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Speaker 1: Hey, Daniel, what are we talking about today?

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Speaker 2: On the episode, we are talking about avoid.

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Speaker 1: As in you're gonna avoid my questions.

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Speaker 2: No voids as in vast empty spaces.

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Speaker 1: Is there a scientist that discovered them? And if so,

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Speaker 1: is it kind of a scam because you just discovered nothing.

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Speaker 2: I'd love to get famous for discovering nothing. That's basically

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Speaker 2: what I've done my whole career.

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Speaker 1: Same here, same here.

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Speaker 2: For that, you got the no Prize instead of the

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Speaker 2: Nobel Prize.

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Speaker 1: Oh, you don't get to eat bells and whistles, so

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Speaker 1: you do get the Nobel Prize.

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Speaker 2: I think I want to avoid myself with these jokes.

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Speaker 1: Avoid. I am Jorge mcgartunez, a author of Oliver's Great

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Speaker 1: Big Universe.

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Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at UC Irvine, and I got into this business to

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Speaker 2: make radical, universe changing discoveries. But I haven't made any.

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Speaker 1: The whole reason we're here, it has been all for nothing.

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Speaker 2: Well, you know, research has no guarantees. You could go

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Speaker 2: out there into the vast plane of undiscovered territory and

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Speaker 2: find all sorts of incredible stuff or just nothing. We

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Speaker 2: have no promises from nature.

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Speaker 1: Well, Daniel, you sound a little defeated. Did you have

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Speaker 1: a lot of years ahead of you in your career?

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Speaker 2: No, I'm not defeated. I rolled the dice and I

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Speaker 2: knew there were risks, and you know, physics is a

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Speaker 2: lot of fun along the way even if you don't

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Speaker 2: make a big discovery.

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Speaker 1: But don't you have like at least twenty thirty years

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Speaker 1: of work still or are you just planning to coast

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Speaker 1: the rest of the.

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Speaker 2: Way on adviceive counsel. I'm going to not answer that question.

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Speaker 1: You're like, it's called being emeritus.

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Speaker 2: I'm rapidly approaching emeritus.

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Speaker 1: Well, whether you're emeritus or active, Welcome to our podcast,

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Speaker 1: Daniel and Jorge Explain the Universe, a production of iHeartRadio.

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Speaker 2: In which we guide you through all of the incredible,

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Speaker 2: mind shattering discoveries of the last few hundred years that

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Speaker 2: have revealed a universe that's weird, that's bizarre, that's strange,

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Speaker 2: and yet somehow maybe understandable, And we also try to

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Speaker 2: guide you through potential discoveries in the next few years,

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Speaker 2: in the next decades, may be made by me or

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Speaker 2: my team, or by some of the listeners to this podcast.

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Speaker 2: Or they are great great grandchildren. Whenever those discoveries come,

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Speaker 2: we want you to be prepared for them by understanding

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Speaker 2: what we do and don't know about the universe.

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Speaker 1: That's right, because it is an incredibly huge and amazing

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Speaker 1: universe out there, full of incredible phenomenon, astounding events, and

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Speaker 1: also a whole lot of moving.

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Speaker 2: Indeed, the universe really is something. Even if that's something

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Speaker 2: is often nothing. But there's lots of mysteries remaining about

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Speaker 2: the nature of the universe. As much as we've discovered

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Speaker 2: in the last one hundred years about how big the

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Speaker 2: universe is, about how it's expanding, about how that expansion

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Speaker 2: is accelerating, about how galaxies swirl around invisible dark matter,

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Speaker 2: there's still a lot of pieces that don't fit together,

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Speaker 2: which tells us probably the next few decades or few

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Speaker 2: hundred years will reveal even more mind blowing discoveries about

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Speaker 2: the nature of our cosmos.

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Speaker 1: Yeah, the amazing thing about this universe and about science

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Speaker 1: is that all the pieces are out there for us

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Speaker 1: to see, for us to discover, for us to observe,

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Speaker 1: and for someone maybe you, maybe us, to put it

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Speaker 1: all together and make sense of this amazing cosmos. Oh wait, wait, sorry, sorry,

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Speaker 1: not Daniel, he's already given up.

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Speaker 2: Hey you know, if it falls to my lap, I'm

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Speaker 2: not saying no.

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Speaker 1: But yeah, well it sound like like you just throw

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Speaker 1: it in the trash.

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Speaker 3: You know.

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Speaker 2: The universe is like a giant mystery novel. Often all

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Speaker 2: of the clues are out there, staring us in the face.

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Speaker 2: This requires the insight, that moment of clarity to see

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Speaker 2: how it all fits together into one coherent story. And

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Speaker 2: currently we're struggling a little bit to understand all of

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Speaker 2: those clues to tell a story that makes sense to

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Speaker 2: us and that holds together mathematically. And it could be

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Speaker 2: that some elements of our current story are drastically wrong.

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Speaker 2: We've certainly done that lots of times in history, gone

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Speaker 2: down the wrong path for decades or even centuries before

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Speaker 2: having to backtrack and come up with a completely new,

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Speaker 2: radical interpretation of how the universe works.

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Speaker 1: Yeah, leaving all those other scientists to have discovered nothing.

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Speaker 1: But all the clues are out there, but one of

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Speaker 1: the problems is that they're really far away. That's because

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Speaker 1: the universe is full of nothing, a lot of big

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Speaker 1: empty void in spaces that are preventing us from reaching

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Speaker 1: and touching some of the important clues that are out there.

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Speaker 1: But there is maybe the idea that some of these

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Speaker 1: huge voids of nothingness could maybe hold the answer to

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Speaker 1: one of the biggest quest questions in the universe.

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Speaker 2: That's right, Maybe the biggest question in modern science today

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Speaker 2: is what is driving the expansion of the universe? Why

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Speaker 2: is it going faster and faster every year? We have

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Speaker 2: a placeholder idea we call dark energy, but as you'll hear,

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Speaker 2: it's not even really a single coherent concept and we

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Speaker 2: might need completely new explanations for it.

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Speaker 1: So today on the podcast, we'll be tackling the question

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Speaker 1: could a huge void cost the illusion of dark energy?

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Speaker 1: So wait, what are you saying, Daniel that dark energy

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Speaker 1: is not something and in fact it might be nothing.

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Speaker 2: Wouldn't it be a huge dramatic plot twist if the

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Speaker 2: answer the biggest question in science was nothing.

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Speaker 1: I feel like we can already preview that, like what

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Speaker 1: came before the universe nothing? What's going to happen after

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Speaker 1: the universe nothing? We're just to blipp and the nothing

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Speaker 1: is I.

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Speaker 2: Think the answer to both of those questions is actually

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Speaker 2: we don't know or we have no idea, which is

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Speaker 2: a little bit different from nothing. And you know, philosophically,

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Speaker 2: nothing is a complicated concept, like what does it even mean? Right?

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Speaker 2: We've talked on the podcast about how space is never

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Speaker 2: really empty and all of it has quantum fields and it,

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Speaker 2: so what does nothing even really mean? It's actually quite

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Speaker 2: a deep philosophical question.

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Speaker 1: It is very tricky.

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Speaker 3: Yeah.

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Speaker 1: For example, I have a doctorate in philosophy, but I

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Speaker 1: know nothing about philosophy.

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Speaker 2: So you're saying you know nothing. Wow, you're an expert

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Speaker 2: in nothing.

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Speaker 1: Well, I guess that's something.

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Speaker 2: I would say. I'm no expert in nothing. Nothing is

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Speaker 2: actually quite complex.

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Speaker 1: I lost track of the negatives there, No, you didn't, No,

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Speaker 1: I didn't. No, I didn't not know nothing about something?

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Speaker 2: There you go. Well, let's check in with the listeners

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Speaker 2: to see if they don't not know nothing about nothing?

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Speaker 1: Yeah, as usual, Daniel went out there to ask people

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Speaker 1: if they think maybe a huge void could be causing

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Speaker 1: what we see as dark energy.

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Speaker 2: Thanks very much to everybody who's sent in their answers.

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Speaker 2: I would love to hear your voice on the podcast.

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Speaker 2: That's right, I'm talking to you. You've been listening for

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Speaker 2: years but never chimed in. Today's the day right to

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Speaker 2: me two questions at Danielanjorge dot com.

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Speaker 1: So think about it for a second. Do you think

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Speaker 1: dark energy could be explained by a huge amount of nothingness?

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Speaker 1: Here's what people had to say.

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Speaker 4: I don't think so. Even without the accelerated expansion of

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Speaker 4: the universe, it's still possible to have huge voids in space.

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Speaker 4: Perhaps if we were able to detect that a huge

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Speaker 4: void wasn't there before, we might be able to use

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Speaker 4: that as evidence towards the cosmological constant, But I think

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Speaker 4: that would take a long time.

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Speaker 3: Perhaps the void is filled with dark energy which we

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Speaker 3: cannot yet detect, So perhaps these areas could be responsible

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Speaker 3: for the accelerated expansion rate, if only we could learn

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Speaker 3: what dark energy truly is.

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Speaker 5: I'm going to assume in your definition of you ascribe

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Speaker 5: to quantum field theory and avoid in space would be

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Speaker 5: an area where the fields from all the fundamental particles

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Speaker 5: are somehow blocked from this area. One could posit that

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Speaker 5: some of these fields might feel a sort of pressure

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Speaker 5: to fill the void, causing an expansion. So, sure, I'll

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Speaker 5: say it could.

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Speaker 6: Aha dark energy explain. Sure it could be space expanding

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Speaker 6: into a void. But then where is that void? What

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Speaker 6: is that void made out of and how is it

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Speaker 6: expanding into it? And what does that even mean? I

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Speaker 6: don't know about this one.

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Speaker 2: I'm confused by that comment. What's the difference between a

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Speaker 2: huge amount of nothingness and a small amount of nothingness?

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Speaker 2: If they're all nothing, it's like ten times zero versus

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Speaker 2: one time zero.

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Speaker 1: I think the difference is a nothing.

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Speaker 2: Nice. Well, I like these listeners answer some really well

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Speaker 2: informed thoughts here. You seem surprised, Daniel, No, I'm impressed

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Speaker 2: as usual.

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Speaker 1: Had you given up on our list as well.

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Speaker 2: I think your reaction is based on nothing. I have

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Speaker 2: nothing but respect for these listeners, their efforts to understand

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Speaker 2: the universe, their willingness to contribute. I'm in awe.

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Speaker 1: Well, they do have some interesting answers here, and it's

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Speaker 1: kind of an interesting question that maybe the biggest part

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Speaker 1: of what we see in the universe, ninety five percent

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Speaker 1: of all the mass and energy in the universe, maybe

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Speaker 1: is not really something or mass or energy. Maybe it's

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Speaker 1: just something that can be easily explained with nothing.

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Speaker 2: Yeah, that's right. In order to explain this accelerating expansion

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Speaker 2: of the universe, we've had to add into our equations,

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Speaker 2: something very weird, very awkward, something we really struggle with,

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Speaker 2: and so people have been working for a long time

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Speaker 2: to find alternative explanations, sort of more prosaic ideas that

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Speaker 2: would explain the strange things we see out there in

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Speaker 2: the universe.

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Speaker 1: My question, Daniel, is why didn't we think of this before?

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Speaker 1: I mean, well, when you see something mysterious, shouldn't the

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Speaker 1: first thing you ask be maybe it's nothing.

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Speaker 2: Yeah, it's a good question. This particular idea that we're

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Speaker 2: going to talk about today is uncomfortable in other ways

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Speaker 2: for scientists. It violates some like philosophical principles that they

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Speaker 2: really hope the universe respects. And that's why it's a

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Speaker 2: little bit weird and a little bit uncomfortable to consider.

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Speaker 2: But hey, sometimes when the universe confronts you with data,

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Speaker 2: you just got to accept it.

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Speaker 1: I mean, after like twenty thirty years of trying to

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Speaker 1: explain it in other ways.

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Speaker 2: I guess, yeah, exactly.

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Speaker 1: Just because it makes it uncomfortable.

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Speaker 2: I like that the universe makes us uncomfortable. I like,

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Speaker 2: when we go what it doesn't make any sense at all?

