Daniel and Jorge Explain the UniverseDaniel and Jorge talk about the hypothesis that there is a cosmological Axis of Evil
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Hey Daniel, what's one of the hardest physics questions someone's ever asked you?
Oh? Well, someone asked me once. If the Earth is round, why don't people fall off the bottom of it?
That is a pretty good question. Yeah. I think we got that one on live radio once, didn't.
We Yeah, we did exactly no preparation.
But why is that a hard question?
Well, the hard part is figuring out why that question makes sense to the person asking it.
You mean, like, how does gravity even work?
Yeah, you have to know like what they are misunderstanding, so that you can find a path to get them some actual understanding.
Mmm.
So what's the answer. Why don't people just, you know, fall off Australia?
How do you know they don't? I mean, have you been to Australia? Maybe the whole thing's a hoax.
You mean Australia as a hoax or gravity as a hoax? Which one kangaroos exist?
I think my lawyers would advise me not to answer any of those questions.
Hi am Hoorhe made cartoonists and the creator of PhD comics.
Hi I'm Daniel. I'm a particle physicist and a professor at uc Irvine and I have never been to Australia or New Zealand.
Really, you've never been down.
On the never been down there, planned it many times, never actually happened. How about you, You've been to Australia. I think I've seen a picture of you talking to kangaroos.
Yeah. Yeah, they're very chatty if you can get them to us. Sit still now, that's amazing. Australia is awesome. I mean it's like going to another continent literally, but it's really like going to another world. Like all the plants are different, they're bigger, all the animals are bigger, they're different. It's pretty amazing.
Definitely on my to do list.
Yeah, but welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we explore all the consonants of modern physics, the weird, the strange, the ones we understand, the ones that are unfamiliar, the ones that seem weird, and the ones that might bite you in the night. We talk about all the biggest questions in the universe, from the scope of the whole shebang, how it started, where it came from, how big is it, how does it all work? Where is it going? All of these questions we talk about them without fear, without shame, and without hesitation, and we explain all of them to you.
Yeah, because physics bites is what you're saying.
I think sometimes you've got an understanding of a problem. They can really sting.
Yeah, but it is pretty cool Australia to think about Australia because if you think about it, they sort of see a whole different side of the space than we do here in North America.
Yeah, and you are used to thinking about the Solar System with the Earth on the sort of top side of it, but that's sort of North Hemisphere centric. If you're on the Southern hemisphere, then that half of the Solar system is sort of looking out and up into the universe just as much as we are. Yeah.
And we have a lot of listeners in Australia. Do you think they listen to it upside down? Or it's sort of weird to think that they're listening to this upside down from us right now?
They are exactly in Australia. You're the physicist and I'm the cartoonist.
That's right. You're the funny one and I'm THEU not so funny.
You can grow go tea in Australia and I can't.
Yeah, it is a pretty interesting universe, and it's a three sixty universe. It's all around us in all directions where we look from anywhere on Earth. But it's sort of interesting to think about directions in space.
It is, and for a long time humans have sort of imagined that the Earth is at the center of the cosmos, that we look at the universe in every direction, but that we are sort of in a special location. And it wasn't until about five hundred years ago with Copernicus that we started to realize home on a second, maybe there is no special location in space. Maybe we're just at some random point, and that gives you a completely different view about the shape and the nature of the universe that we are seeing.
Yeah, it was weird for humans to think that we are not the center of the universe, although I am sort of the center of my universe, or wait, I should maybe I should correct. My kids and my spouse are the center of my universe. Of course.
I think there's an emotional moment there also when kids grow up and realize that they are not the center of everything, that the whole universe doesn't revolve around them, that other people are people too.
Yep, unless your kids are aliens, which case you might have a more interesting realization.
And it's kind of hard to understand what a big mental shift that was, you know, something that we now are very comfortable understanding that we are just in a random spot in the universe. But it was a huge conceptual shift, the kind that I don't think we can even really ever understand because we weren't firmly rooted in the other idea that we are special at the center of the universe. But giving up a long held assumption about the nature of the universe. That's sort of the joy of physics, you know. That's when physics stings, when it like tells you, oops, you've been thinking about things completely the wrong way. The universe is fundamentally really different from the way you imagined it. I long for that kind of cosmic realignment.
When it crawls up your pants and bite behind. That's what you look forward to. Yes, But yeah, at some point humans realize we're not in any kind of special point in space, you know, and it sort of informs everything right and informs the theory sort of the equations about physics. It has to do with symmetry and all that. So there's no specific or special point. We don't even know if we're at the center of the universe or like in a corner of the universe, or we don't even know if it makes sense in an infinite universe to have a point.
Right, Yeah, and the joke you made earlier is actually true. You are at the center of your observable universe. You know, we don't know how big the universe is. We can only see a portion of it, and that portion is limited by the speed of light. And so the part of the universe that you can see is the part where light has had time to get to you since the beginning of the universe. And that's actually a different if you're in our sun and if you're at another sun, because you can see a different portion of the universe because light that has reached you know, Alpha Centauri may not have come yet two hours. And that's also true for my head and your head. So technically speaking, we are the centers of our own observable universes, and so.
