Editing Perpetual motion (section)

== Apparent perpetual motion machines ==
As a perpetual motion machine can only be defined in a finite isolated system with discrete parameters, and since true isolated systems do not exist (among other things, due to [[Uncertainty principle|quantum uncertainty]]<!--These are mathematical theorems, not physical laws: and [[Tarski's undefinability theorem|Tarski's]]/[[Gödel's incompleteness theorems|Gödel's]] theorems-->), "perpetual motion" in the context of this article is better defined as a "perpetual motion machine", since a machine is a "a mechanically, electrically, or electronically operated device for performing a task",<ref>{{cite dictionary |title=Machine Definition & Meaning |date=2024-11-28 |url=https://www.merriam-webster.com/dictionary/machine |dictionary=Merriam Webster |access-date=2024-11-28 |language=en |archive-date=2024-11-28 |archive-url=https://web.archive.org/web/20241128055416/https://www.merriam-webster.com/dictionary/machine |url-status=bot: unknown }}</ref> whereas "motion" is simply movement (such as [[Brownian motion]]). Distinctions aside, on the macro scale, there are concepts and technical drafts that propose "perpetual motion", but on closer analysis it is revealed that they actually "consume" some sort of natural resource or latent energy, such as the phase changes of [[water]] or other fluids or small natural temperature gradients, or simply cannot sustain indefinite operation. In general, extracting work from these devices is impossible.

=== Resource consuming ===
[[Image:Boyle'sSelfFlowingFlask.png|thumb|The "capillary bowl"]]

Some examples of such devices include:
* The [[drinking bird]] toy functions using small ambient temperature gradients and evaporation. It runs until all water is evaporated.
* A [[capillary action]]-based water pump functions using small ambient temperature gradients and [[vapour pressure]] differences. With the "capillary bowl", it was thought that the capillary action would keep the water flowing in the tube, but since the [[cohesion (chemistry)|cohesion force]] that draws the liquid up the tube in the first place holds the droplet from releasing into the bowl, the flow is not perpetual.
* A [[Crookes radiometer]] consists of a partial vacuum glass container with a lightweight propeller moved by (light-induced) temperature gradients.
* Any device picking up minimal amounts of energy from the natural [[electromagnetic radiation]] around it, such as a solar-powered motor.
* Any device powered by changes in air pressure, such as some clocks ([[Cox's timepiece]], [[Beverly Clock]]). The motion leeches energy from moving air which in turn gained its energy from being acted on.
* A [[heat pump]], due to it having a [[Coefficient of performance|COP]] above 1: the energy it consumes as work is less than the energy it moves as heat.
* The [[Atmos clock]] uses changes in the vapor pressure of ethyl chloride with temperature to wind the clock spring.
* A device powered by induced nuclear reactions or by [[radioactive decay]] from an isotope with a relatively long [[half-life]]; such a device could plausibly operate for hundreds or thousands of years.{{Citation needed|date=August 2024}}
* The [[Oxford Electric Bell]] and the {{ill|Karpen Pile|ro|Pilă Karpen}} are driven by [[Voltaic pile|dry pile]] batteries.

=== Low friction ===
* In [[flywheel energy storage]], "modern flywheels can have a zero-load rundown time measurable in years".<ref>{{Ref patent |country=WO
 |number= 2008037004
 |status= application
 |title= An energy storage device and method of use
 |pubdate= 2008-04-03
 |fdate= 2007-09-25
 |pridate= 2006-09-25
 |invent1= Kwok, James
}}</ref>
* Once spun up, objects in the vacuum of space—stars, black holes, planets, moons, [[spin-stabilized satellite]]s, etc.—dissipate energy very slowly, allowing them to spin for long periods. [[Tide]]s on Earth are dissipating the gravitational energy of the Moon/Earth system at an [[average]] rate of about 3.75 [[terawatt]]s.<ref name=Munk1998>{{Cite journal
|last = Munk |first = W.
|year = 1998
|title = Abyssal recipes II: energetics of tidal and wind mixing
|journal = Deep-Sea Research Part I: Oceanographic Research Papers
|volume = 45
|issue = 12
|page = 1977
|doi = 10.1016/S0967-0637(98)00070-3
|last2 = Wunsch
|first2 = C
|bibcode = 1998DSRI...45.1977M }}</ref><ref name=Ray1996>{{Cite journal
|last = Ray | first = R. D.
|year = 1996
|title = Detection of tidal dissipation in the solid Earth by satellite tracking and altimetry
|journal = Nature
|volume = 381
|issue = 6583
|page = 595
|doi = 10.1038/381595a0
|last2 = Eanes
|first2 = R. J.
|last3 = Chao
|first3 = B. F.
|bibcode = 1996Natur.381..595R |s2cid = 4367240
}}</ref>

