The point I'm trying to make here is this: the claim that evidence is the sine qua non of reality has at its heart a very large assumption: that sensory evidence (e.g. the "photons of light" in your example) actually exist and bear some relation to an external reality. In other words there is no way to demonstrate from evidence that sensory "evidence" means anything. For all you or I know, everything we see, hear etc. could all simply be part of a dream, or a hallucination, or some computer simulation. as far as the physical brain is concerned, signal = signal; the brain cells don't care if the signals they are receiving have their origin in some concrete external reality or not. of course, you and I believe that the things we experience via our senses ('evidence") correspond to Real things in the Real world, but we have no way of demonstrating that to be true. We believe in the Real World, but belief is an act of faith. Experience is a subjective process, since it relies on our subjective senses. Therefore, even the "objective" scientific method is ultimately a faith-based system of thought.
So what can one know? We can only know that which we apprehend without recourse to the subjective (and uncertain) physical senses. We do not need eyes to visualize something in our "mind's eye"; we no not need ears to hear ourselves think. Logically, therefore, only those things we apprehend directly can be known to be real. We do not "feel" ourselves to be living; we are ourselves. Placed in a sensory deprivation tank, a man might come to doubt the existence of the sensible world, but he will never doubt his own existence. Therefore, the only thing we can know with 100% certainty is that we ourselves exist. Cogito ergo sum — I think, therefore I am.
The scientific method might seem to be a foolproof way to absolute certainty — but rest assured, it only seems that way. At the heart of the scientific method lies an axiom very much unprovable — that the evidence of our senses corresponds to an external reality in some meaningful way. It may be easy to believe that statement, but by the very "rules" of the scientific method itself, its truth is not demonstrable from evidence, and therefore it is very much an article of faith.
It's both. Epistemology is "a branch of philosophy that investigates the origin, nature, methods, and limits of human knowledge." Ontology is "the branch of metaphysics that studies the nature of existence or being as such." I used 'epistemology' because it includes ontology (in the same sense that semiotics includes semantics,) and because the point I am trying to make is in fact an epistemological one.
The point I'm trying to make here is this: the claim that evidence is the sine qua non of reality has at its heart a very large assumption: that sensory evidence (e.g. the "photons of light" in your example) actually exist and bear some relation to an external reality. In other words there is no way to demonstrate from evidence that sensory "evidence" means anything. For all you or I know, everything we see, hear etc. could all simply be part of a dream, or a hallucination, or some computer simulation. ...of course, you and I believe that the things we experience via our senses ('evidence") correspond to Real things in the Real world, but we have no way of demonstrating that to be true. We believe in the Real World, but belief is an act of faith. Experience is a subjective process, since it relies on our subjective senses. Therefore, even the "objective" scientific method is ultimately a faith-based system of thought.
Firstly, the question of whether or not human senses faithfully report 'real' information about 'the real world' to the human brain is an example of the issue of the interpretation of tokenized information I spoke of earlier. Wrongly believing that sensory data represents information about 'the real world' would be an example of an interpretive error. The information would be true, but wrongly interpreted. The sensory signals received by our brain are what they are. It's up to us to figure out what they mean. That's one of the central issues of epistemology.
Secondly, 'believing in the actual existence' of what we like to think of as 'the real world external to ourselves' may or may not be an act of faith. To paraphrase a certain former President of the US, it depends on what the meaning of 'believe' is. I address that more deeply below.
So what can one know? We can only know that which we apprehend without recourse to the subjective (and uncertain) physical senses. ...Logically, therefore, only those things we apprehend directly can be known to be real. ...Placed in a sensory deprivation tank, a man might come to doubt the existence of the sensible world, but he will never doubt his own existence. Therefore, the only thing we can know with 100% certainty is that we ourselves exist. Cogito ergo sum — I think, therefore I am.
The epistemological problem goes even deeper than that. Remember, epistemology is all about what can be known, and how it can be known. As it turns out, what can be known also depends on what the meaning of 'know' is. But again, I'll go into that more deeply below.
But I will point out that a person placed in a perfectly effective sensory deprivation tank would have no way of knowing whether he was alive as a biological entity, or simply a simulation being run on a computer the likes of which doesn't yet exist (in our time and place.) Nor would he have any way of knowing which of his thoughts were his, and which were injected by some external agent.
The scientific method might seem to be a foolproof way to absolute certainty — but rest assured, it only seems that way. At the heart of the scientific method lies an axiom very much unprovable — that the evidence of our senses corresponds to an external reality in some meaningful way. It may be easy to believe that statement, but by the very "rules" of the scientific method itself, its truth is not demonstrable from evidence, and therefore it is very much an article of faith.
Yes and no. Yes, the truth of the belief that "the evidence of our senses corresponds to an external reality in some meaningful way" is not provable. No, that doesn't mean it has to be taken on faith.
What can be proven? You can prove things to be true by definition. And you can formulate a system of logic, and statements that are well-formed according to the syntactic rules of your system of logic can be proven to be true or false (or perhaps undecidable,) according to the rules of your system of logic. And that's it. Nothing else can be 'proven' in any absolute sense.
Note that the meaning of the terms 'true,' 'false,' and 'prove' in the above paragraph are defined by a formal system of logic, and that systems of logic are inherently based on the manipulation of symbols. Also note that 'true,' 'false' and 'prove' are themselves symbols.
Reality is composed of tokens that aren't symbols. This matters because symbols can be used to state that which is not true--and in the case where such statements are about 'the real world,' there's no way to prove in any absolute sense that what the statement says about 'the real world' is true--even if you can 'prove' it's truth according to the rules of logic. A logical proof is still a statement composed of symbols.
Absolute proof requires symbols, and is necessarily restricted to the domain of symbols. Once one goes beyond the symbolic domain, 'absolute proof' does not exist. Statements made up of symbols that are about 'the real world' serve as maps or models of reality. But the map is not the territory, and there's no way to prove (in any absolute sense) that the map or model is an accurate reflection of what is being mapped or modelled.
For any statement that purports to state an absolute proof about 'the real world,' one can always ask, "And why is that true?" There is no assertion of fact that is not subject to such a challenge. The answer to any such challenge must itself be another assertion of one or more facts, each of which will again be subject to the same challenge. There is no transitive closure. That's why there is no such thing as absolute proof, outside of the domain of symbols.
A lot of confusion has been caused by the fact that logic and science both use the term 'prove,' but don't mean the same thing by it. So what's the difference between a logical proof and a scientific proof?
Ultimately, a logical proof shows that something is true or false by definition. A system of logic can be considered to be a symbolic machine whose purpose and effect is to compute the meaning (definition!) of a statement, where the meaning must be one of the possible truth values permitted by the system (usually these are 'true,' 'false' and 'undecidable/undefined,' although the latter is often tacked on as an afterthought.)
In contrast, a scietific proof of a theory shows that the theory is more likely to be true than any alternative so far considered. Science is not a definitional system based on symbols, but an obersvational system based on the most probably (or even the most scientifically useful/productive) interpretation of the evidence (non-symbolic tokens.) Science can't work any other way, precisely because absolute proof does not exist outside of the domain of symbols. So logic and science use different epistemological paradigms. In logic, it's all about what can be absolutely proven or disproven. In science, it's all about which theories best stand up to criticism--and that can and does change over time.
As long as the scientist understands that ALL his beliefs are subject to criticism, and that the result of that criticism may be that he will come to prefer a different belief, and that that applies equally to each and every one of his beliefs, then he can fairly say that his beliefs are not based in any way on faith.
Note that belief in rationalism and objective evidence must be one of the beliefs held to be subject to criticism (and hence falsifiable.)