Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.physics > #512491 > unrolled thread

Re: 'Dark Matter'

Back to article view | Back to sci.physics

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-10 21:18 +0200
    Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-10 13:51 -0700
      Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-10 15:58 -0500
        Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-11 01:04 +0200
          Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-11 07:49 -0500
            Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 06:26 -0700
              Re: 'Dark Matter' Sam Wormley <swormley1@gmail.com> - 2015-08-11 08:31 -0500
              Re: 'Dark Matter' HVAC <Mr.HVAC@gmail.com> - 2015-08-11 09:41 -0400
                Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 06:51 -0700
                  Re: 'Dark Matter' HVAC <Mr.HVAC@gmail.com> - 2015-08-11 13:44 -0400
                    Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 11:00 -0700
                      Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-11 18:44 +0000
                Re: 'Dark Matter' Sam Wormley <swormley1@gmail.com> - 2015-08-11 08:51 -0500
                  Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 07:17 -0700
                    Re: 'Dark Matter' Sam Wormley <swormley1@gmail.com> - 2015-08-11 10:45 -0500
                      Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 09:50 -0700
                        Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-11 10:01 -0700
                  Re: 'Dark Matter' Mahipal <mahipal7638@gmail.com> - 2015-08-11 08:10 -0700
            Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 13:44 +0200
              Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-13 07:51 -0500
    Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-10 21:28 +0000
      Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-10 14:35 -0700
        Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-10 23:31 +0000
          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 15:22 +0200
            Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 14:43 +0000
              Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 19:39 +0200
                Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 18:06 +0000
                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 20:23 +0200
                    Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 19:37 +0000
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 00:39 +0200
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 15:38 +0200
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:25 +0200
                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 17:15 +0200
                              Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 17:31 +0200
                                Re: 'Dark Matter' R Kym Horsell <kym@kymhorsell.com> - 2015-08-16 16:09 +0000
                                  Re: 'Dark Matter' [OT] Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 18:47 +0200
                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 10:38 +0200
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 11:09 +0200
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 12:40 +0200
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:17 +0200
                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 16:46 +0200
                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 10:42 +0200
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 11:21 +0200
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 12:58 +0200
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:19 +0200
                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 16:49 +0200
                  light is magneto-electrical noTthaTguY <abu.kuanysh05@gmail.com> - 2015-08-13 19:10 -0700
                Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-13 13:49 -0500
                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 20:50 +0200
                    Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-13 14:03 -0500
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 00:43 +0200
                        Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-15 17:53 -0700
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 09:34 +0200
                          Re: 'Dark Matter' HVAC <Mr.HVAC@gmail.com> - 2015-08-16 08:05 -0400
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 11:36 +0200
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:00 +0200
                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 16:22 +0200
                              Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:30 +0200
                                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 16:56 +0200
                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 11:17 +0200
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 11:26 +0200
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 13:01 +0200
            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 10:14 +0200
              Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 10:43 +0200
                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 13:07 +0200
                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:21 +0200
                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 17:07 +0200
      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-11 01:03 +0200
        Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-10 23:40 +0000
          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 13:41 +0200
            Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 14:54 +0000
              Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-13 08:13 -0700
                Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-13 10:46 -0500
                  Re: 'Dark Matter' noTthaTguY <abu.kuanysh05@gmail.com> - 2015-08-13 09:48 -0700
                  Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-13 10:00 -0700
                    Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-13 13:45 -0500
                Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 16:01 +0000
                Re: 'Dark Matter' HVAC <Mr.HVAC@gmail.com> - 2015-08-14 07:07 -0400
                  Re: 'Dark Matter' noTthaTguY <abu.kuanysh05@gmail.com> - 2015-08-14 10:39 -0700
              Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 20:29 +0200
                Re: 'Dark Matter' moroney@world.std.spaamtrap.com (Michael Moroney) - 2015-08-13 19:14 +0000
                  Re: 'Dark Matter' Felipe Delgado <fd@spreadspectrum.org> - 2015-08-13 19:28 +0000
                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-15 15:38 +0200
                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 12:23 +0200
                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:04 +0200
                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 16:32 +0200
                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 16:33 +0200
                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 17:02 +0200
                              Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 19:24 +0200
                                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 20:31 +0200
                                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 22:16 +0200
                                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 22:38 +0200
                                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 20:45 +0200
                                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 22:32 +0200
                                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 22:57 +0200
                                      Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 23:22 +0200
                                        Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 23:34 +0200
                                          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 23:38 +0200
                                            Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-18 07:43 +0200
                                              Re: 'Dark Matter' john <johnsefton288@gmail.com> - 2015-08-18 08:07 -0700
                                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 21:40 +0200
                                Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 22:35 +0200
                                  Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-16 23:36 +0200
                                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-16 23:50 +0200
                                    Re: 'Dark Matter' Poutnik <poutnik4nntp@gmail.com> - 2015-08-17 07:56 +0200
        Re: 'Dark Matter' Odd Bodkin <bodkinodd@gmail.com> - 2015-08-11 07:48 -0500
          Re: 'Dark Matter' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-08-13 13:41 +0200

