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From: gv@hou2e.UUCP (A.VANNUCCI)
Newsgroups: net.physics
Subject: Re: Compton effect & lightsail
Message-ID: <504@hou2e.UUCP>
Date: Tue, 12-Mar-85 19:15:57 EST
Article-I.D.: hou2e.504
Posted: Tue Mar 12 19:15:57 1985
Date-Received: Wed, 13-Mar-85 02:23:05 EST
References: <145@ihlpa.UUCP>
Organization: AT&T Bell Labs, Holmdel NJ
Lines: 16

> I think it bothers some people that the photon doesn't lose energy
> in the lightsail's rest frame. How can the lightsail gain if the
> photon doesn't lose?  Let's resort to a classical analogy to explain
> this.

  The fact is that the frame of reference of the lightsail is not
an inertial frame *precisely* because the lightsail gains energy.
Energy is, obviously, not conserved in a non-inertial frame.

  In the inertial frame tangent to the lightsail just prior to a
photon reflection the reversal in the momentum of the photon is
accompanied by a small increase in the momentum of the lightsail,
such that both energy and momentum are conserved.

                                  G. Vannucci
                                  AT&T Bell Labs, Holmdel