[AsLan^]

There's something that's been bothering me for ages about faster than light travel and the fact that it cannot exist.

If you were to build a box that had another box inside that was in turn connected to a mechanical device that could either push the box out or pull it in, effectively doubling the total length of the box or returning it to its regular length. And you could control this expansion/retraction with a timer of some sort...

Why, couldn't you build a line of these boxes in space 2 light years long (for example) which would be difficult but doesn't require infinite amounts of energy. Then when the boxes expand, the length of the line would be doubled and the endpoints of the boxes will be each be traveling 1 light year from their starting position in the time it takes for the mechanical arm to expand the box.

You couldn't activate the boxes with any particular signal because it would take a light year for any information to travel up or down the line (assuming you started the signal at the center). But with the timers in the mechanical arms it should be possible to ensure the boxes all expanded and contracted at the same time.

So if I was situated at one endpoint and my friend was situated at the future endpoint for the expanded line, why couldn't we exchange information, or even put stuff in the box to be transported... faster than light.

[curiousuburb]

It's all turtle boxes, all the way down.

Plus, the boxes wouldn't work with cats.

Don't bogart the bong, dude.

[Luca]

I'm having trouble visualizing what you're talking about but I remember reading a discussion elsewhere where someone asked if it would be possible to have superluminal communication by constructing a thin, rigid rod several light years long and tapping out messages. Assuming it's possible to build such a thing (no small feat), you could just have either end at a receiving station and communicate by tapping the thing back and forth.

Of course, the relative motion of the objects would mean that both end points would have to be constructed somewhere in space, and furthermore, the process of constructing an absolutely incompressible, totally rigid rod that is light-years long and infinitesimally smaller in the other dimensions is mind-boggling. But assuming it could be done... why not? Or would the motion still travel at the speed of light?

[Dorian Gray]

Originally Posted by Luca But assuming it could be done... why not? Or would the motion still travel at the speed of light?

If you assume it (or AsLan^'s boxes) can be done you may as well keep assuming and assume you can just get in a car and go faster than light. The laws of physics don't co-operate. If I push one end of my computer the other end initially accelerates slightly slower due to the aluminium compressing. Nothing in the universe doesn't compress in a similar fashion.

[AsLan^]

I think with the rod idea, it would take one light year for the molecules to bump into each other eventually transmitting the push.

But, in that case, the molecules at the end of the rod are patiently waiting to be bumped rather than doing anything on their own. At the initial push, the total length of the rod compresses slightly and one year later returns to its normal length.

With my question, it's very similar but the rod has been broken down into boxes which are all exerting force at the same time rather then waiting for a push to come down the line.

Granted, the mechanism in the center box each box would have to be capable of moving the entire chain of boxes but I imagine the energy requirements would still be short of infinity (which is what is currently believed to be the amount of energy required to accelerate something to the speed of light).

[Luca]

Originally Posted by AsLan^ I think with the rod idea, it would take one light year for the molecules to bump into each other eventually transmitting the push. But, in that case, the molecules at the end of the rod are patiently waiting to be bumped rather than doing anything on their own. At the initial push, the total length of the rod compresses slightly and one year later returns to its normal length. With my question, it's very similar but the rod has been broken down into boxes which are all exerting force at the same time rather then waiting for a push to come down the line. Granted, the mechanism in the center box would have to be capable of moving the entire chain of boxes but I imagine the energy requirements would still be short of infinity (which is what is currently believed to be the amount of energy required to accelerate something to the speed of light).

Actually with the rod, the amount of time it would take for the molecules at one end to respond to a movement by the other end would range from one year (given a one light-year rod) to significantly longer than a year, depending on the material used. And like Dorian said, the materials and construction methods necessary to create such a thing are probably just as impossible as true FTL travel itself.

[FFL]

Originally Posted by curiousuburb Don't bogart the bong, dude.

Srsly, dude.... you've been on that thing for quite a few parsecs now....

[Unch]

Are you thinking of something that this kind of telescopic?

Say you had a telescopic device consisting of 3 sections, the outer section remains stationary, the 2nd section is propelled away from the outer section (but still attached) at say 3/4 the speed of light. Inside the second section is the innermost section that is indpendently propelled at 3/4 the speed of light away from the 2nd section.

