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  on the speed of information can it be faster than light?

+ 0 like - 4 dislike
214 views

Let's imagine there is a rod a very long rod. This rod is also very ridged. This very long and very ridged rod is also very easy to move despite its length and ridgetity. Let's say for the sake of easy math and absurdity it is 1 light year long.

At one end of this rod is a button at the other is a finger waiting to press the rod into the button. At the same time there is a very powerful flash light/laser that is for the purposes of easy math and absurdity shines upto 1 light year away. At the end of this beam of light is a button just to the left of the button near the rod, this button however unlike the one to the right can only be depressed by this flashlights beam.

Now we have set up the race. A race between the speed of light and the speed of a rod. Again, for absurdity, we will give the light depressing finger an hours head start. That is an hour before the finger poised to push the rod does so.

My question is witch will depress the button first?

If it is as I believe the rod or right button will be depressed first, would it not be the case the information was conveyed faster than the speed of light?

asked Sep 13 in General Physics by stupidone [ no revision ]

Also let's be charitable assume static points as in from starting point to end point. That is to say don't muddy the question with something to the effect of "it (the targeted button) will have moved..."

If you assume absurd things you get absurd results.

@Arnold Neumailer Thank you for confirming my belief in pedantic responses on the internet. It would have cost you nothing to not comment. Amazing that you are here and cannot grasp a thought experiment!

Do not feed trolls.

1 Answer

+ 1 like - 0 dislike

To be honest, originally I did not want to answer this sort of question. It is to be noted that "stupidone" himself referred to the assumptions in his question as "absurd".

Now for the answer:

A rigid rod:

1) The material objects of our world are made up of atoms, which have mass and interact by electromagnetic forces. Pressing the rod would lead to a displacement of some atoms closest to the pressing finger, this displacement occurring at a speed lower than the speed of light. The displacement leads to a rearrangement of electromagnetic fields in the rod, this change propagating at the speed of light, this change leading to a change of forces on further atoms, causing their acceleration and respective displacement, and so on. As a result, a mechanical wave is travelling along the rod. The atoms therein are moving slower than the speed of light. Therefore, the end of the rod next to the button will move after the light signal has reached its corresponding button.

2) Suppose the rod made of a more exotic material, like nuclear matter (leaving aside the issue of stability of the rod shape here). Then instead of atoms and electromagnetic forces, you will have protons and neutrons (which have mass), and nuclear forces plus electromagnetic forces (which are carried by fields disturbances of which propagate at the speed of light). So, eventually, it is a situation as under 1.

3) Let's be even more exotic and disregard the details of the composition of the rod. The rod is rigid. But what does that mean then? It, by definition, means that as soon as you press one end, the other end moves in the same way as the pressed end does. But in this case the definition necessary to understand your setup (i.e., what does "rigid" mean) already contains the answer to your question. 

4) What can a rod like in 3 be? It either is something utterly different from the physical world we know, not even composed of constituents, maybe. Or it is made up of particles which interact by forces we do not know but which propagate faster than the speed of light. Such particles themselves then are also not known to us. 

Your question therefore boils down to: If I assume things significantly different from known physics, do I predict results significantly different from the predictions of known physics?

answered Sep 14 by Flamma (110 points) [ no revision ]

@flamma

Wow! More idiotic pedantry...

Bad faith discussion. It is obviously a thought experiment about speed of light not materials. Score one for being as described pedant.

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