Time Travel and Conservation Laws

[TheBaker]

I'm doing some research into time travel for a presentation I have to give in a month or so, and I'm currently looking at the compatibility of Time Travel and the Laws of Conservation.

Sending an object back in time would increase the mass - and hence the energy - in the Universe at this time, and would therefore appear to violate the conservation of energy.

However, I found http://www.weburbia.com/physics/time_travel.html" that says that in fact the conservation laws may not violated because conservation laws are local, whereas there may not be a global conservation law.

I've tried to find more information on this, but couldn't nothing obvious came up, so I was wondering what people here thought of the idea.

Assuming that there are no other objections to time travel, do conservation laws necessarily rule out time travel? Or can the two be compatible (even if it requires something strange to be happening)?

 

[JesseM]

However, I found http://www.weburbia.com/physics/time_travel.html" that says that in fact the conservation laws may not violated because conservation laws are local, whereas there may not be a global conservation law.

Here's a good page on the problems with defining what "energy conservation" means globally in general relativity (and general relativity does allow for the possibility of backwards time travel in certain unusual spacetimes):

http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

 

[deathstar]

It would have more mass i think when it speeds up to allow it to go back in time but as soon as it stops it would have the same mass. Asumeing nothing interfears. If it did make it back in time we wouldn't see it because events in time would change it. But it would have more mass at the objects initial entry in time.