Electrical "Circuits"

"The exception proves that the rule is wrong. That is the principle of science.

If there is an exception to any rule, and if it can be proved by observation, that rule is wrong."

    – Richard Feynman, The Meaning of it All, 1999 ­­­

Getting the basics right.
There are many internet sites offering suggestions on the mysteries of electricity. A few are reasonably well presented but avoid any explanation. Others state Ohm's Law and expect the reader to understand what is happening. Some portray a flow of electrons in a circuit but get the explanation horribly wrong. Then, there are many who try to use plumbing and water as an analogy of electrical theory. This merely reinforces in their minds the concept of circular flows, pumps and pressures, but they cannot produce valid water flow models to explain capacitance (electrostatics) or inductance (electromagnetism).


When teaching the basics of electricity many articles start with a battery/switch/light bulb configuration like this:

What does it teach us about electricity? Well, almost nothing. All it really shows is what a switch does.  It  simply leads to a fallacy that they later rely on when explaining electrical theory; there must be a complete circuit for a current to exist. This leads to a further fallacy that within a battery electrons move from the positive terminal to the negative terminal, thus completing a round trip for each electron. Note the flying "angels" magically transporting the electrons to the negative terminal in this screen capture from a site claiming to teach electrical theory.

However the battery/switch/light bulb configuration could be more informative if we just put one more component in the "circuit"; a capacitor.
Watch what happens now.

When the switch is closed the lamp briefly glows but then goes out. Furthermore, repeated action of the switch has no effect whatsoever. I can imagine that those who see the lamp glow will think; "There is a continuous loop". But when the lamp goes out, they have no explanation. To them, there was a continuous loop but now there isn't. In fact, there never was a continuous loop. Not one electron ever passed through the capacitor.

So there are at least two fallacies which are being taught to students as if they were indisputable facts.

• There must be a complete circuit (a continuous loop) for a current to exist.
• Within a battery, electrons flow from the positive terminal to the negative terminal.

There's just so much wrong with these two statements that it's difficult to know where to start.
The use of the word "circuit" is misleading. Describing how a switch works, does not explain electrical theory. So let's forget all that rubbish and start from the beginning.

Protons are the largest objects in an atom. They form the centre of an atom (called the nucleus). The type of atom is determined by the number of protons in the nucleus. Protons are positively charged (shown as red in this animation). The nucleus of the atom contains protons and neutrons. Neutrons (shown as purple) are the same size as protons but they do not have any charge, so they play no part in basic electrical theory. Circling the nucleus are electrons. There are two atomic particles that are important in the study of electricity; protons and electrons.

When we say that the nucleus of an atom is positively charged, the word "positive" is purely arbitrary. But whatever we call it, we do so to distinguish between the charge of a proton and the charge of the electron. Electrons are said to be negatively charged.
In any object, when there are as many protons as there are electrons, it is neutral (uncharged). If there were more electrons than protons then it would be negatively charged. If there were more protons than electrons it would be positively charged.

Now for something to memorize:

1. Like charges repel each other. (Same repel)
2. Unlike charges attract each other. (Opposites attract)

Almost all electrical activity operates on these two principles.

In a solid, like a piece of copper wire, the copper atoms cannot move around. The best they can do is wobble a bit when they get warm. The outermost shell of a copper atom contains just one electron (the white one in the following animation). With enough energy, such as heat, this electron can be easily dislodged from the atom. It is this electron that we now call a free electron.

It is estimated that at room temperature, there will be one free electron for each copper atom. The free electrons are able to move around from atom to atom. Sometimes combining with an atom and sometimes becoming free again. The free electrons are moving around in different directions and at different speeds. But they are always responding to the balance of the forces of attraction and repulsion. Electrons are always in motion.

The next animation shows that electrons will move away from each other and will disperse to fill the available space. In doing so, they transfer the charge. It also shows what happens when a length of copper wire is connected to the positive terminal of a battery and what happens with a wire connected to the negative terminal. Electrons will move into the positive terminal so that the wire is at the same potential (charge) as the positive terminal. Same for the negative, electrons will move out of the battery and disperse to fill the space available, thus making it at the same potential (charge). It also shows how electrons move toward the positive terminal even before the terminal comes in contact with the wire. And how the electrons move away from the negative terminal as it approaches the wire. This demonstrates something called parasitic (stray) capacitance.

