I've always wondered if the 'Roswell' alien (tall, thin, bulbous heads for holding giant brains, gigantic eyes, very small mouths and noses, long fingers, no hair) aren't actually aliens at all, but are us from millions of years in the future after we'd evolved more, darting back in time to conduct their version of archeological research.

That brings to mind a nitpick I always have with science fiction games.

That Tachyon blaster? I want it to drop the opponents shields BEFORE I shoot it. Either give me a proper time-traveling weapon, or don't name it a Tachyon blaster.

Interesting idea! That never occurred to me before.

It's also quite plausible, in theory — more so than practical intergalactic space travel (which will almost certainly require technology even more miraculous than mere time travel), but less so than practical intragalactic space travel. Physicists surmise that traveling backwards through time may be possible via utilizing wormholes in some way.

It's also interesting in that that's basically how we currently appear to apes - taller, thinner, paler, less hair, larger eyes. Apply that template to us, exaggerate it, and you get the classic "grey" alien. Even if they aren't actually real, it's funny we'd view them in the same light that 'lesser' animals view humans in, even down to the "mysterious abduction" angle. (Electronically tagging animals then returning them to the wild = probing.)

That's one of the setting features of Continuum. The P&P, not the plane.

Time travel into the past is disproven by a simple mental exercise, I think.

You send something into the past. Anything. A single photon of light. A jelly donut. Al Gore. Whatever.

This Whatever now exists twice. Time ekes forward until you get to the event that sends the Whatever into the past.

This Whatever now exists three times. Time ekes forward until you get to the event that sends the Whatever into the past.

This Whatever now exists four times.

Five times.

Five thousand times.

...

Infinite times.

The moment time travel to the past is accomplished, infinite expression of the sent item occurs. Of course, sometime before that, the mounting quantities of radiation/jelly donuts/Al Gores results in the time travel event to fail to occur.

That doesn't make much sense to me. If you send a pen to the past, sure, up until the point you sent that pen to the past, there are two versions of that pen in the 'present' (that is, the time traveling pen's present), but once the pen gets to that point in time, then the version of itself that is sent to the past isn't in the present with it anymore, it's back in the past, so, in the present, only one version of the pen exists again. A version that is older than it should be because it went through the same amount of time twice. But one version, none the less.

At 2PM, we send a pen back to 1PM.

Back at 1PM, there's now two pens. 2PM comes around, where the time travel event occurs and one pen gets sent back to 1PM. The second pen keeps existing.

Back at 1PM, there's now three pens. They're the same pen, existing multiple times. 2PM comes around, time travel event, one pen goes to 1PM. There's two pens that keep existing. They're the same pen, existing twice.

Back at 1PM, there's now four pens.

So on.

So on.

Eventually (instantly), the laboratory fills up with pens and the machinery goes kablooie, thus preventing time travel from taking place.

I don't think that's what happens.

At 2pm you send a Pen(A) back to 1pm.

At 1pm there is a Pen(A) which traveled in time and a Pen( B ) which has not traveled yet.

At 2pm you send a Pen( B ) back to 1pm. Now there is just Pen(A) again. At 3pm, only Pen(A) exists.

At 1pm there is a Pen( B ) which traveled in time and a Pen(A) which has not traveled yet.

At 2pm you send Pen(A) back to 1pm. Now there is just Pen( B ) again. At 3pm, only Pen( B ) exists.

And so on.

See?

Your explanation is very compelling. And near as I can tell, far more correct that my take.

My dissatisfaction: fatigue is killing my reasoning ability.

I get where he's going with it, though.

On Sunday, a gold smith refines two gold bars. On Monday, they're in your office, and in a meeting, you decide to send back all your gold bars except for one tomorrow. On Tuesday, you send one back to Monday morning...meaning you have three in your office on Monday, even though only two gold bars have been refined. That's a violation of conservation of matter.

Ah, but it's more complex than that:

At 1400, you send Pen back to 1300.

Pen is indeed gone from 1400 now, but Pen is NOT gone from 1359 and earlier, because you didn't send it back until 1400.

Pen and Pen therefore exist simultaneously from 1300-1359.

You can send yourself back to 1359, then send both Pen and Pen back to 1300 again.

Now there exists Pen, Pen, Pen and Pen at 1300, and they will continue to exist all the way into the future (in theory).

----------------

However, this is not an infinite system, because the time frame isn't infinite.

But, at some point, you'll have caught up with yourself and once again, there will be only one pen. Or two gold bars.

Perhaps, but when exactly does that happen?

If you have four pens at 1300 and time progresses normally from there, at what time do three of them (let's call them the "time-clone" pens) cease to exist? At 1400? If so, why?

I don't know if that's actually the case.

Tuesday comes around, and there's this policy to send back all gold bars except for one. Now, on Monday, you have four gold bars in your office, which means three get sent back, so now there're five gold bars, and onward recursively.

At some point, a Monday rolls around where the meeting can't happen because the conference room is a gold vault, and no one sends any back. What happens? The gold arrives in Tuesday just fine.

EDIT: Ninja, but hey, same point.

That sounds like one of Zeno's paradoxes, assuming you can split the time between 13:00 and 13:59 infinitely such that you can send infinite pens back. Even assuming you have enough control over time to permit the time travel, the actual sending of the pen still takes a finite amount of time, such that you can't perform such an action an infinite number of times in a given finite time period.

I think this is where the paradox comes into play (EDIT: people have posted while I was writing this, but I expected that). Noola, your example only holds true if we're using specific, exact instances in time, I think.

If you send Pen back to 1300 from 1400, is it really gone from 1400? From your point of view (at 1400), Pen, having been sent back to 1300, will immediately reappear in 1400, albeit one hour older than it naturally should be.

So if you send Pen back to 1300, send yourself back to 1359, send Pen (or two Pens, for that matter) back to 1300 again, and so on, you can get a lot of Pens all at 1300.

But will the clones all vanish at precisely 1400? That's the paradox.

Why would the clones vanish at all? If the gold clones vanish from Tuesday, then presumably they also vanish from Monday, which means you're sending gold back to Monday again because the meeting happens, and Wednesday becomes an impossibility. This is even ignoring that things don't spontaneously deconstruct into nothingness, because that too is a violation of conservation.

You guys have done no research.

Kyle Reese comes back in time from the future to protect Sarah Connor. He dies in the present (well, 1984), but not before fathering a son... who sends him back in time in 2029. The dead guy.

This has profound ramifications for time travel that I do not see addressed in any of your fancy-shmancy logimicatin'. Also, no one has discussed the criticality of traveling at 88mph.

Quite true, sending anything (energy or matter) into the past violates the law of conservation of energy, which is why there are grave doubts that travel into the past will ever be possible — wormholes or no wormholes. At some point on the timeline, you'll essentially have created something from nothing.

Future travel, on the other hand, has already been proven quite possible (at velocities approaching the speed of light; actually, any velocity, but the effect is minimal at, say, 88mph) and presents no paradoxes.

EDIT:


Fixed myself.