dunklervater@yahoo.com wrote:

Hello group,

Recently I came across the paper of Miguel Alcubierre at arxiv, and
found it very interesting to see, that there might be physical laws
that allow superluminar velocities.

When I looked on, it seemed, as if there is already strong evidence,
that the base assumptions are flawed.

Is this thing still something that gets debated?

Thanks in advance,

The Alcubierre drive is debunked. There is no way to communicate
outside the warp bubble, so it cannot be navigated or selectively
stopped. Suppose you could go anywhere in the universe instantly, but
had no control over your destination? Reduction to practice is the
small problem.

dunklervater@yahoo.com wrote:

Hello group,

Recently I came across the paper of Miguel Alcubierre at arxiv, and
found it very interesting to see, that there might be physical laws
that allow superluminar velocities.

When I looked on, it seemed, as if there is already strong evidence,
that the base assumptions are flawed.

Is this thing still something that gets debated?

Thanks in advance,

The Alcubierre drive is debunked. There is no way to communicate
outside the warp bubble, so it cannot be navigated or selectively
stopped. Suppose you could go anywhere in the universe instantly, but
had no control over your destination? Reduction to practice is the
small problem.

The most problematic feature of the warp drive geometry is the
behaviour of the negative energy densities in the warp bubble wall [2,
5]. If the Alcubierre spacetime is taken literally, part of the exotic
matter will have to move superluminally with respect to the local
lightcone. It is easy to see that all exotic matter outside some
surface surrounding the center (let us call this the critical
surface), will move in a spacelike direction. For vs > 1, there has to
be exotic matter outside the critical surface, since the function f
must reach the value 0 for some rs (which, of course, can be
infinity), and the negative energy density is proportional to
(df/drs)^2 for an ‘Eulerian observer’ [1]. As noted in [5], the
Alcubierre spacetime is an example of what can happen when the
Einstein equations are run in the ‘wrong’ direction, first specifying
a metric, then calculating the associated energy–momentum tensor.

The problem of tachyonic motion can be interpreted as meaning that
part of the necessary exotic matter is not able to keep up with the
rest of the bubble: if one would try to make a warp bubble go
superluminal, the outer shell would be left behind, destroying the
warp effect.

It is conceivable that the problem can be circumvented, for example by
letting the distribution of exotic matter expand into a ‘tail’ in the
back. It may be possible to do this in a way compatible with both the
QI and the Quantum Interest Conjecture introduced in [13], which
states that a pulse of negative energy must always be followed by a
larger pulse of positive energy. However, it is unlikely that one can
get rid of tachyonic motion of the exotic matter without introducing a
naked curvature singularity in the front of the bubble [14].