So how does a capacitor work?
A capacitor is made of two plates (actually two sheets of metal foil). These two plates are often separated by an insulator so that they can never come in contact with each other. In the following animation, when the lower plate is connected to the negative terminal, the electrons in the upper plate are repelled away. In this case however, the electrons have nowhere to go.

To highlight the fact that electrons do not pass through a capacitor, consider this example:

When a battery is connected to two capacitors in series, Plate 1 becomes negatively charged and Plate 4 becomes positively charged. This causes the electrons in Plate 2 to move to Plate 3 of the other capacitor. The electrons in Plate 2 are repelled away from Plate 1 and attracted toward Plate 4, leaving the capacitors charged as shown. Each capacitor is now charged to half the battery voltage.
When we remove the battery and replace it with a lamp, half of the electrons in Plate 1 will move to Plate 4 thus neutralizing both plates. As this happens, the plates in-between (ie., Plates 2 and 3) will also revert to their normal neutral state of charge as the forces of attraction and repulsion are reduced. The capacitor is now discharged.
Is there a complete circuit with two capacitors in series? No. The electrons in Plates 2 and 3 and the connecting wire will never get to the battery or the lamp.

Those who assert that a closed circuit must exist before a current can exist and that this current must "flow" through each component in the circuit are misleading their students. Not one electron passes from either side of a capacitor to the other side. It is an open circuit, yet a current can exist outside the capacitor. When a capacitor is charging, there will be a current into and out of the capacitor, but never through the capacitor. When a capacitor is discharging, there will be a current into and out of the capacitor, but never through the capacitor. No current exists between the plates of a capacitor.

I can imagine some readers saying, "Oh, but to have a continuous current you must have a continuous loop".

How does this relate to Richard Feynman's quote?
Well, I only need one exception and here it is:
Shown below is a circuit which proves that a continuous loop is not necessary for a continuous current. The component values are not that critical. The 560 ohm resistor should be selected to suit the battery voltage which could be from 3 to 12 volts. For a 6 volt battery, 220 ohms will be sufficient. For a 9 volt battery, 390 ohms, and for 12 volt battery, 560 ohms. The 1M ohm resistor can be up to 5M ohm (I haven't tried greater than 5M ohms).
The point is, with the probe touching a large metal object which is not grounded, (like a toaster that is not plugged into the power outlet) the LED will flash on quickly as the metal charges. If the probe is touched on a metal object which is plugged into the power outlet then the LED will light and stay lit for as long as the probe is connected.  

Please note, there is no other electrical connection, just the probe tip. There is no possible return path. 

Basically, as indicated by ib electrons travel from the negative terminal of the battery, through the base-emitter junctions of the transistors, through the 1 megohm resistor, then to ground (the Earth). They can never return to the battery.
When there is a current ib through the transistors base-emitter junctions, there is now a current ia through the transistors collector-emitter junctions which then connects the LED to the negative battery terminal and the LED lights up.

All of the examples and explanations given above rely on the fact that like charges repel and opposite charges attract. They deal with electrostatic charges and the electrostatic fields around a conductor.
When charges move within a conductor, we call that a current.

As part of the usual excuse to argue that a circuit must have a complete loop, it is often stated that within a battery, electrons must go from the positive terminal to the negative terminal. This of course, is rubbish.
As electrons are repelled from the negative terminal and attracted toward the positive terminal, they slowly reduce the difference in charge between the terminals. The positive terminal becomes slightly less positive and the negative terminal becomes slightly less negative.

If it were possible to "transport" electrons from the positive to the negative terminal inside the battery, then the charge difference would remain the same - the battery's difference in potential (voltage) would always remain the same, even though we are using the energy that it supplies. So the battery would never go flat.

Just as with two capacitors in series, the electrons between the positive and negative terminals will never participate in illuminating the light bulb. As the positive terminal of the battery accumulates electrons from the negative terminal, the chemical ability of the battery to produce electrons in each cell is reduced. The zinc electrodes (negative terminals) are slowly dissolving in the electrolyte. The electrons produced move to the copper electrodes (the positive terminals) without going through the electrolyte. These electrons then combine with Hydrogen ions from the electrolyte to produce Hydrogen gas.

