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First, we have extensive observational data from elsewhere in the universe that tells us that the fundamental interactions work the same everywhere. For example
by pdonis 3y ago
First, we have extensive observational data from elsewhere in the universe that tells us that the fundamental interactions work the same everywhere. For example, we see light coming from regions that have very different gravity, but it still behaves the same.
Second, on the scale of atoms, or even on the scale of ordinary macroscopic objects, gravity is so extremely weak that its effects on things like chemical bonds or the structure of nuclei, atoms, and molecules is negligible. If you have a very massive object like a star (or a white dwarf or neutron star), then of course you have different states of matter possible (degenerate matter in stellar cores, white dwarfs, and neutron stars), but even those states of matter still have all the fundamental interactions working the same way. The different states of matter are due to the extreme density and pressure, not due to any change in the fundamental interactions.
Third, what we usually call "the speed of light in vacuum" is actually a property of spacetime, not specifically of light. So the idea of this speed being "slowed down by gravity" is based on a confusion. That property of spacetime (a better name for it would be local Lorentz invariance) is the same everywhere no matter how weak or strong gravity is.
- rkagerer 3y agoIsn't gravity a property of spacetime? (curvature)
- petschge 3y agoYou can describe it that way. But different parts of spacetime can have different curvature, so you get different impact of gravity. No matter how you describe it, gravity is different on Earth, Moon or in deep space and your theory has to model that no matter if it uses forces, curvature of spacetime or something else.
- pdonis 3y agoMore precisely, tidal gravity is spacetime curvature. What most people think of as "gravity"--for example, feeling weight when you are standing on the surface of the Earth--is actually non-gravitational forces, such as the Earth's surface pushing up on you, that are keeping you from freely falling. If you are in free fall, the "force of gravity" as people normally think of it disappears. (This was the key insight that started Einstein on the path to General Relativity.) What is left over is tidal gravity--freely falling objects converging or diverging because of the geometry of spacetime.
- _8j50 3y ago> For example, we see light coming from regions that have very different gravity, but it still behaves the same. Blackholes bend light for example, isn't that light behaving differently due to gravity? Couldn't pulsars and quasars do the same? > That property of spacetime (a better name for it would be local Lorentz invariance) is the same everywhere no matter how weak or strong gravity is. Isn't gravity a product of spacetime curvature? Normal objects' "speed" changes when they curve, can observational evidence froma distance, especially considering relativistic effects be enough to tell observers on earth thay even during curvatures of spacetime, the speed of light in vaccume locally at that point won't be affected?
- pdonis 3y ago> Blackholes bend light for example, isn't that light behaving differently due to gravity? No. Light "bending" due to gravity isn't a change in the behavior of light. The light is still traveling on the straightest possible path and obeying the same Maxwell's Equations. It's just doing it in a curved spacetime instead of a flat one.
- pdonis 3y ago> Isn't gravity a product of spacetime curvature? See my response to rkagerer downthread.
- pdonis 3y ago> Normal objects' "speed" changes when they curve The fact that you put "speed" in scare-quotes shows that, even if you don't realize it, you intuitively grasp that the concept you are trying to use doesn't work the way you are saying it does. Normal objects in free fall, i.e., moving only under the influence of "gravity", move on straight lines in spacetime, just like light does. (They are different straight lines because normal objects have mass while light is massless. But they're still straight lines in both cases.) The apparent "curvature" comes from the curvature of spacetime, not any change in the behavior of the objects. The objects have no way of telling locally whether the spacetime they are in is flat or curved. > the speed of light in vaccume locally at that point won't be affected? No. You can't tell anything about spacetime curvature or gravity by local measurements of the speed of light in vacuum.