A Brief History Of Time

Stephen W. Hawking

Summary: the most commonly unfinished book of all times–hard to digest but a real treat for a curious mind

Score: 80 / 100

One could still imagine that God created the universe at the instant of the big bang, or even afterwards in just such a way as to make it look as though there had been a big bang,

A theory is a good theory if it satisfies two requirements. It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.

Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it.

Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation.

For example, if the sun were to cease to shine at this very moment, it would not affect things on earth at the present time because they would be in the elsewhere of the event when the sun went out

Newton’s laws of motion put an end to the idea of absolute position in space. The theory of relativity gets rid of absolute time.

This is known as the twins paradox, but it is a paradox only if one has the idea of absolute time at the back of one’s mind.

In the theory of relativity there is no unique absolute time, but instead each individual has his own personal measure of time that depends on where he is and how he is moving.

In Friedmann’s model the speed at which any two galaxies are moving apart is proportional to the distance between them.

All we know is that the universe is expanding by between 5 percent and 10 percent every thousand million years.

Werner Heisenberg, formulated his famous uncertainty principle.

The more accurately you try to measure the position of the particle, the less accurately you can measure its speed, and vice versa.

“God does not play dice.”

The electric repulsive force between two electrons is due to the exchange of virtual photons, which can never be directly detected.

Our own sun contains about 2 percent of these heavier elements, because it is a second-or third-generation star,

The first primitive forms of life consumed various materials, including hydrogen sulfide, and released oxygen. This gradually changed the atmosphere to the composition that it has today, and allowed the development of higher forms of life such as fish, reptiles, mammals, and ultimately the human race.

The total energy of the universe is zero.

What we call real is just an idea that we invent to help us describe what we think the universe is like.

Psychological arrow is determined by the thermodynamic arrow.

It seems to me much better and less confusing if you admit in print that you were wrong. A good example of this was Einstein, who called the cosmological constant, which he introduced when he was trying to make a static model of the universe, the biggest mistake of his life.

If a two-dimensional creature ate something it could not digest completely, it would have to bring up the remains the same way it swallowed them, because if there were a passage right through its body, it would divide the creature into two separate halves: our two-dimensional being would fall apart.