Eternal Inflation Theory|The beginning of Universe

In order to get the large scale structureof the Universe we see today, cosmologists have proposed the idea of inflation, thatthe Universe expanded an enormous amount in the earliest moments. But if inflation really happened, then ithas even stranger implications for the nature of the Universe and the search for multiverses. We’ve covered the topic of inflation a coupleof times in the past, but I’ll give you the short version one more time.

The Big Bang exquisitely explains the expansionof the Universe we see today. When we look out as far as we can, to theedge of the observable Universe we see the afterglow of the Big Bang: the cosmic microwavebackground radiation. This light was released the moment the Universehad cooled down a little, and has been traveling for almost 13.8 billion years to reach us. Thanks to the expansion of the Universe, it’sbeen redshifted to just a few degrees above absolute zero. When astronomers measure the temperature ofthis background, it’s incredibly consistent, with only tiny fluctuations measurable withthe most sensitive instruments. This means that the entire Universe that wecan see had time to transfer temperature to each other before it expanded. But the original Big Bang Theory suggeststhat the expansion of the Universe didn’t give the material time to even out its temperature. In order to explain this, cosmologists developedthe concept of inflation. There was a period in the earliest Universewhen the energy in matter was bound up in the fabric of space itself. The Universe expanded so quickly, that a regionthe size of a subatomic particle would have been stretched to the size of the visibleUniverse in a fraction of a second. Inflation also answered other challenges thatthe original Big Bang couldn’t explain, such as the flatness of the Universe, andtotal lack of monopoles. Like I said, we’ve done a whole video aboutinflation. But inflation has introduced its own set ofstrange ideas, including the concept of “eternal inflation”; that inflation didn’t endfor the entire Universe like it did in our local area. There are regions undergoing inflation allover the place, creating multiple universes within our Universe. You know, a multiverse.

I’ll be honest, though, the concept of eternalinflation is beyond my comprehension. And so, in times like this, I like to bringin a ringer. Today, I’m glad to bring you Dr. Ethan Siegel,an astrophysicist and science writer. His most recent book is Treknology, all aboutthe science of Star Trek. Ethan tackles some of the most complex topicsout there in an understandable way, and I could really use his help. Ethan, welcome to the Guide to Space Before we get started, was there anythingyou wanted to add to my description of inflation? Hi there Fraser, it's my pleasure to be hereand I'm more than happy to tell you all about the eternal inflation and why it lasts forever. Lasts forever, it's going all the time? I don't even know where to start. Can you explain or add anything to the wayI described inflation to set the stage for how we're going to move into this idea ofeternal inflation. Sure, you did a great job. You know that's something that people don'trealize when they hear the Big Bang. When people hear the Big Bang, they thinkoh, that's the origin of everythign, that's where the whole Universe can from, and that'sthe birth of space and time. And as far as we're concerned, the answersto that, the answers to that are yes, yes and not quite. The reason is that if you imagine the Universetoday, you see it expanding, you see it cooling, you see galaxies moving farther and fartherapart from one another and you say to yourself, oh, right, well if things are expanding now,and cooling now, the red shift you talk about, because as space expands as the fabric ofspace stretches, you say oh, right, you have this wavelength of light and that definesits energy. So as space stretches, the wavelength getslonger, and that means the Universe gets cooler. So if instead you look back in the past andask what were things like in the distant past, you say oh right, that means that the Universewas smaller and space was smaller, and things were closer together. So rather than being larger and getting largerand getting cooler, that means that in the past it was hotter, it was denser, thingswere closer together. And because it's had less time for thingsto clump together, the Universe was also more uniform. So you extrapolate back and say, well, ifthings were hotter and hotter and more uniform, I should be able to go back to a time whenthere were no stars and no galaxies. And we think we've seen that time, and wethink that the James Webb Space Telescope is going to reveal those first stars and galaxies. And you go back even more and you say, wellat some point it must have been so hot and these wavelengths must have been so shortthat couldn't even have formed neutral atoms at that time. And absolutely, that's correct, there wasa time when the Universe was just full of an ionized plasma because all of the radiationin it was too powerful, that as soon as you formed a neutral atom, an incoming photonwould strike that atom, knock the electron off, and you've have a plasma again.

