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How is general relativity wrong? · Daniel and Kelly’s Extraordinary Universe

• 0:09
  Speaker 1: Hey, Daniel, do you get a lot of emails claiming
• 0:11
  Speaker 1: that Einstein was wrong?
• 0:14
  Speaker 2: Oh? Yeah, just about every day I get an email
• 0:16
  Speaker 2: from some retired engineer who sends me there Einstein was
• 0:19
  Speaker 2: wrong paper.
• 0:22
  Speaker 1: Is that the stereotype they retired engineer who has a
• 0:25
  Speaker 1: lot of time in their hands.
• 0:26
  Speaker 2: Not just the stereotype, it's also the reality.
• 0:30
  Speaker 1: Do you not get emails from retired physicists? Also, physicists
• 0:33
  Speaker 1: don't retire. I guess they wouldn't asked you questions if
• 0:36
  Speaker 1: they were physicists.
• 0:37
  Speaker 2: Yeah, they would just publish the papers themselves.
• 0:39
  Speaker 1: Or physicists never retire. Maybe the only engineers are smart
• 0:43
  Speaker 1: enough never retire.
• 0:45
  Speaker 2: We just read eat away.
• 0:47
  Speaker 1: But do you read these emails or do you just
• 0:49
  Speaker 1: you know, send them to your trash box.
• 0:51
  Speaker 2: No. I give each of them like ten or fifteen minutes.
• 0:53
  Speaker 2: See maybe if they're onto something.
• 0:55
  Speaker 1: Oh well, ten to fifteen minutes, that's a that's a
• 0:57
  Speaker 1: pretty good amount. Do you do it because you think
• 0:59
  Speaker 1: they might? You're right?
• 1:00
  Speaker 2: Well, I believe in curiosity and maybe somebody out there
• 1:03
  Speaker 2: does have a great idea. I mean, their heart's in
• 1:06
  Speaker 2: the right place, even if usually the details are wrong.
• 1:09
  Speaker 1: So you do think they might be right.
• 1:11
  Speaker 2: Well, they're definitely right that Einstein was wrong. It just
• 1:14
  Speaker 2: so happens that so are most of these engineers.
• 1:17
  Speaker 1: Well, I guess that's wrong. Is Einstein is not a
• 1:19
  Speaker 1: bad title. I mean, if he couldn't get it right,
• 1:21
  Speaker 1: at least the engineers are trying.
• 1:23
  Speaker 2: Eventually, one of these engineers is going to figure it out.
• 1:25
  Speaker 1: But what if they figure it out on like the
• 1:27
  Speaker 1: sixteenth minute of their paper. Maybe you should double your
• 1:31
  Speaker 1: efforts until you retire.
• 1:34
  Speaker 2: There you go, that's going to retire me.
• 1:51
  Speaker 1: I am horeham May, cartoonists and the author of Oliver's
• 1:54
  Speaker 1: Great Big Universe.
• 1:55
  Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:58
  Speaker 2: at UC Irvine, and I want to be around when
• 2:01
  Speaker 2: we figure out how Einstein was wrong.
• 2:04
  Speaker 1: But you don't want to be the one who figures
• 2:05
  Speaker 1: it out? Do you just want to be around?
• 2:08
  Speaker 2: I just want to cling on to my tenured position
• 2:11
  Speaker 2: for long enough to be here for the party when
• 2:14
  Speaker 2: somebody else figures it out. Now, I'd love to figure
• 2:16
  Speaker 2: it out myself. I'm just not that egotistical.
• 2:19
  Speaker 1: Hmm. Do you think there'll be a big party when
• 2:21
  Speaker 1: they prove Einstein was wrong? Wouldn't that be sort of like,
• 2:24
  Speaker 1: you know, spinning on the grave of a great genius.
• 2:29
  Speaker 2: No, I think it was a tremendous accomplishment when Einstein
• 2:32
  Speaker 2: proved Newton wrong, and no shade on Newton. You know,
• 2:36
  Speaker 2: Newton made a huge advance, a big leap forward, just
• 2:40
  Speaker 2: not all the way to the final truth, and same
• 2:43
  Speaker 2: way its Einstein. And you know the history of physics
• 2:45
  Speaker 2: is littered with these pivotal moments when we made a
• 2:48
  Speaker 2: leap forward in understanding. And I want to be around
• 2:50
  Speaker 2: when we have one of those.
• 2:52
  Speaker 1: But do you think Eistein held a party like and
• 2:55
  Speaker 1: Newton was wrong?
• 2:56
  Speaker 2: Party was wrong party? I don't know if you put
• 2:59
  Speaker 2: it that way, you know, but when his theory of
• 3:02
  Speaker 2: john relativity was so publicly proven right by the eclipse
• 3:06
  Speaker 2: and the visible bending of light, I bet he had
• 3:08
  Speaker 2: a glass of champagne or something.
• 3:10
  Speaker 1: Or maybe he was, you know, nice enough not to
• 3:13
  Speaker 1: dis ut.
• 3:16
  Speaker 2: We're all standing on the shoulders of giants. We don't
• 3:18
  Speaker 2: have to denigrate those giants.
• 3:19
  Speaker 1: That's why you only like to stand under grave and dance.
• 3:23
  Speaker 1: But anyways, welcome to our podcast. Daniel and Jorge explain
• 3:26
  Speaker 1: the Universe, a production of iHeartRadio.
• 3:28
  Speaker 2: In which we try to climb onto the shoulders of
• 3:30
  Speaker 2: those giants with you to bring you along on this
• 3:33
  Speaker 2: fascinating journey the humans have been engaged in for thousands
• 3:37
  Speaker 2: of years to try to understand the nature of our universe.
• 3:41
  Speaker 2: Is there a single law that explains how everything works
• 3:44
  Speaker 2: out there? Is there a final truth for us to discover.
• 3:47
  Speaker 2: Are we on the path to deeply understanding the nature
• 3:50
  Speaker 2: of reality? Or is an endless quest, a long ladder
• 3:54
  Speaker 2: of improvements without ever actually reaching the truth.
• 3:57
  Speaker 1: That's right because as much as science has discovered about
• 3:59
  Speaker 1: the universe, about how how it all works, why it's
• 4:00
  Speaker 1: all made off, there's still a whole bunch of stuff
• 4:03
  Speaker 1: that we don't know about, big mysteries out during the
• 4:05
  Speaker 1: cosmos that we are still trying to figure out, and
• 4:08
  Speaker 1: that we have lots of ideas for. But sometimes those
• 4:10
  Speaker 1: ideas are not quite right.
• 4:12
  Speaker 2: Because science is a process, not a destination, and we
• 4:16
  Speaker 2: are continually updating, improving, and revising our theories for how
• 4:20
  Speaker 2: things work. We think we understand something, and then decad
• 4:24
  Speaker 2: later an engineer shows.
• 4:25
  Speaker 1: Us we were wrong, as is always the case.
• 4:27
  Speaker 2: But those are happy moments in science. Those are the
• 4:30
  Speaker 2: critical pivotal steps forward, those bring us closer to the truth.
• 4:34
  Speaker 2: We're not here to defend the ideas of the ancients,
• 4:37
  Speaker 2: to hold up Aristotilian physics for everybody to believe in,
• 4:40
  Speaker 2: but to bring ourselves closer to the truth by revising
• 4:44
  Speaker 2: the ideas of geniuses who have come before us.
• 4:47
  Speaker 1: Yeah. I feel like that's a very core principle of
• 4:49
  Speaker 1: science that makes it so special, is that there's always
• 4:51
  Speaker 1: the possibility that you could be wrong.
• 4:53
  Speaker 2: Yeah. In fact, probably everything we know about science is
• 4:55
  Speaker 2: wrong in some sense. Everything we do is some approximation
• 5:00
  Speaker 2: of the truth which we might never actually reach.
• 5:03
  Speaker 1: What do you mean, never reach? Are you giving up now?
• 5:08
  Speaker 2: I'm not giving up. I'm promising job security for future physicists.
• 5:12
  Speaker 2: I'm saying it's an infinite task.
• 5:15
  Speaker 1: You're saying, if you're a physicist, you're never going to retire,
• 5:19
  Speaker 1: So choose engineering if you want to at some point
• 5:22
  Speaker 1: stop working.
• 5:23
  Speaker 2: I'm just trying to be humble. You know, every idea
• 5:25
  Speaker 2: we've had in physics has eventually been supplanted by something
• 5:28
  Speaker 2: more precise, something we think is more deeply true. It'd
• 5:32
  Speaker 2: be really egotistical to say, well, the idea we have now,
• 5:36
  Speaker 2: now this is the one that's going to hold up forever.
• 5:40
  Speaker 1: Well, this has been going on for centuries and maybe
• 5:42
  Speaker 1: even thousands of years, and even big names like Einstein
• 5:46
  Speaker 1: people think might not be quite right.
• 5:47
  Speaker 2: Some of these theories we've developed are not just very
• 5:50
  Speaker 2: very accurate, they're beautiful. They give us deep insights into
• 5:54
  Speaker 2: how the universe might work. They tell us a story
• 5:57
  Speaker 2: about how the universe functions, sometimes in a way it's
• 6:00
  Speaker 2: very surprising and intuitive for us. So it's hard to believe.
• 6:04
  Speaker 2: But we think most of these theories might still be wrong.
• 6:07
  Speaker 1: So today on the podcast, we'll be tackling the question
• 6:14
  Speaker 1: how is general relativity wrong? Shouldn't mean to first talk
• 6:19
  Speaker 1: about how it's right.
• 6:22
  Speaker 2: We should, but I just.
• 6:25
  Speaker 1: Or is that what we've been doing for the last
• 6:27
  Speaker 1: five hundred episodes?
• 6:28
  Speaker 2: Yeah, the last one hundred years has been how general
• 6:30
  Speaker 2: relativity is right? But I was going to say, welcome
• 6:33
  Speaker 2: to the group of retired engineers, but then I realized,
• 6:36
  Speaker 2: are you a retired engineer? A? Right?
• 6:39
  Speaker 1: I am an engineer technically, I guess you don't lose
• 6:41
  Speaker 1: the title. Yeah, I'm not quite retired. I'm not sure
• 6:44
  Speaker 1: anyone would trust me to design a bridge or any
• 6:47
  Speaker 1: kind of a car or anything. Maybe a robot. Robots me,
• 6:52
  Speaker 1: what could go wrong.
• 6:52
  Speaker 2: With exactly, I've never read a story about robots.
• 6:57
  Speaker 1: Robots are totally safe. But yeah, I know. But I
• 7:00
  Speaker 1: look forward to to the day where I can, When
• 7:01
  Speaker 1: I can retire for sure, then I can send you questions.
• 7:06
  Speaker 2: You'll get your fifteen minutes, just like everybody.
