M-theory is the unified theory Einstein was hoping to find.

Imaginary time is a new dimension, at right angles to ordinary, real time.

Often one postulates that a priori, all states are equally probable. This is not true in the world as we see it. This world is not correctly described by the physics which assumes this postulate.

In my school, the brightest boys did math and physics, the less bright did physics and chemistry, and the least bright did biology. I wanted to do math and physics, but my father made me do chemistry because he thought there would be no jobs for mathematicians.

Gravitation is, so far, not understandable in terms of other phenomena.

I think you should always bear in mind that entropy is not on your side.

The missing link in cosmology is the nature of dark matter and dark energy.

When I was a young man, Dirac was my hero. He made a breakthrough, a new method of doing physics. He had the courage to simply guess at the form of an equation, the equation we now call the Dirac equation, and to try to interpret it afterwards.

An object in motion tends to remain in motion along a straight line unless acted upon by an outside force.

The cyclic universe theory predicts no gravitational waves from the early universe.

There are children playing in the streets who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago.

Physics is really figuring out how to discover new things that are counterintuitive, like quantum mechanics. It’s really counterintuitive.

My first popular book, ‚A Brief History of Time,‘ aroused a great deal of interest, but many found it difficult to understand.

Atoms are very special: they like certain particular partners, certain particular directions, and so on. It is the job of physics to analyze why each one wants what it wants.

Working out another system to replace Newton’s laws took a long time because phenomena at the atomic level were quite strange. One had to lose one’s common sense in order to perceive what was happening at the atomic level.

My discovery that black holes emit radiation raised serious problems of consistency with the rest of physics. I have now resolved these problems, but the answer turned out to be not what I expected.

Time can behave like another direction in space under extreme conditions.

I tell you the solemn truth, that the doctrine of the Trinity is not so difficult to accept for a working proposition as any one of the axioms of physics.

In the past, there was active discrimination against women in science. That has now gone, and although there are residual effects, these are not enough to account for the small numbers of women, particularly in mathematics and physics.

I think we all change each other’s paths. I don’t know which law idea that is in physics, but I don’t think any of us can live without affecting one another.

To every action there is always opposed an equal reaction.

We are the product of quantum fluctuations in the very early universe.

It always seems odd to me that the fundamental laws of physics, when discovered, can appear in so many different forms that are not apparently identical at first, but, with a little mathematical fiddling, you can show the relationship.

Today, all physicists know from studying Einstein and Bohr that sometimes an idea which looks completely paradoxical at first, if analyzed to completion in all detail and in experimental situations, may, in fact, not be paradoxical.

I am not enough of a mathematician to be able to judge either the well-foundedness or the limits of relativity in physics.

It is now quite lawful for a Catholic woman to avoid pregnancy by a resort to mathematics, though she is still forbidden to resort to physics or chemistry.

The drawing teacher has this problem of communicating how to draw by osmosis and not by instruction, while the physics teacher has the problem of always teaching techniques, rather than the spirit, of how to go about solving physical problems.

If the rate of expansion one second after the Big Bang had been smaller by even one part in a hundred thousand million million, it would have recollapsed before it reached its present size. On the other hand, if it had been greater by a part in a million, the universe would have expanded too rapidly for stars and planets to form.

I need physics more than friends.

From the point of view of basic physics, the most interesting phenomena are, of course, in the new places, the places where the rules do not work – not the places where they do work! That is the way in which we discover new rules.

Some scientists think it may be possible to capture a wormhole and enlarge it many trillions of times to make it big enough for a human or even a spaceship to enter.

No one undertakes research in physics with the intention of winning a prize. It is the joy of discovering something no one knew before.

The same thing is to be understood of all bodies, revolved in any orbits. They all endeavour to recede from the centres of their orbits, and were it not for the opposition of a contrary force which restrains them to and detains them in their orbits, which I therefore call Centripetal, would fly off in right lines with a uniform motion.

It is generally recognised that women are better than men at languages, personal relations and multi-tasking, but less good at map-reading and spatial awareness. It is therefore not unreasonable to suppose that women might be less good at mathematics and physics.

There is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to the laws of physics.

There are no black holes in the sense of regimes from which light can’t escape to infinity.

Although almost every theoretical physicist agrees with my prediction that a black hole should glow like a hot body, it would be very difficult to verify experimentally because the temperature of a macroscopic black hole is so low.

While physics and mathematics may tell us how the universe began, they are not much use in predicting human behavior because there are far too many equations to solve. I’m no better than anyone else at understanding what makes people tick, particularly women.

Quarks came in a number of varieties – in fact, at first, only three were needed to explain all the hundreds of particles and the different kinds of quarks – they are called u-type, d-type, s-type.

The first amazing fact about gravitation is that the ratio of inertial mass to gravitational mass is constant wherever we have checked it. The second amazing thing about gravitation is how weak it is.

Mediocre theoretical physicists make no progress. They spend all their time understanding other people’s progress.

Physics has a history of synthesizing many phenomena into a few theories.

Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe?

I think equation guessing might be the best method to proceed to obtain the laws for the part of physics which is presently unknown. Yet, when I was much younger, I tried this equation guessing, and I have seen many students try this, but it is very easy to go off in wildly incorrect and impossible directions.

There happen to be a lot of people around who spent an hour on the Internet and think they know a lot of physics, but it doesn’t work like that… There’s a reason there are graduate schools in these departments.

According to ‚M‘ theory, ours is not the only universe. Instead, ‚M‘ theory predicts that a great many universes were created out of nothing.

Chemistry, until my childhood, not that long ago, was regarded as a calculating device. Because you couldn’t reduce to physics. So it’s just some way of calculating the result of experiments. The Bohr atom was treated that way.

Resistance is usually ascribed to bodies at rest, and impulse to those in motion, but motion and rest, as commonly conceived, are only relatively distinguished; nor are those bodies always truly at rest, which commonly are taken to be so.

I was never top of the class at school, but my classmates must have seen potential in me, because my nickname was ‚Einstein.‘

It is theoretically possible to warp spacetime itself, so you’re not actually moving faster than the speed of light, but it’s actually space that’s moving.

If a projectile were deprived of the force of gravity, it would not be deflected toward the earth but would go off in a straight line into the heavens and do so with uniform motion, provided that the resistance of the air were removed.

Most people don’t have time to master the very mathematical details of theoretical physics.

What goes up must come down.

The same law takes place in a system, consisting of many bodies, as in one single body, with regard to their persevering in their state of motion or of rest. For the progressive motion, whether of one single body or of a whole system of bodies, is always to be estimated from the motion of the center of gravity.

Philosophers have not kept up with modern developments in science. Particularly physics.

OK, so what’s the speed of dark?

Theoretical physics is one of the few fields in which being disabled is no handicap – it is all in the mind.

Science is beautiful when it makes simple explanations of phenomena or connections between different observations. Examples include the double helix in biology and the fundamental equations of physics.

With the exception of gravitation and radioactivity, all of the phenomena known to physicists and chemists in 1911 have their ultimate explanation in the laws of quantum electrodynamics.

I hope I have helped to raise the profile of science and to show that physics is not a mystery but can be understood by ordinary people.

I had a project for my life which involved 10 years of wandering, then some years of medical studies and, if any time was left, the great adventure of physics.