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  • We know a lot about time. We know that time in some sense is at rock bottom that which

  • allows change to take place, right. When we say that time has elapsed we notice that because

  • things now are different from how they were a little while ago. That’s what we mean

  • by time elapsing. But is time some fundamental quality of reality or is it something that

  • our brains impose on our perceptions to organize our experience into some coherent framework

  • that allows us to survive. I mean I can well imagine that we have been under evolutionary

  • pressure over the millennia to organize perception so that we can survive, get the next meal,

  • plan for the future. All of that would seemingly require that we have a conception of time

  • that we apply to what we experience out there. But that doesn’t mean time as we experience

  • it is real. It doesn’t mean that time as we experience it is how the world is actually

  • structured. I mean there are many ideas that people put forward. The possibility for instance

  • that, you know, we all know that matter is made of molecules and atoms. Could it be that

  • time is also made of some kind of ingredient? A molecule of time? An atom of time? Is that

  • really what time is at a

  • fundamental level?

  • Time travel is absolutely possible. And this is not some sort of weird sci-fi thing that

  • I’m talking about here. Albert Einstein taught us more than 100 years ago that time

  • travel is possible if youre focusing upon time travel to the future. And I’m not referring

  • to the silly thing that we all age, right. Were all going into the future. Sure, I’m

  • talking about if you wanted to leapfrog into the future, if you wanted to see what the

  • Earth will be like a million years from now, Albert Einstein told us how to do that. In

  • fact he told us two ways of how to do it. You can build a spaceship, go out into space

  • near the speed of light, turn around and come back. Imagine you go out for six months and

  • you turn around and you come back for six months. You will be one year older. But he

  • taught us that your time is elapsing much slower than time back on Earth. So when you

  • step out of your ship youre one year older but Earth has gone through many, many years.

  • It can have gone through 10,000, 100,000 or a million years depending on how close to

  • the speed of light you traveled.

  • And he also taught us if you go and hang out near the edge of a black hole time again will

  • elapse more slowly for you at the edge of the black hole than back on Earth. So you

  • hang out there for a while, you come back and again you get out of your ship and it

  • will be any number of years into the future, whatever you want all depending on how close

  • you got to the edge of the black hole and how long you hung out there. That is time

  • travel to the future. Now of course what people really want to know about is getting back.

  • Can you travel back to the past? I don’t think so. We don’t know for sure. No one

  • has given a definitive proof that you can’t travel to the past. In fact, some very reputable

  • scientists have suggested ways that you might travel to the past. But every time we look

  • at the proposals and detail it seems kind of clear that theyre right at the edge

  • of the known laws of physics. And most of us feel that when physics progresses to a

  • point that we understand things even better, these proposals just will be ruled out, they

  • won’t work. But I guess I would say there’s a long shot possibility based on what we know

  • today that time travel to the past might be possible. But most of us wouldn’t bet our

  • life on it.

We know a lot about time. We know that time in some sense is at rock bottom that which

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Brian Greene: Time Travel is Possible

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    林峰生 posted on 2020/03/27
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