Are Photons Massless? | Inquiry & Confusion

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    Massless Photons
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Discussion Overview

The discussion centers around the nature of photons, specifically whether they are massless and the implications of this property on their ability to travel at the speed of light. Participants explore theoretical and experimental perspectives on the mass of photons, as well as the distinction between energy and matter-form energy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant recalls that objects with mass require infinite energy to reach the speed of light, suggesting that photons can travel at this speed because they are massless.
  • Another participant expresses confusion about the distinction between energy (like light) and matter-form energy, indicating a desire for clarification.
  • Some participants assert that, according to current knowledge, photons are indeed massless, which allows them to travel at the speed of light.
  • One participant presents a theoretical perspective that if photons had mass, the electric potential energy of charged particles would behave differently than it does under the current understanding.
  • Another participant emphasizes that experimental measurements of the photon's mass are consistent with zero, but the upper limit is extremely small compared to known masses.

Areas of Agreement / Disagreement

Participants generally agree that photons are considered massless based on current knowledge and experimental evidence, but there are nuances in how this is interpreted and understood, leading to some uncertainty and differing perspectives.

Contextual Notes

There are unresolved questions regarding the implications of a massless photon on physical theories, and the discussion reflects a mix of theoretical assertions and experimental findings without reaching a definitive conclusion.

Kurushimi
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This is just a random inquiry that's confusing me. I remember hearing at one point that the reason no object could travel at the speed of light is that an object with mass going at the speed of light would require an infinite amount of energy to get moving that fast. And that photons could do it because they were massless. But, then, I also recall hearing that photons aren't truly massless...which seems contradictory to me. I can't remember my sources. Was I misinformed about one (or, perhaps both) of these?
 
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I'd like to know too. I'm on a desparete journy to understand the difference between energy (ei light) and matter-form energy.
 
Yes, to the best of our knowledge photons are exactly massless, which means they travel at c (which we refer to as "the speed of light" only because photons appear to be massless).

Any massive object will have a speed that is strictly less than c no matter how much energy it has.
 
There are two answers to this question. The theorist's answer is "yes, the photon is massless. Were it not, the elecric potential energy of a charged particle would vary like \frac{1}{r}e^{-m_\gamma r} instead of just \frac{1}{r}, among other effects." The experimentalist's answer is "probably. Our best measurements of the photon's mass are consistent with 0 and the upper bound they set is 15 or 16 orders of magnitude smaller than any other known mass."
 
Parlyne said:
The experimentalist's answer is "probably. Our best measurements of the photon's mass are consistent with 0 and the upper bound they set is 15 or 16 orders of magnitude smaller than any other known mass."
I would say this as "yes, to within experimental error".
 

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