Faster than Light - Summary Wanted

[abri]

Faster than Light travel is often discussed, but it seems that facts and fiction are often mixed together. (FTL not nessesarily from point A to point B at a velocity greater than C, just move object from A to B faster than light could travel.)

To make it quick; there are some theories right now on Faster than Light (hereafter FTL) travel. Many theories are just humbug from some viral video, with no scientiffic basis at all, theese are not the subject here.

I'm interested in the theories with real scientiffic background. I've bee searching for an "introduction to the different theories" with a summary of what scientiffic grouns each theory holds. Has anybody seen a summary like this?

Dr. Ael Rin Sirion has written something about FTL from a quantum-theoretical viewpoint, are his claims good or bad? corner.net/admiral/warptek.htm

-----NOTE-----
The 'humbug-theories' like "aliens planted a blueprint in my head" are not the subject in this thread.

 

[ghwellsjr]

It's all fiction.

 

[phinds]

It's all fiction.

And not even very interesting fiction at that.

 

[abri]

So at this point there is no valid theory, not even the slightest hint, of traveling from point A to point B faster than light would in a straight trajectory (space folding and so on)?

 

[mfb]

After the OPERA publication, some theories were developed which had some FTL-effects inside, some of them from notable scientists. They all created some sort of violation of Lorentz-invariance.
But I don't think any of them got attention after the OPERA collaboration announced their measurement issues.

You can find a lot of arXiv articles with OPERA or neutrino as keywords.

Stream of dark matter as a possible cause of the opera clocks' synchronization signals delay <- this one has a funny abstract

 

[abri]

After the OPERA publication

Thank you for an extensive answer, I'm unfamilliar with the "OPERA Publication". As soon as I've done my finals in June, I'll dive right into that.

 

[jtbell]

I'm unfamilliar with the "OPERA Publication"

We had a lot of discussion about it here, for several months:

https://www.physicsforums.com/showthread.php?t=532620

 

[abri]

We had a lot of discussion about it here

Looks like I've found my excuse for not studying this summer-vacation either.

 

[Matterwave]

In Short: OPERA reports FTL neutrinos; a lot of publications were made to explain FTL neutrinos or where OPERA error'd in their measurements; OPERA reports that a GPS timing error could be at fault due to a not fully plugged in fiber optic cable.

 

[Nugatory]

Looks like I've found my excuse for not studying this summer-vacation either.

Hmmm... Sounds to me more like you'll be studying, just not what that you're supposed to be studying :)

If that's your plan... Be aware that Dr. Ael Rin Sirion's (could that possibly be an anagram?) stuff is worse than mere science fiction... It makes incorrect statements about things that we already know and have confirmed through experiment. In particular, all that stuff about light pulses propagating at speed v-c behind you and v+c in front of you... It's nonsense, that's not how light behaves.

Dig up a decent textbook, spend a few months working through it, and you'll understand special relativity in a way that "Ael Rin Sirion" never will... and that is way more interesting, exciting, and rewarding than anything that he'll ever come up with. There's a reason why smart people devote their lives to understanding and advancing physics... and it's not how well it pays.

 

[Gulli]

So at this point there is no valid theory, not even the slightest hint, of traveling from point A to point B faster than light would in a straight trajectory (space folding and so on)?

Well there's wormholes and Alcubierre drive, but the latter is probably impossible to achieve without the energy of say, an entire galaxy, while we don't know how to create the former, it may not even be possible to create a wormhole, though the universe might have created some for us to "harvest" (but we've never found one).

If there will ever be FTL travel it would probably happen via wormholes.

 

[GeorgeDishman]

.. Alcubierre drive .. is probably impossible to achieve without the energy of say, an entire galaxy ..

Isn't the problem even worse, it needs galaxies worth of negative mass?

 

[Chestermiller]

There was a TV video staring Stephen Hawking which covered time travel, and, by implication, distance travel. I think it was on the Science Channel or National Geographic. You should find it interesting. The material covered is not bull.

I'm surprised that none of the responders mentioned a "kind of" FTL travel associated with Special Relativity. If you get in a spaceship and move at speeds very close to the speed of light relative to our galaxy, then, as reckoned from your frame of reference, the distances in our galaxy are contracted, and, to the residents in our galaxy, the clocks in your spaceship (and your biological clock) are running very slowly. To the residents of our galaxy, you may have covered, for example, 30000 light years in about 30000 years, but, from your frame of reference, you have covered 30 light years in about 30 years. Thus, in neither frame of reference have you exceeded the speed of light, but you have still covered the 30000 light years across the galaxy during your lifetime. Of course, from a practical standpoint, enormous amounts of energy are required for you to reach speeds such as implied here. But still, it is conceptually possible.