A battery is not a pump, endlessly recycling electrons. Electrons cannot pass from the positive terminal to the negative terminal. There are no "angels" magically transporting electrons to the negative battery terminal.

Finally, electrical theory is far more complex than a simple switch or any plumbing analogy.
If a student later goes on to study radio/TV transmissions then a proper understanding of electrostatics and electromagnetics will provide a segue to understanding more complex electrical and electronic equipment.

So, for students trying to understand electrical theory, beware of instructors who say things like;
"Energy is required to force the electrons to move from the zinc to the copper electrode...", or "There must be a complete loop for a current to exist",  or "Within a battery, electrons flow from the positive to the negative terminal".

It is better to think of a battery as being like a very big charged capacitor.

• Not one electron will ever return to the negative terminal of a battery.
• A circuit with batteries or capacitors is not a complete loop.
• A current can exist without a complete loop.

In AC circuits, the electrons don't actually go anywhere, they just wiggle back and forth.

This article contains artwork and animation provided by Carnegie Mellon University.

It also contains a screenshot from PhET Simulations.

The ground detector circuit and the Voltaic Pile images are mine.

Proving a Negative

1. Double negatives
    Just as with someone who says, "I haven't done no crime!". Do they mean:

    a.  There is no crime that they haven't committed?
    b.  That they have done no crime? I.e. They have committed no crime.
    c.  That they haven't done a crime? I.e. They haven't committed a crime.
    d.  That they have done crime? I.e. What they have done, was a crime.

    So too with "You can't prove a negative". Do they mean (for example):

    a.  You can't prove that pigs can't fly. (Or even; You can't prove that flying pigs don't exist.)
    b.  You can prove that pigs can't fly.
    c.  You can't prove that pigs can fly.
    d.  You can prove that pigs can fly.

    In the first case (the suspected criminal), it's generally interpretations b or c, which the claimant means with their double negative.

    Claims b and c (in each example), mean the same thing, as do a and d.

    When people use a double negative, It is important to get them to clarify which of the three interpretations (b, c or d) do they mean. Double negatives are ambiguous.

2. Unfalsifiable
    If something is unprovable, then it is untestable and unscientific.

    When someone says, "You cannot prove ..." then they are warning me that what follows is probably unfalsifiable and unscientific.

    E.g. You can't prove that God exists. Or, you can't prove that God doesn't exist.

    Questions of religion or the supernatural are not scientific. Science is about the natural, the provable, the repeatable, the testable, the evidence.

3. Examples of provable negatives
    Here are five negative claims which are provable.
    I.e. You can prove that...:

        2 + 2 ≠ 5
        Sir Isaac Newton did not watch television.
        Kangaroos do not exist on the moon.
        I am not the smartest person in the world. (That should be self-evident)
        Automobiles did not exist in the 16th century.

    These are just a few exceptions to the "rule" that you can't prove a negative.

"The exception proves that the rule is wrong. That is the principle of science. If there is an exception to any rule, and if it can be proved by observation, that rule is wrong." – Richard Feynman, according to The Meaning of it All, 1999 ­­­

4. Can you prove that?
    The claim, "You can't prove a negative" is itself, a negative.

    Can you prove that you can't prove a negative?

    If you can, then you've contradicted your claim and the claim is false.
    If you can't, then the claim is meaningless and unfalsifiable.

    A negative claim which is not provable; "You cannot prove a negative".


5. "Universal, existential negative"
 If it is impossible to prove an existential universal negative then it is equally impossible to prove an existential universal affirmative. I.e. If it is impossible to prove that something does not exist somewhere in the universe, then it is equally impossible to prove that the same something does exist somewhere in the universe.

    For every negative claim which is impossible to prove then the opposite claim is also impossible to prove.
    If it is impossible to prove that pigs can't fly then it is impossible to prove that pigs can fly.
    If it is impossible to prove that God doesn't exist then it is impossible to prove that God does exist.

