Does the Law of Conservation of Matter/Energy Disallow Time Travel?

[Ari Sheffield]

I was thinking about this recently while talking to one of my friends. I was playing devil's advocate with what he was saying, when all the sudden I realized something-

The law of conservation of mass and energy states that matter/energy can neither be created no destroyed. However, if you were to time travel, either you, or if you don't exist anymore, the particles that made you, would still be there. And so would you. That means there will be more matter in the time you travel back to than there is supposed to be.

I apologize if this is a really stupid topic, or if this has an obvious answer. 
I have not consulted Google yet. I wanted to see some other people's thoughts on this first.

[vorlon13]

No fate . . . . .

[ignoramus]

That's probably why it's impossible?

[robvalue]

That would appear to be one of the paradoxes that could occur, yeah.

I don't think "time travel" is well-defined enough to be coherent, honestly.

[Alex K]

Good question! I agree with rob though, one would probably have to be more specific how the time travel one envisions is supposed to be accomplished, to say something further. If there is e.g. a wormhole connecting two times in the same universe, forgetting about causal paradoxes for a moment, I don't see why they couldn't possibly act as sources and sinks of energy - energy conservation is not to be taken for granted in general relativity - but I haven't done the calculation. It's quite possible that the energy would be borrowed/ reabsorbed from or into the wormhole itself such that it would look more massive once you've gone through to compensate that you're gone, or in the past, gets lighter when you come out.But I'm just guessing.

[Anomalocaris]

In that case, wouldn't the appearent mass of a wormhole foretell the outside observer how much stuff can go through time to come out of it into the observer's time?

[Alex K]

In that case, wouldn't the appearent mass of a wormhole foretell the outside observer how much stuff can go through time to come out of it into the observer's time?

Yeah, I guess so, but I haven't really thought this through. Would it be a conceptional problem if that were so?

[Anomalocaris]

In that case, wouldn't the appearent mass of a wormhole foretell the outside observer how much stuff can go through time to come out of it into the observer's time?

Yeah, I guess so, but I haven't really thought this through. Would it be a conceptional problem if that were so?

If we assume conservation of mass and energy over any span of time means a backward time travel portal wormhole with mass can't just suddenly be caused to appear by the time traveler at his destination time, then the worm hole must predate any potential destination time it can access and have some uncertain origin not tied to the time travel.  Uunless the wormhole is a primordial feature of the universe, this means time travel can't access any arbitrary time, but only times during which the wormhole exists.

Perhaps one could build a wormhole time machine, but the machine can only access times after its own construction. It can't truly allow anyone go back in time to before the machine was built.

It also suggests an observer in the past can observe the preexisting wormhole and know something about where, if not when, a time travel from the far future going back in time would appear in the observer's near future to visit the observer, and alos perhaps put other constraints on what could come through the wormhole into his time, and perhaps add another layer of paradox by using this foreknowledge of future time travel to avoiding his visitor from the future?

[Alex K]

@Anomalo

Doesn't opening up and stabilizing a worm hole require negative energy density? Maybe they cancel ... But yes, if one plopped into existence that seems to violate energy conservation either way. Ok, homework for us: how does conservation of energy present itself if there are timelike curves?

[LostLocke]

No fate . . . . .

Charlie disagrees...