25:11
Mars, for instance, was a habitable place. Could be that life arose there. We're all Martians. Hello and welcome to Instant Genius, a byite-size masterclass in podcast form. I'm Jason Goodger, commissioning editor at BBC Science Focus. In this episode, we catch up with science writer and longtime BBC Science Focus contributor, Marcus Chow, to talk about the biggest unsolved mysteries in cosmology. So, Marcus Chow, welcome to the podcast. Thanks for inviting me. Thanks so much for joining us. So today we're talking about the mysteries of cosmology. So why there's no question that over the years we've developed a pretty impressive picture of the
universe. But as always in science there's always lots to learn. So I thought the best place to start then we've established that the big bang was the start of the universe. But what does that mean and how did we figure that out? Well, um I to tell you that physicists or astronomers have been dragged kicking and screaming to that idea because obviously once you know that the universe had a beginning then everyone says what happened before. So most people were wedded or before the big bang idea was um proved most pe most physicists were wedded to the idea that the universe had existed forever. But basically the universe the building blocks of the universe are galaxies. two trillion of them, of which
our Milky Way where we live is just one of them. And they're all flying apart like pieces of cosmic shrapnel in the aftermath of some titanic explosion. And if we run that expansion backwards, you know, uh in our minds like a movie in reverse, we come to a time 13.82 billion years ago when everything was compressed into a small space. And when you compress anything, it gets very hot as anyone who squeezed the air in a bicycle pump knows. So the big bang, this explosion was a hot big bang. And the evidence of that is in the room where we are now because the afterglow of the big bang, the afterglow of the fireball of the big bang is all around us. So incredibly 99.9% of all the
photons those are particles of light in the universe are tied up in the afterlow of the big bang and only.1% come from the stars and galaxies. That fireable light has been degraded by the expansion of the universe to lower energies and it appears at microwave wavelengths. You know the wavelengths used by your phone by a microwave oven that kind of thing. So that's why we can't actually see it. But if we were to be out in space and we were to have glasses, magic glasses that could see microwaves rather than visible light, we would see the entire universe glowing white. Not black at all. Everything would be white. It' be like being inside a giant light bulb. Uh and that afterlow of the Big Bang, which
is the final proof that it happened, is the most striking feature of the universe. And that's still something that astronomers study now, isn't it? With special instruments. Yeah. I mean it turns out that imprinted on this afterlow is um basically the universe beginning to go from a uniform state in the big bang to a clumpy state. So today it's in a very clumpy state um you know with galaxies and big gaps in between but in the beginning it wasn't like that. So we can actually see the seeds of structures the seeds of great clusters of galaxies impressed on this afterglow. So when I said you look at the sky and it should you know appears white all over
there are slight fluctuations in that whiteness and they are those fluctuations are due to uh matter uh being slightly clumped. So we can see the beginning of the structures in the universe forming. So after that time uh anywhere that was slightly denser than average pulled in had slightly stronger gravity and pulled in material slightly faster and in a process which is kind of like the rich getting ever richer uh the galaxies like our Milky Way formed. Yeah. So I think the obvious question that someone is a curious scientist is going to obviously that's a really took a lot of really clever people a long time to figure out but you think well what happened before the big bang.
