What Happened At The Beginning Of Time? - with Dan Hooper

Thank you, thank you all for coming. I want to start by saying that it is really exciting to see a room so full of science enthusiasts, at least in my country, people constantly lament about the lack of public support or interest in science and yet when I go out to give talks like this everyone shows up so they are wrong and thank you for helping me prove them wrong tonight so when you think about history people of all

time

s and all cultures have something in common they all looked into the night . sky and everyone was wondering about their universe and how it came to exist.

In this sense, we have a lot in common with our ancient ancestors, but in some ways we are very different, in fact, we are different because we live in a very special

time

. in history where for the first time when we look at the night sky we understand more or less

what

we are looking at, it is a privileged moment in this sense, take this image, for example, this is an image from the space telescope called Hubble. It is part of the program we know as the Hubble Deep Field. Most of the spots you see in this image.

These spots of light are images of galaxies similar in size and shape to our own Milky Way, but because it takes time for light to travel through space This image does not accurately represent

what

those galaxies look like today, but rather what they looked like more than 13 billion years ago, just a few hundred million years after the Big Bang, our universe was a very different from then, it is much more compact and much hotter. It's full of different kinds of things and we understand more or less how and why it has evolved and changed into the way it has to become in the universe we live in a little over a hundred years ago, physicists didn't even have the slightest We had no idea how to ask these types of questions let alone how to answer them, we had no idea how our universe had changed, evolved or started, in fact we didn't even know how to ask a question like how space could change, we thought space was immutable. backdrop something through which objects could move but we never used verbs in connection with space space never did anything in Newtonian physics but we now think of space as something that can change and evolve expand contract deformation curve and we can think that the change or give thanks for that change to the ideas of Albert Einstein then he thought that it was he who taught us that space was more exciting than the static backdrop that Isaac Newton told us about in 1915 with his theory General relativity taught us that space can change, it can do things, it can be dynamic, and in fact, you can use these equations that he published in 1915 to show that the space that makes up our universe can do many things, but it cannot remain the same if you take those equations and imagine a body of more or less uniform space filled with a certain amount of matter with which you invariably, without exception, fight, it has to expand or contract and in 1929 the great astronomer Edwin Hubble observed for the first time that Our In fact, the universe is expanding, points in space are moving further away from each other as time progresses, causing the universe to become increasingly colder, less dense and larger than it was. in the past, so I guess everyone in this room has heard at some point that space is expanding that our universe is expanding over time, but my other guests is that most of you don't really know what that means , you are probably imagining a situation where there are a lot of things in space or a part of space. slowly moving out of it occupying a larger volume I want to remove that image from your brains that's not what cosmologists mean when they say space is expanding what Hubble really saw through his telescope in the 1920s was that All the galaxies I could see were moving away from us, and the farther away a given galaxy was, the faster I observed it moving away.

Now it's possible that that data is consistent with the idea that we were in the middle of a big cosmic explosion—everything is just moving. far away from us, but in fact that is not the case if you look at the universe as a whole combining all the data that we have, what you find is that if you were in a different galaxy and you looked at your neighboring galaxies you would see the same thing Hubble did everything, moves away from all other points in space all the time, if you're like most people you're probably asking yourself what seems to me to be a very predictable question in this day and age, they're predictable guys, I've given enough talks like this to know that's probably what's going through 7-3 80% of your minds right now and you're wondering what space expanding to the right is, show me your hand if you're wondering that, yeah, okay, ya I told him.

It's a reasonable question, but it doesn't have a good answer, it doesn't have a good answer because if space expanded into something, what would we call that something? Space. Well, that's not what we mean when I tell you that space is expanding. When cosmologists say that space is expanding, what they mean is that all of space, not some part, is expanding. The volume of any face piece is greater in hell than in the past and will be even greater in the future if you have a It's hard to imagine space expanding without something to expand into.

