A steel pole is built from planet A to planet B one light year away..

[CycloWizard]

Originally posted by: DrPizza
I've never read about this before - is the speed of sound in a solid a constant, regardless of the frequency of the sound?

i.e. in many (most?) mediums, the speed of light isn't the same constant for all frequencies. Hence, we have prisms.

The speed of sound is generally frequency dependent. To go with Paperdoc's excellent explanation, the way an engineer would quantify the real and imaginary parts of these vibrations is by looking at the viscoelastic behavior of the solid. The real part corresponds to stored energy, while the imaginary part corresponds to "lost" (i.e. dissipated) energy. The former is usually associated with elasticity and is quantified by the storage modulus, whereas the latter is usually associated with viscous dissipation effects and is quantified by viscosity (or loss modulus, which is simply viscosity divided by frequency). Both of these quantities generally vary with frequency, though both exhibit high-frequency plateaus in all real materials (at least, in all materials I've ever seen data for). This testing has traditionally been done using dynamic mechanical analysis (DMA) for relatively stiff samples of the type we're talking about here, though there are various other methods for testing (indentation for softer and/or inhomogeneous solids; various types of rheometry for liquid-like materials). Entire books have been written on the subject.

 

[Fenixgoon]

the fastest you'd be able to move information through a material would be the motion of the atoms, electrons, and phonons. which is to say, you're still constrained by matter, and therefore, cannot achieve faster than light travel.

the (maximum) speed of sound in a material is dependent on the material's moduli - elastic modulus (E), shear modulus (G) and bulk modulus (K) - as well as Poisson's ratio, IIRC.

 

[Machupo]

I'm waiting for someone to ask about a nail/pole made out of entangled particles

 

[Jedi2155]

We wouldn't be able to see the hammer hit to know the original state .

 

[QuantumPion]

Originally posted by: jdjbuffalo
Paratus and TastesLikeChicken did a good job of following up why this wouldn't work.

Hopefully we will have FTL drives and communications one day (soon, I hope). But right now we don't have any way of even theoretically doing this.

I do not think FTL travel OR communication is physically possible. The reason is that if it were possible to communicate faster than light, it would be possible to set up a situation where you could send information back in time, which leads to all sorts of logical paradoxes.

 

[MStele]

I do not think FTL travel OR communication is physically possible. The reason is that if it were possible to communicate faster than light, it would be possible to set up a situation where you could send information back in time, which leads to all sorts of logical paradoxes.

As to faster than light travel, relativity in regards to the speed of light only applies to local space. If you jump into your mega-awesome spaceship and attempted to accelerate to the speed of light, you might find yourself a little bit disappointed and a little bit heavier, as well as tired due to the energy needed...but in the long run you'll fall short. However, there are theories about wormholes where large distances can be covered virtually instantaneously. If you travel in this manner from point A to point B at a distance of 1 light year, then you can see that although your trip was quick, in local space you would literally have crossed 1 light year of space in a instant, or for this purpose I'll arbitrarily choose 1 second of travel. Since speed is distance/time, we would have traveled 9,460,730,472,580,800 meters over 1 second, which would mean we had a linear velocity 31,557,600 times that of the speed of light. Long story short, we still have alot to learn.

As for the pole, mechanical waves operate differently from electromagnetic waves. Even if your perfectly rigid pole was possible, the amount of energy required to move it would be ridiculous, since you have inertia working against you, even if its as thin as a nail.

 

[Red Squirrel]

This is kind of mind boggling stuff. But yeah I've also read that when an object is moved, there is actually a delay between the time one side of the object is moved, and the other side. Ex: you slide your phone across the desk. During a certain period of time you are actually squishing the phone as the other side has not yet started to move. This of course happens at an insane speed. So even a very solid rigid material bends/squishes/stretches.

