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“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.”
Did the universe have a beginning, and if so, what happened before then?
The earth’s shadow on the moon was always round, which would be true only if the earth was spherical.
The Greeks even had a third argument that the earth must be round, for why else does one first see the sails of a ship coming over the horizon, and only later see the hull?
All Newton himself ever said was that the idea of gravity came to him as he sat “in a contemplative mood” and “was occasioned by the fall of an apple.”)
“What did God do before he created the universe?” Augustine didn’t reply: “He was preparing Hell for people who asked such questions.” Instead, he said that time was a property of the universe that God created, and that time did not exist before the beginning of the universe.
But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant galaxies are moving rapidly away from us. In other words, the universe is expanding.
Hubble’s observations suggested that there was a time, called the big bang, when the universe was infinitesimally small and infinitely dense.
If there were events earlier than this time, then they could not affect what happens at the present time. Their existence can be ignored because it would have no observational consequences.
Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory.
The general theory of relativity describes the force of gravity and the large-scale structure of the universe,
Quantum mechanics, on the other hand, deals with phenomena on extremely small scales,
Our present ideas about the motion of bodies date back to Galileo and Newton.
Galileo’s measurements were used by Newton as the basis of his laws of motion.
The lack of an absolute standard of rest meant that one could not determine whether two events that took place at different times occurred in the same position in space.
The nonexistence of absolute rest therefore meant that one could not give an event an absolute position in space, as Aristotle had believed.
Both Aristotle and Newton believed in absolute time. That is, they believed that one could unambiguously measure the interval of time between two events, and that this time would be the same whoever measured it, provided they used a good clock.
Newton’s theory had got rid of the idea of absolute rest, so if light was supposed to travel at a fixed speed, one would have to say what that fixed speed was to be measured relative to. It was therefore suggested that there was a substance called the “ether” that was present everywhere, even in “empty” space.
Albert Einstein, pointed out that the whole idea of an ether was unnecessary, providing one was willing to abandon the idea of absolute time.
Only light, or other waves that have no intrinsic mass, can move at the speed of light.
In other words, the theory of relativity put an end to the idea of absolute time!
In effect, the meter is defined to be the distance traveled by light in 0.000000003335640952 second, as measured by a cesium clock. (The reason for that particular number is that it corresponds to the historical definition of the meter—in terms of two marks on a particular platinum bar kept in Paris.)
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.
The nearest star, called Proxima Centauri, is found to be about four light-years away (the light from it takes about four years to reach earth), or about twenty-three million million miles.
And that meant that the universe could not be static, as everyone previously had thought, but is in fact expanding; the distance between the different galaxies is growing all the time.
As the balloon expands, the distance between any two spots increases, but there is no spot that can be said to be the center of the expansion.
It is perhaps ironic that, having changed my mind, I am now trying to convince other physicists that there was in fact no singularity at the beginning of the universe—as
Laplace suggested that there should be a set of scientific laws that would allow us to predict everything that would happen in the universe,
The doctrine of scientific determinism was strongly resisted by many people, who felt that it infringed God’s freedom to intervene in the world,
Heisenberg showed that the uncertainty in the position of the particle times the uncertainty in its velocity times the mass of the particle can never be smaller than a certain quantity, which is known as Planck’s constant.
This approach led Heisenberg, Erwin Schrödinger, and Paul Dirac in the 1920s to reformulate mechanics into a new theory called quantum mechanics, based on the uncertainty principle.
Quantum mechanics therefore introduces an unavoidable element of unpredictability or randomness into science.
Einstein never accepted that the universe was governed by chance; his feelings were summed up in his famous statement “God does not play dice.”
The only areas of physical science into which quantum mechanics has not yet been properly incorporated are gravity and the large-scale structure of the universe.
There is thus a duality between waves and particles in quantum mechanics:
Aristotle believed that all the matter in the universe was made up of four basic elements—earth, air, fire, and water.
the electromagnetic force between two electrons is about a million million million million million million million (1 with forty-two zeros after it) times bigger than the gravitational force.
a star that was sufficiently massive and compact would have such a strong gravitational field that light could not escape: any light emitted from the surface of the star would be dragged back by the star’s gravitational attraction before it could get very far.
(According to some accounts, a journalist told Eddington in the early 1920s that he had heard there were only three people in the world who understood general relativity. Eddington paused, then replied, “I am trying to think who the third person is.”)
but the problem of understanding what would happen to such a star, according to general relativity, was first solved by a young American, Robert Oppenheimer, in 1939. His result, however, suggested that there would be no observational consequences that could be detected by the telescopes of the day. Then World War II intervened and Oppenheimer himself became closely involved in the atom bomb project.
One could well say of the event horizon what the poet Dante said of the entrance to Hell: “All hope abandon, ye who enter here.”
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.
How could we hope to detect a black hole, as by its very definition it does not emit any light? It might seem a bit like looking for a black cat in a coal cellar.
We also have some evidence that there is a much larger black hole, with a mass of about a hundred thousand times that of the sun, at the center of our galaxy.
A black hole with a mass a few times that of the sun would have a temperature of only one ten millionth of a degree above absolute zero.
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.
One possible answer is to say that God chose the initial configuration of the universe for reasons that we cannot hope to understand. This would certainly have been within the power of an omnipotent being, but if he had started it off in such an incomprehensible way, why did he choose to let it evolve according to laws that we could understand?
(If each configuration is equally probable, it is likely that the universe started out in a chaotic and disordered state, simply because there are so many more of them.)
If the universe is indeed spatially infinite, or if there are infinitely many universes, there would probably be some large regions somewhere that started out in a smooth and uniform manner. It is a bit like the well-known horde of monkeys hammering away on typewriters—most of what they write will be garbage, but very occasionally by pure chance they will type out one of Shakespeare’s sonnets.
why is the universe so smooth? This is an example of the application of what is known as the anthropic principle, which can be paraphrased as “We see the universe the way it is because we exist.”
