WEBVTT - How is general relativity wrong?

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<v Speaker 1>Hey, Daniel, do you get a lot of emails claiming

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<v Speaker 1>that Einstein was wrong?

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<v Speaker 2>Oh? Yeah, just about every day I get an email

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<v Speaker 2>from some retired engineer who sends me there Einstein was

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<v Speaker 2>wrong paper.

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<v Speaker 1>Is that the stereotype they retired engineer who has a

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<v Speaker 1>lot of time in their hands.

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<v Speaker 2>Not just the stereotype, it's also the reality.

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<v Speaker 1>Do you not get emails from retired physicists? Also, physicists

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<v Speaker 1>don't retire. I guess they wouldn't asked you questions if

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<v Speaker 1>they were physicists.

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<v Speaker 2>Yeah, they would just publish the papers themselves.

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<v Speaker 1>Or physicists never retire. Maybe the only engineers are smart

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<v Speaker 1>enough never retire.

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<v Speaker 2>We just read eat away.

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<v Speaker 1>But do you read these emails or do you just

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<v Speaker 1>you know, send them to your trash box.

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<v Speaker 2>No. I give each of them like ten or fifteen minutes.

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<v Speaker 2>See maybe if they're onto something.

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<v Speaker 1>Oh well, ten to fifteen minutes, that's a that's a

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<v Speaker 1>pretty good amount. Do you do it because you think

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<v Speaker 1>they might? You're right?

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<v Speaker 2>Well, I believe in curiosity and maybe somebody out there

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<v Speaker 2>does have a great idea. I mean, their heart's in

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<v Speaker 2>the right place, even if usually the details are wrong.

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<v Speaker 1>So you do think they might be right.

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<v Speaker 2>Well, they're definitely right that Einstein was wrong. It just

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<v Speaker 2>so happens that so are most of these engineers.

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<v Speaker 1>Well, I guess that's wrong. Is Einstein is not a

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<v Speaker 1>bad title. I mean, if he couldn't get it right,

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<v Speaker 1>at least the engineers are trying.

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<v Speaker 2>Eventually, one of these engineers is going to figure it out.

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<v Speaker 1>But what if they figure it out on like the

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<v Speaker 1>sixteenth minute of their paper. Maybe you should double your

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<v Speaker 1>efforts until you retire.

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<v Speaker 2>There you go, that's going to retire me.

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<v Speaker 1>I am horeham May, cartoonists and the author of Oliver's

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<v Speaker 1>Great Big Universe.

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<v Speaker 2>Hi, I'm Daniel. I'm a particle physicist and a professor

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<v Speaker 2>at UC Irvine, and I want to be around when

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<v Speaker 2>we figure out how Einstein was wrong.

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<v Speaker 1>But you don't want to be the one who figures

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<v Speaker 1>it out? Do you just want to be around?

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<v Speaker 2>I just want to cling on to my tenured position

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<v Speaker 2>for long enough to be here for the party when

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<v Speaker 2>somebody else figures it out. Now, I'd love to figure

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<v Speaker 2>it out myself. I'm just not that egotistical.

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<v Speaker 1>Hmm. Do you think there'll be a big party when

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<v Speaker 1>they prove Einstein was wrong? Wouldn't that be sort of like,

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<v Speaker 1>you know, spinning on the grave of a great genius.

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<v Speaker 2>No, I think it was a tremendous accomplishment when Einstein

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<v Speaker 2>proved Newton wrong, and no shade on Newton. You know,

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<v Speaker 2>Newton made a huge advance, a big leap forward, just

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<v Speaker 2>not all the way to the final truth, and same

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<v Speaker 2>way its Einstein. And you know the history of physics

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<v Speaker 2>is littered with these pivotal moments when we made a

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<v Speaker 2>leap forward in understanding. And I want to be around

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<v Speaker 2>when we have one of those.

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<v Speaker 1>But do you think Eistein held a party like and

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<v Speaker 1>Newton was wrong?

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<v Speaker 2>Party was wrong party? I don't know if you put

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<v Speaker 2>it that way, you know, but when his theory of

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<v Speaker 2>john relativity was so publicly proven right by the eclipse

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<v Speaker 2>and the visible bending of light, I bet he had

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<v Speaker 2>a glass of champagne or something.

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<v Speaker 1>Or maybe he was, you know, nice enough not to

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<v Speaker 1>dis ut.

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<v Speaker 2>We're all standing on the shoulders of giants. We don't

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<v Speaker 2>have to denigrate those giants.

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<v Speaker 1>That's why you only like to stand under grave and dance.

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<v Speaker 1>But anyways, welcome to our podcast. Daniel and Jorge explain

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<v Speaker 1>the Universe, a production of iHeartRadio.

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<v Speaker 2>In which we try to climb onto the shoulders of

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<v Speaker 2>those giants with you to bring you along on this

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<v Speaker 2>fascinating journey the humans have been engaged in for thousands

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<v Speaker 2>of years to try to understand the nature of our universe.

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<v Speaker 2>Is there a single law that explains how everything works

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<v Speaker 2>out there? Is there a final truth for us to discover.

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<v Speaker 2>Are we on the path to deeply understanding the nature

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<v Speaker 2>of reality? Or is an endless quest, a long ladder

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<v Speaker 2>of improvements without ever actually reaching the truth.

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<v Speaker 1>That's right because as much as science has discovered about

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<v Speaker 1>the universe, about how how it all works, why it's

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<v Speaker 1>all made off, there's still a whole bunch of stuff

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<v Speaker 1>that we don't know about, big mysteries out during the

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<v Speaker 1>cosmos that we are still trying to figure out, and

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<v Speaker 1>that we have lots of ideas for. But sometimes those

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<v Speaker 1>ideas are not quite right.

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<v Speaker 2>Because science is a process, not a destination, and we

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<v Speaker 2>are continually updating, improving, and revising our theories for how

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<v Speaker 2>things work. We think we understand something, and then decad

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<v Speaker 2>later an engineer shows.

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<v Speaker 1>Us we were wrong, as is always the case.

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<v Speaker 2>But those are happy moments in science. Those are the

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<v Speaker 2>critical pivotal steps forward, those bring us closer to the truth.

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<v Speaker 2>We're not here to defend the ideas of the ancients,

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<v Speaker 2>to hold up Aristotilian physics for everybody to believe in,

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<v Speaker 2>but to bring ourselves closer to the truth by revising

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<v Speaker 2>the ideas of geniuses who have come before us.

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<v Speaker 1>Yeah. I feel like that's a very core principle of

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<v Speaker 1>science that makes it so special, is that there's always

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<v Speaker 1>the possibility that you could be wrong.

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<v Speaker 2>Yeah. In fact, probably everything we know about science is

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<v Speaker 2>wrong in some sense. Everything we do is some approximation

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<v Speaker 2>of the truth which we might never actually reach.

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<v Speaker 1>What do you mean, never reach? Are you giving up now?

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<v Speaker 2>I'm not giving up. I'm promising job security for future physicists.

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<v Speaker 2>I'm saying it's an infinite task.

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<v Speaker 1>You're saying, if you're a physicist, you're never going to retire,

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<v Speaker 1>So choose engineering if you want to at some point

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<v Speaker 1>stop working.

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<v Speaker 2>I'm just trying to be humble. You know, every idea

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<v Speaker 2>we've had in physics has eventually been supplanted by something

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<v Speaker 2>more precise, something we think is more deeply true. It'd

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<v Speaker 2>be really egotistical to say, well, the idea we have now,

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<v Speaker 2>now this is the one that's going to hold up forever.

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<v Speaker 1>Well, this has been going on for centuries and maybe

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<v Speaker 1>even thousands of years, and even big names like Einstein

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<v Speaker 1>people think might not be quite right.

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<v Speaker 2>Some of these theories we've developed are not just very

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<v Speaker 2>very accurate, they're beautiful. They give us deep insights into

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<v Speaker 2>how the universe might work. They tell us a story

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<v Speaker 2>about how the universe functions, sometimes in a way it's

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<v Speaker 2>very surprising and intuitive for us. So it's hard to believe.

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<v Speaker 2>But we think most of these theories might still be wrong.

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<v Speaker 1>So today on the podcast, we'll be tackling the question

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<v Speaker 1>how is general relativity wrong? Shouldn't mean to first talk

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<v Speaker 1>about how it's right.

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<v Speaker 2>We should, but I just.

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<v Speaker 1>Or is that what we've been doing for the last

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<v Speaker 1>five hundred episodes?

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<v Speaker 2>Yeah, the last one hundred years has been how general

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<v Speaker 2>relativity is right? But I was going to say, welcome

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<v Speaker 2>to the group of retired engineers, but then I realized,

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<v Speaker 2>are you a retired engineer? A? Right?

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<v Speaker 1>I am an engineer technically, I guess you don't lose

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<v Speaker 1>the title. Yeah, I'm not quite retired. I'm not sure

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<v Speaker 1>anyone would trust me to design a bridge or any

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<v Speaker 1>kind of a car or anything. Maybe a robot. Robots me,

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<v Speaker 1>what could go wrong.

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<v Speaker 2>With exactly, I've never read a story about robots.

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<v Speaker 1>Robots are totally safe. But yeah, I know. But I

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<v Speaker 1>look forward to to the day where I can, When

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<v Speaker 1>I can retire for sure, then I can send you questions.

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<v Speaker 2>You'll get your fifteen minutes, just like everybody.

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<v Speaker 1>Else, my fifteen minutes of physics. Yes, exactly, that's right,

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<v Speaker 1>most people along for fifteen minutes of fame. The entire

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<v Speaker 1>engineer is long for fifteen minutes of a physicist time.

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<v Speaker 1>But yeah, this is an interesting question to talk about.

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<v Speaker 1>How general relativity, which is I guess, the main theory

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<v Speaker 1>or one of the main theories that Einstein discovered, right, Yeah.

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<v Speaker 2>Einstein made lots of contributions to physics, even inspiring quantum

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<v Speaker 2>mechanics with his explanation of the photoelectric effect, which is

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<v Speaker 2>what he actually won the Nobel Prize for. But a

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<v Speaker 2>lot of people think that his greatest contribution to physics

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<v Speaker 2>really were the theories of special relativity and then general

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<v Speaker 2>relativity and tell us about how light operates, what space

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<v Speaker 2>time really is, and explain that gravity is not actually

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<v Speaker 2>a force, it's just a product of the curvature of

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<v Speaker 2>space and time.

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<v Speaker 1>I would have thought his greatest contribution was hair. Do

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<v Speaker 1>you know. I feel like it's so iconic in the culture,

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<v Speaker 1>and it's given permission to every physicist since then not

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<v Speaker 1>get a haircut.

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<v Speaker 2>But it's so effortless, right, that's the whole point of

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<v Speaker 2>his hair due is like, I don't even care what

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<v Speaker 2>he looks like up there. I don't I don't have

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<v Speaker 2>to look at it. You got to look at.

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<v Speaker 1>It, That's what I mean. That's what I mean. You

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<v Speaker 1>gave permission for the rest of you see, to give

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<v Speaker 1>all of the the other physicists standing on his shoulders

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<v Speaker 1>to just let it all hang out.

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<v Speaker 2>Well, you're standing on his shoulders. You got your head

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<v Speaker 2>stuck right in that hair. You know, you can't really.

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<v Speaker 1>Avoid it everywhere, that's right, Yeah, yeah, yeah, don't drop

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<v Speaker 1>a pan or anything, you might lose it in that hair. Well,

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<v Speaker 1>as usually, we were wondering how many people out there

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<v Speaker 1>had thought about the idea that Einstein might be wrong,

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<v Speaker 1>that general relativity is not quite right, and in which

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<v Speaker 1>way isn't it right?

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<v Speaker 2>So thanks very much to everybody who answers these questions.

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<v Speaker 2>If you would like to join our group of volunteers.

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<v Speaker 2>Please write to me two questions at Danielandjorge dot com.

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<v Speaker 2>We'd love to hear your voice.

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<v Speaker 1>But do you have to be a retired engineer to

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<v Speaker 1>join the group.

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<v Speaker 2>You can be a current engineer, you can be a

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<v Speaker 2>retired engineer, you can be an inspiring engineer, you can

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<v Speaker 2>be a chocolate engineer. Any kind of engineer is welcome,

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<v Speaker 2>even non engineers.

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<v Speaker 1>Well, think about it for a second. How do you

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<v Speaker 1>think general relativity might be wrong? Here's what people had

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<v Speaker 1>to say.

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<v Speaker 3>And I think general relativity is wrong or has to

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<v Speaker 3>be wrong because in its sort of proposition of singularity

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<v Speaker 3>in the middle of black holes, because that's just like impossible, right,

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<v Speaker 3>somehow that has got to be not true.

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<v Speaker 4>I'm I'm entirely sure how general relativity is wrong. It's

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<v Speaker 4>actually been something that's bothering me, so I'll be very

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<v Speaker 4>interested to hear. And I suspect it is quantum physics

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<v Speaker 4>that has disproved, So I'm not entirely sure how the.

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<v Speaker 5>Hi Daniel and Hawaii love your show. Keep up the

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<v Speaker 5>great I think the biggest thing that seems off with

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<v Speaker 5>general relativity to me is the idea that there is

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<v Speaker 5>an infinity. If you think about other concepts like absolute zero,

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<v Speaker 5>there's reasons in real life why we can't reach that temperature.

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<v Speaker 5>And I think if we can understand what those reasons

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<v Speaker 5>are for black holes, for example, then maybe we'll be

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<v Speaker 5>able to understand what the problem is with general relativity.

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<v Speaker 6>Well, it doesn't account for quantum physics and quantum particles,

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<v Speaker 6>and I think with how the Big Bang started, it

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<v Speaker 6>doesn't count for the very initial moments after the Big

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<v Speaker 6>Bang because that includes quantum particles.

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<v Speaker 1>All Right, I feel like maybe we've talked about this

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<v Speaker 1>enough in our podcast, yet people seem pretty familiar with

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<v Speaker 1>this idea.

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<v Speaker 2>Yeah. I think we've been sort of gent nagging general

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<v Speaker 2>relativity for a while now.

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<v Speaker 1>If people have some clues where we're trying to seduce

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<v Speaker 1>general relativity here, what's your plan here?

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<v Speaker 2>No, we've been sort of warming people up to the

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<v Speaker 2>idea that maybe general relativity isn't telling us the truth

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<v Speaker 2>about nature.

