My Perception Of Time Travel

[Darby]

I worry about the law of conservation of matter/energy. Suppose that there is a finite amount of matter/energy in the universe. Every plank second that matter/energy moves into the next time dimension just like when we walk we move into the next physical dimension. Since the law of conservation of matter/energy states matter/energy cannot be created or destroyed we are composed of the same matter/energy that existed in the previous time dimension just like when you walk into the next physical dimension you no longer exist in the previous physical dimension.

schonovic,

In most common cases conservation of mass/energy holds. But this isn't a common case. It's time travel and the answer is deeply embedded in general relativity. The short answer is that these conservation laws are local, not universal. Here's an example that you can ponder:

Einstein stated that adding the cosmological constant to general relativity was his biggest mistake. In the sense that the reason he added it as a "fudge factor" to make the numbers come out correct maybe it was a mistake. However, experimental evidence ultimately determined that he was correct. There is a universal constant energy density everywhere. In the most empty vacuum it is still there and it is the same everywhere. So far, so good: there is a constant energy in a vacuum.

Along come late 20th Century cosmologists and they determine that the universe is expanding. Not so good. If the cosmological constant is, well, constant and the universe is expanding (increasing in volume) then a boatload of "new" energy must be coming from somewhere. Non-locally the conservation of mass/energy law is violated.