I'll teach you a trick. This is something that occurred to me when I was a graduate student and I was struggling with these ideas as I imagine many of you are doing now. The mind trick involves this, so I say: I look at this room. I want to measure the size of this room. So what I do, I find a three-foot stick. I run there. I leave the meter stick one after another until I find it. It turns out that this is, you know, 15 meters from side to side. I waited a bit while I do it again.

I made the same similar measurement, but this time I find that 16 meters are needed. Links How do I interpret this information live? Two ways you could do it. I could say ah, I just measured that the room is expanding, it's growing over time, or equally well, I can say ah, the meter is shrinking, both of which are completely compatible with the data I just described, but I could imagine objections that we could say, well, you can tell if this meter is shrinking by comparing it. I can go here and see if this requires eight feet or eight feet or something and that changes because if the foot is shrinking, then you could tell. comparing it to other things, so I say, okay, I'm going to refine my hypothesis by saying that everything in this room is shrinking in unison, which will look like the room is expanding, so let's return this to cosmology if you don't mind.

If you are comfortable with the idea that space expands without expanding into anything, you can instead conveniently think of everything in space, including constants like the speed of light, contracting at the same time, so if the space is expanding, which it is and has been for a long time, we can deduce that in the past and the given space must have been smaller and since it contains the same types of matter and things, it must have been denser in the past and when you take a particle gas and compress it, it heats up, which is why Hubble's observation took place.

With its profound implications for our past universes, this is at the heart of what we mean by the big bang theory, the idea that over billions of years our universe expanded and evolved from a dense, hot state into the universe that we see around us today. When you think about the Big Bang or what it is usually described as, you are probably tempted to imagine something like a cosmic explosion when someone says that the temperature one trillionth of a second after the Big Bang was something like the density one minute after the Big Bang. Big Bang.

The explosion was whatever or the nuclear fusion took place one second after the Big Bang. You might think it

happened

somewhere in space. That's not what we mean when I tell you that the Big Bang had a certain temperature, the universe had a certain temperature right after the Big Bang, what I mean is that all of space, the temperature was everywhere, those densities They were everywhere, there were mind-blowing extreme conditions that the Big Bang describes as a state that persisted throughout space, everywhere in the universe, it's not an explosion, it's not an event. It's not a location, it's not an object, it's a state our entire universe was in 13.8 billion years ago.

Okay, so let's take a step back and walk through a timeline of the cosmic history of our universe so that on this scale we see a couple of key events. You can start a couple of hundred million years after the Big Bang, that's when the first stars start to form. Those stars were quite different from the ones we see in our universe today. The first stars were much larger and had shorter lives. They were very hot. volatile objects and exploded in a short period of time seeding the conditions for the next generations of stars to begin for it, we are only now acquiring the technology that we believe will be necessary to image some of these stars to see the first images of these stars with Our telescopes, something like 9 billion years later, our star, the Sun, and the various planets formed to form our solar system and then, over the next five billion years or so, after those four Approximately one and a half billion years ago, life evolved on Earth. and if you look at that image, all of human history is contained in about one pixel, in this sense humanity has played a very insignificant role in our cosmic universe in other ways, of course we play the only important role, so there is no nothing wrong with this timeline.

OK, not bad, but cosmologists look at this and say it's a really boring way to describe the history of our universe. It's a terrible way to show it because all the most interesting things

happened

far to the left or at the extreme. You can't see the left side on this scale, so let's rescale it instead of showing it on a linear axis, let's make it a logarithmic one so that now, when you stretch everything out to powers of 10, you can look back to much earlier times. . Getting closer to the Big Bang in particular you can see the special moment about 380,000 years after the Big Bang when the first atoms were formed.

This transition was really important for many reasons that I will explain, but the reason it happened had a lot to do with the temperature of the universe today, our universe is filled with a radiation background that is only two point seven degrees above the absolute zero, very, very cold, but if you step back, compress that radiation, the expansion of space done in reverse makes those photons shorter and hotter. If you go back to this point 380,000 years ago, you will find a point in our history where the entire universe was filled with a 3,000 degree background radiation, this is comparable to the surface temperature of a red star, okay, but It filled all the space.

