The title is quite a claim. First, what does it even mean?
First and foremost, it says something about reality (that it’s physical). What is reality? Surely defining reality is “fraught with difficulty”(1). Yet not so much. Reality is simply whatever exists. I think that any difficulty comes in not at the level of definition, but at the level of gauging which things, in fact, exist. So, in the title, I use the word as that totality of things that exist.
Some may quibble here that ‘existence’ is itself fraught with difficulty in any attempt to define it. That’s true in the sense that if we attempt to look to some other term to explain or illuminate our understanding, we are reaching a sort of metaphysical bedrock, that of being itself. Things are–what more could be said than this? There exists something because there isn’t just nothing. In Cartesian reasoning, even denying something exists is proof enough that something exists, namely a denying that something exists. This denial has an existence. What sort, exactly, can be up for debate. The difficulty of “defining” reality sets in in trying to figure out exactly which things exist and how they relate to one another. This is perhaps the chief project of metaphysics, and something we all think about and consider from time to time. Everyone has a world view, after all.
So much for reality. Next, the title says about reality that it is more than physical, or that there are some parts of reality that are not physical. What is meant by ‘physical’? Things that are physical are those things that are explained or understood in light of physical science. In particular, physical things are the fundamental particles as they interact under the fundamental forces. These would include electrons, up and down quarks, and photons for particles; and strong and weak nuclear forces, gravity, and electromagnetism for forces. There may be more besides these (perhaps dark matter and energy, if they exist), but this is what ‘physical’ will mean for the purposes of this post: anything identical with or understood only in terms of the aforementioned particles and forces.
Now, it’s generally thought that most things are physical in the sense just outlined. Yet, is everything that exists physical? No, I will show using Frank Jackson’s Mary argument.
Mary, The Setup
Mary is a neuroscientist with a complete knowledge and understanding of physics. She knows the brain and how it causally interacts with the environment, which includes when the eyes are open and looking at something that is red. She knows the range of electromagnetic radiation that constitutes red light, and the particular interactions that reflect such light from red surfaces. As indicated before, she also knows the cascade of processes that begin with such light hitting the back of the retina and the axonal path through the thalamus to the visual cortex and so on. In short, Mary knows all the physical facts involved in seeing red (and more processes besides).
Yet Mary has lived in a black and white laboratory her entire life, learning from black and white books. She has never seen red. When she opens the door to see colors for the first time, she learns something new. She learns a fact that was not contained in her study of physics. Namely, she learns what it is like to see a color.
The Mary argument concludes with a fact that is not physical in the sense I outlined above. It includes as part of what exists a feeling or experience of colors.
One View on The Nature of Colors Where The Mary Argument Fails
The Mary Argument, it seems to me, works for any view of colors that allow for any sort of separation between the physics of color as a wavelength on the electromagnetic spectrum on the one hand, and the qualitative aspect of color on the other. It is common to think that the qualitative aspect of color is not a constituent of the color of the public world that physics studies at all, but is rather entirely a constituent of one’s experience.
However, this is not the only possible view of colors. A view that makes a necessary connection between the qualitative features of colors and their respective wavelengths will thereby get the qualitative features through their wavelengths, as I said, necessarily. However, this would, I think is clear, assume a view of physical things that Frank Jackson’s Mary was not assuming, namely that physical things include (even necessarily!) qualitative features that we are directed to or made aware of in opening our eyes. Under such a view of the nature of colors, completely understanding red as a wavelength on the electromagnetic spectrum would plausibly also involve the specific way that it would be sensed by any organism equipped to sense it in real time, since Mary knows this process well (i.e. completely), and such an understanding would also allow Mary to know this qualitative feature of the color. Again, I don’t think this is included in normal accounts of what is physical, but it is a view that I think is possible.
Barring this view, Jackson’s Mary shows that reality is more than physical. However, granting the view, then what’s physical is also qualitative. The physical is much richer than is typically thought. Either way is a gain in understanding reality.