• 7:08
  Speaker 1: Else, my fifteen minutes of physics. Yes, exactly, that's right,
• 7:13
  Speaker 1: most people along for fifteen minutes of fame. The entire
• 7:17
  Speaker 1: engineer is long for fifteen minutes of a physicist time.
• 7:20
  Speaker 1: But yeah, this is an interesting question to talk about.
• 7:23
  Speaker 1: How general relativity, which is I guess, the main theory
• 7:26
  Speaker 1: or one of the main theories that Einstein discovered, right, Yeah.
• 7:30
  Speaker 2: Einstein made lots of contributions to physics, even inspiring quantum
• 7:33
  Speaker 2: mechanics with his explanation of the photoelectric effect, which is
• 7:37
  Speaker 2: what he actually won the Nobel Prize for. But a
• 7:40
  Speaker 2: lot of people think that his greatest contribution to physics
• 7:42
  Speaker 2: really were the theories of special relativity and then general
• 7:45
  Speaker 2: relativity and tell us about how light operates, what space
• 7:49
  Speaker 2: time really is, and explain that gravity is not actually
• 7:53
  Speaker 2: a force, it's just a product of the curvature of
• 7:56
  Speaker 2: space and time.
• 7:58
  Speaker 1: I would have thought his greatest contribution was hair. Do
• 8:00
  Speaker 1: you know. I feel like it's so iconic in the culture,
• 8:04
  Speaker 1: and it's given permission to every physicist since then not
• 8:09
  Speaker 1: get a haircut.
• 8:10
  Speaker 2: But it's so effortless, right, that's the whole point of
• 8:13
  Speaker 2: his hair due is like, I don't even care what
• 8:14
  Speaker 2: he looks like up there. I don't I don't have
• 8:16
  Speaker 2: to look at it. You got to look at.
• 8:17
  Speaker 1: It, That's what I mean. That's what I mean. You
• 8:19
  Speaker 1: gave permission for the rest of you see, to give
• 8:22
  Speaker 1: all of the the other physicists standing on his shoulders
• 8:25
  Speaker 1: to just let it all hang out.
• 8:26
  Speaker 2: Well, you're standing on his shoulders. You got your head
• 8:28
  Speaker 2: stuck right in that hair. You know, you can't really.
• 8:30
  Speaker 1: Avoid it everywhere, that's right, Yeah, yeah, yeah, don't drop
• 8:34
  Speaker 1: a pan or anything, you might lose it in that hair. Well,
• 8:37
  Speaker 1: as usually, we were wondering how many people out there
• 8:39
  Speaker 1: had thought about the idea that Einstein might be wrong,
• 8:42
  Speaker 1: that general relativity is not quite right, and in which
• 8:45
  Speaker 1: way isn't it right?
• 8:46
  Speaker 2: So thanks very much to everybody who answers these questions.
• 8:49
  Speaker 2: If you would like to join our group of volunteers.
• 8:51
  Speaker 2: Please write to me two questions at Danielandjorge dot com.
• 8:55
  Speaker 2: We'd love to hear your voice.
• 8:57
  Speaker 1: But do you have to be a retired engineer to
• 8:59
  Speaker 1: join the group.
• 9:00
  Speaker 2: You can be a current engineer, you can be a
• 9:01
  Speaker 2: retired engineer, you can be an inspiring engineer, you can
• 9:04
  Speaker 2: be a chocolate engineer. Any kind of engineer is welcome,
• 9:08
  Speaker 2: even non engineers.
• 9:09
  Speaker 1: Well, think about it for a second. How do you
• 9:11
  Speaker 1: think general relativity might be wrong? Here's what people had
• 9:14
  Speaker 1: to say.
• 9:15
  Speaker 3: And I think general relativity is wrong or has to
• 9:21
  Speaker 3: be wrong because in its sort of proposition of singularity
• 9:28
  Speaker 3: in the middle of black holes, because that's just like impossible, right,
• 9:33
  Speaker 3: somehow that has got to be not true.
• 9:36
  Speaker 4: I'm I'm entirely sure how general relativity is wrong. It's
• 9:41
  Speaker 4: actually been something that's bothering me, so I'll be very
• 9:44
  Speaker 4: interested to hear. And I suspect it is quantum physics
• 9:50
  Speaker 4: that has disproved, So I'm not entirely sure how the.
• 9:57
  Speaker 5: Hi Daniel and Hawaii love your show. Keep up the
• 9:59
  Speaker 5: great I think the biggest thing that seems off with
• 10:04
  Speaker 5: general relativity to me is the idea that there is
• 10:07
  Speaker 5: an infinity. If you think about other concepts like absolute zero,
• 10:13
  Speaker 5: there's reasons in real life why we can't reach that temperature.
• 10:17
  Speaker 5: And I think if we can understand what those reasons
• 10:20
  Speaker 5: are for black holes, for example, then maybe we'll be
• 10:24
  Speaker 5: able to understand what the problem is with general relativity.
• 10:29
  Speaker 6: Well, it doesn't account for quantum physics and quantum particles,
• 10:37
  Speaker 6: and I think with how the Big Bang started, it
• 10:43
  Speaker 6: doesn't count for the very initial moments after the Big
• 10:49
  Speaker 6: Bang because that includes quantum particles.
• 10:52
  Speaker 1: All Right, I feel like maybe we've talked about this
• 10:54
  Speaker 1: enough in our podcast, yet people seem pretty familiar with
• 10:56
  Speaker 1: this idea.
• 10:57
  Speaker 2: Yeah. I think we've been sort of gent nagging general
• 11:01
  Speaker 2: relativity for a while now.
• 11:03
  Speaker 1: If people have some clues where we're trying to seduce
• 11:06
  Speaker 1: general relativity here, what's your plan here?
• 11:10
  Speaker 2: No, we've been sort of warming people up to the
• 11:12
  Speaker 2: idea that maybe general relativity isn't telling us the truth
• 11:16
  Speaker 2: about nature.
• 11:17
  Speaker 1: Well, let's dig into Daniel. First of all, what is
• 11:20
  Speaker 1: general relativity and how is it different than other kinds
• 11:22
  Speaker 1: of relativity.
• 11:25
  Speaker 2: So Einstein's first theory of relativity was special relativity, and
• 11:29
  Speaker 2: this was in response to weird mysteries about the speed
• 11:33
  Speaker 2: of light, the Michaelson Morley experiment, electromagnetism and frame dependence
• 11:38
  Speaker 2: and all that stuff. And the theory of special relativity
• 11:41
  Speaker 2: is the one that tells us that light moves at
• 11:42
  Speaker 2: the same speed for all observers, and it leads us
• 11:46
  Speaker 2: to understand how time flows and how events can be
• 11:49
  Speaker 2: simultaneous for one person and not simultaneous for another, and
• 11:53
  Speaker 2: things get shorter at high speeds, and there's a maximum
• 11:56
  Speaker 2: speed at which things could travel. That's all the fascinating
• 11:59
  Speaker 2: physics of space relativity, which already was like a huge
• 12:03
  Speaker 2: brain twist for people back then, right, it was very
• 12:06
  Speaker 2: hard to accept very new idea for how the universe worked.
• 12:11
  Speaker 2: That was special relativity.
• 12:13
  Speaker 1: But is it called special relativity? What is it special
• 12:16
  Speaker 1: from or about?
• 12:17
  Speaker 2: Because it's only relevant in one particular circumstance, and that's
• 12:21
  Speaker 2: when you assume that space is flat, that space has
• 12:24
  Speaker 2: no curvature to it. General relativity is his generalization of
• 12:29
  Speaker 2: special relativity to much broader set of cases, scenarios where
• 12:33
  Speaker 2: the universe has big lumps of mass in it and
• 12:36
  Speaker 2: that mass curves space. Instead of thinking about light pulses
• 12:40
  Speaker 2: moving through space in straight lines and staying parallel to
• 12:43
  Speaker 2: each other. Now, he developed the mathematics to consider what
• 12:46
  Speaker 2: happened when space itself was curved, when light moved in
• 12:49
  Speaker 2: what seemed like curved paths.
• 12:52
  Speaker 1: But did he call it special relativity when he came
• 12:55
  Speaker 1: up with it? Like, did he know as a special
• 12:56
  Speaker 1: case and maybe it wouldn't didn't apply to the rest
• 12:59
  Speaker 1: of the universe.
• 13:00
  Speaker 5: Mm hmm.
• 13:00
  Speaker 2: I'm sure some of our German listeners will know how
• 13:03
  Speaker 2: to say it in German, because these original papers, of course,
• 13:05
  Speaker 2: were not in English. But yeah, he originally called it
• 13:08
  Speaker 2: special relativity and then general relativity.
• 13:11
  Speaker 1: But does that mean then that special relativity is automatically
• 13:14
  Speaker 1: wrong because it only works when space is flat. But
• 13:17
  Speaker 1: space is never flat, is it. Yeah, that's a great question,
• 13:20
  Speaker 1: and it sort of begs the philosophical question what do
• 13:22
  Speaker 1: we mean by wrong? Because the universe is never totally empty.
• 13:25
  Speaker 1: Space is always a little bit curved here, a little
• 13:27
  Speaker 1: bit curved there. I mean, even if you just have
• 13:29
  Speaker 1: a photon passing through space, that is curving space itself, right,
• 13:33
  Speaker 1: because photons have energy. So in that sense, special relativity
• 13:37
  Speaker 1: is approximately right. It's never deeply truly right because it
• 13:41
  Speaker 1: doesn't describe our universe.
• 13:43
  Speaker 2: That doesn't mean the rules of special relativity are wrong, right.
• 13:46
  Speaker 2: It could be that the rules of special relativity are correct,
• 13:49
  Speaker 2: they're just never applicable because the situation describes an energy
• 13:53
  Speaker 2: less universe never actually arises.
• 13:56
  Speaker 1: Wait, so special relativity sort of only works in a
• 13:59
  Speaker 1: new tone in kind of universe. Like you have to
• 14:02
  Speaker 1: assume that Newton was right first.
• 14:04
  Speaker 2: Well, no, Newton had a different theory of space and time.
• 14:06
  Speaker 2: He thought that space and time were absolute backdrops that
• 14:09
  Speaker 2: you could like measure your velocity relative to space, that
• 14:13
  Speaker 2: space was this like stage upon which everything happened. Special
• 14:17
  Speaker 2: relativity already tells you that things like velocity are relative.
• 14:21
  Speaker 2: There is no absolute frame of reference to the universe.
• 14:24
  Speaker 2: So even special relativity is a big departure from Newton's
• 14:27
  Speaker 2: view of how the universe worked.
• 14:29
  Speaker 1: But it sort of also assumed that, like a giant universe,
• 14:32
  Speaker 1: it is not vendable, that's like fixed, kind.
• 14:34
  Speaker 2: Of in the same sense that Newton assumed that, like
• 14:37
  Speaker 2: the X axis runs perfectly straight out to infinity. Special
• 14:41
  Speaker 2: relativity also assumes that.