 

[Shadow Conception]

As to faster than light travel, relativity in regards to the speed of light only applies to local space. If you jump into your mega-awesome spaceship and attempted to accelerate to the speed of light, you might find yourself a little bit disappointed and a little bit heavier, as well as tired due to the energy needed...but in the long run you'll fall short. However, there are theories about wormholes where large distances can be covered virtually instantaneously. If you travel in this manner from point A to point B at a distance of 1 light year, then you can see that although your trip was quick, in local space you would literally have crossed 1 light year of space in a instant, or for this purpose I'll arbitrarily choose 1 second of travel. Since speed is distance/time, we would have traveled 9,460,730,472,580,800 meters over 1 second, which would mean we had a linear velocity 31,557,600 times that of the speed of light. Long story short, we still have alot to learn.

As for the pole, mechanical waves operate differently from electromagnetic waves. Even if your perfectly rigid pole was possible, the amount of energy required to move it would be ridiculous, since you have inertia working against you, even if its as thin as a nail.

That makes no sense to me. Isn't that like digging a "secant" hole through the Earth and traveling through it, coming out the other end, and then saying you traveled the curved distance in a shorter amount of time?

Wouldn't the case just be that you traveled a shorter distance, and therefore a shorter time?

 

[Cutterhead]

That makes no sense to me. Isn't that like digging a "secant" hole through the Earth and traveling through it, coming out the other end, and then saying you traveled the curved distance in a shorter amount of time?

Wouldn't the case just be that you traveled a shorter distance, and therefore a shorter time?

For theoretical FTL travel such as this to occur, we would probably need some manner of bending space. It helps to think of it that way - instead of traveling through space as we typically do, we would need to bend space around ourselves. Like a piece of paper with one hole on either end, and bending the paper to bring each hole into direct contact, as opposed to traveling a straight line across the paper from hole to hole.

As for the OP's proposition for instantaneous communication over long distances, there is the interesting phenomenon of quantum entanglement - where an action (measurement taken) on one particle has an instant and opposite effect on another entangled particle, regardless of distance. That is one potential area of observable physics that could one day make something like FTL communication possible.

 

[MStele]

That makes no sense to me. Isn't that like digging a "secant" hole through the Earth and traveling through it, coming out the other end, and then saying you traveled the curved distance in a shorter amount of time?

Wouldn't the case just be that you traveled a shorter distance, and therefore a shorter time?

Remember that everything is relative, based on the observer. In local space, going from point A to point B means traversing the space between them. Even if the ship was instantly transported from point A to point B through a worm hole of sort, in local space there is still one light year between them, therefore the ship did in fact travel one light year, even if it took a short cut to get there.

I'm not saying worm hole theory is sound, since there is no way to prove it one way or the other at the moment. If it were in fact possible however, it would provide a method of exceeding the speed of light without violating Special relativity, since the object never actually attempts to accelerate to the speed of light.

I'm a geologist and not a physicist, so if my understanding on the worm hole theory is wrong please correct me.

 

[TanisHalfElven]

well i am not even gonna talk about the OP since that is already answered.
but you can go faster than light in a different medium, like say water. infact submerged nuclear reactors frequently emit electrons that move faster than light (in the water).

 

[CycloWizard]

well i am not even gonna talk about the OP since that is already answered.
but you can go faster than light in a different medium, like say water. infact submerged nuclear reactors frequently emit electrons that move faster than light (in the water).

Huh? The speed of light in water is much slower than in air or vacuum. The speed of light in pure water is only 75% of that in vacuum, as indicated by its refractive index of 1.333. I'd be interested to see if water transmits anything faster than light in water.

 

[silverpig]

Huh? The speed of light in water is much slower than in air or vacuum. The speed of light in pure water is only 75% of that in vacuum, as indicated by its refractive index of 1.333. I'd be interested to see if water transmits anything faster than light in water.

Cerenkov radiation.

 

[Shadow Conception]

Remember that everything is relative, based on the observer. In local space, going from point A to point B means traversing the space between them. Even if the ship was instantly transported from point A to point B through a worm hole of sort, in local space there is still one light year between them, therefore the ship did in fact travel one light year, even if it took a short cut to get there.

