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Speaker 3: Hey, Daniel, do you ever wonder if physics might be

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Speaker 3: like really wrong?

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Speaker 1: Are you talking about me or like the entire community?

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Speaker 3: Well, I know you're never wrong, Daniel, that's unthinkable, but

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Speaker 3: you know, like, has physics ever gotten something about the

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Speaker 3: very nature of the universe?

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Speaker 4: Kind of uh? Not right?

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Speaker 1: You mean, like what's the best snack food? Or what

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Speaker 1: colored lab coach should we wear?

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Speaker 4: Hey?

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Speaker 3: Yeah, you know, like can I eat antimatter or not?

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Speaker 3: Maybe it's delicious.

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Speaker 1: Physics could definitely be wrong about snack foods.

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Speaker 3: Well, I mean think bigger, Like, is it possible that

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Speaker 3: maybe things are not quite what they seem?

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Speaker 1: Well, it wouldn't be the first time physics is wrong,

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Speaker 1: and I hope it's not the last time.

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Speaker 3: I am Horhem, a cartoonist and the creator of PhD comics. Hi.

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Speaker 1: I'm Daniel. I'm a particle physicist, and I've never been

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Speaker 1: wrong about snack foods.

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Speaker 3: And I've never been wrong about being wrong, So I

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Speaker 3: think that means that I'm always wrong. I don't know,

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Speaker 3: but welcome to our podcast. I'm definitely right about that.

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Speaker 3: This is our podcast, Daniel and Jorge Explain the Universe,

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Speaker 3: a production of iHeartRadio.

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Speaker 1: That's right, our podcast in which we take a mental

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Speaker 1: tour of all the crazy stuff that's out there in

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Speaker 1: the universe and try to bring it into your head.

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Speaker 1: We try to wrap up the entire universe, all those

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Speaker 1: trillions and trillions of stars and weird blobs of gas

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Speaker 1: and dust and invisible stuff and insert it through a

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Speaker 1: little hole in your ear into your brain.

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Speaker 3: Yeah, all of the amazing and incredible stuff out there

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Speaker 3: in universe, and also all of the stuff that's normal.

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Speaker 3: You know, And sometimes I think when you examine what's

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Speaker 3: pearce to be normal in your everyday lives, it turns

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Speaker 3: out to have all kinds of wonders and all kinds

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Speaker 3: of small miracles in it.

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Speaker 1: Are there small miracles in your snack foods? Is that

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Speaker 1: what you're talking about?

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Speaker 5: Like?

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Speaker 1: Ooh, look, there's chocolate chips in this trail mix.

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Speaker 3: Every snack is a miracle, Daniel, especially banana's net.

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Speaker 1: But in this podcast, we go beyond the miracles of

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Speaker 1: banana based snack foods and talk about the incredible things

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Speaker 1: that scientists are trying to figure out, because contrary to

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Speaker 1: popular perceptions, scientists don't have it all figured out. There

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Speaker 1: are lots of really big mysteries out there, and wondering

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Speaker 1: about the universe is something that belongs to including you.

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Speaker 3: Yeah, so they're one of the biggest mysteries out there

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Speaker 3: in the universe. And literally is sort of like not

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Speaker 3: just like because we don't know it, but also because

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Speaker 3: it's a huge part of the universe.

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Speaker 4: Is dark matter?

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Speaker 3: Dark matter is a little bit crazy, right, It's like

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Speaker 3: twenty seven percent of the universe, but we have no

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Speaker 3: idea what it is.

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Speaker 1: That's right of the energy budget of the universe, it's

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Speaker 1: a pretty big slice. It's like a little bit more

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Speaker 1: than a quarter of all the energy in the universe.

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Speaker 1: Is this weird stuff and we've never seen it directly.

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Speaker 1: We're pretty sure it's there, but we don't really know

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Speaker 1: what is it. Is it made out of particles? Is

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Speaker 1: it made out of black holes? Is it made out

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Speaker 1: of lost socks? It's a really huge mystery in modern physics.

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Speaker 1: In fact, I would say it's one of the biggest

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Speaker 1: open questions in science.

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Speaker 3: I think it's just dark socks. Actually, wouldn't that make sense?

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Speaker 3: I always lose those.

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Speaker 1: How many dark socks have you lost for our head?

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Speaker 1: I mean, we're talking a whole lot of socks.

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Speaker 3: Well, to be honest, I'm a cartoonist, so I don't

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Speaker 3: have to wear dark socks very often, or socks at all,

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Speaker 3: because I also live in California.

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Speaker 4: But yeah, dark matter, I mean it's a big deal.

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Speaker 3: There's five times more dark matter then there is regular

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Speaker 3: matter like planets and stars and gas and dust and

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Speaker 3: black holes.

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Speaker 4: There's all that stuff.

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Speaker 3: There's actually it's only like twenty percent of the stuff

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Speaker 3: in the universe.

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Speaker 1: Yeah, which means the normal matter, the regular matter, the

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Speaker 1: stuff that you're familiar with, is not actually regular or normal.

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Speaker 1: It's the unusual stuff. If you just took like a

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Speaker 1: survey of stuff in the universe, most of the stuff

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Speaker 1: is dark matter, the things that make up stars and

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Speaker 1: planets and galaxies and hamsters and me and you and

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Speaker 1: bananas and snack foods that's unusual in the universe. It's

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Speaker 1: a minority of what's out there in the universe, and

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Speaker 1: yet we still don't know what this dark matter is.

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Speaker 3: It's a big mystery and a lot of times, you know,

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Speaker 3: whenever people talk about dark matter, I feel like a

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Speaker 3: common question we get, at least in talks and appearances,

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Speaker 3: is that people ask us like, what if dark matter

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Speaker 3: doesn't exist? Like what if it's just an error in

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Speaker 3: the equations that you have about physics in the universe,

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Speaker 3: Like what if we just maybe like misunderstood gravity, or

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Speaker 3: haven't counted all the stars in the galaxy, or you know,

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Speaker 3: what if there's something else that is maybe normal but

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Speaker 3: we just haven't thought about it.

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Speaker 1: Yeah, And it's a great question because most of the

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Speaker 1: evidence we have for dark matter is a little bit indirect, Like,

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Speaker 1: because dark matter is so dark and hard to interact with,

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Speaker 1: we don't have clear pictures of it, right, we haven't

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Speaker 1: seen what it's made out of. We've only sort of

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Speaker 1: seen its effects and sometimes secondhand, and so it's tempting

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Speaker 1: to wonder if it's really there. You know, It's like

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Speaker 1: if you've only seen the footprints of an animal, are

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Speaker 1: you really sure it exists, or could it be something

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Speaker 1: else spoofing you Until you really capture one or see

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Speaker 1: one in the wild, you don't really believe it exists, right,

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Speaker 1: And dark matter has been eluding our searches for decades

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Speaker 1: and makes people wonder like, well, maybe people have it wrong.

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Speaker 6: Yeah.

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Speaker 3: I mean it's kind of a crazy idea, right to

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Speaker 3: think that there's that much stuff out there, and conveniently

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Speaker 3: it's invisible and you can't see it, you know what

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Speaker 3: I mean? Like I would be like maybe you should

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Speaker 3: take your math or you know, maybe you should have

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Speaker 3: another grad student do the calculation.

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Speaker 1: So, which do you think is the conspiracy theory dark matter,

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Speaker 1: like there's so much of it and you can't see

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Speaker 1: it because it's so dark and that proves that it exists,

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Speaker 1: or the anti dark matter conspiracy theories?

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Speaker 3: Oh wait, anti dark matter? That's another episode right there?

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Speaker 3: Can you have anti dark matter Danny?

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Speaker 1: Yeah, no, that's another great question. We think probably not

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Speaker 1: because then it would annihilate with dark matter and turn

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Speaker 1: into photons, which we would see.

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Speaker 3: What if it turns into dark photons?

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Speaker 1: Yeah, that's actually a thing, dark photons.

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Speaker 4: Really, it really is a man. Yeah, it goes double price.

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Speaker 1: You don't get credit for that one. But you know

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Speaker 1: which idea sounds more bonkers, right, that the universe is

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Speaker 1: filled with an incredible amount of invisible matter nobody had

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Speaker 1: to text it until recently, or that it's not Yeah.

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Speaker 3: So today on the podcast, we'll be asking the question

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Speaker 3: does these need dark matter? Is it an essential part

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Speaker 3: of the unitse like, could you have a universe without

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Speaker 3: dark matter? Would that make sense? Or is it maybe

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Speaker 3: that the universe doesn't need it? And maybe it is

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Speaker 3: kind of an error that we have in our calculations

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Speaker 3: and observations about the universe.

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Speaker 1: And this kind of skepticism is very healthy when you

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Speaker 1: have a crazy idea you're trying to accommodate when you

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Speaker 1: see results in your experiments you don't understand. You need

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Speaker 1: to be flexible about this sort of theoretical framework with

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Speaker 1: which you come at the problem. You need to be

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Speaker 1: open to crazy new ideas, but you also need to

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Speaker 1: be open to the fact that maybe you got your

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Speaker 1: measurements wrong. There always can be an alternative explanation. So

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Speaker 1: before you go big and say, wow, we're going to

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Speaker 1: revolutionize our understanding of the universe, you got to rule

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Speaker 1: out all the more prosaic, basic, simpler explanations, and so

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Speaker 1: it's always a good idea to keep those ideas in mind.

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Speaker 3: Yeah, so, how sure are we that dark matter exists

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Speaker 3: in the universe? And could it be something else?

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Speaker 1: So I went out there into the internet and I

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Speaker 1: ask people, can we explain what we see in the

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Speaker 1: universe without dark matter? Are there good alternative theories that

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Speaker 1: don't require a new particle or new blob of stuff.

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Speaker 3: So before you listen to these answers from the internet,

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Speaker 3: think about it for a second. Do you think dark

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Speaker 3: matter is necessary in the universe or do you think

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Speaker 3: the universe could ignore it or live without it. Here's

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Speaker 3: what people had to say.

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Speaker 7: I would think we would be much more baffled if

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Speaker 7: we didn't have dark matter to explain the expansion of

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Speaker 7: the universe.

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Speaker 8: Oh man, this is tough because I still don't have

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Speaker 8: a good handle on what dark matter really is. But

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Speaker 8: I think I think we really don't know what dark

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Speaker 8: matter is. So I'm going to say, yeah, we could

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Speaker 8: definitely explain what we see without it, because we're kind

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Speaker 8: of just making up what it is.

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Speaker 9: I yes, dark matter is just a made up term

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Speaker 9: for the stuff that's there that we can't explain so truly,

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Speaker 9: any theory is under the umbrella of dark matter.

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Speaker 10: I have a strong vision that the thing could be

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Speaker 10: explained without dark matter. I recall Daniel saying that dark

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Speaker 10: matter is just a name that we've come up with

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Speaker 10: for the phenomenon that we get explained.

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Speaker 6: I don't know what we would see without dark matter,

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Speaker 6: And my understanding is that we do know that there's

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Speaker 6: dark matter because the math doesn't work out.

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Speaker 4: At some point we will have to explain the universe

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Speaker 4: without dark matter, because like the dark in the matter

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Speaker 4: sort of implies that we don't know what it is.

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Speaker 11: I believe that dark matter is a theory that we

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Speaker 11: came up with to help explain why we couldn't account

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Speaker 11: for all of the gravity that we see in the universe.

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Speaker 11: I think it's a fairly recent discovery. I don't believe

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Speaker 11: Einstein knew about it, so he must have had some

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Speaker 11: other way to account for all of the gravity.

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Speaker 4: All right, some pretty good answers there, Yeah.

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Speaker 1: I like the people who treat dark matters just sort

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Speaker 1: of like as an umbrella idea for all the things

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Speaker 1: we don't understand, and so whatever we find out there

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Speaker 1: we just call that dark matter, and I think that

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Speaker 1: really touches on the sense people have that we don't

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Speaker 1: really have a clue what's out there. We just sort

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Speaker 1: of labeled it dark matter, and we're talking about it

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Speaker 1: as if it's a thing, but it's really just a

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Speaker 1: name we applied to our cluelessness.