The universe doesn't seem to have any kind of preference for any particular point in space, but there's sort of a bigger question about whether it has a special direction in space that it likes.
Yeah, they're connected questions, but they actually are separate. One's connected to the question of are the laws of physics the same everywhere in the universe? You know, if you do an experiment here, does it matter would you get a different answer if you do it somewhere else, or if you do it in another star system or alien physicists measuring the same law physics. We're pretty sure that they are. But there's another question, which is does the universe have a preferred direction? Right? Like, if you rotate your experiment, could you possibly get a different answer? Could you measure some like preferred direction of the universe?
Is there an up and or down in the universe kind of or left or right?
Yeah, or like a special direction around which the universe prefers or something like an axis.
All right, So on the podcast, we'll be asking the question does the universe have a preferred direction?
Now?
I assume this is there like a like a spatial direction, not like an emotional direction or acting direction.
Creative direction. Yeah, the universe prefers method actors.
Yeah, you know, prefer as a comedies as opposed to dramas. What's the tone of the universe, Daniel, Maybe it's.
All universe hoaks now. And that's why this is a physics podcast and not a Hollywood industry podcast. We're not talking about the latest trends in you know, representation in Hollywood movies or anything. We are talking about directions in space. You know, if the universe had some specific direction that was different from the other ones, then in principle, you might be able to measure that. You could like design an experiment that would be sensitive to it. The way, for example, the surface of the Earth does have preferred directions or different directions. Right, there is a north on the Earth and the south on the Earth, and you can design experiment it's called the compass, to measure it, to detect it, and to use that to navigate.
Or like if you're on Earth, there's sort of an up and down, right, I mean it depends on where you are on Earth, but there's sort of like a towards the center of the Earth or away from the center of the Earth. Is that kind of what that also count as a direction?
Absolutely? Yeah, Gravity defines a direction on the surface of the Earth. Absolutely, and as you say, it's towards the center, which is actually the answer of the question why don't people fall off Australia.
I'm sure people fall in Australia, but do they fall off of Australia.
I don't think they trip and then fly off into space. You know, I think we would have seen that on YouTube if that was happening.
Maybe you have a rocket power, you know, parachute or.
Something, right, And the answer is intuitive and obvious to everybody who understands the Earth is a sphere. But obviously down is towards the center of the Earth, which is why people fall down towards the cider of the Earth everywhere they are on the planet. And you're right, like the direction there is relative to the center of the Earth. But that's just arbitrary, right, you could pick anything. But the question is, you know, is there a non arbitrary choice? Is there are which makes sense no matter where you are in the universe.
Well, you just made me think that. You know, we feel gravity towards the center of the Earth, but we're also being attracted by the sun a lot, right, So does that mean that our gravitational vector, or the rection of gravity is sort of slight, always slightly tweaked towards the sun.
Yeah. Absolutely, the gravity of everything is affecting how much you weigh, and so as the Earth rotates, your weight changes a very small amount. But you know, the amount that the Sun pulls on you versus the Earth pulls on you is very small.
So at noon is when I'm lightest. Right, technically it is when I weigh less.
That's right. At noon, the Sun is pulling you off of the Earth, and at midnight the Sun is helping the Earth pull you towards its center, so you gain weight at night. So this is the travel the Earth's are always at noon diet.
That's right. That This is why I eat a big lunch because I can.
Right, every meal is lunch, the physics diet.
I avoid meals at midnight, although sometimes you cannot.
There. I've been traveling with you.
I know you eat meals at midnight, eight, at midnight, at one am, two am. I have no preferred time for by directing my meals. So I guess the question is the Earth has a preferred sort of gravitational direction. But you're saying, like does the universe have maybe not a gravitational direction, but just like you know, a different direction or some sort of different effect that changes depending on which way you're pointing in out there in space.
Yeah, and really sort of the cleanest way to define this is imagine getting transported to an arbitrary location in the universe. Could you build an apparatus which could measure some location so that if you're transported to some other location and randomly rotated, you could like tell how far you've been rotated. You could measure it. And you know, like on the surface of the Earth, you can tell your direction because you could just use the magnet. But you know that doesn't work obviously, like off the surface of the Earth. So could you build like a universal compass that always tells you, you know, a reference direction, and the universe has no preferred direction, then that's impossible because there's no physical mechanism which prefers one direction over another.
Right, that would help you sort of navigate the universe in a way, right, Like if you get lost in the universe, you could sort of look at your cosmological compass and be like, oh, I need to go you know, east or whatever in space and I might reach Earth again.
It certainly would help you navigate, but it would also like blow up our idea of how the universe works. Right now, we really assume that the universe has no preferred direction and no preferred rotation. But recently there have been some ideas that suggest that maybe there is a preferred direction, and these go buy sort of a cosmically silly name.
Yeah, because we've been assuming that if there is a special direction, it would be the universe's preferred direction. But what if there's a direction that the universe does not like, Like, what if it's the opposite, what if it's like the least favorite direction in the universe.
