Name: Inflation & the Universe in a Grapefruit - Sixty Symbols
Uploaded: 2020-03-30T04:14:17.000Z
Duration: 24 min 8 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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.

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.

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.

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.

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.

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.

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.

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.

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.

If you take a photo of your family, then blow it up and put on cameras on the wall.

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.

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.

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.

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.

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.

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.

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.

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.

Subtitles ListPlay Video

Inflation & the Universe in a Grapefruit - Sixty Symbols

potential

process

majority

slightly