# Life of pi in no danger - Experts cold-shoulder campaign to replace with tau

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- Published 30.06.11

**New Delhi, June 29:** The reign of pi is in no imminent danger in the world of mathematics.

Experts appear to have ignored a proposal from within their own ranks to retire the circle constant that is taught in schools and appears throughout mathematics and replace it with 2pi, or tau.

Proponents of the proposal to reject pi and embrace tau — whose value is twice that of pi, or 6.283 — celebrated tau day on June 28, arguing that tau is the natural circle constant as it links a circle’s circumference to its radius, and not, as pi does, to its diameter.

University of Utah mathematician Bob Palais had pitched the idea that 2pi may be a better choice for a circle constant than pi in a publication *Mathematical Intelligencer *nearly 10 years ago. Palais wanted to name 2pi “1-turn”.

However, others who share his views have campaigned for assigning the Greek letter tau.

But leading mathematicians in India, the UK and the US appeared oblivious to this campaign today and asserted that there has been no debate or even discussion over replacing 2pi with tau in serious mathematical circles.

“This has not been part of any serious mathematical discourse,” said Madabusi Santanam Raghunathan, professor emeritus at the Tata Institute of Fundamental Research, Mumbai. “The only benefit I see is that you could write one symbol (tau) instead of two symbols (2pi) and save on ink — nothing more than that,” Raghunathan told **The Telegraph**.

Some senior mathematicians caution that moves to do away with pi and introduce 2pi may be counterproductive.

“The inconvenience and confusion that would ensue in the transition phase (from pi to 2pi) would far outweigh benefits if any,” a University of California Berkeley-educated mathematician, who is now a faculty member at an institution in Bengal, said.

A US-based physicist, educator and tau proponent, Michael Hartl, has in a document he calls The Tau Manifesto, argued that tau, or 2pi, appears with “astonishing frequency throughout mathematics” and that tau is superior to pi which he describes as “a confusing and unnatural choice for the inner circle”.

But mathematicians say there’s no need for any change. “Yes, 2pi does come up in extremely natural ways across mathematics, but a shift from pi to tau will be utterly inconsequential for the way mathematics is practised,” said Gautam Bharali, a mathematician at the Indian Institute of Science (IISc), Bangalore.

“This isn’t a mathematical debate,” said Tom Coates, a reader in pure mathematics at Imperial College, London.

Across the Atlantic, mathematician Alexandru Ionescu at Princeton University also appeared unimpressed by tau. “Pi or 2pi — either one is just fine, it won’t make any difference to mathematics,” Ionescu said.

“The whole notion of replacing pi by 2pi is silly since we all are very comfortable with pi and multiplication by two,” said Siddhartha Gadgil, a mathematician at the IISc. “And one of the most remarkable formula found in mathematics is based on pi, not 2pi,” Gadgil said.

Palais himself on his website has said “it is apparent that we can’t eliminate pi, but it seems helpful to be aware of its pitfalls, and introduce an alternative for those who might wish to use one”.

Citing one of its pitfalls, Palais says the area of a circle is described using pi and the radius, but the circumference is described using pi and the diameter.