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Philosophical Significance of the Special Theory of Relativity
or
What does it all mean?

Skeptical Morals

John D. Norton
Department of History and Philosophy of Science
University of Pittsburgh

The Project

Special relativity has changed our understanding of the nature of space, time, energy and other physical quantities. There is a very widespread feeling that the advent of special relativity has somehow changed the way we look at things in a sense that goes beyond these narrow physical results. What might that sense be?

The problem in answering is that there is scarcely a viewpoint or movement in modern philosophical thought that does not claim support in one way or another from Einstein's achievement. Clearly they cannot all be right. Quite often radically opposed viewpoints claim support from Einstein's achievement. In the end it is up to you to decide, since the issue remains controversial. You should use your knowledge of Einstein's theory and the circumstances surrounding its emergence to assist you.

The Method

Deciding what this significance might be is a philosophical problem of no small interest. It must be resolved by the standard methods of philosophical analysis. These methods are simple to describe and not so difficult to learn. To begin, we need to keep two notions in mind:

The thesis or claim.

Just what is it that is being claimed? This must be stated in as simple and clear a manner as possible. No real progress can be made until we know what this is in precise and unambiguous terms. Often merely finding the clear statement is an advance in itself.

The arguments that support the claim.

A thesis or claim by itself is only of so much value. What now matters is what reasons can be given to believe the claim. These reasons should be laid out in as cogent a form as possible. Typically these reasons will take the form of an explicit argument. To support a claim we might try to show that if you believe the widely accepted X, Y and Z, then logic forces you to accept the new claim C. Or the argument might be that if you fail to believe the thesis you will be caught up in some undesirable consequence, even an outright contradiction.

Our goal is to take something that is puzzling, vague and elusive and make it precise and definite. If we do it right, the resolution of the puzzle should seem so straightforward that we wonder why it ever seemed otherwise.

Candidate Morals

The obvious candidate is just the basic content of the theory itself. It tells us some pretty surprising things about space and time and the matter they contain: that c is a fundamental barrier to all motions; that moving clocks slow; that simultaneity is relative; that energy and mass are equivalent; and so on. In so far as a perennial problem of philosophy has been to discern the nature of space and time, this is a reasonable answer. However it is usually thought that the advent of relativity somehow changed something fundamental, perhaps in how we see ourselves in the universe, or, more narrowly, in how we conduct our scientific investigations of that universe. Our quest is for morals of that type.

This and the next two chapters will describe some candidate morals of this broader type. I will give you my reaction to them to give you an example of how these claims may be analyzed and also to let you know what I think. Do you agree? Make up your own mind and you proceed. Your decision will be reported in the assignment.

This chapter will develop skeptical morals.

1a. Skepticism about common sense ideas

Relativity shows us that we cannot expect our common sense ideas about the physical world to be reliable.

Here is a reconstruction in terms of thesis and argument.

Thesis: Common sense is an unreliable guide to truth.

Argument:
1. If common sense is a reliable guide to truth, then it will not assure us of falsehoods. (Premise)
2. Common sense assures us that well-made rods and clocks are unaffected by their motion. (Premise)
3. Relativity tells us that well-made rods and clocks shrink and slow when they are moving. (Premise)
4. Common sense assures us of falsehoods. (From 2., 3.)
5. Common sense is not a reliable guide to the truth. (From 1., 4.)

On its face, this is acceptable. This claim is clear enough. The argument employs true premises and valid inferences. Informally, we had commonsense ideas about rods, clocks, simultaneity and more. We believed them because they seemed, well, commonsensical. Relativity showed that they were incorrect. Therefore commonsense ideas are untrustworthy, or at least on some occasions.

While the thesis and argument are acceptable, the view is oversimplified and the oversimplification is misleading.

It suggests that we needed relativity theory to tell us that common sense is unreliable. Anyone who has ever attended to developments in science will find numerous examples of science revealing the fragility of commonsense ideas. Copernicus did just that to our commonsense idea that we are at rest; he showed that we hurl through space at great speed in space, spinning all the while.

More seriously, the implicit assumption is that science and common sense are opposed. That is, they are two distinct ways that we know about the world. They are not distinct. There is an important connection between scientific breakthroughs and common sense.

Here's a list of things that we know through commonsense:

The sky cannot fall down.
Cows cannot jump over the moon.
The earth is spherical.
People venturing to the other side will not fall off.
The earth spins on its axis and orbits the sun.
Matter is made of atoms too small to see.
Nothing goes faster than light.

The items of the list become successively more sophisticated. Indeed inspecting them reveals that each item of today's commonsense is a major result of yesterday's science.

What this suggests is that there is no independent notion of a common sense idea that somehow sits outside what we know through systematic investigations. Rather commonsense is a by-product of those investigation. The broad acceptance of common sense ideas about our physical world is merely the final stage of absorption of the results of scientific investigation. That is why today's common sense is yesterday's scientific breakthrough.

From this we can infer a more subtle moral: there is a kind of reliability in common sense ideas since they are ultimately, though indirectly, grounded in something more solid. Rather than needing a blanket skepticism about common sense ideas, the real thing to guard against is common sense that does not keep pace with newer investigations.

