[Fyron]

My appologies if you feel insulted, that was not my intention.

Apology accepted. Please refrain from statements akin to "you don't know jack" (no pun intended) in the future.

First of all, I do acknowlege the fact that space and time are not physical (having mass) objects! You refuse to acknowledge that they exist without having mass or energy.

No, I don't refuse to acknowledge that. Reread my statement. It specifically says "...unless it is a dimensional concept (such as space and time)...". I do not know how much more specific I can get... And, I also said this:
"Since you refuse to acknowledge it... dimensions are not physical objects, and so do not have mass. Space and time are dimensions, not objects. I have amended my statements; there is nothing to reconcile."

What is the exact value of the mass of a given photon?

The exact value is unknown. I can not give you an exact value.

Are you saying that if humans can't observe something then it doesn't exist?

I thought I had already addressed that, but it must have been deleted from a draft. So... I am saying that if humans can not observe something (directly, indirectly, through mathematical models, etc., etc.) then it has no more value than mere fantasy until such a time as it can be observed in some form. Unsupported hypothesis are a dime a dozen, and can be safely ignored (except when testing to see if they are true or not, of course). I could easily claim that there are invisible (on all frequencies), undetectable, flying, pink elephants floating around. Such a hypothesis is just as valid as any other, until some form of work is done to try to disprove it or find some form of concrete evidence (see earlier post) is found that supports it (and there is not a better alternative hypothesis that more accurately reflects the data).

Originally posted by Slick:
Yes, I have heard of a solar sail (did some R&D at TRW). Photons do indeed carry momentum to impart to a sail. They do not have mass. There is your mistake. For a photon, momentum is given by:

p = (Plank's Const.)/(Wavelength)

See? momentum with no mass. Any basic physics book has this in it.

Photoreceptive fans react to the change in momentum when a photon encounters the fan, not because the photon has mass.

"...everything that exists either has mass or has mass-like properties..." (abbreviated). Momentum is a "mass-like property" in that it transfers inertia like mass does. It falls under the rest of my statement. Even if a photon has no mass (which is open for debate in the wide world of physics), having momentum qualifies it just the same.

[ August 18, 2003, 06:00: Message edited by: Imperator Fyron ]