## Is energy faster than light?

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

Scooter_xkcd
Posts: 2
Joined: Thu Aug 18, 2011 6:24 am UTC

### Is energy faster than light?

If you have a massively long non-compressible object, say a light-second long rod though space, and push it, the other end moves instantaneously with the rest of it.

However, if you have a photon head from one end to the other without any interference, obviously it would take a second.

How is this possible? Not even the forces of gravity and electromagnetism are faster than the speed of light, yet the force applied to the rod travels to all particles in the rod in zero time? If this is the case, then energy would be instantaneous too, and therefore the travel of heat (radiation?).

gmalivuk
GNU Terry Pratchett
Posts: 26765
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

### Re: Is energy faster than light?

It's not possible. Absolute incompressibility violates special relativity, because impulses travel through a material at the speed of sound in that material, which is mediated by the electromagnetic force between atoms and therefore can't be faster than light.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

Technical Ben
Posts: 2986
Joined: Tue May 27, 2008 10:42 pm UTC

### Re: Is energy faster than light?

Has this been asked 4 times in a month now? Perhaps some large sticky, banner or cheese grater for "long rod".
It's all physics and stamp collecting.
It's not a particle or a wave. It's just an exchange.

Scooter_xkcd
Posts: 2
Joined: Thu Aug 18, 2011 6:24 am UTC

### Re: Is energy faster than light?

Technical Ben wrote:Has this been asked 4 times in a month now? Perhaps some large sticky, banner or cheese grater for "long rod".

I saw one like this, but it asked something slightly different, such as how to make a photon traveling through the substance move faster than light.

douglasm
Posts: 630
Joined: Mon Apr 21, 2008 4:53 am UTC

### Re: Is energy faster than light?

I've seen something like this discussed many times in this forum, though I can't give a good estimate of how often.

The misconception to be cleared up is always that no, the other end actually doesn't move immediately. The other end moves when the compression wave, which travels at the speed of sound in the rod, reaches it. A true non-compressible object would be one with an infinite speed of sound, which is impossible. Nothing can have a speed of sound greater than c without violating Relativity, and it takes something like a neutron star to even get close to that.

Coffee
Posts: 637
Joined: Mon Aug 18, 2008 5:56 am UTC
Location: Far away

### Re: Is energy faster than light?

Good luck pushing a rod made of neutronium.
Far away boys, far away boys, away from you now.
I'm lying with my sweetheart, in her arms I'll be found.

KittenKaboodle
Posts: 158
Joined: Thu Dec 16, 2010 6:36 am UTC

### Re: Is energy faster than light?

"Random thought on transmitting info @ C+ velocities" viewtopic.php?f=18&t=73157 still on the first page of "Science", almost precisly the same question, and got some decent answers, videlicet , movement travel at the speed of sound which is allways less than the speed of light in a vacuum and in ordinary materials, much much less. (there was some doubt about neutronium, but still, the speed of sound would not exceed c)
ShuRugal wrote:A perfectly straight rod of a material with low compressibility (such as high-speed steel or, to be silly, diamond) measuring 1 light-second in length is set up with an actuator on one end and a contact sensor on the other.

Set up parallel beside the actuator is a device which will, when the actuator pushes the rod, emit a photon towards a photocell beside the contact sensor.

The actuator pushes the rod, and simultaneously a photon is emitted. Does the photon arrive at the other end of the rod before, after, or concurrently with the movement of the other end of the rod?

dumbzebra
Posts: 275
Joined: Thu Dec 10, 2009 4:59 pm UTC
Location: Somewhere on the moon.

### Re: Is energy faster than light?

Oh Trollphysics...
As the great philosopher Socrates once said: "No."