Density of common salt is about 2g/cc.
So a grain that was at the limit of (unaided) vision 1/10 mm / side would weigh about 2 microgram, Ten thousand times than we are talking about. So we need to go down to a grain about 4 microns (4/1,000 mm) on the side. A red blood cell is about 8 micron in diameter. This about ten times the limit of vision with an optical microscope.
This explanation is intriguing to me. Thanks so much for trying to explain this, and I'm trying to figure out why I'm having trouble making sense out of it.
The notion of using a "grain" of sand or salt, is a common point of reference that most people will know or understand as being tiny in the familiar everyday kind of experience.
In the context of microscopic measurements, which can't be seen by the eye unaided by magnification, or even with simple glass lens magnification, the phrase "grain" is not helpful in assessing the quality or strength of scientific measurements, and hence the evidence at issue.
It's a poor analogy for comparing the reliability of a particular DNA result, because any DNA test below the threshold of visibility to the eye, will seem equally challenged. So its a poor analogy in the context it was brought up, namely, to challenge the validity of a DNA result at issue.
It is however instructive, in getting a sense of the physical challenges at issue, in the collection, preservation testing and susceptibility to contamination at issue in this type of scientific evidence. It gives us the chance to comprehend the relative size of sample, in comparison to a common familiar object. It shows us how far down the scale of measurement we are going, in order to grasp the nature of the substance at issue.
So then, what do these measurements actually mean?
1.
"Density of common salt is about 2g/cc".
Ok, 2g means two grams. What is "cc"'s? Is this a measure of volume known as centiliters? (1/100th of a liter?).
2.
So a grain that was at the limit of (unaided) vision 1/10 mm / side would weigh about 2 microgram, Ten thousand times than we are talking about.
A. So "a grain of sand has a 1/10 mm /side" - does this mean a grain of sand with a width (or length) of 1/10th of a millimeter? (does MM stand for millimeters?).
B. "... would weigh about 2 micro-grams" (If a milligram is 1,000th of a gram, is a micro gram equal to 1/1,000th of a milligram?).
C. ... "Ten thousand times that we are talking about." (What are we talking about? I've lost the object reference).
3.
"So we need to go down to a grain about 4 microns (4/1,000 mm) on the side. A red blood cell is about 8 micron in diameter. This about ten times the limit of vision with an optical microscope."
A. ...So we need to go down to a grain of about 4 microns (4/1,000 mm) on the side... (What is a micron? Is it a 1,000th of a MM (millimeter?)
B. "A red blood cell is about 8 micron in diameter." (still not sure what a micron is, so maybe this is why I'm getting confused).
C. "This about ten times the limit of vision with an optical microscope." (Still not sure what a micron is).
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The point of this exercise, is to explore how easy it is to get lost in technical explanations, and how hard it is to gauge the audience with whom one is hopefully communicating.
I've seen this over and over, where technical explanations become hard to follow because of a gap in vocabulary and basic concepts, that make arguments harder to understand than they need to be.
Without knowledgeable people to help lead us through the darkness, we really would be lost. But talking over the heads of the audience is frustrating to the listener and speaker both. Yet it happens so often, and so often the results of the conversation go astray, are misinterpreted, or put to improper use.
Mach, Ergon, and other folks think they are experts, and routinely spout numbers, challenge experts, and generally mislead people. Their arguments are best challenged on the merits. But that's hard to do without a grounding in the facts, and its hard to be an expert in all things, so we rely on experts to help us. But I advocate following the arguments rigorously, not just blind acceptance of what experts say.
So Planingale, thanks so much for your efforts and willingness to try to explain this 'sciency stuff'. For my own part, I know I've got a seat reserved on the short yellow bus, but I'm trying.