Kickstarting the UniverseCosmology is honestly a mind-blowing field. It’s basically all about

Kickstarting the UniverseCosmology is honestly a mind-blowing field. It’s basically all about understanding the universe on a huge scale, like where did it come from? How did it evolve, and according to what fundamental laws? Will it come to an end? If so, how and when?In the 1980s, cosmologists had two major problems to solve: the flatness problem and the horizon problem. The flatness problem is the fact that the universe seems to be geometrically flat. It’s expanding at an accelerating rate, and if it’s flat, it means that the rate of expansion is balanced very precisely with the amount of matter in the universe. Basically, this means that there’s enough stuff to eventually halt the universe’s expansion, but not enough to make it collapse back in on itself again afterwards. Image Credit: io9It also means that the universe was even more perfectly balanced near the time of the Big Bang, because if there were any deviations from the nice, flat, smoothness, then these ‘defects’ would have grown very dramatically and very obviously over the past 14 billion years – and yet, we see nothing of the sort. This is so coincidental that it’s almost unbelievable – there’s no reason for it to be this way. Another issue is the horizon problem. Wherever you look in the universe, it seems to be roughly the same. When we measure the temperature of the cosmic microwave background (CMB, pictured above), we see that it’s exactly the same temperature in every single direction. This is weird, because for two regions to have the same conditions (like the exact same temperature), they must be close enough to exchange ‘information’ and come into equilibrium with each other. But since the universe is expanding, the photons from the CMB haven’t actually had time to reach and exchange heat with photons on the other side of the universe. These distant regions of the universe are isolated from each other, so how can they have the exact same temperature?Image CreditTo answer these questions, astronomers put forth the idea of inflation: a period right after the Big Bang when the universe experienced ultra-fast, exponential expansion. Before this massive acceleration, the entire universe would have been in contact – regions that are now hugely separated would have been close enough to come to equilibrium, which explains the horizon problem. The rapidly expanding space also would have flattened the universe by “expanding away” any large curvatures, so now everything looks flat from our local perspective. To understand that, imagine if the Earth were the size of a basketball. We’d easily notice that it’s a sphere, but if we then expanded it to the size it is now, the curvature would be harder to see – and indeed in most places on Earth, the surface appears almost flat. Now imagine if it expanded to the size of the universe – everything would look completely flat in every direction, because it would just be so massive relative to us.While inflation explains these problems, we have no idea about the mechanisms behind it – what started the ultra-fast expansion? And what stopped it again? Cosmologists generally agree that the idea is correct, but there are still a lot of kinks to be expanded out. -- source link

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