The way he thinks about aliens is a little short sighted. I see the logic in it, but to state that we're alone is unknowable. Now, we may be functionally alone, ie: perhaps intelligent life is rare enough that it only happens once every 10,000 galaxies, but the first human emitted signals have only traveled about 200 light years, which on a cosmic scale is basically nothing. It's estimated there are 100 to 200 billion galaxies and the average distance between galaxies is 100 million light years. That's not even a fraction of the size of our own galaxy. One single light year is ~9.46 TRILLION kilometers. The scale of the cosmos is so incredibly vast that it is statistically improbable that intelligent life hasn't evolved elsewhere. Now, we may never be able to communicate so we're functionally alone, but it's ridiculous to say that intelligent life hasn't evolved elsewhere. But perhaps that's just me putting words in his mouth and his view is more nuanced. Now, it's likely the only way we'll ever experience contact with one of these civilizations is if inter-dimensional travel becomes a reality...