Matter Bends Light Not Gravity
Gravity does not bend light unless the light is passing through a medium.
The gravitational field exerts the free fall to give the atmosphere a tendency to fall.
This leads to an uneven density.
Light slows down in a medium as it gets absorbed and re-emitted in different densities, affecting the time taken through the medium.
In a prism this behavior of light in a medium becomes very visible as the light slows down at different rates based on the width of the beam slowing its path through different densities or durations.
The surface of water results in its own light bending behaviors with the abrupt change in density between the path in air or in water.
On Earth (or any other celestial body) gravity pulls air toward the surface. The air temperature reflects the kinetic energy of the molecules maintaining a pressure directly proportional to temperature. The nature of the atmosphere changes with the greatest pressure at the lowest elevation or the lowest pressure at the highest elevation.
During an evening sunset the beam of light slows at different rates through the layers of different densities so light bends with the slowest path at the surface.
I have read that Newton's gravitational field accounted for only half of the observed angular deviation at the Sun's surface in 1919.
The Sun's atmosphere is plasma or charged matter. The Sun's electric field would have affected the plasma so it behaved differently with both a gravitational field and an electric field than if those EM fields were not present.
Gravity does not bend light, matter does.
With no gravity or any electromagnetic force affecting the free flow of gases the path of light will remain straight.
I have posted about how a gravitational field cannot affect electric and magnetic fields, or electromagnetic radiation, like light.
That remains true. But I do need to correct the wrong impression. Gravity has an indirect role.
However we do not live in a vacuum and gravity affects whatever matter is about.
I expect on the moon as long there is no atmosphere, and I do not expect it to develop an electric field so I expect light will never bend on the moon.
Gravity does not bend light; matter does.
This comment about 2 days later:
Matter has mass. Mass has gravity. Therefore, gravity bends light. Hence, Gravitational Lensing, which is light bent by gravity, not matter, as no direct contact with matter is made by the light being bent.
Another's comment a few hours later:
I thought gravity bends space and light follows that bend
My response after those comments above:
The point is light goes straight through a vacuum or matter of uniform density and thickness.
A transition at the surface of matter will bend light like a glass prism or the surface of water.
Different densities of the earth's atmosphere will bend light.
Different densities of the sun's atmosphere will bend light.
I know of no test of gravity affecting light in a vacuum.
The Moon could be used but its gravity is weak so the deviation is probably too small to detect. That would be the true test.
Using a gas giant is impossible given its immense atmosphere, so there is no defined surface with nothing above it. A galaxy also has no surface edge.
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