It is not just any temperature, it is particularly important because it is what I like to call the melting point of atoms. what do I want to say with that? I mean if I take a box full of a gas with some particles, there are some particles. atoms, it doesn't really matter what type and I started heating them right when they got to 3000 degrees, the electrons would start to fall out instead of having a gas of electrically neutral atoms, you would have a plasma of electrons, protons and other nuclei, so in the history of our universe before this transition, the universe did not contain any atoms, but instead consisted of electrons, protons and other nuclei and then, around 380,000 years, those electrons join those nuclei forming the first atoms in our history, The reason What excites cosmologists so much is that before that transition, when the universe was still a plasma, all space was opaque to light.

If you had a flashlight just 200,000 years after the Big Bang and you tried to shine it, all those photons would just sort of bounce off of you, it would be just as successful as if you tried to shine a flashlight and across the earth they just wouldn't make it any distance. , but as those atoms began to form, the light became or space became more and more transparent and suddenly a huge amount of light was released into space and it has been traveling through the universe since then more or less endlessly now I'm a scientist and inherently deep down in my heart I'm a skeptic if you want To convince me that something like what I just described actually happened is not just speculation but actually happened you'll probably have to provide me with some empirical evidence pretty convincing, some kind of measurement or some kind of observation.

I think it's okay, this clearly solves thematter at hand and you would think that since this happened 13.8 billion years ago, evidence like that simply won't be possible to acquire, after all, something so far in the past. There is no way we could plausibly measure that kind of thing, but in that sense you would be wrong because this is an image of that light that was released into our universe only 380,000 years after the Big Bang, we call it the Cosmic Microwave Background, it was 3,000 degrees when it was released, but then, as the universe expanded, those photons stretched and cooled and today it is that 2.7 degree radiation that fills all the space we are bathed in right now, every cubic centimeter it has about 411 photons of that transition that is everywhere.

It's so if you take an old old television, you know the kind that has rabbit ears and you turn it on right, except in the United States, if you turn it on to channel one where there's no broadcast, maybe you have a channel one here. I don't know you. You will find that you get this white static. A small percentage comes from the Big Bang. This was first measured, it was first detected in the mid-1960s, and cosmologists have been eagerly measuring it at higher levels ever since. and higher precision, this is an image taken from the Planck satellite, which is a telescope designed to study this particular radiation and provides our most detailed high-resolution map of this era of our cosmic history.

Those little yellow-orange and blue spots you see are a representation. Of the small temperature variations in this radiation, the hottest spots are about one part in a hundred thousand hotter than the coldest spots are about one part in a hundred thousand colder than the average, which corresponds to a distribution of matter and energy that existed during the time these atoms were forming, by studying this we know what our universe was like so close to the Big Bang just a few hundred thousand years after the origin of time, let's go back to our timeline, let's go back even further more this time.

We will go back to the first minutes and seconds after the Big Bang, we are the first nuclei that were forming before this moment, the universe had things like protons and neutrons, but like the melting point of atoms, it was too hot for the nuclei joined together to form nuclei, but at this point, at about a billion degrees of temperature, those nuclei began to undergo nuclear fusion. The way I like to think about this is that this was a point where the universe was so dense and so hot that the entire universe, all of space, was functioning like an incredibly efficient nuclear fusion reactor, doing the kinds of things that found today in the masts and cores of massive stars, except it was much faster because there were many more neutrons for those protons and neutrons to bind. into things like deuterium, tritium, helium-3, and finally helium as we know it in the universe today;

In fact, about a quarter of all protons and neutrons found their way into helium during this time period along with some heavier elements like lithium. and beryllium we can use the equations of general relativity and some equations that dictate the behavior of nuclear physics to calculate how much helium lithium beryllium we think should have formed this way and we can go out into the universe and try to measure it and see if we find those quantities and We do the best we can to measure, this nucleosynthesis process occurred exactly the way the theory does and that gives us a lot of confidence that we understand how it has evolved from the first seconds after the Big Bang to the present, let's go back even further But now, we will return to this point, something like a millionth of a second after the Big Bang, this is when the first protons and neutrons were forming before this point.

