Gravity's effect on speed and direction of light

[Learner]

I have a complete novice question: what is the effect of gravity on the speed and direction of light?

When we see starlight in the sky, could gravity have bent the light such that the stars are actually located in a slightly different position than how they appear to our eyes (or would that effect be negligible over such large distances)?

[Richard Norman]

On Fri, 18 Apr 2014 06:56:47 -0700 (PDT), Learner <nat...@gmail.com>
wrote:

>I have a complete novice question: what is the effect of gravity on the speed and direction of light?
>
>When we see starlight in the sky, could gravity have bent the light such that the stars are actually located in a slightly different position than how they appear to our eyes (or would that effect be negligible over such large distances)?

Google "gravitational lens".

[deadrat]

On 4/18/14 8:56 AM, Learner wrote:
> I have a complete novice question: what is the effect of gravity on the speed and direction of light?
>
> When we see starlight in the sky, could gravity have bent the light such that the stars are actually located in a slightly different position than how they appear to our eyes (or would that effect be negligible over such large distances)?
>

This is, in fact, one of the confirmations of Einstein's theory. During
a solar eclipse, astronomers can measure the position of stars with
lines of sight close to the sun at totality and compare the positions
measured when the sun isn't close by. Sir Arthur Eddington first did
this in 1919 using the bright stars in the Hyades cluster in the
constellation Taurus. The sun's gravity bends the light in accordance
the theory of relativity.

The speed of light in a particular medium is always constant.

[John Stockwell]

You are describing gravitational lensing. The speed of light does not change, but light is bent by massive bodies.

John

[Robert Carnegie]

On Friday, 18 April 2014 17:19:03 UTC+1, John Stockwell wrote:
> You are describing gravitational lensing. The speed of light
> does not change, but light is bent by massive bodies.

Is the speed of light different - slower - in "dark matter",
like it is in glass and water and so on?

[jillery]

On Fri, 18 Apr 2014 06:56:47 -0700 (PDT), Learner <nat...@gmail.com>
wrote:

>I have a complete novice question: what is the effect of gravity on the speed and direction of light?
>
>When we see starlight in the sky, could gravity have bent the light such that the stars are actually located in a slightly different position than how they appear to our eyes (or would that effect be negligible over such large distances)?

Short version: Empty space is flat, so light moves through it in a
straight line. Mass creates gravity, which "dimples" or curves space.
Light dips into and out of those "dimples", and so changes direction,
or "bends".

But the effect is very small. The mass of the Sun, which has over 99%
of all the mass of the entire Solar System, deflects light's path only
one quarter of a thousandth of a degree. This is about the same as the
apparent diameter of a compact disc viewed from a distance of about 20
miles away.

Collect enough mass together, say several galaxies in a tight cluster,
and it will create enough gravity to curve space enough to cause light
from behind it to come to a point in front of it; a gravitational
lens.

Collect even more mass together and/or more densely, and it will
create enough gravity to curve space so much that light that goes into
the dimple can't get back out; a black hole.

In all cases, the speed of light is constant. What gravity changes is
not the speed of light, but its frequency. As gravity increases,
light from it loses energy and so gets "redder".

[Paul Ciszek]

In article <d0370fcd-5f67-4291...@googlegroups.com>,

Find us some dark matter, and there will be a lot of guys who will want
to perform that experiment as well as many, many others.

Supposedly, dark matter doesn't interact with the electromagnetic force,
including light (hence the name), only gravity. Now, here is where things
might get weird: If you had a dense clump of dark matter somewhere, light
should be able to pass right through it--but would there be any funky time
dialation effects inside the mass? Might that affect the transit time
of light through the clump as measured by outside observers?

--
Money is Speech
Corporations are People
Freedom is Slavery
Ignorance is Strength

[jillery]

I'm no expert, but I'm almost certain that it's not. Gravity doesn't
effect the speed of light, but it reduces its energy, ie redshifts it.

[Richard Norman]

On Fri, 18 Apr 2014 14:39:13 -0400, jillery <69jp...@gmail.com>
wrote:

<snip>

>... What gravity changes is

>not the speed of light, but its frequency. As gravity increases,
>light from it loses energy and so gets "redder".

