Now, this is an impossible object, but the idea of it raised a question in my mind.
Let's imagine that there is in space, a one light-year long rigid object, and there is a person on each side of this object *you and I.*
Let's imagine I have the ability to push it foward.
Now the problem arises.
When I push this object foward, let's say just a few centimeters, as not to harm you, what happens?
Will it take 1 year for your side of the object to move few centimeters foward?
If so, what would it look like from the side?
Will it be instantaneous? *meaning the second I push it, it is moved on the other side for you.*
This is a dumb question, that I hope I can get a smart answer from.
Will it take 1 year for your side of the object to move few centimeters foward?
It depends on the material. If it were, for example, steel, the compressive wave that travels down the bar (and thus transmits information about you having pressed on it) travels at around 6.1 km/s, so it'd take a little over 49000 years for the other end of the bar to react.
It can't be instantaneous because then information would be travelling greater than the speed of light which would allow you to actually violate causality.
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It can't be instantaneous because then information would be travelling greater than the speed of light which would allow you to actually violate causality.
That's what I thought, but then I thought *since I'm pushing it not faster than the speed of light, none of it ever travels faster than the speed of light.*
The speed at which you push it is actually irrelevant, that only tells you how fast the molecules move. The disturbance that tells the rest of the beam that the end has moved propagates at the speed of sound in the bar. The actual particles move very little.
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Never attribute to malice what can adequately be explained by incompetence.
What's interesting about this thought experiment is that it also describes how electrical impulses work. The energy of you pushing the bar, just like the energy of an electrical impulse, travels much faster and further than any of the particles of the bar.
1) How in the world would you even get an object that long? (yes i know the problem is hypothetical and stuff)
2) How would you keep it upright in order to send the signal?
3) What even is one light year away that someone would be able to recieve the signal from?
But then again, this was probably derived from a troll science picture anyways.
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Last I checked electricity moves at the speed of light(far from instant). The electrons themselves moves super slow but the motion of one cause a wave where all the other move too.
Last I checked electricity moves at the speed of light(far from instant).
It can travel up to the speed of light, but is often less (and can sometimes be significantly less) and depends on the dielectric constant of the material carrying the current. Even putting insulation around a wire can affect it (usually slowing the speed of propagation down).
The electrons themselves moves super slow but the motion of one cause a wave where all the other move too.
In a DC circuit the drift velocity of electrons is ridiculously slow. We're talking on the order of micrometers per second. In an AC circuit (most household electronics) the electrons don't really move anywhere at all but just vibrate in place. This is one of the important things to understand about wave phenomena: the wave itself can move much faster than the material that it propagates in.
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Bah, macro and micro physics bug me. In macro things start to get weird due to the speed of light. In micro things start to get weird due to the size of particles and the fact that they have a wavelength(more speed of light blah).
There has to be some way to break the speed of light, should make things interesting...
Bah, macro and micro physics bug me. In macro things start to get weird due to the speed of light. In micro things start to get weird due to the size of particles and the fact that they have a wavelength(more speed of light blah).
There has to be some way to break the speed of light, should make things interesting...
If I recall correctly, they made a photon (a particle of light) travel faster than the speed of light. I don't know if it actually did anything weird.
Bah, macro and micro physics bug me. In macro things start to get weird due to the speed of light. In micro things start to get weird due to the size of particles and the fact that they have a wavelength(more speed of light blah).
There has to be some way to break the speed of light, should make things interesting...
If I recall correctly, they made a photon (a particle of light) travel faster than the speed of light. I don't know if it actually did anything weird.
The sum of energy of the photon never traveled faster than the speed of light.
This is correct. They can do things like make the phase velocity of light (since it's a wave) exceed the speed of light. The group velocity (and therefore the photons themselves) do not exceed the speed of light ever. Nothing that carries information can exceed the speed of light. However there are a number of things that can exceed the speed of light with no violation of special relativity since they don't carry information (so for the purposes of superluminal travel or communication they're completely worthless).
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Never attribute to malice what can adequately be explained by incompetence.
Wow, thinking about this, my head feels like it might explode.
