# Unified fields in BB

1. Sep 12, 2011

### easyrider

Hello guys/gals, I understand this is a probably a stupid/impossible question in yalls eyes, but considering that todays scientists are working towards understanding the entirety of the beginning of the universe, and we would all like to understand it too, so bare with me here.

In the earliest times of the universe/BB, what would "it" have been made of? The way I understand it is it was made up of all 4 forces at such high intensities they came together into one force. So, does this mean the forces came before their corresponding bosons? What would that unified field/energy look like?
Also what would the electroweak force look like and could it still do the same things light does?

2. Sep 13, 2011

### bapowell

It is indeed believed that at high enough energies, at least the strong, weak, and electromagnetic forces were unified. As the universe cooled, these split off from the unified force in a process called spontaneous symmetry breaking. When the forces are unified, only the bosons associated with the "superforce" exist. When the symmetries break, and the forces disentangle, the superforce bosons "become" the bosons associated with the separate forces.

The electroweak force was the unified interaction comprised of the weak nuclear force and electromagnetism. At even earlier times, the electroweak interaction was unified with the strong force.

3. Sep 13, 2011

### easyrider

So there was still bosons during the earliest times of BB?

What would be the name of these superforce bosons/what is the evidence for them?

Does the electroweak force have a single boson thats different from the photon and the w and z bosons?

Also, what exactly would the unified and electroweak force look like, how would it behave?

And during this time, was there a point in which no matter, not even quarks, was there?

Last edited: Sep 13, 2011
4. Sep 13, 2011

### bapowell

Yup.

Currently, there is no perfectly successful GUT. One of the more important predictions that come out of GUTs is the lifetime of the proton, since in traditional GUTs there are baryon number-violating interactions that enable proton decay. Another testable prediction is the scale of unification -- the energy at which the three forces: strong, weak, electromagnetic -- come together. The number of bosons in the GUT depend on the "size" of the symmetry of the theory.

Sort of. The electroweak force is mediated by 4 massless bosons. When the symmetry breaks, 3 of them acquire masses (the Ws and Z) and one remains massless (the photon).

The simplest GUT (Georgi-Glashow) has X and Y bosons analogous to the W and Zs of electroweak theory. They mediate interactions between quarks and leptons, leading to violations of lepton and baryon number. More elaborate GUTs can lead to other types of interactions.

Modern cosmology picks up just after the big bang occurred. At this time, the universe was a hot bath of radiation, leptons, quarks, and gluons.

5. Sep 14, 2011

### easyrider

Thank you, so when they say radiation dominated universe, there was some matter in there as well?

Also, ignoring singularities, and talking about the big bang when it was at the planck energy density, would it have been made up of energy in the form of the unified forces or matter or a mix of both?

6. Sep 14, 2011

### bapowell

Yeah, I sort of misspoke at the end of my last post. What is meant by radiation is any particle species that is moving relativistically -- $T \gg m$, where T is the temperature and m is the mass of the particle. So in the very early universe, virtually all species of particle -- force carriers and matter alike -- were relativistic and behaved gravitationally like radiation. As the universe cooled, particles with mass $m \sim T$ became non-relativistic, but photons and neutrinos, for example, are relativistic. Therefore, before the universe transitioned to a matter dominated phase, it passed through a radiation dominated phase that had matter components as well, since the photons and neutrinos dominated the energy density early on.

7. Sep 14, 2011

### easyrider

Oh okay, so there was all types of particles in there but they wouldve been just about indistinguishable from photons? And then when it started cooling down matter started taking on its current properties?

8. Sep 14, 2011

### bapowell

While all particle species right after the BB were relativistic, it's not quite correct to say that they were all indistinguishable (for example, fermions and bosons have different statistical properties which give them different thermodynamics). What all relativistic species do have in common is how their energy densities evolve in the expanding universe -- they satisfy $\rho \propto a^{-4}(t)$, where a(t) is the scale factor governing the expansion of the spacetime. It's important to stress that matter still retained its properties back then -- an electron was still an electron. It's perhaps more correct to say that a relativistic electron emphasizes its wave-like properties (gravitationally evolves like radiation) whereas a non-relativistic one exhibits more particle-like behavior (gravitationally evolves like pressureless dust)

9. Sep 14, 2011

### easyrider

Thanks, when talking about GUTs, what exactly is meant by "mass, charge, flavour, and color charge would have been meaningless"? This must be an older/obsolete way of looking at it?

Also, what is most currently accepted view on the big bang and string theory?

And just a random question, but is it possible for a superstring to be by itself so to speak and not make up anything larger? What properties would it exhibit? Would it be able to propagate/travel along by itself?

10. Sep 15, 2011

### bapowell

I believe this is getting at the fact that the "charges" that generate the four fundamental interactions: mass/energy, electric charge, color charge, and weak isospin, do not generate these interactions during the GUT era. Instead, only the charges of the GUT force are relevant.

That the big bang does fine without string theory

Superstrings are not believed to necessarily make up anything larger. For example, an electron is fundamental and identified as a vibrating string in string theory.

11. Sep 15, 2011

### easyrider

I didnt really mean it like that, like which theory(Id assume string theory or LQG) is considered to be more favored right now among most top cosmologists and/or particle physicists? Ive heard string theory hasnt really turned up a whole lot results/predictions wise..

Last edited: Sep 16, 2011
12. Sep 16, 2011

### bapowell

I'd say neither theory is more favored right now since they are both tremendously light on predictions. And as with anything else in science, the acceptance of theories and ideas is an evidence-based endeavor. Neither theory is complete, and so cosmologists must be cautious when developing models based on them. That doesn't mean that it isn't worthwhile to investigate the implications that each theory has on cosmology, but we are certainly a far way from saying which theory is more correct.