Practice English Speaking&Listening with: The Arrow of Time feat. Sean Carroll

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It's perfectly obvious the time has a direction

All we mean by that is that the past is different from the future in lots of different ways

We were younger in the past, we will be older in the future

We remember the past, we don't remember the future

The surprise is that that difference between past and future

is nowhere to be found in the deep down laws of physics

Time is actually a lot like space if you're out in a space suit flying around

there will be no difference between up, down, left, right

likewise, there is no intrinsic difference between the past and the future

in the laws of physics. Now that's not completely a mystery to us

we know that what actually happens in the real world

is that you're not just made of one or two particles

bumping into each other, you're a very very complicated collection

of many many particles and they're becoming more disorderly with time.

this is just saying that entropy increases.

The interesting thing is that every difference between the past and the future

will utimately be traced to the fact that the entropy was lower

in the past and is growing. That's the Second Law of Thermodynamics

The universe was orderly, it's becoming more disorderly

That's not a surprise. There is more ways to be disorderly than to be orderly.

The suprise is that the universe was ever low entropy to begin with.

If we go all the way back to the Big Bang, 13.7 billion years ago, the universe began

in a highly ordered state. So, modern cosmologists are trying to understand

right now why the early universe was in a such precise state.

why it was so low entropy. Once we understand that,

it will make perfect sense to us why the arrow of time stretches

as it does from the past to today all the way toward the future.

The Description of The Arrow of Time feat. Sean Carroll