This is not quite true. If light originates in a region of high
gravity and "climbs out of" the gravitational field, then it does lose
energy and shows a red shift. However light falling into the
gravitational field is blue shifted and light that passes by, being
deflected or lensed by an intense gravitational region, returns to its
original color.

It is correct that the speed does not change.

[Paul Ciszek]

In article <c2r2l91506a96lmhu...@4ax.com>,

jillery <69jp...@gmail.com> wrote:
>
>In all cases, the speed of light is constant. What gravity changes is
>not the speed of light, but its frequency. As gravity increases,
>light from it loses energy and so gets "redder".

If you prefer to think of light as a continuous wave rather than discrete
photons, this same effect is explained using time dialation (I think).

Picture a radio station operating at the bottom of a gravity well. Let's
say the station's clock is operating off of the same frequency standard
that they use to generate their carrier wave. If you listen to the station
from outside the gravity well, not only will the frequency be slower
(i.e., red-shifted) but the DJ will be talking slower, it will take 20
minutes to play "Alice's Restaurant", the "top of the hour" news bite will
be later and later each hour, etc.

[jillery]

Then the light isn't from there. My point stands.

[jillery]

That's how I understand it, that time in a gravity well/accelerating
frame slows down. It's not clear to me if you think that implies the
speed of light itself slows down. IIUC it does not.

[Richard Norman]

On Fri, 18 Apr 2014 15:18:13 -0400, jillery <69jp...@gmail.com>

wrote:

>On Fri, 18 Apr 2014 14:53:25 -0400, Richard Norman
><r_s_n...@comcast.net> wrote:
>
>>On Fri, 18 Apr 2014 14:39:13 -0400, jillery <69jp...@gmail.com>
>>wrote:
>>
>><snip>
>>
>>>... What gravity changes is
>>>not the speed of light, but its frequency. As gravity increases,
>>>light from it loses energy and so gets "redder".
>>
>>This is not quite true. If light originates in a region of high
>>gravity and "climbs out of" the gravitational field, then it does lose
>>energy and shows a red shift. However light falling into the
>>gravitational field is blue shifted and light that passes by, being
>>deflected or lensed by an intense gravitational region, returns to its
>>original color.
>
>
>Then the light isn't from there. My point stands.
>
>
>>It is correct that the speed does not change.

"As gravity increases"?? What does that mean?

[jillery]

On Fri, 18 Apr 2014 15:51:57 -0400, Richard Norman
<r_s_n...@comcast.net> wrote:

>"As gravity increases"?? What does that mean?

Is that an acutal question, as in you don't understand the point I'm
making? Or is that an rhetorical retort, as in you don't think it's a
coherent statement?

[Richard Norman]

On Fri, 18 Apr 2014 16:10:50 -0400, jillery <69jp...@gmail.com>
wrote:

I don't understand the point you are making in talking about light
moving in a situation which, in your terminology, occurs "as gravity
increases". In particular, the phrase you wrote but now snipped
reads "As gravity increases, light from it...". What is the "it"
which involves gravity increasing? It seems to me that if light moves
away from a mass then gravity should decrease.

[jillery]

On Fri, 18 Apr 2014 16:36:17 -0400, Richard Norman

<r_s_n...@comcast.net> wrote:

>On Fri, 18 Apr 2014 16:10:50 -0400, jillery <69jp...@gmail.com>
>wrote:
>
>>On Fri, 18 Apr 2014 15:51:57 -0400, Richard Norman
>><r_s_n...@comcast.net> wrote:
>>
>>>"As gravity increases"?? What does that mean?
>>
>>
>>Is that an acutal question, as in you don't understand the point I'm
>>making? Or is that an rhetorical retort, as in you don't think it's a
>>coherent statement?
>
>I don't understand the point you are making in talking about light
>moving in a situation which, in your terminology, occurs "as gravity
>increases". In particular, the phrase you wrote but now snipped
>reads "As gravity increases, light from it...". What is the "it"
>which involves gravity increasing? It seems to me that if light moves
>away from a mass then gravity should decrease.

If you don't understand, then you have no basis for claiming that my
statement isn't quite right. Yet that is exactly what you led with,
as if you do think you understand what I meant.

Given your long, consistent, and continuous behavior up to now, of
posting one YASMA after another, you should understand that I remain
skeptical of your claim of sincerity above.