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Speaker 2: How could the universe be that way? Those are the

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Speaker 2: moments we really learn something when we really have to

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Speaker 2: confront some fundamental assumption that is probably wrong.

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Speaker 1: Right, right, you like it, but only if you're sitting

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Speaker 1: comfortably in your couch.

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Speaker 2: Right, yeah, exactly. Let me get comfortable before you make

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Speaker 2: me uncomfortable.

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Speaker 1: Yeah, let's draw online here. I want to be physically

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Speaker 1: comfortable but intellectually uncomfortable.

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Speaker 2: Is that what you're saying, Yes, serve me some chocolate

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Speaker 2: while you tell me the results of this study. Yes, absolutely,

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Speaker 2: a little bit of sugar makes the medicine go down.

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Speaker 1: Right, right, you've given up even getting up up for

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Speaker 1: your couch. But anyways, Daniel, for those of us who

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Speaker 1: are sitting in our couches, wait to hear the answer.

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Speaker 1: What you start us with the basics? What is this

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Speaker 1: thing that we call dark energy?

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Speaker 2: Yeah, so the thing that we're struggling to explain is

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Speaker 2: something we call dark energy. But dark energy is not

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Speaker 2: really like a theory as much as a description of

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Speaker 2: something we observe in the universe for which we don't

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Speaker 2: have a great explanation. And that's the fact that the

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Speaker 2: universe is expanding, and it's not just expanding the same

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Speaker 2: rate every year. It's expanding at an accelerated rate. It

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Speaker 2: seems like the distances between clusters of galaxies is increasing,

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Speaker 2: so that's expansion, but it's increasing faster and faster every year.

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Speaker 2: This is something we discovered about twenty five years ago now,

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Speaker 2: when we first learned how to figure out how far

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Speaker 2: away things are in the universe, and it was really

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Speaker 2: a shocker. You know, people before that were wondering how

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Speaker 2: quickly the expansion of the universe was slowing down. That

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Speaker 2: was the big question in science because you have the

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Speaker 2: universe expanding when it's very very young, but then it's

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Speaker 2: filled with matter. There's all this heavy stuff in the universe,

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Speaker 2: galaxies and black holes and whatever that tends to pull

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Speaker 2: stuff back together, and so people were wondering, hey, is

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Speaker 2: there enough gravity to pull stuff back together to make

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Speaker 2: like a reverse big bang, like a big crunch, or

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Speaker 2: is there not enough and it's just going to gradually

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Speaker 2: slow down for a long time to keep drifting apart.

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Speaker 2: And when they went out to measure it, they discovered, shocker,

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Speaker 2: neither of those were true. The universe preferred secret answer CEE,

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Speaker 2: which is that things are getting further apart faster and faster.

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Speaker 2: So dark energy is sort of like our placeholder name

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Speaker 2: to explain how that might be happening.

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Speaker 1: So, I think we've known that the universe is expanding

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Speaker 1: for about one hundred years, right, But you're saying it's

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Speaker 1: only recently we figured out it's accelerating.

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Speaker 2: Yeah, if you want to go further back into history,

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Speaker 2: around the time that Einstein was developing the theory of relativity,

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Speaker 2: we thought the universe was static. We thought that there

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Speaker 2: was just like our galaxy hanging out there in empty

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Speaker 2: space and that was it. Then Edwin Hubble and Henrietta

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Speaker 2: Levitt developed this way to measure the distance to things

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Speaker 2: in the sky to tell how far away they were,

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Speaker 2: And what they discovered is that some smudgets we saw

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Speaker 2: in the sky that we thought were just like clouds

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Speaker 2: of gas in our galaxy were actually much further away.

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Speaker 2: There were further than any of the stars in the sky.

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Speaker 2: There were actually other galaxies. And on top of that,

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Speaker 2: those galaxies were moving away from us. So we discovered

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Speaker 2: that the universe was not only just our galaxy, it

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Speaker 2: was filled with galaxies, and that the universe was expanding.

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Speaker 2: Everything was running away from us. That was about one

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Speaker 2: hundred years ago.

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Speaker 1: And how do we know they were moving away from

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Speaker 1: us from the red shifting the Doppler.

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Speaker 2: Effect, Yeah, exactly. You can look at the light from

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Speaker 2: those galaxies and you can see how its frequency shifted

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Speaker 2: things that are moving away from us. As you said,

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Speaker 2: the Doppler effect, the light from those things is shift

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Speaker 2: in frequency, and you can tell because we have an

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Speaker 2: idea for what frequency of light should be emitted by

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Speaker 2: galaxies to have these particular fingerprints, and so when they're

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Speaker 2: shifted over twenty nanometers or one hundred nanimeters or whatever

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Speaker 2: in wavelength, then we can tell. And that we use

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Speaker 2: that to measure the velocity.

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Speaker 1: And so back then, did we think or measure that

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Speaker 1: everything was moving away from us at the same speed

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Speaker 1: or we just didn't know enough to know at what

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Speaker 1: rate things were moving away from us.

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Speaker 2: Back then, Hubble's discovery allowed us to measure the distance

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Speaker 2: to other galaxies, but sort of only in us nearby sphere.

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Speaker 2: Hubble couldn't tell that the universe was expanding and accelerating

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Speaker 2: because he couldn't measure the distance to far away enough stuff.

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Speaker 2: He and Henriette Levitt developed this technique to measure the

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Speaker 2: distance to stuff looking at these particular variable stars called cephids.

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Speaker 2: But you had to be able to see them, and

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Speaker 2: if galaxies were far enough away, then you couldn't see

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Speaker 2: those stars in the galaxies, so he could sort of

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Speaker 2: only see a little bubble. But about twenty five years

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Speaker 2: ago we developed a new technique that allowed us to

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Speaker 2: see much further and to measure the distance much further,

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Speaker 2: and so then we could see the change over time

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Speaker 2: as we look back into the history of the universe,

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Speaker 2: and we noticed this effect. So Hubble couldn't see it

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Speaker 2: because they didn't have enough data. It didn't have a

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Speaker 2: long enough lever arm in history to see things changing.

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Speaker 1: It was being able to tell how far away things

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Speaker 1: were and then measuring on top of that their velocity

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Speaker 1: that let us figure out that things we're accelerating.

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Speaker 2: Yeah, exactly. It was the development of this technique using

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Speaker 2: type one a supernova supernova of course, the implosion of

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Speaker 2: stars leading to an extraordinarily bright explosion, so bright that

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Speaker 2: they outshine the galaxies therein. And so you can measure

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Speaker 2: these things for very very distant galaxies, and understanding the

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Speaker 2: physics of it, and understanding how bright they are at

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Speaker 2: their source without knowing how far away they are, lets

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Speaker 2: you figure out how far away they are by looking

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Speaker 2: at how bright they are here on Earth, because things

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Speaker 2: here are dimmer when they arrive, so they'll lets you

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Speaker 2: know how far away things are, and that's absolutely crucial

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Speaker 2: because knowing how far away some thing is tells you

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Speaker 2: when the light left it right. And so as we

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Speaker 2: look further into space, we're looking further back in time.

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Speaker 2: So that's how we can see the history of the

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Speaker 2: expansion of the universe. We can see how fast is

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Speaker 2: stuff moving away from us that's close by i e.

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Speaker 2: Recent history, and then we can ask how fast it

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Speaker 2: was stuff moving away from us earlier in the universe

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Speaker 2: by looking further away. So this is absolutely crucial to

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Speaker 2: understanding how dark energy works and also how it might

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Speaker 2: be wrong. What we see is that the expansion is

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Speaker 2: faster for things that are closer to us, and we

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Speaker 2: interpret that to mean the expansion is speeding up, so

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Speaker 2: deeper into space the expansion looks slower. Closer to us,

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Speaker 2: the expansion looks faster. That's what leads us to conclude

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Speaker 2: that the expansion is accelerating.

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Speaker 1: So things we can tell are really far away don't

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Speaker 1: have as much of a red shift as the things

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Speaker 1: that we can see that are closer to us.

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Speaker 2: They're further away, so their actual distance, the red shift

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Speaker 2: is larger, but hasn't accumulated over time, So it's the

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Speaker 2: acceleration is like the slope of that velocity curve. So

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Speaker 2: those things are very far away, they are very very

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Speaker 2: red shifted, but the change in that slope we can

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Speaker 2: see over time as we look at these things from

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Speaker 2: further away to closer in.

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Speaker 1: All right, So then that tells us that the universe

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Speaker 1: is expanding more and more rapidly. And we have a

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Speaker 1: name for that, which is dark energy, or at least

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Speaker 1: the thing that might be causing this acceleration. That's what

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Speaker 1: we call dark energy.

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Speaker 2: Yeah, we call it dark energy. And I feel like

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Speaker 2: there's a lot of confusion out there about what we

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Speaker 2: do and don't know, and I think this is really

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Speaker 2: interesting insight into sort of the way physics works. Like

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Speaker 2: we often begin thinking about an idea before we have

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Speaker 2: it all worked out. We just sort of like start

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Speaker 2: fleshing it out the way you might like design your house,

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Speaker 2: starting from what you wanted to look on the outside

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Speaker 2: before you figured it out, Like, hey, what are all

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Speaker 2: the structural supports and can I really have pipes over here?

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Speaker 2: And is it possible to have a shower on the

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Speaker 2: roof or whatever. You know, you haven't always figured out

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Speaker 2: the details, some of which might be absolutely essential. And

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Speaker 2: so if you look at the beginning days of the.

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Speaker 1: Development, I know every house you would have a shower

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Speaker 1: on the roof.

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Speaker 2: My wife is a big fan of an outside shower.

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Speaker 2: She's always wanted to put one in. So I'm always suggesting,

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Speaker 2: let's put it on the roof. And I don't know

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Speaker 2: why that's not a popular idea. But anyway, if you

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Speaker 2: look at the history of the development of big ideas

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Speaker 2: and physics, this is how it works. And so we've

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Speaker 2: done that with dark energy. We're like, wow, this is weird.

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Speaker 2: How do we explain this? Okay, first, let's give it

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Speaker 2: a cool name. Now, let's start to think about how

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Speaker 2: it might be possible. And we definitely don't have all

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Speaker 2: the details worked out. We have some conception of how

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Speaker 2: in general relativity you might generate this effect, we definitely

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Speaker 2: don't have all the pieces together.

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Speaker 1: And we say that it's ninety five percent of the energy, mass,

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Speaker 1: and energy of the whole universe, because that's how much

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Speaker 1: energy you need to explain something that's accelerating the entire

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Speaker 1: observable universe.

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Speaker 2: Yeah, it's something like seventy percent. Dark matter and dark

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Speaker 2: energy together make ninety five percent, but the dark energy

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Speaker 2: portion is set tventy percent. Yeah, and you're exactly right.

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Speaker 2: And the way we get that seventy percent is a

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Speaker 2: few different ways. But one way is to say, all right,

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Speaker 2: how in general relativity could you cause the universe to expand?

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Speaker 2: Because usually gravity causes things to come together. Right, you

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Speaker 2: have two masses in space, they curve space, they tend

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Speaker 2: to move together. But general relativity is much more complex

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Speaker 2: than Newtonian gravity includes all sorts of complicated terms and

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Speaker 2: effects in there. And one of the possible effects in

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Speaker 2: general relativity is if you have a field in space,

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Speaker 2: like the electromagnetic field or the weak field or the

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Speaker 2: electron field. We know space is filled with these fields,

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Speaker 2: but if these fields have a lot of potential energy,

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Speaker 2: meaning they have like stored energy inside of them because

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Speaker 2: of their configuration the way the Higgs field does. For example,

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Speaker 2: having a lot of potential energy in space will generate

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Speaker 2: this expansion. Just like part of the mathematics of general relativity.

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Speaker 2: You have a negative sign in front of this term

401
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Speaker 2: in the equations, and so it generates expansion of space.

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Speaker 2: So if you had a field with a lot of

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Speaker 2: potential energy, it would generate the expansion. So we calculate

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Speaker 2: how much potential energy do you need, and that comes

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Speaker 2: out to be about seventy percent of the energy in

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Speaker 2: the universe.

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Speaker 1: So this whole idea that dark energy is seventy percent

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Speaker 1: of the universe comes from the assumption, if I'm understanding right,

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Speaker 1: the assumption that what's causing the acceleration of the universe

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Speaker 1: is something kind of baked into space itself.

