How Old is Time?

How old is time?

This is a question a child might ask, and it is worthy of an answer. But who will answer it? Astronomers might say, "Fifteen billion years," referring to the approximate age of the universe according to modern cosmology. The child might ask, "Why?" or "How do you know?" or "Says who?"

An adult might rephrase this as, "By what standard?"

There are many means to measure time. But there is no such thing as an absolute time standard.

The writings of some religions depict the Creation much as the Big Bang theory does. Time had no meaning. There was no up, no down, no form. But there was a tremendous amount of something, being and not being, like and unlike matter. It was energy of a form not known even to the most vivid imagination, shining from a single point into an absolute void.

Cosmologists, those people who delve into the mysteries of the structure and origin of the universe, have probed back closer and closer to the beginning of time--an hour, a minute, a fraction of a second--but never have they been able to reach the exact moment of Genesis. It would seem that the details of that instant are for the Divine mind alone to know.

The most widely accepted modern theory of the universe is called the Big Bang, because it depicts the whole cosmos as having blown up like a superbomb about fifteen billion years ago. All the stuff of galaxies, stars and planets was once, it is thought, contained in a space smaller than an atom. Few dare attempt to explain from where this primeval seed came.

* * *

A year is the time for the earth to circle the sun. Our planet has revolved around its parent star some five billion times. Before that, there was no sun and no earth, and there was no year.

Other solar systems surely existed, before the formation of the earth and sun, with planets having similar orbital cycles. These can suffice as the standard for a year before the earth and sun were born.

Probing further back, a time presents itself in which the face of the universe was of another sort: no stars nor planets, but only a cooling, expanding, curdling primordial mass. How can one then speak of a year? Probing into the still more remote past, the cosmos was of a stuff unlike anything known or imaginable. This muddles the meaning of matter, energy, space and time.

Is there light if no one sees? Is there warmth, if there is no face for it to shine on? Perhaps. But it is the light and warmth of the unthinking, unconscious cell.

Some absolute standard for time is needed to truly know the age of the universe. What standard? Is there some aspect of the cosmos that has existed since the exact moment of Genesis?

All chemical elements emit and absorb energy at certain frequencies, at thousands, millions, billions or more times per second. For any given element, these frenzied vibrations are always the same, like atomic fingerprints. They are identical in the university lab and on Mars, Alpha Centauri and in the Andromeda galaxy.

The most abundant element in the cosmos is hydrogen, one electron orbiting one proton. A strong oscillation of this element occurs at a wavelength of twenty-one centimeters, in the ultra-high radio frequency band. This wavelength of energy is so common that some astronomers think alien civilizations might transmit beacon signals near the frequency, about 1.4 gigahertz (1.4 billion cycles per second).

A single cycle of this atom is a miniscule parcel of time, but a constant one. What better standard to use, than the regular heartbeat of the simplest and most abundant substance?

A year could be defined as the number of oscillations of hydrogen, at the twenty-one-centimeter wavelength, that take place during one orbit of the earth around the sun. It's a big number, but a constant one. Hydrogen is far older than the solar system. It is a better standard for measuring time.

But, as there was a time when there was no earth and no sun, there were once no electrons nor protons, and therefore no hydrogen. The hydrogen standard can work only back to a certain point. Maybe there's some basis for time even more fundamental than the simplest atomic element. What is it? Would it not break down, too, upon probing far enough back?

* * *

In the very first moments of its existence, the cosmos was unlike anything familiar today. Astrophysicist George Gamow has called this stuff ylem, from which all the known universe is made. Where did this fireball come from? Some people have flatly said that it was created by Divine will. Others say a scientific answer must exist, but that it, by its nature, defies resolution.

The ylem exploded with great outward force. All the galaxies in the universe are receding from each other, still carried by the momentum of the big bang. Some astronomers have devised other ways to explain the expansion of the universe, but most today agree that the cosmos was born in a primordial holocaust. The echo of this cataclysm has been heard with radio telescopes, like a whisper from the sky, betraying a secret. So ethereal is this cosmic sigh, that its discovery, in 1965, was an accident, a fluke in the apparatus of two engineers working for the Bell Labs.

What was the ylem like? It was dense, it was hot and it was bright. It did not have particles like protons, neutrons and electrons. Even the most fundamental specks known today, the quarks, might have sprung from something else, made in turn from still something else. It depends on how far back scientists are able to look.

