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Hi,

Solar wrote:Nononono... the speed of light is constant. It's the space-time that's distorted by gravity, not the speed of light.

You are incorrect there.Matter ( or wave ) has dual nature, it exhibits particle nature as well as wave nature.The particle nature of light is used to explain photo electric effect and everyone knows Einstein got Nobel prize for photoelectric effect . So speed of light will be affected by force and gravity is a force.Speed of light =c only in vacuum with no force applied

--Thomas

Thomas wrote:Hi,

Solar wrote:Nononono... the speed of light is constant. It's the space-time that's distorted by gravity, not the speed of light.

You are incorrect there.Matter ( or wave ) has dual nature, it exhibits particle nature as well as wave nature.The particle nature of light is used to explain photo electric effect and everyone knows Einstein got Nobel prize for photoelectric effect . So speed of light will be affected by force and gravity is a force.Speed of light =c only in vacuum with no force applied

--Thomas

One of the underlying precepts of relativity theory (special and general) is that the speed of light is the same for all observers, no matter their relative motion (that is why it's called relativity theory). The different speed of light in mediums like air and water have nothing to do with gravity; it occurs due to the electromagnetic properties of the medium. Gravity can only affect the direction, not the speed of light. If you solve the EFEs for a photon travelling straight into / out of a black hole, it is still traveling at only the speed of light.

Thomas is correct. Gravity changes the speed of light.

But, it depends how I measure it. If I am near the light, and not resisting the gravitational field, I'll measure speed = c. Speed of light is always c if I am in the same inertial frame as the light.

However, if I measure from another inertial frame then gravity does have an effect. The statement that c is an absolute constant for all observers only applies in special relativity. Gravity changes that.

gerryg400 wrote:Thomas is correct. Gravity changes the speed of light.

But, it depends how I measure it. If I am near the light, and not resisting the gravitational field, I'll measure speed = c. Speed of light is always c if I am in the same inertial frame as the light.

However, if I measure from another inertial frame then gravity does have an effect. The statement that c is an absolute constant for all observers only applies in special relativity. Gravity changes that.

If that were true, there would be no constant "c", since general relativity prefers no reference frame over another. Every observer in a different gravitational situation would observe a different "c" value, and no value would be more correct than any other. The Equivalence Principle would also be violated, because the laws of physics would appear to be different from different reference frames. More specifically, fine structure constant (electromagnetic constant) would be different in different reference frames, and insanely different predictions would appear (for example, while an observer on a star would predict nuclear fusion would take place, as it does, an observer on earth would predict that the weaker electric constant would cause the star to implode due to the loss of electromagnetic force).

If I measure the speed of light to be c[me], and you have a gravitation potential of V with respect to me then you will measure the speed of that same light as This is one of Einstein's equations. He published this long before general relativity. As you can see, c is still a constant. It's just that neither you nor I necessarily measure the speed of light to be c.

I hope your childhood dream is to argue about speed of light so you don't do it for nothing in childhood dream topic.

I hope your childhood dream is to argue about speed of light so you don't do it for nothing in childhood dream topic.

For me, I guess it was really. I wanted to be physicist but never made it. I'm restricted to just reading other people's work.

Gravity does not change the speed of light. What you are talking about is the measured speed of light from an observers viewpoint. The speed of light is still a constant.

Light as you probably know has no mass and can not be effected by gravity in the normal sense. What gravity does is that it effects time. If you have a massive body like a black hole, light traveling close to it (but not too close or it will get sucked in) will bend around the hole because time goes slower on the side of the photon facing the hole compared to the opposite side.

Light as you probably know has no mass and can not be effected by gravity in the normal sense. What gravity does is that it effects time. If you have a massive body like a black hole, light traveling close to it (but not too close or it will get sucked in) will bend around the hole because time goes slower on the side of the photon facing the hole compared to the opposite side.

What if I were right there, in gravitational free fall when the photon went past the black hole. I'd report that the light went in a straight line past me at precisely c m/s. You, outside the gravitational field of the black hole would say that the light curved around the black hole and that one side of the beam went slower than the other. So you see the light bend and slow-down. Why do you believe the bending but not the slowing down ?

Yes to me seeing the bend it would look like the light is traveling slower. But I must take into account that when time is moving slower for the light beam compared to me the distance between the measuring points I would use to calculate it's speed have to decrease as well.

err...
wow. that changed topic quick!

Yes to me seeing the bend it would look like the light is traveling slower. But I must take into account that when time is moving slower for the light beam compared to me the distance between the measuring points I would use to calculate it's speed have to decrease as well.

I think we agree. Although I don't think we know what the light is really doing.

Someone further up said that

One of the underlying precepts of relativity theory (special and general) is that the speed of light is the same for all observers, no matter their relative motion (that is why it's called relativity theory).

I was just pointing out that that statement is not true and only holds if the observers are in the same inertial frame.

Yes, we are way off topic..... although studying this stuff was my childhood dream.

My dream was to eat a sandwich, then I ate one and everything went back to normal again.
Yea university next year, I should probably sign up for something.

My dream was to grow up.

I had a pretty weird night mare when I was very young, involving a laughing burger (which is weird as I don't actually think I'd ever seen a burger before), but other than that I can recall any childhood dream. All the computer and programming stuff have of course been a very big part of my life for a long time, but that didn't actually start before the age of 15 or something like that, so I don't think that it counts.

Guess I've always wanted to be a race driver, but since I don't even have a drivers license and that my driving experience is very limited, I think this dream will have to wait