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<blockquote data-quote="Umbran" data-source="post: 6738382" data-attributes="member: 177">Er.&nbsp; We should be careful about how we say such things, really.&nbsp; Sometimes I'm sloppy.Technically, at the moment, we expect that those conservation laws hold strictly, and that FTL is not possible.&nbsp; We do not know for absolute certain they are both strictly and totally true.&nbsp;&nbsp; If they are both strictly true, we do not know that one *causes* the other (and which way that causality goes), or if both are merely axioms of the universe (such that both must be true in order to have a consistent universe, and neither one really has priority), or if both are merely logical results of some even higher set of principles.In reality, when we say, &quot;You can't do time travel, because that violates causality/conservation, etc,&quot; what we are really saying is, if you plug in numbers faster than light, the rules as we understand them give results that do not make sense.&nbsp; But, there are ways...As an example, we can imagine a universe with those conservation laws, in which time/FTL travel is possible, in a limited sense.&nbsp; It turns out that so long as your time travel never violates causality, no conservation rules get broken.&nbsp; This is equivalent to a universe in which no logical paradoxes occur as a result of time travel.&nbsp; Robert L. Forward wrote a novel, Timemaster, that takes place in such a universe, that has a form of cosmic sensorship.&nbsp; In the book, this manifests as a sort of predestination for the time traveller - he feels at every particular moment like he has free will, but once he starts time travelling, he really doesn't.Forward was not the best at characterization, but for finding things to write about that seemed really wacky, but were technically allowed (as of the time of his writing, at least), he was pretty awesome.We can, less easily, imagine a world in which the conservation laws do not *strictly* hold - that there are ways they may break.&nbsp; Those ways must be pretty arcane, but they may be in the back corners of how things work, such that we haven't ever seen them.&nbsp; But, maybe the ban on FTL still holds, for other reasons.</blockquote>

[QUOTE="Umbran, post: 6738382, member: 177"] Er. We should be careful about how we say such things, really. Sometimes I'm sloppy. Technically, at the moment, we expect that those conservation laws hold strictly, and that FTL is not possible. We do not know for absolute certain they are both strictly and totally true. If they are both strictly true, we do not know that one *causes* the other (and which way that causality goes), or if both are merely axioms of the universe (such that both must be true in order to have a consistent universe, and neither one really has priority), or if both are merely logical results of some even higher set of principles. In reality, when we say, "You can't do time travel, because that violates causality/conservation, etc," what we are really saying is, if you plug in numbers faster than light, the rules as we understand them give results that do not make sense. But, there are ways... As an example, we can imagine a universe with those conservation laws, in which time/FTL travel is possible, in a limited sense. It turns out that so long as your time travel never violates causality, no conservation rules get broken. This is equivalent to a universe in which no logical paradoxes occur as a result of time travel. Robert L. Forward wrote a novel, [i]Timemaster[/i], that takes place in such a universe, that has a form of cosmic sensorship. In the book, this manifests as a sort of predestination for the time traveller - he feels at every particular moment like he has free will, but once he starts time travelling, he really doesn't. Forward was not the best at characterization, but for finding things to write about that seemed really wacky, but were technically allowed (as of the time of his writing, at least), he was pretty awesome. We can, less easily, imagine a world in which the conservation laws do not *strictly* hold - that there are ways they may break. Those ways must be pretty arcane, but they may be in the back corners of how things work, such that we haven't ever seen them. But, maybe the ban on FTL still holds, for other reasons. [/QUOTE]

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