[The black hole] teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as “sacred,” as immutable, are anything but.

If there’s one thing in physics I feel more responsible for than any other, it’s this perception of how everything fits together. I like to think of myself as having a sense of judgment. I’m willing to go anywhere, talk to anybody, ask any question that will make headway. I confess to being an optimist about things, especially about someday being able to understand how things are put together. So many young people are forced to specialize in one line or another that a young person can’t afford to try and cover this waterfront — only an old fogy who can afford to make a fool of himself. If I don't, who will?

If this is what the McCarran Act means in practice, it seems to us a form of organized cultural suicide.
In a letter co-signed with his Princeton University physics professor colleagues, Walker Bleakney and Milton G. White, protesting that Nobel Prize-winning, Cambridge professor, Dirac having been invited for a year's visit to Princeton, had been denied a visa by the U.S. State Department under section 212A of the Immigration and Naturalization Act (McCarran Act). Quoting a report in Physics Today, this regulation includes 'categories of undesireables ranging from vagrants to stowaways.' The real reason remains unclear, but was perhaps related to Dirac's prior science-related visits to Russia. Robert Oppenheimer's security clearance had recently been revoked, and this was the era of McCarthy's rabid anti-Communism hearings.

No theory of physics that deals only with physics will ever explain physics. I believe that as we go on trying to understand the universe, we are at the same time trying to understand man.

The laws of physics must provide a mechanism for the universe to come into being.

The only thing harder to understand than a law of statistical origin would be a law that is not of statistical origin, for then there would be no way for it—or its progenitor principles—to come into being. On the other hand, when we view each of the laws of physics—and no laws are more magnificent in scope or better tested—as at bottom statistical in character, then we are at last able to forego the idea of a law that endures from everlasting to everlasting.

The universe came into being in a big bang, before which, Einstein’s theory instructs us, there was no before. Not only particles and fields of force had to come into being at the big bang, but the laws of physics themselves, and this by a process as higgledy-piggledy as genetic mutation or the second law of thermodynamics.

The universe does not exist “out there,” independent of us. We are inescapably involved in bringing about that which appears to be happening. We are not only observers. We are participators. In some strange sense, this is a participatory universe. Physics is no longer satisfied with insights only into particles, fields of force, into geometry, or even into time and space. Today we demand of physics some understanding of existence itself.

Wheeler’s First Moral Principle: Never make a calculation until you know the answer. Make an estimate before every calculation, try a simple physical argument (symmetry! invariance! conservation!) before every derivation, guess the answer to every paradox and puzzle. Courage: No one else needs to know what the guess is. Therefore make it quickly, by instinct. A right guess reinforces this instinct. A wrong guess brings the refreshment of surprise. In either case life as a spacetime expert, however long, is more fun!