- #1

Andrew Wright

- 118

- 19

- TL;DR Summary
- Objects falling into an event horizon seem to gain infinite kinetic energy.

Hi,

When objects fall in a gravitational field, they convert gravitational potential energy into kinetic energy. Because energy is always conserved:

amount of kinetic energy gained = amount of gravitational potential energy lost.

Now the gravitational energy lost should be equal to the amount of energy gained by doing the journey in reverse.

This is where I have a problem. An object that is near the event horizon would require a near infinite amount of energy to make the journey in reverse out of the black hole. So this means a near infinite amount of gravitational potential energy is lost. In turn, that the kinetic energy gained by falling into an event horizon is infinite. So, this feels wrong since black holes are real objects that exist out there and infinite energy sounds like nonsense.

Have I made a mistake? Why/Why not?

When objects fall in a gravitational field, they convert gravitational potential energy into kinetic energy. Because energy is always conserved:

amount of kinetic energy gained = amount of gravitational potential energy lost.

Now the gravitational energy lost should be equal to the amount of energy gained by doing the journey in reverse.

This is where I have a problem. An object that is near the event horizon would require a near infinite amount of energy to make the journey in reverse out of the black hole. So this means a near infinite amount of gravitational potential energy is lost. In turn, that the kinetic energy gained by falling into an event horizon is infinite. So, this feels wrong since black holes are real objects that exist out there and infinite energy sounds like nonsense.

Have I made a mistake? Why/Why not?