Major scientific reasons that alien UFOs have never existed

There is no proven life of any kind outside of the Earth. No life has been found on any planet in our solar system with one exception. NASA has certainly contaminated Mars with Earth microbes. Scientists have spent billions of dollars expecting to detect intelligent signals from one of the 200 billions of solar systems in our Milky Way Galaxy or from one of the 100 billion other galaxies, only to be disappointed. No intelligent signals exist. Nobody is out there. We are alone.