Page 2 of 6 — ← Prev page 1 [2] 3 4 5 6  Next page →

#512527

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>Odd Bodkin wrote:

>> When that photon left the sun, the sun also recoiled a little in the
>> opposite direction.

>Your other ideas aside: What about the other photons?

It recoils from them as well.

Since the sun is spherically symmetric with photons going in all
direction, it all pretty much adds up to zero, and the sun doesn't move.  
(not that we could measure the recoil from a single photon of something as
massive as the sun)

[toc] | [prev] | [next] | [standalone]

#512533

And, Michael, once those photons
leave the sun, does it make any
difference to that sun what they do or do not
encounter? Momentum-wise or anything
else-wise?

No.

[toc] | [prev] | [next] | [standalone]

#512588

john <johnsefton288@gmail.com> writes:

>And, Michael, once those photons
>leave the sun, does it make any
>difference to that sun what they do or do not
>encounter? Momentum-wise or anything
>else-wise?

>No.

You finally got something right.

There are two events.  The sun emits a photon and recoils (actually the
emitting plasma particle recoils as the sun is not solid, as was pointed
out)  The photon later hits your eye (or a tree) and transmits its
momentum and energy to you (or the tree).

[toc] | [prev] | [next] | [standalone]

#513247

Michael Moroney wrote:

> john <johnsefton288@gmail.com> writes:
>> And, Michael, once those photons
>> leave the sun, does it make any
>> difference to that sun what they do or do not
>> encounter? Momentum-wise or anything
>> else-wise?
>> 
>> No.
> 
> You finally got something right.
> 
> There are two events.  The sun emits a photon and recoils (actually the
> emitting plasma particle recoils as the sun is not solid, as was pointed
> out) 

A “recoiling emitting plasma particle”, what crankish nonsense.  Read on the 
plasma state of matter, and stellar nucleosynthesis, before further 
comments, will you?

> The photon later hits your eye (or a tree) and transmits its
> momentum and energy to you (or the tree).

Nonsense.  One photon, which emerges as such when it hits the observer’s 
retina, carries energy E = pc = ℎc∕λ = ℎf (IOW: p = ℎ∕λ) which is used to 
activate the proteins in the photoreceptor cells in the retina.  (It has 
been shown [I can cite papers] that one photon suffices for that, but 
naturally there are considerably more photons involved in visual 
perception.)  Only in *that* sense momentum p of the photon is involved at 
the observer’s side of the process.


PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#513268

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>Michael Moroney wrote:

>> There are two events.  The sun emits a photon and recoils (actually the
>> emitting plasma particle recoils as the sun is not solid, as was pointed
>> out) 

>A "recoiling emitting plasma particle", what crankish nonsense.  Read on 
>the plasma state of matter, and stellar nucleosynthesis, before further
>comments, will you?