Exactly. And as I said, this is why nobody wanted to believe in the big bang, you know. I mean, they really the prevailing idea, the competing idea was you've probably all heard the steady state theory which would been promoted by uh the British physicist Fred Hy. This said that the universe has basically existed forever and you know which if that's the case, you don't have to worry about the beginning. M but of course once we were began to be able to look a long way across space so when we light actually is incredibly fast but on cosmic uh distances it kind of crawls like a snail towards us you know so when we look at very distant objects billions of light years away we're seeing them as they were billions of years ago and the
steady state predicted that the universe should look exactly the same back then as it does now but it doesn't there are things for instance called quazars which were discovered in 1963 3. These are basically super luminous galaxies which are pumping out hundreds of times more energy than a typical galaxy. We now know they're powered by super massive black holes and they existed in the past but they don't exist today. So they were the proof that the universe has actually changed and it's evolved. So how about this idea of inflation? Um sort of eternal inflation as it's called. Yeah. Well, okay. So we have this basic big bang that we know is true, right? We know that the universe began in a hot
dense phase and has been expanding uh and cooling and the galaxies congealing out of that cooling debris. We know that's true. We know that's true because of the existence of the fireball radiation, what we call the cosmic background radiation which is everywhere. So we've got the evidence of that. But the big bang theory um conflicts with our observations in three major ways. So you just mentioned one of them, but I'll just quickly say that we need an awful lot of what's called dark matter, invisible stuff that's uh has, you know, we can feel it gravity, but we can't see it. And we also need you another thing called dark energy, which we often cover in science focus. Um stuff with repulsive gravity
that fills a lot of the universe. And a third thing you have to So basically you have this big bang model which is hot dense phase um you know universe expanding and cooling. we have to bolt on dark matter, dark energy and as you say inflation and the re the reason for inflation is um so I say inflation was a kind of super fast expansion that happened before the big bang. So if you imagine like the explosion of a nuclear bomb compared to a stick of dynamite, the nuclear bomb would be inflation and the explosion of the dynamite would be the sedate inflate expansion that's taken over since. The reason we need this is because when we look at this after go of the big bang, you know,
the whole sky appearing white, there are correlations between bits of the sky which are 180 degrees apart. But if we run the expansion of the universe back to the time when that radiation was formed, um about 380,000 years after the moment of creation, we find those regions could not possibly have been in contact. there was no way that any signal could have gone between them. So, how do they know to be at the same brightness, the same temperature? So, what we've realized is there had to been a super fast expansion very early on. And so, um that would mean that these regions would have been in contact when we don't think they were. And this is inflation. So, inflation, if you want the real description, it's of it's a really
unusual state of the vacuum. Okay? So, the vacuum we think of is empty. But in quantum theory, the vacuum is not empty. But this is a weird state of the vacuum with actually repulsive gravity. And this repulsive gravity causes this vacuum to expand. So in the beginning there was literally nothing but this vacuum. It's called the force vacuum or the inflationary vacuum. But it expanded u because it had this repulsive gravity and it created more of itself. So it's like the ultimate free lunch. You know, you've got a you've got some banknotes between your hands. You move them apart, you get more banknotes. So, basically, inflation creates more and more of this vacuum for free. And but as it
expands, it's what we call a quantum thing. And quantum things are unpredictable. And so all over the uh this expan ever expanding faster expanding nothingness, little tiny bits decay into normal vacuum. So the vacuum that's all around us today. And all the energy of this higher uh inflationary vacuum has to go somewhere and it goes into creating matter in these tiny little bubbles forming everywhere. And that matter is heated to millions of degrees. Those are the big bangs. So in this picture, the big bang is not a one-off. There are big bangs going off all over this inflationary vacuum like kind of like fireworks just going off all over the place. And we just happen to be in one
of these big bang universes. And that's sort of uh one of the ideas of the multiverse which is known as the bubble universe. Is that right? Exactly right. So if we're in one of these bubbles, it turns out that the vacuum between us and the next bubble is basically expanding so fast that we can never ever have contact with that. So in effect that's another universe you know and uh so uh and this inflation unfortunately goes on forever because if you imagine these little bubbles are forming imagine it's like a moth eating coat right so the moths and the coat is expanding the moths can't eat the coat fast enough you know as fast as
they eat the coat more of it expands so this inflation goes on forever and creates all of these disconnected bubble universes, big bang universes. Yeah. So, so it does actually force on us the idea of the multiverse and that is a real downer because the idea of inflation was that it was going to give us a theory of everything, not that we're going, you know, one universe, one explanation, not we were going to have this infinity of universes. So, let's go on to you mentioned there dark matter. Yeah. So, this is another thing that's um just been a mystery for decades now, isn't it? So um how did we first come across it and you know where are we now?
