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So my question is completely a theoritical question. For example i have a stick made of the strongest material and lightest material and its lenght is as long as the solar system's diameter. The end of the stick is A and the other end in space is B where a man is sitting. So here on earth i am holding the stick A and move it an angle that the B side covers 1 light year in the same time as the time it required for me to turn the stick to that angle. So does it mean that we can travel faster than light?

Ok so keep aside these things like how will i make that big stick or what will be the effects of the man travelling at that speed blah..blah..blah.. because its just a theoritical question.

Qmechanic
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Bhavesh
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1 Answers1

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No, because of the large scale. Doing things like this only seems instantaneous. The speed of a push on this object is actually the speed of sound in the object.

Jimmy360
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  • Ok so when its signal is reached on the B side then will it go instantaneous? – Bhavesh Apr 23 '15 at 10:38
  • No, it seems instantaneous, because on earth, you have never pushed an object big enough for the finite speed to matter. The will go at the speed of sound, incredibly slowly on a cosmological scale. – Jimmy360 Apr 23 '15 at 11:10
  • Once the signal reaches B, the whole rod will be in motion, but not he speed of light. – Jimmy360 Apr 23 '15 at 11:11
  • Why is that so? – Bhavesh Apr 23 '15 at 12:10
  • @Bhavesh Imagine the rod on the atomic scale. When you push it, the first row of atoms move, pushing the next row like a domino effect. But this is also what happens when we make a sound, a molecular domino effect. – Jimmy360 Apr 23 '15 at 12:44
  • Ok i have already understood that but i am asking that why can't it move instantly after the signal from A reaches B? as the signals are continuousy travelling not indivisually right so the B side should move instanly right? Also my question is marked as duplicate of this "Is it possible for information to be transmitted faster than light by using a rigid pole?" and there its written speed of light not speed of sound so... – Bhavesh Apr 23 '15 at 15:07
  • @Bhavesh A rigid pole like you are describing is impossible. There is another upper bound on the rod's speed, but before I begin, I must ask, are you familiar with QFT? – Jimmy360 Apr 24 '15 at 02:33
  • No i am not familiar with QFT – Bhavesh Apr 24 '15 at 03:10
  • @Bhavesh Ok, all you need to know to understand my answer about to the final upper bound is that all fundamental forces are there because particles make them work. Does that kind of make since. For example, the gravity particle is a graviton. – Jimmy360 Apr 24 '15 at 03:27
  • Ok so i understood that but after the force of push from A reaaches B can't it move intanteneously as the force of push will be constanlty travelling saying that move move move and it must go at a speed higher than the speed of light. – Bhavesh Apr 24 '15 at 10:15
  • @Bhavesh In QFT, electric repulsion is due to photons. How can the rod go faster than its mediator. Thus, the upper bound for a rod that somehow avoids the sound limit ( which won't happen) is the speed of light. – Jimmy360 Apr 24 '15 at 12:58