# Why do we know the particle/quantum field theory is phys of symmetries

1. Jan 11, 2014

### ndung200790

Why do we know that particle physics/quantum field theory is a physics of symmetries?What leads we to the gauge symmetries of all interactions?.Why we can not assume a physics without symmetry?

2. Jan 11, 2014

### bhobba

Of course you can do it without symmetries. Its just most beautiful and elegant that way.

Thanks
Bill

3. Jan 11, 2014

### Staff: Mentor

This comes from Noether's theorem.

4. Jan 11, 2014

### ZapperZ

Staff Emeritus
I'm a bit puzzled by this question.

Since you're asking specifically in reference to "particle physics/quantum field theory", does that mean that you have no issues with the concept of symmetries being used in classical physics and other areas? If so, then this makes no sense, since the SAME principle and idea are at work here. DaleSpam has eluded to such a principle.

So what is it about "particle physics/quantum field theory" that made you ask such a question, but not for classical physics?

Zz.

5. Jan 11, 2014

### Staff: Mentor

A symmetry implies the existence of a conserved quantity, and we know by observation and experiment that the world (both quantum and classical, as ZZ points out) is full of conserved quantities. That's a pretty good hint that investigating symmetries will be a fruitful way of investigating the world, and so far experience has supported that approach.

That doesn't necessarily make it the only approach, but as long as it works and no one has found a better approach, it's going to be the one that's most widely used.

6. Jan 11, 2014

### Jilang

If you were starting out to make a theory you would like it to work no matter where you choose to set the origin in space (x=0), whenever you choose the zero of time to be (t=0) whatever you set the zero of velocity of the frame of reference to be, wherever you set the direction of angle of zero to be and wherever you chose to set the zero of the EM field etc. This is necessary if you think about it as we make these choices of where the zeros are and they are arbitrary. These are the symmetries of the theories.

By making the model describing the physics invariant under all these choices leads naturally to the conservation of certain quantities. For example
Invariance under time translation leads to conservation of energy
Invariance under rotation leads to conversation of angular momentum
EM gauge invariance leads to conservation of charge
Etc.

Which is in line with what we find in experiments. It's pretty amazing!

7. Jan 11, 2014

### samalkhaiat

No, we can not do QFT without symmetries.