How do Forces "split"?

Factual Questions
1

I’ve been reading and thinking (I know… I’m not supposed to), and Physics is always wonderful but I always have a tendency to start reading about things I don’t understand, and lacking the ambition to read 80 books, and the time limits of Physics classes I need to ask these questions.

From what I understand in my shakey knowlege (I think this specific tidbit came from watching something) the singular… entity before the big bang had all 4 nuclear forces unified. Makes sense to me, if everything (or pretty much so) is condensed so is all the force and such. But then (again, please don’t hurt me if I’m wrong, my knowlege is shakey at best) it said that gravity “broke off” resulting in all hell breaking loose, basically the big bang and since all the forces were unified (minus the weakest one) everything was expanded faster than c for a moment or so afterwards.

I have no idea on the time window for this but I assume the strong force broke off next (I’m basing this off the term “electroweak” which my physics teacher described while half dodging my question as the force when electromagnetism and the weak force were unified). And then assumedly weak and electromagnetic broke apart elaving us with our four “fundamental” nuclear forces of strong, weak, electromagnetic, and gravitational.

My question (okay lots of quesitons) is (and please correct any of my above paragraphs if it will help) how, and under what circumstances can this breaking of forces happen? I’d assume it would take quite a bit. Even so I have to ask that, even though I’m almost certain the answer is “a non-zero probability that is nonetheless ridiculously close to zero” what is the chance of this happening again? And how would it affect us in the long run and the immediately presuming it did happen?

Like I said, I’m probably graspign at things way beyond my level right now. I don’t mind complicated physics terms when nescessary, but when applicable be gentle, I think Wikipedia is wanting a little “alone time” from me since I’ve been overusing it lately. :wink:

2

The Big Bang wasn’t caused by gravity splitting off from the other forces. That happened after.

The basic idea behind symmetry breaking is that at very high energies all the forces of nature behave identically. However at lower energies the fundamental characteristics of the vacuum cause them to behave differently.

Imagine it this way: When a balloon is inflated it curves smoothly in all directions. It’s symmetrical. That’s the high-energy situation. Let the air out of the balloon and its wrinkled and nubbly. It’s no longer symmetrical. The precise patterns of the wrinkles and nubs are determined by the fundamental nature of the balloon (the vacuum) itself.

Shortly after the Big Bang the universe was in an extremely high energy state. Any fundamental characteristics of the vacuum were masked. All the forces (gravity, electromagnetism, the strong and weak nuclear forces) had identical properties in this high energy environment.

As the universe expanded and cooled the properties of the vaccuum began to manifest themselves. The balloon deflated and wrinkles and nubs appeared. These wrinkles and nubs “broke symmetry” and gave the fundamental forces the properties we observe today.

Current research is focused on reinflating the balloon just a little. The Large Hadron Collider at Fermilab will hopefully create strong enough collisions to temorarily reverse the symmetry break between the electromagnetic and weak nuclear forces.

People have wondered if its possible for the vacuum to spontaneously change properties. The current assumption is that the vacuum is the lowest energy configuration the universe can assume. But maybe it’s really a “false vacuum” and with a little coaxing a little more air could be squeezed out of the balloon. This would destroy the universe as we know it. As the properties of the vacuum changed every fundamental law of the universe would change as well. Forces would operate differently, the masses of particles would change. Existance as we know it would instantaneously cease.

Don’t worry. It’s not likely to happen. The universe has been around for billions of years and if there really was a lower energy configuration than our current vacuum it probably would have manifested itself already.

3

It’s not like particle decay; the forces didn’t decide to split at a random time. It’s an energy scale thing. Just after the Big Bang, particle energies were very high. As the fledgling universe cooled, typical energies dropped in proportion, and it’s the energies involved that govern how the interactions behave. A cosmologist might talk about the forces splitting (since energies drop with cosmological time), while a particle physicist might talk about forces unifying (since the energy reach of particle accelerators improves with time).

The electromagnetic and weak forces make for a clean example. Consider two electrons heading toward each other at typical atomic energies (few eV).



\elec.
 \
  \
   v
   
   ^
  /
 /
/elec.

The quantum field theoretic view of the interaction is (approximately) that a virtual photon is exchanged between the two electrons, transferring momentum and energy.



\       ^
 \     / elec.
  \   /  
   \ /   
    |
    |virtual photon
    |
   / \
  /   \
 /     \ elec.
/       v

Calculating the probability of this exchange happening gives you the strength of the force. However, electrons also interact via the weak force, which involves the exchange of rather massive W and Z particles (rather than photons). In fact, the electron scattering process above can occur via the weak force:



\       ^
 \     / elec.
  \   /  
   \ /   
    |
    |virtual Z
    |
   / \
  /   \
 /     \ elec.
/       v

In reality, both processes occur simultaneously. However, a Z is heavy (mass=91 GeV/c[sup]2[/sup]), so making even a virtual one to exchange when you’ve got only a few eV of energy to spare is exceedingly difficult. Thus, the weak force plays a negligible role in the calculation.

But… if the electrons instead have 100 GeV of energy (obtainable in particle accelerators and Big Bangs), it’s just as easy to exchange an photon or a Z, and the electromagnetic and weak forces play equal roles in the interaction. They are said to be unified. (The unification is considerably more elegant than this makes it sound, though. The photon and Z (and W) are cut from the same cloth in the standard model. The fact that the photon ends up massless while the others are heavy is a longer story.)

At energies well beyond current human reach (10[sup]15[/sup] GeV), the strong force is expected to unite with the “electroweak” force. While the standard model does well with electroweak unification, new theoretic frameworks are needed (and many exist) to describe the latter strong+electroweak unification. Most of these new theories include predictions that will be checked in the next round of particle physics experiements at the upcoming Large Hadron Collider. Even absent this possibility, the puny energy range available to us has been sufficient to show that the strengths of the electromagnetic, weak, and strong forces trend with energy in more or less the right way such that they might converge in the 10[sup]15[/sup] GeV ballpark.

No satisfactory theoretical framework exists to describe the unification of gravitation with the above three forces. From fairly general arguments, it is expected that the unification would occur around 10[sup]19[/sup] GeV.

4

Nit pick, of sorts: The LHC is being built at CERN (Switzerland), not at Fermilab (Illinois).

5

Here’s what I don’t understand. If all the forces had identical properties what was it about them that differentiated them at that time? How were they different forces? Weren’t they the same force (if it walks like a duck, etc)? And if so, how would that force resolve itself into different forces?

6

If there had been physicists around in a pre-splitting era, then yes, they would have viewed (say) the electromagnetic and weak forces as part of one unified force. The splitting happens because there are certain energy scales associated with different aspects of the force. If you’re dealing with objects that have much higher energies than this special energy scale, then the fine structure of how the force behaves isn’t going to affect your answers much; but if you’re dealing with objects that have a much lower energy than this special energy scale, then it’s going to matter to your experiments a great deal.

As an analogy, imagine playing billiards on a giant washboard. If you hit the billiard balls hard enough, they’ll skitter over the surface and won’t much care that the grooves run in a particular direction. However, if you only give your billiard balls a tiny bit of energy, they might not have enough energy to cross one of the ridges in the washboard, and so their motion in the direction along the grooves will be very different from their motion perpendicular to the grooves.

7

Duh … I knew that. Thanks.