Would the innermost section be travelling away from the outermost section at 1.5 the speed of light? Is that the kind of thing you are thinking of?

[Kickaha]

If that's the case, he might want to read up on Lorentz transformations.

[AsLan^]

Originally Posted by Unch Are you thinking of something that this kind of telescopic? Say you had a telescopic device consisting of 3 sections, the outer section remains stationary, the 2nd section is propelled away from the outer section (but still attached) at say 3/4 the speed of light. Inside the second section is the innermost section that is indpendently propelled at 3/4 the speed of light away from the 2nd section. Would the innermost section be travelling away from the outermost section at 1.5 the speed of light? Is that the kind of thing you are thinking of?

Basically yes, although it would be many thousands of sections (or boxes).

In my question it's true that the end sections would be traveling away from each other at many times the speed of light but it wouldn't be useful because transmitting information between them would still only be at the speed of light.

That's why I postulated that I would be at one end and the person I wished to transmit FTL information to would be at the future endpoint of that same endpoint of the expanded line.

The reason I suggested a line of boxes two light years in length is to account for the fact that each box would simultaneously be acting in both directions. The total length of the boxes after expansion would be four light years, with each endpoint having traveled one light year.

[Kickaha]

Aslan^, this is equivalent to a ship going 0.5c, and shining a light straight forward off its nose - how fast is that beam of light going, to an observer standing to one side? How about to an observer on the ship?

Remember, the speed of light is a constant, regardless of frame of reference...

[AsLan^]

The beam of light thing has always confused me too. Wouldn't an observer only see the beams of light that flew directly toward them and were detected by their eyes?

Isn't the only reason we can see "beams" of light because it is really light that has been reflected by dust or vapor and eventually ended up at our eyes?

[Mugge]

I would expect that the boxes would tear apart or stretch like when stuff goes into a black hole.

[Kickaha]

Originally Posted by AsLan^ The beam of light thing has always confused me too. Wouldn't an observer only see the beams of light that flew directly toward them and were detected by their eyes? Isn't the only reason we can see "beams" of light because it is really light that has been reflected by dust or vapor and eventually ended up at our eyes?

Yes, but it still has to get from dust mote A to dust mote B at some rate, correct?

What's the rate?

Here, make it easier - there's a planet straight ahead, and the observer is on the planet looking straight at the beam coming at him. No atmosphere. It's just a thought experiment.

So you have someone on the back end of the beam, on a ship going 0.5c, and an observer on the front end of the beam, staying still.

How fast is the light beam according to each person?

If you were in a car going 10kph, and threw a ball forward at 10kph, a person in front of you catching it would have it hit their mitt at 20kph.

[ezkcdude]

Originally Posted by AsLan^ The reason I suggested a line of boxes two light years in length is to account for the fact that each box would simultaneously be acting in both directions. The total length of the boxes after expansion would be four light years, with each endpoint having traveled one light year.

Not exactly. In a "real-world" scenario, you would need to take into account wave transmission. For example, if you tap one end of a flag pole with your finger, it will take some finite amount of time to propagate to the other side. The time depends on the material characteristics of the material. This is actually the basis for measurement techniques like ultrasound.

Long story short: there's still no free lunch.

[AsLan^]

I know the correct answer is c but my question is slightly different.

In your space ship example, we are talking about electromagnetic radiation.

My question is about the forces being exerted between the molecules comprising the boxes. Each box would only have to wait for the push from the box before it and they are all acting simultaneously.

[AsLan^]

Originally Posted by ezkcdude Not exactly. In a "real-world" scenario, you would need to take into account wave transmission. For example, if you tap one end of a flag pole with your finger, it will take some finite amount of time to propagate to the other side. The time depends on the material characteristics of the material. This is actually the basis for measurement techniques like ultrasound. Long story short: there's still no free lunch.

Well, I had hoped to account for this by the use of timers. In my boxes there is no need to wait for the propagation of a signal telling them when to activate.

[Kraetos]

Alright so as long as this thread is here, I simply have to ask this question:

In your opinion, what is the most probable way humans could find a way to move mass faster than light?

I am aware the answer is "it can't be done." So lets put that aside for a moment, for the sake of discussion.

