グレープフルーツの中のインフレーションと宇宙 - 60のシンボル (Inflation & the Universe in a Grapefruit - Sixty Symbols)

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flesh is not the big bang.
No, the big Bang is inflation.
If you like, gives the initial conditions for the big bank.
Well, the big Bang by itself is that initial singularity, which we don't understand.
No one can go back to the very beginning.
And anyone who tells you that can is there's a little bit of mystique going on in, to say the least.
So what we normally think of as the Big Bang your is your thinking of just a a few nanoseconds after the actual initial singularity.
The Big Bang has certain assumptions in it.
I'm going to come to inflation.
Why you need inflation, what it is.
The Big Bang has certain assumptions in it is best on what was called the cosmological principle, which is something Einstein introduced in solving his equations.
The cosmological principle states that the universe on large scales his homogeneous.
That means we're in no unique place in the universe where just representative of the whole universe and its eyes a tropic.
That means it looks the same in all directions.
Once you've got those initial that initial principle in place, and once you've got something that's expanding out of the particles are expending out.
Then you can begin to work out what the temperatures of the universe, how rapidly the universe should expand, what it should look like today and you can make all sorts of predictions.
And they worked really well.
It gives you concepts.
It gives you time.
Scales like windows.
Nuclear synthesis occur.
When did the first nuclear secure?
After about three minutes, it tells you when the microwave background radiation emerged about 300,000 years after the Big Bang, it tells you when radiation matter had the same density on when we moved into a matter dominated universe and structures would begin to form.
And so it gives you all of these nice results.
It does not tell you where did structures come from in the first place?
What provided the initial seeds for structures?
It does not tell you why in the very early universe, it should be so homogeneous and ice a tropic wag.
Did that happen on dhe?
It does not tell you how to get rid of objects that could have formed in phase transitions in the early universe.
In particular, objects called multiples which could form in grand unified theories.
And if you can't get rid of these modern polls there so massive that they would have caused the universe to collapse very quickly.
So there were these issues which the Big Bang has associated with it, that need explaining it was to try and understand why the universe was as it is.
So flat is especially incredibly flat, homogeneous and Nyssa tropic that led to people like, in particular Alan Booth from M I t.
On.
Then Soviet physicists like Alexis Torbinski on Andrei Linde came up with these ideas to provide you if you like, with the initial preceding dynamics, which would then feed into what way now called the Big Bang Andi that was called inflation way we go on.
Inflation corresponds to a period where the universe actually accelerates.
The size of the universe actually grows exponentially quickly and so on.
And the reason it and it's a very short period of time in the early universe, This occurred for about about 10 to the minus 30 seconds.
That's all you require.
In order to satisfy all these conditions, it could have spent much, much longer.
But the amount you we require to explain the observed universe is about this amount.
It Z.
It's not very long at all.
You have an initial very small patch of the university is represented by a gap there.
Okay, on that initial small patch is such that all the radiation that's present in there has had time to interact with each other.
It is in what's known as causal contact.
So Light has had a chance to proper get from one side to the other side that, in other words, you expect this pit of the universe to be at the same temperature.
Now this piece of the universe just then begins to grow really rapidly.
It just gets stretched by the expansion.
The expansion stretches of exponentially rapidly for this short period of time, but it grows so rapidly that within it it's no easy tohave, a piece of value which becomes our observable universe.
Within this huge, huge, humongous piece, it's now easy to have a smoke smaller patch which becomes our observable universe on because it's begun from this region, which was causally connected and is nice and smooth and homogeneous.
It emerges as this smooth, homogeneous ice a tropic region, which is what we know, see?
And so you have an explanation of how you can go from the universe, which is on huge scales, smooth and hope, a NASA tropic homogeneous from a region which was much smaller.
Your on line.
If you take a photo of your family, then blow it up and put on cameras on the wall.
It's gonna be the same picture.
It's just it's it's much bigger.
Yeah, but the difference is that the that the university you might correspond to might just be the ear off one of those of that of that photograph.
It doesn't have to be the whole thing anymore.
I should.
I should explain when, When?
When?
When?
When we look at the uniform nature of the this microwave background, right, it's it's got this beautiful, smooth temperature.
