ArmchairGeneral

Incorrect. Escape velocity is a lot more complicated than that. I'll be honest, I don't really understand how to calculate it, but I will point out that while Earth's gravitational acceleration is 9.8 m/s/s, escape velocity at the surface is approximately 11,200 m/s.

Helpful link: Escape velocity - Wikipedia, the free encyclopedia

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ArmchairGeneral

That is correct. Negative acceleration (deceleration) is what you feel whenever you slow down.

ArmchairGeneral

I'm no physics whiz, but I think you're making a unnecessary distinction between massy and massless objects. As I understand it, what we think of as a gravitational attraction is considered in relativity to be nothing more than the curvature of spacetime. Thus, everything that exists in spacetime, including photons, is affected by gravity.

dave lukins

Measurements taken during an eclipse in 1919 showed that light from a distant Galaxy was bent by the mass of the Sun... that was in accordance with Einstein's law of gravitation

ArmchairGeneral

Technically, what was bent was space. Light was following the shortest path through space, which is by definition a straight line. A good analogy is seen in the flight paths of airplanes, which follow great circles (circles that bisect the Earth). On a Mercator projection, the path will look curved, but it's actually the shortest line between two points, and thus a straight line in spherical geometry.

dave lukins

Yes, in theory of general relativity, light would be bent by the deformation of the space-time continuum around an object such as a Planet

highsea

I was trying to point out that the description of photons being somehow accelerated by gravitational force is not the case. Photons do not "fall back" into a black hole, for example.

Photons are NOT affected by gravity. The space that they exist in IS. That is not an unnecessary distinction to physists, I can assure you. Gravity has absolutely no effect on a photon (or any other massless particle). If it did, photons could be sped up and slowed down, and the speed of light would not be a universal constant.

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omon

oh, ok i see it makes sence now, is it like magnets have force or pressure, but flux itself(the force it self) has no weight, or does it?

ArmchairGeneral

But, if I understand correctly, in general relativity, there is no such thing as a gravitational force. What we think of as gravity is nothing more than an effect of curved space. Which is what affects photons, and everything else. So what's the difference between gravity (space-time curvature) affecting mass, and space-time curvature (gravity) affecting light?

gunnut

Ahh, but I did make the difference.

I stated the earth's gravitational acceleration is 9.8m/s/s

I never once said the earth's escape velocity is 9.8m/s

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gunnut

OK, got it. That makes sense.

gunnut

Actually, light was not bent.

The space that light travels in was bent by the gravity of the star. So it "appears" that light was bent. But in reality light travels in a straight line, but if we curve the space, we can bent light.

ArmchairGeneral

No, but you stated that since the escape velocity of a black hole must be at least 300 million m/s, the gravitational acceleration of a black hole must be at least negative 300 million m/s/s. Thus, by the same reasoning, since the escape velocity of the earth is 11,200 m/s, the gravitational acceleration must be 11,200 m/s/s. Which it ain't.

My apologies for leaving an /s on my previous post.

dave lukins

So you ARE saying that light was bent If not, I'm gonna wake Albert up and tell him he was wrong, and send him to your address

If you don't agree with "Bent" lets agree with the term "Deflected" (for now)

dave lukins

For a Black Hole to stop emitting Light it has to shrink under its own gravity. As it shrinks the gravitational field at the surface becomes stronger and the escape velocity increases. By the time the Radius is down to 30km its escape velocity would have increased to 300,000 kps.. the velocity of light. After that, any light emitted by the star would not be able to escape to infinity and would be dragged back by the grav. field