• 14:44
  Speaker 1: Okay, So then did Einstein know that he had relativity
• 14:49
  Speaker 1: in his boget when he came up with special relativity
• 14:51
  Speaker 1: or was it like a progression of theories.
• 14:54
  Speaker 2: It was definitely a progression. He had not yet solved
• 14:56
  Speaker 2: general relativity. This is not like a staged release where
• 14:59
  Speaker 2: he's like, I got big idea, but I got to
• 15:01
  Speaker 2: like drip it out to the public.
• 15:02
  Speaker 1: This is not like a poor camp But he sort
• 15:06
  Speaker 1: of knew that he special or if he called it
• 15:08
  Speaker 1: special relativity, he knew that only applied to a special case.
• 15:11
  Speaker 2: Yeah, but he hadn't solved the general case yet. It
• 15:13
  Speaker 2: took him years and years to figure it out because
• 15:16
  Speaker 2: the mathematics was super hairy, and he relied on like
• 15:19
  Speaker 2: clever ideas from other mathematical geniuses that he talked to
• 15:23
  Speaker 2: to make his theory of general relativity work. And it's
• 15:26
  Speaker 2: still famously almost impossible to deal with. Like, the equations
• 15:29
  Speaker 2: of general relativity are so complicated, we mostly can't even
• 15:32
  Speaker 2: solve them for anything that looks like our universe. Like
• 15:36
  Speaker 2: we've solved general relativity for scenarios like the universe is
• 15:39
  Speaker 2: filled smoothly with mass, where the universe has nothing in
• 15:42
  Speaker 2: it but a black hole, we can't exactly solve the
• 15:45
  Speaker 2: equations of general relativity for any realistic scenarios because they're
• 15:48
  Speaker 2: so hairy. So it took Einstein years to come up
• 15:51
  Speaker 2: with his theory.
• 15:52
  Speaker 5: Mm.
• 15:52
  Speaker 1: But I guess maybe my question is, like, when he
• 15:55
  Speaker 1: came up with special relativity, did he know that space
• 15:58
  Speaker 1: could actually bend and that the universe actually very different
• 16:03
  Speaker 1: or did that come about when he discovered general relativity.
• 16:07
  Speaker 2: Now, he had that idea that he wanted to incorporate
• 16:09
  Speaker 2: curvature into the fabric of space time as a way
• 16:12
  Speaker 2: to explain gravity. He just hadn't figured out how to
• 16:14
  Speaker 2: make the mathematics of it all work, and that took
• 16:17
  Speaker 2: years and sort of novel mathematics at the time. You know,
• 16:20
  Speaker 2: differential geometry, the idea of like thinking about how things
• 16:23
  Speaker 2: move along curve services. That was kind of new stuff
• 16:26
  Speaker 2: one hundred years ago.
• 16:28
  Speaker 1: All right, well, maybe break it down for us, How
• 16:32
  Speaker 1: would you explain what general relativity is.
• 16:34
  Speaker 2: General relativity is an explanation for why we think there's
• 16:38
  Speaker 2: a force of gravity. It tells us that as things
• 16:41
  Speaker 2: move through space, it's not as Newton described, that they
• 16:44
  Speaker 2: have mass and that mass gives them a force that
• 16:46
  Speaker 2: attract each other, but instead that mass bends space and
• 16:50
  Speaker 2: then they move according to the curvature of that space.
• 16:53
  Speaker 2: So when you jump off a building and you fall
• 16:56
  Speaker 2: towards the Earth, it's not that the Earth's gravity is
• 16:59
  Speaker 2: pulling on you, accelerating you towards the center of the Earth.
• 17:02
  Speaker 2: But now you're moving according to the curvature of space.
• 17:04
  Speaker 2: The Earth has bent space, and you're moving along that
• 17:08
  Speaker 2: curvature towards the center of the Earth. So it's a
• 17:11
  Speaker 2: different picture.
• 17:12
  Speaker 1: And I guess you mean space time right, because you
• 17:15
  Speaker 1: have to kind of mix time into it, right, because
• 17:17
  Speaker 1: like something the bowling belt doesn't fall towards the Earth
• 17:20
  Speaker 1: like it needs time to do that.
• 17:22
  Speaker 2: Right. Time is definitely important factor. And special relativity already
• 17:25
  Speaker 2: showed us that space and time are very closely connected
• 17:28
  Speaker 2: and actually linked them together into four dimensional object. And
• 17:32
  Speaker 2: in that sort of four dimensional way of thinking, a
• 17:34
  Speaker 2: lot of things that didn't make sense in three D
• 17:37
  Speaker 2: space and one D time now click together to make
• 17:40
  Speaker 2: these really beautiful symmetries that you just don't have if
• 17:43
  Speaker 2: you think about space and time separately. The same way
• 17:46
  Speaker 2: that like linking electricity and magnetism together into one object
• 17:49
  Speaker 2: explains a lot of mysteries between them, linking space and
• 17:52
  Speaker 2: time together into one object really makes the mathematics crisp
• 17:55
  Speaker 2: and clear and beautiful, so you have special relativity is
• 17:58
  Speaker 2: based on the idea that space and time, and general
• 18:00
  Speaker 2: relativity just expands that. So absolutely space time is curved,
• 18:04
  Speaker 2: and general relativity also predicts the distortion of time. As
• 18:08
  Speaker 2: things pass through curvature, their time ticks more slowly. General
• 18:12
  Speaker 2: relativity describes the curvature of space time.
• 18:16
  Speaker 1: But the way you're describing it is sort of like
• 18:18
  Speaker 1: it's all about gravity.
• 18:19
  Speaker 2: Gravity comes out as a consequence of this story. Really,
• 18:22
  Speaker 2: what we're trying to do is describe the nature of reality,
• 18:25
  Speaker 2: like what's out there? Why do things move the way
• 18:27
  Speaker 2: we see them moving? If you're in a spaceship and
• 18:30
  Speaker 2: you're looking at the Earth orbiting the sull and you
• 18:32
  Speaker 2: want to know why is it. Newton tells you one story.
• 18:34
  Speaker 2: He says there's a force between these objects pulling on them.
• 18:37
  Speaker 2: Einstein tells you a different story. He says there's no
• 18:40
  Speaker 2: force there, there's no acceleration. That's the inertial motion of
• 18:44
  Speaker 2: the Earth through curved space time. Both stories are trying
• 18:48
  Speaker 2: to explain what we see, but they are describing very
• 18:51
  Speaker 2: different realities.
• 18:53
  Speaker 1: I guess what I mean is like, let's say you
• 18:54
  Speaker 1: take gravity out of the equation. Like, you're just talking
• 18:57
  Speaker 1: about two electrons in space repelling each other from their
• 19:01
  Speaker 1: electrical charge. Do you still need general relativity to describe
• 19:06
  Speaker 1: that motion. No.
• 19:07
  Speaker 2: In fact, we don't know how to do general relativity
• 19:10
  Speaker 2: on electrons. That's one of the problems.
• 19:12
  Speaker 1: Oh well, sounds like I just skipped ahead exactly.
• 19:16
  Speaker 2: So no, you do not need general relativity to describe
• 19:19
  Speaker 2: all the quantum interactions that exist, like in flat space,
• 19:23
  Speaker 2: two electrons out there, assume they're not perturbing space because
• 19:26
  Speaker 2: their masses are so small. Then no, we can do
• 19:28
  Speaker 2: quantum mechanics and explain all those electron interactions without general
• 19:32
  Speaker 2: relativity at all. Generalativity tells us about space and time
• 19:36
  Speaker 2: and gravity, and that's it. I mean, that's a lot
• 19:39
  Speaker 2: of stuff, but that's it all right.
• 19:40
  Speaker 1: So then what do you mean by how that this
• 19:43
  Speaker 1: theory might be wrong? Like, what would it mean for
• 19:47
  Speaker 1: iSight to be wrong?
• 19:48
  Speaker 2: Well, one way for theory to be wrong is for
• 19:50
  Speaker 2: it to make an incorrect prediction. Right If I say, look,
• 19:53
  Speaker 2: I'm fifty years old, and from zero to fifty I've
• 19:57
  Speaker 2: grown about a meter and a half. So therefore, in
• 19:59
  Speaker 2: my fifty years, I'm also going to grow a meter
• 20:01
  Speaker 2: and a half. That's a prediction. It's dumb, obviously, and
• 20:05
  Speaker 2: it's going to be disproven if I live another fifty
• 20:07
  Speaker 2: years and measure my height. So that's a theory that
• 20:09
  Speaker 2: can be proven wrong. Right, So if Einstein's theory makes
• 20:12
  Speaker 2: a prediction and that isn't born out by reality, we
• 20:15
  Speaker 2: do experiments that show that his predictions are wrong, that's
• 20:18
  Speaker 2: a scenario where we would say Einstein was wrong. How Else,
• 20:23
  Speaker 2: there's a sort of philosophical sense in which Einstein could
• 20:26
  Speaker 2: be wrong, which is all these theories of physics are
• 20:29
  Speaker 2: telling us the story. They're an explanation, and all of
• 20:31
  Speaker 2: our explanations in the end, are scientific stories about what's happening,
• 20:35
  Speaker 2: like why is the Earth moving this way? It's moving
• 20:37
  Speaker 2: this way because of the curvature of space time. But
• 20:40
  Speaker 2: those stories involve things we can't see, like we can't
• 20:43
  Speaker 2: directly observe the curvature of space time, we can't directly
• 20:46
  Speaker 2: see electric fields. These stories always involve invisible things that
• 20:50
  Speaker 2: we can't detect directly, And so then we wonder like, well,
• 20:53
  Speaker 2: what if those stories are wrong, do they actually describe
• 20:57
  Speaker 2: reality what's really happening, or are they just sort of
• 20:59
  Speaker 2: like the stories we're telling, even if they predict all
• 21:03
  Speaker 2: the experiments correctly, could they still be sort of philosophically wrong?
• 21:07
  Speaker 1: Is it sort of like, you know, how we thought
• 21:09
  Speaker 1: Newton was right for a long time, and it worked
• 21:12
  Speaker 1: to describe the motion of baseballs and billard balls, and
• 21:15
  Speaker 1: you know, the orbits of the planets, but it's not
• 21:18
  Speaker 1: really right at the end of the.
• 21:19
  Speaker 2: Day, exactly. We don't think that Newton's story is correct.
• 21:22
  Speaker 2: Newton's explanation for billiard balls and planets is not what's
• 21:25
  Speaker 2: actually happening, right, and so Newton can't be right. And
• 21:29
  Speaker 2: so in that sense we wonder like, well, if it's
• 21:31
  Speaker 2: not really philosophically true, is it possible that sometime in
• 21:35
  Speaker 2: the future, maybe not today, maybe well beyond our current capabilities,
• 21:39
  Speaker 2: that Einstein's theory could be proven wrong in some deep
• 21:43
  Speaker 2: future experiment. If it's fundamentally not described in the nature
• 21:46
  Speaker 2: of the universe, it might be possible to find a
• 21:48
  Speaker 2: way to prove that.