[John Stockwell]

I would have to say "no" on that. Dark matter is alleged to interact
with regular matter only through gravitation. So, lensing yes, but
slowing down no, because there is supposed to be no electromagetic interaction
with dark matter.

-John

[John Stockwell]

Yet, relativity holds that the speed of light will be the same in either the inside or outside
frame.

-John

[Richard Norman]

On Fri, 18 Apr 2014 17:39:21 -0400, jillery <69jp...@gmail.com>

Believe what you want. You wrote something that was terribly unclear
and included a phrase that seemed to deny what you claimed. I did
acknowledge that your statement was partially true because there is a
circumstance under which gravity causes a red shift. But gravity can
also cause a blue shift or no shift at all and you did not distinguish
these cases. So in certain circumstances you are right but in others
you are wrong.

But since you do not with to explain just what you meant by gravity
increasing or what the "it" is in ""As gravity increases, light from
it..." then so be it. You are skeptical of my sincerity. I doubt you
understand the issue. End of story.

[Josko Daimonie]

By means of context, I would say that he was referring to his analogy.
The light passes through, or originates, in a potential well; by 'when
gravity increases' he means that the well becomes deeper.

At least, that's what I thought when reading it and it seemed fairly
obvious using his short version at the start.

[jillery]

On Fri, 18 Apr 2014 18:50:31 -0400, Richard Norman

What you say above doesn't help to convince me of your sincerity. To
the contrary, it helps to affirm your lack of it. And that is the end
of the story.

[jillery]

Apparently Rnorman isn't really interested in what I meant, only in
how he can misrepresent it.

[deadrat]

I believe that as the light approaches a massive object (which is to say
that the force the light feels increases as the distance decreases), the
light's frequency will be blue-shifted. As the light recedes from the
massive object (which is tot say that the force the lights feels
decreases as the distance increases), the light will be red-shifted by
the same amount. Thus the gravitational effect of the massive object
will not be reflected in the measured frequency of the light. The light
will however be deflected.

I am sure of three things. First, that someone who knows more physics
than I can correct me if I'm wrong. Secondly, that for jillery, the
issue now has nothing to do with physics but with your shortcomings as a
human being. Thirdly, she will have the last word on that topic.

[jillery]

On Fri, 18 Apr 2014 19:01:28 -0500, deadrat <a...@b.com> wrote:


Just to throw your own argument back at you, who invited you into this
subthread? Go away.

[deadrat]

Actually, no one was talking to *you*. My comment was directed to RN.
If he'd like to invite me out, that's fine.

If you're sure you've been as clear as possible (and especially if only
one person has voiced confusion), then you're done. If you think you
could have been clearer or just in an abundance of caution (and
especially if multiple people seem confused), then rephrase and amplify.
There's no need to invite the drama by reading people's minds for
their level of sincerity.

But you knew that.

As I predicted, you won the last thread, the one that ended with your
bizarre comments about sadism and blackface.

And I predict you'll win this one too. You can't help yourself.

[rnorman]

On Fri, 18 Apr 2014 21:13:22 -0400, jillery <69jp...@gmail.com>
wrote:

I didn't realize anyone had to get your permission to participate in
a public forum. But if you really must know, I did.

[jillery]

On Fri, 18 Apr 2014 20:26:52 -0500, deadrat <a...@b.com> wrote:

>Actually, no one was talking to *you*. My comment was directed to RN.
>If he'd like to invite me out, that's fine.

Actually, no one was talking to *you*. Now go away.

[jillery]

On Fri, 18 Apr 2014 21:55:12 -0400, rnorman <r_s_n...@comcast.net>

wrote:

>On Fri, 18 Apr 2014 21:13:22 -0400, jillery <69jp...@gmail.com>
>wrote:
>> On Fri, 18 Apr 2014 19:01:28 -0500, deadrat <a...@b.com> wrote:
>
>
>
>
>> Just to throw your own argument back at you, who invited you into
>this
>> subthread? Go away.
>
>I didn't realize anyone had to get your permission to participate in
>a public forum. But if you really must know, I did.

Cite?

[Robert Carnegie]

This is a field where misunderstandings are common, and
language should be used carefully.

Perhaps you had in mind that, for instance, if I'm in orbit
at a safe distance around a black hole, and I drop a white LED
flashlight into it, I will observe the light reddened.
But if I drop Richard Norman into the black hole /holding/
the flashlight, he will see it as white light.

