While it's presently a topic of heated debate, the current majority opinion is that the universe began in an event that we call the [b]big bang[/b]. This term was coined by Fred Hoyle, an opponent of the theory, in a derogatory manner while doing a BBC radio interview in 1949. Hoyle didn't like the theory because he - as most scientists of his era - was convinced the universe was static. That notion followed from ancient Greek philosopher Aristotle and others, and was still the view of science at the turn of the 20[sup]th[/sup] century. [br][br]The idea of the universe having a beginning - and a violent one - entered into science in the 1910s-1920s. To the static (and eternal) universe proponents this was a revolution with scientific and philosophical implications. The incorrect view of a static universe was so pervasive, that Einstein himself was misled. He had noticed in 1917 that his own equations of general relativity predicted an expanding universe, and artificially inserted a term called the [b]cosmological constant[/b] in order to force his equations to predict a static universe. Einstein later referred to this as the biggest blunder of his life.[br][br]Using Einstein's field equations from general relativity, in 1922 a Russian named Alexander Friedmann showed that the equations implied the universe may be expanding and was the first to propose an expanding universe. [br][br]Later, in 1927, but independently the Belgian Jesuit priest and astronomer Georges Lemaître came to the same conclusion. It was Lemaître who extended the idea to include a calculation of the rate of expansion, widely and incorrectly attributed to Edwin Hubble. Lemaître also connected the theory to experimentally-measured galactic spectral red-shifts that were being recordeded in his day. Lemaître also first published the idea he called the "hypothesis of the primeval atom" which Hoyle later referred to as the big bang during that 1949 BBC radio interview. The name stuck. In spite of all the empirical and theoretical evidence, Hoyle continued to believe in a static universe until his death in 2001. His opposition rested on his opinion that the big bang too much resembled philosophical arguments for a creator.

The current view of the big bang until the present day goes like this:[br][list=1][*]An event takes place which establishes the beginning of both space and time. It is incorrect to think of space being there before the big bang.  It is also incorrect to assume that time existed before the big bang.  It is the material universe and the processes within it that give rise to the notion of, and the ability to quantify time.[/*][*]Equations of physics tell us that the universe initially was made of only light (no matter) of enormous energy density.  Think of all the sunlight from all the stars in all the galaxies in a pinhead, and that's a grave underestimate.[/*][*]Soon after it began, after only 10[sup]-35 [/sup]seconds, a period of inflation took place where the universe suddenly grew by a factor of around 10[sup]27[/sup] times.  We don't know why inflation took place, and the truth is that we presently are debating whether it really did take place. In fact, while this inflationary stage is mentioned in any big bang timeline, we do not have data to support it. Planck mission data from 2015 actually suggested we may be wrong about inflation. The idea was proposed initially to solve a problem that we see in the heavens - that the temperature seems too uniform to be a product of chance. This is another instance of "uncanny fine-tuning" requiring a physical explanation. So inflation supposes that the material of the universe had been in close proximity and near equilibrium early on, and only after that was carried faster than light speed apart by the expansion of spacetime. If inflation did not occur, then we have even more great mysteries to be solved. [/*][*]The universe continued to grow at a slower rate, and cooled. Matter formed - at first quarks formed protons and neutrons (and other hadrons), then electrons formed. [/*][*]Within 3 minutes protons, deuterium and some helium nuclei had formed.[/*][*]For around 380,000 years the matter was too dense and hot to allow light to travel far. The universe was opaque. Electrons had not yet combined with nuclei.[/*][*]Recombination took place after this time and electrons combined with the nuclei to form the first neutral atoms. The universe became transparent at this time and the remnant of radiation released at this time forms what we see today as the cosmic microwave background radiation, or the afterglow of the big bang that we see in every direction of space.[/*][*]The universe went through its own dark ages in the intervening time between recombination and reionization which occured once gravity had caused large clouds of atoms to form into dense hot clusters which would soon become stars. Even before igniting fusion, there was once again light in the universe due to blackbody radiation.[/*][*]Stars form and are fueled by nuclear fusion from which we get heavier elements up to iron.[/*][*]At the end of their lives, large, exploding stars run the endothermic (ones which require energy rather than liberating it) nuclear reactions (fission in reverse) to create the rest of the periodic table. That being said, we now know that there are direct-collapse black holes in which large clouds of gas avoid ever becoming stars, and instead go from dust cloud to black hole. Being true, there is enough energy there to produce any elements we see without having to wait for a star to form, to live and to die an explosive death.[/*][/list]