Could there be some connection between so called 'dark matter' and the
old Michelson/Morley experiments? Do the theories about dark matter
shed new light (sorry!) on the existance of the 'ether' since dark
matter appears to be transparent to light?

Hello Buffycat,
   
          I usually am in agreement with views expressed by learned commenters,
like  kottekoe-ga, qed100-ga or iang-ga ... but in this case I will
take an opposite view, a positive view of your question. I will join
you in a speculation (a scientific version of a wild goose chase).
 Just do not quote me, :-) OK?


 On an intuitive, conceptual level, there may be some connection between
 the old and new issues, between ether and current discrepancies between 
 theory and experiment observed in alge scale measurements. 

First, I have to admit that I do not like the 'dark matter'.
 To quote myself (which is also suspect) I need to say:
"People speak of the 'dark matter' - but fact is that no-one ever saw it. Only
reason it was invented was to save some theories which are otherwise
falsified by recent experiments...new lease on life .."

http://answers.google.com/answers/threadview?id=460093

I hope that evolution of science will go that way: that gravitation laws
will be refined, corrected, and dark matter will not be needed. It may go the
other way - a 'second leg' may be found, but it did not happened yet.

  Note on the legs: New physics theories need at least two two legs,
to stand on. For example GRT (Einstein's gravity) got one leg when it
explained Mercury deviation and second when it explained 'bending of
light' by the Sun.
http://en.wikipedia.org/wiki/Talk:Tests_of_general_relativity

 Here is the first connection: Before Einstein, the discrepancies
between experiment and theory were explained by postulating  unseen
masses.
It worked - Neptun and Pluto were discovered this way.
Those are  SEARCH TERMS: discovery Neptun, Pluto .. e.g.
http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Neptune_and_Pluto.html

When they pointed a telescope to a calculated location - there was a dark mass.
That was a very robust second leg.

They tried that with Mercury - and it did not work. Einstein hypothesis, that
Newtons laws are only aproximate and that  there (near the Sun = high
intensity) these slight correction will be measurable was the right
solution - a second leg for GTR.

So, I expect that now, in the oposite extreme, at very weak fields, on
a large scale, the observed discrepancies may be a harbinger of next
change of theories.

That would have to connect with GTR in some very new and fundamental way.

The GTR (which really started with STR and MM experiment) kicked us in direction
of relativity and 'no Ether'. But now, 100 years later, Ether which we did throw
out of the door, is crawling back through the window: Vacuum has energy !
 Huh?  It is called 'zero point energy'.  It may have something to do
with cosmological constant (which was also dusted off to explain these
discrepancies) and it may, just may provide some 'preferred frame of
reference' - a euphemism for 'absolute space'.

None of that is implying that Einstein was wrong.
 But some of that may be saying that human knowledge is evolving in
spirals. Sometimes discarded concepts find a new use, in the new
context.
Newton's 'corpuscural (=particle) theory of light, which was rejected in favor
of wave theory in the 19 century, found a new life in the 20 century
in the Quantum Mechanics. (Not that we are happy about this two headed
monstrum).

So, on this long time scale, and in speculative realm, I would say 'yes'.
They may be some connection. May be someone will boldly reject 'dark matter'
and postulates better laws of gravity, just a Einstein boldly rejected absolute
space and postulated relativity.

Hedgie

---

Request for Answer Clarification by buffycat-ga on 02 Mar 2006 15:40 PST

I thought the 'dark matter' theory was put foreward to account for a
*huge* discrepancy between observed 'normal' matter and measurable
gravetational effects: something like a 70% difference between what we
can see and what we can measure. This seems a big gap to explain by
your theories.

---

Clarification of Answer by hedgie-ga on 02 Mar 2006 21:48 PST

BuffyCat

 The expression 

 "to explain by your theories.."

 is (I hope unintentionally) offensive in this context. 

  I have not presented any theories in my answer,
   certainly not any of mine theories.

  There is not much controversy about the fact that there is a
discrepancy betwen measurement and predictions in this area (large
scale gravity).

 I was explaining that at this time, the explanation based on the existence of
 'dark matter' is a hypothesis (not even a theory).
There are other explanations, published by other physicists.
I find those other explanations more plausible = but the jury is still out.
For this reason I have called discussion of that alternative 'a speculation'.

Kindly, reread the answer. If you need any clarification related to what I
actually wrote, feel free to do another RFC.

Hedgie

---

Request for Answer Clarification by buffycat-ga on 02 Mar 2006 23:37 PST

I'm sorry. Any offense was accidental. I had the impression that you
believed that the differences between what we can see, and the
gravitational effects we can measure, were the result of inaccurate,
or inefficient measurement, rather than being a real discrepancy which
needed a whole new theory to explain it. If  was wrong I apologise.

---

Clarification of Answer by hedgie-ga on 03 Mar 2006 16:09 PST

The mismatch between measurement and current theory is not disputed.