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Speaker 3: Interesting, like if you put an s a DN, it

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Speaker 3: becomes dark matters, and then it's sort of like an

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Speaker 3: umbrella term for things that are dark.

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Speaker 1: That's true, and you know that is definitely true of

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Speaker 1: dark energy. Dark energy is another piece of the universe pie. Right,

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Speaker 1: The universe pie is five percent normal matter, twenty five

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Speaker 1: percent dark matter, seventy percent dark energy. Dark energy definitely

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Speaker 1: in the category of just stuff we don't understand. We

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Speaker 1: gave a fancy sounding name dark energy, this stuff that's

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Speaker 1: making the universe expand right. Dark matter, on the other hand,

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Speaker 1: is much better understood, is much more concrete an idea,

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Speaker 1: much more detailed observation. They're both called dark both things

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Speaker 1: we don't understand. But dark energy definitely a label for

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Speaker 1: our cluelessness, while dark matter is a much better founded,

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Speaker 1: well described theory.

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Speaker 3: It's less dark. I guess we're less in the dark

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Speaker 3: about exactly.

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Speaker 1: We are less in the dark. Our minds are not

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Speaker 1: quite so filled with dark shadows.

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Speaker 3: All right, Well that's the question for today, And that's

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Speaker 3: the question is you know, do we need dark matter?

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Speaker 3: Like is it a concept that is totally necessary for

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Speaker 3: the universe to makes sense or is it just something

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Speaker 3: weird that exists out there and that maybe we could

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Speaker 3: have a totally wrong idea about it.

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Speaker 1: Yeah, and are there other theories that are being worked

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Speaker 1: on in the scientific community that might explain it without

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Speaker 1: needing to add some new kind of stuff to the universe.

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Speaker 1: Darker matter the darkest matter. And you'll find that in

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Speaker 1: science there are always competing voices. You know, there's often

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Speaker 1: like a mainstream most people think the answer is X,

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Speaker 1: but there's always somebody out there who thinks it's why,

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Speaker 1: somebody who thinks it's Z. And you got to give

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Speaker 1: these people room because sometimes they're right, and sometimes their

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Speaker 1: ideas are the ones that turn into the mainstream. That's

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Speaker 1: how the mainstream became mainstream. It used to once be

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Speaker 1: lunatic fringe.

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Speaker 3: Are they're alternative physicists, you know, French physicists.

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Speaker 1: There definitely are there are people out there once they

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Speaker 1: get tenure start working on crazy bonkers theories and sometimes

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Speaker 1: for decades, then nobody pays attention, nobody really reads their papers.

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Speaker 1: That people even laugh behind their hands, but sometimes they're right,

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Speaker 1: you know. Literally, the history of physics is filled with

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Speaker 1: revolutions that started as crazy ideas, right, and so we

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Speaker 1: definitely got to pour water on some of those seedlings

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Speaker 1: because they could sprout into huge new intellectual trees.

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Speaker 3: Wow, awesome dark physics trees I'm picturing. All right, Well,

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Speaker 3: step us through, like what's the main argument for dark matter,

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Speaker 3: Like what's the main evidence about it? And what makes

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Speaker 3: us think that, you know, it's something new and different

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Speaker 3: as opposed to maybe it's just more stuff out there

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Speaker 3: that we can see.

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Speaker 1: Yeah, So if you're going to come up with another

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Speaker 1: theory of the universe, another way to explain the way

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Speaker 1: the universe works, you have to explain what we do see, right,

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Speaker 1: I mean that's the whole idea behind making a theory

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Speaker 1: of physics. So if you're gonna come up with your theory,

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Speaker 1: you have to understand what are the observations, what are

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Speaker 1: the experiments reveal that need to be explained that you know,

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Speaker 1: what's the motivation we're creating this idea of dark matter,

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Speaker 1: and the short version is it's all gravity. Like everything

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Speaker 1: we see out there in the universe that we need

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Speaker 1: dark matter to explain are weird gravitational effects that we

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Speaker 1: can't explain with all the other stuff, just the gas

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Speaker 1: and the dust and the stars.

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Speaker 3: Right with the universe feels dark matter in terms of gravity,

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Speaker 3: like it's there affecting the gravity of other things, but

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Speaker 3: you can't see it.

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Speaker 4: That's the main evidence for it.

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Speaker 1: Yeah, basically there's unexplained gravity, like we thought we knew

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Speaker 1: where all the stuff was in the universe from the

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Speaker 1: stars and the gas and the dust, and from that

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Speaker 1: you can calculate how much gravity there should be, and

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Speaker 1: we can see the effects of gravity, and we'll go

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Speaker 1: through in a list of how we see the effects

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Speaker 1: of gravity. But there's more gravity than we expected, so

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Speaker 1: that there's more stuff i e. Dark matter or gravity

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Speaker 1: is weird and different.

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Speaker 3: And so it's all about the gravity then, right, because

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Speaker 3: that's kind of at the basis of the theory about

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Speaker 3: dark matter, is that it feels gravity but not anything.

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Speaker 1: Else exactly, and that's why it's dark, because if it

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Speaker 1: felt electromagnetism, it would reflect light or it would give

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Speaker 1: off light like everything else does than the universe it glows,

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Speaker 1: or if it felt the strong force, it would bind

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Speaker 1: with quarks and form nucleons and interact with us. So

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Speaker 1: it doesn't interact with us in any way that we

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Speaker 1: know of other than gravitational And that's why we call

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Speaker 1: it matter because we think it's something that has new gravity.

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Speaker 1: But you know, it could also just be a tweak

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Speaker 1: to the way we understand gravity. But at its core,

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Speaker 1: it's really an observation that our theory of gravity doesn't work,

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Speaker 1: either because there's missing mass or the theory is wrong, right,

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Speaker 1: So those are two sides of the.

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Speaker 3: Coin, right, Like, according to what we know about how

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Speaker 3: gravity works, there's a lot of gravity missing, or there's

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Speaker 3: too much gravity in the universe.

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Speaker 4: Almost.

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Speaker 1: Yeah, there's gravity out there and we don't have masks

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Speaker 1: to explain it, and so we have to sort of

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Speaker 1: fill in those gaps. And that's an uncomfortable feeling, right.

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Speaker 1: You're like, well, you can't just like fill in the

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Speaker 1: gaps and assume that your theory is right and add

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Speaker 1: extra stuff to make it work out. You know, that

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Speaker 1: feels uncomfortable.

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Speaker 3: Right, Like there's snack food missing from my fridge. Surely

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Speaker 3: it was my son who cut up in the middle

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Speaker 3: of the night to eat it. But you can't you

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Speaker 3: can't just assume that.

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Speaker 1: You can't just assume that could have been your daughter.

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Speaker 4: Maybe you sleepwalked right or And.

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Speaker 1: That's why you install a camera in front of your

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Speaker 1: fridge and get those weird videos to yourself at four

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Speaker 1: am stuffing cake in your face. You speak from experience, then, hypothetically, hypothetically.

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Speaker 3: Hypothetically, right, all right, So we think dark matter is

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Speaker 3: there because of gravity, and there are several ways that

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Speaker 3: we have seen this kind of missing gravity, right, It's

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Speaker 3: in the galaxy rotations. The way galaxies rotate is kind

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Speaker 3: of one of the first one, maybe even Yeah.

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Speaker 1: One of the most dramatic and earliest pieces of evidence

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Speaker 1: that there was more gravity in the universe than we

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Speaker 1: expected was looking at how galaxies rotate. And we can

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Speaker 1: add up all the mass of the stars and the

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Speaker 1: stuff in the galaxy and say, okay, we know how

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Speaker 1: much gravity there should be, and then we can calculate

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Speaker 1: how fast those galaxies are rotating. And you know, for

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Speaker 1: a galaxy, when it's rotating, it's trying to push stuff off,

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Speaker 1: it's trying to like throw stuff off the edge. Like

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Speaker 1: if you put ping pong balls on a merry go

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Speaker 1: round and spin it, the ping pong balls fly out.

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Speaker 1: The thing that keeps the galaxy from tearing itself, apart

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Speaker 1: from throwing those ping pong balls out into inter galactic space,

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Speaker 1: is the gravity. So you can ask how fast is

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Speaker 1: the galaxy spinning and is there enough gravity to hold

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Speaker 1: it together? Because the faster it spins, the more gravity

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Speaker 1: you need.

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Speaker 3: Right, Yeah, it's kind of like our Solar system, right,

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Speaker 3: Like you know, the mass of the Sun is what

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Speaker 3: keeps all the planets kind of spinning around it. But

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Speaker 3: what if, like the plants were spinning faster than what

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Speaker 3: you could explain by the mass of the Sun. You

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Speaker 3: would need some other explanation.

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Speaker 1: That's right, You'd need more force to hold them into

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Speaker 1: their orbits. And so you say, well, maybe there's extra

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Speaker 1: gravity or some other force or something. And so we

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Speaker 1: know there's something else holding the galaxy together. And so

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Speaker 1: the first explanation is, oh, well, what if there's more

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Speaker 1: invisible mass. There's just some stuff in the galaxy that's

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Speaker 1: providing gravity and we just can't see it, And you

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Speaker 1: can explain these rotation curves the way the stars move

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Speaker 1: around centers of galaxies. If you distribute a bunch of

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Speaker 1: mass sort of smoothly, it's like a big clump in

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Speaker 1: the middle, and then sort of smoothly out past the

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Speaker 1: edge of the galaxy into a big halo that's even

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Speaker 1: actually bigger than the galaxy. That explains to that says,

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Speaker 1: that would give you the kind of gravity that we

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Speaker 1: are seeing.

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Speaker 3: Right, because if you look at a galaxy doesn't have

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Speaker 3: that enough mass, right, like, there aren't enough stars or

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Speaker 3: planets in it that you can see.

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Speaker 1: That's right. We count up all the visible stuff and

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Speaker 1: we say how much mass does it have? And that

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Speaker 1: just doesn't give us enough gravity to explain how those

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Speaker 1: galaxies are holding themselves together. And that was the sort

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Speaker 1: of genesis of it. I mean, for a long time

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Speaker 1: people were like, well, wow, that's must be a mistake,

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Speaker 1: you know, because coming to the idea that there's five

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Speaker 1: times as much mass as you can see is a

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Speaker 1: really big idea. It's not something people just came to

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Speaker 1: an afternoon and then accept it.

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Speaker 4: Yeah, it doesn't seem likely.

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Speaker 1: It does not seem likely. It seems more likely that

402
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Speaker 1: you mismeasured something that you got the velocities wrong, or

403
00:19:17,720 --> 00:19:20,360
Speaker 1: you know your grad student is pranking you or something.

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00:19:20,560 --> 00:19:22,679
Speaker 3: It's a big idea, right, It's like jumping to the

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Speaker 3: conclusion right away that maybe there are five ghosts in

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Speaker 3: my house eating my snacks. You know, that's like a

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Speaker 3: big that's a big leap from like, hey, maybe it's

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Speaker 3: just your just your son hungry.

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Speaker 1: And so it took other pieces of evidence before dark

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Speaker 1: matter became mainstream.

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Speaker 3: Right, all right, let's get into those other ways that

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Speaker 3: we know dark matter is there, and let's get into

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Speaker 3: whether or not it is there or maybe we just

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Speaker 3: have gravity wrong.

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Speaker 3: All right, Daniel, we're talking about whether dark matter is necessary.

466
00:22:34,320 --> 00:22:36,720
Speaker 3: In the universe, or you know, maybe it's just a

467
00:22:36,760 --> 00:22:39,600
Speaker 3: hanger on and the universe could care less about dark matter.

468
00:22:40,280 --> 00:22:42,480
Speaker 3: But we know it's definitely there because we see it

469
00:22:42,520 --> 00:22:45,679
Speaker 3: from the rotation of galaxies, and also we've sort of

470
00:22:45,960 --> 00:22:47,960
Speaker 3: kind of can see it, right, We can see it

471
00:22:48,000 --> 00:22:51,520
Speaker 3: in the way that distorts the light from other faraway stars.