• 21:51
  Speaker 1: Well, apparently there's a whole cottage industry of people trying
• 21:54
  Speaker 1: to prove Einstein wrong. There have been many experiments, a
• 21:57
  Speaker 1: lot of different theories trying to bring the man down
• 22:01
  Speaker 1: and so let's dig into that and how exactly general
• 22:03
  Speaker 1: relativity is wrong. But first let's take a quick break.
• 22:20
  Speaker 1: All right, we're talking about how general relativity might be wrong,
• 22:24
  Speaker 1: might be or is wrong.
• 22:26
  Speaker 2: I'm pretty sure it is wrong. I mean, we don't
• 22:28
  Speaker 2: know for sure. But if I had the place a bet,
• 22:31
  Speaker 2: I put my money on Einstein is wrong.
• 22:34
  Speaker 1: Are you taking bets? Is there a pool online that
• 22:36
  Speaker 1: I can sign up for?
• 22:39
  Speaker 2: Oh, you want to bet against me?
• 22:41
  Speaker 1: You're betting against Einstein. I don't know who has the
• 22:48
  Speaker 1: better hair. You're Einstein.
• 22:52
  Speaker 2: Einstein is many things I aspire to, especially this hair
• 22:56
  Speaker 2: was all there yet. I know I'm not there yet.
• 23:00
  Speaker 1: You could die it.
• 23:00
  Speaker 2: I guess who dyes their hair white?
• 23:06
  Speaker 1: I don't know. Yeah, you could be the first person.
• 23:09
  Speaker 2: Yeah, I think dan Quayle died his Temple's great to
• 23:11
  Speaker 2: get a little bit more gravitas. There you go, But
• 23:14
  Speaker 2: I prefer the youthful look.
• 23:15
  Speaker 1: I see, I see, I'm.
• 23:17
  Speaker 2: No longer mistaken for a grad student in my department.
• 23:20
  Speaker 1: You don't need great hair in a while. You don't
• 23:23
  Speaker 1: need gravitas to prove gravity is wrong.
• 23:25
  Speaker 2: No, apparently you don't even need gray hairs. You just
• 23:29
  Speaker 2: need a great idea.
• 23:32
  Speaker 1: That is a grave bar too to pass. Well, it
• 23:37
  Speaker 1: sounds like a lot of people are trying or have
• 23:38
  Speaker 1: been trying to prove einsign wrong, or at least they've
• 23:41
  Speaker 1: been trying to make sure his theory is right. I
• 23:44
  Speaker 1: guess maybe is that a better way to put it.
• 23:46
  Speaker 2: Yeah, we have been trying to verify Einstein's theory, or
• 23:49
  Speaker 2: at least to check it or to see if it's wrong.
• 23:52
  Speaker 2: Because Einstein's theory of gravity doesn't just replace Newton's gravity,
• 23:56
  Speaker 2: it changes it. It makes different predictions from newton theory, and
• 24:00
  Speaker 2: that allows us to test it, to look for those
• 24:03
  Speaker 2: very specific predictions, those consequences of gravity actually being a
• 24:07
  Speaker 2: curvature of space time and not a force between two masses.
• 24:11
  Speaker 2: So for the last one hundred years or so, we've
• 24:13
  Speaker 2: been doing those tests.
• 24:15
  Speaker 1: Yeah, doing those tests and also making observations about the universe,
• 24:18
  Speaker 1: right as a way to test the theory.
• 24:21
  Speaker 2: Yeah, exactly. One way to look for new stuff is
• 24:24
  Speaker 2: just like build a new telescope, look deep into the universe,
• 24:26
  Speaker 2: wait for surprises. Another very very valuable way to discover
• 24:30
  Speaker 2: new stuff is to make very high precision tests of
• 24:34
  Speaker 2: your theory. You know, if your theory makes a very
• 24:36
  Speaker 2: specific prediction about what's going to happen, then go out
• 24:39
  Speaker 2: and do an experiment that's really really precise and check it.
• 24:42
  Speaker 2: Because if there's a small discrepancy, that's a hint maybe
• 24:45
  Speaker 2: this is something new going on, there's something wrong with
• 24:48
  Speaker 2: your theory or some piece of it you haven't accounted for.
• 24:50
  Speaker 2: We do that all the time in particle physics, for example,
• 24:53
  Speaker 2: we measure the mass of something super duper precisely and
• 24:56
  Speaker 2: see if the theory predicts it. Measure the interaction of
• 24:59
  Speaker 2: some particle really really precisely, and see if the theory
• 25:02
  Speaker 2: predicts it correctly.
• 25:03
  Speaker 1: All right, well, what are some of the ways in
• 25:05
  Speaker 1: which we've tested Einstein theories.
• 25:07
  Speaker 2: Well, one of the early successes was understanding the orbit
• 25:10
  Speaker 2: of mercury. You know, the planets orbit the Sun, and
• 25:14
  Speaker 2: in Newtonian physics, this is because there's a force there,
• 25:17
  Speaker 2: and Newton and Kepler were able to even describe not
• 25:20
  Speaker 2: just the circular motion of the planet, but the elliptical
• 25:23
  Speaker 2: motion of the planets. Right, the planets don't orbit in
• 25:26
  Speaker 2: perfect circles. They orbit in ellipses. But that's okay. In
• 25:29
  Speaker 2: Newtonian mechanics, you can have an elliptical orbit that's stable. Right,
• 25:33
  Speaker 2: the Sun pulls on things and then it goes faster when
• 25:35
  Speaker 2: it's closer and slower when it's further away. The math
• 25:38
  Speaker 2: all works out, But an ellipse has a direction to it. Right,
• 25:42
  Speaker 2: there's a bit of the ellipse that's longer and a
• 25:44
  Speaker 2: bit of the ellipse that's shorter, and procession means that
• 25:47
  Speaker 2: that ellipse is turning, like the direction that the ellipse
• 25:50
  Speaker 2: is longer and the pointy bits of the football is turning.
• 25:53
  Speaker 2: So that's what we call that the procession of the ellipse,
• 25:56
  Speaker 2: and Newton can also predict that procession. But what we
• 26:00
  Speaker 2: discovered is that the procession of the orbit of Mercury
• 26:03
  Speaker 2: was a little bit different from what Newton predicted, and
• 26:07
  Speaker 2: Einstein's theory predicted it correctly because it's a different story
• 26:10
  Speaker 2: about how gravity works.
• 26:13
  Speaker 1: But wait, why mercury, Like, what's different about mercury.
• 26:16
  Speaker 2: Well, Mercury is closest to the Sun. And one of
• 26:19
  Speaker 2: the crucial differences between Newtonian and Einsteinian gravity is what
• 26:23
  Speaker 2: happens when something is spinning. Like Newton says, if an
• 26:27
  Speaker 2: object has mass, then you're going to feel it's gravity,
• 26:29
  Speaker 2: and it doesn't matter if it's spinning. Take a sphere
• 26:31
  Speaker 2: of mass, if it's spinning or not. Newton says it
• 26:34
  Speaker 2: has the same gravity. It doesn't matter if it's spinning,
• 26:36
  Speaker 2: if it's a perfect sphere, because you always have masses
• 26:39
  Speaker 2: in the same place. But Einstein says it does matter
• 26:43
  Speaker 2: because Einstein's theory responds not just to the presence of
• 26:46
  Speaker 2: mass but energy, and something that's spinning has a different
• 26:50
  Speaker 2: energy than something that isn't spinning, and it actually twists
• 26:53
  Speaker 2: space time a little bit in a way that twists
• 26:56
  Speaker 2: things nearby, gives them little twists. So the Sun is
• 26:59
  Speaker 2: giving a little torque to Mercury's procession, according to Einstein
• 27:03
  Speaker 2: and not to Newton, and that little torque was enough
• 27:06
  Speaker 2: to explain the deviation in the orbit of Mercury.
• 27:09
  Speaker 1: WHOA, but you wouldn't feel this here on Earth.
• 27:12
  Speaker 2: It's a much smaller effect as you get further and
• 27:14
  Speaker 2: further away. But we've actually measured this ourselves. We've put
• 27:17
  Speaker 2: super precise satellites in orbit around the Earth to detect
• 27:21
  Speaker 2: the effect of the Earth spinning on stuff in orbit
• 27:25
  Speaker 2: around the Earth. We had an episode about gravity Probe
• 27:28
  Speaker 2: B which involves these incredible gyroscopes, which are the smoothest
• 27:32
  Speaker 2: objects known to man, These like incredible balls of quartz
• 27:36
  Speaker 2: mined in Brazil and polished by Grammas in Germany until
• 27:39
  Speaker 2: they're like incredibly spherical so that they're super precise, and
• 27:43
  Speaker 2: they have detected the same thing around the orbit of
• 27:46
  Speaker 2: the Earth.
• 27:47
  Speaker 1: WHOA, that's another way in which we've proven that Einstein
• 27:50
  Speaker 1: was right.
• 27:51
  Speaker 2: Yeah, exactly. All of these experiments and some of these
• 27:53
  Speaker 2: like they take decades to develop to make so precise,
• 27:57
  Speaker 2: and they always come out bang on ein Stein's prediction.
• 28:01
  Speaker 2: It's kind of infuriating.
• 28:03
  Speaker 1: What do you mean infuriating, Well, we.
• 28:05
  Speaker 2: Think Einstein is wrong, and so it's frustrating to not
• 28:08
  Speaker 2: be able to prove it right. As soon as we
• 28:11
  Speaker 2: find an example where Einstein is wrong, that's a thread
• 28:14
  Speaker 2: we can pull on. We can say, okay, here we go,
• 28:16
  Speaker 2: here's the lead. The thing is, we think Einstein was
• 28:19
  Speaker 2: probably wrong, but we don't know how to improve his theory,
• 28:22
  Speaker 2: and until we find a place to where it fails,
• 28:25
  Speaker 2: it's difficult to know how to proceed.
• 28:28
  Speaker 1: So in the gravity of things and how spinning things
• 28:31
  Speaker 1: affect gravity, because Einstein predicted that it would, right.
• 28:35
  Speaker 2: Einstein predicted that it would.
• 28:36
  Speaker 1: So something that spinning has more gravity to it, Like
• 28:39
  Speaker 1: if the Earth was spinning faster, we'd all be heavier.
• 28:42
  Speaker 2: It's not just more gravity, right. Newton's equation is one equation,
• 28:45
  Speaker 2: it's a single force equation. It tells you the magnitude
• 28:49
  Speaker 2: of the force and the direction of it. But Einstein's
• 28:51
  Speaker 2: equation is a tenser equation. It's like a big matrix
• 28:55
  Speaker 2: of equations and tells you gravity is much more complicated
• 28:58
  Speaker 2: than just like a force and a direction, and it
• 29:00
  Speaker 2: can also apply a torque. There's all sorts of complicated things.
