What is dark en­ergy do­ing to our uni­verse?

All About Space - - Ask Space -

Dark en­ergy re­mains per­haps the great­est un­solved mys­tery in cos­mol­ogy, aside from the ques­tion of how the uni­verse got started in the first place!

Cur­rently dark en­ergy has mostly be­nign ef­fects, caus­ing the uni­verse to ex­pand at a mod­er­ate, though ac­cel­er­at­ing pace. If dark en­ergy’s prop­er­ties re­main sta­ble in the fu­ture, or if dark en­ergy is sim­i­lar to Ein­stein’s fa­mous ‘cos­mo­log­i­cal con­stant’, the uni­verse will ex­pand in­def­i­nitely.

There are, broadly speak­ing, two other pos­si­ble al­ter­na­tive sce­nar­ios where dark en­ergy’s den­sity changes over cos­mic time. Nei­ther sce­nario is par­tic­u­larly hope­ful. In one, dark en­ergy loses its power, de­cay­ing to zero and caus­ing the ac­cel­er­a­tion to stop. In some mod­els, the de­cay of its strength can lead to a ‘Big Crunch’, the col­lapse of all the mat­ter in the uni­verse, per­haps lead­ing to a ‘bounce’ that causes an­other Big Bang.

In the sec­ond al­ter­na­tive sce­nario, in the ex­tremely deep fu­ture, dark en­ergy’s strength in­creases with time, pos­si­bly caus­ing the so-called ‘Big Rip’ where the force as­so­ci­ated with dark en­ergy’s ac­cel­er­a­tion dom­i­nates over all other forces, in­clud­ing the chem­i­cal bond forces that hold atoms in our bod­ies to­gether. But don’t worry – that would not hap­pen for an­other 70 bil­lion years or more… so keep pay­ing your taxes!

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