- #1
Logic314
- 10
- 7
I have read in several popular physics texts that general relativity predicts that gravity deflects light, but that Newtonian mechanics, in contrast, predicts that the trajectory of light is not affected by gravity. However, I am very skeptical and confused about this result.
We of course have the common famous result of Newtonian mechanics, which states that objects of different masses all accelerate the same way under the same local gravitational field (this is the basis for the experimental fact that a feather and a rock fall at nearly the same acceleration inside a vacuum chamber).
But if this is indeed what Newtonian mechanics predicts (that is, if the acceleration in a local gravitational field really is independent of the mass of the particle, according to Newtonian mechanics), then Newtonian mechanics should predict that light has the same acceleration as a rock does within the same local gravitational field, despite the fact that they have different masses (one being nonzero and the other being 0), and thus, Newtonian mechanics should predict that gravity bends light.
So, I'm very confused about why popular physics textbooks seem to emphasize that Newtonian mechanics predicts that light is unaffected by gravity, even though this seems to contradict the general principle from Newtonian gravity theory (that the way objects accelerate under the influence of gravity does not depend on their masses).
We of course have the common famous result of Newtonian mechanics, which states that objects of different masses all accelerate the same way under the same local gravitational field (this is the basis for the experimental fact that a feather and a rock fall at nearly the same acceleration inside a vacuum chamber).
But if this is indeed what Newtonian mechanics predicts (that is, if the acceleration in a local gravitational field really is independent of the mass of the particle, according to Newtonian mechanics), then Newtonian mechanics should predict that light has the same acceleration as a rock does within the same local gravitational field, despite the fact that they have different masses (one being nonzero and the other being 0), and thus, Newtonian mechanics should predict that gravity bends light.
So, I'm very confused about why popular physics textbooks seem to emphasize that Newtonian mechanics predicts that light is unaffected by gravity, even though this seems to contradict the general principle from Newtonian gravity theory (that the way objects accelerate under the influence of gravity does not depend on their masses).