Gravity is the primary force that causes nebulae to collapse, not the force that prevents it. Nebulae are vast interstellar clouds of gas and dust that are held together by their own gravitational forces. Without gravity, nebulae would simply disperse and fade away.

Pressure, on the other hand, can play a role in counteracting the force of gravity and preventing nebulae from collapsing too quickly. Thermal pressure, which is created by the heating of gas and dust within the nebula, can push outward and help to balance the inward pull of gravity. Magnetic pressure, which is generated by the interaction of magnetic fields within the nebula, can also contribute to the overall pressure balance.

However, it's important to note that pressure forces alone cannot indefinitely prevent a nebula from collapsing. Over time, the gravitational forces acting within the nebula will overcome any opposing pressures, leading to the eventual collapse of the cloud and the formation of stars and planetary systems.