The other day, we went to a designer's fashion shop whose owner was rather adamant that he was never ever going to wear a face mask, and that he didn't believe the COVID-19 thing was real. When I argued for the opposing position, he pretty much dismissed what I said out of hand, claiming that "the hospitals are empty dude" and "it's all a lie". When I told him that this really isn't true, he went like "well, that's just your opinion". Well, no -- certain things are facts, not opinions. Even if you don't believe that this disease kills people, the idea that this is a matter of opinion is missing the ball by so much that I was pretty much stunned by the level of ignorance.
His whole demeanor pissed me off rather quickly. While I disagree with the position that it should be your decision whether or not to wear a mask, it's certainly possible to have that opinion. However, whether or not people need to go to hospitals is not an opinion -- it's something else entirely.
After calming down, the encounter got me thinking, and made me focus on something I'd been thinking about before but hadn't fully forumlated: the fact that some people in this world seem to misunderstand the nature of what it is to do science, and end up, under the claim of being "sceptical", with various nonsense things -- see scientology, flat earth societies, conspiracy theories, and whathaveyou.
So, here's something that might (but probably won't) help some people figuring out stuff. Even if it doesn't, it's been bothering me and I want to write it down so it won't bother me again. If you know all this stuff, it might be boring and you might want to skip this post. Otherwise, take a deep breath and read on...
Statements are things people say. They can be true or false; "the sun is blue" is an example of a statement that is trivially false. "The sun produces light" is another one that is trivially true. "The sun produces light through a process that includes hydrogen fusion" is another statement, one that is a bit more difficult to prove true or false. Another example is "Wouter Verhelst does not have a favourite color". That happens to be a true statement, but it's fairly difficult for anyone that isn't me (or any one of the other Wouters Verhelst out there) to validate as true.
While statements can be true or false, combining statements without more context is not always possible. As an example, the statement "Wouter Verhelst is a Debian Developer" is a true statement, as is the statement "Wouter Verhelst is a professional Volleybal player"; but the statement "Wouter Verhelst is a professional Volleybal player and a Debian Developer" is not, because while I am a Debian Developer, I am not a professional Volleybal player -- I just happen to share a name with someone who is.
A statement is never a fact, but it can describe a fact. When a statement is a true statement, either because we trivially know what it states to be true or because we have performed an experiment that proved beyond any possible doubt that the statement is true, then what the statement describes is a fact. For example, "Red is a color" is a statement that describes a fact (because, yes, red is definitely a color, that is a fact). Such statements are called statements of fact. There are other possible statements. "Grass is purple" is a statement, but it is not a statement of fact; because as everyone knows, grass is (usually) green.
A statement can also describe an opinion. "The Porsche 911 is a nice car" is a statement of opinion. It is one I happen to agree with, but it is certainly valid for someone else to make a statement that conflicts with this position, and there is nothing wrong with that. As the saying goes, "opinions are like assholes: everyone has one". Statements describing opinions are known as statements of opinion.
The differentiating factor between facts and opinions is that facts are universally true, whereas opinions only hold for the people who state the opinion and anyone who agrees with them. Sometimes it's difficult or even impossible to determine whether a statement is true or not. The statement "The numbers that win the South African Powerball lottery on the 31st of July 2020 are 2, 3, 5, 19, 35, and powerball 14" is not a statement of fact, because at the time of writing, the 31st of July 2020 is in the future, which at this point gives it a 1 in 24,435,180 chance to be true). However, that does not make it a statement of opinion; it is not my opinion that the above numbers will win the South African powerball; instead, it is my guess that those numbers will be correct. Another word for "guess" is hypothesis: a hypothesis is a statement that may be universally true or universally false, but for which the truth -- or its lack thereof -- cannot currently be proven beyond doubt. On Saturday, August 1st, 2020 the above statement about the South African Powerball may become a statement of fact; most likely however, it will instead become a false statement.
