**Why are
we asking this now?**

A French computer

programmer has calculated pi to a world record of almost 2,700 billion

decimal places. Fabrice Bellard said he did it for the programming

challenge rather than any particular interest in this infinitely

long number. All the more remarkable is that he did it on a desktop

computer costing less than £2,000. It took 131 days to complete

the calculation and the resulting number took up more than 1,000

gigabytes of memory on his hard drive. Downloading it would take

10 days and reciting it aloud would take about 49,000 years.

**What was
the old record?**

It was achieved

using a multi-million pound supercomputer at the University of Tsukuba

in Japan last August. Mathematician Daisuke Takahashi calculated

pi to 2,577 billion decimal places. But his computer was roughly

2,000 times faster at processing data than Bellard’s machine. The

Japanese supercomputer calculated pi at a speed of 94.2 teraflops,

which is 94.2 trillion floating point operations or calculations

per second. It took 29 days.

**What exactly
is pi?**

As every schoolchild

should be able to describe, pi is the ratio of the circumference

of a circle to its diameter. In other words, divide the distance

around the edge of a circle by its diameter – a straight line

through its centre connecting one edge to another – and you

always get the same constant, denoted by pi. The problem is that

this number is infinitely long. For most purposes the value of pi

can be estimated to two decimal places, i.e. 3.14. But keep dividing

the circumference by the diameter and you soon get to 3.14159265358979323846.

Keep on dividing and you will eventually get to the number achieved

by Bellard.

**Is there
another way of describing this number?**

Sometimes it’s

denoted as 22/7 [i.e. 22 over 7] which is an approximation. In Europe

this is celebrated by assigning 22 July as pi Approximation Day.

In the US, however, they celebrate pi on 14 March – World pi

Day – which of course in American date notation is written

as 3/14. Either way, you have two opportunities in the year to celebrate

the cerebral pleasures of pi.

**Why does
pi fascinate people so much?**

It fascinates

experts because it is a number that is considered both irrational

and transcendental. It is irrational because it cannot be written

as a simple ratio of whole numbers and transcendental because pi

is living proof that you cannot square a circle. "The mathematics

of pi is often rather pretty," explained Ian Stewart, professor

of mathematics at Warwick University. "All numbers are interesting

but some are more interesting than others and pi is the most interesting

of the lot."

**When did
we first learn of pi?**

It seems to

go back to the ancient Babylonians. When the town planners of Babylon

began to build the city they took a keen interest in geometry and

it became evident to them as early as the 20th century BC that when

any circle’s circumference was divided by its diameter the resulting

number was always about three. In fact they calculated the value

of this ratio as equal to 25/8 [25 over 8] which is 3.125 –

within 0.5 per cent of the true value of pi.

Interestingly,

a less exact value of pi is given in the Bible (Kings 7:23) which

described a round basin with the dimensions: 10 cubits in diameter

and 30 cubits in circumference. This conveniently results in pi

being a nice round number – three – but it is quite inaccurate.

Mathematicians would reel back in horror at such a tidy calculation,

which is why Professor Fink in an episode of The Simpsons managed

to gain the full attention of hall full of babbling scientists when

he shouted "pi is exactly three!"

January

9, 2010