472
00:22:51,560 --> 00:22:54,159
Speaker 1: That's right. These days, we have a good handful of

473
00:22:54,200 --> 00:22:57,879
Speaker 1: ways to indirectly detect dark matter, and one of the

474
00:22:57,960 --> 00:23:01,800
Speaker 1: coolest is seeing it like a lens in the sky

475
00:23:02,400 --> 00:23:06,480
Speaker 1: because dark matter only has gravitational forces, but gravity can

476
00:23:06,560 --> 00:23:10,000
Speaker 1: bend space, right, It's a bending of space and time.

477
00:23:10,119 --> 00:23:12,959
Speaker 1: So if you have a big blob of invisible stuff

478
00:23:13,000 --> 00:23:16,000
Speaker 1: in the sky, it will curve the space it's in

479
00:23:16,480 --> 00:23:19,120
Speaker 1: so that photons traveling through it will get bent as

480
00:23:19,160 --> 00:23:22,000
Speaker 1: if they're moving through a huge lens. So if there's

481
00:23:22,040 --> 00:23:24,280
Speaker 1: a big blob of dark matter between you and some

482
00:23:24,440 --> 00:23:28,000
Speaker 1: really far away galaxy, it will distort that galaxy, creating

483
00:23:28,080 --> 00:23:31,159
Speaker 1: duplicates of it, stretching it, just as if there was

484
00:23:31,200 --> 00:23:32,639
Speaker 1: a huge lens in the sky.

485
00:23:32,560 --> 00:23:34,439
Speaker 3: Right, And so we can see that, like if you

486
00:23:34,560 --> 00:23:36,679
Speaker 3: look at pictures of the sky, you see these kind

487
00:23:36,720 --> 00:23:39,840
Speaker 3: of distortions these ripples, these lensing effects. Yep, you can

488
00:23:39,840 --> 00:23:41,800
Speaker 3: sort of see dark matter almost.

489
00:23:41,520 --> 00:23:43,600
Speaker 1: You can definitely see it. And there's sort of two categories.

490
00:23:43,640 --> 00:23:47,000
Speaker 1: There's strong lensing, like there's a big dense blob and

491
00:23:47,080 --> 00:23:50,120
Speaker 1: it's distorting the galaxies and it's pretty hard to explain

492
00:23:50,200 --> 00:23:52,879
Speaker 1: that kind of lensing in any other way. And then

493
00:23:52,920 --> 00:23:55,479
Speaker 1: there's weak lensing. We just sort of like look at

494
00:23:55,520 --> 00:23:58,000
Speaker 1: all the galaxies out there to see like, are any

495
00:23:58,040 --> 00:23:59,959
Speaker 1: of them sort of just a little distortedd or just

496
00:24:00,080 --> 00:24:02,359
Speaker 1: looking a little tweaked. And from that we can get

497
00:24:02,400 --> 00:24:04,600
Speaker 1: sort of like a map of where in the sky

498
00:24:04,720 --> 00:24:07,520
Speaker 1: we think the dark matter is just by looking at

499
00:24:07,600 --> 00:24:10,840
Speaker 1: small distortions, and that's how we've gotten a pretty good

500
00:24:10,920 --> 00:24:13,280
Speaker 1: map for where we think this missing mass is. How

501
00:24:13,320 --> 00:24:15,159
Speaker 1: we know that it's mostly in the center of the

502
00:24:15,200 --> 00:24:17,840
Speaker 1: galaxy and how far out past the edge of the

503
00:24:17,920 --> 00:24:20,920
Speaker 1: visible galaxy the dark matter halo might go. So it's

504
00:24:20,960 --> 00:24:22,720
Speaker 1: a really powerful technique.

505
00:24:22,359 --> 00:24:24,520
Speaker 3: Right, And so that's kind of how dark matter entered

506
00:24:24,600 --> 00:24:27,240
Speaker 3: in kind of our view of the universe was these

507
00:24:27,320 --> 00:24:31,040
Speaker 3: first initial ways. But since then we sort of have

508
00:24:31,119 --> 00:24:34,120
Speaker 3: put more nails into sort of the coffin of whether

509
00:24:34,200 --> 00:24:36,080
Speaker 3: or not dark matter is out there, right. I mean

510
00:24:36,600 --> 00:24:39,879
Speaker 3: it's now sort of shows up in pictures of the universe,

511
00:24:39,920 --> 00:24:42,560
Speaker 3: the early universe, it kind of shows up in our

512
00:24:42,640 --> 00:24:45,720
Speaker 3: calculations about all the energy in the universe. Right, It's

513
00:24:45,760 --> 00:24:48,280
Speaker 3: gotten more and more convincing that there's something there.

514
00:24:48,080 --> 00:24:50,959
Speaker 1: That's right, it becomes very difficult to explain the universe

515
00:24:51,000 --> 00:24:54,479
Speaker 1: you see without dark matter. For example, we see the

516
00:24:54,480 --> 00:24:57,919
Speaker 1: influence of dark matter on the formation of structures in

517
00:24:57,960 --> 00:25:00,720
Speaker 1: the universe. Like the universe began as a sort of

518
00:25:00,840 --> 00:25:04,399
Speaker 1: diffuse cloud, you know, just of gas, mostly hydrogen, and

519
00:25:04,440 --> 00:25:08,520
Speaker 1: then it started clumping together, and that clumping comes from gravity. Right,

520
00:25:08,560 --> 00:25:11,040
Speaker 1: So gravity is a thing that draws these things together

521
00:25:11,080 --> 00:25:14,280
Speaker 1: and eventually gives you stars and galaxies and planets and

522
00:25:14,320 --> 00:25:16,280
Speaker 1: all that cool stuff. If you run a simulation of

523
00:25:16,280 --> 00:25:18,960
Speaker 1: the universe without any dark matter, then you don't get

524
00:25:19,000 --> 00:25:21,679
Speaker 1: galaxies in the first ten billion years. It takes like

525
00:25:21,720 --> 00:25:25,119
Speaker 1: another ten or twenty billion years. So it's dark matter

526
00:25:25,160 --> 00:25:28,800
Speaker 1: that's that's created these like gravitational wells for stuff to

527
00:25:28,880 --> 00:25:32,160
Speaker 1: fall into to make the stars in the galaxies and us.

528
00:25:32,800 --> 00:25:35,040
Speaker 1: So just like the whole structure of the universe would

529
00:25:35,080 --> 00:25:39,480
Speaker 1: look very different without some kind of gravitational stuff out there,

530
00:25:40,440 --> 00:25:40,760
Speaker 1: and we.

531
00:25:40,720 --> 00:25:45,400
Speaker 3: Should have just called them dark clumps or dark doits.

532
00:25:45,520 --> 00:25:47,760
Speaker 1: And even earlier in the universe, like we've talked on

533
00:25:47,800 --> 00:25:51,640
Speaker 1: this program about the cosmic microwave background radiation. Those are

534
00:25:51,640 --> 00:25:55,360
Speaker 1: photons from the very very early universe, three hundred thousand

535
00:25:55,400 --> 00:25:58,480
Speaker 1: years after the universe was created, the first moment when

536
00:25:58,520 --> 00:26:02,119
Speaker 1: the universe became trans parent to light. Before that it

537
00:26:02,160 --> 00:26:05,000
Speaker 1: was thick and soupy and light got reabsorbed. And after

538
00:26:05,040 --> 00:26:07,120
Speaker 1: that it was cool enough that light could travel through

539
00:26:07,160 --> 00:26:10,199
Speaker 1: the universe without being absorbed, right, And the shape of

540
00:26:10,240 --> 00:26:13,400
Speaker 1: that plasma that gave off that light was affected by

541
00:26:13,600 --> 00:26:15,800
Speaker 1: dark matter and how much dark matter there was and

542
00:26:15,880 --> 00:26:18,399
Speaker 1: how much normal matter there was, and that stuff like

543
00:26:18,640 --> 00:26:21,760
Speaker 1: bounced off each other and oscillated and like squeezed and

544
00:26:21,800 --> 00:26:25,320
Speaker 1: squished that plasma. So the amount of dark matter in

545
00:26:25,359 --> 00:26:28,600
Speaker 1: that moment of the universe affects the shape of that light,

546
00:26:28,640 --> 00:26:31,000
Speaker 1: the currents, the sort of patterns we see in that

547
00:26:31,080 --> 00:26:34,639
Speaker 1: light in a very very precise way. That's hard to

548
00:26:34,680 --> 00:26:38,080
Speaker 1: describe in any other way other than there's some other

549
00:26:38,240 --> 00:26:41,320
Speaker 1: kind of stuff out there. So that's giving us this gravity.

550
00:26:41,720 --> 00:26:44,200
Speaker 3: Yeah, you can see like it's imprint in the light.

551
00:26:44,240 --> 00:26:47,719
Speaker 3: From the early universe, like it's visually and like tangibly

552
00:26:47,800 --> 00:26:50,240
Speaker 3: and like you know, you can calculate it or it

553
00:26:50,560 --> 00:26:51,360
Speaker 3: distorts that light.

554
00:26:51,440 --> 00:26:53,600
Speaker 1: That's right. And so if you just take the universe

555
00:26:53,600 --> 00:26:56,600
Speaker 1: and you add to it a new particle, a particle

556
00:26:56,600 --> 00:26:59,359
Speaker 1: that doesn't move really fast, we call it cold and

557
00:26:59,480 --> 00:27:03,080
Speaker 1: doesn't feel anything but gravity, it explains all of this stuff.

558
00:27:03,119 --> 00:27:06,480
Speaker 1: It explains why galaxies rotate the way they do, why

559
00:27:06,520 --> 00:27:09,639
Speaker 1: the cosmic microwave background radiation looks the way it does,

560
00:27:09,920 --> 00:27:13,560
Speaker 1: why the structure of the universe has this structure at

561
00:27:13,560 --> 00:27:17,280
Speaker 1: this time in the universe. And also there are very specific,

562
00:27:17,600 --> 00:27:20,639
Speaker 1: awesome experiments that the universe has done to sort of

563
00:27:20,680 --> 00:27:22,360
Speaker 1: demonstrate dark matter to us.

564
00:27:23,200 --> 00:27:25,679
Speaker 3: Yeah, I guess, you know, I think maybe a question

565
00:27:25,760 --> 00:27:28,120
Speaker 3: that a lot of people have, and I'm sure physicists

566
00:27:28,160 --> 00:27:30,359
Speaker 3: had at the beginning, was, you know, why does it

567
00:27:30,400 --> 00:27:33,400
Speaker 3: need to be something special? Like why does it need

568
00:27:33,480 --> 00:27:36,439
Speaker 3: to be a new kind of particle or matter? Couldn't

569
00:27:36,440 --> 00:27:39,960
Speaker 3: it also just be something regular but that you just

570
00:27:40,000 --> 00:27:42,280
Speaker 3: can't see, Like, you know, what if there's a whole

571
00:27:42,280 --> 00:27:44,840
Speaker 3: bunch of black asteroids out there that are hard to see,

572
00:27:45,080 --> 00:27:47,840
Speaker 3: or you know a lot of small dust that we

573
00:27:47,880 --> 00:27:50,000
Speaker 3: can see, or maybe even like a whole bunch of

574
00:27:50,040 --> 00:27:52,320
Speaker 3: little black holes kind of spread around the universe.

575
00:27:52,400 --> 00:27:54,159
Speaker 1: Yeah, that's a great question, like why do we know

576
00:27:54,200 --> 00:27:56,600
Speaker 1: it's a new kind of thing. Why can't it just

577
00:27:56,640 --> 00:27:59,719
Speaker 1: be more of the same, but just kind of dark, right, Yeah, well,

578
00:28:00,280 --> 00:28:02,960
Speaker 1: well we don't really know anything in our current set

579
00:28:02,960 --> 00:28:06,920
Speaker 1: of particles that is that dark. I mean, other than neutrinos.

580
00:28:07,440 --> 00:28:10,200
Speaker 1: Everything else has some kind of interaction, like if it's

581
00:28:10,200 --> 00:28:13,560
Speaker 1: a black rock or something, well that does reflect light,

582
00:28:13,640 --> 00:28:16,160
Speaker 1: it does give off light. So if it's made out

583
00:28:16,160 --> 00:28:17,919
Speaker 1: of the normal kind of matter, it's going to have

584
00:28:17,960 --> 00:28:21,720
Speaker 1: the kind of interactions we have, and therefore we would

585
00:28:21,720 --> 00:28:25,399
Speaker 1: be able to see it, except of course, neutrinos. Neutrinos

586
00:28:25,400 --> 00:28:27,280
Speaker 1: were a candidate for dark matter for a long time.