Instead, there were no protons and neutrons, there were just the particles that make up protons and neutrons, things we call quarks along with things we call gluons. After all, a proton is nothing more than a few quarks held together by gluons, just like a neutron as the universe cools. These quarks begin to unite forming the first protons and neutrons at an incredible temperature of about 10 billion degrees now when I described the formation of the first atoms in the formation of the first nuclei I told you what we observed on Earth from the early universe to convince them that we knew this really happened and in those two cases we are pretty sure it really happened, but we have no way of observing the epoch of proton and neutron formation, we don't know in any way with current technology that allows us to go back to the first millionth of a second in cosmic history, but that doesn't mean we can't progress.

What we do, however, what we have to rely on for the moment with our current technology is trying to recreate. the conditions that were found in our universe in these early times and we do it using these fantastic machines that we call particle accelerators this is an image of the Large Hadron Collider the Large Hadron Collider is a huge 17 mile underground tunnel that passes underneath from the city of Geneva Switzerland and then it goes into nearby France, it is too big to fit under Switzerland, under Geneva, and along that tunnel we have 21st century magnets, super powerful magnets, superconducting magnets that accelerate protons up to just below the speed of light and when I say just below the speed. of light, I mean 99.999999, 7% of the speed of light.

I think I got the right number of 9, sir, sometimes I get one or two wrong, but I get really close to the speed of light and then those particle beams head straight into each other. others in key locations within these devices called particle detectors, they are about the size of a gymnasium and they are all built with 21st century electronics in those detectors the particle beams collide and approximately 600 million times every second the protons collide and are its energy. it transforms into new forms of matter and energy the reason we do this the reason particles collide with each other is not immediately obvious if I wanted to learn more about automotive mechanics I don't get to the cars and crash them into each other as fast as Possibly Maybe, that wouldn't be a very effective technique, but when it comes to particle physics, this is our best tool.

We are taking advantage here of Einstein's most famous equation equals MC squared. What Einstein's equation really means is mass as a form of energy. and if you put enough energy in one place at a time you can convert that energy, at least in principle, into other kinds of things that carry a lot of mass, so that in the collisions at the Large Hadron Collider we are able to create a long and great variety of particles forms a matter in energy to transport a large amount of mass that we do not find in our universe; Otherwise today at least not in appreciable quantities we produce things like top quarks and W bosons and Higgs bosons and tau leptons and the The list goes on and on and on and on, all these particles are explosive, these particles are really rare in our world today, but a trillionth of a second after the Big Bang, the universe was full of them, all of them, that is due to the type of collisions that the Large Hadron Collider produces and we still have to study the type of collisions that they occurred a billionth of a second after the Big Bang under that type of temperature and density conditions.

This is a graph showing all the particles we have. We have observed and studied at the Large Hadron Collider and other particle accelerators and the top left are the six quarks, the up and down quarks are the types that form protons and neutrons, the others are more exotic matter and shorter life, the top quark was discovered at my own Fermilab long before I worked there at the bottom left are the six leptons, this includes the electron which is very well known and its heavier cousins, the muon and tau, are also three neutrinos, neutrinos are somewhat exceptional because they interact so weakly that they can pass through the entire Earth without knowing that they are there, but we can still study them, we know how to do it and then on the right we have the force that communicates the particles, for example, the reason for which there is an electromagnetic force, the force. that Michael Faraday presented here in this same scenario the force has been around for over a century and a half, we now understand that because photons pass back and forth through the space between charged particles, the gluon generates a nuclear force that is too strong and the particles known as The W and Z bosons give rise to the weak nuclear force of the early universe a trillionth of a second after the Big Bang.