When you talked about the cosmic microwavebackground, that refers to the time when atoms finally became neutral that the scatteringdidn't occur any more. And that's the leftover glow we see from theBig Bang, which happened when the Universe was 380,000 years old. You go back further and it becomes so hotthat you can't even have atomic nuclei, that they get blasted apart. So we can do the calculations for the lightelements for the abundence of the light elements for how nuclear fusion happened in the firstfew minutes and seconds of the Universe. And that's something that we make predictionsfor that we have observations that you learn about the Universe. But if you want to go all the way back toarbitrarily high densities, to arbitrarily high temperatures, you run into a problem. You start saying, well, if that's what I got,then what I should see for example in this pattern of fluctuations in the microwave backgroundis that different regions should have different temperatures of a certain magnitude. There should be big big massive temperaturefluctuations that we don't see.

We don't see one part in one or one part in10 or one point in 100 fluctuations. We see like one part in 30,000 which tellsus, no, there's a lower energy scale there. We would expect that if you look 13.8 billionlight years in one direction and 13.8 billion light years in the opposite direction, there'sno way for these two regions to have exchanged information, to have exchanged photons, tohave come to thermal equilibrium. And yet, completely opposite regions of thesky started out with the same properties. You also talked about spacial curvature, andwe measure this spacial curvature of the Universe to be zero, to be absolutely flat, even thoughwe know that spacial curvature increases as time goes on, so that means when the Universewas 10 to the minus some really large number of seconds old, it would have had some kindof curvature that was super miniscule, like 10 to the -100 in order to give roughly zer0curvature that we see now. So all these things are motivations to sayyou know, either to get the Big Bang, we had to start with these incredibly fine tunedinitial conditions or you can appeal to physics and say, you know, what kind of dynamics couldhave occurred to set this up. This is the beginnings of where you get anyscientific theory from. You have a period, the Big Bang, that worksreally well in a certain regeme. But when you go all the way back to the verybeginning, you start to ask questions that you don't have a good answer to. You either have to say well, it was eitherlike this and that's the story, or you have to say that well, it started out with thesesets of conditions, it was flat, it was the same temperature everywhere, we don't havethese high energy left over relics that these extensions predict. Either we start with those conditions andthose were the conditions that the Universe was born with, or something happened to setthe Universe up like this. And if that's the case, what are the otherthings that this theory would predict and how can we go out and test them? So that's what inflation is. Right and so that sort of sets up what inflationis, it's this expansion that I mentioned and what you were talking about, but in my mindI imagine it being this same, this thing that happened across the entire Universe. This stretching that happened at all placesat once and then that phase is over. So how does this play into the idea of eternalinflation. Okay, so that's a great explanation, you'vegot this space and it's stretching exponentially. And just so everyone explains what exponentionallymeans, imagine I've got this cube that's one cm on a side and I let it expand for one timestep. So I take a time step and now it's two ona side and two on a side and two on a side, so it's two by two by two. And then I take another time step so now eachof these has expanded again so it's 4 by 4 by 4. And then I take another time step and eachof those again doubles so it's 8 by 8 by 8, you can see with inflation, that if you justtake a small number of time steps, like 64 time steps or so, all the sudden you get somethingthat's like 10 to the 30 times as large as you started with. Which is to say that if inflation goes onfor just 10 to the minus 33 seconds, then you can go from something the size of theplancke scale, the smallest conceivable scale that makes sense to the size of the observableUniverse today in just 10 to the minus 33 seconds. So that's how rapidly space expands, that'swhat it means that it's expanding exponentially.

