Around 13.8 billion years ago our universe started to exist. As far as science knows, the big bang was the beginning of everything, the beginning of space, time and all the energy and matter there is.
It was unimaginably hot, a raging explosion and expansion. Since then our universe has started to expand rapidly. Until today the universe is expanding continuously and the rate of expansion continues to increase.
In our universe, energy conservation applies, which means that all of today’s energy was already created at the beginning of the Big Bang, something that we humans cannot understand. This initial total energy could divide into matter, dark matter and dark energy. A relic of the Big Bang is today’s Cosmic microwave background.