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Speaker 2: Yeah, exactly, And there's some supporting evidence for it, and

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Speaker 2: there's also a bunch of stuff that doesn't work about it.

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Speaker 2: Like one supporting piece of evidence is that we can

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Speaker 2: go out and measure all of the energy in the universe,

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Speaker 2: because it affects the overall curvature of the universe, Like

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Speaker 2: is the universe overall flat or curve negatively or curved positively.

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Speaker 2: That depends very sensitively on how much energy is there

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Speaker 2: in the universe. And we go out and we measure that,

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Speaker 2: and then we measure the energy out there in the

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Speaker 2: universe to be exactly what we need to make it

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Speaker 2: flat and to add up very nicely with this seventy

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Speaker 2: percent number. So the dark matter, the normal matter, and

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Speaker 2: the dark energy in the universe all adds up perfectly

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Speaker 2: to make the universe flat, which is what we observe.

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Speaker 2: That's very cool.

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Speaker 1: Oh interesting, All right, Well, let's get into the things

427
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Speaker 1: that don't work about dark energy and why maybe nothingness

428
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Speaker 1: could be the key to understanding how it all works.

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Speaker 1: So let's dig into that. But first let's take a

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Speaker 1: quick break. All right, we're talking about dark energy and

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Speaker 1: giant voids in the universe, and could those two things

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Speaker 1: be related. Could dark energy just be a whole bunch

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Speaker 1: of nothing. Could it be explained by perhaps the absence

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Speaker 1: of things in space? And so we talked a little

435
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Speaker 1: bit about dark energy what it is, but we know

436
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Speaker 1: about it. But Daniel, there's something wrong with that picture

437
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Speaker 1: of dark energy. What's wrong with it.

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Speaker 2: What's wrong with it is that we have no idea

439
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Speaker 2: where all this potential energy would be coming from. In

440
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Speaker 2: order to have the universe expand and accelerate at the

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Speaker 2: rate that it has been, we need space to be

442
00:21:58,359 --> 00:22:00,919
Speaker 2: filled with some kind oftential energy.

443
00:22:01,119 --> 00:22:04,119
Speaker 1: Well, here's a question, like, does dark energy need to

444
00:22:04,160 --> 00:22:07,119
Speaker 1: be something that's like a field or baked into space,

445
00:22:07,280 --> 00:22:10,040
Speaker 1: or could it be some maybe hidden property of gravity

446
00:22:10,080 --> 00:22:12,880
Speaker 1: perhaps or electromagnetism, or is that the same thing.

447
00:22:13,240 --> 00:22:16,480
Speaker 2: It could definitely be something totally brand new, some new

448
00:22:16,600 --> 00:22:19,600
Speaker 2: kind of physics we've never seen before, or change in

449
00:22:19,680 --> 00:22:22,439
Speaker 2: general relativity. That's definitely possible, and there are people out

450
00:22:22,480 --> 00:22:26,480
Speaker 2: there working on other crazy ideas. But so the mainstream

451
00:22:26,520 --> 00:22:28,600
Speaker 2: effort is to say, like, well, can we incorporate this

452
00:22:28,680 --> 00:22:31,760
Speaker 2: into general relativity, because it's kind of interesting that general

453
00:22:31,760 --> 00:22:36,359
Speaker 2: relativity has this capacity already. It's something that Einstein's relativity

454
00:22:36,400 --> 00:22:40,440
Speaker 2: can do expand space and accelerate that expansion. The problem

455
00:22:40,520 --> 00:22:42,879
Speaker 2: is that to make that happen, you need to fill

456
00:22:42,960 --> 00:22:45,840
Speaker 2: space with all of this energy. Either you say, look,

457
00:22:45,960 --> 00:22:47,560
Speaker 2: that's just the way it is. You just put a

458
00:22:47,640 --> 00:22:50,280
Speaker 2: number in there, and that's called the cosmological constant and

459
00:22:50,359 --> 00:22:52,960
Speaker 2: you say, like, it's not explained, that's just the nature

460
00:22:52,960 --> 00:22:56,000
Speaker 2: of space. It just has this energy, kind of unsatisfying,

461
00:22:56,560 --> 00:22:58,800
Speaker 2: or you find the source of that energy you say, oh,

462
00:22:58,840 --> 00:23:01,679
Speaker 2: look it's this particular quantum field that can do it.

463
00:23:02,000 --> 00:23:04,880
Speaker 2: And we look through our list of quantum fields we ask, well,

464
00:23:04,920 --> 00:23:07,360
Speaker 2: how much potential energy do they have? And one of them,

465
00:23:07,440 --> 00:23:09,919
Speaker 2: has a lot of potential energy. The Higgs field is

466
00:23:09,960 --> 00:23:13,240
Speaker 2: filled with potential energy. Remember that most of the fields

467
00:23:13,240 --> 00:23:16,000
Speaker 2: in the universe like to relax down to zero. They

468
00:23:16,119 --> 00:23:18,680
Speaker 2: like to be in their lowest energy state. But the

469
00:23:18,760 --> 00:23:21,240
Speaker 2: Higgs field is really weird, has this wrinkle in it,

470
00:23:21,280 --> 00:23:23,919
Speaker 2: so it sort of gets stuck at high potential energy

471
00:23:24,119 --> 00:23:27,359
Speaker 2: when the universe is cooling. The Higgs field doesn't collapse

472
00:23:27,400 --> 00:23:29,000
Speaker 2: down to zero the way the other ones do. It

473
00:23:29,040 --> 00:23:31,320
Speaker 2: has all this potential energy. All right, So this is

474
00:23:31,359 --> 00:23:35,040
Speaker 2: really exciting, right. Dark energy needs some field filled with

475
00:23:35,119 --> 00:23:38,240
Speaker 2: potential energy to explain the accelerating expansion in the universe,

476
00:23:38,440 --> 00:23:42,240
Speaker 2: and over here we have a field filled with potential energy. Awesome.

477
00:23:42,600 --> 00:23:44,879
Speaker 2: So people sat down to do the calculations and say,

478
00:23:45,200 --> 00:23:47,800
Speaker 2: does the Higgs field have enough energy to explain the

479
00:23:47,840 --> 00:23:51,680
Speaker 2: accelerating expansion the universe. The answer is no, and it's

480
00:23:51,720 --> 00:23:54,600
Speaker 2: not even close. The answer is off by ten to

481
00:23:54,680 --> 00:23:57,960
Speaker 2: the one hundred and twenty. So the fields we have

482
00:23:58,080 --> 00:24:01,440
Speaker 2: can definitely not explain the expansion of the universe as

483
00:24:01,440 --> 00:24:01,919
Speaker 2: we see it.

484
00:24:02,880 --> 00:24:05,200
Speaker 1: But I guess if it's not a field, if it's

485
00:24:05,200 --> 00:24:07,520
Speaker 1: something else, would it still account for seventy percent of

486
00:24:07,600 --> 00:24:10,520
Speaker 1: the universe, or like, what are some of these other

487
00:24:10,560 --> 00:24:11,280
Speaker 1: things that could.

488
00:24:11,119 --> 00:24:15,800
Speaker 2: Be ooh not a field, man, That blows my mind. Currently,

489
00:24:15,840 --> 00:24:18,760
Speaker 2: our theories of the universe are that everything's a field, right,

490
00:24:18,840 --> 00:24:21,680
Speaker 2: Like all the particles are ripples in fields, and all

491
00:24:21,720 --> 00:24:23,920
Speaker 2: the energy out there is stored in some kind of field.

492
00:24:24,000 --> 00:24:27,080
Speaker 2: So mostly people are developing like new kinds of fields.

493
00:24:27,400 --> 00:24:29,640
Speaker 2: Maybe there's some other kind of field, not the Higgs field,

494
00:24:29,720 --> 00:24:32,320
Speaker 2: something else out there in the universe that contains all

495
00:24:32,320 --> 00:24:34,399
Speaker 2: of this energy, and then you have to explain, like

496
00:24:34,400 --> 00:24:36,080
Speaker 2: why we wouldn't have seen it and has no other

497
00:24:36,119 --> 00:24:38,760
Speaker 2: effects that we could detect. For example, that's the way

498
00:24:38,800 --> 00:24:41,679
Speaker 2: a lot of people are going. Non field explanations for

499
00:24:41,720 --> 00:24:44,720
Speaker 2: the accelerating expansion in the universe. Those are pretty far

500
00:24:44,760 --> 00:24:47,880
Speaker 2: out of the mainstream, but you know, it could be right.

501
00:24:48,840 --> 00:24:51,159
Speaker 2: Physicists tend to work like within the framework of the

502
00:24:51,160 --> 00:24:53,119
Speaker 2: ideas we have. Doesn't mean that that's where we're going

503
00:24:53,160 --> 00:24:53,879
Speaker 2: to find the answer.

504
00:24:55,080 --> 00:24:57,679
Speaker 1: Or what if it's like a part of gravity itself

505
00:24:57,760 --> 00:25:01,280
Speaker 1: or general relativity like maybe Grouty gets it turns the

506
00:25:01,280 --> 00:25:04,400
Speaker 1: negative if you get really far away from something, would

507
00:25:04,400 --> 00:25:06,600
Speaker 1: that still be a field? Technically?

508
00:25:07,200 --> 00:25:10,399
Speaker 2: I don't think that's compatible with general relativity. So in

509
00:25:10,480 --> 00:25:12,159
Speaker 2: order to have that be the explanation, you have to

510
00:25:12,240 --> 00:25:15,080
Speaker 2: change general relativity. And the thing people like about this

511
00:25:15,240 --> 00:25:17,480
Speaker 2: dark energy framework is that you don't have to change

512
00:25:17,480 --> 00:25:19,879
Speaker 2: general relativity because it's been tested up and down the

513
00:25:19,920 --> 00:25:23,600
Speaker 2: wazoo and it really is accurate for huge distances or

514
00:25:23,680 --> 00:25:26,840
Speaker 2: huge distances yeah, I mean, it explains an enormous amount

515
00:25:26,880 --> 00:25:29,120
Speaker 2: about the structure of the universe as we see it,

516
00:25:29,760 --> 00:25:34,040
Speaker 2: and so changing general relativity is pretty uncomfortable, except in

517
00:25:34,080 --> 00:25:37,520
Speaker 2: places where it hasn't been tested, like inside black holes

518
00:25:37,720 --> 00:25:40,280
Speaker 2: or the very very early universe, things we haven't been

519
00:25:40,320 --> 00:25:44,560
Speaker 2: able to observe yet, basically where quantum mechanics arises. So

520
00:25:44,640 --> 00:25:48,119
Speaker 2: it's difficult to make changes to general relativity without messing

521
00:25:48,200 --> 00:25:49,160
Speaker 2: up a lot of other.

522
00:25:48,960 --> 00:25:52,639
Speaker 1: Stuff that would just be uncomfortable and also require a

523
00:25:52,680 --> 00:25:53,400
Speaker 1: lot of work.

524
00:25:54,160 --> 00:25:56,919
Speaker 2: And it could be the path to huge discoveries. But

525
00:25:57,080 --> 00:25:58,840
Speaker 2: you know, the way physics works is, hey, let's try

526
00:25:58,840 --> 00:26:01,359
Speaker 2: the easiest thing first. And so there is this door

527
00:26:01,400 --> 00:26:03,560
Speaker 2: open in general relativity, like, let's see if we can

528
00:26:03,600 --> 00:26:07,240
Speaker 2: explain it using the framework we have, which requires discovering

529
00:26:07,280 --> 00:26:09,840
Speaker 2: this field that explains where all the energy is and

530
00:26:10,080 --> 00:26:11,360
Speaker 2: that we don't have an answer for.

531
00:26:12,240 --> 00:26:15,240
Speaker 1: So then that's the problem with our current theories about

532
00:26:15,280 --> 00:26:17,639
Speaker 1: dark energy is that you think it requires a field,

533
00:26:17,640 --> 00:26:19,320
Speaker 1: but we don't know what field it could be, because

534
00:26:19,359 --> 00:26:21,560
Speaker 1: it needs to have more energy than anything we know about.

