What do you mean by “simultanously”? You’ve used it to refer to events which do not occur at the same place.
The details are not significant. Simultaneously in the rest frame of earth. Whatever. Or send a timing signal from Mars to Earth at the same time as the radio message is emitted toward Alpha Centauri, then leave Earth when you receive the timing signal. You’ll still arrive before the radio message, even though you’ve given it a head start.
I think that you’ve shown that the distance between your departure point and Mars is six light years;
The distance between Earth and Mars is 225 million km on average, or 12.5 light minutes.
If you like, you can send your radio message from the same location as your departure point. First emit a (directional) radio signal from earth toward Alpha Centauri. Then depart in your spaceship, just making sure not to collide with the radio signal on your way there (go a different way, say by taking a pit stop at Vega). You’ll still get there before the light signal.
you’ve done that by moving space around such that the point you departed from is in the vicinity of Alpha Centauri.
In a sense, yes, that is exactly what an alcubierre drive is meant to do. The trajectory that starts at Earth, enters the bubble, sits there a while, exits the bubble and arrives at Alpha Centauri travels “locally” less than six light years. The bubble train might be analogised to a wormhole in that it establishes a shorter path between two otherwise distance places.
But unlike a wormhole, the Alcubierre drive doesn’t require you set up the path and destination in advance (unless Krasnikov is right, and there aren’t any tachyons), and it’s an effect confined to the vicinity—in space and time—of the ship using it. So in all meaningful senses it can reasonably be described as a faster than light drive, as opposed to a bridge, which is what a wormhole is.
That ‘directional radio signal’ is taking a longer path, as noted by the fact that a different directional radio signal (one that went with the traveler) would get there first.
Are you using a Euclidean definition of speed? Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
Sanity check: before, during, and after the trip, shine a laser continuously ‘forward’, toward the destination. Turn off the bubble well short of arrivial. What pattern of red shifting should the destination expect to see?
Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
I’m sure it only looks like insanity to people who haven’t studied general relativity.
The point is that an Alcubierre drive lets you get from here to Alpha Centauri (which I now discover is actually 4.4 light years away, since I finally decided to look it up just then) in less than 4.4 years. Whether it does that by temporarily making the distance shorter along a certain path is mostly irrelevant for the purpose of classifying it as a particular kind of starship drive.
The point which started the discussion is that you don’t get to look back and see yourself leave. (probably; I’m not certain how light behaves when there is more than one ‘straight line’ path, of different lengths, to the destination; that seems like is could happen if you took a dogleg around the most direct path.
The details are not significant. Simultaneously in the rest frame of earth. Whatever. Or send a timing signal from Mars to Earth at the same time as the radio message is emitted toward Alpha Centauri, then leave Earth when you receive the timing signal. You’ll still arrive before the radio message, even though you’ve given it a head start.
The distance between Earth and Mars is 225 million km on average, or 12.5 light minutes.
If you like, you can send your radio message from the same location as your departure point. First emit a (directional) radio signal from earth toward Alpha Centauri. Then depart in your spaceship, just making sure not to collide with the radio signal on your way there (go a different way, say by taking a pit stop at Vega). You’ll still get there before the light signal.
In a sense, yes, that is exactly what an alcubierre drive is meant to do. The trajectory that starts at Earth, enters the bubble, sits there a while, exits the bubble and arrives at Alpha Centauri travels “locally” less than six light years. The bubble train might be analogised to a wormhole in that it establishes a shorter path between two otherwise distance places.
But unlike a wormhole, the Alcubierre drive doesn’t require you set up the path and destination in advance (unless Krasnikov is right, and there aren’t any tachyons), and it’s an effect confined to the vicinity—in space and time—of the ship using it. So in all meaningful senses it can reasonably be described as a faster than light drive, as opposed to a bridge, which is what a wormhole is.
That ‘directional radio signal’ is taking a longer path, as noted by the fact that a different directional radio signal (one that went with the traveler) would get there first.
Are you using a Euclidean definition of speed? Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
Sanity check: before, during, and after the trip, shine a laser continuously ‘forward’, toward the destination. Turn off the bubble well short of arrivial. What pattern of red shifting should the destination expect to see?
I’m sure it only looks like insanity to people who haven’t studied general relativity.
The point is that an Alcubierre drive lets you get from here to Alpha Centauri (which I now discover is actually 4.4 light years away, since I finally decided to look it up just then) in less than 4.4 years. Whether it does that by temporarily making the distance shorter along a certain path is mostly irrelevant for the purpose of classifying it as a particular kind of starship drive.
The point which started the discussion is that you don’t get to look back and see yourself leave. (probably; I’m not certain how light behaves when there is more than one ‘straight line’ path, of different lengths, to the destination; that seems like is could happen if you took a dogleg around the most direct path.