Is time travel possible?
Question asked by: knowitall
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The answer to this depends on four key factors:
- what you mean by time travel (definition)
- do you mean travel to the past, future, or scope (direction)
- what metaphysical entities you allow to exist (dimensions)
- do you mean logically possible, or practically possible (dynamics)
Clearly as you vary what you allow the answer will change, viz:
- if by time travel you mean the agent is consciously aware of less time passing than another, then someone in a coma or in a state of hibernation is a time traveller. If you allow wormholes and other purely theoretical devices to exist, then again the answer to the question of jumping through time will change.
The definition for time travel in this answer is thus fixed as follows, a generally accepted definition:
"A person X, will be said to have time travelled relative to a person Y if, having his wristwatch set to the same time as Y, at some future point the time does not correlate between their watches".
We of course assume that the watch has a battery that never runs out and the time on it is 100% accurate for this hypothetical case. We just need a clear definition to measure.
With this definition, the answer to the question 'can we travel to the future' is straightforwardly 'yes', and has actually been proven in tests. The way to time travel is to speed yourself up relative to the other person.
For instance, if Y is your average human on earth, and X is sent into geostationery orbit around the earth, over a period of time X will experience marginally less time than Y (very small fractions of a second, but on this definition time travel none the less). That this works has been proven with very accurate caesium clocks.
To get really pronounced time travel, unfortunately X will have to travel at speeds approaching light speed - so still very much theoretically possible, though of course practically impossible for humans at present. Alternatively, one would have to experience extremely strong gravitational effects, such as hovering around the event horizon of a black hole.
If we switch to talk about travel to the past, the answer would seem to be 'no'. That is unless you start to create theoretical devices like wormholes, which if they exist, just might let you move back and forth through space. However postulating an entity that we don't understand, nor know if it exists, is a pretty unsatisfactory way to answer a question.
To all intents and purposes, backward travel is not possible, as it appears to entail logical contradictions in the chain of cause and event. These cannot be gone into here, but in short it does not appear that these can be overcome.
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