Magnetic fields go to the maximum

By Aussiegirl

Well, heck -- I won't even pretend to fully understand this, but you gotta love a new calculation that puts the previous calculation as being off by a factor of a billion! Seems like this is going to have some implications for String Theory.

Magnetic fields go to the maximum (May 2006) - News - PhysicsWeb

What is the maximum possible magnetic field allowed in our universe? According to two theoretical physicists in Russia and Israel, it is 1042 Gauss -- a value that is a billion times smaller than the previous estimate for the upper limit. As well as being of fundamental interest, the new finding -- if correct -- may rule out theories on "superconductive cosmic strings" and also some accepted mechanisms of producing other hypothetical objects such as magnetic monopoles (Phys. Rev. Lett. 96 180401).

All compact astronomical objects, such as white dwarfs, neutron stars and black holes, have enormous magnetic fields -- as high as 1017 G -- associated with them. The Earth's magnetic field, in contrast, is less than 1 G. However, theorists have also predicted that hypothetical objects called superconductive cosmic strings could have even higher magnetic fields near them of 1047 to 1048 G.

Cosmic strings are believed to be extremely thin 1D topological defects in the fabric of spacetime that stretch across the universe, perhaps making up structures like galaxies as they loop around themselves. They are invoked in grand unified particle physics models and are thought to have been produced just after the Big Bang.

However, the new maximum value for magnetic fields of 1042 G, which has been calculated by Anatoly Shabad of the Lebedev Physics Institute in Moscow and Vladimir Usov at the Weizmann Institute of Science in Rehovot, is lower than that associated with cosmic strings. If correct, it would rule out the existence of extremely strong magnetic fields in the vicinity of these objects.

The value obtained is 109 times lower than the previous upper limit of 1051 G, which had the drawback that it assumed that "Dirac monopoles" exist in Nature. Predicted by some theories that seek to unify the electroweak and strong interactions, these particles have never yet been observed experimentally.

Shabad and Usov obtained their result by considering what the maximum possible value of the magnetic field could be in pure quantum electrodynamics (QED), which describes the fundamental forces between particles as being due to the exchange of "field quanta". Until now, scientists believed that a magnetic field could take on arbitrarily high values in QED.