Daniel and Jorge Explain the UniverseWhat would happen if dark matter and dark energy disappeared?
Dark matter and dark energy are 95% of the energy in the Universe. But do we need them?
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Hey, jor, Hey, let's do a physics thought experiment.
So I have to think about it.
You have to have thoughts.
Well, does it involve you know, Einstein on a moving train looking through a prison or something.
No, No, we're going bigger than.
That thiker, than like a super massive even bigger. What could be bigger than billions of suns?
Well, imagine that you could visit the universe's control room and just like turn something off. What would you remove from our units?
I imagine that all the time Daniel waited, did you say, what would I remove, or who would I remove?
Let's not make it personal. What would you remove from the.
Universe in that case, probably Twitter? Twitter, I would probably remove immediately.
I thought you were going to say, alarm clocks or emails.
Yeah, those are pretty bad too, deadlines. If I can flip multiple switches, yeah, they're all being flipped.
Well, if that sounds good to you. The next time we have an election, vote for Jorge for Universe control room operator.
Champ twenty twenty four. Hi'm horhemming cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist, and I'm terrified to let Jorge into the control room of the universe.
Are you worried I'm gonna do like a Homer Simpson and eat my donuts and excellent lea press the red switch.
No, I'm terrified because you ask really good questions, and so you'd be like, hmm, what happens if I push this all the way up? Or if I just flip all these knobs and the physicists would be like, what, don't even think about that, that's impossible.
What if I flip the switch on that everyone gets a physics degree?
I would love that. That is actually our goal, that's one of the missions of this podcast, in fact, is to educate everybody out there with a little bit of physics.
Yeah, to turn the switch on in your head, to make you think about the universe and to look out into the cosmos in maybe a whole different way.
One of my proudest moments in this podcast was seeing somebody tweet that they had learned more physics from our podcast than in eight years as a PhD student in physics. No way what but it was on Twitter. Who knows if it was real?
Also, could it have been one of your grad students?
Oh or my sock puppet account on Twitter?
One of your students is trying to tell you something, Daniel like, I hear more from my professor through this podcast than in actual life.
I pay plenty of attention to my students, but thank you for standing up for them.
Well.
Yeah, so, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio, in which we.
Talk about everything that's amazing in the universe, everything that's mysterious, everything that we do know, everything that we don't know, everything that we would like to know, and everything that Daniel's students want to ask him but can't seem to find him in his office.
For Yeah, I think they know by now to pretend to be somebody else and then send you a question.
That's right because we think that everything that you wonder about, everything that we wonder about, everything that scientists are trying to figure out, we think that those questions belong to everybody, and that everybody deserves to know what's going on and what we know and what we don't know. So our goal is to transport you to the very forefront of human knowledge, and to do it without using any fancy.
Words, because there are still a lot of questions out there in the universe. There are a lot of big mysteries that scientists are actively wondering about, and so science is for everyone. We should all be involved in this quest to understand where we are and how it is that we're here.
Yeah, And one of the biggest questions we have about the universe is just why is it the way it is? Did it have to be this way? Is there some rule that tells us that the universe could only have been this way or could it have been totally different? So sometimes we look around, we think, well, could the universe work without this bit or that bit? Or what if we flip these knobs with things still operate?
Yeah, you mean, Daniel, we can't just say it is what it is.
It definitely is what it is, but the question is why is it what it is and not something else?
Yeah? Because I think you know, pondering these fundamental, almost philosophical questions is also a big part of physics, you know, asking what if questions like why is it like that and not something else?
Yeah?
If the universe was totally different.
Why isn't it what it Isn't that would be on my tombstone?
Right?
Why you just made me think there, Daniel.
There's too many negatives in that one. Yeah, And we are curious about that, and so we play these mind games sometimes like do we need this bit or do we need that bit? Or how do these two things work together? And that's very helpful because it helps you understand why we have the various pieces of the universe that we have. We look out into the universe and we see the way it works, and we try to explain it, and we build up the minimal set of bits that we need to explain everything. That we see in the universe, and so it's helpful to understand what would happen if you yanked at one part of the universe or yanked out another, or turned something off.
Yeah, and you know, it's not just kind of a fun game to play, but it's also, you know, kind of a fundamental way in which science is done. Right. I mean, when you ask yourself why something is like that in signe, you kind of have to ask yourself, what if it wasn't like that? You know, I'm thinking about the null hypothesis.
Yeah, exactly. Sometimes you have to ask, like, do we really need this bit? Because the simpler explanation is always preferred. And so if you can explain the universe without some little extra you know, whiz bang bit in your theory, then great. Like if you have the current theory of the universe, plus you have one with like invisible space kittens, well you don't really need the invisible space kittens. They don't add anything to your theory. Yes you do, Yes, you like the invisible space kittens. You don't need the invisible space kittens.
I would totally flip that switch.
