Tin foil hat
A tin foil hat is a piece of headgear made from one or more sheets of aluminium foil or similar material. Alternatively it may be a conventional hat lined with foil. One may wear the hat in the belief that it shields the brain from electromagnetic fields, to prevent mind control and/or mind reading, or 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, persecutory delusions and belief in conspiracy theories. This stereotype is popular in pop culture, with tin foil hats making appearances in movies such as Signs and Futurama: Into the Wild Green Yonder.
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.
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; belief in their necessity is popularly associated with paranoia.
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. A well-constructed tin foil enclosure would approximate a Faraday cage, reducing the amount of (typically harmless) radiofrequency electromagnetic radiation passing through to the interior of the structure. 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-millimetre-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.
The effectiveness of the tin foil hat as electromagnetic shielding for stopping radio waves is greatly reduced by it not being a complete enclosure. Placing an AM radio under a metal bucket without a conductive layer underneath demonstrates the relative ineffectiveness of such a setup. Indeed, 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 attenuate incoming radiation depending on frequency. At WIFI frequencies - 2.4 GHz is attenuated by up to 90 dB; the effect was observed to be roughly independent of the relative placement of the wearer and radiation source. At GHz wavelengths, the skin depth is less than the thickness of even the thinnest foil.
Tin foil hats are seen by some[who?] as a protective measure against the effects of electromagnetic radiation (EMR). Despite some allegations that EMR exposure has negative health consequences, 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.
Humans are able to detect modulated radio-frequency electromagnetic signals in the microwave range, hearing them as sounds. The perceived source of induced sound is located inside of or directly behind the head of the recipient, regardless of the location of the transmitter. The effect is believed to be caused by interaction of the cochlea to microwaves.
During the Cold War, electromagnetic hearing was clinically studied in the United States for applications including covert message transmission and use as a non-lethal weapon. As a declassified National Ground Intelligence Center document points out:
- Huxley, Julian (1927). The Tissue-Culture King. "Well, we had discovered that metal was relatively impervious to the telepathic effect, and had prepared for ourselves a sort of tin pulpit, behind which we could stand while conducting experiments. This, combined with caps of metal foil, enormously reduced the effects on ourselves."
- "Hey Crazy--Get a New Hat". Bostonist. 15 November 2005. Retrieved 2007-04-05.
- Adey, W. R. (December, 1979). Neurophysiologic effects of Radiofrequency and Microwave Radiation, Bulletin of New York Academy of Medicine, vol. 55, no. 11,. pp. 1079–1093.
- Jackson, John David (1998). Classical Electrodynamics. Wiley Press. ISBN 0-471-30932-X.
- Rahimi, Ali; Ben Recht, Jason Taylor, Noah Vawter (17 February 2005). "On the Effectiveness of Aluminium Foil Helmets: An Empirical Study". Ali Rahimi.
- Lean, Geoffrey (2006-05-07). "Electronic smog - Environment - The Independent". London: Independent.co.uk. Retrieved 2009-06-09.
- "Safety and Health Topics: Radiofrequency and Microwave Radiation - Health Effects". Osha.gov. Retrieved 2009-06-09.[dead link]
- Elder, Joe A.; Chou, C.K. (2003). "Auditory response to pulsed radiofrequency energy". Bioelectromagnetics (Wiley-Liss) 24 (S6): S162–73. doi:10.1002/bem.10163. ISSN 0197-8462. PMID 14628312.
- "Bioeffects of Selected Nonlethal Weapons". Nonlethal Technologies – Worldwide. National Ground Intelligence Center. 1998.
|Wikimedia Commons has media related to: Tin foil hats|
- Do tinfoil helmets provide adequate protection against mind control rays? – from The Straight Dope
- Tinfoil hats attract mind-control signals, boffins learn
- Mind Games -Washington Post
- On the Effectiveness of Aluminium Foil Helmets: An Empirical Study, Electrical Engineering and Computer Science department, MIT