Any particle existing in space constantly interacted with its neighbors in a frenzy of activity that was created and destroyed in rapid succession a year. after the other, one electron would become a top quark, which would become a gluon, which would become a photon, which would become a neutrino and then, again, it was an incredibly active time, full of creation, full of transformation and everything we know about that period of Now we can thank the Large Hadron Collider and other accelerator experiments for helping us build and understand. Well, at this point in the lecture you might get the impression that I'm trying to tell you that first we really understand a lot about our universes. fraction of a second, but that is not true, we have a wonderful theory, a spectacularly successful theory when we combine everything Einstein taught us about space and time with everything we have learned about particle physics and quantum physics from accelerators of particles and other experiments that we can explain.

Much of what we see we can explain the detailed patterns of light we see since the formation of the first atoms. We can understand how galaxies and galaxy clusters formed and why they have these types of characteristics. We observe. We can understand how light nuclear elements were formed. They formed just a few seconds after the Big Bang, but when we get to a time before that, there is every reason to think that our theories may be incomplete or simply wrong, since we can't observe those eras, so there is plenty of opportunity to getting things wrong and then secondly, there are a number of puzzles or problems that cosmologists have discovered in the last few decades that turn out to be really difficult to solve and they all seem to point to this early era.

These riddles make me at least suspect that I have done it right. I don't know, maybe we'll tie up these loose ends as the story progresses with better measurements and better observations. I may be a bit theorizing or perhaps these puzzles are indications that we've done this all wrong and need to radically rewrite the first second of our universes' history book. Let me describe to you some of these puzzles that I am talking about. The first of these puzzles has to do with the simple fact that matter exists in our universe. When we study it in particle accelerators, we learn that each type of matter is accompanied by something that is an equal and opposite version of that matter that we call antimatter.

For example, the electron exists alongside something called a positron, they have the same mass, they basically have the same properties except the electron has a negative electrical charge and the positron has a positive electrical charge, quarks have their antimatter counterparts and antiquarks, neutrinos, antineutrinos, etc., there seems to be a perfect symmetry between the laws that describe matter and antimatter. You can't have one without the The other thing and the best we can say is that you can't create antimatter without creating an equal amount of matter and you can't destroy antimatter without destroying an equal amount of matter, they come in and out of the existence in unison, their destinies are intertwined, so when cosmologists think about this they run into a big problem.

They have every reason to think about the laws of physics, since we currently understand that the early universe should have been filled with equal amounts of matter and antimatter. They follow the same laws of physics, regardless of what created the universe. matter would have been created at the same time with the same amount of antimatter, but then as the universe expands and cools, the matter and antimatter should have destroyed each other, but this would have left us in a universe without electrons , without protons, without neutrons, without atoms, without any stars, without planets, without galaxies and without life, that is clearly not the universe we live in, so we know we have something wrong about how this developed in the universe primitive, but we don't know what the answer is that we have. a lot of guesses but we don't know which ones are correct the second problem also has to do with matter but not the type of matter thatconsists of atoms something else what I'm showing you here is an image of the Andromeda galaxy it's one of our closest neighbor to the Milky Way, we can look at an object like that and we can see how any star that contains how much gas does it contain basically we can We get a pretty good inventory of all your visible matter when we do that.

We can calculate simply using the laws of gravity how the stars should move around a galaxy like this and you get something like this. This is a predicted rotation curve of a galaxy like Andromeda. As you move away from the center of the galaxy, we find that the stars should move in slower and slower orbits because they are farther and farther away from the concentration of mass. This is basically the same reason why Pluto moves in a very slow orbit and we move in a much faster one. It's the same basic idea in the In the 70s, although astronomers began measuring the rotation curves, they looked more like this top line, these galaxies seem to house much more mass than we could explain in terms of stars, gas, dust and planets, in addition, the mass that we could not observe seems to be more swollen. extending to much greater distances from the centers of galaxies, we had many discussions and debates, but eventually we came to a consensus that what was happening here is that most of the mass and galaxies are not made of luminous material, no They are made of things that appreciably radiate, absorb or reflect light, instead they are made of something else, something that for lack of a better name we simply call dark matter, we don't know what dark matter is, just so we can give it a name.