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<v Speaker 1>Well, let's dig into Daniel. First of all, what is

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<v Speaker 1>general relativity and how is it different than other kinds

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<v Speaker 1>of relativity.

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<v Speaker 2>So Einstein's first theory of relativity was special relativity, and

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<v Speaker 2>this was in response to weird mysteries about the speed

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<v Speaker 2>of light, the Michaelson Morley experiment, electromagnetism and frame dependence

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<v Speaker 2>and all that stuff. And the theory of special relativity

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<v Speaker 2>is the one that tells us that light moves at

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<v Speaker 2>the same speed for all observers, and it leads us

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<v Speaker 2>to understand how time flows and how events can be

0:11:49.960 --> 0:11:53.000
<v Speaker 2>simultaneous for one person and not simultaneous for another, and

0:11:53.280 --> 0:11:56.199
<v Speaker 2>things get shorter at high speeds, and there's a maximum

0:11:56.240 --> 0:11:59.240
<v Speaker 2>speed at which things could travel. That's all the fascinating

0:11:59.280 --> 0:12:02.880
<v Speaker 2>physics of space relativity, which already was like a huge

0:12:03.040 --> 0:12:06.360
<v Speaker 2>brain twist for people back then, right, it was very

0:12:06.400 --> 0:12:11.000
<v Speaker 2>hard to accept very new idea for how the universe worked.

0:12:11.160 --> 0:12:12.520
<v Speaker 2>That was special relativity.

0:12:13.080 --> 0:12:15.840
<v Speaker 1>But is it called special relativity? What is it special

0:12:16.800 --> 0:12:17.679
<v Speaker 1>from or about?

0:12:17.920 --> 0:12:21.440
<v Speaker 2>Because it's only relevant in one particular circumstance, and that's

0:12:21.480 --> 0:12:24.720
<v Speaker 2>when you assume that space is flat, that space has

0:12:24.760 --> 0:12:29.400
<v Speaker 2>no curvature to it. General relativity is his generalization of

0:12:29.440 --> 0:12:33.800
<v Speaker 2>special relativity to much broader set of cases, scenarios where

0:12:33.960 --> 0:12:36.480
<v Speaker 2>the universe has big lumps of mass in it and

0:12:36.520 --> 0:12:40.000
<v Speaker 2>that mass curves space. Instead of thinking about light pulses

0:12:40.280 --> 0:12:43.640
<v Speaker 2>moving through space in straight lines and staying parallel to

0:12:43.679 --> 0:12:46.440
<v Speaker 2>each other. Now, he developed the mathematics to consider what

0:12:46.520 --> 0:12:49.880
<v Speaker 2>happened when space itself was curved, when light moved in

0:12:49.960 --> 0:12:51.720
<v Speaker 2>what seemed like curved paths.

0:12:52.600 --> 0:12:54.960
<v Speaker 1>But did he call it special relativity when he came

0:12:55.040 --> 0:12:56.920
<v Speaker 1>up with it? Like, did he know as a special

0:12:56.960 --> 0:12:59.320
<v Speaker 1>case and maybe it wouldn't didn't apply to the rest

0:12:59.320 --> 0:12:59.920
<v Speaker 1>of the universe.

0:13:00.080 --> 0:13:00.400
<v Speaker 5>Mm hmm.

0:13:00.440 --> 0:13:03.120
<v Speaker 2>I'm sure some of our German listeners will know how

0:13:03.160 --> 0:13:05.360
<v Speaker 2>to say it in German, because these original papers, of course,

0:13:05.400 --> 0:13:08.000
<v Speaker 2>were not in English. But yeah, he originally called it

0:13:08.000 --> 0:13:10.320
<v Speaker 2>special relativity and then general relativity.

0:13:11.000 --> 0:13:14.160
<v Speaker 1>But does that mean then that special relativity is automatically

0:13:14.200 --> 0:13:17.440
<v Speaker 1>wrong because it only works when space is flat. But

0:13:17.520 --> 0:13:19.960
<v Speaker 1>space is never flat, is it. Yeah, that's a great question,

0:13:20.240 --> 0:13:22.600
<v Speaker 1>and it sort of begs the philosophical question what do

0:13:22.600 --> 0:13:25.760
<v Speaker 1>we mean by wrong? Because the universe is never totally empty.

0:13:25.800 --> 0:13:27.760
<v Speaker 1>Space is always a little bit curved here, a little

0:13:27.760 --> 0:13:29.840
<v Speaker 1>bit curved there. I mean, even if you just have

0:13:29.880 --> 0:13:33.600
<v Speaker 1>a photon passing through space, that is curving space itself, right,

0:13:33.679 --> 0:13:37.480
<v Speaker 1>because photons have energy. So in that sense, special relativity

0:13:37.720 --> 0:13:41.560
<v Speaker 1>is approximately right. It's never deeply truly right because it

0:13:41.559 --> 0:13:43.120
<v Speaker 1>doesn't describe our universe.

0:13:43.440 --> 0:13:46.839
<v Speaker 2>That doesn't mean the rules of special relativity are wrong, right.

0:13:46.880 --> 0:13:49.600
<v Speaker 2>It could be that the rules of special relativity are correct,

0:13:49.840 --> 0:13:53.800
<v Speaker 2>they're just never applicable because the situation describes an energy

0:13:53.880 --> 0:13:55.840
<v Speaker 2>less universe never actually arises.

0:13:56.440 --> 0:13:59.040
<v Speaker 1>Wait, so special relativity sort of only works in a

0:13:59.280 --> 0:14:02.080
<v Speaker 1>new tone in kind of universe. Like you have to

0:14:02.120 --> 0:14:03.679
<v Speaker 1>assume that Newton was right first.

0:14:04.080 --> 0:14:06.520
<v Speaker 2>Well, no, Newton had a different theory of space and time.

0:14:06.600 --> 0:14:09.720
<v Speaker 2>He thought that space and time were absolute backdrops that

0:14:09.760 --> 0:14:13.280
<v Speaker 2>you could like measure your velocity relative to space, that

0:14:13.400 --> 0:14:17.000
<v Speaker 2>space was this like stage upon which everything happened. Special

0:14:17.000 --> 0:14:20.920
<v Speaker 2>relativity already tells you that things like velocity are relative.

0:14:21.120 --> 0:14:23.760
<v Speaker 2>There is no absolute frame of reference to the universe.

0:14:24.000 --> 0:14:27.680
<v Speaker 2>So even special relativity is a big departure from Newton's

0:14:27.720 --> 0:14:29.240
<v Speaker 2>view of how the universe worked.

0:14:29.880 --> 0:14:32.480
<v Speaker 1>But it sort of also assumed that, like a giant universe,

0:14:32.520 --> 0:14:35.080
<v Speaker 1>it is not vendable, that's like fixed, kind.

0:14:34.880 --> 0:14:37.440
<v Speaker 2>Of in the same sense that Newton assumed that, like

0:14:37.560 --> 0:14:41.720
<v Speaker 2>the X axis runs perfectly straight out to infinity. Special

0:14:41.760 --> 0:14:43.160
<v Speaker 2>relativity also assumes that.

0:14:44.560 --> 0:14:49.640
<v Speaker 1>Okay, So then did Einstein know that he had relativity

0:14:49.640 --> 0:14:51.560
<v Speaker 1>in his boget when he came up with special relativity

0:14:51.640 --> 0:14:53.920
<v Speaker 1>or was it like a progression of theories.

0:14:54.480 --> 0:14:56.640
<v Speaker 2>It was definitely a progression. He had not yet solved

0:14:56.640 --> 0:14:59.440
<v Speaker 2>general relativity. This is not like a staged release where

0:14:59.440 --> 0:15:01.240
<v Speaker 2>he's like, I got big idea, but I got to

0:15:01.280 --> 0:15:02.880
<v Speaker 2>like drip it out to the public.

0:15:02.920 --> 0:15:05.960
<v Speaker 1>This is not like a poor camp But he sort

0:15:06.000 --> 0:15:08.200
<v Speaker 1>of knew that he special or if he called it

0:15:08.200 --> 0:15:10.960
<v Speaker 1>special relativity, he knew that only applied to a special case.

0:15:11.360 --> 0:15:13.720
<v Speaker 2>Yeah, but he hadn't solved the general case yet. It

0:15:13.800 --> 0:15:16.320
<v Speaker 2>took him years and years to figure it out because

0:15:16.320 --> 0:15:19.880
<v Speaker 2>the mathematics was super hairy, and he relied on like

0:15:19.960 --> 0:15:23.480
<v Speaker 2>clever ideas from other mathematical geniuses that he talked to

0:15:23.480 --> 0:15:26.040
<v Speaker 2>to make his theory of general relativity work. And it's

0:15:26.040 --> 0:15:29.440
<v Speaker 2>still famously almost impossible to deal with. Like, the equations

0:15:29.440 --> 0:15:32.800
<v Speaker 2>of general relativity are so complicated, we mostly can't even

0:15:32.880 --> 0:15:36.120
<v Speaker 2>solve them for anything that looks like our universe. Like

0:15:36.200 --> 0:15:39.400
<v Speaker 2>we've solved general relativity for scenarios like the universe is

0:15:39.400 --> 0:15:42.360
<v Speaker 2>filled smoothly with mass, where the universe has nothing in

0:15:42.400 --> 0:15:45.000
<v Speaker 2>it but a black hole, we can't exactly solve the

0:15:45.000 --> 0:15:48.280
<v Speaker 2>equations of general relativity for any realistic scenarios because they're

0:15:48.320 --> 0:15:51.160
<v Speaker 2>so hairy. So it took Einstein years to come up

0:15:51.320 --> 0:15:52.040
<v Speaker 2>with his theory.

0:15:52.320 --> 0:15:52.520
<v Speaker 5>Mm.

0:15:52.920 --> 0:15:55.640
<v Speaker 1>But I guess maybe my question is, like, when he

0:15:55.680 --> 0:15:58.720
<v Speaker 1>came up with special relativity, did he know that space

0:15:58.760 --> 0:16:03.200
<v Speaker 1>could actually bend and that the universe actually very different

0:16:03.400 --> 0:16:06.640
<v Speaker 1>or did that come about when he discovered general relativity.

0:16:07.320 --> 0:16:09.560
<v Speaker 2>Now, he had that idea that he wanted to incorporate

0:16:09.720 --> 0:16:12.640
<v Speaker 2>curvature into the fabric of space time as a way

0:16:12.680 --> 0:16:14.800
<v Speaker 2>to explain gravity. He just hadn't figured out how to

0:16:14.800 --> 0:16:17.160
<v Speaker 2>make the mathematics of it all work, and that took

0:16:17.200 --> 0:16:20.160
<v Speaker 2>years and sort of novel mathematics at the time. You know,

0:16:20.200 --> 0:16:23.760
<v Speaker 2>differential geometry, the idea of like thinking about how things

0:16:23.840 --> 0:16:26.800
<v Speaker 2>move along curve services. That was kind of new stuff

0:16:26.800 --> 0:16:27.680
<v Speaker 2>one hundred years ago.

0:16:28.720 --> 0:16:32.400
<v Speaker 1>All right, well, maybe break it down for us, How

0:16:32.400 --> 0:16:34.480
<v Speaker 1>would you explain what general relativity is.

0:16:34.840 --> 0:16:38.400
<v Speaker 2>General relativity is an explanation for why we think there's

0:16:38.440 --> 0:16:41.440
<v Speaker 2>a force of gravity. It tells us that as things

0:16:41.480 --> 0:16:44.520
<v Speaker 2>move through space, it's not as Newton described, that they

0:16:44.560 --> 0:16:46.680
<v Speaker 2>have mass and that mass gives them a force that

0:16:46.680 --> 0:16:50.320
<v Speaker 2>attract each other, but instead that mass bends space and

0:16:50.360 --> 0:16:53.440
<v Speaker 2>then they move according to the curvature of that space.

0:16:53.960 --> 0:16:56.160
<v Speaker 2>So when you jump off a building and you fall

0:16:56.160 --> 0:16:58.960
<v Speaker 2>towards the Earth, it's not that the Earth's gravity is

0:16:59.040 --> 0:17:02.160
<v Speaker 2>pulling on you, accelerating you towards the center of the Earth.

0:17:02.400 --> 0:17:04.639
<v Speaker 2>But now you're moving according to the curvature of space.

0:17:04.680 --> 0:17:07.920
<v Speaker 2>The Earth has bent space, and you're moving along that

0:17:08.040 --> 0:17:11.600
<v Speaker 2>curvature towards the center of the Earth. So it's a

0:17:11.600 --> 0:17:12.359
<v Speaker 2>different picture.

0:17:12.680 --> 0:17:15.560
<v Speaker 1>And I guess you mean space time right, because you

0:17:15.600 --> 0:17:17.760
<v Speaker 1>have to kind of mix time into it, right, because

0:17:17.840 --> 0:17:20.560
<v Speaker 1>like something the bowling belt doesn't fall towards the Earth

0:17:20.880 --> 0:17:21.919
<v Speaker 1>like it needs time to do that.

0:17:22.000 --> 0:17:25.360
<v Speaker 2>Right. Time is definitely important factor. And special relativity already

0:17:25.400 --> 0:17:28.320
<v Speaker 2>showed us that space and time are very closely connected

0:17:28.800 --> 0:17:32.320
<v Speaker 2>and actually linked them together into four dimensional object. And

0:17:32.359 --> 0:17:34.840
<v Speaker 2>in that sort of four dimensional way of thinking, a

0:17:34.840 --> 0:17:36.679
<v Speaker 2>lot of things that didn't make sense in three D

0:17:37.040 --> 0:17:40.320
<v Speaker 2>space and one D time now click together to make

0:17:40.359 --> 0:17:43.320
<v Speaker 2>these really beautiful symmetries that you just don't have if

0:17:43.359 --> 0:17:46.000
<v Speaker 2>you think about space and time separately. The same way

0:17:46.000 --> 0:17:49.160
<v Speaker 2>that like linking electricity and magnetism together into one object

0:17:49.160 --> 0:17:52.240
<v Speaker 2>explains a lot of mysteries between them, linking space and

0:17:52.280 --> 0:17:55.600
<v Speaker 2>time together into one object really makes the mathematics crisp

0:17:55.640 --> 0:17:58.359
<v Speaker 2>and clear and beautiful, so you have special relativity is

0:17:58.359 --> 0:18:00.560
<v Speaker 2>based on the idea that space and time, and general

0:18:00.560 --> 0:18:04.480
<v Speaker 2>relativity just expands that. So absolutely space time is curved,

0:18:04.640 --> 0:18:08.240
<v Speaker 2>and general relativity also predicts the distortion of time. As

0:18:08.320 --> 0:18:12.920
<v Speaker 2>things pass through curvature, their time ticks more slowly. General

0:18:12.960 --> 0:18:15.120
<v Speaker 2>relativity describes the curvature of space time.