To highlight the lengths that some people will go to hold onto their "you can't prove a negative" myth, I came across this: (my bolding)

"You can't prove a negative" This Error is propagating across the internet, because of this article. People are beginning to say "ha you can prove SOME negatives so this rule doesn't hold". Actually "You can't prove a negative" is actually common short hand for “you can’t prove a universal negative,” or better "existential negative". In other words, you cannot prove that some hypothetical does not exist, anywhere in the universe, because that would require that you be able to look everywhere at the same moment. And, of course, if the hypothetical something, in question is claimed to be invisible and undetectable by any means, in principle, it gets even sillier to attempt to disprove that hypothetical's existence. e.g. God or telepathy etc.Stewgreen2 (talk) 10:11, 7 May 2013 (UTC)

http://en.wikipedia.org/wiki/Talk:Evidence_of_absence

If Stewgreen2 thinks this proves that one can't prove a universal,existential negative then he should consider the following:
The obvious response to this is; you cannot prove that some hypothetical does  not  exist, anywhere in the universe, because that would require that you be able to look everywhere at the same moment. And, of course, if the hypothetical something, in question is claimed to be invisible and undetectable by any means, in principle, it gets even sillier to attempt to dis prove that hypothetical's existence. e.g. God or telepathy etc.


6. A real life proof

The Michaelson/Morley experiment showed how a claim that luminiferous aether, “an invisible and infinite material with no interaction with physical objects”, was proven to not exist. The generalisations that one can't prove a negative, or that one can't prove universal or absolute non-existence [of something], have been disproven. They are false statements. 

I need only one example to disprove the generalisations, just as a single black swan refutes the assumption that all swans are white.

 

Test

Making Things Human

One of the more common things we do when writing poetry or prose is to infer that objects and animals can have human attributes or qualities. So we hear about a cruel storm, a car that refuses to start or how a male bird will seek out a female so that he can pass on his genes to his offspring. The storm may cause severe damage and loss of life, but it doesn't do so because it is vindictive or cruel. The car is unable to start because there is some mechanical fault, not because it doesn't want to go somewhere. The male bird has no knowledge of genetics so it is unlikely that it would be his motivation to procreate.

We call this anthropomorphism, particularly when referring to non-human animals. When applied to non-living things like storms or cars, in the field of logic it's called a pathetic fallacy.

The use of anthropomorphisms in poetry, general prose and fiction is an acceptable, descriptive, even a desirable quality of communication. However in science and the teaching of science it often indicates that whoever uses such techniques is attempting to conceal the fact that they don't understand the principle that they are discussing.

On a recent online forum a scientist was attempting to describe the Laws of Thermodynamics to non-scientists. He referred to an experiment involving two solid metal spheres in a vacuum, close, but not touching each other and he wrote, "They each detect the temperature of the other because they detect the peak frequency and that frequency is proportional to the absolute temperature". The only word that should concern us for the moment is the use of the word detect. Now detect means, to find out, or discover the existence or presence of something. A simple solid metal sphere cannot detect anything! The use of the word detect in this example is inappropriate and misleading.

A glass thermometer contains a liquid which expands when it is heated. We can use this device to detect when the temperature rises or falls, but the liquid itself cannot detect anything. The liquid simply expands or contracts relative to its temperature. It would be misleading and scientifically incorrect to say that the liquid detects the temperature of the room and adjusts its volume accordingly.

Can non-living things be manufactured such that they appear to detect the presence of other things? Well, yes! A thermostat can control a heater in a room and can respond to a change in the temperature of that room. If the temperature is below a certain point, the thermostat switches the heater on and when the temperature is above another point the thermostat switches the heater off. In this sense however the thermostat merely appears to us as though it is detecting the room temperature.

Prior to the discovery of electricity and the invention of thermostats and electric heaters, suggesting that a thing could "detect" and control the temperature of a room would be considered as laughable. Today, it is considered acceptable and normal. However we must always be alert to the misuse of such words when we talk about any technological advancement such as computers. As Sir Arthur C. Clarke wrote, "Any sufficiently advanced technology is indistinguishable from magic". Behind every magic trick there is a practical explanation of how the trick was performed. We know the woman was not actually cut in half, it just appears that way.

