Nieminen Juha skrev i meldingen <37f31566@news.povray.org>...
>Simen Kvaal <sim### [at] studentmatnatuiono> wrote:
>: Light has mass too! According to Einstein, light has no resting mass, but
>: relativistic mass.
>
>  I wouldn't say that light actually has mass.
>  AFAIK light has no mass. Period.
>  This is only my opinion of what I have understood about physics:
>  For some calculations it may be easier to consider the light having mass,
>but it's only a mathematical trick. It doesn't really have any mass. The


Light has mass. Period!! It's not just a mathematical trick. Light *has*
relativistic mass, and so have you. When travelling faster and faster, you
gain weight. You cannot travel at the speed of light, because you'd have
infinite mass:

m = m0 / sqrt(1 - (v*v/c*c))

If m0 is your resting mass, v is your velocity and c is the speed of light,
then relativistic mass (aka REAL mass) is m. You can see from the equation
that when your speed approaches the speed of light, your mass diverges into
infinity. These are the equations Einstein found, and they have been
*empirically* verified!

The reason why light has mass, is Einsteins formula:

E = mc^2.

Light has energy, right? Then, light must have mass. It cannot have resting
mass, because light doesn't rest. But as the light travels at the speed of,
say, light, it must have relativistic mass. The energy of a photon is:

E = f * k

where f is the frequency and k is a constant (which i cannot remember; it's
three years since i learnt this). Put this into the "emc" and you get:

m = f*k/c^2

This is the mass of light. Period.




>reason why light bends near massive objects is because the space is curved
>there and the light tends to move along the geodesic lines of the space
>(which are actually the shortest way from one point to another). The
>massive object doesn't attract the light, it's just bending the space.
>

Correct, afaik.


>
>  You are confused here. Solar wind is not light, it's gaseous matter that
>the Sun is emitting (mainly ions). See:
>http://www-spof.gsfc.nasa.gov/Education/wsolwind.html
>

Okay. I was wrong there. But light has mass! The solar winds was just a
(very) bad example. You can verify that photons actually may cause pressure!
This is the empirical prof of the mass of light. You cannot have pressure
without mass.

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