Question

Within which time frame from the initial Big Bang do we believe all four fundamental forces of nature were united into a single force?

Answer 1

It is thought that the fundamental forces were unified less then `10^(-36)` seconds after the Big Bang.

Explanation:

In terms of unifying the fundamental force only the electromagnetic and weak forces have been unified. The theories show that the photon and Z boson become indistinguishable at high energies.

The next theory which is required is a Grand Unified Theory (GUT) with unifies the strong and electroweak forces. The problem is that we don't know how to make a particle accelerator powerful enough to reach the energies to detect the particle required for a GUT. There are candidate theories and it is estimated that the three forces were unified some `10^(-36)` seconds after the Big Bang.

It is thought that the GUT forces separated around `10^(-12)` seconds after the Big Bang.

Unifying gravity with a GUT to form a Theory of Everything is a long way off. The GUT forces are described by quantum theories. Gravity is described geometrically as the curvature of spacetime. We need a quantum theory of gravity before any unification can be attempted.

Any unification of all four forces would have to be much earlier than `10^(-36)` seconds aftr the Big Bang.