What's the symbol called that's behind and to the right of Einstein's head in this picture? Bonus if you can tell me what the whole formula is!
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$\begingroup$ you are used to the E=mc**2 form of the formula, where m is the relativistic mass, and do not recognize it when represented by using the behavior of the rest mass. hyperphysics.phy-astr.gsu.edu/hbase/relativ/conrel.html $\endgroup$– anna vCommented Jan 6, 2015 at 5:34
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1$\begingroup$ Cross-posted from math.stackexchange.com/q/1092619 (closed) $\endgroup$– David ZCommented Jan 6, 2015 at 5:55
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8$\begingroup$ This question appears to be off-topic because it is about mathematical symbol identification. $\endgroup$– Brandon EnrightCommented Jan 6, 2015 at 6:39
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1$\begingroup$ It's not something I feel strongly about, but I think the close votes are a bit unfair. The question is basically asking what the equation is, and that seems a fair question. $\endgroup$– John RennieCommented Jan 6, 2015 at 8:24
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$\begingroup$ @JohnRennie Doesn't it not ask a specific physics question ? Just because it's related to physics doesn't mean it's fit for physics.se. Such questions are better asked on chat. $\endgroup$– GauravCommented Jan 6, 2015 at 8:56
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2 Answers
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Here is a link to the Einstein archives online. You will see the same cursive letter E used in his signature.
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$\begingroup$ This seems more suited for a comment (to Goodies' post?) than an answer. $\endgroup$ Commented Jan 6, 2015 at 13:57
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$\begingroup$ Thanks @Louis. I appreciate everyone's responses and feedback but I found the link you provided to be the most useful and pertinent to the root of my question. Thanks again to everyone for all the great feedback. $\endgroup$– Old NameCommented Jan 6, 2015 at 16:05
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1$\begingroup$ The answer does identify the symbol as a cursive $E$, so as far as I'm concerned it meets the criterion to be considered an answer. $\endgroup$– David ZCommented Jan 6, 2015 at 18:03
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$\begingroup$ I only intended to confirm what had already been posted in other comments by citing a proper reference. I will accept the reputation points, with humility, since they now enable the comment privilege. Thank you all for your patience, support and constructive criticism. $\endgroup$– LouisBCommented Jan 6, 2015 at 20:21
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The equation is that of the relativistic energy of a 'particle' with a nonzero mass. $$ E=\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}} $$
The symbol itself I've never seen before. However, I think it's important to mention that $1/\sqrt{1-\frac{v^2}{c^2}}$ is represented by $\gamma$ ($\text{gamma}$).
The factor $\gamma$ is often used in special relativity in Lorentz Length Contraction and Time Dilation (space and time contract with relativistic speed).
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$\begingroup$ Yes. Ignore the initial left swoop, and you'll see it. $\endgroup$– BMSCommented Jan 6, 2015 at 5:43
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$\begingroup$ Also worth noting that with a little algebra, you can show this formula is equivalent to $E^2 = m^2 c^4 + p^2 c^2$, where $p = mv / \sqrt{1 - v^2/c^2}$ is the relativistic momentum. So the formula is telling you the total energy in a given frame is a combination of the rest mass energy and energy due to motion in that frame. $\endgroup$ Commented Jan 6, 2015 at 6:10
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2$\begingroup$ By the way, on the blackboard, the symbol for the speed is really $q$, not $v$, see comments about Geschwindigkeit $q'$ here: einsteinpapers.press.princeton.edu/vol4-doc/71 $\endgroup$ Commented Jan 6, 2015 at 7:14