On the issue of whether it is possible to introduce new evidence:
1. I assert that things can be true. This is not an assertion that
we know them to be true, but that there are facts, and this is an independent variable to human consciousness.
2. Given acceptance of one, it follows that some things are true, and likewise, some things must be impossible. For example, if A is true, and mutually exclusive conditions are not possible, then we can state, with authority, that ~A is impossible. If it is true I am holding only 1 macroscopic object, an apple, in my left hand, therefore it is impossible that I am not holding an apple in my left hand. It is also impossible that I am holding a dog in my left hand. etc.
3. Let us distinguish between evidence and valid evidence. I'm not trying to play word games here. Take 'evidence' as a data point. Look out the window at the thermometer on your deck and you see it is 40 (C or F, your choice). Plenty of room for error. You read it wrong. The needle is stuck. Somebody snuck in and replaced your trusty American (F) thermometer for a nasty Canadian (C) one and you are using the wrong scale. You are having a stroke and hallucinated the whole thing. 'Valid evidence' is, in contrast, evidence that actually reflects the real world, within the error bars of the instrument. It reads 40C? Well, that means pretty darn hot, plus or minus a few degrees. The reading was accurate. I am not talking (yet) of our
knowledge of whether the reading is accurate, just whether it actually reflects reality. If it does, it is a valid data point.
4. No
valid evidence can be introduced to support an impossible event. If we reason based on valid evidence, we will conclude true things, and describe reality accurately (albeit with limitations). (elementary logic - not going through this step by step for now)
5. Therefore,
if and only if we have valid evidence, we can state that something is true, or impossible, and know that it is not possible, no matter what, for new valid evidence to come into our possesion to contradict that point.
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Okay, so can we in fact know that we possess what I am calling valid evidence? I don't want to slide in my definition and just somehow assume our human brains are capable of determining that.
Karl Popper would say no, I think. He views (I'm so simplifing his position, forgive me, this is one sentence in a internet forum post) evidence as a long chain of inductions. See enough white swans, and you conclude there are not black swans. But, you could always see a black swan, so you are never 100% certain. He actually uses the swan argument early in his book.
I, Piggy, and others say bunk to that. Valid measurements are possible (assertion at this point).
allow me a thought experiment that does not
prove the above, but allows us to think about it.
Take a GPS receiver. If it receives one satellite, you know (evidence level, not valid evidence level) your position is somewhere in a big three dimensional, hollow sphere.
If it receives two satellites, take the two big hollow spheres each satellite predicts, take their intersections, and that intersection describes the boundary of your position (with error bars, of course).
By the time you have 4 satellites, your position is pretty much pinpointed, within the aforementioned error bars.
Objections: satellites can be broken. You are assuming the world is round (actually, shaped as WGS-84 states). The receiver could be messed up. How do you know the receiver is correct (i.e., it's essential theory of operation - working perfectly within it's design, but wrongly)? etc.
Replies: First, this is a thought experiment, so let's not infinitely regress. The idea here is that once you know you have a valid data point, you can start
triangulating your new data against it, establishing known limits for its fidelity to the real world. Triangulate literally in the case of the GPS, figuratively for non-geometric problem spaces. GPS receivers and satellites have built in error detection, and they work. How? Because they know the limit of what is possible, and can discard data outside of that. Did the calculated position become the surface of the moon? Something is defective, because we know that the satellites circle the earth, and there is no possible set of measurements that would allow placement on the moon so long as the measured distance from receiver to satellite is earth distance apart.
even if by some unknown event the moon suddenly entered the earth's atsmosphere, and somehow you ended up standing on it in the position predicted by the receiver,
we still know the receiver is broken, because that would have been pure coincidence. Something in the math or display
must be wrong. Furthermore, by adding just one more data point, say, looking at your feet and noting you aren't, in fact, a few hundred thousand miles away on the moon, would suffice to disprove the idea that the receiver was correct. Oh, but I might be on LSD, and hallucinating I'm on the earth. Could be, but the next person who reads that reading ain't on LSD. Nor is the computer system designed to diagnose GPS receiver problems. Etc. Just adding a few pieces of evidence (yes, evidence, not valid evidence) allows us to weed out what is possible and impossible), and move from evidence, to valid evidence. There are combinations of truths which are impossible: we can remove possibilities from consideration. Remove enough, and we have validated our data point. We have valid evidence.
Naturally, that chain of proof started far before the GPS. We started back at the 2 rocks + 2 rocks stage, and fire burns stage, and levers multiply forces stage. We move forward, building knowledge. As I sit here typing, it is not
probable that MOSFET junctions work - it
are working.
I recognize the above is not rigorously airtight, but whatda expect from a forum post?
I assert making it airtight is the matter of tying up the loose ends, the subject matter of a book or two. One I've always wanted to write, but eh, life intrudes.
