An experiment in Zurich brings us nearer to a black hole’s mysteries
The equations that describe the universe at the smallest and largest scales — how the tiniest elementary particles dance, how the space-time of the cosmos bends — predicted a slight incongruity, a tiny unbalancing in the numbers of certain particles under certain circumstances.
But physicists have yet to observe this phenomenon — with the unwieldy name of mixed axial-gravitational anomaly — and confirm the prediction. The imbalance is negligible except when the warping of space-time is extreme, like next to a black hole or the moment after the Big Bang. It turns out there was somewhere else to look, and it was much closer. An international team of scientists discovered this anomaly in a tabletop apparatus in Zurich examining the properties of a tiny metallic ribbon.
“There was no way to test this effect until now,” said Johannes Gooth, a scientist at IBM Research in Zurich who is the lead author of a paper published July 19 by the journal Nature.
The IBM experiment did not involve black holes, or even gravity. Instead, it took advantage of a class of exotic materials known as Weyl semimetals named for a German scientist, Hermann Weyl, whose equation first gave rise to the possibility of such materials. A solid Weyl semimetal crystal was first created a couple of years ago, enabling the IBM study. The motion of electrons inside a ribbon of a semimetal is governed by essentially the same space-time-warping equations as the original mixed axial-gravitational anomaly. The advance could have practical uses in electronics, similar to how the invention of the transistor led to computer chips.