Latest / Daniel and Kelly’s Extraordinary Universe / Could a huge void cause the illusion of dark energy?

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Could a huge void cause the illusion of dark energy? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: Hey, Daniel, what are we talking about today?
• 0:09
  Speaker 2: On the episode, we are talking about avoid.
• 0:13
  Speaker 1: As in you're gonna avoid my questions.
• 0:16
  Speaker 2: No voids as in vast empty spaces.
• 0:21
  Speaker 1: Is there a scientist that discovered them? And if so,
• 0:24
  Speaker 1: is it kind of a scam because you just discovered nothing.
• 0:27
  Speaker 2: I'd love to get famous for discovering nothing. That's basically
• 0:30
  Speaker 2: what I've done my whole career.
• 0:32
  Speaker 1: Same here, same here.
• 0:33
  Speaker 2: For that, you got the no Prize instead of the
• 0:35
  Speaker 2: Nobel Prize.
• 0:36
  Speaker 1: Oh, you don't get to eat bells and whistles, so
• 0:38
  Speaker 1: you do get the Nobel Prize.
• 0:41
  Speaker 2: I think I want to avoid myself with these jokes.
• 0:43
  Speaker 1: Avoid. I am Jorge mcgartunez, a author of Oliver's Great
• 1:02
  Speaker 1: Big Universe.
• 1:03
  Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:06
  Speaker 2: at UC Irvine, and I got into this business to
• 1:09
  Speaker 2: make radical, universe changing discoveries. But I haven't made any.
• 1:14
  Speaker 1: The whole reason we're here, it has been all for nothing.
• 1:18
  Speaker 2: Well, you know, research has no guarantees. You could go
• 1:21
  Speaker 2: out there into the vast plane of undiscovered territory and
• 1:25
  Speaker 2: find all sorts of incredible stuff or just nothing. We
• 1:28
  Speaker 2: have no promises from nature.
• 1:30
  Speaker 1: Well, Daniel, you sound a little defeated. Did you have
• 1:33
  Speaker 1: a lot of years ahead of you in your career?
• 1:37
  Speaker 2: No, I'm not defeated. I rolled the dice and I
• 1:39
  Speaker 2: knew there were risks, and you know, physics is a
• 1:42
  Speaker 2: lot of fun along the way even if you don't
• 1:44
  Speaker 2: make a big discovery.
• 1:45
  Speaker 1: But don't you have like at least twenty thirty years
• 1:48
  Speaker 1: of work still or are you just planning to coast
• 1:52
  Speaker 1: the rest of the.
• 1:53
  Speaker 2: Way on adviceive counsel. I'm going to not answer that question.
• 1:58
  Speaker 1: You're like, it's called being emeritus.
• 2:02
  Speaker 2: I'm rapidly approaching emeritus.
• 2:04
  Speaker 1: Well, whether you're emeritus or active, Welcome to our podcast,
• 2:07
  Speaker 1: Daniel and Jorge Explain the Universe, a production of iHeartRadio.
• 2:11
  Speaker 2: In which we guide you through all of the incredible,
• 2:14
  Speaker 2: mind shattering discoveries of the last few hundred years that
• 2:17
  Speaker 2: have revealed a universe that's weird, that's bizarre, that's strange,
• 2:21
  Speaker 2: and yet somehow maybe understandable, And we also try to
• 2:25
  Speaker 2: guide you through potential discoveries in the next few years,
• 2:28
  Speaker 2: in the next decades, may be made by me or
• 2:30
  Speaker 2: my team, or by some of the listeners to this podcast.
• 2:33
  Speaker 2: Or they are great great grandchildren. Whenever those discoveries come,
• 2:37
  Speaker 2: we want you to be prepared for them by understanding
• 2:39
  Speaker 2: what we do and don't know about the universe.
• 2:43
  Speaker 1: That's right, because it is an incredibly huge and amazing
• 2:46
  Speaker 1: universe out there, full of incredible phenomenon, astounding events, and
• 2:50
  Speaker 1: also a whole lot of moving.
• 2:53
  Speaker 2: Indeed, the universe really is something. Even if that's something
• 2:56
  Speaker 2: is often nothing. But there's lots of mysteries remaining about
• 3:00
  Speaker 2: the nature of the universe. As much as we've discovered
• 3:02
  Speaker 2: in the last one hundred years about how big the
• 3:05
  Speaker 2: universe is, about how it's expanding, about how that expansion
• 3:08
  Speaker 2: is accelerating, about how galaxies swirl around invisible dark matter,
• 3:13
  Speaker 2: there's still a lot of pieces that don't fit together,
• 3:16
  Speaker 2: which tells us probably the next few decades or few
• 3:19
  Speaker 2: hundred years will reveal even more mind blowing discoveries about
• 3:23
  Speaker 2: the nature of our cosmos.
• 3:25
  Speaker 1: Yeah, the amazing thing about this universe and about science
• 3:28
  Speaker 1: is that all the pieces are out there for us
• 3:31
  Speaker 1: to see, for us to discover, for us to observe,
• 3:34
  Speaker 1: and for someone maybe you, maybe us, to put it
• 3:37
  Speaker 1: all together and make sense of this amazing cosmos. Oh wait, wait, sorry, sorry,
• 3:42
  Speaker 1: not Daniel, he's already given up.
• 3:45
  Speaker 2: Hey you know, if it falls to my lap, I'm
• 3:47
  Speaker 2: not saying no.
• 3:48
  Speaker 1: But yeah, well it sound like like you just throw
• 3:51
  Speaker 1: it in the trash.
• 3:53
  Speaker 3: You know.
• 3:53
  Speaker 2: The universe is like a giant mystery novel. Often all
• 3:57
  Speaker 2: of the clues are out there, staring us in the face.
• 4:00
  Speaker 2: This requires the insight, that moment of clarity to see
• 4:03
  Speaker 2: how it all fits together into one coherent story. And
• 4:07
  Speaker 2: currently we're struggling a little bit to understand all of
• 4:09
  Speaker 2: those clues to tell a story that makes sense to
• 4:12
  Speaker 2: us and that holds together mathematically. And it could be
• 4:16
  Speaker 2: that some elements of our current story are drastically wrong.
• 4:19
  Speaker 2: We've certainly done that lots of times in history, gone
• 4:22
  Speaker 2: down the wrong path for decades or even centuries before
• 4:25
  Speaker 2: having to backtrack and come up with a completely new,
• 4:28
  Speaker 2: radical interpretation of how the universe works.
• 4:32
  Speaker 1: Yeah, leaving all those other scientists to have discovered nothing.
• 4:36
  Speaker 1: But all the clues are out there, but one of
• 4:39
  Speaker 1: the problems is that they're really far away. That's because
• 4:41
  Speaker 1: the universe is full of nothing, a lot of big
• 4:44
  Speaker 1: empty void in spaces that are preventing us from reaching
• 4:48
  Speaker 1: and touching some of the important clues that are out there.
• 4:50
  Speaker 1: But there is maybe the idea that some of these
• 4:54
  Speaker 1: huge voids of nothingness could maybe hold the answer to
• 4:59
  Speaker 1: one of the biggest quest questions in the universe.
• 5:01
  Speaker 2: That's right, Maybe the biggest question in modern science today
• 5:05
  Speaker 2: is what is driving the expansion of the universe? Why
• 5:08
  Speaker 2: is it going faster and faster every year? We have
• 5:11
  Speaker 2: a placeholder idea we call dark energy, but as you'll hear,
• 5:15
  Speaker 2: it's not even really a single coherent concept and we
• 5:18
  Speaker 2: might need completely new explanations for it.
• 5:21
  Speaker 1: So today on the podcast, we'll be tackling the question
• 5:29
  Speaker 1: could a huge void cost the illusion of dark energy?
• 5:35
  Speaker 1: So wait, what are you saying, Daniel that dark energy
• 5:37
  Speaker 1: is not something and in fact it might be nothing.
• 5:41
  Speaker 2: Wouldn't it be a huge dramatic plot twist if the
• 5:43
  Speaker 2: answer the biggest question in science was nothing.
• 5:50
  Speaker 1: I feel like we can already preview that, like what
• 5:53
  Speaker 1: came before the universe nothing? What's going to happen after
• 5:56
  Speaker 1: the universe nothing? We're just to blipp and the nothing
• 5:59
  Speaker 1: is I.
• 6:01
  Speaker 2: Think the answer to both of those questions is actually
• 6:03
  Speaker 2: we don't know or we have no idea, which is
• 6:05
  Speaker 2: a little bit different from nothing. And you know, philosophically,
• 6:08
  Speaker 2: nothing is a complicated concept, like what does it even mean? Right?
• 6:12
  Speaker 2: We've talked on the podcast about how space is never
• 6:15
  Speaker 2: really empty and all of it has quantum fields and it,
• 6:18
  Speaker 2: so what does nothing even really mean? It's actually quite
• 6:21
  Speaker 2: a deep philosophical question.
• 6:23
  Speaker 1: It is very tricky.
• 6:24
  Speaker 3: Yeah.
• 6:24
  Speaker 1: For example, I have a doctorate in philosophy, but I
• 6:27
  Speaker 1: know nothing about philosophy.
• 6:30
  Speaker 2: So you're saying you know nothing. Wow, you're an expert
• 6:32
  Speaker 2: in nothing.
• 6:34
  Speaker 1: Well, I guess that's something.
• 6:37
  Speaker 2: I would say. I'm no expert in nothing. Nothing is
• 6:40
  Speaker 2: actually quite complex.
• 6:41
  Speaker 1: I lost track of the negatives there, No, you didn't, No,
• 6:45
  Speaker 1: I didn't. No, I didn't not know nothing about something?
• 6:50
  Speaker 2: There you go. Well, let's check in with the listeners
• 6:52
  Speaker 2: to see if they don't not know nothing about nothing?
• 6:54
  Speaker 1: Yeah, as usual, Daniel went out there to ask people
• 6:56
  Speaker 1: if they think maybe a huge void could be causing
• 7:00
  Speaker 1: what we see as dark energy.
• 7:02
  Speaker 2: Thanks very much to everybody who's sent in their answers.
• 7:05
  Speaker 2: I would love to hear your voice on the podcast.
