Why would'nt this work?
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A perfectly rigid object would be usable as a tool of FTL communication
Would it though? I feel like the theoretical limit is still c
Yes, the speed of sound in an object is how fast neighboring atoms can react to each other, and not only is that information (therefore limited to C already) but specifically it's the electric field caused by the electrons that keep atoms certain distances from each other and push each other around. And changes in the electric/magnetic fields are famously carried by photons (light) specifically - so even in bulk those changes move at the speed of light at most
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A perfectly rigid object would be usable as a tool of FTL communication
Would it though? I feel like the theoretical limit is still c
Yes, that's the point. The limit c denies the possibility of a perfectly rigid body existing physically. It can only exist as a thought experiment.
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Perhaps also worth pointing out that the speed of light is that exact speed, because light itself hits a speed limit.
As far as we know, light has no mass, so if it is accelerated in any way, it should immediately have infinite acceleration and therefore infinite speed (this is simplifying too much by using a classical physics formula, but basically it's like this:
a = f/m = f/0 = ∞). And well, light doesn't go at infinite speed, presumably because it hits that speed limit, which is somehow inherent to the universe.That speed limit is referred to as the "speed of causality" and we assume it to apply to everything. That's also why other massless things happen to travel at the speed of causality/light, too, like for example gravitational waves. Well, and it would definitely also apply to that pole.
Here's a video of someone going into much more depth on this: https://www.pbs.org/video/pbs-space-time-speed-light-not-about-light/
I think relativity demonstrates that light does have mass?
They might not have "rest mass" but they do have mass!
The eclipse experiment proved it, solar sails whilst hypothetical demonstrate it.
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I think relativity demonstrates that light does have mass?
They might not have "rest mass" but they do have mass!
The eclipse experiment proved it, solar sails whilst hypothetical demonstrate it.
Photons don't have mass, but they do have momentum.
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The problem is that when you push an object, the push happens at the speed of sound in that object. It's very fast but not anywhere near the speed of light. If you tapped one end of the stick, you would hear it on the moon after the wave had traveled the distance.
Wow, TIL that the speed of sound has this equivalence
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I swear I've seen a video of someone timing the speed of pushing a very long pole to prove this very thing. If I can find it I'll post it here.
AlphaPhoenix is definitely one of the best scientists on YouTube, that video is good.
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A perfectly rigid object would be usable as a tool of FTL communication
Would it though? I feel like the theoretical limit is still c
What about using c++ or rust?
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
If you're openminded enough to listen to those who disagree with the standard model,
take an elastic band and twist it, that's what will happen to the stick and this travels at lightspeed,
as this is what light does. Do it fast enough and the 'elastic band'/stick/'atom on the other end' breaks. -
Perhaps also worth pointing out that the speed of light is that exact speed, because light itself hits a speed limit.
As far as we know, light has no mass, so if it is accelerated in any way, it should immediately have infinite acceleration and therefore infinite speed (this is simplifying too much by using a classical physics formula, but basically it's like this:
a = f/m = f/0 = ∞). And well, light doesn't go at infinite speed, presumably because it hits that speed limit, which is somehow inherent to the universe.That speed limit is referred to as the "speed of causality" and we assume it to apply to everything. That's also why other massless things happen to travel at the speed of causality/light, too, like for example gravitational waves. Well, and it would definitely also apply to that pole.
Here's a video of someone going into much more depth on this: https://www.pbs.org/video/pbs-space-time-speed-light-not-about-light/
Actually, the thing that applies to the pole is the speed of sound (of the pole material), which is the speed the atoms in the pole move at. Not even close to the speed of light.
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If you're openminded enough to listen to those who disagree with the standard model,
take an elastic band and twist it, that's what will happen to the stick and this travels at lightspeed,
as this is what light does. Do it fast enough and the 'elastic band'/stick/'atom on the other end' breaks.Gravity waves doesn't go faster than light though?
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You think its instantaneous because you never held such a long stick.
Speak for yourself!
Is it instantaneous though?
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Gravity waves doesn't go faster than light though?
Iirc from the 2 YouTube videos I watched light can theoretically bend thanks to gravity, black holes anyone?
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It would work, but only in the impossible world where you have a perfectly rigid unbreakable stick. But such an object cannot exist in this universe.
Pick up a solid rigid object near you. Anything will do, a coffee cup, a comb, a water bottle, anything. Pick it up from the top and lift it vertically. Observe it.
It seems as though the whole object moves instantaneously, does it not? It seems that the bottom of the object starts moving at the exact same instant as the top. But it is actually not the case. Every material has a certain elasticity to it. Everything deforms slightly under the tiniest of forces. Even a solid titanium rod deforms a little bit from the weight of a feather placed upon it. And this lack of perfect rigidity means that there is a very, very slight delay from when you start lifting the top of the object to when the bottom of it starts moving.
For small objects that you can manipulate with your hands, this delay is imperceptible to your senses. But if you observed an object being lifted with very precise scientific equipment, you could actually measure this delay. Motion can only transfer through objects at a finite speed. Specifically, it can only move at the speed of sound through the material. Your perfectly rigid object would have an infinite speed of sound within it. So yes, it would instantly transfer that motion. But with any real material, the delay wouldn't just be noticeable, but comically large.
Imagine this stick were made of steel. The speed of sound in steel is about 5120 m/s. The distance to the Moon is about 400,000 km. Converting and dividing shows that it would actually take about 22 hours for a pulse like that to travel through a steel pole that long. (Ignoring how the steel pole would be supported.)
So in fact, you are both right and wrong. You are correct for the object you describe. A perfectly rigid object would be usable as a tool of FTL communication. But such an object simply cannot exist in this universe.
Username checks out.
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I think relativity demonstrates that light does have mass?
They might not have "rest mass" but they do have mass!
The eclipse experiment proved it, solar sails whilst hypothetical demonstrate it.
Relativistic mass is not helpful to our everyday understanding of mass, it's more helpful to discuss momentum, like the other commenter pointed out
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Iirc from the 2 YouTube videos I watched light can theoretically bend thanks to gravity, black holes anyone?
Space bends due to gravity. Light continues in a straight line through the now non-linear space, thus appearing to bend.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
This is actually a great example for why that stick must not exist.
You can also do this with a unbreakable stick and an unbreakable shorter tube. Throw the stick at a high velocity through the tube and it contracts for the point of view of the tube. Then close it shut. Now you have a stick that's longer than the tube fully contained in it.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
Go find a 30' stick and let us know if you can point it at the moon.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
Next, I suppose you'll want to know about the speed of dark 🤨
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Actually, the thing that applies to the pole is the speed of sound (of the pole material), which is the speed the atoms in the pole move at. Not even close to the speed of light.
Correct answer is here.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
