Friday, August 26, 2011

Dude looks like a lady

When I was talking recently in Barcelona at a music conference, I was interviewed by a Spanish newspaper, which has now published the piece. From what I can tell (courtesy of Google Translate), it is I think best described as a loose improvisation based around our conversation. And perhaps the better for it, who knows? But I like best one of the reader comments:
“Language is very intellectual, good photo, but looks like a woman, perhaps the combination has made the smart person.”
In my experience, however, that is a little unfair to Spanish women.

Wednesday, August 24, 2011

Did Einstein discover E=mc2?

A lot of people have strong opinions about that, as is clear from the comments that have followed on from my article of this title for Physics World. (I particularly liked "For an objective account, see Albert Einstein: The Incorrigible Plagiarist." Yup, sounds like an objective book to me.) The piece is here, but the pre-edited version is below. There's a fair bit more that I'd have liked to explore here - it's a deeply interesting issue. The biggest revelation for me was not so much seeing that there were several well-founded precursors for the equivalence of mass and energy, but finding that this equivalence seems to have virtually nothing to do with special relativity. Tony Rothman said to me that "I've long maintained that the conventional history of science, as presented in the media, textbooks and by the stories scientists tell themselves is basically a collection of fairy tales." I'd concur with that.

Who discovered that E=mc2? It’s not as easy a question as you might think. Scientists ranging from James Clerk Maxwell and Max von Laue to a string of now obscure early twentieth-century physicists have been proposed as the true discovers of the mass-energy equivalence now popularly credited to Einstein’s theory of special relativity. These claims have spawned headlines accusing Einstein of plagiarism, but many are spurious or barely supported. Yet two physicists have now shown that Einstein’s famous formula does have a complicated and somewhat ambiguous genesis – which has little to do with relativity.

One of the more plausible precursors to E=mc2 is attributed to Fritz Hasenörhl, a physics professor at the University of Vienna. In a 1904 paper, Hasenörhl clearly wrote down the equation E=3/8mc2. Where did he get it from, and why is the constant of proportionality wrong? Stephen Boughn of Haverford College in Pennsylvania and Tony Rothman of Princeton University examine this question in a preprint.

“I had run across Hasenöhrl's name a number of times with no real explanation as to what he did”, Rothman explains. “One of my old professors, E.C.G. Sudarshan, once remarked that he gave Hasenöhrl credit for mass-energy equivalence. So around Christmas time last year, I said to Steve, ‘why don't we spend a couple hours after lunch one day looking at Hasenöhrl's papers and see what he did wrong?’ Well, two hours turned into eight months, because the problem ended up being extremely difficult.”

Hasenöhrl’s name has a certain notoriety now, as he is commonly invoked by anti-Einstein cranks. His reputation as the man who really discovered E=mc2 owes much to the efforts of the anti-Semitic and pro-Nazi physics Nobel laureate Philipp Lenard, who sought to separate Einstein’s name from the theory of relativity so that it was not seen as a product of ‘Jewish science’.

Yet all this does Hasenörhl a disservice. He was Ludwig Boltzmann’s student and successor at Vienna, and was lauded by Erwin Schrödinger among others. “Hasenohrl was probably the leading Austrian physicist of his day”, says Rothman. He might have achieved much more if he had not been killed in the First World War.

The relationship of energy and mass was already widely discussed by the time Hasenörhl considered the matter. Henri Poincaré had stated that electromagnetic radiation had a momentum and thus effectively a mass according to E=mc2. German physicist Max Abraham argued that a moving electron interacts with its own field E0 to acquire an apparent mass given by E0=3/4mc2. All this was based on classical electrodynamics, assuming an ether theory. “Hasenöhrl, Poincaré, Abraham and others suggested that there must be an inertial mass associated with electromagnetic energy, even though they may have disagreed on the constant of proportionality”, says Boughn.

Robert Crease, a philosopher and historian of science at Stony Brook University in New York, agrees. “Historians often say that, had there been no Einstein, the community would have converged on special relativity shortly”, he says. “Events were pushing them kicking and screaming in that direction.” Boughn and Rothman’s work, he says, shows that Hasenöhrl was among those headed this way.

Hasenörhl approached the problem by asking whether a black body emitting radiation changes in mass when it is moving relative to the observer. He calculated that the motion adds a mass of 3/8c2 times the radiant energy. The following year he corrected this to 3/4c2.

However, no-one has properly studied Hasenörhl’s derivation to understand his reasoning or why the prefactor is wrong, say Bough and Rothman. That’s not easy, they admit. “The papers are by today’s standards presented in a cumbersome manner and are not free of error. The greatest hindrance is that they are written from an obsolete world view, which can only confuse the reader steeped in relativistic physics.” Even Enrico Fermi apparently did not bother to read Hasenörhl’s papers properly before concluding wrongly that the discrepant 3/4 prefactor was due to the electron self-energy identified by Abraham.

“What Hasenörhl really missed in his calculation was the idea that if the radiators in his cavity are emitting radiation, they must be losing mass, so his calculation wasn't consistent”, says Rothman. “Nevertheless, he got half of it right. If he had merely said that E is proportional to m, history would probably have been kinder to him.”

But if that’s the case, where does relativity come into it? Actually, it doesn’t. While Einstein’s celebrated 1905 paper ‘On the electrodynamics of moving bodies’ clearly laid down the foundations of relativity by abandoning the ether and making the speed of light invariant, his derivation of E=mc2 did not depend on those assumptions. You can get the right answer with classical physics, says Rothman, all in an ether theory without c being either constant or the limiting speed. “Although Einstein begins relativistically, he approximates away all the relativistic bits, and you are left with what is basically a classical calculation."

