What scientists find when they find nothing Premium

Null results can yield profound insights: from Michelson-Morley's experiment leading to the special theory of relativity, to searches for dark matter particles prompting new theories. Null results can also be a sign of progress, as seen in the hunt for dark matter and new forces, and in experiments like LIGO. Such results can also be a reminder of our own mortality, as with the search for proton decay.

Say you have a friend who asserts that they can smell water. You are sceptical, yet also curious. To test their claim, you fill up 50 cups out of 100 with water and instruct your blindfolded friend to sniff away.

If your scepticism – the null hypothesis – is justified, the odds of your friend identifying all 50 filled cups are very slim. In fact, they will get it right only about half the time, through simple luck. This would be the “null result” of the test.

Any careful investigation proceeds in this spirit, with a null hypothesis determined by the context. In court, you are innocent until proven guilty. In experiments of fundamental physics, you will often hear that today’s discovery is tomorrow’s null hypothesis.

Even today, thousands of physicists are searching for hitherto undiscovered particles and forces. This is because they want to defy the Standard Model, the best theory physicists have to explain the universe – and today’s null hypothesis. But since the discovery of the Higgs boson in 2012, no conclusive positive results have been reported.

What should we make of that?

Sea change

In the late 19th century, Albert Michelson and Edward Morley conducted an experiment to look for “luminiferous ether” in their laboratory. According to the science of their time, the luminiferous ether was the universal medium through which light waves travelled. As earth moves through the ether, the physicist duo had to show that the speed of light varied according to its direction. But despite meticulous care, they couldn’t show that.