> Since the speed of light is the fastest possible movement, there is no way to arrive at the event location faster than that, any faster movement means you would be time traveling back into the past in attempt to reach the event before it happens.

I don't quite get the time travel bit. I've seen too many sci fi and fantasy shows where time is effectively frozen while supernatural entities move about. Other than the supernatural entities moving about, the instant is the same everywhere, it doesn't go back.

And if I see an event at Alpha Centauri, and immediately teleport there, the light wave is still at Earth. I haven't traveled back in time to the origination of the light wave at Alpha Centauri. And my light wave will not reach Earth until another ~4.3 years has passed after the first light wave that prompted my journey to Alpha Centauri. So the observer will not see anything unusual. I will not have rewritten the light pattern they saw.

Also I think astronomers do see events which appear to be violations of causality, but are actually just gravitational distortions of the light traveling from an event. So interference with the travel of light from an event can't really be seen as traveling back in time.

If you were to teleport to the appropriate space coordinates upon seeing the event, the event being in the past (since you are seeing the event with light delay), you would not arrive in time to see it up close.

If you wanted to see it up close, you would have to travel into the past, since your teleportation would have to include a translation of time coordinates, not just of space coordinates.

Also, although order of events is variable, causality is (I believe) currently assumed to be absolute, so while two observers can differ on which came first between events A and B, this is only possible if A and B’s light (really, information) cones do not intersect such that one precedes the other causally.

Suppose A does not intersect B by light cone, and you can instantly teleport. Then you can interact at A, teleport and interact at B, then immediate teleport everywhere in the universe, causally intertwining all frames before causality can physically propagate to those coordinates. Then you have time traveled to such an extent that I have no idea how the universe reconciles such a thing.

It seems to me a bit like scattering a bunch of sand onto a still body of water. The sand hits simultaneously at all points, creating waves that interfere and reinforce each other. Why does the universe have to reconcile? Just let the waves do what they do and move on from that.

The simultaneity and single reference frame of the sand hitting example means there are no contradictions present.

Assuming a finite speed limit to information transfer exists, exceeding that limit means you can create a potentially unlimited number of contradictions in state.

It would be like watching the waves do what they do, but none of it happened, because no matter what you think you saw, there is at least one contradiction (due to the teleporting meddler). Like if you imagine any one state, and you meddle it to be impossible, as if doing Cantor’s diagonalization on the potential state space (if you can do literally instant teleportation and action with no cooldown).

The sand hitting is an analogy for the transition from a 3-dimensional reference frame to a 2-dimensional reference frame (ala Flatland).

I honestly don't understand what you're talking about with respect to contradictions. You aren't traveling back in time by instantaneously jumping. Is the universe supposed to be one cohesive thing? What are you talking about when you reference states in relation to the universe?

I lost the edit window so I'll tack on that I've been thinking about this with respect to conventional faster than light travel. I think that sort of relativistic speed travel basically requires traveling back in time, because time is supposed to slow as one gets close to the speed of light. If hitting the speed of light was actually possible for a massive particle, then presumably time would stop (I think)? So for that case I guess time would have to reverse if speed could increase, though I don't know that causality would have to reverse. Maybe under these conditions there could be paradoxes of various kinds.

I'm not a relativity physicist, and don't even know if these questions and suppositions are even the right things to be asking. If one could travel faster than the speed of light by teleportation, I don't think time travel or an unsyncing of the fabric of reality seems like it would need to happen. But what do I know. Thought experiments don't always reflect reality.

Since fast moving objects appear to contract (to an outside observer) the faster they go, if you have an object traveling at near light speed, it will appear vanishingly short, regardless of its true length.

So let there be a one mile long object, let it travel at nearly light speed for five seconds. As God, freeze time after 5 seconds and place two measuring stations: one touching the head of Object from Observer's point of view, and one touching the tail of Object from Object's point of view (we can teleport around instantly so we can verify that we've got everything set up correctly with no penalty).

Observer Head thinks Object Head and Object Tail are at about 5 light-seconds + 1 mile from origin (because Object is vanishingly short, and Object Head started at 1 mile from origin). But within Object, the Tail is 1 mile behind.

So Object Tail will signal Observer Tail at about 1 mile/c before it reaches where it supposedly is, and Observer Tail instantly signals Observer Head, thus Observer Head receives causality from its signal before it sends its signal.

