Name: 【TED】Sean Carroll: Distant time and the hint of a multiverse (Sean Carroll: Distant time and the hint of a multiverse)
Uploaded: 2017-03-20T19:21:36.000Z
Duration: 15 min 55 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...

We live in a galaxy, the Milky Way Galaxy.

There are about a hundred billion stars in the Milky Way Galaxy.

and you point it at a random part of the sky,

as long as your camera is attached to the Hubble Space Telescope,

is a galaxy roughly the size of our Milky Way --

a hundred billion stars in each of those blobs.

There are approximately a hundred billion galaxies

100 billion is the only number you need to know.

The age of the universe, between now and the Big Bang,

Which tells you something about our place in the universe.

One thing you can do with a picture like this is simply admire it.

I've often wondered, what is the evolutionary pressure

that made our ancestors in the Veldt adapt and evolve

As a cosmologist, I want to ask, why is the universe like this?

One big clue we have is that the universe is changing with time.

If you looked at one of these galaxies and measured its velocity,

And if you look at a galaxy even farther away,

What that means, of course, is that, in the past,

In the past, the universe was more dense,

If you squeeze things together, the temperature goes up.

The thing that doesn't make sense to us as much

is that the universe, at early times, near the Big Bang,

You might think that that's not a surprise.

You might say, "Well, maybe things just smoothed themselves out."

But the conditions near the Big Bang are very, very different

than the conditions of the air in this room.

is we have a universe with a hundred billion galaxies,

At early times, those hundred billion galaxies

were squeezed into a region about this big --

And you have to imagine doing that squeezing

where there were a few more atoms than somewhere else.

Because if there had been, they would have collapsed under the gravitational pull

Keeping the universe very, very smooth at early times

is not easy; it's a delicate arrangement.

that the early universe is not chosen randomly.

There is something that made it that way.

So part of our understanding of this was given to us by Ludwig Boltzmann,

an Austrian physicist in the 19th century.

And Boltzmann's contribution was that he helped us understand entropy.

It's the randomness, the disorder, the chaoticness of some systems.

we can rearrange the constituents of a system so that you don't notice,

so that macroscopically it looks the same.

is one in which there's only a few arrangements that look that way.

is one that there are many arrangements that look that way.

the law that says that entropy increases in the universe,

is simply because there are many more ways

to be high entropy than to be low entropy.

This insight that entropy increases, by the way,

is what's behind what we call the arrow of time,

the difference between the past and the future.

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【TED】Sean Carroll: Distant time and the hint of a multiverse (Sean Carroll: Distant time and the hint of a multiverse)

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