A cosmological axis of evails.
Yeah, that's the sort of name that you have for in the in the in the physics community, right, the cosmological axis of evil.
That's right. There's been this idea of bubbling up that maybe we were wrong in thinking that the universe has no preferred direction.
Maybe it does or a non preferred direction, right.
I think the origin of the idea axis of evil is that it undermines our idea that the universe doesn't prefer anything. It's like, nobody should be preferred to the axis of evil is like spoiling an otherwise pristine and beautiful idea.
Oh I see, but it is a phrase that people use in the physics community to like, oh, you're talking about the cosmological axis of evil?
Oh?
Absolutely, or cee for sure.
Absolutely. There's a paper titled the axis of evil, which I just read yesterday. Like, this is not something I came up with or just a joke on podcasts. It's really a physics term for a deep concept.
I feel like you just used I read it in a paper as in, like that's supposed to be an ultimate authority. I saw it on YouTube. It must be right. I saw it on archive dot X. It must be true.
I don't know if the physics is sound or if it's actually right, but it is something people actually say in the physics community. So there's that.
Much cosmological access of evil. That's what will they get into today. And so, as usual, we were wondering how many people out there had heard of this cosmological access of evil and whether they have any idea about what it means. So Daniel went out there into the internet to ask people this question. Here's what they had to say on a.
Guess cosmological something to do with very large scale structures in the universe access of evil. Perhaps it's something to do with the way that certain fields are calculated and there's some weird mathematical structure that causes problems. I have no idea.
I have no idea.
I couldn't even begin to guess.
It sounds familiar, but I don't know what it is. Probably i'm watching too much theory.
I can tell you right off the bat, I'm stealing that and that is going to be the name for my new punk rock band. But aside from that, I have no My only guess is that that is what we would call the things that are going to be responsible for the end of the universe. So maybe dark energy and entropy are the cosmological access of evil.
The cosmological axis of evil is the nexus in the universe where everything that is evil intersects.
Think the dark side of the force.
Live causibral backwards is live.
What does that have to do with the access of evil. I guess that's a good enough answer because I have no idea either, So I'll go with it's something with the bow taste void and the great Attractor and the void is somehow funneling all of the matter from the universe into the Great Attractor to create a super giant black hole that's going to swallow everything. How does that sound? That's an axis of evil. We could throw mustache twirling enemies in there, or I guess go te Jorge because he was in one of those parallel universe episodes before. So I have no idea what tomological axis of evil is.
Somehow I see Austin powers and battling the cosmogical access of evil in my brain when I read this question, I don't know anything beyond that.
All Right, nobody has any idea, Daniel. It has not broken out of the physics community out into the larger population.
And that's our job is to funnel the craziest, funnest, most interesting, wackiest ideas that are poorly named out into the larger community.
Yeah. So you call it an acts of evil because I guess an access is sort of like a direction, and you're saying that maybe this direction is sort of evil in the sense that it sort of ruins the universe or ruins your sort of perfect symmetry picture of the universe.
Yeah, I think that's right. Although historically and sort of philosophically, it's fascinating because I think, you know, the idea that the universe doesn't have a preferred direction went up against a lot of theological friction, you know, five hundred years ago, because people preferred the concept, you know, that the Earth was at the center of the universe and in a special location and sort of at the heart of the cosmos. So the idea that the universe didn't have a preferred direction was sort of seen as evil five hundred years ago, and now doubting that idea is again seen as evil. So in that sense, maybe evil is just like you know, the upstart.
Well, I think if there's anything movies has taught us is that evil is a relatives you know, maybe not the Marvel movies, but you know, more artful movies.
Yeah, I think it's a pretty ridiculous name.
You mean, like in religious times or in a religious sense, like would you want the universe who have a preferred direction? You know, you want your DT to have some sort of point of view.
Well, I think the Catholic Church, for example, was not a big fan of the idea that the Earth was not at the center of the cosmos. Galileo spent a long time under house arrest for insisting that it was. And I don't think that Copernicus was like number one favored person by the pope either. So I think that, you know, the scientist's got a lot of flak several hundred years ago for suggesting that the Earth was not at the center of the cosmos.
But now there's maybe an inkling or a suggestion that maybe the universe does have a special axis, a special direction it likes. And so break it down first, what does that mean and where does that come from.
So we've been operating under this assumption for a long time now that we don't have a special place in the universe, that there is no special place, that there is no preferred direction. And this really has grown out of like the Copernican principle, you know, from five hundred years ago, and these days we call it the cosmological principle because we say it even more broadly. We say that the whole universe is homogeneous, is isotropic, that on a large scale, everywhere in the universe is basically the same. There's no center, there's no edge, there's no place that's different from any other. Place, and so if you spotted a deviation from that, if you like, detected something which seemed to prefer a direction, that would spoil something really deeply fundamental at the heart of basically all of modern cosmology.
Are those two things tied together, you know, like a special or preferred location and a preferred direction, or are those you know independent, like can you have a preferred direction without a preferred location?