• 29:03
  Speaker 2: So it's not just about more gravity, it's about what
• 29:06
  Speaker 2: that gravity is doing.
• 29:08
  Speaker 1: But is that true? If the Earth was spinning faster,
• 29:10
  Speaker 1: I would be heavier.
• 29:11
  Speaker 2: If the Earth was spinning faster, the Earth would be
• 29:13
  Speaker 2: twisting you a little bit. It wouldn't necessarily make you heavier,
• 29:17
  Speaker 2: it'd be spinning you.
• 29:19
  Speaker 3: Oh.
• 29:19
  Speaker 1: But then you say, like it affects the gravity, like
• 29:21
  Speaker 1: it maybe increases the gravity of the Earth.
• 29:24
  Speaker 2: Yeah. I think that's true. Because the overall energy is higher,
• 29:27
  Speaker 2: then you would get more curvature. But also that curvature
• 29:31
  Speaker 2: is more complicated, so it induces a little torque on
• 29:33
  Speaker 2: objects nearby.
• 29:35
  Speaker 1: There's sort of like a little eddy current in gravity.
• 29:38
  Speaker 2: Right, This is called frame dragging. Check out our episodes
• 29:40
  Speaker 2: about that if you want more details.
• 29:41
  Speaker 1: Yeah, what are some of the other ways in which
• 29:44
  Speaker 1: people have tested Einstein?
• 29:46
  Speaker 2: So a lot of these tests we just described are
• 29:48
  Speaker 2: sort of weak field gravity gravity in places where space
• 29:51
  Speaker 2: is curved, but not like dramatically curved. One of the
• 29:54
  Speaker 2: really dramatic predictions of Einstein's theory is that space can curve,
• 29:58
  Speaker 2: incredibly powerfully curve and create things like black holes. And
• 30:02
  Speaker 2: for a long time people thought, well, that's obviously wrong, right,
• 30:06
  Speaker 2: that's ridiculous. But then we went out and we saw
• 30:08
  Speaker 2: black holes in the universe. And so the fact that
• 30:11
  Speaker 2: black holes exist is that there's an event horizon beyond
• 30:15
  Speaker 2: which information cannot escape is a direct prediction of general relativity,
• 30:19
  Speaker 2: not of Newtonian physics, and something we've seen in the
• 30:22
  Speaker 2: universe but we.
• 30:23
  Speaker 1: Think we've seen. Right, then we talk about before how
• 30:26
  Speaker 1: nobody has actually technically seen a black hole or confirmed
• 30:30
  Speaker 1: its existence.
• 30:31
  Speaker 2: Yeah, that's an important caveat right, We've seen things that
• 30:34
  Speaker 2: are very consistent with black holes. There are some alternative
• 30:37
  Speaker 2: theories dark stars, boson stars, fuzzy string balls, et cetera,
• 30:41
  Speaker 2: et cetera. The most mainstream interpretation of those is that
• 30:45
  Speaker 2: they are black holes. They're totally consistent with black holes.
• 30:48
  Speaker 2: But you're right, we've never actually confirmed the existence of
• 30:51
  Speaker 2: an event horizon in the universe.
• 30:54
  Speaker 1: Right, or what's inside of it, right.
• 30:56
  Speaker 2: Yeah, or what's inside of it.
• 30:57
  Speaker 1: But we have to sort of used black holes in
• 31:00
  Speaker 1: to prove that the gravitational waves exist, which is part
• 31:03
  Speaker 1: of Eystein's theory, right exactly.
• 31:06
  Speaker 2: Another important distinction between Einsteinian and Newtonian gravity is that
• 31:10
  Speaker 2: gravity takes time. That information is not instantly propagated in
• 31:14
  Speaker 2: the universe. Newton says, if you delete the Sun from
• 31:17
  Speaker 2: the universe, it's gravity disappears instantly. But Einstein's spent a
• 31:20
  Speaker 2: lot of time thinking about how information is propagated. He
• 31:23
  Speaker 2: developed the theory of special relativity, and so in general
• 31:26
  Speaker 2: relativity he accounts for this. He says that it takes
• 31:28
  Speaker 2: time for gravitational information to propagate, and that propagates via
• 31:32
  Speaker 2: gravitational waves. So you take a black hole, for example,
• 31:35
  Speaker 2: or even a sun or a big rock and you
• 31:37
  Speaker 2: wiggle it. Then the curvature it's causing wiggles as you
• 31:41
  Speaker 2: wiggle the rock. You can detect this if you have
• 31:44
  Speaker 2: really big sources of gravitational waves, like black holes eating
• 31:48
  Speaker 2: each other as they spiral around each other, they make
• 31:50
  Speaker 2: these gravitational waves and we've detected them. This is another
• 31:54
  Speaker 2: crazy prediction that I personally thought would never be borne out.
• 31:58
  Speaker 2: But again due to like amazing seeing technical and experimental bravado,
• 32:02
  Speaker 2: they figured out how to see these things and we've
• 32:04
  Speaker 2: confirmed them and the predictions are bang on Einstein's calculations.
• 32:09
  Speaker 1: Yeah, that's some amazing engineering going on there, right.
• 32:12
  Speaker 2: It really is impressive.
• 32:15
  Speaker 1: They probably deserve their retirement engineers.
• 32:17
  Speaker 2: Well, they definitely deserve the Nobel Prizes that they won
• 32:21
  Speaker 2: for it. I was thinking about where to go to
• 32:22
  Speaker 2: grad school in the late nineties and thinking about, you know,
• 32:25
  Speaker 2: particle physics at Berkeley or gravitational waves at Caltech, and
• 32:29
  Speaker 2: I definitely chose particle physics at Berkeley because I thought
• 32:32
  Speaker 2: they would never see those gravitational waves.
• 32:34
  Speaker 1: I thought it was crazy, and you could own part
• 32:37
  Speaker 1: of a Nobel Prize right now had you chosen another.
• 32:40
  Speaker 2: Path, absolutely, you know, have the path not taken.
• 32:43
  Speaker 1: But instead now they are retired engineers who have part
• 32:46
  Speaker 1: of a Nobel Prize, but you don't.
• 32:47
  Speaker 2: Yeah exactly. But you know there's another version of that
• 32:50
  Speaker 2: story where I did join the project and I messed
• 32:52
  Speaker 2: it all up and they never discovered gravitation. Oh yeah,
• 32:55
  Speaker 2: So maybe I was doing everybody a favor by staying
• 32:57
  Speaker 2: out of it.
• 32:58
  Speaker 1: That's right, you get account for all plus abilit.
• 33:00
  Speaker 2: I'm what I'm saying is I get to share that
• 33:02
  Speaker 2: Nobel Prize by not messing it up.
• 33:04
  Speaker 1: Really, Daniel done, so does everybody else who's ever existed.
• 33:12
  Speaker 2: I mean we're always saying everybody is a scientist, right,
• 33:15
  Speaker 2: so shouldn't we all reap the benefits.
• 33:17
  Speaker 1: Well, I think we all get the benefits, but not
• 33:19
  Speaker 1: necessarily the credit or the not credit for not getting
• 33:24
  Speaker 1: the way.
• 33:24
  Speaker 2: I mean, there's so many discoveries out there that I
• 33:27
  Speaker 2: didn't mess up. I don't know why I'm not getting
• 33:28
  Speaker 2: credit for that.
• 33:29
  Speaker 1: I know there should be just a prize just for you.
• 33:32
  Speaker 1: They should thank me.
• 33:33
  Speaker 2: Every year, Thank you Daniel for not being involved and
• 33:36
  Speaker 2: not messing this one up.
• 33:38
  Speaker 1: That's right. Daniel Whitson ignored us a price.
• 33:43
  Speaker 2: Yeah exactly, But anyway, it's an incredible accomplishment. Nobel Prize
• 33:47
  Speaker 2: is very well deserved.
• 33:48
  Speaker 1: Yeah, and so that's one way in which we confirm
• 33:51
  Speaker 1: general relativity, right, because you can only get gravitational waves
• 33:54
  Speaker 1: with general relativity, or is there another explanation for them?
• 33:59
  Speaker 2: There's no other explanation for gravitational waves. I mean other
• 34:02
  Speaker 2: variations of general relativity that we might talk about, you know,
• 34:06
  Speaker 2: ways to build on general relativity. But you can't get
• 34:08
  Speaker 2: gravitational waves in Newtonian gravity. You need the curvature of
• 34:13
  Speaker 2: space time and general relativity to have that prediction, all.
• 34:18
  Speaker 1: Right, So that's another box that general relativity checked. What
• 34:22
  Speaker 1: are some of the other boxes that it has passed well?
• 34:25
  Speaker 2: Affects like gravitational lensing because space is curved when light
• 34:29
  Speaker 2: passes through it, it follows that curvature, and so light moving
• 34:33
  Speaker 2: around really massive objects doesn't move and what looks like
• 34:36
  Speaker 2: a straight line to us if we're far away and
• 34:39
  Speaker 2: we can see this in the sky, we can see
• 34:41
  Speaker 2: light bending around invisible dark matter and creating distortions in
• 34:45
  Speaker 2: background galaxies. This effect occurs all over the place in
• 34:49
  Speaker 2: the sky and it's been confirmed many, many times. So
• 34:53
  Speaker 2: we definitely know that light is curved as it passes
• 34:55
  Speaker 2: through bend space.
• 34:58
  Speaker 1: This is an interesting one because I feel like anyone
• 35:00
  Speaker 1: can confirm and look out there into the universe to
• 35:03
  Speaker 1: do this right, Like you don't need to build a
• 35:05
  Speaker 1: super special satellite or a super giant detector, Like you
• 35:08
  Speaker 1: could just look out into this into space and confirm
• 35:11
  Speaker 1: that space is being bent out there.
• 35:14
  Speaker 2: Yeah, I'm not sure you could do it with like
• 35:16
  Speaker 2: a backyard telescope. You need sort of precise measurements, but.
• 35:19
  Speaker 1: You haven't seen my backyard.
• 35:20
  Speaker 2: Then retired engineers have a lot of disposable income and
• 35:26
  Speaker 2: maybe they have really fancy telescopes in their backyard. But yeah,
• 35:30
  Speaker 2: you can.
• 35:31
  Speaker 1: See or like you know, you could go to a
• 35:32
  Speaker 1: local observatory maybe yeah, or a big one and like
• 35:35
  Speaker 1: you can step right up to the lens and take a.
• 35:38
  Speaker 2: Look right exactly. Sometimes you can see galaxies duplicated, like
• 35:42
  Speaker 2: the same galaxy in two places in the sky because
• 35:45
  Speaker 2: photons from that galaxy bend around some object and appear
• 35:48
  Speaker 2: to be coming from two different directions. You can see
• 35:51
  Speaker 2: what's called an Einstein cross, effectively like an optical distortion
• 35:55
  Speaker 2: of our vision because of this curvature. So yeah, you
• 35:58
  Speaker 2: can just look through a telescope and you can see
• 36:01
  Speaker 2: gravitational lensing.
