# Cheap way to test relativity?

#### Rockazella

Here’s a quick thought I had.
Since electrons experience relativistic effects just like any other matter, would you be able to detect a mass increase in a wire if you sent a current through it?

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#### Integral

Staff Emeritus
Gold Member
The actual net movement of electrons in a current carring wire is very small. The actual electon drift velocity is not even close to c.

#### quartodeciman

Einstein wrote in his second relativity paper that one might check out E=MC2 by weighing radioactive material at two different times and comparing the weight difference to the total radioactive energy emitted in between. He later admitted it was a foolish idea.

#### Rockazella

The actual net movement of electrons in a current carring wire is very small. The actual electon drift velocity is not even close to c.
Isn't it true that the signals speed is near c? I guess I dont really understand what you mean by electron drift velocity, mind explaining?

#### Integral

Staff Emeritus
Gold Member
The name is very discriptive. The actual speed of a single electron or its drift velocity is much smaller then c. Signal probogation on the other hand is a signifigent fraction of c. This is not an uncommon phenonemn, even in water waves a molecule of water remaings nearly stationary horizontanly as the wave passes.

#### Jonathan

On a similar note, in particle accelerators, they can get particles to go quite fast, so do the particles ever get heavy enough from their speed that putting a plumb line a few feet from the accelerator would be noticably perturbed when the accelerator is running? Granted, this wouldn't be as cheap as running a current through a wire.

#### Integral

Staff Emeritus
Gold Member
Originally posted by Jonathan
On a similar note, in particle accelerators, they can get particles to go quite fast, so do the particles ever get heavy enough from their speed that putting a plumb line a few feet from the accelerator would be noticably perturbed when the accelerator is running? Granted, this wouldn't be as cheap as running a current through a wire.
Just what would that prove?

Even thought particle accelerators have had sufficient energy to push particles well beyond c, if we lived in the world of Newtonian Physics, they have been unable to. Why? because of relativity, the speeds achieved for the energy input match the predictions of relativity to many decimal places.

#### Jonathan

Integral: I don't understand your post, but my point was that maybe the paricle would get heavy enough to have a noticable attraction for the plumb line. I really doubt it though, it was just an idea.
Mr. Robin Parsons: According to relativtity, it should be unmeasurably heavier while hot, not the other way around. Maybe water condensation?

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#### russ_watters

Mentor
Johnathan, its a lot easier than you're making it out to be: since the particle accelerator has to accelerate the particle, you can tell exactly how much energy you put into the particle and then measure its speed. Even a mediocre particle accelerator puts enough energy into a particle to accelerate it well beyond C under Newtonian mechanics. So the relativistic effects are clear as day.

#### Jonathan

Oh! Upon rereading Integral and Russ_water's posts, They are clear know, I don't know how I missed the point before.

#### arcnets

Originally posted by Rockazella
would you be able to detect a mass increase in a wire if you sent a current through it?
Probably not.
But there is an easy relativistic explanation of forces between parallel wires:
Let's assume that positive charges are at rest, and negative charges flowing (OK, OK,...)
Imagine how one electron in wire A 'sees' wire B.
- If the currents have the same direction, then the electron will see the positive charges length-contracted, i.e. condensed. No change on negative charges. So wire B appears net positive, so attraction.
- If the currents have opposite directions, then the positive charges appear condensed, but the negative charges more condensed. So net negative charge, so repulsion.

I know that drift velocities are only some cm/s, but on the other hand you have a very large number of electrons. When doing the math, you arrive at the correct force, believe me.

And of course, this doesn't 'prove' anything about relativity.

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