He’s not saying they are not out there. He is throwing cold water on our chances of contacting them.
Some things, he admits, have changed:
Thanks to advances in astrophysics, we now know that there are billions of exoplanets in the Milky Way alone, leading most of the scientific community to conclude that life probably does exist elsewhere in the universe. Those who do not believe so are now considered the kooks. And while alien abductions are still not in the mainstream, UFOs are — so much so that the U.S. intelligence community just issued a report on them.Alex Berezow, “We are effectively alone in the universe” at Big Think (August 17, 2021)
But while many are willing to acknowledge that simple life forms, at least, could exist in principle on many planets, he sees two major roadblocks to assuming that they do. First, no one really understands how life got started (abiogenesis) on Earth. Berezow notes, “There are several different theories on the origin of life, and none of them are any good.” Eminent chemist James Tour has made the same point in some detail:
He also doubts the easy assumption that interstellar travel is at all practical: “Sure, we could get on a spaceship today and head for a planet orbiting the nearest star, Proxima Centauri, but we better pack a lot of fun-sized bags of pretzels because it will take about 6,300 years to get there.”
Speed of light travel? Even so, he says, Proxima Centauri is four light years away. The other side of the galaxy? Over 100,000 light years away. Even black holes are (thankfully) many hundreds of light years from Earth. And wormholes are, at present, a speculative concept, he says.
The wormhole theory postulates that a theoretical passage through space-time could create shortcuts for long journeys across the universe. Wormholes are predicted by the theory of general relativity…
In 1935, Einstein and physicist Nathan Rosen used the theory of general relativity to elaborate on the idea, proposing the existence of “bridges” through space-time. These bridges connect two different points in space-time, theoretically creating a shortcut that could reduce travel time and distance. The shortcuts came to be called Einstein-Rosen bridges, or wormholes.Nola Taylor Redd, “What Is Wormhole Theory?” at Space.com (October 20, 2017)
The theory of general relativity predicts wormholes though we have not yet found any. So the takeaway here is that for serious interstellar travel, we would really need to find wormholes:
You may also wish to read: Quantum physicist: Aliens may communicate by starlight Terry Rudolph of Imperial College, London, argues that they may have evolved so as to take advantage of quantum mechanics via photonics more easily than we can. Photonics is a form of communication that takes advantage of the fact that light moves
faster than electricity. Fibre optics (light) is used to transmit data via the internet but on the stationary computer, it’s the slower electrons that rule. Some researchers hope to change that. Many now think that we cannot rely on “Moores’s Law” to just keep improving electronics. We may need to recalibrate to the speed of light.