535
00:26:21,800 --> 00:26:25,040
Speaker 2: Yeah, that's the major problem, sort of the conceptual problem.

536
00:26:25,080 --> 00:26:28,239
Speaker 2: There are also a few smaller problems, experimental problems, like

537
00:26:28,560 --> 00:26:32,040
Speaker 2: our picture of the universe as being mostly dark energy

538
00:26:32,080 --> 00:26:34,080
Speaker 2: and a big chunk dark matter and a little bit

539
00:26:34,080 --> 00:26:37,760
Speaker 2: of baryonic matter and normal matter. It explains an enormous amount.

540
00:26:37,840 --> 00:26:40,960
Speaker 2: It explains how the universe started out filled with radiation,

541
00:26:41,119 --> 00:26:44,000
Speaker 2: and then that radiation got diluted and it was matter dominated,

542
00:26:44,040 --> 00:26:47,159
Speaker 2: and it was expanding, but that expansion was slowing down.

543
00:26:47,560 --> 00:26:49,880
Speaker 2: But the expansion led to more dark energy, which then

544
00:26:49,920 --> 00:26:53,320
Speaker 2: accelerated the expansion, and the universe became dark energy dominated

545
00:26:53,359 --> 00:26:56,600
Speaker 2: like six billion years ago. It's an amazing, beautiful story

546
00:26:56,600 --> 00:26:59,879
Speaker 2: that explains an enormous amount, but it doesn't quite explain everything.

547
00:27:00,359 --> 00:27:03,800
Speaker 2: Like there's this discrepancy between our observation of how fast

548
00:27:03,880 --> 00:27:06,320
Speaker 2: the universe is expanding now and how fast it was

549
00:27:06,400 --> 00:27:09,359
Speaker 2: expanding the very early days. This is called the Hubble

550
00:27:09,400 --> 00:27:11,760
Speaker 2: tension because the Hubble constant is kind of a measure

551
00:27:11,760 --> 00:27:14,200
Speaker 2: of the expansion rate, and that's not something we can

552
00:27:14,240 --> 00:27:17,840
Speaker 2: really explain. We don't really understand how the expansion the

553
00:27:17,920 --> 00:27:21,480
Speaker 2: early universe connects for the expansion in late times. At first,

554
00:27:21,560 --> 00:27:23,720
Speaker 2: it was very fuzzy measurements. We thought, I will figure

555
00:27:23,760 --> 00:27:26,240
Speaker 2: it out. But as we make more and more precise measurements,

556
00:27:26,240 --> 00:27:29,040
Speaker 2: they don't really agree. So that might require a tweak

557
00:27:29,080 --> 00:27:31,320
Speaker 2: to this, or it might be a crack that undermines

558
00:27:31,359 --> 00:27:33,760
Speaker 2: the whole theory. So it's not like it's a perfect

559
00:27:33,800 --> 00:27:36,720
Speaker 2: description of everything we see, even if you knew where

560
00:27:36,720 --> 00:27:38,840
Speaker 2: this energy was coming from.

561
00:27:38,880 --> 00:27:41,679
Speaker 1: So then I guess what's the alternative if it's not

562
00:27:42,200 --> 00:27:43,320
Speaker 1: something like a field.

563
00:27:43,520 --> 00:27:45,680
Speaker 2: So one of the alternatives is to question one of

564
00:27:45,760 --> 00:27:48,879
Speaker 2: the basic assumptions of this whole picture of the universe

565
00:27:48,920 --> 00:27:51,159
Speaker 2: that we've been talking about. We usually talk about the

566
00:27:51,240 --> 00:27:53,960
Speaker 2: universe in terms of density, Like when we say seventy

567
00:27:54,000 --> 00:27:56,960
Speaker 2: percent or twenty five percent, we're saying, take a random

568
00:27:57,040 --> 00:27:59,240
Speaker 2: chunk of the universe, how much of that is dark

569
00:27:59,359 --> 00:28:02,480
Speaker 2: energy that is normal energy. When you do that, you're

570
00:28:02,560 --> 00:28:05,000
Speaker 2: kind of making an implicit assumption that all chunks of

571
00:28:05,040 --> 00:28:07,760
Speaker 2: the universe are about the same the stuff is spread

572
00:28:07,760 --> 00:28:10,680
Speaker 2: out through the universe basically evenly, like we know, it's

573
00:28:10,720 --> 00:28:13,639
Speaker 2: not completely evenly. There's definitely clumpiness, like we're a big

574
00:28:13,720 --> 00:28:16,120
Speaker 2: clump in the universe. The Earth, the Sun, the galaxy

575
00:28:16,200 --> 00:28:18,760
Speaker 2: is a clump. But that if you zoom out far enough,

576
00:28:18,800 --> 00:28:22,520
Speaker 2: the universe is evenly spread out on the giant scales.

577
00:28:22,760 --> 00:28:25,760
Speaker 2: The universe is basically the same everywhere. That's kind of

578
00:28:25,760 --> 00:28:29,240
Speaker 2: a philosophical preference. They call it the cosmological principle or

579
00:28:29,280 --> 00:28:32,600
Speaker 2: the Copernican principle. But one of the ideas to explain

580
00:28:32,680 --> 00:28:35,399
Speaker 2: the accelerating expansion of the universe is to say, maybe

581
00:28:35,400 --> 00:28:38,040
Speaker 2: it's not expanding in an accelerating way. Maybe it just

582
00:28:38,160 --> 00:28:40,600
Speaker 2: looks like it is because we're stuck at the center

583
00:28:40,600 --> 00:28:43,360
Speaker 2: of a huge void where there's less stuff in this

584
00:28:43,480 --> 00:28:46,000
Speaker 2: bubble than outside of it, and that gives us the

585
00:28:46,040 --> 00:28:50,040
Speaker 2: illusion that the universe's expansion is accelerating, even if it isn't.

586
00:28:50,480 --> 00:28:53,600
Speaker 1: Whoa, whoa, whoa Wait a minute, how does this even work?

587
00:28:54,400 --> 00:28:58,040
Speaker 1: Is the idea then that maybe outside of the absorbable

588
00:28:58,120 --> 00:29:00,560
Speaker 1: universe there's a whole bunch of nothingness for a while.

589
00:29:00,840 --> 00:29:03,000
Speaker 1: Is that kind of what the picture you're thinking about.

590
00:29:02,880 --> 00:29:04,840
Speaker 2: The idea is that the bubble we're living in, even

591
00:29:04,880 --> 00:29:08,000
Speaker 2: though it has galaxies and stars and whatever, is less

592
00:29:08,040 --> 00:29:10,520
Speaker 2: dense than the stuff outside some bubble.

593
00:29:10,960 --> 00:29:13,680
Speaker 1: But then wouldn't we be able to see those things

594
00:29:13,720 --> 00:29:17,280
Speaker 1: outside the bubble and tell if it's more or less dense.

595
00:29:17,720 --> 00:29:19,920
Speaker 2: Yeah, and we can get into the observations and whether

596
00:29:19,920 --> 00:29:22,239
Speaker 2: this idea actually lines up with what we see in

597
00:29:22,280 --> 00:29:25,640
Speaker 2: the universe. But if this bubble exists, it'd be a

598
00:29:25,680 --> 00:29:28,160
Speaker 2: little tricky to see because we'd be looking really, really

599
00:29:28,200 --> 00:29:30,800
Speaker 2: far out, and our sort of three D map of

600
00:29:30,840 --> 00:29:33,440
Speaker 2: the universe is best for close by stuff, and it

601
00:29:33,480 --> 00:29:35,800
Speaker 2: sort of fades out a little bit as you get

602
00:29:35,840 --> 00:29:38,040
Speaker 2: further out. It's hard to make these big three D

603
00:29:38,120 --> 00:29:40,960
Speaker 2: maps of the universe at this void, if it exists,

604
00:29:41,240 --> 00:29:44,480
Speaker 2: would basically describe everything we see so far. So it's

605
00:29:44,480 --> 00:29:46,840
Speaker 2: sort of suggesting that out there in the deep dark

606
00:29:46,880 --> 00:29:50,160
Speaker 2: reaches of space where we haven't really mapped very well yet,

607
00:29:50,880 --> 00:29:53,560
Speaker 2: galaxies might be a lot denser than they are here.

608
00:29:54,280 --> 00:29:57,000
Speaker 2: Then that might be confusing us about the expansion of

609
00:29:57,040 --> 00:29:57,680
Speaker 2: the universe.

610
00:29:58,200 --> 00:30:00,640
Speaker 1: Wait, I think you're saying that maybe you know the

611
00:30:00,680 --> 00:30:03,800
Speaker 1: galaxies we've seen to come to the conclusion that the

612
00:30:03,920 --> 00:30:07,280
Speaker 1: universe is expanding in an accelerated way. You know, we

613
00:30:07,400 --> 00:30:10,360
Speaker 1: use galaxies we've seen, but maybe those galaxies we seem

614
00:30:10,400 --> 00:30:11,720
Speaker 1: don't go all the way to the edge of the

615
00:30:11,760 --> 00:30:13,480
Speaker 1: observable universe. Is that what you're saying.

616
00:30:13,680 --> 00:30:15,720
Speaker 2: We've used those galaxies and they do go all the

617
00:30:15,760 --> 00:30:18,280
Speaker 2: way to the edge of the observable universe, but it

618
00:30:18,400 --> 00:30:20,480
Speaker 2: might be the things change as you go from here

619
00:30:20,520 --> 00:30:23,040
Speaker 2: to the edge of the observable universe, and that could

620
00:30:23,080 --> 00:30:27,440
Speaker 2: be confusing us about this accelerated expansion. The key concept is,

621
00:30:27,520 --> 00:30:29,800
Speaker 2: remember that we decided that the expansion of the universe

622
00:30:29,880 --> 00:30:33,000
Speaker 2: was accelerating because we saw that changing as we look

623
00:30:33,040 --> 00:30:36,000
Speaker 2: further and further into space, right, And we decided that's

624
00:30:36,040 --> 00:30:39,000
Speaker 2: because things are changing over time. But what if things

625
00:30:39,000 --> 00:30:43,280
Speaker 2: aren't changing over time, they're just changing over space. Right.

626
00:30:43,720 --> 00:30:46,200
Speaker 2: What if the universe is different as you go further

627
00:30:46,280 --> 00:30:49,160
Speaker 2: away than it is here. What if the universe is

628
00:30:49,240 --> 00:30:52,840
Speaker 2: denser further away and then it is closer by, and

629
00:30:52,880 --> 00:30:56,280
Speaker 2: that's what's creating this effect. We see an effect in space,

630
00:30:56,320 --> 00:30:58,760
Speaker 2: and we're assuming that it means an effect over time,

631
00:30:58,800 --> 00:31:01,160
Speaker 2: But what if it's just an effect over space. What

632
00:31:01,200 --> 00:31:03,440
Speaker 2: if the universe is different further away.

633
00:31:04,160 --> 00:31:05,880
Speaker 1: I see what you're saying. I think you're saying that

634
00:31:05,920 --> 00:31:08,880
Speaker 1: some of those galaxies we're using to measure the expansion

635
00:31:08,880 --> 00:31:11,680
Speaker 1: of the universe maybe where they're not where we think

636
00:31:11,680 --> 00:31:12,000
Speaker 1: they are.

637
00:31:12,120 --> 00:31:15,600
Speaker 2: I'm saying that we see faster expansion close by and

638
00:31:15,760 --> 00:31:19,240
Speaker 2: slower expansion further away, right, And we interpret that to

639
00:31:19,320 --> 00:31:22,400
Speaker 2: mean that there was slower expansion earlier in the universe,

640
00:31:22,720 --> 00:31:25,440
Speaker 2: and there's faster expansion later in the universe. So the

641
00:31:25,480 --> 00:31:28,600
Speaker 2: expansion is accelerating. But what if the universe is just

642
00:31:28,720 --> 00:31:31,400
Speaker 2: denser further away, and so it's not expanding as fast

643
00:31:31,440 --> 00:31:34,520
Speaker 2: because there's more gravity, it's holding stuff together. And so

644
00:31:34,640 --> 00:31:39,800
Speaker 2: what if we're confusing nearby faster expansion for expansion increasing

645
00:31:39,840 --> 00:31:42,920
Speaker 2: more recently, right, what if it's not increasing more recently.