It doesn't mean that Understand further, as time went on we became convinced that dark matter must consist of one or more new types of substances, perhaps some type of new elements, root particles or particles that fill all of space and basically act interacting under the force of gravity, if so. It is true that we could begin to understand how our universe came to have the structures it does. This is a sequence of images taken from a computer simulation of dark matter particles that evolved from an early time, shortly after the Big Bang, on the left and then. in a sequence that allows the universe to expand and the force of gravity to pull on Dark Matter and collapse it back into things we call halos.

When we look at the distribution of those halos in the lower right panel, we see a distribution that looks the same. like the distribution of galaxies and galaxy clusters in our universe today, so in a universe its mass is dominated by dark matter, by which I mean that about 5/6 of the total matter is made of dark matter, We can explain why the distribution of galaxies and galaxy clusters in our universe looks the way they do, if you asked me 10 years ago what dark matter would probably consist of, I would have given you a pretty confident speech about how the weak ones are the most likely class of candidates. wimp means a massive, weakly interacting particle. and we thought they were really compelling because if particles like that existed, then we could calculate how many would have been produced in the Big Bang, how many would have been destroyed and how many would have survived and, lo and behold, the number that survived was about right. amount you needed to explain things like this in those galaxy rotation curves, so it left us thinking that's probably the answer, it's pretty simple, it's very easy to write a theory of particle physics that behaves this way , that's probably it and the best of all. was that if it were true, we knew how to test it, we could build these really sensitive underground dark matter detectors, we knew how to do it or at least we thought we could figure it out and you know, we thought that in another, you know, 5 or 10 years to discover these things was a no-brainer, so we went to deep underground laboratories and when I say we, I mean the people who do experimental physics, they don't let me near the experiments for a good reason, so this is an example of an underground world. laboratory in Italy, the Gran Sasso laboratory and in this little kind of graph you can see the xenon and the dark side and the lady and the crest, all of them are dark matter detectors.

There are many others in other laboratories around the world and they have worked very well. science to the scientists who built and designed these things, operated them, have surpassed all expectations in terms of sensitivity and performance, are something like a hundred million times more sensitive than when I started working on dark matter as a graduate. student 100 million is a big number but they haven't seen anything no one can blame the experimentalist a theorist told them this is what you need to find this is how to use the type of experiment you would have to perform to be able to do it they said okay we are prepared for that challenge, they went out and did it, they did it well, but the things we told them to look for were not the best, we can say that the weak ones are more difficult to look for than we thought. and that is possible.

I can write some weak theories that can evade these limitations. I have to do some work, but it's a little harder than it used to be, but it can be done or maybe it's telling us that dark matter wasn't. produced in the early universe in the way we have long imagined perhaps things developed differently in the universe perhaps space expanded at a different rate perhaps there were other forms of matter and energy present perhaps the origin of the Dark Matter was not in these thermal baths as we imagined but perhaps it occurred in some other way.

Any of those things could be possible and I would just say that the elusiveness of dark matter that has surprised me and others is at least suggestive of some events in the early universe that we didn't expect there. Not part of the standard story, okay, the third puzzle I'll talk about has to do with the rate at which space has been expanding over time. If you take Einstein's theory of relativity and deduce how an expanding universe should change over time. Let's end up with predictions like this depending on exactly how much matter there is in the universe and the universe could be that it gets bigger for a while, reaches a maximum size and then starts to contract and finally experiences something like a big bang and a verse we call a big contraction which is the bottom line, it could also be like in the top line, the universe just gets bigger without limit, slowing down but still constantly increasing in size as time goes on and then there is a sort of intermediate case where the one that gets bigger and somehow. from plateaus to a more or less maximum size, ultimately those are all logical possibilities.

For most of the 20th century, cosmologists were trying to figure out which of these universes we lived in, they thought this was a multiple choice question, a B or a C. In the 90s we finally had the kind of telescopes needed to definitively answer this question once and for all and what did they find? D none of the above which is approximately the type of curve we learned was the case in fact okay, okay, In the 90s we learned that space is not only expanding, but it is expanding at an accelerated rate. Space is expanding faster today than it was a billion years ago, and by all indications it will expand even faster a billion years from now.