Those are independent, They're and the same family of ideas, but there are actually two separate things. And you know, it really is interesting. The idea that the universe has no preferred location is a symmetry, right. It says you do an experiment here, you do an experiment there, you get the same answer. Space is the same here and there. That leads to a conservation law. We talked about it once in the podcast. Emmy Nuther's theorems tells you that every symmetry gives a conservation law. And in the case of having no preferred location, that's why momentum is conserved. And in the case of rotation, the idea that if you rotate the universe you should always get the same answers to your experiments. That's what gives you conservation of angular momentum. So there are two separate ideas, but they are closely connected, right, They're both connected to momentum.
But I guess when did people start questioning whether there was a preferred direction? Because I've never heard of this idea that it could have a preferred direction, Right.
It comes out of some observations that have been made in the last few years. People have been assuming that things are equally smooth and the same in every direction, but recently there's been this sort of like strange, unexplained alignment of various measurements that should be random, And when you see a bunch of coincidences line up, you start to wonder, like, hmm, are these coincidences or are these sort of like the first clues into a new way to look at the universe?
Interesting? So this is based on some experimental results.
Yeah, these are unexplained coincidences that have people starting to wonder if the universe might actually have a preferred direction.
Well, you make it seem like a conspiracy or like a sort of secret secret undercurrent, some dark undermelly kangaroo pouch of.
The universe, exactly like some access of evil hatching some plan to spoil our view of cosmology.
A bunch of Australians thinking about how to keep from falling out the Earth.
Yeah, and I think it's worth exploring for a moment what this principle that we're doubting means the idea of the universe is the same everywhere, because obviously it's not exactly the same where, Like, you know, there's a star here and it's not a star there. There's a galaxy over here, but it's not a galaxy over there. It's not true that every place in the universe is exactly identical. It's a statement we make about very very large scales, like if you really zoom out out past galaxies and past galaxy clusters, out to galaxy superclusters, and you look at sort of like the filaments and the foam of the largest scale structure of the universe, things should be about the same everywhere.
It just made me think, like, is it possible to go out there into space and measure gravity and whether or not gravity kind of pulls in one particular direction. Would that tell you if you're at the edge of a universe, a finite universe or not.
Yeah, And that would be a deviation, right and so on the very largest scales, you should basically feel no effect of gravity because there should be an even distribution of stuff in every direction. Pick a random place in the universe and there should be you know, like superclusters over there and superclusters over here, and in the end they should all roughly balance. Of course, if you land near a black hole, you're going to feel some gravity, but on average there should be you know, effective tugging, and that comes from you know, we think the universe was created smoothly and created homogeneously, and you know, the variations that we do see, the fact that there's a galaxy here and not a galaxy there, those come from the little perturbations, the little fluctuations in that smooth beginning of the universe. I see.
All right, So there's some experimental measurements that tells that maybe things are not homogenous, that maybe things do have a preferred direction. So let's get into this secret result. But first, let's take a quick break.
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All right, we are determining whether the universe has a specific direction it likes or dislikes or I guess we're asking whether the universe leans a certain way Daniel, right? Or what's the universe's orientation?
That's right? Is it a chocolate universe? Is it a vanilla universe?
I was gonna say, you know, bananas or pears.
Is it Marvel or is it DC?
Right?
Mm?
Yeah, And that would determine whether I like the universe or not.
Although both of those universes have villains in it, right, Which do you think actually has more Which is the darker universe?
Oh for sure, DC? Yeah. In the Marvel universe, people are more more three dimensional. I think evil has more dimensions to it.
There's certainly more ridiculous jokes in the Marvel universe.
All right, So we were talking about how maybe there is some sort of result or some sort of experimental observation that maybe doesn't look like it's random, and maybe Hints said that maybe there could be a special direction in the universe.
Yeah, and there are actually several of these measurements which together are very suggestive because they're all sort of line up to scene to prefer one direction. And the first one comes from information which should be very familiar to listeners of the podcast. It's the cosmic microwave background radiation. This is light that comes from the very very early universe. Remember when the universe started, it was very hot and very dense, but it was also very opaque. It was sort of like the center of the sun. When things are really hot and nasty. Then light gets absorbed by other molecules as soon as it's made. But then the universe expanded and it cooled, and at some moment, around three hundred and eighty thousand years after the Big Bang, it cooled enough to become transparent. And so the cosmic microwave background radiation are those photons that were created at that moment, the first moment the universe was transparent, and are still flying around the universe today.
Yeah, like if you point your antenna anywhere in space, you sort of get a hum, right, you get a little like a static hiss that it actually turns out to be from the Big Bang.
Yeah, And the universe was super duper hot back then. It was like three thousand degrees kelvin. But in the fourteen billion years that those photons have been flying around, the universe has expanded and so they've been sort of red shifted. They've been pulled into longer wavelengths, which we then translate into a temperature. And so the temperature of the CMB is around two point seven kelvin, and so it's very very long wavelengths, which is why like you can't see the CMB with your eyes. You need a special antenna. And it was discovered, you know, several decades ago. We have a whole episode about it, and it was really nice piece of evidence that the universe was at one point a very hot and dense plasma.