Pointed Ears, the momentum of a photon is p = hf/c.  Momentum is always
conserved.  Therefore, *something* *must* recoil with momentum p = -hf/c.
That something would be, initially, the plasma particle(s) that were 
involved with emitting the photon.  As these transfer their momentum to
the sun as a whole through collisions or other interactions, the sun as a
whole would have to acquire a momentum of -hf/c.  Simple physics.
As Odd pointed out, that amount of momentum applied to something as 
massive as the sun results in a ridiculously small velocity, but it is 
(must be) nonzero.

[toc] | [prev] | [next] | [standalone]

#513302

Michael Moroney wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>> Michael Moroney wrote:
>>> There are two events.  The sun emits a photon and recoils (actually the
>>> emitting plasma particle recoils as the sun is not solid, as was pointed
>>> out)
>> A "recoiling emitting plasma particle", what crankish nonsense.  Read on
>> the plasma state of matter, and stellar nucleosynthesis, before further
>> comments, will you?
> 
> Pointed Ears, the momentum of a photon is p = hf/c.
         ^
Without the space.  Yes, it is.

> Momentum is always conserved.

Yes.  AISB.

> Therefore, *something* *must* recoil with momentum p = -hf/c.

No.  I think we have finally determined the underlying, oversimplying 
fallacy of (the two of) you.  Your disregard of the *direction* of momentum 
(it is a *vector* quantity) aside:

  E = E_kin = p c

and

  p = ℎ f∕c

are *only* true for particles with mass m = 0, as assumed for photons, 
because of

  E_kin = √((m c²)² + (p c)²) − m c²

(the kinetic energy gained by a body is the difference between the energy it 
has in relative motion and the energy it has at relative rest), and

  E² = p² c² + m² c⁴

which *only for m = 0* leads to

   p = E∕c

and for photons with

   E = ℎ f

to

   p = ℎ f∕c.

But the Sun does not consist only of photons.  In fact, it consists of more 
stuff that does not manifest itself as a photon than vice-versa.  Stuff 
whose mass is not zero.  Stuff that does not emit those photons in the first 
place.


PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#513312

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>Michael Moroney wrote:

>> Momentum is always conserved.

>Yes.  AISB.

>> Therefore, *something* *must* recoil with momentum p = -hf/c.

>No.  I think we have finally determined the underlying, oversimplying 
>fallacy of (the two of) you.  Your disregard of the *direction* of momentum 
>(it is a *vector* quantity) aside:

Yes it is a vector, but with the simplification of the photon moving
in the x direction, the y and z components are both zero.  Therefore,
photon's momentum is p = hf/c in the x direction, and the recoil must be
-hf/c (that is, in the -x direction) to keep the sum zero (and conserve 
momentum).

Are you thinking that in the recoil "f" is somehow the frequency of the
recoiling particle?  It's not; it's the frequency of the departing photon.
It has to be mentioned here to balance momentum.  The recoiling particle(s)
electrons and/or nuclei, obviously have mass and p=hf/c doesn't apply
to them directly, it's just that they have momentum equal to and opposite
of that of the photon's.

[toc] | [prev] | [next] | [standalone]

#513315

Michael Moroney wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>>Michael Moroney wrote:
>>> Momentum is always conserved.
>> Yes.  AISB.
>>> Therefore, *something* *must* recoil with momentum p = -hf/c.
>> No.  I think we have finally determined the underlying, oversimplying
>> fallacy of (the two of) you.  Your disregard of the *direction* of
>> momentum (it is a *vector* quantity) aside:
> 
> Yes it is a vector, but with the simplification of the photon moving
> in the x direction, the y and z components are both zero.

That is the *other* *oversimplification* you are doing.

> Therefore, photon's momentum is p = hf/c in the x direction, and the
> recoil must be -hf/c (that is, in the -x direction) to keep the sum zero
> (and conserve momentum).

Again, no.  Whatever could recoil is _not_ a photon; it has a mass not equal 
to zero.  Its momentum is calculated *differently* than that of a photon.
 
> Are you thinking that in the recoil "f" is somehow the frequency of the
> recoiling particle? 

No, I think you have no idea what you are talking about to begin with.

> It's not; it's the frequency of the departing photon.

I know.

