Particle Physics to Explain the First Few Minutes of the Big Bang
Following the same theory we used to explain the opaque universe we can predict the temperature of the universe at various stages of its development.
NB/ We said that the cosmic microwave background today is ~2.7K, and the universe is ~12 billion years old. Extrapolation back we said that about 1 million years after the big bang the background was ~3000K, and prior to this the universe was opaque (all matter was in plasma form).
As we go back further in time (closer to the big bang), the temperature of the universe increases. Since temperature is a measure of the kinetic energy of a particle, we can recreate the conditions of the universe by accelerating particles to very high speeds and observing their properties - hence particle accelerators.
At temperatures above 107K (~ 100s) nuclei become unstable and the protons and neutrons within it dissociate. The plasma becomes a sea of electrons, protons and neutrons moving independently of each other.
At temperatures above 1013K (~ 0.001s after the big bang) the protons and neutrons themselves breakdown into their fundamental particles called quarks (NB. Electrons are believed to be a fundamental particle in their own right from a family called leptons ). Quarks can have different 'flavours' and different combinations of these 'flavours' produce protons and neutrons.
To understand the ways in which the universe might have developed in its earliest stages, we must know about the forces governing the particles that it was made of at each stage.
Obviously today the observable universe is made of matter and radiation and is thus governed by the forces of gravity and electromagnetism.
But as we go back in time and the universe heats up the 4 forces (Weak, Strong, EM and Gravity) become indistinguishable.
The theory behind this last statement is that if the electromagnetic force is responsible for holding the electrons in the region around the atomic nuclei, then in the plasma state of the early universe, where electrons were not associated with atomic nuclei, then the EM force was irrelevant and indistinct from the other forces.
Similarly at higher temperatures where the protons and neutrons of the nucleus separate into their constituent quarks, the strong force, which binds the quarks together to form these particles, becomes indistinct.
To cover the idea completely we must talk about the messenger particles for each of the forces. Current theory suggests and is backed up by some evidence from particle accelerators that the way in which each of the forces is propagated is by massless, high energy particles similar to photons which exchange energy between the interacting particles. Each force has its own messenger particle, but this is not on your syllabus.
Anti matter
We have evidence to show that when a photon in the early universe condensed into matter, producing for instance an electron, then a corresponding piece of anti matter is also formed, in this case a positron.
When a particle meets its equivalent anti-particle, then the two annihilate each other and produce a photon. Below certain energies and the reaction can only go mass à energy, which explains why photons aren't constantly creating matter/ anti-matter pairs.
The mass produced in a matter/ anti matter pair when a photon condenses is governed by the energy of the photon in the relationship: E = mc2
If this was the case though, surely there should be equal amounts of matter and anti matter in the universe and the two should have annihilated each other leaving only energy. So why is there matter in the universe?
Questions:
- Suggest an appropriate time to suggest for the end of the big bang.
- How far back to the beginning of the big bang is there any experimental evidence to support the cosmologists’ story of the Universe?