A Brief History of Time

A Brief History of Time

by

Stephen Hawking

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Theories of Relativity Term Analysis

Albert Einstein first suggested the theory of relativity in 1905, which states every observer has their own unique measure of time, though the laws of science and the speed of light are the same for all observers. The later proposed special theory of relativity neglects gravitational effects. Einstein proposed the general theory of relativity in 1915, which is widely used today. It incorporates gravity, not as a force, but as a consequence of the fact space-time is not flat. Instead, it is curved by mass and energy, and objects take as straight a line as they can as they move through this warped space-time.
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Theories of Relativity Term Timeline in A Brief History of Time

The timeline below shows where the term Theories of Relativity appears in A Brief History of Time. The colored dots and icons indicate which themes are associated with that appearance.
Chapter 1
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...applying Newton’s law of gravity. Albert Einstein’s slightly different prediction, via his general theory of relativity, matched with what was seen, a critical confirmation of his new theory. Newton’s theory is... (full context)
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Scientists now describe the universe in terms of the general theory of relativity and quantum mechanics—both great achievements of the first half of the 20th century. The first... (full context)
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...searching for the ultimate theory becomes hard to justify. Then again,  people argued this about relativity and quantum mechanics, which eventually gave us nuclear power and microelectronics. Thus, the search for... (full context)
Chapter 2
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This new idea was called the theory of relativity, which meant that the laws of science were the same for all freely moving observers.... (full context)
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...amount of energy to do so. Normal objects are thus stuck within the limits of relativity and cannot reach light speed. Only light, or other things with no mass, i.e. waves,... (full context)
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Relativity has changed the way we see space and time forever. Under Newton's theory, observers would... (full context)
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Under the theory of relativity, distance is determined by time and light speed, so every observer must agree on the... (full context)
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...and Poincaré did back in 1905, the resulting theory is called the special theory of relativity. All light cones would be identical and point in the same direction as light speed... (full context)
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...This implies gravitational effects take effect instantly, which doesn't work with the special theory of relativity's idea that nothing moves at or above the speed of light. (full context)
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In 1915, Einstein put forward the idea of the general theory of relativity. He suggested that gravity is not like other forces. Rather, it is the result of... (full context)
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In general relativity, objects take a straight route in curved, four-dimensional space-time, but seem to take curved routes... (full context)
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...straight paths through three-dimensional space. Light should also be bent by gravity, according to general relativity. Light cones near the sun ought to bend slightly inward, because of the sun's mass.... (full context)
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According to general relativity, time should also run more slowly when closer to objects with large mass, like the... (full context)
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Newton's laws ended the idea of absolute space and relativity ended the idea of absolute time. If twins separated, with one living on top of... (full context)
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...what took place within them. People thought they both went on forever. But with general relativity that thinking has changed considerably. Space and time are affected by objects' movement and forces,... (full context)
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...in theoretical physics, and later he showed with Roger Penrose that Einstein's general theory of relativity suggested there was indeed a beginning and end to the universe. (full context)
Chapter 3
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...believing in a static universe. Even Einstein overlooked this idea in his general theory of relativity. Instead he thought up a kind of anti-gravitational force he called the cosmological constant. (full context)
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...space is curved, like the surface of the earth. When combining the general theory of relativity with quantum mechanics (as discussed later), space and time can be finite without a boundary.... (full context)
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...bang. They did show that a big bang was possible under the general theory of relativity. (full context)
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...our understanding has changed significantly. Penrose and Hawking’s work showed that Einstein’s general theory of relativity is only a partial theory. It breaks down at the beginning of the universe. When... (full context)
Chapter 4
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Einstein’s general theory of relativity is considered a classical theory because it does not include quantum mechanics. This does not... (full context)
Chapter 5
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...Dirac was the first to propose a theory consistent with both the general theory of relativity and quantum mechanics. He showed mathematically how spin ½ works and predicted that electrons should... (full context)
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...in the same way as our own. Any theory that obeys the general theory of relativity and quantum mechanics must follow the symmetry of CPT. J. W. Cronin and Val Fitch... (full context)
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...is what happens in that time, when they become a black hole, that draws general relativity and quantum mechanics together. (full context)
Chapter 6
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...1928 to work with Sir Arthur Eddington, one of the only people who understood general relativity at the time, Subrahmanyan Chandrasekhar worked out how big a star needed to be to... (full context)
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Some options available within general relativity let the astronaut escape through a wormhole, to appear somewhere else in the universe. But... (full context)
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General relativity states that moving objects give off gravitational waves, which bend space-time. These waves carry energy... (full context)
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...of the same size would be identical. One could use Karl Schwarzschild’s solutions to general relativity equations to describe them. (full context)
Chapter 7
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...radiation rubbed people up the wrong way, and was the first significant example of general relativity and quantum theory combining. John G. Taylor opposed Hawking when he announced these discoveries. But... (full context)
Chapter 8
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Einstein’s general relativity predicted that space-time began as a singularity in the big bang, and ends in the... (full context)
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General relativity alone cannot answer these questions. Its laws and all laws we have so far break... (full context)
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To know how the universe started, we need laws that hold at the beginning. General relativity relies on singularities, which involve the break down of scientific law. Really, what singularity theories... (full context)
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Another feature of the unified theory of quantum mechanics and general relativity is that gravity is represented in a curved space-time. Applying the sum over histories to... (full context)
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In both quantum and general relativity theory, if we know the make up of the universe at the beginning, we can... (full context)
Chapter 9
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General relativity cannot tell us what happened at the very beginning or what happens in singularities, because... (full context)
Chapter 10
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Mathematician Kurt Gödel suggested a new model of space-time in 1949 under general relativity. He said the whole universe was rotating in the direction spinning tops point. As a... (full context)
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Other space-times allowed by the rules of general relativity do allow for time travel, and fit what one can observe in the universe. For... (full context)
Chapter 11
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Previous chapters covered general relativity, incomplete gravity theories,  and the three forces that can be combined in grand unified theories,... (full context)
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Thus, the first step is to combine the uncertainty principle and general relativity. This has already resulted in significant rethinks, such as black holes not being black and... (full context)
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...predict these values, which is a serious drawback. When incorporating the uncertainty principle and general relativity one can either adjust the strength of gravity or the cosmological constant. But this still... (full context)
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...gravity, but only if the tension were significantly higher. This would leave most of general relativity’s predictions unchanged, except on the miniscule level. Their work didn’t gain much attention at first.... (full context)
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...to date on all subjects. Eddington suggested only two people understood the theory of general relativity in his day. Today many thousands do. If we were to find the unifying theory... (full context)
Chapter 12
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General relativity states there must have been a point of infinite density at the beginning, the big... (full context)