• 7:08
  Speaker 2: That's right, I'm talking to you. You've been listening for
• 7:11
  Speaker 2: years but never chimed in. Today's the day right to
• 7:14
  Speaker 2: me two questions at Danielanjorge dot com.
• 7:17
  Speaker 1: So think about it for a second. Do you think
• 7:19
  Speaker 1: dark energy could be explained by a huge amount of nothingness?
• 7:25
  Speaker 1: Here's what people had to say.
• 7:26
  Speaker 4: I don't think so. Even without the accelerated expansion of
• 7:29
  Speaker 4: the universe, it's still possible to have huge voids in space.
• 7:34
  Speaker 4: Perhaps if we were able to detect that a huge
• 7:36
  Speaker 4: void wasn't there before, we might be able to use
• 7:40
  Speaker 4: that as evidence towards the cosmological constant, But I think
• 7:44
  Speaker 4: that would take a long time.
• 7:46
  Speaker 3: Perhaps the void is filled with dark energy which we
• 7:48
  Speaker 3: cannot yet detect, So perhaps these areas could be responsible
• 7:52
  Speaker 3: for the accelerated expansion rate, if only we could learn
• 7:55
  Speaker 3: what dark energy truly is.
• 7:57
  Speaker 5: I'm going to assume in your definition of you ascribe
• 8:01
  Speaker 5: to quantum field theory and avoid in space would be
• 8:04
  Speaker 5: an area where the fields from all the fundamental particles
• 8:08
  Speaker 5: are somehow blocked from this area. One could posit that
• 8:12
  Speaker 5: some of these fields might feel a sort of pressure
• 8:14
  Speaker 5: to fill the void, causing an expansion. So, sure, I'll
• 8:17
  Speaker 5: say it could.
• 8:19
  Speaker 6: Aha dark energy explain. Sure it could be space expanding
• 8:24
  Speaker 6: into a void. But then where is that void? What
• 8:28
  Speaker 6: is that void made out of and how is it
• 8:31
  Speaker 6: expanding into it? And what does that even mean? I
• 8:34
  Speaker 6: don't know about this one.
• 8:36
  Speaker 2: I'm confused by that comment. What's the difference between a
• 8:39
  Speaker 2: huge amount of nothingness and a small amount of nothingness?
• 8:41
  Speaker 2: If they're all nothing, it's like ten times zero versus
• 8:44
  Speaker 2: one time zero.
• 8:45
  Speaker 1: I think the difference is a nothing.
• 8:50
  Speaker 2: Nice. Well, I like these listeners answer some really well
• 8:54
  Speaker 2: informed thoughts here. You seem surprised, Daniel, No, I'm impressed
• 8:57
  Speaker 2: as usual.
• 8:58
  Speaker 1: Had you given up on our list as well.
• 9:01
  Speaker 2: I think your reaction is based on nothing. I have
• 9:04
  Speaker 2: nothing but respect for these listeners, their efforts to understand
• 9:07
  Speaker 2: the universe, their willingness to contribute. I'm in awe.
• 9:10
  Speaker 1: Well, they do have some interesting answers here, and it's
• 9:13
  Speaker 1: kind of an interesting question that maybe the biggest part
• 9:17
  Speaker 1: of what we see in the universe, ninety five percent
• 9:20
  Speaker 1: of all the mass and energy in the universe, maybe
• 9:23
  Speaker 1: is not really something or mass or energy. Maybe it's
• 9:26
  Speaker 1: just something that can be easily explained with nothing.
• 9:29
  Speaker 2: Yeah, that's right. In order to explain this accelerating expansion
• 9:33
  Speaker 2: of the universe, we've had to add into our equations,
• 9:36
  Speaker 2: something very weird, very awkward, something we really struggle with,
• 9:40
  Speaker 2: and so people have been working for a long time
• 9:41
  Speaker 2: to find alternative explanations, sort of more prosaic ideas that
• 9:46
  Speaker 2: would explain the strange things we see out there in
• 9:48
  Speaker 2: the universe.
• 9:50
  Speaker 1: My question, Daniel, is why didn't we think of this before?
• 9:53
  Speaker 1: I mean, well, when you see something mysterious, shouldn't the
• 9:57
  Speaker 1: first thing you ask be maybe it's nothing.
• 10:00
  Speaker 2: Yeah, it's a good question. This particular idea that we're
• 10:02
  Speaker 2: going to talk about today is uncomfortable in other ways
• 10:05
  Speaker 2: for scientists. It violates some like philosophical principles that they
• 10:10
  Speaker 2: really hope the universe respects. And that's why it's a
• 10:14
  Speaker 2: little bit weird and a little bit uncomfortable to consider.
• 10:17
  Speaker 2: But hey, sometimes when the universe confronts you with data,
• 10:20
  Speaker 2: you just got to accept it.
• 10:21
  Speaker 1: I mean, after like twenty thirty years of trying to
• 10:23
  Speaker 1: explain it in other ways.
• 10:24
  Speaker 2: I guess, yeah, exactly.
• 10:27
  Speaker 1: Just because it makes it uncomfortable.
• 10:29
  Speaker 2: I like that the universe makes us uncomfortable. I like,
• 10:31
  Speaker 2: when we go what it doesn't make any sense at all?
• 10:33
  Speaker 2: How could the universe be that way? Those are the
• 10:36
  Speaker 2: moments we really learn something when we really have to
• 10:39
  Speaker 2: confront some fundamental assumption that is probably wrong.
• 10:43
  Speaker 1: Right, right, you like it, but only if you're sitting
• 10:45
  Speaker 1: comfortably in your couch.
• 10:46
  Speaker 2: Right, yeah, exactly. Let me get comfortable before you make
• 10:51
  Speaker 2: me uncomfortable.
• 10:52
  Speaker 1: Yeah, let's draw online here. I want to be physically
• 10:56
  Speaker 1: comfortable but intellectually uncomfortable.
• 10:58
  Speaker 2: Is that what you're saying, Yes, serve me some chocolate
• 11:00
  Speaker 2: while you tell me the results of this study. Yes, absolutely,
• 11:05
  Speaker 2: a little bit of sugar makes the medicine go down.
• 11:07
  Speaker 1: Right, right, you've given up even getting up up for
• 11:09
  Speaker 1: your couch. But anyways, Daniel, for those of us who
• 11:13
  Speaker 1: are sitting in our couches, wait to hear the answer.
• 11:17
  Speaker 1: What you start us with the basics? What is this
• 11:20
  Speaker 1: thing that we call dark energy?
• 11:22
  Speaker 2: Yeah, so the thing that we're struggling to explain is
• 11:25
  Speaker 2: something we call dark energy. But dark energy is not
• 11:28
  Speaker 2: really like a theory as much as a description of
• 11:32
  Speaker 2: something we observe in the universe for which we don't
• 11:35
  Speaker 2: have a great explanation. And that's the fact that the
• 11:38
  Speaker 2: universe is expanding, and it's not just expanding the same
• 11:41
  Speaker 2: rate every year. It's expanding at an accelerated rate. It
• 11:45
  Speaker 2: seems like the distances between clusters of galaxies is increasing,
• 11:49
  Speaker 2: so that's expansion, but it's increasing faster and faster every year.
• 11:54
  Speaker 2: This is something we discovered about twenty five years ago now,
• 11:57
  Speaker 2: when we first learned how to figure out how far
• 12:00
  Speaker 2: away things are in the universe, and it was really
• 12:03
  Speaker 2: a shocker. You know, people before that were wondering how
• 12:06
  Speaker 2: quickly the expansion of the universe was slowing down. That
• 12:09
  Speaker 2: was the big question in science because you have the
• 12:12
  Speaker 2: universe expanding when it's very very young, but then it's
• 12:15
  Speaker 2: filled with matter. There's all this heavy stuff in the universe,
• 12:17
  Speaker 2: galaxies and black holes and whatever that tends to pull
• 12:20
  Speaker 2: stuff back together, and so people were wondering, hey, is
• 12:23
  Speaker 2: there enough gravity to pull stuff back together to make
• 12:26
  Speaker 2: like a reverse big bang, like a big crunch, or
• 12:29
  Speaker 2: is there not enough and it's just going to gradually
• 12:31
  Speaker 2: slow down for a long time to keep drifting apart.
• 12:34
  Speaker 2: And when they went out to measure it, they discovered, shocker,
• 12:37
  Speaker 2: neither of those were true. The universe preferred secret answer CEE,
• 12:41
  Speaker 2: which is that things are getting further apart faster and faster.
• 12:44
  Speaker 2: So dark energy is sort of like our placeholder name
• 12:47
  Speaker 2: to explain how that might be happening.
• 12:49
  Speaker 1: So, I think we've known that the universe is expanding
• 12:52
  Speaker 1: for about one hundred years, right, But you're saying it's
• 12:55
  Speaker 1: only recently we figured out it's accelerating.
• 12:58
  Speaker 2: Yeah, if you want to go further back into history,
• 13:00
  Speaker 2: around the time that Einstein was developing the theory of relativity,
• 13:04
  Speaker 2: we thought the universe was static. We thought that there
• 13:07
  Speaker 2: was just like our galaxy hanging out there in empty
• 13:09
  Speaker 2: space and that was it. Then Edwin Hubble and Henrietta
• 13:12
  Speaker 2: Levitt developed this way to measure the distance to things
• 13:15
  Speaker 2: in the sky to tell how far away they were,
• 13:18
  Speaker 2: And what they discovered is that some smudgets we saw
• 13:21
  Speaker 2: in the sky that we thought were just like clouds
• 13:23
  Speaker 2: of gas in our galaxy were actually much further away.
• 13:26
  Speaker 2: There were further than any of the stars in the sky.
• 13:29
  Speaker 2: There were actually other galaxies. And on top of that,
• 13:32
  Speaker 2: those galaxies were moving away from us. So we discovered
• 13:35
  Speaker 2: that the universe was not only just our galaxy, it
• 13:37
  Speaker 2: was filled with galaxies, and that the universe was expanding.
• 13:41
  Speaker 2: Everything was running away from us. That was about one
• 13:43
  Speaker 2: hundred years ago.
• 13:44
  Speaker 1: And how do we know they were moving away from
• 13:46
  Speaker 1: us from the red shifting the Doppler.