646
00:31:42,960 --> 00:31:45,640
Speaker 2: It's just we're in a bubble that's expanding faster. If

647
00:31:45,640 --> 00:31:48,000
Speaker 2: you go further away from us in the universe, things

648
00:31:48,040 --> 00:31:51,040
Speaker 2: are expanding more slowly because the universe is denser there

649
00:31:51,080 --> 00:31:54,680
Speaker 2: there's more gravity to hold it together. So instead of saying, oh,

650
00:31:54,720 --> 00:31:59,000
Speaker 2: the universe was expanding slower further away, back further in time,

651
00:31:59,320 --> 00:32:03,200
Speaker 2: and it's expanding faster closer to us, more recently, what

652
00:32:03,280 --> 00:32:05,120
Speaker 2: if it's not a function of time, it's just a

653
00:32:05,160 --> 00:32:08,160
Speaker 2: function of space because we're in this bubble that happens

654
00:32:08,200 --> 00:32:11,320
Speaker 2: to be under dense and so has faster expansion because

655
00:32:11,320 --> 00:32:12,880
Speaker 2: it's less stuff to hold it together.

656
00:32:13,480 --> 00:32:18,720
Speaker 1: Who I feel like my mind is a void right now, Daniel.

657
00:32:19,120 --> 00:32:21,120
Speaker 2: Yeah, if you have more stuff in the universe, if

658
00:32:21,160 --> 00:32:24,480
Speaker 2: these more galaxies, for example, then there's more gravity to

659
00:32:24,520 --> 00:32:27,240
Speaker 2: battle against this expansion. Stuff stays closer together.

660
00:32:27,520 --> 00:32:29,479
Speaker 1: So there is still an expansion of the universe.

661
00:32:29,560 --> 00:32:31,600
Speaker 2: Yes, there would still be an expansion, but it wouldn't

662
00:32:31,600 --> 00:32:34,800
Speaker 2: be accelerating. It's just the expansion depends on how much

663
00:32:34,800 --> 00:32:36,880
Speaker 2: stuff you have around you, which makes perfect sense.

664
00:32:37,200 --> 00:32:39,080
Speaker 1: So you're saying that there is an expansion of the

665
00:32:39,200 --> 00:32:43,040
Speaker 1: universe that's still happening. Yeah, but you're saying, maybe, what

666
00:32:43,080 --> 00:32:46,360
Speaker 1: if it's maybe even and not accelerating. Maybe it's just

667
00:32:46,360 --> 00:32:49,920
Speaker 1: a constant, steady expansion of the universe, which would still

668
00:32:49,960 --> 00:32:50,840
Speaker 1: be a mystery. Though.

669
00:32:50,920 --> 00:32:53,000
Speaker 2: Right now, you can have the expansion of the universe

670
00:32:53,000 --> 00:32:56,040
Speaker 2: without any sort of like weird dark energy in the universe.

671
00:32:57,240 --> 00:32:59,960
Speaker 1: Okay, so then we are assuming still a steady expand

672
00:33:00,800 --> 00:33:04,520
Speaker 1: But you're saying that maybe the acceilerit that expansion looks

673
00:33:04,560 --> 00:33:08,240
Speaker 1: faster around us, even though it's not. It just looks faster.

674
00:33:08,720 --> 00:33:11,480
Speaker 2: It is faster around us. It's just that it's faster

675
00:33:11,480 --> 00:33:14,520
Speaker 2: around us because there isn't as much stuff, not because

676
00:33:14,520 --> 00:33:18,120
Speaker 2: the expansion is changing over time. There's less stuff near us,

677
00:33:18,240 --> 00:33:20,240
Speaker 2: and so there's less stuff to hold stuff together, and

678
00:33:20,280 --> 00:33:23,640
Speaker 2: so that's why it's expanding faster closer than further away.

679
00:33:23,800 --> 00:33:27,360
Speaker 1: Oh, because you're saying that gravity somehow affects the expansion

680
00:33:27,440 --> 00:33:27,840
Speaker 1: of space.

681
00:33:27,960 --> 00:33:30,760
Speaker 2: Absolutely, Yes, gravity holds stuff together. If there was more

682
00:33:30,840 --> 00:33:33,320
Speaker 2: stuff in the universe, then things expand more solely because

683
00:33:33,320 --> 00:33:34,520
Speaker 2: gravity is pulling on them.

684
00:33:34,600 --> 00:33:34,760
Speaker 4: Right.

685
00:33:35,160 --> 00:33:37,800
Speaker 1: Well, but space itself, it doesn't hold space together, or

686
00:33:37,800 --> 00:33:39,400
Speaker 1: does it. Is that what you're saying, that it somehow

687
00:33:39,480 --> 00:33:40,960
Speaker 1: holds space itself together?

688
00:33:41,160 --> 00:33:44,040
Speaker 2: Absolutely, the more stuff you have in the universe, the

689
00:33:44,120 --> 00:33:46,600
Speaker 2: slower things move apart from each other. Remember, we talk

690
00:33:46,640 --> 00:33:48,680
Speaker 2: about creating a new space, but really we're talking about

691
00:33:48,680 --> 00:33:52,840
Speaker 2: increasing the distance between galaxies, and that's all we can measure. Right,

692
00:33:52,880 --> 00:33:55,560
Speaker 2: Space itself is not something where you can measure distances

693
00:33:55,600 --> 00:33:58,640
Speaker 2: relative to space. It's always distance is measured between objects.

694
00:33:58,880 --> 00:34:02,240
Speaker 1: The things are being held together because in the same

695
00:34:02,240 --> 00:34:04,640
Speaker 1: way that I'm being held together with the Earth. Or

696
00:34:04,720 --> 00:34:10,279
Speaker 1: are we talking about some you know, relativistic or something something.

697
00:34:11,000 --> 00:34:12,879
Speaker 2: No, the first way. Yeah, the same way that you're

698
00:34:12,920 --> 00:34:14,120
Speaker 2: being held near the Earth.

699
00:34:14,600 --> 00:34:16,560
Speaker 1: Oh okay, but I always thought that, like I'm being

700
00:34:16,560 --> 00:34:18,880
Speaker 1: held to Earth, and so I'm not expanding away from

701
00:34:18,880 --> 00:34:21,279
Speaker 1: the Earth, but the space that we're both sitting in

702
00:34:21,480 --> 00:34:22,160
Speaker 1: is expanding.

703
00:34:22,440 --> 00:34:25,319
Speaker 2: Yeah, there's two effects happening there, right, Gravity is holding

704
00:34:25,400 --> 00:34:28,279
Speaker 2: you together, and dark energy is expanding that space. But

705
00:34:28,400 --> 00:34:32,839
Speaker 2: gravity winds because gravity is much more powerful over great distances,

706
00:34:33,160 --> 00:34:36,040
Speaker 2: Gravity weakens, right, and you can't hold things together, so

707
00:34:36,120 --> 00:34:37,200
Speaker 2: dark energy takes over.

708
00:34:37,520 --> 00:34:39,399
Speaker 1: Right, But like right here on Earth, I'm sitting here

709
00:34:39,400 --> 00:34:41,080
Speaker 1: on Earth and being held together on Earth. I'm not

710
00:34:41,080 --> 00:34:43,800
Speaker 1: expanding away from the Earth, but sort of like somebody's

711
00:34:43,840 --> 00:34:46,160
Speaker 1: moving the chair under me or somebody's stretching the rug

712
00:34:46,239 --> 00:34:49,200
Speaker 1: under me, the space we're sitting in is expanding, isn't it.

713
00:34:49,440 --> 00:34:50,920
Speaker 2: Yeah that's a helpful way to think about it, but

714
00:34:51,239 --> 00:34:54,279
Speaker 2: it can also be misleading, right, Like, really, what we're

715
00:34:54,280 --> 00:34:56,960
Speaker 2: saying there is if you deleted the Earth and replaced

716
00:34:56,960 --> 00:35:00,359
Speaker 2: it with like a point particle proton, for example, dark

717
00:35:00,440 --> 00:35:03,080
Speaker 2: energy be increasing the space between you and that point

718
00:35:03,120 --> 00:35:07,160
Speaker 2: particle that proton. Yes, absolutely, because there is dark energy everywhere.

719
00:35:07,200 --> 00:35:10,120
Speaker 2: That's the point of that comparison. But these are like

720
00:35:10,160 --> 00:35:12,319
Speaker 2: two things happening in the equations at the same time.

721
00:35:12,400 --> 00:35:15,279
Speaker 2: The net effect, because gravity dominates, is that you and

722
00:35:15,360 --> 00:35:17,800
Speaker 2: the Earth stay close to each other. You can't really

723
00:35:17,840 --> 00:35:21,080
Speaker 2: separate them out and say they're both simultaneously happening. It's

724
00:35:21,160 --> 00:35:24,400
Speaker 2: like two force vectors that you add together. If you

725
00:35:24,400 --> 00:35:26,200
Speaker 2: have a huge amount of force on an object from

726
00:35:26,200 --> 00:35:29,600
Speaker 2: two directions, it adds up to zero force, right this

727
00:35:29,840 --> 00:35:32,080
Speaker 2: net zero force. You can talk about what would happen

728
00:35:32,120 --> 00:35:33,719
Speaker 2: if you were removed one, or you could talk about

729
00:35:33,719 --> 00:35:36,239
Speaker 2: what happened if you remove the other, but you can't

730
00:35:36,280 --> 00:35:38,879
Speaker 2: really say that there's any force on that object because

731
00:35:38,920 --> 00:35:41,120
Speaker 2: they balance each other out in the same way. Dark

732
00:35:41,200 --> 00:35:44,200
Speaker 2: energy tends to push things apart and curvature tends to

733
00:35:44,200 --> 00:35:46,600
Speaker 2: pull things together. So you could talk about what would

734
00:35:46,600 --> 00:35:49,000
Speaker 2: happen if you only had one or the other, but

735
00:35:49,160 --> 00:35:51,719
Speaker 2: really what's happening to you is a combination of the two.

736
00:35:52,280 --> 00:35:54,879
Speaker 1: All right, So then the idea is that maybe we're

737
00:35:54,920 --> 00:35:58,120
Speaker 1: wrong that the universe is expanding faster and faster. It's

738
00:35:58,280 --> 00:36:01,120
Speaker 1: just sort of looks like it because things are denser

739
00:36:01,160 --> 00:36:04,440
Speaker 1: out there, and so they're moving apart from each other less.

740
00:36:05,000 --> 00:36:08,280
Speaker 2: Yeah, exactly. So as we look further into the universe,

741
00:36:08,640 --> 00:36:12,600
Speaker 2: which is further back in time, we see less expansion.

742
00:36:12,960 --> 00:36:15,919
Speaker 2: But maybe that expansion isn't changing with time, maybe it's

743
00:36:16,000 --> 00:36:20,319
Speaker 2: fixed with time, but it's happening less further away than

744
00:36:20,440 --> 00:36:23,680
Speaker 2: closer by because there's more stuff further away. Maybe we

745
00:36:23,800 --> 00:36:26,720
Speaker 2: happen to be in some huge bubble where the stuff

746
00:36:26,760 --> 00:36:29,880
Speaker 2: near us is under dance. This less stuff in our bubble,

747
00:36:29,880 --> 00:36:33,080
Speaker 2: and so things can expand further and further away because

748
00:36:33,200 --> 00:36:36,360
Speaker 2: there's less mass to sort of counteract that expansion.

749
00:36:36,600 --> 00:36:38,880
Speaker 1: I guess what's confusing me is that if it's denser

750
00:36:39,040 --> 00:36:42,640
Speaker 1: out there in the far reaches of space, things are

751
00:36:42,640 --> 00:36:45,719
Speaker 1: being held together there. But wouldn't I still see an

752
00:36:45,719 --> 00:36:49,799
Speaker 1: acceleration or not an acceleration from relative to me.

753
00:36:50,239 --> 00:36:52,360
Speaker 2: An acceleration of the expansion.

