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wisp
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The equivalence principle (EP) - which is the basis of general relativity – states that you cannot distinguish between an object’s behaviour in a uniform gravitational field from that in a uniformly accelerating frame.
If light travels vertically in a gravity field it loses or gains energy, and experiments confirm that gravity pulls on light as if it possessed inertial mass m=E/c^2. So light traveling vertically obeys the EP.
When Einstein first calculated the bending of light near the sun he got a value of 0.8 arcsec, using the above reasoning. But later corrected this to 1.75 arcsec, because light refracts in a gravitational field. So the light bends doubly.
Consider the two cases:
1. An astronaut is in a room inside a rocket that is accelerating. A beam of light passes horizontally across the room and strikes the opposite wall lower down by distance d.
2. An astronaut is in a room inside a rocket that is stationary on the earth. A beam of light passes horizontally across the room and strikes the opposite wall lower down.
Does light fall by d (gravity pulling on light’s inertial mass only)?
Or does it fall by 2d (due to refraction and gravitational pull)?
If it’s 2d, doesn’t that violate the EP?
If light travels vertically in a gravity field it loses or gains energy, and experiments confirm that gravity pulls on light as if it possessed inertial mass m=E/c^2. So light traveling vertically obeys the EP.
When Einstein first calculated the bending of light near the sun he got a value of 0.8 arcsec, using the above reasoning. But later corrected this to 1.75 arcsec, because light refracts in a gravitational field. So the light bends doubly.
Consider the two cases:
1. An astronaut is in a room inside a rocket that is accelerating. A beam of light passes horizontally across the room and strikes the opposite wall lower down by distance d.
2. An astronaut is in a room inside a rocket that is stationary on the earth. A beam of light passes horizontally across the room and strikes the opposite wall lower down.
Does light fall by d (gravity pulling on light’s inertial mass only)?
Or does it fall by 2d (due to refraction and gravitational pull)?
If it’s 2d, doesn’t that violate the EP?