• 13:48
  Speaker 2: Effect, Yeah, exactly. You can look at the light from
• 13:51
  Speaker 2: those galaxies and you can see how its frequency shifted
• 13:55
  Speaker 2: things that are moving away from us. As you said,
• 13:57
  Speaker 2: the Doppler effect, the light from those things is shift
• 14:00
  Speaker 2: in frequency, and you can tell because we have an
• 14:02
  Speaker 2: idea for what frequency of light should be emitted by
• 14:05
  Speaker 2: galaxies to have these particular fingerprints, and so when they're
• 14:08
  Speaker 2: shifted over twenty nanometers or one hundred nanimeters or whatever
• 14:13
  Speaker 2: in wavelength, then we can tell. And that we use
• 14:15
  Speaker 2: that to measure the velocity.
• 14:17
  Speaker 1: And so back then, did we think or measure that
• 14:21
  Speaker 1: everything was moving away from us at the same speed
• 14:24
  Speaker 1: or we just didn't know enough to know at what
• 14:27
  Speaker 1: rate things were moving away from us.
• 14:29
  Speaker 2: Back then, Hubble's discovery allowed us to measure the distance
• 14:31
  Speaker 2: to other galaxies, but sort of only in us nearby sphere.
• 14:35
  Speaker 2: Hubble couldn't tell that the universe was expanding and accelerating
• 14:38
  Speaker 2: because he couldn't measure the distance to far away enough stuff.
• 14:42
  Speaker 2: He and Henriette Levitt developed this technique to measure the
• 14:45
  Speaker 2: distance to stuff looking at these particular variable stars called cephids.
• 14:49
  Speaker 2: But you had to be able to see them, and
• 14:51
  Speaker 2: if galaxies were far enough away, then you couldn't see
• 14:53
  Speaker 2: those stars in the galaxies, so he could sort of
• 14:56
  Speaker 2: only see a little bubble. But about twenty five years
• 14:59
  Speaker 2: ago we developed a new technique that allowed us to
• 15:01
  Speaker 2: see much further and to measure the distance much further,
• 15:03
  Speaker 2: and so then we could see the change over time
• 15:06
  Speaker 2: as we look back into the history of the universe,
• 15:09
  Speaker 2: and we noticed this effect. So Hubble couldn't see it
• 15:12
  Speaker 2: because they didn't have enough data. It didn't have a
• 15:14
  Speaker 2: long enough lever arm in history to see things changing.
• 15:17
  Speaker 1: It was being able to tell how far away things
• 15:19
  Speaker 1: were and then measuring on top of that their velocity
• 15:22
  Speaker 1: that let us figure out that things we're accelerating.
• 15:25
  Speaker 2: Yeah, exactly. It was the development of this technique using
• 15:28
  Speaker 2: type one a supernova supernova of course, the implosion of
• 15:31
  Speaker 2: stars leading to an extraordinarily bright explosion, so bright that
• 15:35
  Speaker 2: they outshine the galaxies therein. And so you can measure
• 15:39
  Speaker 2: these things for very very distant galaxies, and understanding the
• 15:42
  Speaker 2: physics of it, and understanding how bright they are at
• 15:45
  Speaker 2: their source without knowing how far away they are, lets
• 15:48
  Speaker 2: you figure out how far away they are by looking
• 15:50
  Speaker 2: at how bright they are here on Earth, because things
• 15:52
  Speaker 2: here are dimmer when they arrive, so they'll lets you
• 15:55
  Speaker 2: know how far away things are, and that's absolutely crucial
• 15:58
  Speaker 2: because knowing how far away some thing is tells you
• 16:01
  Speaker 2: when the light left it right. And so as we
• 16:04
  Speaker 2: look further into space, we're looking further back in time.
• 16:07
  Speaker 2: So that's how we can see the history of the
• 16:09
  Speaker 2: expansion of the universe. We can see how fast is
• 16:12
  Speaker 2: stuff moving away from us that's close by i e.
• 16:14
  Speaker 2: Recent history, and then we can ask how fast it
• 16:17
  Speaker 2: was stuff moving away from us earlier in the universe
• 16:20
  Speaker 2: by looking further away. So this is absolutely crucial to
• 16:23
  Speaker 2: understanding how dark energy works and also how it might
• 16:27
  Speaker 2: be wrong. What we see is that the expansion is
• 16:30
  Speaker 2: faster for things that are closer to us, and we
• 16:33
  Speaker 2: interpret that to mean the expansion is speeding up, so
• 16:36
  Speaker 2: deeper into space the expansion looks slower. Closer to us,
• 16:40
  Speaker 2: the expansion looks faster. That's what leads us to conclude
• 16:43
  Speaker 2: that the expansion is accelerating.
• 16:45
  Speaker 1: So things we can tell are really far away don't
• 16:49
  Speaker 1: have as much of a red shift as the things
• 16:51
  Speaker 1: that we can see that are closer to us.
• 16:53
  Speaker 2: They're further away, so their actual distance, the red shift
• 16:56
  Speaker 2: is larger, but hasn't accumulated over time, So it's the
• 17:00
  Speaker 2: acceleration is like the slope of that velocity curve. So
• 17:04
  Speaker 2: those things are very far away, they are very very
• 17:06
  Speaker 2: red shifted, but the change in that slope we can
• 17:10
  Speaker 2: see over time as we look at these things from
• 17:13
  Speaker 2: further away to closer in.
• 17:14
  Speaker 1: All right, So then that tells us that the universe
• 17:16
  Speaker 1: is expanding more and more rapidly. And we have a
• 17:20
  Speaker 1: name for that, which is dark energy, or at least
• 17:23
  Speaker 1: the thing that might be causing this acceleration. That's what
• 17:25
  Speaker 1: we call dark energy.
• 17:27
  Speaker 2: Yeah, we call it dark energy. And I feel like
• 17:29
  Speaker 2: there's a lot of confusion out there about what we
• 17:31
  Speaker 2: do and don't know, and I think this is really
• 17:34
  Speaker 2: interesting insight into sort of the way physics works. Like
• 17:37
  Speaker 2: we often begin thinking about an idea before we have
• 17:40
  Speaker 2: it all worked out. We just sort of like start
• 17:42
  Speaker 2: fleshing it out the way you might like design your house,
• 17:45
  Speaker 2: starting from what you wanted to look on the outside
• 17:47
  Speaker 2: before you figured it out, Like, hey, what are all
• 17:49
  Speaker 2: the structural supports and can I really have pipes over here?
• 17:52
  Speaker 2: And is it possible to have a shower on the
• 17:54
  Speaker 2: roof or whatever. You know, you haven't always figured out
• 17:56
  Speaker 2: the details, some of which might be absolutely essential. And
• 18:00
  Speaker 2: so if you look at the beginning days of the.
• 18:01
  Speaker 1: Development, I know every house you would have a shower
• 18:03
  Speaker 1: on the roof.
• 18:05
  Speaker 2: My wife is a big fan of an outside shower.
• 18:07
  Speaker 2: She's always wanted to put one in. So I'm always suggesting,
• 18:09
  Speaker 2: let's put it on the roof. And I don't know
• 18:11
  Speaker 2: why that's not a popular idea. But anyway, if you
• 18:15
  Speaker 2: look at the history of the development of big ideas
• 18:17
  Speaker 2: and physics, this is how it works. And so we've
• 18:19
  Speaker 2: done that with dark energy. We're like, wow, this is weird.
• 18:21
  Speaker 2: How do we explain this? Okay, first, let's give it
• 18:23
  Speaker 2: a cool name. Now, let's start to think about how
• 18:27
  Speaker 2: it might be possible. And we definitely don't have all
• 18:30
  Speaker 2: the details worked out. We have some conception of how
• 18:33
  Speaker 2: in general relativity you might generate this effect, we definitely
• 18:37
  Speaker 2: don't have all the pieces together.
• 18:39
  Speaker 1: And we say that it's ninety five percent of the energy, mass,
• 18:43
  Speaker 1: and energy of the whole universe, because that's how much
• 18:46
  Speaker 1: energy you need to explain something that's accelerating the entire
• 18:50
  Speaker 1: observable universe.
• 18:52
  Speaker 2: Yeah, it's something like seventy percent. Dark matter and dark
• 18:55
  Speaker 2: energy together make ninety five percent, but the dark energy
• 18:58
  Speaker 2: portion is set tventy percent. Yeah, and you're exactly right.
• 19:02
  Speaker 2: And the way we get that seventy percent is a
• 19:04
  Speaker 2: few different ways. But one way is to say, all right,
• 19:07
  Speaker 2: how in general relativity could you cause the universe to expand?
• 19:11
  Speaker 2: Because usually gravity causes things to come together. Right, you
• 19:14
  Speaker 2: have two masses in space, they curve space, they tend
• 19:16
  Speaker 2: to move together. But general relativity is much more complex
• 19:20
  Speaker 2: than Newtonian gravity includes all sorts of complicated terms and
• 19:23
  Speaker 2: effects in there. And one of the possible effects in
• 19:25
  Speaker 2: general relativity is if you have a field in space,
• 19:29
  Speaker 2: like the electromagnetic field or the weak field or the
• 19:31
  Speaker 2: electron field. We know space is filled with these fields,
• 19:34
  Speaker 2: but if these fields have a lot of potential energy,
• 19:36
  Speaker 2: meaning they have like stored energy inside of them because
• 19:38
  Speaker 2: of their configuration the way the Higgs field does. For example,
• 19:42
  Speaker 2: having a lot of potential energy in space will generate
• 19:45
  Speaker 2: this expansion. Just like part of the mathematics of general relativity.
• 19:49
  Speaker 2: You have a negative sign in front of this term
• 19:51
  Speaker 2: in the equations, and so it generates expansion of space.
• 19:55
  Speaker 2: So if you had a field with a lot of
• 19:56
  Speaker 2: potential energy, it would generate the expansion. So we calculate
• 19:59
  Speaker 2: how much potential energy do you need, and that comes
• 20:01
  Speaker 2: out to be about seventy percent of the energy in
• 20:04
  Speaker 2: the universe.
