Range (mathematics)

Template:Italic title The Sand Reckoner (Fitter (Basic ) Bud from Rosemere, has lots of pursuits that include robotics, property developers service Apartments in singapore singapore and aerobics. Has just concluded a trip to City of Cuzco.) is a work by Archimedes in which he set out to determine an upper bound for the number of grains of sand that fit into the universe. In order to do this, he had to estimate the size of the universe according to the contemporary model, and invent a way to talk about extremely large numbers. The work, also known in Latin as Archimedis Syracusani Arenarius & Dimensio Circuli, which is about 8 pages long in translation, is addressed to the Syracusan king Gelo II (son of Hiero II), and is probably the most accessible work of Archimedes; in some sense, it is the first research-expository paper.

Naming large numbers

First, Archimedes had to invent a system of naming large numbers. The number system in use at that time could express numbers up to a myriad (μυριάς — 10,000), and by utilizing the word "myriad" itself, one can immediately extend this to naming all numbers up to a myriad myriads (10⁸). Archimedes called the numbers up to 10⁸ "first numbers" and called 10⁸ itself the "unit of the second numbers". Multiples of this unit then became the second numbers, up to this unit taken a myriad-myriad times, 10⁸·10⁸=10¹⁶. This became the "unit of the third numbers", whose multiples were the third numbers, and so on. Archimedes continued naming numbers in this way up to a myriad-myriad times the unit of the 10⁸-th numbers, i.e., $(10^{8})^{(10^{8})}=10^{8\cdot 10^{8}}$.

After having done this, Archimedes called the numbers he had defined the "numbers of the first period", and called the last one, $(10^{8})^{(10^{8})}$, the "unit of the second period". He then constructed the numbers of the second period by taking multiples of this unit in a way analogous to the way in which the numbers of the first period were constructed. Continuing in this manner, he eventually arrived at the numbers of the myriad-myriadth period. The largest number named by Archimedes was the last number in this period, which is

$\left((10^{8})^{(10^{8})}\right)^{(10^{8})}=10^{8\cdot 10^{16}}.$

Another way of describing this number is a one followed by (short scale) eighty quadrillion (80·10¹⁵) zeroes.

Archimedes' system is reminiscent of a positional numeral system with base 10⁸, which is remarkable because the ancient Greeks used a very simple system for writing numbers, which employs 27 different letters of the alphabet for the units 1 through 9, the tens 10 through 90 and the hundreds 100 through 900.

Archimedes also discovered and proved the law of exponents, $10^{a}10^{b}=10^{a+b}$, necessary to manipulate powers of 10.

Estimation of the size of the universe

Archimedes then estimated an upper bound for the number of grains of sand required to fill the Universe. To do this, he used the heliocentric model of Aristarchus of Samos. The original work by Aristarchus has been lost. This work by Archimedes however is one of the few surviving references to his theory, whereby the Sun remains unmoved while the Earth revolves about the Sun. In Archimedes' own words:

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The reason for the large size of this model is that the Greeks were unable to observe stellar parallax with available techniques, which implies that any parallax is extremely subtle and so the stars must be placed at great distances from the Earth (assuming heliocentrism to be true).

According to Archimedes, Aristarchus did not state how far the stars were from the Earth. Archimedes therefore had to make an assumption; he assumed that the Universe was spherical and that the ratio of the diameter of the Universe to the diameter of the orbit of the Earth around the Sun equalled the ratio of the diameter of the orbit of the Earth around the Sun to the diameter of the Earth. This assumption can also be expressed by saying that the stellar parallax caused by the motion of the Earth around its orbit equals the solar parallax caused by motion around the Earth.

In order to obtain an upper bound, Archimedes used overestimates of his data by assuming:

• that the perimeter of the Earth was no bigger than 300 myriad stadia (5,55·10⁵ km).
• that the Moon was no larger than the Earth, and that the Sun was no more than thirty times larger than the Moon.
• that the angular diameter of the Sun, as seen from the Earth, was greater than 1/200th of a right angle ( π/400 radians, 0.45° degrees.

Archimedes then computed that the diameter of the Universe was no more than 10¹⁴ stadia (in modern units, about 2 light years), and that it would require no more than 10⁶³ grains of sand to fill it.

Archimedes made some interesting experiments and computations along the way. One experiment was to estimate the angular size of the Sun, as seen from the Earth. Archimedes' method is especially interesting as it takes into account the finite size of the eye's pupil, and therefore may be the first known example of experimentation in psychophysics, the branch of psychology dealing with the mechanics of human perception, whose development is generally attributed to Hermann von Helmholtz. Another interesting computation accounts for solar parallax and the different distances between the viewer and the Sun, whether viewed from the center of the Earth or from the surface of the Earth at sunrise. This may be the first known computation dealing with solar parallax.

Equality between Archimedes' number and Eddington's number

The total number of nucleons in the observable universe of roughly the Hubble radius is the Eddington number, currently estimated at 10⁸⁰. Archimedes' 10⁶³ grains of sand contain 10⁸⁰ nucleons, which means that Archimedes' number equals Eddington's number.

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Further reading

The Sand-Reckoner, by Gillian Bradshaw. Forge (2000), 348pp, ISBN 0-312-87581-9.

External links

• Original Greek text
• The Sand Reckoner
• The Sand Reckoner (annotated)
• Archimedes, The Sand Reckoner, by Ilan Vardi; includes a literal English version of the original Greek text