The Question Of Reality

As we have seen, testability is crucial for any scientific theory. However, as crucial as it might be, it is not enough to test a theory against the observations that led to its creation. A scientific theory must also be able to predict unknown facts that can only be confirmed by fresh observations. If any of the predictions are proven wrong, the theory must be deemed incorrect. This potential refutability is a powerful criterion that can help distinguish scientific from most non-scientific theories, as can be demonstrated by comparing astronomy with astrology.

For thousands of years astrologers had been using the apparent movement of the sun, moon, and the five known extraterrestrial planets (Mercury, Venus, Mars, Jupiter and Saturn) to foretell earthly events. Once the sixth planet, Uranus, was discovered in 1781, astrologers adjusted their charts to include the new planet and continued with their forecasting as before.

Astronomers, on the other hand, were fervidly striving to calculate the orbit of the new planet. Their calculations, however, did not match the actual path of Uranus. The discrepancy could be explained by assuming that either Newton’s theory of gravity was wrong, or that the gravity of an unknown heavenly object, farther from Uranus, was responsible for the deviation. Using the law of gravitation, astronomers calculated the assumed celestial position of the undiscovered planet. They confirmed their calculations in 1846 when, by means of a telescope, they managed to view Neptune at the predicted location.

Just as discrepancies in the orbit of Uranus had led to the search for Neptune, irregularities in the orbit of Neptune, and to a lesser extent in the orbits of Uranus and Saturn, had led scientists to suspect the existence of a ninth planet. Again, it was theoretical calculations that led to the discovery of Pluto in 1930. The theory of Gravity is therefore a scientific theory.

To demonstrate how established scientific theories can be refuted, let’s look at the theory of ether, which was the established theory for an entire generation of scientists.

Since Maxwell (1831–1879) formulated the electromagnetic theory in 1865, 19th century scientists had puzzled how electromagnetic waves, such as light, traveled through vacuum and the emptiness of space. Just like waves in water or sound in air, the argument went, electromagnetic waves needed a physical medium to travel through. For this reason alone, a new substance, ether, was proposed. (Although the term ‘ether’ was borrowed from Aristotle, the 19th century’s ether was a different concept altogether.)

According to the theory, ether filled in the entire universe, including vacuum and the inside of material bodies. As such, it had to be a weightless, transparent, frictionless matter that did not take part in any physical or chemical interaction, and was, therefore, impossible to test or verify.

Yet, the theory of ether could predict that light emanating from a moving object in the direction of its movement would travel faster than light emanating from the same object in any other direction. (To illustrate, imagine an item thrown from a moving car. Clearly, if we threw it in the direction of the travel it would travel faster than if we threw it in the opposite direction.)

Michelson and Morley relied on this hypothesis in 1887, when they attempted to determine the speed of earth relative to ether by measuring the difference between the speed of a beam of light traveling with the movement of earth, and that of a beam of light traveling perpendicular to earth’s movement. (The importance of this experiment was that according to Galilean/Newtonian physics, motion is always relative, and there is no way to distinguish a body at rest from a body moving at a constant velocity. Ether could have offered a reference point and define absolute movement.)

Had Michelson and Morley detected the difference as expected, it would have put their names, in a side note, as the first scientists to measure the absolute speed of earth. As it turned out, the experiment failed and no difference could be detected. Even though Michelson and Morley could not explain their result, it was sufficient to inflict a death sentence on the theory of ether, and to win Michelson the 1907 Nobel Prize for physics. This was the experiment that subsequently it led Einstein to develop the theory of special relativity.