I think this is an effect that GPS satellites have to be
adjusted for. Their operation depends on a highly accurate
"atomic" clock on board the satellite, but time itself
measured on the satellite is very slightly different to
time measured on the ground on planet Earth.

But if that is what you meant, I too didn't see it clearly.

Gravity is a geometric property of four-dimensional
space-and-time. It's confusing.

[Robert Carnegie]

OK. I suppose if there was /any/ optical effect from dark matter
itself, then dark matter would have been found sooner.

And apparently we're swimming through it here on Earth... but it
isn't very dense at all. Glass with the physical density of
dark matter would have next to no refraction at all...?

[Robert Carnegie]

On Friday, 18 April 2014 14:56:47 UTC+1, Learner wrote:
> I have a complete novice question: what is the effect of gravity
> on the speed and direction of light?
>
> When we see starlight in the sky, could gravity have bent
> the light such that the stars are actually located in a
> slightly different position than how they appear to our eyes
> (or would that effect be negligible over such large distances)?

I think we've been treating this question in terms
of the science, and not in terms of arguments made
to support "Young Earth Creationism". Is that O.K.
with you?

For instance, there was a claim that, well, I didn't
exactly see how it was meant to work, maybe it's safe
to say that it was only meant to sound good, but I
think it was supposed to allow God to create the
Earth, Sun, other planets and the rest of the universe
all at the same time, with the universe now
13.8 billion years old (Wikipedia says) while
on the Earth only a few thousand years have passed.

Well, anyway, you mentioned the positions of stars,
and gravity causing light to bend, and that put us
onto talking about that particular effect.

But there's also the expansion of the universe to
talk about.

I hope I get this right: Distant galaxies appear
red-shifted because the universe is expanding.
I think it's not really right to say that space
itself is stretching and getting bigger, but
I think it will do as a simple mental picture.
I think also the distant galaxies are not
/moving/ away from us, it isn't a real velocity -
they just /are/ further and further away, because
space is expanding.

It isn't a significant effect inside this galaxy,
which is enough stars to be going on with - but
I think it bears on how far away the distant
galaxies "really" are, although I can't figure
out how. But... apparently the expansion of
the universe is /increasing/. So for that reason -
as well as the fact that we are seeing remote
galaxies as they were billions of years ago anyway,
which is easier to allow for - I think that any given
galaxy logically "is" farther away now than it
appears to be.

On the other hand, astronomers rarely mention that
they're looking at stars and galaxies that are
many light-years away, and therefore they are seen
in their state and position of that many years ago
(even before you take into account the accelerating
expansion of the universe). If you see a star
explode today, then you talk about it as though
it happened "today", although physically it happened
years ago - maybe very many years. This works
because everyone on the Earth sees it at around
the same time.

But, of course, if a science fiction space-ship is
two light years away, and you see it suddenly flying
away at 0.5 of the speed of light, then in fact it
is three light years away right now, since it has
been moving at that speed for two years. (Assuming
that that's what it continued to do.)

On the other hand, in "special relativity" - Einstein's
first kind of relativity - there isn't a reliable
definition of "now" elsewhere, because - well, because
it's "spacetime", and being in motion means that you
have a different frame of reference for space, and time,
and "now". But maybe I shouldn't have brought this up,
because it's probably even more confusing.

[jillery]

On Sat, 19 Apr 2014 00:52:33 -0700 (PDT), Robert Carnegie
<rja.ca...@excite.com> wrote:

[...]

>This is a field where misunderstandings are common, and
>language should be used carefully.

I agree, and manufacturing argument don't help with that.

>Perhaps you had in mind that, for instance, if I'm in orbit
>at a safe distance around a black hole, and I drop a white LED
>flashlight into it, I will observe the light reddened.
>But if I drop Richard Norman into the black hole /holding/
>the flashlight, he will see it as white light.
>
>I think this is an effect that GPS satellites have to be
>adjusted for. Their operation depends on a highly accurate
>"atomic" clock on board the satellite, but time itself
>measured on the satellite is very slightly different to
>time measured on the ground on planet Earth.
>
>But if that is what you meant, I too didn't see it clearly.
>
>Gravity is a geometric property of four-dimensional
>space-and-time. It's confusing.