587
00:28:27,359 --> 00:28:30,720
Speaker 1: The problem is neutrinos move way too fast. They zoom

588
00:28:30,760 --> 00:28:33,440
Speaker 1: around the universe because they're so light, so they don't

589
00:28:33,480 --> 00:28:36,040
Speaker 1: give the same sort of structure to the universe that

590
00:28:36,119 --> 00:28:38,240
Speaker 1: dark matter does. You need this thing to be sort

591
00:28:38,240 --> 00:28:41,240
Speaker 1: of slow moving and cold in order to stick around

592
00:28:41,280 --> 00:28:43,840
Speaker 1: long enough to give the structure of galaxies.

593
00:28:44,320 --> 00:28:47,480
Speaker 3: Couldn't you have cold neutrinos like slow moving neutrinos didn't

594
00:28:47,480 --> 00:28:49,600
Speaker 3: we talk about that the other in another episode.

595
00:28:49,640 --> 00:28:52,920
Speaker 1: Could you have cold neutrinos? Yes, but we don't think

596
00:28:52,920 --> 00:28:56,640
Speaker 1: that neutrinos are that cold. We haven't seen cold neutrinos.

597
00:28:56,680 --> 00:28:59,760
Speaker 1: Neutrinos are so light they have almost no mass that

598
00:28:59,800 --> 00:29:02,720
Speaker 1: they essentially almost always travel near the speed of light.

599
00:29:03,520 --> 00:29:05,880
Speaker 1: They're always in a rush, they're always in a hurry. Yes,

600
00:29:06,160 --> 00:29:11,400
Speaker 1: neutrinos are hot, as we call them in particle physics.

601
00:29:10,240 --> 00:29:14,520
Speaker 3: And literally and figuratively, is it's a pretty big trend

602
00:29:14,560 --> 00:29:14,920
Speaker 3: right now?

603
00:29:15,080 --> 00:29:15,520
Speaker 1: That's right?

604
00:29:15,560 --> 00:29:15,840
Speaker 4: All right?

605
00:29:15,880 --> 00:29:18,520
Speaker 3: Well, I guess if it's not maybe something we know about,

606
00:29:18,680 --> 00:29:20,720
Speaker 3: could it be that just maybe we have our theories

607
00:29:20,800 --> 00:29:23,400
Speaker 3: wrong about how things work, Like, you know, maybe it's

608
00:29:23,440 --> 00:29:25,400
Speaker 3: not a new particle or a new kind of matter,

609
00:29:25,520 --> 00:29:29,560
Speaker 3: but maybe we just have gravity wrong. Like maybe gravity

610
00:29:29,640 --> 00:29:31,360
Speaker 3: doesn't work the way we think it is. And maybe

611
00:29:31,520 --> 00:29:36,080
Speaker 3: these larger universe size scales could gravity, you know, could

612
00:29:36,080 --> 00:29:38,280
Speaker 3: there be a different theory of gravity that would maybe

613
00:29:38,360 --> 00:29:40,200
Speaker 3: account for what we think is dark matter.

614
00:29:40,400 --> 00:29:44,040
Speaker 1: It's definitely something to consider, right because all these observations

615
00:29:44,080 --> 00:29:47,280
Speaker 1: are just observations of gravity, and what we're doing is

616
00:29:47,280 --> 00:29:49,720
Speaker 1: we're saying we assume there's a certain amount of mass

617
00:29:49,720 --> 00:29:52,360
Speaker 1: out there. We assume we know how gravity works. We

618
00:29:52,760 --> 00:29:56,080
Speaker 1: estimate how much gravity there should be based on that mass, right,

619
00:29:56,120 --> 00:29:58,400
Speaker 1: But there are two steps in there. There's figure out

620
00:29:58,440 --> 00:30:01,320
Speaker 1: where the mass is and then calculate how much gravity

621
00:30:01,320 --> 00:30:04,720
Speaker 1: there is from that mass. If that second step is wrong, right,

622
00:30:04,920 --> 00:30:07,600
Speaker 1: if the theory of gravity works differently from what we expected,

623
00:30:07,880 --> 00:30:10,960
Speaker 1: then yeah, that could possibly explain it. Because remember, yeah,

624
00:30:11,080 --> 00:30:14,280
Speaker 1: gravity is very very weak, which makes it very very

625
00:30:14,280 --> 00:30:17,800
Speaker 1: hard to test, Like it's difficult to measure the force

626
00:30:17,840 --> 00:30:21,120
Speaker 1: of gravity at the scale of one centimeter between two

627
00:30:21,200 --> 00:30:25,600
Speaker 1: pebbles because this force there is almost zero, Like you

628
00:30:25,720 --> 00:30:28,640
Speaker 1: need to build a very sensitive instrument to measure the

629
00:30:28,640 --> 00:30:32,120
Speaker 1: gravitational force between anything that's smaller than you know, planets

630
00:30:32,120 --> 00:30:32,720
Speaker 1: and moons.

631
00:30:32,840 --> 00:30:35,480
Speaker 3: Yeah, because you know, like our current theory of gravity

632
00:30:35,720 --> 00:30:39,560
Speaker 3: says that, you know, gravity changes by one over are squared,

633
00:30:39,800 --> 00:30:42,000
Speaker 3: like the force of gravity kind of depends on the

634
00:30:42,360 --> 00:30:45,240
Speaker 3: distance between two things squared, And then you put that

635
00:30:45,360 --> 00:30:48,560
Speaker 3: in the denominator, and that always seems kind of almost

636
00:30:48,640 --> 00:30:51,120
Speaker 3: too simple to me, Like, what are the chances that

637
00:30:51,120 --> 00:30:53,640
Speaker 3: the universe would pick such a simple little formula to

638
00:30:53,640 --> 00:30:56,520
Speaker 3: calculate gravity? You know, why isn't it like one over

639
00:30:56,600 --> 00:31:01,160
Speaker 3: our squared times are to the zero points se and five.

640
00:31:01,200 --> 00:31:02,200
Speaker 3: You know, do you know what I mean? Like it

641
00:31:02,280 --> 00:31:04,560
Speaker 3: seems so simple. Maybe what if it's wrong, Like what

642
00:31:04,600 --> 00:31:07,640
Speaker 3: if gravity isn't one of our square but maybe changes

643
00:31:07,640 --> 00:31:10,720
Speaker 3: over distances in a way that could maybe explain dark matter.

644
00:31:10,760 --> 00:31:13,360
Speaker 1: Yeah, that's a totally realistic thing to think. Although you know,

645
00:31:13,400 --> 00:31:15,160
Speaker 1: there's a lot of these patterns, these one of our

646
00:31:15,320 --> 00:31:18,360
Speaker 1: square patterns in physics and in forces, and there is

647
00:31:18,400 --> 00:31:20,200
Speaker 1: a good reason for it and a fairly simple way

648
00:31:20,200 --> 00:31:23,080
Speaker 1: to understand it. If you imagine like the surface of

649
00:31:23,120 --> 00:31:25,640
Speaker 1: a sphere surrounding a point. Think about like all the

650
00:31:25,680 --> 00:31:28,640
Speaker 1: gravitational energy coming out of a point, the surface of

651
00:31:28,640 --> 00:31:32,080
Speaker 1: a sphere surrounding it, all the gravitational energy passes through

652
00:31:32,080 --> 00:31:34,920
Speaker 1: that sphere, and then as the radius of that sphere

653
00:31:34,960 --> 00:31:37,560
Speaker 1: gets larger, what's the surface of that sphere? Well, it

654
00:31:37,600 --> 00:31:41,080
Speaker 1: goes like are squared, and so the power at any

655
00:31:41,080 --> 00:31:44,520
Speaker 1: point should go like one over are squared. It sort

656
00:31:44,560 --> 00:31:46,960
Speaker 1: of makes sense geometrically.

657
00:31:46,520 --> 00:31:48,200
Speaker 4: But what if geometry is wrong?

658
00:31:48,280 --> 00:31:51,360
Speaker 1: What if geometry is wrong? Right? What is wrong? What

659
00:31:51,400 --> 00:31:52,800
Speaker 1: if podcasting is wrong?

660
00:31:54,240 --> 00:31:55,520
Speaker 4: What if one plus one is wrong?

661
00:31:55,760 --> 00:31:58,080
Speaker 3: Well kind of, I mean you know, we talk about

662
00:31:58,200 --> 00:32:01,160
Speaker 3: sometimes about how space is not, you know, this nice

663
00:32:01,160 --> 00:32:03,480
Speaker 3: and neat, orderly thing, and that sometimes you could even

664
00:32:03,520 --> 00:32:07,800
Speaker 3: like measure triangles in real space that have angles that

665
00:32:07,840 --> 00:32:11,560
Speaker 3: are bigger than one hundred and eighty degrees, could maybe

666
00:32:11,600 --> 00:32:13,880
Speaker 3: like space be weird in such a way that it's

667
00:32:13,920 --> 00:32:15,280
Speaker 3: not really one over our square.

668
00:32:15,440 --> 00:32:17,960
Speaker 1: Yeah. Absolutely, And there are forces that don't go like

669
00:32:18,000 --> 00:32:20,280
Speaker 1: one of our square, Like the strong force doesn't go

670
00:32:20,400 --> 00:32:22,640
Speaker 1: like one of O R squared at small distances. It

671
00:32:22,680 --> 00:32:25,560
Speaker 1: gets even stronger as you get further away. So you

672
00:32:25,680 --> 00:32:28,840
Speaker 1: definitely got to be open to weirdness. And so around

673
00:32:28,840 --> 00:32:30,960
Speaker 1: the time when dark matter was sort of coming up

674
00:32:31,000 --> 00:32:33,400
Speaker 1: in the world as an idea, when it was based

675
00:32:33,480 --> 00:32:36,239
Speaker 1: mostly on galaxy rotations, people thought, well, how can I

676
00:32:36,320 --> 00:32:40,400
Speaker 1: tweak gravity to explain what I'm seeing without dark matter?

677
00:32:40,600 --> 00:32:42,440
Speaker 1: What would I need to change? How what would you

678
00:32:42,480 --> 00:32:44,280
Speaker 1: have to be like one over R to the third

679
00:32:44,360 --> 00:32:45,920
Speaker 1: or one of R to the one point five or

680
00:32:45,920 --> 00:32:50,240
Speaker 1: whatever in order to explain these galaxy rotations without dark matter?

681
00:32:50,640 --> 00:32:52,920
Speaker 1: And so they came up with a different theory. It's

682
00:32:52,920 --> 00:32:59,200
Speaker 1: called mond MO n D for modified Newtonian dynamics.

683
00:32:59,400 --> 00:33:02,880
Speaker 3: Oh no, I would have just called it dark math.

684
00:33:03,280 --> 00:33:04,880
Speaker 1: I wish you could get it in a time machine

685
00:33:04,880 --> 00:33:07,160
Speaker 1: and go back and tell them because I hate Mond.

686
00:33:07,160 --> 00:33:13,080
Speaker 3: Wouldn't that be a lot catch here in front dark math? Well, Mond,

687
00:33:13,120 --> 00:33:15,360
Speaker 3: I guess if you're French then it's like, oh yeah,

688
00:33:15,520 --> 00:33:16,320
Speaker 3: it means the world.

689
00:33:16,480 --> 00:33:18,880
Speaker 1: I suppose though, except it's missing the E and it

690
00:33:18,880 --> 00:33:21,800
Speaker 1: commits the terrible acronym crime of taking two letters from

691
00:33:21,840 --> 00:33:24,320
Speaker 1: one of the words. You know, modified heat.

692
00:33:24,520 --> 00:33:27,160
Speaker 3: Is yeah, all right, So that there is kind of

693
00:33:27,200 --> 00:33:29,600
Speaker 3: a theory in physics that says like, maybe we do

694
00:33:29,680 --> 00:33:32,160
Speaker 3: have gravity wrong, right, Is this like an idea you

695
00:33:32,160 --> 00:33:34,800
Speaker 3: guys take seriously, like maybe there is no dark matter,

696
00:33:34,920 --> 00:33:35,800
Speaker 3: it's just dark math.

