Pedro Domingos

Or we live in a simulation and the programmers didn't include aliens.

...and that no sentient being is able to overcome relativity to reduce that cost.

Most life forms in the university are AI, and not biological in nature.

eh...mostly because we don't have warp drive, or some FTL technology (yet). Without it, we are going nowhere....

Humans just aren’t that tasty.

It's possible that intelligent races eventually get reaaallly good at hacking their brains and creating infinitely creative VR worlds to live in. They simply lose interest in anything but harnessing more energy for their local compute ... kind of like a teenager.

Earth is the only place in the universe that has intelligent life, even if the odd planet was to have a few microbes here and there. Microbes can't build rockets and spaceships.

It took life on earth about 4 billion years to develop radio communication. Aliens would have thought there is nobody here for 4 billion years. Unless they could detect biological signs of life. Ofcourse the universe is full of life. Nothing in the universe happens just once.