An unproven hypothesis may be expressed as a matter of belief. The statement "There is a God who rules the heavens and the Earth" cannot currently (or ever) be proven beyond doubt to be either true or false, which by definition makes it a hypothesis; however, for matters of religion this is entirely unimportant, as for believers the belief that the statement is correct is all that matters, whereas for nonbelievers the truth of that statement is not at all relevant. A belief is not an opinion; an opinion is not a belief.
Scientists do not deal with unproven hypotheses, except insofar that they attempt to prove, through direct observation of nature (either out in the field or in a controlled laboratory setting) that the hypothesis is, in fact, a statement of fact. This makes unprovable hypotheses unscientific -- but that does not mean that they are false, or even that they are uninteresting statements. Unscientific statements are merely statements that science cannot either prove or disprove, and that therefore lie outside of the realm of what science deals with.
Given that background, I have always found the so-called "conflict" between science and religion to be a non-sequitur. Religion deals in one type of statements; science deals in another. The do not overlap, since a statement can either be proven or it cannot, and religious statements by their very nature focus on unprovable belief rather than universal truth. Sure, the range of things that science has figured out the facts about has grown over time, which implies that religious statements have sometimes been proven false; but is it heresy to say that "animals exist that can run 120 kph" if that is the truth, even if such animals don't exist in, say, Rome?
Something very similar can be said about conspiracy theories. Yes, it is possible to hypothesize that NASA did not send men to the moon, and that all the proof contrary to that statement was somehow fabricated. However, by its very nature such a hypothesis cannot be proven or disproven (because the statement states that all proof was fabricated), which therefore implies that it is an unscientific statement.
It is good to be sceptical about what is being said to you. People can have various ideas about how the world works, but only one of those ideas -- one of the possible hypotheses -- can be true. As long as a hypothesis remains unproven, scientists love to be sceptical themselves. In fact, if you can somehow prove beyond doubt that a scientific hypothesis is false, scientists will love you -- it means they now know something more about the world and that they'll have to come up with something else, which is a lot of fun.
When a scientific experiment or observation proves that a certain hypothesis is true, then this probably turns the hypothesis into a statement of fact. That is, it is of course possible that there's a flaw in the proof, or that the experiment failed (but that the failure was somehow missed), or that no observance of a particular event happened when a scientist tried to observe something, but that this was only because the scientist missed it. If you can show that any of those possibilities hold for a scientific proof, then you'll have turned a statement of fact back into a hypothesis, or even (depending on the exact nature of the flaw) into a false statement.
There's more. It's human nature to want to be rich and famous, sometimes no matter what the cost. As such, there have been scientists who have falsified experimental results, or who have claimed to have observed something when this was not the case. For that reason, a scientific paper that gets written after an experiment turned a hypothesis into fact describes not only the results of the experiment and the observed behavior, but also the methodology: the way in which the experiment was run, with enough details so that anyone can retry the experiment.
Sometimes that may mean spending a large amount of money just to be able to run the experiment (most people don't have an LHC in their backyard, say), and in some cases some of the required materials won't be available (the latter is expecially true for, e.g., certain chemical experiments that involve highly explosive things); but the information is always there, and if you spend enough time and money reading through the available papers, you will be able to independently prove the hypothesis yourself. Scientists tend to do just that; when the results of a new experiment are published, they will try to rerun the experiment, partially because they want to see things with their own eyes; but partially also because if they can find fault in the experiment or the observed behavior, they'll have reason to write a paper of their own, which will make them a bit more rich and famous.
I guess you could say that there's three types of people who deal with
statements: scientists, who deal with provable hypotheses and
statements of fact (but who have no use for unprovable hypotheses and
statements of opinion); religious people and conspiracy theorists,
who deal with unprovable hypotheses (where the religious people deal
with these to serve a large cause, while conspiracy theorists only
care about the unprovable hypotheses); and politicians, who should
care about proven statements of fact and produce statements of
opinion, but who usually attempt the reverse of those two these days 
Anyway...
