The answer to the OP is “where do you want to end up?”. More specifically, “where do you want your characters to end up?”. Time travel is fiction, make up your own rules as to how it works. As long as you’re consistent, your readers won’t object to any rules you make.
I guess it would depend on who made the time machine, right? If it’s a Yugo, you’d have a pretty good chance of getting stuck in some kind of frightening semidimension where the ground is made of monkey vomit and the wind sounds like “Never Gonna Give You Up” when it blows past your head.
Ooooh, can we add two arbitrary dimensions and use 0/0/0/0/0/0?
Because unless he’s changed it since his Oval Office visit, that’ll also unlock Kanye’s iPhone. And then we can all Venmo ourselves some cash.
Doesn’t CPT symmetry imply that it’s impossible, even in theory, to distinguish between “normal” matter moving forward through time, and antimatter moving backwards in time? And conversely, antimatter moving forward in time would also be indistinguishable from normal matter moving backwards in time, AIUI.
Set me straight, eh?
Symmetry is one thing, but what is “moving backwards through time” supposed to mean??
If you define it correctly (so a time-reversed particle will have opposite momentum, etc.) then it should change matter to antimatter in a mirror.
The most reliable form of time machine requires a machine at either end of the travel period. It might even be the same machine since time machines tend to exist at some time in all timelines. So if you want to go back in time to say Aug. 19, 1985, there has to be a time machine someplace on Aug. 19, 1985, and that’s where you’d end up when you travel through time. It should be much easier to travel into the future because time machines are more likely to exist there. If you want travel back in time to now then you’d have to build a time machine now and wait to travel back to it.
In this thread about time travel? It is supposed to mean exactly what it sounds like: “experiencing/manifesting time in the opposite direction of what we normal-matter beings experience/manifest it.” Going from t=1 to t=0 to t=-1, if that helps. Inverse entropy. 2nd Law in reverse.
I honestly thought “moving backwards through time” was clearer than the above. Shows what I know.
I am not sure it is as straightforward as you are implying, in this context. Consider a positron just sitting there. Is it moving forwards, or backwards, in time? Both?
I would suggest that in fact the concept (that anti-matter is “matter moving backwards in time”) is actually pretty straightforward, it’s just that it’s wrong.
Consider a positron that was created by a particle collision at time t=0. Is the positron still there at time t=1? Was it there at time t=-1, prior to the collision? If the answers are “yes” and “no”, respectively, as they typically would be, then the positron has the same trajectory along the timeline as any other matter.
Serious question. Can there be such a thing as a positron “just sitting there”?
Okay, let’s illustrate with a hypothetical.
“Hey, that electron over there just drifted a bit north.”
“Bah! I say that that positron over there just drifted south, and it only appears to have moved north because you and it are moving in opposite directions through time.”
“That’s silly, because, uh …”
AIUI, there’s no measurement that can even theoretically distinguish between the two interpretations. My understanding is surely flawed. If someone can complete the “That’s silly, because …” objection, have at it. I’m always up for more knowledge.
… unless of course, your interpretation of the positron having been created at t=0 is biased by your personal Time’s Arrow. Perhaps it’s a virtual particle annihilating itself and its antiparticle at t=0, having come into existence at t=23 or some such.
AIUI, “Yes, but it takes a special effort to create the necessary conditions.”
I think you’re needlessly over-complicating and muddling the question. My observation of the arrow of time (not the rate of flow of time, but the direction of it, as determined by properties like entropy and the relation of cause and effect) has to be regarded as fundamentally objective, in the same way as other fundamental observations like entropy must be regarded as objective, because otherwise no observation at all is meaningful and we can’t make useful statements about anything.
I must strenuously disagree. In the last 2 days, I’ve personally traveled about 48 hours into the future.
Now if I could just figure out how to speed this process up…
I think you’re missing a salient point, and surely that’s due to my failure to express this concept to you effectively. First, I agree that you and I and all the “normal” matter in the world experience time in the direction indicated by the 2nd Law of Thermodynamics.
What I’m asking you to imagine is what a particle of antimatter, traveling through time in the opposite direction to you and I, would look like to an observer (such as yourself) traveling in the “usual/proper” direction of time.
You say, “Look, it gets created right here, at t=0. And here it is later at t=1.”
I say, “But it’s moving backwards through time, so when it goes from t=1 to t=0 and disappears, you’re actually witnessing its annihilation. The energy consumed to create the particle (in your/our “forward” time) is, in “reverse time,” the same energy produced from its annihilation.” [NB: That’s an illustrative turn of phrase, not a quantitative equation, nor a claim that energy exists outside of time or anything like that.]
Your Arrow of Time is surely objectively true for you and me and everybody else. But we’re not antimatter!
ETA: I have clearly spent too much time doing drugs and reading Victor J. Stenger books, albeit never simultaneously.
ETA²: … as far as I can recall.
Fine, that clarifies what you meant (and I presume you would say that what we later observe as the positron’s annihilation was actually its “creation” in its time-reversed universe). But I stand by my point, because this sort of speculation has neither explanatory nor predictive utility AFAIK, and therefore isn’t actually science. It’s much like the speculation about the tachyon, which really does travel backwards through time – that is, if it exists, which it almost certainly does not.
Right. And if I were at a physicists’ conference I’d have dummied up until I could find an appropriate venue for idle physical/metaphysical spitballin’ with like-minded folks, preferably online if possible …
Wasn’t it Richard Feynman who first introduced the notion that antimatter is ordinary matter traveling backwards in time?
This made a number of people unhappy then, and my understanding is that even fewer are happier about it now.
But two physicists, three opinions also applies.
One of the ways I’ve heard it explained… If you’re not moving in space you’re moving thru time at maximum “speed” (whatever that means), but as you move thru space you slow down the movement thru time. Which implies you can only go slower into the future.