One of the biggest questions is whether we are alone in the universe — could there be other intelligent life, besides us, out there? Currently, we don't have any evidence aliens exist. There may have been a chance for a civilization to start billions of years before life began on Earth — one that is far more advanced, technologically speaking, than us. However, they're not making it very obvious. We have no proof of this. If such an advanced civilization exists, though, it probably relies on solar energy to fuels its everyday activities.