Editing Tachyon (section)

{{Short description|Hypothetical faster-than-light particle}}
{{About|hypothetical faster-than-light particles|quantum fields with imaginary mass|Tachyonic field|other uses}}
{{Use dmy dates|date=June 2023}}
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| name = Tachyon
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| classification = [[Elementary particle]]
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| status = Hypothetical 
| theorized = 1967 
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A '''tachyon''' ({{IPAc-en|ˈ|t|æ|k|i|ɒ|n}}) or '''tachyonic particle''' is a hypothetical [[particle]] that always travels [[Faster-than-light|faster than light]]. [[Physicist]]s posit that faster-than-light particles cannot exist because they are inconsistent with the known [[Scientific law#Laws of physics|laws of physics]].<ref name="Tipler" /><ref name="Randall 2005 p286">{{cite book |last=Randall |first=Lisa |date=2005 |title=Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions |isbn=9780060531089 |quote=People initially thought of tachyons as particles traveling faster than the speed of light ... But we now know that a tachyon indicates an instability in a theory that contains it. Regrettably, for science fiction fans, tachyons are not real physical particles that appear in nature. |page=286 |publisher=Harper Collins }}</ref> If such particles did exist they perhaps could be used to send signals faster than light and into the past. According to the [[theory of relativity]] this would violate [[Causality (physics)|causality]], leading to [[logical paradox]]es such as the [[grandfather paradox]].<ref name="Tipler" /> Tachyons would exhibit the unusual property of increasing in speed as their energy decreases, and would require infinite energy to slow to the speed of light. No verifiable experimental evidence for the existence of such particles has been found.

In the 1967 paper that coined the term, [[Gerald Feinberg]] proposed that tachyonic particles could be made from excitations of a [[Quantum field theory|quantum field]] with [[imaginary mass]].<ref name="Feinberg 1967-1969" /> However, it was soon realized that Feinberg's model did not in fact allow for [[superluminal]] (faster than light) particles or signals and that tachyonic fields merely give rise to instabilities, not causality violations.<ref name="Aharonov-etal-1969" /> The term [[tachyonic field]] refers to imaginary mass fields rather than to faster-than-light particles.<ref name="Randall 2005 p286" /><ref name="Sen" />