What starts with a Big Bang ends with a Big Crunch
The universe is about 13.8 billion years old is the largest thing known to man. If a photon left the edge of the observable universe today, it would take more than 46 billion light years to get to us. You may have noticed the distance to the edge of the observable universe is much greater than its age. This happens due to Cosmic inflation. While a photon has been travelling in space, the universe itself expanded, causing the distance between objects to increase in all directions.
This Cosmic inflation is based on Einstein’s theory of relativity which suggests that since the universe is constantly expanding, it must have come from a singular point. The explosive expansion from this point is known as the Big Bang.
Einstein predicted the Big Bang 100 years ago with his groundbreaking mathematics. His work tells us that the universe is expanding at an increased rate and will eventually reach a point where it collapses on itself. What happens next is known as the big crunch. The collapse of the universe will create the largest black hole ever. It will form a singularity which will eventually start another big bang.
The big crunch can only occur if the strength of the gravitational forces between objects increase. The gravitational waves depend on the density and pressure of matter in the universe. These components make up the critical density of the universe. If the density of the universe is greater than the critical density, then the gravitational forces will be strong enough to stop the universe expanding and will collapse back on itself.
Recent observations of distant supernovae have shown that the universe is expanding at an increased rate, which means there must be some form of matter with a strong negative pressure. This energy, known as dark energy, works in the opposite way to gravity; whereby it increases the expansion of space.
What happens if the density of the universe stays below the critical density? well it continues to expand until it gets so large that the universe is inhospitable to life. This scenario is known as the Big Freeze or heat death. In order for this event to occur, the universe has to become so big that it reaches a maximum value. The moment this happens, all the heat gets distributed across the universe equally allowing no space left for heat energy.