=== Thought experiments ===
In some cases a [[thought experiment]] appears to suggest that perpetual motion may be possible through accepted and understood physical processes. However, in all cases, a flaw has been found when all of the relevant physics is considered. Examples include:
* [[Maxwell's demon]]: This was originally proposed to show that the [[second law of thermodynamics]] applied in the statistical sense only, by postulating a "demon" that could select energetic molecules and extract their energy. Subsequent analysis (and experiment) have shown there is no way to physically implement such a system that does not result in an overall increase in [[entropy]].
* [[Brownian ratchet]]: In this thought experiment, one imagines a paddle wheel connected to a ratchet. [[Brownian motion]] would cause surrounding gas molecules to strike the paddles, but the ratchet would only allow it to turn in one direction. A more thorough analysis showed that when a physical ratchet was considered at this molecular scale, Brownian motion would also affect the ratchet and cause it to randomly fail resulting in no net gain. Thus, the device would not violate the [[laws of thermodynamics]].
* [[Vacuum energy]] and [[zero-point energy]]: In order to explain effects such as [[virtual particles]] and the [[Casimir effect]], many formulations of [[quantum physics]] include a background energy which pervades empty space, known as vacuum or zero-point energy. The ability to harness zero-point energy for useful work is considered [[pseudoscience]] by the scientific community at large.<ref name="army">{{cite web|publisher=[[U.S. Army]] [[National Ground Intelligence Center]]|url=http://info.publicintelligence.net/USArmy-ZeroPointEnergy.pdf|title=Zero-Point Energy: Can We Get Something From Nothing?|first=Amber M. |last=Aiken |quote=Forays into 'free energy' inventions and perpetual-motion machines using ZPE are considered by the broader scientific community to be pseudoscience.}}</ref><ref name=saf>{{Scientific American Frontiers |8 |2}}</ref> Inventors have proposed various methods for extracting useful work from zero-point energy, but none have been found to be viable,<ref name="army"/><ref name=Gardner>[[Martin Gardner]], [http://www.csicop.org/si/show/dr._bearden_vacuum_energy/ {{"'}}Dr' Bearden's Vacuum Energy"]. ''[[Skeptical Inquirer]]''. January/February 2007. {{Webarchive|url=https://web.archive.org/web/20190403000514/http://www.csicop.org/si/show/dr._bearden_vacuum_energy/ |date=2019-04-03 }}.</ref> no claims for extraction of zero-point energy have ever been validated by the scientific community,<ref>{{cite news |title=What is the 'zero-point energy' (or 'vacuum energy') in quantum physics? Is it really possible that we could harness this energy? |first=Matt |last=Visser |url=http://homepages.mcs.vuw.ac.nz/~visser/general.shtml#what-zpe|newspaper=Phlogistin / Scientific American|date=3 October 1996
|archive-url=https://web.archive.org/web/20080714115109/http://homepages.mcs.vuw.ac.nz/~visser/general.shtml#what-zpe|archive-date= July 14, 2008
|access-date=31 May 2013}} [http://www.sciam.com/article.cfm?id=follow-up-what-is-the-zer Alternative link]</ref> and there is no evidence that zero-point energy can be used in violation of conservation of energy.<ref>{{cite journal |journal=[[Scientific American]]|date=18 August 1997|url=http://www.sciam.com/article.cfm?id=follow-up-what-is-the-zer|title=FOLLOW-UP: What is the 'zero-point energy' (or 'vacuum energy') in quantum physics? Is it really possible that we could harness this energy?}}</ref>
*[[Ellipsoid paradox]]: This paradox considers a perfectly reflecting cavity with two [[Black body|black bodies]] at points ''A'' and ''B''. The reflecting surface is composed of two elliptical sections ''E''<sub>1</sub> and ''E''<sub>2</sub> and a spherical section ''S'', and the bodies at ''A'' and ''B'' are located at the joint foci of the two ellipses and ''B'' is at the center of ''S''. This configuration is such that the black body at ''B'' heats up relative to ''A'': the radiation originating from the black body at ''A'' will land on and be absorbed by the blackbody at ''B''. Similarly, rays originating from point ''B'' that land on ''E''<sub>1</sub> and ''E''<sub>2</sub> will be reflected to ''A''. However, a significant proportion of rays that start from ''B'' will land on ''S'' will be reflected back to ''B''. This paradox is solved when the black bodies' finite sizes are considered instead of punctual black bodies.<ref>{{Cite journal|last1=Yoder|first1=Theodore J.|last2=Adkins|first2=Gregory S.|date=2011|title=Resolution of the ellipsoid paradox in thermodynamics|journal=American Journal of Physics|language=en|volume=79|issue=8|pages=811–818|doi=10.1119/1.3596430|bibcode=2011AmJPh..79..811Y|issn=0002-9505}}</ref><ref>{{Cite web|last=Mutalik|first=Pradeep|title=How to Design a Perpetual Energy Machine|url=https://www.quantamagazine.org/how-to-design-a-perpetual-energy-machine-20200401/|access-date=2020-06-08|website=Quanta Magazine|date=April 2020|language=en}}</ref>
[[File:Ellipsoid_paradox.svg|alt=|center|thumb|upright=1.6|Ellipsoid paradox surface and rays emitted by body {{mvar|A}} in the direction of body {{mvar|B}}. ({{mvar|a}}) When bodies {{mvar|A}} and {{mvar|B}} are point like, all rays from {{mvar|A}} must be incident on {{mvar|B}}. ({{mvar|b}}) When bodies {{mvar|A}} and {{mvar|B}} are extended, some rays from {{mvar|A}} will not be incident on {{mvar|B}} and may eventually return to {{mvar|A}}.]]