In philosophy, there is a long-standing debate -very long standing, over thousands of years! - about the fundamental nature of reality. On one side, realists claim that the world we think we see and experience around us is indeed real, made of matter and energy, and that the things we see around us exist apart from our awareness of them. Idealists on the other hand believe that the only reality we know for sure is what is in our minds. Everything else is simply sensations we experience with our minds. There may be no external reality, or it may be quite different from what we think we experience.
https://en.wikipedia.org/wiki/Philosophical_realism
While idealism seems very odd to most at first glance, it is actually a well-founded position, giving rise to the "brain in a vat" idea, or more recently, The Matrix movie series, where what we experience inside our heads does not correspond with what is really happening. Indeed, everything we think we experience is merely nerve impulses coming into our brains. Who knows whether those impulses relate to anything real? Maybe some mad scientist is sending us prepared nerve signals as part of his experiment. Moreover, even the concept of nerves and a brain are based on a supposed external physical reality (EPR) that we have no direct access to. We could, in principle, be a simulation in a computer, or worse, a scripted fictional character just passing through the plot as someone else turns the pages. As weird as it may seem, there is no way to be absolutely certain that one of these situations is not true.
In one current manifestation, idealism is sometimes called Mental Reality Theory (MRT), the claim that all of reality is mere mental activity in some non-physical reality. There is no EPR, no external world. The entire world consists only of mental activity, perhaps shared with other minds at times, but nonetheless, devoid of any actual physical matter or energy. Everything we claim to experience is just sensation of mental activity in our minds.
The proponents of MRT claim that they can prove their case, and they point to a variety of evidence in support. As well as the above fact that all experience is based on sensations perceived only by the mind, they have related arguments. For instance Descartes' "cogito ergo sum" (I think, therefore I am) is the only thing anyone can know for absolutely certain. Any other "fact" is based on assumptions, tenets, or presuppositions that cannot be proven.
Recently, MRT advocates also point to quantum physics to "prove" that matter does not truly exist - it is all just interacting wave functions. And they apply the Copenhagen interpretation of quantum physics to say that mental activity - the observer effect - determines even physical reality. By discounting matter and energy and expanding the role of thought, they claim support for their views.
But no so fast! While the alternative of believing in an external physical reality cannot be "proven" mathematically, I believe there is considerable evidence available to each of us to cast MRT into doubt and perhaps balance the debate again. I will present several such arguments: consistency, interactions with others, shared reality, children, and surprises, as well as countering the quantum arguments.
First of all, my experience of the apparent external physical reality (EPR) is very consistent over time, far more consistent than I could maintain in my own mind. The room I'm in seems to me very solid, detailed and unchanging except for the normal coherent changes with my movements and attention, and the passage of time. When I wake up each morning, the world seems just as I remember it from the previous day, even if I cannot describe all the details. To create and constantly maintain such consistency only in my mind would be far more than I feel capable of doing. What a waste of mental energy if it is not real!
Of course there are counter arguments. How do I know what I remember is what actually existed the last time I looked? Maybe my memories are being adjusted on the fly. And if my mind is incapable, then some sort of Universal Mind existing in the same mental reality would be more than capable of maintaining the illusion of consistency, which I only tap into from my smaller mind.
Next, there is the question of other minds. Unless I am a solipsist (believing mine is the only mind in existence), then MRT has to account for other people - or rather, other minds. They assume the other minds exist in the same mental reality universe. That is OK, albeit rather vague, but look at how these minds interact. If MRT is true, one would think telepathy would be the obvious way for minds to interact. However, that does not seem to be the case in our experience. Rather, we seem to need to convert thoughts into nerve impulses that control muscles and body parts to create speech, which then goes as sound waves to the other person's ears, to be converted to nerve impulses into his brain before becoming a communication. Interaction at a distance involves additional transducers and physical signal media, like telephones, computers, wireless and electrical circuits, etc. Why depend on such cumbersome, convoluted methods for mind-to-mind interaction if it isn't real? And what does "distance" even mean in a mental reality? If all of this apparent physical reality is an illusion, how did it come about and why does it seem so real to each one of us? Perhaps some demon mind is running the experiment, having better control of mental "space" than we have managed, and using it to fool us all?
When these two arguments are combined, they provide a third one: shared experiences. When two people sit down together, they can communicate sufficiently well to be sure that the EPR they experience is identical. The table between us is this colour, that material, an agreed size and shape, and so on, to an almost arbitrary level of detail. They can see, touch, hear and experience the same things and events, without unexplainable differences, aside from the obvious ones of precise location, which way they are each looking, and so on. In an MRT world, how would that work? How could two minds "move" to meet together, see the world shift as they move, and then experience the same "reality" around them from slightly different, but compatible perspectives, all without prior collusion? That is never explained, other than by some reference to the Universal Mind controlling everything; perhaps the same mad scientist or demon?
In philosophy, it is often useful to reflect on how children grow and develop in order to address deep questions. MRT has no problem with minds being immature or minds learning and maturing - that is what minds do. But how does that apply to what children actually do while learning? Almost all of their learning is based on interaction with the EPR, through touch, sight, movement, sound, etc. Despite parents' and teachers' best efforts, children do not learn much by direct, verbal communication. Nor do they soak up wisdom by osmosis from some Universal Mind. And then there is the question of how such children come to exist? What is the mental reproduction process that seems to require physical interaction between two and only two different minds? While I haven't read a lot from them, MRT proponents would seem to provide little help there.
An interesting consideration is the concept of "surprise". All through life, unexpected things happen to us all. We stub our toe, we lose our keys, we find a long lost book, we have a surprise party, or an unexpected visit from a friend (or the police!), and so on. If MRT is true, where are these surprises coming from? I cannot be creating them myself or they would not be surprising. One could argue that my subconscious is creating them, but what does that even mean in MRT theory? Does my mind have purely mental "parts" that work together? The other answer would, again be the Universal Mind creating these situations for me.
The last point, regarding quantum physics, is somewhat different. MRT people seem not to notice the irony of depending on the results of physics experiments done in the EPR as evidence that the EPR does not exist. If MRT is all there is, then particles, waves and energy, not to mention all of physical reality, including physics itself, are illusory. How can an illusion be used to prove its own non-existence? I expect MRT has some explanation for this seeming contradiction, but at first blush, it looks like an odd approach.
As I see it, to be credible, MRT must fall back on some sort of Universal Mind, which to us would be indistinguishable from "God". This suggests that MRT is metaphysical at its core, and perhaps religious as well. That is OK as long as MRT people do not then try to debunk actual religions and other people's metaphysics. Indeed, there are related theories that the EPR we experience, including ourselves, is a simulation at some god-like level. That may be conceivable, but it is not quite the same as MRT. In any case, personally I am going to stick with realism, trusting the existence of an EPR, as my view of reality. And I suggest that MRT advocates operate 99% of the time as if they too accept EPR as the basis for their ongoing existence and experiences.
I did say the debate has been around for awhile. These few paragraphs will not settle it, of course, but it was fun exploring some aspects of the two competing views, and I now wonder, are there only two, or is there a third possibility?
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