Gravity's Effects on Light: Mass & Black Holes

In summary, light is affected by gravity because it has relativistic mass, even though it has no rest mass. This is why it can be trapped in a circular orbit around a black hole, but only if it enters on the correct trajectory. However, due to the large number of photons coming from all directions, a steady flow of light would not be seen in this orbit.
  • #36
DaveC426913 said:
No. Gravity curves spacetime. Light, like mass, follows the geodeisc of this curved space. It is not necessary for light to have mass in order to do this.
I don't know why so many people here are allergic to specifying which mass they are talking about, which causes all kinds of disagreements over terms and formulae where there should be none.

Light has no rest mass. It has gravitational mass. In a gravitational field, it has a weight. If you take lights dp/dt in gravitational field, you get a non-zero value. That's a force. That's weight. It's an inertial force, yes, but so is the weight of any other object.
 
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  • #37
OK I think light has mass because it's affected by gravity

Not likely in the sense you mean it...but light does have relativistic mass if that's what you mean. See post # 4 in this thread.

From E = mc2 we know energy and mass are two sides of the same entity...Einstein's work showed that in either form, mass or energy, gravity has an influence. It turns out pressure also has gravitational effects.
 
  • #38
DaleSpam said:
Even Newtonian gravity does not require an object to have mass in order to be affected by gravity:

F=GMm/r²
ma=GMm/r²
a=GM/r²

So the acceleration is independent of the mass of the object.

No.. Newtonian gravity requires an object to have mass in order to be affected by gravity
that is clear from the law . if we put m=0 then f=0 so acceleration = o according to Newton's first law.
What is independent of mass is the magnitude of acceleration and not the existence of acceleration
In GR yes .. because acceleration is a result of space-time curvature (caused by M) which is independent of m
This is one of the differences between GR and Newtonian theory
 
  • #39
Mueiz said:
if we put m=0 then f=0 so acceleration = o according to Newton's first law.
How much force does it take to produce a finite acceleration of a particle of 0 mass?
 
  • #41
DaleSpam said:
Even Newtonian gravity does not require an object to have mass in order to be affected by gravity:

F=GMm/r²
ma=GMm/r²
a=GM/r²

So the acceleration is independent of the mass of the object.

Oh Yes. I never accually thought of the acceleration and it's true, but it's still affected from something. I think if a substance is not affected by gravity then it would have no problem passing the light barrier. 1000 years ago people never dreamed of cars or planes, but we can now beak the sound barrier. Why not the light barrier, if we found a substance that is not affected by time, space or gravity.

Thanks for pointing the acceleration.

Masih,13
 
  • #42
DaleSpam said:
Even Newtonian gravity does not require an object to have mass in order to be affected by gravity:

F=GMm/r²
ma=GMm/r²
a=GM/r²

So the acceleration is independent of the mass of the object.

DaveC426913 said:
This thread is two years old.

No. Gravity curves spacetime. Light, like mass, follows the geodeisc of this curved space. It is not necessary for light to have mass in order to do this.




Stay in school. Learn.


Please I thought you were man of logics. Why is it that humans are so stupid, especially adults. They kill, they waste and all they want is power, but kids are smarter and yet because of jealousy and power all adults do to kids it make them have a bad life. By the way I can't imagine you being a 13 year and thinking the way I have and done and what have you discovered all your life with your stupid education. Yes I know education is good but what's more important is the way you think.

Masih,13
 
  • #43
Fast77 said:
if we found a substance that is not affected by time, space or gravity.
That's a pretty big "if". But yes, something like that would clearly not behave according to current physical laws.

Fast77 said:
Thanks for pointing the acceleration.
You are very welcome!
 
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  • #44
DaleSpam said:
That's a pretty big "if". But yes, something like that would clearly not behave according to current physical laws.

You are very welcome!

