OMG, are you a future version of me?
Has anyone mentioned The Man Who Folded Himself yet?
I just like to give a shout out to C. L. Moore whenever I can. She was the best writer of the era, hands down.
I did ten minutes from now.
The two main interpretations of Time Travel are:
Predestination: The stadium in 2027 has always contained as many Johns as there ever will be, and none of them will be able to affect the events that occurred in the past, any action they take will only ensure things continue on. 2027 John could have looked around and seen all the future versions of himself (and maybe he did, and that’s why he knew time travel was possible).
Many Worlds: Every time John goes back in time to the stadium he creates a new timeline where events might play out differently due to his added presence. Also when 2040 John arrives would see 2027 John, but not 2045 John, because that John won’t travel back in time to create another timeline for 5 more years. 2050 John, crazed by guilt, could bring a sniper rifle and kill 2027 John, but that would not erase the other versions of himself because they all came from timelines where that didn’t happen.
Ironically, in both instances you can’t actually change the past. Either you can’t make any change, or you can only create a different future for everyone but you.
As has been said, if you pick coordinates in space (the stadium) you may or may not find John there. But if you have coordinates in space and time, John is guaranteed to be there. The stadium will have many Johns on that day. All of them will have been present on the day of the meeting. A photograph of the stadium taken by the Ur John on his first visit would show all the Johns who ever visited/will visit.
ETA
I’ve read Cyberiad. I’ve read Memoirs Found In A Bathtub. I have a copy of Solaris (the book not one of the films) around here somewhere. I love me some Lem.
The Time Traveler’s Wife has something like this scenario; the protagonist visits and revisits a crucial time in his life. If he’s watching out for it, he usually recognizes himself and knows if it’s a future or past version. That part of repetitively revisiting the death of his mother over and over was left out of the movie and we only saw two versions of him in that scene.
To think of space and time as two separtate things is the mistake that always trips up the human mind. There is only the one thing, which we are calling space/time for now until we better understand the ONE thing.
Until we can wrap our minds around thinking of it as one thing, time is just a semantic idea. Time does not really exist.
Try telling that to your mother, when she asks you what time you’ll be home after school. 
IIRC they do, essentially. The guy’s house happens to be a prime spot for viewing the asteroid impact, or whatever it was, and one group of time travellers rents rooms from him. Then a second group shows up and attempts to sabotage them with sonic weapons and the like, and to buy the entire house, in an attempt to kick them out.
I don’t think that’s physically correct. Yes, there is one thing we now label “spacetime”. But it’s thought to be made up of two fundamentally different things that are always found together: space and time.
Very, very metaphorically it’s like electric and magnetic fields. One can never exist without the other. But they are NOT the same thing, not even remotely. They are two very different manifestations of a single underlying phenomenon.
Within the context of fictional or speculational accounts of time travel, it’s almost irrelevant what the underlying physical reality is. We’re exploring philosophical or logical space, not physics space.
Yeah, but two groups is nothing like the massive overcrowding that Silverberg suggests.
Not quite. That was one-on-one: Calvin vs. the physical manifestation of his good side. The five duplicates were created earlier; they were supposed to go to school in his stead, but of course they were as work-avoidant as he was.
There was a time-travel sequence, though. Starts here. Two Hobbeses, three Calvins.
Well, I know who I am, but who are all you zombies?
Most movies, TV shows, and fictional books are fast and loose with time travel premises. Most involve causal loops, which are paradoxes that can’t be resolved and hence they are impossible. The Terminator (like Back to the Future, and many others) involves causal loops. Its time travel scenarios are impossible.
One movie that comes closest to reality (possibly) is Interstellar. It’s hard sci-fi. Caltech professor Kip Thorne contributed to the movie’s research, so the science behind the movie is spot on. This doesn’t mean time travel is possible (especially traveling into the past), but if it is, it will most likely follow Interstellar-style physics.
Of course, the 5th-dimensional being’s tesseract is nonsense.
Only in a four-dimensional universe. 3-space + one time dimension.
If you go back and change the past, you create a different timeline in an additional direction, which we can call the fifth dimension. The fifth dimension holds all the possible timelines; all the plausible worlds that might exist, whether you travel in time to create them or not.
However, I don’t know what happens in the sixth dimension - perhaps that’s where all the impossible timelines hang out.
Another is Primer.
Who is “we”? I’ve never seen a scientist make this claim. Or a novelist for that matter.
I wasn’t necessarily including ‘you’ in this ‘we’. But in some timelines you may be included thusly.