And that's why we're not letting you into the control room. But the point is we want the simplest theory, the one that explains everything we see, with a minimal set of ideas, with a minimal set of numbers and details and complicated bits. Because we think, we hope the universe is simple, and we can have long philosophical disagreements about whether the universe should be beautiful and should be pretty, but the goal of looking for simplicity has succeeded for a long time.
Right, I'm thinking simple space kittens. Then you can argue.
So single colors, for example, you don't have any calico invisible space kittens.
All right, Well, on today's episode, we'll be asking a really big what if question, maybe about as big as you can ask about the universe, right, yeah, I mean we're talking about ninety five percent of the universe. What if it disappeared?
That's right. We are gonna let Jorge delete ninety five percent of the universe. Thanos could only do half the universe. But Orge has even more power.
That's right. I am even more inevitable. I am inevitably inevitable.
Everybody out there, tremble in your headphones.
That's right. I'll just snap my fingers, lean put on my infinity glove here. Actually I need two gloves to get to er.
That's right. Yeah, that's right. That's the whole second arc of the Avengers sequence, right, Avengers, return of the Invisible Space Kittens, Jorges Army to destroy.
The universe or maybe destroyed Avengers after game postgame, still gaming anyways. So today on the program, we'll be asking the question what if dark matter dark energy disappear.
Bump bom bomb or I guess the sound effects would be like yow, I like that.
You should do that all the time here on the podcast. I know.
Oh, I make those sound effects when I talk to my students in the meetings, and.
That's why they prefer to listen to the podcast.
No, no, But it's a really fun question because, as you know, dark matter and dark energy are huge for actions of the universe. They play an enormous role, not just in how the universe looks today, but how it looked in its early stages when it was a baby.
Yeah, dark matter represents about twenty seven percent of all the mass and energy in the universe, and dark energy represents about sixty seven percent, right, Daniel, of all everything that there is.
Yeah, that's right, And we often get questions from listeners about what that really means, like what's the denominator? You know, if you don't know how big the universe is, how can you say that dark matter is twenty seven percent twenty seven percent of what? And it's a great question.
Of the whole thing. You don't need a denominator.
The whole thing. You don't need a denominator because we usually think about it in terms of density. Like take any size blob of the universe. We're talking about twenty seven percent of that, and not just of the matter, but of the energy density. Because remember that matter, that mass, the stuff that makes of me and you, is just another form of energy. And we talk about the energy density because that's really what controls the curvature of space in general relativity. It's not just stuff, but it's energy density. So when we talk about this pie that five percent of the universe is the kind of matter we're made out of in twenty seven percent is dark matter and sixty eight percent is dark energy. We're really talking about the fractions of the energy density of any volume of the universe.
Right, And so the universe is really big or really small or infinite it's kind of still means the same thing.
Yeah, and let's us talk about it without knowing the answer to that other super massive, incredibly important question that we're amazingly totally clueless about it.
And so we're asking the question, what would happen if you take it away, like if you went to the control room of the universe and just like flip the off switch on those two things.
That's right, and made that dramatic sucking sound.
And Daniel, do we mean like if we turned them off now, or if we like went back in time and took them out of the birth of the universe.
Yeah, well, immediately when you ask that question, then I want to say, let's do all of them, right, because they're all really fascinating different experiments, right, and if you're going to understand the impact of these things on the universe, you want to play different games. And so yeah, we'll talk about if there had never been dark matter and dark energy in the universe, what would our universe look like? And also what would happen if you just deleted them from the universe like instantaneously right now.
We're going to cancel dark matter and dark energy.
Have you heard what dark matter dark energy said one hundred years ago. Boy, in a modern context, it's embarrassing.
We heard of their workplace policies, oh.
Man, exactly, they were not very tolerant. But first, I was curious what our listeners knew about this subject.
And so, as usual, Daniel went out there into the wilds of the Internet to ask people what they thought would happen if dark matter and dark energy disappear.
So, if you're curious to play intellectual thought experiments for future episodes, please write to us to questions at Daniel and Jorge dot com. We'd love to get your voice on the podcast.
Yeah, so think about it for a second. What do you think would happen if both of those big things disappeared. Here's what people had to say.
If dark matter disappeared, assuming that it didn't exist before and now it disappeared, then I would assume that the galaxies would start to fall apart. The solar systems will probably be okay because gravity there is enough to hold it together, but there wouldn't be enough matter to hold the galaxies together. If dark energy disappeared, then the universe would continue to expand, it would stop accelerating.
I believe I'm going to go ahead and assume that the universe is functioning the way it is now. I would imagine if dark energy disappeared, there'd be enough momentum of the expanding universe that it would continue expanding, and that if dark matter disappeared, I don't know if there would be enough regular matter to stop that expansion. Galaxies would start flying apart, and possibly even solar systems might start flying apart, so it'd be kind of a chaotic experience there.