Equations lose meaning at the moment of Creation. Denominators become zero. Division by zero is not defined.

In his book The First Three Minutes, Steven Weinberg describes events just after the primordial ylem exploded.  He divides events into frames. The first frame lasts about a hundredth of a second after the initial flash. It is implicitly assumed that the density and temperature were infinite, or practically so, at the exact moment of Creation.

When the cosmos was a hundredth of a second old, the temperature was extremely high. The density was phenomenal: all the matter in the entire known universe resided in a tiny parcel of space. The brilliance was not seen with living eyes, nor was it imaginable to mortal minds. A few photons of this radiation, greatly enfeebled by their long journey through time and space, fell into the antennas of Arno Penzias and Robert Wilson in 1965.

Weinberg takes time to etch a mental image of events in this first frame of the cosmic movie. Great things can and do take place in just a hundredth of a second: the invasion of a cell by a virus, the penetration of a sperm into an egg, the breaking-off of a part of a gene, the replication of DNA. All of the events to follow were encoded in that first few moments, as if the universe were indeed some living, evolving cell. In this span of time, says Weinberg, the young cosmos cooled from an infinite temperature, or one unknowably hot, to a mere hundred billion degrees Kelvin.

After the first hundredth of a second, Weinberg shows a universe that cools by a factor of about three for each frame succeeding.

At the end of the frame two, the temperature is thirty billion degrees. At the close of frame three, the temperature has fallen to ten billion degrees. But the hydrogen clock does not yet work, because protons and electrons don't yet exist. How old is the universe at this time? Weinberg gives the figure of one second at the end of frame three. Two frames later, at the end of the fifth quantum in Weinberg's model, the temperature has cooled to a billion degrees, and hydrogen has begun to form, electrons and protons having congealed from the hot quark matter. Now it is possible to define time by hydrogen oscillation. The clock has started to tick.

This leaves the first three minutes undefined according to any known standard. Who is to say, then, that it was really three minutes, and not three years, or three quadrillion years?

Someday, scientists will come up with a time standard even more fundamental than the oscillation of hydrogen atoms. How about the time it takes for light to travel the diameter of a proton? This will work as long as there were protons. But there weren't always protons. How about the time for light to go across a quark? That's okay as long as there were quarks. But even these particles could have formed from something else, still earlier in the evolution of the universe.

Could this unraveling process go on without end?

Perhaps the rate of time depends on the size and density of the universe. This effect is known to take place inside black holes, and it has been suggested that our universe is a black hole. Limitless speculation is possible when the equations say nothing. If there is no absolute time standard--and there can be none, if there exists nothing to act as an absolute clock--then the true age of the universe becomes a Godelian question. That is, there might be an answer, but science cannot find it.

* * *

The structure of atoms was not known until physicists mustered enough energy to bombard materials with high-speed, heavy particles. Probing the nucleus of the atom needed still more energy. Finally, protons were blasted and scientists learned that they are "bumpy." This took more energy yet.

In the early universe, temperatures were hot, and energy was concentrated. Matter could exist only in primitive states. Before a certain time there was only hydrogen. Further back, there were only protons and electrons. Earlier still, there were just quarks. But there was always energy.

s there a truly elementary particle that can't be divided? Yes: it is a particle that would need more energy, for its fragmentation, than is available from the whole universe. This is perhaps the sort of particle from which the cosmos sprang. When, and why, did it unfold as it has? A child asks, and no adult can answer.

You've probably heard of the hypothetical space traveler who leaves for some distant star, and comes back to see his own daughter older than himself. At speeds near the speed of light, the rate of time is slowed, so that moments are stretched out into hours, days or eons.

No one has yet traveled through space at a speed anything like that necessary to produce dilation of time. The Apollo vessels cruised at a few tens of thousands of miles per hour; relativistic effects take place at more than a hundred thousand miles per second.

In a space ship of the future, moving at a great speed, a person might travel ten million light years, and age only a few months. This makes it possible to traverse distances that would otherwise be unreachable. It also creates, in effect, a time machine. Events on the earth would proceed as always, while a deep-space traveler aged slowly. You might get into a space ship for a year, and come back to find--what? An earth a million centuries older. There would be no return, at least not by any means known to scientists today. Time dilation might someday become a very real concern to astronauts. It will pose moral and ethical, as well as scientific, problems. Who will want to go somewhere and make discoveries that cannot be brought back to fellow humans in the same generation? Or even after a hundred generations? What astronaut will be willing to risk leaving civilization forever, to return to an earth that might not be hospitable?

