As they move, atoms collide with each other, bounce, and rotate; some hook together (whenever their shapes are complementary) and assemble in a multitude of arrangements, forming all kinds of macroscopic (compound) objects that appear “as water or fire, plant or man,”3 or unhook and disassemble, deforming (destroying) the objects. As atoms aggregate, objects form and increase in size, and as atoms segregate, objects change form and decrease in size (i.e., they perish). Just as the words “tragedy” and “comedy” are formed when letters (which can be thought of as atoms) from the same alphabet are combined differently, Aristotle had explained, the immense plethora of diverse objects is formed when atoms are arranged in space differently through their motion.4 In fact, atoms were required by Leucippus and Democritus to explain exactly this diversity in nature: “For from what is truly one a plurality could not come to be, nor from what is truly many a unity, but this is impossible.”5 Remarkably, for Democritus the aggregations and segregations of unseen atoms in the void produced not only our own world (with the earth, moon, sun, planets, stars, plants, fish, animals, and including humans) but also countless others. Earthlike (thus habitable) planets are a commonplace in the universe according to the latest astronomical findings!
Atoms have none of the conventional properties of matter such as color, taste, smell, sound, temperature, or even weight. The indication for this, Democritus thought, is in the fact that various objects are perceived differently by different people. Something sweet to me might be spicy to you. “To some honey tastes sweet to others bitter but it is neither,” said Democritus.6 So he explained the conventional properties in terms of the shape of the atoms and their motion in the void; shape and motion cause unique macroscopic arrangements (in objects, in people) and thus unique conventional (emergent) properties. For example, the atoms of a hard object are more closely packed with less empty space (void) between them than the atoms of a soft object. Now, since the atoms of a soft object have more void to roam around they can be pushed there more easily. Hence, such objects feel squeezable and soft. Metals are made of atoms with hooks that hold them firmly interlocked, but liquids are made of round atoms so they can flow by each other easily. Sweet objects are composed of round good-sized atoms; bitter of round, smooth, crooked, and small; acid of sharp (so they can sting the tongue) and angular in body, bent, fine; oily of fine, round, and small. Even light was made of atoms (particles)—incidentally, Einstein won the Nobel Prize in Physics by interpreting light (pure energy) in terms of discrete particles: the photons. Black, white, red, and yellow were considered primary colors and associated with different shapes and arrangements of atoms.7 Combinations of these four colors were in turn used to account for all color variations. Democritus worked out a detail theory on sensation. In general he argued that the constant motion of the atoms, which persists even when a composite object is seemingly at rest, causes some of them to be emitted by the object. Flying through the void, these atoms in turn ultimately collide with the atoms of a sense organ and create a unique sensation (a flavor, smell, color, an image).
All changes of the apparent world of sense perception, animate and inanimate, were reduced to the irreducible atoms and their motion in the void. This scientific reductionism is ambitious. In principle, it is also the goal of the modern theory of the elementary particles of matter, the quarks and leptons. But while there are striking similarities between these modern particles of matter and the ancient atoms, there are also serious differences. Only for purposes of comparison let us call the ancient atoms Democritean or D-atoms, and today’s building blocks of matter, the quarks and leptons, QL-atoms.
D-Atoms and QL-Atoms: Similarities and Differences
Before we proceed with this comparison, let us first briefly summarize the historic developments in search of the D-atom, the ultimate uncuttable piece of matter. Until about the end of the nineteenth century, chemical atoms, such as hydrogen, carbon, oxygen, and so on, of the periodic table of chemistry, were thought to be the fundamental particles of matter, the D-atoms. But this idea turned out to be incorrect when the structure of the chemical atom was probed further and it was found that it was cuttable, made up of electrons and a nucleus. In 1897 physicist J. J. Thomson (1856–1940) discovered the electron, and in 1911 his student physicist Ernest Rutherford (1871–1937) discovered the nucleus. Electrons (one of the six types of leptons) are still thought indivisible, but atomic nuclei not so; the latter are made from divisible protons and neutrons, though they are themselves composed of indivisible quarks. Six types of quarks were postulated to exist as elementary particles in the 1960s, and all six types had been discovered by the end of the twentieth century. Hence, chemical atoms are not fundamental; they have substructure (they are divisible) and in fact are made of the QL-atoms. Like the shadows, which were real but were not the real objects in Plato’s parable of the cave, chemical atoms are real but are not the real fundamental particles (the smallest cuts of matter as envisioned by Leucippus and Democritus)—although the name “atom” has been undeservingly stuck on them, for it’s really a misnomer (inaccuracy) when used to refer to the chemical elements.
On the other hand, both D- and QL-atoms are fundamental because they are not made from other particles; they are disconnected pieces of matter, indivisible (uncuttable), invisible, and the smallest, and their various combinations make up all material things in the universe. Neither the D-atoms nor the QL-atoms have any of the conventional properties of composite objects. These properties are really a consequence of the collective behavior of the D- and QL-atoms that make up these objects.