• 20:05
  Speaker 1: So this whole idea that dark energy is seventy percent
• 20:07
  Speaker 1: of the universe comes from the assumption, if I'm understanding right,
• 20:11
  Speaker 1: the assumption that what's causing the acceleration of the universe
• 20:14
  Speaker 1: is something kind of baked into space itself.
• 20:17
  Speaker 2: Yeah, exactly, And there's some supporting evidence for it, and
• 20:20
  Speaker 2: there's also a bunch of stuff that doesn't work about it.
• 20:23
  Speaker 2: Like one supporting piece of evidence is that we can
• 20:25
  Speaker 2: go out and measure all of the energy in the universe,
• 20:28
  Speaker 2: because it affects the overall curvature of the universe, Like
• 20:31
  Speaker 2: is the universe overall flat or curve negatively or curved positively.
• 20:35
  Speaker 2: That depends very sensitively on how much energy is there
• 20:38
  Speaker 2: in the universe. And we go out and we measure that,
• 20:40
  Speaker 2: and then we measure the energy out there in the
• 20:42
  Speaker 2: universe to be exactly what we need to make it
• 20:43
  Speaker 2: flat and to add up very nicely with this seventy
• 20:47
  Speaker 2: percent number. So the dark matter, the normal matter, and
• 20:50
  Speaker 2: the dark energy in the universe all adds up perfectly
• 20:52
  Speaker 2: to make the universe flat, which is what we observe.
• 20:55
  Speaker 2: That's very cool.
• 20:56
  Speaker 1: Oh interesting, All right, Well, let's get into the things
• 20:59
  Speaker 1: that don't work about dark energy and why maybe nothingness
• 21:03
  Speaker 1: could be the key to understanding how it all works.
• 21:06
  Speaker 1: So let's dig into that. But first let's take a
• 21:09
  Speaker 1: quick break. All right, we're talking about dark energy and
• 21:24
  Speaker 1: giant voids in the universe, and could those two things
• 21:27
  Speaker 1: be related. Could dark energy just be a whole bunch
• 21:30
  Speaker 1: of nothing. Could it be explained by perhaps the absence
• 21:36
  Speaker 1: of things in space? And so we talked a little
• 21:39
  Speaker 1: bit about dark energy what it is, but we know
• 21:42
  Speaker 1: about it. But Daniel, there's something wrong with that picture
• 21:45
  Speaker 1: of dark energy. What's wrong with it.
• 21:47
  Speaker 2: What's wrong with it is that we have no idea
• 21:49
  Speaker 2: where all this potential energy would be coming from. In
• 21:52
  Speaker 2: order to have the universe expand and accelerate at the
• 21:55
  Speaker 2: rate that it has been, we need space to be
• 21:58
  Speaker 2: filled with some kind oftential energy.
• 22:01
  Speaker 1: Well, here's a question, like, does dark energy need to
• 22:04
  Speaker 1: be something that's like a field or baked into space,
• 22:07
  Speaker 1: or could it be some maybe hidden property of gravity
• 22:10
  Speaker 1: perhaps or electromagnetism, or is that the same thing.
• 22:13
  Speaker 2: It could definitely be something totally brand new, some new
• 22:16
  Speaker 2: kind of physics we've never seen before, or change in
• 22:19
  Speaker 2: general relativity. That's definitely possible, and there are people out
• 22:22
  Speaker 2: there working on other crazy ideas. But so the mainstream
• 22:26
  Speaker 2: effort is to say, like, well, can we incorporate this
• 22:28
  Speaker 2: into general relativity, because it's kind of interesting that general
• 22:31
  Speaker 2: relativity has this capacity already. It's something that Einstein's relativity
• 22:36
  Speaker 2: can do expand space and accelerate that expansion. The problem
• 22:40
  Speaker 2: is that to make that happen, you need to fill
• 22:42
  Speaker 2: space with all of this energy. Either you say, look,
• 22:45
  Speaker 2: that's just the way it is. You just put a
• 22:47
  Speaker 2: number in there, and that's called the cosmological constant and
• 22:50
  Speaker 2: you say, like, it's not explained, that's just the nature
• 22:52
  Speaker 2: of space. It just has this energy, kind of unsatisfying,
• 22:56
  Speaker 2: or you find the source of that energy you say, oh,
• 22:58
  Speaker 2: look it's this particular quantum field that can do it.
• 23:02
  Speaker 2: And we look through our list of quantum fields we ask, well,
• 23:04
  Speaker 2: how much potential energy do they have? And one of them,
• 23:07
  Speaker 2: has a lot of potential energy. The Higgs field is
• 23:09
  Speaker 2: filled with potential energy. Remember that most of the fields
• 23:13
  Speaker 2: in the universe like to relax down to zero. They
• 23:16
  Speaker 2: like to be in their lowest energy state. But the
• 23:18
  Speaker 2: Higgs field is really weird, has this wrinkle in it,
• 23:21
  Speaker 2: so it sort of gets stuck at high potential energy
• 23:24
  Speaker 2: when the universe is cooling. The Higgs field doesn't collapse
• 23:27
  Speaker 2: down to zero the way the other ones do. It
• 23:29
  Speaker 2: has all this potential energy. All right, So this is
• 23:31
  Speaker 2: really exciting, right. Dark energy needs some field filled with
• 23:35
  Speaker 2: potential energy to explain the accelerating expansion in the universe,
• 23:38
  Speaker 2: and over here we have a field filled with potential energy. Awesome.
• 23:42
  Speaker 2: So people sat down to do the calculations and say,
• 23:45
  Speaker 2: does the Higgs field have enough energy to explain the
• 23:47
  Speaker 2: accelerating expansion the universe. The answer is no, and it's
• 23:51
  Speaker 2: not even close. The answer is off by ten to
• 23:54
  Speaker 2: the one hundred and twenty. So the fields we have
• 23:58
  Speaker 2: can definitely not explain the expansion of the universe as
• 24:01
  Speaker 2: we see it.
• 24:02
  Speaker 1: But I guess if it's not a field, if it's
• 24:05
  Speaker 1: something else, would it still account for seventy percent of
• 24:07
  Speaker 1: the universe, or like, what are some of these other
• 24:10
  Speaker 1: things that could.
• 24:11
  Speaker 2: Be ooh not a field, man, That blows my mind. Currently,
• 24:15
  Speaker 2: our theories of the universe are that everything's a field, right,
• 24:18
  Speaker 2: Like all the particles are ripples in fields, and all
• 24:21
  Speaker 2: the energy out there is stored in some kind of field.
• 24:24
  Speaker 2: So mostly people are developing like new kinds of fields.
• 24:27
  Speaker 2: Maybe there's some other kind of field, not the Higgs field,
• 24:29
  Speaker 2: something else out there in the universe that contains all
• 24:32
  Speaker 2: of this energy, and then you have to explain, like
• 24:34
  Speaker 2: why we wouldn't have seen it and has no other
• 24:36
  Speaker 2: effects that we could detect. For example, that's the way
• 24:38
  Speaker 2: a lot of people are going. Non field explanations for
• 24:41
  Speaker 2: the accelerating expansion in the universe. Those are pretty far
• 24:44
  Speaker 2: out of the mainstream, but you know, it could be right.
• 24:48
  Speaker 2: Physicists tend to work like within the framework of the
• 24:51
  Speaker 2: ideas we have. Doesn't mean that that's where we're going
• 24:53
  Speaker 2: to find the answer.
• 24:55
  Speaker 1: Or what if it's like a part of gravity itself
• 24:57
  Speaker 1: or general relativity like maybe Grouty gets it turns the
• 25:01
  Speaker 1: negative if you get really far away from something, would
• 25:04
  Speaker 1: that still be a field? Technically?
• 25:07
  Speaker 2: I don't think that's compatible with general relativity. So in
• 25:10
  Speaker 2: order to have that be the explanation, you have to
• 25:12
  Speaker 2: change general relativity. And the thing people like about this
• 25:15
  Speaker 2: dark energy framework is that you don't have to change
• 25:17
  Speaker 2: general relativity because it's been tested up and down the
• 25:19
  Speaker 2: wazoo and it really is accurate for huge distances or
• 25:23
  Speaker 2: huge distances yeah, I mean, it explains an enormous amount
• 25:26
  Speaker 2: about the structure of the universe as we see it,
• 25:29
  Speaker 2: and so changing general relativity is pretty uncomfortable, except in
• 25:34
  Speaker 2: places where it hasn't been tested, like inside black holes
• 25:37
  Speaker 2: or the very very early universe, things we haven't been
• 25:40
  Speaker 2: able to observe yet, basically where quantum mechanics arises. So
• 25:44
  Speaker 2: it's difficult to make changes to general relativity without messing
• 25:48
  Speaker 2: up a lot of other.
• 25:48
  Speaker 1: Stuff that would just be uncomfortable and also require a
• 25:52
  Speaker 1: lot of work.
• 25:54
  Speaker 2: And it could be the path to huge discoveries. But
• 25:57
  Speaker 2: you know, the way physics works is, hey, let's try
• 25:58
  Speaker 2: the easiest thing first. And so there is this door
• 26:01
  Speaker 2: open in general relativity, like, let's see if we can
• 26:03
  Speaker 2: explain it using the framework we have, which requires discovering
• 26:07
  Speaker 2: this field that explains where all the energy is and
• 26:10
  Speaker 2: that we don't have an answer for.
• 26:12
  Speaker 1: So then that's the problem with our current theories about
• 26:15
  Speaker 1: dark energy is that you think it requires a field,
• 26:17
  Speaker 1: but we don't know what field it could be, because
• 26:19
  Speaker 1: it needs to have more energy than anything we know about.
• 26:21
  Speaker 2: Yeah, that's the major problem, sort of the conceptual problem.
• 26:25
  Speaker 2: There are also a few smaller problems, experimental problems, like
• 26:28
  Speaker 2: our picture of the universe as being mostly dark energy
• 26:32
  Speaker 2: and a big chunk dark matter and a little bit
• 26:34
  Speaker 2: of baryonic matter and normal matter. It explains an enormous amount.
• 26:37
  Speaker 2: It explains how the universe started out filled with radiation,
• 26:41
  Speaker 2: and then that radiation got diluted and it was matter dominated,
• 26:44
  Speaker 2: and it was expanding, but that expansion was slowing down.
