astrophysics Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the h ...

, the Eddington number, , is the number of

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

s in the

observable universe The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these ob ...

. Eddington originally calculated it as about ; current estimates make it approximately . The term is named for British astrophysicist

Arthur Eddington Sir Arthur Stanley Eddington (28 December 1882 – 22 November 1944) was an English astronomer, physicist, and mathematician. He was also a philosopher of science and a populariser of science. The Eddington limit, the natural limit to the lumi ...

, who in 1940 was the first to propose a value of and to explain why this number might be important for

physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of f ...

and the foundations of

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

History

Eddington argued that the value of the

fine-structure constant In physics, the fine-structure constant, also known as the Sommerfeld constant, commonly denoted by (the Greek letter ''alpha''), is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between el ...

, ''α'', could be obtained by pure deduction. He related ''α'' to the Eddington number, which was his estimate of the number of protons in the universe. This led him in 1929 to conjecture that ''α'' was exactly 1/136. He devised a "proof" that N_Edd = 136 × 2²⁵⁶, or about 1.57×10⁷⁹. Other physicists did not adopt this conjecture and did not accept his argument. In the late 1930s, the best experimental value of the fine-structure constant, ''α'', was approximately 1/137. Eddington then argued, from aesthetic and

numerological Numerology (also known as arithmancy) is the belief in an occult, divine or mystical relationship between a number and one or more coinciding events. It is also the study of the numerical value, via an alphanumeric system, of the letters in w ...

considerations, that ''α'' should be exactly 1/137. Current estimates of ''N''_Edd point to a value of about . These estimates assume that all matter can be taken to be

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

and require assumed values for the number and size of

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

and

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s in the universe. Attempts to find a mathematical basis for this dimensionless constant have continued up to the present time. During a course of lectures that he delivered in 1938 as Tarner Lecturer at

Trinity College, Cambridge Trinity College is a constituent college of the University of Cambridge. Founded in 1546 by King Henry VIII, Trinity is one of the largest Cambridge colleges, with the largest financial endowment of any college at either Cambridge or Oxford. ...

, Eddington averred that: This large number was soon named the "Eddington number". Shortly thereafter, improved measurements of ''α'' yielded values closer to 1/137, whereupon Eddington changed his "proof" to show that ''α'' had to be exactly 1/137.

Recent theory

The most precise value of ''α'' (obtained experimentally in 2012) is: Consequently, no reliable source any longer maintains that ''α'' is the

reciprocal Reciprocal may refer to: In mathematics * Multiplicative inverse, in mathematics, the number 1/''x'', which multiplied by ''x'' gives the product 1, also known as a ''reciprocal'' * Reciprocal polynomial, a polynomial obtained from another pol ...

of an integer. Nor does anyone take seriously a mathematical relationship between ''α'' and ''N''_Edd. On possible roles for ''N''_Edd in contemporary cosmology, especially its connection with large number coincidences, see Barrow (2002) (easier) and Barrow and Tipler (1986: 224–31) (harder).

References

Bibliography

* * * * * * * * * * * {{Large numbers Large integers Proton Astrophysics Physical cosmology

History

Recent theory

See also

References

Bibliography