Frank Close, OBE, is a Professor of Physics at Oxford University and a Fellow of Exeter College. In his new book, The Void Close tells the story of scientists’ efforts to understand the Void and in the process helps us understand that by seeking to understand the nature of the Void, we are confronting the enigma of why anything should exist at all. In the excerpt below Close looks at ancient conceptions of the Void.
The paradox of creation from the void, of Being and Non-Being, has tantalized all recorded cultures. As early as 1,700, years BC, the Creation Hymn of the Rigveda states that
There was neither non-existence nor existence then. There was neither the realm of space nor the sky which is beyond. What stirred? Where?
Such questions were debated by the philosophers of ancient Greece. Around 600 BC, Thales denied the existence of No thing: for Thales, something cannot emerge from No-thing, nor can things disappear into No-thing. He elevated this principle to the entire universe: the Universe cannot have come from No-thing.
The concept of No-thing was confronted with the laws of logic, Thales posing the question: does thinking about nothing make it something? The answer, according to the Greek logician, is that there can only be nothing if there is no one to contemplate it. My question whether there could be nothing if there was no one to know there was nothing had apparently been answered in the affirmative 3,000 years earlier, though it seems to me to have been an axiomatic assertion rather than established by argument. My quest continued but it appeared that no one after Thales defined nothing other than as an absence of something.
Having disposed of No-thing Thales then moved on to the nature of things. He successfully predicted the eclipse of the sun of 28 May 585 BC, which was a remarkable achievement and bears testimony to his ability. No wonder that his ideas were held in such high regard. He argued that if things cannot come from No-thing, there must be some all pervading essence from which all things have materialized. The question ‘where did everything come from?’ has inspired another: suppose that we removed everything from a region of space, would what is left be the primeval ‘No-Thing’? Thales offered his solution of this mystery too: his prime suspect was water. Ice, steam, and liquid are three manifestations of water and so Thales supposed that water can take on an infinity of other forms, condensing into rocks and everything. As puddles of water seemingly disappeared, later to fall as rain from above, the idea of vaporization emerged and with it the recognition of the cycle that water provides. Space for Thales is as empty as it can be when all matter in it has been turned into its primeval form, liquid water like the ocean. Water thus contains every possible form of matter.∗
∗ 3,000 years later this idea is defunct but modern ideas of the vacuum maintain the conceptual nomenclature by supposing it to contain an infinitely deep ‘sea’ of fundamental particles;
After seventy-eight years of consciousness Thales returned to the permanent void in 548 BC but the idea that there is an ubiquitous primeval essence or ‘ur-matter’ lived on. The nature of the ur-matter, however, was debated. On the one hand Heraclitus insisted it to be fire. So where does fire come from? Answer, it is eternal, and as such could be identified with ideas on a deity, creator of the world. By contrast Anaximenes argued that it is air. Air can be conceived of as extending infinitely, unlike water, its very ubiquity making it the preferred candidate for the universal source of all matter.
In the middle of the fifth century BC, Empedocles was faced with the question whether air was a substance or empty space. The tentative beginnings of experimental methods were brought to bear with a device known as a hydra—a glass tube, open at one end and with a spherical bulb at the other, the bulb containing holes out of which water can pour—so long as the open end of the place your finger over it, no water flows. If you empty the water from the hydra and then submerge it, water will pour in and refill it so long as the open end remains open. However, if the end is covered with your finger, no water enters the holes and no air escapes either. This demonstrated that air and water coexist in the same space; no water can enter until the air leaves; air is a substance and not empty space. It would not be until the seventeenth century that Toricelli explained what was happening.
Empedocles extended the concept of ur-matter to four elements: air, water, fire, and earth. He also introduced primitive ideas on forces: for him they were love and discord, forerunners of attraction and repulsion. He was certainly the first to differentiate between matter and forces, but he still insisted that there can be no such thing as empty space.
Many forms of matter are granular. When spheres are packed together they leave spaces. So that there is no possibility of a void occurring in the ‘empty’ space thus created, Empedocles introduced the ether, lighter than air, which fills those spaces, indeed all space. Ether gets into everywhere, and prevents a vacuum occurring. He even imagined this ubiquitous ether being able to transmit influence from one body to another. In modern thought this is like a gravitational field.
Anaxagoras also denied the possibility of empty space and of creation of something from nothing. For him creation was order emerging from chaos rather than a material universe appearing from nothing. Order from chaos admits that things can evolve and change, as when food turns into us. This permanence of basic elements while changing their overall structure gave the idea of seeds and the birth of atomism. For Anaxagoras, there was no smallest atom, no limit to the divisibility of matter, and so no need to worry about the spaces between touching spheres, no need for gap-filling ether.
Epicurus (341–270 BC), with Leucippus and Democritus, continued the denial that something can come from nothing. They are regarded as the originators of the idea of atoms, small basic indivisible seeds common to matter. Here is born the idea that there can be a void, an empty space through which atoms move. The thinking was that if there is something already at some point, then an atom cannot move into that place; in order for motion to be possible there must be empty space into which atoms can move. They even imagined an infinite evacuated universe filled with moving atoms, which were too small to see individually but which cluster into visible macroscopic forms. Atoms are in motion but their whole is a blur, seemingly at rest. The image is like an ant hill; seen from afar it is a static mound but in closeup would be revealed to consist of millions of tiny individuals in seething motion.
Although the ideas of the atomists more nearly describe our modern picture of matter, it was Aristotle’s contrarian ideas that held sway for 2,000 years. For Aristotle, a void would have to be utterly uniform and symmetric, unable to differentiate front from back, right from left, or up from down. This concept had also appeared in the Creation Hymn of the Rigveda which mused:
Was there below?
Was there above?
Within such a philosophy an object cannot fall or move, it can only exist in a state of rest, an idea which would eventually form a basis of Newton’s mechanics. However, for Aristotle such properties denied the existence of nothing and he brought the logical arguments for the absence of a void to their clearest form. If empty space is something, and if now you place a body in this empty space, you would have two ‘somethings’ at the same point at the same time. If that were possible, then it would generalize to allowing any something to be in the same place as any other something, which is nonsense. So for Aristotle, logic seemed to require that empty space cannot be something and therefore is non-existent. He defined the void as where there is no body, and since the basic elements of things exist eternally, there can be no place that is completely empty.
All in all, Aristotelian logic denied the existence of the void and led to the received wisdom that nature abhors a vacuum. This was regarded as self-evident; nonetheless it was wrong, as we shall now see.