This is the weekly Q & A blog post by our Research Professor in Philosophy, Dr. William Lane Craig.

Question

Hi Dr Craig,

Once again let me thank you for all your contribution to the cause of the Gospel. In your 2013 debate with Dr Alex Rosenberg you mentioned that there are "10 different physical interpretations for quantum mechanics" and "3 different interpretations of special relativity" which are "all empirically equivalent and yet they're different theories and each one is a legitimate scientific theory".

So my question would be,

  1. Does that mean that all these different theories hold the same truth value? Can they all be said to be equally true?
  2. If not, can you explain what you meant by "empirically equivalent"?
  3. If yes, then how does it fit in light of the Law of non-contradiction?
  4. Also does the Law of non-contradiction hold for the entirety of the universe and everything within? Eager to get it clarified.

In Christ,

Jacob

Flag of India.

India

Dr. William Lane Craig's Response

Dr. William Lane Craig

1) No and No. Some scientists, still under the influence of verificationism, think that two theories which have the same empirical consequences are in reality the same theory, merely presented in different ways. By contrast, I hold that two different theories may have the same empirical consequences and yet be different theories because of the different physical structures that they postulate. For example, a theory which postulates 4-dimensional objects in spacetime has a very different view of physical reality than a theory which postulates 3-dimensional objects in space enduring through time. Verificationism suppresses these fundamental differences and so distorts the theories’ descriptions of reality.

2) By “empirically equivalent” one means that the theories make the same testable predictions. You can’t tell which is true or false by examining the scientific evidence because they both have the same observable consequences. Of course, the hope in such an impasse is that new tests may be devised or predictions made that will enable us to discern which, if either, is true. For example, as I explain in my Time and Eternity (2001), the experimental consequences concerning Bell’s Theorem lend powerful support to a neo-Lorentzian, as opposed to Einsteinian, theory of special relativity, on pain of having signals going backwards in time relative to some reference frames.

3) The answer to 2) is not Yes, but No.

4) So no violation of the Law of Contradiction arises from empirically equivalent theories. On the contrary, if they postulate different physical structures of reality, then at most one of them may be true. Logical laws or rules of inference are independent of physical reality, being necessary and a priori, and therefore “hold for the entirety of the universe and everything within.”

This Q&A and other resources are available on Dr. William Lane Craig's website.