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

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.

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

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.

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

In some sort of crude sense, which no vulgarity, no humor, no overstatement can quite extinguish, the physicists have known sin; and this is a knowledge which they cannot lose.

Before 1915, space and time were thought of as a fixed arena in which events took place, but which was not affected by what happened in it. Space and time are now dynamic quantities… space and time not only affect but are also affected by everything that happens in the universe.

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 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.

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.

The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself.

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

Einstein’s gravitational theory, which is said to be the greatest single achievement of theoretical physics, resulted in beautiful relations connecting gravitational phenomena with the geometry of space; this was an exciting idea.

Science is global. Einstein’s equation, E=mc2, has to reach everywhere. Science is a beautiful gift to humanity, we should not distort it. Science does not differentiate between multiple races.

It now appears that the way the universe began can indeed be determined, using imaginary time.

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

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.

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

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 fundamental concept in social science is Power, in the same sense in which Energy is the fundamental concept in physics.

The greatest progress is in the sciences that study the simplest systems. So take, say, physics – greatest progress there. But one of the reasons is that the physicists have an advantage that no other branch of sciences has. If something gets too complicated, they hand it to someone else.

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.

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.

There is no physical law precluding particles from being organised in ways that perform even more advanced computations than the arrangements of particles in human brains.

It should be possible to explain the laws of physics to a barmaid.

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.

My father was a research scientist in tropical medicine, so I always assumed I would be a scientist, too. I felt that medicine was too vague and inexact, so I chose physics.

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.

There could be no fairer destiny for any physical theory than that it should point the way to a more comprehensive theory in which it lives on as a limiting case.

To every action there is always opposed an equal reaction.

Just as the system of the sun, planets and comets is put in motion by the forces of gravity, and its parts persist in their motions, so the smaller systems of bodies also seem to be set in motion by other forces and their particles to be variously moved in relation to each other and, especially, by the electric force.

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.

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

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.

There were several possible solutions of the difficulty of classical electrodynamics, any one of which might serve as a good starting point to the solution of the difficulties of quantum electrodynamics.

All the evidence, experimental and even a little theoretical, seems to indicate that it is the energy content which is involved in gravitation, and therefore, since matter and antimatter both represent positive energies, gravitation makes no distinction.

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.

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.

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

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.

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.

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

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.

Man can be understood only by ascending from physics, chemistry, biology, and geology. In other words, he is first of all a cosmic problem.

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.

If you are in a spaceship that is traveling at the speed of light, and you turn on the headlights, does anything happen?

Because atomic behavior is so unlike ordinary experience, it is very difficult to get used to, and it appears peculiar and mysterious to everyone – both to the novice and to the experienced physicist.

We get the exciting result that the total energy of the universe is zero. Why this should be so is one of the great mysteries – and therefore one of the important questions of physics. After all, what would be the use of studying physics if the mysteries were not the most important things to investigate?

Because there is a law such as gravity, the universe can and will create itself from nothing.

We seem gradually to be groping toward an understanding of the world of subatomic particles, but we really do not know how far we have yet to go in this task.

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

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.

My background educationally is physics and economics, and I grew up in sort of an engineering environment – my father is an electromechanical engineer. And so there were lots of engineery things around me.

It is reasonable that forces directed toward bodies depend on the nature and the quantity of matter of such bodies, as happens in the case of magnetic bodies.

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

I went to Princeton specifically to study physics.

I need physics more than friends.

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.

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.

It was Einstein’s dream to discover the grand design of the universe, a single theory that explains everything. However, physicists in Einstein’s day hadn’t made enough progress in understanding the forces of nature for that to be a realistic goal.

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