But it's not like a perfectly smooth picture. It is kind of like bumpy and lumpy, and it has a certain texture to it. If you point your intenna in one in some directions, the sort of the sky feels hotter than other spots.
Yeah, And it's a great way to visualize what we mean by the universe being like smooth and isotropic, because if you look at the CNB, there are variations in it. There's little spots that are hotter and little spots that are But that doesn't mean that's any preferred direction. It just means that there are some random quantum fluctuations in the early universe over this smooth background, and those fluctuations are exactly what led to you know, like a galaxy forming here or a supercluster forming over there. These were like the seeds of structure of the later universe, and so we study this in great detail to understand exactly how the universe formed, and those seeds of structure really controlled the rest of the evolution of the universe. So it's super interesting to look at that, and that's sort of the scale on which we study the universe to understand whether it's smooth. We'd like take a big chunk of the CMB and say, is this on average the same as another big chunk of the CMB. So mostly it's very smooth, but you're right, there are these variations like one part in one hundred thousand where spots are a little hotter.
Or a little colder, right, and you sort of look at a picture of it, it sort of looks like a camouflage pattern almost in a way, right, Like it's sort of blobby, and it has these kind of texture to it.
And that's when that has been exaggerated.
Right.
If you just looked at a plot of CMB on a normal scale, it would look perfectly smooth. It's only when you like really zoom in or you exaggerate these fluctuations that you can even see them. And we've been sending satellites up into the sky to sample it for decades now, and we started out looking like a very fuzzy picture of it, and then clear and crisper and crisper, and now we could see it like with really high resolution and great accuracy. We can measure all these ripples, and it allows for incredible studies of the nature of the universe. The shapes of those fluctuations tell us about like how much dark matter there was back then in the early universe, and how much dark energy there was, and how the universe has expanded since then. It's an incredible treasure trove of information about how the universe looked back then at the very beginning, and how it's evolved in the meantime.
Yeah, and so it's sort of textured like a camouflage pattern, and so which sort of varies locally in like a small spot. But if you sort of step away from the camouflage pattern, it all sort of generally looks the same, or it looks of homogeneously kind of a textured. But I guess here you're saying that maybe there's a larger a symmetry to it, like maybe some areas of the sky are differently texture than other areas of the sky.
That's right. It turns out there is a little bit of an asymmetry. If you look at the top half of the sky, that is the part of the universe that's like above the plane of the Solar System, it turns out to be a tiny little bit colder. Those photons have a wavelength that's a little bit longer, and if you look down sort at the bottom half of the Solar system, then that portion of the sky is a little bit hotter, those photons are a little bit bluer.
Well, that makes sense, right. Australia is a little bit hotter.
In general, it's so hot it's heating the entire universe.
I'm just kidding. But wait, when you say like the top half and the bottom half, do you mean like the north, like if you look in the northern hemisphere of the sky, or do you mean like some other direction?
I mean roughly the north, But I'm talking about relative to the Solar system. So the Sun has a north pole in a south pole, and the planet's orbit around the Sun in a plane that's perpendicular to the Sun's north pole and south pole.
I mean, like the disc that where all the planets are spinning. It sort of forms like a plate.
Yeah, it forms a plate, and the Sun's north pole south pole goes like straight up and down through that plate, and the Earth moves along that plane. We call it the ecliptic. The Earth is a little bit tilted, so the Earth's north and the Sun's north are not quite aligned. But when we study these things about the universe, we try to orient ourselves relative to the Sun or to the center of the galaxy, rather than to the Earth. It turns out that the cosmic microwave background radiation in the Sun's northern hemisphere, that is the portion of the universe that's like above the plane of the Solar System is a little bit colder than the rest of the universe below the Solar System.
Interesting, and so we're sure it's not like an error in measurement, like maybe they're using different units done in Australia or Argentina where they're measuring this or No.
It's definitely a real thing. It's super fascinating, and there's two things to understand about it. One is like, what does it mean? And the other is what does it mean that it's oriented with the plane of the Solar System? Like it's not necessarily a huge surprise that there is an asymmetry, because you can interpret this as the Earth or the Solar System at least moving through the cosmic microwave background radiation. Like the universe doesn't have to have a preferred location or a preferred direction or velocity. But the stuff in the universe, that plasma that made that light fourteen billion years ago, it was somewhere, It had a location, It had a rest frame, a place where you could say, okay, I'm at rest relative to that plasma, and so then you can say, well, you can be at rest relative to this cosmic microwave background radiation, and it turns out that we are sort of moving through that radiation, which red shifts some of it and blue shifts other parts of it.
Right.
It's almost like if you were running really fast towards a flashlight being pointed at you, you would see the light slightly not perfectly white, but a slightly different color. And if someone was pointing a flash light and you running away, you would also when you look back, see that light slightly shifted in color.
Yeah, And so it's nice to think about the cosmic microwave background radiation as sort of a cosmic rest frame, something against which you can measure your velocity. That doesn't mean the universe has a restrame, right, It's just like these things do exist there out there, there are shining lights at us, and so you can measure these Doppler shifts, as you said, these red shifting and blue shifting, and so we are moving through the CMB at like three hundred and seventy kilometers per second.