It's about 2.75 Calvin today, and it was much hotter earlier on, but it's 2.75 and that's incredibly small deviations on either side of it.
A few parts in the 100,000 so it's almost uniform throughout, and that's how whole observable universe okay, now best radiation was was released about 300,000 years after the big bang.
It's when the cosmic microwave background was released, when the when the first electrons began to bind with the protons to form he hydrogen atoms.
If you look at the size of the universe at that point 300,000 years after the Big Bang and say Right, let me compare that size of the universe to what we see now it turns out that there is simply no way that one region of the sky that we can see today, which has this temperature of 2.75 degrees Calvin, could have communicated with this region of the sky, which also has a temperature of 2.75 degrees covered.
Each of these patches couldn't have grown took to meet each other.
And so this is again another motivation for having the idea of inflation.
Those two patches, which today look completely distinct from one actually came from the same initial small connected patch, which then grew exponentially rapidly.
This seems like what we don't know that we overnight everything was really, really small, then expanded.
Yeah, no, no.
You see the standard cosmology.
It does have things expanding, but not at the rate at which you require.
So if you just solve your equations for a universe full of radiation or full of matter, it will expand.
You're quite right on.
But when you work out the rate at which it will expand, its not enough to then account for these this observation of the uniformity of the cosmic microwave background This isn't like a car rolling down a hill.
Someone has pressed.
Yes, yes, someone's press the accelerator.
And so something has got to provide the initial energy, energy density, energy per unit volume in order to cause the universe to do this.
And this is where we once again introduced the cosmologist of particle cosmologist favorite friend, which is a scale of field.
And then, up until March of this year, we used to say Scale of field.
But no one's ever seen a fundamental scale of field.
Of course, Signals got the Higgs.
It's got Nobel Prize associated with it, so we can all proudly talk about scale of fields, and this is another example of a different type of scale of feel.
It's not a not necessarily a Higgs field, it's it, but it's a it's an object that's just got a value magnitude on dhe.
It has a potential energy associated with it.
And in the early universe, this potential energy dominates over everything else, all the energy in the radiation and any matter that's there.
It's much less than the potential energy of this scale of field on.
That is enough to drive this period of acceleration and then eventually, as the universe is expanding, excellent, you know, growing exponentially quickly.
This field, it doesn't stay on the top of this hill.
You can imagine the field as if it's on a very on a hill that Sze got a very flats region and then it drops down right.
It's going down to its minimum.
The field is gradually rolling down this hill, and as it's up at the top here, it's it's it's fairly stationery.
This energy is constant.
Is this potential energy is constant, and then eventually it begins to experience Too steep a part of the hill on the field quickens up, and at that point, as it quickens up this natural period of of in flesh and this acceleration stops and you, you leave that accelerating period, the universe then has to go into what's called reheating.
All of that energy stored in this field has to get transferred over into the particles that you and I a maid off because that they've all been diluted away during this period of expect exponential expansion.
Anything in the universe has just been diluted away as the universe expands so rapidly.
So we've got to re re energize the universe.
We've got to create the particles again, and this process is is called reheating.
And it's a very tech, difficult process to actually understand because it's in the sense of the field has to couple to lots of other particles, and we have to understand how they're created.
And that's a non going area of research trying to understand how efficiently this is done.
But the universe reheats it creates the particles that you and I are married off on that that then enters a radiation dominated era, and that, if you like, is what we would call the beginning of the Big Bang.
In that sense, I think of if you think of the Big Bang as being best on the idea of the cosmology of the cosmological principle, being satisfied and an expanding universe is its initial conditions than inflation will give you that.
It doesn't.
Inflation still hasn't addressed this bit about the very beginning, right?
I've avoided it again because I don't know the answer to that.
I don't know what actually banged.
Give me the big even to spark off that periods in flashes.
Mr.
Thomas, we don't understand with this.
Yeah, yeah.
Big Bang one inflation, then inflation thing One is being the initial.
What happens at that?
Very inflated.
Yeah.
Where did that come from?
That was banged out of the mystery.
Yeah, the creation of space time has to create.
Yes.
So whatever managed to launched the universal creates best time wherever that energy initial energy.
