# LHC 99% of speed of light

The LHC has two counter-rotating beams of particles both travelling at 99% of the speed of light.

If I was standing on one of the particles, how fast would the other beam appear to travelling ?

I know it’s less than c but wonder how much the ‘other’ 99% contributes.

You’re looking for the formula for relativistic addition of velocities; in this case, the resulting velocity would be around 0.99995 times the speed of light, if I haven’t jumbled any numbers.

I’m sure I’m wrong, but remember a couple years ago when the Earth HAD to be the center of the universe so the perceived motion in the sky of the other planets was explained by giving them retrograde motions in their orbits–as ridiculous and counterintuitive as that sounded, it provided an explanation and yielded predictability when plotting a planet’s path.

Fitzgerald contraction sounds a lot like that to me. Someone decided that c was the speed limit…

Actually, someone observed that the speed of light when added to (or subtracted from) another large velocity didn’t change. This was not at all what was expected. the Michelson-Morley Experiment

It’s the opposite, actually. c was assumed to be the speed of transmission of light waves in a medium known as the luminiferous aether by observation and theoretically formalized in the classical electrodynamics theory that is described by Maxwell’s equations. This medium was assumed to be a fixed background against which the Earth moved, and so two chaps, first Albert Michelson and then with Edward Morley, ran a series of experiments over roughly an eight year period using an interferometer that measured the phase shift between a beam moving one direction and one moving orthogonal (perpendicular) to it, with the intent of trying to determine the Earth’s relative motion against the aether. Since the existence of the aether and the purely classical wave theory of light transmission was a default assumption at that time, this was not a controversial experiment; they simply sought to refine and confirm existing theory. Instead, what they found was that they got the same speed regardless of what direction they oriented the apparatus. A lot of hypotheses were advanced to deal with this, mostly involving some kind of frame-dragging effect where the aether was stuck to the Earth locally but otherwise fixed, but several experiments to test these theories (notably the Trouton–Rankine experiment, Hammar experiment, Kennedy–Thorndike experiment) but all indicated that the speed of light was invariant in all directions and at all relative speeds, and confirmed the Lorentz–FitzGerald contraction hypothesis and Henri Poincaré and Albert Einstein’s independent theories of special relativity.

The time contraction has been observed in many different experiments, and is in fact used in synchronizing GPS satellites (though due to an effect from general relativity rather than SR). Whether the length contraction effect could be physically observed is somewhat contentious; Roger Penrose and James Terrell contend that it would actually be seen as a rotation of the object (as if seeing it in perspective) relative to the observer, an effect known as Terrell rotation or the Terrell-Penrose effect. It is both theoretically accepted and experimentally established to the point of virtual certainty for all but the lunatic fringe of physicists and astronomers, and has been used to predict observed phenomena to as high a precision as extant instrumentation can measure.

Also Ptolomy’s Almagest, with its theories of planetary epicycles, was published was more than “a couple of years ago.”

Stranger

What would determine the direction of rotation?

Never mind, the Wikipedia article answers my quesition. Passing objects (not approaching objects) would appear to rotate, which I assume means the direction of rotation would be determined by the direction of movement past the observer.