0:18:16.480 --> 0:18:18.639
<v Speaker 1>But the way you're describing it is sort of like

0:18:18.960 --> 0:18:19.880
<v Speaker 1>it's all about gravity.

0:18:19.920 --> 0:18:22.800
<v Speaker 2>Gravity comes out as a consequence of this story. Really,

0:18:22.800 --> 0:18:25.080
<v Speaker 2>what we're trying to do is describe the nature of reality,

0:18:25.320 --> 0:18:27.880
<v Speaker 2>like what's out there? Why do things move the way

0:18:27.920 --> 0:18:30.280
<v Speaker 2>we see them moving? If you're in a spaceship and

0:18:30.280 --> 0:18:32.159
<v Speaker 2>you're looking at the Earth orbiting the sull and you

0:18:32.200 --> 0:18:34.720
<v Speaker 2>want to know why is it. Newton tells you one story.

0:18:34.720 --> 0:18:37.240
<v Speaker 2>He says there's a force between these objects pulling on them.

0:18:37.320 --> 0:18:39.960
<v Speaker 2>Einstein tells you a different story. He says there's no

0:18:40.080 --> 0:18:44.000
<v Speaker 2>force there, there's no acceleration. That's the inertial motion of

0:18:44.119 --> 0:18:48.400
<v Speaker 2>the Earth through curved space time. Both stories are trying

0:18:48.440 --> 0:18:51.320
<v Speaker 2>to explain what we see, but they are describing very

0:18:51.320 --> 0:18:52.320
<v Speaker 2>different realities.

0:18:53.040 --> 0:18:54.600
<v Speaker 1>I guess what I mean is like, let's say you

0:18:54.640 --> 0:18:57.800
<v Speaker 1>take gravity out of the equation. Like, you're just talking

0:18:57.840 --> 0:19:01.920
<v Speaker 1>about two electrons in space repelling each other from their

0:19:01.960 --> 0:19:06.160
<v Speaker 1>electrical charge. Do you still need general relativity to describe

0:19:06.160 --> 0:19:07.639
<v Speaker 1>that motion. No.

0:19:07.760 --> 0:19:10.000
<v Speaker 2>In fact, we don't know how to do general relativity

0:19:10.080 --> 0:19:12.200
<v Speaker 2>on electrons. That's one of the problems.

0:19:12.840 --> 0:19:16.600
<v Speaker 1>Oh well, sounds like I just skipped ahead exactly.

0:19:16.680 --> 0:19:19.199
<v Speaker 2>So no, you do not need general relativity to describe

0:19:19.440 --> 0:19:23.000
<v Speaker 2>all the quantum interactions that exist, like in flat space,

0:19:23.040 --> 0:19:26.120
<v Speaker 2>two electrons out there, assume they're not perturbing space because

0:19:26.160 --> 0:19:28.439
<v Speaker 2>their masses are so small. Then no, we can do

0:19:28.520 --> 0:19:32.440
<v Speaker 2>quantum mechanics and explain all those electron interactions without general

0:19:32.480 --> 0:19:35.920
<v Speaker 2>relativity at all. Generalativity tells us about space and time

0:19:36.000 --> 0:19:39.240
<v Speaker 2>and gravity, and that's it. I mean, that's a lot

0:19:39.240 --> 0:19:40.720
<v Speaker 2>of stuff, but that's it all right.

0:19:40.720 --> 0:19:43.080
<v Speaker 1>So then what do you mean by how that this

0:19:43.200 --> 0:19:45.240
<v Speaker 1>theory might be wrong? Like, what would it mean for

0:19:47.000 --> 0:19:47.920
<v Speaker 1>iSight to be wrong?

0:19:48.160 --> 0:19:50.280
<v Speaker 2>Well, one way for theory to be wrong is for

0:19:50.359 --> 0:19:53.800
<v Speaker 2>it to make an incorrect prediction. Right If I say, look,

0:19:53.880 --> 0:19:57.080
<v Speaker 2>I'm fifty years old, and from zero to fifty I've

0:19:57.080 --> 0:19:59.679
<v Speaker 2>grown about a meter and a half. So therefore, in

0:19:59.720 --> 0:20:01.680
<v Speaker 2>my fifty years, I'm also going to grow a meter

0:20:01.720 --> 0:20:04.960
<v Speaker 2>and a half. That's a prediction. It's dumb, obviously, and

0:20:05.000 --> 0:20:07.359
<v Speaker 2>it's going to be disproven if I live another fifty

0:20:07.440 --> 0:20:09.760
<v Speaker 2>years and measure my height. So that's a theory that

0:20:09.760 --> 0:20:12.840
<v Speaker 2>can be proven wrong. Right, So if Einstein's theory makes

0:20:12.840 --> 0:20:15.600
<v Speaker 2>a prediction and that isn't born out by reality, we

0:20:15.640 --> 0:20:18.440
<v Speaker 2>do experiments that show that his predictions are wrong, that's

0:20:18.440 --> 0:20:23.680
<v Speaker 2>a scenario where we would say Einstein was wrong. How Else,

0:20:23.960 --> 0:20:26.520
<v Speaker 2>there's a sort of philosophical sense in which Einstein could

0:20:26.560 --> 0:20:29.320
<v Speaker 2>be wrong, which is all these theories of physics are

0:20:29.359 --> 0:20:31.760
<v Speaker 2>telling us the story. They're an explanation, and all of

0:20:31.800 --> 0:20:35.040
<v Speaker 2>our explanations in the end, are scientific stories about what's happening,

0:20:35.119 --> 0:20:37.520
<v Speaker 2>like why is the Earth moving this way? It's moving

0:20:37.560 --> 0:20:40.320
<v Speaker 2>this way because of the curvature of space time. But

0:20:40.440 --> 0:20:42.960
<v Speaker 2>those stories involve things we can't see, like we can't

0:20:43.000 --> 0:20:46.800
<v Speaker 2>directly observe the curvature of space time, we can't directly

0:20:46.840 --> 0:20:50.919
<v Speaker 2>see electric fields. These stories always involve invisible things that

0:20:50.960 --> 0:20:53.840
<v Speaker 2>we can't detect directly, And so then we wonder like, well,

0:20:53.880 --> 0:20:57.120
<v Speaker 2>what if those stories are wrong, do they actually describe

0:20:57.240 --> 0:20:59.879
<v Speaker 2>reality what's really happening, or are they just sort of

0:20:59.920 --> 0:21:03.159
<v Speaker 2>like the stories we're telling, even if they predict all

0:21:03.160 --> 0:21:06.879
<v Speaker 2>the experiments correctly, could they still be sort of philosophically wrong?

0:21:07.680 --> 0:21:09.720
<v Speaker 1>Is it sort of like, you know, how we thought

0:21:09.800 --> 0:21:12.200
<v Speaker 1>Newton was right for a long time, and it worked

0:21:12.240 --> 0:21:15.080
<v Speaker 1>to describe the motion of baseballs and billard balls, and

0:21:15.760 --> 0:21:18.199
<v Speaker 1>you know, the orbits of the planets, but it's not

0:21:18.359 --> 0:21:19.679
<v Speaker 1>really right at the end of the.

0:21:19.680 --> 0:21:22.600
<v Speaker 2>Day, exactly. We don't think that Newton's story is correct.

0:21:22.640 --> 0:21:25.920
<v Speaker 2>Newton's explanation for billiard balls and planets is not what's

0:21:25.960 --> 0:21:29.719
<v Speaker 2>actually happening, right, and so Newton can't be right. And

0:21:29.760 --> 0:21:31.920
<v Speaker 2>so in that sense we wonder like, well, if it's

0:21:31.960 --> 0:21:35.679
<v Speaker 2>not really philosophically true, is it possible that sometime in

0:21:35.720 --> 0:21:39.080
<v Speaker 2>the future, maybe not today, maybe well beyond our current capabilities,

0:21:39.359 --> 0:21:43.000
<v Speaker 2>that Einstein's theory could be proven wrong in some deep

0:21:43.080 --> 0:21:46.560
<v Speaker 2>future experiment. If it's fundamentally not described in the nature

0:21:46.560 --> 0:21:48.960
<v Speaker 2>of the universe, it might be possible to find a

0:21:48.960 --> 0:21:49.639
<v Speaker 2>way to prove that.

0:21:51.400 --> 0:21:54.359
<v Speaker 1>Well, apparently there's a whole cottage industry of people trying

0:21:54.400 --> 0:21:57.879
<v Speaker 1>to prove Einstein wrong. There have been many experiments, a

0:21:57.880 --> 0:22:01.160
<v Speaker 1>lot of different theories trying to bring the man down

0:22:01.440 --> 0:22:03.879
<v Speaker 1>and so let's dig into that and how exactly general

0:22:03.920 --> 0:22:16.760
<v Speaker 1>relativity is wrong. But first let's take a quick break.

0:22:20.320 --> 0:22:24.200
<v Speaker 1>All right, we're talking about how general relativity might be wrong,

0:22:24.600 --> 0:22:25.639
<v Speaker 1>might be or is wrong.

0:22:26.440 --> 0:22:28.840
<v Speaker 2>I'm pretty sure it is wrong. I mean, we don't

0:22:28.880 --> 0:22:31.000
<v Speaker 2>know for sure. But if I had the place a bet,

0:22:31.119 --> 0:22:32.920
<v Speaker 2>I put my money on Einstein is wrong.

0:22:34.400 --> 0:22:36.320
<v Speaker 1>Are you taking bets? Is there a pool online that

0:22:36.359 --> 0:22:37.840
<v Speaker 1>I can sign up for?

0:22:39.119 --> 0:22:40.239
<v Speaker 2>Oh, you want to bet against me?

0:22:41.920 --> 0:22:48.679
<v Speaker 1>You're betting against Einstein. I don't know who has the

0:22:48.720 --> 0:22:49.920
<v Speaker 1>better hair. You're Einstein.

0:22:52.680 --> 0:22:56.760
<v Speaker 2>Einstein is many things I aspire to, especially this hair

0:22:56.880 --> 0:22:59.160
<v Speaker 2>was all there yet. I know I'm not there yet.

0:23:00.080 --> 0:23:00.639
<v Speaker 1>You could die it.

0:23:00.680 --> 0:23:04.880
<v Speaker 2>I guess who dyes their hair white?

0:23:06.160 --> 0:23:09.240
<v Speaker 1>I don't know. Yeah, you could be the first person.

0:23:09.440 --> 0:23:11.760
<v Speaker 2>Yeah, I think dan Quayle died his Temple's great to

0:23:11.960 --> 0:23:14.080
<v Speaker 2>get a little bit more gravitas. There you go, But

0:23:14.200 --> 0:23:15.359
<v Speaker 2>I prefer the youthful look.

0:23:15.640 --> 0:23:18.000
<v Speaker 1>I see, I see, I'm.

0:23:17.840 --> 0:23:20.160
<v Speaker 2>No longer mistaken for a grad student in my department.

0:23:20.440 --> 0:23:23.320
<v Speaker 1>You don't need great hair in a while. You don't

0:23:23.320 --> 0:23:25.680
<v Speaker 1>need gravitas to prove gravity is wrong.

0:23:25.920 --> 0:23:28.960
<v Speaker 2>No, apparently you don't even need gray hairs. You just

0:23:29.040 --> 0:23:30.680
<v Speaker 2>need a great idea.

0:23:32.000 --> 0:23:37.119
<v Speaker 1>That is a grave bar too to pass. Well, it

0:23:37.160 --> 0:23:38.879
<v Speaker 1>sounds like a lot of people are trying or have

0:23:38.960 --> 0:23:41.720
<v Speaker 1>been trying to prove einsign wrong, or at least they've

0:23:41.800 --> 0:23:44.320
<v Speaker 1>been trying to make sure his theory is right. I

0:23:44.320 --> 0:23:45.959
<v Speaker 1>guess maybe is that a better way to put it.

0:23:46.560 --> 0:23:49.760
<v Speaker 2>Yeah, we have been trying to verify Einstein's theory, or

0:23:49.760 --> 0:23:52.119
<v Speaker 2>at least to check it or to see if it's wrong.

0:23:52.680 --> 0:23:56.640
<v Speaker 2>Because Einstein's theory of gravity doesn't just replace Newton's gravity,

0:23:56.720 --> 0:24:00.840
<v Speaker 2>it changes it. It makes different predictions from newton theory, and

0:24:00.880 --> 0:24:03.200
<v Speaker 2>that allows us to test it, to look for those

0:24:03.320 --> 0:24:07.520
<v Speaker 2>very specific predictions, those consequences of gravity actually being a

0:24:07.560 --> 0:24:10.960
<v Speaker 2>curvature of space time and not a force between two masses.

0:24:11.640 --> 0:24:13.600
<v Speaker 2>So for the last one hundred years or so, we've

0:24:13.600 --> 0:24:14.840
<v Speaker 2>been doing those tests.

0:24:15.160 --> 0:24:18.560
<v Speaker 1>Yeah, doing those tests and also making observations about the universe,

0:24:18.640 --> 0:24:20.919
<v Speaker 1>right as a way to test the theory.

0:24:21.240 --> 0:24:24.240
<v Speaker 2>Yeah, exactly. One way to look for new stuff is

0:24:24.280 --> 0:24:26.880
<v Speaker 2>just like build a new telescope, look deep into the universe,

0:24:26.880 --> 0:24:30.640
<v Speaker 2>wait for surprises. Another very very valuable way to discover

0:24:30.720 --> 0:24:34.119
<v Speaker 2>new stuff is to make very high precision tests of

0:24:34.160 --> 0:24:36.560
<v Speaker 2>your theory. You know, if your theory makes a very

0:24:36.560 --> 0:24:39.160
<v Speaker 2>specific prediction about what's going to happen, then go out

0:24:39.200 --> 0:24:42.280
<v Speaker 2>and do an experiment that's really really precise and check it.

0:24:42.359 --> 0:24:45.760
<v Speaker 2>Because if there's a small discrepancy, that's a hint maybe

0:24:45.760 --> 0:24:47.960
<v Speaker 2>this is something new going on, there's something wrong with

0:24:48.080 --> 0:24:50.520
<v Speaker 2>your theory or some piece of it you haven't accounted for.

