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A Brief History of Time | Context


Three Giants of Astronomy

It was English mathematician and physicist Sir Isaac Newton who stated in a 1675 letter to another scientist, Robert Hooke, that "if I have seen further, it is by standing upon the shoulders of giants." Such implied humility that any scientist's achievements are not possible without understanding those who have paved the way is a thought Stephen Hawking makes frequent mention of in A Brief History of Time. In the back matter following Chapter 12 of his book, Hawking acknowledges three giants of astronomy upon whose shoulders his own achievements in physics depended.

Despite his grumpy nature, Newton advanced the range of mathematics into calculus, without which the theorems of physics would not be possible. He also expanded our understanding of optics (the science of light), making it possible to speculate on the origin and future of the universe. And Newton's discovery of three laws of motion plus one on gravity is the starting point in developing an understanding of the miniscule and the vast properties of matter.

Another giant of astronomy Hawking acknowledges is German theoretical physicist Albert Einstein, whose famous equation E = mc2 pointed the way to the theories of relativity. Einstein's explanation of the photoelectric effect (how particles that have absorbed electromagnetic radiation are emitted) not only brought him the Nobel Prize in 1921 but also gave Hawking a stepping stone for explaining the nature of black holes.

The struggles of the Italian astronomer Galileo Galilei to gain acceptance for his observations is a reminder that any startling departure from accepted truth (such as the existence of black holes) will always be met with opposition. Galileo's advancements in mathematics as the language of "the book of nature" by which observations can be understood was certainly a "shoulder" upon which both Newton and Hawking stood to gain a more complete picture of the world.

The Theory of Relativity versus the Theory of Quantum Mechanics

Hawking and other physicists, supported by increasingly sophisticated technology, draw ever closer to a reconciliation between theories of relativity and quantum mechanics. But the laws governing large bodies of matter at great distance such as stars and galaxies (the theory of relativity), and those governing subatomic units of matter such as photons, neutrons, and quarks at miniscule distances (quantum mechanics) do not agree.

The main obstacle to getting these fundamental theories to agree is the force of gravity, which behaves differently in the realm of the vast than it does in the realm of the very tiny. Hawking defines gravity from Newton's model in Chapter 1 as a relation between the mass of a body and its distance from another body of lesser or greater mass (Chapter 1). But this means that if the force of gravity is dependent on both mass and distance, then items at the quantum level that have little or no mass at tiny distances cannot obey the laws of gravity. It is in the study of black holes and what their behavior (in terms of gravity) tell us about the big bang theory of the origin of the universe (a theory that the universe began with a cosmic explosion) that Hawking believes will lead to a basic, encompassing theory to explain everything from the tiniest units of matter to the largest galaxies (Chapters 6, 7, and 8).

A General Unified Theory and Grand Universal Theories

As Hawking states in Chapter 5, grand universal theories (GUTs), such as quantum field theory, aren't all that grand or universal because they do not include gravity. Still, he does not discount them entirely: "Nevertheless, they may be a step toward a complete, fully unified theory." As of the publication of A Brief History of Time, Hawking describes the use of GUTs in physics as something like the way we use maps: "Each map is valid only in a limited region, but different maps will have a region of overlap" (Chapter 11). And although physicists have not yet come up with a general unified theory that brings together overlapping GUTs, they do know what some of the properties it is likely to have.

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