Farewell to Reality (14 page)

Figure 2
The standard model of particle physics describes the interactions of three generations of matter particles through three kinds of force, mediated by a collection of field particles or ‘force carriers'. Note that only ‘left-handed' leptons and quarks experience the weak nuclear force. The masses of the matter and force particles are determined by their interactions with the Higgs field.

But we now know that protons and neutrons are made of quarks. So, we conclude that the mass of the paperweight resides in the cumulative masses of the quarks from which they are composed. Right?

Wrong. Because the quarks are confined, it's quite difficult to determine their masses, but it is known that they are substantially smaller and lighter than the protons and neutrons that they comprise.
For example, the Particle Data Group quotes mass ranges for both up and down quarks. If we pick masses at the higher end of these ranges and add the masses of two up quarks and a down quark, we get a result that represents about 1 per cent of the mass of a proton.

Hang on a minute. If 99 per cent of the mass of a proton is not to be found in its constituent quarks, where is it?

The answer to this question demands an understanding of colour charge. The Ancient Greeks used to claim that nature abhors a vacuum. A contemporary version of this aphorism might read: ‘nature abhors a naked colour charge'.

In principle, the energy of a single isolated quark is infinite, which is why individual quarks have never been observed. It is much less expensive in energy terms to mask the colour charge that would be exposed by an individual quark either by pairing it with an anti-quark of the corresponding anti-colour or combining it with two other quarks of different colour such that the net colour charge is zero.

However, even within the confines of a proton or neutron, it is not possible to mask the exposed colour charges completely. This would require that nature somehow pile the quarks directly on top of one another, so that they all occupy the same location in space and time. But quarks are quantum wave particles, and they can't be pinned down this way — Heisenberg's uncertainty principle forbids it.

Nature settles for a compromise. Inside a proton or neutron the colour charges are exposed and the energy — manifested in the associated gluons that are exchanged between them — increases. The increase is manageable, but it is also substantial. The energy of the gluons inside the proton or neutron builds up, and although the gluons are massless, through m = E/c
²
their energy accounts for the other 99 per cent of the particle's mass.

And there you have it. For centuries we believed that it would one day be possible to identify the ultimate constituents of material substance, the ultimate ‘atoms' of matter from which everything is constructed. This was Dirac's dream. We assumed that such constituents would possess certain characteristic physical properties, such as the primary quality of mass.

What the standard model of particle physics tells us is far stranger and, consequently, far more interesting. There do appear to be ultimate constituents (at least for now), and they do have characteristic physical
properties, but mass is not really one of them. Instead of mass we have interactions between constituents that would otherwise be massless and the Higgs field. These interactions slow the particles down, giving rise to behaviour that we interpret as mass. As the constituents combine, the energy of the massless force particles passing between them builds, adding to the impression of solidity and substance.

Nobody said that science would deliver a description of empirical reality that was guaranteed to be easily comprehensible. But it is nevertheless rather disconcerting to have the rug of our common experience of light and matter pulled from beneath our feet in this way.

^*
At first sight this might seem an odd thing to demand, but it ensures that the ‘laws' of nature that we deal with in our theories are genuine laws, independent of any specific point of view.

^*
On 23 September 2011, physicists at CERN's OPERA experiment reported results that suggested that neutrinos travelling the 730 kilometres from Geneva to Italy's Gran Sasso laboratory do so with a speed slightly greater than that of light. Data collected from over 16,000 events recorded over a three-year period suggested that the particles were arriving about 61 billionths of a second earlier than expected. Such faster-than-light neutrinos would have represented a fundamental unravelling of Einstein's special theory of relativity and thus the current authorizsed version of reality. Many scientists were sceptical of the results and some argued that they couldn't be correct. On 22 February 2012, the OPERA results were shown to be erroneous, and a loose fibre-optic cable was blamed. The claims were withdrawn, and a couple of high-profile members of the collaboration resigned their positions.

^*
Note that it is accelerated motion which is impeded. Panicles moving at a constant velocity are not affected by the Higgs field. For this reason the Higgs field is not in conflict with the demands of Einstein's special theory of relativity.

^*
Or over-emphasized, depending on your point of view.

^*
At around the same time, American physicist George Zweig developed an entirely equivalent scheme based on a fundamental triplet of particles that he called ‘aces'. Zweig struggled to get his papers published, but Gell-Mann subsequently made strenuous efforts to ensure Zweig's contributions were recognized.

^*
This might suggest that the theory applies only to quarks, but the different kinds of leptons (electron, muon, tau and their corresponding neutrinos) are also sometimes referred to as ‘flavours'.

^**
Provided, that is, that the particle recently discovered at CERN proves to be the standard model Higgs boson.

4

Beautiful Beyond Comparison

Space, Time and the Special and General Theories of Relativity

The theory is beautiful beyond comparison. However, only one colleague has really been able to understand it
…

Albert Einstein
¹

When Newton published his classic work
Philosophiœ Naturalis Principia Mathematica (The Mathematical Principles of Natural Philosophy)
in 1687, he defined an authorized version of reality that was to prevail for more than two hundred years. Newton's mechanics became the basis on which we sought to understand almost everything in the physical world. There appeared to be no limits to its scope, from the familiar objects of everyday experience here on earth to objects in the furthest reaches of the visible universe.

But Newton had been obliged to sweep at least two fundamental problems under the carpet. The first of these appeared to be largely philosophical, and therefore (it could be argued) a matter of personal preference. The second seemed no less philosophical but was more visibly physical, and disconcerting. It would fall to Einstein, and those physicists and philosophers who inspired him and on whose work he built, to resolve these problems from within his special and general theories of relativity.

