The World Explained

the beginning of everything. the big bang. the idea that the universe was suddenlyborn and is not infinite. up to the middle of the 20th century,most scientists thought of the universe as infinite and ageless. until einstein’s theory of relativity gaveus a better understanding of gravity, and edwin hubble discovered that galaxiesare moving apart from one another in a way that fits previous predictions. in 1964, by accident, cosmic backgroundradiation was discovered,

a relic of the early universe, which, together with other observationalevidence, made the big bang the accepted theory in science. since then, improved technology like thehubble telescope has given us a pretty good picture of thebig bang and the structure of the cosmos. recent observations even seem to suggestthat the expansion of the universe is accelerating. but how did this big bang work? how can something come from nothing?

let’s explore what we know. we can ignore the beginning partfor now. first of all, the big bang was notan explosion. it was all space stretchingeverywhere all at once. the universe startedvery, very, very small and quickly expanded to thesize of a football. the universe didn’t expand into anything,space was just expanding into itself. the universe cannot expand into anythingbecause the universe has no borders; there is, by definition, no “outside”the universe.

the universe is all there is. in this hot, dense environment, energymanifested itself in particles that existed only for thetiniest glimpses of time. >from gluons, pairs of quarks were created,which destroyed one another, perhaps after giving off more gluons. these found other short-lived quarksto interact with, forming new quark pairs andgluons again. matter and energy were not justtheoretically equivalent, it was so hot they were practicallythe same stuff.

somewhere around this time, matterwon over antimatter. today, we’re left with almost allmatter and nearly no antimatter at all. somehow, one billion and one matterparticles were formed for every one billion particles ofantimatter. instead of one massive ultimate forcein the universe, there were now several refined versionsof it acting under different rules. by now the universe has stretched to abillion kilometers in diameter, which leads to a decrease in temperature. the cycle of quarks being born andconverted back to energy

suddenly stops. >from now on, we work with what we have. quarks begin forming new particles,hadrons, like protons and neutrons. there are many, many combinations ofquarks that can form all sorts of hadrons, but only very few are reasonably stablefor any length of time. please take a moment to appreciate thatby now, only one second has passed since the beginning of everything. the universe, which has grown to onehundred billion kilometers, is now cold enough to allow most of theneutrons to decay into protons

and form the first atom, hydrogen. imagine the universe at this point as anextremely hot soup, ten billion degrees celsius, filled withcountless particles and energy. over the next few minutes, things cooledand settled down very fast. atoms formed out of hadrons and electrons, making for a stable and electricallyneutral environment. some call this period the dark age,because there were no stars and the hydrogen gas didn’t allow visiblelight to move around. but what’s the meaning of visible light,anyway, when there’s nothing alive yet

that could have eyes? when the hydrogen gas clumped togetherafter millions of years and gravity put it under great pressure, starsand galaxies began to form. their radiation dissolved the stablehydrogen gas into a plasma that still permeates the universe todayand allows visible light to pass. finally, there was light! okay, but what about the partwe didn’t talk about? what happened right at the beginning? this part can be defined as the big bang.

we don’t know at all what happened here. at this point, our tools break down. natural laws stop making sense,time itself becomes wibbly-wobbly. to understand what happened here,we need a theory that unifies einstein’s relativity and quantummechanics, something countless scientists are working on right now. but this leaves us with lots ofunanswered questions. were there universes before our own? is this the first and only universe?

what started the big bang, or did itjust occur naturally, based on laws we don’t understand yet? we don’t know, and maybe we never will. but what we do know is that the universeas we know it started here and gave birth to particles, galaxies,stars, the earth, and you. since were ourselves are made ofdead stars, we are not separate from the universe; we are part of it. you could even say that we are theuniverse’s way of experiencing itself. so, let’s keep on experiencing it, untilthere are no more questions to ask.

subtitles by the amara.org community

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