0:24:50.880 --> 0:24:53.080
<v Speaker 2>We do that all the time in particle physics, for example,

0:24:53.280 --> 0:24:56.679
<v Speaker 2>we measure the mass of something super duper precisely and

0:24:56.720 --> 0:24:59.439
<v Speaker 2>see if the theory predicts it. Measure the interaction of

0:24:59.440 --> 0:25:02.359
<v Speaker 2>some particle really really precisely, and see if the theory

0:25:02.359 --> 0:25:03.360
<v Speaker 2>predicts it correctly.

0:25:03.440 --> 0:25:04.960
<v Speaker 1>All right, well, what are some of the ways in

0:25:05.000 --> 0:25:07.000
<v Speaker 1>which we've tested Einstein theories.

0:25:07.400 --> 0:25:10.680
<v Speaker 2>Well, one of the early successes was understanding the orbit

0:25:10.760 --> 0:25:14.160
<v Speaker 2>of mercury. You know, the planets orbit the Sun, and

0:25:14.240 --> 0:25:17.040
<v Speaker 2>in Newtonian physics, this is because there's a force there,

0:25:17.640 --> 0:25:20.560
<v Speaker 2>and Newton and Kepler were able to even describe not

0:25:20.640 --> 0:25:23.000
<v Speaker 2>just the circular motion of the planet, but the elliptical

0:25:23.080 --> 0:25:25.919
<v Speaker 2>motion of the planets. Right, the planets don't orbit in

0:25:26.000 --> 0:25:29.199
<v Speaker 2>perfect circles. They orbit in ellipses. But that's okay. In

0:25:29.240 --> 0:25:33.360
<v Speaker 2>Newtonian mechanics, you can have an elliptical orbit that's stable. Right,

0:25:33.400 --> 0:25:35.720
<v Speaker 2>the Sun pulls on things and then it goes faster when

0:25:35.720 --> 0:25:38.280
<v Speaker 2>it's closer and slower when it's further away. The math

0:25:38.320 --> 0:25:42.800
<v Speaker 2>all works out, But an ellipse has a direction to it. Right,

0:25:42.800 --> 0:25:44.720
<v Speaker 2>there's a bit of the ellipse that's longer and a

0:25:44.760 --> 0:25:47.760
<v Speaker 2>bit of the ellipse that's shorter, and procession means that

0:25:47.760 --> 0:25:50.560
<v Speaker 2>that ellipse is turning, like the direction that the ellipse

0:25:50.640 --> 0:25:53.560
<v Speaker 2>is longer and the pointy bits of the football is turning.

0:25:53.640 --> 0:25:56.000
<v Speaker 2>So that's what we call that the procession of the ellipse,

0:25:56.800 --> 0:26:00.199
<v Speaker 2>and Newton can also predict that procession. But what we

0:26:00.240 --> 0:26:03.400
<v Speaker 2>discovered is that the procession of the orbit of Mercury

0:26:03.600 --> 0:26:07.080
<v Speaker 2>was a little bit different from what Newton predicted, and

0:26:07.119 --> 0:26:10.720
<v Speaker 2>Einstein's theory predicted it correctly because it's a different story

0:26:10.920 --> 0:26:12.200
<v Speaker 2>about how gravity works.

0:26:13.200 --> 0:26:15.960
<v Speaker 1>But wait, why mercury, Like, what's different about mercury.

0:26:16.600 --> 0:26:19.040
<v Speaker 2>Well, Mercury is closest to the Sun. And one of

0:26:19.080 --> 0:26:23.639
<v Speaker 2>the crucial differences between Newtonian and Einsteinian gravity is what

0:26:23.760 --> 0:26:27.280
<v Speaker 2>happens when something is spinning. Like Newton says, if an

0:26:27.280 --> 0:26:29.560
<v Speaker 2>object has mass, then you're going to feel it's gravity,

0:26:29.640 --> 0:26:31.879
<v Speaker 2>and it doesn't matter if it's spinning. Take a sphere

0:26:31.880 --> 0:26:34.040
<v Speaker 2>of mass, if it's spinning or not. Newton says it

0:26:34.080 --> 0:26:36.879
<v Speaker 2>has the same gravity. It doesn't matter if it's spinning,

0:26:36.880 --> 0:26:39.640
<v Speaker 2>if it's a perfect sphere, because you always have masses

0:26:39.720 --> 0:26:42.760
<v Speaker 2>in the same place. But Einstein says it does matter

0:26:43.240 --> 0:26:46.280
<v Speaker 2>because Einstein's theory responds not just to the presence of

0:26:46.359 --> 0:26:49.880
<v Speaker 2>mass but energy, and something that's spinning has a different

0:26:50.080 --> 0:26:53.480
<v Speaker 2>energy than something that isn't spinning, and it actually twists

0:26:53.640 --> 0:26:56.440
<v Speaker 2>space time a little bit in a way that twists

0:26:56.480 --> 0:26:59.760
<v Speaker 2>things nearby, gives them little twists. So the Sun is

0:26:59.760 --> 0:27:03.640
<v Speaker 2>giving a little torque to Mercury's procession, according to Einstein

0:27:03.760 --> 0:27:06.480
<v Speaker 2>and not to Newton, and that little torque was enough

0:27:06.480 --> 0:27:09.080
<v Speaker 2>to explain the deviation in the orbit of Mercury.

0:27:09.320 --> 0:27:11.720
<v Speaker 1>WHOA, but you wouldn't feel this here on Earth.

0:27:12.000 --> 0:27:14.119
<v Speaker 2>It's a much smaller effect as you get further and

0:27:14.160 --> 0:27:17.520
<v Speaker 2>further away. But we've actually measured this ourselves. We've put

0:27:17.800 --> 0:27:21.680
<v Speaker 2>super precise satellites in orbit around the Earth to detect

0:27:21.760 --> 0:27:25.080
<v Speaker 2>the effect of the Earth spinning on stuff in orbit

0:27:25.119 --> 0:27:28.040
<v Speaker 2>around the Earth. We had an episode about gravity Probe

0:27:28.080 --> 0:27:32.200
<v Speaker 2>B which involves these incredible gyroscopes, which are the smoothest

0:27:32.280 --> 0:27:36.360
<v Speaker 2>objects known to man, These like incredible balls of quartz

0:27:36.440 --> 0:27:39.560
<v Speaker 2>mined in Brazil and polished by Grammas in Germany until

0:27:39.600 --> 0:27:43.439
<v Speaker 2>they're like incredibly spherical so that they're super precise, and

0:27:43.480 --> 0:27:46.320
<v Speaker 2>they have detected the same thing around the orbit of

0:27:46.320 --> 0:27:46.760
<v Speaker 2>the Earth.

0:27:47.359 --> 0:27:50.240
<v Speaker 1>WHOA, that's another way in which we've proven that Einstein

0:27:50.359 --> 0:27:50.640
<v Speaker 1>was right.

0:27:51.080 --> 0:27:53.800
<v Speaker 2>Yeah, exactly. All of these experiments and some of these

0:27:53.920 --> 0:27:57.080
<v Speaker 2>like they take decades to develop to make so precise,

0:27:57.359 --> 0:28:00.800
<v Speaker 2>and they always come out bang on ein Stein's prediction.

0:28:01.280 --> 0:28:02.440
<v Speaker 2>It's kind of infuriating.

0:28:03.000 --> 0:28:05.520
<v Speaker 1>What do you mean infuriating, Well, we.

0:28:05.480 --> 0:28:08.800
<v Speaker 2>Think Einstein is wrong, and so it's frustrating to not

0:28:08.920 --> 0:28:11.119
<v Speaker 2>be able to prove it right. As soon as we

0:28:11.240 --> 0:28:14.600
<v Speaker 2>find an example where Einstein is wrong, that's a thread

0:28:14.640 --> 0:28:16.560
<v Speaker 2>we can pull on. We can say, okay, here we go,

0:28:16.600 --> 0:28:19.359
<v Speaker 2>here's the lead. The thing is, we think Einstein was

0:28:19.400 --> 0:28:21.919
<v Speaker 2>probably wrong, but we don't know how to improve his theory,

0:28:22.320 --> 0:28:24.840
<v Speaker 2>and until we find a place to where it fails,

0:28:25.200 --> 0:28:26.800
<v Speaker 2>it's difficult to know how to proceed.

0:28:28.920 --> 0:28:31.480
<v Speaker 1>So in the gravity of things and how spinning things

0:28:31.600 --> 0:28:34.359
<v Speaker 1>affect gravity, because Einstein predicted that it would, right.

0:28:35.160 --> 0:28:36.480
<v Speaker 2>Einstein predicted that it would.

0:28:36.560 --> 0:28:39.200
<v Speaker 1>So something that spinning has more gravity to it, Like

0:28:39.240 --> 0:28:41.640
<v Speaker 1>if the Earth was spinning faster, we'd all be heavier.

0:28:42.160 --> 0:28:45.920
<v Speaker 2>It's not just more gravity, right. Newton's equation is one equation,

0:28:45.960 --> 0:28:49.240
<v Speaker 2>it's a single force equation. It tells you the magnitude

0:28:49.280 --> 0:28:51.719
<v Speaker 2>of the force and the direction of it. But Einstein's

0:28:51.760 --> 0:28:55.240
<v Speaker 2>equation is a tenser equation. It's like a big matrix

0:28:55.360 --> 0:28:58.280
<v Speaker 2>of equations and tells you gravity is much more complicated

0:28:58.320 --> 0:29:00.320
<v Speaker 2>than just like a force and a direction, and it

0:29:00.320 --> 0:29:03.680
<v Speaker 2>can also apply a torque. There's all sorts of complicated things.

0:29:03.960 --> 0:29:06.320
<v Speaker 2>So it's not just about more gravity, it's about what

0:29:06.360 --> 0:29:07.480
<v Speaker 2>that gravity is doing.

0:29:08.320 --> 0:29:10.520
<v Speaker 1>But is that true? If the Earth was spinning faster,

0:29:10.600 --> 0:29:11.360
<v Speaker 1>I would be heavier.

0:29:11.520 --> 0:29:13.680
<v Speaker 2>If the Earth was spinning faster, the Earth would be

0:29:13.680 --> 0:29:17.240
<v Speaker 2>twisting you a little bit. It wouldn't necessarily make you heavier,

0:29:17.400 --> 0:29:18.320
<v Speaker 2>it'd be spinning you.

0:29:19.080 --> 0:29:19.320
<v Speaker 3>Oh.

0:29:19.360 --> 0:29:21.840
<v Speaker 1>But then you say, like it affects the gravity, like

0:29:21.880 --> 0:29:24.080
<v Speaker 1>it maybe increases the gravity of the Earth.

0:29:24.320 --> 0:29:27.320
<v Speaker 2>Yeah. I think that's true. Because the overall energy is higher,

0:29:27.840 --> 0:29:31.000
<v Speaker 2>then you would get more curvature. But also that curvature

0:29:31.080 --> 0:29:33.840
<v Speaker 2>is more complicated, so it induces a little torque on

0:29:33.960 --> 0:29:34.880
<v Speaker 2>objects nearby.

0:29:35.640 --> 0:29:38.280
<v Speaker 1>There's sort of like a little eddy current in gravity.

0:29:38.320 --> 0:29:40.640
<v Speaker 2>Right, This is called frame dragging. Check out our episodes

0:29:40.680 --> 0:29:41.880
<v Speaker 2>about that if you want more details.

0:29:41.960 --> 0:29:44.280
<v Speaker 1>Yeah, what are some of the other ways in which

0:29:44.480 --> 0:29:46.000
<v Speaker 1>people have tested Einstein?

0:29:46.360 --> 0:29:48.280
<v Speaker 2>So a lot of these tests we just described are

0:29:48.320 --> 0:29:51.840
<v Speaker 2>sort of weak field gravity gravity in places where space

0:29:51.920 --> 0:29:54.640
<v Speaker 2>is curved, but not like dramatically curved. One of the

0:29:54.680 --> 0:29:58.400
<v Speaker 2>really dramatic predictions of Einstein's theory is that space can curve,

0:29:58.560 --> 0:30:02.880
<v Speaker 2>incredibly powerfully curve and create things like black holes. And

0:30:02.920 --> 0:30:06.000
<v Speaker 2>for a long time people thought, well, that's obviously wrong, right,

0:30:06.000 --> 0:30:08.840
<v Speaker 2>that's ridiculous. But then we went out and we saw

0:30:08.920 --> 0:30:11.920
<v Speaker 2>black holes in the universe. And so the fact that

0:30:11.960 --> 0:30:15.240
<v Speaker 2>black holes exist is that there's an event horizon beyond

0:30:15.320 --> 0:30:19.440
<v Speaker 2>which information cannot escape is a direct prediction of general relativity,

0:30:19.640 --> 0:30:22.640
<v Speaker 2>not of Newtonian physics, and something we've seen in the

0:30:22.760 --> 0:30:23.720
<v Speaker 2>universe but we.

0:30:23.720 --> 0:30:26.640
<v Speaker 1>Think we've seen. Right, then we talk about before how

0:30:26.960 --> 0:30:30.280
<v Speaker 1>nobody has actually technically seen a black hole or confirmed

0:30:30.520 --> 0:30:31.200
<v Speaker 1>its existence.

0:30:31.480 --> 0:30:34.080
<v Speaker 2>Yeah, that's an important caveat right, We've seen things that

0:30:34.080 --> 0:30:37.360
<v Speaker 2>are very consistent with black holes. There are some alternative

0:30:37.360 --> 0:30:41.680
<v Speaker 2>theories dark stars, boson stars, fuzzy string balls, et cetera,

0:30:41.720 --> 0:30:45.080
<v Speaker 2>et cetera. The most mainstream interpretation of those is that

0:30:45.120 --> 0:30:48.560
<v Speaker 2>they are black holes. They're totally consistent with black holes.

0:30:48.800 --> 0:30:51.640
<v Speaker 2>But you're right, we've never actually confirmed the existence of

0:30:51.680 --> 0:30:54.360
<v Speaker 2>an event horizon in the universe.

0:30:54.240 --> 0:30:56.160
<v Speaker 1>Right, or what's inside of it, right.

0:30:56.160 --> 0:30:57.560
<v Speaker 2>Yeah, or what's inside of it.

0:30:57.640 --> 0:30:59.840
<v Speaker 1>But we have to sort of used black holes in

0:31:00.400 --> 0:31:03.520
<v Speaker 1>to prove that the gravitational waves exist, which is part

0:31:03.560 --> 0:31:05.640
<v Speaker 1>of Eystein's theory, right exactly.

