Now that everyone has seen the new Star Wars flick at least once, I can use some cheesy puns to talk about physics. Case in point: the force. We're familiar with the four known forces of nature. Electromagnetism, governing everything from light to your fridge magnets. Strong nuclear, binding quarks together to make protons and neutrons, and gluing those together to make atomic nuclei. Weak nuclear, responsible for radioactive decay. And lastly gravity, which connects all matter and energy in the universe.
Why are there four forces, not more or less? Why is gravity so weak? Why is the strong force so short-ranged? Is there any connection at all between them?
Obviously we don't have all the answers, but some intriguing hints have been discovered in the past few decades. For one, we've discovered that at very high energies the electromagnetic and weak nuclear forces merge together. Inside our particle collider experiments, there are only three forces of nature.
We have good mathematical reasons to think that at even higher energies the strong nuclear force disappears too, and based on that we suspect that at extremely high energies, like those found in the first instants of the universe, there was only a single unified force. Not The Force, but close enough.