For the sake of the question, there is no distinction between actual and apparent FTL. I imagine that any FTL idea with even a drop of plausibility will fall into the apparent FTL category, anyway. Don't worry about energy requirements either, unless the energy requirement is infinite.

Is Alcubierre drive plausible on any level, or is it pure, baseless speculation? Is there another FTL theory which involves the expansion/contraction of space time around a "warp bubble" created by a ship which is more feasible?

What about a traversable wormhole? Could one be created artificially? Big enough to move a spaceship through? Could the location of the terminus of an artificial wormhole be chosen at any point in space, or would there need to be parties on both ends of the wormhole before it's created?

Jump drive? Be it instantaneous travel through a wormhole-like phenomenon, or some other type of teleportation.

A different realm or dimension, i.e. hyperspace?

Something else?

[Moogs]

2009 Millennium Falcon LL Bean Edition.

[AsLan^]

Originally Posted by Kickaha Here, make it easier - there's a planet straight ahead, and the observer is on the planet looking straight at the beam coming at him. No atmosphere. It's just a thought experiment. So you have someone on the back end of the beam, on a ship going 0.5c, and an observer on the front end of the beam, staying still. How fast is the light beam according to each person? If you were in a car going 10kph, and threw a ball forward at 10kph, a person in front of you catching it would have it hit their mitt at 20kph.

Actually, thinking about this a bit more, if the observer on the planet observed the light it would be blue shifted and the person on the planet would be able to deduce that the light source was moving at 0.5c.

Which means that although the lights velocity is not being affected, it is still undergoing change as a result of being emitted at 0.5c (the wave is bunching up?) Do particles undergo this same phenomenon?

[ezkcdude]

Originally Posted by AsLan^ Well, I had hoped to account for this by the use of timers. In my boxes there is no need to wait for the propagation of a signal telling them when to activate.

I see now what you mean. At the middle of your line of boxes, there is very little displacement. But - theoretically - at either end the displacement of a box is equal to L/2 (assuming the initial length is L). I don't think you need such an intricate example to ask this question, though. It's essentially the same idea if you think about a rod of length L growing to length 2L instantaneously. I would assume that the speed of light is a real physical constraint that can't be avoided. The boxes in the middle (or a point in the middle of a growing rod) are ok. But the further you go away from the middle and toward either end, the limit of the speed of light would come into play and prevent anything moving faster.

[Kickaha]

Yup, it's a Lorentz contraction - the ship looks longer or shorter depending on who is doing the observation. So as your boxes approach the speed of light, they start to get shorter to an external observer... and the speed of light is preserved.

And you still can't get around the propagation issue - what do you think holds the matter together, and lets it interact? The main two forces are electromagnetism and gravity, and gravity at those scales is miniscule. EM is covered by the speed of light. Same situation.

Time and space are truly intertwined, and the speed of light is the unifying factor. Try and push one, and the other gives to compensate.

That's why it's the Theory of Relativity.

[ezkcdude]

Also, the mechanical force for each box "pushing" the neighboring box is still limited by wave propagation. Even with timers I'm afraid.

[AsLan^]

Originally Posted by ezkcdude I would assume that the speed of light is a real physical constraint that can't be avoided. The boxes in the middle (or a point in the middle of a growing rod) are ok. But the further you go away from the middle and toward either end, the limit of the speed of light would come into play and prevent anything moving faster.

That's pretty much the crux of the issue! With the speed of light as a real physical constraint FTL is impossible

Originally Posted by Kickaha Yup, it's a Lorentz contraction - the ship looks longer or shorter depending on who is doing the observation. So as your boxes approach the speed of light, they start to get shorter to an external observer... and the speed of light is preserved. And you still can't get around the propagation issue - what do you think holds the matter together, and lets it interact? The main two forces are electromagnetism and gravity, and gravity at those scales is miniscule. EM is covered by the speed of light. Same situation. Time and space are truly intertwined, and the speed of light is the unifying factor. Try and push one, and the other gives to compensate. That's why it's the Theory of Relativity.

So, the molecules making up the boxes would become compressed as the outlying boxes approached the speed of light... then as the molecules uncompressed, they would do so only at the speed of light?

[Foj]

We need to think outside the box.

