The Fabric of the Cosmos: Space, Time, and the Texture of Reality

by Brian Greene

Although there is still controversy over precisely how these developments should be interpreted, most physicists agree that probability is deeply woven into the fabric of quantum reality.

With the ensuing twists of scientific progress, Einstein’s paper can now be viewed as among the first to point out that quantum mechanics— if taken at face value—implies that something you do over here can be instantaneously linked to something happening over there, regardless of distance.

We take for granted that there is a direction to the way things unfold in time. Eggs break, but they don’t unbreak; candles melt, but they don’t unmelt; memories are of the past, never of the future; people age, but they don’t unage.

These asymmetries govern our lives; the distinction between forward and backward in time is a prevailing element of experiential reality.

But where does time’s asymmetry come from? What is responsible for this most basic of all time’s properties?

It turns out that the known and accepted laws of physics show no such asymmetry (Chapter 6): each direction in time, forward and backward, is treated by the laws without distinction. And that’s the origin of a huge puzzle.Nothing in the equations of fundamental physics shows any sign of treating one direction in time differently from the other, and that is totally at odds with everything we experience.

As we will see, special physical conditions at the universe’s inception (a highly ordered environment at or just after the big bang) may have imprinted a direction on time, rather as winding up a clock, twisting its spring into a highly ordered initial state, allows it to tick forward.

If superstring theory is proven correct, we will be forced to accept that the reality we have known is but a delicate chiffon draped over a thick and richly textured cosmic fabric.

The discovery of extra dimensions would show that the entirety of human experience had left us completely unaware of a basic and essential aspect of the universe.

The arrow of time, through the defining role it plays in everyday life and its intimate link with the origin of the universe, lies at a singular threshold between the reality we experience and the more refined reality cutting-edge science seeks to uncover.

Yet Camus found much hope in the ability of Sisyphus to exert free will, to press on against insurmountable obstacles, and to assert his choice to survive even when condemned to an absurd task within an indifferent universe. By relinquishing everything beyond immediate experience, and ceasing to search for any kind of deeper understanding or deeper meaning, Sisyphus, Camus argued, triumphs.

Faraday’s key breakthrough was the concept of the field. Later expanded on by Maxwell and many others, this concept has had an enormous influence on the development of physics during the last two centuries, and underlies many of the little mysteries we encounter in everyday life.

In June 1905, Einstein wrote a paper with the unassuming title “On the Electrodynamics of Moving Bodies,” which once and for all spelled the end of the luminiferous aether.

As a teenager, Einstein struggled with the question of what a light wave would look like if you were to chase after it at exactly light speed.

Maxwell’s theory does not allow for stationary light because light never is stationary; regardless of your state of motion, whether you chase a light beam, or run from it, or just stand still, the light retains its one fixed and never changing speed of 670 million miles per hour. But, we naturally ask, how can light possibly behave in such a strange manner?

From the well-worn statement that the speed of light is constant, we conclude that space and time are in the eye of the beholder.

It is not the depth of mathematics that makes Einstein’s special relativity challenging. It is the degree to which the ideas are foreign and apparently inconsistent with our everyday experiences.

We are used to the fact that objects can move through space, but there is another kind of motion that is equally important: objects also move through time.

When you look at something like a parked car, which from your viewpoint is stationary—not moving through space, that is—all of its motion is through time. The car, its driver, the street, you, your clothes are all moving through time in perfect synch: second followed by second, ticking away uniformly. But if the car speeds away, some of its motion through time is diverted into motion through space.

Nevertheless, these results, coming from both theoretical and experimental considerations, strongly support the conclusion that the universe admits interconnections that are not local.

This means that space cannot be thought of as it once was: intervening space, regardless of how much there is, does not ensure that two objects are separate, since quantum mechanics allows an entanglement, a kind of connection, to exist between them.

The wave, he claimed, is not a smeared-out electron, nor is it anything ever previously encountered in science. The wave, Born proposed, is a probability wave.

the size of a wave at a given point in space is proportional to the probability that the electron is located at that point in space.

Thus, the success of quantum mechanics forces us to accept that the electron, a constituent of matter that we normally envision as occupying a tiny, pointlike region of space, also has a description involving a wave that, to the contrary, is spread through the entire universe.

In the quantum world, we’ve learned that everything has both particlelike and wavelike attributes.

As an example, the more precisely you know where a particle is, the less precisely you can possibly know its speed.