• 26:47
  Speaker 2: But the expansion led to more dark energy, which then
• 26:49
  Speaker 2: accelerated the expansion, and the universe became dark energy dominated
• 26:53
  Speaker 2: like six billion years ago. It's an amazing, beautiful story
• 26:56
  Speaker 2: that explains an enormous amount, but it doesn't quite explain everything.
• 27:00
  Speaker 2: Like there's this discrepancy between our observation of how fast
• 27:03
  Speaker 2: the universe is expanding now and how fast it was
• 27:06
  Speaker 2: expanding the very early days. This is called the Hubble
• 27:09
  Speaker 2: tension because the Hubble constant is kind of a measure
• 27:11
  Speaker 2: of the expansion rate, and that's not something we can
• 27:14
  Speaker 2: really explain. We don't really understand how the expansion the
• 27:17
  Speaker 2: early universe connects for the expansion in late times. At first,
• 27:21
  Speaker 2: it was very fuzzy measurements. We thought, I will figure
• 27:23
  Speaker 2: it out. But as we make more and more precise measurements,
• 27:26
  Speaker 2: they don't really agree. So that might require a tweak
• 27:29
  Speaker 2: to this, or it might be a crack that undermines
• 27:31
  Speaker 2: the whole theory. So it's not like it's a perfect
• 27:33
  Speaker 2: description of everything we see, even if you knew where
• 27:36
  Speaker 2: this energy was coming from.
• 27:38
  Speaker 1: So then I guess what's the alternative if it's not
• 27:42
  Speaker 1: something like a field.
• 27:43
  Speaker 2: So one of the alternatives is to question one of
• 27:45
  Speaker 2: the basic assumptions of this whole picture of the universe
• 27:48
  Speaker 2: that we've been talking about. We usually talk about the
• 27:51
  Speaker 2: universe in terms of density, Like when we say seventy
• 27:54
  Speaker 2: percent or twenty five percent, we're saying, take a random
• 27:57
  Speaker 2: chunk of the universe, how much of that is dark
• 27:59
  Speaker 2: energy that is normal energy. When you do that, you're
• 28:02
  Speaker 2: kind of making an implicit assumption that all chunks of
• 28:05
  Speaker 2: the universe are about the same the stuff is spread
• 28:07
  Speaker 2: out through the universe basically evenly, like we know, it's
• 28:10
  Speaker 2: not completely evenly. There's definitely clumpiness, like we're a big
• 28:13
  Speaker 2: clump in the universe. The Earth, the Sun, the galaxy
• 28:16
  Speaker 2: is a clump. But that if you zoom out far enough,
• 28:18
  Speaker 2: the universe is evenly spread out on the giant scales.
• 28:22
  Speaker 2: The universe is basically the same everywhere. That's kind of
• 28:25
  Speaker 2: a philosophical preference. They call it the cosmological principle or
• 28:29
  Speaker 2: the Copernican principle. But one of the ideas to explain
• 28:32
  Speaker 2: the accelerating expansion of the universe is to say, maybe
• 28:35
  Speaker 2: it's not expanding in an accelerating way. Maybe it just
• 28:38
  Speaker 2: looks like it is because we're stuck at the center
• 28:40
  Speaker 2: of a huge void where there's less stuff in this
• 28:43
  Speaker 2: bubble than outside of it, and that gives us the
• 28:46
  Speaker 2: illusion that the universe's expansion is accelerating, even if it isn't.
• 28:50
  Speaker 1: Whoa, whoa, whoa Wait a minute, how does this even work?
• 28:54
  Speaker 1: Is the idea then that maybe outside of the absorbable
• 28:58
  Speaker 1: universe there's a whole bunch of nothingness for a while.
• 29:00
  Speaker 1: Is that kind of what the picture you're thinking about.
• 29:02
  Speaker 2: The idea is that the bubble we're living in, even
• 29:04
  Speaker 2: though it has galaxies and stars and whatever, is less
• 29:08
  Speaker 2: dense than the stuff outside some bubble.
• 29:10
  Speaker 1: But then wouldn't we be able to see those things
• 29:13
  Speaker 1: outside the bubble and tell if it's more or less dense.
• 29:17
  Speaker 2: Yeah, and we can get into the observations and whether
• 29:19
  Speaker 2: this idea actually lines up with what we see in
• 29:22
  Speaker 2: the universe. But if this bubble exists, it'd be a
• 29:25
  Speaker 2: little tricky to see because we'd be looking really, really
• 29:28
  Speaker 2: far out, and our sort of three D map of
• 29:30
  Speaker 2: the universe is best for close by stuff, and it
• 29:33
  Speaker 2: sort of fades out a little bit as you get
• 29:35
  Speaker 2: further out. It's hard to make these big three D
• 29:38
  Speaker 2: maps of the universe at this void, if it exists,
• 29:41
  Speaker 2: would basically describe everything we see so far. So it's
• 29:44
  Speaker 2: sort of suggesting that out there in the deep dark
• 29:46
  Speaker 2: reaches of space where we haven't really mapped very well yet,
• 29:50
  Speaker 2: galaxies might be a lot denser than they are here.
• 29:54
  Speaker 2: Then that might be confusing us about the expansion of
• 29:57
  Speaker 2: the universe.
• 29:58
  Speaker 1: Wait, I think you're saying that maybe you know the
• 30:00
  Speaker 1: galaxies we've seen to come to the conclusion that the
• 30:03
  Speaker 1: universe is expanding in an accelerated way. You know, we
• 30:07
  Speaker 1: use galaxies we've seen, but maybe those galaxies we seem
• 30:10
  Speaker 1: don't go all the way to the edge of the
• 30:11
  Speaker 1: observable universe. Is that what you're saying.
• 30:13
  Speaker 2: We've used those galaxies and they do go all the
• 30:15
  Speaker 2: way to the edge of the observable universe, but it
• 30:18
  Speaker 2: might be the things change as you go from here
• 30:20
  Speaker 2: to the edge of the observable universe, and that could
• 30:23
  Speaker 2: be confusing us about this accelerated expansion. The key concept is,
• 30:27
  Speaker 2: remember that we decided that the expansion of the universe
• 30:29
  Speaker 2: was accelerating because we saw that changing as we look
• 30:33
  Speaker 2: further and further into space, right, And we decided that's
• 30:36
  Speaker 2: because things are changing over time. But what if things
• 30:39
  Speaker 2: aren't changing over time, they're just changing over space. Right.
• 30:43
  Speaker 2: What if the universe is different as you go further
• 30:46
  Speaker 2: away than it is here. What if the universe is
• 30:49
  Speaker 2: denser further away and then it is closer by, and
• 30:52
  Speaker 2: that's what's creating this effect. We see an effect in space,
• 30:56
  Speaker 2: and we're assuming that it means an effect over time,
• 30:58
  Speaker 2: But what if it's just an effect over space. What
• 31:01
  Speaker 2: if the universe is different further away.
• 31:04
  Speaker 1: I see what you're saying. I think you're saying that
• 31:05
  Speaker 1: some of those galaxies we're using to measure the expansion
• 31:08
  Speaker 1: of the universe maybe where they're not where we think
• 31:11
  Speaker 1: they are.
• 31:12
  Speaker 2: I'm saying that we see faster expansion close by and
• 31:15
  Speaker 2: slower expansion further away, right, And we interpret that to
• 31:19
  Speaker 2: mean that there was slower expansion earlier in the universe,
• 31:22
  Speaker 2: and there's faster expansion later in the universe. So the
• 31:25
  Speaker 2: expansion is accelerating. But what if the universe is just
• 31:28
  Speaker 2: denser further away, and so it's not expanding as fast
• 31:31
  Speaker 2: because there's more gravity, it's holding stuff together. And so
• 31:34
  Speaker 2: what if we're confusing nearby faster expansion for expansion increasing
• 31:39
  Speaker 2: more recently, right, what if it's not increasing more recently.
• 31:42
  Speaker 2: It's just we're in a bubble that's expanding faster. If
• 31:45
  Speaker 2: you go further away from us in the universe, things
• 31:48
  Speaker 2: are expanding more slowly because the universe is denser there
• 31:51
  Speaker 2: there's more gravity to hold it together. So instead of saying, oh,
• 31:54
  Speaker 2: the universe was expanding slower further away, back further in time,
• 31:59
  Speaker 2: and it's expanding faster closer to us, more recently, what
• 32:03
  Speaker 2: if it's not a function of time, it's just a
• 32:05
  Speaker 2: function of space because we're in this bubble that happens
• 32:08
  Speaker 2: to be under dense and so has faster expansion because
• 32:11
  Speaker 2: it's less stuff to hold it together.
• 32:13
  Speaker 1: Who I feel like my mind is a void right now, Daniel.
• 32:19
  Speaker 2: Yeah, if you have more stuff in the universe, if
• 32:21
  Speaker 2: these more galaxies, for example, then there's more gravity to
• 32:24
  Speaker 2: battle against this expansion. Stuff stays closer together.
• 32:27
  Speaker 1: So there is still an expansion of the universe.
• 32:29
  Speaker 2: Yes, there would still be an expansion, but it wouldn't
• 32:31
  Speaker 2: be accelerating. It's just the expansion depends on how much
• 32:34
  Speaker 2: stuff you have around you, which makes perfect sense.
• 32:37
  Speaker 1: So you're saying that there is an expansion of the
• 32:39
  Speaker 1: universe that's still happening. Yeah, but you're saying, maybe, what
• 32:43
  Speaker 1: if it's maybe even and not accelerating. Maybe it's just
• 32:46
  Speaker 1: a constant, steady expansion of the universe, which would still
• 32:49
  Speaker 1: be a mystery. Though.
• 32:50
  Speaker 2: Right now, you can have the expansion of the universe
• 32:53
  Speaker 2: without any sort of like weird dark energy in the universe.
• 32:57
  Speaker 1: Okay, so then we are assuming still a steady expand
• 33:00
  Speaker 1: But you're saying that maybe the acceilerit that expansion looks
• 33:04
  Speaker 1: faster around us, even though it's not. It just looks faster.