If we're saying dark energy is somehow involved with the expansion of the universe, then I'm assuming that that's not going to happen anymore. Plus, listening to the latest episode on black Holes, I'm not sure what's actually going to happen there. But I'm not sure that it actually interacts with us in any other way that we know of right now, So that's a total unknown for me.
Probably disaster. First of all, dark matter.
Dark matter is between twenty to thirty percent of the universe. That would be pretty pretty bad. Everything would go crazy for sure.
If dark matter disappears. We know that that is the thing keeping us inside of a galaxy, and at the rate that galaxy is spinning. All the planets and all the star starts would shoot out. And dark energy is a thing that's expanding our universe, right, so maybe expanding stops or maybe or Nuverse start to implode or something.
All right, it sounds like the main message here is disaster. That's right, nothing good, that's right.
The message is basically keep Johe out of the control room.
Lessage, call the Avengers, call the Avengers back.
No one should have that much power, even the Avengers.
I think Tanners was nothinging big enough, right.
Yeah, exactly, that was his problem. Yeah, he was not ambitious enough.
It actually wasn't one of the Infinity stones dark matter or dark energy.
They had like a dark name. I don't remember the physics of it. But one of the cubes is supposed to be powered by dark energy, if I remember, isn't one of the Infinity stones, the same cube that Thor was fighting over and that was powered by dark energy.
You're getting me excited here, Daniel. We can spend the rest of the podcast going back through the testa rack and the power.
That's it. The test ract is powered by dark energy, that's the one.
Yeah, But that turned out to have a stone inside of it whoa. Anyways, back to physics, So not a lot of people predicted good things would happen. Most people seem to think that the universe would sort of fall apart.
Yeah, nobody is in favor of this proposal.
Everyone wants to keep those things around as much as.
Possible, which is why we're doing it as a thought experiment and not in reality. That you know of, Daniel, and you know, there's a long and great history of thought experiments. Einstein's development of relativity was aided by thought experiments, just thinking what would happen if and sometimes they're just very useful to get you to think about the extreme situations. You can't really do the experiment of flying in a spaceship at ninety nine percent of the speed of light and turning on a laser, but you can think about what the rules that we have suggest. You can think about what it would happen if you did that experiment. Now, we'd love to actually do it and to make those measurements, but even when we can't, we can still do the thought experiment to test the boundaries of the idea.
Right, and you also kind of do thought experiments before you do actual experiments.
I hope.
So, like you probably work through all the possible ways that it could go, and then that's how you know what to look for.
Yeah, we definitely thought about it before we built the large change on collider. For example, good will this destroy the world or not? We thought about that, and we also thought about what we could discover and how to build it, and so yeah, there's a lot of fore planning involved in all of these experiments.
All right, Well, just for those of you who might not be familiar, let's recap really quickly what dark matter and dark energy is. So let's start with dark matter. Explain dark matter in three minutes.
Before we delete it from the universe. Let's remind people what it is. So dark matter we know is matter. It's some invisible stuff that's out there. And we know that it's matter and that it's out there because we see its gravitational effects. It's holding galaxies together that are otherwise spinning way too fast to be held together by the gravity of the stars. That we can see. It controls the whole structure of the universe, seeding the formation of galaxies and all kinds of stuff. And we've measured that it's about twenty seven percent of the energy budget of the universe, which is about five times as much as the normal matter, the stuff that makes up stars and gas and planets and bananas and all that good.
Stuff, right, and dark bananas obviously, But it's a big deal. I mean, it's not just like some small thing out there in space. It's literally five times more than the kind of stuff that we're made out of in stars and black and you know, black holes and galaxies.
Yeah, we are literally the tip of the matter iceberg. And it's a wonderful lesson that there's so much going on out there that we weren't aware of until very recently, which means that there are big surprises coming around the Bend in the future. And so we know that it's out there. We know that it's matter. It's definitely made of stuff because it has gravity, but we don't know what it is. We don't know if it's a particle, we don't know if it's something else, we don't know if it's seventy seven kinds of particles. We don't know a lot about it other than that it's dark and that it's matter, hence the name dark matter.
Right, And so that's dark matter and so dark energy also, how would you describe it?
So dark energy is similar to dark matter in the sense that it's important, it's a big chunk of the universe, and we don't know very much about it. Otherwise, that's about all it has in common with dark matter, just basically the word dark.
Dark because we can't see it with visual light.
Right, Yeah, we can't see it with visual light. And also we just don't really understand it. Dark energy is not really a thing. It's not something we understand, it's not something we have a theory about. It's just the observation that the universe is expanding and that that expansion is accelerating. So space is getting bigger and bigger, but it's getting bigger, faster and faster every year, and that takes energy. It takes a lot of energy. And we only recently, like twenty twenty five years ago, discovered that this expansion is accelerating. So dark energy is a description of that acceleration of the expansion. We don't have a theory that describes it. We don't have a model that makes it work. We've just seen that this happens and we know that it's important.
