[A Navy Vet]

"The universe has a certain amount of mass and energy. If you travel to another time, forward or backward, you would increase the ‘mass’ of the universe, because ever atom and subatomic particle of your body has always been around in some form or another since the beginning. T travel to another ‘time’ your atoms would then be duplicated, which is a no-no. To offset the duplication you would be immediately turned into energy."

Interesting. I haven't thought of that. The best sci-fi time travel movies are about unknown dimensional travel like "Arrival". Not sure if your thesis would be applicable in that case.

[Red Badger]

In Asimov’s short story, The Ugly Little Boy, and later full novel version with Silverberg, they handled the problem of ‘mass’ by having the boy and every little thing, grass, dirt, etc, they captured in the past and brought to the present, by having it stay in a ‘bubble of energy’ that was neither in the past or the present, but in between. Of course it too huge amounts of energy to keep the ‘bubble’ going, so it couldn’t be kept up for a long time.

https://en.wikipedia.org/wiki/The_Ugly_Little_Boy