Chet

 

[HallsofIvy]

Probably not mentioned because that is NOT "FTL" of any kind. As measured from your moving reference frame the distance you have covered is much less than 30 light years while, as measured from a frame stationary with respect to the planets, you have taken much longer than 30 years. In order to get it to look like "FTL" you have to mix reference frames.

 

[PAllen]

Well there's wormholes and Alcubierre drive, but the latter is probably impossible to achieve without the energy of say, an entire galaxy, while we don't know how to create the former, it may not even be possible to create a wormhole, though the universe might have created some for us to "harvest" (but we've never found one).

If there will ever be FTL travel it would probably happen via wormholes.

Both require negative energy. The worm hole is not traversible by matter unless stabilized with negative energy. Note that classically, there is no such thing as negative energy. In QM there are effects (Casimir) that are effectively negative energy, but they are subject to strict constraints. It is likely, based on trends in recent research, that it will be established that neither traversible wormholes nor Alcubierre drive are achievable, even in principle (based on the tight negative energy constraints in QM).

(Separately, Alcubierre drive, even if achieved, would incinerate both the spaceship and the destination).

 

[Chestermiller]

Probably not mentioned because that is NOT "FTL" of any kind. As measured from your moving reference frame the distance you have covered is much less than 30 light years while, as measured from a frame stationary with respect to the planets, you have taken much longer than 30 years. In order to get it to look like "FTL" you have to mix reference frames.

I believe that is what I said. And, after all, I did call it "kind of" FTL, didn't I? I just thought the OP would find this interesting.

Chet

 

[DaveC426913]

There are other ways of time traveling, and thus getting from A to B faster than light.

Some solutions that satisfy Einsteinian relativity - such as infinitely long relativistically-rotating cylinders and toroidal black holes - result in being able to travel along a time-like curve instead of a space-like curve. Once you can do that, you;ve got all the time in the world to get to your destination.

But they're even less feasible than Alcubierre Drives and wormholes.

 

[Nugatory]

I'm surprised that none of the responders mentioned a "kind of" FTL travel associated with Special Relativity. If you get in a spaceship and move at speeds very close to the speed of light relative to our galaxy, then, as reckoned from your frame of reference, the distances in our galaxy are contracted, and, to the residents in our galaxy, the clocks in your spaceship (and your biological clock) are running very slowly. To the residents of our galaxy, you may have covered, for example, 30000 light years in about 30000 years, but, from your frame of reference, you have covered 30 light years in about 30 years. Thus, in neither frame of reference have you exceeded the speed of light, but you have still covered the 30000 light years across the galaxy during your lifetime.

It might be more accurate to call this "one-way time travel"...

Still sounds pretty cool... Until you realize that we've all been doing this since we were born, and after about fifty years or so the coolness wears off.

 

[whiskybob]

I'm thinking something else - imagine point A to point B distance of say 10 light seconds.

What happens if a body at point B starts traveling towards point A at the same exact moment that a body originating at point A starts traveling towards point B (they both travel with C)
Even though the distance was 10 light seconds , the 2 bodies will meet in the center of the road in 5 seconds each of them having traveled only 1/2 the distance.

I don't understand how this is not ftl travel - the 2 bodies are moving towards each other (as seen by an independent observer) at a speed of 2C.

I don't understand how there can be a maximum speed if the only way to measure speed is to compare the rate of movement of the body to a point of origin - does that mean that when traveling between the stars you can accelerate infinitely since there's no point of origin?

Maybe I'm too stoopid :P to wrap my mind around "max speed"

 

[DaveC426913]

Even though the distance was 10 light seconds , the 2 bodies will meet in the center of the road in 5 seconds each of them having traveled only 1/2 the distance.

So each body travels 5 light-seconds in 5 seconds; where is the ftl part?

 

[whiskybob]

The FTL part is that the 2 bodies were 10 light seconds apart and yet they met after 5 seconds - they met in half the time that light could have traveled from 1 to the other body.

That's what I'm saying - how do you say there's max speed if all I have to do to prove you wrong is choose another point of reference ?