754
00:36:52,680 --> 00:36:54,640
Speaker 1: Yeah, Like I always thought that the acceleration of the

755
00:36:54,680 --> 00:36:59,600
Speaker 1: expansion is because like, the thing I see really far

756
00:36:59,640 --> 00:37:03,000
Speaker 1: away is moving away from me slower than the things

757
00:37:03,000 --> 00:37:03,920
Speaker 1: that are closer to me.

758
00:37:04,320 --> 00:37:07,960
Speaker 2: Yeah, that's exactly right. But maybe the reason things are

759
00:37:08,040 --> 00:37:11,640
Speaker 2: moving away from you. Closer is because of an under density,

760
00:37:11,760 --> 00:37:14,880
Speaker 2: not because of a change in the expansion over time. Right,

761
00:37:14,960 --> 00:37:17,839
Speaker 2: Maybe everything has the same expansion over time. The things

762
00:37:17,840 --> 00:37:20,560
Speaker 2: that are farther away have a smaller expansion because of

763
00:37:20,560 --> 00:37:23,600
Speaker 2: the conditions over there, not because of some change in

764
00:37:23,640 --> 00:37:24,800
Speaker 2: the universe over time.

765
00:37:25,080 --> 00:37:25,239
Speaker 5: Right.

766
00:37:25,280 --> 00:37:27,200
Speaker 2: We can only see this one slice of the universe

767
00:37:27,239 --> 00:37:29,600
Speaker 2: in space and time. We can look further back in time.

768
00:37:29,680 --> 00:37:32,319
Speaker 2: We can see the universe really far away as it

769
00:37:32,400 --> 00:37:34,880
Speaker 2: was a long time ago, and we don't know what

770
00:37:35,040 --> 00:37:37,440
Speaker 2: is that part of the universe like now, And so

771
00:37:37,680 --> 00:37:39,879
Speaker 2: we see this one particular slice where we can see

772
00:37:39,880 --> 00:37:42,959
Speaker 2: close by stuff recently and far away stuff a long

773
00:37:43,000 --> 00:37:45,800
Speaker 2: time ago. So it's hard to tell the difference between

774
00:37:45,800 --> 00:37:48,640
Speaker 2: things that change over space and things that change over time.

775
00:37:49,200 --> 00:37:51,400
Speaker 2: And we see a change in that story, and we

776
00:37:51,440 --> 00:37:53,399
Speaker 2: interpret that as a change over time, but it could

777
00:37:53,400 --> 00:37:55,880
Speaker 2: be that it's the same over time. It's just changing over.

778
00:37:55,760 --> 00:37:59,759
Speaker 1: Space, meaning that we are measurements of the distance of

779
00:37:59,760 --> 00:38:01,800
Speaker 1: those things. How far away they are from us or

780
00:38:01,880 --> 00:38:03,520
Speaker 1: from each other is wrong.

781
00:38:03,560 --> 00:38:06,480
Speaker 2: How far away they are from us? Yeah, imagine you

782
00:38:06,520 --> 00:38:09,200
Speaker 2: looked out into the universe and you saw that aliens

783
00:38:09,239 --> 00:38:12,600
Speaker 2: on nearby planets were all eating white chocolate, and as

784
00:38:12,600 --> 00:38:15,400
Speaker 2: you look deeper and deeper in the universe, you discovered, oh,

785
00:38:15,400 --> 00:38:18,080
Speaker 2: they're all eating dark chocolate. And you say, well, oh, well,

786
00:38:18,200 --> 00:38:21,239
Speaker 2: that's older information. The dark chocolate information has taken a

787
00:38:21,280 --> 00:38:24,320
Speaker 2: long time to get here, and so maybe what's happened

788
00:38:24,360 --> 00:38:26,800
Speaker 2: over time is that everybody switched from dark chocolate to

789
00:38:26,840 --> 00:38:30,400
Speaker 2: white chocolate. And that explains why my older observations from

790
00:38:30,520 --> 00:38:33,560
Speaker 2: distant galaxies the aliens are eating dark chocolate, and my

791
00:38:34,000 --> 00:38:37,520
Speaker 2: recent observations from nearby galaxies the aliens are eating white chocolate.

792
00:38:37,840 --> 00:38:40,520
Speaker 2: And then another scientist goes, no, no, no, maybe they

793
00:38:40,600 --> 00:38:42,920
Speaker 2: just prefer dark chocolate out there and the deep reaches

794
00:38:42,960 --> 00:38:44,960
Speaker 2: of space, and we live in a white chocolate bubble

795
00:38:44,960 --> 00:38:48,000
Speaker 2: where everybody seems to eat white chocolate. Those two explanations

796
00:38:48,080 --> 00:38:50,680
Speaker 2: both work. One is a change over space, the other

797
00:38:50,760 --> 00:38:52,719
Speaker 2: is a change over time, and we can't tell the

798
00:38:52,760 --> 00:38:56,000
Speaker 2: difference because we have this one set of observations linked

799
00:38:56,000 --> 00:38:56,879
Speaker 2: in space and time.

800
00:38:57,640 --> 00:39:00,960
Speaker 1: I'm not sure adding flavor to the this is helping.

801
00:39:02,320 --> 00:39:05,000
Speaker 1: So then you're saying, like, maybe what's explaining dark energy

802
00:39:05,160 --> 00:39:07,520
Speaker 1: is that there's more stuff in the periphery of the

803
00:39:07,560 --> 00:39:10,040
Speaker 1: universe there's more stuff in the perimeter of our vision

804
00:39:10,960 --> 00:39:14,160
Speaker 1: or of what we can see. Yeah, exactly, but still

805
00:39:14,200 --> 00:39:15,480
Speaker 1: within the observable universe.

806
00:39:15,480 --> 00:39:18,520
Speaker 2: Still within the observable universe. Yes, of course this is

807
00:39:18,520 --> 00:39:20,840
Speaker 2: a big idea, and if it's true, you have to

808
00:39:20,840 --> 00:39:23,160
Speaker 2: make sense of it and why we would be living

809
00:39:23,160 --> 00:39:24,879
Speaker 2: in the middle of this big void and what else

810
00:39:24,880 --> 00:39:27,000
Speaker 2: it would mean. And there's lots of ways we can

811
00:39:27,120 --> 00:39:27,880
Speaker 2: check this idea.

812
00:39:28,400 --> 00:39:31,240
Speaker 1: All right, Well, let's dig into how we're testing this idea.

813
00:39:31,719 --> 00:39:34,000
Speaker 1: Is it a stretch or is it a whole bunch

814
00:39:34,040 --> 00:39:36,560
Speaker 1: of nothing as well? So let's dig into that. But

815
00:39:36,600 --> 00:39:52,240
Speaker 1: first let's take another quick break. All right, we're talking

816
00:39:52,320 --> 00:39:55,719
Speaker 1: about nothing, Dan, Is this like the Seinfeld episode of

817
00:39:55,760 --> 00:39:57,920
Speaker 1: the podcast? Just about nothing?

818
00:40:00,040 --> 00:40:02,120
Speaker 2: Long as that can be Sifeld instead of George.

819
00:40:01,760 --> 00:40:05,640
Speaker 1: Than sure, YadA YadA, YadA the universe.

820
00:40:07,360 --> 00:40:09,160
Speaker 2: Or maybe I should be Kramer. I don't know, as

821
00:40:09,200 --> 00:40:11,080
Speaker 2: long as I'm not Newman, oh Man.

822
00:40:12,480 --> 00:40:14,680
Speaker 1: I want to be Lean. She's the coolest one.

823
00:40:15,640 --> 00:40:19,319
Speaker 2: She definitely is. It is a really fun idea, and

824
00:40:19,360 --> 00:40:22,759
Speaker 2: it's always cool to think about how your conception of

825
00:40:22,840 --> 00:40:26,239
Speaker 2: the universe could be totally different from what everybody's been imagining.

826
00:40:26,320 --> 00:40:30,000
Speaker 2: Right the biggest ideas are the sexiest because they also

827
00:40:30,040 --> 00:40:32,640
Speaker 2: give you those moments you're like, Wow, the universe is

828
00:40:32,680 --> 00:40:35,279
Speaker 2: this way and not some other way. And this would

829
00:40:35,280 --> 00:40:37,600
Speaker 2: be a pretty big idea. I mean, this would be

830
00:40:37,640 --> 00:40:42,680
Speaker 2: putting our galaxy near the center of an enormous cosmic

831
00:40:42,760 --> 00:40:46,400
Speaker 2: feature in order to explain the redshifts that we are seeing.

832
00:40:46,480 --> 00:40:49,040
Speaker 2: To fit this to the data, you have to have

833
00:40:49,239 --> 00:40:54,080
Speaker 2: a big void, something that's three billion light years in

834
00:40:54,280 --> 00:40:56,320
Speaker 2: radius a giga parsec.

835
00:40:57,000 --> 00:40:58,920
Speaker 1: And that's the only way this works. Or what does

836
00:40:58,960 --> 00:40:59,279
Speaker 1: that mean?

837
00:40:59,440 --> 00:41:00,720
Speaker 2: That's the only way this works.

838
00:41:00,960 --> 00:41:04,440
Speaker 1: See only nothing explanation that fits what we currently see.

839
00:41:04,920 --> 00:41:07,080
Speaker 2: Yeah, because when we look out into the universe, we

840
00:41:07,120 --> 00:41:10,560
Speaker 2: see the sort of same history in every direction. Right,

841
00:41:10,640 --> 00:41:13,920
Speaker 2: So if you look one direction, you see things closer

842
00:41:14,000 --> 00:41:17,120
Speaker 2: by expanding more quickly than things further away. If you

843
00:41:17,160 --> 00:41:20,880
Speaker 2: look in another direction, another direction, another direction, it's very isotropic.

844
00:41:21,400 --> 00:41:24,120
Speaker 2: And so to explain that by like a coincidence of

845
00:41:24,200 --> 00:41:27,440
Speaker 2: the density, you need the universe to be more dense

846
00:41:27,800 --> 00:41:31,680
Speaker 2: basically in every direction, which requires a huge void, and

847
00:41:31,800 --> 00:41:34,160
Speaker 2: it requires us to be at the center of it,

848
00:41:34,560 --> 00:41:37,640
Speaker 2: and it requires that void to be basically spherical, So

849
00:41:37,680 --> 00:41:40,319
Speaker 2: you have the same weird density as a function of

850
00:41:40,360 --> 00:41:45,359
Speaker 2: distance effect in every direction, and so yeah, that's kind

851
00:41:45,360 --> 00:41:47,880
Speaker 2: of a big cosmic coincidence if it's.

852
00:41:47,760 --> 00:41:50,719
Speaker 1: True, meaning like we're right smack in the middle of

853
00:41:50,760 --> 00:41:51,760
Speaker 1: this giant void.

854
00:41:52,320 --> 00:41:54,560
Speaker 2: Yeah, and like it doesn't have to be exactly in

855
00:41:54,600 --> 00:41:57,640
Speaker 2: the middle to within like a centimeter, but on cosmic

856
00:41:57,680 --> 00:41:59,680
Speaker 2: distance scales, we'd have to be very close to the

857
00:41:59,680 --> 00:42:03,239
Speaker 2: center because we've measured this expansion effect in lots of

858
00:42:03,239 --> 00:42:06,400
Speaker 2: different directions and it seems the same in every direction.

859
00:42:06,480 --> 00:42:08,520
Speaker 2: So yeah, we'd have to be at the center of it.

860
00:42:08,960 --> 00:42:12,960
Speaker 2: And this really violates this Copernican principle, this idea that

861
00:42:13,040 --> 00:42:16,719
Speaker 2: like the universe is basically the same everywhere, and like, yeah,

862
00:42:16,719 --> 00:42:19,680
Speaker 2: there's a little bit of clumpiness, but there's no huge

863
00:42:19,719 --> 00:42:23,200
Speaker 2: features that make this neighborhood totally different from that neighborhood.

864
00:42:23,719 --> 00:42:25,840
Speaker 2: And you know that's not something we know, it's just

865
00:42:25,880 --> 00:42:28,680
Speaker 2: something we've assumed. It makes sense, it fits with the

866
00:42:28,719 --> 00:42:31,560
Speaker 2: way we like to think about the universe. Until nature

867
00:42:31,600 --> 00:42:33,480
Speaker 2: shows us that it's not true. We're kind of going

868
00:42:33,560 --> 00:42:35,720
Speaker 2: to go with it because we like the idea doesn't

869
00:42:35,760 --> 00:42:37,440
Speaker 2: mean that it is true, right, It doesn't mean that

870
00:42:37,480 --> 00:42:39,440
Speaker 2: the universe has to be the same everywhere.

