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Notes from About Time, 1996

by Paul Davies

Time has always lain outside the domain of quantum physics and attempts to incorporate it end up by eliminating it. Time vanishes!

One second is no longer 1/86,400 of a day: it is 9,192,631,770 beats of a cesium atom.

Running like a common thread through the history of human thought, East and West, North and South, is a belief that time is an illusion, an elaborate product of the human mind.

Time itself is but an imperfect “moving image of Eternity which remains forever at one.”

During the nineteenth century most astronomers believed that the universe remained on average much the same from epoch to epoch.

In neutron stars matter is in the neutron state and has a density of a billion metric tons per cubic centimetre. The enormous gravity of these objects enables some of them to rotate over a thousand times a second.

The sun circles the earth at about thirty kilometres per second (100,000 kilometres per hour) and the sun orbits the galaxy at 220 kilometres per second.

The idea that events in time are laid out “all at once” motivated Einstein to write, ‘The distinction between past, present and future is only an illusion, even if a stubborn one.’

Common sense is that layer of prejudices laid down in the mind prior to the age of eighteen.

Albert Einstein

Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.

Hermann Minkowski

At first Einstein dismissed Minkowski’s new four-dimensional geometry as “superfluous pedantry.” But he came round to the idea in due course.

Herman Weyl once wrote: ‘The world does not happen, it simply is.’ Thus the proverb ‘What’s done is done’ would seem to apply with equal force to the future as to the past.

Near the end of his days Einstein confessed that the problem of the now “worried him seriously.” In conversation with the philosopher Rudolf Carnap he conceded that there is “something essential about the now,” but expressed the belief that, whatever it was, it lay, “just outside the realm of science.”

In fact the theory of relativity does not say that ‘nothing can go faster than light.’ Rather it forbids any particle from crossing the light barrier.

About 90 percent of physicists would be against the idea of tacheons (faster than light particles).

The best clock is accurate to better than one part in a hundred trillion over three hundred seconds.

According to Einstein’s general theory of relativity both time and space are warped. A gravitational field is not a field of force at all, but a curvature in the geometry of spacetime.

In 1919 the highly respected British astronomer Sir Arthur Eddington had managed to confirm a key prediction of the general theory of relativity the very slight bending of a starbeam by the sun’s gravity.

Einstein never took his Jewishness very seriously and remained a sort of reverent atheist throughout his life.

There is good evidence that at least one million-solar-mass black hole lurks at the centre of the Milky Way.

In 1929 Edwin Hubble announced one of the most momentous scientific discoveries of all time: the universe is expanding.

Radioactive dating gives a figure of 4.5 billion years for the age of the earth.

The discovery of the cosmic background heat radiation in 1965 knocked the stuffing out of the steady-state theory for good.

In 1927 the Belgian cleric and mathematician Monsignor Georges Lemaitre discovered that Einstein’s proposed tug-of-war between gravitational attraction and the cosmological repulsion couldn’t work because it was unstable. Einstein had introduced the cosmological term thereby marring the mathematical elegance of the gravitational-field equations because of his adherence to the prevailing notion of a static universe. He later called the cosmological term the biggest blunder of his life. Indeed, the term has become known as “Einstein’s fudge factor.”

We all know what light is; but it is not easy to tell what it is.

Samuel Johnson

Einstein wanted to believe that quantum particles such as photons are really ‘out there’ with a complete set of well-defined properties before anyone observes them.

It is not possible in general to say when things ‘actually happen’ in quantum physics.

Quantum cosmology has abolished time as surely as the mystic’s altered state of consciousness.

In a quantum description there is no single spacetime with a well-defined geometry that is ‘there’; instead, you must imagine all possible geometries all possible spacetimes, space warps and timewarps mixed together in a sort of cocktail, or ‘foam.’

The general rule is: once foamy and fuzzy, always foamy and fuzzy. Apparently, only very special initial conditions that is, only universes which start out with very specially configured foam will evolve into approximately ‘classical’ (i.e. nonquantum) realities, possessing time, space and well-defined macroscopic material objects.

The great cosmic drama could be like a movie a sequence of static frames, run past us at such a speed we don’t notice the joins. It may just give the illusion of continuity. On the experimental front, physicists routinely study sequences of events happening on a time scale of about a hundred-trillion-trillionth of a second, and no hint of temporal discontinuity has shown up yet.

The crucial property of quantum physics is that cause and effect aren’t rigidly linked, as they are in classical, commonsense physics. There is indeterminism, which means some events ‘just occur’ spontaneously so to speak without a prior cause in the normal meaning of the word.

