Absence cannot be sensed.

In the material world, bumping (i.e. encountering) is the essence. Two objects must bump when they attempt to occupy the same space at the same time. Two objects cannot occupy the same space at any given time. Any one object cannot occupy two spaces at any given time. Therefore, bumping happens.

When they bump, they interact—first, changing their kinetic energy without changing their mass and shape. Changes in their relative momentum. If they share or exchange their mass, new shapes emerge. Not only the kinetic energy but also the original two objects change into new objects that did not exist before the bump.

The frequency of bumping depends on the concentrations of the two objects and their relative momentum.

Senses are unique properties of life. We do not use this word to describe inanimate objects. What are senses?

Humans have seven senses, at least. Visual, that is sensed by the eyes, audible, that is sensed by the ears, smells by the nose, and tastes by the tongue. The skin senses touch and heat. The inner ear senses gravity. They are completely independent physical properties. None can replace or supplement others. The eyes cannot hear.

Of course, our material world consists of more than seven physical properties. We cannot sense outside of our seven senses.  For example, we cannot sense UV light, while our skin cells can be damaged by it, causing sunburn.  Although we can sense the pain of sunburn, we cannot sense UV light. X-rays and infrared radiation are in the same situation. In this line, we cannot sense oxygen, either. We can sense the subsequent damage as short of breath. Because we cannot sense it, we cannot tell where oxygen is. Therefore, people can accidentally encounter a lack of oxygen in mines and other small, confined spaces without ventilation.

Senses can help change the frequency of bumping and encountering. It is important to realize that the senses themselves are physical bumping/encountering.

Here, there are two layers of bumping. The first layer is what I would call the real encounters. Bumping into foods, mates and predators. The frequency of encounters depends on their concentrations and their relative momentum.

Senses are the physical encounters forming the second layer before the real encounters. Sensing is the detection of preceding physical events associated with real encounters. By detecting the associated physical events, it becomes possible to change the frequency of real encounters through reaction.

A set of sensing-reaction can modify the frequency of real encounters, facilitating the finding of food and mates, and avoiding bumping into predators.

This process can be automated and does not require any cognitive effort. Imagine automated doors or escalators. Sensing objects and reacting. One stereotypical reaction after one specific sensing.  Again, sensing is a highly specific detection of one physical property associated with a subsequent real encounter.

It is essential to acknowledge that there is no way to sense everything present on Earth. Our human cognitive world is sense-dependent. Something we can sense reproducibly is ‘exist’. Something we cannot sense is ‘inexist’.

Then, how do we know the existence of UV, X-rays, infrared and oxygen? Because we made them reproducibly sensible using tools (i.e. experimental tools like a telescope, microscope, various detectors). Using tools, the invisible became visible reproducibly.  Although the original physical properties are not directly sensed, we have obtained a means to sense their existence indirectly. This is the history of modern science. Something that cannot be sensed directly is visualized indirectly using tools. Reproducible indirect observations are evidence of the existence of the invisible. This has been the way that modern science has progressed. Based on the reproducible indirect observable evidence, we cognize the existence of insensible.

We recognize an object using our senses. Based on the senses, we know it exists. Can we sense something that does not exist? We cannot. We cannot sense insensible. Insensible is inexistence.

Absence cannot be sensed, while presence can be sensed. Absence only exists in cognition, that is, the memory of a set of sense-reaction.  A set of sense-reaction can change the frequency of real encounters.  This series of sense, reaction, and encounter is equivalent to the logic, that is, an event sequence. Find a smell – follow the smell – find a food. The accuracy of this logic is highly varied. For example, the chance of finding a food could be 99% or less than 1%. If one knows the chance rate, one gets disappointed or pleased. Expectation. This expectation allows cognition of absence. Something occurs in the sense, but no subsequent encounter. Without this memory, no disappointment. No way to notice the absence.

Can we sense an insufficiency or shortcoming? When you cook a dish, you notice that one ingredient or seasoning is missing or is not enough. You have likely noticed this at the moment when you use it. Do you pause to get a new one, or do you improvise? 

