In theoretical physics, a "Boogeyman" is a "monstrous" theory, model or idea – a hypothetical or notional model defined by its theoretical ability to "kill and eat" a popular theory. A boogeyman can be considered as a "what if" scenario - the Boogeyman is not guaranteed to exist, and its existence may even be considered vanishingly unlikely ... however the more unlikely a Boogeyman appears to be, the more constraints there are on its existence, and the more specific we can be about its potential properties.
If the Boogeyman's constraints are sufficiently severe, then so such theory may be possible. However, the point of the Boogeyman exercise is to test our own preconceptions and try to deliberately design a "nightmare scenario" for a popular theory ... it is less about arguing that the Boogeyman cannot exist, and more about deriving the characteristics (however unlikely) that it would need to have in order to exist, so that we can then assess probabilities.
Properties of a Boogeyman
In common with the "Boogeyman" in children's stories, a scientific Boogeyman is (a) a threat, (b) scary, (c) indistinctly defined (at least, at first), and (d) not believed-in by experienced adults. As a scientific theory, a Boogeyman also has to have "stealth" properties – in order to be "lurking in the background", there needs to be some reason why the theory has not previously been thoroughly examined, either because it sidesteps existing definitions, contravenes assumed behaviours, or if its validity would have terrible consequences or would require us to rethink our belief systems in ways that are so repugnant as to make the very idea unthinkable, or ... ideally ... all of the above.
The value of the Boogeymen exercise
The Boogeyman approach lets us short-circuit our existing beliefs and explore possibilities which, if correct, might overturn existing thinking.
Potential past "Boogeyman" candidates:
- For the Pythagorean Brotherhood, whose core project was the construction of a logical system of the universe in which all reality was based on integers and integer ratios, Hippasus' suggestion of the existence of numbers which did not represent integer ratios – the so-called "irrational" numbers – challenged core beliefs and required a revolution in thinking. Legend has it that Hippasus was put to death for mathematical heresy before the validity of his argument was accepted.
- In geometry, the early subject of fractals (before it acquired the name) was originally rejected as aberrant and pathological, with fractal shapes dismissed as "monsters". Supposedly, an early argument against the validity of the Mandelbrot Set as a legitimate field of mathematical study was that the shape had to be an artefact of the computer systems that generated it, perhaps caused by rounding errors or bad coding.
- In C18th English physics, Isaac Newton's status was regarded as almost godlike, and the idea that he had almost single-handedly rescued the reputation of English natural philosophy against the predations of the Continentals meant that Newton's system was then considered "too big to fail". When Continental scientists started using wave theory to suggest different energy/wavelength relationships to Newton's, the English response was to dismiss wave theory as obviously wrong, and its proponents as foolish and ignorant. In this context, the "Boogeyman" for C18th Newtonian theory could stem from the question, "What if the continentals are right, and Newton's system contains a terrible mistake?". Studying this question could have allowed English scientists to construct a corrected version of Newton's system, in advance of the experimental results from ~1800 onwards that showed that the original Newtonian system – unthinkably – was wrong.
- Bogeyman (wikipedia.org) – see also "Bogie", an unidentified radar signal requiring investigation