Unification of Forces: Heating Up Spacetime & 4 Forces

[DiracPool]

Why is it that the farther we go back in time where there was a higher and higher average temperature, the 4 fundamental forces begin to unify one by one? What is it about "heating up spacetime" that causes the forces to unify? And by unify, do we mean that they become indistinguishable from one another, or do we mean that they remain distinct, only the strengths of the forces begin to reach parity?

 

[mfb]

They become more fundamental interactions, which look different from the usual interactions.

I would not say "interaction x and y get unified to z" - I think the other direction is more natural. There is an interaction (like the electroweak interaction), which can be described with two or more effective interactions for low energies.
As an example: the electromagnetic interaction, if all velocities are slow, can be approximated with electrostatics and magnetostatics.

 

[Mordred]

Why is it that the farther we go back in time where there was a higher and higher average temperature, the 4 fundamental forces begin to unify one by one? What is it about "heating up spacetime" that causes the forces to unify? And by unify, do we mean that they become indistinguishable from one another, or do we mean that they remain distinct, only the strengths of the forces begin to reach parity?

I can't recall which source it was on early universe particle physics, but I recall the statement "at high energies they become indistinquishable from one another"

anyways here is a resource article you may find handy

http://arxiv.org/pdf/0904.1556v2.pdf "The Algebra of Grand Unified Theories"

There is a couple of books I would recommend as well.

Particle Physics of the Early Universe by John Baez and John Huerta.

INTRODUCTION TO ELEMENTARY PARTICLES by David Griffiths