Chapter 16, Problem 43A

From our frame of reference on Earth, objects slow to a stop as they approach black holes in space because time gets infinitely stretched by the strong gravity near the black hole. If astronauts accidentally falling into a black hole tried to signal back to Earth by flashing a light, what kind of wave-lengths of light would best be looked for in Earth-based telescopes?

To determine

The kind of wavelength signaled by an astronaut accidentally falling into a black hole by flashing a light.

Answer to Problem 43A

The wavelength would be far infrared.

Explanation of Solution

Introduction:

According to Einstein’s third prediction, gravity causes time to run slow.

When an astronaut fall into the black hole then due to gravity of black hole, time runs with extremely slow nearly stops. When light travels against the gravity then frequency of the light observed by the Earth-based telescopes will decrease to an extent that wavelength observed will be far infrared.

Conclusion:

Thus, the light emitted by the astronaut from the black hole will be of far infrared wavelength.