Other than the spectacle of an obscured event horizon quivering before a bright sheet of background light, the most spectacular blackhole phenomenon astronomers can witness from the remoteness of Earth is a relativistic jet of plasma piercing the darkness of intergalactic space. Among the most dizzying cosmic displays in nature, these funnels of energetic particles probe the medium surrounding roughly one in 20 known supermassive black holes. A prominent jet was evident on the very first quasar photograph (of 3C 273), and glows even more brilliantly as a high-energy ray of light in modern Chandra images (see Fig. 1.2). For the most part, however, black-hole jets manifest themselves in a “parallel” universe – indeed, their ghostly apparitions pre-empted the discovery of supermassive black holes by several decades, though without any portent of what they would later reveal. And once again, astronomers can thank the telephone company for facilitating one of the most amazing advances in the history of science, on a par with the discovery – six decades later – of the cosmic microwave background radiation through the commercialization of space.

Not long after a demonstration that the substance of light behaves like a series of waves undulating through time and space, Guglielmo Marconi (1874–1937) successfully initiated transatlantic communications in 1901 using wireless radio.

Though some Hubble images of distant galaxies feature destructive collisions that could trigger quasar activity, others show that many normal, undisturbed aggregates of stars are oblivious to the cosmic thunder within their midst. This is an indication that a variety of mechanisms – some quite subtle – may be responsible for igniting a quasar. Whatever the formative process is, however, these supermassive objects seem to have spared their hosts from any obvious damage, so their prodigious outpouring of matter and radiation may be a shortlived phenomenon. Still, this observation is not sufficient to guide astronomers toward the identification of a coherent, single pattern of quasar birth and growth.

For years, astrophysicists concerned with the nature of supermassive black holes have been asking themselves a cosmological “chicken and the egg” question: “Which came first, the gargantuan pit of closed spacetime, or the lively panorama of gilded stars and glowing gas that we call a galaxy?”

Prior to a remarkable recent discovery that now seems to have answered this question for the majority of cases, the evidence in favor of black holes appearing first was anchored by the telling observation that the number of quasars peaked 10 billion years ago, early in the universe's existence. The light from galaxies, on the other hand, originated much later – after the cosmos had aged another 2 to 4 billion years.

Settling on the banks of the Tiber river, the Latini would establish a city in the seventh century BC that later came to dominate much of the civilized world. They used the word gravis to denote heavy or serious, and the corresponding noun gravitas for heaviness and weight. Our modern word gravity, and its more precise derivative gravitation, trace their roots to this early usage, which itself is linked to a yet older root that includes the Sanskrit guru (for weighty or venerable), among others. The ancients were evidently quite aware of this ever-present property of matter – that it should have an unwavering attraction toward the Earth – though up to the time of Galileo and Newton, gravity simply remained a name for the phenomenon, without any explanation or even an adequate description.

THE INEXORABLE FORCE OF GRAVITY

Toward the end of the seventeenth century, attempts to account for the behavior of objects changing their motion in response to external influences were primarily concerned with the nature of forces that one could easily identify. In the story of Goliath's slaying, for example, the stone was dispatched toward his forehead after David released the sling. Prior to that moment, the diminutive combatant was able to restrain the motion of the stone with a force applied by his hand mediated through the string. Newton argued that the Earth must itself be exerting an attractive force on matter since everything falls down in the same direction.

Supermassive black holes are certainly the most powerful objects in the universe, yet even this attribution may not adequately convey the severity with which they stress their surroundings. Yes, their force of attraction is inexorable, but more than this, it is – as far as we can tell – infinitely unassailable once matter approaches so close that even something moving at the speed of light cannot break free. The radius at which this happens is known as the black hole's event horizon, for nothing within it can communicate with the universe outside. Thus, we have no way of directly seeing such an object. Instead, its presence may be deduced on the basis of the shadow it casts before a bright screen, such as a dense cluster of stars. To have any hope of carrying out such an observation, however, we must be close enough to the highly concentrated mass to actually resolve the dark depression among the myriad other details likely to be present in its environment.

We become aware of a supermassive black hole primarily because of the incomparable cosmic power it exudes. For example, the image of 3C 273 in Fig. 1.2 attests to its nature as one of the brightest beacons in the visible universe. Yet it should be black, drawing everything into a catastrophic fall toward oblivion, releasing nothing – particles or light – to breach its cloak of secrecy.