697
00:33:35,880 --> 00:33:38,720
Speaker 1: It's definitely an idea that physics should take seriously in

698
00:33:38,760 --> 00:33:41,680
Speaker 1: the sense that we should think about alternatives. This one

699
00:33:41,720 --> 00:33:44,440
Speaker 1: theory in particular doesn't have a lot of supporters, and

700
00:33:44,440 --> 00:33:46,880
Speaker 1: we'll get into exactly why, but you know, it's an

701
00:33:46,880 --> 00:33:51,440
Speaker 1: interesting idea, and it says like maybe gravity works differently

702
00:33:51,560 --> 00:33:54,880
Speaker 1: at very very large distances. Like you know, we've tested

703
00:33:54,880 --> 00:33:57,240
Speaker 1: gravity here on Earth, we know how it works. We've

704
00:33:57,280 --> 00:34:00,280
Speaker 1: tested gravity in the Solar System pretty well, but you know,

705
00:34:00,360 --> 00:34:03,520
Speaker 1: maybe the first time we're looking at gravity on galaxy scales.

706
00:34:03,560 --> 00:34:07,000
Speaker 1: Maybe gravity just works differently over like, you know, fifty

707
00:34:07,120 --> 00:34:10,560
Speaker 1: thousand light years, right, we haven't done that experiment before.

708
00:34:10,640 --> 00:34:13,520
Speaker 3: Maybe it gets going, like, maybe it gets stronger in

709
00:34:13,680 --> 00:34:15,040
Speaker 3: galaxy size scales.

710
00:34:15,120 --> 00:34:17,520
Speaker 1: Yeah, and so the idea is actually even weirder than that.

711
00:34:17,600 --> 00:34:21,840
Speaker 1: It says, maybe gravity works differently when you have a

712
00:34:21,960 --> 00:34:26,480
Speaker 1: very very small acceleration, when things are not being pulled

713
00:34:26,600 --> 00:34:30,799
Speaker 1: very hard. Maybe gravity works a little bit different.

714
00:34:30,920 --> 00:34:32,279
Speaker 4: Oh my god, you just blew my mind.

715
00:34:32,280 --> 00:34:35,720
Speaker 3: All right, let's get into this crazy idea that gravity

716
00:34:35,800 --> 00:34:38,880
Speaker 3: depends on how you're moving maybe, and whether or not

717
00:34:38,960 --> 00:34:41,680
Speaker 3: that could work. But first, let's take another quick great.

718
00:34:45,840 --> 00:34:47,640
Speaker 1: When you pop a piece of cheese into your mouth

719
00:34:47,760 --> 00:34:50,880
Speaker 1: or enjoy a rich spoonful of Greek yogurt, you're probably

720
00:34:50,960 --> 00:34:54,919
Speaker 1: not thinking about the environmental impact of each and every bite.

721
00:34:55,040 --> 00:34:57,640
Speaker 1: But the people in the dairy industry are US Dairy

722
00:34:57,680 --> 00:35:01,960
Speaker 1: has set themselves some ambitious sustainability goals, including being greenhouse

723
00:35:02,000 --> 00:35:04,600
Speaker 1: gas neutral by twenty to fifty. That's why they're working

724
00:35:04,600 --> 00:35:06,960
Speaker 1: hard every day to find new ways to reduce waste,

725
00:35:07,000 --> 00:35:11,239
Speaker 1: conserve natural resources, and drive down greenhouse gas emissions. Take water,

726
00:35:11,280 --> 00:35:14,880
Speaker 1: for example, most dairy farms reuse water up to four times.

727
00:35:14,920 --> 00:35:18,280
Speaker 1: The same water cools the milk, cleans equipment, washes the barn,

728
00:35:18,400 --> 00:35:22,120
Speaker 1: and irrigates the crops. How is US Dairy tackling greenhouse gases?

729
00:35:22,160 --> 00:35:25,120
Speaker 1: Many farms use anaerobic digestors that turn the methane from

730
00:35:25,160 --> 00:35:28,560
Speaker 1: maneuver into renewable energy that can power farms, towns, and

731
00:35:28,600 --> 00:35:30,839
Speaker 1: electric cars. So the next time you grab a slice

732
00:35:30,840 --> 00:35:32,759
Speaker 1: of pizza or lick an ice cream cone, know that

733
00:35:32,840 --> 00:35:35,480
Speaker 1: dairy farmers and processors around the country are using the

734
00:35:35,560 --> 00:35:39,320
Speaker 1: latest practices and innovations to provide the nutrient dense dairy

735
00:35:39,320 --> 00:35:42,000
Speaker 1: products we love with less of an impact. Visit us

736
00:35:42,080 --> 00:35:44,560
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737
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748
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Speaker 4: Hi.

749
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Speaker 7: I'm David Eagleman from the podcast Inner Cosmos, which recently

750
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Speaker 7: hit the number one science podcast in America. I mean

751
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752
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755
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756
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757
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758
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763
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764
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765
00:37:56,160 --> 00:37:59,520
Speaker 3: Right, Daniel, we're talking about dark math to maybe explain

766
00:37:59,600 --> 00:38:02,600
Speaker 3: dark manth. And so there's an idea that maybe our

767
00:38:02,719 --> 00:38:05,399
Speaker 3: formulation of gravity or how we think gravity works, could

768
00:38:05,440 --> 00:38:08,600
Speaker 3: be wrong, maybe and it could maybe act very differently

769
00:38:08,640 --> 00:38:12,040
Speaker 3: over larger scales, like maybe it gets stronger the galaxy scale,

770
00:38:12,280 --> 00:38:15,720
Speaker 3: or you're telling me it's actually when there's lower actileerations.

771
00:38:15,760 --> 00:38:17,480
Speaker 4: And this is just an idea again, right.

772
00:38:17,440 --> 00:38:20,279
Speaker 1: This is just an idea. But hey, everything's just an idea, right,

773
00:38:20,320 --> 00:38:22,200
Speaker 1: even lunch lunch is just an idea.

774
00:38:22,320 --> 00:38:24,880
Speaker 4: Remember, Oh no, Daniel, lunch is very real to me.

775
00:38:26,040 --> 00:38:27,920
Speaker 1: Well, the idea is, you know, somehow you have to

776
00:38:27,920 --> 00:38:31,480
Speaker 1: get gravity to be stronger without breaking things we already know.

777
00:38:31,640 --> 00:38:34,279
Speaker 1: So what if you know affecting things in the edge

778
00:38:34,320 --> 00:38:36,919
Speaker 1: of the galaxy, you could have gravity instead of going

779
00:38:36,960 --> 00:38:39,520
Speaker 1: like one over are squared, which would make it very

780
00:38:39,600 --> 00:38:41,880
Speaker 1: very weak. As R gets large, you can make it

781
00:38:41,920 --> 00:38:44,920
Speaker 1: go like one over R. It doesn't fall off as quickly.

782
00:38:44,920 --> 00:38:48,080
Speaker 1: It doesn't get weak as quickly with large distances.

783
00:38:48,080 --> 00:38:51,760
Speaker 3: Interesting, So, like the gravity I feel with another planet

784
00:38:51,840 --> 00:38:54,120
Speaker 3: on the other side of the Milky Way, maybe it's

785
00:38:54,160 --> 00:38:55,719
Speaker 3: stronger than I think.

786
00:38:55,840 --> 00:38:57,879
Speaker 1: Yeah, maybe it's not like one over our square, it's

787
00:38:57,920 --> 00:39:00,319
Speaker 1: more like one over R and R is still really

788
00:39:00,320 --> 00:39:02,759
Speaker 1: really large. So you know, those planets don't affect you

789
00:39:02,840 --> 00:39:06,120
Speaker 1: because the gravity from them is still really tiny. But

790
00:39:06,239 --> 00:39:08,200
Speaker 1: if you're adding up lots of planets and you're trying

791
00:39:08,200 --> 00:39:11,120
Speaker 1: to calculate, like how a whole galaxy spins, then it

792
00:39:11,160 --> 00:39:13,279
Speaker 1: really does make a big difference to go like one

793
00:39:13,320 --> 00:39:15,880
Speaker 1: of our are instead of one of her are squared.

794
00:39:16,200 --> 00:39:18,919
Speaker 1: But it seems a bit hacky as opposed to dark matter.

795
00:39:19,880 --> 00:39:22,799
Speaker 1: Dark matter doesn't seem hacky. Well, dark matter, you know,

796
00:39:22,800 --> 00:39:25,680
Speaker 1: you can explain a lot of really different things adding

797
00:39:25,800 --> 00:39:28,239
Speaker 1: just one simple idea, like hey, what if there's a

798
00:39:28,280 --> 00:39:31,040
Speaker 1: new particle that's not hacky, Like we don't know why

799
00:39:31,080 --> 00:39:33,160
Speaker 1: there's a certain number of particles in the universe and

800
00:39:33,200 --> 00:39:35,879
Speaker 1: not more, or if there are more, So adding one

801
00:39:35,920 --> 00:39:38,560
Speaker 1: new particle doesn't feel as hacky as like let's have

802
00:39:38,640 --> 00:39:41,120
Speaker 1: gravity have a knob on it, or like a distance

803
00:39:41,200 --> 00:39:44,319
Speaker 1: above which it starts behaving different rules, or you know,

804
00:39:44,440 --> 00:39:47,600
Speaker 1: small accelerations below which it starts behaving differently.

805
00:39:47,719 --> 00:39:50,319
Speaker 3: Really, why does it need to be low accelerations? How

806
00:39:50,360 --> 00:39:50,839
Speaker 3: does that work?

807
00:39:50,880 --> 00:39:53,520
Speaker 1: In it doesn't really work as I think I heard

808
00:39:53,520 --> 00:39:56,640
Speaker 1: you react because like acceleration with respect to what right,

809
00:39:56,680 --> 00:39:59,239
Speaker 1: all of a sudden, the gravity you feel depends on

810
00:39:59,280 --> 00:40:02,680
Speaker 1: your reference and it breaks all sorts of symmetries. But

811
00:40:02,719 --> 00:40:06,479
Speaker 1: there is that one idea that accelerations like one ten

812
00:40:06,600 --> 00:40:09,000
Speaker 1: trillionth of the gravity on Earth. If you feel an

813
00:40:09,040 --> 00:40:12,440
Speaker 1: acceleration less than that, then the gravity on you behaves

814
00:40:12,480 --> 00:40:15,080
Speaker 1: differently than it does for larger accelerations.

815
00:40:15,200 --> 00:40:17,480
Speaker 3: Oh, I see, it's not you're not saying when you're

816
00:40:17,480 --> 00:40:21,240
Speaker 3: going at a low acceleration is just when the effects

817
00:40:21,280 --> 00:40:23,440
Speaker 3: of gravity are small, maybe it doesn't behave as one

818
00:40:23,440 --> 00:40:24,120
Speaker 3: over our square.

819
00:40:24,200 --> 00:40:26,359
Speaker 1: Yeah, And the effects of gravity at very very far

820
00:40:26,520 --> 00:40:30,440
Speaker 1: distances are really small. Like what is the acceleration on

821
00:40:30,520 --> 00:40:33,359
Speaker 1: some star at the edge of the galaxy due to

822
00:40:33,400 --> 00:40:35,360
Speaker 1: the black hole the center of the galaxy. Well, the

823
00:40:35,400 --> 00:40:38,840
Speaker 1: distance is fifty thousand light years, so the acceleration is

824
00:40:39,080 --> 00:40:42,319
Speaker 1: very small, also because the masses are large. And so

825
00:40:42,360 --> 00:40:44,560
Speaker 1: it's just a way to say, let's have it have

826
00:40:44,600 --> 00:40:47,799
Speaker 1: an effect where we see this weirdness and not have

827
00:40:47,880 --> 00:40:50,560
Speaker 1: an effect anywhere else. Let's try not to break what

828
00:40:50,600 --> 00:40:53,360
Speaker 1: we already know and understand and only have this theory

829
00:40:53,360 --> 00:40:54,880
Speaker 1: turn on in special cases.