D-atoms are unchangeable; they do not transform. But QL-atoms do; they transform from one type of material particle to another and also into and from energy (although they do not transform into something more fundamental). But like matter, energy also comes as discrete bundles, as particles (e.g., photons), and so Leucippus’s and Democritus’s notion of discreteness as a property of nature is preserved and applies to energy, too. Furthermore, like D-atoms, which are made of the same substance, QL-atoms are made of the same substance, too, mass and energy (which are equivalent as per special relativity). And since D-atoms are indestructible, so is their substance, but so is the substance of QL-atoms, for the total amount of mass-energy in the universe is constant (as per the law of conservation of mass-energy). So the substance of both, the ancient and modern atoms, endures, while nature is constantly changing.
D-atoms have shapes and thus have nonzero size; QL-atoms are considered point-like and thus shapeless and size-less.8 There is both a challenge and a simplicity associated with each view. In the D-atoms we need to imagine all sorts of complex atomic shapes, but we need not worry about forces. Democritus did not introduce any (a topic to be revisited later). D-atoms, he explained, coalesce into composite objects as a result of their perpetual motion and complementary shapes. Also, composite objects have size since they are made of D-atoms, which themselves have size. On the other hand, QL-atoms lack shape and size, but they still combine. They do so via the exchange of the particles of force (the photons, the W’s, the Z’s, the gluons, also the gravitons if we find them). Being point-like thus shapeless is in a sense a simplicity, for it means that QL-atoms are internally structureless like the D-atoms. But it is also a complexity, for how can something of zero size, of zero extension in space, have properties such as mass, electric charge, energy, spin, and so on, and, even worse, how can composite objects have size and extension in space when their constituents do not? Within the context of the Parmenidean theory, the “size” question may be restated as follows: how can size come from not-size? That is, how can Being (the nonzero size of macroscopic objects) come to be from Not-Being (from zero-size constituents)? This was impossible for Parmenides. Democritus solved the size challenge by postulating that matter cannot be divisible (cuttable) ad infinitum; it must be finitely divisible with the smallest cuts to be the indivisible, the uncuttable D-atoms of nonzero size. For only then, he thought, could composite
objects have size, if they are composed of things that themselves have size. Interestingly, the strings of string theory do have size. If these turn out to exist, we may not need to worry about size (Being) coming to be from not-size (Not-Being), an idea that would be pleasing to both Parmenides and Democritus. The size challenge is revisited in the section on “Void or Not?”
On the one hand, D-atoms are postulated to move in order to comply with the apparent world and explain change. On the other hand, since motion is an ambiguous concept from the modern point of view, QL-atoms are postulated to move only as an adequate way of understanding the phenomena. Furthermore, in quantum theory, material particles (the QL-atoms) are less materialistic in the sense that they no longer have key properties that material particles were once thought to have in order to be called material: they are neither permanent, nor indestructible, nor unchangeable, nor deterministic, nor have they well-defined shapes or trajectories through space and time, and as a consequence nor have they identity and individuality. Thus, QL-atoms are best regarded as events and not as permanent Parmenidean Being-like entities (as are the D-atoms). And the properties of QL-atoms are best described in terms of the quantum probability, a number that expresses only a potential event: for example, which type of QL-atom might be observed, where, and with which properties and behavior.
Are the QL-atoms the smallest cuts of matter and, within this context, thus the ultimate D-atoms? It is generally not thought so. Are the QL-atoms different forms of the same type of universal substance, the same type of particle, and what might that be? While the Higgs boson particles have some qualities required of a universal substance, the standard model that predicts them does not include the most puzzling force in the universe, namely, gravity. Therefore, although useful, any model of nature that does not incorporate gravity is incomplete.
The basic concept of the ancient atomic theory was highly valued by Nobel laureate Richard Feynman. He said: “If, in some cataclysm, all scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most [scientific] information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact . . .) that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.”9 On a related note, in his book The God Particle Nobel laureate Leon Lederman graded thousands of scientists (including himself) for their efforts in their quest for a primary substance of the universe. He started with Thales all the way to 1993, the completion date of his book. Democritus received the only A in the class!10
So as a general idea, the D-atoms, the uncuttable discrete and fundamental pieces of matter that everything is made of, are still part of our most advanced theories of nature, for these basic but important properties are properties of the QL-atoms, too—in fact, also of the strings of string theory. But whether the QL-atoms (together with the force-carrying particles of the standard model as well as the Higgs boson, a total of sixty-one particles all confirmed to exist), a zoo of other unconfirmed particles of matter and energy (including the graviton, predicted by various other scientific models), or some new particles of one and the same type (a much-desired scientific simplicity of Democritean grandeur) that manifest themselves by way of the familiar particles are or will be the truly uncuttable discrete and fundamental pieces of matter remains to be seen. How about the void? Does it exist or not? Is it needed, or can it be avoided?
Void or Not?
