Is the ‘new muon’ really a great scientific discovery? For now, I’m cautious | Carlo Rovelli

Physicists are always looking for eureka moments - but we should be careful with headline-grabbing announcements

There is something curious about the great experiments and discoveries in fundamental physics from the past few decades. They have covered black holes, gravitational waves, the Higgs particle and quantum entanglement. They have led to Nobel prizes, reached the front pages of newspapers and made the scientific community proud. But they haven't told us anything new: they have confirmed what we expected about the world. All these phenomena were in the university textbooks I studied almost half a century ago. Their existence was predicted by our best established theories. I do not mean to diminish the awe. On the contrary. It is amazing that the phenomena were observed, and even more amazing that they were figured out before we could see them. Their detection is a celebration of the power of scientific thinking to see into the unseen. Yet a malignant voice could have whispered in our ears at each step: What's the great surprise? We expected this." Fundamental experimental physics has long been, in this sense, quite conservative. It has simply been confirming the best theories of last century over and over again.

Last week findings from Fermilab, the US's particle physics and accelerator laboratory, appeared to contradict what we thought to be the case. The laboratory announced a new measurement of the magnetic moment" of the muon - one of the universe's elementary particles, a heavier brother of the electron. The measured value of the muon seems to disagree with the value predicted by the theory. It is an observation that does not complement our established theories; it clashes with them.