Faster than light travel

[Umbran]

I recall a book series (was it by Vernor Vinge?) in which an ancient race has set up compact cylinders of stellar mass, rotating at near light speed, to act as anchor points for folding space. My memory of it is quite vague, as I read it decades ago, but this was based at least loosely on the understanding of physics at the time. Simply put you would approach at a given vector in order to "link up" two of these points, so that you could enter a space fold that would transit you to your destination.

Yeah. I think that solution came from Tipler. He thought of it as a time machine, but in those solutions, time travel implies FTL space travel, so you can use it for that too.

Mind you, it isn't enough for it to be of stellar mass. It has to be of high density. IIRC, the original solution requires an infinite cylinder of neutronium, spinning so its surface is moving at relativistic speeds. It has been conjectured that havingthe cylinder of finite length is also workable, but if the edge effects don't make you into spaghetti, they limit where/when you can go to further.

 

[Mustrum_Ridcully]

Does this particular method actually still even allow FTL travel, or does it just allow you to travel non-relativistically close to the speed of light? I seem to remember someone commenting on that detail, but I am not sure if it was correct. I don't expect to be able to understand the actual paper, unfortunately.
But it would be something I read before about the Alcubierre Drive - aside from needing exotic matter with negative energy, you would still need something moving superluminally to create the desired configuration of masses for FTL travel. Which is kinda begging the question.But there was an alternate approach were you basically first build a space high way placing the masses where they need to be by "foot" at non-FTL speed, and from that point on, you can travel on that route at FTL speed. So no Star Trek warp drive and going anywhere interesting outside our star system would still take humanity decades, centuries or millennia, but once they build their warp highways, people could move quickly between planets. Or we're lucky and someone built one for us already and we just need to find the next drive up ramp.

 

[Ryujin]

Yeah. I think that solution came from Tipler. He thought of it as a time machine, but you can use it for space travel too.

Mind you, it isn't enough for it to be of stellar mass. It has to be of high density. IIRC, the original solution requires an infinite cylinder of neutronium, spinning so its surface is moving at relativistic speeds. It has been conjectured that havingthe cylinder of finite length is also workable, but if the edge effects don't make you into spaghetti, they limits the where/when you can go to further.

The book that I was thinking of was "The Avatar" by Poul Anderson, though Vinge did use it by a different name and configuration.

Tipler cylinder - Wikipedia

en.wikipedia.org

 

[darjr]

It assumes that a local area of space time can travel faster than the speed of light. We already know that waves in space time cannot. It, in itself, is kind of educated speculation.

I think.

 

[Umbran]

Does this particular method actually still even allow FTL travel, or does it just allow you to travel non-relativistically close to the speed of light?

The claim on this one is outright FTL. I haven't been over the paper myself yet. My tensor calculus is rusty enough that it'll be a chore.

I seem to remember someone commenting on that detail, but I am not sure if it was correct. I don't expect to be able to understand the actual paper, unfortunately.
But it would be something I read before about the Alcubierre Drive - aside from needing exotic matter with negative energy, you would still need something moving superluminally to create the desired configuration of masses for FTL travel.

Maybe yes, maybe no. It basically depends on one basic issue.

In the original formulation, the Alcubierre Drive has a flaw (actually several, but I'm talking about one)- the people inside the bubble are causally disconnected from the rest of the universe while it is in operation. You configure it, launch, and it does its thing until you arrive at your destination. You cannot do things like, say, steer an Alcubierre Drive, because the passengers cannot communicate with the bubble.

A workaround for that may exist. It amounts to firing little Alcubierre Drive packets from within the bubble to the main bubble. The same solution can get around the problem you mention, if it works.

On a personal note - I get wistful with this stuff. I learned General Relativity from Larry Ford at Tufts, who has done a significant amount of work on the Alcubierre Drive solutions. If he'd had funding, I'd likely have been his grad student, and I'd have been working on this really cool stuff, and probably still be in academia as a result. sigh.

 

[Umbran]

It assumes that a local area of space time can travel faster than the speed of light. We already know that waves in space time cannot. It, in itself, is kind of educated speculation.

I think.

I'm not sure what "It" is assuming. But in general, no. The solutions work out - the basic questions are over whether other things prevent them from working. For example... stopping an Alcubierre drive may sterilize any system you are entering with a massive burst of radiation.

 

[Ryujin]

I'm not sure what "It" is assuming. But in general, no. The solutiosn work out - the basic questions are over whether other things prevent them from working. For example... stopping an Alcubierre drive may sterilize any system you are entering with a massive burst of radiation.

Whoops! Shades of the Voyager Probe, from "Space: 1999." Suddenly alien societies are looking for the race that committed genocide, while transmitting messages of friendship.

 

[darjr]

There are a lot of solutions that work out. Being real and verifiable with experiment or observations is a whole other thing

 

[Umbran]

There are a lot of solutions that work out. Being real and verifiable with experiment or observations is a whole other thing

Of course. However, when so many things about General Relativity are verified by experiment and observations, the first place to look for a failure point isn't in the very basic math. The more likely culprits are around the requirements (like exotic matter), or the fact that it may vaporize anything inside it with Hawking radiation.

 

[darjr]

I thinks that’s survivors bias. After all originally it was a steady state theory of the universe. The counter was shown through observation. Also I believe there was supporting work showing why black holes were impossible. That too fell to observation. Most of the counter things that “checked out” and later shown to be wrong through experiment and observation are forgotten.

it is WHY Enstiens theory is so remarkable.