Our view of the night sky is a panoply of stars choreographed to the galaxy's spiral melody. A deep exploration of the universe beyond our immediate neighborhood would therefore not be possible were it not for the occasional chance alignment of interstices among these swarming points of light. For ten consecutive days in December of 1995, the Hubble Space Telescope peered through just such a clearing, and produced our deepest ever view of the universe, graced with thousands of galaxies bursting into life at the dawn of time.

THE HUBBLE DEEP FIELD

Called the “Hubble Deep Field” (see Fig. 6.1), this image contains not only classical spiral and elliptical galaxies, but also boasts a rich variety of other galaxy shapes and colors that hint at the influences governing the evolution of the early universe. Some of these objects may have condensed within 1 billion years of the Big Bang.

Covering a speck of sky only one-thirtieth the diameter of the full moon, the view of the Hubble Deep Field (one quarter of which is shown here) is so narrow that just a few foreground stars in our galaxy are visible. Most of the objects contained within it are instead so distant that our eyes would have to be four billion times more sensitive in order for us to see them without the aid of a telescope.

If you were to imagine a description of nature whose constituents are so bizarre that even its originator refuses to allow for their actual manifestation, you would not have to go past the theory of general relativity. Created almost a century ago, it was perhaps the most anticipatory advancement in the history of physics. Its development was so visionary that none of the four significant tests applied to it since – two of which were adjudged to be of Nobel quality – have truly exposed the core of this remarkable theory, where the most abstruse distortions to the fabric of space and time are imprinted.

Einstein suspended his belief at the thought of a universe that would permit singularities to form, in which matter collapses inexorably to a point and becomes forever entombed. Yet this was the boldest consequence of his new description of gravity.

Remarkably, the idea that a gravitational field ought to bend the path of light so severely that the heaviest stars should then be dark was actually forged much earlier, in the context of Newtonian mechanics, toward the end of the eighteenth century. The Reverend John Michell argued in a paper published by the Philosophical Transactions of the Royal Society that, if a star was sufficiently massive, its escape velocity would have a magnitude exceeding even the speed of light, which, being comprised of particles, would then slow down and fall back to the surface.

Consciousness is a nonphysical property that cannot be defined in physical terms, and indeed does not exist in the physical universe. It is impossible to determine by any physical means if an object is conscious. When presented with miscellaneous objects, such as an orange, a chair, a clock, a human being, a candle flame, and a crystal, an experimenter cannot determine by means of experiments with physical equipment which of these objects is conscious. This normally would constitute sufficient proof that consciousness does not exist anywhere in any form. One of the objects, however, could be myself, and I know beyond all doubt that I am a conscious being. I am more certain of my consciousness than was Dr. Johnson of the concreteness of his stone. Consciousness beyond all doubt exists, yet demonstrably does not exist in the physical universe. Consciousness belongs to the Universe not the physical universe. No other conclusion seems possible.

Everything is spread out in time. Things stretch away into the recent past as recalled in our memories and newspapers, and into the distant past as recounted by historians and geologists. They also stretch away into the near future as anticipated in our plans and foretold by fortune tellers, and into the distant future as predicted by geologists and astronomers.

Say no more of time! If you want a peaceful mind go no farther. Every step in quest of understanding time leads to greater bewilderment. Much of the problem is that our languages inadequately express our experiences of time.

“What, then, is time?” asked Augustine of Hippo in the Confessions. “If no one asks me, I know what it is. If I wish to explain what it is to him who asks me, I do not know.” He viewed time as a continuous temporal sequence from the past to the future, from Creation in the beginning to Judgment in the end. Time thus displays a historiography ordained by either God, fate, or natural law. This is much the same as our present commonsense general view. It caused him much perplexity, some of which is expressed by Austin Dobson in The Paradox of Time:

Some of the problem is easily stated: Nothing displayed in time can change! If you think of time in terms of space, as an extension, a sort of one-dimensional space, with everything displayed in it, such as birthdays, anniversaries, holidays, then everything has its fixed moment in time and cannot possibly change.