Right, It's kind of like your five year old when they don't want to go to sleep and they're jumping on the bed. You're like, where do they get this energy? It's not like they're glowing through. They're just acting in a funny way.
That's right. But they both contribute to this pie. Right. Dark energy takes a lot of energy. We can calculate how much energy it takes to expand the universe and to accelerate that expansion, and it's just under seventy percent of the energy density of the universe, and dark matter is twenty seven percent. And they fit together in this pie. And the pie is important because various elements of the pie work together to control whether the universe is expanding or contract and whether stuff is being formed like galaxies and stars, or whether everything's just sort of floating out their diffuse and so as we'll learn, these two elements are very important for the formation of our universe and to keep it blowing up or to make it contract or all of those things. So these are the most important parameters into like determining the whole structure and the shape and the size of the universe.
Right, It's almost in a way like if you like the universe the way it is now, Like we are more expendable than dark matter or dark energy. Like you can take away all the galaxies and stars and humans and bananas, and the universe would be less effective than if you took out one of these two things.
That's right. If dark hoor Hay gets into the universe control room, Dark Daniel will say, yeah, sure, turn off all the bananas and other matter. It doesn't make any difference. Yeah, let's just delete ourselves. But then who build the control room Daniel? Well, you know, we don't know. But we are a tiny, maybe irrelevant fraction of the universe, and so we can't expect that everything is made in our image.
Right, All right, let's get into what would happen to the universe if these two things suddenly disappeared. But first, let's take a quick break.
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All right, Daniel, you've led me into the control room of the universe, and I see a big switch here that says DarkMatter with two options on off. I'm gonna go with off here. I'm gonna flip the switch.
Are you ready hold on to something?
Click? All right, I've just made dark matter this year. What's gonna happen?
All right, Well, it's important to know when we are in the universe simulation, like, are we going to remove dark matter from the very very beginning so there never was any or are we gonna delete it? We're gonna cancel dark matter in the universe today.
I guess two different things might happen, right, yeah, all right, So let's start with the early universe. Let's say we pulled it back to the future, went back to the early universe, and then got rid of dark matter. Would the universe be very different?
The universe would be really different fourteen billion years later if there had never been any dark matter in it, because dark matter is really the thing that makes the universe interesting. Briefly, its gravity is the reason that we have formed stars and galaxies and all sorts of interesting stuff. Like the gravity from our kind of matter is not sufficient to pull together into interesting structures this early in the universe without the gravitational assist of dark matter.
Because I guess without the gravity that dark matter brings, things wouldn't have clump together as much or as interestingly. Which one are you saying, yeah, both of them.
I mean. The brief history of the universe is that you have very small over densities, little places where stuff is denser than other stuff that came out of quantum fluctuations in the very early universe, and then gravity takes over and stuff that's denser has more gravity at tracks more stuff, which makes more gravity, which attracts more stuff. It's a feedback cycle, and what you need is stuff for that to happen. And so if you have dark matter and it's five times as much stuff as there is normal matter, then that happens a lot faster. And something that people don't typically understand is that dark matter is not just like everywhere in the universe it's clumped. There are big blobs of it, and those blobs are centered everywhere there is normal matter, and it's not coincidence. Right. Think about dark matter as forming like depressions in the shape of the universe to collect normal matter, so that gas and hydrogen and helium falls into those depressions, and then it squeezed together into stars and galaxies, et cetera. Without them, it'd be much smoother. It'd take a lot longer for gravity to pull the hydrogen together and to form stars and galaxies.
Now, was dark matter clumped initially or was it out there in the Big Bang pretty smooth or were there quantum fluctuations in the dark matter as well?
Well, it was the quantum fluctuations that caused any structure at all, Like everything else, the universe would have started out perfectly smooth if not for these quantum fluctuations, and then we would have even dark matter, even dark matter. Yeah, absolutely, because dark matter and normal matter were made in the Big Bang, right when we went from really really hot and dense so that all the fields were crazy and they broke down and created the particles as the universe started to expand and cooled. They're all made essentially during this initial expansion of the universe. But as you say, it would have been perfectly smooth without those quantum fluctuations, and so dark matter like accentuates it, like exaggerates the effect of these fluctuations, and it speeds things up. If you do a simulation of the universe without dark matter, we've literally done this, then you just don't get stars and galaxies fourteen billion years into the universe, but.
You get them eventually. Like, is the effect of dark matter just speeding things up or is it like we would never clump together as a galaxy.