I think you can actually say a century because the first person who realized that there had to be a lot of hidden stuff was Fritz Wiki uh a Swiss American physicist in California. But yeah so everywhere we see evidence of the visible stuff being pulled or pulled by the gravity of something invisible. But the main reason for dark matter is that without it we couldn't possibly be here. The big bang predicts that we shouldn't be here. So I told you that there were these slight um density enhancements in the big bang fireball and because they were slightly enhance they had slightly stronger gravity they dragged in material faster. As I say the rich getting richer that kind of process. If you think of that process, it would take 10 times the current age
of the universe to make our Milky Way. Okay? So, we cannot possibly exist unless there is an enormous amount of other stuff whose gravity speeded up that process of gathering matter together. So, it's it's roughly this the dark matter, the invisible stuff outweighs the visible stuff by about a factor of six. Yeah. And um we still haven't figured out what this is, have we? There's been dozens of theories, wimps, um you know, tiny black holes, all sorts of things. So, what the current what do you think the current top contenders are? It's just really hard to know. I mean, there have literally been hundreds of proposals. You know, this stuff, which is clearly in this room with us now, um uh but we can't we it doesn't interact with ordinary matter. Um
it could be just give out very little light or it could give out no light. Uh and as you just alluded to um many theories of particle physics do predict the existence of stuff. There's a theory called super symmetry that predicts a whole load of new particles. But all searches at the Large Hadron Collider in Geneva uh in laboratories stuck down mines all over the world have failed to find absolutely anything. Basically, you got to wait until some bit of dark matter bumps into something that your, you know, your detector and note the vibration or something like that. That's what you got to do. But since we've got no idea what the dark matter is, you know, there's a um very difficult to look for it and as you say, all earthbound
experiments have completely drawn a blank. So, we don't really have uh much of a handle on it. But interestingly, you mentioned black holes there. And the very interesting thing about black holes is of all these hypothetical things, we know they exist. So in my mind, they are the least outrageous possibility for the dark matter. But we've done these searches called macho searches. There's a process called gravitational lensing. So, so when we the light of a distant galaxy goes past a mass, it's kind of bent and focused and we can see this effect. Uh, and we've used this effect to search for these things called
massive compact halo objects. You know, could the dark matter be made of asteroids, dead stars, black holes? And the searches have actually um drawn a blank. So there is still a possibility that black holes could be the dark matter but there's a very small window uh of mass range where they could possibly exist. Yeah. So let's go on to black holes then another really fascinating topic. So as you said a bit back the event horizon telescope actually made an image of a black hole. So you know we know that they're out there. Um so what is a black hole? Well, I mean a black hole is a region of space where gravity is so strong that nothing not even light can escape. So incredibly uh at the height of the uh first world war
Einstein um presented his new theory of gravity in Berlin um in a series of four lectures in November 1915. Um and I should tell you that he realized that gravity is the curvature of space. We can't see it because it's the curvature of four-dimensional spacetime and we are threedimensional beings. We can't see it. So that's why it took the genius of Einstein to realize it. So you think the earth is held going around the sun on an invisible held on an invisible tether between the sun and the earth, you know, gravity. But in fact, the sun makes a depression or a valley in the spaceime around it and the earth goes around the outer uh regions of this valley like a roulette ball in a roulette wheel. And I just should
tell you that Einstein replaced the one formula that Newton had to describe gravity with 10. So finding the curvature of space which is gravity for any realistic mass he considered impossible. But within a few weeks a man working uh on the western front on the Alsas front at a place called Mole House um found a solution found a description for the spaceime around a compact mass. His name was Carl Schwarzfield and he wrote this letter to Einstein and Einstein was amazed to get a letter from the Western Front and even more amazed to find that this thing that he thought was impossible um was you know was possible. But Schwarz should hadn't finished. The beginning of 1916, he wrote to Einstein. He said, "If this if
this um if the mass became ever more concentrated, the valley of spacetime would become steeper and steeper until it became a bottomless pit from which nothing or even light could escape and that's a black hole." So Schwarz is the person who discovered that they but then there follows an entire century where pretty much everyone thought these things cannot possibly exist. I mean they are just too ridiculous. Einstein never believed in black holes because if the there's nothing to stop once the mass starts shrinking under its own gravity there's nothing to stop it and it will shrink down to a point it become infinitely dense this is called a singularity and when you get a singularity in a in any theory it tells you your theory is
