# Geek Trivia: Eye for an Einstein

How did Albert Einstein express his infamous energy-mass equivalence equation in its original 1905 publication, wherein the mathematical construct bore little resemblance to its most famous incarnation, E=mc<sup>2</sup>?

How did Albert Einstein express his infamous energy-mass equivalence equation in its original 1905 publication, wherein the mathematical construct bore little resemblance to its most famous incarnation, E=mc2?

A lot of quantum physics history geeks (they're out there) will tell you that Einstein originally wrote E=mc2 as m=L/c2, where L was a stand-in for E as the variable representing energy. These folks are closer to right but still not there.

The m=L/c2 advocates are working off a 1920s-era English translation of Einstein's original paper, "Does the Inertia of a Body Depend Upon Its Energy Content?" as published in the 1905 German Annals of Physics. What's missing from this Einsteinian I-told-you-so is the key fact that c was not a widely observed stand-in for the speed of light until the 1920s.

Einstein instead used the letter V for light speed, as had been standard practice since the 1890s. Thus, what Einstein actually wrote would have been m=L/V2.

Except that he didn't write that either. The absolute gotcha of all this is that in Einstein's first paper introducing his theory of energy-mass equivalence, he didn't write a summary equation at all. Instead, he explained his conclusion in prose, writing:

"Gibt ein Körper die Energie L in Form von Strahlung ab, so verkleinert sich seine Masse um L/V2."

This translates as:

"If a body gives off the energy L in the form of radiation, its mass diminishes by L/V2."

Thus, one could easily surmise the equation m=L/V2 — where m is mass, L is energy, V is the speed of light — fromwhat Uncle Albert laid out, but he never explicitly wrote it. (One might more accurately write it as delta-m=L/V2, as Einstein was discussing a change in mass.)

Just as c came to supplant V as shorthand for the speed of light, E overtook L as a stand-in for energy. So, m=L/V2 became m=E/c2. Anyone who got a passing grade in Algebra 101 could reconfigure this into the fraction-free equation E=mc2.

This simplified form of Einstein's famous equation was the one cited by newspapers when Einstein began gaining international acclaim, even among laypersons, in the 1920s through the 1940s. As to which version is more "legitimate," it's all relative, but it does make for some theoretically thought-provoking Geek Trivia.

## The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area. Every week, yours truly will choose the best post from the assembled masses and discuss it in a future edition of Geek Trivia.

This week's quibble comes from the October 24 edition of Geek Trivia, "Flying by the (ejection) seat of your pants." TechRepublic member rollo.ross got upset with my use of the term jerry-rig.

"[You wrote] 'This jerry-rig is necessary because the space shuttle's design has never allowed for unmanned recovery from orbit.' I think you mean jury-rig, meaning a temporary fix. Surely you don't mean jerry-built, meaning shoddy construction."

Luckily, members bittoo_m and RealGem stood up for me, the latter writing:

"If you try Dictionary.com, you see that jerry-rig is an alteration of jury-rig that was influenced by jerry-built... Jay is not incorrect in using jerry-rig, although I personally prefer jury-rig."

Free etymology lesson time: Jury-rig is a nautical term that comes from jury mast, a temporary mast raised to replace or aid a standard sail mast. Jerry-built is a derogative term meaning poorly built, derived from the World War II Allied slang for German forces, the Jerries. The two terms have since morphed into jerry-rig.

The terms are probably interchangeable, but it appears my audience errs on the side of tradition. Thanks for pointing it out, and keep those quibbles coming!

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