Category Archives: physique sodomie

L’ horizon

Imagine that it’s possible to build a spaceship that constantly accelerates. We don’t really care how it does this; this is a thought experiment in physics, not an exercise in interstellar spacecraft engineering. Because we’re dealing with relativistic velocities, we need to be precise and say that the spaceship undergoes constant proper acceleration: passengers will measure a constant inertial force pushing them towards the back of the ship, whereas observers in motion relative to the ship will necessarily describe its acceleration differently.

If we start out by treating the spaceship as a single point, we can describe its world line in an inertial reference frame with coordinates (t,x) as:

x(τ) = (t(τ), x(τ)) = (sinh(a τ)/a, cosh(a τ)/a)

where τ is proper time measured by a clock in the spaceship (set to zero when t=0), a is the acceleration the passengers feel, and we have chosen coordinates so that x=1/a when t=τ=0. (We are using units where the speed of light is set equal to 1, and this means that whenever we talk about an inverse acceleration being equal to a distance, or vice versa, their product will equal c2 in conventional units. For example 1/g, where g is the gravitional acceleration at the Earth’s surface, corresponds to a distance of 9.18 x 1015m, or about a light-year, while 1/x, where x is one metre, corresponds to an acceleration of 9.18 x 1015g.)

The world line of the spaceship is a hyperbola:

Constant aceleration world line

This hyperbola can also be described by the equation:

a2x2 – a2t2 – 1 = 0, or
x.x = 1/a2

The best style is the style you don’t notice. Somerset Maugham


Nous n’avons pas connu sa tête prodigieuse

où les pupilles murissaient. Mais son torse

encore luit ainsi qu’un candélabre

dans lequel son regard, vrillé vers l’intérieur,

se fixe et étincelle. Sinon, tu ne serais

ébloui par la poupe du sein, et la légère

volte des reins ne serait parcourue du sourire

qui s’en va vers ce centre où s’érigea le sexe.

Et la pierre sinon, écourtée, déformée,

serait soumise sous le linteau diaphane des épaules

et ne scintillerait comme fourrure fauve

ni ne déborderait toutes ses limites

comme une étoile : car il n’y est point de point

qui ne te voie. Tu dois changer ta vie.