• 33:08
  Speaker 2: It is faster around us. It's just that it's faster
• 33:11
  Speaker 2: around us because there isn't as much stuff, not because
• 33:14
  Speaker 2: the expansion is changing over time. There's less stuff near us,
• 33:18
  Speaker 2: and so there's less stuff to hold stuff together, and
• 33:20
  Speaker 2: so that's why it's expanding faster closer than further away.
• 33:23
  Speaker 1: Oh, because you're saying that gravity somehow affects the expansion
• 33:27
  Speaker 1: of space.
• 33:27
  Speaker 2: Absolutely, Yes, gravity holds stuff together. If there was more
• 33:30
  Speaker 2: stuff in the universe, then things expand more solely because
• 33:33
  Speaker 2: gravity is pulling on them.
• 33:34
  Speaker 4: Right.
• 33:35
  Speaker 1: Well, but space itself, it doesn't hold space together, or
• 33:37
  Speaker 1: does it. Is that what you're saying, that it somehow
• 33:39
  Speaker 1: holds space itself together?
• 33:41
  Speaker 2: Absolutely, the more stuff you have in the universe, the
• 33:44
  Speaker 2: slower things move apart from each other. Remember, we talk
• 33:46
  Speaker 2: about creating a new space, but really we're talking about
• 33:48
  Speaker 2: increasing the distance between galaxies, and that's all we can measure. Right,
• 33:52
  Speaker 2: Space itself is not something where you can measure distances
• 33:55
  Speaker 2: relative to space. It's always distance is measured between objects.
• 33:58
  Speaker 1: The things are being held together because in the same
• 34:02
  Speaker 1: way that I'm being held together with the Earth. Or
• 34:04
  Speaker 1: are we talking about some you know, relativistic or something something.
• 34:11
  Speaker 2: No, the first way. Yeah, the same way that you're
• 34:12
  Speaker 2: being held near the Earth.
• 34:14
  Speaker 1: Oh okay, but I always thought that, like I'm being
• 34:16
  Speaker 1: held to Earth, and so I'm not expanding away from
• 34:18
  Speaker 1: the Earth, but the space that we're both sitting in
• 34:21
  Speaker 1: is expanding.
• 34:22
  Speaker 2: Yeah, there's two effects happening there, right, Gravity is holding
• 34:25
  Speaker 2: you together, and dark energy is expanding that space. But
• 34:28
  Speaker 2: gravity winds because gravity is much more powerful over great distances,
• 34:33
  Speaker 2: Gravity weakens, right, and you can't hold things together, so
• 34:36
  Speaker 2: dark energy takes over.
• 34:37
  Speaker 1: Right, But like right here on Earth, I'm sitting here
• 34:39
  Speaker 1: on Earth and being held together on Earth. I'm not
• 34:41
  Speaker 1: expanding away from the Earth, but sort of like somebody's
• 34:43
  Speaker 1: moving the chair under me or somebody's stretching the rug
• 34:46
  Speaker 1: under me, the space we're sitting in is expanding, isn't it.
• 34:49
  Speaker 2: Yeah that's a helpful way to think about it, but
• 34:51
  Speaker 2: it can also be misleading, right, Like, really, what we're
• 34:54
  Speaker 2: saying there is if you deleted the Earth and replaced
• 34:56
  Speaker 2: it with like a point particle proton, for example, dark
• 35:00
  Speaker 2: energy be increasing the space between you and that point
• 35:03
  Speaker 2: particle that proton. Yes, absolutely, because there is dark energy everywhere.
• 35:07
  Speaker 2: That's the point of that comparison. But these are like
• 35:10
  Speaker 2: two things happening in the equations at the same time.
• 35:12
  Speaker 2: The net effect, because gravity dominates, is that you and
• 35:15
  Speaker 2: the Earth stay close to each other. You can't really
• 35:17
  Speaker 2: separate them out and say they're both simultaneously happening. It's
• 35:21
  Speaker 2: like two force vectors that you add together. If you
• 35:24
  Speaker 2: have a huge amount of force on an object from
• 35:26
  Speaker 2: two directions, it adds up to zero force, right this
• 35:29
  Speaker 2: net zero force. You can talk about what would happen
• 35:32
  Speaker 2: if you were removed one, or you could talk about
• 35:33
  Speaker 2: what happened if you remove the other, but you can't
• 35:36
  Speaker 2: really say that there's any force on that object because
• 35:38
  Speaker 2: they balance each other out in the same way. Dark
• 35:41
  Speaker 2: energy tends to push things apart and curvature tends to
• 35:44
  Speaker 2: pull things together. So you could talk about what would
• 35:46
  Speaker 2: happen if you only had one or the other, but
• 35:49
  Speaker 2: really what's happening to you is a combination of the two.
• 35:52
  Speaker 1: All right, So then the idea is that maybe we're
• 35:54
  Speaker 1: wrong that the universe is expanding faster and faster. It's
• 35:58
  Speaker 1: just sort of looks like it because things are denser
• 36:01
  Speaker 1: out there, and so they're moving apart from each other less.
• 36:05
  Speaker 2: Yeah, exactly. So as we look further into the universe,
• 36:08
  Speaker 2: which is further back in time, we see less expansion.
• 36:12
  Speaker 2: But maybe that expansion isn't changing with time, maybe it's
• 36:16
  Speaker 2: fixed with time, but it's happening less further away than
• 36:20
  Speaker 2: closer by because there's more stuff further away. Maybe we
• 36:23
  Speaker 2: happen to be in some huge bubble where the stuff
• 36:26
  Speaker 2: near us is under dance. This less stuff in our bubble,
• 36:29
  Speaker 2: and so things can expand further and further away because
• 36:33
  Speaker 2: there's less mass to sort of counteract that expansion.
• 36:36
  Speaker 1: I guess what's confusing me is that if it's denser
• 36:39
  Speaker 1: out there in the far reaches of space, things are
• 36:42
  Speaker 1: being held together there. But wouldn't I still see an
• 36:45
  Speaker 1: acceleration or not an acceleration from relative to me.
• 36:50
  Speaker 2: An acceleration of the expansion.
• 36:52
  Speaker 1: Yeah, Like I always thought that the acceleration of the
• 36:54
  Speaker 1: expansion is because like, the thing I see really far
• 36:59
  Speaker 1: away is moving away from me slower than the things
• 37:03
  Speaker 1: that are closer to me.
• 37:04
  Speaker 2: Yeah, that's exactly right. But maybe the reason things are
• 37:08
  Speaker 2: moving away from you. Closer is because of an under density,
• 37:11
  Speaker 2: not because of a change in the expansion over time. Right,
• 37:14
  Speaker 2: Maybe everything has the same expansion over time. The things
• 37:17
  Speaker 2: that are farther away have a smaller expansion because of
• 37:20
  Speaker 2: the conditions over there, not because of some change in
• 37:23
  Speaker 2: the universe over time.
• 37:25
  Speaker 5: Right.
• 37:25
  Speaker 2: We can only see this one slice of the universe
• 37:27
  Speaker 2: in space and time. We can look further back in time.
• 37:29
  Speaker 2: We can see the universe really far away as it
• 37:32
  Speaker 2: was a long time ago, and we don't know what
• 37:35
  Speaker 2: is that part of the universe like now, And so
• 37:37
  Speaker 2: we see this one particular slice where we can see
• 37:39
  Speaker 2: close by stuff recently and far away stuff a long
• 37:43
  Speaker 2: time ago. So it's hard to tell the difference between
• 37:45
  Speaker 2: things that change over space and things that change over time.
• 37:49
  Speaker 2: And we see a change in that story, and we
• 37:51
  Speaker 2: interpret that as a change over time, but it could
• 37:53
  Speaker 2: be that it's the same over time. It's just changing over.
• 37:55
  Speaker 1: Space, meaning that we are measurements of the distance of
• 37:59
  Speaker 1: those things. How far away they are from us or
• 38:01
  Speaker 1: from each other is wrong.
• 38:03
  Speaker 2: How far away they are from us? Yeah, imagine you
• 38:06
  Speaker 2: looked out into the universe and you saw that aliens
• 38:09
  Speaker 2: on nearby planets were all eating white chocolate, and as
• 38:12
  Speaker 2: you look deeper and deeper in the universe, you discovered, oh,
• 38:15
  Speaker 2: they're all eating dark chocolate. And you say, well, oh, well,
• 38:18
  Speaker 2: that's older information. The dark chocolate information has taken a
• 38:21
  Speaker 2: long time to get here, and so maybe what's happened
• 38:24
  Speaker 2: over time is that everybody switched from dark chocolate to
• 38:26
  Speaker 2: white chocolate. And that explains why my older observations from
• 38:30
  Speaker 2: distant galaxies the aliens are eating dark chocolate, and my
• 38:34
  Speaker 2: recent observations from nearby galaxies the aliens are eating white chocolate.
• 38:37
  Speaker 2: And then another scientist goes, no, no, no, maybe they
• 38:40
  Speaker 2: just prefer dark chocolate out there and the deep reaches
• 38:42
  Speaker 2: of space, and we live in a white chocolate bubble
• 38:44
  Speaker 2: where everybody seems to eat white chocolate. Those two explanations
• 38:48
  Speaker 2: both work. One is a change over space, the other
• 38:50
  Speaker 2: is a change over time, and we can't tell the
• 38:52
  Speaker 2: difference because we have this one set of observations linked
• 38:56
  Speaker 2: in space and time.
• 38:57
  Speaker 1: I'm not sure adding flavor to the this is helping.
• 39:02
  Speaker 1: So then you're saying, like, maybe what's explaining dark energy
• 39:05
  Speaker 1: is that there's more stuff in the periphery of the
• 39:07
  Speaker 1: universe there's more stuff in the perimeter of our vision
• 39:10
  Speaker 1: or of what we can see. Yeah, exactly, but still
• 39:14
  Speaker 1: within the observable universe.
• 39:15
  Speaker 2: Still within the observable universe. Yes, of course this is
• 39:18
  Speaker 2: a big idea, and if it's true, you have to
• 39:20
  Speaker 2: make sense of it and why we would be living
• 39:23
  Speaker 2: in the middle of this big void and what else
• 39:24
  Speaker 2: it would mean. And there's lots of ways we can
• 39:27
  Speaker 2: check this idea.
• 39:28
  Speaker 1: All right, Well, let's dig into how we're testing this idea.
