Claims that cannot be tested, assertions immune to disproof are veridically worthless, whatever value the may have in inspiring us or in exciting our sense of wonder.

Extraordinary claims require extraordinary evidence.

I'm frequently asked, "Do you believe there's extraterrestrial intelligence?" I give the standard arguments- there are a lot of places out there, the molecules of life are everywhere, I use the word billions, and so on. Then I say it would be astonishing to me if there weren't extraterrestrial intelligence, but of course there is as yet no compelling evidence for it.
Often, I'm asked next, "What do you really think?"
I say, "I just told you what I really think."
"Yes, but what's your gut feeling?"
But I try not to think with my gut. If I'm serious about understanding the world, thinking with anything besides my brain, as tempting as that might be, is likely to get me into trouble. Really, it's okay to reserve judgment until the evidence is in.

Think of how many religions attempt to validate themselves with prophecy. Think of how many people rely on these prophecies, however vague, however unfulfilled, to support or prop up their beliefs. Yet has there ever been a religion with the prophetic accuracy and reliability of science? ... No other human institution comes close.

Just as there are those who accept every UFO report at face value, there are also those who dismiss the idea of alien visitation out of hand and with great passion. It is, they say, unnecessary to examine the evidence, and “unscientific” even to contemplate the issue. I once helped to organize a public debate at the annual meeting of the American Association for the Advancement of Science between proponent and opponent scientists of the proposition that some UFOs were spaceships; whereupon a distinguished physicist, whose judgment in many other matters I respected, threatened to sic the Vice President of the United States on me if I persisted in this madness. (Nevertheless, the debate was held and published, the issues were a little better clarified, and I did not hear from Spiro T. Agnew.)

. . .a scientific theory is just a mathematical model we make to describe our observations: it exists only in our minds. So it is meaningless to ask: which is real, "real" or "imaginary" time? It is simply a matter of which is the more useful description.