Final answer:
Gravitational fields can influence matter/antimatter collisions, such as near a black hole where one particle may be captured and the other escapes, leading to energy loss for the black hole. In the broader universe, matter/antimatter annihilation is not broadly observed, indicating a matter-dominated universe.
Step-by-step explanation:
The effect of a gravitational field during a matter/antimatter collision can have spectacular outcomes. In the vicinity of a black hole, for instance, the combination of gravity and quantum mechanics can result in particle-antiparticle pair production, a phenomenon predicted by quantum field theories. If a pair is produced at the event horizon of a black hole, one particle may get trapped by the black hole's gravity and fall in, while the other escapes. This results in a net loss of energy for the black hole, a process theorized as Hawking radiation, which could lead to the black hole shrinking over time.
In the universe at large, when matter and antimatter meet, they annihilate each other, transforming into pure energy, often in the form of gamma-ray radiation. Observations show that the universe is matter-dominated as we do not observe the expected levels of gamma-rays that would be produced if antimatter were abundant. The rarity of antimatter in the observable universe is supported by the lack of annihilation radiation, especially the 0.511-MeV gamma rays from electron-positron annihilation.