17. 11. 2020

A Brief History Of Time

by Stephen W. Hawking


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, (Saturday, March 09, 2013, 07:42 AM, page 177-78)

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. (Saturday, March 09, 2013, 07:43 AM, page 183-84)

Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. (Saturday, March 09, 2013, 07:44 AM, page 188-89)

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. (Saturday, March 09, 2013, 07:45 AM, page 191-92)

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 (Saturday, March 09, 2013, 10:34 AM, page 435-36)

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. (Saturday, March 09, 2013, 10:45 AM, page 492-93)

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. (Saturday, March 09, 2013, 10:47 AM, page 498)

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. (Saturday, March 09, 2013, 10:49 AM, page 498-500)

in Friedmann’s model the speed at which any two galaxies are moving apart is proportional to the distance between them. (Saturday, March 09, 2013, 11:18 AM, page 635-36)

all we know is that the universe is expanding by between 5 percent and 10 percent every thousand million years. (Saturday, March 09, 2013, 11:26 AM, page 674-75)

Werner Heisenberg, formulated his famous uncertainty principle. (Saturday, March 09, 2013, 08:25 PM, page 795)

the more accurately you try to measure the position of the particle, the less accurately you can measure its speed, and vice versa. (Sunday, March 10, 2013, 04:50 PM, page 802-3)

“God does not play dice.” (Sunday, March 10, 2013, 04:59 PM, page 824-25)

the electric repulsive force between two electrons is due to the exchange of virtual photons, which can never be directly detected; (Sunday, March 10, 2013, 11:45 PM, page 1004-5)

Our own sun contains about 2 percent of these heavier elements, because it is a second-or third-generation star, (Friday, March 15, 2013, 09:22 PM, page 1708-9)

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. (Friday, March 15, 2013, 10:57 PM, page 1722-24)

the total energy of the universe is zero. (Monday, March 18, 2013, 06:27 AM, page 1860-61)

what we call real is just an idea that we invent to help us describe what we think the universe is like. (Wednesday, March 20, 2013, 08:08 AM, page 2027)

psychological arrow is determined by the thermodynamic arrow, (Wednesday, March 20, 2013, 03:35 PM, page 2094-95)

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. (Wednesday, March 20, 2013, 08:46 PM, page 2187-89)

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 (Thursday, March 21, 2013, 05:58 PM, page 2518-20)