Date: Wed, 06 Feb 2002 09:59:46 -0800

Author: Ron Ebert

Subject: Re: FW: Special Relativity


At 07:11 AM 2/6/2002 -0800, S M Ryan wrote:

>"Physical impossibility" is the easy way out. Make it a
>couple photons, or a quarks if you prefer. Forget the
>"how" of them being constrained to circular motion around a
>common central point at an identical angular velocity, just
>take that it is. One, "P", at radius "R", the other, "p",
>at smaller radius "r". Now give it some thought.
>It no longer falls under "special relativity" (which limits
>itself to constant velocities) as there is circular
>acceleration involved. Still... if the instantaneous
>linear velocity of P is c, and that of p is slightly less
>than c - what will their perceptions of each other be?
>What would our perception of them be? Or can we not look
>at the "instantaneous"?

Now you're invoking a complicated situation that goes way beyond what the
original questioner proposed. Photons are massless and travel in the
straightest line they can - called null geodesics in general relativity. In
order to get them to travel in a curved path you have to have them
traveling through curved spacetime, and in order to get them to travel in a
circle you'd need them traveling along the event horizon of a black hole.

Quarks don't exist as free particles. They make up particles such as
neutrons and protons. Aside from the photon, there are no massless
particles that travel at the speed of light for long ranges though there
are a few which are short-lived or confined to short ranges, typically the
length of atomic nuclei. So you'd need to deal with long-lived
long-traveling particles such as electrons or protons.

These do not and cannot travel at the speed of light, so you're confined to
asking what happens when they travel close to the speed of light. To get
them to do that you need to apply large electrostatic or magnetic forces.
Particle accelerators routinely do this, and they have to compensate for
the effects of relativity as someone else pointed out. A specific question
about what they do can be answered if a specific situation is proposed.

Ron Ebert
Physics is the attempt to look at things as they really are.
Urs Lauterburg - Tap-L list