Saturday, 28 September 2013

the difference between superstition and science

Science generally makes statements or theories predicated on evidence. Most of the time, scientists won't claim that they have a fact, but rather a correlation. A correlation tells you that two things co-relate. That is, as one changes, the other changes. You might recall y = f(x) from mathematics at school; this means that the y axis is a function of the x axis, or correlates or changes with the x axis.

Many people misunderstand scientific findings and think that scientists are often giving facts (causal relationships between x and y, say), when in fact they're just giving correlations. Consider booze, violence and poverty. In such a case, if there's a correlation, it's not an established fact that booze causes violence when coupled with poverty. Why? Because counterexample anecdotes can be found that fall outside of the booze - is - proportional - to - poverty - and - violence graph; these are called 'outliers'. Thus the theory is only generally accurate rather than a fact. Consider a rich guy who beats his wife. Booze in this case might not be involved, nor poverty. Therefore booze and poverty are not necessary or sufficient causes of assault. 

A cause is a correlation for which a mechanism can be found. A correlation is a relationship between two sets of data for which no mechanism has yet been found. The job of scientific theory is to supply that mechanism as a theory.

Now: What is superstition? I venture the following definition. A superstition is a belief based on either (a) anecdotal evidence, i.e. too few cases, or, (b) a belief based on a false assumption that causation exists where there's merely anecdotal correlation.

So, here's an example of a superstitious remark: My aunt died when a black cat crossed her path, therefore, black cats are to be avoided because they are harbingers of death. No. That's just one anecdote; so the correlation between death and black cats is anecdotal, and the theory that derives from it, is a superstition because (a) it's not giving a mechanism, and (b) it's one anecdote; we need a few thousand. 

The key differences between a scientific correlation (a law or theory), and a superstition, is the presence of a causal mechanism and quantifiers. So the following description is NOT superstitious: My aunt believed in the black cat superstition. She was driving one day, and a black cat crossed her path. Due to her panic at the sight of the black cat, she swerved into a concrete pillar at sufficient speed and mass to cause sufficient impact velocity, and died. So, in a sense, the black cat could be said to have been the cause of her death, but actually her fear was the cause of her death; the sighting of the cat was merely one component. Had she been a cat lover, say, and had a white cat had crossed her path, she still would have swerved, and she still would have died. Therefore, it is not the black cat that was the issue, but any cat at all, of any colour.

See the difference? One story connects specifically a black cat with specifically one death, and claims that that means that a general rule about black cats is true. That's also called 'fallacy of affirming the consequent': You see a black cat. When you see a black cat, you will die. You died. Therefore it was because of the black cat. In the scientific case, we have the same logical structure (a fallacy or generalisation), but look at the difference! Here we go: The scientific story connnects ANY cat with this specific death by explaining in terms of the car's momentum and speed, and the driver's mortal fear of colliding with the cat. She swerved, therefore, given her momentum, speed and direction, she hit a pillar and died. This model quantifies (gives speeds, momentum, etc), and it explains the mechanism.

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