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I am conducting research on photons and was wondering if they have relativistic mass. I already know that they they have zero rest mass. Any answers are welcome!

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    $\begingroup$ Did you look at the relativistic energy-momentum relationship?en.wikipedia.org/wiki/Energy%E2%80%93momentum_relation $\endgroup$ – CuriousOne Oct 11 '14 at 19:40
  • $\begingroup$ Duplicate: directly answered here - physics.stackexchange.com/q/34067 $\endgroup$ – Rob Jeffries Oct 11 '14 at 19:46
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    $\begingroup$ @RobJeffries true that the answer to this question is given in that question, but they're not quite asking the same thing, I think, so I'd hesitate to call it a duplicate. $\endgroup$ – David Z Oct 11 '14 at 19:48
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    $\begingroup$ If you are researching photons, I recommend this article by Nobel laureate Willis Lamb. It discusses the history of the photon concept, and the misconceptions around the concept. (Like Lamb, I avoid the use of the word as much as possible.) $\endgroup$ – garyp Oct 12 '14 at 0:39
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    $\begingroup$ The relevance to my comment (not answer) is that the OP is conducting research on photons, and Lamb's article provides a history of the concept. There's nothing kooky about his Anit-photon paper. As for your dismissal of his analysis of the photoelectric effect: not so fast. I don't know if Lamb was a kook or not, but in the two cases considered here, he is not. But I'm with you on one thing. It's easy to come up with a list of Nobel laureates who are kooks. $\endgroup$ – garyp Oct 14 '14 at 12:37
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Relativistic mass is obsolete. See Why is there a controversy on whether mass increases with speed? . Therefore this is not a question that modern physicists would consider of interest. Furthermore, the usual motivation given for using the relativistic mass convention is that it lets you use Newton's second law without modification, but Newton's second law isn't going to apply to a photon, no matter how hard you try.

If you did want to assign a photon a relativistic mass, there is no other parameter that could determine the mass besides its energy $E$, and based on units the mass would then have to be of the form $m=kE/c^2$, where $k$ is a unitless constant. Probably $k=1$, since we can take $p=mv$ as the definition of the relativistic mass, and $p=E/c$ for a photon.

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It's quite wrong to assert that relativistic mass is obsolete. Gary Oas of Standford university did a study of a sample of the SR and GR textbooks. Of the ones published between 1995 and 2005 there were 60% of them which use relativistic mass.

In this video, Alan H. Guth of MIT describes why the mass of a photon is not zero. http://www.newenglandphysics.org/common_misconceptions/DSC_0003.MOV

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    $\begingroup$ Curiously another answer of Ben's cites the Oas paper and comes to the exact opposite conclusion as you have. $\endgroup$ – Kyle Kanos Jul 21 '15 at 15:15

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