871
00:42:39,800 --> 00:42:41,880
Speaker 1: I guess you know. What's confusing me is like, couldn't

872
00:42:41,880 --> 00:42:43,960
Speaker 1: we tell if we were in a void, Like you know,

873
00:42:44,040 --> 00:42:47,080
Speaker 1: we can look with our telescopes and we can see

874
00:42:47,120 --> 00:42:49,800
Speaker 1: galaxies all the way out to the observable universe. Wouldn't

875
00:42:49,800 --> 00:42:52,440
Speaker 1: we have noticed by now that there are more of

876
00:42:52,480 --> 00:42:55,480
Speaker 1: them further away than what we can see close to us.

877
00:42:55,600 --> 00:42:59,040
Speaker 2: Yeah, absolutely, we could tell if we had seen all

878
00:42:59,080 --> 00:43:02,360
Speaker 2: the galaxies out there and map the density. But you know,

879
00:43:02,480 --> 00:43:05,400
Speaker 2: things that are really far away are hard to see.

880
00:43:05,760 --> 00:43:07,799
Speaker 2: In order to see things super duper far away, you

881
00:43:07,800 --> 00:43:09,960
Speaker 2: have to point a very powerful telescope at them, and

882
00:43:10,040 --> 00:43:12,840
Speaker 2: you have to look for a while because these galaxies

883
00:43:12,880 --> 00:43:15,840
Speaker 2: are very very dim and they're very very red shifted.

884
00:43:16,440 --> 00:43:18,000
Speaker 2: So we have a telescope that can do that, Like

885
00:43:18,120 --> 00:43:21,520
Speaker 2: James Web has been breaking records and seeing galaxies really

886
00:43:21,560 --> 00:43:24,279
Speaker 2: really far away into the early universe. But James Web

887
00:43:24,360 --> 00:43:26,480
Speaker 2: is very expensive, and we have one of it, and

888
00:43:26,520 --> 00:43:28,680
Speaker 2: it can only point in some directions at a time,

889
00:43:28,760 --> 00:43:31,719
Speaker 2: and space is extraordinarily vast. The number of galaxies we're

890
00:43:31,760 --> 00:43:34,920
Speaker 2: talking about are huge, so we basically just haven't really

891
00:43:34,920 --> 00:43:38,239
Speaker 2: looked far enough like we've seen nearby stuff. And we'd

892
00:43:38,280 --> 00:43:39,680
Speaker 2: like to think that we've seen to the edge of

893
00:43:39,680 --> 00:43:42,359
Speaker 2: the observable universe. We only have really done that in

894
00:43:42,400 --> 00:43:46,200
Speaker 2: a few tiny directions, and so like our detailed three

895
00:43:46,280 --> 00:43:48,759
Speaker 2: D map of the universe definitely does not extend all

896
00:43:48,800 --> 00:43:51,239
Speaker 2: the way out to the observable universe. There are lots

897
00:43:51,239 --> 00:43:53,280
Speaker 2: of places out there where it's very fuzzy.

898
00:43:53,800 --> 00:43:55,840
Speaker 1: But I guess you wouldn't need to see all of

899
00:43:55,840 --> 00:43:58,200
Speaker 1: the universe. You just need to see whether things are

900
00:43:58,200 --> 00:44:00,840
Speaker 1: dense or out there near the edge of the abstorbable

901
00:44:00,920 --> 00:44:03,799
Speaker 1: universe than they are here. Isn't that sort of a

902
00:44:04,440 --> 00:44:05,120
Speaker 1: easy check?

903
00:44:07,080 --> 00:44:09,319
Speaker 2: Well, we don't see any evidence of that, right, But

904
00:44:09,360 --> 00:44:12,160
Speaker 2: they could still make the data fit. Because our observations

905
00:44:12,200 --> 00:44:14,920
Speaker 2: are still limited. They can make this data fit. And

906
00:44:14,960 --> 00:44:16,920
Speaker 2: so you can come up with a theory of the

907
00:44:17,000 --> 00:44:21,160
Speaker 2: universe that respects general relativity and describes all of the

908
00:44:21,200 --> 00:44:24,839
Speaker 2: redshifts that we see from type one A supernova and

909
00:44:25,040 --> 00:44:29,800
Speaker 2: our observations of galaxy density so far, and doesn't require

910
00:44:29,880 --> 00:44:32,360
Speaker 2: any dark energy. But it does require this sort of

911
00:44:32,520 --> 00:44:35,320
Speaker 2: like bubble where the density of the universe is smaller

912
00:44:35,560 --> 00:44:37,960
Speaker 2: in her neighborhood. But you can still do that and

913
00:44:38,040 --> 00:44:40,719
Speaker 2: be consistent with all of these observations. I know that

914
00:44:40,800 --> 00:44:41,520
Speaker 2: sounds crazy.

915
00:44:41,600 --> 00:44:43,440
Speaker 1: Oh, I see what you're saying. You're saying like maybe

916
00:44:44,000 --> 00:44:46,480
Speaker 1: it could be that all of are checks of the

917
00:44:46,520 --> 00:44:49,560
Speaker 1: density of the universe out there where somehow we just

918
00:44:49,600 --> 00:44:52,960
Speaker 1: looked in the wrong places kind of, So what you're saying.

919
00:44:52,840 --> 00:44:55,359
Speaker 2: Kind of and I think probably people overestimate how much

920
00:44:55,400 --> 00:44:58,480
Speaker 2: we've looked into the deep universe. We really don't have

921
00:44:58,560 --> 00:45:01,520
Speaker 2: that much data. So it's not that hard to squeak

922
00:45:01,560 --> 00:45:03,840
Speaker 2: it a little bit and still be consistent with the

923
00:45:03,880 --> 00:45:07,120
Speaker 2: deep images of the distant universe, because those are pretty rare.

924
00:45:07,200 --> 00:45:09,160
Speaker 2: But there are other ways that we could tell whether

925
00:45:09,239 --> 00:45:11,560
Speaker 2: we were in a bubble. There are other impacts this

926
00:45:11,640 --> 00:45:14,160
Speaker 2: theory has on things that we can measure much more

927
00:45:14,200 --> 00:45:18,000
Speaker 2: precisely than just like actually looking and measuring the density.

928
00:45:18,600 --> 00:45:21,560
Speaker 2: This idea has consequences for other things that we have

929
00:45:21,680 --> 00:45:22,920
Speaker 2: very sensitive probes for.

930
00:45:23,239 --> 00:45:25,120
Speaker 1: All Right, what are some of those ways.

931
00:45:25,160 --> 00:45:28,400
Speaker 2: Well, maybe the most powerful is the cosmic microwave background radiation.

932
00:45:28,920 --> 00:45:30,920
Speaker 2: Like we look at the structure of the universe. Now,

933
00:45:30,920 --> 00:45:33,319
Speaker 2: as you're saying, how much density is there? Where are

934
00:45:33,400 --> 00:45:36,479
Speaker 2: the galaxies? But all that structure is seeded in little

935
00:45:36,560 --> 00:45:40,040
Speaker 2: density fluctuations from the early universe. Right. The whole reason

936
00:45:40,080 --> 00:45:42,200
Speaker 2: we have structure, the reason we have a galaxy here

937
00:45:42,239 --> 00:45:44,640
Speaker 2: and not a galaxy there, is because in the early

938
00:45:44,719 --> 00:45:46,880
Speaker 2: universe there was a little spot that was the denser,

939
00:45:46,880 --> 00:45:50,200
Speaker 2: and gravity gathered stuff together to make galaxies, for example.

940
00:45:50,600 --> 00:45:52,960
Speaker 2: So we can predict how stuff should be distributed in

941
00:45:52,960 --> 00:45:56,640
Speaker 2: the universe today based on those fluctuations in the cosmic

942
00:45:56,680 --> 00:45:59,720
Speaker 2: microwave background radiation. That light from the very early universe,

943
00:46:00,560 --> 00:46:02,759
Speaker 2: and that life from the very early universe is very,

944
00:46:02,840 --> 00:46:03,480
Speaker 2: very smooth.

945
00:46:03,920 --> 00:46:04,120
Speaker 3: Right.

946
00:46:04,200 --> 00:46:06,880
Speaker 2: It tells us that there should be no huge features.

947
00:46:07,280 --> 00:46:10,640
Speaker 2: It tells us exactly how big those density fluctuations should be,

948
00:46:11,120 --> 00:46:13,600
Speaker 2: and it lines up with what we see. Right. The

949
00:46:13,640 --> 00:46:16,480
Speaker 2: stuff we see in the universe, both close and far away,

950
00:46:16,880 --> 00:46:20,560
Speaker 2: has just about the right density fluctuations, meaning like galaxies

951
00:46:20,560 --> 00:46:24,400
Speaker 2: and clumps of galaxies and actually big voids between those galaxies.

952
00:46:24,680 --> 00:46:28,520
Speaker 2: We have seen huge voids between clusters of galaxies, not

953
00:46:28,560 --> 00:46:30,920
Speaker 2: as big as the one this requires, but there are

954
00:46:31,000 --> 00:46:33,200
Speaker 2: big voids out there in space, and all that is

955
00:46:33,200 --> 00:46:37,040
Speaker 2: perfectly described by the cosmic microwave background radiation. And a

956
00:46:37,160 --> 00:46:39,839
Speaker 2: huge megavoid that we're at the center of is not

957
00:46:40,000 --> 00:46:43,279
Speaker 2: consistent with what we see in the CMB. There's no

958
00:46:43,400 --> 00:46:46,640
Speaker 2: fluctuations in it that would give such an enormous.

959
00:46:46,239 --> 00:46:49,920
Speaker 1: Feature, Like you don't see other voids in the cosmic

960
00:46:50,080 --> 00:46:53,520
Speaker 1: microwrate background. But would you see this void, this potential

961
00:46:53,640 --> 00:46:56,480
Speaker 1: giant void we're in in the cosmic micro rate background

962
00:46:56,560 --> 00:46:59,000
Speaker 1: or does it tell you that there isn't avoid the.

963
00:46:58,960 --> 00:47:01,160
Speaker 2: Cosmic microwave background tells you that there should be no

964
00:47:01,400 --> 00:47:04,600
Speaker 2: huge void, and it does predict other voids. It does

965
00:47:04,680 --> 00:47:07,319
Speaker 2: predict that we should see big gaps between galaxies, and

966
00:47:07,360 --> 00:47:10,200
Speaker 2: we see those and we measure those, but it suggests

967
00:47:10,200 --> 00:47:13,480
Speaker 2: that you should not get voids this big. Right. Basically,

968
00:47:13,680 --> 00:47:16,759
Speaker 2: the size of the wiggles in the early universe limits

969
00:47:17,000 --> 00:47:20,520
Speaker 2: how big the features can be in our current universe. Right,

970
00:47:20,560 --> 00:47:23,400
Speaker 2: you'd need huge wiggles in the CMB to make huge

971
00:47:23,440 --> 00:47:26,640
Speaker 2: wiggles now. We only see small wiggles in the early universe,

972
00:47:26,880 --> 00:47:29,680
Speaker 2: So we should only have small voids in small clumps now,

973
00:47:29,719 --> 00:47:31,280
Speaker 2: And that's basically what we see.

974
00:47:31,560 --> 00:47:33,840
Speaker 1: Wait, it tells you that it's impossible or does it

975
00:47:33,880 --> 00:47:35,840
Speaker 1: tell you that it's rare for us to be in

976
00:47:35,880 --> 00:47:36,879
Speaker 1: a huge void like that?

977
00:47:37,080 --> 00:47:39,160
Speaker 2: I think technically it tells you that it's very very

978
00:47:39,480 --> 00:47:43,279
Speaker 2: unlikely because the light we're seeing from the CMB is

979
00:47:43,440 --> 00:47:46,239
Speaker 2: not the light from the plasma that was here that

980
00:47:46,360 --> 00:47:49,400
Speaker 2: formed our structures. It's the light from the plasma that

981
00:47:49,480 --> 00:47:51,680
Speaker 2: was very far away, and it's been traveling to us

982
00:47:51,840 --> 00:47:54,560
Speaker 2: the whole history of the universe. So we're not actually

983
00:47:54,560 --> 00:47:57,480
Speaker 2: seeing the patterns that led to the formation of our structure.