Computers do not think, they do not know. In fact they can only repeat to us those things that we have previously instructed them to repeat to us. Just as the humble thermostat was designed to respond to the temperature of a room, it doesn't find out or discover the temperature. Or, like a typewriter, a computer doesn't know anything about the words that I type; it merely displays the letters represented by the keys on the keyboard. It is up to me to press the keys in the right order to produce the words which form the sentences.

In some far distant future time, it may be appropriate to refer to some incredibly complex machine as thinking or knowing etc., but for now such terms are misleading at least in the scientific sense.

I have selected the use of the word detect because it illustrates the fine line between a scientific explanation and a simple anthropomorphism. In matters of science and technology it is important to choose your words carefully and avoid anthropomorphism. If you are listening to someone giving a scientific explanation then be sceptical when they use anthropomorphisms. If possible, ask them to rephrase their explanation because they have resorted to a pathetic fallacy.

James Randi Lecture @ CalTech in 1992.

http://www.youtube.com/watch?v=qWJTUAezxAI

James Randi describes, in a humourous way, a thought experiment, intended to demonstrate that one cannot prove a negative.  He imagines taking 1000 reindeer to the top of the World Trade Centre to push them, one at a time, off the roof. "You're going to test whether or not reindeer can fly."
As expected, they all fall to their deaths. His comedic way is quite entertaining, but tapers off as he gets closer to making his point.

"Now, what have we proven with this experiment?
Have we proven that reindeer cannot fly? No! Of course not.
Think about it now. We've only shown that; on this occasion, under these conditions of atmospheric pressure, temperature, radiation, all these sort of things, at this position geographically, on this season etc. that these 1000 reindeer either could not fly or, chose not to..."

These 1000 reindeer did not fly, however it may have been the "atmospheric pressure" etc, that prevented them from flying? By that same reasoning, you can't prove that dead sparrows or rocks, can't fly because, it may be the atmospheric pressure etc, preventing them from flying.

"Now, if the second, then we know something certainly about the IQ of the average reindeer...
However, we have not proven a negative. We cannot prove a negative, technically, rationally and philosophically speaking.
However, people will often look at this example and say, 'Well, how many reindeer would you have to test?' Now I'm not going to get into the statistics of the thing... I'm not going to get into the arguments on the matter, I will only tell you that you cannot prove a negative and I think that's a rather good example that you might wish to use in illustrating your point.
The other folks who claim that it is so are required to prove it. And, if it's so, it's very easy. Just show me one flying reindeer!
Of course then they come up with the rationalizations and they say, 'Oh no it's only the 8 tiny reindeer who live at the north pole who can and will, on the evening of December the 24th, fly to do that specific job'. In that case you have to throw up your hands and say, 'Well, I don't think that your hypothesis is very testable."

Let's start with his first question; "Now, what have we proven with this experiment?".
Have we proven that reindeer cannot fly? Mr Randi's answer : No!
Have we proven that reindeer can fly? Answer : No!
So what have we proven with this experiment?  Answer : If you throw reindeer off a tall building, they will probably die.
So the rest of his performance is simply to reiterate his assertion that you cannot prove a negative.

What was the point of his thought experiment?
"We cannot prove a negative, technically, rationally and philosophically speaking". Where is the evidence?

Note the association; those who would argue against his "You can't prove a negative" assertion, would also argue that reindeer can fly. And of course, people who would argue that reindeer can fly are stupid, just like those who would argue against his statement.
Like all good comedians, the punchline is stated as a quick one-liner: "The other folks who claim that it is so, are required to prove it. And, if it's so, it's very easy. Just show me one flying reindeer!".

This is a common misdirection technique used by con-men and magicians.
He plays his audience as any professional magician or comedian would. He distracts his audience with the preposterous concept of throwing 1000 reindeer off the (then) world's tallest buildings. While the audience is still visualizing such a ghastly, ridiculous scenario, he quickly slips in his message that he wants the audience to believe.
Now comes the switch. Let everyone know that only those people who believe that reindeer can fly, would also believe that it is possible to prove a negative. So, after watching his show, if you believe that he has proved that "You cannot prove a negative", then you have been conned.

