Our ability to detect light – we call photon to the particle/wave of light – is limited to a very narrow frequency range (or alternatively, wavelength range, as the product frequency x wavelength equals the light propagation velocity) within the very wide spectrum of electromagnetic waves, as represented in the figure. Our human detection capability spans a narrow range of photon frequencies (or wavelengths; or colors, as we conveniently say) but this range has proven sufficient for our survival in Nature. The sensory organ that detects light for us is the multitude of photoreceptors imbedded in the retinas of our eyes, as they convert the detected photon information into chemical and electrical signals of various types that go to the brain for processing. Other animal species see the world differently, typically extending their light detection capabilities further into the deep blue and ultraviolet to improve night vision for hunting, survival and/or navigation. As a result, cats, dogs and many other species do not perceive the clear sky as blue but as violet.

Through Science and Technology, however, we have developed instruments that allow us to ‘see’ through basically any other spectral window that we may choose. At lower frequencies (or equivalently, longer wavelengths), signals encoded in radio waves bring us communications, news and music from all over the world; our microwave ovens safely cook food using light in the microwave region; our wi-fi and bluetooth-equipped devices ensure wireless communications and infrared heaters bring comfort in winter; and signals encoded in infrared light pulses propagate along hundreds of thousands of kilometres of optical fibres to provide worldwide communications and the internet. At higher frequencies (or equivalently, shorter wavelengths), ultraviolet radiation from the sun interacts with Nature and stimulates a number of biological processes essential for life and the food chain that is now ours; X-rays show our bone and tissue structures in ever greater detail and Gamma rays bring information from distant cosmic events.

What we call “reality” has very little to do with what is out there. What we call reality is a very simple and crude representation of the Universe as our sensory organs allow our brain to build a picture that is effective or “good enough” for human survival. In the Universe there are no colors, no sounds, no smells, no pressures, no textures, no temperatures, not even ‘objects’ of any kind; there are just particles (elementary particles; atoms and molecules, themselves composed of elementary particles) and waves of various types propagating, bouncing around and/or bunching together. The Universe is alien to us, often violent and brutal, and we are imbedded in it. Elusive but fascinating elementary particles known as ‘neutrinos’ pass trough our bodies without us perceiving anything, to the rate of 65 billion neutrinos per each square centimeter of our body area, every second. In turn, we exist because all atoms that incorporate our bodies were previously fabricated inside distant stars that once exploded or collided, scattering those atoms in the Universe thus making them available for many types of ventures. Through our minds and the Science that the human mind has developed and continues to develop, we have been learning more and more about how Nature works and thus how we function.

Note that I am limiting these comments to the perspective offered by classical Physics. If I were to plunge deeper into the perspective offered by the more fundamental quantum Physics, the Universe world not be simply strange but utterly bizarre.

Life is good.

PS: Humans can only perceive slow variations in light intensity; fast variations are interpreted by our brain as being equivalent to no variations at all. This happens when the rate is larger than about 30 Hz or ‘cycles per second’. That’s how cinema was invented as a fast succession of images that gives the impression of continuity. We can only detect faster rates of change by using technology.