Black holes are stars that have collapsed into one very small point. This small point is called a "singularity".This singularity is a point of space-time which rotates at a high speed.That is the reason that black holes have no time. Black holes suck things into their center because its gravity is very strong. Some of the things it can suck in are light and stars. Only very large stars, called "super-giants", are big enough to become a black hole. The star must be one and a half times the mass of the sun or larger to turn into a black hole. This number is called the "Chandrasekhar limit". If the mass of a star is less than the Chandrasekhar limit, it will not turn into a black hole; instead, it will turn into a different, smaller type of star. The boundary of the black hole is called the "event horizon". If something is in the event horizon, it will never get out of the black hole.
Black holes can be shaped differently. Some black holes are perfectly spherical - like a ball. Other black holes bulge in the middle. Black holes will be spherical if they do not rotate. Black holes will bulge in the middle if they rotate.
Black holes are difficult to find because they do not let out any light. They can be found when black holes suck in other stars. When black holes suck in other stars, the black hole lets out X-rays, which can be seen by telescopes. Hawking talks about his bet with another scientist, Kip Thorne. Hawking bet that black holes did not exist, because he did not want his work on black holes to be wasted. He lost the bet.
Hawking realized that the event horizon of a black hole could only get bigger, not smaller. The area of the event horizon of a black hole gets bigger whenever something falls into the black hole. He also realized that when two black holes combine, the size of the new event horizon is greater than or equal to the sum of the event horizons of the two other black holes. This means that a black hole's event horizon can never get smaller.
Disorder, also known as "entropy", is related to black holes. There is a scientific law that has to do with entropy. This law is called the "second law of thermodynamics", and it says that entropy (or disorder) will always increase in an isolated system (for example, the universe). The relation between the amount of entropy in a black hole and the size of the black hole's event horizon was first thought of by a research student (Jacob Bekenstein) and proven by Hawking, whose calculations said that black holes emit radiation. This was strange, because it was already said that nothing can escape from a black hole's event horizon.
This problem was solved when the idea of pairs of "virtual particles" was thought of. One of the pair of particles would fall into the black hole, and the other would escape. This would look like the black hole was emitting particles. This idea seemed strange at first, but many people accepted it after a while.
Most scientists believe that the universe started in an explosion called the Big Bang. The model for this is called the "hot big bang model". When the universe starts getting bigger, the things inside of it also begin to get cooler. When the universe was first beginning, it was infinitely hot. The temperature of the universe cooled and the things inside the universe began to clump together.
Hawking also talks about how the universe could have been. For example, if the universe formed and then collapsed quickly, there would not be enough time for life to form. Another example would be a universe that expanded too quickly. If a universe expanded too quickly, it would become almost empty. The idea of many universes is called the "many-worlds interpretation".
Inflationary models are also discussed in this chapter, and so is the idea of a theory that unifies quantum mechanics and gravity.
Each particle has many histories. This idea is known as Feynman's theory of sum over histories. A theory that unifies quantum mechanics and gravity should have Feynman's theory in it. To find the chance that a particle will pass through a point, the waves of each particle needs to be added up. These waves happen in imaginary time. Imaginary numbers, when multiplied by themselves, make a negative number. For example, 2i X 2i = -4.
Alexander Graham Bell
Alexander Graham Bell (March 3, 1847 - August 2, 1922) was a teacher, scientist, and inventor. He was the founder of the Bell Telephone Company.
Alexander Graham Bell was born in Edinburgh, Scotland. His family was known for teaching people how to speak English clearly (elocution). Both his grandfather, Alexander Bell, and his father, Alexander Melville Bell, taught elocution. His father wrote often about this and is most known for his invention and writings of Visible Speech. In his writings he explained ways of teaching people who were deaf and unable to speak. It also showed how these people could learn to speak words by watching their lips and reading what other people were saying.
Alexander Graham Bell went to the Royal High School of Edinburgh. He graduated at the age of fifteen. At the age of sixteen, he got a job as a student and teacher of elocution and music in Weston House Academy, at Elgin in Morayshire. He spent the next year at the University of Edinburgh. While still in Scotland, he became more interested in the science of sound (acoustics). He hoped to help his deaf mother. From 1866 to 1867, he was a teacher at Somersetshire College in Bath, Somerset.
In 1870 when he was 23 years old, he moved with his family to Canada where they settled at Brantford, Ontario. Bell began to study communication machines. He made a piano that could be heard far away by using electricity. In 1871 he went with his father to Montreal, Quebec in Canada, where he took a job teaching about "visible speech". His father was asked to teach about it at a large school for deaf mutes in Boston, Massachusetts, but instead he gave the job to his son. The younger Bell began teaching there in 1872. Alexander Graham Bell soon became famous in the United States for this important work. He published many writings about it in Washington, D.C.. Because of this work, thousands of deaf mutes in the United States of America are now able to speak, even though they cannot hear.
In 1876, Bell was the first inventor to patent the telephone, and he helped start the Bell Telephone Company with others in July 1877. In 1879, this company joined with the New England Telephone Company to form the National Bell Telephone Company. In 1880, they formed the American Bell Telephone Company, and in 1885, American Telephone and Telegraph Company (AT&T), still a large company today. Along with Thomas Edison, Bell formed the Oriental Telephone Company on January 25, 1881.
Bell married Mabel Hubbard on July 11, 1877. He died of diabetes at his home near Baddeck, Nova Scotia in 1922.
Bell's genius is seen in part by the eighteen patents granted in his name alone and the twelve that he shared with others. These included fifteen for the telephone and telegraph, four for the photophone, one for the phonograph, five for aeronautics, four for hydrofoils, and two for a selenium cell. In 1888, he was one of the original members of the National Geographic Society and became its second president.
He was given many honors.