So then you say, okay, how does this happen,you say well, I imagine it's some kind of quantum field, when you're up at the top ofa hill, right, you get inflation going and then you roll down the hill and inflationcomes to an end. And you say, okay, that's great and you toldme this picture you have. That inflation starts out here, you roll downthe hill and it comes to an end and it does that everywhere. And that's fine if you're a ball rolling downa hill, but we know that inflation like everything else in the Universe should be a quantum field. It's not a ball rolling down the hill, it'sa quantum field running down a quantum potential so now let me ask you something about quantummechanics. If I give you an electron and I say, hey,hang onto this electron and you do, and you hold the electron in your hand, as if thatwere something you could do to electrons. And then I say, just take a chill pill, don'ttake a look at that electron for a while, let that electron sit in your hand. And come back after a couple of seconds. Now where's that electron? Is it in the same spot you left it. And you can go and look. And there's a probability that the electronwill be in the same spot you left it, but one of the properties of quantum wave functionsis that they spread out over time. This is just something inherent to the quantumnature of every particle and wave in the Universe is that it has this inherent uncertainty toit and it has this inherent quantum spreading to its wave function that happens with time. So if you've got your inflationary potential,if you've got the field at the top of the hill, right, the field's at the top of thepotential, and it starts to roll, so it starts to roll down the hill, you can say well, hangon, as it's starts to roll instead of having this one by one by one box, I've got thislet's say, 8 x 8 x 8 box, I've got 8 times 8 times 8, that's a lot, that's 512 independentregions that were the size of that original region. And then you say, okay, well, it's startedto roll down the hill, that's on average. So, on average, it's started to roll downthe hill but because of this quantum nature of things, the field spreads out. What happens then, the field spreads out sothat in some places you've rolled farther down the hill and you're closer to inflationcoming to an end. In some places you're right where you expectto be, where inflation's rolled down the hill the field has rolled down the end and inflation'scoming to an end like you expect. But in other places, inflation has causedthe spreading to expand so much, that you're closer to being back up the hill than youwere initially. In other words, you don't always roll downthe hill, even if it's just a small percentage of the time where you run up the hill, whereyou run against where you expected to be because of this quantum spreading is faster and biggerthan the rolling down the hill, well space grows so fast from one thing to 512 thingsis such a small time that now you see oh no, I have more regions that are inflating evenmore than they were when I started. And so, yes, you're going to have regionswhere inflation rolls down that hill, where it comes to an end, where it comes to an end,that's where the energy inherent to space gets converted into matter, antimatter andradiation and you get that hot Big Bang. And you get the birth of our Universe withall those properties that we talked about. Where it's been stretched flat, where thetemperature is the same in all directions because things were connected during inflation. And where you don't have monopoloes or otherhigh energy relics, because you never got up to that high temperature that you thoughtyou would get if you extrapolated arbitrarily. There's a maximum temperature that we canreach, and we've discovered with WMAP and the Planck satellites, that that's somewherearound a factor of 1000 times or more below the Planke energy. So okay, with inflation you can reproducethose successes of the Big Bang, you can make additional predictions of the fluctuationsof the Universe, of superhorizon fluctuations, about what types of structures you're goingto get. But you can also do this additional thingwhere you say, well, where does inflation end? How likely are we to have inflation end atany particular time? And you can say, well, look, as we move forwardin time, even if inflation comes to an end with every time step in half or more thanhalf of the regions, there were still an infinite number and an increasingly infinite numberof regions as time goes on where inflation continues for eternity. And that's where the idea of eternal inflationcomes from. That as this quantum field rolls down thefield, it has a probability of spreading out. And in some of those regions where it spreadsdown enough, you never roll down that hill, you always stay at the top of the hill, whichmeans that you're always inflating. And so, if we looked across the Universe. If we could somehow move into a God mode andactually look around and observe, we've got our current observable Universe, which isonly some fraction of what is the possible actual Universe and possibly infinite.

But if we could see these other regions ofinflation, what would we see? Okay, so I'm going to ask you to visualizeyou were some higher dimensional creature, that you could see all the 4-dimensions ofour space and time, and you could see what's going on in them from an outside view. Inside, you would see what we call our observableUniverse. This is the stuff we can see from the momentof the Big Bang, the light that's reaching us right now in all directions. It would be this spherical Universe centeredon us because that's where we happen to be. If we were anywhere else it would be centeredon wherever we were. And you would see that's a part of our regionwhere inflation ended. It's getting bigger as time goes on, but wecan't see all of it. Now, if you look beyond that, beyond the partthat's observable to us, you would also see, oh wow, we're getting a big big sphericalregion that is where inflation ended. And it may not be spherical, it may not besymmetrical, we just assume it's spherical. You get this big region where inflation ended,and that's expanding outward at the speed of light, and expanding with the expansionof space. And anywhere in that region, if you put anobserver, and said hey, you've been here since the Big Bang, what do you see. You could draw a sphere about 46 light yearsin radius, about the same as you can for us. That's how far you can see in the expandingUniverse. Except if you're very close to the boundary,you would get there, but you would see a mysterious end. Like you would see a cut off in the structureof the Universe, of the microwave background. There would just be empty space beyond that. So if you asked what's going on beyond thatempty space. Well outside of the region where you had yourhot Big Bang, that's inflating space, that you would have this space where inflationcontinues and every so often you can say, well if I look throughout this inflating space,what else am I seeing? Well, the answer is that I would see a bunchof different pockets in the Universe that looked like our part where inflation ended,except it may have ended at different times. So, the Universe in some places, other universeswithin this multiverse within this eternally expanding space, they may have not ended 13.8billion years ago and said, that's when you have the Big Bang and that's when you getyour little pocket Universe. Instead, you could have had something thatended more recently, you could have had something that ended long before us.

You could have Universes much older than oursis, and you could also have universes where inflation is just stopping right now and you'reonly having the start of that hot Big Bang. But what's very important to recognize aboutinflation is this super rapidness at which it causes space to expand insures that ifyou invision the Universe as okay, we have this bubble that we form within this oceanof inflating space. And you've got another little bubble. Even though these bubbles are expanding atthe speed of light. The space in between them, the space is expandingexponentially and it always pushes these bubbles away.