• 39:31
  Speaker 1: Is it a stretch or is it a whole bunch
• 39:34
  Speaker 1: of nothing as well? So let's dig into that. But
• 39:36
  Speaker 1: first let's take another quick break. All right, we're talking
• 39:52
  Speaker 1: about nothing, Dan, Is this like the Seinfeld episode of
• 39:55
  Speaker 1: the podcast? Just about nothing?
• 40:00
  Speaker 2: Long as that can be Sifeld instead of George.
• 40:01
  Speaker 1: Than sure, YadA YadA, YadA the universe.
• 40:07
  Speaker 2: Or maybe I should be Kramer. I don't know, as
• 40:09
  Speaker 2: long as I'm not Newman, oh Man.
• 40:12
  Speaker 1: I want to be Lean. She's the coolest one.
• 40:15
  Speaker 2: She definitely is. It is a really fun idea, and
• 40:19
  Speaker 2: it's always cool to think about how your conception of
• 40:22
  Speaker 2: the universe could be totally different from what everybody's been imagining.
• 40:26
  Speaker 2: Right the biggest ideas are the sexiest because they also
• 40:30
  Speaker 2: give you those moments you're like, Wow, the universe is
• 40:32
  Speaker 2: this way and not some other way. And this would
• 40:35
  Speaker 2: be a pretty big idea. I mean, this would be
• 40:37
  Speaker 2: putting our galaxy near the center of an enormous cosmic
• 40:42
  Speaker 2: feature in order to explain the redshifts that we are seeing.
• 40:46
  Speaker 2: To fit this to the data, you have to have
• 40:49
  Speaker 2: a big void, something that's three billion light years in
• 40:54
  Speaker 2: radius a giga parsec.
• 40:57
  Speaker 1: And that's the only way this works. Or what does
• 40:58
  Speaker 1: that mean?
• 40:59
  Speaker 2: That's the only way this works.
• 41:00
  Speaker 1: See only nothing explanation that fits what we currently see.
• 41:04
  Speaker 2: Yeah, because when we look out into the universe, we
• 41:07
  Speaker 2: see the sort of same history in every direction. Right,
• 41:10
  Speaker 2: So if you look one direction, you see things closer
• 41:14
  Speaker 2: by expanding more quickly than things further away. If you
• 41:17
  Speaker 2: look in another direction, another direction, another direction, it's very isotropic.
• 41:21
  Speaker 2: And so to explain that by like a coincidence of
• 41:24
  Speaker 2: the density, you need the universe to be more dense
• 41:27
  Speaker 2: basically in every direction, which requires a huge void, and
• 41:31
  Speaker 2: it requires us to be at the center of it,
• 41:34
  Speaker 2: and it requires that void to be basically spherical, So
• 41:37
  Speaker 2: you have the same weird density as a function of
• 41:40
  Speaker 2: distance effect in every direction, and so yeah, that's kind
• 41:45
  Speaker 2: of a big cosmic coincidence if it's.
• 41:47
  Speaker 1: True, meaning like we're right smack in the middle of
• 41:50
  Speaker 1: this giant void.
• 41:52
  Speaker 2: Yeah, and like it doesn't have to be exactly in
• 41:54
  Speaker 2: the middle to within like a centimeter, but on cosmic
• 41:57
  Speaker 2: distance scales, we'd have to be very close to the
• 41:59
  Speaker 2: center because we've measured this expansion effect in lots of
• 42:03
  Speaker 2: different directions and it seems the same in every direction.
• 42:06
  Speaker 2: So yeah, we'd have to be at the center of it.
• 42:08
  Speaker 2: And this really violates this Copernican principle, this idea that
• 42:13
  Speaker 2: like the universe is basically the same everywhere, and like, yeah,
• 42:16
  Speaker 2: there's a little bit of clumpiness, but there's no huge
• 42:19
  Speaker 2: features that make this neighborhood totally different from that neighborhood.
• 42:23
  Speaker 2: And you know that's not something we know, it's just
• 42:25
  Speaker 2: something we've assumed. It makes sense, it fits with the
• 42:28
  Speaker 2: way we like to think about the universe. Until nature
• 42:31
  Speaker 2: shows us that it's not true. We're kind of going
• 42:33
  Speaker 2: to go with it because we like the idea doesn't
• 42:35
  Speaker 2: mean that it is true, right, It doesn't mean that
• 42:37
  Speaker 2: the universe has to be the same everywhere.
• 42:39
  Speaker 1: I guess you know. What's confusing me is like, couldn't
• 42:41
  Speaker 1: we tell if we were in a void, Like you know,
• 42:44
  Speaker 1: we can look with our telescopes and we can see
• 42:47
  Speaker 1: galaxies all the way out to the observable universe. Wouldn't
• 42:49
  Speaker 1: we have noticed by now that there are more of
• 42:52
  Speaker 1: them further away than what we can see close to us.
• 42:55
  Speaker 2: Yeah, absolutely, we could tell if we had seen all
• 42:59
  Speaker 2: the galaxies out there and map the density. But you know,
• 43:02
  Speaker 2: things that are really far away are hard to see.
• 43:05
  Speaker 2: In order to see things super duper far away, you
• 43:07
  Speaker 2: have to point a very powerful telescope at them, and
• 43:10
  Speaker 2: you have to look for a while because these galaxies
• 43:12
  Speaker 2: are very very dim and they're very very red shifted.
• 43:16
  Speaker 2: So we have a telescope that can do that, Like
• 43:18
  Speaker 2: James Web has been breaking records and seeing galaxies really
• 43:21
  Speaker 2: really far away into the early universe. But James Web
• 43:24
  Speaker 2: is very expensive, and we have one of it, and
• 43:26
  Speaker 2: it can only point in some directions at a time,
• 43:28
  Speaker 2: and space is extraordinarily vast. The number of galaxies we're
• 43:31
  Speaker 2: talking about are huge, so we basically just haven't really
• 43:34
  Speaker 2: looked far enough like we've seen nearby stuff. And we'd
• 43:38
  Speaker 2: like to think that we've seen to the edge of
• 43:39
  Speaker 2: the observable universe. We only have really done that in
• 43:42
  Speaker 2: a few tiny directions, and so like our detailed three
• 43:46
  Speaker 2: D map of the universe definitely does not extend all
• 43:48
  Speaker 2: the way out to the observable universe. There are lots
• 43:51
  Speaker 2: of places out there where it's very fuzzy.
• 43:53
  Speaker 1: But I guess you wouldn't need to see all of
• 43:55
  Speaker 1: the universe. You just need to see whether things are
• 43:58
  Speaker 1: dense or out there near the edge of the abstorbable
• 44:00
  Speaker 1: universe than they are here. Isn't that sort of a
• 44:04
  Speaker 1: easy check?
• 44:07
  Speaker 2: Well, we don't see any evidence of that, right, But
• 44:09
  Speaker 2: they could still make the data fit. Because our observations
• 44:12
  Speaker 2: are still limited. They can make this data fit. And
• 44:14
  Speaker 2: so you can come up with a theory of the
• 44:17
  Speaker 2: universe that respects general relativity and describes all of the
• 44:21
  Speaker 2: redshifts that we see from type one A supernova and
• 44:25
  Speaker 2: our observations of galaxy density so far, and doesn't require
• 44:29
  Speaker 2: any dark energy. But it does require this sort of
• 44:32
  Speaker 2: like bubble where the density of the universe is smaller
• 44:35
  Speaker 2: in her neighborhood. But you can still do that and
• 44:38
  Speaker 2: be consistent with all of these observations. I know that
• 44:40
  Speaker 2: sounds crazy.
• 44:41
  Speaker 1: Oh, I see what you're saying. You're saying like maybe
• 44:44
  Speaker 1: it could be that all of are checks of the
• 44:46
  Speaker 1: density of the universe out there where somehow we just
• 44:49
  Speaker 1: looked in the wrong places kind of, So what you're saying.
• 44:52
  Speaker 2: Kind of and I think probably people overestimate how much
• 44:55
  Speaker 2: we've looked into the deep universe. We really don't have
• 44:58
  Speaker 2: that much data. So it's not that hard to squeak
• 45:01
  Speaker 2: it a little bit and still be consistent with the
• 45:03
  Speaker 2: deep images of the distant universe, because those are pretty rare.
• 45:07
  Speaker 2: But there are other ways that we could tell whether
• 45:09
  Speaker 2: we were in a bubble. There are other impacts this
• 45:11
  Speaker 2: theory has on things that we can measure much more
• 45:14
  Speaker 2: precisely than just like actually looking and measuring the density.
• 45:18
  Speaker 2: This idea has consequences for other things that we have
• 45:21
  Speaker 2: very sensitive probes for.
• 45:23
  Speaker 1: All Right, what are some of those ways.
• 45:25
  Speaker 2: Well, maybe the most powerful is the cosmic microwave background radiation.
• 45:28
  Speaker 2: Like we look at the structure of the universe. Now,
• 45:30
  Speaker 2: as you're saying, how much density is there? Where are
• 45:33
  Speaker 2: the galaxies? But all that structure is seeded in little
• 45:36
  Speaker 2: density fluctuations from the early universe. Right. The whole reason
• 45:40
  Speaker 2: we have structure, the reason we have a galaxy here
• 45:42
  Speaker 2: and not a galaxy there, is because in the early
• 45:44
  Speaker 2: universe there was a little spot that was the denser,
• 45:46
  Speaker 2: and gravity gathered stuff together to make galaxies, for example.
• 45:50
  Speaker 2: So we can predict how stuff should be distributed in
• 45:52
  Speaker 2: the universe today based on those fluctuations in the cosmic
• 45:56
  Speaker 2: microwave background radiation. That light from the very early universe,
• 46:00
  Speaker 2: and that life from the very early universe is very,
• 46:02
  Speaker 2: very smooth.
• 46:03
  Speaker 3: Right.
• 46:04
  Speaker 2: It tells us that there should be no huge features.
• 46:07
  Speaker 2: It tells us exactly how big those density fluctuations should be,
• 46:11
  Speaker 2: and it lines up with what we see. Right. The
• 46:13
  Speaker 2: stuff we see in the universe, both close and far away,
• 46:16
  Speaker 2: has just about the right density fluctuations, meaning like galaxies
• 46:20
  Speaker 2: and clumps of galaxies and actually big voids between those galaxies.
