# Fudge factor

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{{short description|Ad hoc element introduced into a calculation}}
A '''fudge factor''' is an [ad hoc](/source/ad_hoc) quantity or element introduced into a [calculation](/source/calculation), [formula](/source/formula) or [model](/source/Scientific_modelling) in order to make it fit observations or expectations.  Also known as a '''correction coefficient''', which is defined by
<math display="block">
 \kappa_\text{c} = \frac{\text{experimental value}}{\text{theoretical value}}.
</math>

Examples include Einstein's [cosmological constant](/source/cosmological_constant), [dark energy](/source/dark_energy), the initial proposals of [dark matter](/source/dark_matter) and [inflation](/source/inflation_(cosmology)).<ref>{{citation |title=Einstein's Greatest Blunder?: The Cosmological Constant and Other Fudge Factors in the Physics of the Universe |author=Donald Goldsmith |publisher=Harvard University Press |year=1997 |isbn=9780674242425}}</ref>

== Examples in science ==
Some quantities in scientific theory are set arbitrarily according to measured results rather than by calculation (for example, the [Planck constant](/source/Planck_constant)). However, in the case of these [fundamental constants](/source/fundamental_constants), their arbitrariness is usually explicit. To suggest that other calculations may include a "fudge factor" may suggest that the calculation has been somehow tampered with to make results give a misleadingly good match to experimental data.

=== Cosmological constant ===
In theoretical physics, when [Albert Einstein](/source/Albert_Einstein) originally tried to produce a [general theory of relativity](/source/general_theory_of_relativity), he found that the theory seemed to predict the gravitational collapse of the universe: it seemed that the universe should be collapsing, and to produce a model in which the universe was ''static and stable'' (which seemed to Einstein at the time to be the "proper" result), he introduced an expansionist variable (called the [cosmological constant](/source/cosmological_constant)), whose sole purpose was to cancel out the cumulative effects of gravitation. He later called this "the biggest blunder of my life".<ref>{{citation |url=https://books.google.com/books?id=UM2agAdvbXkC&pg=PA246 |title=The Quantum World: Quantum Physics for Everyone |author=Kenneth William Ford |publisher=Harvard University Press |year=2004 |isbn=9780674037144}}</ref>

== See also ==
* [Anthropic principle](/source/Anthropic_principle)
* [Confidence interval](/source/Confidence_interval)
* [Plug (accounting)](/source/Plug_(accounting))

== References ==
{{reflist}}

Category:Heuristics
Category:Error

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Adapted from the Wikipedia article [Fudge factor](https://en.wikipedia.org/wiki/Fudge_factor) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Fudge_factor?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.