• 36:02
  Speaker 1: Now, and now this is significant because it basically shows
• 36:05
  Speaker 1: that light is affected by gravity, which is significant because
• 36:09
  Speaker 1: light doesn't have any mass, right, yeah, so it wouldn't, nominally,
• 36:14
  Speaker 1: according to Newton, feel a force of gravity, and yet
• 36:19
  Speaker 1: it's being pulled and pushed by the mass of other objects.
• 36:23
  Speaker 2: Exactly because it's moving through that curved space, and masses
• 36:28
  Speaker 2: bend space and everything moves through that curved space.
• 36:32
  Speaker 1: Although doesn't it also maybe depend on what you mean
• 36:34
  Speaker 1: by mass, Like if you mean any kind of energy
• 36:37
  Speaker 1: is massd then could that also explain the curvature of
• 36:40
  Speaker 1: light without general relativity? You know, like let's say a
• 36:44
  Speaker 1: photon doesn't have any mass in the traditional sense, but
• 36:47
  Speaker 1: it has energy to it it does. Yeah, yeah, And
• 36:50
  Speaker 1: now let's say that I call mass something different like
• 36:53
  Speaker 1: mass now not just the mass we used to call mass,
• 36:55
  Speaker 1: but also energy like the energy of photon might have,
• 36:59
  Speaker 1: and then it was a force from gravity because of
• 37:03
  Speaker 1: this energy mass. Couldn't I also maybe explain the curvature
• 37:07
  Speaker 1: of light with Newtonian physics?
• 37:09
  Speaker 3: Oh?
• 37:10
  Speaker 2: I see, could you make some sort of like Newtonian
• 37:12
  Speaker 2: version of gravity where you generalize it from just mass
• 37:16
  Speaker 2: to energy and say, you know, the Whoregey theory of
• 37:18
  Speaker 2: gravity is that there's a force between objects with energy,
• 37:21
  Speaker 2: not just with mass.
• 37:23
  Speaker 1: Yes, the Whoregey theory of light and gravity future novel
• 37:28
  Speaker 1: prize winning theory.
• 37:30
  Speaker 2: Yeah, yeah, absolutely, you can do that. And people have
• 37:33
  Speaker 2: actually tried to do this to build like a bridge
• 37:35
  Speaker 2: between Newtonian and Einsteinian theories. One thing we do when
• 37:39
  Speaker 2: we come up with a brand new theory is we
• 37:41
  Speaker 2: try to understand, like, is the old theory a special
• 37:43
  Speaker 2: case of this new theory. How do they fit together?
• 37:45
  Speaker 2: Is one at generalization of the other one? And so
• 37:48
  Speaker 2: people have actually gone back and tried to like patch
• 37:50
  Speaker 2: these things together and say, could you go from Newtonian
• 37:53
  Speaker 2: physics to Einsteinian physics using that direction to avoid the
• 37:56
  Speaker 2: interpretation of curvature. And there are some that you can
• 38:00
  Speaker 2: get right. For example, you can describe how light bends
• 38:04
  Speaker 2: using this apparent force between energy rather than a force
• 38:08
  Speaker 2: between mass. But you can't get all the details right
• 38:11
  Speaker 2: of the curvature of space time. There's more information in
• 38:14
  Speaker 2: there in the metric and the curvature of space time
• 38:17
  Speaker 2: that can just be described by the force. It's sort
• 38:19
  Speaker 2: of like a richer theory.
• 38:22
  Speaker 1: I see, so I think. I guess what I was
• 38:23
  Speaker 1: trying to get to is that, you know, gravitational lensing
• 38:26
  Speaker 1: is a test of gravity, but it's not like a
• 38:29
  Speaker 1: slam dunk case of gravity, right of general relativity exactly.
• 38:34
  Speaker 2: You can add bells and whistles to Newton's theory to
• 38:37
  Speaker 2: make gravitational lensing happen.
• 38:39
  Speaker 1: Yeah. Yeah, it's called the bells and whistles theory of
• 38:42
  Speaker 1: the universe, the B and W. All right, well, let's
• 38:47
  Speaker 1: get into how else we know that general relativity is wrong,
• 38:51
  Speaker 1: and let's talk about how it's wrong and where we
• 38:53
  Speaker 1: think it might finally break. So let's stick into that.
• 38:56
  Speaker 1: But first let's take another quick break. All right, we're
• 39:11
  Speaker 1: talking about general relativity, the big theory that Einstein came
• 39:14
  Speaker 1: up with. The talks about gravity and how space can
• 39:17
  Speaker 1: bend and how space time gets bent by things like
• 39:21
  Speaker 1: mass and energy, and how it might be wrong. Although
• 39:24
  Speaker 1: it seems pretty right from all the experiments we've done.
• 39:27
  Speaker 2: So far, it's been endlessly vinegated, which is frustrating because
• 39:31
  Speaker 2: I'm pretty sure it's wrong.
• 39:32
  Speaker 1: What are you so short?
• 39:35
  Speaker 2: Even though every test we've done has confirmed Einstein's prediction,
• 39:39
  Speaker 2: we think that there are scenarios where it must break down.
• 39:42
  Speaker 2: Not tests we can do today, but test we can
• 39:45
  Speaker 2: imagine with thought experiments places in the universe where we
• 39:48
  Speaker 2: think Einstein's theory can't be right.
• 39:51
  Speaker 1: Interesting. So you're saying, like, it's as right as far
• 39:54
  Speaker 1: as we know and the phenomena we've seen, but there
• 39:58
  Speaker 1: might be situations where it breaks down.
• 40:00
  Speaker 2: We think that there are situations where it has to
• 40:02
  Speaker 2: be wrong, even though we haven't yet been able to
• 40:05
  Speaker 2: engineer any of those situations in the lab to prove it.
• 40:09
  Speaker 2: But there are sort of thought experiments or future experiments
• 40:11
  Speaker 2: we can predict or places in the universe where we
• 40:15
  Speaker 2: think it's got to be wrong.
• 40:16
  Speaker 1: Uh. Interesting, All right, well let's step through these scenarios.
• 40:19
  Speaker 1: What are these places?
• 40:20
  Speaker 2: Yeah, well, one was the scenario you brought up earlier,
• 40:23
  Speaker 2: like what happens between two electrons? What is the gravitational
• 40:27
  Speaker 2: force between two electrons? Because electrons are not just like
• 40:30
  Speaker 2: tiny little versions of planets. They're not just like small
• 40:34
  Speaker 2: planets with tiny little masses in them where you can
• 40:37
  Speaker 2: apply Newtonian physics or think about the curvature of space.
• 40:40
  Speaker 2: They're fundamentally different from planets. They're probabilistic. We know that
• 40:44
  Speaker 2: electrons are quantum objects. They don't have a definitive location.
• 40:49
  Speaker 2: They have a probability for being here and a probability
• 40:51
  Speaker 2: for being there. They can interfere with each other, and
• 40:55
  Speaker 2: Einstein's theory doesn't account for that. It doesn't allow for that.
• 40:58
  Speaker 2: It says, Look, things have locations, and those locations determine
• 41:03
  Speaker 2: how space curves. So we don't know what to do
• 41:05
  Speaker 2: when things don't have locations, The space curve randomly the
• 41:10
  Speaker 2: space curve probabilistically. What's going on?
• 41:13
  Speaker 1: But other theories can can deal with that, like could
• 41:16
  Speaker 1: Neaton handle a quantum object? No.
• 41:18
  Speaker 2: Newton's theory also requires you to know where something is,
• 41:22
  Speaker 2: Like if you're going to feel the force of gravity
• 41:24
  Speaker 2: from an electron, you got to know how far away
• 41:25
  Speaker 2: it is and in what direction. If an electron like
• 41:28
  Speaker 2: could be to your left and could be to your right,
• 41:31
  Speaker 2: then what gravity are you feeling? Are you feeling gravity
• 41:33
  Speaker 2: to the left, are you feeling gravity to the right?
• 41:35
  Speaker 2: Are you feeling fifty to fifty gravity to the left
• 41:38
  Speaker 2: and right? So it cancels itself out, like Newton also
• 41:40
  Speaker 2: doesn't know what to do in that situation.
• 41:43
  Speaker 1: Wait, what so then how do you do anything with
• 41:46
  Speaker 1: quantum mechanics, like how do you how do you compute
• 41:48
  Speaker 1: the path of an electron?
• 41:49
  Speaker 2: Yeah, mostly we ignore gravity. Like when we compute the
• 41:52
  Speaker 2: path with an electron or electrons interacting, we assume that
• 41:55
  Speaker 2: there's no gravity. We do those all in flat space.
• 41:59
  Speaker 1: But then how do you how do you like, if
• 42:01
  Speaker 1: another electron pushes it or pulls it, how do you
• 42:04
  Speaker 1: make that calculation of where it's going to go?
• 42:07
  Speaker 2: Well, we just assume that there is no gravity, and
• 42:09
  Speaker 2: we do the quant mechanical version of things. Because all
• 42:12
  Speaker 2: the other forces, the pushing and the pulling of electromagnetism
• 42:16
  Speaker 2: that allows for this probabilistic stuff. We have a quantum
• 42:19
  Speaker 2: theory of electromagnetic forces, and a quantum theory of the
• 42:22
  Speaker 2: strong force and the weak force. All the forces in
• 42:24
  Speaker 2: the universe we can describe using quantum mechanics, and those
• 42:28
  Speaker 2: quantum descriptions can totally accommodate these sort of probabilities and interference.
• 42:34
  Speaker 1: And it just lets you compute like the arc or
• 42:37
  Speaker 1: trajectory of an electron.
• 42:39
  Speaker 2: It lets you compute the probability of various outcomes. Absolutely,
• 42:43
  Speaker 2: so quantum mechanics is totally cool with that. And when
• 42:47
  Speaker 2: we do that, we have to ignore gravity. You might ask, well,
• 42:49
  Speaker 2: how can you get the right answer if you're ignoring gravity. Well,
• 42:52
  Speaker 2: gravity is super duper weak. It's so much weaker than
• 42:55
  Speaker 2: any of these other forces, so it's basically negligible. Like
• 42:58
  Speaker 2: we couldn't actually even measure the mass of an electron
• 43:02
  Speaker 2: using gravity. We talked recently on the podcast about like
• 43:05
  Speaker 2: the smallest thing we've ever measured the gravity for. It
• 43:08
  Speaker 2: was like around a kilogram or a little bit smaller.
• 43:11
  Speaker 2: You know, zillions and zillions of atoms, So we can't
• 43:14
  Speaker 2: detect the gravity these particles. We just ignore it in
• 43:17
  Speaker 2: our calculations for particle physics because we also don't know
• 43:20
  Speaker 2: how to do those calculations.
