Tin foil hat

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A tin foil hat is a piece of headgear made from one or more sheets of aluminum foil or similar material. Alternatively it may be a conventional hat lined with foil. One may wear the hat in the belief that it acts to shield the brain from such influences as electromagnetic fields, or against mind control and/or mind reading; or attempt to limit the transmission of voices directly into the brain.

The concept of wearing a tin foil hat for protection from such threats has become a popular stereotype and term of derision; the phrase serves as a byword for paranoia and persecutory delusions, and is associated with conspiracy theorists.


Origin of concept

The concept was mentioned in a science fiction story by Julian Huxley, "The Tissue-Culture King," first published in 1927, in which the protagonist discovers that "caps of metal foil" can be used to block the effects of telepathy.[1]

Since then, the usage of the term has been associated with paranoia and conspiracy theories. The supposed reasons for their use include the prevention of perceived harassment from governments, spies or paranormal beings. These draw on the stereotypical images of mind control operating by ESP or technological means, like microwave radiation. The effectiveness of tin foil hats is disputable; however, the belief in their necessity is popularly associated with paranoia.[2]

Scientific basis

The notion that a tin foil hat can significantly reduce the intensity of incident radio frequency radiation on the wearer's brain has some scientific validity, as the effect of strong radio waves has been documented for quite some time.[3] A well-constructed tin foil enclosure would approximate a Faraday cage, reducing the amount of (typically harmless) radiofrequency electromagnetic radiation inside. A common high school physics demonstration involves placing an AM radio on tin foil, and then covering the radio with a metal bucket. This leads to a noticeable reduction in signal strength (probably because of the bucket and not the tinfoil, eliminating the utility of the foil). The efficiency of such an enclosure in blocking such radiation depends on the thickness of the tin foil, as dictated by the skin depth, the distance the radiation can propagate in a particular non-ideal conductor. For half-millimeter-thick tin foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked, although tin foil is not sold in this thickness, so numerous layers of tin foil would be required to achieve this effect.[4]

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