In the original Star Trek pilot, their engine was a “time warp” one. Maybe they had this until someone pointed out it was impossible.
They are one coordinate.
But if you notice, even though Doc Brown only sets time coordinates in his machine, he essentially arrives at his destination at the same relative spot that he left. While he hasn’t moved anywhere (beyond the 88 mph thing) from Marty’s point-of-view, his Delorean still moved the same amount of distance as the Earth, solar system, and galaxy moved over the time interval Doc Brown programmed in.
So the Delorean is accepting the “Here” part of the “Here, Now” coordinate (x[sub]1[/sub]y[sub]1[/sub]) as an absolute position relative to the Earth, but then calculating a (y[sub]1[/sub] - y[sub]2[/sub]) amount of planetary, solar, and galactic drift, and calling that x[sub]2[/sub].
So Doc Brown still arrives at the same point X, but it’s only the same point X relative to the Earth; not to the sun, nor to the galaxy, nor to the universe. He must have one hell of a computer in that Delorean. Or maybe that’s what the Flux Capacitor does.
I’m seriously pushing the limits of my knowledge of relativistic physics; if I push any further, my head might asplode.
Hi, Neighbor,
Yeah, but your body is also moving along with the earth, sun, solar sytem, galaxy, etc. In a time machine, or at least the ones I have seen portrayed, they disappear, only to appear at some other time, but in the same place. This would indicate that they go “somewhere else” only to appear at the right time and place. However, in your case, in order for the time machine to stay in the same place, it would always be there. Which I guess would work. But then people in the past would have seen this machine thingy that had always been around. And I have seen Primer and I guess that is pretty close to the concept in that movie.
For example, if the Delorean in “Back to the Future” really worked and it stayed on the earth, you should be able to see it at every point in time between 1985 and 1955, if it’s moving along with the earth. Right?
No, what he’s saying is that the delorian is keeping track of all of the movements of the earth.
More so with HG Wells’ Time Machine, where he could see his surroundings changing.
But the BTTF time machine might arguably be jumping directly from one point in time to another, without passing through the intervening period at all - a bit like tunnelling electrons.
I have a proposed solution (which might have been touched upon in previous posts, I’m now too lazy to look back):
You want to travel in time - the effect of this is that you inherit a vector that is exactly equivalent to your motion at the precise point of departure (vector is reversed if you’re going back in time) - you very literally fly off at a tangent, travelling a distance commensurate with the interval of time travelled.
This has been answered in Chapter 1 of The Time Machine:
Which is fine, until someone builds a wall there. You may not be able to see the spokes of a wheel, but you sure notice what happens when you shove a stick in between them.
But you can’t inherit the vector and wind up where you want, since the direction of the vector of traveling is continually changing thanks to gravity pulling you down and keeping you on the ground as the earth rotates. Your vector at any moment will point you away from the earth. The earth would also be pulled away from you thanks to the sun’s gravity.
The Wells solution might work if you make contact with the forces often enough to be pulled along. In the movie he winds up inside a mountain for a while. In the book he says that this would be okay while traveling, since he’d slip through the mountain, but stopping inside would be a problem. In the book the ground never seems to rise or fall, so he doesn’t have the suspended in air problem.
I wonder that every time I see McGyver hop through the Stargate.
Something else I wondered. Wells’ machine just seemed to be a device for creating a slower bubble of time, surely everyone would see George sitting in his machine, looking blankly into space as they passed.
In the Strontium Dog comic they have time bombs which are like grenades - you throw it at someone and it transports them (and their immediate environs) a short time into the future, by which time the planet has moved on and they end up floating in space without a spacesuit.
The TARDIS approach would be, I think, the most plausible. For an interesting story, our time traveler usually needs to end up in something like “the same place”; and since that’s very hard to define, the best narrative option seems to be that you control both time and place of emergence.
There are, of course, other alternatives. Larry Niven’s “Flight of the Horse” stories involve the notion “what if ‘time travel’ really is a fantasy literary device?” – that is, a device or mechanism which travels in fantasy? So Our Hero is sent back into time to retrieve a horse (long extinct), and returns with a unicorn…
But then there’s the notion implicit in Asimov’s “End of Eternity”, and also a story by John Brunner which I’m forgetting the name of. If time travel and affecting the past are possible, then at some point a time traveler will take actions which guarantee that the invention of the time machine doesn’t happen. In consequence, if time travel is possible that leads to a universe in which there is no time travel …
That was the conclusion of Larry Niven’s story Theory and Practice of Time Travel
If time is a dimension, like length, height, and width, couldn’t we start at, say, 1,1,1 on the x, y and z axes, and just slide along the tau axis and wind up where 1,1,1 on the x, y, and z axes intersect the tau axis? That is, not 1,1,1 in some absolute frame of reference, and thus millions of miles away from the position of “then-Earth,” but at the point that “then-Earth” was touching the tau axis…thus appearing in the same place relative to earth?
Does that make any sense? Earth as a four-dimensional object, we move along one axis of the greater whole?
Not necessarily - if you position yourself very carefully and launch at a precise time when your vector points to where another (or the same) point on Earth will be in the future, or was in the past.
It would take an almost impossible level of precision, but with the Earth rotating as it does, and orbiting as it does, and moving around the galaxy as it does, there must be tangents from certain times and places that align with others in other times and places.
That’s nine hundered miles an hour, but I gotcha right away. 
Well, that would explain why there wasn’t a horde of time travelers at the crucifixion, etc. The only time you can travel back to without winding up in the middle of space is February 15, 186778543 BC.
I actually roughed the tangents idea out as the premise for a sf story years and years ago - it imposes lots of interesting restrictions and risks, at the same time as permitting just enough interesting possibilities.
If you’re skipping over intervening space instantaneously, you are traveling in time. If I could blip from here to our nearest star, I’d be getting there 4 years before light from Sol could make it there. Leaving aside issues like quantum entanglement, in normal space no information can travel faster than light. Relative to Earth, I’d be able to see things four years in the past.
With fictional time machines, you pretty much have to assume that if someone could make the time part work, the space adjustments would be solvable too. You’d have a built-in warp drive along with your time machine. Makes the time part seem banal in comparison since you could find out what the extent of the universe is with a few days of popping around and taking measurements from various spots.
He also skips over the question of what happens when a billiard ball traveling at near lightspeed interacts with the mass of the guy’s body. What happens when something is traveling at a velocity relative to something else is that some fraction of the kinetic energy of that object is converted to heat at the time of impact and it imparts some or all of its kinetic energy into the other object, depending on whether or not it’s an elastic collision.
This one ain’t elastic. It wouldn’t go through and make a neat little hole, it would obliterate itself and the guy, and atoms and particles would go flying off in all directions, generating essentially nuclear interactions. CERN uses gigawatts of power to accelerate particles — not even atoms, but little bits of atoms — to near lightspeed in order to study the subatomic particles that are generated when the particles hit some atoms.
A 150 g mass is going to release quite a bit more energy at impact than a few measly gigawatts. The party guests in Asimov’s story would have been at the center of a thermonuclear fireball, not witnesses to a clever murder.
Decent story though.