830
00:40:55,320 --> 00:40:57,600
Speaker 3: All right, so that's a possibility. But where did this

831
00:40:57,640 --> 00:40:59,840
Speaker 3: idea come from? Like why would we think that maybe

832
00:41:00,000 --> 00:41:00,680
Speaker 3: gravity is wrong?

833
00:41:00,760 --> 00:41:02,720
Speaker 1: So for a long time there wasn't really a good idea.

834
00:41:02,760 --> 00:41:04,520
Speaker 1: There was just like, well, I don't know, but if

835
00:41:04,560 --> 00:41:07,360
Speaker 1: I put in this other formula, I can explain the galaxy.

836
00:41:07,360 --> 00:41:09,799
Speaker 4: I rotation curves without dark matter.

837
00:41:09,640 --> 00:41:11,480
Speaker 1: Without dark matter. Yeah, so they're like, all right, so

838
00:41:11,600 --> 00:41:15,200
Speaker 1: either there's missing mass or gravity works this other weird way.

839
00:41:15,480 --> 00:41:18,200
Speaker 1: And then people started thinking, well, why would gravity work

840
00:41:18,239 --> 00:41:20,399
Speaker 1: that way? Is there any reason for it? And that's

841
00:41:20,440 --> 00:41:23,040
Speaker 1: a totally valid line of inquiry, right, like what theory

842
00:41:23,080 --> 00:41:25,000
Speaker 1: do we have to have to explain the data? And

843
00:41:25,400 --> 00:41:27,400
Speaker 1: does that theory make sense? Can we come up with

844
00:41:27,480 --> 00:41:30,400
Speaker 1: a reason why maybe that theory is right? A theory

845
00:41:30,440 --> 00:41:34,520
Speaker 1: about a theory underpinnings of the theory, right. We always

846
00:41:34,560 --> 00:41:37,160
Speaker 1: in physics want to have a microscopic understanding. We don't

847
00:41:37,160 --> 00:41:39,480
Speaker 1: want to just say gravity just has this number on it.

848
00:41:39,520 --> 00:41:41,239
Speaker 1: We want to know why does it, Where does that

849
00:41:41,280 --> 00:41:43,440
Speaker 1: come from? Why isn't it something else? Just like you

850
00:41:43,440 --> 00:41:45,520
Speaker 1: were saying earlier, why is it one of our square

851
00:41:45,640 --> 00:41:47,760
Speaker 1: not one over are two point one or whatever?

852
00:41:47,960 --> 00:41:49,239
Speaker 4: That's the next version.

853
00:41:50,360 --> 00:41:54,120
Speaker 1: That upgraded gravity. And so recently there is an idea

854
00:41:54,560 --> 00:41:57,520
Speaker 1: from a guy in Holland, Eric Verlinda, and he has

855
00:41:57,600 --> 00:42:01,319
Speaker 1: this crazy idea of gravity called in tropic gravity that

856
00:42:01,600 --> 00:42:05,520
Speaker 1: might be able to explain why gravity works differently at

857
00:42:05,520 --> 00:42:06,480
Speaker 1: these distance scales.

858
00:42:06,560 --> 00:42:09,680
Speaker 3: Hmmm, I feel like maybe he just grab two cool

859
00:42:09,719 --> 00:42:13,680
Speaker 3: sounding things and put them together. Tropic he did sort

860
00:42:13,719 --> 00:42:16,000
Speaker 3: of like dynamic gravity or something, but it.

861
00:42:15,960 --> 00:42:17,000
Speaker 1: Comes from a cool place.

862
00:42:17,040 --> 00:42:17,200
Speaker 8: You know.

863
00:42:17,400 --> 00:42:21,640
Speaker 1: It was Stephen Hawking who first connected sort of thermodynamics

864
00:42:22,040 --> 00:42:26,160
Speaker 1: and gravity. He started thinking about the temperature of black

865
00:42:26,200 --> 00:42:29,399
Speaker 1: holes and thinking, you know, if black holes have temperatures,

866
00:42:29,680 --> 00:42:32,800
Speaker 1: that means they should radiate. Oh wait, and that's Hawking radiation.

867
00:42:33,320 --> 00:42:35,319
Speaker 1: So in the last sort of forty years, people have

868
00:42:35,360 --> 00:42:38,720
Speaker 1: been thinking about gravity and thormour dynamics as a connection.

869
00:42:38,800 --> 00:42:42,080
Speaker 1: They're trying to understand like, you know, actually, maybe gravity

870
00:42:42,200 --> 00:42:46,280
Speaker 1: isn't a fundamental force. And maybe, you know Einstein's idea

871
00:42:46,360 --> 00:42:49,160
Speaker 1: that gravity is just a curvature of space time, maybe

872
00:42:49,200 --> 00:42:52,960
Speaker 1: that's also wrong. Maybe instead, gravity is just like an

873
00:42:52,960 --> 00:42:58,200
Speaker 1: emergent phenomena of thermodynamics. Maybe it's just like comes out

874
00:42:58,239 --> 00:43:01,960
Speaker 1: of the manipulation and an interaction of some tiny little

875
00:43:02,000 --> 00:43:05,239
Speaker 1: bits of space in a way that feels like gravity

876
00:43:05,280 --> 00:43:05,879
Speaker 1: to us.

877
00:43:06,160 --> 00:43:07,960
Speaker 4: That's a little bit mind blowing.

878
00:43:08,080 --> 00:43:10,400
Speaker 1: Yeah, it's a little bit mind blowing. This whole idea

879
00:43:10,600 --> 00:43:13,440
Speaker 1: emergent phenomena can be hard to get your mind around,

880
00:43:13,440 --> 00:43:15,799
Speaker 1: but it's actually very familiar, you know, Like we can

881
00:43:15,880 --> 00:43:19,120
Speaker 1: talk about wind, right. Wind is an emergent phenomena. It's

882
00:43:19,120 --> 00:43:21,879
Speaker 1: not a fundamental force in the universe. You know, two

883
00:43:21,920 --> 00:43:25,920
Speaker 1: particles interacting don't feel wind. Wind is a combination of

884
00:43:25,960 --> 00:43:28,440
Speaker 1: lots of other things we do understand on a microscopic

885
00:43:28,560 --> 00:43:33,320
Speaker 1: level that has a macroscopic effect, or like economics. You know,

886
00:43:33,360 --> 00:43:35,960
Speaker 1: there are laws of economics that come from you know,

887
00:43:36,040 --> 00:43:38,719
Speaker 1: supply and demand or whatever. It's not a fundamental force

888
00:43:38,760 --> 00:43:41,200
Speaker 1: in the universe, but still you could have an understanding

889
00:43:41,239 --> 00:43:44,000
Speaker 1: of it. And so they think maybe gravity is just

890
00:43:44,120 --> 00:43:49,040
Speaker 1: like a macroscopic effect of something microscopic. Maybe the thermodynamics

891
00:43:49,040 --> 00:43:50,319
Speaker 1: of space design.

892
00:43:50,680 --> 00:43:53,239
Speaker 3: Like there is no gravity, it's just kind of like

893
00:43:53,400 --> 00:43:56,480
Speaker 3: how space itself kind of arranges itself.

894
00:43:56,520 --> 00:43:59,640
Speaker 1: Yeah, because we know that space likes to increase entropy,

895
00:44:00,120 --> 00:44:04,239
Speaker 1: increase disorder, and so we think entropy always increases in

896
00:44:04,280 --> 00:44:06,760
Speaker 1: the universe, and so maybe gravity is just an effect

897
00:44:06,760 --> 00:44:09,279
Speaker 1: of that. You know, the argument goes something like when

898
00:44:09,360 --> 00:44:12,560
Speaker 1: things fall into a black hole, for example, that increases

899
00:44:12,600 --> 00:44:15,520
Speaker 1: the entropy of the black hole, because otherwise it would

900
00:44:15,640 --> 00:44:17,840
Speaker 1: violate the second law of thermo dynamics. Things can't just

901
00:44:17,960 --> 00:44:21,520
Speaker 1: disappear into the black hole. But maybe it's the opposite.

902
00:44:21,640 --> 00:44:24,319
Speaker 1: Maybe it's not that gravity pulls things into the black

903
00:44:24,360 --> 00:44:28,120
Speaker 1: hole and then increases the entropy. Maybe it's entropy that's

904
00:44:28,120 --> 00:44:31,359
Speaker 1: pushing things into black holes, and that's actually what gravity is.

905
00:44:31,560 --> 00:44:35,200
Speaker 1: That's just like you know, the way gas diffuses in

906
00:44:35,239 --> 00:44:37,319
Speaker 1: a box. You put a blob of gas in the

907
00:44:37,320 --> 00:44:40,040
Speaker 1: corner of a box and it spreads out into the box.

908
00:44:40,320 --> 00:44:43,360
Speaker 1: That's entropy in the same way. Maybe entropy is stuff

909
00:44:43,520 --> 00:44:47,239
Speaker 1: falling into itself, like you know, having more stuff near

910
00:44:47,320 --> 00:44:51,640
Speaker 1: itself dense blobs of mass increases the temperature, which changes

911
00:44:51,680 --> 00:44:54,280
Speaker 1: the entropy of the situation. I mean, it's a complicated

912
00:44:54,400 --> 00:44:58,040
Speaker 1: argument involving like quantum entangled space time, but I think

913
00:44:58,040 --> 00:44:58,799
Speaker 1: that's the gist of it.

914
00:44:58,880 --> 00:45:01,520
Speaker 3: Well, and all of that kind crazy idea is just

915
00:45:01,560 --> 00:45:04,319
Speaker 3: to explain how maybe gravity could not be one over

916
00:45:04,400 --> 00:45:04,920
Speaker 3: our square.

917
00:45:05,000 --> 00:45:07,680
Speaker 1: Yeah, if you have in tropic gravity, so maybe if

918
00:45:07,719 --> 00:45:10,719
Speaker 1: gravity is not a fundamental force in the universe, but

919
00:45:10,880 --> 00:45:14,359
Speaker 1: just like an emergent property of quantum space time, and

920
00:45:14,520 --> 00:45:18,760
Speaker 1: you have dark energy, then Verlindis theory predicts that space

921
00:45:18,840 --> 00:45:22,440
Speaker 1: curves in this way, that gravity, the effective force of gravity,

922
00:45:22,760 --> 00:45:26,120
Speaker 1: goes the way Mond needs it to explain the galactic

923
00:45:26,160 --> 00:45:30,560
Speaker 1: rotation curves. So that's kind of interesting. That's an alternative

924
00:45:30,600 --> 00:45:32,960
Speaker 1: to dark matter. That is one alternative to dark matters

925
00:45:32,960 --> 00:45:37,560
Speaker 1: to say we have this weird gravitational thermodynamics idea that

926
00:45:37,680 --> 00:45:40,920
Speaker 1: changes the way gravity works. That explains why we thought

927
00:45:40,920 --> 00:45:43,799
Speaker 1: there was missing stuff. Instead, it's just the gravity works

928
00:45:43,800 --> 00:45:44,960
Speaker 1: differently than we expect it.

929
00:45:45,120 --> 00:45:47,280
Speaker 3: Interesting, all right, So then I guess the big question

930
00:45:47,400 --> 00:45:51,120
Speaker 3: is could that work? Is that a valid or plausible

931
00:45:51,160 --> 00:45:55,279
Speaker 3: theory that maybe explains gravity in a different way that

932
00:45:55,360 --> 00:45:58,719
Speaker 3: then explains dark matter and so that it's not just

933
00:45:58,760 --> 00:46:00,720
Speaker 3: another particle or kind of stuff.

934
00:46:01,080 --> 00:46:01,719
Speaker 4: Could that work?

935
00:46:01,840 --> 00:46:04,920
Speaker 1: Well, it's a cool idea, and it does explain galaxy

936
00:46:05,000 --> 00:46:09,480
Speaker 1: rotation curves, and it actually explains galaxy rotation curves better

937
00:46:09,560 --> 00:46:12,200
Speaker 1: than dark matterness. What there's some galaxies out there that

938
00:46:12,239 --> 00:46:14,960
Speaker 1: we still can't explain using dark matter, like they rotate

939
00:46:14,960 --> 00:46:17,600
Speaker 1: in weird ways and we don't understand it, and you know,

940
00:46:17,640 --> 00:46:20,799
Speaker 1: but hey, galaxies are weird, but they sort of fit.

