The Uni­verse Has a Cold Spot (That Can't be Ex­plained)

The tem­per­a­ture is the same through­out the uni­verse – ex­cept from in one cold spot. Sci­en­tists thought that the spot was an op­ti­cal il­lu­sion, but ac­cord­ing to a new the­ory, it may be ev­i­dence of a col­li­sion.

Science Illustrated - - SPACE -

In 2015, the Planck satel­lite mapped out a cold spot in the back­ground ra­di­a­tion of the uni­verse. The ra­di­a­tion, which was emit­ted by the young uni­verse 380,000 years af­ter the Big Bang, fills the en­tire uni­verse. Orig­i­nally, the ra­di­a­tion was very en­er­getic (or hot), but the ex­pan­sion of the uni­verse has ex­tended the rays into much cooler mi­crowaves with a tem­per­a­ture of 2.73 de­grees above ab­so­lute zero. Ex­cept for slight vari­a­tions of a few mil­lionths of a de­gree, the tem­per­a­ture of the uni­verse is gen­er­ally the same, and so, the cold spot fas­ci­nated as­tronomers. First, they thought that the spot had been caused by a huge void

be­tween the spot and Earth. On the way through the void, the wave­length of light is stretched, get­ting colder than when light travels through space with a nor­mal quan­tity of gal­ax­ies. How­ever, new ob­ser­va­tions by English sci­en­tists show that this void does not ex­ist and so, it can­not ex­plain the cold area.

Right af­ter the Big Bang, the young uni­verse ex­panded from the size of an elec­tron to the vol­ume of a foot­ball. The in­fla­tion hap­pened ex­tremely fast, i.e. at a speed higher than that of light, and lasted a tril­lionth of a tril­lionth of a tril­lionth of a sec­ond. Sub­se­quently, the ex­pan­sion con­tin­ued at a slower pace.

The process is known as in­fla­tion, and cos­mol­ogy rests on this one, fun­da­men­tal foun­da­tion stone. How­ever, the in­fla­tion the­ory in­volves a ma­jor chal­lenge to our un­der­stand­ing of how space is or­gan­ised. It pre­dicts that in­fla­tion did not only take place in the small area that grew into our uni­verse. In­stead, the process was more chaotic, tak­ing place in a much larger space, in which myr­i­ads of uni­verses popped up at the same time just like pop­corn in a pot of hot oil. Ac­cord­ing to the the­ory, bil­lions of uni­verse bub­bles ex­ist around our own uni­verse – we are liv­ing in a multiverse.

For decades, as­tronomers have de­bated whether the the­ory’s pre­dic­tion of the multiverse can be true, and now, sci­en­tists have found the first pos­si­ble ev­i­dence: the uni­verse in­cludes a mys­te­ri­ous cold spot, which could be a crater re­sult­ing from a col­li­sion with an­other uni­verse.

In­fla­tion ex­plains the uni­verse

The in­fla­tion the­ory was in­tro­duced into sci­en­tists’ model of the Big Bang in the 1980s to ex­plain why gal­ax­ies are evenly dis­trib­uted across the uni­verse. If the ex­pan­sion of the uni­verse had hap­pened at an even pace fol­low­ing the Big Bang, grav­ity would make gal­axy clus­ters clump to­gether to pro­duce ma­jor dif­fer­ences in the dis­tri­bu­tion of mass. The rapid in­fla­tion dis­trib­uted the mass evenly from the very be­gin­ning of the uni­verse – like when air is evenly dis­trib­uted in a bal­loon that is in­flated.

In­fla­tion als o ex­plains why the tem­per­a­ture is al­most the same through­out the uni­verse. When our new­born uni­verse was the size of an elec­tron, all mat­ter had the same tem­per­a­ture. Dur­ing the in­fla­tion, the tem­per­a­ture av­er­aged out to be more or less the same no mat­ter which way we look.

The uni­form tem­per­a­ture can be ob­served from the cos­mic back­ground ra­di­a­tion of the uni­verse. The ra­di­a­tion was emit­ted in the young uni­verse, 380,000 years af­ter the Big Bang. Be­fore, the uni­verse was so hot that ra­di­a­tion was con­stantly con­verted into mat­ter, so no light es­caped. But when the uni­verse had grown big and cold enough for the first hy­dro­gen atoms to form, light es­caped from the mat­ter in a glimpse. Sub­se­quently, the uni­verse turned dark again, as the new, neu­tral hy­dro­gen atoms do not emit any vis­i­ble light. The light did not re­turn, un­til the first gal­ax­ies formed hun­dreds of mil­lions of years later.

Decades of ob­ser­va­tions of cos­mic back­ground ra­di­a­tion show that the tem­per­a­ture gen­er­ally only varies a few mil­lionths of a de­gree – ex­cept in one place. In 2004, as­tronomers dis­cov­ered a par­tic­u­larly cold spot in the back­ground ra­di­a­tion three bil­lion light years from Earth. The spot cov­ers an area of five de­grees of the sky and is 0.00015 de­grees colder than the gen­eral ra­di­a­tion tem­per­a­ture of 2.73 de­grees above ab­so­lute zero.

Un­til re­cently, sci­en­tists thought that the cold area was due to a huge void ex­tend­ing 1.8 bil­lion light years be­tween us and the cold spot. When light waves from the back­ground ra­di­a­tion travel through such a void, the light waves lose en­ergy on their way into the void, re­gain­ing en­ergy on their way out. As­tronomers com­pare the phe­nom­e­non to a ball that loses en­ergy on its way up­hill, rolling faster down the other side. In a stag­nant uni­verse, the light would es­cape the void with the ex­act same en­ergy with which the waves en­tered. But be­cause the uni­verse has ex­panded over the 1.8 bil­lion years that the light took to travel through the su­per-void, the hill on the way out of the void will be less steep. So, the light will not re­gain all the en­ergy, be­com­ing slightly more long wave and colder. Hence, sci­en­tists thought that the cold spot was an op­ti­cal il­lu­sion caused by the void.

Now, English as­tronomers from Durham Univer­sity have re­jected the orig­i­nal ex­pla­na­tion by show­ing that the huge void does not ex­ist. There are as many gal­ax­ies be­tween Earth and the cold spot as be­tween our world and all other places of the back­ground ra­di­a­tion. So, as­tronomers tend to pre­fer an­other ex­pla­na­tion: The spot is a crater caused by a col­li­sion be­tween our uni­verse and an­other one un­der in­fla­tion.

PRE­VI­OUS ION EXPLANAT COLD SPOT B A C K G R O U N D R A D I AT I O N L I G H T WAV E S RA­DI­A­TION SHOWS TEM­PER­A­TURE The back­ground 1 ra­di­a­tion in the uni­verse has the same tem­per­a­ture – ex­cept a par­tic­u­larly cold spot 3 bil­lion light years from Earth. VOID IS FULL OF GAL­AX­IES New stud­ies 3 have shown that the void is not empty. It in­cludes just as many gal­ax­ies as other places in space. VOID CAUSES OP­TI­CAL IL­LU­SION Sci­en­tists thought 2 that a huge void be­tween Earth and the cold spot made light lose en­ergy, so the light waves are stretched, and the spot seems cold. THEORETICAL VOID EARTH

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