0:31:06.000 --> 0:31:10.239
<v Speaker 2>Another important distinction between Einsteinian and Newtonian gravity is that

0:31:10.280 --> 0:31:14.240
<v Speaker 2>gravity takes time. That information is not instantly propagated in

0:31:14.240 --> 0:31:17.080
<v Speaker 2>the universe. Newton says, if you delete the Sun from

0:31:17.120 --> 0:31:20.800
<v Speaker 2>the universe, it's gravity disappears instantly. But Einstein's spent a

0:31:20.800 --> 0:31:23.200
<v Speaker 2>lot of time thinking about how information is propagated. He

0:31:23.240 --> 0:31:26.000
<v Speaker 2>developed the theory of special relativity, and so in general

0:31:26.040 --> 0:31:28.520
<v Speaker 2>relativity he accounts for this. He says that it takes

0:31:28.560 --> 0:31:32.320
<v Speaker 2>time for gravitational information to propagate, and that propagates via

0:31:32.400 --> 0:31:35.640
<v Speaker 2>gravitational waves. So you take a black hole, for example,

0:31:35.720 --> 0:31:37.800
<v Speaker 2>or even a sun or a big rock and you

0:31:37.840 --> 0:31:41.600
<v Speaker 2>wiggle it. Then the curvature it's causing wiggles as you

0:31:41.680 --> 0:31:44.360
<v Speaker 2>wiggle the rock. You can detect this if you have

0:31:44.440 --> 0:31:48.080
<v Speaker 2>really big sources of gravitational waves, like black holes eating

0:31:48.120 --> 0:31:50.480
<v Speaker 2>each other as they spiral around each other, they make

0:31:50.520 --> 0:31:54.280
<v Speaker 2>these gravitational waves and we've detected them. This is another

0:31:54.440 --> 0:31:58.240
<v Speaker 2>crazy prediction that I personally thought would never be borne out.

0:31:58.400 --> 0:32:02.240
<v Speaker 2>But again due to like amazing seeing technical and experimental bravado,

0:32:02.560 --> 0:32:04.680
<v Speaker 2>they figured out how to see these things and we've

0:32:04.720 --> 0:32:09.000
<v Speaker 2>confirmed them and the predictions are bang on Einstein's calculations.

0:32:09.360 --> 0:32:12.000
<v Speaker 1>Yeah, that's some amazing engineering going on there, right.

0:32:12.120 --> 0:32:13.120
<v Speaker 2>It really is impressive.

0:32:15.040 --> 0:32:17.520
<v Speaker 1>They probably deserve their retirement engineers.

0:32:17.960 --> 0:32:20.960
<v Speaker 2>Well, they definitely deserve the Nobel Prizes that they won

0:32:21.000 --> 0:32:22.760
<v Speaker 2>for it. I was thinking about where to go to

0:32:22.800 --> 0:32:25.280
<v Speaker 2>grad school in the late nineties and thinking about, you know,

0:32:25.320 --> 0:32:29.080
<v Speaker 2>particle physics at Berkeley or gravitational waves at Caltech, and

0:32:29.160 --> 0:32:32.440
<v Speaker 2>I definitely chose particle physics at Berkeley because I thought

0:32:32.440 --> 0:32:34.920
<v Speaker 2>they would never see those gravitational waves.

0:32:34.960 --> 0:32:37.920
<v Speaker 1>I thought it was crazy, and you could own part

0:32:37.960 --> 0:32:40.720
<v Speaker 1>of a Nobel Prize right now had you chosen another.

0:32:40.440 --> 0:32:43.280
<v Speaker 2>Path, absolutely, you know, have the path not taken.

0:32:43.640 --> 0:32:46.000
<v Speaker 1>But instead now they are retired engineers who have part

0:32:46.040 --> 0:32:47.320
<v Speaker 1>of a Nobel Prize, but you don't.

0:32:47.400 --> 0:32:50.000
<v Speaker 2>Yeah exactly. But you know there's another version of that

0:32:50.080 --> 0:32:52.720
<v Speaker 2>story where I did join the project and I messed

0:32:52.720 --> 0:32:55.080
<v Speaker 2>it all up and they never discovered gravitation. Oh yeah,

0:32:55.160 --> 0:32:57.920
<v Speaker 2>So maybe I was doing everybody a favor by staying

0:32:57.920 --> 0:32:58.280
<v Speaker 2>out of it.

0:32:58.440 --> 0:33:00.600
<v Speaker 1>That's right, you get account for all plus abilit.

0:33:00.520 --> 0:33:02.040
<v Speaker 2>I'm what I'm saying is I get to share that

0:33:02.080 --> 0:33:04.160
<v Speaker 2>Nobel Prize by not messing it up.

0:33:04.360 --> 0:33:12.400
<v Speaker 1>Really, Daniel done, so does everybody else who's ever existed.

0:33:12.520 --> 0:33:14.959
<v Speaker 2>I mean we're always saying everybody is a scientist, right,

0:33:15.000 --> 0:33:17.000
<v Speaker 2>so shouldn't we all reap the benefits.

0:33:17.480 --> 0:33:19.360
<v Speaker 1>Well, I think we all get the benefits, but not

0:33:19.400 --> 0:33:24.400
<v Speaker 1>necessarily the credit or the not credit for not getting

0:33:24.400 --> 0:33:24.680
<v Speaker 1>the way.

0:33:24.840 --> 0:33:27.120
<v Speaker 2>I mean, there's so many discoveries out there that I

0:33:27.160 --> 0:33:28.840
<v Speaker 2>didn't mess up. I don't know why I'm not getting

0:33:28.840 --> 0:33:29.400
<v Speaker 2>credit for that.

0:33:29.520 --> 0:33:31.960
<v Speaker 1>I know there should be just a prize just for you.

0:33:32.280 --> 0:33:33.120
<v Speaker 1>They should thank me.

0:33:33.360 --> 0:33:36.080
<v Speaker 2>Every year, Thank you Daniel for not being involved and

0:33:36.160 --> 0:33:37.120
<v Speaker 2>not messing this one up.

0:33:38.000 --> 0:33:41.840
<v Speaker 1>That's right. Daniel Whitson ignored us a price.

0:33:43.360 --> 0:33:47.280
<v Speaker 2>Yeah exactly, But anyway, it's an incredible accomplishment. Nobel Prize

0:33:47.320 --> 0:33:48.440
<v Speaker 2>is very well deserved.

0:33:48.560 --> 0:33:50.760
<v Speaker 1>Yeah, and so that's one way in which we confirm

0:33:51.440 --> 0:33:54.320
<v Speaker 1>general relativity, right, because you can only get gravitational waves

0:33:54.480 --> 0:33:59.000
<v Speaker 1>with general relativity, or is there another explanation for them?

0:33:59.200 --> 0:34:02.560
<v Speaker 2>There's no other explanation for gravitational waves. I mean other

0:34:02.760 --> 0:34:06.200
<v Speaker 2>variations of general relativity that we might talk about, you know,

0:34:06.240 --> 0:34:08.799
<v Speaker 2>ways to build on general relativity. But you can't get

0:34:08.840 --> 0:34:13.239
<v Speaker 2>gravitational waves in Newtonian gravity. You need the curvature of

0:34:13.239 --> 0:34:18.560
<v Speaker 2>space time and general relativity to have that prediction, all.

0:34:18.520 --> 0:34:22.400
<v Speaker 1>Right, So that's another box that general relativity checked. What

0:34:22.640 --> 0:34:25.399
<v Speaker 1>are some of the other boxes that it has passed well?

0:34:25.440 --> 0:34:29.680
<v Speaker 2>Affects like gravitational lensing because space is curved when light

0:34:29.760 --> 0:34:33.280
<v Speaker 2>passes through it, it follows that curvature, and so light moving

0:34:33.320 --> 0:34:36.799
<v Speaker 2>around really massive objects doesn't move and what looks like

0:34:36.840 --> 0:34:39.480
<v Speaker 2>a straight line to us if we're far away and

0:34:39.520 --> 0:34:41.200
<v Speaker 2>we can see this in the sky, we can see

0:34:41.320 --> 0:34:45.279
<v Speaker 2>light bending around invisible dark matter and creating distortions in

0:34:45.400 --> 0:34:49.319
<v Speaker 2>background galaxies. This effect occurs all over the place in

0:34:49.360 --> 0:34:52.640
<v Speaker 2>the sky and it's been confirmed many, many times. So

0:34:53.040 --> 0:34:55.880
<v Speaker 2>we definitely know that light is curved as it passes

0:34:55.920 --> 0:34:56.880
<v Speaker 2>through bend space.

0:34:58.080 --> 0:35:00.360
<v Speaker 1>This is an interesting one because I feel like anyone

0:35:00.440 --> 0:35:03.319
<v Speaker 1>can confirm and look out there into the universe to

0:35:03.320 --> 0:35:05.440
<v Speaker 1>do this right, Like you don't need to build a

0:35:05.480 --> 0:35:08.759
<v Speaker 1>super special satellite or a super giant detector, Like you

0:35:08.760 --> 0:35:11.600
<v Speaker 1>could just look out into this into space and confirm

0:35:11.840 --> 0:35:14.600
<v Speaker 1>that space is being bent out there.

0:35:14.920 --> 0:35:16.560
<v Speaker 2>Yeah, I'm not sure you could do it with like

0:35:16.600 --> 0:35:19.759
<v Speaker 2>a backyard telescope. You need sort of precise measurements, but.

0:35:19.840 --> 0:35:20.840
<v Speaker 1>You haven't seen my backyard.

0:35:20.920 --> 0:35:26.759
<v Speaker 2>Then retired engineers have a lot of disposable income and

0:35:26.840 --> 0:35:30.799
<v Speaker 2>maybe they have really fancy telescopes in their backyard. But yeah,

0:35:30.800 --> 0:35:31.120
<v Speaker 2>you can.

0:35:31.000 --> 0:35:32.440
<v Speaker 1>See or like you know, you could go to a

0:35:32.480 --> 0:35:35.920
<v Speaker 1>local observatory maybe yeah, or a big one and like

0:35:35.960 --> 0:35:38.319
<v Speaker 1>you can step right up to the lens and take a.

0:35:38.280 --> 0:35:42.239
<v Speaker 2>Look right exactly. Sometimes you can see galaxies duplicated, like

0:35:42.280 --> 0:35:45.320
<v Speaker 2>the same galaxy in two places in the sky because

0:35:45.320 --> 0:35:48.520
<v Speaker 2>photons from that galaxy bend around some object and appear

0:35:48.560 --> 0:35:51.319
<v Speaker 2>to be coming from two different directions. You can see

0:35:51.320 --> 0:35:55.239
<v Speaker 2>what's called an Einstein cross, effectively like an optical distortion

0:35:55.920 --> 0:35:58.480
<v Speaker 2>of our vision because of this curvature. So yeah, you

0:35:58.520 --> 0:36:00.840
<v Speaker 2>can just look through a telescope and you can see

0:36:01.080 --> 0:36:02.160
<v Speaker 2>gravitational lensing.

0:36:02.520 --> 0:36:05.280
<v Speaker 1>Now, and now this is significant because it basically shows

0:36:05.320 --> 0:36:09.400
<v Speaker 1>that light is affected by gravity, which is significant because

0:36:09.800 --> 0:36:13.680
<v Speaker 1>light doesn't have any mass, right, yeah, so it wouldn't, nominally,

0:36:14.520 --> 0:36:19.560
<v Speaker 1>according to Newton, feel a force of gravity, and yet

0:36:19.640 --> 0:36:23.680
<v Speaker 1>it's being pulled and pushed by the mass of other objects.

0:36:23.400 --> 0:36:28.040
<v Speaker 2>Exactly because it's moving through that curved space, and masses

0:36:28.120 --> 0:36:31.280
<v Speaker 2>bend space and everything moves through that curved space.

0:36:32.040 --> 0:36:34.879
<v Speaker 1>Although doesn't it also maybe depend on what you mean

0:36:34.920 --> 0:36:37.800
<v Speaker 1>by mass, Like if you mean any kind of energy

0:36:37.880 --> 0:36:40.520
<v Speaker 1>is massd then could that also explain the curvature of

0:36:40.600 --> 0:36:44.000
<v Speaker 1>light without general relativity? You know, like let's say a

0:36:44.000 --> 0:36:47.600
<v Speaker 1>photon doesn't have any mass in the traditional sense, but

0:36:47.680 --> 0:36:50.400
<v Speaker 1>it has energy to it it does. Yeah, yeah, And

0:36:50.440 --> 0:36:52.920
<v Speaker 1>now let's say that I call mass something different like

0:36:53.040 --> 0:36:55.960
<v Speaker 1>mass now not just the mass we used to call mass,

0:36:55.960 --> 0:36:58.480
<v Speaker 1>but also energy like the energy of photon might have,

0:36:59.280 --> 0:37:03.400
<v Speaker 1>and then it was a force from gravity because of

0:37:03.400 --> 0:37:07.239
<v Speaker 1>this energy mass. Couldn't I also maybe explain the curvature

0:37:07.400 --> 0:37:09.800
<v Speaker 1>of light with Newtonian physics?

0:37:09.920 --> 0:37:10.000
<v Speaker 3>Oh?

0:37:10.080 --> 0:37:12.399
<v Speaker 2>I see, could you make some sort of like Newtonian

0:37:12.560 --> 0:37:16.040
<v Speaker 2>version of gravity where you generalize it from just mass

0:37:16.040 --> 0:37:18.799
<v Speaker 2>to energy and say, you know, the Whoregey theory of

0:37:18.840 --> 0:37:21.600
<v Speaker 2>gravity is that there's a force between objects with energy,

0:37:21.719 --> 0:37:22.840
<v Speaker 2>not just with mass.

0:37:23.000 --> 0:37:28.280
<v Speaker 1>Yes, the Whoregey theory of light and gravity future novel

0:37:28.360 --> 0:37:30.200
<v Speaker 1>prize winning theory.

0:37:30.840 --> 0:37:33.120
<v Speaker 2>Yeah, yeah, absolutely, you can do that. And people have

0:37:33.120 --> 0:37:35.840
<v Speaker 2>actually tried to do this to build like a bridge

0:37:35.880 --> 0:37:39.640
<v Speaker 2>between Newtonian and Einsteinian theories. One thing we do when

0:37:39.640 --> 0:37:41.040
<v Speaker 2>we come up with a brand new theory is we

0:37:41.080 --> 0:37:43.640
<v Speaker 2>try to understand, like, is the old theory a special

0:37:43.680 --> 0:37:45.560
<v Speaker 2>case of this new theory. How do they fit together?

