Section 16–1 Relativity and the philosophers

(Relativism / Empiricism / Mach’s Positivism)

In this section, Feynman discusses relativism, empiricism, and Mach’s positivism.

1. Relativism:

“That all is relative is a consequence of Einstein, and it has profound influences on our ideas (Feynman et al., 1963, section 16–1 Relativity and the philosophers).”

According to Feynman, cocktail-party philosophers simply interpret Einstein’s theory as “all is relative.” These philosophers would explain that phenomena depend on one’s frame of reference has been demonstrated in physics. That is, the idea of “things depend upon your frame of reference” has a profound effect on modern thought. The philosophical view that “all is relative” is sometimes described as relativism. In a sense, this misconception of the special theory of relativity can be attributed to the term relativity. On the contrary, there are absolute truths and invariant quantities in special relativity.

One may expect Feynman to elaborate on the importance of invariants that is in contrast to relativism. For example, in Jammer’s (1999) words, “mathematician Felix Klein and physicist Arnold Sommerfeld suggested that the name ‘theory of relativity’ should be replaced by ‘theory of invariants’ because the theory is merely a theory of the invariants of the Lorentz transformation (p. 33).” On the other hand, Minkowski (1907) has developed the concept of invariant (absolute) space-time interval and suggested the name “the postulate of the absolute world (p. 117).” Importantly, the light postulate states that the speed of light is invariant (or absolute) in all inertial frames of reference. Furthermore, the equations (e.g., four-momentum) in the special theory of relativity are invariant.

2. Empiricism:

“Our inability to detect absolute motion is a result of experiment and not a result of plain thought, as we can easily illustrate (Feynman et al., 1963, section 16–1 Relativity and the philosophers).”

Feynman explains that a consequence of relativity was the development of empiricism which said, “You can only define what you can measure.... The physicists should have realized that they can talk only about what they can measure.” In other words, the whole problem of whether one can define absolute velocity is the same as the problem of whether one can measure absolute velocity in an experiment without looking outside. However, another consequence is the development of operationalism: the idea of an operational definition in which “the concept is synonymous with the corresponding set of operations (Bridgman, 1927, p. 5).” Bridgman further suggests that a dozen operating procedures in measuring a physical quantity may lead to a dozen of different concepts.

Empiricism is a philosophy of science that emphasizes the importance of experimental evidence. In a lecture delivered in Cornell University, Feynman (1965) says that “[i]t does not make any difference how beautiful your guess is. It does not make any difference how smart you are, who made the guess, or what his name is - if it disagrees with experiment it is wrong (p. 156).” Thus, some may argue that Feynman is an empiricist because he advocates the role of empirical evidence in the development of physical laws. However, in “Surely, You’re Joking, Mr. Feynman!,” Feynman questioned empirical results of Telegdi’s experiment on parity violation. Interestingly, Telegdi (1989) praises Feynman and writes that “[h]e understood experiments deeply and could suggest sources of error that had escaped the experimenters themselves (p. 85).”

3. Mach’s Positivism:

“Now that the motion is no longer absolute, but is a motion relative to the nebulae, it becomes a mysterious question, and a question that can be answered only by experiment (Feynman et al., 1963, section 16–1 Relativity and the philosophers).”

Feynman states Mach’s philosophy as one cannot detect any motion except by looking outside. (Mach distrusts concepts that cannot be verified by observable evidence.) Moreover, Feynman argues that Mach’s philosophy is not true because the Earth’s rotation on its axis can be determined using Foucault pendulum without looking at the stars. However, Bondi and Samuel (1997) applies Mach’s principle to explain a small precession (or Lense-Thirring precession) of the Foucault plane. More important, Einstein recognized Mach’s influence in questioning the notion of absolute space and time that helped to develop the special theory of relativity. Mach’s philosophy of science is more appropriately known as Mach’s positivism instead of simply positivism or phenomenalism.

Mach’s positivism can be described by Einstein’s words: “Science is nothing else but the comparing and ordering of our observations according to the methods and angles which we learn particularly by trial and error... As results of this ordering abstract concepts and the rules of their connection appear... Concepts have meaning only if we can point to objects to which they refer and to the rules by which they are assigned to these objects (Frank, 1952, p. 271).” Despite his criticisms of Mach’s positivism, Feynman explores how to incorporate Mach’s principle in quantum mechanics and gravitation theory (Feynman, Morinigo, & Wagner, 1995). Furthermore, Feynman discussed Mach’s principle with Wheeler before performing a sprinkler’s experiment that resulted in Feynman banished from the laboratory (Wheeler, 1989).

Note: The philosophical underpinning of Poincaré’s principle of relativity is essentially geometric conventionalism. For example, Poincaré (1902) writes that ‘[e]xperiment guides us in this choice, which it does not impose on us. It tells us not what is the truest, but what is the most convenient geometry (pp. 71-72).” Poincare’s conventionalism can be described as a “philosophy asserted that fundamental scientific principles are not reflections of the ‘real’ nature of the universe but are convenient ways of describing the natural world insofar as they are not contradicted by observation or experiment (Nye, 1979, p. 107). Thus, Feynman could have clarified whether the method of synchronizing clocks in special relativity is also a matter of convention.

Questions for discussion:

1. Why is relativism (“all is relative”) a misconception of Einstein’s special theory of relativity?

2. How would you justify empiricism which is related to “you can only define what you can measure?”

3. How do you explain that “one cannot detect any motion except by looking outside” (using a smartphone that has a built-in GPS)?

The moral of the lesson: currently, we have a much more humble point of view of our physical laws—everything can be wrong! (Mach’s philosophy may seem silly to physicists, but it helps to question the notion of absolute space and time.)

References:

1. Bondi, H., & Samuel, J. (1997). The Lense-Thirring effect and Mach’s principle. Physics Letters A, 228(3), 121-126.

2. Bridgman, P. W. (1927). The Logic of Modern Physics. New York: Macmillan.

3. Feynman, R. P. (1965). The character of physical law. Cambridge: MIT Press.

4. Feynman, R. P., Leighton, R. B., & Sands, M. (1963). The Feynman Lectures on Physics, Vol I: Mainly mechanics, radiation, and heat. Reading, MA: Addison-Wesley.

5. Feynman, R. P., Morinigo, F. B., & Wagner, W. G. (1995). Feynman Lectures on gravitation (B. Hatfield, ed.). Reading, MA: Addison-Wesley.

6. Frank, P. (1951). Einstein, Mach, and logical positivism. In Paul Schilpp (Ed.), Albert Einstein: Philosopher-Scientist. La Salle, Illinois: Open Court Press. pp. 270-286.

7. Jammer, M. (1999). Einstein and Religion: Physics and Theology. Princeton: Princeton University Press.

8. Minkowski, H. (1907). Space and Time. In Petkov, V., (Ed.), Minkowski’s Papers on Relativity. Moscu: Minkowski Institute Press.

9. Nye, M. J. (1979). The Boutroux circle and Poincaré's conventionalism. Journal of the History of Ideas, 40(1), 107-120.

10. Poincaré, H. (1902/1952). Science and hypothesis. Mineola, NY: Dover.

11. Telegdi, V. (1989). A Lowbrow's View of Feynman. Physics Today, 42(2), 85.

12. Wheeler, J. A. (1989). The Young Feynman. Physics Today, 42(2), 24-28.