Another way that time can be stretched is by the presence of an extreme gravitational field, or by huge accelerations. This kind of time dilation is not significant on the surface of the earth, because the gravity is nowhere near strong enough. Even near the sun, it is hardly significant. But it might become a very great factor when, or if, humans ever venture near black holes, or accelerate at moderate rates for vast distances through space.

A clock in a strong gravitational field runs more slowly than a clock in interstellar space, or on the surface of a planet such as the earth.

Time dilation, whether caused by high speeds or by strong gravity or acceleration, is explained by the theory of relativity, developed by Albert Einstein in the early part of the twentieth century.

A space ship, capable of traveling near the speed of light, could be used as a time machine to go into the future. At about nine-tenths of the speed of light, time is stretched by a factor of two. At 99.99 percent of the speed of light, time is stretched by a much greater amount, a factor of about seventy. No amount of energy can drive a space ship to the speed of light, but it is, in theory, possible to get so close that the time-stretching factor might become a thousand, or a million, or even more.

A similar phenomenon would take place if you ventured close to a black hole. But this would be a dangerous and critical maneuver. If you made the slightest miscalculation, you would fall in. This would throw you entirely off the time line you have lived in all your life. Besides that, in an ordinary-sized black hole, you would be crushed to death by the force of gravity, and wouldn't even get to find out what sort of time line you had happened onto.

All forward time travel is, it seems, a one-way deal. Once you've committed yourself to the future, you cannot return. For this, you would have to travel backwards in time. For various reasons, most scientists think that is impossible.

The problem with backward time travel is that it gives rise to absurd possibilities. Suppose you could build a time machine, get inside it, and travel back a few years. Maybe you could go back and destroy the plans for the time machine itself. What would happen then? You would never have made the trip, and therefore you couldn't have gone back to destroy the plans. Or you could go back and convince your father and mother not to get married. This might take the form of anything from gentle persuasion to outright murder. In any case, doing this would prevent your own birth.

Backward time travel is great stuff for science fiction. But most scientists seem to agree that traveling backward in time will have to remain fiction, except in certain theoretical problems of physics. Backward time travel is like speeding faster than light, or climbing out of a black hole. These things, too, are beyond material realization.

* * *

In physics, the equations predict the existence of various particles. Some are later observed; some aren't. Some apparently move faster than light. These strange particles are known as tachyons. The prefix tachy means, in the physicist's lingo, "very fast." They have not yet been directly seen.

According to relativity theory, time slows down as an object approaches the speed of light. The nearer to the speed of light that the object gets, the more time is slowed, until, if it were possible to reach the speed of light, time would stop. Some physicists extrapolate past the speed of light, and say that time would, at these speeds, run backwards.

Although this is of theoretical interest, relativity theory also says that no material object, such as a space ship, can ever be accelerated to speeds faster than that of light. In fact, an infinite amount of energy would be needed just to reach the speed of light. It is not likely that anyone will ever be able to go backward in time by flying around faster than light.

If you were to jump, or fall, into a black hole, time might turn around. Of course you'd never know. If you weren't squeezed into thread, your mind would still perceive time as moving forward.

When something falls into a black hole, it seems, to an outside observer, to come to rest at the event horizon. If you could watch a clock fall into a black hole, the clock would run more and more slowly. As it fell, it would seem to freeze at the event horizon, never quite passing through. But if you traveled down into the dark maw with the clock, it would continue to operate at normal speed.

If anybody ever jumps into a collapsed star, assuming one is actually found someplace by space travelers, the hapless adventurers will be stretched into spaghetti by the gravitational force. In an extremely large black hole, such as might be found at the center of our Milky Way galaxy, the astronauts might not be crushed, but they would be forever gone from this universe. It would not matter whether they had gone back in time or not, since they would be in some other place infinitely far away, and couldn't come back to play any historical mischief in this universe!

There is still another possibility for time travel, and this doesn't give rise to the contradictions of backward time travel. This is so-called imaginary time, in which you go from one time line onto another. It might also be called alternative time or sideways time travel.

