The nineteenth letter of the Greek Alphabet.

In particle physics, the tau is the third generation lepton. It's very massive and thus requires very high-energy collisions to create. The process of creating taus usually involves colliding beams of electrons and positrons (antielectrons). At high enough energies, this results in the production of tau and antitau, which decay almost instantly (in the range of 10-13 seconds).

The tau's corresponding neutrino (the tau neutrino) was recently discovered at Fermilab in Illinois, providing experimental verification for its prediction in the Standard Model.

In the world of Warhammer 40,000, the Tau are a relatively young species among those contesting for power in the galaxy. Though young by the standards of the Empire, having attained basic technological proficiency within the last 6,000 years, the Tau have achieved a high level of technical sophistication- perhaps even higher than the level of the Empire itself. Unlike many of the Games Workshop Warhammer 40k races, the Tau are not simply a fantasy race put into space (like the Orks, Eldar, Dark Eldar, and Chaos forces). They are hominid in form (two arms, two legs, and a head), with bluish, hairless skin, flat faces with no discernable nose, and a wide mouth.

The Tau evolved on an arid, semi-desert world, where different groups of Tau were forced into different areas of the planet in order to specialize and survive. These specialized groups evolved into the four major castes that provide the basic organization of Tau society. Water caste Tau are merchants, beaurocrats, and negotiators. Fire caste Tau are fierce warriors. Earth caste Tau are craftsmen, farmers, and engineers. Air Tau are messangers, explorers, and staff that Tau offworld navy. A fifth cast, the Ethereal, serves as the leaders of Tau society, occupying a role somewhere between royalty and priesthood. The Ethereal seek to convince all Tau to serve the Greater Good of all Tau. The first members of the Ethereal caste settled a world-wide caste war that threatened to eliminate the Tau shortly after they achieved a modest level of technological achievement. Because of their mystique and the reverence in which they are held, the presence of an Etherial on the battlefield can inspire Tau warriors to great feats of bravery and daring. Conversely, the death of an Ethereal can send tremors through a Tau army that can cause chaos./p>

After the rise of the Ethereal class and the settlement of the war, Tau society began to advance at a rapid pace. Technological development outpaced the expected rate, and soon resulted in limited space flight and other advances. The Tau began to encounter nearby sentient races, most of whom were absorbed into the growing Tau empire. Most important among these were the Kroot, a barbaric race of warriors that have been regularly employed as mercenaries by the Tau to enhance their combat abilities. Contact with the Empire and other space-age races was limited. While a number of battles were fought with Orks, a large and persistant warpstorm blocked Imperial and other forces from entering Tau space for thousands of years. As a result of local space conditions and the warpstorm, the Tau did not develop long-range warp jump capabilities. Curiously, they also never developed psykers of any sort.

As the Tau developed technologically, contact with the Empire finally came (a few Imperial scouts had contacted the Tau prior to the development of the warpstorm, and a fleet dispatched to 'cleanse' the aliens, but the effort was stopped when the storm developed). Tau exploration vessels wandered into Imperial space, where they were engaged and destroyed. The Empire, recognizing the Tau from genetic samples taken by the early explorer missions, set out to destroy this new alien threat. Thus was born the Damocles crusade. A number of outlying Tau worlds were conquered or destroyed. But as the Empire pressed deeper into Tau space, they met with increased resistance, until they were forced to sue for peace. The Empire withdrew, only to be replaced by a threat to the Tau from Tyranid marauders. Such is life in the grim future ;).

Though they regularly take to the battlefield to defend their fledgling empire, the Tau are not a particularly warlike people (certainly not by the standards of Warhammer 40k!). Even the warriors of the Fire caste look upon hand-to-hand combat with disdain, seeing it as brutish and foolish. Not coincidently, Tau are ill-equipped for direct assault. They prefer to use their technology to their advantage, laying down a field of fire with pulse rifles and plasma weapons and employing networked drones and heavily armed and armored battlesuits. Even enraged Tau will usually let loose a withering hail of missle fire rather than dashing off into close combat. The Kroot, alies of the Tau, do most of their close fighting, while Tau Fire warriors, battlesuits, drones and artillery pound enemy positions from afar.

The circumference of a circle is 2π times its radius. This is a bit confusing, having to stare at a factor TWO in an expression that is supposed to produce the circumference of ONE whole circle. Also, if you rotate the circle radius ONE full turn (360 degrees), your radian expression will contain an irrelevant factor TWO. Inelegant, clumsy, unnerving.

But these (and plenty more) annoyances can be resolved, if you care to define a different circle constant, τ (Greek letter tau):

τ= circumference/radius

Now, using this new circle constant τ , one full rotation (360 degrees) of a unit radius becomes simply 1 x τ = τ radians. Similarly, turning the radius 60 degrees means turning it one sixth (1/6) of a full turn and hence τ/6 radians, turning it 90 degrees is equivalent to ¼ of a full turn and hence τ/4 radians, and so on. Immensely more intuitive and straightforward, when there is no fooling around with an inexplicable factor 2, isn’t it?

The inspiration of using the circumference/radius definition as the proper (and the one-and-only) circle constant first occurred to mathematician Bob Palais (in the article “Pi is wrong!”), but the idea of using the Greek letter τ (Tau) to denote it is due to physicist Michael Hartl. Hartl declared June 28 2010 “Tau Day”, and he will probably celebrate the first Tau Day anniversary on June 28, 2011.

2π occurs in a large number of important mathematical expressions (Gaussian probability distribution, Fourier transform, Cauchy’s integral formula, etc.), so replacing 2π by τ makes things easier and simpler.

The price of this simplicity is that the expression for the area of a circle becomes A = ½τr2, which contains an inconvenient factor ½. But Michael Hartl maintains that there are a lot of quadratic forms of this type in mathematics and physics (distance fallen: ½gt2, spring energy: ½kx2, kinetic energy: ½mv2, etc.), so the area formula for a circle will be easy to remember.

So τ = 6.283185 ... is the only circle constant worth remembering. Forget all others – there can only be one winner! But victory may take some time, I guess.


Tau (?), n. [Gr. tay^ the letter τ (English T).] (Zoöl.)

The common American toadfish; -- so called from a marking resembling the Greek letter tau (τ).

Tau cross. See Illust. 6, of Cross.


© Webster 1913

Tau (tou), n. [Gr. tay^.]

The nineteenth letter (Τ, τ) of the Greek alphabet, equivalent to English t.


© Webster 1913

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