The issue here is not whether what I wrote was good, bad, clear,
confusing, correct, invalid, or any other bald assertion anyone may
choose to apply to it. The issue here is that Rnorman declared that
what I wrote was wrong even before he understood what I said, and to
claim that I don't know what I'm talking about. There's no point to a
trial when I'm already hung.

[jillery]

Correct. Gravity from dark matter manifests itself on galactic scales
and beyond. It's only apparent interaction with "normal" matter is
gravitationally. That's the reason why some postulated that the the
theory of gravity should be modified at larger scales. But for
various reasons, that doesn't work out so well.

[J. J. Lodder]

Believers in MOND claim otherwise,

Jan

MOND for MOdified Newtonian Dynamics.

[jillery]

Very true, but evidence counters their beliefs.

[Steven Carlip]

In article <LrOdnekxE5dFIczO...@giganews.com>,
deadrat <a...@b.com> wrote:

[...]

> I believe that as the light approaches a massive object (which is to say
> that the force the light feels increases as the distance decreases), the
> light's frequency will be blue-shifted. As the light recedes from the
> massive object (which is tot say that the force the lights feels
> decreases as the distance increases), the light will be red-shifted by
> the same amount. Thus the gravitational effect of the massive object
> will not be reflected in the measured frequency of the light. The light
> will however be deflected.

This is correct, except for one quibble, which is actually
important to cosmology. If the massive object is a super-
cluster of galaxies (or a "supervoid," which acts as if it
has negative mass relative to the average), its gravitational
potential can change during the time the light is passing,
because the expansion of the Universe can stretch it out.
If this happens, the red shift going out will not exactly
match the blue shift going in. This effect is called the
"integrated Sachs-Wolfe effect," and it's particularly
sensitive to any acceleration in the expansion; while it's
hard to observe, it can in principle be used as an independent
measure of "dark energy."

(This can only happen at very large scales -- objects as small
as galaxies and smaller clusters are held together strongly
enough by their own gravity that they are not affected much
by the expansion.)

The other thing that might be worth mentioning is that the
deflection of light can be used to "map" the location of
matter, including dark matter, throughout the Universe.
This has been started, and there are plans underway to use
future telescopes such as the LSST to make detailed three-
dimensional maps of the mass density of the observable
Universe.

Steve Carlip

[erik simpson]

Pretty much right, but a small, maybe semantic quibble:

Light can't really 'feel' any force, particularly gravitational, even in
the Newtonian limit, since the photon is massless. In GR, massless particles
are constrained to move on 'lightlike' geodesics, along which 'proper time'
(as measured by a comoving clock) does not vary. Photons of known emitted
frequency can be red- or blue-shifted as measured by an observer either by
relative motion between the emitter and the observer (Doppler shift) or by
relatively different spacetime curvature at the emitter and observer
('gravitational' shift). In the latter case, it's really due to the fact
that identical clocks run at apparently different rates in regions of
different curvature (gravitational field).

[jillery]

Thank you, Steve Carlip, for once again restoring order and reason to
a chaotic thread.

[deadrat]

Hanged. Unless you're, ....

Oh, never mind.

[jillery]

On Sat, 19 Apr 2014 13:13:43 -0500, deadrat <a...@b.com> wrote:


I wasn't taking to you. Go away

[deadrat]

On 4/19/14 2:11 PM, jillery wrote:
> On Sat, 19 Apr 2014 13:13:43 -0500, deadrat <a...@b.com> wrote:
>
>
> I wasn't taking to you. Go away
>

No.

Sound familiar?

[jillery]

So much for your self-awareness. Let's see if the irony fairy
remembers who said what first.