• 43:22
  Speaker 1: But I wonder if you mean, like only at the
• 43:23
  Speaker 1: microscopic level, Like, for example, can I treat an electron
• 43:28
  Speaker 1: as a little point particle like a little tiny baseball
• 43:31
  Speaker 1: and throw it at the Earth. Wouldn't even like Newtonian
• 43:34
  Speaker 1: physics tell me at least the most likely path that
• 43:37
  Speaker 1: electron is going to take.
• 43:39
  Speaker 2: Yeah, absolutely, you can do those calculations, and we actually
• 43:42
  Speaker 2: do those calculations. When we think about like the atmosphere,
• 43:45
  Speaker 2: how much atmosphere are we losing. Well, it depends on
• 43:48
  Speaker 2: the velocity and the gravity of the atoms in the
• 43:51
  Speaker 2: upper atmosphere. We lose more hydrogen and helium than the
• 43:54
  Speaker 2: heavier elements because they have more gravity. The Earth is
• 43:57
  Speaker 2: pulling on them harder. But there we're doing a classical calculation.
• 44:01
  Speaker 2: We're ignoring the quantum nature of those objects. Whenever the
• 44:04
  Speaker 2: quantum nature is relevant, gravity becomes irrelevant. And that's one
• 44:08
  Speaker 2: of the frustrating things about testing Einstein's theory is that
• 44:11
  Speaker 2: it's mostly irrelevant in places where we think it's going
• 44:14
  Speaker 2: to fail. Like we think that Einstein's theory breaks down
• 44:19
  Speaker 2: for quantum particles, but it's also irrelevant for quantum particles
• 44:23
  Speaker 2: because quantum particles have almost no mass.
• 44:26
  Speaker 1: Well, I think what you're saying is that it does
• 44:28
  Speaker 1: work for quantum particles, just not at a certain level. Right, Like,
• 44:33
  Speaker 1: you can use general relativity and Newtonian physics on an
• 44:37
  Speaker 1: electron to predict whether it's going to leave the Earth
• 44:40
  Speaker 1: or not, or what pass is going to take around
• 44:42
  Speaker 1: the Earth, but when you get down to the microscopic level,
• 44:45
  Speaker 1: you don't know what to do.
• 44:46
  Speaker 2: Yeah, when the quantum nature of those particles is important,
• 44:50
  Speaker 2: general relativity breaks down, we don't know what to do
• 44:52
  Speaker 2: with it there, and that's exactly where we also can't
• 44:55
  Speaker 2: detect the effects of general relativity. If you ignore the
• 44:58
  Speaker 2: quantum nature of the electron or the atom, then yes,
• 45:01
  Speaker 2: you can use general relativity or even Newtonian physics to
• 45:04
  Speaker 2: predict the path of the particle. But when the quantum
• 45:07
  Speaker 2: nature is important, that's when it breaks down, and that's
• 45:10
  Speaker 2: when we can't detect the effects of general relativity.
• 45:14
  Speaker 1: All right, well, what are some of the other extreme
• 45:17
  Speaker 1: situations where you think, I think theory might burong.
• 45:20
  Speaker 2: The other famous concern, and the one that Listeners raised,
• 45:22
  Speaker 2: is singularities. What's inside a black hole? General relativity tells
• 45:26
  Speaker 2: us that the things that fall past the event horizon
• 45:29
  Speaker 2: slide towards the center of the black hole, where curvature
• 45:32
  Speaker 2: gets stronger and stronger, and it gets so strong that
• 45:35
  Speaker 2: essentially it's a runaway effect and becomes infinitely dense. You
• 45:39
  Speaker 2: have this point in space where you have mass but
• 45:42
  Speaker 2: zero volume, and so we call that a singularity because
• 45:45
  Speaker 2: the density is essentially infinite or undefined. So that's the
• 45:49
  Speaker 2: prediction of general relativity. But most people think that that's
• 45:52
  Speaker 2: not really a prediction that's a sign that the theory
• 45:55
  Speaker 2: is broken. It's predicting something we think is unphysical and
• 45:59
  Speaker 2: it has to be replaced by another theory. That we've
• 46:01
  Speaker 2: gone beyond the boundary of where the theory is valid.
• 46:05
  Speaker 2: Just like me predicting that I'll grow another meter and
• 46:07
  Speaker 2: a half in the next half of my life.
• 46:09
  Speaker 1: What do you mean, Like you're saying that the idea
• 46:11
  Speaker 1: of a singularity is the prediction of general relativity. Exactly,
• 46:16
  Speaker 1: which is at the center of a black hole?
• 46:17
  Speaker 2: Yeah, exactly, that's what general relativity tells us is at
• 46:20
  Speaker 2: the center of a black hole. But we don't believe it.
• 46:23
  Speaker 2: We don't think it's actually there. We think it's a
• 46:25
  Speaker 2: sign that general relativity is wrong, that we've pushed it
• 46:29
  Speaker 2: beyond the bounds where you can no longer really use
• 46:31
  Speaker 2: the theory.
• 46:32
  Speaker 1: But why not, Why couldn't you have some point something
• 46:35
  Speaker 1: in the center of a black hole.
• 46:36
  Speaker 2: Well, one reason is quantum mechanics. Right, if something becomes
• 46:39
  Speaker 2: that small, then its quantum properties are important because quantum
• 46:43
  Speaker 2: mechanics rules when things are super dup or small. Everything
• 46:46
  Speaker 2: in the universe that's super tiny follows the rules of
• 46:48
  Speaker 2: quantum mechanics and quantum mechanics says you can't have something
• 46:52
  Speaker 2: so massive, so much energy in such a tiny little space,
• 46:55
  Speaker 2: as like an inherent fuzziness to the universe that a
• 46:59
  Speaker 2: singularity violates. And so if we could look inside a
• 47:01
  Speaker 2: black hole and see what's there. Is it a singularity,
• 47:04
  Speaker 2: is it something else, a weird quantum fuzzy blob, is
• 47:07
  Speaker 2: it something completely different, then we would know how to
• 47:10
  Speaker 2: update and correct general relativity. But of course we can't.
• 47:14
  Speaker 1: But isn't it sort of the same as like an electron.
• 47:16
  Speaker 1: Like an electron you can treat as a point particle,
• 47:18
  Speaker 1: which is also an impossibility. And yet do you still
• 47:21
  Speaker 1: assume that in quantum mechanics, In sort.
• 47:23
  Speaker 2: Of old school quantum mechanics, we do treat the electron
• 47:25
  Speaker 2: as a point particle, and that's valid in some scenarios
• 47:28
  Speaker 2: right where it doesn't really matter. But you're right, if
• 47:30
  Speaker 2: you zoom in on the electron, it can't actually be
• 47:33
  Speaker 2: a point particle. And if you do quantum field theory,
• 47:36
  Speaker 2: then you replace this idea of a point particle with
• 47:39
  Speaker 2: like a little blob of energy density in the quantum
• 47:42
  Speaker 2: field of the electron. And so we have like different
• 47:45
  Speaker 2: pictures for sort of different scales of work in particle physics.
• 47:49
  Speaker 2: But you're right, from some points of view, the point
• 47:51
  Speaker 2: particle description works just fine. And so if like from
• 47:54
  Speaker 2: the outside of a black hole, having a singularity on
• 47:56
  Speaker 2: the inside is okay. But once you zoom in on
• 47:59
  Speaker 2: it that you get in and observe the quantum details
• 48:02
  Speaker 2: of it, we're wondering like, is it really a singularity
• 48:04
  Speaker 2: or is it something else? And that would be a
• 48:07
  Speaker 2: deviation from Einstein's prediction. If it's not a singularity, then
• 48:11
  Speaker 2: that would be a clue something we could pull on
• 48:13
  Speaker 2: to help unravel or update Einstein's theory.
• 48:16
  Speaker 1: Well, I feel like in this case, you know, it
• 48:18
  Speaker 1: wouldn't prove that Eystein was wrong. It's just that at
• 48:22
  Speaker 1: that level you have to use a different set of rules.
• 48:24
  Speaker 2: Yeah, that's a good point. It's not showing Einstein is wrong.
• 48:26
  Speaker 2: It's showing that his theory is valid only under certain circumstances.
• 48:30
  Speaker 2: And that's cool. It's like saying, you know, as fluid
• 48:33
  Speaker 2: mechanics wrong, Well, it works great for fluids. You can't
• 48:36
  Speaker 2: apply it to like crowds or to steam or crystals.
• 48:39
  Speaker 2: Doesn't mean it's wrong. It means that it's relevant to
• 48:42
  Speaker 2: a certain set of conditions, And so that's sort of
• 48:46
  Speaker 2: the question we were asking philosophically, Like, if Einstein's theory
• 48:49
  Speaker 2: of gravity is deeply true, it's the actual story of
• 48:52
  Speaker 2: what the universe is doing, then it should always be right.
• 48:55
  Speaker 2: But if it's just an approximation, if it's just something
• 48:58
  Speaker 2: that works under some certain conditions like fluid mechanics, then
• 49:02
  Speaker 2: you know, it's just a story we're telling ourselves that
• 49:04
  Speaker 2: helps us do calculations. It might not be like the
• 49:06
  Speaker 2: actual story of the universe if there are bounds on
• 49:10
  Speaker 2: where it's relevant.
• 49:11
  Speaker 1: Or I wonder if another possibilities that it is right
• 49:13
  Speaker 1: all the way down to the center of the universe.
• 49:16
  Speaker 1: You just have to add quantum mechanics on top, meaning
• 49:19
  Speaker 1: that they're each right in their own way.
• 49:21
  Speaker 2: Yeah, but they disagree about what happens at the heart
• 49:24
  Speaker 2: of a black hole, right, so they can't both be right.
• 49:26
  Speaker 1: I don't know. Maybe they don't disagree.
• 49:29
  Speaker 2: But they do. They disagree. You know, there might be
• 49:32
  Speaker 2: some version of quantum gravity, an extension of Einstein's idea
• 49:36
  Speaker 2: modification of Einstein's ideas that describes more accurately what's going
• 49:41
  Speaker 2: on inside a black hole. But if there's no singularity. There,
• 49:45
  Speaker 2: then Einstein's prediction is wrong.
• 49:48
  Speaker 1: Well, as a particle physicist and a quantum mechanic person,
• 49:51
  Speaker 1: I would say, maybe you're a little biased.
• 49:53
  Speaker 2: Yeah, yeah, sure, I believe.
• 49:57
  Speaker 1: It all right. What are some of the other situation
• 50:00
  Speaker 1: where you think Einstein might be wrong?
• 50:02
  Speaker 2: Well, another famous singularity is the Big Bang. You know,
• 50:06
  Speaker 2: if you take the universe as we see it, it's
• 50:08
  Speaker 2: sort of cold and dilute, but we see that it's expanding.