broken you've got to you know you can't say anything sensible so that's why Einstein hated this black hole solution because he spent 10 years of blood and sweat developing his new theory of gravity, he didn't want to know within a few weeks that there was a flaw in it, you know, but you know, nature has despite the fact we thought they can't possibly exist these things. We have actually confirmed that they do. The actual definitive evidence was the signal on the 14th of September 2015 when gravitational wave detectors in America. So these detect ripples in the fabric of spaceime um detected gravitational waves from the merger of two black holes and the signal that they got was the definitive signature. But as you say in
an event horizon telescope which is eight radio dishes spread over the planet. There was one in Antarctica, one in Mexico, you know, all over the place. they uh jointly um observed the same object which was a galaxy called M87 uh and which we believe had a 6.5 billion solar mass black hole in the center and the signals from all these telescopes are all identical were flown together to supercomputers in uh haststack in Massachusetts and barn in Germany and they on a computer we were able to get the image we would have had we had a telescope the size of the earth and the bigger the telescope the finer the detail you can see and we got that amazing image of this donut this glowing orange donut of material
swirling down onto this black void which was the black hole. Yeah. In the office we call it the eye of Sauron. It is like the eye of Sauron. Yeah. But it took three more years to actually image the black hole at the center of our galaxy which is called Sagittarius a star that was discovered in uh 51 years ago. And um if I it's bizarrely it's a thousand times smaller than the one in M87, but it's a thousand times nearer. So the two objects look exactly the same size on the sky. But the reason it took so long is because it's so much smaller. Stuff whirls around it much, much faster. So it's kind of like very easy to photograph an elderly Labrador sleeping on your lawn because it doesn't move much. But try photographing a puppy
that's that's that's flying about. The puppy's kind of Sagittarius A star and the Labrador is M87. So you mentioned there that um a black hole not even light can escape from. So the big question then is what's going on inside it? Well, I mean this is one of my bug bears because uh in 1963 uh Roy K who he's still alive. He's he's 91. He's a New Zealander. He's still publishing papers. Uh and he did something that everyone thought was impossible. He found the shape of the curvature of space round a spinning black hole. So a realistic black hole and it was the first solution to Einstein's equations for 47 years. Uh and he then thought to myself self, I need to find out what's what's the curvature of space inside the black hole
and he gave up. It's impossible. So it's not been possible for anyone to use Einstein's theory to predict what's inside a black hole. So everything you hear, you know, oh my god, you know, if you go into the center of the black hole, you're appearing another time. You're here in another universe. This is all complete speculation. We have no idea. Uh I mean the theory predicts that there is a singularity which is a point of infinite density and for a spinning black hole that's actually a circular thing. It's actually a circular singularity. Um, but we know that singularities are impossible. So, we're waiting for what's called a quantum theory of gravity because we think that Einstein theory breaks down and we
need a better theory. Uh, but we haven't made much progress there. But that will tell us what's actually at the center of a black hole. I should tell you that outside a black hole, space and time are highly distorted. So, as you get near the black hole, uh, in strong gravity, uh, time slows down. So if you would see someone falling into a black hole um they would be moved more and more in slow motion as they got closer to the point of no return which is called the event horizon. You know uh that person they would cross the event horizon into the black hole quite quickly but it from your point of view outside it would take forever. Uh and bizarrely this
distortion of space and time becomes even more ridiculous when you cross the horizon because the direction of space and time switch. So the direction to the center of the black hole is no longer a distance in space. It's a distance in time. So you can't avoid the singularity for the same reason you can't avoid tomorrow because you can't. It's in the future. So let's have a look at gravity then. We mentioned there that this idea of quantum gravity um and we've got um the standard model of particle physics uh the three forces that explains the strong force, the weak force, the electromagnetic force and they all have a particle associated with them. Um and we found those you know there are several in some in the weak force for example, aren't
