Light

Dose Light have mass? The last I heard it didn't. Einstein was
supposed to have proved it. However the other day my friend said tat
newer research showed that it did. We argued over it for a while, and
then I thought " I know, I'll ask all those helpful Physicists at
IFIS!!!" So, can you help?

James Hanley, bloke with out-of-date data?

Yes it does, that's why light is affected by gravity.

I thought that was because the space the light was moving through was
bet by gravity. So the light its self is not bent, by the space it is
moving through is, so the light appears to be bent, but isn't. I know
that isn't a good way of putting it, and that it is probably a load of
nonsense, that's how it was tough to me...

James Hanley, clutching at straws!

I don't think this is the case. I remember being taught that light
consists
of photons, which have mass, but it is negligible. Unless of course you
are referring to theories about Dark Matter, which is well above my
head...

In article <7163823F2EDACF1188610000C0F06ACF0106DC11@>, Hanley F <F.Hanley@> wrote:
That was my impression too.

I should point out that when we talk about "mass", we are actually talking
about two things: inertia and gravity. Inertia is the thing that makes it
harder to push (or stop) heavy things, and gravitational susceptibility is
the thing that makes them harder to pick up.

It turns out that these two properties are always in exact proportion for
all materials - but I am not at all sure that they are in exact proportion
for light. Light does get bent by gravity (or the space through which it
travels is bent by gravity) and it does have something like inertia, which
is demonstrated in those little whirly glass things that spin around when
you shine light on them. They have a white side and a dark side - on the
dark side the light sticks to the surface, while on the light side it
bounces off. The difference in inertia between the sticking and the
bouncing off creates a tiny, tiny force that pushes the wheel around.


The inertia-of-light is the property upon which "light-sail" spacecraft are
considered to operate - an essential feature of such diverse stories as "The
Number of the Beast", "The Fourth Profession", "Sunjammer" and "The Mote in
God's Eye".

The bending of light by gravity appears in pretty well all the black-hole
stories ever written.

Can any real (mathematical, up-to-date) physicists tell us if "inertial
mass" and "gravitational mass" are in proportion for light?



Simon

---
"This too is meaningless, a chasing after the wind" -Ecclesiastes 4:16

simon@ | Not affiliated to any religion
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H (+44/0)1784 431998 | Not affiliated to any ideology
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"I have been asked to point out, as if you couldn't guess, that my rantings
are not the opinions of One Chip Solutions. So now you know, don't you..?"

Hmm. My A-level physics teacher said it was because the little glass
bulb containing the spinning bit didn't hold a complete vacuum, and when
light hit the dark sides of the little vanes, that side heated up
slightly, causing the gas near them to expand a little bit, and thus
pushing the whirly thing around. At least, I think that was the
explanation he gave us, but he could have been winding us up. It was
either that or the dark sides getting given the same static charge as
the gas by the light hitting them, pushing the gas away from that side,
and making the spinny thing spin. But I'm even more dubious about that
theory.

Later,

Steve :-)
_
__
(oO)
/||\

Light can't escape a black hole (that's why it's black). This appears to support the point of view that light is affected by gravity.


...............................................................................
clyth@
In relativity, matter tells space how to curve, and space tells matter
how to move. The Heart of Gold told space to get knotted...
D. Adams Life, The Universe and Everything

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From: Hanley F
Sent: 10 February 1998 12:56
To: 'chat@'
Subject: RE: Light
I thought that was because the space the light was moving through was
bet by gravity. So the light its self is not bent, by the space it is
moving through is, so the light appears to be bent, but isn't. I know
that isn't a good way of putting it, and that it is probably a load of
nonsense, that's how it was tough to me...

James Hanley, clutching at straws!

A smartarse friend has something to say on the subject of light.
Photons have a small negligable mass but as they have this mass they are affected by large gravitational feilds such as found near stars this results in ther path being alterd through an equation produced by sir isac newton which shows the gravatational effects of two bodys.
...............................................................................
clyth@
In relativity, matter tells space how to curve, and space tells matter
how to move. The Heart of Gold told space to get knotted...
D. Adams Life, The Universe and Everything

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