Time travel doesn't necessarily break the laws of thermodynamics, It just means that things will be different in the past when traveling back in time, even if nothing is changed.
Realistically The Flash has an unmanagable and messed up timeline with so may plot holes that the required levels in suspension of disbelief exceed even Doctor Who and Legends given that The Flash is not a time travel show, but nonetheless suffers from variable in inconsistency as if it were.
Unless (this is a big unless) you accept the presence of two things:
1) The laws of thermodynamics allow for the destruction and recreation of new timelines but not new alternate realities.
2) Time constructs (these are different from time remnants) take the place of missing persons out of time or alternate universe. They are very much real beings, but are nonetheless doomed to destruction by their original counterparts.
I am not in physics. I do not math beyond algebra. But I do enjoy Sci-fi.
If you too enjoy sci-fi and the flash, please join me in these AU moments we've never, and can never see.
