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Perpetual motion

For other uses, see Perpetual motion (disambiguation).
"Perpetual Motion Machine" redirects here. For other uses, see Perpetual Motion Machine (disambiguation).
"Free energy device" redirects here. For other meanings of "free energy", see Free energy.
Robert Fludd's 1618 "water screw" perpetual motion machine from a 1660 wood engraving. It is widely credited as the first attempt to describe such a device.[note 1][1]
Something for Nothing (1940), a short film featuring Rube Goldberg illustrating the U.S. Patent Office's policy regarding perpetual motion machines (and the power efficiency of gasoline)

Perpetual motion is the motion of bodies that continues forever in an unperturbed system. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an external energy source. This kind of machine is impossible, since its existence would violate the first and/or second laws of thermodynamics.[2][3][4][5]

These laws of thermodynamics apply regardless of the size of the system. For example, the motions and rotations of celestial bodies such as planets may appear perpetual, but are actually subject to many processes that slowly dissipate their kinetic energy, such as solar wind, interstellar medium resistance, gravitational radiation and thermal radiation, so they will not keep moving forever.[6][7]

Thus, machines that extract energy from finite sources cannot operate indefinitely because they are driven by the energy stored in the source, which will eventually be exhausted. A common example is devices powered by ocean currents, whose energy is ultimately derived from the Sun, which itself will eventually burn out.

In 2016,[8] new states of matter, time crystals, were discovered in which, on a microscopic scale, the component atoms are in continual repetitive motion, thus satisfying the literal definition of "perpetual motion".[9][10][11][12] However, these do not constitute perpetual motion machines in the traditional sense, or violate thermodynamic laws, because they are in their quantum ground state, so no energy can be extracted from them; they exhibit motion without energy.


Cite error: There are <ref group=note> tags on this page, but the references will not show without a {{reflist|group=note}} template (see the help page).

  1. ^ Cite error: The named reference sciam was invoked but never defined (see the help page).
  2. ^ Derry, Gregory N. (2002-03-04). What Science Is and How It Works. Princeton University Press. p. 167. ISBN 978-1400823116.
  3. ^ Roy, Bimalendu Narayan (2002). Fundamentals of Classical and Statistical Thermodynamics. John Wiley & Sons. p. 58. Bibcode:2002fcst.book.....N. ISBN 978-0470843130.
  4. ^ "Definition of perpetual motion". Oxforddictionaries.com. 2012-11-22. Retrieved 2012-11-27.[dead link]
  5. ^ Point, Sébastien. "Free energy: when the web is freewheeling". Skeptikal Inquirer, January–February 2018.
  6. ^ Taylor, J. H.; Weisberg, J. M. (1989). "Further experimental tests of relativistic gravity using the binary pulsar PSR 1913 + 16". Astrophysical Journal. 345: 434–450. Bibcode:1989ApJ...345..434T. doi:10.1086/167917. S2CID 120688730.
  7. ^ Weisberg, J. M.; Nice, D. J.; Taylor, J. H. (2010). "Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16". Astrophysical Journal. 722 (2): 1030–1034. arXiv:1011.0718. Bibcode:2010ApJ...722.1030W. doi:10.1088/0004-637X/722/2/1030. S2CID 118573183.
  8. ^ "Physicists Create World's First Time Crystal".
  9. ^ Grossman, Lisa (18 January 2012). "Death-defying time crystal could outlast the universe". New Scientist. Archived from the original on 2017-02-02.
  10. ^ Cowen, Ron (27 February 2012). ""Time Crystals" Could Be a Legitimate Form of Perpetual Motion". Scientific American. Archived from the original on 2017-02-02.
  11. ^ Powell, Devin (2013). "Can matter cycle through shapes eternally?". Nature. doi:10.1038/nature.2013.13657. ISSN 1476-4687. S2CID 181223762. Archived from the original on 2017-02-03.
  12. ^ Gibney, Elizabeth (2017). "The quest to crystallize time". Nature. 543 (7644): 164–166. Bibcode:2017Natur.543..164G. doi:10.1038/543164a. ISSN 0028-0836. PMID 28277535. S2CID 4460265.

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