• 46:24
  Speaker 2: We have seen huge voids between clusters of galaxies, not
• 46:28
  Speaker 2: as big as the one this requires, but there are
• 46:31
  Speaker 2: big voids out there in space, and all that is
• 46:33
  Speaker 2: perfectly described by the cosmic microwave background radiation. And a
• 46:37
  Speaker 2: huge megavoid that we're at the center of is not
• 46:40
  Speaker 2: consistent with what we see in the CMB. There's no
• 46:43
  Speaker 2: fluctuations in it that would give such an enormous.
• 46:46
  Speaker 1: Feature, Like you don't see other voids in the cosmic
• 46:50
  Speaker 1: microwrate background. But would you see this void, this potential
• 46:53
  Speaker 1: giant void we're in in the cosmic micro rate background
• 46:56
  Speaker 1: or does it tell you that there isn't avoid the.
• 46:58
  Speaker 2: Cosmic microwave background tells you that there should be no
• 47:01
  Speaker 2: huge void, and it does predict other voids. It does
• 47:04
  Speaker 2: predict that we should see big gaps between galaxies, and
• 47:07
  Speaker 2: we see those and we measure those, but it suggests
• 47:10
  Speaker 2: that you should not get voids this big. Right. Basically,
• 47:13
  Speaker 2: the size of the wiggles in the early universe limits
• 47:17
  Speaker 2: how big the features can be in our current universe. Right,
• 47:20
  Speaker 2: you'd need huge wiggles in the CMB to make huge
• 47:23
  Speaker 2: wiggles now. We only see small wiggles in the early universe,
• 47:26
  Speaker 2: So we should only have small voids in small clumps now,
• 47:29
  Speaker 2: And that's basically what we see.
• 47:31
  Speaker 1: Wait, it tells you that it's impossible or does it
• 47:33
  Speaker 1: tell you that it's rare for us to be in
• 47:35
  Speaker 1: a huge void like that?
• 47:37
  Speaker 2: I think technically it tells you that it's very very
• 47:39
  Speaker 2: unlikely because the light we're seeing from the CMB is
• 47:43
  Speaker 2: not the light from the plasma that was here that
• 47:46
  Speaker 2: formed our structures. It's the light from the plasma that
• 47:49
  Speaker 2: was very far away, and it's been traveling to us
• 47:51
  Speaker 2: the whole history of the universe. So we're not actually
• 47:54
  Speaker 2: seeing the patterns that led to the formation of our structure.
• 47:57
  Speaker 2: We're seeing the patterns that led to the formations structure
• 48:00
  Speaker 2: that's very far away now, and so we can't actually
• 48:03
  Speaker 2: see like the blueprints that led to our structure. We
• 48:06
  Speaker 2: can just see the blueprints that led to other structure,
• 48:08
  Speaker 2: and we see nothing like that anywhere else in the universe,
• 48:11
  Speaker 2: and so it'd be very unlikely for that to happen
• 48:14
  Speaker 2: here if it's never happened anywhere else in the universe.
• 48:17
  Speaker 2: So that's sort of the argument.
• 48:19
  Speaker 1: M all right, So the CMB says probably not.
• 48:24
  Speaker 2: Yeah, And there's another argument, which has to do with
• 48:27
  Speaker 2: how elements are made. The early universe was very very dense,
• 48:31
  Speaker 2: dense enough briefly to cause nuclear fusion to make protons
• 48:35
  Speaker 2: and for some of those protons to make helium, and
• 48:38
  Speaker 2: the density of that really determines what elements were made.
• 48:41
  Speaker 2: We have a very good understanding of how that works,
• 48:44
  Speaker 2: and if it lines up very very well with what
• 48:45
  Speaker 2: we see out there in the universe, how much helium
• 48:47
  Speaker 2: and hydrogen and lithium there was made during the Big Bang.
• 48:50
  Speaker 2: This whole field is called Big Bang nucleosynthesis. And so
• 48:54
  Speaker 2: that's a very sensitive probe of the density of the
• 48:57
  Speaker 2: early universe in our neighborhood. And so if we got
• 49:00
  Speaker 2: that wrong somehow, if the universe weirdly was under dense
• 49:03
  Speaker 2: in our region, you would see that in the amount
• 49:06
  Speaker 2: of helium made in the Big Bang, and we don't,
• 49:09
  Speaker 2: and so that's pretty hard to reconcile with what we see. Also,
• 49:13
  Speaker 2: we've more recently measured a lot more Type one A supernova.
• 49:17
  Speaker 2: This idea of the big void was very popular, like
• 49:20
  Speaker 2: maybe ten years ago, when we had many fewer measurements
• 49:24
  Speaker 2: of the supernova and there were some gaps, and so
• 49:26
  Speaker 2: it was easier to sort of like fit this to
• 49:28
  Speaker 2: the data. But more recent measurements by the Slowing Digital
• 49:31
  Speaker 2: Sky Survey, for example, make it much harder to explain
• 49:34
  Speaker 2: the red shifts using this sort of like weird void
• 49:37
  Speaker 2: bubble thing.
• 49:38
  Speaker 1: Meaning we have better data about where things are out there.
• 49:41
  Speaker 2: Yeah, exactly. We sort of filled in some gaps by
• 49:43
  Speaker 2: taking more and more measurements of type one A supernova,
• 49:46
  Speaker 2: and that makes it harder and harder to even explain
• 49:49
  Speaker 2: the red shifts using this.
• 49:51
  Speaker 1: Void meaning we're more confident that things are not dens
• 49:54
  Speaker 1: or out there, yeah, or we're just more confident by
• 49:56
  Speaker 1: where things are.
• 49:57
  Speaker 2: We're more confident about where things are, and that makes
• 49:59
  Speaker 2: it harder to come up with a consistent picture of
• 50:02
  Speaker 2: us being at the center of a void as an
• 50:04
  Speaker 2: alternative explanation for the redshifts that we're seeing. But you know,
• 50:07
  Speaker 2: there's lots of remaining to be understood, Like some of
• 50:10
  Speaker 2: the voids that are out there in space. We don't
• 50:11
  Speaker 2: understand how they formed and how big they got. And
• 50:14
  Speaker 2: there's still the hubble tension like the expansion of the universe.
• 50:17
  Speaker 2: So it's not like the explanation we have is perfect.
• 50:20
  Speaker 2: There's lots of holes in it, lots of things that
• 50:22
  Speaker 2: still don't work, lots of opportunities for other ideas. But
• 50:25
  Speaker 2: I think this void theory, as cool as it sounds,
• 50:28
  Speaker 2: works less well than the current mainstream dark energy idea.
• 50:31
  Speaker 1: This idea that there's this mysterious invisible energy that we
• 50:35
  Speaker 1: can't explain either exactly.
• 50:38
  Speaker 2: There's still a lot of work left to do to
• 50:40
  Speaker 2: make that even like a coherent theory. But it's sort
• 50:42
  Speaker 2: of like our best current idea.
• 50:44
  Speaker 3: Hm.
• 50:45
  Speaker 1: Well, I guess if it has so many counts against it,
• 50:47
  Speaker 1: why are people even considering this? Why do we you
• 50:49
  Speaker 1: just spend an hour talking about it.
• 50:52
  Speaker 2: I think people are still considering other ideas because the
• 50:55
  Speaker 2: whole concept of our dark energy does have flaws, and
• 50:58
  Speaker 2: it is a big idea, And it's healthy to maintain
• 51:01
  Speaker 2: different directions of research because we could run into a
• 51:04
  Speaker 2: big problem. You know, in sketching out the details of
• 51:07
  Speaker 2: dark energy, we could discover a fundamental flaw in the
• 51:10
  Speaker 2: whole plan, so that doesn't hang together.
• 51:12
  Speaker 5: You know.
• 51:13
  Speaker 2: It's like when you build a house and you discover
• 51:14
  Speaker 2: while the plumbing is just not going to fit with
• 51:16
  Speaker 2: the electrical like, we got to go back to the
• 51:18
  Speaker 2: drawing board. So it's important to keep your mind open
• 51:21
  Speaker 2: and consider other ideas.
• 51:23
  Speaker 1: Plus, it's fun, right, right, other ideas for other people
• 51:26
  Speaker 1: to try to figure out their tree right exactly, just
• 51:30
  Speaker 1: not you?
• 51:30
  Speaker 2: Yeah, maybe I should You're done. Maybe I should just
• 51:33
  Speaker 2: sit on the couch, eat chocolate and let somebody else
• 51:36
  Speaker 2: figure it.
• 51:36
  Speaker 1: Out, right, But dark chocolate or white chocolate? Any which
• 51:39
  Speaker 1: part of the universe are you in?
• 51:42
  Speaker 2: If our part of the universe is turning into white chocolate,
• 51:44
  Speaker 2: then I'm thinking about moving.
• 51:46
  Speaker 1: What sounds like you already gave up on the whole universe,
• 51:49
  Speaker 1: so now you're just giving up on the local universe exactly.
• 51:54
  Speaker 3: All right?
• 51:55
  Speaker 1: Well, an interesting discussion about maybe the biggest mystery in
• 51:59
  Speaker 1: the entire universe. What is dark energy? What's costing the
• 52:02
  Speaker 1: universe to expand faster and faster. Is it just all
• 52:05
  Speaker 1: a big illusion or is there really some sort of
• 52:08
  Speaker 1: mysterious energy out there?
• 52:10
  Speaker 2: Well, I think the theory of dark energy is on
• 52:12
  Speaker 2: the right track. It's really important to think about other ideas,
• 52:14
  Speaker 2: and it also helps us understand the strengths and the
• 52:17
  Speaker 2: weaknesses of dark energy, what we do and what we
• 52:20
  Speaker 2: don't really know.
• 52:22
  Speaker 1: We hope you enjoyed that. Thanks for joining us. See
• 52:24
  Speaker 1: you next time.
• 52:30
  Speaker 2: For more science and curiosity. Come find us on social
• 52:32
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• 52:37
  Speaker 2: Instant and now TikTok. Thanks for listening, and remember that
• 52:41
  Speaker 2: Daniel and Jorge explain the universe is a production of iHeartRadio.
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