Gravity's Effects on Light: Mass & Black Holes

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Discussion Overview

The discussion revolves around the effects of gravity on light, particularly in the context of black holes and the concept of mass. Participants explore the implications of light being affected by gravity despite being described as massless, and they examine the conditions under which light might orbit a black hole.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question why light is said to have no mass if it is affected by gravity.
  • It is noted that photons are massless but possess relativistic mass, which may contribute to their interaction with gravity.
  • One participant suggests that there could be circular paths around a black hole that light can follow, but these orbits are unstable, requiring precise trajectories.
  • Another participant discusses the concept of gravitational time dilation and its potential effects on light, likening it to the refractive index.
  • Concerns are raised about the idea of light being trapped in a perfect orbit around a black hole, with some arguing that light would need to be on the correct trajectory to achieve this.
  • Some participants reference the photon sphere and discuss the conditions under which light might be captured or escape from a black hole.
  • There is a mention of energy leaking from black holes and the implications of general relativity on the behavior of light near massive objects.
  • One participant argues against the idea that light's interaction with gravity is due to relativistic mass, suggesting instead that it is a result of curved space-time.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of light's mass and its interaction with gravity, particularly in the context of black holes. There is no consensus on the explanations provided, and the discussion remains unresolved.

Contextual Notes

Some statements rely on specific interpretations of relativistic mass and gravitational effects, which may not be universally accepted. The discussion includes various assumptions about the behavior of light and gravity that are not fully explored.

  • #31
Fast77 said:
OK I think light has mass because it's affected by gravity which means it has weight. So if light had no mass then it would be 0x9.8=0 and no weight, so gravity does not affect it. Which means it must have some mass (0.00000000000000000000000000000000000000000001kg).
By the way, Einstine was wrong and right. "That an atom would get more massive then the universe if it reached near speed of light". A particlee that has no mass or heat does not exist. But what if we could find a particlee that has mass, but no affected by gravity and make our space ships with that substance in the solar system(elevators). I came up with this theory, but since i have not learned calculas yet I don't know the math behind it. I have found this substance/ particlee and would like to share it with the world, if anyone is interested please message me. I also have many more theories to share.
Masih,13

I like the way you think.. I also don't have the proper education.. But imagination is the importent thing.. I would love to discuss theories with you..
 
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  • #32
This thread is two years old.
Fast77 said:
OK I think light has mass because it's affected by gravity which means it has weight.
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.


Fast77 said:
By the way, Einstine was wrong and right. "That an atom would get more massive then the universe if it reached near speed of light". A particlee that has no mass or heat does not exist. But what if we could find a particlee that has mass, but no affected by gravity and make our space ships with that substance in the solar system(elevators). I came up with this theory, but since i have not learned calculas yet I don't know the math behind it. I have found this substance/ particlee and would like to share it with the world,

Stay in school. Learn.
 
  • #33
neh4pres said:
imagination is the importent thing..

Imagination is good. But you will have to choose between doing something practical with it and merely fantasizing.

If you want to do something practical, stay in school. You will learn why these ideas are naive, and you will learn to develop more robust ideas.
 
  • #35
Fast77 said:
OK I think light has mass because it's affected by gravity
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.
 
  • #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.
 
  • #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!
 
Last edited:
  • #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.
 

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