Thank you all for the explanations, but I think until I fully grok special relativity, Lorentz transformations and relativity of simultaneity, the answers won't make any sense to me. Maybe the question I should be asking is "why do we believe there is no absolute time frame", but that would change this question too much, I believe.
I won't delete this on, but leave it up for interested readers and flag it as a dupe. Maybe the answers here will make more sense to them than to me. Cheers, everyone
I keep reading that FTL means traveling back in time would be possible, but all explanations I've read so far seem to concentrate on when it is we perceive the arrival of light as the observer. Maybe the definition of time travel that people are using is different from the one in Sci-Fi, so maybe my incomprehension comes from there.
Here's what I think as a programmer. Could someone please point out in layman terms what I'm misunderstanding?
I assume, were the universe a computer, it'd have a global state that is constantly changing.
In order to perceive this state and its changes, we have evolved with utensils to do so. Our perception is always of something that happened in the past because the fastest thing to transfer that information travels at the speed of light. There is always a lag and the greater the distance from an event, the greater the lag.
Now that we've established state, perception and speed of information travel, let's say we have the possibility of traveling faster than the known maximum speed of information travel / lightspeed.
Scenario 1: actor observing past action
An actor does an action at normal speed, instantaneously travels to a location where the information of that action will take (let's say) max 10 seconds to arrive, and sees itself doing an action from 10 seconds ago. There was no time travel but simply a lag of information transfer.
Scenario 2: two actors at different FTLs
A cataclysmic event happens on earth. Slow FTL actor starts trip to distant planet to transfer information. Time passes and a faster FTL transport is made and fast FTL actor is sent to transfer information again. Fast FTL arrives before Slow FTL. Destination already has information that Slow FTL was bringing, and Slow FTL traveled ahead of light that was also bringing the information.
Destination will get the information 3 times, but the even will always lie in the past. Even if destination mounted a rescue mission and sent help instantaneously to earth, the cataclysm would still have already happened. The global state had already changed.