Some people would argue it is inflation.
That, for example, quantum mechanics allows things allows you to Because of the Heisenberg uncertainty principle, which tells you you can trade off energy for a fraction of time.
You can grab a lot of energy for a short period of time.
For example, in the Heisenberg uncertainty principle on dhe, that energy could be the energy stored in this field.
And so some people would say that's what happened.
That energy it was it was enough to trigger the creation of space time and then off it went.
So in that sense, inflation does it for you.
That patch inflated river became diluted.
It would have had it will have had radiation.
Yet we'll have had some energy in there.
No, no.
No matter where to hide.
Where too high in energy for that.
If an atom was to try and you know what is an atom?
An atom of hydrogen is where an electron is bound to a proton on dhe and brought on itself is made up of quarks.
Okay, but if you if you increase the energy of that electron bound into the proton if you fight it text relatively little energy to for you to rip the energy ripped the electron off again on DSO.
The early universe had way, way more in Egypt in that so, in fact, everything that would be present in the early universe would have been in their most basic fundamental form.
We wouldn't have been out of form structures like protons, even at that stage isn't valid for me to ask how big these things were like how big was how big was the universe?
before after inflation.
So this Yeah, of course I found So for example, a patch.
Um, that is about 10 to the minus 20.
Think about 10 to the minus 27 centimeters and would have grown.
Would have been enough.
Big enough.
Yeah, 10 Mohs, 27 centimeter at about 10 to the minus 30 seconds after the big bang would have been enough to then grow too easily encompass our observable universe, which, at the end, our observable universe at the end of a period of in flesh of would be probably about the size of a grapefruit, and then it could carry on growing after that.
But it would have done enough expansion to then account for the observed I such a way that we see today from very small, great threw a grapefruit myself.
By the end of the period of inflation that will require there could have been much more.
I mean, nobody.
There are models of the universe because they require these scale of fields.
You can chose the potential.
That's the thing that you can play around with get different predictions.
There's a very key thing about inflation, which I need to discussing the second.
But different models will give you different periods of it amounts of inflation.
But we require fixed amounts in order to account for the observed uniformity of this radiation and the observed flatness special flatness of the universe.
But isn't it also happened to the inflation?
Couldn't.
Isn't there a point where you guys will say inflation lasted that long?
That would work.
I mean, if you go, you tell me this level band is this attempt to the well, there's an upper bound.
No, I mean you can have.
There are models of what we call an eternal inflation.
These are models where inflation has been going on in some part of the universe forever.
It's just no happening here.
Well, actually, it is happening right now with dark energy, but it's a different energy scale.
Um, so there isn't enough abound in that sense.
I mean, there are there are models of inflation where your it's constantly popping off different regions of space, growing exponentially quickly.
But they're just not the regions that we live in.
It's it's important our region.
Inflation did end because if inflation carried on, then structures could never fall matter would always be ripped apart rather than it being allowed to clump together.
So we know inflation had to end.
It could have gone on for a long, long time in terms of the amount of doubling of the size of the universe.
But we know that we require the fixed amount at the end of the inflationary period.
In order to account for what we see today, you talk about things you know, the observable universe, but the universe that we so they in flesh and leads to the size of the universe, way bigger than our observable born.
And so we don't know what's going on out in those regions and its indoors regions that we could.
It could still be inflating that could still be regions of the universe and floating up there and sporting more expansion, accelerated expansion.
There's a group Whole group of people don't particularly like the idea of inflation.
And there's it, Andre would Mitt and I've worked on both both both of these sides of the argument on dhe.
One of the reasons is the question of you know, how fine tuned do you have to be in order to get inflation in the very in the early universe.
And there is a big question about this using this agony over this initial patch, for example, why should it have been uniform at this park where we were expect quantum fluctuations to be so big that it could spoil it all for you?
And so there is that there is a question about the fine tune aspects of these inflationary models on dhe.
That's one way you you argue about how, how how likely it is that inflation actually occurred.
And that's enough.
That's still a debate going on as to that.
And there are different models, and there's better models called the cycling universe right where the universe undergoes a series of expansions and collapses on each.
Each time it collapses and bounces back.