Perhaps, when you were in elementary school or high school, there was a "time line" over the blackboard in history class. Do you remember the teacher pointing at it with her long stick? It was probably divided into years, decades or centuries. You can make a time line with divisions representing microseconds or millenia, moments or eons. But the general principle is the same in every case: you always move along the line from the past toward the future. The point "right now" is the present.

Isaac Newton saw humankind moving inexorably and constantly along, and time as flowing smoothly and always at the same, fixed Divine rate. Now people know better. But time still moves, and it still forms lines in the mind.

Time is regarded by scientists as a spatial dimension. You can place at most three yardsticks so that their ends are all at one point and they're all perpendicular. Time, as a dimension, can be portrayed as perpendicular to all three yardsticks, not directly visible, but nonetheless real.

Drawings can be made in which time is shown as a dimension. To do this, you have to cut out one or two of the three space dimensions. A circling airplane might be drawn as a helix, with the time dimension corresponding to the axis of the helix. A wavefront of the flash from the big bang might look like a cone.

Suppose for a moment that it were possible to travel freely forward and backward in time, for any span you might desire, from a minute to an hour, a day, a year, a millenium. This is truly the same thing as being able to fly through a mysterious, invisible fourth dimension.

If you could pass into a fourth dimension of space, how easy it would be to get out of a sealed cell! You would only have to propel yourself around the walls of the cell and emerge, just as easily as you could step out of a circle drawn on a pavement.

In relativity theory, time becomes this fourth dimension of space. To get out of a sealed cell, you could travel into the future until the whole building was torn down, step over a few feet, and then travel back. Or you could hurtle backward to a time before the structure was built, step aside, and return. Or you could go back in time and uncommit the crime you committed, so that no one would have had cause to put you into prison in the first place.

You envision time as a line, marked off in units like seconds or years. On this line, you move forward. You can accelerate your forward movement by means of relativistic spacecraft, but you cannot, apparently, move backwards. You cannot make time stop, even though, at times, it seems to stand still.

In space, it's easy to imagine myriad lines, running in all kinds of directions. Some of them intersect each other. Some are parallel. Some are askew. These are space lines, the things about which they taught you in high-school geometry class.

There are time lines, too. Except for the one on which humankind is trapped, multiple time lines are impossible to visualize, because of the very narrowness of vision that this imprisonment creates.
How can you go sideways in time? Or off at an angle of sixty degrees? The experience can be imagined more easily if you realize that, if you could do these things, you wouldn't notice anything peculiar at all!

Other time lines lay out other universes, places you do not see, have never been, and will never go. Not, anyway, until something truly cosmic happens. Past infinity, beyond eternity, and before all things, there are other time lines.

Mathematicians, physicists and even electrical engineers make use of imaginary numbers, so called because their existence is not easy to envision. The unit imaginary number is the square root of -1. If you multiply this number, usually written as the letter i, by itself, you get -1. This number is just as real as any other number, but it refuses to fall onto the number line to which your teacher pointed with her long stick.

In certain astrophysical equations, there are fundamental time units equal to i seconds. These are fragments of imaginary time. Imaginary time explains some things perfectly. Its reality is therefore based on more than just idle brainstorming. Just as imaginary numbers are as real as the real numbers, so imaginary time is as real as real time.

The idea of many time lines gives rise to the notion of a time plane or a three-dimensional time continuum. Even more bizarre are universes in which there are dozens, hundreds or thousands of time dimensions. Or infinitely many!

Ideas like this have no practical use in physics--yet. But they are rich territory for science fiction. Their existence cannot easily be verified by known laboratory methods. But this does not mean they aren't "there," somewhere.

How many dimensions of time are there? An answer must exist, a Godelian truth; a provable and specific answer is something you can't get at.

If you could jump into a black hole, you would propel yourself into imaginary time. If there were some other black hole in that new universe, it would have a third line of time. Another black hole inside this would run according to a fourth line of time. All of creation might well consist of black holes within black holes within black holes, a spacetime foam resembling the Mandelbrot set, leading either infinitely inward or infinitely outward, as well as sideways, inside-out and heels-over-head. In this environment, "then" and "now" blur and lose meaning. You might begin to think that in the Divine eye, time doesn't flow at all, and that all things, wherever and whenever they are, simply exist. Stephen Hawking, the cosmologist who has followed in the footsteps of such notables as Isaac Newton, comes to this conclusion in his book, A Brief History of Time.