Einstein's theories of relativity were radically to transform how we seek to comprehend space and time, and the ways in which space and time respond to the presence of material substance.

After Einstein, reality would never be quite the same again.

Newton's bucket

The first problem Newton had to confront concerned the very nature of space and time. Are these things aspects of an independent physical reality? Do they exist independently of objects and of perception or measurement? In other words, are they ‘absolute' things-in-themselves?

Take your eyes away from this book and look around you. What do you see? That's easy. You see objects in your immediate environment — perhaps chairs, a table, a TV in the corner of the room. These, you conclude, are objects in space.

But what, precisely,
is
space? Can you see it? Can you touch it? Well, no, you can't. Space is not something that we perceive directly. We perceive objects, and these objects have certain relations with one another which we might be tempted to call spatial relations, but space itself does not form part of the content of our direct experience. Our interpretation of the objects as existing in a three-dimensional space is the result of a synthesis of sense impressions in our brains translated by our minds.
^*

Similarly, you can't reach out and touch time. Time is not a tangible object. Your sense of time would seem to be derived from your sense of yourself and the objects around you changing their relative positions, or changing their nature, from one type of thing into another.

The pragmatists among us shrug their shoulders (again). So what? Just because we can't perceive these things directly doesn't mean they aren't ‘real'. Newton was inclined to agree, although he was willing to acknowledge the essential relativity of space and time in our ‘vulgar' experience. Objects move towards or away from each other, changing their relative positions in space and in time. This is relative motion, occurring in a space and time defined only by their relationships to the objects of reality.

But Newton's mechanics demanded an
absolute
motion. He argued that, although we can't directly perceive them, absolute space and time really do exist, forming a ‘container' within which matter and energy can interact. Take all the matter and energy out of the universe, he
decreed, and the empty container would remain: there would still be ‘something'.

Some of Newton's contemporaries (most notably his arch-rival, German philosopher and mathematician Gottfried Liebniz) were not satisfied. They preferred a more empiricist perspective, dismissing theoretical objects or structures that cannot be directly perceived as intellectual fantasies, akin to God or angels.

Newton believed that although absolute space and time cannot be directly perceived, we can nevertheless perceive phenomena that can only be explained in terms of an absolute space and time. To answer his critics, he devised a thought experiment to demonstrate this possibility. This is Newton's famous bucket argument.

Suppose we go into the garden.
^*
We tie one end of a rope to the handle of a bucket and the other around the branch of a tree, so that the bucket is suspended in mid-air. We fill the bucket three quarters full with water. Now we turn the bucket so that the rope twists tighter and tighter. When the rope is twisted as tight as we can make it, we let go of the bucket and watch what happens.

The bucket begins to spin around as the rope untwists. At first, we see that the water in the bucket remains still, its surface flat and calm. Then, as the bucket picks up speed, the water itself starts to spin and its surface becomes concave — the water is pushed by the rotation out towards the circumference and up the inside of the bucket. Eventually, the rate of spin of the water catches up with the rate of spin of the bucket, and both spin around together.

Watching over your shoulder, Newton smiles. He wrote:

This ascent of the water [up the side of the bucket] shows its endeavour to recede from the axis of its motion; and the true and absolute circular motion of the water, which is here directly contrary to the relative, discovers itself, and may be measured by this endeavour.
²

Here's the essence of Newton's argument. The surface of the water becomes concave because the water is moving. This motion must
be either absolute or relative. But the water remains concave as its rate of spin relative to the bucket changes, and it remains concave when the water and the bucket are spinning around at the same rate. The concave surface cannot therefore be caused by the motion of the water relative to the bucket. It must be caused by the absolute motion of the water. Absolute motion must therefore exist. Absolute motion can only exist in absolute space. So, absolute space exists.

Have you spotted the potential flaw in Newton's argument yet?

If flaw it is, it is the assumption implicit in Newton's logic that if the concave surface of the water is not caused by motion relative to the bucket, then it surely cannot be caused by motion relative to the tree, the garden, me, you, the earth, the sun and all the stars in the universe.

Why not? Well, if this really were an example of motion relative to the rest of the universe, then by definition we cannot tell which component of such a system is stationary and which is moving. This is what relative motion means. Relative motion demands that if the bucket and the water in it were perfectly still, and we could somehow spin the entire universe around it, we would expect that the surface of the water would become concave.

Ridiculous! How could the entire universe have this kind of influence without appearing to exert a force on the water of any kind? Newton's assumption is surely valid, and absolute space must therefore exist.

Simultaneity and the speed of light

We might be inclined to think that the question of whether or not absolute space and time exist is a largely philosophical question. Indeed, absolute space and time suggest some kind of privileged frame of reference, a ‘God's eye view', and Newton was quite willing to assign responsibility for it to God. We might conclude that the question of the existence or otherwise of such a privileged frame is interesting, likely to provoke interesting arguments, but ultimately unanswerable.

Einstein didn't think so. As he pondered this question whilst working as a ‘technical expert, third class' at the Swiss Patent Office in Bern in 1905, he realized that it did, indeed, have an answer. He concluded that absolute space and time cannot exist, because the speed of light is a constant, independent of the speed of its source.

Although he was later to become a diehard realist, the youthful Einstein was greatly influenced by empiricist philosophy; particularly that of the Austrian physicist Ernst Mach. Mach had criticized Newton's concepts of absolute space and time and dismissed them as useless metaphysics.