Or an illusion, anyway. (If you’re confused by that sentence, go read the title).
This is what you see:
Pretty, right? All that green grass and blue-ish water…
What’s actually happening is that (deep breath and simplifying):
- Electromagnetic radiation of many different wavelengths (also known as ‘light of many different colours and some that’s invisible to us’) is radiated by the sun and arrives on earth (see more here).
- The light hits objects and, depending on the properties of that object, different amounts and colours of light are reflected.
- Some of that light hits the cornea of the human eye and is directed onto the retina.
- The retina consists of light-detecting cells called rods and cones, which, through some complex chemical reactions, produce different electrical impulses depending on the light that hits them.
- These electrical impulses travel down the optic nerve and arrive in the brain (see more here).
- The brain then interprets these electrical impulses to produce an image of the world.
But the really clever thing is that what you (that’s the conscious, thinking you) see is not what’s actually there (lots and lots of atoms which consist mostly of empty space) or even what’s actually hitting your retina (electromagnetic radiation of varying wavelengths). The brain uses the input from your eyes (both at this moment and in the past) to produce a model of the world that is as efficient and useful (though not necessarily as accurate) as possible.
You have a blind spot in the centre of each eye where the optic nerve passes through the retina to the brain. Mostly the brain fills it in by using information from the other eye. And if you’re only using one eye? It makes it up. Try this.
This is just one example of how the brain takes limited data and turns it into useful information. For excruciating detail on the subject, see here.
The talk that actually inspired me to write this post is here: