To add to red's reply, the answer also depends on what you mean by "significant". Gravity is a weak force, relative to the three others, but it is has the greatest capacity to act over long distances. So even in the early universe, when it existed as a separate force (with the caveats red described), it would have been a minor force in comparison to the strong/weak forces and electromagnatism. As the density of matter decreased, gravity would have had a larger and larger role, compared to those other forces.

Bryan

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