941
00:46:21,840 --> 00:46:24,200
Speaker 4: They have their own history.

942
00:46:24,560 --> 00:46:29,280
Speaker 1: No, my theory, that's right, My theory that the universe

943
00:46:29,360 --> 00:46:31,239
Speaker 1: is just weird explains everything.

944
00:46:31,000 --> 00:46:33,960
Speaker 3: Oh man, the whites and theory of everything.

945
00:46:34,120 --> 00:46:37,239
Speaker 1: The whites and theory of weirdness. But it explains the

946
00:46:37,239 --> 00:46:41,520
Speaker 1: galaxy rotation curves really nicely. But there's a big caveat there,

947
00:46:41,520 --> 00:46:45,400
Speaker 1: which is it was sort of invented to explain those curves,

948
00:46:45,440 --> 00:46:49,520
Speaker 1: like you came up with a theory to fit that data. Really,

949
00:46:49,600 --> 00:46:52,120
Speaker 1: a good test of a theory is does it explain

950
00:46:52,320 --> 00:46:56,080
Speaker 1: other data? Is it a real general principle about the universe,

951
00:46:56,120 --> 00:46:58,640
Speaker 1: something which is really deeply true, or is it just

952
00:46:58,719 --> 00:47:01,760
Speaker 1: a mathematical tweak to the one plot this one figure

953
00:47:01,960 --> 00:47:02,320
Speaker 1: to make it.

954
00:47:02,320 --> 00:47:04,399
Speaker 3: Because if it only works to explain one thing, it's

955
00:47:04,440 --> 00:47:06,120
Speaker 3: it's kind of suspicious, right exactly.

956
00:47:06,360 --> 00:47:08,919
Speaker 1: And if it only works to explain the one thing

957
00:47:08,960 --> 00:47:11,840
Speaker 1: that motivated it, then probably it's not a deep truth

958
00:47:11,920 --> 00:47:13,320
Speaker 1: of the universe, right.

959
00:47:14,000 --> 00:47:17,000
Speaker 3: All right, So maybe it doesn't work. Can it explain

960
00:47:17,080 --> 00:47:19,040
Speaker 3: some of the other things that we know about dark matter,

961
00:47:19,160 --> 00:47:23,640
Speaker 3: like the lensing and the cosmic microwave background and the

962
00:47:23,680 --> 00:47:26,600
Speaker 3: structure of the universe. A tweak to our theory of

963
00:47:26,640 --> 00:47:28,320
Speaker 3: gravity also explain all these.

964
00:47:28,160 --> 00:47:31,879
Speaker 1: Things in a word, No, it just doesn't work.

965
00:47:32,040 --> 00:47:33,440
Speaker 4: No, galaxies are just weird.

966
00:47:33,560 --> 00:47:35,960
Speaker 1: No, galaxes is just weird. No, it does not explain

967
00:47:36,040 --> 00:47:39,360
Speaker 1: the cosmic microwave background. Like, it's very difficult to explain

968
00:47:39,440 --> 00:47:43,520
Speaker 1: that using anything else other than some new kind of

969
00:47:43,560 --> 00:47:46,959
Speaker 1: particle or primordial black hole or something, some new kind

970
00:47:47,000 --> 00:47:49,719
Speaker 1: of stuff. You just can't explain it using deviation and

971
00:47:49,760 --> 00:47:51,960
Speaker 1: gravity because it was on a really small scale. This

972
00:47:52,080 --> 00:47:54,479
Speaker 1: is like, really, you know, things were nearby each other.

973
00:47:54,800 --> 00:47:58,360
Speaker 1: This wasn't galactic distances interesting, and it's very difficult to

974
00:47:58,400 --> 00:48:00,759
Speaker 1: explain the structure of the universe. And then there's this

975
00:48:00,800 --> 00:48:03,480
Speaker 1: one really awesome example of dark matter that's sort of

976
00:48:03,520 --> 00:48:06,759
Speaker 1: like a smoking gun that makes it almost impossible to

977
00:48:06,800 --> 00:48:10,600
Speaker 1: explain using anything but some new kind of matter, some

978
00:48:10,640 --> 00:48:13,480
Speaker 1: new kind of stuff. Yeah, and that's this bullet cluster.

979
00:48:13,880 --> 00:48:16,959
Speaker 1: There was this collision millions and millions of years ago,

980
00:48:17,200 --> 00:48:20,840
Speaker 1: far far away between two clusters of galaxy that passed

981
00:48:20,880 --> 00:48:23,400
Speaker 1: through each other. And we thought that those clusters of

982
00:48:23,440 --> 00:48:26,840
Speaker 1: galaxies they had normal matter like stars and planets, et cetera,

983
00:48:27,080 --> 00:48:29,880
Speaker 1: and then also clumps of dark matter. So what happened

984
00:48:29,960 --> 00:48:33,279
Speaker 1: is they passed through each other, and the gas and

985
00:48:33,320 --> 00:48:35,759
Speaker 1: the dust it all collided and made big collisions and

986
00:48:35,840 --> 00:48:38,399
Speaker 1: slowed down and all that stuff. But the dark matter,

987
00:48:38,440 --> 00:48:40,479
Speaker 1: it doesn't interact with the normal matter, and it doesn't

988
00:48:40,520 --> 00:48:43,520
Speaker 1: interact with itself very much at all either because gravity

989
00:48:43,600 --> 00:48:45,560
Speaker 1: is so weak. So the dark matters just sort of

990
00:48:45,600 --> 00:48:48,000
Speaker 1: passed through. So what we see when we look up

991
00:48:48,040 --> 00:48:49,920
Speaker 1: in the skies, we see like a big blob in

992
00:48:49,960 --> 00:48:52,480
Speaker 1: the center of all the gas and dust that interacted,

993
00:48:52,760 --> 00:48:55,439
Speaker 1: and then on either side we see the dark matter

994
00:48:55,480 --> 00:48:57,880
Speaker 1: that passed through, and we can see that because of

995
00:48:57,920 --> 00:48:59,120
Speaker 1: the gravitational lensing.

996
00:48:59,360 --> 00:49:01,000
Speaker 3: But doesn't it all I know, we talked about the

997
00:49:01,040 --> 00:49:03,719
Speaker 3: bullet cluster before, but doesn't it still just come down

998
00:49:03,800 --> 00:49:09,160
Speaker 3: to gravitational lensing? Like, what if gravity can explain gravitational lensing,

999
00:49:09,640 --> 00:49:12,799
Speaker 3: could that also explain the bullet cluster that we see.

1000
00:49:12,880 --> 00:49:15,120
Speaker 1: It's very difficult to explain the bullet cluster in any

1001
00:49:15,120 --> 00:49:17,319
Speaker 1: other way because you need to have gravitational lensing in

1002
00:49:17,400 --> 00:49:21,759
Speaker 1: exactly those right spots on opposite sides of this very

1003
00:49:21,800 --> 00:49:25,440
Speaker 1: obvious collision. So it's a very nice explanation to think, Oh,

1004
00:49:25,440 --> 00:49:27,839
Speaker 1: there's some invisible matter that passed through and it's now

1005
00:49:27,880 --> 00:49:30,440
Speaker 1: sitting there distorting the background galaxy.

1006
00:49:30,520 --> 00:49:30,799
Speaker 4: I see.

1007
00:49:30,800 --> 00:49:34,279
Speaker 3: The bullet cluster is like proof that whatever's causing these

1008
00:49:34,320 --> 00:49:38,200
Speaker 3: gravitational things is mobile, like it can move like stuff.

1009
00:49:38,520 --> 00:49:41,880
Speaker 3: But if it was just a gravitational theory tweak, that

1010
00:49:41,880 --> 00:49:44,440
Speaker 3: wouldn't like keep going or move or change from here

1011
00:49:44,440 --> 00:49:44,840
Speaker 3: to there.

1012
00:49:44,800 --> 00:49:47,799
Speaker 1: Exactly, and it can be separated from the normal matter.

1013
00:49:47,880 --> 00:49:51,000
Speaker 1: It's not just a gravitational tweak from the normal matter, right,

1014
00:49:51,000 --> 00:49:53,759
Speaker 1: the normal matter was left behind in the middle. It's

1015
00:49:53,800 --> 00:49:56,640
Speaker 1: its own kind of stuff. It has its own gravity,

1016
00:49:57,120 --> 00:49:59,360
Speaker 1: and so that's sort of like a bullet in the

1017
00:49:59,400 --> 00:50:02,560
Speaker 1: brain of the you know, non dark matter theories. Wow,

1018
00:50:02,640 --> 00:50:07,080
Speaker 1: the bullet cluster is a bullet. People really took Mond

1019
00:50:07,239 --> 00:50:09,920
Speaker 1: sort of seriously until then. And then when the bullet

1020
00:50:09,920 --> 00:50:12,840
Speaker 1: cluster was discovered, people were like, oh, well that's it.

1021
00:50:12,920 --> 00:50:13,600
Speaker 1: Dark matter is.

1022
00:50:13,600 --> 00:50:16,440
Speaker 4: Real and Mond is dead never mind.

1023
00:50:17,760 --> 00:50:20,680
Speaker 1: And at that point people really didn't take Mond seriously.

1024
00:50:20,760 --> 00:50:23,799
Speaker 1: So since then, Mond has been much more of a

1025
00:50:23,840 --> 00:50:26,920
Speaker 1: fringe theory. I mean, Virlin's idea is more recent and

1026
00:50:26,960 --> 00:50:29,560
Speaker 1: it's sort of cool, but it sort of explains something

1027
00:50:29,600 --> 00:50:33,880
Speaker 1: that nobody really takes seriously anymore. So it's very fringe.

1028
00:50:33,440 --> 00:50:33,799
Speaker 4: In a way.

1029
00:50:33,840 --> 00:50:36,840
Speaker 3: The bullet cluster shows you that dark matter or whatever

1030
00:50:36,920 --> 00:50:41,000
Speaker 3: is causing these gravitational distortions and footprints is mobile like

1031
00:50:41,040 --> 00:50:42,520
Speaker 3: it's it can move like stuff.

1032
00:50:42,560 --> 00:50:43,919
Speaker 4: It moves like stuff can move.

1033
00:50:44,360 --> 00:50:48,000
Speaker 1: Yeah, and so again it's unsatisfying because we don't know

1034
00:50:48,080 --> 00:50:50,440
Speaker 1: what it is, and and we've been looking for for

1035
00:50:50,480 --> 00:50:52,359
Speaker 1: a while. It's not like we're just like, oh, it's

1036
00:50:52,520 --> 00:50:56,600
Speaker 1: some invisible stuff, let's move on. We've built dedicated experiments

1037
00:50:56,600 --> 00:50:59,040
Speaker 1: to look for it. We've thought several times that we

1038
00:50:59,080 --> 00:51:02,279
Speaker 1: would definitely find and then haven't seen it. So there's

1039
00:51:02,280 --> 00:51:04,440
Speaker 1: definitely some tension there. It's not like dark matter is

1040
00:51:04,440 --> 00:51:07,160
Speaker 1: a beautiful theory that's all wrapped up, like we don't

1041
00:51:07,280 --> 00:51:10,200
Speaker 1: understand why we haven't been able to find the dark

1042
00:51:10,280 --> 00:51:13,520
Speaker 1: matter yet. There's definitely something weird going on there. And

1043
00:51:13,560 --> 00:51:16,480
Speaker 1: it's very healthy to think about new ideas, but mond

1044
00:51:16,640 --> 00:51:19,879
Speaker 1: doesn't quite work. There is no other idea out there

1045
00:51:19,920 --> 00:51:23,279
Speaker 1: that explains what we see nearly as well as some

1046
00:51:23,400 --> 00:51:26,760
Speaker 1: new cold particle hey idea, is it snack based?

1047
00:51:27,360 --> 00:51:29,480
Speaker 4: It's called Hey, maybe dark matter is weird.

