# The fundamental forces and elementary particles at absolute zero

1. Jan 13, 2014

### ns_phonon

We all know that there four fundamental forces in nature, viz.
The gravitational force
The electromagnetic force
The strong nuclear force
The weak nuclear force

Now also we know that temperature of any system is the average kinetic energy possessed by the particles of the system

Now my question is very simple and to the point, no beating about the bush, if we reduce the temperature so much almost to the absolute zero.
"WILL THE DECREASE IN TEMPERATURE CAUSE A CHANGE IN THE MAGNITUDE OF ANY OF THESE FOUR FUNDAMENTAL FORCES....???"

If it does then please try to explain the mechanism behind and giving citations from any loyal and honest sources will be appreciated.

2. Jan 13, 2014

### Staff: Mentor

There is no reason to use caps lock.

The forces you listed are all elementary, and you can consider the forces between individual particles.
Individual particles do not have a temperature - temperature is an effective description for a large set of particles. Therefore, temperature cannot have an effect on those forces on a fundamental level. Temperature can have an indirect effect - it can influence particle positions, for example, and the forces depend on the particle positions, but that does not change the way the forces act.

To give a comparison: we (humans) cannot change chemistry - we can decide which substances we mix in our lab, but chemistry itself does not depend on that.

3. Jan 13, 2014

### kurros

Is this really true? I know nothing about finite temperature field theory, but I would have thought that since couplings run with energy scale they would also run with temperature.

4. Jan 13, 2014

### ZapperZ

Staff Emeritus
Look at the Coulomb force between two charges. Next, look at the gravitational force between two bodies.

Do you see any temperature dependence?

Zz.

5. Jan 13, 2014

### ns_phonon

But if the temperature does not affect the fundamental forces then would not a question arise of how a Bose- Einstein Condensate is formed.

Most sites tell that when we lower the temperature to extreme low then all(most of the) the atoms(boson atoms) go into the ground state and they lose their individual properties and gets condensed into a blob which can be represented by a single wave function. And so we cannot differentiate an atom of calcium from rubidium.

All this explanation seems really very enchanting at quantum and particle physics level.

But if all the atoms gets condensed then wont they suffer an electrostatic replusion in between them due to electron shells trying to push away from each other.Then how can we have a superatom(union of boson atoms) as described in Bose- Einstein condensate if the coloumb force magnitude remains the same in lowering the temperature.

6. Jan 13, 2014

### ns_phonon

http://discovermagazine.com/1993/feb/thebiggestchill174#.UtDQB8u3RAg

7. Jan 13, 2014

### ZapperZ

Staff Emeritus
Reread what mfb wrote about temperature being a STATISTICAL property. The BE condensation is a MANY-BODY property. It doesn't happen in isolated or even few particles!

I can easily turn this around. If you claim that the BE condensate is an indication that the fundamental forces are temp dependent, then how come the coulomb forces and gravitational forces have no temp dependence? This important fact is something you seem to glaringly ignore.

Zz.

8. Jan 14, 2014

### Staff: Mentor

Running couplings are not variations of the forces, in the same way different distances don't lead to a different law of gravity for Sun/Mercury and Sun/Earth. In addition, see ZapperZ's reply.

We can. We cannot distinguish two rubidium atoms.
The classic notion of "distance" cannot be applied to BECs in this way, but it does not change how the forces work.

9. Jan 14, 2014

### kurros

Well what would count as a variation of the strength of the forces then? At different renormalisation scale we could be describing the forces with a completely different looking effective theory; it's a pretty dramatic change, far more so than the simple scaling that happens with distance in classical gravity/electromagnetism. Sure, it is in some sense a distance-related effect, but it is a distance-related effect that can fundamentally change how the forces manifest.

10. Jan 15, 2014

### Staff: Mentor

A coupling constant that is different at different locations or at different times, or different charges for different particles of the same type, or something similar you would not expect from a fundamental interaction.

The same laws of gravity describe both neutron stars and the orbit of earth around the sun, even if the effects are completely different.

11. Jan 15, 2014

### kurros

But you don't suddenly describe gravity with particles of a different mass and spin, like say switching from talk about gluons to pions, or from fermi interactions to Z exchanges, or from massive Z's and W's and photons to massless SU(2)xU(1) gauge bosons.

12. Jan 16, 2014

### Staff: Mentor

Exactly, and you don't do that for other interactions.

That's like comparing friction and the forces between two electrons. The interaction acts the same way, you just consider different effects on completely different scales.
Also note that temperature has no meaning for your examples.

13. Jan 16, 2014

### kurros

Ahh, ok well this point I would like to be clear on. Are you saying that in the sufficiently early universe we would not actually describe the physics in terms of massless gauge bosons and so on? Like I said I know no finite temperature field theory, so I don't know what happens here. I have always assumed that some kind of renormalisation-like procedure still occurs though, and that the renormalisation scale would correspond to the temperature of the plasma, or some such.