• 50:12
  Speaker 2: Then you rewind the clock back to the early universe.
• 50:14
  Speaker 2: You see the universe getting hotter and hotter and denser
• 50:17
  Speaker 2: and denser and denser, and you could rewind that back,
• 50:20
  Speaker 2: like all the way back to an infinite density, a singularity,
• 50:24
  Speaker 2: a moment when the universe is filled with infinitely dense matter.
• 50:28
  Speaker 2: And I gotta clarify a lot of people think of
• 50:30
  Speaker 2: the Big Bang as like a single point of matter
• 50:33
  Speaker 2: which then exploded out into space. But instead we imagine
• 50:36
  Speaker 2: the Big Bang is something that happened everywhere that the
• 50:38
  Speaker 2: whole universe filled with this incredibly dense matter. So Einstein's
• 50:42
  Speaker 2: theory lets you unwind all the way back to this
• 50:45
  Speaker 2: moment of infinite density. But nobody believes that. People think that, well,
• 50:49
  Speaker 2: you get back to some hot dense state up to
• 50:52
  Speaker 2: like the Plank temperature, some really hot moment, and beyond that,
• 50:56
  Speaker 2: some quantum effects are going to be relevant. You can't
• 50:58
  Speaker 2: just use general relativity to extrapolate all the way back
• 51:01
  Speaker 2: to infinite.
• 51:02
  Speaker 1: Density unless quantum mechanics breaks down at that point. Like
• 51:06
  Speaker 1: you're assuming that quantum mechanics is still valid at that point.
• 51:10
  Speaker 2: Right, Yeah, And but quantum mechanics is another theory that's
• 51:13
  Speaker 2: been tested in great detail and very exquisitely, and we
• 51:17
  Speaker 2: think describes the fundamental nature of the universe. So what
• 51:21
  Speaker 2: happens when these two theories come into conflict is the
• 51:24
  Speaker 2: big question. And so, like inside the heart of a
• 51:27
  Speaker 2: black hole or in the very very early universe, these
• 51:29
  Speaker 2: are the moments when quantum mechanics and general relativity are
• 51:33
  Speaker 2: both relevant. They both have something to say about what happens,
• 51:36
  Speaker 2: and they say different things. And so most people believe,
• 51:39
  Speaker 2: and maybe I'm biased because I'm a part of the
• 51:41
  Speaker 2: physicist that the universe is quantum mechanical and that general
• 51:44
  Speaker 2: relativity will break down at those moments and will not
• 51:47
  Speaker 2: accurately predict the universe.
• 51:49
  Speaker 1: I see, by most people you mean you and your friends.
• 51:55
  Speaker 2: Yes, me and the rest of the physicists in the universe.
• 51:58
  Speaker 2: Most people believe that our relativity is wrong, but we
• 52:01
  Speaker 2: haven't proven it. We have not proven it right. It's
• 52:03
  Speaker 2: a belief, it's a theory, it's a speculation.
• 52:06
  Speaker 1: Feels a little like faith.
• 52:07
  Speaker 2: Daniel, Well, you know, science is subjective in the sense
• 52:11
  Speaker 2: of like what we try to believe, what we tried
• 52:13
  Speaker 2: to prove, what we explore. We have hunches, we have creativity.
• 52:17
  Speaker 2: It's not like science is a process that tells you
• 52:19
  Speaker 2: what to try and what experiments to do, et cetera,
• 52:23
  Speaker 2: et cetera. You have to have ideas and intuition and
• 52:26
  Speaker 2: hunches and creativity, but then you have to listen to
• 52:28
  Speaker 2: the experiments, you know, and so that's what we're waiting for.
• 52:32
  Speaker 1: But I guess you would concede that right now. There's
• 52:35
  Speaker 1: nothing that maybe would say that one or the other
• 52:39
  Speaker 1: is right or wrong. You just feel that one is
• 52:42
  Speaker 1: more right than the other.
• 52:43
  Speaker 2: Yeah, we have no evidence that Einstein was wrong. We
• 52:46
  Speaker 2: just suspect very very strongly that he's got to be
• 52:49
  Speaker 2: wrong eventually. But no, we do not have any evidence
• 52:53
  Speaker 2: that Einstein was wrong.
• 52:56
  Speaker 1: In fact, it almost seems like you have the evidence
• 52:58
  Speaker 1: to the contrary.
• 52:59
  Speaker 2: Yeah, we have lots of evidence that he's right. Frustrating
• 53:02
  Speaker 2: the huge amounts of evidence that he was right. But
• 53:05
  Speaker 2: under these scenarios that we can't engineer ourselves. We can't
• 53:08
  Speaker 2: look inside a black hole, we can't rewind time at
• 53:10
  Speaker 2: the beginning of the universe. We have a hard time
• 53:14
  Speaker 2: coming up with ways of testing quantum mechanics and gravity.
• 53:17
  Speaker 2: That we did a whole episode about quantum gravity experiments
• 53:19
  Speaker 2: and a tabletop that might be able to break that barrier.
• 53:22
  Speaker 2: Nobody's yet been able to engineer a scenario to prove
• 53:26
  Speaker 2: Einstein wrong.
• 53:27
  Speaker 1: It kind of feels like a conspiracy theory, Daniel, Is
• 53:29
  Speaker 1: that where the queue in q andon comes from?
• 53:32
  Speaker 2: That does mean quantum Wait? Is Einstein the conspiracy theorist?
• 53:35
  Speaker 2: Or are you saying particle physics?
• 53:38
  Speaker 1: I'm saying maybe quantum mechanics. You can see this is
• 53:41
  Speaker 1: the conspiracy theory. That's where the Q and q andon
• 53:44
  Speaker 1: comes from.
• 53:45
  Speaker 2: Oh I see quantum anon.
• 53:46
  Speaker 1: Yes, yeah, In fact, even sounds like a particle like
• 53:49
  Speaker 1: electrode q and on. Oh man, I just broke the conspiracy.
• 53:55
  Speaker 1: It's all tied secret Cabala physicists.
• 53:59
  Speaker 2: Yeah, that's the exactly right. Well, you could make the
• 54:01
  Speaker 2: same arguments in the other direction, right, you could say, like, look,
• 54:03
  Speaker 2: quantum mechanics has been proven right through a huge number
• 54:06
  Speaker 2: of experiments, but it conflicts with general relativity the heart
• 54:10
  Speaker 2: of black holes in the early universe, so maybe it's wrong.
• 54:13
  Speaker 2: You could take that entirely other perspective. We have two
• 54:16
  Speaker 2: great theories that disagree, and one of them's got to
• 54:20
  Speaker 2: be wrong.
• 54:21
  Speaker 1: Right, I'm just saying, probably we don't know that conspiracy
• 54:23
  Speaker 1: starts with a que and so that to me is
• 54:26
  Speaker 1: a big hint. It sounds like a particle too. All right, Well,
• 54:31
  Speaker 1: what does it all mean, Daniel, doesn't mean that we
• 54:33
  Speaker 1: have these two titanic gigantic theories about the universe. You're
• 54:37
  Speaker 1: saying that the conflict in a lot of situations. So
• 54:40
  Speaker 1: there's plenty of scientific evidence that for each of them
• 54:43
  Speaker 1: to be both right. But they can both be right
• 54:47
  Speaker 1: in the center of the universe.
• 54:48
  Speaker 2: Yeah, we have so many scenarios where we've tested each
• 54:51
  Speaker 2: of them individually with great precision, and all the scenarios
• 54:55
  Speaker 2: where both of them should be relevant are scenarios we
• 54:57
  Speaker 2: can't engineer, or we can't study or hit from us.
• 55:01
  Speaker 2: So it's endlessly frustrating, but there's a lot of creative
• 55:03
  Speaker 2: people out there coming up with ideas for how we
• 55:06
  Speaker 2: might be able to test them, new ways to bring
• 55:09
  Speaker 2: these two theories together. It's been one hundred years. We
• 55:11
  Speaker 2: haven't figured this out, but we're still working on it.
• 55:14
  Speaker 2: M Is it possible they're both right. They can't really
• 55:18
  Speaker 2: both be right because they make different predictions about the
• 55:21
  Speaker 2: same scenarios, but they could both be wrong. In fact,
• 55:25
  Speaker 2: most likely scenario is that they're both wrong and there's
• 55:28
  Speaker 2: some other deeper theory which tells us a completely different
• 55:31
  Speaker 2: story about the nature of the universe. You know, one
• 55:33
  Speaker 2: of my favorite things about these theories is that they
• 55:35
  Speaker 2: do tell a story. There's an explanation for why things happen.
• 55:39
  Speaker 2: But as these theories are replaced by other theories, you
• 55:41
  Speaker 2: get a different story, like, oh, it's not actually fields
• 55:44
  Speaker 2: out there or a curvature of space time, it's something
• 55:46
  Speaker 2: else going on that explains the whole universe. So yeah,
• 55:50
  Speaker 2: I want to be around when we figure that all
• 55:52
  Speaker 2: out and we hear the next story of the true
• 55:54
  Speaker 2: nature of the universe.
• 55:55
  Speaker 1: Pretty cool. It might be that the universe is made
• 55:57
  Speaker 1: out of qnons man and then hey, it'll turn out
• 56:03
  Speaker 1: the Internet was right.
• 56:04
  Speaker 2: I think it's bigfoot particles.
• 56:05
  Speaker 1: Einstein was wrong, Newton was wrong. The Internet was right
• 56:09
  Speaker 1: all along.
• 56:10
  Speaker 2: It's all tiny big foots at the microscopic scale. Yes,
• 56:12
  Speaker 2: that's right, yeah, pulling and pushing. Wait, Sasquatch has a
• 56:15
  Speaker 2: Q in it doesn't it? Oh?
• 56:17
  Speaker 1: It does? Yeah? Oh my, well I also has an
• 56:20
  Speaker 1: S and a couple of a's.
• 56:24
  Speaker 2: Details details.
• 56:25
  Speaker 1: Maybe Sasquatch is a retired engineer and she'll break the
• 56:28
  Speaker 1: whole case open.
• 56:29
  Speaker 2: There.
• 56:30
  Speaker 1: You just have to read past the fifteen minutes Daniel
• 56:32
  Speaker 1: of that email Sasquatch sent you all right, Well, we
• 56:35
  Speaker 1: hope you enjoyed that. Thanks for joining us. See you
• 56:38
  Speaker 1: next time.
• 56:44
  Speaker 2: For more science and curiosity, come find us on social media,
• 56:47
  Speaker 2: where we answer questions and post videos. We're on Twitter, Discord, Instant,
• 56:51
  Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel
• 56:55
  Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
• 56:59
  Speaker 2: For more podcast asked from iHeartRadio, visit the iHeartRadio app,
• 57:03
  Speaker 2: Apple Podcasts, or wherever you listen to your favorite shows