An important question, and one that may have occurred to you, is whether the uncertainty principle is a statement about what we can know about reality or whether it is a statement about reality itself.

“One should no more rack one’s brain about the problem of whether something one cannot know anything about exists all the same, than about the ancient question of how many angels are able to sit on the point of a needle.”

Half a century later, theoretical insights and experimental results inspired by their work require us to turn their analysis on its head and conclude that the most basic, intuitively reasonable, classically sensible part of their reasoning is wrong: the universe is not local. The outcome of what you do at one place can be linked with what happens at another place, even if nothing travels between the two locations—even if there isn’t enough time for anything to complete the journey between the two locations.

Is time a truly fundamental ingredient in the makeup of the cosmos, or simply a useful construct to organize our perceptions, but one not found in the lexicon with which the most fundamental laws of the universe are written? Could time be a derivative notion, emerging from some more basic concept that has yet to be discovered?

As I type these words, I clearly feel time flowing. With every keystroke, each now gives way to the next. As you read these words, you no doubt feel time flowing, too, as your eyes scan from word to word across the page. Yet, as hard as physicists have tried, no one has found any convincing evidence within the laws of physics that supports this intuitive sense that time flows.

We are all within spacetime. Every experience you or I ever have occurs at some location in space at some moment of time.

We can envision a light that illuminates one time slice after another, momentarily making the slice come alive in the present—making it the momentary now—only to let it go instantly dark again as the light moves on to the next slice.

But, again, while this image seems to match experience, scientists have been unable to find anything in the laws of physics that embodies such a moving light. They have found no physical mechanism that singles out moment after moment to be momentarily real—to be the momentary now—as the mechanism flows ever onward toward the future.

A less than widely appreciated implication of Einstein’s work is that special relativistic reality treats all times equally. Although the notion of now plays a central role in our worldview, relativity subverts our intuition once again and declares ours an egalitarian universe in which every moment is as real as any other.

We argue that every part of the spacetime loaf in Figure 5.1 exists on the same footing as every other, suggesting, as Einstein believed, that reality embraces past, present, and future equally and that the flow we envision bringing one section to light as another goes dark is illusory.

To understand Einstein’s perspective, we need a working definition of reality, an algorithm, if you will, for determining what things exist at a given moment.

So: if you buy the notion that reality consists of the things in your freeze-frame mental image right now, and if you agree that your now is no more valid than the now of someone located far away in space who can move freely, then reality encompasses all of the events in spacetime. The total loaf exists. Just as we envision all of space as really being out there, as really existing, we should also envision all of time as really being out there, as really existing,

In this way of thinking, events, regardless of when they happen from any particular perspective, just are.

They all exist. They eternally occupy their particular point in spacetime. There is no flow. If you were having a great time at the stroke of midnight on New Year’s Eve, 1999, you still are, since that is just one immutable location in spacetime.

to the you who is in any such moment, it is the now, it is the moment you experience at that moment. And it always will be.

To experience illumination—to be “alive,” to be the present, to be the now—and to then experience darkness—to be “dormant,” to be the past, to be what was—is to experience change. But the concept of change has no meaning with respect to a single moment in time.

The intuitive image of a projector light that brings each new now to life just doesn’t hold up to careful examination. Instead, every moment is illuminated, and every moment remains illuminated.

Under close scrutiny, the flowing river of time more closely resembles a giant block of ice with every moment forever frozen into place.7

Is science unable to grasp a fundamental quality of time that the human mind embraces as readily as the lungs take in air, or does the human mind impose on time a quality of its own making, one that is artificial and that hence does not show up in the laws of physics?

Certainly, though, the feeling that time flows is deeply ingrained in our experience and thoroughly pervades our thinking and language. So much so, that we have lapsed, and will continue to lapse, into habitual, colloquial descriptions that refer to a flowing time. But don’t confuse language with reality.

A thousand times a day, our experiences reveal a distinction between things unfolding one way in time and the reverse. A piping hot pizza cools down en route from Domino’s, but we never find a pizza arriving hotter than when it was removed from the oven.

Perhaps the most pointed example of all is that our minds seem to have access to a collection of events that we call the past—our memories—but none of us seems able to remember the collection of events we call the future.

This is what we mean by time’s having an orientation, a direction, or an arrow.1

Even though experience reveals over and over again that there is an arrow of how events unfold in time, this arrow seems not to be found in the fundamental laws of physics.