Is the speed of interaction faster than light?

Question

Bare with me.. This is a philosophical question, I know it can't realistically be done, but..........

If I got a really long metal rod, say, about 1 light year in length.

I used it to poke my friend who was stood at the other end, would he feel the poke some time sooner than 1 year later? If so, I've just send a signal faster than light.

I know the rod will compress slightly, but let's say that it is a very dense rod.

Answer 1

if the rod is a light year long, then thats unfair for the light, smart one.

Answer 2

It makes no difference how dense the rod is. Your poke is not transmitted by magic. It's transmitted by the electrochemical interactions of the molecules in the rod, which propagate at less than c.

Answer 3

It is theoretical, not philosophical.

When you move the end of the rod, a compression wave will speed down the rod at the speed of sound in the rod. No matter how dense it is. The -stiffer- it is, the faster the speed of sound, but it will never travel even at the speed of light.

So he'll feel it considerably more than a year later.

Electricity doesn't travel at the speed of light. So if you sent a current down the metal rod to a bell, it would take quite a bit longer than a year for the bell to ring.

That is because 1. Electrons have mass and don't travel at the speed of light and 2. The electrons in the wire travel a meandering path that just averages out to moving in the direction of current.

PS The expression is "bear with me". If you're asking us to get naked with you, no thanks. ;')

Answer 4

if hes one light year away your friend wont feel anything cos he'll be dead

Answer 5

I once thought about this same question and spoke to a physics professor on the topic, and no a light year long rod, would take a light year to move.When you push an object a atom's push each atom in front of it, and other end moves as a result of the energy passing through it, speed depending on the density, but  even at absolute density this would not travel faster than light.

Answer 6

lol