no doubt

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The fact that I really only have real knowledge of this experience in this moment doesn't mean that (reliable) knowledge is impossible. Otherwise, ordinary life would be unmanageably difficult. Observation, logical reasoning, and the scientific method do in fact yield results and are usually meaningful. What, at least to me, makes little or no sense is speculation—especially philosophical or "spiritual" speculation. That is, at best, entertainment, not truth. "Life after death" or "universal consciousness"—no one knows or can know whether these are real or not, no matter what they tell me. I can choose to believe these things. But belief is not knowledge, not even "relative" knowledge.

However, some forms of thought do have a solid, reliable foundation and can therefore be used effectively in everyday life or as a basis for developing technology. We call this "knowledge." There is reliable knowledge when there is sufficient evidence for it.

In this writing, not all forms of "knowledge" are the same. For example, I can think of the arithmetic sum of the natural numbers 5 and 3 and seem to "know" that it equals 8. Do I really know that? Not in the same way as the knowing of this moment. I don't have to think about the knowing of this moment. For the arithmetic operation, I still have to think, however briefly, and use my memory. It's not direct, immediate knowing.

Much of what we call knowledge—like arithmetic—is implicit. It presupposes a lot of science that I no longer think about—because it has become so familiar. When I was about 5 or 6 years old, it took me a lot more effort and I actually had to count my sum in my head. The rules of arithmetic had not yet been fully absorbed and had to be consciously consulted.

This is similar to the implicit knowledge of how to ride a bike or swim. All of it learned activities. After a while, the body "knows" how to do it and you don't think about it anymore.

It seems like we are certain of some things, but in fact that certainty still comes from memory—even when we no longer consciously think about it.

I can imagine all kinds of things and be told all kinds of things—but which imagined idea, which claim, is correct and which is not or less correct?

Claims can be trusted if there is sufficient evidence for their validity. The validity of a claim will always be relative. It is not about absolute proof, but it must be (provisionally) sufficient to make effective decisions based on the claim.

Sufficient evidence

Sufficient evidence can be obtained in the following ways:

1. Through observation.
   The factuality of a sensory observation as such, in my view, is beyond dispute. The accuracy of the interpretation of what is being observed is not. It may be a hallucination or a dream. So, some degree of skepticism is in order. Of course, everything can be doubted (except the fact that there is doubt), even observation (which leads to the position of 'radical skepticism'). But in practice we don't do that, because it wouldn't be very practical in everyday life or scientific work. On the other hand, one can simply be mistaken. Between seeing something and recognizing it—that is, putting it into words and naming what one sees—there occurs a process of interpretation: memory is consulted, and an attempt is made to find the best possible 'match' with previously acquired knowledge. The interpretation may then be more or less effective. You think you see a snake, but it turns out to be a piece of rope. Oops.
   
   But if in my world I see something that looks like an apple and I have no reason to assume I'm hallucinating, dreaming, or be mistaken, I see no problem at all in eating that apple. In the case of observation, explicit proof is normally not required. The observation itself is the proof.
2. Demonstrability through logical deduction.
   Take a simple statement that can be derived through basic logic (a 'modus ponens,' for example):
   1. Infrared radiation is electromagnetic radiation with wavelengths between roughly 780 nanometers and 1 millimeter (10⁶ nm) that is not visible to the human eye. Such radiation is perceived as heat.
   2. This lamp emits radiation of 3 µm (3000 nm).
   3. If the lamp is on, and I sit in front of it, I will feel warmth.

   Solid as a rock. No hole to poke through.

   In formal logic, demonstrability is an automatic process based on correctly applying a number of rules derived from the axioms of the system. Demonstrability in formal logic is therefore not the same as truth. To mark something as true requires an interpretation of reality. And ever since Gödel, we know that no formal system can be fully derived from its axioms. There will always be statements that are not provable, but may nonetheless be true...
   Still, as long as we don't have to rely on a formal system but simply on 'common sense', a valid logical formulation is sufficient to characterize something as knowledge.
3. Demonstrability through the scientific method.
   In science, the procedure of the 'empirical cycle' is usually followed to arrive at scientific knowledge. This cycle is used to gain knowledge from experience by formulating hypotheses and testing them. This occurs not only in the natural sciences but also in psychology, often through experimentation.
   The scientific method is a systematic way in which scientists explore and try to understand the world around us. It involves a sequence of steps to gather evidence, test hypotheses, and draw conclusions.
   First, scientists begin with observations or questions about something they want to understand. These observations help them form a hypothesis—a well-informed guess about how something works or why something happens.
   Next, scientists design experiments or gather data to test their hypotheses. They carefully control variables to ensure that their results are reliable and repeatable. By collecting and analyzing the data, scientists can determine whether their hypothesis is supported or not.
   If the data supports the hypothesis, scientists may repeat the experiment several times to confirm the results. They may also share their findings with other scientists through journals or conferences.
   If the data does not support the hypothesis, scientists go back to the drawing board and revise their ideas. They may form a new hypothesis and set up new experiments to test it. This process of revising and refining hypotheses is a vital part of the scientific method.
   In this way, scientific knowledge is acquired, which can always be adjusted when new facts become available.