1048
00:51:30,560 --> 00:51:34,200
Speaker 1: Maybe that's weird. Yeah, and that's why people are sort

1049
00:51:34,200 --> 00:51:36,760
Speaker 1: of digging further and further into the barrel of ideas

1050
00:51:36,760 --> 00:51:38,919
Speaker 1: for dark matter. People thought for a long time, okay,

1051
00:51:38,960 --> 00:51:42,800
Speaker 1: dark matter must just be some weakly interacting massive particle,

1052
00:51:42,840 --> 00:51:45,480
Speaker 1: some new blob of stuff, but we haven't seen it.

1053
00:51:45,800 --> 00:51:48,000
Speaker 1: And so then people are like, well, maybe it's axions,

1054
00:51:48,080 --> 00:51:50,839
Speaker 1: or maybe it's primordial black holes or and there are

1055
00:51:50,840 --> 00:51:54,399
Speaker 1: some other even crazier ideas, like squermions, what.

1056
00:51:55,000 --> 00:51:57,760
Speaker 4: Like they're uncomfortable in social situations. What do you mean.

1057
00:51:59,160 --> 00:52:03,160
Speaker 1: Introvert on? Yeah, No, squirmyons are this crazy idea that

1058
00:52:03,560 --> 00:52:06,720
Speaker 1: you know, how particles are like excitations of quantum fields.

1059
00:52:06,719 --> 00:52:09,360
Speaker 1: They're like little bundles of energy in a quantum field.

1060
00:52:09,800 --> 00:52:12,760
Speaker 1: People think, well, maybe not all energy and quantum fields

1061
00:52:12,800 --> 00:52:15,640
Speaker 1: are particles. Maybe some of them are like more distributed

1062
00:52:15,760 --> 00:52:18,279
Speaker 1: or spread out in weird ways. And they found that

1063
00:52:18,360 --> 00:52:21,720
Speaker 1: you can like tangle up quantum fields in these weird ways,

1064
00:52:22,080 --> 00:52:25,120
Speaker 1: like make knots in them, and that's what they call squirmyons.

1065
00:52:25,239 --> 00:52:27,560
Speaker 4: These could create gravity.

1066
00:52:27,800 --> 00:52:30,360
Speaker 1: Yeah, because any energy density creates gravity.

1067
00:52:31,239 --> 00:52:34,600
Speaker 3: Well, we will have to dig into that for another episode.

1068
00:52:34,719 --> 00:52:38,000
Speaker 3: Sounds pretty sure. That's pretty squirmy for sure. So there's

1069
00:52:38,000 --> 00:52:40,160
Speaker 3: lots of ideas, the whole spectrum. Right, dark matter is

1070
00:52:40,200 --> 00:52:43,400
Speaker 3: not just one idea, the sort of spectrum of ideas,

1071
00:52:43,520 --> 00:52:46,360
Speaker 3: all satisfied the condition that it's some new kind of

1072
00:52:46,520 --> 00:52:49,719
Speaker 3: cold object. But what that object is. It could be

1073
00:52:49,719 --> 00:52:52,640
Speaker 3: one particle, could be many kinds of particles. It could

1074
00:52:52,640 --> 00:52:55,000
Speaker 3: be black holes, it could be square meyons, it could

1075
00:52:55,000 --> 00:52:57,600
Speaker 3: be something else we haven't even thought of yet. But

1076
00:52:57,640 --> 00:53:00,600
Speaker 3: whatever it is, we're pretty sure it's stuff. It's something that.

1077
00:53:00,560 --> 00:53:02,280
Speaker 4: Has gravity, stuff, and it's there.

1078
00:53:02,400 --> 00:53:02,799
Speaker 1: That's right.

1079
00:53:02,840 --> 00:53:04,840
Speaker 3: But I mean, it's really interesting because I feel like

1080
00:53:04,880 --> 00:53:07,000
Speaker 3: we've known dark matters there for a while now, and

1081
00:53:07,040 --> 00:53:07,760
Speaker 3: we just can't.

1082
00:53:07,560 --> 00:53:08,200
Speaker 4: Seem to crack it.

1083
00:53:08,280 --> 00:53:09,760
Speaker 1: We can't seem to find it keeps.

1084
00:53:09,840 --> 00:53:12,800
Speaker 3: Eluding us, you know, like it just keeps on hiding

1085
00:53:12,840 --> 00:53:15,120
Speaker 3: there and not letting us know what it is.

1086
00:53:15,160 --> 00:53:16,880
Speaker 1: That's right, But we don't know how long the story is.

1087
00:53:16,920 --> 00:53:17,080
Speaker 10: You know.

1088
00:53:17,120 --> 00:53:19,560
Speaker 1: We were looking for the Higgs boson for fifty years

1089
00:53:19,640 --> 00:53:21,960
Speaker 1: and then we found it. We were looking for the

1090
00:53:22,000 --> 00:53:24,680
Speaker 1: top quark for twenty years before we found it. A

1091
00:53:24,680 --> 00:53:26,640
Speaker 1: lot of those things. People thought, oh, we'll find this

1092
00:53:26,680 --> 00:53:28,279
Speaker 1: in the next year or two, and then they were

1093
00:53:28,520 --> 00:53:31,319
Speaker 1: confused and disappointed. To not discover it soon, but you know,

1094
00:53:31,400 --> 00:53:34,000
Speaker 1: eventually we got there and we figured it out. So

1095
00:53:34,040 --> 00:53:36,960
Speaker 1: maybe we're just five years away from discovering dark matter,

1096
00:53:37,040 --> 00:53:39,040
Speaker 1: or maybe it's going to be another hundred. Maybe we

1097
00:53:39,080 --> 00:53:41,600
Speaker 1: need a new crazy idea for what dark matter is.

1098
00:53:41,640 --> 00:53:43,240
Speaker 1: But dark matter, I'm pretty sure.

1099
00:53:43,600 --> 00:53:48,520
Speaker 3: Is so all those physicists squirming around, relax. Maybe dark

1100
00:53:48,560 --> 00:53:49,440
Speaker 3: matter is in our future.

1101
00:53:49,480 --> 00:53:51,880
Speaker 1: That's right. I certainly hope it is. It'd be fascinating.

1102
00:53:51,920 --> 00:53:54,520
Speaker 1: And remember that it's most of the stuff out there

1103
00:53:54,520 --> 00:53:57,960
Speaker 1: in the universe. Like, what a crazy opportunity to learn

1104
00:53:58,000 --> 00:54:00,880
Speaker 1: about the way the universe works. Yeah, to know that

1105
00:54:00,920 --> 00:54:02,760
Speaker 1: eighty percent of the stuff out there in the universe

1106
00:54:02,800 --> 00:54:05,120
Speaker 1: has been hidden from us. The day we crack that

1107
00:54:05,200 --> 00:54:07,279
Speaker 1: open and get to learn about it, like, it could

1108
00:54:07,320 --> 00:54:11,279
Speaker 1: have incredibly complex structure, it could have interactions and biology

1109
00:54:11,320 --> 00:54:14,120
Speaker 1: and chemistry and all sorts of crazy stuff. Most of

1110
00:54:14,160 --> 00:54:16,239
Speaker 1: the stuff out there in the universe we haven't yet

1111
00:54:16,280 --> 00:54:19,200
Speaker 1: gotten to play with, and so we're eager, we're desperate

1112
00:54:19,200 --> 00:54:20,440
Speaker 1: to figure out what this stuff is.

1113
00:54:20,520 --> 00:54:22,959
Speaker 3: Yeah, because if you're the scientist that discovers what dark

1114
00:54:23,000 --> 00:54:26,000
Speaker 3: matter is, I mean, that's like a lot of street cred,

1115
00:54:26,160 --> 00:54:28,560
Speaker 3: you know, It's like you could say that you discovered

1116
00:54:28,640 --> 00:54:32,480
Speaker 3: eighty percent, eighty percent of everything in the universe. I

1117
00:54:32,480 --> 00:54:34,720
Speaker 3: think they would have to give you five Nobel Prizes,

1118
00:54:34,760 --> 00:54:36,640
Speaker 3: you know, just for that one discovery.

1119
00:54:36,280 --> 00:54:37,759
Speaker 1: They'd have to give you eighty percent of all the

1120
00:54:37,760 --> 00:54:38,480
Speaker 1: Nobel prizes.

1121
00:54:38,520 --> 00:54:40,560
Speaker 4: I think, yeah, yeah, yeah, there you go.

1122
00:54:40,960 --> 00:54:42,719
Speaker 1: You get all the Nobel prices for the next four

1123
00:54:42,800 --> 00:54:44,359
Speaker 1: hundred years, just to balance it out.

1124
00:54:44,920 --> 00:54:45,240
Speaker 4: Yeah.

1125
00:54:45,280 --> 00:54:47,200
Speaker 3: So it's a big question, and who knows, Maybe one

1126
00:54:47,239 --> 00:54:49,960
Speaker 3: of our listeners will be the one who discovers it.

1127
00:54:50,000 --> 00:54:51,520
Speaker 1: That's right, It could be you out there, it could

1128
00:54:51,520 --> 00:54:53,600
Speaker 1: be your kids out there. What we definitely need to

1129
00:54:53,600 --> 00:54:55,400
Speaker 1: do or keep our minds open and come up with

1130
00:54:55,480 --> 00:54:57,040
Speaker 1: new ideas for what dark matter is.

1131
00:54:57,080 --> 00:54:57,600
Speaker 4: Pretty cool?

1132
00:54:57,800 --> 00:55:01,200
Speaker 3: All right, Well, we hope you enjoyed that view into

1133
00:55:01,239 --> 00:55:03,719
Speaker 3: this mysterious dark matter and how we know it's there

1134
00:55:03,760 --> 00:55:06,480
Speaker 3: and how we know it's not just a weird fluke

1135
00:55:06,520 --> 00:55:08,319
Speaker 3: of gravitational equations.

1136
00:55:08,440 --> 00:55:10,160
Speaker 4: Thanks for tuning in, See you next time.

1137
00:55:18,120 --> 00:55:20,920
Speaker 1: Thanks for listening, and remember that. Daniel and Jorge Explain

1138
00:55:21,000 --> 00:55:24,960
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1139
00:55:25,000 --> 00:55:29,160
Speaker 1: from iHeart Radio, visit the iHeartRadio app, Apple Podcasts or

1140
00:55:29,200 --> 00:55:45,239
Speaker 1: wherever you listen to your favorite shows. When you pop

1141
00:55:45,280 --> 00:55:47,279
Speaker 1: a piece of cheese into your mouth, you're probably not

1142
00:55:47,320 --> 00:55:50,239
Speaker 1: thinking about the environmental impact. But the people in the

1143
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Speaker 1: dairy industry are. That's why they're working hard every day

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Speaker 1: to find new ways to reduce waste, conserve natural resources,

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Speaker 1: and drive down greenhouse gas emissions. House US dairy tackling

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Speaker 1: methane from manure into renewable energy that can power farms, towns,

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Speaker 1: and electric cars. Visit you as dairy dot COM's Last

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Speaker 1: Sustainability to learn more.

1150
00:56:14,560 --> 00:56:17,919
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1151
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1157
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1158
00:56:45,760 --> 00:56:45,880
Speaker 10: Hi.

1159
00:56:46,040 --> 00:56:49,680
Speaker 7: I'm David Eagleman. From the podcast Inner Cosmos, which recently

1160
00:56:49,760 --> 00:56:52,480
Speaker 7: hit the number one science podcast in America. I mean

1161
00:56:52,600 --> 00:56:56,239
Speaker 7: neuroscientists at Stanford, and I've spent my career exploring the

1162
00:56:56,360 --> 00:56:57,160
Speaker 7: three pound.

1163
00:56:57,040 --> 00:57:01,640
Speaker 4: Universe in our heads. Join me weekly to or the relationship.

1164
00:57:01,080 --> 00:57:03,960
Speaker 7: Between your brain and your life, because the more we

1165
00:57:04,120 --> 00:57:06,960
Speaker 7: know about what's running under the hood, better we can

1166
00:57:07,120 --> 00:57:10,760
Speaker 7: steer our lives. Listen to Inner Cosmos with David Eagelman

1167
00:57:10,880 --> 00:57:14,080
Speaker 7: on the iHeartRadio app, Apple Podcasts, or wherever you get

1168
00:57:14,120 --> 00:57:15,000
Speaker 7: your podcasts.