Warp Drive Might Be Less Impossible Than Previously Thought

You can't go backwards in time using FTL. You can violate Causality, but that's not the same thing and isn't actually a big deal.

Picture it this way: You have a ship that can travel to Jupiter in 5 seconds. The method doesn't matter. You leave Earth, go to Jupiter, come back faster than light, and it's still 10 seconds into the Earth's future. You did not go so fast that you ended up in the Earth's past. You did not return while they were still counting down to your launch.

But what DID happen is that you outpaced your own light cone [wikipedia.org].

Since relativistic observers cannot exceed the speed of light themselves, and events can only propagate at the speed of light, then for all events, all relativistic observers will see the cause before the effect. That's Causality. But a lot of people get caught up on the whole "no absolute reference" thing and they take it a bit too far. Once something happens, it's done. You might not know about it yet, but it already happened and there's nothing you can do about it.

So what would it mean if we could outpace our own light cone? Not much, actually.

You could see the effect of some events before the cause, but you wouldn't be able to do anything about it. The cause already happened. The cause has its own light cone, but you're coming at it from a weird angle, so you haven't run into it yet. You might not even see the cause until you slow down and let it catch up to you "naturally".

Similarly, some observers would see you as moving backwards, but that's just because you're moving faster than the photons you're emitting. Anyone who saw that wouldn't be able to do anything about it, though, even if they could travel instantaneously. You've already long since passed them. If they could travel faster than you, they might be able to intercept you in the future by plotting out your course from what they observered, but they wouldn't actually be able to use what they saw to affect the past. Like if I found a blog post from you that said you were hiking from DC to Hollywood starting a week ago, so I figure out how long that will take and board a plane to meet you there. The Universe wouldn't much care.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/i16weThFhjQ/warp-drive-might-be-less-impossible-than-previously-thought

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