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Brian Greene: I'm Brian Greene, professor of physics and mathematics at Columbia University and co-founder of the World Science Festival. It's critical that you realize that there are two types of time travel, and they are radically different. Time travel to the future? Definitely possible.
As I read this, even though I do not have extensive scientific training, I understood this article. For my PhD research I read through Einstein's text 'Relativity', photo and cited below. I gathered basically the view below, from my PhD reading.
He showed that if you go out into space and travel near the speed of light, and you turn around, and you come back, your clock will be ticking off time more slowly. So, when you step off it's going to be the future on planet Earth. You will have time traveled into the future.
He also showed that if you hang out near a nice strong source of gravity — a neutron star, a black hole — and you kind of get right near the edge of that object, time also for you would slow down real slow relative to everybody else. And therefore, when you come back to Earth, for instance, it'll again be far into the future.
This is not controversial stuff. Any physicist who knows what they're talking about agrees with this.
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But the other kind of time travel — to the past is where the arguments start to happen because many of us don't think that time travel to the past is possible. The main proposal that people at least consider worthy of attention for traveling to the past does make use of a weird concept called wormholes.
A wormhole is something that really … Albert Einstein again discovered. The guy has like got his name written over everything in this field. It's a bridge, if you will, from one location space to another. It's kind of a tunnel that gives you a shortcut to go from here to here.
Now he discovered this in 1935 but it was subsequently realized that if you manipulate the openings of a wormhole — put one near a black hole or take one on a high-speed journey — then time of the two openings of this wormhole tunnel will not take off at the same rate, so that you will no longer just go from one location in space to another, if you go through this tunnel — through this wormhole — you'll go from one moment in time to a different moment in time. Go one way, you'll travel to the past, the other way, travel to the future.
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Now again, we don't know if wormholes are real. We don't know if they are real whether you'll be able to go through them. So, there are all sorts of uncertainties here. Most of us think that you're not going to actually go on a whirlwind journey through a wormhole to the past. But it's still not ruled out.
I can accept documented, empirical, reasonable, science and accepted these premises during my PhD reading. The first type of time travel is reasonable and possible.
Philosophically, I seriously doubt that a finite entity can naturally, within the physical, material realm, technically time travel to the past. I reason this would be logically impossible.
I suppose that supernaturally, theoretically, God could reverse and repeat events and/or simulate the past. I can grant solar time could be slowed down or sped up. If God did create a situation where events were reversed and repeated, this would be a repeat of events (more than once) and not, technically, time travel. However, biblically, time in this physical universe is linear only, by implication from Genesis to Revelation. Therefore, although I reason that God could dabble with the past, he clearly will not.
Einstein, Albert (1961) Relativity: The Special and General Theory, Translated by Robert W. Lawson, New York, Wings Books.