Physicist Clifford Will of Washington University in St Louis, a specialist on relativity, considers the preprint “very interesting”. Boughn and Rothman “are well regarded physicists”, he says, and as a result he “tend[s] to trust their analysis”. However, the controversies that have been previously aroused over the issue of priority perhaps accounts for some of the reluctance of historians of physics to comment when contacted by Physics World.

Did Einstein know of Hasenörhl’s work? “I can't prove it, but I am reasonably certain that Einstein must done, and just decided to do it better”, says Rothman. But failure to cite it was not inconsistent with the conventions of the time. In any event, Einstein asserted his priority for the mass-energy relationship when this was challenged by Johannes Stark (who credited it in 1907 to Max Planck). Both Hasenörhl and Einstein were at the famous first Solvay conference in 1911, along with most of the other illustrious physicists of the time. “One can only imagine the conversations”, say Boughn and Rothman.

Tuesday, August 02, 2011

A philosophical question

Here’s my latest Crucible column for Chemistry World.

“Philosophy is dead” is an assertion that, coming from most people, would be dismissed as idle, unconsidered, even meaningless. (What, all of it? Political philosophy? Moral philosophy? The philosophy of music?) But when Stephen Hawking announced this in his recent book with Leonard Mlodinow, The Grand Design, it was greeted as the devastating judgement of a sage and sent philosophers scurrying to the discussion boards to defend their subject (more properly, to defend Hawking’s presumed target of metaphysics).

Yet many chemists may be unaware that a philosophy of chemistry existed in the first place. Isn’t chemistry about practical, tangible matters, or – when theoretical issues are concerned – questions of right and wrong, not the fuzzy and abstract issues popularly associated with philosophy? On the contrary, at least two journals (Hyle and Foundations of Chemistry) and the International Society for the Philosophy of Chemistry have insisted for some years that there are profound chemical questions of a philosophical nature.

These questions might not seem quite as urgent as how to make stereoselective carbon-carbon bonds, but they should at the very least make chemists reflect about the nature of their daily craft. What is the ontological status of ‘laws’ of chemistry? To what extent are molecular structures metaphorical? What’s more, the philosophy of chemistry impinges directly on chemistry’s public image. As Eric Scerri, editor-in-chief of Foundations of Chemistry, says, “Most philosophers of science believe that chemistry has been reduced to physics and is therefore of no fundamental interest. They believe that chemistry has no ‘big ideas’ to compare with quantum mechanics and relativity in physics and Darwin’s theory in biology” [1].

The philosophy of chemistry excites lively, often impassioned debate. Those unquiet waters have recently been agitated by an extensive overview of the topic published in the Stanford Encyclopedia of Philosophy, a widely used online reference source, by Michael Weisberg, Paul Needham and Robin Hendry, all three respected philosophers of science [2]. It’s an ambitious affair, accommodating everything from the evolution since ancient times of theories of matter to the nature of the chemical bond and interpretations of quantum theory. The piece has proved controversial because the authors have presented points of view on several of these issues that are not universally shared.

Much of the debate hinges on the fact that the concepts and principles used by chemists – the notion of elements, molecules, bonds, structure, or the idea much debated by these philosophers that ‘water is H2O’ – lack philosophical rigour. Arguments about whether gaseous helium contains atoms or molecules, or whether the element sodium refers to a grey metal or to atoms with 11 protons, are frequently rehearsed in lab coffee rooms. That these hardly affect the practicalities of chemical synthesis doesn’t detract from their validity as philosophical conundrums.

Take, for example, Needham’s claim that isotopes of the ‘same’ element should in fact be considered different elements [3]. Clearly there is rather little difference between 35Cl and 37Cl, but if ‘element’ is pinned to chemical identity, are H and D really the ‘same’? Indeed, does not even the tiniest isotope effect blur any strict definition based on chemical behaviour rather than proton number? Perhaps the Austrian chemist Friedrich Paneth was right to regard the notion of an element as something ‘transcendental’.

Even more controversially, Hendry takes a view long developed by him and others such as Guy Woolley that the concept of molecular structure is mere metaphor, rendered logically incoherent by quantum mechanics. To distinguish methanol from dimethyl ether, we need to first put the nuclei in position by hand and then apply the Born-Oppenheimer approximation to the quantum equations so that only the electrons move. Without this approximation, the raw Hamiltonian for nuclei and electrons is identical for both isomers.

Hendry asserts that the isomers exist as quantum superpositions, from which a particular isomer emerges only when the wavefunction is collapsed by observation. Scerri argues [4], in contrast, that this collapse happens naturally and inevitably because of environment-induced decoherence. Even if so, the image is disconcerting: molecular structures exist because of their environment, not as intrinsic entities. What of molecules isolated in interstellar space, almost a closed system? Regardless of the position one takes, it remains unclear how, or if, molecular structure can be extracted directly from quantum theory, as opposed to being rationalized post hoc – relative energies can be computed, for sure, but that’s not the same. Ultimately these questions might have answers in physics; at least for the moment, they are philosophical.

1. E. R. Scerri, J. Chem. Ed. 77, 522-526 (2000).
2. M. Weisberg, P. Needham & R. Hendry, ‘Philosophy of Chemistry’, Stanford Encyclopedia of Philosophy.
3. P. Needham, Stud. Hist. Phil. Sci., 39, 66–77 (2008).
4. E. R. Scerri, Found. Chem. 13, 1-7 (2011).