Your favourite dish might be ruined. You may regret not checking all the ingredients before starting to cook.  You couldn’t cognize the problem in advance until you face (i.e. sense) it. Your improvisation skills may mask the problem, but depending on what is missing, the prepared dish could be something entirely different from the originally intended dish.

Absence cannot be sensed. But only cognized based on memory and logic. If one has the knowledge, the absence is addressed before it causes a problem. On the other hand, the problem caused by the absence is sensed and initiates a reaction – compensation (or improvisation). Again, without cognition, absence is not realized. Because absence is insensible to avoid, accidental encounters with the problems caused by absence are inevitable in certain environments.

How did the sense evolve in living organisms?

At the onset of life, no sense is needed. Life is the cyclic activities of growth, replication and reproduction. Everything necessary for life was available, abundant and ubiquitous in the adjacent local environment. Without senses, enough encounters to continue in the local environment. Simultaneously, the continuity of the cyclic activities is constrained by the local abundance. Whatever the reasons, if one’s local environment changes due to one’s own movement or changes in the local environment, the continuity of the cyclic activities is compromised. The end of life.

No sense. Therefore, no chance to avoid for individual organisms. Everything is by chance.

No point in sensing anything abundant. Something that is abundant in one place or time but not abundant in another place or time, and its absence causes a problem in the continuity of the cyclic activities. That is worth sensing because sensing allows them to avoid the problem.

The cyclic activities of growth, replication and reproduction are the sequential phases. Importantly, not all phases are equally sensitive to perturbation. Growth is relatively easily paused, while replication and reproduction are not. Rather than pausing, it is better not to initiate it.  

Life started because everything necessary was available in the vicinity. Non-stop cycling without any sense. The fluctuation in available resources compromises the non-stop cycling and leads to failure. Some can escape this because the vulnerability to the resource fluctuation is phase-dependent. If one can sense the fluctuation and pause at the phase less vulnerable to the fluctuation, the chance of its continuation increases.

However, I mentioned that absence cannot be sensed. Is there any way?

If the absence of one thing can cause the presence of the other, the absence is sensible as the presence of something else. This type of mechanism is used in sensing amino acid deprivation in a cell. Amino acids are the essential substrates to generate proteins. When amino acids are in short supply, cells sense that and pause protein translation from mRNAs. Simultaneously, activate autophagy to recycle amino acids from proteins. How is this sensed?

In a normal situation, amino acids saturate tRNAs, which are the vectors of amino acids to synthesize proteins on mRNA. All tRNAs bind to their specific amino acids. When amino acids are short, free tRNAs become available.  This is sensed as the absence of amino acids. In this way, initiation of protein translation will be on hold at the tolerable phase, rather than being stalled in the middle. Sensing helps the continuation in the situation of fluctuation, but is not required in the original abundance and ubiquity.

Without sensing, any encounters depend on concentration and relative momentum. Sensing and reaction modify the frequency of the encounters. Some encounters are good, like finding food and a mate; some others are bad, like bumping into a predator or jumping into a fire. Bad encounters can be tolerated/compensated for, like running faster than a predator or with a fireproof jacket. But not always. One could have just had a leg injury or eaten too much a minute ago. Unable to run fast enough. Or the jacket had holes because it was used too often. Sensing allows one to avoid bad encounters. On the other hand, compensation has limitations.

Knowledge is the statement of the recognition of repetitiveness in a reproduced event in the past. Repetitiveness in a reproduced event is a temporal series of subevents within a reproduced event. This is logic in knowledge. Because of repetitiveness, knowledge can be projected to the future for making predictions. Good knowledge and correct logic are highly reproducible.

Absence and inexistence in senses can be cognized, based on knowledge. Knowledge is memorized statements of the repetitiveness in the past. Statements are words and language. Without cognition of repetitiveness, absence cannot be cognized. Words play tremendous roles in the cognition of repetitiveness.

Language created the concept of absence and inexistence. They only exist in the language-based cognitive world.