Well, it depends a little bit on what's going on with dark energy. It speats things up, right, and so given enough time without dark energy expanding the universe, then yeah, it would form these gravitational structures and you would get stars and galaxies. But there's a bit of a race here, right. Dark energy is coming on the scene and it's pulling the universe apart. It's making it harder for gravity to form structures. So we got a little bit of a window there right before dark energy yanks the universe apart and makes everything too far up to do anything interesting. You've got a window there to form interesting structures. So you don't have infinite time to get stuff done, You've got a deadline. I mean, you have fourteen billion years, but you still got a deadline, right.
Well, assuming that dark energy keeps going.
That's right, Assuming that dark energy keeps going, and that you know, you don't stumble into the control room and turn it off or accidentally double it or something. Stay tuned, Stay tuned. That's the last part of their podcast. So we wouldn't get interesting structures. So what would the universe look like today? It would just look sparser, like there wouldn't be like galaxies and stars would be more spread out apart, or there'd be less stars. Yeah, we would essentially just be earlier in the development of structure. And so whereas in our universe we had the first population of stars form in less than a billion years after the Big Bang, that would have happened much later, and galaxies formed, you know, in the first billion years or so, that would also happen much much later. And so at this point in the universe. It depends a little bit on the details of how you're modeling dark energy, but we would probably have some stars, but not big complicated galaxies like we have today.
So dark matter is like the steroids of the growth of the universe. All right. I thought the universe was organic and you know, hormone free. But I guess even the universe dopes a little.
That's right. Market pressures, man, market.
Pressures, all right. So then the other scenario that's interesting is like, what if you trend off dark matter. Now, like we are where we are now, it is what it is, but then suddenly something happened to dark matter.
That's right, Say you had dark matter that super charged the acceleration of structure in the universe, gave us stars and galaxies, and then you deleted it Feno's style from the universe. Well, you know, the structures that we have now depend on dark matter. It's not just like, oh, well, we needed dark matter to get where we are, but now that we're rich and famous, we could forget about our friends from our hometown. We still need dark matter because it's holding our galaxy together. Like our galaxy is spinning, right, and things that are spinning tend to fly apart if it's not something holding them together. Like we say often in the podcast, you put ping pong balls on a merry go round and spin it. Ping pong balls fly out. The reason that the stars in our galaxy which is spinning, don't fly out into intergalactic space. Is because gravity is holding them together, and mostly that's dark matter. So if you deleted dark matter from the galaxy, then it'd be like as if you suddenly turned the Merry go around on five times as fast, and you know, the stuff in the outer ring of the galaxy would get tossed out into intergalactic space. There wouldn't be enough gravity to hold it together.
Would it just fly off or would it just you know, the galaxy would just get bigger in terms of things being more spread out.
It would get bigger. But the stuff on the outside would essentially have escape velocity suddenly, so they would get tossed into intergalactic space. We would lose all those stars in the sort of exurbs of the galaxy.
Well wait, we don't really need those stars to we.
There's a lot of crucial votes in those districts, man, so be careful.
Which is a lot of politics here today, Daniel.
But your fate depends sort of on your distance from the center of the galaxy. If you're in the very edge of the galaxy, you're getting tossed out into space. You're becoming a rogue star, which is, hey, maybe not that bad. Like, what did you really need the galaxy for anyway? You know, if you believe in inlimited galaxies, then maybe that's good for your philosophy.
Well, what would happen to us in particular, Like would our solar system be affected at all? Like would life go on the same for us? Or would we also fall apart.
Well, we're in sort of that middle region and we would stay still gravitationally bound to the main galaxy, but we'd get a little further from the center, and probably what would happen is that all the stars in our vicinity would clump together to form basically like a little dwarf galaxy. You may not be aware, but our galaxy has little satellites, Like you know our planet has a moon, right, our galaxy has its own satellites, things that orbit it called dwarf galaxies, little clusters of stars that form many galaxies. So probably our sun would end up in one of these little clumps that would be orbiting the old core of the Milky Way.
Really, but maybe further out or something, yeah.
Further out, So instead of being like in the suburbs, we'd be a little town out deep in the wilderness.
So you're saying, without dark matter, you would get more of these satellite galaxies. Why would we get more.
Well, because the middle part of the galaxy, this middle band where we live, wouldn't be held into the galaxy anymore, would sort of get spread out, and instead of having been tossed all the way into space, we don't have enough velocity for that, we don't have escape velocity. We'd become gravitationally bound to the galaxy, but in sort of a clump. And so this middle part of the galaxy would sort of break up into a bunch of little galaxies that are then orbiting the old core.
All right, Well, it sounds like if we took it out early in the universe, we wouldn't be here. The universe would look really different. But if he took it out today, you know daily life. We mean, we would sort of orbit around things differently, but it maybe wouldn't affect us in our daily lives.
Yeah, we're almost not affected at all by the structure of the galaxy. It doesn't really matter to us at all whether those other stars are there. You know, we're dominating by the experience of the Sun. But whether there are other stellar neighbors is not really a big deal, and you know, it affects maybe our prospects for galaxy spanning civilizations. Once in the future we end up in a little dwarf galaxy further from the main core. But you know, if our ambitions are closer to home, then it doesn't really change our lives if dark matter is deleted today.
