Quotes from Stephen Hawking

Why do we see only three space dimensions and one time dimension? The suggestion is that the other dimensions are curved up into a space of very small size, something like a million million million million millionth of an inch. This is so small that we just don't notice it: we see only one time dimension and three space dimensions, in which space-time is fairly flat.

The nonexistence of absolute rest therefore meant that one could not give an event an absolute position in space, as Aristotle had believed. The positions of events and the distances between them would be different for a person on the train and one on the track, and there would be no reason to prefer one person's position to the other's.

Se chegássemos ao fim da linha, o espírito humano definharia e morreria. Mas não creio que um dia sossegaremos: aumentaremos em complexidade, se não em profundidade, e seremos sempre o centro de um horizonte de possibilidades em expansão.

Anthropic principle: We see the universe the way it is because if it were different we would not be here to observe it. Antiparticle:

In 1956 two American physicists, Tsung-Dao Lee and Chen Ning Yang, suggested that the weak force does not in fact obey the symmetry P.

The electromagnetic attraction between negatively charged electrons and positively charged protons in the nucleus causes the electrons to orbit the nucleus of the atom, just as gravitational attraction causes the earth to orbit the sun.

The present evidence therefore suggests that the universe will probably expand forever, but all we can really be sure of is that even if the universe is going to recollapse, it won't do so for at least another ten thousand million years, since it has already been expanding for at least that long. This should not unduly worry us:

it is surely better to strive for a complete understanding than to despair of the human mind.

Now, if you believe that the universe is not arbitrary, but is governed by definite laws, you ultimately have to combine the partial theories into a complete unified theory that will describe everything in the universe.

to some accounts, a journalist told Eddington in the early 1920s that he had heard there were only three people in the world who understood general relativity. Eddington paused, then replied, "I am trying to think who the third person is.")

Maybe it says something about human nature that the only form of life we have created so far is purely destructive.

At first, I believed that disorder would decrease when the universe recollapsed. This was because I thought that the universe had to return to a smooth and ordered state when it became small again. This would mean that the contracting phase would be like the time reverse of the expanding phase. People in the contracting phase would live their lives backward: they would die before they were born and get younger as the universe contracted.

Bodies such as stars or black holes cannot just appear out of nothing. But a whole universe can.

When you look at the vast size of the universe, and how insignificant and accidental human life is in it, that seems most implausible.

It also predicted that the electron should have a partner: an antielectron, or positron. The discovery of the positron in 1932 confirmed Dirac's theory and led to his being awarded the Nobel prize for physics in 1933.

However, we now believe such an equilibrium would be unstable: if the stars in some region got only slightly nearer each other, the attractive forces between them would become stronger and dominate over the repulsive forces so that the stars would continue to fall toward each other. On the other hand, if the stars got a bit farther away from each other, the repulsive forces would dominate and drive them farther apart.

What place, then, for a creator?

In general, quantum mechanics does not predict a single definite result for an observation. Instead, it predicts a number of different possible outcomes and tells us how likely each of these is.

the universe expanded by a factor of 1,000,000,000,000,000,000,000,000,000,000 in .00000000000000000000000000000000001 second. It was as if a coin 1 centimeter in diameter suddenly blew up to ten million times the width of the Milky Way.

The uncertainty principle signaled an end to Laplace's dream of a theory of science, a model of the universe that would be completely deterministic: one certainly cannot predict future events exactly if one cannot even measure the present state of the universe precisely!

The fact that light travels at a finite, but very high, speed was first discovered in 1676 by the Danish astronomer Ole Christensen Roemer.

We also now have evidence for several other black holes in systems like Cygnus X-l in our galaxy and in two neighboring galaxies called the Magellanic Clouds. The

The mass of the sun curves space-time in such a way that although the earth follows a straight path in four-dimensional space-time, it appears to us to move along a circular orbit in three-dimensional space.

In an infinite universe, every point can be regarded as the center, because every point has an infinite number of stars on each side of it.