Information Theory and Intelligent Design.

True Not true Unless you want to use antiquated terminology from 60 years past. They have "relativistic mass" which is not actually mass at all. They have momentum, hence your solar sail, and from the momentum a mass-like equivalent measure is derived... but it is not mass.

Sorry, this is not on-topic here, so I'll keep my asnwer brief (for me) Oh dear But Baez's site is very sound. No, absolutely not. Rest mass is an invariant quantity. Relativistic mass is an observer dependent quantity, and hence largely meaningless. If I ask you for your height, what do I expect? A measurement depending on your particular position? On how far away you are from me? On how fast you happen to be moving at that time? Because mass is not the only generator of inertia and gravitation. In this case one could say that it is the momentum of the photons that is causing the difference - it is certainly not their mass as that is zero. The trouble is there are too many uses of the word mass being floated around. The "mass" of a composite body is the gravitational "mass" - something that we actually often call stress/energy to avoid confusion. This is very different to the rest mass of a particle and to the relativistic "mass" of a particle. Meyer is simply talking nonsense and he has no clue to the real nature of mass and its various defintions - it's not his field. Why would I be intersted in any of his definitions?