And that means that wherever you are in theUniverse, your pocket universe should never collide with another pocket universe. The space in between them should always beexpanding eternally. And even though you're always producing acountless number of these universes, they'll never interact with each other and you'llnever be able to see them. All that we can experience is our observableUniverse within it. So we could never reach these other universes. We're stuck just doing the math and imaginingthem. That's sad. Right unless you turn on God mode, like yousaid. If you turn on the God mode, then you cansee all the things. And this is an interesting thing, and a lotof people argue that is the multiverse and is eternal inflation actually science. And I would argue that it is, but you haveto be very careful. The reason that I would argue that it is,is you say, well, we've got this theory of cosmic inflation and the evidence for it isoverwhelming. Right? We've got some very good evidence for it,cosmic inflation has been validated, it's very robust, we're very happy with it. Then you come to the next thing, you say well,we also understand that the Universe and everything in it is quantum in nature. So you say okay, you've got cosmic inflation,you've got the quantum nature of the Universe. We put these two things together and whatare the consequences we get out of eternal inflation is one of them. This tells you no matter how long ago or howrecently ago inflation began, once it begins, it should continue eternally into the future. This doesn't mean it continued eternally intothe past. Inflation may have had a beginning.

The Universe may have had a beginning, orit may have been eternal to the past. The problem is that for us within our observableUniverse, because of how rapidly inflation causes an expansion, when we look to one endof the Universe and when we look to the other end of the Universe in two opposite directions,we say okay, we're looking at the entire observable Universe, we ask how much of inflation dowe have access to, do we have information about that exists in something observableto us. The answer is unfortunately, we only haveaccess to only about 10 -33 seconds. The final 10 to the -33 seconds of inflation. This is something that could have gone onfor fractions of a second, or could have gone on for many seconds, or many years, or billionsof years, or googols of years, or forever, or forever. But we only have access to that tiny bit ofinformation, so on one hand, it's incredible how much we can learn about the Universe,just from this tiny bit we can access. But it does make you wonder because we havethis tremendous extrapolation that we've done from it, is there some kind of physics somewhere. Or is there some physics that we've gottenwrong along the path that means that this conclusion is invalid.

And as a scientists, it's very important tokeep an open mind about it. We're doing the best science we can with allthe information we have. We've validated every part of this theorythat we can physically validate. And for the parts that we haven't validatedyet, we're looking for ways to do that. But as we come forward we hope to learn moreand more things but at some point you're going to hit a limit. You're going to hit a limit, there's a finitenumber of particles in the universe, there's a finite number of degrees of freedom thatthey have, there's a finite number of bits of information encoded in it. And even with everything we have, with 10to the 90 particles or so, and how they're correlated and how they interact with eachother, that's finite. So if you say, I want to know what happenedbefore these last 10 to the -33 seconds of inflation. That information might not exist in the waythat human beings or anything within our Universe can ever gain access to. Well, in a moment, Ethan and I are going totalk about his new book, but first I'd like thank: Lucas HúngaroKane Doyle Jackson van Deinsen And the rest of our 812 patrons for theirgenerous support. If you love what we’re doing and want toget in on the action, head over to patreon.com/universetoday. Ethan, well thank you very much for blowingmy mind with this bittersweet ending. But tell me about your book. Congratulations. Yeah, so thank you, I have a new book out,it's called Treknology, it's a book about Star Trek, the science of it in particular. It's about the science of Star Trek, fromtricorders to warp drive. And what we've done in this book is that we'vetaken a look at 28 of the different technologies featured in Star Trek, from warp drive totransporters to Georgie's visor to any of the military or civilian communication advancesyou can think of to the ship's technology to even Borg implants. You take all these technologies and you wantto ask yourself, Star Trek the original series was 51 years ago. Star Trek the Next Generation premiered 30years ago. How many of these technologies have alreadybecome reality? You've got these things like flip communicationsand universal translator ear pieces, and touchscreen computers like PADDs or electronic clipboardsand sliding doors and you're like that's yesterday's technology, and that's true.

In the mean time, we've made tremendous advancesto some technologies you might not realize are almost here, from a holodeck, we've gotvirtual reality with multi-sensory experiences, not just sight and sounds, but using infrasonicsensors we've also got touch. You might say what about things like syntheholand believe it or not, we've actually got drugs and pharmacological compounds that haveus well on our way to having this synthetic version of alcohol that will give you allthe positive effects without any of the negative effects with the addition you can take anantidote pill that will sober yourself up almost instantaneously.