There are two ways to explain it.
1) postulate unseen mass
2) change the theory

It is not an issue of my believes. Here is an article from Scientific American
which explains alternative 2).

" The dark matter problem arose because of a mismatch in the masses of
galaxies and larger cosmic structures. The constituents of these
systems-stars and gas in the case of galaxies, gas and galaxies in the
case of galaxy clusters-move about but do not escape, because they are
checked by the gravitational pull from the rest of the system. The
laws of physics tell us how much mass has to be present to
counterbalance the motions and thereby prevent the dispersal of the
system. Disconcertingly, the tally of mass that astronomers actually
observe falls far short of that..."
[
http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=724C1E4B-FFD5-46F4-963E-7610EC8B7EC
]

Whole long URL above needs to be pasted into the browser.

Hedgie

The official answer denied the validity of my original question! I am
trying to find out as much about 'dark matter' as possible. The person
who answered my question doesn't really believe dark matter exists.
I'm not denying he has the right to such an opinion,but to take my
money for telling me my question doesn't make sense, strikes me as
unfair.From what others have written, via comments, it seems that the
answerer is in a very small minority by denying the very existance of
'dark matter'. That alone should didqualify him from trying to answer
my question.  From buffycat ga

denying the validity of my question is not a good way to answer it!

Please bear with me, but I must ask the following before pursuing this
any further: Why do you suppose the M&M experiment *would* have any
important relationship to dark matter?

From 'buffycat-ga'. In answer to the first comment, I didn't say
"would". I just wondered if the existance of an ether , perhaps made
of dark matter, had become an open question again.. If the ether is
made of dark matter, transparent to light, then Michelson and Morley's
experiments to establish the speed of the earth's travel through it
wouldn't have succeeded. Therefore their experiments cannot be used to
'disprove' the existance of an ether.

The aether was supposed to be the medium through which light travelled
- the MM experiment showed there was no medium.  Introducing dark
matter doesn't change that.  There are still some free thinkers who
believe in the "luminiferous aether", but I've never heard of a
suggested link between it and dark matter.

Ian G.

Ok, I see. Well what the M&M experiment did, or actually didn't, do
was to clearly demonstrate the existence of the "luminiferous" ether,
which was an important feature of 19th century physical modeling of
space. It was understood by way of classical electrodynamics that
light was a wave, and waves were presumed to require a classically
envisioned stuff to mechanically vibrate. This vibration of the ether,
like that of a guitar string, would be light itself. But in classical
theory the group velocity of that wave would add linearly to that of
the emissive source against the background of a fixed coordinate
system, that of the ether itself. The purpose of the experiment was to
detect this source dependency of the speed of light by observing very
slight changes in an interference pattern. It failed to make any such
detection, despite that the instrument's sensitivity was well within
the that required to see changes predicted by classical theory.

   The gist of it is, that the M&M experiment showed, and special
relativity predicted (after the fact of the experiment), that no such
frame dependent speed of light can be detected, and so the classical
ether became irrelevant. If it exists, it can't be detected, either in
theory or in prtactice, and so is outside of scientific realism.

   This doesn't preclude however the presence of space-filling
"stuff". It's only the specifics of the classical ether which are
ruled out. As it turns out, since the late 1920s quantum field theory
(QFT) has pretty much required that space be filled with a variety of
fields, one for each known particle. A particle, for example a photon,
is a "unit" wave in that field. But such a field has rules that it has
to obey; it can't be classical in nature, since it's been ruled out.
These space-filling fields are certainly much in the spirit of the
notion of an ether, even though they differ in details. They are
required to be Lorentz invariant for example. They are detectable if
quantum-field-theoretical predictions are born out in experiment. But
those predictions don't, of course, include source dependency for the
speed of light. To demonstrate this would be a major (catastrophic)
failure of both quantum field and relativistic theory.

   It's important to stress that Lorentz invariance is not a function
of the speed of light. Rather, it's more accurate to say that the
speed of light, c, is a function of Lorentz invariance. The value of c
is not really just the speed at which light travels. It is, in context
of relativisitic theory, the asymptotic limit towards which all motion
can tend, but never exceed. A massive object, such as an electron, can
in principle approach ever closer to c, so long as force is applied to
change the particle's velocity, but never, ever arrive at c. The
closer a massive object gets to c, the more slowly it is able to get
yet closer. A massless particle such as a photon has an undefined rest
frame of reference and can travel only at c, no faster, no slower,
between the moment at which it is emitted by an electric charge and
the moment at which another one absorbs the photon's energy. c is an
intrinsic property of space-time.

    So a dark matter field (ether) could exist. But a dark matter
ether would presumably also be Lorentz invariant even if it is
transparent to light itself, and so the M&M experiment wouldn't be
particularly relevant to it.

   Does this help?

QED: Well said!