984
00:47:57,840 --> 00:48:00,400
Speaker 2: We're seeing the patterns that led to the formations structure

985
00:48:00,400 --> 00:48:03,640
Speaker 2: that's very far away now, and so we can't actually

986
00:48:03,680 --> 00:48:06,440
Speaker 2: see like the blueprints that led to our structure. We

987
00:48:06,480 --> 00:48:08,640
Speaker 2: can just see the blueprints that led to other structure,

988
00:48:08,880 --> 00:48:11,760
Speaker 2: and we see nothing like that anywhere else in the universe,

989
00:48:11,800 --> 00:48:14,160
Speaker 2: and so it'd be very unlikely for that to happen

990
00:48:14,200 --> 00:48:17,000
Speaker 2: here if it's never happened anywhere else in the universe.

991
00:48:17,719 --> 00:48:19,319
Speaker 2: So that's sort of the argument.

992
00:48:19,440 --> 00:48:24,319
Speaker 1: M all right, So the CMB says probably not.

993
00:48:24,960 --> 00:48:27,319
Speaker 2: Yeah, And there's another argument, which has to do with

994
00:48:27,560 --> 00:48:31,360
Speaker 2: how elements are made. The early universe was very very dense,

995
00:48:31,600 --> 00:48:35,360
Speaker 2: dense enough briefly to cause nuclear fusion to make protons

996
00:48:35,400 --> 00:48:38,160
Speaker 2: and for some of those protons to make helium, and

997
00:48:38,200 --> 00:48:41,240
Speaker 2: the density of that really determines what elements were made.

998
00:48:41,640 --> 00:48:44,000
Speaker 2: We have a very good understanding of how that works,

999
00:48:44,080 --> 00:48:45,640
Speaker 2: and if it lines up very very well with what

1000
00:48:45,680 --> 00:48:47,640
Speaker 2: we see out there in the universe, how much helium

1001
00:48:47,640 --> 00:48:50,640
Speaker 2: and hydrogen and lithium there was made during the Big Bang.

1002
00:48:50,680 --> 00:48:54,400
Speaker 2: This whole field is called Big Bang nucleosynthesis. And so

1003
00:48:54,480 --> 00:48:57,239
Speaker 2: that's a very sensitive probe of the density of the

1004
00:48:57,320 --> 00:49:00,799
Speaker 2: early universe in our neighborhood. And so if we got

1005
00:49:00,800 --> 00:49:03,760
Speaker 2: that wrong somehow, if the universe weirdly was under dense

1006
00:49:03,800 --> 00:49:06,320
Speaker 2: in our region, you would see that in the amount

1007
00:49:06,360 --> 00:49:08,680
Speaker 2: of helium made in the Big Bang, and we don't,

1008
00:49:09,320 --> 00:49:13,280
Speaker 2: and so that's pretty hard to reconcile with what we see. Also,

1009
00:49:13,400 --> 00:49:17,480
Speaker 2: we've more recently measured a lot more Type one A supernova.

1010
00:49:17,560 --> 00:49:20,440
Speaker 2: This idea of the big void was very popular, like

1011
00:49:20,520 --> 00:49:24,000
Speaker 2: maybe ten years ago, when we had many fewer measurements

1012
00:49:24,040 --> 00:49:26,200
Speaker 2: of the supernova and there were some gaps, and so

1013
00:49:26,239 --> 00:49:28,040
Speaker 2: it was easier to sort of like fit this to

1014
00:49:28,080 --> 00:49:31,360
Speaker 2: the data. But more recent measurements by the Slowing Digital

1015
00:49:31,400 --> 00:49:34,440
Speaker 2: Sky Survey, for example, make it much harder to explain

1016
00:49:34,480 --> 00:49:37,240
Speaker 2: the red shifts using this sort of like weird void

1017
00:49:37,280 --> 00:49:38,040
Speaker 2: bubble thing.

1018
00:49:38,320 --> 00:49:41,320
Speaker 1: Meaning we have better data about where things are out there.

1019
00:49:41,239 --> 00:49:43,520
Speaker 2: Yeah, exactly. We sort of filled in some gaps by

1020
00:49:43,560 --> 00:49:46,640
Speaker 2: taking more and more measurements of type one A supernova,

1021
00:49:46,719 --> 00:49:49,400
Speaker 2: and that makes it harder and harder to even explain

1022
00:49:49,600 --> 00:49:51,239
Speaker 2: the red shifts using this.

1023
00:49:51,239 --> 00:49:54,200
Speaker 1: Void meaning we're more confident that things are not dens

1024
00:49:54,280 --> 00:49:56,880
Speaker 1: or out there, yeah, or we're just more confident by

1025
00:49:56,880 --> 00:49:57,520
Speaker 1: where things are.

1026
00:49:57,680 --> 00:49:59,799
Speaker 2: We're more confident about where things are, and that makes

1027
00:49:59,800 --> 00:50:02,440
Speaker 2: it harder to come up with a consistent picture of

1028
00:50:02,560 --> 00:50:04,600
Speaker 2: us being at the center of a void as an

1029
00:50:04,640 --> 00:50:07,680
Speaker 2: alternative explanation for the redshifts that we're seeing. But you know,

1030
00:50:07,760 --> 00:50:10,040
Speaker 2: there's lots of remaining to be understood, Like some of

1031
00:50:10,040 --> 00:50:11,640
Speaker 2: the voids that are out there in space. We don't

1032
00:50:11,719 --> 00:50:14,279
Speaker 2: understand how they formed and how big they got. And

1033
00:50:14,320 --> 00:50:17,000
Speaker 2: there's still the hubble tension like the expansion of the universe.

1034
00:50:17,040 --> 00:50:20,040
Speaker 2: So it's not like the explanation we have is perfect.

1035
00:50:20,200 --> 00:50:22,040
Speaker 2: There's lots of holes in it, lots of things that

1036
00:50:22,080 --> 00:50:25,080
Speaker 2: still don't work, lots of opportunities for other ideas. But

1037
00:50:25,160 --> 00:50:28,040
Speaker 2: I think this void theory, as cool as it sounds,

1038
00:50:28,400 --> 00:50:31,880
Speaker 2: works less well than the current mainstream dark energy idea.

1039
00:50:31,920 --> 00:50:35,520
Speaker 1: This idea that there's this mysterious invisible energy that we

1040
00:50:35,840 --> 00:50:37,920
Speaker 1: can't explain either exactly.

1041
00:50:38,600 --> 00:50:40,120
Speaker 2: There's still a lot of work left to do to

1042
00:50:40,160 --> 00:50:42,319
Speaker 2: make that even like a coherent theory. But it's sort

1043
00:50:42,360 --> 00:50:44,080
Speaker 2: of like our best current idea.

1044
00:50:44,560 --> 00:50:44,719
Speaker 3: Hm.

1045
00:50:45,480 --> 00:50:47,640
Speaker 1: Well, I guess if it has so many counts against it,

1046
00:50:47,680 --> 00:50:49,880
Speaker 1: why are people even considering this? Why do we you

1047
00:50:49,880 --> 00:50:51,120
Speaker 1: just spend an hour talking about it.

1048
00:50:52,920 --> 00:50:55,440
Speaker 2: I think people are still considering other ideas because the

1049
00:50:55,440 --> 00:50:58,160
Speaker 2: whole concept of our dark energy does have flaws, and

1050
00:50:58,239 --> 00:51:01,440
Speaker 2: it is a big idea, And it's healthy to maintain

1051
00:51:01,880 --> 00:51:04,920
Speaker 2: different directions of research because we could run into a

1052
00:51:04,920 --> 00:51:07,719
Speaker 2: big problem. You know, in sketching out the details of

1053
00:51:07,760 --> 00:51:10,400
Speaker 2: dark energy, we could discover a fundamental flaw in the

1054
00:51:10,440 --> 00:51:12,240
Speaker 2: whole plan, so that doesn't hang together.

1055
00:51:12,800 --> 00:51:13,000
Speaker 5: You know.

1056
00:51:13,040 --> 00:51:14,600
Speaker 2: It's like when you build a house and you discover

1057
00:51:14,840 --> 00:51:16,840
Speaker 2: while the plumbing is just not going to fit with

1058
00:51:16,880 --> 00:51:18,759
Speaker 2: the electrical like, we got to go back to the

1059
00:51:18,840 --> 00:51:21,800
Speaker 2: drawing board. So it's important to keep your mind open

1060
00:51:21,880 --> 00:51:23,280
Speaker 2: and consider other ideas.

1061
00:51:23,560 --> 00:51:26,520
Speaker 1: Plus, it's fun, right, right, other ideas for other people

1062
00:51:26,560 --> 00:51:30,239
Speaker 1: to try to figure out their tree right exactly, just

1063
00:51:30,239 --> 00:51:30,520
Speaker 1: not you?

1064
00:51:30,719 --> 00:51:33,680
Speaker 2: Yeah, maybe I should You're done. Maybe I should just

1065
00:51:33,719 --> 00:51:36,000
Speaker 2: sit on the couch, eat chocolate and let somebody else

1066
00:51:36,000 --> 00:51:36,440
Speaker 2: figure it.

1067
00:51:36,360 --> 00:51:39,479
Speaker 1: Out, right, But dark chocolate or white chocolate? Any which

1068
00:51:39,480 --> 00:51:40,600
Speaker 1: part of the universe are you in?

1069
00:51:42,480 --> 00:51:44,480
Speaker 2: If our part of the universe is turning into white chocolate,

1070
00:51:44,520 --> 00:51:45,640
Speaker 2: then I'm thinking about moving.

1071
00:51:46,880 --> 00:51:49,920
Speaker 1: What sounds like you already gave up on the whole universe,

1072
00:51:49,960 --> 00:51:54,920
Speaker 1: so now you're just giving up on the local universe exactly.

1073
00:51:54,719 --> 00:51:55,040
Speaker 3: All right?

1074
00:51:55,080 --> 00:51:59,080
Speaker 1: Well, an interesting discussion about maybe the biggest mystery in

1075
00:51:59,120 --> 00:52:02,160
Speaker 1: the entire universe. What is dark energy? What's costing the

1076
00:52:02,239 --> 00:52:05,080
Speaker 1: universe to expand faster and faster. Is it just all

1077
00:52:05,120 --> 00:52:08,759
Speaker 1: a big illusion or is there really some sort of

1078
00:52:08,800 --> 00:52:10,320
Speaker 1: mysterious energy out there?

1079
00:52:10,480 --> 00:52:12,040
Speaker 2: Well, I think the theory of dark energy is on

1080
00:52:12,080 --> 00:52:14,760
Speaker 2: the right track. It's really important to think about other ideas,

1081
00:52:14,840 --> 00:52:17,480
Speaker 2: and it also helps us understand the strengths and the

1082
00:52:17,520 --> 00:52:20,360
Speaker 2: weaknesses of dark energy, what we do and what we

1083
00:52:20,440 --> 00:52:21,279
Speaker 2: don't really know.

1084
00:52:22,040 --> 00:52:24,640
Speaker 1: We hope you enjoyed that. Thanks for joining us. See

1085
00:52:24,680 --> 00:52:25,239
Speaker 1: you next time.

1086
00:52:30,000 --> 00:52:32,880
Speaker 2: For more science and curiosity. Come find us on social

1087
00:52:32,920 --> 00:52:37,400
Speaker 2: media where we answer questions and post videos. We're on Twitter, This, Org,

1088
00:52:37,520 --> 00:52:41,160
Speaker 2: Instant and now TikTok. Thanks for listening, and remember that

1089
00:52:41,280 --> 00:52:45,080
Speaker 2: Daniel and Jorge explain the universe is a production of iHeartRadio.

1090
00:52:45,400 --> 00:52:50,520
Speaker 2: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,

1091
00:52:50,680 --> 00:52:53,000
Speaker 2: or wherever you listen to your favorite shows.