The Big Questions: Physics (27 page)

One of the central rules of programming is that you don’t waste precious computing resources. That means that any simulation will not be infinitely smooth. It will be built well enough to give its conscious avatars a sense of continuity in the world around them –
but no better than is necessary. That means a sudden, close look might expose the gaps in the programming.

We may, in fact, have already done so. We already know that the theories we have devised to describe our reality have apparent inconsistencies. The quantum world, which seems to describe things we encounter at subatomic scales, for instance, does not make sense to the human mind. It allows particles to have multiple existences, occupying two spatial positions at the same time or simultaneously moving in opposite directions.

Similarly, relativity, which we use to describe reality when we are considering large, cosmological scales, fails to describe the most extreme of cosmological conditions, such as the interior of a black hole, or the geometry of the moment of the Big Bang. Could it be that these frustrating limitations to our theories reflect the limits of the programming behind our reality?

There is further evidence to consider. One of the most significant aims of modern science is to ‘unify’ the laws of physics. At the moment, the main thrust of that is to marry together relativity and quantum theory. However, it is a marriage that no one has yet managed to broker. Might that be because it is fundamentally impossible?

When creating today’s simulations, programmers use a particular method for coding the finer details – the movement of hairs in a polar bear’s fur, say. The methods for creating a facsimile of a pastoral landscape are different. Similarly, the creators of our simulation may have used different methods for programming our reality on different scales, so we should not expect to be able to marry them together. If that is the case, the frustrations of science might be a clue to the nature of our existence.

A further clue might be found in our genetic code. Our DNA tends to make mistakes when replicating. Left uncorrected, these mistakes would be enough to give any species a short shelf life – perhaps too short to evolve. The simulated story of life would
have crashed quickly had it not been for error-correcting routines embedded in the function of our genes. We do the same with our computer programs: we incorporate error-correcting routines that put things right before things go irretrievably awry. It is not a big stretch, therefore, to imagine that the simulation’s programmers would have to employ the same methods.

One suggestion that has been made by serious physicists is that a correction to the simulation might create cracks, or even breaks, in the laws of physics. Some things might not behave as expected. Have we made any such observations? As a matter of fact, yes. Astronomers have suggested, for instance, that the light reaching Earth from the furthest galaxies observable shows signs that the laws of physics have suffered a tweak at some point in the distant past. The light was emitted 12 billion years ago, and its interactions with matter during its journey across the universe have a slightly different character than one might reasonably expect.

The observation seems to suggest that one of the constants of physics, the constant that governs the fine details of how light and matter interact, was subtly different in the past. Is this a programming error, or part of an error-correction routine? Though the scientific inference about the varying constant seems solid enough, the suggestion that it provides support for the idea that we live in a simulation remains controversial.

None of these ‘tests’ are knock-down convincing. The idea that we are living in a computer simulation is an intriguing one, and in many ways it offers a highly plausible answer to one of the most vexing problems of modern physics. Whether it can be proved or falsified remains an open question. Maybe that’s why some philosophers have argued that the only way we will know for sure is if the humans propagating the idea are mysteriously ‘deleted’ from the simulation because they pose a threat to its continued success. Others have made a similarly playful, but far more appealing suggestion. Now that we have made this discovery, it seems entirely possible that we could soon find a huge message rending the sky asunder: ‘Congratulations: please proceed to Level 2’.

The ties that bind the universe, and their origin in the superforce

It’s a question straight out of Hollywood. Take two imposing but very different beasts, and set them against one another. We have had Alien vs Predator and King Kong vs Godzilla; how about Gravity vs the Strong Force? Or the Weak Nuclear Force vs Electromagnetism? You won’t be surprised to hear that the answers to such questions are unattainable. The reason for that might come as a surprise, however.

If physicists’ suspicions are proved right, we are not dealing with four forces, but one. Just as a skilled puppeteer can control more than one marionette, there seems to be one superforce behind what we see as the different forces of nature. It could be that gravity, electromagnetism and the strong and weak nuclear forces (see table:
How the Superforce Split
) were once united.

In the preface to his great work
Philosophiae Naturalis Principia Mathematica
, Newton wrote that he harboured a deep suspicion that all the phenomena of nature ‘depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards each other, and cohere in regular figures, or are repelled and recede from each other.’ The forces of nature, in other words, are at the core of physics.

This idea was in marked contrast to what had gone before. The Greek mode of scientific investigation was to assume and
respect the role of a ‘prime mover’, an ultimate cause that also governed notions of justice and morality. Seeking purely physical mechanisms for natural events, without searching for the ethical and moral dimensions they related to, was just not done. But we now know that the forces of physics hold true for everyone but mean nothing in moral terms. Gravity, to paraphrase the Gospel of Matthew, ‘sendeth rain on the just and on the unjust’.

Not all the forces are so inclusive. The electromagnetic force, for example, only acts between particles containing electrical charge. The strong force only acts over a short range, and between the particles in the nucleus. This raises a question. If they are all so different, why do we believe they are all of the same origin? To answer that, we look first at our ideas of gravity – and where they fall short.

