“The most incomprehensible thing about the Universe is that it is comprehensible.”

Albert Einstein (1879-1955).

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“If, in the last few years, you haven't discarded a major opinion or acquired a new one, check your pulse. You may be dead.”

American poet Gelett Burgess (1866-1951).

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“We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture.”

Hannes Alfvén (1908-1995), the father of Magnetohydrodynamics.

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“You don't really understand something until you can compute it.”

Computational astrophysicist Michael L. Norman, on numerous occasions.

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“Brag of your country. When I am abroad, I brag of everything that Nova Scotia is, has, or can produce and, if they beat me at everything else, I say: `How high do your tides rise?'.”

Joseph Howe (1804-1873); journalist, politician, poet, referring to the 16 m tides in the Bay of Fundy. It is because of his success at defending himself against a charge of seditious libel in 1835 that Canada has a free press.

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“Numquam ponenda est pluralitas sine necessitate; Plurality must never be posited without necessity.”

William of Ockham (1287-1347), though versions of "Occam's Razor" can be traced to Ptolomy (90-168 AD): We consider it a good principle to explain the phenomenon by the simplest hypothesis possible. Modern versions include: The simplest explanation is usually the best.

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“If I have seen further than others, it is by standing upon the shoulders of giants.”

Sir Isaac Newton (1642-1727).

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“I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”

attributed to Sir Isaac Newton shortly before his death in 1727.

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“He must be a dull man who can examine the exquisite structure of a comb, so beautifully adapted to its end, without enthusiastic admiration.”

Charles Darwin (1809-1882) in his On the Origin of Species, when introducing the role of instinct in the construction of "humble-bee" hives.

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“Prediction is very difficult, especially about the future.”

Niels Bohr (1885-1962), often (but incorrectly) attributed to Yogi Berra.

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“Those who are not shocked when they first come across quantum theory cannot possibly have understood it.”

Niels Bohr.

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“I cannot seriously believe in quantum theory because it cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance.”

Albert Einstein, 1948, on his favourite critique of quantum mechanics where, so the theory requires, a measurement at location B can instantaneously have an influence at location A. On this he had stated the year before: My instinct for physics bristles at this, and in 1935 he wrote: No reasonable definition of reality could be expected to permit this. To Niels Bohr's quotation, Albert Einstein was certainly shocked!

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“I have stated previously that the arrow of time should follow the arrow of universal expansion, and if the universe should start to collapse, we'd all start getting younger. I was wrong.”

Stephen Hawking (1942-2018) in an address to the XIII Texas Symposium on Relativistic Astrophysics, Chicago, 1986.

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“Only two things are infinite: the universe and human stupidity, and I'm not sure about the former.”

Albert Einstein.

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“I haven't an inkling, and it takes a thousand inklings to make a clue!”

Origin unknown. While it appears in the 1997 novel Larry's Party by Carol Shields, it was my father's response to unanswerable questions since long before then.

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“Freedom has to be armed no worse than tyranny.”

Ukrainian President Volodymyr Zelenskyy.

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“And I find it kinda funny, I find it kinda sad; the dreams in which I'm dying are the best I've ever had; I find it hard to tell you, 'cause I find it hard to take; when people run in circles, it's a very very mad world, mad world.”

from Mad World by Roland Orzabal and Curt Smith, Tears for Fears (1982); covered in 2001 by Michael Andrews and Gary Jules for the soundtrack of Donnie Darko.