Einstein and Bohr, the two leading authorities of the day, were locked in conflict (the word conflict was used by Einstein himself). To take sides meant choosing between the two most revered physicists.

Einstein never ceased to ponder the meaning of the quantum theory.

On the face of it, the universe, according to the picture that has now emerged, is destined to expand for all eternity, at an ever-increasing rate.

The … results have given physicists confidence that we understand the origin of the universe to within a fraction of a second after the Big Bang. However, we are still left with the embarrassing questions of what preceded the Big Bang and why it occurred.

[I]t is often stated that of all the theories proposed in this century, the silliest is quantum theory. Some say that the only thing that quantum theory has going for it, in fact, is that it is unquestionably correct.

At the beginning of time, when temperatures were incredibly hot, our universe must have been perfectly symmetrical.

To Einstein, terms like ‘the gravitational field’, ‘the structure of space-time’, and ‘the ether’ were all synonymous.

Quantum mechanics, that mysterious, confusing discipline, which none of us really understands but which we know how to use … is not a theory, but rather a framework within which we believe any correct theory must fit.

We are more likely to develop a correct theory of nature from a meaningful theory than from a meaningless one.