0:37:45.680 --> 0:37:48.200
<v Speaker 2>Is one at generalization of the other one? And so

0:37:48.239 --> 0:37:50.440
<v Speaker 2>people have actually gone back and tried to like patch

0:37:50.520 --> 0:37:53.440
<v Speaker 2>these things together and say, could you go from Newtonian

0:37:53.480 --> 0:37:56.960
<v Speaker 2>physics to Einsteinian physics using that direction to avoid the

0:37:56.960 --> 0:38:00.719
<v Speaker 2>interpretation of curvature. And there are some that you can

0:38:00.800 --> 0:38:04.480
<v Speaker 2>get right. For example, you can describe how light bends

0:38:04.760 --> 0:38:08.680
<v Speaker 2>using this apparent force between energy rather than a force

0:38:08.719 --> 0:38:11.440
<v Speaker 2>between mass. But you can't get all the details right

0:38:11.760 --> 0:38:14.400
<v Speaker 2>of the curvature of space time. There's more information in

0:38:14.440 --> 0:38:17.080
<v Speaker 2>there in the metric and the curvature of space time

0:38:17.280 --> 0:38:19.279
<v Speaker 2>that can just be described by the force. It's sort

0:38:19.320 --> 0:38:20.560
<v Speaker 2>of like a richer theory.

0:38:22.200 --> 0:38:23.640
<v Speaker 1>I see, so I think. I guess what I was

0:38:23.680 --> 0:38:26.280
<v Speaker 1>trying to get to is that, you know, gravitational lensing

0:38:26.640 --> 0:38:29.040
<v Speaker 1>is a test of gravity, but it's not like a

0:38:29.080 --> 0:38:34.400
<v Speaker 1>slam dunk case of gravity, right of general relativity exactly.

0:38:34.800 --> 0:38:37.440
<v Speaker 2>You can add bells and whistles to Newton's theory to

0:38:37.600 --> 0:38:39.200
<v Speaker 2>make gravitational lensing happen.

0:38:39.360 --> 0:38:42.400
<v Speaker 1>Yeah. Yeah, it's called the bells and whistles theory of

0:38:42.440 --> 0:38:47.359
<v Speaker 1>the universe, the B and W. All right, well, let's

0:38:47.400 --> 0:38:50.920
<v Speaker 1>get into how else we know that general relativity is wrong,

0:38:51.000 --> 0:38:53.640
<v Speaker 1>and let's talk about how it's wrong and where we

0:38:53.640 --> 0:38:56.279
<v Speaker 1>think it might finally break. So let's stick into that.

0:38:56.360 --> 0:39:11.440
<v Speaker 1>But first let's take another quick break. All right, we're

0:39:11.440 --> 0:39:14.920
<v Speaker 1>talking about general relativity, the big theory that Einstein came

0:39:14.960 --> 0:39:17.319
<v Speaker 1>up with. The talks about gravity and how space can

0:39:17.440 --> 0:39:21.200
<v Speaker 1>bend and how space time gets bent by things like

0:39:21.280 --> 0:39:24.440
<v Speaker 1>mass and energy, and how it might be wrong. Although

0:39:24.480 --> 0:39:26.880
<v Speaker 1>it seems pretty right from all the experiments we've done.

0:39:27.560 --> 0:39:31.120
<v Speaker 2>So far, it's been endlessly vinegated, which is frustrating because

0:39:31.200 --> 0:39:32.360
<v Speaker 2>I'm pretty sure it's wrong.

0:39:32.840 --> 0:39:33.920
<v Speaker 1>What are you so short?

0:39:35.560 --> 0:39:38.840
<v Speaker 2>Even though every test we've done has confirmed Einstein's prediction,

0:39:39.280 --> 0:39:42.440
<v Speaker 2>we think that there are scenarios where it must break down.

0:39:42.880 --> 0:39:45.399
<v Speaker 2>Not tests we can do today, but test we can

0:39:45.440 --> 0:39:48.600
<v Speaker 2>imagine with thought experiments places in the universe where we

0:39:48.600 --> 0:39:50.640
<v Speaker 2>think Einstein's theory can't be right.

0:39:51.160 --> 0:39:54.440
<v Speaker 1>Interesting. So you're saying, like, it's as right as far

0:39:54.480 --> 0:39:57.960
<v Speaker 1>as we know and the phenomena we've seen, but there

0:39:58.000 --> 0:40:00.640
<v Speaker 1>might be situations where it breaks down.

0:40:00.880 --> 0:40:02.840
<v Speaker 2>We think that there are situations where it has to

0:40:02.880 --> 0:40:05.120
<v Speaker 2>be wrong, even though we haven't yet been able to

0:40:05.160 --> 0:40:09.160
<v Speaker 2>engineer any of those situations in the lab to prove it.

0:40:09.200 --> 0:40:11.920
<v Speaker 2>But there are sort of thought experiments or future experiments

0:40:11.920 --> 0:40:15.120
<v Speaker 2>we can predict or places in the universe where we

0:40:15.160 --> 0:40:16.479
<v Speaker 2>think it's got to be wrong.

0:40:16.880 --> 0:40:19.680
<v Speaker 1>Uh. Interesting, All right, well let's step through these scenarios.

0:40:19.719 --> 0:40:20.600
<v Speaker 1>What are these places?

0:40:20.800 --> 0:40:23.120
<v Speaker 2>Yeah, well, one was the scenario you brought up earlier,

0:40:23.200 --> 0:40:26.960
<v Speaker 2>like what happens between two electrons? What is the gravitational

0:40:27.040 --> 0:40:30.520
<v Speaker 2>force between two electrons? Because electrons are not just like

0:40:30.680 --> 0:40:34.359
<v Speaker 2>tiny little versions of planets. They're not just like small

0:40:34.440 --> 0:40:37.279
<v Speaker 2>planets with tiny little masses in them where you can

0:40:37.320 --> 0:40:40.240
<v Speaker 2>apply Newtonian physics or think about the curvature of space.

0:40:40.600 --> 0:40:44.719
<v Speaker 2>They're fundamentally different from planets. They're probabilistic. We know that

0:40:44.760 --> 0:40:49.240
<v Speaker 2>electrons are quantum objects. They don't have a definitive location.

0:40:49.320 --> 0:40:51.959
<v Speaker 2>They have a probability for being here and a probability

0:40:51.960 --> 0:40:55.480
<v Speaker 2>for being there. They can interfere with each other, and

0:40:55.600 --> 0:40:58.640
<v Speaker 2>Einstein's theory doesn't account for that. It doesn't allow for that.

0:40:58.680 --> 0:41:03.160
<v Speaker 2>It says, Look, things have locations, and those locations determine

0:41:03.160 --> 0:41:05.879
<v Speaker 2>how space curves. So we don't know what to do

0:41:05.920 --> 0:41:09.960
<v Speaker 2>when things don't have locations, The space curve randomly the

0:41:10.000 --> 0:41:12.799
<v Speaker 2>space curve probabilistically. What's going on?

0:41:13.239 --> 0:41:16.120
<v Speaker 1>But other theories can can deal with that, like could

0:41:16.160 --> 0:41:18.200
<v Speaker 1>Neaton handle a quantum object? No.

0:41:18.360 --> 0:41:21.839
<v Speaker 2>Newton's theory also requires you to know where something is,

0:41:22.120 --> 0:41:24.160
<v Speaker 2>Like if you're going to feel the force of gravity

0:41:24.200 --> 0:41:25.879
<v Speaker 2>from an electron, you got to know how far away

0:41:25.920 --> 0:41:28.440
<v Speaker 2>it is and in what direction. If an electron like

0:41:28.480 --> 0:41:30.640
<v Speaker 2>could be to your left and could be to your right,

0:41:31.160 --> 0:41:33.720
<v Speaker 2>then what gravity are you feeling? Are you feeling gravity

0:41:33.719 --> 0:41:35.520
<v Speaker 2>to the left, are you feeling gravity to the right?

0:41:35.719 --> 0:41:38.000
<v Speaker 2>Are you feeling fifty to fifty gravity to the left

0:41:38.040 --> 0:41:40.879
<v Speaker 2>and right? So it cancels itself out, like Newton also

0:41:40.960 --> 0:41:42.840
<v Speaker 2>doesn't know what to do in that situation.

0:41:43.160 --> 0:41:45.960
<v Speaker 1>Wait, what so then how do you do anything with

0:41:46.040 --> 0:41:48.360
<v Speaker 1>quantum mechanics, like how do you how do you compute

0:41:48.360 --> 0:41:49.560
<v Speaker 1>the path of an electron?

0:41:49.719 --> 0:41:52.840
<v Speaker 2>Yeah, mostly we ignore gravity. Like when we compute the

0:41:52.840 --> 0:41:55.799
<v Speaker 2>path with an electron or electrons interacting, we assume that

0:41:55.800 --> 0:41:58.800
<v Speaker 2>there's no gravity. We do those all in flat space.

0:41:59.239 --> 0:42:01.279
<v Speaker 1>But then how do you how do you like, if

0:42:01.719 --> 0:42:04.400
<v Speaker 1>another electron pushes it or pulls it, how do you

0:42:04.480 --> 0:42:06.759
<v Speaker 1>make that calculation of where it's going to go?

0:42:07.440 --> 0:42:09.480
<v Speaker 2>Well, we just assume that there is no gravity, and

0:42:09.520 --> 0:42:12.080
<v Speaker 2>we do the quant mechanical version of things. Because all

0:42:12.120 --> 0:42:15.480
<v Speaker 2>the other forces, the pushing and the pulling of electromagnetism

0:42:16.040 --> 0:42:19.320
<v Speaker 2>that allows for this probabilistic stuff. We have a quantum

0:42:19.400 --> 0:42:22.279
<v Speaker 2>theory of electromagnetic forces, and a quantum theory of the

0:42:22.320 --> 0:42:24.840
<v Speaker 2>strong force and the weak force. All the forces in

0:42:24.880 --> 0:42:28.719
<v Speaker 2>the universe we can describe using quantum mechanics, and those

0:42:28.760 --> 0:42:33.239
<v Speaker 2>quantum descriptions can totally accommodate these sort of probabilities and interference.

0:42:34.120 --> 0:42:37.600
<v Speaker 1>And it just lets you compute like the arc or

0:42:37.760 --> 0:42:39.160
<v Speaker 1>trajectory of an electron.

0:42:39.400 --> 0:42:43.200
<v Speaker 2>It lets you compute the probability of various outcomes. Absolutely,

0:42:43.640 --> 0:42:47.040
<v Speaker 2>so quantum mechanics is totally cool with that. And when

0:42:47.080 --> 0:42:49.239
<v Speaker 2>we do that, we have to ignore gravity. You might ask, well,

0:42:49.320 --> 0:42:52.399
<v Speaker 2>how can you get the right answer if you're ignoring gravity. Well,

0:42:52.440 --> 0:42:55.560
<v Speaker 2>gravity is super duper weak. It's so much weaker than

0:42:55.600 --> 0:42:58.839
<v Speaker 2>any of these other forces, so it's basically negligible. Like

0:42:58.960 --> 0:43:01.680
<v Speaker 2>we couldn't actually even measure the mass of an electron

0:43:02.160 --> 0:43:04.719
<v Speaker 2>using gravity. We talked recently on the podcast about like

0:43:05.040 --> 0:43:08.719
<v Speaker 2>the smallest thing we've ever measured the gravity for. It

0:43:08.760 --> 0:43:11.160
<v Speaker 2>was like around a kilogram or a little bit smaller.

0:43:11.200 --> 0:43:14.680
<v Speaker 2>You know, zillions and zillions of atoms, So we can't

0:43:14.719 --> 0:43:17.560
<v Speaker 2>detect the gravity these particles. We just ignore it in

0:43:17.560 --> 0:43:20.279
<v Speaker 2>our calculations for particle physics because we also don't know

0:43:20.320 --> 0:43:21.680
<v Speaker 2>how to do those calculations.

0:43:22.040 --> 0:43:23.600
<v Speaker 1>But I wonder if you mean, like only at the

0:43:23.800 --> 0:43:27.560
<v Speaker 1>microscopic level, Like, for example, can I treat an electron

0:43:28.120 --> 0:43:31.280
<v Speaker 1>as a little point particle like a little tiny baseball

0:43:31.520 --> 0:43:34.320
<v Speaker 1>and throw it at the Earth. Wouldn't even like Newtonian

0:43:34.320 --> 0:43:37.839
<v Speaker 1>physics tell me at least the most likely path that

0:43:37.880 --> 0:43:38.839
<v Speaker 1>electron is going to take.

0:43:39.560 --> 0:43:42.640
<v Speaker 2>Yeah, absolutely, you can do those calculations, and we actually

0:43:42.640 --> 0:43:45.359
<v Speaker 2>do those calculations. When we think about like the atmosphere,

0:43:45.680 --> 0:43:48.440
<v Speaker 2>how much atmosphere are we losing. Well, it depends on

0:43:48.480 --> 0:43:51.840
<v Speaker 2>the velocity and the gravity of the atoms in the

0:43:51.920 --> 0:43:54.560
<v Speaker 2>upper atmosphere. We lose more hydrogen and helium than the

0:43:54.600 --> 0:43:57.880
<v Speaker 2>heavier elements because they have more gravity. The Earth is

0:43:57.920 --> 0:44:01.280
<v Speaker 2>pulling on them harder. But there we're doing a classical calculation.

0:44:01.280 --> 0:44:04.800
<v Speaker 2>We're ignoring the quantum nature of those objects. Whenever the

0:44:04.880 --> 0:44:08.839
<v Speaker 2>quantum nature is relevant, gravity becomes irrelevant. And that's one

0:44:08.840 --> 0:44:11.840
<v Speaker 2>of the frustrating things about testing Einstein's theory is that

0:44:11.880 --> 0:44:14.759
<v Speaker 2>it's mostly irrelevant in places where we think it's going

0:44:14.840 --> 0:44:19.879
<v Speaker 2>to fail. Like we think that Einstein's theory breaks down

0:44:19.920 --> 0:44:23.840
<v Speaker 2>for quantum particles, but it's also irrelevant for quantum particles

0:44:23.840 --> 0:44:26.000
<v Speaker 2>because quantum particles have almost no mass.

