How Real Is Your World

How Real Is Your World

It is a rare person who uses the word“realism” in everyday conversations. Realism is a noun that philosophers use when they discuss what exists independent from an observer. Stephen Hawking and Leonard Mlodinow believe no living thing truly experiences reality in its raw form. They coined the term “model-dependent realism” in their book, The Grand Design. Model-dependent realism asserts that every living creature has sensory organs that cherry-pick sights, sounds, and/or other sensations that have evolved to allow each species to survive and reproduce.

For example, what humans see is dramatically different from what a snake sees; neither picture of the world matches the “real” reality more accurately. A human could barely notice a rat at night because we have not needed to eat rats in the dark to survive. Rodent eating snakes could not have survived as a species were it not for their acute infrared vision.

Each species has a unique set of senses but none have an unaltered conduit to “reality”. We humans and other animals tend to assume what we see, for example, is what is actually before our eyes. We act as if we have a clear window through which we directly experience what’s OUT THERE. There is no doubt that there is something OUT THERE that allows humans to enjoy and share common experiences. Model-dependent realism is all about how our perceptions relate to an independent reality assuming one exists.

I will use sight as an example. What we see on a sunny day incorrectly appears to us as if photons travel an unobstructed path to our personal “TV-like” screen showing us exactly what’s OUT THERE. But we don’t directly experience the light that enables vision; photons pass through our pupils but they die as they hit light-sensitive cells, rods and cones, at the back of the eyeball (there ends the unobstructed path to our TV screen -- from our eyeball on, light itself plays no role in our vision, there is no light inside the pitch-black recesses of our brains). The photons stimulate rods and cones that generate electrical signals which travel (in the dark) up the optic nerve to the brain’s visual cortex. The visual cortex “decodes” the electrical signals (analogous to your TV or computer screen decoding electrical signals). But, unlike your TV, those electrical signals in your brain don’t produce light on a screen. Inside the visual cortex, a model of what’s OUT THERE is constructed to appear as if it were light but actually is an assembly of electrical signals scrambling through your neurons masquerading as light. Here is a short video showing an example of how neurons can coordinate with one another (in the dark, of course) to help us build a big picture of where we are in the world.

To keep neurons from overwhelming and confusing us with sensations, interneurons and chemical processes tame the active neurons and maintain enough order to provide just enough of a view of “reality” to function. For example, our eye is capable of registering a single photon but a chemical process requires at least 10 photons to stimulate rods to transfer information to the brain; cones demand 10,000 photons to register (rods are primarily used for night vision and cones for vision in daylight).

Other animals are presented with a different visual reality. Many birds see a range of ultraviolet colors that allow birds of prey to spot urine trails of rodents and voles; many fruits and berries reflect ultraviolet light that makes them stand out against green foliage highlighting food sources. What “exists” for birds and bees is quite different than what “exists” for humans and snakes; realism is modeled differently according to the needs of each creature.

Of course, we humans know this, not because our sensory organs perceive what other animals see, but because humans developed the capability to invent instruments and use logical processes to detecting things our senses cannot experience, thus expanding our understanding of realism beyond what our bodies sense. Nevertheless, we only know what nature has allowed us to know, limiting our knowledge of how expansive is the reality that is OUT THERE. Even our extended understanding of reality is incalculably limited to what our sensory organs and our logical abilities facilitate. Our realism is as model-dependent as that of the snake stalking a rat in the dark.