Does Light Have Mass? Gravity Effects Explained

  • Context: Undergrad 
  • Thread starter Thread starter Safamm
  • Start date Start date
  • Tags Tags
    Light Mass
Click For Summary

Discussion Overview

The discussion revolves around the nature of light in relation to mass and gravity, exploring whether light has mass, how it is affected by gravity, and what characteristics an entity must possess to be influenced by gravitational forces. The conversation touches on theoretical frameworks, particularly General Relativity, and the implications of energy in gravitational interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that light does not have mass but does possess energy, which is relevant to its interaction with gravity.
  • Others emphasize that according to General Relativity, gravity is a result of curved spacetime, affecting all entities traveling through it, including massless electromagnetic radiation.
  • A participant questions the implications of energy in relation to gravity, pondering whether all things are affected by gravity regardless of their energy state.
  • There is a discussion about whether curved spacetime can be likened to potential energy, similar to a spring, and how this relates to gravity affecting itself.
  • Some participants argue that gravity does affect itself, complicating the understanding of gravitational interactions and suggesting that this leads to challenges in applying renormalization to gravity.
  • A later reply raises the idea of an infinite space curve akin to a black hole, questioning how gravity could affect itself without mass in a localized area.
  • One participant notes that within current experimental accuracy, no mass for light has been observed, yet acknowledges that light is affected by gravity as it travels through curved spacetime.

Areas of Agreement / Disagreement

Participants generally agree that light does not have mass but is affected by gravity. However, there are multiple competing views regarding the implications of energy and the self-affecting nature of gravity, leaving the discussion unresolved on these points.

Contextual Notes

Some claims depend on interpretations of General Relativity and the nature of energy in gravitational contexts, which remain open to further exploration and clarification.

Safamm
Messages
8
Reaction score
0
Does light have mass?
Is light affected by gravity?
What should something have to be affected by gravity?
 
Astronomy news on Phys.org
Safamm said:
Does light have mass?
No.
Is light affected by gravity?
yes.
What should something have to be affected by gravity?
energy.

These are questions that are well covered online though.
The main confusion comes from trying to relate the behavior of light near a massive body and Newtonian gravity.
Understand that Newton's gravity is wrong and has been supplanted by General Relativity, where gravity is understood in terms of local curvature in 4D space-time.
In GR, the gravitational interaction is covered by the stress-energy tensor.
 
Safamm said:
Does light have mass?

No, but it has energy.

Is light affected by gravity?

Yes! Gravity according to General Relativity, which is our leading theory of gravity, is the result of curved spacetime. Anything traveling through spacetime will be affected, including EM radiation that is massless.

What should something have to be affected by gravity?

Well, energy is one answer. But I would ask that if something has absolutely zero energy, does it even exist? Could it just be that all things are affected by gravity?
 
Drakkith said:
No, but it has energy.



Yes! Gravity according to General Relativity, which is our leading theory of gravity, is the result of curved spacetime. Anything traveling through spacetime will be affected, including EM radiation that is massless.



Well, energy is one answer. But I would ask that if something has absolutely zero energy, does it even exist? Could it just be that all things are affected by gravity?

Would curved space time have potential energy in same way a spring is just waiting to be relased by the release of the matter in space time?
I ask because if gravity effects everything with energy, that would then mean it would effect itself which we know gravity doesn't effect gravity.
 
sirchick said:
Would curved space time have potential energy in same way a spring is just waiting to be relased by the release of the matter in space time?
I ask because if gravity effects everything with energy, that would then mean it would effect itself which we know gravity doesn't effect gravity.

Except that it does affect itself. This is why you cannot apply renormalization to gravity. (Or so I'm told)
http://www.einstein-online.info/spotlights/gravity_of_gravity
 
Drakkith said:
Except that it does affect itself. This is why you cannot apply renormalization to gravity. (Or so I'm told)

How does it effect itself? If gravity effects energy and gravity can have energy, wouldn't there be a infinite space curve like a black hole only not effected by mass in a small area but rather - itself.
 
sirchick said:
How does it effect itself? If gravity effects energy and gravity can have energy, wouldn't there be a infinite space curve like a black hole only not effected by mass in a small area but rather - itself.

I don't know GR well enough to answer this. Check this thread though.
https://www.physicsforums.com/showthread.php?t=640266
 
If gravity contributes to itself, you end up with free energy.
 
Hi.

Safamm said:
Does light have mass?

Within accuracy in current experiment standard, no mass is observed for light.
You can find the maximum possible value of light mass easily in books or web.

Safamm said:
Is light affected by gravity?

Yes, it runs 'straight' in curved space-time.

Safamm said:
What should something have to be affected by gravity?

Gravity itself express geometry of space-time.

Regards.
 
  • #10
Thank you all for your enlightening and educational comments.
 
  • #11
Chronos said:
If gravity contributes to itself, you end up with free energy.
Do you have a reference for that?
Did you see the reference in Drakkith's earlier post?

Anyway - seems we have satisfied OP ;)
 

Similar threads

Undergrad Why Does Gravity Remain when Star Mass Dissipates?
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad How Does Gravity Affect Spectral Line Strength?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Effects of gravity on planetary core structure
  • · Replies 9 ·
Replies
9
Views
3K
Undergrad The initial density of an object and its compression into a black hole
  • · Replies 17 ·
Replies
17
Views
6K
Undergrad How Do Moons Influence the James Webb Telescope's Position at Lagrange Point L2?
  • · Replies 4 ·
Replies
4
Views
2K
Graduate Does modified gravity somehow explain galaxies that don't need it?
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Gravity inside an exponential mass disk
  • · Replies 16 ·
Replies
16
Views
2K
Undergrad Visible light Over Large Distances
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Does light bend around black holes?
  • · Replies 49 ·
2
Replies
49
Views
7K
Undergrad Dark matter + gravity is 'right', or our understanding of gravity is wrong?
  • · Replies 35 ·
2
Replies
35
Views
5K