How Does Gravity Affect Light with Zero Mass?

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Discussion Overview

The discussion revolves around the interaction between gravity and light, specifically addressing how light, which is massless, can be affected by gravitational fields. Participants explore concepts from both classical mechanics and relativity, questioning the applicability of traditional formulas in relativistic contexts.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that an object can only move at the speed of light if it has zero mass, questioning how light can be bent by gravity.
  • One participant suggests that when massless particles move, their mass may not be considered zero due to the energy-mass relationship described by E=mc².
  • Another participant clarifies that gravity interacts with energy and momentum rather than mass, noting that photons possess energy despite having zero mass.
  • A participant expresses confusion regarding the application of classical mechanics formulas in relativistic scenarios, particularly when mass is considered to be zero.
  • It is mentioned that the bending of light, or gravitational lensing, occurs due to the curvature of spacetime around massive objects, affecting the path of light traveling nearby.
  • One participant emphasizes that the momentum of photons influences how much their paths are curved in a gravitational field.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the relationship between gravity and light, with no consensus reached on the applicability of classical mechanics in relativistic contexts or the implications of massless particles in gravitational fields.

Contextual Notes

Some participants highlight limitations in their understanding of relativity, indicating that their knowledge may not encompass all relevant aspects of the discussion. There is also uncertainty regarding the conditions under which classical mechanics can be applied to relativistic situations.

squareroot
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So, an object can move with c if and only if it has 0 mass.So howcome that light is bended by gravity? How can smth with 0 mass be bend by gravity?


Ty
 
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squareroot said:
So, an object can move with c if and only if it has 0 mass.So howcome that light is bended by gravity? How can smth with 0 mass be bend by gravity?


Ty
Well,I think when the 0 mass moves,it's mass is no longer 0 according to the formula E=m*c^2
 
Because gravity couples to energy (and momentum, and stress), not mass. A photon has zero mass but nonzero energy.
 
ty for your answers .I haven't studied relativity in school yet but from what i know gravity is mass times gravitational acc.,but.if u apply that here m is zero so G is zero

Are the formulas from classic mechanics applicable in any relativistic situation?
 
squareroot said:
So, an object can move with c if and only if it has 0 mass.So howcome that light is bended by gravity? How can smth with 0 mass be bend by gravity?Ty

The bending of light around objects with mass, gravitational lensing, occurs because the spacetime around a massive object (such as the sun, a galaxy, etc.), is curved, and distorts the path of the light traveling near that object.

See this image for an example:

http://scienceblogs.com/startswithabang/upload/2010/07/see_a_quasar_gravitationally_l/gravitational-lens-01.jpeg

As Bill K said, it is the momentum of the photons that determines how dramatically they are curved away from their original path.
 
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squareroot said:
ty for your answers .I haven't studied relativity in school yet but from what i know gravity is mass times gravitational acc.,but.if u apply that here m is zero so G is zero

Are the formulas from classic mechanics applicable in any relativistic situation?
Only as approximations in the "v much less than c" case.
 

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