Or that there is t a singular timeline for all events; that there is a multiverse and traveling back in time may lead you to a different past than whence you came. So, say, the future travelled came from a universe where 9/11 didn’t happen, so had no way of prefetching it. And, also, that our present may not lead to the time traveler’s future, as we’re in different universes with different timelines.
Do I believe that as a possibility? I mean, I really don’t know, but I wouldn’t discount it.
If you’re going to argue that lunacy is actually just the first stage of genius, I think you need to count all the lunatics who just turned out to be genuine lunatics.
I think this is no reason at all. For one thing, if time travel landed you someplace dangerous or fatal, that’s a nasty consequence of time traveling, not proof there is no such thing. I think there’s a similar non-proof that people traveling by jet cannot be achieved, because it’s hard to navigate to within a hundred feet vertically at the end of a long trip, and people would wind up falling or being interred.
For another thing, we can too choose a frame of reference. We can choose the frame that is stationary with respect to our time traveller at the beginning of their time travel. Or a frame moving at any arbitrary velocity WRT our time traveller. Again, the traveller may or may not appreciate their arrival circumstances, but that doesn’t prove the travel can’t be achieved.
We might quibble as to what constitutes time travel. In the H. G. Wells story “The Time Machine” the traveller sits in the machine, exposed to the elements, and sees the world speed up around them. Drifting in and out of sleep for a few hours arguably produces a similar effect. So does hibernation or suspended animation, except seeing the world is difficult or impossible for the traveller due to their own ability during the trip. All of these kind of default to the long term physical stability of the traveller’s departure platform.
Anything that gets us into our own past, with agency rather than as a ghostly observer, would be something very much more special, because we generate paradoxes and break causality. I doubt this is possible, and think it’s easy to prove it’s impossible, except for my reservations about physical mastery of the universe that might as well be magic to uninitiated eyes after many millions of years of intellectual advancement.
I’m sure my latest time machine will work properly as soon as I can test it. The problem is that it is only a time transmitter that can transport matter to a time receiver someplace in the future that is broadcasting a homing signal across the past. I haven’t figured out how to make that receiver yet. Apparently I never will and no one else will either. Oh well, back to the drawing app.
Given enough instances of time travel, we’d eventually have reliable reports of people suddenly appearing in our timeline who weren’t there a second ago. Even if they couldn’t accurately predict anything about our future, their sudden appearance, taken by itself, should leave us wondering how they achieved such a feat.
Plus, one would expect that travelers from the future - any future - would arrive with some really incredible technology that’s not-at-all within our capability yet, the equivalent of arriving in the mid 1800s with a PC (and a rather large battery that can power it long enough for a credible tech demo).
And if there’s a long future in which time travel to the past is possible, we’d eventually expect our own timeline (and all other timelines) to become crowded with future-to-past time travelers.
The absence of all of this, even in a multiverse, still suggests that time travel is not possible, or that we go extinct before we figure it out.
That’s a distinct possibility. If the universe forbids paradoxes, then anyone going back in time can only act in a way that is consistent with established history; this is called Novikov Self-Consistency, and it would severely constrain the activities of prospective time-travellers.
However there is an alternative; travelling back in time might allow you to change history, but this just creates a different timeline and the future you create is different from the one you came from.
The exact mechanisms of the laws of time that would allow travellers to change history are debatable; does the original timeline ‘fade away’ or suddenly vanish; like in Back to the Future?
Or do both timelines continue to exist, and you might be able to travel back to either alternative? If you use the wormhole method I described way back in post 19, then there is a good chance that the original wormhole still exists, and with it a link back to the original timeline with unchanged history.
I’ve written a short story or two about time travel, and once you introduce alternate futures and alternate timelines things get complex very quickly.
Yeah, because time travel stories are otherwise so straightforward and simple.
I have seen two different sources (X-Men First Class and La Brea) where not only does the original timeline exist, but the following happens:
Personally, I am in the “if backwards time travel is possible, it is to a parallel universe where it won’t affect the one that the travelers left” (and that the past is the same in both universes up to the point where the travelers arrive) camp.