How black holes will shed light on the fourth di­men­sion and the var­i­ous the­o­ries about time

BBC Earth (Asia) - - Front Page - WORDS: PROF ROBERT MATTHEWS


As sci­ence sto­ries go, it was huge in every sense: the first-ever de­tec­tion of grav­i­ta­tional waves, rip­ples in the very fab­ric of space and time, trig­gered by the col­li­sion of two black holes far beyond the Milky Way.

Grav­i­ta­tional waves were pre­dicted by Ein­stein a cen­tury ago and picked up in Septem­ber 2015 by colos­sal laser de­tec­tors in the United States. Now, they are be­ing hailed as a whole new way to ob­serve the Uni­verse. And one physi­cist be­lieves they may soon al­low sci­en­tists to wit­ness a truly mind-bog­gling event: the emer­gence of time.

Ac­cord­ing to Prof Richard Muller of the Univer­sity of Cal­i­for­nia, Berke­ley, when black holes col­lide they do more than dis­rupt the space around them. They also cre­ate what he calls “nows”: brief new in­stants of time.

It’s an as­ton­ish­ing idea, but ac­cord­ing to Muller it’s no sci-fi fan­tasy. Within a few years, he says, the same de­tec­tors that dis­cov­ered grav­i­ta­tional waves may pro­vide hard ev­i­dence of in­stants of time be­ing cre­ated in deep space.


Such claims put Muller at the fore­front of re­search aimed at un­der­stand­ing this most in­ef­fa­ble com­po­nent of our Uni­verse. From Aris­to­tle to Ein­stein, some of the most bril­liant minds in his­tory have pon­dered the na­ture of time, only to come away baf­fled. Around 1,500 years ago, the philoso­pher Au­gus­tine cap­tured the views of many sci­en­tists, and his words con­tinue to res­onate to­day: “What then is time? If no one asks me, I know what it is. If I wish to ex­plain it to him who asks, I do not know.”

Muller be­lieves re­cent ad­vances in physics make it pos­si­ble to cut through the con­fu­sion to re­veal the truth. At present, that truth is based on Ein­stein’s relativity. Ac­cord­ing to this, the com­mon-sense view that we in­habit a Uni­verse with three di­men­sions of space, with time flow­ing from past to fu­ture, is an il­lu­sion. Ein­stein in­sisted that space and time are just dif­fer­ent as­pects of one uni­fied whole that he called ‘space-time’.

While Ein­stein was in his twen­ties, he went on to show that this leads to a host of unexpected ef­fects. Ob­jects that zip past at close to light speed will appear dis­torted, and com­pressed in the di­rec­tion of travel. Clocks mov­ing at such speeds will appear to run slow.

De­spite their out­landish­ness, the pre­dic­tions of relativity have all been tested – and all have proved cor­rect. Yet there re­mains some­thing odd about the sup­posed ‘one­ness’ of space and time. As Muller points out, there’s a sim­ple ex­per­i­ment any­one can per­form: “We can stand still in space – but not in time”.

There are other puz­zles too. The fun­da­men­tal laws of na­ture take no ac­count of the flow of time, giv­ing the same answer whether time flows for­wards or back­wards. Yet we’re sur­rounded by events that seem to show that time re­ally does have an ‘ar­row’ point­ing from the past to the fu­ture, from the ero­sion of moun­tains to the de­cay of all liv­ing things.

Muller started pulling to­gether all his thoughts on this, in order to write a book. He then had a flash of in­spi­ra­tion. “As I wrote and con­tin­ued to think… it sud­denly oc­curred to me that the flow of time was re­ally a grad­ual ad­di­tion of new mo­ments of time, new ‘nows’.”

But what could pos­si­bly cre­ate pack­ets of time? Muller found the answer in the fun­da­men­tal unity of space and time. Ever since the dis­cov­ery of the

ex­pan­sion of the Uni­verse more than 90 years ago, sci­en­tists have had to ac­cept that space re­ally can be cre­ated out of nowhere. And as space and time are just dif­fer­ent as­pects of the same thing, that means time can be cre­ated as well.

“Every mo­ment the Uni­verse gets a lit­tle big­ger, and there is a lit­tle more time,” ex­plains Miller.

That, in turn, pro­vides a stun­ningly sim­ple ex­pla­na­tion for the sup­posed flow of time: “The fore­front, ex­pand­ing edge of time is what we re­fer to as now, and the flow of time is the con­tin­ual cre­ation of new nows,” he says. “It all fits to­gether.”


Muller wasn’t con­tent to stop there, with just an in­trigu­ing idea. He wanted to find a way of putting it to the test. And he could see no way to do it. “I had some ideas based on cos­mol­ogy, but I couldn’t fig­ure out how to ac­tu­ally per­form the tests, at least within my ex­pected life­time.” So Muller pressed on with writ­ing his book, which ap­peared last year as

Now: The Physics Of Time.

But just as he was fin­ish­ing his book, he learned of the dis­cov­ery of grav­i­ta­tional waves by the sci­en­tists at the Laser In­ter­fer­om­e­ter Grav­i­ta­tional-wave Ob­ser­va­tory (LIGO). That changed ev­ery­thing.

One of LIGO’s mir­rors, which are used to de­tect grav­i­ta­tional waves

Prof Richard Muller thinks black holes could hold the se­cret to de­tect­ing the cre­ation of time

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Sky map of the south­ern hemi­sphere, re­veal­ing the lo­ca­tion of the source of the grav­i­ta­tional waves de­tected by LIGO

Wavelet graph of two black holes merg­ing, as de­tected by LIGO in 2015

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