[Moogs]

The thing of it is, you'd have to go way FTL to get to a point where you could travel to even nearby star systems in any reasonable amount of time that humans could endure without running into massive health and/or psych problems in isolated, zero G environs. Also communicating with home would become a grizzly situation me thinks. It will be tough enough with the 20 minute delay to Mars or whatever it is. Imagine a delay that took not hours, days or even weeks but uncountable long years, Gandalf. Teleporting FTLW.

[Kickaha]

Originally Posted by AsLan^ That's pretty much the crux of the issue! With the speed of light as a real physical constraint FTL is impossible So, the molecules making up the boxes would become compressed as the outlying boxes approached the speed of light... then as the molecules uncompressed, they would do so only at the speed of light?

Noooo... the faster you go, the shorter the space contracts. This is one of those 'speed of light is an absolute limit' things - if you were to hit the speed of light, the space you took up would contract to zero. To you, it would look like the universe contracted to a singularity. Woot relativity!

[Enki]

The only hope for FTL is to find a way to travel across a higher dimension, so the path taken within that higher dimension adheres to the constraints of information travel across it, and that it also allows travel through the "interior" of the balloon rather than constrained to the curved path of the membrane of the balloon (where the visible universe is the balloon membrane). The String Theory wonks are talking about 10 dimensions so there are some candidates, but we are at a bit of a Flatland type of disadvantage when contemplating dimensions higher than 4.

It also doesn't necessarily mean physical humans can do that FTL travel, I have to agree with Kurzweil on that particular point.

[Dave]

Originally Posted by Kraetos Alright so as long as this thread is here, I simply have to ask this question: In your opinion, what is the most probable way humans could find a way to move mass faster than light? I am aware the answer is "it can't be done." So lets put that aside for a moment, for the sake of discussion.

The relevant equations give pretty interesting results if you give yourself a complex velocity and/or negative mass.

[AsLan^]

Originally Posted by Kickaha Noooo... the faster you go, the shorter the space contracts. This is one of those 'speed of light is an absolute limit' things - if you were to hit the speed of light, the space you took up would contract to zero. To you, it would look like the universe contracted to a singularity. Woot relativity!

This doesn't make sense to me. If the universe were a singularity to something traveling at light speed, then anything moving at light speed would either be everywhere at once, or at least have the ability to travel anyplace within the universe instantaneously.

Also, with space and time being intertwined, I was under the impression that this was just a mathematical model used to assist in simplifying calculations and that space and time are not really the same thing. How could they be, it's like saying that any one of the spatial dimensions is the same as another when they obviously are not.

As far as the observed effects of time dilation, I'm not convinced that this is occurring either (due in no small part to me not understanding the theories involved, but to me it doesn't pass the common sense test).

For starters, what is time? Time is an abstract concept, it is really just the position of where something was in three dimensional space before it got to where it is now. I don't see how time could stop or be made to go backwards etc. If everything in the universe simply stopped, there would be no way to measure time but time would still be passing. The position of objects in three dimensional space at any point after the universe stopped would simply be the position they were at when the universe stopped. Time would still be passing though.

Is it not more plausible to just say that when particles are moving at high speeds the changes they are normally undergoing that allow us to measure time slow down? This certainly seems more plausible to me then warping the entire universe to account for an atomic clock slowing down when moving at high speeds.

I mean even with the twins example, whilst it's plausible to me that the twin who leaves earth at light speed returns to find his brother older, why do we say that this is due to time dilation? Is is not more plausible that when moving at higher speeds, the interactions between atoms that cause aging require more energy and simply happen slower or not at all? In that case, while the twin moving at light speed appears not to have aged, we know that he has existed for the same amount of time as his brother by virtue of the fact that we know he occupied a position in the universe at all the times.

If two atoms were next to each other in a lab and one was cooled close to absolute zero, measuring time by examining the physical changes the atoms have undergone would reveal that the cooled atom had experienced time dilation. This is obviously non-nonsensical because the cooled atom existed at all times its non-cooled friend did.

I hope this doesn't come off as a rant, I don't understand the theory of relativity and the layman's examples that are often used to try and explain it only serve to confuse me more. I'm slightly biased by the fact that I hope relativity is wrong because if it is right then things like interstellar travel at FTL speeds really are impossible

Thanks for helping