Question

The principle of equivalence states that all experiments done in a lab in a uniform gravitational field cannot be distinguished from those done in a lab that is not in a gravitational field but is uniformly accelerating. For the latter case, consider what happens to a laser beam at some height shot perfectly horizontally to the floor, across the accelerating lab. (View this from a nonaccelerating frame outside the lab.) Relative to the height of the laser, where will the laser beam hit the far wall? What does this say about the effect of a gravitational field on light? Does the fact that light has no mass make any difference to the argument?; As a person approaches the Schwarzschild radius of a black hole, outside observers see all the processes of that person (their clocks, their heart rate, etc.) slowing down, and coming to a halt as they reach the Schwarzschild radius. (The person falling into the black hole sees their own processes unaffected.) But the speed of light is the same everywhere for all observers. What does this say about space as you approach the black hole?

a) The laser beam hits lower; gravitational field bends light.
b) The laser beam hits higher; gravitational field accelerates light.
c) Light's constant speed is unaffected by gravity.
d) Light's behavior near a black hole is unpredictable.

Answer 1

In an accelerating lab, a horizontally shot laser beam hits lower on the far wall, illustrating that gravity affects the path of light. This effect mirrors the bending of light due to gravitational fields, independent of light's masslessness, signifying gravity's influence on spacetime. Near a black hole's Schwarzschild radius, observed processes slow, indicating spacetime's extreme distortion.

Step-by-step explanation:

The principle of equivalence, as posited by Einstein in his theory of general relativity, suggests that the effects of a uniform gravitational field are indistinguishable from those of uniform acceleration. When considering a laser beam shot horizontally across an accelerating lab, the beam would hit the far wall at a lower point than the source. This phenomenon occurs because the lab is moving upwards during the time it takes the light to cross the room, causing the beam to strike lower on the opposite wall than where it originated. This effect is analogous to the deflection of light by a gravitational field, indicating that gravity bends light, as Einstein reasoned. Notably, the fact that light has no mass does not prevent gravity from affecting its path, highlighting a key prediction of general relativity: the curvature of spacetime itself influences the path of light.

Regarding the Schwarzschild radius of a black hole, Einstein's theory predicts that as an observer approaches the event horizon (the Schwarzschild radius), all of their processes appear to slow down to an outside observer, while their own experience remains unchanged. This dramatic effect demonstrates the intense distortion of spacetime near a black hole, where the gravitational field is so strong that light itself appears to stop at the event horizon when viewed from the outside.