Not sure how the universe resolves that. Unless the universe can "overclock" and become indefinitely fast at propagating and processing information when need be.

I think my example isn't entirely sound because I forget the exact math (it's been a long time), so you might have to tweak the example to be fully mathematically sound, but the general concept of causal contradiction within one's own frame of reference should be sound, I think.

I think I've understood your example. I'm just not sure how important it is. We have things such as optical illusions already. Does this have a material effect on the structure of the universe? On objects in the universe? Or is it just causing mathematical paradoxes?

I've played around with the fantastic idea of instant portals between places (or simple teleportation), and assume this would have unusual effects on gravity when, for instance, portalling from one side of a planet to the other.

I think I lack the theoretical basis to really understand whether this is a problem for the universe as it is. And I don't think a lay explanation can be satisfactory. I appreciate your attempt.

An optical illusion is an appearance of something amuck without it actually being so.

In this case, something is actually (not illusory) happening before it happens, if we assume some actor that can act faster than causality can keep up.

I have also come to the conclusion I have forgotten too much of my math haha, was a fun exercise trying to recover some part of it.

> I don't quite get the time travel bit. I've seen too many sci fi and fantasy shows where time is effectively frozen while supernatural entities move about. Other than the supernatural entities moving about, the instant is the same everywhere, it doesn't go back.

Those representations are inaccurate.

If time is truly frozen, that means photons should be frozen in place, unless photons are somehow exempt due to having no mass and thus no time.

If the frozen photon theory is correct, you would have to see things by moving your eye into rays of light and letting photons hit your receptors and get consumed. But because these photons are being consumed and not replaced, you will leave pockets of darkness where your eyes will see no signal if you pass through there again.

At normal everyday distances you will see everything frozen in place with this method. However, at long distances such as light years, moving into the light source will run its animation over time at the speed you are moving toward it. So you will see the event occur before your eyes right up until you reach the destination where the event has already occurred, and you can observe firsthand what we already knew to be true.

> Those representations are inaccurate.

Yes, I know Sci Fi and fantasy are inaccurate depictions of reality.

> So you will see the event occur before your eyes right up until you reach the destination where the event has already occurred, and you can observe firsthand what we already knew to be true.

I get this.

I just don't get how moving faster than the speed of light (or causality) necessarily invokes literal time travel. And while I've read that physical scientists are amazed at how well mathematics model and predict reality, if this time travel is a result of the mathematics, then I need to be convinced that in this case the mathematics really are modeling reality.

Look at it this way, let’s say you’re at the event site and seeing it happen right in front of you.

Suddenly, some travelers arrive and say they also came to witness the event, but they came from light years away.

How? The light of the event would have only traveled for a few light minutes, and no other type of information would travel faster than that. There’s no way someone light years away would know about it yet.

The only explanation, assuming they didn’t perfectly predict the event, is that they time traveled. From your perspective they covered a distance of light years in the span of time between the event’s start and you first meeting them.

Sure. But assuming time is traveling the same for you, their origin point, and the photons going between the two, they won't suddenly appear when the event has just begun, even if they travel instantaneously. Because, as you say, the point at which they first saw the event had yet to receive the light image of the event.

And if they do seem to suddenly appear much faster than you would believe possible, you suddenly know that you're at the bottom of a time-dilation gravity well (or the equivalent). Though you probably could have figured this out beforehand from the red-shift of the light traveling between the two points. Or you know that they observed the event from a closer point of view, instantaneously traveled to a most distant location to change clothes, and then traveled again to your location. Time travel is only one of at least three possibilities.

If you are in a time dilation gravity well, the mere act of outsiders traveling into it might be time travel itself, as they are traversing the well from the outside (what you would think of as the future) to reach a point inside where time is lagging behind.

Time may be lagging behind, but you aren't traveling backward in it. Merely transitioning to a slower tick-tock cycle.

So in that case traveling into the heart of the well would feel like you are fast forwarding the events of the well until you gradually synchronize with the tick cycle and things move at normal speeds? In which case you could never reach the exact moment of the event you set out to see.

The object has been fully dragged across the event horizon into the black hole?

Or you can consider the event as "inevitably will happen." Just as valid.