The atomists Leucippus and Democritus called an atom a thing, Being (what-is), and the void nothing (not thing), Not-Being (what-is-not).11 And they agreed with the theory of Parmenides (with one interpretation of it, anyway, for which the properties of Being are understood literally) that motion is impossible without the void. But whereas Parmenides denied the existence of the void by considering it Not-Being, the atomists postulated the opposite: Not-Being, the void, exists, for only then, they thought, can motion and change be accounted for. It is the place to put the atoms and enable them to move. For the atomists the void is empty space, and so in it there is nothing. But for Parmenides it, the void, empty space itself, is nothing, Not-Being; not in it there is nothing. The nature of the void has created mind-boggling debates since the time of Parmenides. For if something, for example, the void, is really nothing, how can it exist? How does one define “nothingness”? The answer is not easy.
But first let’s summarize Democritus’s arguments favoring the void. By accepting the phenomena of motion, change, and diversity to be real, he deduced the void to be real as well, for without the void his impenetrable, indivisible atoms could not move and consequently the phenomena of change and diversity would not occur; but they do occur, so the void must be real. Similarly, by accepting also multiplicity and division of composite objects to be real, he again deduced void to be real, for without it, composite objects could not be divided (cut) into smaller pieces: “division resulted from the presence of void in bodies.”12 As explained further by philosopher and mathematician Bertrand Russell (by paraphrasing Democritus), “When you use a knife to cut an apple, the knife has to find empty places where it can penetrate; if the apple contained no void, it would be infinitely hard and therefore physically indivisible.”13 Here we recall of course that for Democritus divisibility does not continue ad infinitum; it applies only to composite objects and stops at his physically indivisible atoms. So for Democritus both the atoms and the void are real: “thing [atoms] is [exist] no more than not-thing [void].”14
Now what does modern physics think of the void? Does it exist or not? Is it a true nothing, the Parmenidean Not-Being, or something else? While “nature abhors a vacuum,”15 a popular phrase since the Renaissance, yet “nothing works without, well, nothing.”16
Void?
On the one hand, void is still a useful concept for the understanding of many phenomena. According to quantum theory, electrons in a chemical atom, for example, “move” around their nucleus by keeping their distance from one another as if space between them is empty, devoid of matter—“a regulation against overcrowding”17 formally known as the Pauli exclusion principle. As a consequence of this principle, the electrons of chemical atoms keep their distance from each other; they do not like to be squeezed together into a small region, so they act as if they were rigid: the closer they get, the faster they move apart—a statement in agreement with the Heisenberg uncertainty principle, for, according to it, the uncertainties in the position and velocity are inversely proportional, so the smaller a particle’s region of confinement (the smaller its position uncertainty), the faster its motion to escape such a region (the greater its velocity uncertainty), “almost as if it [the particle] were overcome with claustrophobia,” Brian Greene wrote.18 The exclusion principle explains why chemical atoms are mostly empty space and why macroscopic objects (which are made of chemical atoms) have a degree of rigidity, size, and shape—e.g., the distance that tiny particles keep from each other translates into the size and shape of a macroscopic object. D-atoms are rigid; consequently, in a sense they, too, obey the regulation against overcrowding, for one D-atom cannot occupy the same region of space as another D-atom. Had the exclusion principle not been true, the QL-atoms, which obey it, would not endure as disconnected pieces of matter, thus nuclei would not form, nor would chemical atoms or the molecules of organic chemistry, and consequently nor would the matter that living things are made of; generally, all matter in such a scenario would collapse into a uniform, undifferentiated, and lifeless state. The diversity in nature is in a sense a consequence of the exclusion principle: diversity is a law of nature!
Or Not?
On the other hand (that is, to be able to explain other phenomena), in the quantum realm the void is not really devoid of
matter but a very busy place, seething with all-pervasive fields of energy (e.g., light and gravity waves, even the much-required Higgs field that explains mass—see section “Worlds Without Forces” later), known as vacuum energy. These fields cannot be zero, even in seemingly empty space, because the time-energy uncertainty principle would be in violation (recall the section titled “Nothing Comes from Nothing” in chapter 8). And they are actually fluctuating constantly, creating and annihilating pairs of particles with their corresponding antiparticles. These particles, which are called virtual, are not created out of nothing or annihilated into nothing but are made out of energy and return to be energy (the vacuum energy). Unlike real particles, which can be directly observed, virtual particles cannot, even though they can still cause measurable effects on real particles, an indication that “empty” space is really not empty.
Moreover, according to the theory of general relativity, the whole of space is filled by a gravitational field with properties (such as strength) that vary from place to place and from one moment to the next. Einstein explained gravity by assigning properties to “empty” space; empty space (and time) is a flexible medium that gets distorted by a mass, and gravity is space’s (and time’s) distortions. These properties are the void, and so in the theory of general relativity the void is not the Parmenidean Not-Being, for Not-Being, a true nothing, is property-less.
In Search of a Theory of Everything Page 18