Right or I wonder how long before we would even notice dark matter was gone?
Oh my gosh, are you are you trying to admit? Are you trying to confess to having done something last night? What are they going to notice?
I'm like the bad guy and Watchman. It's like I flipped the switch twenty four hours ago, Daniel.
This is the modern version of the telltale heart. Can anybody tell? They're all looking at me?
Yeah, Like, how long ago could I have flipped the switch before we even notice?
That's a good question, and it goes to like how well we know the structure of our galaxy, which is a whole fascinating podcast topic. We have scheduled for a couple of weeks from now, But we know the structure of the galaxy pretty well, and we can tell the distance too nearby stars, and so if that's suddenly changed, we would be able to tell, but not for a few years, right, because the information we're getting is years old, because the closest stars are a few light years away and most of the rest of the galaxy is five ten hundred thousand light years away. So it'd be a while before we actually.
Saw it, hundreds of years or something, right.
Yeah, it could be hundreds or thousands of years before we figure.
That out, before we're like, hooray, what did you do?
Or he is great great great great great grandchildren or to be held to account.
So what would it look like? Would we see less stars out in space when we looked at the nice guy.
Yeah, we would see less stars out in space, and we'd be separated from the main core of the galaxy. Now, the core of the galaxy wouldn't change very much because it's got so much gravity already in the supermassive black hole would hang on to that. Instead of seeing the Milky Way as a band across the sky, we would see the core of the galaxy in our sky. Be pretty spectacular.
Actually, m it would get more intense maybe, yeah, it might get more intense, all right, well, that's dark matter. Thank you for playing dark better. We like what you're doing. We'll keep it.
I guess I vote yes on dark.
You don't even know what it is, Daniel.
I don't know what it is, but I want to keep it up. I like it. I fear change.
All right, let's talk about what would happen if we took dark energy away. But first, let's take another quick break.
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All right, Dan, and we're talking about what would happen if we took out these big chunks with the universe away, dark matter and dark energy. And so let's talk about what would happen if I made dark energy disappear. And again, I guess you can talk about taking it away at the beginning of the universe and today, So what would happen if I took it out when the universe started.
It's fascinating because these two different components, dark matter and dark energy sort of dominate the stage at different part of the history of the universe, Like dark matter controls the structure of the universe from very early days, whereas dark energy really only takes over in the last few billion years. And so they really play a different role here, which is.
Fast really bloom.
Yeah. To understand this, we have to understand a little bit about the history of the expansion of the universe. So go all the way back to the very beginning, and the universe somehow is created. We don't understand that at all. And then there's inflation, when the universe goes from very hot and very dense to suddenly much larger, and again we don't really understand that at all. But from that going forward, we think we have an understanding of how the universe expands and how that expansion accelerates or decelerates, and it's controlled by how much matter and radiation there is, how much energy there is in the universe, and also in this dark energy, and the two forces are usually working at odds with each other.
Wait, so dark energy wasn't very instrumental in the Big Bang, was an inflation sort of partly due to dark energy.
So we don't know. Inflation has a very similar effect to dark energy, and that expands the universe very rapidly, But we don't know if then mechanism of inflation is the same as the mechanism of dark energy, like they both have the same effect. We don't know if they're the same thing. They could be, and in some theories they are and some theories they're totally different. But we're really just the very beginning stages of understanding these things at all. And so we can't really say that inflation is the same as dark energy. So let's put inflation aside and think about what happens post inflation, right basically after the Big Bang if there was no dark energy.
Oh, I see, all right, So that the universe just exploded or expanded rapidly after inflation, and now everything's kind of hanging out there. So what would happen if I turn off dark energy?
So really not very much like in the early universe, dark energy plays almost no role. And the reason is that things are still really very hot and dense. You have a lot of radiation in the first forty seven thousand years of the universe. Mostly the universe is just radiation. We're talking like photons like crazy, bouncing around everywhere for the first forty seven thousand years. And it's a little counterintuitive, but what happened in the very the beginning of the universe is that you had expansion of the universe, even though it's mostly just filled with stuff, right, And Typically you think of stuff causing gravity, which causes you know, contraction, But the matter in the radiation in the universe actually caused some expansion early on made the universe get bigger. Now the effect of dark energy is to accelerate that expansion, is to make that expansion happen faster and faster and faster. Gravity works the other way, it makes the expansion happen slower.
Are you saying that dark energy didn't play a role, Like it wasn't important or it was just turned down in the early moments of the universe.