It makes about as much sense as if you took a rock and threw it up and it kept moving faster away from the earth. something is driving it. Gravity should pull on it slowing it down, but it's not happening the only way we have. To understand this is that if we pause it, space itself intrinsically contains a fixed amount of energy, a fixed density of energy that we call subdark energy, and that energy must have approximately the same density everywhere in the universe. and approximately the same density at every moment in the universe in the history of our universe, which means that when one cubic meter of space becomes two cubic meters of space as it expands, everything else is diluted, all matter , the density decreases by a factor at all energy.

The density of light decreases and the energy density in dark energy remains the same, meaning that over time an increasing fraction of the total energy of our universe is in the form of dark energy and when it becomes the component Mainly, accelerated expansion is predicted to take place. So today we think that 70% of the energy-dense inner universes are in the form of dark energy. We don't understand what it is, we certainly don't understand why it exists in the quantity that it does, and I don't know where we are. I'm going to change that, the fourth and final cosmological puzzle I'll mention is an effort to solve the fact that if I look as far back as I can in that direction with a telescope and I look as far back as I can in that direction with the telescope and I compare what I see.

I basically see the same thing. Our universe at the largest scales is remarkably homogeneous. The same amount of things everywhere. The same temperature everywhere. In fact, the Cosmic Microwave Background in that direction is within one hundred thousandth part. same temperature as a Cosmic Microwave Background in that direction and it shouldn't be because that part of space never had the opportunity to be in contact with that part of space, it's what happens to people who have never met or met. communicated with each other, they just wrote the same song if you find two people and they both claim to have written the same song, you would say that one of them or both of them maybe learned it from a common source if you don't want to accuse them of being liars, you say I heard it somewhere part and got into your head unconsciously, but these people in these parts of our universe never had a chance to meet or interact, in fact, based on what we understand about the laws of physics, even if you travel at the speed of light , that thing never could.

We have contacted that thing simply not possible, so to address this we have been forced Alan Guth and others in the 1980s began to entertain the possibility that shortly after the Big Bang space may have had a period of expansion. hyperfast that we call cosmic inflation. The idea here is to take two points in space in contact with each other and have them expand much faster than the speed of light, separating them from each other so that the space grows so fast that it takes them to very different places being propelled. by an An energy field similar to dark energy but much more intense and then that energy is converted into normal radiation and particles that start the Big Bang as we know it and then you have an explanation of why that part of the universe in that part .

Parts of the universe became very similar because they were once neighbors, but you need something like these bursts of hyperrapid expansion that we call cosmic inflation if you're trying to explain that particularly interesting, in my opinion, facet or result of Considering Inflation is that It doesn't tend to end if I have a piece of space and it's inflating, there will be a small portion that stops inflating and fills up with matter and energy and starts expanding like a normal universe. and it becomes a normal universe, but the rest of the inflated space continues to inflate and then a part of that stops inflating and creates a universe and then another part into another passion forever, it never ends.

You produce an incredibly large number of universes this way. So in other words, if inflation occurred, we have every reason to think that our universe is one of many within a larger multiverse. I wouldn't say that a multiverse is a scientific fact which is certainly not true, but the more we learn about inflation the more likely it is. It seems that our universe is one of many, so let me pivot a little here we have an incredibly successful theory, we can explain the details of the Cosmic Microwave Background, the expansion history of our universe and the formation of light nuclei that we know about.

I understand these things very well and yet there are these puzzling loose ends dark matter dark energy what happened to all the antimatter and why cosmic inflation occurred all of these things are impossible or really challenging outstanding questions that we have been wrestling with for the last few years and decades and as time goes on they haven't proven to get any easier, if anything, the experiments we've run have only made these questions harder to address, so when I want to frustrate and/or entertain my colleagues, I I like to ask them the next question and they will come back to this.