For example, it still seems to be a part of common sense that "airs" can be good for you. Don't we know of the benefits of clear mountain air? Similarly the wrong "airs" were thought to be unhealthy. The disease of malaria--literally "bad air" mal aria--was thought to be caused by them. Of course we now know that malaria is really caused by infection from mosquito borne parasites with the mosquitoes coming from swamps that might also emit bad smells. So the idea of avoiding bad smelling places to avoid the disease was right, but only indirectly.

1b. Skepticism about science

Relativity shows us that even the best of our theories--classical mechanics--are unreliable. Why should we believe any of the theories of modern science? Should we not expect the Einsteins of tomorrow to overturn them all?

Alchemist searching for the philosopher's stone that will convert base metals into gold.

Here is a reconstruction of the thesis and argument:

Thesis: All present scientific theories are false.

Argument:
1. Relativity theory showed that classical Newtonian physics, an apparently secure theory, was false. (Premise)
2. This refutation is common: many apparently secure theories have subsequently been overturned by later theories. (Premise)
3. We should expect this pattern to continue. (Premise)
4. Our best scientific theories will eventually be overturned by new theories, if we persist in seeking new theories. (From 1., 2., 3.)
5. All present scientific theories are false. (From 4.)

The thesis is clear. The argument is also clear. Relativity is just the latest of many instances of new science overturning old theories we thought secure. So we should expect our latest theories will eventually also be overturned, so don't believe them.

In my view this is a lamentable argument, defective because it rests on false premises. Both 1. and 2. are false. Relativity theory did not wipe away all the physics that went before. The bulk of that physics stays intact. Classical physics only needs relativistic corrections when we deal with velocities close to the speed of light. In virtually all applications, from designing bridges to launching Apollo astronauts, classical physics suffices. Premise 2. fails in the same way for other sciences.

The real pattern is that, once a science reaches some level of maturity, it becomes a fixture in the domains in which it was developed. The much publicized revolutions that eventually do arise supply adjustments outside of those domains. Here are some examples:

There is a much more benign moral in all this: do not trust theories in domains remote from those in which they were devised. The persistence of the skeptical argument is a puzzle to me. It simply rests on defective history of science, yet it remains popular among many historians of science who should know better.

2. A General Relativism

Einstein has shown us that the fundamental quantities of physics are relative. Is this not a quite general moral? Is not what is true or false or what is right or wrong relative to the individual? Should we not say "Everything is relative"?

Here's the thesis and argument reconstructed:

Thesis: Everything is relative.

Argument:
1. All quantities in relativity theory have a meaning only relative to an inertial frame or to an inertially moving observer. (Premise)
2. Relativity theory revealed that we were mistaken in our earlier belief in absolute quantities in physics. (Premise)
3. Other notions (truth, moral rightness) are like the quantities of physics.
4. The moral of relativity theory can be applied elsewhere. (1., 2., 3., by analogy)
3. Everything is relative. (From 1., 2., 3.)

Reconstructing the argument explicitly is already pretty damning. One sees that the moral is poorly drawn. Although it is obvious, let us spell out why.

First, the argument is invalid. It seeks to use an argument by analogy. (This is like that in some aspects; therefore this is like that in other aspects.) The analogy fails. That certain quantities in relativity theory are relative to the observer or, better said, state of motion of the observer, has no real bearing on whether there is one true standard for the good or the morally right. The same word--relativism--is used in all cases, but the similarity of meaning is so superficial as not to allow success in one domain to carry to another.

Second, the first premise is false. It is not true in relativity theory that "everything is relativity". Only certain quantities are, albeit more that in classical physics. Some quantities are not relative. The simplest examples are the so-called "rest" quantities: rest mass, rest length etc. These are by definition the masses and lengths measured by a co-moving observer. They are characteristic properties of bodies and are of fundamental physical importance; (obviously) all observers must agree on their values. They are an absolute.

It is something of an accident of history to do with Einstein's way of thinking about relativity theory that we stress the "relative" aspect of the theory. In the more mathematical approach to the theory, what draws most attention is what is not relative, the so-called "invariants." So early in the history Einstein agreed with the great mathematician Felix Klein that a better name for the theory would have been "theory of invariants."

Working in that mathematical tradition, Hermann Minkowski, who introduced the notion of spacetime, wrote in his 1908 lecture "Space and Time":
"...the word[s] relativity-postulate for the requirement of an invariance with the group G_c seem to me feeble. Since the postulate comes to mean that only the four-dimensional world in space and time is given by phenomena, but that the projection in space and in time may still be undertaken with a certain degree of freedom, I prefer to call it the postulate of the absolute world (or briefly the world-postulate)."

Had history paid more attention to Minkowski's advocacy of the absolute world, might I now be lamenting the fallacy of inferring that "everything is absolute" from Einstein's theory?!

In the two chapters following, we will see more candidate morals described and analysed. The morals will not be displayed formally in terms of thesis and argument, as was done above. You should, however, remember that they are all to be held to the same standards of clarity of expression and cogency of argument. If thinking about them becomes troublesome, you should revert to the standard philosopher's questions:

What is the thesis? What is the argument?

What you should know

• The various philosophical morals people have tried to draw from relativity theory.
• How to identify a clear thesis and the argument that supports it.
• How to criticize the statement of a thesis and the argument that supports it.
• Your own view of which philosophical morals can be drawn from relativity theory.

Copyright John D. Norton. February 2001; October 2002; July 2006; February 2, 13, September, 23, 2008; February 1, 2010; February 10, 2013.