Why Doesn't a Photon's Energy Knock Us Out?

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Discussion Overview

The discussion centers around the nature of photons, particularly their energy, mass, and interaction with matter. Participants explore why photons do not have the expected physical effects on humans despite their energy, touching on concepts from relativity and quantum mechanics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that photons have zero rest mass and travel at the speed of light from their creation, challenging the idea that they gain mass or energy as they approach light speed.
  • Others question the instantaneous nature of photons reaching light speed, seeking clarification on their behavior in different media.
  • There are claims that photons possess momentum despite having no rest mass, with discussions on the implications of this for their interactions with matter.
  • Some participants argue that gravity affects photons, raising questions about how something with zero mass can be influenced by a gravitational field.
  • A few contributors suggest that if photons had mass, it would necessitate a significant revision of existing physics, as all current experiments would contradict this notion.
  • There are speculative ideas about the nature of photons and their relationship with electrons, including discussions on energy density and the stress-energy tensor in general relativity.

Areas of Agreement / Disagreement

Participants express a range of views regarding the mass and behavior of photons, with no consensus reached. Some agree on the lack of rest mass, while others propose alternative interpretations of their properties and interactions.

Contextual Notes

Discussions include unresolved questions about the nature of photons, the implications of their mass (or lack thereof), and the effects of gravity on light. Participants reference various theoretical frameworks without reaching definitive conclusions.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly in the fields of quantum mechanics and relativity, as well as anyone curious about the fundamental properties of light and energy.

  • #31
Thanks, Nereid. Those neutrinos sound like a fine can of worms to try to sort out.
 
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  • #32
Nereid, the gluons, which of course are not observed, are also massless, along with the photon. These are all bosons. The neutrinos, before the recent discoveries, were regarded as the only massless fermions.
 
  • #33
selfAdjoint said:
Nereid, the gluons, which of course are not observed, are also massless, along with the photon. These are all bosons. The neutrinos, before the recent discoveries, were regarded as the only massless fermions.
Oops, :redface: Clearly my coffee wasn't strong enough (or last night's wine too good).

So the carriers of two of the forces are massless, and the carriers of one quite massive (and the graviton is hypothetical), with all force carriers being bosons.

Does the gluon travel at c?
 
  • #34
Nereid said:
Does the gluon travel at c?

Necessarily it does, since it's massless, and the standard model obeys special relativity, because the Lorentz transformations require that for a massless body.
 
  • #35
Neutrinos are flavorful, gluons are colorful.

"In quantum chromodynamics (QCD), today's accepted theory for the description of the strong nuclear force, gluons are exchanged when particles with a color charge interact. When two quarks exchange a gluon, their color charges change; the gluon carries an anti-color charge to compensate for the quark's old color charge, as well as the quark's new color charge. Since gluons thus carry a color-charge themselves, they can also interact with other gluons, which makes the mathematical analysis of the strong nuclear force quite complicated and difficult. Even though there are theoretically nine unique colour combinations for gluons, (r-ar, r-ag, r-ab, g-ar, g-ag, g-ab, b-ar, b-ag, and b-ab) in reality there are only eight."


Gluon
Address:http://www.fact-index.com/g/gl/gluon.html
 
  • #36
That account might be a little confusing unless you know that in QCD, each gluon carries two charges, one of the colors and one of the anticolors. Each gluon is represented by a 3X3 matrix, in a representation of the gauge group SU(3). Rows correspond to the color charges and columns to the anti-color ones. Since there are three choices for each of these, the number of possibilities would seem to be 3X3 = 9. But the requirement that the matrices representing the gluons be unitary means you can derive algebraic relations from which given any eight components you can calculate the ninth. So there are really only eight INDEPENDENT components of the 3X3 gluon matrix.
 

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