With all due respect, perhaps it’s time for Steven Hawking to retire, take down his “scientist” shingle, and quit embarrassing himself. While we all know today that the only kind of science that seems to sell books and Discovery channel advertising, is that flavor attracting conspiracy theorist and extraterrestrial intelligent life enthusiasts, it is sad that a physicist of Hawking's caliber and contribution to the field would now stoop to pseudo-science to make a buck. To add insult to injury, Hawking's idea that Aliens represent a threat to humanity is not original and may well represent a case of quasi-plagiarism.
In his book “The Dreams of Reason” (c. 1988), renowned Physicist Dr. Heinz Pagels reasoned: “Given the vastness of space and the available differences in evolutionary times, the likelihood is that extraterrestrial life will either be to primitive to be able to contact us or it will be millions of years in advance of us, know the state of affairs rather well, and have little interest in us.” Perhaps Hawking's own notions are a spin-off on Pagels’ or some other physicist’s or astronomer’s ideas, who themselves has exercised greater discretion in making public, or not, their speculative notions.
As Dr. Call Sagan so eloquently stated in regard to extraterrestrial intelligence, “extraordinary claims require extraordinary evidence,” and in this case, all Hawking can muster is mere speculation and conjectural thesis. That's fine when the burden of proof is lowered to simply dazzling the minds of undereducated Discovery Channel viewers seeking sensationalism, and who lack the critical thinking skills to discern the difference between pseudo-science and real science. But for “real scientists” of the stature of a Steven Hawkins to begin to invest in whimsical notions and back them up with their credentials only tarnishes their reputable status. There was a day, and not so long ago, when no self respecting scientist would ever advance an unfounded theory or posit they could not support with at least some kind of evidence. Hawking can’t even offer the flimsiest of evidentiary substantiation for his otherwise whimsical notions, but because it is the venerable Steven Hawkins saying so, it must be right; right?
Even Frank Drake’s 1960 equation purporting the high probability extraterrestrial life should be a common occurrence in the galaxy, now appears to be lacking some variable or constant to bolster its validity; perhaps some vector to account for human wishful thinking. Most reputable scientist today question whether extraterrestrial life exists at all, even some who are part of SETI (Search for Extraterrestrial Intelligence). Of course, you won’t see such naysayer’s booked by the discovery channel to refute the suppositions of more hopeful speculators. For one thing, these guys and gals(scientists) at SETI along with other astrophysicists and astronomers depend on grants and donations to support themselves while they search the heavens for habitable planets and extraterrestrials. They are certainly not going to shoot their own golden goose by suggesting they are wasting their time and your money.