0:44:26.560 --> 0:44:28.759
<v Speaker 1>Well, I think what you're saying is that it does

0:44:28.800 --> 0:44:33.000
<v Speaker 1>work for quantum particles, just not at a certain level. Right, Like,

0:44:33.200 --> 0:44:37.239
<v Speaker 1>you can use general relativity and Newtonian physics on an

0:44:37.320 --> 0:44:40.160
<v Speaker 1>electron to predict whether it's going to leave the Earth

0:44:40.239 --> 0:44:42.840
<v Speaker 1>or not, or what pass is going to take around

0:44:42.880 --> 0:44:45.520
<v Speaker 1>the Earth, but when you get down to the microscopic level,

0:44:45.840 --> 0:44:46.719
<v Speaker 1>you don't know what to do.

0:44:46.840 --> 0:44:49.960
<v Speaker 2>Yeah, when the quantum nature of those particles is important,

0:44:50.360 --> 0:44:52.759
<v Speaker 2>general relativity breaks down, we don't know what to do

0:44:52.840 --> 0:44:55.560
<v Speaker 2>with it there, and that's exactly where we also can't

0:44:55.600 --> 0:44:58.600
<v Speaker 2>detect the effects of general relativity. If you ignore the

0:44:58.640 --> 0:45:01.480
<v Speaker 2>quantum nature of the electron or the atom, then yes,

0:45:01.560 --> 0:45:04.440
<v Speaker 2>you can use general relativity or even Newtonian physics to

0:45:04.520 --> 0:45:07.520
<v Speaker 2>predict the path of the particle. But when the quantum

0:45:07.640 --> 0:45:10.240
<v Speaker 2>nature is important, that's when it breaks down, and that's

0:45:10.520 --> 0:45:13.239
<v Speaker 2>when we can't detect the effects of general relativity.

0:45:14.880 --> 0:45:16.960
<v Speaker 1>All right, well, what are some of the other extreme

0:45:17.040 --> 0:45:19.960
<v Speaker 1>situations where you think, I think theory might burong.

0:45:20.200 --> 0:45:22.720
<v Speaker 2>The other famous concern, and the one that Listeners raised,

0:45:22.920 --> 0:45:26.759
<v Speaker 2>is singularities. What's inside a black hole? General relativity tells

0:45:26.840 --> 0:45:28.880
<v Speaker 2>us that the things that fall past the event horizon

0:45:29.320 --> 0:45:32.800
<v Speaker 2>slide towards the center of the black hole, where curvature

0:45:32.880 --> 0:45:35.440
<v Speaker 2>gets stronger and stronger, and it gets so strong that

0:45:35.560 --> 0:45:39.400
<v Speaker 2>essentially it's a runaway effect and becomes infinitely dense. You

0:45:39.480 --> 0:45:42.160
<v Speaker 2>have this point in space where you have mass but

0:45:42.560 --> 0:45:45.839
<v Speaker 2>zero volume, and so we call that a singularity because

0:45:45.880 --> 0:45:49.520
<v Speaker 2>the density is essentially infinite or undefined. So that's the

0:45:49.520 --> 0:45:52.480
<v Speaker 2>prediction of general relativity. But most people think that that's

0:45:52.520 --> 0:45:55.160
<v Speaker 2>not really a prediction that's a sign that the theory

0:45:55.320 --> 0:45:59.200
<v Speaker 2>is broken. It's predicting something we think is unphysical and

0:45:59.239 --> 0:46:01.319
<v Speaker 2>it has to be replaced by another theory. That we've

0:46:01.320 --> 0:46:04.680
<v Speaker 2>gone beyond the boundary of where the theory is valid.

0:46:05.040 --> 0:46:07.600
<v Speaker 2>Just like me predicting that I'll grow another meter and

0:46:07.640 --> 0:46:09.279
<v Speaker 2>a half in the next half of my life.

0:46:09.760 --> 0:46:11.439
<v Speaker 1>What do you mean, Like you're saying that the idea

0:46:11.440 --> 0:46:15.800
<v Speaker 1>of a singularity is the prediction of general relativity. Exactly,

0:46:16.360 --> 0:46:17.879
<v Speaker 1>which is at the center of a black hole?

0:46:17.960 --> 0:46:20.440
<v Speaker 2>Yeah, exactly, that's what general relativity tells us is at

0:46:20.440 --> 0:46:23.360
<v Speaker 2>the center of a black hole. But we don't believe it.

0:46:23.400 --> 0:46:25.719
<v Speaker 2>We don't think it's actually there. We think it's a

0:46:25.760 --> 0:46:28.799
<v Speaker 2>sign that general relativity is wrong, that we've pushed it

0:46:29.120 --> 0:46:31.479
<v Speaker 2>beyond the bounds where you can no longer really use

0:46:31.560 --> 0:46:32.080
<v Speaker 2>the theory.

0:46:32.360 --> 0:46:35.120
<v Speaker 1>But why not, Why couldn't you have some point something

0:46:35.160 --> 0:46:36.399
<v Speaker 1>in the center of a black hole.

0:46:36.640 --> 0:46:39.720
<v Speaker 2>Well, one reason is quantum mechanics. Right, if something becomes

0:46:39.840 --> 0:46:43.640
<v Speaker 2>that small, then its quantum properties are important because quantum

0:46:43.640 --> 0:46:46.360
<v Speaker 2>mechanics rules when things are super dup or small. Everything

0:46:46.360 --> 0:46:48.560
<v Speaker 2>in the universe that's super tiny follows the rules of

0:46:48.640 --> 0:46:52.280
<v Speaker 2>quantum mechanics and quantum mechanics says you can't have something

0:46:52.400 --> 0:46:55.600
<v Speaker 2>so massive, so much energy in such a tiny little space,

0:46:55.640 --> 0:46:59.040
<v Speaker 2>as like an inherent fuzziness to the universe that a

0:46:59.120 --> 0:47:01.800
<v Speaker 2>singularity violates. And so if we could look inside a

0:47:01.840 --> 0:47:04.160
<v Speaker 2>black hole and see what's there. Is it a singularity,

0:47:04.440 --> 0:47:07.279
<v Speaker 2>is it something else, a weird quantum fuzzy blob, is

0:47:07.280 --> 0:47:10.239
<v Speaker 2>it something completely different, then we would know how to

0:47:10.480 --> 0:47:13.800
<v Speaker 2>update and correct general relativity. But of course we can't.

0:47:14.040 --> 0:47:16.239
<v Speaker 1>But isn't it sort of the same as like an electron.

0:47:16.320 --> 0:47:18.480
<v Speaker 1>Like an electron you can treat as a point particle,

0:47:18.480 --> 0:47:21.239
<v Speaker 1>which is also an impossibility. And yet do you still

0:47:21.239 --> 0:47:23.560
<v Speaker 1>assume that in quantum mechanics, In sort.

0:47:23.360 --> 0:47:25.560
<v Speaker 2>Of old school quantum mechanics, we do treat the electron

0:47:25.600 --> 0:47:28.480
<v Speaker 2>as a point particle, and that's valid in some scenarios

0:47:28.560 --> 0:47:30.600
<v Speaker 2>right where it doesn't really matter. But you're right, if

0:47:30.640 --> 0:47:33.200
<v Speaker 2>you zoom in on the electron, it can't actually be

0:47:33.440 --> 0:47:36.640
<v Speaker 2>a point particle. And if you do quantum field theory,

0:47:36.680 --> 0:47:39.160
<v Speaker 2>then you replace this idea of a point particle with

0:47:39.239 --> 0:47:42.120
<v Speaker 2>like a little blob of energy density in the quantum

0:47:42.239 --> 0:47:45.560
<v Speaker 2>field of the electron. And so we have like different

0:47:45.600 --> 0:47:49.319
<v Speaker 2>pictures for sort of different scales of work in particle physics.

0:47:49.600 --> 0:47:51.560
<v Speaker 2>But you're right, from some points of view, the point

0:47:51.560 --> 0:47:54.239
<v Speaker 2>particle description works just fine. And so if like from

0:47:54.280 --> 0:47:56.560
<v Speaker 2>the outside of a black hole, having a singularity on

0:47:56.600 --> 0:47:59.520
<v Speaker 2>the inside is okay. But once you zoom in on

0:47:59.600 --> 0:48:02.080
<v Speaker 2>it that you get in and observe the quantum details

0:48:02.120 --> 0:48:04.759
<v Speaker 2>of it, we're wondering like, is it really a singularity

0:48:04.840 --> 0:48:07.239
<v Speaker 2>or is it something else? And that would be a

0:48:07.280 --> 0:48:11.120
<v Speaker 2>deviation from Einstein's prediction. If it's not a singularity, then

0:48:11.160 --> 0:48:13.000
<v Speaker 2>that would be a clue something we could pull on

0:48:13.080 --> 0:48:15.880
<v Speaker 2>to help unravel or update Einstein's theory.

0:48:16.920 --> 0:48:18.440
<v Speaker 1>Well, I feel like in this case, you know, it

0:48:18.440 --> 0:48:22.399
<v Speaker 1>wouldn't prove that Eystein was wrong. It's just that at

0:48:22.400 --> 0:48:24.520
<v Speaker 1>that level you have to use a different set of rules.

0:48:24.640 --> 0:48:26.879
<v Speaker 2>Yeah, that's a good point. It's not showing Einstein is wrong.

0:48:26.920 --> 0:48:30.600
<v Speaker 2>It's showing that his theory is valid only under certain circumstances.

0:48:30.960 --> 0:48:33.680
<v Speaker 2>And that's cool. It's like saying, you know, as fluid

0:48:33.719 --> 0:48:36.520
<v Speaker 2>mechanics wrong, Well, it works great for fluids. You can't

0:48:36.520 --> 0:48:39.800
<v Speaker 2>apply it to like crowds or to steam or crystals.

0:48:39.800 --> 0:48:42.560
<v Speaker 2>Doesn't mean it's wrong. It means that it's relevant to

0:48:42.640 --> 0:48:46.560
<v Speaker 2>a certain set of conditions, And so that's sort of

0:48:46.600 --> 0:48:49.279
<v Speaker 2>the question we were asking philosophically, Like, if Einstein's theory

0:48:49.320 --> 0:48:52.640
<v Speaker 2>of gravity is deeply true, it's the actual story of

0:48:52.640 --> 0:48:55.560
<v Speaker 2>what the universe is doing, then it should always be right.

0:48:55.960 --> 0:48:58.040
<v Speaker 2>But if it's just an approximation, if it's just something

0:48:58.080 --> 0:49:02.239
<v Speaker 2>that works under some certain conditions like fluid mechanics, then

0:49:02.320 --> 0:49:04.160
<v Speaker 2>you know, it's just a story we're telling ourselves that

0:49:04.239 --> 0:49:06.520
<v Speaker 2>helps us do calculations. It might not be like the

0:49:06.560 --> 0:49:09.960
<v Speaker 2>actual story of the universe if there are bounds on

0:49:10.080 --> 0:49:11.560
<v Speaker 2>where it's relevant.

0:49:11.400 --> 0:49:13.719
<v Speaker 1>Or I wonder if another possibilities that it is right

0:49:13.800 --> 0:49:16.200
<v Speaker 1>all the way down to the center of the universe.

0:49:16.640 --> 0:49:19.880
<v Speaker 1>You just have to add quantum mechanics on top, meaning

0:49:19.880 --> 0:49:21.279
<v Speaker 1>that they're each right in their own way.

0:49:21.680 --> 0:49:24.160
<v Speaker 2>Yeah, but they disagree about what happens at the heart

0:49:24.200 --> 0:49:26.680
<v Speaker 2>of a black hole, right, so they can't both be right.

0:49:26.960 --> 0:49:29.000
<v Speaker 1>I don't know. Maybe they don't disagree.

0:49:29.600 --> 0:49:32.680
<v Speaker 2>But they do. They disagree. You know, there might be

0:49:32.719 --> 0:49:36.760
<v Speaker 2>some version of quantum gravity, an extension of Einstein's idea

0:49:36.840 --> 0:49:41.399
<v Speaker 2>modification of Einstein's ideas that describes more accurately what's going

0:49:41.520 --> 0:49:45.319
<v Speaker 2>on inside a black hole. But if there's no singularity. There,

0:49:45.360 --> 0:49:46.959
<v Speaker 2>then Einstein's prediction is wrong.

0:49:48.120 --> 0:49:51.360
<v Speaker 1>Well, as a particle physicist and a quantum mechanic person,

0:49:51.840 --> 0:49:53.440
<v Speaker 1>I would say, maybe you're a little biased.

0:49:53.880 --> 0:49:57.640
<v Speaker 2>Yeah, yeah, sure, I believe.

0:49:57.360 --> 0:50:00.200
<v Speaker 1>It all right. What are some of the other situation

0:50:00.320 --> 0:50:02.399
<v Speaker 1>where you think Einstein might be wrong?

0:50:02.840 --> 0:50:06.239
<v Speaker 2>Well, another famous singularity is the Big Bang. You know,

0:50:06.280 --> 0:50:08.359
<v Speaker 2>if you take the universe as we see it, it's

0:50:08.400 --> 0:50:12.040
<v Speaker 2>sort of cold and dilute, but we see that it's expanding.

0:50:12.280 --> 0:50:14.760
<v Speaker 2>Then you rewind the clock back to the early universe.

0:50:14.760 --> 0:50:17.360
<v Speaker 2>You see the universe getting hotter and hotter and denser

0:50:17.400 --> 0:50:20.239
<v Speaker 2>and denser and denser, and you could rewind that back,

0:50:20.360 --> 0:50:24.600
<v Speaker 2>like all the way back to an infinite density, a singularity,

0:50:24.640 --> 0:50:27.720
<v Speaker 2>a moment when the universe is filled with infinitely dense matter.

0:50:28.400 --> 0:50:30.360
<v Speaker 2>And I gotta clarify a lot of people think of

0:50:30.440 --> 0:50:33.160
<v Speaker 2>the Big Bang as like a single point of matter

0:50:33.200 --> 0:50:36.520
<v Speaker 2>which then exploded out into space. But instead we imagine

0:50:36.520 --> 0:50:38.560
<v Speaker 2>the Big Bang is something that happened everywhere that the

0:50:38.600 --> 0:50:42.840
<v Speaker 2>whole universe filled with this incredibly dense matter. So Einstein's

0:50:42.840 --> 0:50:45.359
<v Speaker 2>theory lets you unwind all the way back to this

0:50:45.480 --> 0:50:49.879
<v Speaker 2>moment of infinite density. But nobody believes that. People think that, well,

0:50:49.960 --> 0:50:52.400
<v Speaker 2>you get back to some hot dense state up to

0:50:52.440 --> 0:50:55.920
<v Speaker 2>like the Plank temperature, some really hot moment, and beyond that,

0:50:56.000 --> 0:50:58.440
<v Speaker 2>some quantum effects are going to be relevant. You can't

0:50:58.480 --> 0:51:01.359
<v Speaker 2>just use general relativity to extrapolate all the way back

0:51:01.400 --> 0:51:02.799
<v Speaker 2>to infinite.