It didn't really play a role at all. Dark energy gets more important as the universe gets bigger because it has one really weird property is that it doesn't get diluted. Like every chunk of space has the same amount of dark energy, and if you double the space, you make space bigger, you get more dark energy, whereas with matter and radiation, like if you double the size of space, then the matter gets less dense because you have the same amount of matter, Like you have two protons in a cubic meter of space, and then you expand the universe to be twice as big. Now you have two protons in two cubic meters of space, so you have less matter density, but dark energy just doubles when you double the space. So as space gets bigger, dark energy gets more and more important. So dark energy, you could have deleted it from the very early universe, it would have had no role. But as the universe gets bigger and bigger, it starts to take over and become dominant.
Right.
I guess it's kind of like if you took it out before it grew, then it wouldn't make a difference. But now as the universe grew, dark energy also grew, and so it just became more consequential.
That's right. And so if you had deleted it from the early universe and it never had happened, right, we never had dark energy, then the history of the universe would be like, you have the Big Bang, you have all this matter, you have all this radiation. You still have expansion of the universe in the very early universe. But then gravity is taking over. It's slowing down that expansion. Eventually it stops the expansion and it turns things around. We have a contraction, and the universe reverses and comes back into a big crunch. So dark energy is the reason.
We're still around.
Why we're still around is the reason why we haven't had a big crunch. But you wouldn't have noticed it in the very early universe because it didn't really take over until a little bit later.
Oh so wait, if I took out dark energy at the beginning, the universe would have expanded, And are you saying that by now, like fourteen years into it, we wouldn't be here, like the universe would have crunched already.
Absolutely. Yeah. Without dark energy in the universe, gravity would have won. It would have slowed down the expansion. It would have stopped it and turned it around and crunched us. We wouldn't have this universe without dark energy.
Like none of the stars would have form, or they would have been starting to form, but then the universe would crunch.
Yeah, because you still have dark matter, you would have formed stars and galaxies. But then without dark energy, all that gravity would have gone into a runaway effect and collapsed the universe back into a very very dense thing.
Okay, so that's if you took it out early. What have you waited a little bit before taking out dark energy?
Yeah, so there's a bit of a dial there, right, if you take it out too early, the universe crunches. If you leave it in a little bit longer, then it allows the universe to expand more, fights gravity longer, and it gives you a longer and longer window at some point. If you turn off dark energy late enough, it's too late, like gravity can no longer win. Like in our universe today with dark energy, we have the acceleration of the universe happening right now, like the space is expanding, and it's expanding faster and faster. So, for example, if it turns it off today, gravity could not pull the universe back into adopt It's already too late for gravity.
Really, is it, Because if you take out dark energy, the universe stops expanding. It's like it's fixed in size. Wouldn't gravity eventually bring everything together?
Yes, But if you take out dark energy, you don't stop the expansion. You stop the acceleration of the expansion. You stop adding to thelocity. Things still have a velocity. Remember Newton's loss tell us that things in motion stay in motion unless you apply a force to them, and so dark energy is that force. If you stop pushing on things, they're still flying out. Their space is still expanding, and so dark energy is the acceleration of the expansion, not the expansion itself. So if you take out dark energy, you stop the acceleration, but things are still expanding and gravity does not have the power to turn that around.
Wait, what is still expanding like the distance between stars and galaxies? Or would space itself still be you know, multiplying and growing both.
We're talking about the expansion of space itself, right, Oh, I see, and that expansion is accelerated by dark energy. But you still get expansion even without dark energy.
Really, so if you took out dark energy, space would still be growing. What is making it grow? Don't you need energy for that?
Well, the expansion can continue without dark energy. But matter itself causes the expansion of the universe, like we were talking about earlier in the very early universe. It's just matter that causes the universe to expand. Now, gravity gives you a negative derivative on that expansion. It slows down that expansion, and dark energy increases that expansion. So sort of two things to talk about there, like the velocity of space and its acceleration. So matter gives space velocity to expand outwards. Gravity gives you a negative acceleration on that, and dark energy gives you positive acceler.
Dark energy is kind of like the booster rocket or like the torbo yeah in the universe.
Crow yeah. So if you take away dark energy in the very very early universe, so it never happened, then gravity would win and things would crunch. If you take it away today, right then it's sort of too late. It's already won the game, and gravity can't turn things around, Like things are moving out too fast and too far away for things to turn around. And there's like a middle time there where if you deleted dark energy just the right moment, you would find like a balance there. And there's some moment there there's a tipping point, and I'm not sure you could actually walk that line and stay on that tipping point, but there's some point at which if you don't delete dark energy before that moment, it's going to win.
So I guess you're saying that dark energy could retire right now. It's done. Its job is to put in its time, and now the universe will never crunch back down into right, I mean without yeah, even if you took out dark energy, the universe will never crunch back down into an inverse big bang.
That's right. To make an inverse big bang, now you need dark energy to reverse, not just to disappear. You needed to turn around and somehow cause the contraction of the universe. And you might think, well, but it's only ever caused the expansion of the universe. Why would it cause contraction, which is a great question, But remember that we don't know anything about dark energy. We have speculations that it might be the cosmological constant or something else, or the energy of empty space, but we really have no understanding of what it is, which means we can't predict its future. And it could do something bonkers like turnaround and change direction and cause the contraction of the universe.
