In the beginning, it was infinity and then, the beginning.
13.4 Billion years ago
This is the beginning. There was no time, no existence, not even empty space. Our universe we recognize today was an infinitely dense, infinitely hot, infinitely small object. This is the moment of creation when everything we see exploded out of existence: Space, time, matter and energy.
* * *
About one ten-million-trillion-trillion-trillionth of a second after the moment of creation, the universe we know is a hundred-thousand-billion-billion-billion degrees hot. To write that out in number will look like this: 100,000,000,000,000,000,000,000,000,000,000.
At this point of time, all things in the universe we see (and might not see) today are pack in such a tiny place and all the four fundamental forces of nature: gravity, electromagnetic, weak nuclear and strong force are indistinguishable from each other due to the astronomical amount of energy being concentrated at such a tiny point. The laws of physics set a start here and until today, physicists are still trying to understand the mechanisms of the cosmos at this point of time.
Just an instant after this time, gravity, out of the other three fundamental forces of nature cut itself loose and thus set the fundamental clockwork of gravity throughout the universe. As the universe now aged 10 to the power of minus 35 seconds, cooling begins and space expands and the forces split again. This time, the strong force went independent, left behind the electro-weak force. Later still, the electro-weak force split again into the weak force and electromagnetic force; making all the four fundamental forces of nature separated nicely and each has their functions. The strong force is responsible to bind the protons and neutrons in the nucleus of an atom, the weak force is responsible for the radioactive decay of atoms, and the electromagnetic force is what we now commonly experience as light, electricity and magnetism.
By now, the universe was merely trillionth of a second old.