Some examples of the 'empirical' classification presented in our past post are given below. Not all phenomena are observable as we see. Many of them are non-observable and cannot be sensed in any way.
Observable and cyclic:
- Conspicuous astronomical events: apparent movement of celestial bodies, eclipses of the sun, moon, tides - rise and fall of sea level;
- Seasonal ocurrrences: change of color of leaves in the beginning of autumn, the menstrual cycle;
Observable and noncyclic:
A large category of natural ocurrences such as:
- Weather and climate: storms, lightning, hurricanes;
- Life (biology): an interesting example are bat´s sounds at the threshold of what can be heard by humans (below 20KHz). Most of bat´s interaction with the environment is ultrasonic and, therefore (according to our nomenclature) 'invisible' (non-audible), almost all life occurrences are noncyclic and shows a strong cause and effect link;
- Geology: vulcanic eruptions (including geysers) and earthquakes. Other geological occurrences are too slow to be witnessed during the human life interval;
- Astronomy: the sudden appearance of a bright supernova (ex. SN1987A);
- Medicine: many symptons are observables and are related to (nonobservable) causes.
- Astronomy: the observation through a telescope of Jupiter´s moons transits or eclipses;
- Biology: observation of the cyclic cell division through microscopes;
- Astronomy: observation of solar prominences. Interesting enough, solar prominences are observable only during total solar eclipses.In normal conditions, the sun bright photosphere outshines their appearance that can only be observed with the use of special equipments. In general, all nonperiodic astronomical events (such as supernavas in distant galaxies) share the same features;
- Biology: observation though microscope of all types of nonperiodic biological phenomena;
- General: low amplitude sound effects: throught the use of amplifiers, unhearble sounds can become hearable;
- Medical techniques: Positron emission tomography. A remarkable example of something hidden (observable body structures) that can become visible through a PET scan device.
Nonobservable, invisible and noncyclic
- Thermophysics, optics: Schlieren imaging reveals very small changes in the refraction index of transparent media. Thermal plumes rising from human bodies can not be seen in any way, but are visible throught Schlieren imaging tecniques (intervening medium). The technique also allows the visualization of sound waves;
- Radio: all sorts of electromagnetic phenomena can become audible using a radio. The range of frequencies is very wide;
- Astronomy: X-ray, infrared, Ultraviolet astronomy revealing an universe we are totally blind to;
- Astrophysics and Cosmology: ~74% of what exists in the universe is invisible (and nonobservable), the so called dark energy. Dark matter is the term used to describe another special matter state that respond for 22% of what exist.The remaining 4% is made up of atoms and, therefore, matter of our ordinary knowledge.
How do we know about the existence of non-observable, invisible and sporadic events ? The secret lies in the theories or rational structures that provide ways to experimentally access them.