We have a picture of a seamless spacetime projecting into the space and time of each observer's world line. Though elegant and economic, in one sense it differs little from the Newtonian picture. Space in the Newtonian scheme was just a sort of nothing (a sideless box) spanning everything, and time was a similar sort of nothing in which everything also had location. In the theory of special relativity both came together to form an expanse of spacetime containing everything that again was just a sort of nothing (just a bigger sideless box).

Then in 1916 Einstein advanced the theory of general relativity and the picture changed dramatically. (How dramatically was not fully realized for many years.) Spacetime lost its state of nothingness and acquired a tangible physical reality. Gravity ceased to be a mysterious astral force acting instantaneously at a distance and became a property of dynamic curved spacetime.

In the new scheme spacetime itself guides the heavenly bodies and the old astrological action at a distance turned out to be the curvature of space and time combined into spacetime. We now have a spacetime that pulls and pushes and transmits shivers and shakes at the speed of light. We cannot eat spacetime, but it can be hit, and can hit back, and can eat us if we stray too close to a black hole. Spacetime in general relativity springs to life and becomes an active participant in the physical universe.

In the preface to the first edition of Masks of Universe I wrote: “At first I thought this book would take me only a few months to write. After all, the basic idea was simple, and only a few words should suffice to make it clear and convincing. But soon this illusion was shattered. A few months grew into three years, and now I realize that thirty years would not suffice. But enough! Other work presses, and life is too short.” Here I am, not thirty years but almost two decades later writing the preface to the second edition and struggling again to make clear the “simple idea.”

The idea rests on the distinction between Universe and universes. The Universe by definition is everything and includes us experiencing and thinking about it. The universes are the models of the Universe that we construct to explain our observations and experiences. Beneath the deceptive simplicity of this idea lies a little-explored realm of thought.

No person can live in a society of intelligent members unless equipped with grand ideas of the world around. These grand ideas – or cosmic formulations – establish the universe in which that society lives. The universes that human beings devise and in which they live, or believe they live, organize and give meaning to their experiences.

The Universe is everything. It includes us and the rational universes we collectively devise. Each universe unifies a society and dictates the “true” facts. Individuals suppose with unfailing confidence that their particular universe is the Universe, and their confidence is not in the least shaken by the fact that our ancestors lived in very different universes and our descendants in the future will live also in totally different universes. In all universes things have their causes, often hidden from ordinary mortals. We depend on our wise men – emperors, kings, shamans, priests, sages, prophets, and professors – to put us right and tell us the “true” facts. As long as somebody reliable knows the truth, all is right with the universe.

All universes have their rules of containment that define what is included as fitting and what is excluded as unfitting. Thales said the Ionian universe consisted of water; Anaximenes said air; Heraclitus said fire; Xenophanes said earth; Empedocles said earth, water, air, and fire. Democritus said the Atomist universe consisted only of atoms and the void; all else was illusion and opinion. Plato said the Platonic universe consisted of the eternal verities of the Mind; all else was shadow and deception. Aristotle said the Aristotelian universe consisted of earth, water, air, fire, and ether in ascending order, animated by Ideas, and nothing existed beyond the sphere of the stars. Saint Augustine said the Christian universe consisted of the Word of God, and all else was heresy.

The telescope, microscope, thermometer, barometer, precision clock, air pump, and other seventeenth-century inventions preceded the Age of Reason in the eighteenth century. The age of enlightened reason commenced with prophets proclaiming visions of a new universe: “I feel engulfed in the infinite immensity of spaces whereof I know nothing and which know nothing of me, I am terrified. … The eternal silence of these infinite spaces alarms me,” said Blaise Pascal. And “behold a universe so immense that I am lost in it. I no longer know where I am. I am just nothing at all. Our world is terrifying in its insignificance,” said Bernard de Fontenelle.

The mechanistic universe of the eighteenth century more than fulfilled the promise of the prophets. Outfitted with laws uniting the Earth and the heavens, with self-running celestial mechanistic systems distributed throughout endless space, with time ticking away regularly as in Huygens's precision pendulum clock, the mechanistic universe opened up the prospect of the human mind able at last to solve all the riddles of nature.

