# A question about an alternate version of the Alcubierre Drive

1. Feb 6, 2014

### MonkeyKid

I'm not sure if this is the right forum.

I'm sorry, but I'm not good at Physics or English (which is not my first language). I was just wondering, after watching a show on the Discovery Channel that mentioned the Alcubierre Drive. Then I went on the internet and read about it and all the difficulties (and probable impossibility) of actually building one. Then I kept on reading and found out about the Krasnikov tube which is a little more confusing.

Anyway, I don't understand the equations at all (I'm just a regular 14yo), so I can't figure this out by myself:

Assuming an Alcubierre drive is hypothetically possible, would also be possible to build something similar to an Alcubierre drive (in the sense that it would contract space in front of the craft and expand it behind it), but that wouldn't allow faster than light travel, but just regular slower than light travel instead?

And in case that such slower than light drive would be hypothetically possible, are all the things that are not plausible (like negative energy) in an Alcubierre drive still needed if you wanted to build this slower version of it?

Would this slower than light version of the Alcubierre drive be faster than our current means of space travel?

And lastly, would this form of transportation be more easily accomplished if made in the form of a Krasnikov tunnel instead?

Thank you. Sorry if it's badly written, but it took me a long long time (49 minutes) to write it, so it's the best I could do.

2. Feb 6, 2014

### Mordred

welcome to the forum, assuming that the drive is possible.

yes its possible to use for slower than light travel at any speed up to and beyond c. The Alcubierre drive and the Krasnikov tunnel are similar but the Krasnikov tunnel is far less likely a possibility. For both methods require a huge amount of energy. However the Alcubierre drive theoretically would require far less. I've read some peer reviewed published papers that show that the Alcubierre drive may have a problem with gamma radiation. In that paper they showed that the amount of radiation developed is proportional to the speed and time of the drives usage. the faster you go and father you go the greater the radiation at both the start and end of the journey. Possibly radiating the location you left and arrive at. Not sure if I still have that paper. Either way its highly doubtful we will see either usage implemented anytime soon, assuming those methods prove viable.

3. Feb 6, 2014

### MonkeyKid

What I could understand is that with an Alcubierre drive you already go from 0 to any speed you want, so a device that would do what an Alcubierre drive does, but without the requirement of being able to accelerate to a faster than light speed IS an Alcubierre drive, just used for a shorter time. Did I understand correctly?

And the only thing that would change would be the amount of gamma radiation, that in the case of a slower and thus shorter travel, would not be so much.

So, the only way to create a propulsion system based on contracting-expanding space is using the equations of Alcubierre, which comes with their the limitations attached (such as the need for huge amounts of hypothetical negative mass matter). Is that right?

Last edited: Feb 6, 2014
4. Feb 6, 2014

### jcsd

The Alcubierre drive requires negative energy regardless of whether the global velocity of the warp bubble is below c.

5. Feb 7, 2014

### waitedavid137

The only modification of the Alcubierre warp drive that I know of that limits the speed of the warp to the speed of light, but completely eliminates the negative energy requirement is
$ds^2 = \left(1-\beta f(x,y,z-ct)\right)dct^2 - \frac{\left(dz-\beta f(x,y,z-ct)dct\right)^2 }{\left(1-\beta f(x,y,z-ct)\right)}-dy^2 -dx^2$
where you place the ship in front of the warp and surf the warp up to the speed $\beta c$. If you write $f=\frac{-h}{1-h}$ you may recognize this spacetime as the Brinkmann exact solution to Einstein's field equations for pp electromagnetic and gravitational plane waves.

Last edited: Feb 7, 2014
6. Feb 7, 2014

### MonkeyKid

Is this version more plausible? Or does it still stumble upon things that are probably unachievable, other than negative energy.

7. Feb 7, 2014

### waitedavid137

Its Brinkmann's exact solution to Einstein's field equations for ordinary plane polorized electromagnetic and gravitational waves.

8. Feb 7, 2014

### MonkeyKid

From what I read, what those equations model are well known scientific facts, like eletromagnetic radiation and gravitational radiation traveling through space in a specific manner. I couldn't find anything about how could such model be used as a form of propulsion for space travel.

9. Feb 7, 2014

### waitedavid137

Yep, this result is something no one I know of is as yet looking into.