Final answer:
The gravitational force between particles increases with energy at scales relevant to the theory of everything due to the unification of fundamental forces and pronounced spacetime curvature in high-energy conditions.
Step-by-step explanation:
As the energy of interacting particles increases, especially at the scale where the theory of everything is considered, it is believed that the gravitational force between them increases. This occurs because, in high-energy conditions, such as those present a fraction of a second after the Big Bang, particles are subjected to immense pressure and temperatures which could feasibly cause all four fundamental forces of nature to unite into a single force. Under such extreme conditions, the nature of spacetime and particles changes drastically.
According to theories including string theory, the fundamental particles are replaced by one-dimensional strings that vibrate at different frequencies in an 11-dimensional space. The increase in energy could potentially lead to changes in how these strings vibrate, thus affecting the forces between them. Furthermore, as the early universe was incredibly dense and hot, the idea is that interactions between particles were governed by this unified force, which, as energy decreased, separated into the four distinct forces we observe today.
Therefore, it's the extreme conditions and high energies that render the gravitational force more pronounced, as spacetime curvature becomes more significant due to the increased energy/mass of the particles as they approach the conditions that might be described by a theory of everything.