Planck epoch
Up to 10–43 seconds after the Big Bang Main article: Planck epoch
At the energy levels that prevailed during the Planck epoch the four fundamental forces—electromagnetism, gravitation, weak nuclear interaction, and strong nuclear interaction—may all have the same strength, so they are possibly unified in one fundamental force. Little is known about this epoch, and different theories propose different scenarios. General relativity predicts a gravitational singularity before this time, but under these conditions the theory is expected to break down due to quantum effects. Physicists hope that proposed theories of quantum gravitation, such as string theory, loop quantum gravity, and causal sets, will eventually lead to a better understanding of this epoch.