[deadrat]

On 4/19/14 11:07 AM, Steven Carlip wrote:
> In article <LrOdnekxE5dFIczO...@giganews.com>,
> deadrat <a...@b.com> wrote:
>
> [...]
>> I believe that as the light approaches a massive object (which is to say
>> that the force the light feels increases as the distance decreases), the
>> light's frequency will be blue-shifted. As the light recedes from the
>> massive object (which is tot say that the force the lights feels
>> decreases as the distance increases), the light will be red-shifted by
>> the same amount. Thus the gravitational effect of the massive object
>> will not be reflected in the measured frequency of the light. The light
>> will however be deflected.
>
> This is correct, except for one quibble, which is actually
> important to cosmology. If the massive object is a super-
> cluster of galaxies (or a "supervoid," which acts as if it
> has negative mass relative to the average), its gravitational
> potential can change during the time the light is passing,
> because the expansion of the Universe can stretch it out.
> If this happens, the red shift going out will not exactly
> match the blue shift going in. This effect is called the
> "integrated Sachs-Wolfe effect," and it's particularly

> sensitive to any acceleration in the expansion; <snip/>

Perhaps a quibble, but nevertheless important for a fuller
understanding. Thanks for the noting it.

> Steve Carlip
>

[deadrat]

Your use of scare quotes is quite apt and I was remiss to not to use
them. For me, saying that one particle "feels a force" means that the
particle's movement is affected by an exchange of a force-carrying
particle. Not the case for gravity, as you explain below.

In this sense, photons can't "feel" the electromagnetic force either
since they carry no charge. My (strictly qualitative) understanding is
that the coupling in photon-photon scattering is explained by the
creation of fermion-antifermion pairs (say, electron-positron) that can
feel electromagnetism. The creation, can be documented by Feynman
diagrams, and it is backed by the full faith and credit of the
Heisenberg Uncertainty Principle.

[erik simpson]

My understanding of photon-photon interaction is as yours, and also strictly
qualitative. I find QED (and even worse, QCD) repels my deeper understanding
very effectively.

[deadrat]

I am fully aware that I rudely told you to butt out in a previous
conversation.

When the irony fairy shows up at your house, I'm sure she'll explain the
irony in your telling me to go away given that your response to me was a
you're-not-the-boss-of-me bluster that I couldn't make you.

When the self-awareness pixie shows up, I'm sure he'll discuss your
demand for the written invitation for a conversation between two other
people.

I'm sorry that you didn't like my little hung/hanged joke enough to call
me Mr. LP. At least give me some credit for not commenting on your 4/18
claim that "Gravity doesn't effect the speed of light."

Oops.

P.S. Congratulations on winning the sadism/blackface subthread.

P.P.S. Congratulations in advance on winning this subthread.

[jillery]

On Sun, 20 Apr 2014 00:34:55 -0500, deadrat <a...@b.com> wrote:


Go away.

[deadrat]

On 4/20/14 1:05 AM, jillery wrote:
> On Sun, 20 Apr 2014 00:34:55 -0500, deadrat <a...@b.com> wrote:

<restore>

I am fully aware that I rudely told you to butt out in a previous
conversation.

When the irony fairy shows up at your house, I'm sure she'll explain the
irony in your telling me to go away given that your response to me was a
you're-not-the-boss-of-me bluster that I couldn't make you.

When the self-awareness pixie shows up, I'm sure he'll discuss your
demand for the written invitation for a conversation between two other
people.

I'm sorry that you didn't like my little hung/hanged joke enough to call
me Mr. LP. At least give me some credit for not commenting on your 4/18
claim that "Gravity doesn't effect the speed of light."

Oops.

P.S. Congratulations on winning the sadism/blackface subthread.

P.P.S. Congratulations in advance on winning this subthread.

</restore>

> Go away.

[jillery]

On Sun, 20 Apr 2014 03:03:38 -0500, deadrat <a...@b.com> wrote:


There is nothing you can say that I need to hear. Go away.

[Kleuskes & Moos]

On Fri, 18 Apr 2014 18:49:22 +0000, Paul Ciszek wrote:

> In article <d0370fcd-5f67-4291...@googlegroups.com>,

> Robert Carnegie <rja.ca...@excite.com> wrote:
>>On Friday, 18 April 2014 17:19:03 UTC+1, John Stockwell wrote:
>>> You are describing gravitational lensing. The speed of light does not
>>> change, but light is bent by massive bodies.
>>
>>Is the speed of light different - slower - in "dark matter", like it is
>>in glass and water and so on?
>

> Find us some dark matter, and there will be a lot of guys who will want
> to perform that experiment as well as many, many others.

Given the fact that dark matter, according to theory as far as i
understand it, is all around us, it should not effect the speed of light.
If it did, science would have noticed aberrations in the speed of light.

IIRC the speed of light in various circumstances is *very* well explored.