> [snip nonsense]

You have a misconception as to what “conservation of momentum” means.  The 
whole thing goes: “In an *isolated* system, total momentum is conserved.”
An isolated system is one where there are no interactions with its 
surroundings at all.

Even if one views the Sun as a isolated system, which it is not, the total 
momentum of all of its particles is conserved; not only that of two of them 
participating in the interaction that you are wishing for, and which does 
not happen in the first place.

More could be said about this, but I let you chew on this first.


PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#513334

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>Michael Moroney wrote:

>> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>>>> Therefore, *something* *must* recoil with momentum p = -hf/c.
>>> No.  I think we have finally determined the underlying, oversimplying
>>> fallacy of (the two of) you.  Your disregard of the *direction* of
>>> momentum (it is a *vector* quantity) aside:
>> 
>> Yes it is a vector, but with the simplification of the photon moving
>> in the x direction, the y and z components are both zero.

>That is the *other* *oversimplification* you are doing.

OK.  Give me a vector example of a particle emitting a photon and
recoiling, which can *not* be simplified from a 3 vector to a case of
momentums of p and -p in the x direction, with y & z components zero, 
simply by aligning the x axis with the direction of the photon.

>> Therefore, photon's momentum is p = hf/c in the x direction, and the
>> recoil must be -hf/c (that is, in the -x direction) to keep the sum zero
>> (and conserve momentum).

>Again, no.  Whatever could recoil is _not_ a photon; it has a mass not equal 
>to zero.  Its momentum is calculated *differently* than that of a photon.
> 
>> Are you thinking that in the recoil "f" is somehow the frequency of the
>> recoiling particle? 

>No,

Yes you do, by your answer above stating what's recoiling is not a photon.
It's not, of course, but its momentum is still -hf/c, where f is the
frequency of the photon emitted, *NOT* some frequency of the recoiling
particle.

Its momentum is mv; and for momentum to be conserved, mv = -hf/c,
which is why I wrote its momentum is -hf/c.

[toc] | [prev] | [next] | [standalone]

#513997

Michael Moroney wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>> Michael Moroney wrote:
>>> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>>>>> Therefore, *something* *must* recoil with momentum p = -hf/c.
>>>> No.  I think we have finally determined the underlying, oversimplying
>>>> fallacy of (the two of) you.  Your disregard of the *direction* of
>>>> momentum (it is a *vector* quantity) aside:
>>> Yes it is a vector, but with the simplification of the photon moving
>>> in the x direction, the y and z components are both zero.
>> That is the *other* *oversimplification* you are doing.
> 
> OK.  Give me a vector example of a particle emitting a photon and
> recoiling, which can *not* be simplified from a 3 vector to a case of
> momentums of p and -p in the x direction, with y & z components zero,
> simply by aligning the x axis with the direction of the photon.

Well, where photons are first produced in the Sun, in proton–proton 
collisions in the core, at about 1.57 × 10⁷ K, there is no linear recoiling 
to begin with.  Whether there is any recoiling at all is very questionable.  
And there is actually no thing that emits them: they are simply a product of 
the fusion, and because momentum is preserved, the photon and the resulting 
helium-2 nucleus go off in different directions that cannot be traced to a 
single originating entity.

Likewise later, when photons are produced in electron–positron annihilation 
and deuterium–hydrogen fusion at 7 × 10⁶ to 2 × 10⁶ K.

And those photos are absorbed by the solar plasma after having traveled only 
short distances.  When they are re-emitted, that happens “in a random 
direction and usually at a slightly lower energy”.  So you can see that a 
recoiling in a particular direction cannot take place.  As that is not the 
case, statistically any individual recoiling or group of recoilings – which 
cannot be computed as simply as you claim – is neutralized by those in the 
respective opposite directions.  *Total* momentum is conserved.

<https://en.wikipedia.org/wiki/Sun#Photosphere>
<https://en.wikipedia.org/wiki/Sun#Photons_and_neutrinos>

AISB, the Sun does _not_ recoil from photon emission (and it does not shrink 
because of transfer of momentum).  Nor does the observer when a photon hits 
their retina (they would if the energy E = p c the photon carries was not 
fully converted in activating the photoreceptor cell; light pressure is an 
actual phenomenon).

