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How did a false vacuum create a repulsive force during early cosmic inflation?

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During the early stages of the universe, such as the grand unification (GUT) era, certain fields existed in a high-energy state known as a "false vacuum." In the framework of general relativity, this state is characterized by a unique combination of mass density and negative pressure.1

While ordinary matter and radiation exert attractive gravity, this specific configuration of the false vacuum results in a large, gravitationally repulsive force. This force can be mathematically represented as a cosmological constant that was significantly larger in the early universe than it is today. The resulting repulsion caused the universe to undergo exponential expansion, or inflation, doubling in size at an extremely rapid rate.12

Eventually, as the universe cooled, it underwent a phase transition from the false vacuum to a lower-energy "true vacuum" state, similar to the way liquid water releases latent heat when freezing into ice. This transition ended the inflationary period and reheated the universe, providing the energy necessary for the subsequent emergence of particles and the standard evolution of the big bang model.1