I'm not saying worm hole theory is sound, since there is no way to prove it one way or the other at the moment. If it were in fact possible however, it would provide a method of exceeding the speed of light without violating Special relativity, since the object never actually attempts to accelerate to the speed of light.

I'm a geologist and not a physicist, so if my understanding on the worm hole theory is wrong please correct me.

I'm still lost.

Isn't that like saying if I travel 1 mile against the diameter of the Earth, I just moved 7925 miles in the other direction?

If you take a shortcut to get 1 light year away, you will be 1 light year away from the starting point measuring the unbent spacetime between the destination and initial point. But the distance you would have traveled would be less, because the wormhole shortens the distance needed to get to the destination...

Basically, the distance you travel in the wormhole is less than the distance you would travel without a wormhole and through regular space. Therefore, if you tried both at the same speed, you'd get to your destination faster because of the shorter distance; a shortcut.

 

[WalkerDPlank]

This question is completely silly. Everyone knows that it would be much more efficient for the pole to go back and forth, not side to side.

 

[CycloWizard]

Cerenkov radiation.

Huh, never heard of that before. Interesting Wiki article though.

 

[MStele]

I'm still lost.

Isn't that like saying if I travel 1 mile against the diameter of the Earth, I just moved 7925 miles in the other direction?

If you take a shortcut to get 1 light year away, you will be 1 light year away from the starting point measuring the unbent spacetime between the destination and initial point. But the distance you would have traveled would be less, because the wormhole shortens the distance needed to get to the destination...

Basically, the distance you travel in the wormhole is less than the distance you would travel without a wormhole and through regular space. Therefore, if you tried both at the same speed, you'd get to your destination faster because of the shorter distance; a shortcut.

There are a couple of points. First, I was arguing that faster than light travel is possible without violating special relativity. I used a simple distance/time equation to show that in local space a person could travel 1 light year in less time than you could at the speed of light, therefore on paper they did in fact travel faster than light. I chose an arbitrary 1 second transit time just to make it work. I do get your point that distance travelled is distance traveled, and that if I went through a worm hole, then I should only count that distance. My point is that wormholes do not count as local space and any distance covered can only be measured through local space. If I could step through a "stargate" here on earth and appear magically on the moon, I still travelled the ~238 thousand miles or so, even if in real terms I only walked 5 feet. I realize that "stargates" and "wormholes" are different things but they are analogous in regards to what I am saying, in that they both represent an ability to bypass portions of local space which would otherwise had to be traversed.

What's amazing is that if you were watching for my arrival on the moon with a telescope, I would have been there for 1.5 seconds before you would see me arrive, and from then on, you would be looking into my past. And since on the moon I would be at a higher velocity relative to the earth, time will travel more swiftly on earth and thus I would age slower. The difference is negligable given the small difference in velocity, but its still cool to think about.

Here is a excerpt from wiki that explains what I meant about distance traveled a little better.

"Special relativity only applies locally. Wormholes allow superluminal (faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole, the time taken to traverse it would be less than the time it would take a light beam to make the journey if it took a path through the space outside the wormhole. However, a light beam traveling through the wormhole would always beat the traveler. As an analogy, running around to the opposite side of a mountain at maximum speed may take longer than walking through a tunnel crossing it. You can walk slowly while reaching your destination more quickly because the distance is smaller."

 

[Shadow Conception]

Ah that makes total sense. Thanks for clearing it up.

 

[KIAman]

I'd believe in superluminal speeds than bending the physical shape of reality, somehow creating a stable transport in between, then skipping right through.

If there was a reality fairy-tale scale of 1-10 (1 being possible, 10 impossible), then superluminal is a solid 10 and wormholes are a solid 15.

 

[MStele]

I'd believe in superluminal speeds than bending the physical shape of reality, somehow creating a stable transport in between, then skipping right through.