Lofty thoughts that formerly soared among the towers of the Eternal City descended to street level in an exhilarating new Earthly City. Pious otherworldly preoccupations transformed into practical worldly occupations. The reborn world was bright and young, free of the late medieval conviction that all was senile and exhausted. The rejuvenated human sciences, led by “lapsed Christians,” surged forward, achieving reforms that nowadays we take for granted as characteristic of Western society.

We take space and time for granted. Normally they do not trouble us, yet whenever we think about them we become puzzled.

Space seems simple enough. Here it is, all around us, stretching away and spanning everything in the external world. We are surprised when told that people in other cultures have different ways of regarding space. What is there about it that can possibly be different? Edward Hall in The Hidden Dimension says, “there is no alternative to accepting the fact that people reared in different cultures live in different sensory worlds” – in other worlds of space. It seems that the Arabs, Japanese, Hopi, and the people of many other cultures have different modes of expression concerning arrangements and relations in space; they live in different mental worlds – in other worlds of space.

Time is much more puzzling. Here it is in our imagination, stretching away, spanning everything in the past, present, and future. But unlike space it is not all around us and directly accessible. We experience time within ourselves, it seems, and cannot perceive it directly in the external world. Those intervals of minutes and hours on the face of a clock are actually intervals of space. A second cannot be displayed directly in pure form in the external world in the same way as a centimeter.

We live in the Solar System on the planet Earth that revolves with other planets around a star called the Sun. Light from the Sun hurrying at great speed takes 500 seconds to reach the Earth and five hours to reach the far-flung planet Pluto. The Earth that to us seems large is dwarfed by the Solar System with its whirling planets.

Starlight from the nearest stars travels for years before reaching the Earth. If we imagine the Sun having the size of a grain of sand, the nearby stars on the same scale would be at a distance of one hour's drive on an interstate highway. Scattered out to enormous distances in all directions are a hundred billion stars that constitute the whirlpool system called our Galaxy. The Galaxy – a glittering carousel of stars across which light takes 100,000 years to travel and around which the Sun journeys once every 200 million years – seems incomprehensibly large compared with the solar system.

Much has been discovered about the Galaxy: its many kinds of stars, sunlike stars, blue, yellow, and red giants, binary stars, white dwarfs, and dense neutron stars; its great spiral disk seen by us as the Milky Way where clouds of glowing gas and obscuring dust give birth to new stars; its even greater halo of very old stars and globular clusters; and still much that remains to be discovered.

Newton's universe of uniformly distributed stars has become Wright's universe.

Etienne Tempier, Bishop of Paris, roundly condemned all who dared to trifle with the power of the supreme being. Scholars and divines were free to admit reason into matters of faith provided full acknowledgment was made to God as an all-powerful being free of self-contradiction. Here was the Trojan Horse, introduced by the well-intentioned bishop, from which sallied forth in years to come thoughts that would topple the towers of the medieval universe.

Professors at Oxford and Paris in the fourteenth century made great progress in clarifying the nature of space, time, and motion. William Heytesbury and his colleagues at Merton College defined velocity and acceleration and then succeeded in calculating by graphical methods the distance traveled in an interval of time by a body having constant acceleration. William of Ockham participated in these studies while fighting a battle against needless abstractions. His celebrated principle of theoretical parsimony – known as Ockham's razor – states that in the use of concepts “it is foolish to accomplish with a greater number what can be done with fewer.”

Jean Buridan, a professor at Paris and formerly Ockham's student, revived the notion of impetus that can be traced back to Hipparchus in the second century B.C. and is now referred to as momentum. According to Buridan, impetus is proportional to the velocity of a body and also its quantity of matter (now referred to as mass), and the impetus of a thrown body maintains the body in a state of motion.

An unidentified English author of the fourteenth century, who was probably a priest, wrote

Like other contemplative mystics of the Middle Ages the author discovered that thought could not unveil the face of God: “By love may he be gotten and holden; but by thought neither.” God, the Cloud of Unknowing, was beyond articulation, and the source of all articulations.

Contemplative mystics in the Middle Ages – Christian, Jewish, and Muslim – ranked among the most advanced thinkers of their time. Thus, Nicholas of Cusa, prince and statesman of the Roman Church, sagely recorded that “scientific superstition” is the expectation that science answers our every question.

In the West, and wherever else the modern physical universe now holds sway, sections of the public have caught up with the agnostic intellectuals of the nineteenth century.