Did I not recommend to you that you get yourself informed about stellar 
nuclear fusion, among other things?

>> […]  Whatever could recoil is _not_ a photon; it has a mass not
>> equal to zero.  Its momentum is calculated *differently* than that of a 
>> photon.
>>> Are you thinking that in the recoil "f" is somehow the frequency of the
>>> recoiling particle?
>> No,
> 
> Yes you do,

I think I know better what I am thinking than you, thank you very much.

> by your answer above stating what's recoiling is not a photon.

Non sequitur.

> It's not, of course, but its momentum is still -hf/c,

It is not, because the momentum of the origin of the emission, if it can be 
traced, is calculated differently – it cannot be defined by a frequency at 
all; because it does not need to be a full transfer of momentum (and in fact 
it is not: put simply, the Sun still exists although it is shining): and 
because it involves a direction that you are simply ignoring.


PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#514249

Dne 16/08/2015 v 00:39 Thomas 'PointedEars' Lahn napsal(a):

> AISB, the Sun does _not_ recoil from photon emission ...

It does, but it is cancelled by spherical symmetry.

"light pressure is an actual phenomenon".

It is light pressure seen from the other side, at the source.
As both operations, emission and absorption, are symmetrical.

Like 2 boys on 2 boats, mutually throwing the ball,
effectively repulsing themselves by "ball pressure"
at both sides, throwing and catching.

> ............... (and it does not shrink
> because of transfer of momentum).

It does, by departing light pressure, but it can be neglected,
and is supported by dynamic equilibrium.

> Nor does the observer when a photon hits 
> their retina (they would if the energy E = p c the photon carries was not 
> fully converted in activating the photoreceptor cell; light pressure is an 
> actual phenomenon).

Linear nor angular momentum transfer
from the photon to atoms / molecules
is given by law.

It is not detemined
by way how the absorbed energy is transformed.
It only detemines, how they are redistributed.


-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514289

Poutnik wrote:

> Dne 16/08/2015 v 00:39 Thomas 'PointedEars' Lahn napsal(a):
>> AISB, the Sun does _not_ recoil from photon emission ...
> 
> It does,

The Sun *itself* does _not_ recoil.  Period.

> but it is cancelled by spherical symmetry.

Nonsense.

> "light pressure is an actual phenomenon".
> 
> It is light pressure seen from the other side, at the source.
> As both operations, emission and absorption, are symmetrical.

Light pressure in the Sun – the proper term there is radiation pressure – is 
directed *outward* from the center.  It was claimed that it would be 
directed *inward* in some way, which is nonsense.

Learn to read before I decide to killfile you.

Did I already say that I detest people who do not even extend others the 
simple courtesy of introducing themselves, and stand by their statements, 
with their real name?

-- 
PointedEars

[toc] | [prev] | [next] | [standalone]

#514307

Dne 16/08/2015 v 16:25 Thomas 'PointedEars' Lahn napsal(a):
> Poutnik wrote:
> 
>> Dne 16/08/2015 v 00:39 Thomas 'PointedEars' Lahn napsal(a):
>>> AISB, the Sun does _not_ recoil from photon emission ...
>>
>> It does,
> 
> The Sun *itself* does _not_ recoil.  Period.


> 
>> but it is cancelled by spherical symmetry.
> 
> Nonsense.

So you agree with the first line.
> 
>> "light pressure is an actual phenomenon".
>>
>> It is light pressure seen from the other side, at the source.
>> As both operations, emission and absorption, are symmetrical.
> 
> Light pressure in the Sun – the proper term there is radiation pressure – is 
> directed *outward* from the center.  It was claimed that it would be 
> directed *inward* in some way, which is nonsense.

Light pressure IN the Sun aka radiation pressure
is different phenomena.

I have spoken about radiation to space.

> 
> Learn to read before I decide to killfile you.