> Supposedly, dark matter doesn't interact with the electromagnetic force,
> including light (hence the name), only gravity. Now, here is where
> things might get weird: If you had a dense clump of dark matter
> somewhere, light should be able to pass right through it--but would
> there be any funky time dialation effects inside the mass? Might that
> affect the transit time of light through the clump as measured by
> outside observers?

Good question, but the answer depends on locating such a clump.

[Walter Bushell]

In article <lj04u0$hdd$1...@dont-email.me>,

Kleuskes & Moos <kle...@somewhere.else.net> wrote:

> Good question, but the answer depends on locating such a clump.

Which shouldn't form. You see our type of matter can radiate energy
and thus lose energy but normal ( dark) matter can't radiate energy
and therefore can't clump.

--
Never attribute to stupidity that which can be explained by greed. Me.

[Walter Bushell]

In article <bd15b9cb-4dc4-40f9...@googlegroups.com>,
John Stockwell <john.1...@gmail.com> wrote:

> On Friday, April 18, 2014 12:29:34 PM UTC-6, Robert Carnegie wrote:
> > On Friday, 18 April 2014 17:19:03 UTC+1, John Stockwell wrote:
> >
> > > You are describing gravitational lensing. The speed of light
> >
> > > does not change, but light is bent by massive bodies.
> >
> >
> >
> > Is the speed of light different - slower - in "dark matter",
> >
> > like it is in glass and water and so on?
>

> I would have to say "no" on that. Dark matter is alleged to interact
> with regular matter only through gravitation. So, lensing yes, but
> slowing down no, because there is supposed to be no electromagetic interaction
> with dark matter.
>

> -John

Except that nearly all the matter is dark and hence must be considered
normal matter. Baryonic matter is an bizarre anomaly.

[deadrat]

On 4/20/14 3:13 AM, jillery wrote:
> On Sun, 20 Apr 2014 03:03:38 -0500, deadrat <a...@b.com> wrote:
>
>
> There is nothing you can say that I need to hear. Go away.

This stance is consistent with your ongoing mode of operation. For
instance, it took you three exchanges with RN to decide that the issue
lay with his bad character and not your own phrasing.

I won't expect this behavior to change until the self-awareness pixie
shows up at your house. He will then carefully explain that people are
not wrong simply because you don't like them.

And that even if they are wrong about what you wrote, an explication on
your part will increase your understanding at little cost to yourself.

[jillery]

[deadrat]

On 4/20/14 3:09 PM, jillery wrote:
> On Sun, 20 Apr 2014 13:54:28 -0500, deadrat <a...@b.com> wrote:

<restore>

This stance is consistent with your ongoing mode of operation. For
instance, it took you three exchanges with RN to decide that the issue
lay with his bad character and not your own phrasing.

I won't expect this behavior to change until the self-awareness pixie
shows up at your house. He will then carefully explain that people are
not wrong simply because you don't like them.

And that even if they are wrong about what you wrote, an explication on
your part will increase your understanding at little cost to yourself.

</restore>

> Go away.

[jillery]

[deadrat]

On 4/20/14 6:12 PM, jillery wrote:
> On Sun, 20 Apr 2014 17:33:37 -0500, deadrat <a...@b.com> wrote:
>
> Go away.
>

<quote poster="jillery" date="4/2/14" time="9:22P">
Make me. You're not the boss around here. You don't own this group
or this topic. Why don't you go away?
</quote>

Have you seen the irony fairy or the self-awareness pixie yet?

[jillery]

[deadrat]

On 4/20/14 6:58 PM, jillery wrote:
> On Sun, 20 Apr 2014 18:36:26 -0500, deadrat <a...@b.com> wrote:
>
> Go away
>

[jillery]

On Wed, 02 Apr 2014 22:19:14 -0500, deadrat <a...@b.com> wrote:

>Just. Go. Away. From. Here.


You have no credibility. Now go away.

[deadrat]

Because I'm using your own words? How does that work?

Now go away.

See the quote above.

[jillery]

On Sun, 20 Apr 2014 22:50:20 -0500, deadrat <a...@b.com> wrote:

Go away.

[deadrat]

On 4/20/14 11:16 PM, jillery wrote:
> On Sun, 20 Apr 2014 22:50:20 -0500, deadrat <a...@b.com> autoreplied:
>
> Go away.

