Science magazine headline declares a purported physics paradox resolved
DOI: 10.1063/PT.4.0127
Adrian Cho’s one-page News and Analysis article in the 27 April 2012 issue of Science opened this way:
A basic equation of electricity and magnetism is wrong, one scientist claims. The classic formula for the force exerted by electric and magnetic fields—the so-called Lorentz force—clashes with Einstein’s special theory of relativity, says Masud Mansuripur, an electrical engineer at the University of Arizona in Tucson. Others doubt the claim but have not found a flaw in the simple argument that challenges century-old textbook physics.
Doubters are now about to speak. Under the headline ‘Purported relativity paradox resolved,’ Cho offers a detailed update on the Science website. It opens this way:
You can rest easier now: A purported conflict between the century-old theory of classical electrodynamics and Einstein’s theory of special relativity doesn’t exist, a chorus of physicists says.
In April, as reported and commented on in this venue, Cho reviewed the nature of the Lorentz force, cited what he called the irony that physicists invoke it ‘in the textbook example of how electrodynamics and relativity mesh,’ and then summarized the claim of paradox. Now he reports that four physicists independently say, in comments in press at Physical Review Letters, that they have resolved it.
Mansuripur’s gedanken experiment, writes Cho, involved a tiny magnet at a fixed distance from a pointlike electric charge. Here’s the key paragraph in Cho’s update:
But Mansuripur forgot something, all four commenters argue. Thanks to the bizarreness of special relativity, the magnet also possesses an odd ‘hidden angular momentum’ that in the moving frame constantly increases. By its very definition, a torque equals a change in angular momentum. So instead of twisting the magnet, the torque in the moving frame simply feeds the increase in hidden angular momentum. Problem solved.
Cho notes that Mansuripur ‘is sticking to his guns,’ arguing that hidden momentum ‘is an ill-defined concept that merely papers over the problem’ and that his approach eliminates the need for it. But others, Cho says, call hidden momentum ‘part and parcel of relativity.’
Steven T. Corneliussen, a media analyst for the American Institute of Physics, monitors three national newspapers, the weeklies Nature and Science, and occasionally other publications. He has published op-eds in the Washington Post and other newspapers, has written for NASA’s history program, and is a science writer at a particle-accelerator laboratory.