But:

“[...] Even results that are peer-reviewed and published can be wrong. [...] I want to stress that science is not just a collection of results handed down from on high—it's a process. We can be wrong. We make assumptions, hypotheses, guesses, and we go out and check whether they work or not. And that's not a flaw, it's a feature. That's how science works.”

— Theoretical physicist Sean Carroll

An example of reliable scientific knowledge is, for instance, the Theory of Evolution. The evidence for the existence of evolution is extensive and comes from a variety of scientific disciplines. Here are some of the key pieces of evidence:

Fossil record: The fossil record offers a wealth of evidence for evolution. Fossils show the existence of many extinct species and provide a timeline of transitional forms connecting various groups of organisms. For example, the discovery of transitional fossils like Archaeopteryx, which shows characteristics of both reptiles and birds, supports the idea that birds evolved from reptilian ancestors.

Comparative anatomy: This involves studying similarities and differences in the structures of different organisms. The theory of evolution predicts that species with a common ancestor will have similar structures. Homologous structures, like the five-fingered limb in humans, cats, whales, and bats, are evidence of a shared ancestor.

Embryology: The study of embryos reveals similarities in the early developmental stages of different species. For example, embryos of fish, reptiles, birds, and mammals all display similar features early on, such as gill slits and tails, pointing to a shared evolutionary history.

Molecular biology: Molecular biology provides compelling evidence through DNA sequences, which allow scientists to compare the genetic information of different species. The more closely related two species are, the more similar their DNA. DNA analysis has revealed shared sequences and patterns of inheritance that support the idea of common descent.

Biogeography: The distribution of species across geographic regions supports evolution. The presence of closely related species on nearby islands or continents suggests they descended from a common ancestor and diverged due to geographic isolation.

Observable evidence: Scientists have documented examples of evolution happening in real time. One well-known example is the evolution of antibiotic resistance in bacteria. In response to antibiotics, bacteria can undergo genetic changes that enable them to survive and reproduce, resulting in resistant strains.

These are just a few examples of the evidence that supports the reality of evolution. The cumulative evidence from many different fields of study forms a robust foundation for the theory, which is widely accepted in the scientific community.

Another example is the Standard Model of particle physics. It describes the smallest particles in our universe and the forces acting upon them. The accuracy and success of this theory are astonishing. For instance, its prediction of the measured value of the fine-structure constant has a precision of 1 in 10⁹! At the same time, scientists are fairly certain that this theory cannot be complete, since certain observed phenomena in particle physics cannot be explained by it.

A real scientific theory is therefore not "just a theory." Theories like evolution and the Standard Model have earned the status of factual reliability and are considered highly trustworthy forms of knowledge.

However, as we'll see later, scientists are humans too, and thus susceptible to biases and equally prone to being misled by illusory (and unconscious) thought.

As long as we keep our questions — and therefore our knowledge — practical and pragmatic, there's usually no problem. Problems arise when one keeps questioning. You can always keep asking further, until you reach the boundary of our knowledge. Beyond that boundary, no verifiable answers are possible. Rational reasoning comes to a halt. We have reached the ultimate questions — a descent or ascent to the foundation or edge of knowledge. "Does life, does the universe have a meaning?, What is consciousness?, What ultimately are matter and energy?, Is there a beginning or an end?" Some will say these are the questions that really matter. Others will shrug.

Note well: only knowledge has limits. Belief is boundless — to the point of absurdity. And in direct experience, in knowing, everything is self-evident and no questions arise at all.

Here is my provisional conclusion:
Answers to ultimate questions that are taken as final are legion, but they will always remain hypotheses and, if believed, amount to a form of self-deception. In other words: as soon as answers are found to ultimate questions and these "Answers" are accepted, knowledge vanishes and religeous belief emerges.