We can't possibly know how what we don't know now would alter what we think is true, now, were we to come to know it. And we clearly do not know all. So we cannot possibly (logically) be certain that what we currently think is true or false, is true or false. And to just blindly pretend otherwise would be both illogical and dishonest. We would be deceiving ourselves deliberately. And that's a dangerous position to take in relation to the world.
All we can do is be honest about this, and trust that what we think is true will continue to function as true when we act on it.
Again, no.
I believe it was Lawrence Krauss that once said the following:
"
Science is not in the business of proving things. In fact, you could say that science is rather in the business of disproving things".
What that means, is that science can't tell you what is "absolutely true", but it certainly can tell you what is "absolutely false".
The myths under discussion here are stories that make testable predictions. And when tested, if the predictions don't check out, then we can say with certainty that the claims are
false. Because that's how you disprove claims: you look at the testable predictions and then test those predictions. When those tests fail, it means the predictions are wrong and by extension, so is the model / claim from which the predictions flow.
I'll illustrate with a less controversial (for this audience, anyway) example to drive that point home...
Suppose I'm a suspect in a murder case. I claim to have an alibi.
Say the murder took place in Brussels at noon on the third of april.
I claim that I was in Paris that whole day on a business trip and I say that my wife can confirm that, since I told her and that I also talked to her on the phone while in Paris. They interrogate my wife to confirm this story and she confirms it that I left very early in the morning by car (it's a 4 hour drive) and told her I had to go to Paris for work and that we indeed talked on the phone during the day.
So far, so good, right?
Now they check my phone records and sure enough, there are a few calls between me and my wife.
Here's the kicker: in phone records, they can track where the signal came from. If location services on my phone are up, my phone itself also has a trace of where I was. They check both and as it turns out, I was in fact in Brussels at the time of the calls.
Result: my claims have just been disproven. I was not in Paris. My phone, which I used to call my wife, was in Brussels. So so was I.
My claims have just been exposed as being lies to the detectives as well as my wife.
My claims made testable predictions: my phone signal and location services should be traced to Paris during that day.
When tested, it turns out this isn't the case. So the predictions are false. By extension, so is the claim from which the predictions followed.
So, in summary: yes, we can very very much know when a claim is "absolutely false" if and when the testable predictions are shown to fail.