time travel

Remembrance of Things Future: The Mystery of Time from nytimes

"There was a conference for time travelers at M.I.T. earlier this spring.
I'm still hoping to attend, and although the odds are slim, they are apparently not zero despite the efforts and hopes of deterministically minded physicists who would like to eliminate the possibility of your creating a paradox by going back in time and killing your grandfather."
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"The mystery of time is connected with some of the thorniest questions in physics, as well as in philosophy, like why we remember the past but not the future, how causality works, why you can't stir cream out of your coffee or put perfume back in a bottle."
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"She added in an e-mail message: "I have always thought that there has to be some basic fundamental notion of causality, even if it doesn't look at all like the one of the space-time we live in. I can't see how to get causality from something that has none; neither have I ever seen anyone succeed in doing so.""
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"But nobody knows if phantom, or exotic, energy is really allowed in nature and most physicists would be happy if it is not. Its existence would lead to paradoxes, like negative kinetic energy, where something could lose energy by speeding up, violating what is left of common sense in modern physics.
Dr. Krauss said, "From the point of view of realistic theories, phantom energy just doesn't exist.""
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"Being a good physicist, Dr. Polchinski phrased the problem in terms of billiard balls. A billiard ball, he suggested, could roll into one end of a time machine, come back out the other end a little earlier and collide with its earlier self, thereby preventing itself from entering the time machine to begin with. "

very very fascinating indeed.