# GetWiki

*Einstein synchronisation*

ARTICLE SUBJECTS

being →

database →

ethics →

fiction →

history →

internet →

language →

linux →

logic →

method →

news →

policy →

purpose →

religion →

science →

software →

truth →

unix →

wiki →

ARTICLE TYPES

essay →

feed →

help →

system →

wiki →

ARTICLE ORIGINS

critical →

forked →

imported →

original →

Einstein synchronisation

[ temporary import ]

**please note:**

- the content below is remote from Wikipedia

- it has been imported raw for GetWiki

**Einstein synchronisation**(or

**PoincarÃ©–Einstein synchronisation**) is a convention for synchronising clocks at different places by means of signal exchanges. This synchronisation method was used by telegraphers in the middle 19th century, but was popularized by Henri PoincarÃ© and Albert Einstein who applied it to light signals and recognized its fundamental role in relativity theory. Its principal value is for clocks within a single inertial frame.

## Einstein

According to Albert Einstein's prescription from 1905, a light signal is sent at time tau_1 from clock 1 to clock 2 and immediately back, e.g. by means of a mirror. Its arrival time back at clock 1 is tau_2. This synchronisation convention sets clock 2 so that the time tau_3 of signal reflection is defined to be
tau_3 = tau_1 + tfrac{1}{2}(tau_2 - tau_1) = tfrac{1}{2}(tau_1 + tau_2).{{Citation | author=Einstein, A. | year=1905 | title=Zur Elektrodynamik bewegter KÃ¶rper | journal=Annalen der Physik | volume=17 | pages=891â€“921 | bibcode=1905AnP...322..891E | doi=10.1002/andp.19053221004 | issue=10 | url=http://www.pro-physik.de/Phy/pdfs/ger_890_921.pdf | deadurl=yes | archiveurl=https://web.archive.org/web/20091229162203weblink | archivedate=2009-12-29 | df= }}.

See also English translationThe same synchronisation is achieved by "slowly" transporting a third clock from clock 1 to clock 2, in the limit of vanishing transport velocity. The literature discusses many other thought experiments for clock synchronisation giving the same result.The problem is whether this synchronisation does really succeed in assigning a time label to any event in a consistent way. To that end one should find conditions under which:
(a) clocks once synchronised remain synchronised,
(b1) the synchronisation is reflexive, that is any clock is synchronised with itself (automatically satisfied),
(b2) the synchronisation is symmetric, that is if clock A is synchronised with clock B then clock B is synchronised with clock A,
(b3) the synchronisation is transitive, that is if clock A is synchronised with clock B and clock B is synchronised with clock C then clock A is synchronised with clock C.

If point (a) holds then it makes sense to say that clocks are synchronised. Given (a), if (b1)–(b3) hold then the synchronisation allows us to build a global time function t. The slices t=const. are called "simultaneity slices".Einstein (1905) did not recognize the possibility of reducing (a) and (b1)–(b3) to easily verifiable physical properties of light propagation (see below). Instead he just wrote "*We assume that this definition of synchronism is free from contradictions, and possible for any number of points; and that the following*(that is b2–b3)

*relations are universally valid*."Max Von Laue{{Citation | author=Laue, M. | year=1911 | title=Das RelativitÃ¤tsprinzip | publisher=Friedr. Vieweg & Sohn | place=Braunschweig }}. was the first to study the problem of the consistency of Einstein's synchronisation (for an account of the early history see Minguzzi, 2011{{Citation | author=Minguzzi, E. | year=2011 | title=The PoincarÃ©-Einstein synchronization: historical aspects and new developments | journal= J. Phys.: Conf. Ser. | volume =306 | issue=1 | pages =012059 | doi=10.1088/1742-6596/306/1/012059 |bibcode = 2011JPhCS.306a2059M }}). L. Silberstein{{Citation | author=Silberstein, L. | year=1914 | title=The theory of relativity | publisher=Macmillan | place=London }}. presented a similar study although he left most of his claims as an exercise for the readers of his textbook on relativity. Max von Laue's arguments were taken up again by H. Reichenbach,{{Citation | author=Reichenbach, H. | year=1969 | title=Axiomatization of the Theory of Relativity | publisher=University of California Press | place=Berkeley }}. and found a final shape in a work by A. Macdonald.{{Citation | author=Macdonald, A. | year=1983 | title=Clock synchronization, a universal light speed, and the terrestrial red-shift experiment | journal=American Journal of Physics | volume =51 | pages =795â€“797 | doi=10.1119/1.13500|bibcode = 1983AmJPh..51..795M | issue=9 | citeseerx=10.1.1.698.3727 }} The solution is that the Einstein synchronisation satisfies the previous requirements if and only if the following two conditions hold:

- (
*No redshift*) If from point A two flashes are emitted separated by a time interval Î”t as recorded by a clock at A, then they reach B separated by the same time interval Î”t as recorded by a clock at B. - (
*Reichenbach's round-trip condition*) If a light beam is sent over the triangle ABC, starting from A and reflected by mirrors at B and C, then its arrival time back to A is independent of the direction followed (ABCA or ACBA).