there? But um when it comes to gravity there's we haven't been able to find its associated particle. So what's the idea behind that and why is that so tough? The reason for that is that gravity is unbelievably weak. You know it's one followed by 40 zeros weaker than the electric force that is holding together the atoms in your body. is it is so weak that I can hold my arm out and the entire mass of the earth with all of its gravity cannot pull my arm down. I mean that's how weak gravity is. So in terms of um you're talking about the other forces they have a quantum explanation. So we imagine that the forces arise because of an exchange of what we call force carrying particles. So as you say with the electromagnetic force that glues
together the atoms in the bodies it's it's change of photons and with gravity it's gravitons and weakness is associated with infrequency of interaction. So it means that those because it's so weak the gravittons hardly ever interact you know uh and when you do a calculation Freeman Dyson that the British physicist who lived in America most of his career he did a calculation and I think he realized that you would need a detector the size of Jupiter operating for more than the age of the universe to expect one graviton to interact with it. So I don't think we're going to I mean there is a lot of interest now in incredibly in maybe tabletop experiments that might be able to yield
evidence of gravitons. But we have every reason to believe that the gravitational force just like the other three has a quantum explanation in terms of the exchange of gravitons. It's just weird that um uniquely gravity can be described as geometry. Okay. So, because everything falls at the same rate, you can imagine it's all falling, you know, in the same curved spaceime. You can't do that for the electromagnetic force because the force that's experienced by a mass depends on its charge. So, that's a different geometry for every charge. But in the particular case of gravity which is a universal force that affects every
single um mass the same there is this geometrical explanation but that doesn't necessarily mean that there isn't a quantum explanation as well. H so a sort of another big mystery that um physicists particle physicists and cosmologists have been trying to figure out is the fact that where is all the antimatter because the theories say that there should be essentially equal parts of matter and antimatter but there's way more matter than antimatter. Yeah. Well, first of all, we ought to say that one of getting back one of the really shocking aspects of modern science is that only 5% of the universe have we seen. Okay, so the majority to 95% is this dark matter and dark energy.
We don't actually know what it is at all. And the 5% is made of atoms. So we, you know, we really haven't really seen much of the universe. But as you just said that 5% should come in two types because every single experiment we do with particles when we generate a particle of matter we automatically generate a part particle of antimatter. So the electron has a partner called the posetron which has particular significance to Bristol where science focus is based because Paul Durk the Bristol physicist is the person who predicted dark matter in 19 not dark matter antimatter in about 1928. Um but yeah so um there is a clue to where the antimatter is and that is there are 10 billion photons in the universe particles of light for every
particle of matter. Okay so that tells you that because when matter and electrons and posetrons meet they annihilate and end up as photons. So that tells you that in the beginning for every 10 billion particles of antimatter there were 10 billion and one particles of matter and then there was this allg of destruction and all and pretty much all of it turned into photons leaving this just one particle per 10 billion of matter. So there's a tiny asymmetry in the laws of physics which must have resulted in all the antimatter uh vanishing. And really when you think about it that has to exist because if it didn't exist there would be no universe because all matter would have been destroyed and annihilated if there was equal
amounts of anti-atter and antimatter. So the person who actually um really discovered what has to be part of the solution is a woman called Cheng Woo who was scand scandly overlooked for the Nobel Prize in 1957. She did this tremendous um experiment which everyone thought was impossible and she found that there was a skewess to the laws of physics that the weak interaction the weak nuclear one of the three four forces called the weak force the weak force um behaves differently when it pulls on particles which are spinning one way to the other way. Okay. And it's called parity u violation. And there were great physicists of the day like wolf going pow bet their house that it couldn't possibly exist and she proved
it was correct but the two theorists who predicted it won the Nobel prize and she didn't get a share but somehow the solution has to involve that. So either there was a process in the big bang that produced a surplus of matter over antimatter or there was a process that destroyed antimatter preferentially but we haven't found it yet. So um let's finish up with a classic sci-fi favorite then the search for alien life particularly intelligent life. Yeah. So, a lot of people say, "Well, if it exists, surely at least if we hadn't found it, it would have found us." So, what's the idea there?
