If a tree falls in a forest and no one is around to hear it, does it make a sound?

The title of this post is a reworking of a philosophical argument originally formulated to address the possibility that things don’t exist unless they are perceived. The statement in its reformulated form posits a scientific question regarding the nature of perception.
 
In this post I will be writing about the very basic first order perception of reality that is relayed to us through our senses, not the complex cultural, social, emotional, psychological, and many other -al aspects of human perception. Many people would like to think that our perception of the world around us is a complete and true representation of reality. However, scientists have studied the phenomenon of perception for many years and they have come up with some amazing findings.
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We perceive the reality that surrounds us through our senses. These traditionally have included sight, smell, taste, touch, and hearing. On top of these we have additional senses such as the ability to perceive heat or cold, the ability to perceive noxious stimuli (pain), and the ability to perceive acceleration and balance, among others. Each of these senses detects aspects of the world around or inside us and is associated with certain receptors in our body. Despite all that you may have read in sensationalist publications, no claim of extrasensory perception (ESP) has ever been validated. To perceive an aspect of reality, we need to have a receptor in our bodies that will detect it, and one of the consequences of this is that if we don’t have said receptor, we will not perceive it.
 
From studying other organisms in our planet we have learned that their perception of reality is different from ours. For example, a human, a dog, a cat, a bird, a snake, and a butterfly can look at the same image and perceive it different ways. And this example only covers the sense of sight. Part of the reason this is the case is that other living things have receptors that we lack. Many snakes can “see” heat emission in great detail, which allows them to identify a prey or a predator in absolute darkness. Various organisms, including species of insects, birds, fish, and mollusks, can detect ultraviolet light. Migratory birds and other animals can detect magnetic fields, which allow them to navigate accurately following the Earth’s magnetic field on long treks. Sharks, rays, and skates, and other species can detect weak electric fields, a sense that they use to communicate or detect prey. Insects such as locusts and bees can see polarized light and use it for navigation. Some species of shrimp can detect ionizing radiation.
 
The above examples point to the existence of hidden aspects of reality that are beyond our experience, and indicate that our perception of reality is not complete. It must be acknowledged, however, that we have been able to compensate for our limitations with our intellect. We can build devices such as infrared or polarized light glasses, compasses, Geiger counters, and other type of detectors that can allow us to perceive or at least measure and exploit these hidden realities. In fact, we have gone beyond that and developed devices capable of perceiving realities that no other life form in our planet can perceive such as imaging the inner structures of our bodies and cells, or detecting gravitational waves produced by colliding black holes.
 
But, even if our perception of reality is not complete, isn’t what we do perceive an accurate representation of said reality? Our brain utilizes the information relayed by our senses to form a representation of the reality around us; however, this representation is not necessarily true. Everyone, for example, has seen the spokes of the wheel in a moving vehicle slow down, become stationary, and even begin spinning in the opposite direction. There are situations in which our senses can fool us, and many such illusions have been catalogued and even used in art. However, it can be argued that, despite these exceptions, in the majority of cases our perception of reality must be essentially true; otherwise life would not be possible.
 
There is no question that our perception of reality must correlate with reality enough to make life possible. However, this does not mean that our perception has to be a true representation of said reality. Scientists have performed simulations pitting true (veridical) perceptions of reality against utilitarian ones where not all aspects of reality are perceived, but rather just those that make life possible with the least expenditure of energy. In these simulations, the utilitarian perceptions won out in the long term. To understand this concept, consider your computer screen. You have a number of files that show up as icons of a certain shape, color, and pattern. This utilitarian representation of computer files allows for you to efficiently interact with the computer mechanisms that make the creation, editing, archiving, and deleting of files possible, but the actual physical (veridical) reality of what a computer file looks like is nowhere near anything visualized as a desktop icon. Thus we and other living things may be wired to perceive reality in such a similar functional way that stresses utility over veracity.
 
Now that we have seen that not only our perception of reality is incomplete, but that there is also not a one to one correspondence between our perception and reality or even an overriding reason why it should be accurate, we are ready to answer the question presented in the title of this post.
 
If a tree falls in a forest and no one is around to hear it, does it make a sound?
 
When the tree hits the ground it will give rise to compression waves which will propagate through the air and the ground startling nearby wildlife. But if by “sound” we mean the unique perception by our species of these waves, then the surprising answer is: no!

Photograph by the author.