Learn to read and behave or I will killfile you again.
> 
> Did I already say that I detest people who do not even extend others the 
> simple courtesy of introducing themselves, and stand by their statements, 
> with their real name?
> 
Did you say Usenet never expose the use adresses
in spite of I have seen them exposed many times ?

Was it mistake or lie ?

BTW, my name is Libor Striz,
but as internet is so anonymous, it does not matter much.

You say I am a liar, so I must have invented it.

-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514309

Dne 16/08/2015 v 17:15 Poutnik napsal(a):
> Dne 16/08/2015 v 16:25 Thomas 'PointedEars' Lahn napsal(a):
>> Poutnik wrote:
>>

>>
>> Did I already say that I detest people who do not even extend others the 
>> simple courtesy of introducing themselves, and stand by their statements, 
>> with their real name?
>>
> Did you say Usenet never expose the use adresses
> in spite of I have seen them exposed many times ?
> 
> Was it mistake or lie ?
> 
> BTW, my name is Libor Striz,, more exactly Stříž
> but as internet is so anonymous, it does not matter much.
> 
> You say I am a liar, so I must have invented it.
> 
OTOH, You claim to be Thomas Lahn,
but it may or may not be true.

Some people come with fake real name,( I do not mean you )
while others come with nickname they honour.

I use my nick Poutnik  or Poutnikl ( l as Libor, as it is common among
Czechs ), as I honour it, being my real nickname and penname as well.


-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514318

Poutnik <poutnik4nntp@gmail.com> wrote:
> Dne 16/08/2015 v 17:15 Poutnik napsal(a):
>> Dne 16/08/2015 v 16:25 Thomas 'PointedEars' Lahn napsal(a):
>>> Poutnik wrote:
>>> Did I already say that I detest people who do not even extend others the 
>>> simple courtesy of introducing themselves, and stand by their statements, 
>>> with their real name?
>> Did you say Usenet never expose the use adresses
>> in spite of I have seen them exposed many times ?
>> Was it mistake or lie ?
>> BTW, my name is Libor Striz,, more exactly St???
>> but as internet is so anonymous, it does not matter much.
>> You say I am a liar, so I must have invented it.
> OTOH, You claim to be Thomas Lahn,


Unfortunately for his parents, it's true.

> but it may or may not be true.
> Some people come with fake real name,( I do not mean you )
> while others come with nickname they honour.
> I use my nick Poutnik  or Poutnikl ( l as Libor, as it is common among
> Czechs ), as I honour it, being my real nickname and penname as well.

-- 
> What's causing Global Warming, Will?
Why do you care, Sam?
Myself, I do not know and that is fine with me.
There many more important things that I do not know! 
-- Will Janoschkadiction, 21 Apr 2012

[toc] | [prev] | [next] | [standalone]

#514344 — Re: 'Dark Matter' [OT]

Dne 16/08/2015 v 18:09 R Kym Horsell napsal(a):

>> What's causing Global Warming, Will?
> Why do you care, Sam?
> Myself, I do not know and that is fine with me.
> There many more important things that I do not know! 
> -- Will Janoschkadiction, 21 Apr 2012
> 

While I was disputing with Will a lot in past,
this quote is fine, regarding real life.

We have to choose
from what we do not know
to get it known for us.

-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514170

Dne 13/08/2015 v 20:23 Thomas 'PointedEars' Lahn napsal(a):
> Michael Moroney wrote:
> 

> 
>> Therefore, photon's momentum is p = hf/c in the x direction, and the
>> recoil must be -hf/c (that is, in the -x direction) to keep the sum zero
>> (and conserve momentum).
> 
> Again, no.  Whatever could recoil is _not_ a photon; it has a mass not equal 
> to zero.  Its momentum is calculated *differently* than that of a photon.
>  

Sure, but it does change momentum conservation.

If massless photon has momentum vec p,
recoiling massive ion get momentum difference -vec p.

Eventual relativistic effects do not change it.

The ion velocity change has in such a case
to be calculated by SR formula
from the momentum change,  and not otherwise.