Hawking speaks of the arrow of time. Time seems to move forward because human minds think forwards. If time ran backwards, it would appear natural, and would therefore be defined as forwards.

Some scientific principles can work without defining time as going forwards or backwards. Others cannot.

You can try to imagine what it would be like if your perception of time were suddenly to turn around and run backwards. You would see things like water flowing into the nozzle of a hoze. Hot things would absorb energy rather than emitting it. Ice would radiate coldness. You could dive out of a pool but not in. Food could be uncooked but not cooked. The hands on a clock would go around counterclockwise. The sun would rise in the west. You would rise from the earth to be born old. You would crawl into your mother's womb to be absorbed.

What about things such as the force of gravity? You could drop things up; does this mean you would fly off into space? That is a puzzle! A ball might fly up into your hand on command, as if you were levitating it. You could fall up into a twentieth-story window. But you'd have to have been lying dead on the ground first.

Obviously, there are problems with backward time. There are other senses in which time direction can be defined, besides the way people perceive it as flowing.

There are real differences in effect between forward time and backward time. Shattered glass does not form itself into windowpanes. Neutrons don't fly all by themselves into atomic nuclei and make the atoms get heavier. Brilliant fireballs do not coalesce into little blimp-shaped hydrogen bombs. Black holes don't unfold into stars. The so-called thermodynamic arrow of time always points in a direction that allows certain things to happen, but forbids other things.

According to this standard for the direction of time, time moves forward if and only if disorder increases. If things got more and more orderly, time would be running in reverse, in the sense that the psychological and thermodynamic arrows of time would be in conflict, instead of pointing in the same direction, as they do in the real cosmos. If the psychological and thermodynamic arrows were pointing opposite ways, then tomorrow's weather would be remembered, rather than speculated on. People would try to forecast the past. All of the aforementioned ridiculous things would be commonplace.

Hawking also defines a cosmological arrow of time, in which the universe is growing in size. If the universe were shrinking, then the direction of this arrow would be reversed.

The light from distant galaxies is shifted toward longer wavelength, so that the spectral lines are "redder." This famous red shift was discovered when powerful telescopes and sensitive photographic devices were turned toward the heavens. This shift is attributed to a flying apart of the whole universe, the momentum from the original explosion, the big bang.

Will this expansion ever be halted by gravity? Every atom in the universe is pulling at every other. This slows the expansion down. If it reverses, it will be a long, long time in coming--many billions of years. Whether it will take place or not depends on the amount of invisible matter floating around. This is still a mystery. The more invisible matter, the greater the gravity, and the more resistance it offers to the outward flee of the galaxies. The question of an eventual collapse is unanswered by present knowledge.

Right now, psychological time, thermodynamic time and cosmological time are all in agreement. All three arrows point in the same direction. By the time any contraction takes place, if it ever does, the sun will long since have burned out. The cosmological arrow of time will turn around and point the other way. The thermodynamic arrow will stay the same. Therefore, order will increase. The universe will become hotter and will end in a mighty falling-in, a fireball in reverse motion.

What will follow this big crunch or gnab gib (big bang spelled backwards)? Perhaps everything will start up all over again, with a new big bang, a new universe, and new galaxies, stars and planets. This has been called the Oscillating Universe theory, because it allows for cycles to take place again and again without end, and presumably without any beginning. But it can only be the wildest of speculation. Human knowledge doesn't yet go back past the most recent bang.

Time is a line, just as are lines in space. The universe is a four-dimensional object, with its past, present and future all mapped out. In the collection of all intelligence that has ever been, is now, and will ever be, this object stands out in clear sight.

* * *

Scientific and philosophical debate has raged for centuries over the question of predestiny. The theory of statistics and probability answers some of the questions, but not all. For many events, there remain only two possibilities: either they will happen, or they won't. Humans can only wait and see.

The universe is a huge entity of four dimensions, through which humans travel, their timewise vision narrowed to a line. This line had its beginnings in a brilliant and violent conflagration. Perhaps it will end similarly. Some even say that this line is actually a gigantic circle.

In timespace, the future is laid out just as surely as the past. The only difference is that the immediate past can be recalled, and the immediate future cannot. On a larger scale, the past and the future are equally obscure. Except, perhaps, to psychics. But that is a realm to be addressed elsewhere and elsewhen.

Copyright 1998, 1999, 2000 by Francisco Carrera.