Gravity, to us the weakest of the forces, was the first to be tamed. Newton made the initial move in his universal law of gravitation, offering a formula that described how any bodies with mass would interact. In Newton’s scheme, the pull of gravity accounted for the motions of the planets with an astonishing degree of accuracy. Newton’s gravitational ideas fell short in two ways, however. One was that they offered a description but no
explanation
of gravity. The other was that they did not describe every facet of how gravity works in the universe: some phenomena defied explanation.

The precession of the perihelion of Mercury is perhaps the most famous example. The perihelion is the point of closest approach in an elliptical orbit. Mercury’s trip round the Sun has just such a point, which moves, or precesses, with successive orbits. The precession is a result of the gravitational pull of the other planets in the solar system, and, in 1845, the French astronomer Urbain Joseph Le Verrier used Newton’s law to work out what it should be. There seemed to be an error. Le Verrier’s calculation missed the observed precession by 43 seconds of an arc per century. Every hundred years, the calculations were out by just one hundredth of a degree, but they were wrong nonetheless.

Fortunately, Einstein’s general theory of relativity provided the required correction. Relativity describes the gravitational fields as arising from the influence of mass and energy on the fabric of the universe: gravity comes from a warping of space–time. It is an astonishingly successful theory, and has never failed an experimental test. Nonetheless, for all relativity’s grand successes in describing what we see in the universe, a proper explanation for the why and how of gravity remains elusive. And until we have one, we cannot be sure that gravity really is so weak – especially when we examine the next force to succumb to science.

Electromagnetism is a much stronger force than gravity. Take two electrons: the electromagnetic repulsion between them is 10
⁴³
times larger than their mutual gravitational attraction. But this relative strength may be an illusion. The clue lies in the fact that electromagnetism is a unification of two theories: electricity and magnetism.

In the 1840s, the English physicist Michael Faraday had come up with the concept of a field to explain why iron filings formed lines when scattered around a magnet. To Faraday, these ‘lines of force’ were associated with some physical properties of the space around the magnet. The link to electricity came easily: Faraday also discovered that a changing magnetic field creates an electric field.

But there was a complication. When Faraday’s friend James Clerk Maxwell tried to pull Faraday’s discoveries, and the equations that described them, together, he could only make sense of the result if he added another factor into the mix. It is not enough that changing magnetic fields create electric fields. The converse must also be true: changing electric fields, Maxwell said, must create magnetic fields.

Maxwell’s new equations glowed with a beautiful consistency: electricity and magnetism were two sides of the same coin. This unification led to another beautiful result. When Maxwell looked at the consequence of a changing magnetic field growing an electric field, which grew a magnetic field in turn, and
so on for infinity, he realized he had discovered the root of electromagnetic radiation. What’s more, the speed of propagation of this disturbance was the speed of light. Light, it became immediately clear, is an electromagnetic wave.

The significance of this discovery is hard to overestimate. It led to the discovery of the electromagnetic spectrum, to radio waves and gamma rays and everything in-between. It showed how energy could be transferred from point to point through space, doing away with the idea of some ghostly interactions that had no physical source. Perhaps most importantly, it paved the way for an instant revolution in physics. Maxwell’s equations didn’t work when the source of radiation was moving relative to an observer, an observation that prompted Einstein to resolve the anomaly with special relativity (see
What is Time?
) in 1905. What’s more, the unification of electricity and magnetism was only the start. We now know that another of nature’s forces is delivered from the same hand.

Einstein was highly motivated by the idea of unification. After the success of relativity, he spent his life trying to construct a ‘unified field theory’ that pulled electromagnetism out of the geometry of space–time, just as he had done with gravity. As a result, he and his few followers ignored the development of quantum theory. Einstein had never liked it, and hoped it would go away.

But it didn’t, and explorations of the new theory, along with the fast post-war development of particle physics, pointed to the existence of two new forces: the strong and weak nuclear forces. Einstein never addressed these, but carried on playing exclusively with electromagnetism and gravity. By the time he died in 1955, physics had moved on without him.

It is a particular shame because the weak nuclear force, which acts between the particles of the nucleus – the neutron and the proton – and has an extremely short range of 10
^–17
metres, is now known to be closely related to the electromagnetic force. We know this because the weak force is responsible for ‘beta’ radiation,
where an atom emits an electron or its positively charged counterpart, a positron. The beta-emission of an electron involves a neutron turning into a proton, which can only happen if a ‘W boson’, the source of the weak force, is emitted first: it is this particle that then decays to produce the electron.

The link was made stronger when we realized that the weak force and the electromagnetic force result from the same process, known to physicists as ‘spontaneous symmetry-breaking’. This is rather like what happens when you assemble a crowd of strangers in a room. As they get talking, some will find common points of interest in one area, some in another, and, given enough time, they will form into distinct groups that end up talking about different things. Initially, there was ‘symmetry’: there was nothing to distinguish the strangers from one another, no way to group them. But, as they talked, that symmetry was spontaneously broken, and groups formed.

In the 1960s, Steven Weinberg, Sheldon Glashow and Abdus Salaam showed that the same process of spontaneous symmetry breaking created the electromagnetic and weak forces from another force. They named it the ‘electroweak force’, and suggested that it had only existed in its unbroken form in the high-energy conditions at the beginning of the universe. The work was a masterstroke, and won the trio the 1979 Nobel Prize in physics. The theory made specific theoretical predictions: the existence of the W and Z bosons, for example, which were found, complete with all the assumed characteristics, in 1983.