These air usually brains that bouncing out of string theory of bouncing back out.
You call that your big bank, but there are issues.
There is well concerning how you actually deal with the bounce itself.
All of these models, where you end up dealing with regions of high curvature where singularities conform, you always ending up because the mathematics usually is breaking down on you.
Degree of speculations required to actually fully try and map from one region to another.
We're not speculation, but but But you need to acknowledge that we may not have full control of the mathematics and that we need to try and understand that better.
It's an amazing idea.
It's so now let me come to the big guy said.
I needed to talk about which many people would say it classes it on really solid ground, which is in many ways the big key breakthrough or the key result out of inflation isn't necessarily this fact that it provides me with their naturally a natural where to get a smooth, homogeneous psychotropic universe.
That's not the key thing.
The key thing is that it provides me with a way of obtaining the initial fluctuations in the matter content in the universe.
It provides me with those seed primordial fluctuations with which Galaxies can then begin to grow, that which the microwave background that no Satrapi's can be observed to be what they are and the reason inflation does this for me is this inflict on this scale of field again?
Remember, I drew the picture in over here where I said imagine the field is on a potential which is flat and then getting steeper.
Okay, so and it's evolving down, and I drew it very smoothly, justly, Boulding down.
But in reality, what's happening is this field is a quantum field is not a classical feel like a ball rolling down it's got.
It's a quantum object.
Quantum objects inherently have fluctuations just through the Heisenberg uncertainty principle.
So as it's mean, value is indeed going down.
It's wanting to just fall down all the time.
It's fluctuating backwards and forwards backwards and forwards backwards and forwards.
These fluctuations mean that in some regions of the universe, it's slightly higher up the potential in other regions.
It's slightly lower down the potential.
That means it's got slightly more energy here in this region, slightly less energy in this region.
So now, in different parts of the universe, I've got these slight deviations in energy.
Those feed into the equations they affect, how gravity works, where it's slightly more energy in the particles, slightly less energy in the particle, and it provides you with this small fluctuations in the pull of matter towards matter from this region to this region, photons of light experienced slightly different gravitational poles as they go through.
And they lead naturally to the onset of these fluctuations, which is the microcosmic Mac with background on no such place which we discussed with about plank on, then letter on.
From those fluctuations, you see the structures of the universe.
What inflation seems to do quite remarkably is when you look at the distribution of these fluctuations of the microwave background and you look at these Doppler peaks, okay, and they can now pick out about seven of these Doppler peaks and you fit it to your inflationary scenario.
It just works like a dream.
It just maps all of them.
There are some slight issues in some regions which people are homing in on because they're desperate to find something that might be wrong with inflation.
But the US that we don't yet understand about it.
But the general feature seems to be there that the inflationary prediction due to these fluctuations of this field seemed to map brilliantly over to the cosmic microwave background.
And so there's a whole group of people would say inflation is on really firm footing.
I'm not quite there because I see inflation is this wonderful paradigm that works really well that that the idea works really well.
But where did this infant on field come from?
Where did this scale of field come from?
It's got some forms from some fundamental theory on dhe.
They We begin to struggle, actually, if you try to, and that's where I have been doing the bulk of my work.
If you try and incorporate inflation in the world of particle physics and are in string theory, it's actually not that easy.
It's quite difficult to get a scale of field, which does everything you want it to do in terms of the cosmic microwave background on, yet also fits very nicely into the dynamics of the universe.
From the world of string theory exist.
Escape field existed where it is gone.
The bulk of its energy has gone.
Yes, and there are some models of the of the universe.
Remember, I said, there are many models of their sinful, so in the majority of them is gone that the field has has decayed on dhe.
That's the reheating process at the end of inflation, and it's declared its energy has gone into creating a ll the particles.
But there are some models called one particular set.
Wallace called quintessential inflation, where that that inflict on energy hasn't yet old gone on dhe.
Some of it is still driving the current acceleration of the universe.
The universe is accelerating again today at a much lower energy scale.
Then it was accelerating in the early universe.
But it's still it is accelerating on dhe.
Some bottles have that energy there, but the majority of the models would say it's something else, causing that exoneration today and that inflict on energy has indeed gone.