“There are some the­o­ries of ex­tra di­men­sions that you can’t probe with the large scales that we worked with”

Fi­nal di­men­sion

All About Space - - Final Dimension -

around the world are look­ing for physics be­yond the Stan­dard Model. An­other is the search for dark mat­ter, the mys­te­ri­ous shad­owy en­tity that acts like a glue hold­ing large struc­tures in the uni­verse to­gether. “There’s noth­ing in the Stan­dard Model to ex­plain that,” says Tina Pot­ter from the Univer­sity of Cam­bridge, UK.

She is work­ing on the AT­LAS ex­per­i­ment at the LHC in the hope of find­ing ev­i­dence of a the­ory called su­per­sym­me­try – the most pop­u­lar the­ory of physics be­yond the Stan­dard Model. It says that ev­ery par­ti­cle in the Stan­dard Model has an as-yetundis­cov­ered part­ner. That in­stantly dou­bles the num­ber of par­ti­cles physi­cists are search­ing for. “Some of these par­ti­cles are fan­tas­tic can­di­dates for dark mat­ter – so if we find them it would plug one of the big holes in our knowl­edge about the uni­verse,” Pot­ter says.

It isn’t the the­ory’s only ap­peal – some ver­sions of string the­ory also rely on su­per­sym­me­try be­ing true. Those that do are called su­per­sym­met­ri­cal string the­o­ries – or su­per­string the­o­ries. There are five ver­sions in to­tal. How­ever, in or­der to get the maths to work, all five su­per­string the­o­ries re­quire there to be ten di­men­sions. That’s the three of space and one of time we ex­pe­ri­ence, plus six so-called ‘hy­per­space’ di­men­sions that we don’t. Those hy­per­space di­men­sions would be small enough to re­main out of sight. An al­ter­na­tive the­ory known as M-the­ory sug­gests that all five su­per­string the­o­ries are vari­ants of an 11-di­men­sional re­al­ity. These su­per­string the­o­ries be­came fash­ion­able in the 1980s and over­took the orig­i­nal ver­sion of string the­ory in pop­u­lar­ity. That’s called bosonic string the­ory, and it sug­gests the strings vi­brate across a stag­ger­ing 26 di­men­sions!

Find­ing ev­i­dence of su­per­sym­me­try won’t in it­self con­firm su­per­string the­ory, but a fail­ure to do so would make the whole idea even harder to stom­ach. In that re­gard the LHC may be able to help. It has just reached the end of its lat­est run of par­ti­cle-smash­ing ex­per­i­ments, pro­duc­ing a swarm of im­por­tant data for physi­cists to pick over.

“We are hop­ing to find some­thing there,” says Pot­ter. “It’s all hands on deck to an­a­lyse it as quickly as pos­si­ble.” Mean­while, the LHC will be shut down in De­cem­ber 2018 and up­graded ready to pro­duce even more en­er­getic col­li­sions in around 18 months’ time. “Next time we turn on we’ll dou­ble the amount of data we have now,” Pot­ter says. “Any hints of su­per­sym­me­try we see in this dataset will be con­firmed in the next one.”

So slowly but surely physi­cists are mak­ing head­way. Larger ad­di­tional di­men­sions ap­pear ruled out by the lat­est grav­i­ta­tional wave dis­cov­er­ies, but there re­mains hope that ex­per­i­ments such as the Large Hadron Col­lider could con­firm su­per­sym­me­try and bol­ster the some­what flimsy cir­cum­stan­tial case for string the­ory with its smaller hy­per­spaces. As al­ways in physics, more ex­per­i­ments and bet­ter data bring sharper in­sights. They could one day prove that Na­ture paints on a can­vas of many more di­men­sions than meet the eye. Cu­ri­ouser and cu­ri­ouser in­deed.

Kris Pardo

The AT­LAS ex­per­i­ment at the Large Hadron Col­lider is just one way physi­cists are look­ing for ev­i­dence of su­per­sym­me­try

A neu­tron star merger known as GW170817 was picked up by the LIGO de­tec­tor in 2017

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.