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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 you’re focusing upon time travel to the future. And I’m not referring
to the silly thing that we all age, right. We’re 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 you’re 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 they’re 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.
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Brian Greene: Time Travel is Possible

60 Folder Collection
林峰生 published on March 27, 2020
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