Yeah, it's almost like there are flashlights pointed at us from every direction. That's kind of the CMB, right, And so if we're moving with and then we're going to see some of those flashlights a different color than the ones, for example, behind us.
Yeah, I think it's a point of confusion here. A lot of people write in asking like why is it we can see the CMB right now and not earlier or not later? And I think the conceptual idea here to unpack is that the CMB was everywhere. This plasma filled the whole universe and generated light in every direction. What we are seeing now is just the portion of it which happens to be arriving right now. So, as you said, imagine people shining flashlights fourteen billion years ago in every direction, which flashlights would we see right now? We'd see like a shell of flashlights that are super far away from us that happened to arrive right now. As time goes on, we see a different slice of the CMB, So we don't see the whole CMB. We see sort of like a spherical shell of it at any moment.
All right, So us moving through this radiation this light would explain why it feels cooler and hotter on one side of the Solar system north pole or not. But that doesn't mean that the universe has a preferred direction. It just means we're moving through it in as certain direction.
That's right. The weird thing is that it's aligned with the plane of our solar system, Like why is that the CMB having some rest frame in us moving through it? No big deal? Why are we moving through it exactly aligned with the plane of our solar system because our solar system, you know, has no connection to the CMB. It just is what it is. It's not even that well aligned with the plane of our galaxy, which is not well aligned with the CMB. So it's a little bit odd. It's like strange, maybe a coincidence, maybe not, that the plane of our solar system is aligned with this other cosmic plane.
Well, if it's not a coincidence, what else could it be.
Well, that's the question. Like, if it's not coincidence, it needs to have some explanation. There needs to be some mechanism that says, like, all right, the universe has a preferred direction which causes both of these things to line up in this direction. If you didn't know what a compass was, and you saw two compasses and they're like, oh, look, the red arrows are both pointing in the same direction. I wonder why. Then you've got to dig deeper and find some like mechanism that explains what aligns those two in the same direction. And so we're just the beginning of like understanding what that might be. You know, large scale gravitational effects on the outside of our observable universe could like distort the whole universe in a way that makes things aligned in this way.
For example, Uh, I think I see what you're saying. You're saying that the fact that we see the CMB colder in one direction and harder in another direction, it's not evidence that the universe is somehow biased. It's the coincidence that our solar system is aligned to this direction. That's the weird thing. Like maybe whatever caused us to be moving in that direction and whatever caused our solar system to be pointed in that direction, maybe it's somehow related.
Yes, and it's a little weird, and you might just brush it off and say, like, oh, it's just coincidence whatever. They both have to have a direction. But there are other things aligned with our solar system that have been like slowly piling up the coincidences enough that people are like, hmm, maybe this.
Is a thing, all right, yeah, so what are those things?
Well, a second one also relates to the CMB, because people were wondering, like are we moving relative to the CMB, or is the whole universe moving relative to the CNB, Like is the entire current existing stuff in the universe is that at rest with respect to the CMB. So people tried to make another measurement of our velocity independent of the CMB. They try to measure the Earth or the Solar system's velocity relative to the whole universe of stuff that exists right.
Now, you mean, the stuff that we can see.
The stuff that we can see. Yes, And so instead of using the CMB, they're like, let's look at the stuff that exists right now, the stuff we can see. So what they did is they looked at a bunch of quasars. These are very energetic black holes the hearts of galaxies and black holes of course are themselves dark, but these black holes are so powerful they have millions or billions of times the mass of the Sun that they create incredible radiation around them because of the tidal forces causing friction in the gases that are falling into the black holes. So these are some of the brightest things in the universe, which is really helpful because then you can see a lot of them, and you can see them really far away, and you can see a distortion in them because if they're like shifted in one frequency or shifted in another frequency, you can use that to measure our velocity relative to these quasars. So people ask this question. They're like, are we moving relative to like all the quasars that we can see out there in the universe.
I see, trying to get a sense of like in the observable universe, are we moving left right?
And what they found is that we are moving relative to those quasars. We're moving around six hundred kilometers per second relative to those quasars, which is a big surprise. First of all, people are like, what why are we moving so fast relative to like the a stuff in the universe.
But when you say we're moving, do you mean like our solar system or our Milky Way or our galaxy cluster? What do you mean?
I mean our solar system?
Okay, but don't we know how our solar system is moving relative to the Milky Way?
Yeah? Absolutely, we do, all.
Right, So you're saying that our galaxy itself is sort of moving through the observable universe.
Yeah, our galaxy seems to be moving through the observable universe. And the really surprising thing is that it seems to be moving relative to these quasars in the direction aligned with this cmb anisotropy. That is, it seems to be moving in the same direction along the Sun's north and south pole.