Non Newtonian Fluids behave differntly then regular fluids. Even antimatter, so there is a possibility that just mabey Dark Matter might be the key to breaking the light barrier or reach that speed. That is what I believe and think. Another soloution might be to make a spaceship from space itself. I know it sounds stupid and insane but our universe is believed to be living in a ball of space.

Masih,13
 
  • #45
Fast77 said:
there is a possibility that just mabey Dark Matter might be the key to breaking the light barrier or reach that speed. That is what I believe and think. ...

Masih,13
Look Masih, I hope when my kids are 13 that they will be as excited about physics as you, but you need to be careful. The rule against overly speculative posts is strongly enforced here.
 
  • #46
DaleSpam said:
Look Masih, I hope when my kids are 13 that they will be as excited about physics as you, but you need to be careful. The rule against overly speculative posts is strongly enforced here.

Yes I understand and I shall take your advice, but all I am doing is including the possiblities that are not being presented. Thanks for the that.

By the way is that a rule in this website?



Masih
 
  • #47
Fast77 said:
Yes I understand and I shall take your advice, but all I am doing is including the possiblities that are not being presented. Thanks for the that.
No problem, I hope you will continue to enjoy physics in general and PF in particular. It can be a great resource.

Fast77 said:
By the way is that a rule in this website?
Yes, there is a link to the rules at the top of each page, rught under the Physics Forums banner. It is under the bold heading "Overly Speculative Posts". I do realize that speculating can be a lot of fun, but that it the purpose of friendly chats and science fiction novels, not this site. There is plenty of enjoyable stuff to discuss that is well understood and not speculative.
 
<h2>1. How does gravity affect the speed of light?</h2><p>Gravity does not affect the speed of light. The speed of light is a fundamental constant in the universe and is not affected by any external forces, including gravity. This is known as the principle of the constancy of the speed of light.</p><h2>2. How does mass affect the path of light?</h2><p>Mass can affect the path of light through the phenomenon of gravitational lensing. When light passes near a massive object, such as a galaxy or black hole, its path can be bent due to the gravitational pull of the object. This can cause the light to appear distorted or even create multiple images of the same object.</p><h2>3. Can gravity bend light?</h2><p>Yes, gravity can bend light. This is known as gravitational lensing and is a result of Einstein's theory of general relativity. The more massive an object is, the stronger its gravitational pull and the more it can bend light.</p><h2>4. How do black holes affect light?</h2><p>Black holes have an extremely strong gravitational pull due to their immense mass, which can bend light and cause it to be trapped within the black hole's event horizon. This means that light cannot escape from a black hole, making it appear completely black to an outside observer.</p><h2>5. Can light escape a black hole?</h2><p>No, light cannot escape a black hole. The escape velocity of a black hole is greater than the speed of light, meaning that even light is not fast enough to overcome the gravitational pull and escape from a black hole. This is why black holes are often referred to as "light traps".</p>

1. How does gravity affect the speed of light?

Gravity does not affect the speed of light. The speed of light is a fundamental constant in the universe and is not affected by any external forces, including gravity. This is known as the principle of the constancy of the speed of light.

2. How does mass affect the path of light?

Mass can affect the path of light through the phenomenon of gravitational lensing. When light passes near a massive object, such as a galaxy or black hole, its path can be bent due to the gravitational pull of the object. This can cause the light to appear distorted or even create multiple images of the same object.

3. Can gravity bend light?

Yes, gravity can bend light. This is known as gravitational lensing and is a result of Einstein's theory of general relativity. The more massive an object is, the stronger its gravitational pull and the more it can bend light.

4. How do black holes affect light?

Black holes have an extremely strong gravitational pull due to their immense mass, which can bend light and cause it to be trapped within the black hole's event horizon. This means that light cannot escape from a black hole, making it appear completely black to an outside observer.

5. Can light escape a black hole?

No, light cannot escape a black hole. The escape velocity of a black hole is greater than the speed of light, meaning that even light is not fast enough to overcome the gravitational pull and escape from a black hole. This is why black holes are often referred to as "light traps".

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