log in or register to remove this ad

 

Faster than light travel

Umbran

Mod Squad
Staff member
So, there are solutions to Einstein's equations for General Relativity that allow for effective faster than light travel - you may have seen them referred to as real life "warp bubbles". The problem with them is that they need a lot of what physicists call "exotic matter" - matter with really weird properties like negative energy density, stuff that we have not observed in nature, and do not know how to make.

Someone's found some new solutions that don't require exotic matter. However, to move a ship of 100 meter radius, it'd take energies equivalent to the mass of a few hundred Jupiters.

But, that's progress, right?


 

log in or register to remove this ad

darjr

I crit!
Halo Drives still seem the most realistic possibility. Just got to get our selves to the nearest black hole pair.
Maybe the Halo mechanism could be used to provide the energy needed here?
 





Umbran

Mod Squad
Staff member
Halo Drives still seem the most realistic possibility. Just got to get our selves to the nearest black hole pair.

The nearest known black hole is some 1100 light years away. When you want to get to something 4 ly from Earth (like Proxima Centauri), having to first go 1100 ly to QV Telescopii isn't exactly a win.

Maybe the Halo mechanism could be used to provide the energy needed here?

I would question the ability of any normal matter to manage that amount of energy all at once. Using the drive system in the OP requires bringng the energy requirements down by about 30 orders of magnitude.
 

darjr

I crit!
Well yea, but a 30 magnitude reduction is asking a lot. So meet somewhere higher. And yea it’s a hard nut to crack anyway it’s sliced.
 

Umbran

Mod Squad
Staff member
Well yea, but a 30 magnitude reduction is asking a lot. So meet somewhere higher.

I don't think you have the option to meet somewhere higher. The laws of physics are a harsh mistress.

We are talking about how much energy can be in a ship a few hundred yards across.

Consider, if you managed to put all the mass (and so, all the energy) of a single Jupiter in a space about 6 meters across, it would collapse into a black hole. If you put it all in a space between one and five kilometers across, it collapses into a ball of neutronium.

Basicially, in order to power the ship, you need a ball of neutronium ten times larger than the ship! The matter/energy you need cannot fit within the ship, much less be managed by the ship's systems. Not going to the stars in that.

If you bring it down by 30 orders of magnitude, we are talking about completely converting maybe a kilogram material into energy. For scale, all the energy released by the Hiroshima bomb was less than a gram of mass. So, we are then still talking about containing a thousand Hiroshimas within a space of, say, a modern sports stadium. Which may be possible, but still pretty fantastic.

But, above that... you're not going to the stars if you vaporize the ship when you turn the engine on.
 
Last edited:

Ryujin

Hero
I don't think you have the option to meet somewhere higher. The laws of physics are a harsh mistress.

We are talking about how much energy can be in a ship a few hundred yards across.

Consider, if you managed to put all the mass (and so, all the energy) of a single Jupiter in a space about 6 meters across, it would collapse into a black hole. If you put it all in a space between one and five kilometers across, it collapses into a ball of neutronium.

Basicially, in order to power the ship, you need a ball of neutronium ten times larger than the ship! The matter/energy you need cannot fit within the ship, much less be managed by the ship's systems. Not going to the stars in that.

If you bring it down by 30 orders of magnitude, we are talking about completely converting maybe a kilogram material into energy. For scale, all the energy released by the Hiroshima bomb was less than a gram of mass. So, we are then still talking about containing a thousand Hiroshimas within a space of, say, a modern sports stadium. Which may be possible, but still pretty fantastic.

But, above that... you can't go to the stars if you vaporize the ship when you turn the engine on.
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. This removes the necessity for having super massive objects housed within a relatively tiny ship but, then again, there is the issue of getting these anchors in the locations you wish to visit.

So, on that theory, we could have interstellar travel in a few mere millennia ;)
 

Umbran

Mod Squad
Staff member
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.
 
Last edited:

Mustrum_Ridcully

Adventurer
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

Hero
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.

 

darjr

I crit!
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

Mod Squad
Staff member
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

Mod Squad
Staff member
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.
 
Last edited:

Ryujin

Hero
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

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

Umbran

Mod Squad
Staff member
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 crit!
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.
 

An Advertisement

Advertisement4

Top