Personally, I'm not sure whether he was there to give a lecture or to be the comic relief. Unfortunately, so many people believe his joke.

Here's the statement that Mr Randi considers to be a fundamental, self-evident truth (an axiom):
"You cannot prove a negative". The statement itself is a negative.
Can you prove that you cannot prove a negative?
If you can, then you have just proven a negative and contradicted your statement.
If you cannot, then the statement is not an axiom.

From Wikipedia - Evidence of absence. As of 23 Sept 2013 :

"In 1992 during a presentation at Caltech, skeptic James Randi uses the phrase "you can't prove a negative". He claims that he cannot prove a negative (such that telepathy does not exist), but he also argues that an individual who claims telepathy exists must prove so. He discusses that induction is often used as a mode of proving a thesis, but if an individual assumes that something is or is not, then the person must prove so. Further, as he says, he does not take an advocacy position, as a lawyer would. He says that he cannot prove that a negative is true, but he could attempt to use evidence and induction to support a claim that he is biased toward, such as a claim that something does not exist (ex. flying reindeer)."

http://en.wikipedia.org/wiki/Evidence_of_absence

Of course Mr Randi should use evidence and induction to support his claim, that reindeer cannot fly, but what he hasn't proven, nor given any evidence to support, is his assertion that one cannot prove a negative.
All in all, Mr Randi has just dismissed his 1000 dead reindeer evidence as inconclusive, simply because he wants to believe that you can't prove a negative.

Where Falsehoods Begin

In an attempt to discredit and refute Karl Popper, a forum commenter wrote: "It is not falsifiability that makes a conjecture a scientific hypothesis it is being able to test it."

However, what did Karl Popper ("Conjectures and Refutations" - 1963) say about it?

"Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks."

"The criterion of the scientific status of a theory is its falsifiability, or refutability, or testability." — Karl Popper, (Popper, CR, 36)

If "Testability is falsifiability" as Popper says, then the commenter's sentence illustrates his ignorance. By exchanging the word falsifiability with testability we get - It is not falsifiability testability that makes a conjecture a scientific hypothesis it is being able to test it.
So, in trying to show that Popper is wrong, the commenter has shown that Popper is correct. The commenter actually agrees with Popper but, he just doesn't realize it. Had the commenter written; "What makes a conjecture a scientific hypothesis is being able to test it", or, "Testability makes a conjecture a scientific hypothesis", then I'm sure Popper would have agreed with either version.

The commenter also wrote:
"Newtons laws of motion in the context of human scaled dimensions, masses, speeds, and precision cannot be falsified."
Of course, Newton's laws of motion are tested every time we see, and measure, anything in motion. If at anytime something does not move as described by Newton's laws of motion, only then, could we claim that Newton's laws are false, under certain conditions. As such, Newton's laws of motion have been, and continue to be, tested and thus are falsifiable.
As for the commenter's statement, "cannot be falsified", if he means that they must be true, then he is reducing science to the level of religion and dogmatism, because only religions are arrogant enough to deem themselves to be the holders of ultimate, definitive truth. Instead, if he means, the laws of motion have yet to be shown to be false or, are yet to be falsified, then he is correct; in which case, his error is the use of the definitive, "cannot".

Nature does not comply with the laws of physics, the laws of physics merely attempt to describe nature.

In science, we must be careful with the words and phrases used to convey a concept. Slight variations in one interpretation can lead to further exaggeration in another, and so on and so on, until the concept may eventually be completely misrepresented. As it was with, "It is not falsifiability that makes a conjecture a scientific hypothesis it is being able to test it."
The commenter went on to say the following:

"Popper? His brilliant idea is that you cannot know that anything is true. All you can do is show that something is likely false. Hence is[sic] prescription for knowing is lurching from something that is probably false to something else that is probably false until you know everything that is false.
However, by his conjecture (not theory), you cannot know that it is true that you know everything that is false. Somehow that is supposed to constitute knowledge. I do agree that knowing what NOT to do is helpful but if you don’t know what TO do, you are at dead zero and I do mean dead."

"Popper published his poppycock to sell books, talks, and seminars and not to give instructions as to how humans can learn to know anything at all useful. What we need to know about reality is what is life giving, supporting, and enhancing. His method only tells us how to avoid killing our selves by actually killing ourselves. Then it is too late for us to use Popper “Knowledge”."