Well that's a little weird, I guess, because you know, like we're spinning on Earth, and the Earth is spinning around the Sun, and the Sun is spinning around the galaxy, and the galaxy I imagine, is spinning around sort of the larger galaxy cluster. Are you saying, I guess I'm not sure quite what you're saying. You're saying, like all of those sort of velocity vectors, all those directions of motion are somehow pointing in the same direction right now, wouldn't that like, aren't we moving sometimes in this direction and that direction as we're going around the Sun or the galaxy?
Sure, the Earth is moving around the Sun, and the Sun is moving around the center of the galaxy, and the galaxy is orbiting the center of the galaxy cluster, and so each of those has a velocity and a direction relative to the CMB. Right now, we're talking about one of those in particular, which is just the velocity of the Solar system, and that velocity vector seems to point right towards the direction of the hotter part of the CMB, So that's really interesting and also seems to be aligned with the direction of those quasars. And there's no reason to think that these three directions should be aligned. They could have been anything. Now, the question of the Earth's velocity and the galaxies velocity are separate, right, those are different vectors. But the solar system velocity is aligned with the CMB and with those quasars.
Which is somehow aligned with the direction of the Solar system. Is it also aligned with the direction of the milk Is our solar system disc in the disk of the Milky Way?
It's not right. Our Solar system is actually tilted relative to the disc of the Milky Way. So this required just our solar system to somehow be weirdly aligned with this two cosmic axis, the CMB and the quasars. It's a very strange coincidence.
But I guess if we wait a few you know, one hundred years or a thousand years, wouldn't our direction change because we're going around the galaxy.
So our velocity relative to the galaxy does change as we move around the galaxy. The period of that is, you know, very very long. It's millions and millions of years. But the direction of the Solar system shouldn't change. Our conservation of angular mensum should mean that the basically the north and south pole of the Sun shouldn't change even as it moves around the center of the galaxy. The same way like the direction of the earth tilt doesn't change as it moves around the Sun.
I see, but you're saying that, then the Milky Way is moving in the same direction as our solar system is pointed at, which is the same as what we measure with the CMB.
The Solar system is aligned with the direction of the CMB, but the Milky Way is a little bit tilted relative to the Solar system, so it's not quite as aligned. And there's a third weird coincidence in the same direction.
Well what is it?
So people are constantly looking for things that are weirdly liigned, and so what they did is they looked at these spins of galaxies. You can look out deep into the universe and look at all these galaxies and you can measure which direction they're spinning in, Like a galaxy is like a little swirl, and you can tell which direction it's spinning, like is it's spinning left or is it spinning right based on the direction that the arms are sort of trailing behind it. And you can look out and you can count, like how many of them are clockwise and how many of them are anti clockwise. And you might expect if the universe is random and isotropic and no preferred directions, for that to be like roughly even everywhere. Well, what they see is that there isn't asymmetry, and they see this asymmetry again aligned with the plane of the Solar System, that galaxies you can see above the ecliptic are more clockwise, and the galaxy you can see below the ecliptic tend to be more counterclockwise swirling.
What wouldn't that be explained by the fact that you know, like you're looking at the bottoms of some galaxies and you're looking at the tops of some galaxies depending on how you look at them.
Yeah, but if they're randomly oriented, you should see the same number of clockwise and counterclockwise, like the same galaxy. If it's spinning in one direction, you'll see a clockwise or counterclockwise depending on which side of it you are on. But if they're all in random places and all in random directions, you should see the same number in every direction. It's like if you throw a million coins in a room, you should have the same number of heads and tails in every direction. Right, But we see an asymmetry. We see like more heads over here and more tails over here, which is weird already, but that asymmetry is then aligned with these other asymmetries we see the one in the CMB and the motion relative to the quasars interesting.
I mean, it's sort of like the whole toilet slashing in the different direction of the Southern hemisphere.
Right, yeah, yeah, though I don't know if that's really a thing.
Yeah, I think it is a thing, right, because we know that the hurricanes spin in different directions, right.
They do spin in different directions because of the corials. First, you're absolutely right, but I don't know if that actually controls the direction in which toilets flush. So Australian listeners let us know, but.
Don't all flush at the same time, because you're going to drain the continent dress.
You'll slow the earth spin if you all flush at the same time.
All right, Well, so there's a lot of interesting coins in this is that maybe tell you that the universe has a preferred direction. And so let's get into what this all means. But first, let's take a quick break. When you pop a piece of cheese into your mouth, or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times. The same water cools the mill, well clean's equipment, washes the barn, and irrigates the crops. How is US dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com Slash sustainability to learn more.
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All right, Daniel, here's now our favorite question. What does it all mean? Man? What does it mean that the universe hasn't preferred directions? I guess the theory is, the hypothesis is that the universe has some sort of preferred direction that is somehow making galaxies all sort of spin in roughly the same direction, and it's making our solar system roughly spin in that direction, and everyone's moving in that direction. To what does that mean?
