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Primer: Einstein! September 24, 2008

Posted by Will Thomas in EWP Primer.
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OK, I fess up, I’m pulling out my reserve tank of things I can write about if I haven’t given sufficient thought to the weekly Hump-Day History post.  Having been a teaching assistant in a course called the “Einsteinian Revolution”, I think I can rattle off a quick 900-1,000 words on the guy!

AIP Emilio Segre Visual Archives, W. F. Meggers Gallery of Nobel Laureates

Credit: AIP Emilio Segre Visual Archives, W. F. Meggers Gallery of Nobel Laureates

There is, of course, a historiographical industry surrounding Einstein.  Legions of science history enthusiasts are well-aware of his personal biography, his scientific work, his role as a scientific diplomat, his political advocacy.  There’s nothing that I can write here that would be considered remotely new or exciting, so this one goes out to all those who haven’t yet joined the thousands of Einstein groupies out there, those who know him mostly as an icon.  (Certified groupies may feel free to cluck their tongues at the insufficient characterizations offered here).

Let’s focus on the significance and genius of Albert Einstein.  As he himself often pointed out, as a day-to-day physicist, he was comparable in talent to the best minds of the theoretical physics community of his day.  Where Einstein needs to be considered the best mind of his era is in his ability to conceptualize the fundamental questions at the heart of physical inquiry.  Conceptually, there were only a few other physicists in his time who could even really be considered in his league.

Einstein’s interest in the conceptual problems of physics extends from his snotty lack of regard for the graduate training in physics he received at the Eidgenosse Technische Hochschule (ETH) in Zurich, where he did not distinguish himself (though he was extraordinarily gifted mathematically, contrary to legend and the billboard on Hwy 95 through Baltimore saying that “even Einstein was no Einstein”).  What really interested him was not what they were training him to do, but the philosophy of physicist Ernst Mach, who stressed the need for mathematical relationships in physics to represent fundamental physical relationships without quasi-fictional “models” attached to justify them.  He worked out the consequences of his own conceptual thinking at the patent office in Bern, which was the best job he could manage to get out of his undistinguished performance at the ETH.

What bothered Einstein the most about physics circa 1900 was that its theory of electromagnetism, then-recently distilled into “Maxwell’s equations”, allowed observers to determine whether or not they were really moving.  Newton’s equations always yielded the same results regardless of whether one object was flying at a second, whether the second was flying at the first, or they were flying at each other.  All that could really be known was the speed with which they approached each other.

But light behaves like a wave, and waves always move at the same speed through a medium regardless of the source of the wave.  This is why there is a sonic boom when aircraft hit the speed of sound, because the waves the aircraft makes, which travel at the speed of sound, all move along with the aircraft.  Therefore, a light source would measure a different speed of light, moving through a “luminiferous ether” medium, than would the observer of that light, meaning that they would witness different electromagnetic phenomena.  (One of Einstein’s memories of early his thinking had to do with what one would witness if one could travel alongside a light wave).

To get around this problem, to bring electromagnetic theory on par with the relativity experienced in the Newtonian universe, Einstein supposed that all observers always saw light move at the same speed (“c”).  This assumption had a few consequences.  First, it meant that effects due to the existence of the ether could never be detected—its existence became “superfluous” to physical explanation, and thus, following the tenets of Mach, it could be drummed out of physical theory.  Second, again following his reading of Mach, the only way to tell that events were simultaneous was to take measurements of the times that they occurred.  But if everyone saw light moving at the same speed regardless of how they were moving with respect to each other, it meant nobody could agree on the the times the events occurred.  Simultaneity went out the window, as did any sense that time could be objectively measured, as did length.  This was “special relativity”: the physics between reference frames traveling at different but constant speed.

Einstein published his paper detailing all this in 1905, and published another key paper the same year (and a third on “Brownian motion” that I’m going to unjustly neglect).  In this paper, Einstein contended with the fact that his notion of light accorded more with the Newtonian idea of flying objects than with waves traveling in a medium.  Doing this, he could explain some problematic phenomena—most famously, the photoelectric effect, where higher frequency (more purple-y) light, but not brighter light could cause certain metals to produce electrical currents.  However, light obviously behaved like a wave—it diffused, it created interference effects.  Einstein called the particulate approach in his paper a “heuristic”.  He didn’t know what was going on.

And Einstein would pull this trick again in the ensuing years with general relativity, showing acceleration and gravitation to be indistinguishable: there is no way to determine blindly if you are in an accelerating elevator in outer space or sitting still in a gravitational field.

Now, Einstein wasn’t alone in working out the problems of light, time, simultaneity, and length.  Using more traditional models, physicists such as Hendrik Lorentz, George FitzGerald, Joseph Larmour, and Henri Poincaré were working out many of the same implications at the same time as Einstein was thinking.  However, none of them shared Einstein’s commitment to conceptual clarity, which, worked out further—but never resolved completely—opened up not only accurate measurements, but the quantized world in which physicists are now trained.

On the thin differences in thinking between Einstein and other physicists concerned with simultaneity, Peter Galison’s Einstein’s Clocks, Poincaré’s Maps is important reading, and a useful look at the intellectual worlds each lived in.  There are probably other sources now, but on Einstein, Mach, and special relativity, I still go to Gerald Holton’s Thematic Origins of Scientific Thought, section II (“on relativity theory”).  Those inclined toward a more basic primer can look at my employer’s web exhibit: Einstein: Image and Impact.

Having shilled for my advisor’s book, his advisor’s book, and my employer, I bring this wantonly self-serving edition of Hump-Day History to a close.


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