A tin foil hat is a piece of headgear made from one or more sheets of tin foil, aluminium foil or similar material. People wear the hats in the belief that they act to shield the brain from such influences as electromagnetic fields, or against alien interference, mind control and mind reading. The idea 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 is often used to characterize conspiracy theorists.
Tin foil hats and paranoia
Various web sites claim that people believe in the efficacy of tin foil hats and similar devices to stop the voices in their head or prevent the government, paranormal beings, or aliens from reading and/or controlling their minds. These people believe that the foil deflects mind control signals from, for instance, project HAARP, which allegedly transmits mind-control signals from mobile phone towers. These draw on the stereotypical images of mind control operating by ESP or by technological means, like microwave radiation. Belief in the effectiveness of tin foil hats is popularly linked to mental illnesses such as paranoid schizophrenia.[1]
Scientific basis
Two people wearing tin foil hats.
The belief that a tin foil hat can significantly reduce the intensity of incident radio frequency (RF) radiation on the wearer's brain is not completely without a basis in scientific fact. A well constructed tin foil enclosure would approximate a Faraday cage, reducing the amount of radiofrequency electromagnetic radiation entering from outside. 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. 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.[2]
The effectiveness of the tin foil hat as electromagnetic shielding for stopping radio waves is greatly reduced by the fact that it is not a complete enclosure. Placing an AM radio under a metal bucket without a conductive layer underneath demonstrates the relative ineffectiveness of such a setup. Because the effect of an ungrounded Faraday cage is to partially reflect the incident radiation, a radio wave that is incident on the inner surface of the hat (i.e., coming from underneath the hat-wearer) would be reflected and partially 'focused' towards the user's brain. While tin foil hats may have originated in some understanding of the Faraday cage effect, the use of such a hat to attenuate radio waves belongs properly to the realm of pseudoscience.
A study by graduate students at MIT determined that a tin foil hat could either amplify or attenuate incoming radiation depending on frequency. The effect was observed to be roughly independent of the relative placement of the wearer and radiation source.[3] At GHz wavelengths, the skin depth is less than the thickness of even the thinnest foil.
Despite some allegations that electromagnetic radiation (EMR) exposure has harmful effects on health ,[4] at this time, no link has been verifiably proven between the radio-frequency EMR that tin foil hats are meant to protect against and subsequent ill health.
Tin foil hats in popular culture
EastEnders character Joe Wicks was briefly portrayed constructing and wearing his own tin foil hat as part of a storyline which saw him suffering from schizophrenia.
The novel Idiots in the Machine by Edward Savio portrays a character who believes that tin foil keeps harmful gamma rays away and becomes a media sensation, marketing a successful line of foil hats to Chicago.
In an episode of The Simpsons, "Brother's Little Helper", Bart becomes paranoid after taking an ADD drug called Focusin, leading him to believe that Major League Baseball is spying on him and begins donning a tin foil hat.
The tin foil hat was an April Fool's Day item for the MMORPG World of Warcraft, created by Blizzard to parody player paranoia about their character information being searchable on the World of Warcraft armory website.[6]
In M. Night Shyamalan's 2002 film Signs, the Hesses don tin foil hats to protect from invading aliens.
One character in the 2007 film The Signal wears a tin foil hat in an attempt to block the titular "signal" turning people into murderous madmen.
In the 1956 novel Slave Ship by Frederick Pohl, various characters wear tin foil hats to protect themselves from telepathic attacks.
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