Well, it is a puzzle, isn't it? You know, um why we haven't seen any but it's a big universe. If you look at life on Earth, you see that it got stuck at the single cell stage for a long time, about three billion years, something like that. And only in the last about 800 million years or 500 million years has it become complex. And that kind of implies that the step from single cell life to complex life like us is a difficult one. So that the it could be and we're this is a problem that we're arguing from one instance which is very difficult. It could be that there's a lot of life in the universe but it's very simple. you know, it's only single if it's like glows, it's single cell organism and there may not be much intelligent life. Um so we haven't seen
any sign but I mean I just remember that one of the great books that got me interested in physics and that was Carl Sean's the cosmic connection and I remember him saying that there were tribes in New Guinea uh who lived in separate valleys uh and they spent their lives in these separate valleys and they communicated with big drums and he said if you'd asked them how would you communicate with an advanced civilization uh you know a few valleys the way they say use a bigger drum and we are using radio waves you know which we've only been using for a century um almost certainly other forms of communication might be used by extraterrestrials and um you know we are just thinking well we'll just get a bigger radio
telescope you know uh and try and pick it up. So it could be that the extraterrestrial communication is whizzing through us at this very moment and we don't know. But another interesting idea is from Steven Wolfram. Steven Wolram is a uh um he's a physicist from London. He's a billionaire because he invented a computer language called Mathematica. Uh and one of the questions is you know where are they? Um and he thinks that if you look at our communications, they become more and more chaotic. Okay? So to squeeze more and more information into our radio communication, we make them more we there's less and less pattern and so our signals, if you look at our phone communications and whatever, they're looking more and more like
natural sources like the sun. So, you know, we're looking for the interstellar equivalent of radio one. You know, we're looking for a single carrier frequency that's modulated, but that may not be the way anyone is communicating. So, there's lots of possible explanations, but uh I'm pretty certain that there well, I'm pretty certain we'll find evidence of life in our solar system. I'm pretty certain of that because of the simple fact that there are meteorites that arrive on Earth from Mars. You know, something's hit Mars. A meteorite has been uh, you know, ejected into space, circled around for a few
million years and fallen on Earth. And it's possible for u simple organisms like bacteria to survive inside this. And Mars, for instance, was a habitable place about a billion years before the Earth or half a billion years before the Earth. We see evidence on the surface of rivers and seas. So it could be that life arose there first and came here that we're all Martians. But certainly interplanetary span panspermia the idea that simple life could spread between the planets and uh is quite likely and we can see quite a few places in the solar system where life could arise in particular the subse Jupiter's moons or Ganymede um Europa Kalisto maybe and then of course Saturn's moon uh Titan uh Triton
around Uranus there's quite a few places in the solar system where we could find life. Mind-blowing stuff. Thanks for joining us, Marcus. Thank you. It's been a pleasure. Thank you for watching this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Marcus Chow. To discover more about the topics we've just discussed, check out his latest book, A Crack in Everything. If you liked what you just saw, then please do consider liking this episode and subscribing to our channel.
