It's in the news again as the experiments have finally begun.
I'm obviously not a physicist. I'm just a science fiction fan. But honestly? I don't see this coming to anything even though I hope, really hope, that it does.
The speed of light in vacuum is a constant. One cannot exceed it. As one approaches it, all sorts of weird and funny things happen. Your mass increases. Time dialation occurs. Light becomes red and blue shifted. And heaven help you if you hit something. I certainly hope there's no one out there using relativistic weapons, and if they are, they aren't pointed at us. We'll never see the end coming.
Quite a bit of Science-fiction handwaves the speed of light away, and that's fine. If you want to tell a story about adventuers meeting aliens, landing on other planets orbiting other stars, and the like, you rather need that constant to have a loophole, a workaround, or to just be plumb wrong.
Luckily, relativity has such a work around.
"It is shown how, within the framework of general relativity and without the introduction of wormholes, it is possible to modify a spacetime in a way that allows a spaceship to travel with an arbitrarily large speed. By a purely local expansion of spacetime behind the spaceship and an opposite contraction in front of it, motion faster than the speed of light as seen by observers outside the disturbed region is possible. The resulting distortion is reminiscent of the `warp drive' of science fiction. However, just as happens with wormholes, exotic matter will be needed in order to generate a distortion of spacetime like the one discussed here.”But not so luckily, said workaround requires massive amounts of energy. Negative energy. Which does not exist.
Dr. Harold White of the very small NASA Theoretical Propulsion Unit thinks it may be possible to create a very tiny warp field, but it's worth noting that the creator of the metric itself doesn't think so.
Still, one of the most dubious is Dr. Alcubierre himself. He listed a number of concerns, starting with the vast amounts of exotic matter that would be needed.It's important to note that Dr. White is far more cautious than the press coverage, which has been ridiculous. It's also worth noting that the cost for the experiment is tiny: $50,000. That's it. I'm cool with that. Chump change, for a government with a several trillion dollar yearly budget.
“The warp drive on this ground alone is impossible,” he said.
And he posed a more fundamental question: How would you turn it on?
“At speeds larger than the speed of light, the front of the warp bubble cannot be reached by any signal from within the ship,” he said. “This does not just mean we can’t turn it off; it is much worse. It means we can’t even turn it on in the first place.”
There's still the matter of "negative energy" and other exotic matters, which for now I'll label unobtainium. And last but not least, there's the causality problem.
Looking up into the night sky is basically looking back into the past. The sun's light, when it reaches us, is already 8 minutes old. Sirius's light, when it reaches us, is almost a decade old. The light we see from Andromeda left its stars before humanity and its ancestors even evolved. The night sky is a time machine. I am still not sure how the warp bubble manages not to violate causality, even if it slips between the various folds of space time. Then you get into frames of reference and whatnot, and everyone's head starts to hurt.
I'm certainly glad they're doing this experiment, though.
However, honestly speaking, I don't think human beings will be returning to space in numbers until someone finds a way to make a profit over it. It's very expensive to leave the gravity well. It's very difficult to keep people alive in a sealed biosphere. The experiment on Earth more or less failed. Now there are hundreds of thousands of people, if not more, who'd happily sign up for what could be the end of their life on such a mission, but governments are not going to shell out funds to send people to found colonies on Mars and the Moon and elsewhere in the solar system and beyond unless they can recoup that cost. Worth noting the colonization of the Americas were done via public-private corporations and other partnerships. Oh, and outright plunder too.
I actually do think Planetary Resources has something there, though, but they're hamstrung by the same problem. They're stuck at the bottom of the same gravity well as everyone else and as stated, it's expensive to climb out of it.
All that said, I hope Dr. White is successful. Rationally, I don't think his experiment will go anywhere.
Any physics folks out there in dkos land want to weigh in? Let's have a fun discussion about it. (We can even discuss our favorite spacedrives from sci-fi. We can even discuss UFOs.)
Dr. White's paper is here.