It will seem like a starting point, but they will come back to this in a moment. I would like to ask you what you think it would be like to have been a physicist in 1904, why. 1904 I could have chosen any year you think, but no, no, 1904special. 1904 was the year when companies were most confident in their ability to understand the universe. At that time, Newtonian physics had been successful for 200 years. New discoveries continued to be made like electricity and magnetism and heat and other things like this and from the Newtonian mentality or paradigm we continue to be able to address it, we explain more and more with these ideas of mass and force and acceleration and speed and in the space geometry all these things that were introduced by Newton, two centuries earlier, were still working in the majority of physicists, the vast majority of physicists in 1904 were confident that the Newtonian framework would continue to thrive in the distant future, perhaps forever.

Of course, in 1904 there were some loose ends and one of those loose ends. had to do with the nature of light, it had been measured that light always travels at the same speed in any reference frame which is different from other types of waves if I tell you that there is a water wave that moves through the ocean at 20 miles per hour and I got in a boat moving with the wave at 10 miles per hour. I measured the wave was moving at 10 miles per hour in my frame of reference. Everyone expected light to be like this too, but it turns out that light travels at the same speed 3 times 10 to 8 meters per second in each reference frame and no one could understand why the second of these riddles had to do with the planet Mercury.

In its orbit like any other planet Mercury moves along an ellipse and orientation. of that ellipse changes a little from year to year it is processed throughout the 19th century the precession of the perihelion of Mercury was measured very precisely the speed at which it was processed was measured very precisely and was only a little different From what Newton had predicted better, we could see that Newtonian physics did not accurately describe Mercury's orbit. Now, one hypothesis that was popular at the time is that there might be some other planet out there, something called Vulcan, that's where the name comes from and maybe it just was. gently pulling on Mercury ruining its orbit a bit, but astronomers looked for Vulcan and didn't find it, no one had a good explanation for why Mercury behaved that way.

Perhaps the biggest remaining problem had to do with the Sun in In fact, physicists couldn't explain how something the size of the Sun could be emitting so much sunlight for so long over billions of years. This thing had been emitting about the same amount of solar energy. We knew this from geology, but even if the entire Sun were made of gasoline or coal, it should have run out of fuel after just a couple of tens of thousands of years. People also imagined that maybe it was contracting by converting gravitational potential energy into sunlight, but that would last millions, not billions of years, so no one had done it. a clue as to why the Sun was doing what it was doing, and ultimately, physicists had no way to even address the problem of how atoms worked.

Atoms were known to emit these peculiar spectral lines. This kind of light, no one knew why, no one could even begin. To calculate it further, when we tried to calculate what an electron should do in an orbit around a proton, we discovered that those electrons should spiral inward and collide with the nucleus and in almost no time, in other words, atoms should not be stable and yet here we are of course these did not turn out to be loose ends in 1905 Einstein published a series of incredibly revolutionary papers, introduced a theory of relativity and wrote the first paper presenting some of the ideas that would eventually become In quantum physics these papers were not based on the Newtonian paradigm, they tore it down and built something else in its place, the theory of relativity explained why the speed of light was the same for all observers and all frames of reference.

It is because space and time were not as Newton imagined them. The general theory of relativity offered equal mc-squared, which could explain how the Sun could convert a very small fraction of its mass into enough energy to power sunlight for ten billion or more years. The theory of quantum physics that Einstein worked on could explain not only the spectral lines we observe in atoms, but also why they formed. stable and eventually Einstein's general theory of relativity would explain with high precision why Mercury's orbit behaved the way it did, so I ask myself the following question: 2020 the 1904 of cosmology, we have wonderful theories that have been successful for a long time and yet there are things that we cannot explain, at least we have not been able to do so so far, perhaps it will turn out that they are just loose ends that we will clearly resolve with more observational experiments or perhaps we will discover that the only way to solve these persistent problems and puzzles have a new paradigm, one that I can't even imagine what it looks like yet because it hasn't been written well.

Thanks, it's been a lot of fun. I hope to answer a lot of his questions and then I'll come here and we'll sign some books and you can ask me some questions in person. Thank you.