-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514177

Poutnik wrote:

> Dne 13/08/2015 v 20:23 Thomas 'PointedEars' Lahn napsal(a):
>> Michael Moroney wrote:
>>> Therefore, photon's momentum is p = hf/c in the x direction, and the
>>> recoil must be -hf/c (that is, in the -x direction) to keep the sum zero
>>> (and conserve momentum).
>> Again, no.  Whatever could recoil is _not_ a photon; it has a mass not
>> equal to zero.  Its momentum is calculated *differently* than that of a 
>> photon.
> 
> Sure, but it does change momentum conservation.

Come again?

> If massless photon has momentum vec p, recoiling massive ion get momentum
> difference -vec p.

In the ion’s rest frame, if there is only one ion and one photon, and one 
photon for each ion.  No doubt about *that*.

> Eventual relativistic effects do not change it.

Nobody claimed it would.  You are taking statements out of context.

> The ion velocity change has in such a case
> to be calculated by SR formula
> from the momentum change,  and not otherwise.

Exactly.  Which also means that it has to be taken into account how much of 
the photon’s energy comes from or is converted into kinetic energy, with the 
additional caveat that additional kinetic energy does not need to mean the 
kinetic energy of the receiving object itself (but could as well be that of 
its constituents).

You really should read the whole posting and the whole discussion before you 
post a corrective follow-up.  The people whom I have debated have claimed 
that “Newtonian mechanics” suffices to describe the process because of “low 
speeds” on “the surface of the sun” [sic], that *the Sun* would be recoiling 
from photon emissions in the opposite direction of “the emission” (the same 
as *everything* that absorbs photons), and that you could compute that 
“recoiling speed” in a simple way, respectively.  And probably I have 
forgotten to mention more of the nonsense that they claimed.

 
PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

#514189

Dne 16/08/2015 v 11:09 Thomas 'PointedEars' Lahn napsal(a):
> Poutnik wrote:
> 
>> Dne 13/08/2015 v 20:23 Thomas 'PointedEars' Lahn napsal(a):
>>> Michael Moroney wrote:
>>>> Therefore, photon's momentum is p = hf/c in the x direction, and the
>>>> recoil must be -hf/c (that is, in the -x direction) to keep the sum zero
>>>> (and conserve momentum).
>>> Again, no.  Whatever could recoil is _not_ a photon; it has a mass not
>>> equal to zero.  Its momentum is calculated *differently* than that of a 
>>> photon.
>>
>> Sure, but it does change momentum conservation.
> 
> Come again?

Some basic facts come again and again.
> 
>> If massless photon has momentum vec p, recoiling massive ion get momentum
>> difference -vec p.
> 
> In the ion’s rest frame, if there is only one ion and one photon, and one 
> photon for each ion.  No doubt about *that*.

It is unwise to set frame by this way.
Isolated system in context of momentum means, there is no momentum
exchange. If there is, than there is simple superposition
of momentum conservation and exchange.

If Alice gives Bob 2 backs ids not affected
by fact Tom gave to each of them 3 one.

If there are 2 other ions, the momentum change can be redistributed to
them, but will not disappear.

> 
>> Eventual relativistic effects do not change it.
> 
> Nobody claimed it would.  You are taking statements out of context.

then there was no need to mess with relativistic formulas.
> 
>> The ion velocity change has in such a case
>> to be calculated by SR formula
>> from the momentum change,  and not otherwise.
> 
> Exactly.  Which also means that it has to be taken into account how much of 
> the photon’s energy comes from or is converted into kinetic energy, with the 
> additional caveat that additional kinetic energy does not need to mean the 
> kinetic energy of the receiving object itself (but could as well be that of 
> its constituents).

Kinetic energy is not much relevant, as it is not elastic interaction.
Kinetic energy follows here momentum conservation.
KE of moving object will be reflected in higher/lower energy and higher
or lower momentum of departing photon.

> 
> You really should read the whole posting and the whole discussion before you 

I did. You really should expect the worst at others.

