DARK PHYSICS IS STUCK

Is it time to ad­mit that cos­mol­ogy is en­snared by dimly un­der­stood forces? MICHAEL BROOKS in­ves­ti­gates.

Cosmos - - Front Page -

IN 2006, I VEN­TURED to the Carnegie In­sti­tu­tion in Washington DC. There, I had a long con­ver­sa­tion with the as­tronomer Vera Ru­bin. Thirty-six years ear­lier, she was one of the first modern cos­mol­o­gists to sug­gest that a huge part of the uni­verse was miss­ing. At the time, she had sug­gested it might take a decade to find this miss­ing stuff, now best known as “dark mat­ter”.

BY 1990, TWO DECADES later, when dark mat­ter was still miss­ing, the English As­tronomer Royal Martin Rees said it would turn up within a decade. In 1999 dark mat­ter hadn’t made an ap­pear­ance, but Rees was un­bowed: he de­clared him­self “op­ti­mistic” that, in five years’ time, he would be able to re­port what dark mat­ter is.

But by the time Ru­bin and I met in Washington, as­tronomers were all still empty-handed. What’s more, things had got­ten worse: in 1997 as­tronomers had dis­cov­ered “dark en­ergy”, an­other miss­ing com­po­nent of the cos­mos. Now a full 96% of the uni­verse in­volved a form of mat­ter and en­ergy un­known to science.

Has there been progress since then? Not re­ally. In 2018, more than 20 years af­ter we had to ac­knowl­edge our ig­no­rance of the vast ma­jor­ity of the uni­verse, we still haven’t iden­ti­fied what dark mat­ter or dark en­ergy might be. “I’m cer­tainly ready for the great leap for­ward,” says Rocky Kolb, an as­tronomer based at the Univer­sity of Chicago.

And there is not much hope of mak­ing such a leap ei­ther. In fact, some re­searchers are propos­ing that we might be liv­ing through our gen­er­a­tion’s “ether mo­ment”. For cen­turies, main­stream science be­lieved that light prop­a­gated through a space filled with a mys­te­ri­ous stuff – the ether. But by the turn of the 20th cen­tury, the ether’s ex­is­tence had been re­futed. Could both dark mat­ter and dark en­ergy be sim­i­larly se­ductive il­lu­sions?

THE FIRST HINT OF a dark side to the uni­verse came in 1933, when the Swiss as­tronomer Fritz Zwicky no­ticed that the Coma galaxy clus­ter was spin­ning so fast that it should be fall­ing apart due to cen­tripetal forces. Zwicky sug­gested that they might be hold­ing to­gether be­cause of the grav­i­ta­tional ac­tion of em­bed­ded mas­sive par­ti­cles that didn’t be­tray their pres­ence by re­flect­ing light. He called this hy­po­thet­i­cal stuff “Dun­kle

Ma­terie”: dark mat­ter. The search didn’t re­ally get off the ground though un­til the 1970s. It was the hey­day

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