300,000,000

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Cohen, ER; etal. (2007). Quantities, Units and Symbols in Physical Chemistry (3rded.). Royal Society of Chemistry. p.184. ISBN 978-0-85404-433-7. Aoki, K; Mitsui, T (2008). "A small tabletop experiment for a direct measurement of the speed of light". American Journal of Physics. 76 (9): 812–815. arXiv: 0705.3996. Bibcode: 2008AmJPh..76..812A. doi: 10.1119/1.2919743. S2CID 117454437. According to Galileo, the lanterns he used were "at a short distance, less than a mile." Assuming the distance was not too much shorter than a mile, and that "about a thirtieth of a second is the minimum time interval distinguishable by the unaided eye", Boyer notes that Galileo's experiment could at best be said to have established a lower limit of about 60 miles per second for the velocity of light. [119] Panofsky, WKH; Phillips, M (1962). Classical Electricity and Magnetism. Addison-Wesley. p. 182. ISBN 978-0-201-05702-7.

Amelino-Camelia, G (2009). "Astrophysics: Burst of support for relativity". Nature. 462 (7271): 291–292. Bibcode: 2009Natur.462..291A. doi: 10.1038/462291a. PMID 19924200. S2CID 205051022. Buchanan, Mark (11 February 2015). "Physics in finance: Trading at the speed of light". Nature. 518 (7538): 161–163. Bibcode: 2015Natur.518..161B. doi: 10.1038/518161a. PMID 25673397. NPL's Beginner's Guide to Length". UK National Physical Laboratory. Archived from the original on 31 August 2010 . Retrieved 28 October 2009. a b c Essen, L (1950). "The Velocity of Propagation of Electromagnetic Waves Derived from the Resonant Frequencies of a Cylindrical Cavity Resonator". Proceedings of the Royal Society of London A. 204 (1077): 260–277. Bibcode: 1950RSPSA.204..260E. doi: 10.1098/rspa.1950.0172. JSTOR 98433. S2CID 121261770.Cromie, William J. (24 January 2001). "Researchers now able to stop, restart light". Harvard University Gazette. Archived from the original on 28 October 2011 . Retrieved 8 November 2011. a b c Boyer, CB (1941). "Early Estimates of the Velocity of Light". Isis. 33 (1): 24. doi: 10.1086/358523. S2CID 145400212. Radar systems measure the distance to a target by the time it takes a radio-wave pulse to return to the radar antenna after being reflected by the target: the distance to the target is half the round-trip transit time multiplied by the speed of light. A Global Positioning System (GPS) receiver measures its distance to GPS satellites based on how long it takes for a radio signal to arrive from each satellite, and from these distances calculates the receiver's position. Because light travels about 300 000kilometres ( 186 000mi) in one second, these measurements of small fractions of a second must be very precise. The Lunar Laser Ranging experiment, radar astronomy and the Deep Space Network determine distances to the Moon, [89] planets [90] and spacecraft, [91] respectively, by measuring round-trip transit times. Certain quantum effects appear to be transmitted instantaneously and therefore faster than c, as in the EPR paradox. An example involves the quantum states of two particles that can be entangled. Until either of the particles is observed, they exist in a superposition of two quantum states. If the particles are separated and one particle's quantum state is observed, the other particle's quantum state is determined instantaneously. However, it is impossible to control which quantum state the first particle will take on when it is observed, so information cannot be transmitted in this manner. [48] [49]

Similarly, communications between the Earth and spacecraft are not instantaneous. There is a brief delay from the source to the receiver, which becomes more noticeable as distances increase. This delay was significant for communications between ground control and Apollo 8 when it became the first crewed spacecraft to orbit the Moon: for every question, the ground control station had to wait at least threeseconds for the answer to arrive. [82]Taylor, EF; Wheeler, JA (1992). Spacetime Physics. W.H. Freeman. pp. 74–75. ISBN 978-0-7167-2327-1. Optical constants of C (Carbon, diamond, graphite)". refractiveindex.info. Mikhail Polyanskiy . Retrieved 7 November 2017. In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity v p. A physical signal with a finite extent (a pulse of light) travels at a different speed. The overall envelope of the pulse travels at the group velocity v g, and its earliest part travels at the front velocity v f. [63] The blue dot moves at the speed of the ripples, the phase velocity; the green dot moves with the speed of the envelope, the group velocity; and the red dot moves with the speed of the foremost part of the pulse, the front velocity.

a b c Gibbs, P (1997). "Is Faster-Than-Light Travel or Communication Possible?". Usenet Physics FAQ. University of California, Riverside. Archived from the original on 10 March 2010 . Retrieved 20 August 2008. Fearn, H. (10 November 2006). "Dispersion relations and causality: does relativistic causality require that n (ω) → 1 as ω → ∞?". Journal of Modern Optics. 53 (16–17): 2569–2581. Bibcode: 2006JMOp...53.2569F. doi: 10.1080/09500340600952085. ISSN 0950-0340. S2CID 119892992. There are different ways to determine the value of c. One way is to measure the actual speed at which light waves propagate, which can be done in various astronomical and Earth-based setups. It is also possible to determine c from other physical laws where it appears, for example, by determining the values of the electromagnetic constants ε 0 and μ 0 and using their relation to c. Historically, the most accurate results have been obtained by separately determining the frequency and wavelength of a light beam, with their product equalling c. This is described in more detail in the "Interferometry" section below. Terrell, J (1959). "Invisibility of the Lorentz Contraction". Physical Review. 116 (4): 1041–1045. Bibcode: 1959PhRv..116.1041T. doi: 10.1103/PhysRev.116.1041.

Examples of sentences in which the number 300,000,000 is written out in words

Peres, Asher (1993). Quantum Theory: Concepts and Methods. Kluwer. p.170. ISBN 0-7923-2549-4. OCLC 28854083. Sarton, G (1993). Ancient science through the golden age of Greece. Courier Dover. p.248. ISBN 978-0-486-27495-9.

Penrose, R (2004). The Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books. pp. 410–411. ISBN 978-0-679-77631-4. ... the most accurate standard for the metre is conveniently defined so that there are exactly 299 792 458 of them to the distance travelled by light in a standard second, giving a value for the metre that very accurately matches the now inadequately precise standard metre rule in Paris. Tolman, RC (2009) [1917]. "Velocities greater than that of light". The Theory of the Relativity of Motion (Reprinted.). BiblioLife. p.54. ISBN 978-1-103-17233-7. a b c Milonni, Peter W. (2004). Fast light, slow light and left-handed light. CRC Press. pp.25 ff. ISBN 978-0-7503-0926-4. Massless particles and field perturbations, such as gravitational waves, also travel at speed c in vacuum. Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. Particles with nonzero rest mass can be accelerated to approach c but can never reach it, regardless of the frame of reference in which their speed is measured. In the special and general theories of relativity, c interrelates space and time and also appears in the famous equation of mass–energy equivalence, E = mc 2. [9]Schaefer, BE (1999). "Severe limits on variations of the speed of light with frequency". Physical Review Letters. 82 (25): 4964–4966. arXiv: astro-ph/9810479. Bibcode: 1999PhRvL..82.4964S. doi: 10.1103/PhysRevLett.82.4964. S2CID 119339066.