My high-school science courses are hardly an unimpeachable source, but in my opinion, formed by those courses, "falsifiability" is the difference between an hypothesis and a guess. Falsification is the process of proving an assertion false. Assertions can never be proved universally true, but can be proved false in the context of a particular set of circumstances.
It's an important point you make that scientists typically (and "science" as a discipline usually) like it when an hypothesis is proved wrong or especially when a theory (an hypothesis which has already survived many attempts to prove it wrong) is invalidated. They give out prizes for that :^) In my opinion this demonstrates that so-called "forensic science" isn't science at all: forensics is about winning arguments, and not about discovering truth, which is supposed to be the aim of science.
Your post reminded me a lot of concepts in semantics, a sub-field of linguistics. This is the scientific field studying how language is related to the "world". Of course, it's not much concerned with religion or politics.
If you want to dig a little bit deeper, you might want to read up on "possible worlds" and modal logic, e.g. from a quick glance the Stanford Encyclopedia of Philosophy entry on "Possible worlds" looks like a good starting point.
Wouter, are you going into philosophics?
Please don't. We (society) need(s) you more as a Volleybal player.
That Debian Developer should also not go do philosophics nor politics (whichever). Volleybal playing would be fine. I'm sure that would improve the Debian contributions. Philosophics? Unlikely.
We don't have enough either professional nor hobbyist Debian Developers, while we have plenty philosophers. Neither do we have enough professional Volleybal players, while again we have plenty philosophers.
Agreed. The fact that we have plenty of some resource (philosophers) doesn't necessarily mean that we couldn't use more of it ...
Ok yes. Fine. Convert yourself into a philosopher then.
grass is green. I have do disagree with your statement describing a "fact". my grass is currently yellow but it does turn green in the winter. grass may take on a different color based on available light. some people have trouble seeing certain colors, green could be one of them. I hear some animals do not see in color, grass is a shade of gray. to make your statement describing a fact more true, you must add qualifiers, which makes me more and more skeptical of your "fact", as well as your ability to define a fact.
perhaps what you meant to say is "grass is green to me and my buddies", which sounds a lot like an opinion.
expensive experiments. I say info is not enough. the info can be faked. we used to do that back in high school when we didn't have enough time to complete the experiments. we knew what the outcome was supposed to be, so we just had to falsify the data to match.
perhaps a good question is whether a hypothesis can be proven true or false with faked info. I mean, we proved it was possible back then but I'm talking about people who get paid doing science.
Covid. arguing is a bit pointless. everyone is very attached to their always unimpeachable sources of truth.
Don't get me wrong, I'm not a science skeptic, but while I understood the point to be about theoretical "scientists" and "religious" people, I think it's actually unfortunate you are using everyday terms to describe that, because if you look at what's actually going on, a fair bunch of the stuff going on in science isn't really scientific at all. If it were, there wouldn't be a reproducible crisis.
And I get the impression that religious people spend most of their time actually dealing with perhaps generally badly examined (science-wise) human stuff.
I think it's more profitable to think about scientific reasoning, and perhaps religious reasoning.
"facts are universally true". while this is nice to believe, getting universal agreement on facts may be impossible in today's world where anyone can disagree. all it takes is one person to disagree with the fact, then there goes universal.
science without doing it yourself is basically taking it on faith. if you cant afford to do it yourself, then you can't honestly say whether the methodology was followed and as a result, what the results were.
one might say frogs can't swallow with their eyes open is a fact, while many might agree, one person may say it is false. the only proof you might have is that it is on a snapple bottle cap, and he may not find your source credible. if you care and since you have no direct proof, it is up to you to find frogs and prove they can't blink while swallowing. even, then, unless you provide the methodology and have other people run the experiment to independently verify the results and happen to interpret the results to come to the same conclusion, then all you have is a bunch of statements.
we live in a world where if we agree it is true, then it is true. science is no magical path to universal truth, in fact, it requires a certain level of faith to be useful.
as everyone knows, even you, facts that are usually true (like the grass is green even when it always isn't) are close enough. ha ha.
interesting stuff, Wouter.