For The Encyclopedia of the Social Sciences. Copyrighted. Do not copy or distribute. OK to quote.
In everyday usage, reality refers to the universe that exists independently of our thoughts. Dreams or delusions, which we experience when we are asleep or are otherwise not in full possession of our senses, are examples of the nonreal.
In philosophy, this commonsense view is known as realism. The opposing view in which only our thoughts are real is called idealism. An intermediate view is dualism, in which reality is composed of both the concrete objects of experience, which we call matter, and some other nonmaterial element usually associated with mind and perhaps some external supernatural substance called spirit. While dualism is a common belief within most of the world’s religions, it is nonparsimonious in the sense that no evidence requires the complication of dual realities. Spirit can be incorporated into either realism or idealism, although it is explicitly excluded in a form of realism called materialism. In the materialist view, matter and perhaps space and time are all that exist.
Associated with many thinkers since ancient times in both the East and the West, idealism asserts that our only knowledge of the outside world comes from perceptions, which are developed in the mind. So, it is reasoned but not proved that these are the only entities that can be real. The implication of idealism is that our thoughts are somehow more perfect, more truthful than the raw data that impinges our senses. Furthermore, perceptions that may be formed independently of the senses are equally real. Plato (c. 427–347 BCE) told the allegory of the cave, in which the cave’s inhabitants are constrained to view only shadows on the wall and cannot observe the sources of the shadows. He introduced the notion that reality is composed of perfect Forms such as the Form of the Good, which some interpret as Plato’s notion of God. In an example of Plato’s view, the planets travel in perfect circles around earth, and their observed zigzag motion across the sky is a distortion, much as the images of our bodies are distorted when viewed in a funhouse mirror.
In modern times, many mathematicians and theoretical physicists have adopted an updated Platonic view of reality. Mathematical truths seem to exist independently of individual opinions and cultures. Some are not only unproved but also provably unprovable, yet they are known by other means to be correct (Gödel’s theorem). Furthermore, mathematical models in the physical sciences have the remarkable ability to predict future observations with exquisite precision. Surely, the argument goes, mathematics and mathematical physics must carry some aspect of reality. Yet they are still inventions of the human mind. Carried to its extreme, idealism implies that we should be able to make our own reality simply by thinking about it. Clearly this is not the case, despite the claims of some New Age gurus. Try as they might, none have been able to think themselves younger.
Each of us has an intuitive feeling that the concrete objects we confront during our waking experience constitute some aspect of reality. Samuel Johnson (1709–1784) expressed this common view when he heard of the idealistic philosophy espoused by Bishop George Berkeley (1685–1753). As described in James Boswell’s Life of Johnson:
We stood talking for some time together of Bishop Berkeley‘s ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I shall never forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, “I refute it thus.” (1934, Vol. I, p. 471)
When we kick an object and it kicks back, we are pretty certain that we have interacted with some aspect of a world outside our heads (and feet). In simple terms, this describes the processes of everyday observations as well as the most sophisticated scientific experiments. According to physics, when we look at an object with our naked eyes, particles of light called photons bounce off the object into our eyes. This process generates electrical signals that are analyzed by our brains. Essentially the same process takes place with scientific observations, where various particles besides photons and instruments more sensitive than the eye are used.
From the available data, scientists form mathematical models, or theories, to describe their observations and predict future observations. In the twentieth century, physicists developed the remarkably successful theories of relativity and quantum mechanics, leading to the standard model of particles and forces that accurately describes the nature of matter as we observe it. An equally successful standard model of cosmology has resulted from the application of the above theories to astronomical observations of increasing precision. With these theories, we can now describe the basic physics and cosmology of our universe from one trillionth of a second after it came into existence until the present. Surely the quarks and quasars of these models constitute some element of reality.
More than two thousand years ago, the Greek philosophers Leucippus (480–420 BCE</SC>) and Democritus (460–370 BCE) proposed that reality is composed of atoms and the void, where atoms were defined as particles that could not be divided further and the void was the empty space between atoms. This became the working model of Newtonian physics (Sir Isaac Newton, 1642–1727), although it seemed necessary to also include some kind of continuous, smooth background of fields to account for gravity and electromagnetism. In the nineteenth century, atoms came to be associated with the chemical elements, and that term is still used in that context. However, we have now cut the elements into smaller pieces in nuclear reactions.
In the twentieth century, it was found that theoretical quantum fields exist in one-to-one correspondence with particles, the so-called quanta of the fields. The quantum of an electromagnetic field is the particle of light, called the photon. The fields associated with forces that appear at the nuclear level have quanta called weak bosons and gluons. While a quantum theory of gravity has not yet been developed, it is speculated that the gravitational field will be associated with a quantum particle called the graviton.
Thus it remains possible, though not provable, that ultimate reality is composed of only atoms and the void, where the atoms are localized bits of matter, whatever the ultimate uncuttable objects may turn out to be. Einstein’s theory of general relativity, which led him and others to attribute a reality to space and time, suggests a connection between geometry and matter. The currently fashionable string theory supports that connection.
Boswell, James.  1934. Life of Johnson. Ed. G. Birkbeek Hill. Oxford: Oxford Clarendon Press.
Penrose, Roger. 2004. The Road to Reality: A Complete Guide to the Laws of the Universe. New York: Knopf.
Stenger, Victor J. 2000. Timeless Reality: Symmetry, Simplicity, and Multiple Universes. Amherst, NY: Prometheus.
Stenger, Victor J. 2006. The Comprehensible Cosmos: Where Do the Laws of Physics Come From? Amherst, NY: Prometheus.
Susskind, Leonard. 2006. The Cosmic Landscape: String Theory and the Illusion of Intelligent Design. New York: Little Brown.
Victor J. Stenger
Emeritus Professor of Physics and Astronomy
University of Hawaii at Manoa
Adjunct Professor of Philosophy
University of Colorado at Boulder