0:51:02.280 --> 0:51:06.319
<v Speaker 1>Density unless quantum mechanics breaks down at that point. Like

0:51:06.920 --> 0:51:10.560
<v Speaker 1>you're assuming that quantum mechanics is still valid at that point.

0:51:10.360 --> 0:51:13.080
<v Speaker 2>Right, Yeah, And but quantum mechanics is another theory that's

0:51:13.120 --> 0:51:17.759
<v Speaker 2>been tested in great detail and very exquisitely, and we

0:51:17.840 --> 0:51:20.840
<v Speaker 2>think describes the fundamental nature of the universe. So what

0:51:21.080 --> 0:51:24.640
<v Speaker 2>happens when these two theories come into conflict is the

0:51:24.640 --> 0:51:27.279
<v Speaker 2>big question. And so, like inside the heart of a

0:51:27.280 --> 0:51:29.839
<v Speaker 2>black hole or in the very very early universe, these

0:51:29.880 --> 0:51:33.080
<v Speaker 2>are the moments when quantum mechanics and general relativity are

0:51:33.120 --> 0:51:36.120
<v Speaker 2>both relevant. They both have something to say about what happens,

0:51:36.200 --> 0:51:39.800
<v Speaker 2>and they say different things. And so most people believe,

0:51:39.800 --> 0:51:41.719
<v Speaker 2>and maybe I'm biased because I'm a part of the

0:51:41.800 --> 0:51:44.680
<v Speaker 2>physicist that the universe is quantum mechanical and that general

0:51:44.719 --> 0:51:47.759
<v Speaker 2>relativity will break down at those moments and will not

0:51:47.840 --> 0:51:49.360
<v Speaker 2>accurately predict the universe.

0:51:49.560 --> 0:51:52.040
<v Speaker 1>I see, by most people you mean you and your friends.

0:51:55.080 --> 0:51:57.760
<v Speaker 2>Yes, me and the rest of the physicists in the universe.

0:51:58.800 --> 0:52:01.360
<v Speaker 2>Most people believe that our relativity is wrong, but we

0:52:01.440 --> 0:52:03.839
<v Speaker 2>haven't proven it. We have not proven it right. It's

0:52:03.880 --> 0:52:06.359
<v Speaker 2>a belief, it's a theory, it's a speculation.

0:52:06.600 --> 0:52:07.680
<v Speaker 1>Feels a little like faith.

0:52:07.960 --> 0:52:11.359
<v Speaker 2>Daniel, Well, you know, science is subjective in the sense

0:52:11.400 --> 0:52:13.640
<v Speaker 2>of like what we try to believe, what we tried

0:52:13.680 --> 0:52:17.279
<v Speaker 2>to prove, what we explore. We have hunches, we have creativity.

0:52:17.600 --> 0:52:19.880
<v Speaker 2>It's not like science is a process that tells you

0:52:19.960 --> 0:52:23.279
<v Speaker 2>what to try and what experiments to do, et cetera,

0:52:23.320 --> 0:52:26.239
<v Speaker 2>et cetera. You have to have ideas and intuition and

0:52:26.320 --> 0:52:28.799
<v Speaker 2>hunches and creativity, but then you have to listen to

0:52:28.840 --> 0:52:31.759
<v Speaker 2>the experiments, you know, and so that's what we're waiting for.

0:52:32.920 --> 0:52:35.319
<v Speaker 1>But I guess you would concede that right now. There's

0:52:35.760 --> 0:52:39.000
<v Speaker 1>nothing that maybe would say that one or the other

0:52:39.080 --> 0:52:41.920
<v Speaker 1>is right or wrong. You just feel that one is

0:52:42.120 --> 0:52:42.960
<v Speaker 1>more right than the other.

0:52:43.239 --> 0:52:46.560
<v Speaker 2>Yeah, we have no evidence that Einstein was wrong. We

0:52:46.719 --> 0:52:49.840
<v Speaker 2>just suspect very very strongly that he's got to be

0:52:49.880 --> 0:52:53.920
<v Speaker 2>wrong eventually. But no, we do not have any evidence

0:52:53.920 --> 0:52:54.879
<v Speaker 2>that Einstein was wrong.

0:52:56.360 --> 0:52:58.720
<v Speaker 1>In fact, it almost seems like you have the evidence

0:52:58.760 --> 0:52:59.480
<v Speaker 1>to the contrary.

0:52:59.760 --> 0:53:02.200
<v Speaker 2>Yeah, we have lots of evidence that he's right. Frustrating

0:53:02.400 --> 0:53:05.400
<v Speaker 2>the huge amounts of evidence that he was right. But

0:53:05.719 --> 0:53:08.759
<v Speaker 2>under these scenarios that we can't engineer ourselves. We can't

0:53:08.760 --> 0:53:10.960
<v Speaker 2>look inside a black hole, we can't rewind time at

0:53:10.960 --> 0:53:13.919
<v Speaker 2>the beginning of the universe. We have a hard time

0:53:14.000 --> 0:53:16.840
<v Speaker 2>coming up with ways of testing quantum mechanics and gravity.

0:53:17.080 --> 0:53:19.800
<v Speaker 2>That we did a whole episode about quantum gravity experiments

0:53:19.800 --> 0:53:22.360
<v Speaker 2>and a tabletop that might be able to break that barrier.

0:53:22.880 --> 0:53:26.120
<v Speaker 2>Nobody's yet been able to engineer a scenario to prove

0:53:26.200 --> 0:53:27.040
<v Speaker 2>Einstein wrong.

0:53:27.160 --> 0:53:29.480
<v Speaker 1>It kind of feels like a conspiracy theory, Daniel, Is

0:53:29.520 --> 0:53:31.640
<v Speaker 1>that where the queue in q andon comes from?

0:53:32.040 --> 0:53:35.400
<v Speaker 2>That does mean quantum Wait? Is Einstein the conspiracy theorist?

0:53:35.520 --> 0:53:37.160
<v Speaker 2>Or are you saying particle physics?

0:53:38.120 --> 0:53:41.120
<v Speaker 1>I'm saying maybe quantum mechanics. You can see this is

0:53:41.160 --> 0:53:44.120
<v Speaker 1>the conspiracy theory. That's where the Q and q andon

0:53:44.239 --> 0:53:45.080
<v Speaker 1>comes from.

0:53:45.080 --> 0:53:46.400
<v Speaker 2>Oh I see quantum anon.

0:53:46.520 --> 0:53:49.640
<v Speaker 1>Yes, yeah, In fact, even sounds like a particle like

0:53:49.719 --> 0:53:55.000
<v Speaker 1>electrode q and on. Oh man, I just broke the conspiracy.

0:53:55.840 --> 0:53:59.080
<v Speaker 1>It's all tied secret Cabala physicists.

0:53:59.400 --> 0:54:01.320
<v Speaker 2>Yeah, that's the exactly right. Well, you could make the

0:54:01.320 --> 0:54:03.640
<v Speaker 2>same arguments in the other direction, right, you could say, like, look,

0:54:03.680 --> 0:54:06.760
<v Speaker 2>quantum mechanics has been proven right through a huge number

0:54:06.840 --> 0:54:10.239
<v Speaker 2>of experiments, but it conflicts with general relativity the heart

0:54:10.280 --> 0:54:13.160
<v Speaker 2>of black holes in the early universe, so maybe it's wrong.

0:54:13.520 --> 0:54:16.439
<v Speaker 2>You could take that entirely other perspective. We have two

0:54:16.520 --> 0:54:20.239
<v Speaker 2>great theories that disagree, and one of them's got to

0:54:20.280 --> 0:54:20.960
<v Speaker 2>be wrong.

0:54:21.120 --> 0:54:23.120
<v Speaker 1>Right, I'm just saying, probably we don't know that conspiracy

0:54:23.280 --> 0:54:26.440
<v Speaker 1>starts with a que and so that to me is

0:54:26.480 --> 0:54:31.640
<v Speaker 1>a big hint. It sounds like a particle too. All right, Well,

0:54:31.200 --> 0:54:33.440
<v Speaker 1>what does it all mean, Daniel, doesn't mean that we

0:54:33.480 --> 0:54:37.680
<v Speaker 1>have these two titanic gigantic theories about the universe. You're

0:54:37.719 --> 0:54:40.440
<v Speaker 1>saying that the conflict in a lot of situations. So

0:54:40.880 --> 0:54:43.799
<v Speaker 1>there's plenty of scientific evidence that for each of them

0:54:43.840 --> 0:54:46.520
<v Speaker 1>to be both right. But they can both be right

0:54:47.120 --> 0:54:48.520
<v Speaker 1>in the center of the universe.

0:54:48.680 --> 0:54:51.160
<v Speaker 2>Yeah, we have so many scenarios where we've tested each

0:54:51.200 --> 0:54:55.480
<v Speaker 2>of them individually with great precision, and all the scenarios

0:54:55.480 --> 0:54:57.640
<v Speaker 2>where both of them should be relevant are scenarios we

0:54:57.760 --> 0:55:00.799
<v Speaker 2>can't engineer, or we can't study or hit from us.

0:55:01.239 --> 0:55:03.960
<v Speaker 2>So it's endlessly frustrating, but there's a lot of creative

0:55:03.960 --> 0:55:06.440
<v Speaker 2>people out there coming up with ideas for how we

0:55:06.520 --> 0:55:08.959
<v Speaker 2>might be able to test them, new ways to bring

0:55:09.000 --> 0:55:11.840
<v Speaker 2>these two theories together. It's been one hundred years. We

0:55:11.880 --> 0:55:15.720
<v Speaker 2>haven't figured this out, but we're still working on it.

0:55:14.640 --> 0:55:18.479
<v Speaker 2>M Is it possible they're both right. They can't really

0:55:18.520 --> 0:55:21.480
<v Speaker 2>both be right because they make different predictions about the

0:55:21.520 --> 0:55:25.640
<v Speaker 2>same scenarios, but they could both be wrong. In fact,

0:55:25.719 --> 0:55:28.399
<v Speaker 2>most likely scenario is that they're both wrong and there's

0:55:28.400 --> 0:55:31.400
<v Speaker 2>some other deeper theory which tells us a completely different

0:55:31.440 --> 0:55:33.840
<v Speaker 2>story about the nature of the universe. You know, one

0:55:33.880 --> 0:55:35.880
<v Speaker 2>of my favorite things about these theories is that they

0:55:35.880 --> 0:55:38.640
<v Speaker 2>do tell a story. There's an explanation for why things happen.

0:55:39.000 --> 0:55:41.600
<v Speaker 2>But as these theories are replaced by other theories, you

0:55:41.640 --> 0:55:44.120
<v Speaker 2>get a different story, like, oh, it's not actually fields

0:55:44.120 --> 0:55:46.920
<v Speaker 2>out there or a curvature of space time, it's something

0:55:46.920 --> 0:55:50.480
<v Speaker 2>else going on that explains the whole universe. So yeah,

0:55:50.480 --> 0:55:52.080
<v Speaker 2>I want to be around when we figure that all

0:55:52.080 --> 0:55:54.399
<v Speaker 2>out and we hear the next story of the true

0:55:54.480 --> 0:55:55.480
<v Speaker 2>nature of the universe.

0:55:55.719 --> 0:55:57.600
<v Speaker 1>Pretty cool. It might be that the universe is made

0:55:57.600 --> 0:56:03.000
<v Speaker 1>out of qnons man and then hey, it'll turn out

0:56:03.040 --> 0:56:03.839
<v Speaker 1>the Internet was right.

0:56:04.440 --> 0:56:05.800
<v Speaker 2>I think it's bigfoot particles.

0:56:05.840 --> 0:56:09.279
<v Speaker 1>Einstein was wrong, Newton was wrong. The Internet was right

0:56:09.360 --> 0:56:09.920
<v Speaker 1>all along.

0:56:10.239 --> 0:56:12.600
<v Speaker 2>It's all tiny big foots at the microscopic scale. Yes,

0:56:12.680 --> 0:56:15.800
<v Speaker 2>that's right, yeah, pulling and pushing. Wait, Sasquatch has a

0:56:15.880 --> 0:56:17.239
<v Speaker 2>Q in it doesn't it? Oh?

0:56:17.280 --> 0:56:20.359
<v Speaker 1>It does? Yeah? Oh my, well I also has an

0:56:20.480 --> 0:56:22.960
<v Speaker 1>S and a couple of a's.

0:56:24.400 --> 0:56:25.440
<v Speaker 2>Details details.

0:56:25.600 --> 0:56:28.880
<v Speaker 1>Maybe Sasquatch is a retired engineer and she'll break the

0:56:28.960 --> 0:56:29.680
<v Speaker 1>whole case open.

0:56:29.680 --> 0:56:29.839
<v Speaker 2>There.

0:56:30.000 --> 0:56:31.840
<v Speaker 1>You just have to read past the fifteen minutes Daniel

0:56:32.080 --> 0:56:35.680
<v Speaker 1>of that email Sasquatch sent you all right, Well, we

0:56:35.760 --> 0:56:38.920
<v Speaker 1>hope you enjoyed that. Thanks for joining us. See you

0:56:38.920 --> 0:56:39.399
<v Speaker 1>next time.

0:56:44.040 --> 0:56:47.240
<v Speaker 2>For more science and curiosity, come find us on social media,

0:56:47.320 --> 0:56:51.880
<v Speaker 2>where we answer questions and post videos. We're on Twitter, Discord, Instant,

0:56:51.960 --> 0:56:55.400
<v Speaker 2>and now TikTok. Thanks for listening, and remember that Daniel

0:56:55.440 --> 0:56:58.880
<v Speaker 2>and Jorge Explain the Universe is a production of iHeartRadio.

0:56:59.160 --> 0:57:03.040
<v Speaker 2>For more podcast asked from iHeartRadio, visit the iHeartRadio app,

0:57:03.320 --> 0:57:06.800
<v Speaker 2>Apple Podcasts, or wherever you listen to your favorite shows