Common Questions

Frequently asked questions about the relationship between science and the Catholic faith.

Q14: Aren’t human beings and human minds completely explained by physics and chemistry?

This has not even been shown to be true of non-human animals.  In fact, some eminent contemporary philosophers have argued that consciousness (which presumably many animals possess) is not explainable just by physics and chemistry. (This includes philosophers who are religious, such as Saul Kripke, and philosophers who are atheists, such as Thomas Nagel, David Chalmers, and Frank Cameron Jackson).  For example, even though common sense tells us that dogs and cats have consciousness and experience sensations, it would be completely consistent with the laws of physics and chemistry to say that they don’t.  No calculation based on the equations of physics and chemistry can answer whether an animal or any other physical entity is having subjective experiences. While the consciousness of animals is presumably a perfectly natural phenomenon, it does not come out of the equations of physics and chemistry.

This also is the view of some eminent physicists.  For example, Edward Witten, who calls himself a “skeptical agnostic,” has said, “[While I believe that] the workings of the conscious brain will [eventually] be elucidated to a large extent, … why something that we call consciousness goes with those workings I think will remain mysterious … . I don’t think [consciousness] will become part of physics.” 1

In fact, there is an argument, put forward by several of the leading physicists of the twentieth century, that conscious minds (at least, the minds of human beings) are not completely describable or explainable by physics.  (Some of the physicists who made this argument were John von Neumann, Sir Rudolf Peierls, and the Nobel laureate Eugene Wigner.) This argument is based on the logic of quantum mechanics, which requires a distinction between the physical systems described by the equations of physics and the “observers” who make measurements of those systems.  Peierls expressed the conclusion of the argument this way: “The premise that you can describe in terms of physics the whole function of a human being, … including its knowledge and consciousness, is untenable.”  (An explanation of this argument can be found in some of the “resources for further study” given below.)

Aside from consciousness, which other animals also have, human minds have rationality and freedom.  There are philosophical arguments that these powers go beyond the capacities of anything that is purely physical.  Some of these arguments go back at least to Aristotle, while others have been put forward by contemporary philosophers.  Many atheists agree that free will cannot be possessed by anything purely physical. Therefore, because they deny the existence of anything that is not physical, some atheists also deny the reality of free will. They dismiss the widespread belief in free will as mere “folk psychology,” i.e. a naïve myth held by ordinary people.  However, the reality of free will is a fact that we know from our own experience of exercising it.  Moreover, if our minds were not free, and our thoughts were just the product of the physical processes in our brains, then our power of reason would also be an illusion, and there would be no point in arguing about anything.


1.. Edward Witten, Video Interview with Wim Kayzer, “Episode 9: Of Beauty and Consolation,” July 21, 2014,

Resources for further study

The Believing Scientist: Essays on Science and Religion, Stephen M. Barr (Eerdmans, 2016), Chapter 9 (“More Than Machines: Physics and Free Will”)

Modern Physics and Ancient Faith, Stephen M. Barr (University of Notre Dame Press, 2003), Part V.

Video: “The Role of the Observer in Quantum Phenomena,” Stephen M. Barr (Lecture at 2018 conference of SCS, re-recorded)

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