Could someone explain the 'Lorentz invariant' to me. Is it something
to do with lineal shrinkage of matter at near light speeds? Or am I on
the wrong track completely?    From buffycat-ga

Buffycat - Lorentz Invariance is not an easy concept to grasp.
Physicists love to find things that are invariant, meaning they don't
change under a certain operation. This is the same as saying they like
to find symmetries. For example, Galileo understood that the laws of
mechanics were invariant if everything is given a "boost" in velocity.
This is the so-called principle of "Galilean" relativity, which
explains why a game of pool on an airplane traveling at 600 mile per
hour will work the same way as long as the plane is in smooth air.
Einstein discovered that if you want to preserve this notion, but keep
the speed of light constant, you get these weird changes in length
(Fitzgerald or Lorentz contraction) and time dilation. Lorentz
codified this in a set of coordinate transformations that transform
the four time and space coordinates from one reference frame to those
of another frame moving at a constant velocity. This so-called Lorentz
Transformation is the heart and soul of special relativity. One of the
most cherished principles of modern physics, right up there with
conservation of energy, is Lorentz Invariance. That is, the laws of
physics are exactly the same in a reference frame derived by a Lorentz
Transformation (sometimes called a "boost") from another frame. This
is another way of saying that the laws of physics obey the principle
of "Einsteinian" or "Special" Relativity.

As a sometime visitor to this forum , I am usually reluctant to
comment on an "official " answer to a question which I  did not ask.

The third and fourth comments (by iang-ga and qed100-ga)have provided
very good answers to buffycat's  intelligent query.

I am however at a loss therefore to understand what the official GAR's
diatribe is all about. As well as totally confusing the original query
(by buffycat) it also undermines the intelligent comments by the
non-researchers.
 
I hope that buffcat asks for a refund for the this insulting answer.

Yours Truly 

Mongolia

One wonders where are the 'learned commenter' when one needs them.

Thank you Mongolia, for your suggestion. I have asked for a refund.
Thank you kottekoe and (particularly) qed100, for your helpful
comments. Are you interested in becoming paid answerers? Is there
anything I can do to help? PS I still don't understand the Lorentz
Invariance!

Of course, the article in the Scientific American is not the only
publication on the topic.

Here is a more accessible article from the British Guardian:
http://technology.guardian.co.uk/online/science/story/0,12450,894026,00.html

It is not my task to make guesses about which way the progress of science and
understanding will take. My task is to report on what is the current state
of knowledge and research.

Doubts about the traditional explantion started with Pioneer anomaly
http://en.wikipedia.org/wiki/Pioneer_anomaly
already in 1987 . There was a stream of additional articles which show
that this indeed is an open question on todays theories of gravity.
 There are many more papers on this  is peer reviewed journals.

 The fact that  mongolia-ga on 04 Mar 2006 16:31 PST did not bother to
read any reports on the current state of the research is not really anything
I feel responsible for. I have posted the links. It is on the reader to make
his or her mind. I just do want reiterate that these are not my theories.
I do neverthless find them interesting. I hop you do to.

Hedgie

Hey Buffcat,

   Sorry I didn't get back to this sooner; I was pretty busy lately.

   What kottekoe said earlier regarding Lorentz invariance is
accurate. But abstracting away the technicalities, essentially Lorentz
invariance means that, for all inertial reference systems (for
example, a spaceship coasting along on its own momentum), in general
the laws of physics will be observably the same, and more specifically
the value of c will similarly be the same for all inertial systems. In
other words, no matter what the inertial system's velocity relative to
some other system, from within the laws will be invariant.

   This is not, on the other hand, the same as saying that what you
observe happening in *other* relative systems will be invariant.
Indeed, as you in your inertial frame of reference pass by another
system at some relative velocity, the parameters of that system will,
by your reckoning, be "transformed", i.e., Lorentz transformed. The
transformation will manifest itself as length contraction of the other
system along the axis of relative motion (it'll be observably
squashed), and time in that system will run observably slower. (The
time in that system is said to be "dilated".) Both the length
contraction and the time dilation are determined as a function of the
relative velocity between the pair of systems, and both
transformations are by the same scaling factor, what's called the
"gamma" factor:

1/sqrt[1 - v^2/c^2]

   It's interesting to note that this means that, though the speed of
light in your local inertial system will tend to measure out to c, the
speed of light in the distant system will indeed be less than c, and
will be less by the gamma factor. This points out the real meaning of
the proposition "The speed of light is invariant for all inertial
systems"; it is invariant from *within* the system, regardless its
velocity relative to any other such system.

   Of course, your system, as measured from the other system, will be
transformed. You will be measurably squashed & time dilated.

Quoting myself earlier:

"time in that system will run observably slower"

and

"the speed of light in the distant system will indeed be less than c, and
will be less by the gamma factor."

   Excuse me; I got myself backwards. That ought to have been that the
other relatively moving system runs faster, with the value of c in
that system being greater than in your local, inertial system.