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<blockquote data-quote="AbdulAlhazred" data-source="post: 6734638" data-attributes="member: 82106">Modern notions of time travel all involve the construction of some sort of 'closed time-like curve', that is some sort of 'wormhole' into the past. So you would literally pass through. The question then is at what point would you say something had been created or destroyed? Truthfully there are vastly many things that would be broken by time travel, including every single known conservation law I believe, at least from some observer's perspective. This is why physicists are mostly pretty down on the whole concept, it seems most likely to be something that &quot;just can't happen&quot;. Again Noether's Theorum raises its head here, if these conservation laws are broken, then their dual symmetries are also broken.There is an 'out' here though. As best we can interpret the evidence the Universe is truly vast, and the part we can see, and ever be causally connected to, is only a tiny fraction (something on the order of one part in 10^120th power parts) of all that there is. If the Universe is really so extensive, then almost every conceivable configuration of matter must exist somewhere within it. That would include, say, a planet exactly like Earth except just like Earth was 3 weeks ago. If you could go there, would that be time travel? Opening up a wormhole to such a place and stepping through, would that violate any conserved property of the Universe? It would seem not. So, perhaps, we could go any place outside of the portion of the Universe causally connected to Earth. We could go there regardless of any limitations imposed by the speed of light or any other consideration of causality. You just have to find a way to build such a 'wormhole'. Of course there likely simply is no such way, but we really don't know enough to rule it out.</blockquote>

[QUOTE="AbdulAlhazred, post: 6734638, member: 82106"] Modern notions of time travel all involve the construction of some sort of 'closed time-like curve', that is some sort of 'wormhole' into the past. So you would literally pass through. The question then is at what point would you say something had been created or destroyed? Truthfully there are vastly many things that would be broken by time travel, including every single known conservation law I believe, at least from some observer's perspective. This is why physicists are mostly pretty down on the whole concept, it seems most likely to be something that "just can't happen". Again Noether's Theorum raises its head here, if these conservation laws are broken, then their dual symmetries are also broken. There is an 'out' here though. As best we can interpret the evidence the Universe is truly vast, and the part we can see, and ever be causally connected to, is only a tiny fraction (something on the order of one part in 10^120th power parts) of all that there is. If the Universe is really so extensive, then almost every conceivable configuration of matter must exist somewhere within it. That would include, say, a planet exactly like Earth except just like Earth was 3 weeks ago. If you could go there, would that be time travel? Opening up a wormhole to such a place and stepping through, would that violate any conserved property of the Universe? It would seem not. So, perhaps, we could go any place outside of the portion of the Universe causally connected to Earth. We could go there regardless of any limitations imposed by the speed of light or any other consideration of causality. You just have to find a way to build such a 'wormhole'. Of course there likely simply is no such way, but we really don't know enough to rule it out. [/QUOTE]

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