Now if I wanted to travel back in time…to, oh, say the year 1800.
Wouldn’t this throw off the balance of things? All of the matter that makes up me, my clothes, and whatever else I have with me at the time would just be gone from 2000. Would there just be an empty hole? What would happen?
All that matter would be transported back to 1800. But would there be room for it? What would happen when all this matter just suddenly appeared?
So, what would happen if I were to go back in time?
This problem isn’t anything to do with time travel; teleportation would encounter the same problem; you’d have to displace the matter that is at the destination or else materialisation will be… ummm… uncomfortable…
No big problem at the dematerialisation end though; you disappear and there’s a slight ‘pop’ as the air rushes in to fill the gap.
Or is the OP asking about conversation of mass? A human’s worth of mass appearing out of nowhere and than an equal mass disappearing 200 years later is one hell of a quantum fluctuation.
Indeed. It should violate the Second Law of Thermodynamics, but since tinme travel can’t necessarily be ruled out by modern physics, proponents of this or that theory of time travel often base things on a model that would allow transfer of mass without violating the SLT.
In C. S. Lewis’ unfinished novel The Dark Tower, a character argues that time travel should be impossible as it would necessarily violate the conservation of matter, resulting in a person being in two places at the same time; even if a person traveled to an era long before his birth or long after his death, the atoms which constituted his body would still exist, whether as the grass to be eaten by the cow which is a remote ancestor to the one which provided his steak dinner last night, or as dust blowing at some crossroads.
A suggestion I recall reading a few years ago was that if time travel is possible, then the universe may have some self-compensating mechanism; when a person disappears from their era matter is somehow “sucked” into the universe to create a blanace, and it sloshes out again when he arrives at his destination.