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