<font color="yellow"> It follows by conservation[sic] of momentum that if the light is incident to, and reflected from the sail at some angle to the normal then the sail will experience a force in the direction of the normal, i.e. at an angle to the direction of the light source. </font><br /><br />See my above reply to nacnud. Since it is clear that light is not “reflected” from a surface per se, what is really happening there?<br /><br /><font color="yellow"> I do agree that billowing and rotation of the sail may be problematic, but presumably simulations of this can be carried out. </font><br /><br />I have run these simulations, and the result was always the same. I only found one practical way (which does not required input of energy or propellant) to counteract the rotation of the sail.<br /><br /><font color="yellow"> This is consistent with the hypothesis that the emission of a photon provides a push (and this makes perfect sense given that photons have momentum). </font><br /><br />I have always found this to be contradictory, an oxymoron of sorts. People refer to light as electromagnetic waves when it is convenient, and as particles when it is convenient. For instance, it would be difficult to provide an explanation of how an electromagnetic wave would provide “push”. While I understand the basis of the wave-particle duality hypothesis, I suspect that there is something going on there that would explain a lot of things, if we could just figure it out. Wave-particle duality is probably the biggest cop-out by physicists in recent history.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>