- (
*Laue-Weyl's round-trip condition*) The time needed by a light beam to traverse a closed path of length L is L/c, where L is the length of the path and c is a constant independent of the path.

## History: PoincarÃ©

Some features of the conventionality of synchronization were discussed by Henri PoincarÃ©.Galison (2002).Darrigol (2005). In 1898 (in a philosophical paper) he argued that the postulate of light speed constancy in all directions is useful to formulate physical laws in a simple way. He also showed that the definition of simultaneity of events at different places is only a convention.{{Citation|author=PoincarÃ©, Henri|year=1898-1913|title=The foundations of science|chapter=s:The Measure of Time|The Measure of Time]]|place=New York|publisher=Science Press|pages=222–234}} Based on those conventions, but within the framework of the now superseded aether theory, PoincarÃ© in 1900 proposed the following convention for defining clock synchronisation: 2 observers A and B, which are moving in the aether, synchronise their clocks by means of optical signals. Because of the relativity principle they believe themselves to be at rest in the aether and assume that the speed of light is constant in all directions. Therefore, they have to consider only the transmission time of the signals and then crossing their observations to examine whether their clocks are synchronous.} is the speed of light, and v is the speed of the Earth which we suppose is parallel to the x axis, and in the positive direction, then we have: t'=t-tfrac{vx}{V^{2}}.{{Citation|author=PoincarÃ©, Henri|year=1900|title=La thÃ©orie de Lorentz et le principe de rÃ©action|journal=Archives NÃ©erlandaises des Sciences Exactes et Naturelles|volume=5|pages=252â€“278|title-link=s:fr:La thÃ©orie de Lorentz et le principe de rÃ©action}}. See also the English translation.}}In 1904 PoincarÃ© illustrated the same procedure in the following way:}}## See also

## References

{{Reflist}}## Literature

- {{Citation|author=Darrigol, Olivier|title=The Genesis of the theory of relativity|year=2005|journal=SÃ©minaire PoincarÃ©|volume=1|pages=1â€“22|url=http://www.bourbaphy.fr/darrigol2.pdf|doi=10.1007/3-7643-7436-5_1|bibcode=2006eins.book....1D|isbn=978-3-7643-7435-8}}
- D. Dieks,
*Becoming, relativity and locality*, in*The Ontology of Spacetime*, online - D. Dieks (ed.),
*The Ontology of Spacetime*, Elsevier 2006, {{ISBN|0-444-52768-0}} - D. Malament, 1977. "Causal Theories of Time and the Conventionality of Simultaniety," NoÃ»s 11, 293–300.
- Galison, P. (2003), Einstein's Clocks, PoincarÃ©'s Maps: Empires of Time, New York: W.W. Norton, {{ISBN|0-393-32604-7}}
- A. GrÃ¼nbaum.
*David Malament and the Conventionality of Simultaneity: A Reply*, online - S. Sarkar, J. Stachel,
*Did Malament Prove the Non-Conventionality of Simultaneity in the Special Theory of Relativity?*, Philosophy of Science, Vol. 66, No. 2 - H. Reichenbach,
*Axiomatization of the theory of relativity*, Berkeley University Press, 1969 - H. Reichenbach,
*The philosophy of space & time*, Dover, New York, 1958 - H. P. Robertson,
*Postulate versus Observation in the Special Theory of Relativity*, Reviews of Modern Physics, 1949 - R. Rynasiewicz,
*Definition, Convention, and Simultaneity: Malament's Result and Its Alleged Refutation by Sarkar and Stachel*, Philosophy of Science, Vol. 68, No. 3, Supplement, online - Hanoch Ben-Yami,
*Causality and Temporal Order in Special Relativity*, British Jnl. for the Philosophy of Sci., Volume 57, Number 3, pp. 459–479, weblink" title="web.archive.org/web/20061003172711weblink">abstract online

## External links

- Stanford Encyclopedia of Philosophy,
*Conventionality of Simultaneity*weblink (contains extensive bibliography) - Neil Ashby,
*Relativity in the Global Positioning System*, Living Rev. Relativ. 6, (2003), weblink - How to Calibrate a Perfect Clock
*from John de Pillis*: An interactive Flash animation showing how a clock with uniform ticking rate can precisely define a one-second time interval. - Synchronizing Five Clocks
*from John de Pillis.*An interactive Flash animation showing how five clocks are synchronised within a single inertial frame.

**- content above as imported from Wikipedia**

- "

- time: 6:24am EDT - Wed, Aug 21 2019

- "

__Einstein synchronisation__" does not exist on GetWiki (yet)- time: 6:24am EDT - Wed, Aug 21 2019

[ this remote article is provided by Wikipedia ]

LATEST EDITS [ see all ]

GETWIKI 09 JUL 2019

GETWIKI 09 MAY 2016

GETWIKI 18 OCT 2015

GETWIKI 20 AUG 2014

GETWIKI 19 AUG 2014

© 2019 M.R.M. PARROTT | ALL RIGHTS RESERVED