[shanelja]

Question 2: What would happen if you, whilst within this bubble, throw a coin attached to a piece of string out of the space ship, while still connected to the ship by the string and the coin exits the bubble?

For instance, assuming the 'string' was made of a tough alloy, would it snap and the coin remain where it was at that time, would the ship be dragged back to where the coin is, or can the question not yet be answered by science?

I ask because, presumably, if the coin can exit and be fine, this could be the basis for some kind of inter galaxy bus, no need to slow down the bus, merely drive your spaceship off the bus and exit the bubble when at your destination.

[jerf]

The coin experiences massive tidal forces and basically explodes, taking a certain amount of energy out of the warp field in order to do it.

One of the problems with this approach that has been explored in other papers is that even if you have a warp drive and even if you have actually gotten a ship into it and even if you've managed to point it in the direction you want to go, the collision of the interstellar medium with your warp field tears it apart quite violently and the warp field "collapses". And unlike when they "collapse" on Star Trek and the only manifestation is a polite electronic "whirring" noise, being in a collapsing real warp field is a death sentence, with tidal forces on par with black hole gravitational fields.

[jonnathanson]

Honestly? I'm not sure. I know there are at least a few physicists who post on HN, and perhaps one of them could provide a more informed estimation than I.

Bear in mind, this article only addresses one of the many fundamental challenges to the Alcubierre drive: the energy requirements. Typically, the energy requirement has been considered the primary challenge to the feasibility of the device. But it's not the only one. Science hasn't completely worked out what would happen inside the bubble, or what happens to particles of matter interacting with the bubble at its leading edge. I've heard at least one speculation that the bubble would fill up with Hawking radiation and pretty much roast everyone alive inside it, like a big, interstellar dutch oven.

Another issue is the stability of the bubble itself. Again, the article doesn't really address this issue. But it's a pretty big one.

[shanelja]

It sounds like we are as yet a long, long way away from this being a reality, but I suppose it only takes a couple of leaps forward to make it more than just 'maybe possible'.