 

[Nugatory]

The FTL part is that the 2 bodies were 10 light seconds apart and yet they met after 5 seconds - they met in half the time that light could have traveled from 1 to the other body.

That's what I'm saying - how do you say there's max speed if all I have to do to prove you wrong is choose another point of reference ?

Because you can't get them to the meeting point in an arbitrarily short time, as you could if there were no speed limit. Or equivalently, there's no matter what reference point you choose, you'll never see anything moving faster than the speed of light relative to that reference point.

 

[TheEtherWind]

Paragraph 7:

"You hop into your space ship, and move off to the nearest star. All the time, you accelerate smoothly to maintain a 1 G environment. There is a mirror above you, perpendicular to the nosecone. Clearly, the light from your face moves to the mirror at C-(ship's velocity) and bounces back at c+(Ship's velocity) . If you were to keep going for so long that you reached the speed of light, C, then the light moving toward the mirror would be moving at C-C or 0 units per second. Your reflection would vanish. Suddenly, you have sensory proof that you're moving."

Violating postulates 1 and 2 to disprove postulate 1... how clever.

 

[GeorgeDishman]

The FTL part is that the 2 bodies were 10 light seconds apart and yet they met after 5 seconds - they met in half the time that light could have traveled from 1 to the other body.

That's what I'm saying - how do you say there's max speed if all I have to do to prove you wrong is choose another point of reference ?

Well bodies with mass can't travel at the speed of light but they can get arbitrarily close to it. Suppose they take 5.1s instead of 5s. Each travels at 0.9804c. If one measures the speed of the other, they find the speed is 0.9998c, nothing measures anything to be >c.

 

[DaveC426913]

Well bodies with mass can't travel at the speed of light but they can get arbitrarily close to it. Suppose they take 5.1s instead of 5s. Each travels at 0.9804c. If one measures the speed of the other, they find the speed is 0.9998c, nothing measures anything to be >c.

True, but in whiskybob's defense, his argument is that "the 2 bodies are moving towards each other (as seen by an independent observer) at a speed of 2C."

 

[GeorgeDishman]

True, but in whiskybob's defense, his argument is that "the 2 bodies are moving towards each other (as seen by an independent observer) at a speed of 2C."

Sure, and that is valid of course, what is sometimes called "closing speed" is not limited since it is a simple arithmetic sum of two speeds.

 

[DaveC426913]

Sure, and that is valid of course, what is sometimes called "closing speed" is not limited since it is a simple arithmetic sum of two speeds.

Yup. and this is the key to resolving whiskybob's confusion.

When you are a third observer, measuring the closing speeds of two objects, there is nothing wrong with the speed being as high as 2c. But, strictly speaking, in this case no object is traveling at greater than c.

So the next obvious question is: "...except that from the point of view of one of the objects, the other is..."

Ah, but that's a different reference frame!

As two objects approach each other, measuring the closing speed of one from the PoV of the other is not a simple addition. You must use the relativistic velocity addition formula (Lorentz transform). When you do so, you will always get a final closing velocity less than c.

 

[GeorgeDishman]

Yup. and this is the key to resolving whiskybob's confusion.

When you are a third observer, measuring the closing speeds of two objects, there is nothing wrong with the speed being as high as 2c.

Right, and that accords with the terminology I am used to. In all the textbooks and websites I've read, the term "closing speed" is reserved for this case of the third party observer hence the arithmetic sum (conventionally in one dimension) is applicable.

But, strictly speaking, in this case no object is traveling at greater than c.

So the next obvious question is: "...except that from the point of view of one of the objects, the other is..."

Ah, but that's a different reference frame!

And that is the question and result I posted previously.

As two objects approach each other, measuring the closing speed of one from the PoV of the other is not a simple addition. You must use the relativistic velocity addition formula (Lorentz transform). When you do so, you will always get a final closing velocity less than c.

You get a (coordinate) velocity that is less than c but that is not "closing speed" in the way I have seen the term used.

 

[HarryRool]

Faster than Light travel is often discussed, but it seems that facts and fiction are often mixed together. (FTL not nessesarily from point A to point B at a velocity greater than C, just move object from A to B faster than light could travel.)

I'm interested in the theories with real scientiffic background. I've bee searching for an "introduction to the different theories" with a summary of what scientiffic grouns each theory holds. Has anybody seen a summary like this?

Faster Than Light -- Superluminal Loop Holes in Physics by Nick Herbert