The major challenges to the problem of reality in modern physics have come from the theory of relativity and the quantum theory. The philosophical importance of both of their results will be overviewed here in order to appraise their contributions to metaphysics.
2.2.1. The Theory of Relativity. The theory of relativity is a theory of space, time and motion. Albert Einstein (1879-1955) published his paper on the special theory of relativity in 1905, in which he mathematically proved that motion is relative and not absolute. For this he assumed that light has a constant velocity that is never relative to any moving body. This, however, was not just an hypothesis for its factuality was proved by the Michelson-Morley experiment that the velocity of light was never affected by the velocity of the moving body emitting the light itself. Another important principle on which the theory is based is that: a coordinate system (that with reference to which motion is measured) that is moved uniformly and in a straight line relative to an inertial system is likewise an inertial system. Consequently, there is no way to detect absolute motion since the laws of physics are the same in all inertial systems and the coordinate system itself is an inertial system. But then how is it possible for the velocity of light to be constant, then?
According to Einstein, the special theory of relativity finally succeeded in reconciling both the priniciples logically by a modification of kinematics – i.e., of the doctrine of the laws relating to space and time. The contancy of time was ensured by the elasticizing and relativizing of space and time. Thus, in an inertial system moving relative to a coordinate system, the velocity of light emitted from it will appear to be constant; however, the space-time phenomenon of the inertial system will appear to have warped from the coordinate system’s point of view. This space-time distortion is not merely mental but physical. The time of the moving object runs slower in relation to that of the coordinate system. Similarly, the time of the still object runs faster in relation to that of the moving object. To illustrate this, to a passenger in a train, a light beam emitted from a source on to a mirror vertically opposite to it would take exactly the same time (say 2) as the distance (say 4) divided by the speed of light (say 2) to be reflected back. To an outsider in a system relatively slower to the moving train, the velocity of light being constant, the light beam would have to traverse a longer distance diagonally (say 6) and therefore would take (say 3) time to be reflected back. This means that what is (2) to the passenger is (3) to the outsider. This implies that for the passenger time is slower than for the outsider, though from his perspective his time appears to be normal while the outsider’s time (as represented by his clock) seems to run faster. The theory of relativity thus also came to see events as occuring not just in a three-dimensional space but in a four-dimensional space-time. The implications for space were that the moving object appears to have increased in its size in the direction of its motion to the coordinate system. On the other hand, to the moving object the coordinate system decreases in size.
In 1915, Einstein published his general theory which dealt with the problem of gravity. In it Eintein, suggested that gravity was not a force like other forces, but was a consequence of the fact that space-time is not flat but curved or warped by the distribution of mass and energy in it. He went to suggest that the Newtonian notion of gravity as a force is useless. Bodies do not follow orbits because of being acted upon by gravitational force; intead, they follow the nearest thing to a straight path in a curved space, which is called a geodesic. A geodesic on the two-dimesional surface of the earch is called a great circle and, though circular and curved, it is the shortest path between two points. A geodesic in four-dimensional space-time is the shortest path between two points in space-time; however, bodies following it appear to take a curved path (orbit) in three-dimensional space. This space-time warp theory had several implications as predictions. One prediction was that light-rays travelling geodesic paths (shortest paths) would appear to be curved near massive objects, e.g., a star, in space. The prediction was proved true by an observation of an eclipse in 1919. Another prediction was that time should appear to run slower near a massive body like the earth where the force of acceleration is great. This was tested in 1962 using a pair of very accurate clocks mounted at the top and bottom of a water tower.
According to Russell, the philosophical consequences of relativity are not so great as is supposed. Russell may be right in many ways. For instance, the theory does not affect the rationality of logic. In fact, the logical attempt to reconcile conflicting principles produced the theory. However, the results of relativity do have some philosophical consequences for the conception of the universe. For instance, the warping of space-time seems to go against the common-sense view of space and time. It shows that time is not absolute but part of the physical universe, is ‘elastic’ and can be stretched or shrunk. The same is also true of space. For epistemology, this only shows how experience can alter a rationally axiomatic geometry of space devoid of the dimension of time. It cannot just be assumed that the understanding of what a straight line is a priori has nothing to do with experience; for, relativity shows that such Euclidean conception recieves radical alteration in consideration of moving bodies and an empirical hypotheses such as the uniformity of physical laws and the constancy of the velocity of light. Obviously, geometry cannot be cosmically successful without the inclusion of experience.
The association of space and time with mass and energy raises several metaphysical questions. Is reality one or many? Is there a singular coordinate system that includes all these inertial systems? Is that coordinate system inertial or uninertial? If it is inertial, then it can only be so in relation to some other coordinate system which doesn’t qualify it as an overarching coordinate system as such? But if it is uninertial, then is it infinite or finite? Further, in what way can space and time be applied to the concepts of immaterial beings like spirits? In what way can it be said that God is eternal: as enduring in time or as being timeless, since time is related to mass and energy? Is there a rational (or empirical?) justification for applying such concepts to God? Such are questions that the theory of relativity raises against metaphysics.