> post a corrective follow-up.  The people whom I have debated have claimed 
> that “Newtonian mechanics” suffices to describe the process because of “low 
> speeds” on “the surface of the sun” [sic], that *the Sun* would be recoiling 
> from photon emissions in the opposite direction of “the emission” (the same 
> as *everything* that absorbs photons), and that you could compute that 
> “recoiling speed” in a simple way, respectively.  And probably I have 
> forgotten to mention more of the nonsense that they claimed.
> 
At accepted error level, Newtonian mechanic IS sufficient.
But without counting, I estimate the recoiling effect is minimal.

-- 
Poutnik ( the Czech word for a wanderer )

[toc] | [prev] | [next] | [standalone]

#514284

Poutnik wrote:

> Dne 16/08/2015 v 11:09 Thomas 'PointedEars' Lahn napsal(a):
>> Poutnik wrote:
>>> Dne 13/08/2015 v 20:23 Thomas 'PointedEars' Lahn napsal(a):
>>>> Michael Moroney wrote:
>>>>> Therefore, photon's momentum is p = hf/c in the x direction, and the
>>>>> recoil must be -hf/c (that is, in the -x direction) to keep the sum
>>>>> zero (and conserve momentum).
>>>> Again, no.  Whatever could recoil is _not_ a photon; it has a mass not
>>>> equal to zero.  Its momentum is calculated *differently* than that of a
>>>> photon.
>>> Sure, but it does change momentum conservation.
>> Come again?
> 
> Some basic facts come again and again.

“Come again?” is colloquial English for “I beg your pardon?” which means 
“Please repeat what you just said, I did not understand it.”  Which, in this 
case, was sarcastic, of course, as you wrote nonsense.

>>> If massless photon has momentum vec p, recoiling massive ion get
>>> momentum difference -vec p.
>> In the ion’s rest frame, if there is only one ion and one photon, and one
>> photon for each ion.  No doubt about *that*.
> 
> It is unwise to set frame by this way.

No, it is very wise, as it points out the difference between the velocity of 
a particle that is standing still with respect to the rest of the Sun, and a 
particle that is moving with respect to the rest of the Sun, and a moving 
Sun.  Different to what was claimed.

>>> Eventual relativistic effects do not change it.
>> Nobody claimed it would.  You are taking statements out of context.
> 
> then there was no need to mess with relativistic formulas.

You must be joking.  You misrepresented what I said.
 
>>> The ion velocity change has in such a case
>>> to be calculated by SR formula
>>> from the momentum change,  and not otherwise.
>> Exactly.  Which also means that it has to be taken into account how much
>> of the photon’s energy comes from or is converted into kinetic energy,
>> with the additional caveat that additional kinetic energy does not need
>> to mean the kinetic energy of the receiving object itself (but could as
>> well be that of its constituents).
> 
> Kinetic energy is not much relevant, as it is not elastic interaction.

Nonsense.  It is high kinetic energy of nuclei in the Sun that allows 
tunneling through the Coulomb barrier, making nuclear fusion possible
in the first place.  Of course, that kinetic energy is in part transferred 
to particles created, such as photon.  That is why they are *gamma* photons 
in and near the core.

> Kinetic energy follows here momentum conservation.

Yes (insofar as one is willing to ascribe coherent meaning to that 
incoherent statement). There is a “p” for momentum in

  E_kin = √((m c²)² + (p c)²) − m c².

> KE of moving object will be reflected in higher/lower energy and higher
> or lower momentum of departing photon.

AISB.

>> You really should read the whole posting and the whole discussion before
>> you
> 
> I did. You really should expect the worst at others.

If you did, then there is are only two possibilities left: you did not read 
carefully enough, or you did read it carefully but decided to misrepresent 
what I said.  Given your other straw man arguments, the latter is more 
likely.
 

PointedEars
-- 
“Science is empirical: knowing the answer means nothing;
 testing your knowledge means everything.”
   —Dr. Lawrence M. Krauss, theoretical physicist,
    in “A Universe from Nothing” (2009)

[toc] | [prev] | [next] | [standalone]

Page 2 of 6 — ← Prev page 1 [2] 3 4 5 6  Next page →

Back to top | Article view | sci.physics

csiph-web