Unfortunately, the commenter appears to be unfamiliar with the works of Karl Popper. He may have read some of Popper's statements, but is either unable to consider them, or is unwilling to change his preconceived (ill-conceived?) ideas. I could go through his rant, sentence by sentence and try to refute his claims. However, when I read, "His method only tells us how to avoid killing our selves by actually killing ourselves." I think to myself, Nah!

The commenter's words sound assertive and scientific, implying that he is well read on the topic, and as such, many readers will accept them as the truth. They may even repeat the assertions to others when they are discussing Karl Popper's writings.

Of course, that same criticism that the commenter's words sound assertive and scientific etc, can be applied to me. The difference (I hope), is that I have tried to examine his claims and given some argument as to why I think his claims are misleading or inappropriate, whereas, the commenter has not afforded Popper the same courtesy.

This is how falsehoods and misconceptions get transformed, in the minds of some, into axioms.

Fishing For Evidence

Image by Google Maps

Early one morning six boys came across a beautiful stream. None of them had ever tried to catch fish in this stream. Greg, one of the boys, casually looked at the stream and said, "I don't think there are any fish in there". The other boys asked, "Why not? We can't see the bottom of the stream so we can't say there are no fish". They then added, "The absence of evidence is not evidence of absence".

They decided to set up camp near the stream with the intention of spending a few days fishing and camping. They eagerly assembled their fishing tackle and set to the serious business of challenging who would catch the first or the largest or the most fish. The boys each had a preferred technique, some used live bait, some used artificial lures and some had fly fishing gear.

By lunchtime, the boys gathered at their camp. Nobody had caught a fish and nobody even reported a nibble. The mood was starting to change about catching fish in this stream. Some boys even thought Greg was right to declare there were no fish here. A short discussion about the absence of evidence ensued. One boy gave an analogy to explain the idea. He said, "Astronomers know a lot about the planet Mars. They have looked at it through the most powerful telescopes available and are unable to detect any signs of life on Mars. Being unable to detect life at such vast distance is not evidence for the absence of life on Mars."

They all agreed that they would stay and continue fishing. By sunset, still no fish had been caught. As they ate some of the tinned food they brought, the discussion turned again to the absence of evidence. Some asked, "How much absence of fish would it take to declare that there were no fish in this stream?” As the mood, along with the daylight, got darker and darker, it was decided that if no fish had been caught by lunchtime tomorrow they would pack up and find another site.

As agreed the night before, at lunchtime the boys had moved camp and declared that the absence of any evidence of fish is evidence of the absence of fish.

At the new site, which was similar to the old site, Greg mumbled something about how there probably won't be any fish here either. Everyone else groaned. Within half an hour of the first line being cast, fish were caught and Greg was happy to be proven wrong. They enjoyed their fish supper and bragged about the first to catch a fish, catching the biggest and catching the most fish and as all fishermen do, the ones that got away. Later that evening the discussion reverted to the phrase "the absence of evidence".

Greg admitted that he had no way of knowing whether there were fish at either site. He agreed that his absence of evidence was not evidence of the absence of fish. Later another boy reminded them that when they left the first site, they had all agreed that the absence of evidence was evidence of the absence of fish.  They realized, after a day and a half trying to catch fish, that by not catching any, this was evidence that there were no fish to catch.

So how can two such obviously contradictory statements as, "The absence of evidence is not evidence of absence" and "The absence of evidence is evidence of absence" both be correct? The contradiction is due to equivocation (ambiguity) over the meaning of "absence of evidence". Greg had no evidence to support his claim that there were no fish, so his absence of evidence was not evidence of absence (no fish to be caught). After spending a day and a half fishing, the boys now had some evidence that there were no fish to be caught, so the absence of evidence (no fish caught) was evidence of absence (no fish to be caught).

When anyone makes the statement, "The absence of evidence is not evidence of absence" consider carefully what they mean by "the absence of evidence". It may be necessary to ask if evidence has been sought and if it has, then the absence of supporting evidence is indeed evidence against whatever is claimed to exist.