2.2.2. The Quantum Theory. Also known as quantum mechanics in physics, quantum theory is related to the physics of subatomic particles and phenomena that are considered to be the building blocks of material reality. Two important foundations of quantum mechanics are the postulations of Max Planck (1858-1947) and Werner Heisenberg (1901-1976). Another important physicist in the development of quantum mechanics was Erwin Schrödinger (1887-1961). In fact, Heisenberg and Schrödinger get the credit for the origination of the quantum theory, though in very different mathematical formulations. Planck postulated in 1900 that energy can be emitted or absorbed by matter only in small, discrete units called quanta. In 1927, Heisenberg formulated the uncertainty principle which states that the position and momentum of a subatomic particle cannot be specified simultaneously. This is so because it is only by shining light on a particle that the future position or velocity of the particle can be known. However, it needs the light of a short wavelength to measure with precision the position of the particle. However, the smallest amount of light, according to Planck’s theory, was a quantum. This quantum of light (as pack of energy behaving like a particle) would disturb the particle and change its velocity in a way that could not be predicted. Moreover, the only way for the light to be of shorter wavelength is for the quantum to be of a higher energy. But the larger the amount of energy, the greater the disturbance of the particle and the amount of uncertainty. This means that the more accurately one tries to measure the position of the particle, the less accurately its velocity is measurable, and vice versa.
The quantum theory that was formulated on the basis of this uncertainty principle saw particles as no longer having separate, well-defined positions and velocities that could not be observed; they had a quantum state, which was a combination of position and velocity. Quantum came to see particles such as electrons having wave properties, depending on how one chose to observe it. A particle seen as a wave, obviously, has no particular point of location. In this way quantum mechanics introduced an unavoidable element of unpredictability or randomness into science. There is no deterministic reason why a certain particle, say an electron shot from the rear electron gun on to the screen, should follow a particle path to a particular point on the screen. A number of different paths can be predicted for it despite the target of the gun. This unpredictability meant that the universe at the subatomic level was not deterministic. Particles could pop into existence out of nothing without specific causation.
All this, obviously, has a number of philosophical implications. The first to be tackled is the law of non-contradiction. How can something like light be both wave and particle? Obviously, it can either be a wave or a particle: not both at the same time? Further, what does it mean that the measuring system determines whether something, say an electron, appears to be a wave or a particle? Does it mean that phenomenon is determined by intention or that reality is something quite different than what is given in phenomena as appearance? Another important point for philosophy is the breakdown of cause and effect in atomic systems. Classical physics left no room for freewill; however, the new mechanics is seen as a science that frees the future from bondage to the past. As J. J. G. McCue saw it, ‘No murderer can plead Newton’s Laws as the cause of his crime, nor can any physicist, however skilled at calculation, tell for certain which assemblage of particles will win the next Presidential election.’ Finally, the theory makes it possible that the universe originated by itself out of nothing. It doesn’t need a Creator. However, in order for that to be the laws of quantum physics must precede it. ‘Quantum physics has to exist (in some sense) so that a quantum transition can generate the cosmos in the first place.’ Thus, the cosmological problem of philosophy seems to be inescapable despite the development of the new physics.
 Bertrand Russell, ABC of Relativity, 5th rev. edn. (London: Routledge, 1997), p. 29
 Albert Einstein, “What is the Theory of Relativity?” Ideas and Opinions (New Delhi: Rupa & Co, 2002), p. 229
 Ibid, pp. 229-230
 Bertrand Russell, ABC of Relativity, p. 148
 Hawking, A Brief History of Time, pp. 32-33
 Bertrand Russell, ABC of Relativity, p. 148
 Paul Davies, “Time,” The Experience of Philosophy, 2nd edn. (eds. Daniel Kolak & Raymond Martin; Belmont: Wadsworth Publishing Company, 1992), p. 91
 Cf. Albert Einstein, “Geometry and Experience,” Ideas and Opinions, pp. 233-246
 Stephen T. Thornton & Andrew Rex, Modern Physics (Fort Worth: Saunders College Publishing, 1993), p. 208
 “Quantum Theory,” Microsoft Encarta Encyclopedia (Microsoft Corporation, 2001)
 Hawking, A Brief History of Time, pp. 58-59
 Ibid, pp. 59-60
 Paul Davies, “Is the Universe a Free Lunch,” The Experience of Philosophy, p. 429
 J. J. G. McCue, The World of Atoms (New York: The Ronald Press Company, 1956), p. 478
 Paul Davies, “Is the Universe a Free Lunch?” The Experience of Philosophy, p. 430
© Domenic Marbaniang, Philosophy of Science, 2006