Why is universe expanding?

 

There's a lot we don't know about the universe. But one thing we are pretty sure about is that it's constantly expanding. In fact, the evidence for an expanding universe is so strong that it's considered one of the most important discoveries of the 20th century. So why is the universe expanding? We don't really know for sure. But there are a few theories that could explain it. 1. One theory is that the universe is expanding because of the Big Bang. The Big Bang was the moment when the universe began. It's thought that all of the matter and energy in the universe was concentrated in a very small space. Then, for some reason, that space exploded. The explosion sent all of the matter and energy flying outwards. And as it did, the universe began to expand. 2. Another theory is that the universe is expanding because of dark energy. Dark energy is a kind of energy that is pushing the universe apart. We don't really know what dark energy is, but we do know that it exists. It makes up about 68% of the universe. 3. Another theory is that the universe is expanding because of inflation. Inflation is a period of time in the early universe when space itself expanded rapidly. This expansion caused the universe to get bigger very quickly. 4. Another theory is that the universe is expanding because of gravity. Gravity is the force that pulls things together. But it also has a repulsive force. This repulsive force is very weak, but it's enough to cause the universe to expand. 5. Another theory is that the universe is expanding because of quantum mechanics. Quantum mechanics is the study of the behavior of matter and energy at the atomic and subatomic level. According to quantum mechanics, there is a lot of empty space in the universe. This empty space is constantly expanding. As it does, the universe gets bigger. 6. Another theory is that the universe is expanding because of the nature of space. Space is constantly expanding. We don't really know why this is, but it's just the way space is. As space expands, so does the universe. 7. Another theory is that the universe is expanding because of the nature of time. Time is constantly moving forward. As time moves forward, the universe expands. So there are a lot of theories about why the universe is expanding. But the truth is, we don't really know for sure.