Q&A

Focus-Science and Technology - - CONTENTS - HASSAN BUSHNAG, LON­DON RM

Your burn­ing science ques­tions an­swered by our panel of ex­perts.

As its name sug­gests, an­ti­mat­ter is a kind of mir­ror im­age of or­di­nary mat­ter, made up of par­ti­cles like positrons, with the op­po­site charge and spin to elec­trons. (‘Spin’ is a type of an­gu­lar mo­men­tum that all sub­atomic par­ti­cles have, spin can have a value of 1/2 or 1.) But most the­o­rists doubt that an­ti­mat­ter also pro­duces anti­grav­ity. That’s be­cause the so- called chargepar­ity-time (CPT) the­o­rem of quan­tum the­ory sug­gests an­ti­mat­ter’s ‘anti-ness’ does not ex­tend to its mass and grav­i­ta­tional ef­fect. That said, it’s al­ways pos­si­ble there’s a loop­hole in this the­o­rem: it’s had to be tweaked sev­eral times over the decades to ex­plain newly dis­cov­ered phe­nom­ena. Later this year, ex­per­i­men­tal­ists at CERN, home of the Large Hadron Col­lider, plan to look for signs of strange be­hav­iour when par­ti­cles of an­ti­mat­ter are re­leased in a vac­uum. If the par­ti­cles rise, anti­grav­ity may be the ex­pla­na­tion.

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