If there was a reality fairy-tale scale of 1-10 (1 being possible, 10 impossible), then superluminal is a solid 10 and wormholes are a solid 15.

I agree with you about wormholes. I think people like to focus on them because they provide the only reasonable conjecture to answer whether humans will ultimately start colonizing other planets. Mars is reasonable, but without some sort of exemption from special relativity, theres really no way to do it with any meaningful efficiency. Sure, more powerful spacecraft will be invented, but acceleration is limited by the human body, so very long distance travel becomes more of a pipe dream.

Who knows what the future may bring though.

 

[William Gaatjes]

i found this wile reading on the unusual speed of sound in berylium 12900meters/second and aluminium 6320 meters / second.

http://cr4.globalspec.com/thread/7294/Speed-of-sound-in-a-metal-rod

Excellent question! I don't have an answer. A perfectly stiff material (and especially a perfect "specific stiffness" material -- i.e., one with 0 density) does not exist, so we won't be able to do the experiment.

But suppose we have an infinitely stiff rod of 1000 km length. If we push on it, the other end must move at exactly the same time. Likewise, if we pull on it. So if we push and pull at, let's say, 100 times per second, then there will be a sound at the other end. And the start of that sound will be precisely at the same time as the start of the sound at our push-pull end. The motion of the material itself, however, would be much slower. (If the amplitude is 1mm, then the material motion is only 200 mm per second.) So we are not violating the prohibition against matter moving at greater than the speed of light.

So, yes, I guess then the speed of sound in this material (assuming longitudinal waves) would be higher than the speed of light. The speed of the matter would be much lower.

In short it is no. Any material can be compressed and because of this there is always a delay. And that delay is linked to the speed of light. Simply put every atom adds a delay and that delay is a multiple of the wavelength of the speed of light. If you want faster then light communication ? Do not use matter (or antimatter, because it is the same thing in this scenario only with a negative sign). You have to use that from which matter or every "particle" is comprised from. And what that is ? I do not know. Some stuff that operates in waves only i think...


EDIT:

http://www.bamr.co.za/velocity%20of materials.shtml

If we would ever be able to build a material atom for atom exactly as we want it, we can build atomic structures that could do some nice things.

According to another poster in the thread, boron and berylium have a hexagon structure.

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidstate.htm

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch13/structure.php

 

[sao123]

The pole is bendable. Even the hardest materials deform to a certain extent. If you made a pole of diamond it would still deform and that deformation would travel along the pole much like a wave. The rigidity of the material would determine the amplitude of that deformation wave.

under normal matter a, 100% rigidity would be impossible due to the nature of electrostatic forces and the emptty space between them...

however, theoretically would black hole matter, which is infinitely dense exhibit 100% rigiditiy, and therefore possibly be the only matter capable of transmitting at light speed? consequently, would the speed of sound in a black hole = the speed of light?

 

[DominionSeraph]

however, theoretically would black hole matter, which is infinitely dense exhibit 100% rigiditiy, and therefore possibly be the only matter capable of transmitting at light speed?

It's infinitely dense because it takes up no space. If it were to take up space across which to measure distance, it would no longer be infinitely dense.

 

[BarkingGhostar]

This is an interesting discussion. . .What if we modify the original scenario a bit. Just imagine you have a nail made out of some fictional material that is completely and totally rigid and cannot be compressed or bent . . .we'll just assume it is indestructible. This nail is 1 light year in length yet it is no heavier than your average roofing nail. What would happen if you place the point of it on a board lying flat on the surface of the earth and took a hammer to the other end of it a light year away and gave the nail an immense whack? How long would it take for the pointy end of the nail to sink into the board as a result of the whack you gave it a light year away?

I bet the wind would impart for force than any hammer.

 

[earthman]

Paratus and TastesLikeChicken did a good job of following up why this wouldn't work.

Hopefully we will have FTL drives and communications one day (soon, I hope). But right now we don't have any way of even theoretically doing this.

Only in science fiction.