[jillery]

[Mike Painter]

On Sun, 20 Apr 2014 07:05:15 -0400, Walter Bushell <pr...@panix.com>
wrote:

>In article <lj04u0$hdd$1...@dont-email.me>,
> Kleuskes & Moos <kle...@somewhere.else.net> wrote:
>
>> Good question, but the answer depends on locating such a clump.
>
>Which shouldn't form. You see our type of matter can radiate energy
>and thus lose energy but normal ( dark) matter can't radiate energy
>and therefore can't clump.

If the matter can move I would expect it to have areas where the
average density was high.

[jillery]

<http://arxiv.org/pdf/astro-ph/0608407v1.pdf>

A collision of two galactic clusters separated the galaxies from the
gas within and between them, because the interacting gas bunched
up and compressed, while the galaxies themselves, and the
non-interacting dark matter, slid past each other.

The location of the gas, where most of the normal matter resides, is
visible between the two separate galactic clusters. But the
gravitational lensing has two foci, each centered on the separate
galactic clusters and dark matter.

[Paul Ciszek]

In article <vsu2l915kb0f476ms...@4ax.com>,
jillery <69jp...@gmail.com> wrote:
>
>That's how I understand it, that time in a gravity well/accelerating
>frame slows down. It's not clear to me if you think that implies the
>speed of light itself slows down. IIUC it does not.

As I understand it, the speed of light as measured by the folks at the
bottom of the gravity well remains the same. It had better--we measure
the speed of light deep inside Earth's gravity well all the time, and
treat that number as if it were some sort of universal constant. Here
is the part I am less certain of: If someone outside the gravity well
watched the folks down in the gravity well measuring the speed of light,
what would that outside observer see?

--
Please reply to: | "Evolution is a theory that accounts
pciszek at panix dot com | for variety, not superiority."
Autoreply has been disabled | -- Joan Pontius

[David MacMillan]

On Friday, April 25, 2014 3:07:05 PM UTC-5, Paul Ciszek wrote:
> In article,

>
> jillery wrote:
>
> >
> >That's how I understand it, that time in a gravity well/accelerating
> >frame slows down. It's not clear to me if you think that implies the
> >speed of light itself slows down. IIUC it does not.
>
>
> As I understand it, the speed of light as measured by the folks at the
> bottom of the gravity well remains the same. It had better--we measure
> the speed of light deep inside Earth's gravity well all the time, and
> treat that number as if it were some sort of universal constant. Here
> is the part I am less certain of: If someone outside the gravity well
> watched the folks down in the gravity well measuring the speed of light,
> what would that outside observer see?
>

The effects of relativity between one side of the measurement and the other side of the measurement would end up canceling each other out. The outside observer would get different variables for the lightspeed measurement, but the same conclusion.

[erik simpson]

No. The observer outside the 'gravity well' would observe that his clock of
know frequency seemed to be running faster than the identical clock deeper in
the well. This is the source of the 'gravitational redshift'. However, the
outside observer would determine the local speed of light in vacuum to be
identical with the measurement of the inside observer.

[David MacMillan]

Same thing, different words. The variables (e.g. the apparent speed of clocks) would be different, but any calculation of the speed of light (since lightspeed cannot be directly measured) would end up being the same.

[erik simpson]

Where do you get this stuff? The speed of light can be measured by several
means, and depending on what you mean by 'direct', you can quibble, but the
Fizeau-Foucault determination (1850) is as direct as anyone could want.

[David MacMillan]

On Friday, April 25, 2014 4:52:56 PM UTC-5, erik simpson wrote:
>
> Where do you get this stuff? The speed of light can be measured by several means, and depending on what you mean by 'direct', you can quibble, but the Fizeau-Foucault determination (1850) is as direct as anyone could want.
>

Sure. And the results of the Fizeau-Foucault experiment or any other method will be observed to give an identical value for c whether you're the observer outside the well or the observer inside the well. No problem there.

My point is to the original question posed by Paul, noting that the speed of a clock would be observed as different from outside, and wondering whether measurements of the speed of light would be equally different. The clocks do indeed run at different rates, but any measurement of the speed of light will still end up being the same.

[erik simpson]

Ah. Sorry to sound querulous, I was confused by language.