The Big Bang, in today’s society, has countless interpretations. Through all of this, however, it all boils down to one thing. Somehow, something expanded to create our universe. The general theory is that at first, the universe was in an infinitely hot and dense sphere 1/100,000,000,000 the size of a proton. Suddenly came the Planck Epoch. No law of physics can explain what happened during this time, but afterwards gravity split from the previously united four fundamental forces (Gravity, Electromagnetic force, Strong force, and Weak force), and the universe instantly expanded to the size of a football field as it began to cool. In short, the universe expands because it is always cooling down.
A detailed explanation, if you would like to hear it, is as follows: After gravity separated from the four fundamental forces, the era known as the Grand Unification Epoch, the temperature of the universe cooled enough to allow Electroweak force to separate as well, in the time known as the Electroweak Epoch. After this, the universe reached the Inflationary Epoch, where the universe expanded so much that it became perfectly flat and smooth. Around this time, most of the subatomic particles were being formed. Also, the universe was cool at this era because of its expansion, which brings us into the next era of the universe, known as Reheating. During this time, the universe ceased expansion, and the energy that would have been used to continue expansion decayed into heat and radiation, causing quarks, electrons, and neutrinos to form.
After Reheating, the fundamental forces took on the forms they are today, but the universe was still too hot to allow quarks to bind and form hadrons. This is known as the Quark Epoch. Then comes the Hadron Epoch, where the universe finally cooled enough to allow hadrons to form. Soon after came the Lepton Epoch where the hadrons and anti-hadrons annihilated each other, causing Leptons to be the main component of the universe. All of this, back to the beginning of the Big Bang, has happened in 10 seconds. After this came the Photon Epoch, which is where the Leptons and Anti-Leptons annihilated each other to cause Photons to dominate the universe. Three minutes later or so came neucleosynthesis, where the universe cooled enough to let atoms form.
Scientists are able to tell that there once was a dense sphere that became our universe, but nothing explains why it was there. Most people, myself included, believe that it was placed there by God or another Higher Being. However, scientists are reluctant to accept this theory and reject it because of the lack of proof. Will the scientists ever prove the reason for the universe? Only time will tell. Whatever your explanation is for the universe and the Big Bang, none of us will ever know the truth until proof is found. And that might not be as far away as you think.