Like it could start taking energy away from space almost.
And we don't understand it, so we can't predict its future. If dark energy disappeared today, then yes, there's already enough expansion that gravity can't win. And if you kept dark energy doing what it's doing, which is causing the acceleration, then you know it's already game over and we're accelerating towards having more and more distance between galaxies, having these little blobs of stuff being more and more separated, and more and more isolated, and each one gravity is strong enough to hold together. Right, dark energy is not going to rip you from the Earth or rip the Solar system apart. Because gravity has won these little micro battles to hold these little structures together. More likely will collapse into a bunch of black holes then separated with vast distances between other black holes. Not a happy outlook, black holes to the end of time, White's in twenty twenty four.
You have a stark choice here of people between lightness and darkness.
That's right, reality or fantasy.
All right, Well, I'm getting the sense that dark energy and dark matter were super important for us to be here. We needed them to get to where we are, But now that the universe is kind of chugging along, we really don't kind of need either of them right now.
Well that's true.
Yeah, Like you could turn them off now and humanity would probably go on the same trajectory as it would have been.
Yeah.
Well, you know, that's not very grateful. You know, it's just like, what can I remove from my life that I don't need anymore now that I've made it. That's not a very generous attitude. We should remember how we got here and all the little people necessary along the way.
But you know, as Mary Kanda says, you know, think about it and just bring you joy, Daniel, and if not, just throw it out.
Dark matter brings me joy. But you're right, we don't need it. We could delete dark matter from our universe and our solar system would be fine. We can delete dark energy from our universe and it wouldn't really change the fate of our solar system at all. So you're right, there were instrumental in getting us here, but we could cut them out of our entourage.
I guess. I mean like in a way almost like if you get rid of dark energy, it almost makes the universe more accessible, right because if things aren't accelerating further apart, then it increases our chances of you reaching other places in the universe.
Yeah, that's true. It's a bit of a grim picture to imagine that dark energy could be creating these vast distances between superclusters of galaxies, making it literally impossible to explore the universe. And so yeah, I would actually like to turn off dark energy or reverse it a little bit, bring some of that stuff a little closer, give our human rocket engines a chance to explore.
So you mean you would like me to go into the control room and fiddle with the knob, be like.
On off sufficient adult supervision.
Yes, so it'd be like flipping the switch and then just so that the aliens are close enough for you to say hi to them, and then and on switching it back on.
That sounds great, Yeah, do that all right.
Let me put on my infinity gloss here and twiddle my thumbs all right. Well, it sounds like these are really super fun thought experiments, but I feel like they're also a big part of how you know that these things exist, meaning, like you know, you play these experiments in your head, like what if dark matter never existed, Well, the universe wouldn't be the way it is, which sort of tells you that dark matter does exist.
Yeah, exactly. And it's not just these large scale structures the organization and the size of the universe. There are a lot of other details that tell us how much dark matter there is, how much dark energy there is, how they interact, and that come from lots of different observations, you know, from looking at the early light of the universe and all sorts of other crazy detailed measurements, so it really seems like dark matter and dark energy are a thing and that they are necessary things to make the universe the way it is. Then, of course the next question is like why are they at those values? Could there have been more dark matter or more dark energy? Why these numbers and not other numbers?
Right? But we almost don't want to ask those questions because then we wouldn't be here.
I want to ask those questions because I want to know is it an accident that we're here? Or are we inevitable as the only possible universe one that has this kind of structure, or are we totally lucky when in a trillion chance? To me, those are the deepest questions of physics. Those are the reasons I got into physics, is to try to answer these massive philosophical questions about the context of our very lives.
Yeah. See, it's not just Stanus who's inevitable or wants to be inevitable, it's Daniel.
It's questions really, it's wondering about the universe that's inevitable.
All right, Well, I think we've reached the endgame here of our episode. We hope that you look down into the Universe tonight or tomorrow or the next day, and think about what are some of the things that led to us being here and how important they are and what would happen if things were totally different.
And share with us your one and your thoughts and your questions. Please write to us to questions at Daniel and Jorge dot com or interact with us on Twitter at Daniel and Jorge, where we make bad jokes and answer questions.
Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
As a United Explorer card member, you can earn fifty thousand bonus miles plus look forward to extraordinary travel rewards, including a free checked bag, two times the miles on United purchases and two times the miles on dining and at hotels. Become an Explorer and seek out unforgettable places while enjoying rewards everywhere you travel. Cards issued by JP Morgan Chase Bank NA Member FDIC subject to credit approval offer subject to change. Terms apply.
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High Potential series premiere Tuesday, ten ninth Central on ABC and stream on Hulu
