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Wouldn't messages passing from the future to the past imply that the future can then influence the past? Which of course introduces a slew of paradoxes. I reali

Wouldn't messages passing from the future to the past imply that the future can then influence the past? Which of course introduces a slew of paradoxes. I realize the concept is concerned with single particles, but could there exist a series of messages that alters the original particles so much so as to introduce a paradox? (e.g. in the vein of "the grandfather paradox" in human time travel to the past, where a man kills his own grandfather.) edit: clarity.

spiritplumber 12y ago
Outside of physics, the future influences the past all the time, though. Imagine that you are in Stalinist Russia and win a minor scientific prize for a paper you wrote. There is a purge, and while you manage to not get deported to Siberia, the prize is reassigned to a less brilliant but more politically orthodox colleague, to the point that he is listed as first author of your paper. He goes on to have a better career because of this paper, and by the end of the affair, nobody remembers that you wrote the paper to begin with. If all observable effects of an events have been retconned, can that event be said to have occured? Can a similar situation happen in physics, and if so, does it "count" if only macroscopic effects are reversed? (To keep with the analogy, in this case, everything but your memory has been changed, but your memory hasn't been - although it might over time, due to you wanting to avoid cognitive dissonance).
givan 12y ago
> An atom that normally emits light will cease emitting when its surroundings become incapable of absorbing that light. Thus one event (emission) depends on something that does or doesn’t happen in the future (absorption). “That’s one of the examples of a particle probing the future and seeing what’s there, and then making a decision based on it, and just not decaying Using the above analogy the message sent from the future (the man exists) to the past will prevent the grandfather to be killed just like the decaying atom, maybe the messages send back and forth from the future rewrites the events to prevent the paradox, something like backtracking until it works.
DennisP 12y ago
Time travel doesn't necessarily introduce paradox. Imagine you have a billiard table, on which there's a wormhole. If you roll a billiard ball into the wormhole on the right trajectory, it will emerge three seconds prior to entering the wormhole, hit its earlier self a solid blow, and its earlier self will never enter the wormhole, creating a paradox. But when you try, it emerges from the wormhole on an altered trajectory, and strikes itself only a glancing blow. And why did it emerge with an altered trajectory? Because it was struck a glancing blow. This is the Novikov self-consistency principle [1]. Physicists have been unable to find initial conditions that don't allow a consistent solution. On the other hand, nobody has proven that consistent solutions always exist. And sometimes there are lots of consistent solutions. (I wonder whether that's why quantum physics isn't deterministic, but I'm no physicist.) [1] http://en.wikipedia.org/wiki/Novikov_self-consistency_principle http://en.wikipedia.org/wiki/Novikov_self-consistency_princi...

spiritplumber 12y ago

Outside of physics, the future influences the past all the time, though. Imagine that you are in Stalinist Russia and win a minor scientific prize for a paper you wrote. There is a purge, and while you manage to not get deported to Siberia, the prize is reassigned to a less brilliant but more politically orthodox colleague, to the point that he is listed as first author of your paper. He goes on to have a better career because of this paper, and by the end of the affair, nobody remembers that you wrote the paper to begin with. If all observable effects of an events have been retconned, can that event be said to have occured? Can a similar situation happen in physics, and if so, does it "count" if only macroscopic effects are reversed? (To keep with the analogy, in this case, everything but your memory has been changed, but your memory hasn't been - although it might over time, due to you wanting to avoid cognitive dissonance).

givan 12y ago

> An atom that normally emits light will cease emitting when its surroundings become incapable of absorbing that light. Thus one event (emission) depends on something that does or doesn’t happen in the future (absorption). “That’s one of the examples of a particle probing the future and seeing what’s there, and then making a decision based on it, and just not decaying Using the above analogy the message sent from the future (the man exists) to the past will prevent the grandfather to be killed just like the decaying atom, maybe the messages send back and forth from the future rewrites the events to prevent the paradox, something like backtracking until it works.

DennisP 12y ago

Time travel doesn't necessarily introduce paradox. Imagine you have a billiard table, on which there's a wormhole. If you roll a billiard ball into the wormhole on the right trajectory, it will emerge three seconds prior to entering the wormhole, hit its earlier self a solid blow, and its earlier self will never enter the wormhole, creating a paradox. But when you try, it emerges from the wormhole on an altered trajectory, and strikes itself only a glancing blow. And why did it emerge with an altered trajectory? Because it was struck a glancing blow. This is the Novikov self-consistency principle [1]. Physicists have been unable to find initial conditions that don't allow a consistent solution. On the other hand, nobody has proven that consistent solutions always exist. And sometimes there are lots of consistent solutions. (I wonder whether that's why quantum physics isn't deterministic, but I'm no physicist.) [1] http://en.wikipedia.org/wiki/Novikov_self-consistency_principle http://en.wikipedia.org/wiki/Novikov_self-consistency_princi...