We really don't know what it means. And mainstream cosmology is very certain that it's all just random, that it's fluctuations. They are very strong believers in the cosmological principle that the universe is the same everywhere and that there is no preferred direction. It would just be very difficult for them to give up this principle, which is precisely why it's so much fun to think about and to talk about, because it's those kind of like huge mental revolutions that are the best moments in physics. And so what does it mean. It means that people should spend some time thinking about how it might be possible to have a universe with a preferred direction and how that might manifest itself. And so the next step is to like come up with an explanation that could link all these things together and then figure out a way to test that. You know, before you get there, you got to like really make sure that these things are real. So we've done a lot of careful studies, like make sure these aren't like an artifact or some problem with the data processing. You know, that it really is real. But a lot of these things have been confirmed independently by like several different satellites, especially the CMB and isotropy.
All right, so what are some of the possibilities about what could be going on?
Well, I had a hard time finding anything that was really very credible. The only idea I could find that really wasn't immediately dismissible was the idea that there could be some like giant cloud of matter outside the observable universe. You know, we think maybe the universe is infinite. We can see a piece of it, but there should be parts of the universe beyond the things that we can see, and in principle, those could be affecting things in our universe. Like the things outside the observable universe we can't directly see, but things in our observable universe could see them that could be influenced by them gravitationally. So now imagine some like crazy collection of stuff on the outside of the observable universe that's like distorting what's happening inside the observable universe. It's ridiculous, and it would require like incredible cosmic structures and gravitational effects, but it's sort of the only plausible direction to explain.
This interesting, all right, So maybe there's a giant I don't know, kangaroo space kangaroo which is outside of our feet division that is somehow skewing the whole universe. What else could be going on?
It could also just be random, you know, it's very difficult to know what the chances of this are happening. In physics, whenever we want to conclude that something is real. We need to know what are the chances that this could have just happened by a random You know, eventually, if you flip enough coins you will see weird deviation. So we want to not conclude something deep and true about the universe if it just happens to be a strange fluctuation. In this case, it's very difficult to evaluate that because we didn't set out trying to measure this. We sort of noticed it after the fact, and it's easy to notice coincidences after the fact. That it's hard to account for all the coincidences you didn't notice. And so to really like measure what the chances are of this happening, you need to imagine, like what are all the other things you might have seen and noticed, And that's impossible. For example, somebody went through the CMB spectrum and they found that the initials of Stephen Hawking can be read in the cosmic microwave background radiation.
What graffiti the beginning of the universe.
It's ridiculous, But there is a patch in the CMB which, if you're looking for it spells out the letters S and H. You know, what are the chances of that? For example, Well, you know who can know, because you know, who knows what other things you would have looked for in the consert background radiation.
Yeah, that could be a coincidence. But then the other part of it is the part that says was here that one's harder to explain.
There was, here's a joke. The sn H really is there, Like, you can go and look for it. This is not something I'm making up. It's just an example of how things that seem totally implausible really can't just be random because it's very hard to measure. The chances of something happening.
Also depends on your point of view, Like if you look at it upside down, it says HS. So maybe it was really Harry Styles who graffiti the beginning of the universe. That guy seems eternal, you know.
And he's pissed that Stephen Hawking he's getting all of his press.
Yeah, or maybe it's all a big joke. Maybe they're the same person, Harry Styles is sleeping Hawky.
But you know, to really answer this question, you need to either develop a theory which explains these coincidences and make some prediction we could test, or you know, you need to build like another CMB telescope and teleport it to other parts of the universe to see if it measures the same things somewhere else, Because really the question we're asking is are we in a privileged location? Is what we're seeing weird? And the most direct way to answer that is to go to other parts of the universe and to make these measurements there. That's, of course totally impractical, but that would sort of like really deeply answer the question.
Right Or I wonder if it could be that also that the universe doesn't have a preferred direction, but somehow the matter and the way it formed in the universe that we are living in, maybe somehow it started spinning in one direction, just like our Solar system randomly picked the direction to be spinning it.
Yeah, although if the universe is infinite, then we would expect all those things to average out. Right that you do have clumpiness here, and you do have rotation there, but on average things should be even. And the kind of things we're measuring, you know, the spinning of galaxies across these huge distances, we do expect things to average out on those distances. They don't average out on the Solar system distance or the galaxy distance, but you know, across huge superclusters, they really should average out.
All right, Well, I think this all just kind of points to how interesting it is that we're trying to decode the entire universe from this one little spot in the corner that we're sitting on.
You know.
It's like, you know, we're sticking our finger out trying to measure the wind of the universe, but really we're just like confined to this one spot where we are.
Yeah, And it also gives you a glimpse into sort of the process of physics. When you look back on the history of physics, it seems sort of like inevitable, like we found this, then we figured that out, then we figured this other thing out. But at any moment, we're really just clueless. When we're exploring lots of different paths, some of which are totally bonkers and some of which could be the seeds of a future understanding. People could look back in these moments and be like, oh, yeah, people first found out about this crazy thing in the universe back then, and people didn't really believe it for a long time, and it took forever to take hold. That could be this idea, right, now or this would just be another in the long series of science dead ends.
I guess. In the meantime, if you're in Australia, watch your step, don't fall off, and don't flush the toilet at the same time.
That's right, keep spinning everyone, All right, Well.
We hope you enjoyed that. 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 gas emissions. House US Dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit us dairy dot COM's Last Sustainability to learn more.
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