Faster than light travel

[shawnhcorey]

Again, the warp bubble complicates this. It takes the interior of the bubble outside everybody's light cone - things inside are causally disconnected from the rest of the universe while it exists. If the event that is "staring" effectively happens inside, there's no violation.

But eventually the bubble must be popped. So there are still 2 events outside each other's light cone: creating the bubble and popping it.

 

[Umbran]

My brain is just kinda hurting by the concept that something which causes gravity is the very thing that prevents gravity escaping it. I get stuck in this circular self-referential loop, which basically means I don't understand it.

If anyone who doesn't do tensor calculus tells you they understand General Relativity, they are simply incorrect. So, don't sweat it. Grokking in fullness requires heavy math that not everyone gets exposed to.

The point shawn is making is an issue if you only look at gravity as a particle or a wave - the typical quantum mechanical view. But, as we know, QM and Relativity don't get on so well. And, back in classical mechanics, there's a third thing gravity is - spacetime curvature.

General Relativity is all about calculating that spacetime curvature. And, it does not care about the whole particle/wave thing. From this viewpoint, there is nothing traveling from within the hole to the outside world, so the speed with which it does so is irrelevant.

 

[shawnhcorey]

My brain is just kinda hurting by the concept that something which causes gravity is the very thing that prevents gravity escaping it. I get stuck in this circular self-referential loop, which basically means I don't understand it.

And that is why there is a search for alternatives.

"Black holes do not exist—at least, not as we know them, says renowned physicist Stephen Hawking, potentially provoking a rethink of one of space's most mysterious objects." No Black Holes Exist

 

[Umbran]

But eventually the bubble must be popped. So there are still 2 events outside each other's light cone: creating the bubble and popping it.

Sure. But you get no paradox, no closing of the curve, unless a round-trip is allowed, which may not be the case for the Alcubierre Drive.

 

[shawnhcorey]

The point shawn is making is an issue if you only look at gravity as a particle or a wave - the typical quantum mechanical view. But, as we know, QM and Relativity don't get on so well. And, back in classical mechanics, there's a third thing gravity is - spacetime curvature.

Curved space-time means the radial distance is increased to infinite. Since everything must travel the speed of light or slower, nothing can escape a black hole, not even gravity.

Some think that the curved space-time detaches itself from the mass and remains in its inertial frame but this has been shown to be incorrect.

 

[shawnhcorey]

Sure. But you get no paradox, no closing of the curve, unless a round-trip is allowed, which may not be the case for the Alcubierre Drive.

If you can do FTL once, you can do it many times.

 

[Umbran]

And that is why there is a search for alternatives.

"Black holes do not exist—at least, not as we know them, says renowned physicist Stephen Hawking, potentially provoking a rethink of one of space's most mysterious objects." No Black Holes Exist

From that same article: "I would caution against any belief that Hawking has come up with a dramatic new solution answering all questions regarding black holes," said theoretical physicist Sean Carroll at the California Institute of Technology, who did not participate in this study. "These problems are very far from being resolved."

 

[Umbran]

If you can do FTL once, you can do it many times.

Moving slower than light, there are places in spacetime, places outside your light cone, that you cannot reach. If you can move at sub-light speed, you can move many times, but there are places you can't get to.

There's no reason, a priori, that moving FTL removes ALL restrictions on travel. It may be that, though you are moving FTL, you could do so many times, but there would still places you cannot get to.

 

[shawnhcorey]

There's no reason, a priori, that moving FTL removes ALL restrictions on travel. It may be that, though you are moving FTL, you could do so many times, but there would still places you cannot get to.

Except that special relativity allows you to change things by merely changing your velocity. If there are 2 events outside each other's light cone, the order in which they happen can be changed by changing your velocity. The past is not fixed; it depends on your point of view.

 

[tomBitonti]

Not any more than gravity slows down light - which is to say not at all. Things with zero mass (photons and gravitons) move at a fixed speed in vacuum. Rather than slowing down, they lose energy - meaning the their wavelengths get red-shifted. Saying "light cannot escape a black hole" is saying that light originating within the black hole gets red-shifted to nothing.

That's true for light originating at the event horizon. Light originating within the event horizon follows a path that reaches the singularity at the center of the black hole. Any direction in which light can be emitted within a black hole points towards the singularity.
Thanks!
TomB