David Bohm, famed for his writing and philosophical works, particularly among readers of a mystical bent, was a curiously isolated figure in the physics community. He was perhaps best known for his 1950s textbook on quantum mechanics. But very early on he decided he didn’t like quantum mechanics as conventionally formulated by Nils Bohr. Bohm thus took up the lonely torch of quantum dissent where Einstein had left it on his deathbed.

In my opinion progress in science is usually made by dropping assumptions.

David Bohm

The concept of antimatter dates back to about 1930 and a famous prediction by Paul Dirac. Within a year or two Dirac’s ‘positrons’ had been found in cosmic-ray showers.

John Wheeler proposed that all the electrons in the universe are really one and the same particle, simply bouncing back and forth in time!

We like to suppose that cause precedes effect. We would be uncomfortable with the idea that a breaking window causes a stone to be thrown.

Time is nature’s way to keep everything from happening at once.

John Wheeler

In spite of the power and beauty of Einstein’s general theory of relativity, it was relegated to the back-waters of physics for decades, largely because its predicted effects were usually small and hard to test. But postwar developments changed all this. Two decades after Einstein’s death in 1955 the subject of general relativity finally blossomed into a fully developed discipline.

Pressure, in addition to mass and energy, also creates gravity, though its effect is normally negligible. For an ordinary body like the Earth, its internal pressure contributes no more than a billionth of its surface gravity (adding less than a milligram to your weight).

The upshot of the recent flurry of work on time travel is that there is nothing very obvious in the laws of physics to prevent it happening in principle, although in all theoretical examples to date it can be achieved only by manipulating matter and energy in the most extreme and fanciful manner.

Travel into the past, or even the possibility of signalling the past, opens up a Pandora’s box of puzzles and paradoxes.

The laws of the universe must by definition describe a consistent reality.

Since Einstein, physicists have generally rejected the notion that events ‘happen,’ as opposed to merely exist in the four-dimensional spacetime continuum.

The Greek philosopher Zeno argued that all motion was impossible, since at any given instant of time an apparently moving object is in fact static. He considered the flight of an arrow and pointed out that at every moment in its trajectory it occupies one and only one ‘block’ of space. Since it can’t occupy more than one space at a particular moment, it must be stationary at that moment. And as this state of affairs is true at each and every moment, there can be no motion of any kind.

The incompatibility between a moving now and a static time coordinate is manifested in the arresting question: “How fast does time flow?” We all know the answer: one second per second. But how can time move ‘in time?’

For me, ‘now’ is when I experience the world. So why is it the twentieth century now? In other words, why is it ‘now’ now? Is there something special about my now as opposed to the now of historical figures like Napoleon or Caesar.

According to one estimate about 10 percent of the people who have ever lived are living now.

To the physicist our descendants are ‘there’ in the future.

Clocks don’t go ‘tick-tock’ at all; they go ‘tick-tick,’ every tick producing the same sound. It’s just that our consciousness run two successive ticks into a single ‘tick-tock’ experience but only if the duration between ticks is less than about three seconds.

Sensory deprivation can drastically alter the impression of time intervals.

The word Time came not from heaven but from the mouth of man.

John Wheeler

A German research team found that in some cases brain cells start firing as long as a second or more before a voluntary physical movement actually begins. It is almost as if your brain knows what ‘you’ are going to do some moments before you decide to do it!

Given that consciousness runs over half a second late and actions require the brain to ‘get ready’ for up to a second or more, it would seem as if a human being cannot consciously respond to an event in less than about a couple of seconds. This certainly contradicts experience.

In the 1920s Eddington declared that our impression of becoming, of a flowing time, is so powerful and central to our experience that it must correspond to something in the objective world.

Like Laplace, Einstein was a determinist at heart. He found quantum physics, with its inherent uncertainty and indeterminism, utterly repugnant.

A deterministic world is one in which the future is already contained in the present (just as the present was contained in the past) and nothing genuinely new ever happens. The ‘unfolding’ of the future is nothing more than the outworking of pure logic through the laws of dynamics.

A chaotic system is one which, although in a strict mathematical sense deterministic, is nevertheless so highly sensitive to minute disturbances that meaningful prediction over the long term is precluded.

The ‘collapse’ of multiple possibilities, of statistical expectations, into a unique actuality remains one of the great unsolved puzzles of physics.

The special theory of relativity has been tested to unprecedented accuracy, and appears unassailable.

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