

It's official: Time machines won't work - uladzislau
http://latimesblogs.latimes.com/technology/2011/07/time-travel-impossible.html

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hamner
Please link to more reputable sources for scientific articles. For an example,
the university press release is intended for a general audience and more
factual: <http://www.ust.hk/eng/news/press_20110719-893.html>, and the peer-
reviewed publication is here:
[http://www.phys.ust.hk/dusw/Publication/PhysRevLett_106_2436...](http://www.phys.ust.hk/dusw/Publication/PhysRevLett_106_243602.pdf)

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beej71
Dup and ancient. I read this back in 2067.

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glimcat
There was some real science done. Then the media took it and ran with it.

Spoilers: the real science did not in any way involve time travel.

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nohat
The research determined that single photons could not move faster than the
speed of light (sounds obvious, but quantum scale objects don't necessarily
behave). This does not disprove time travel, just one hypothetical phenomena
that could have led to time travel.

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__rkaup__
I've always wondered: isn't travelling to the past the same thing as making
matter from nothing? That is, since then there would be two copies of you.

~~~
Udo
Kind of, I always saw it as leaving this universe irreversibly and entering an
earlier version of it from out of nowhere. But since atoms don't have unique
IDs, it's no problem to have two (almost) identical people beside each other.

Also, contrary to popular fiction, the past isn't changed only because a
blundering human is transported into it, it is _already_ altered by the mere
introduction of additional matter into a system that would have evolved
differently without it. So, if you want to change the past, transport a single
proton back 2 million years into some swamp. Of course, that would be
pointless because nobody would ever know what changed...

The real conundrum is what actually happens to the "old" universe at the
instant of traveling back into the past. Is everything that happened between
those two points in time erased? Or does the old universe continue as if
nothing happened and a new parallel one branches out that is of no consequence
at all? In the infinite universes theory, time travel would merely amount to
"jumping" into the "right" neighboring universe (however, personally this
whole business with infinite branching parallel universes always seemed like a
wasteful and inelegant model to me).

All these theories have one thing in common though: things change only for the
time travelers themselves. So for meaningful time travel, you would have to be
able to transport whole beings across a doorway in spacetime. Twice. In the
right direction. Given the known conditions near theoretically surmised holes
in spacetime, that's not an easy task. Atoms: maybe. Huge fragile collections
of unstable molecules: probably not.

