“I do not pretend to know what many ignorant men are sure of.” ~Clarence S. Darrow
“Dogmatism and skepticism are both, in a sense, absolute philosophies; one is certain of knowing, the other of not knowing. What philosophy should dissipate is certainty, whether of knowledge or ignorance.” ~Bertrand Russell
“The educated in [the critical habit of thought] . . . are slow to believe. They can hold things as possible or probable in all degrees, without certainty and without pain.” ~William Graham Sumner
“What can be asserted without proof can be dismissed without proof.” ~Christopher Hitchens
“Doubt is not a pleasant state of mind, but certainty is absurd.” ~Voltaire
“It is wrong, always, everywhere, and for anyone, to believe anything upon insufficient evidence” ~William K. Clifford
“The presence of those seeking the truth is infinitely to be preferred to the presence of those who think they’ve found it” ~Terry Pratchett
“A belief which leaves no place for doubt is not a belief; it is a superstition.” ~José Bergamín
Red flags go up for me whenever I’m faced with absolute certainty from somebody. My experience tells me that such a person is probably either a fundamentalist Christian or Muslim or is a didactic pedagogue who feels that anybody who disagrees is obviously wrong. Among us atheists, of course, religious fundamentalism is ruled out, so it always turns out (so far) that absolute certainty, in atheists, conceals over-confidence or intransigence or (more likely) both.
I used to feel certain that no entity, all-powerful or not, could possibly produce the unimaginable mass/energy of the entire universe. But as it turns out, cosmologists now believe the universe has a grand sum of zero energy (thanks to "negative energy", like gravity). I used to feel certain that consciousness was entirely subjective and abstract. But observation explicitly factors into quantum theory. And certain phenomena, like quantum entanglement, reveal that data is inherent to subatomic particles. That seems a bit strange for a universe that existed for billions of years without intelligence of any kind (if you assume God does not exist). And, of course, there's the favorite argument of Intelligent Design: our universe, fine-tuned to life on Earth.
I know that there's arguments for and against all these strange things. The point is that, although we have theories that attempt to explain everything, they are only working models that fit observations. They aren't the actual reality or "truth". There were many scientific paradigms preceding modern ones and there will be many more to come. Are there really 11 dimensions? Is life limited to 3 dimensions plus time? What if life existed in higher dimensions? According to the math, if an entity existed in the highest dimension (the 11th?) he would have god-like powers, such as omnipresence.
I know that's a bunch of wild speculation. The point is that there is too much we don't know. So much, in fact, that certainty is an unjustified pretense. The ineffable mystery of existence may never be solved. I reject any certainty where the big questions are concerned.