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have sold more books on physics than Madonna has on sex.
Science slay
“We are lucky to live in an age in which we are still making discoveries….The age in which we live is the age in which we are discovering the fundamental laws of nature.”
Ptolemy
Copernican theory,
Philosophiae Naturalis Principia Mathematica, probably the most important single work ever published in the physical sciences.
(The story that Newton was inspired by an apple hitting his head is almost certainly apocryphal.
When asked: “What did God do before he created the universe?” Augustine didn’t reply: “He was preparing Hell for people who asked such questions.”
This quote goes hard
that time did not exist before the beginning of the universe.
An expanding universe does not preclude a creator, but it does place limits on when he might have carried out his job!
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.
The general theory of relativity describes the force of gravity and the large-scale structure of the universe, that is, the structure on scales from only a few miles to as large as a million million million million (1 with twenty-four zeros after it) miles, the size of the observable universe. Quantum mechanics, on the other hand, deals with phenomena on extremely small scales, such as a millionth of a millionth of an inch.
One of the major endeavors in physics today, and the major theme of this book, is the search for a new theory that will incorporate them both—a quantum theory of gravity.
The big difference between the ideas of Aristotle and those of Galileo and Newton is that Aristotle believed in a preferred state of rest, which any body would take up if it were not driven by some force or impulse.
The fact that light travels at a finite, but very high, speed was first discovered in 1676 by the Danish astronomer Ole Christensen Roemer.
If the wavelength of these waves (the distance between one wave crest and the next) is a meter or more, they are what we now call radio waves. Shorter wavelengths are known as microwaves (a few centimeters) or infrared (more than a ten-thousandth of a centimeter).
Even shorter wavelengths are known as ultraviolet, X rays, and gamma rays.
It was therefore suggested that there was a substance called the “ether” that was present everywhere, even in “empty” space.
Einstein’s famous equation E=mc2 (where E is energy, m is mass, and c is the speed of light),
In Newton’s theory, if a pulse of light is sent from one place to another, different observers would agree on the time that the journey took (since time is absolute), but will not always agree on how far the light traveled (since space is not absolute).
(The time taken is the distance the light has traveled—which the observers do not agree on—divided by the light’s speed—which they do agree on.)
(The surface of the earth is two-dimensional because the position of a point can be specified by two coordinates, latitude and longitude.)
Roger Penrose and I showed that Einstein’s general theory of relativity implied that the universe must have a beginning and, possibly, an end.
The nearest star, called Proxima Centauri, is found to be about four light-years away
Will the universe eventually stop expanding and start contracting, or will it expand forever?
So all we know is that the universe is expanding by between 5 percent and 10 percent every thousand million years.
by that time, unless we have colonized beyond the Solar System, mankind will long since have died out, extinguished along with our sun!
deterministic.
quarks
We now know that every particle has an antiparticle, with which it can annihilate. (In the case of the force-carrying particles, the antiparticles are the same as the particles themselves.)
There could be whole antiworlds and antipeople made out of antiparticles. However, if you meet your antiself, don’t shake hands! You would both vanish in a great flash of light.
mesons,
But why should that lead to more quarks than antiquarks?
The symmetry C means that the laws are the same for particles and antiparticles. The symmetry P means that the laws are the same for any situation and its mirror image (the mirror image of a particle spinning in a right-handed direction is one spinning in a left-handed direction). The symmetry T means that if you reverse the direction of motion of all particles and antiparticles, the system should go back to what it was at earlier times; in other words, the laws are the same in the forward and backward directions of time.
There is a mathematical theorem that says that any theory that obeys quantum mechanics and relativity must always obey the combined symmetry CPT.
The term black hole is of very recent origin. It was coined in 1969
Robert Oppenheimer,
The rate of energy loss in the case of the earth and the sun is very low—about enough to run a small electric heater. This means it will take about a thousand million million million million years for the earth to run into the sun, so there’s no immediate cause for worry!
several gamma ray quanta
As explained above, an early generation of stars first had to form. These stars converted some of the original hydrogen and helium into elements like carbon and oxygen, out of which we are made. The stars then exploded as supernovas, and their debris went to form other stars and planets, among them those of our Solar System, which is about five thousand million years old. The first one or two thousand million years of the earth’s existence were too hot for the development of anything complicated. The remaining three thousand million years or so have been taken up by the slow process of
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We don’t yet have a complete and consistent theory that combines quantum mechanics and gravity.
The real numbers can be represented by a line going from left to right, with zero in the middle, negative numbers like −1, −2, etc. on the left, and positive numbers, 1, 2, etc. on the right. Then imaginary numbers are represented by a line going up and down the page, with i, 2i, etc. above the middle, and −i, −2i, etc. below. Thus imaginary numbers are in a sense numbers at right angles to ordinary real numbers.
So long as the universe had a beginning, we could suppose it had a creator. But if the universe is really completely self-contained, having no boundary or edge, it would have neither beginning nor end: it would simply be. What place, then, for a creator?
The explanation that is usually given as to why we don’t see broken cups gathering themselves together off the floor and jumping back onto the table is that it is forbidden by the second law of thermodynamics.
There are at least three different arrows of time. First, there is the thermodynamic arrow of time, the direction of time in which disorder or entropy increases. Then, there is the psychological arrow of time. This is the direction in which we feel time passes, the direction in which we remember the past but not the future. Finally, there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting.
The first indication that the laws of physics might really allow people to travel in time came in 1949 when Kurt Gödel discovered a new space-time allowed by general relativity.
cosmic strings are objects that are like string in that they have length but a tiny cross section. Actually, they are more like rubber bands because they are under enormous tension, something like a million million million million tons. A cosmic string attached to the earth could accelerate it from 0 to 60 mph in 1/30th of a second.
The point is that the theory of relativity says that there is no unique measure of time that all observers will agree on.
So, one can regard the pair of particles as a single particle moving on a closed loop in space-time. When the pair is moving forward in time (from the event at which it appears to that at which it annihilates), it is called a particle. But when the particle is traveling back in time (from the event at which the pair annihilates to that at which it appears), it is said to be an antiparticle traveling forward in time.
As was explained in the first chapter, it would be very difficult to construct a complete unified theory of everything in the universe all at one go. So instead we have made progress by finding partial theories that describe a limited range of happenings and by neglecting other effects or approximating them by certain numbers.