I would think it would be instantaneous, seeing as it is a single rigid object, it would HAVE to be reacting at the same time lest the object has two parts of it in the same spot.
it would HAVE to be reacting at the same time lest the object has two parts of it in the same spot.
An object being deformable doesn't mean two parts of it can occupy the same spot. Like I said before, and if you'd read the topic, what happens is a wave propagates through the bar much like how waves propagate through air. Objects can bend and compress and change shape and volume.
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Never attribute to malice what can adequately be explained by incompetence.
Then, yes, a rigid object would move instantaneously. That's not very interesting because rigid objects can't exist. Largely for exactly that reason since the interactions between atoms would be limited by the speed of light itself.
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Never attribute to malice what can adequately be explained by incompetence.
Let's imagine that there is in space, a one light-year long rigid object, and there is a person on each side of this object *you and I.*
Let's imagine I have the ability to push it foward.
Now the problem arises.
When I push this object foward, let's say just a few centimeters, as not to harm you, what happens?
Will it take 1 year for your side of the object to move few centimeters foward?
If so, what would it look like from the side?
Will it be instantaneous? *meaning the second I push it, it is moved on the other side for you.*
This is a dumb question, that I hope I can get a smart answer from.
It depends on the material. If it were, for example, steel, the compressive wave that travels down the bar (and thus transmits information about you having pressed on it) travels at around 6.1 km/s, so it'd take a little over 49000 years for the other end of the bar to react.
It can't be instantaneous because then information would be travelling greater than the speed of light which would allow you to actually violate causality.
That's what I thought, but then I thought *since I'm pushing it not faster than the speed of light, none of it ever travels faster than the speed of light.*
I know you're joking, but this still assumes the bar is rigid and it isn't. It will bend.
Every time I come to this board I learn more than I do in an average day at school.
1) How in the world would you even get an object that long? (yes i know the problem is hypothetical and stuff)
2) How would you keep it upright in order to send the signal?
3) What even is one light year away that someone would be able to recieve the signal from?
But then again, this was probably derived from a troll science picture anyways.
[Diamond]
It can travel up to the speed of light, but is often less (and can sometimes be significantly less) and depends on the dielectric constant of the material carrying the current. Even putting insulation around a wire can affect it (usually slowing the speed of propagation down).
In a DC circuit the drift velocity of electrons is ridiculously slow. We're talking on the order of micrometers per second. In an AC circuit (most household electronics) the electrons don't really move anywhere at all but just vibrate in place. This is one of the important things to understand about wave phenomena: the wave itself can move much faster than the material that it propagates in.
would the object overlap itself?
No. What would happen is you'd get a shock wave. It's the same thing that happens when you cross the speed of sound in air.
Of course, in a practical setting what would actually happen is the material would fail (though there still would be shock waves in it).
There has to be some way to break the speed of light, should make things interesting...
[Diamond]
If I recall correctly, they made a photon (a particle of light) travel faster than the speed of light. I don't know if it actually did anything weird.
This is correct. They can do things like make the phase velocity of light (since it's a wave) exceed the speed of light. The group velocity (and therefore the photons themselves) do not exceed the speed of light ever. Nothing that carries information can exceed the speed of light. However there are a number of things that can exceed the speed of light with no violation of special relativity since they don't carry information (so for the purposes of superluminal travel or communication they're completely worthless).
I would think it would be instantaneous, seeing as it is a single rigid object, it would HAVE to be reacting at the same time lest the object has two parts of it in the same spot.
MineScience - viewtopic.php?f=25&t=166560
Dragonator - viewtopic.php?f=25&t=141803
Sand Skiffs - viewtopic.php?f=25&t=233346
But it's not rigid, nothing is.
An object being deformable doesn't mean two parts of it can occupy the same spot. Like I said before, and if you'd read the topic, what happens is a wave propagates through the bar much like how waves propagate through air. Objects can bend and compress and change shape and volume.
MineScience - viewtopic.php?f=25&t=166560
Dragonator - viewtopic.php?f=25&t=141803
Sand Skiffs - viewtopic.php?f=25&t=233346