# Effects gravity have on Superconductors

1. Nov 13, 2009

### thehangedman

The electron pairs, acting as bosons, all fall to the lowest energy state, and can't get enough energy (under normal operating conditions), to make the quantum jump to the next energy level, hence as they move through the conductor they don't lose energy. That is, in a nutshell, my assumptions about how Superconductors work. Question is, wouldn't gravity, though a small effect, cause a splitting of the energy bands? And if so, the electrons would be able to move between the different split bands and hence gain / lose energy, correct? Granted, the splitting would be very very small as compared to the level difference between the lowest and next highest states, but the whole system being "superconducting" seams to me to be dependent on the assumption that no jumps can happen. Any jumps, even very small ones, would result in a gradual lose of energy in the system.

Has anyone measured the distribution of the electrons in a superconductor to find the effect gravity would normally have? Regular conductors show a distribution (more electrons at the bottom of the wire), but if the above is correct, there shouldn't be such a distribution in a SC...

2. Nov 13, 2009

### Bob S

I have never heard of this. Does this mean there is a vertical electric field in the wire due to gravity pulling the electrons down? How high would a wire have to be to charge my cellphone?
Bob S

3. Nov 13, 2009

### Bob_for_short

As the electrons are much more attracted to the lattice than to the Earth, the gravity effect should be negligible in a superconductor as well as in a conductor. The lattice density vertical variation is more noticeable effect of gravity, I think.

4. Nov 13, 2009

### thehangedman

Here are some references I found in a few minutes on Google:

I would assume your post is an attempt to be funny, but it's not. If I was an expert I wouldn't be posting questions here. You can either be helpful, and point out where I'm wrong in my assumptions, or move on and read some other posts.

Last edited by a moderator: May 4, 2017
5. Nov 13, 2009

### thehangedman

Ok, but even being a very small effect, wouldn't that cause the electrons to slowly lose their energy? Or, is the effect so small that it wouldn't be detectable unless measured over a long period of time?

6. Nov 13, 2009

### Bob_for_short

Concerning the second reference, it is about "Gravity-induced emf in superionic conductor", not in superconductor.

"The electric field arising due to redistribution of mobile Ag(+) cations under the action of gravity is observed experimentally...".

Was it a liquid conductor?

7. Nov 13, 2009

### Bob_for_short

I heard from one physicist that a two- or three-year experiment with a superconductor showed no change in its state. Besides, the velocity in SC is quantized. So the loss cannot be small but finite. It makes the superconducting state quasi-stable with a very big decay time.

8. Nov 13, 2009

### JustinLevy

thehangedman,
Yes, there would be a non-uniform distribution of charge because of this. Effectively gravity creates an electric potential difference in a conductor on the order of:
$$V = \frac{mg\Delta h}{q}$$
Assuming there is only one type of charge carrier with mass m and charge q.

And yes, the effect would be very very small. You also would not be able to measure it with a voltmeter since the voltmeter would feel the same effect (that doesn't mean you can't detect its effect other ways though).
I didn't read your references, but if they did use a liquid conductor to see these effects, it is probably for exactly that reason ... the charge carriers are very heavy, making the effect bigger and easier to detect.

Getting back to your main question, no, this would not ruin a superconductor.
Instead of a gravitational field, let's use an external constant electric field. Does this ruin superconductivity? No. Does it split the 'levels'? No.
Charge will just build up on the surface (like in an ordinary conductor), to "expell" the electric field from the conductor. The superconductivity will continue as normal.

In both examples, the external force on the electrons was the same for all electrons. So how could this possibly "split the levels"? It will not.

Imagine an external magnetic field. Since the electrons in the Cooper pair have different spin, they will feel a different force. But again, a superconductor will work to expell this field, and the superconductivity will remain in the bulk (until you exceed the ability of the superconductor to expell the field).

Even in a cold superconductor, surely this potential difference has got to be way below $$k_BT$$?