Light building the standard model

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Discussion Overview

The discussion revolves around the nature of light, specifically questioning the assertion that light has no mass. Participants explore various aspects of light's behavior, including its momentum, interaction with gravity, and wave-particle duality. The conversation touches on theoretical implications, experimental evidence, and historical context regarding the understanding of light in physics.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants argue that light has momentum and is affected by gravity, leading them to conclude that it must have mass.
  • Others challenge this reasoning, stating that momentum and gravitational effects do not necessarily imply mass, and that energy considerations in general relativity provide a different perspective.
  • Several participants mention experimental data that suggests light has no rest mass, with one noting an upper limit on photon mass as extremely small.
  • There is a discussion about the concept of relativistic mass and how it relates to energy, with some asserting that photons cannot have rest mass because it would lead to infinite mass at the speed of light.
  • Some participants express confusion about the transition from classical mechanics to quantum mechanics, questioning how classical principles apply to light and whether they should be discarded in this context.
  • One participant emphasizes that scientific understanding evolves through experimentation and that current theories assume light has no mass based on extensive evidence.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether light has mass. There are multiple competing views regarding the implications of light's momentum, gravitational effects, and the definitions of mass in different contexts.

Contextual Notes

Some discussions highlight limitations in classical mechanics when applied to quantum phenomena, suggesting that classical definitions may not adequately describe light's behavior. There are also references to historical experiments that shaped current understanding, but no specific conclusions are drawn about their implications.

  • #61
How do we know light has its own gravitational field? This certainly was never mentioned in my physics classes so far... and I've not seen any mention of it with electromagnetic waves... Where can I find information on this?
 
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  • #62
Well relativity says that mass energy or pressure bends space-time and light has energy.
If a positron and an electron collide they produce a photon or 2, I am not sure if its 1 or 2, but the electron and positron have mass and I am sure you would agree they have a Gravitational field. So if energy is conserved why would the gravitational field go away. It would seem weird. Even tho the Electric and magnetic field go away. But its something think about. Google gravitational field of light.
 
  • #63
elegysix said:
How do we know light has its own gravitational field? This certainly was never mentioned in my physics classes so far... and I've not seen any mention of it with electromagnetic waves... Where can I find information on this?
It is called a pp-wave spacetime:
http://en.wikipedia.org/wiki/Pp-wave_spacetime
 
  • #64
elegysix said:
This is a major part of what I am questioning. From classical mechanics alone, I see no reason to believe this. We know classical mechanics works. So starting with classical mechanics, How do you figure that these things happen?
Because, in some extreme cases, classical mechanics doesn't work. Specifically, the Michaelson-Morely experiment gives results different from classical mechanics and so do experiments in the photo-electric effect.
 
  • #65
So light has its own gravitational field... even more reason for me to think it has mass. Lol.
Just out of curiosity, does anyone know what the calculated mass from its gravitational field would be? Is this the same as the mass calculated from radiation pressure?

I know that your immediate response is that this is pointless to do, but humor me please lol
 
  • #66
Are you asking what rest mass a particle would have that had an equal G field to a photon. I think they call it Gravitational effective mass. I am sure you could do it with E=mc^2. If light had mass it seems like it would pulverize other things because it is traveling so fast could you imagine the kinetic energy. When we collide protons together in accelerators after the collision we can have the sum of the rest masses of the particles greater than the 2 protons, we are turning kinetic energy into mass. Thats why we build bigger accelerators to find more massive particles. If you think light having its own G field is weird, you could ask does the G-field itself have its own field or does an E or B field have a Gravitational field. Are gravitational waves affected by gravity.
 
  • #67
Anyone know the most important experiments done with light? I want to review them.
 
  • #68
elegysix said:
Anyone know the most important experiments done with light? I want to review them.

Well, a few that spring to mind:

Relativity theory:
Michelson-Morley experiment
Deflection of light by the Sun
Gravitational redshift

Quantum theory:
Young's double-slit experiment
Photoelectric effect
Compton effect
 
  • #69
elegysix said:
So light has its own gravitational field... even more reason for me to think it has mass. Lol.
Did you miss the entire thread?

elegysix said:
Just out of curiosity, does anyone know what the calculated mass from its gravitational field would be? Is this the same as the mass calculated from radiation pressure?

I know that your immediate response is that this is pointless to do, but humor me please lol
It is not pointless, but it is not easy to do either, and it depends very strongly on the exact setup. See the link I posted earlier and google "pp-wave spacetime". You will get several examples, but the math is somewhat intense.
 

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