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## Galaxy motions -> hidden superstructure (DM!)

 Quote by Ian You can see only visible light! not all frequencies are visible to our eyes, dark matter is the same as ordinary matter, we cannot see it or touch it because it is bigger and on another scale.
Understood Ian, but the standard model says DM cannot be the same as ordinary matter, i.e. baryonic, as there is too much of it. Standard GR BB nucleo-synthesis allows only a maximum of 4% critical density as ordinary matter (and that is pushing it) whereas galactic dynamics and lensing observations require about 20%, or more. So what is it?

However if the GR R(t) ~ t^(1/2) then t^(2/3) in the radiation and matter dominated epochs respectively is replaced by R(t) ~ t all the way through in the freely coasting model then nucleo-synthesis allows 20% baryonic density + neutrino etc contributions, so the problem is solved. And you will be right; DM is ordinary matter!

- Garth

 Quote by Garth Understood Ian, but the standard model says DM cannot be the same as ordinary matter, i.e. baryonic, as there is too much of it. Standard GR BB nucleo-synthesis allows only a maximum of 4% critical density as ordinary matter (and that is pushing it) whereas galactic dynamics and lensing observations require about 20%, or more. So what is it?
I've not seen the data. Are the galactic rotation curves and the lensing effects just as strong for Andromeda as for very distant galaxies? Thanks.

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 Quote by Garth They were not - indeed GPB is ideal for testing such alternatives - SCC and Moffat's non-symmetric gravitational theory (NGT) [see "Modified Gravitational Theory and the Gravity Probe-B Gyroscope Experiment" http://arxiv.org/abs/gr-qc/0405091].
Good to hear.
 The question how would a non-GR outcome of the experiment be interpreted should it occur?
Indeed! It should be an exciting time, should it not?
 1. The space-borne interferometer to test whether photons and particles fall 'at the same rate': "Self Creation Cosmology An Alternative Gravitational Theory" http://arXiv:gr-qc/0405094 Section 7.1 pg 17.
I'd be interested to hear whether you think the proposals in Cosmic Visions (or the NASA equivalent) will cover this.
 2. The deep-space Casimir force experiment to test whether there is a cut off of the Casimir force at great distances from the Sun. (ibid)
AFAIK, there are no deep space experiments planned, by anyone, for any purpose (unless you count the Pluto-Kuiper Express, which is all but dead, no?)
 The truncated LIGO type interferometer, to test the same question as 1 above.
To what extent would LISA be able to serve as an alternative? What about the resonant mass gravity wave detectors?
 I can partly understand Nereid's puzzlement over the statement. However I would like to point out that, apart from a motley collection of such as myself who might be called 'crackpots' by some, there are a number of respected figures who have signed the statement such as Bondi, Gold and Narlikar. But why have they?
That's what I'm trying to understand! If none of the missions preclude tests of any alternatives, and if there are but a small number of dedicated missions that the iconclasts would dream of, where's the beef (other than pocket money for tea and biccies)?

 Recognitions: Gold Member Science Advisor Speaking of large scale structure and the standard model, this is interesting http://www.arxiv.org/abs/astro-ph/0404111

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On possible non-GR outcome of GPB experiment:
 Quote by Nereid It should be an exciting time, should it not?
If such an outcome should occur do you think they will devise another epicycle?
 Quote by Nereid I'd be interested to hear whether you think the proposals in Cosmic Visions (or the NASA equivalent) will cover this.
 Quote by Nereid AFAIK, there are no deep space experiments planned, by anyone, for any purpose (unless you count the Pluto-Kuiper Express, which is all but dead, no?).
It has been suggested that a Pioneer Anomaly test be put onboard a low-mass, low-thrust mission to Pluto, the Pluto orbiter Probe or POP. A study of such a mission has been undertaken recently in ESA’s Advanced Concepts Team and detailed results of the system design and trajectory design have been presented in T. Bondo et al, “Preliminary Design of an Advanced Mission to Pluto”. Proceeding of the 24th ISTS, Miyazaki, Japan, June 2004. http://www.esa.int/gsp/ACT/doc/ACT-R...0-ISTS2004.pdf . I have no idea as to whether or when it would get off the ground.
 Quote by Nereid To what extent would LISA be able to serve as an alternative? What about the resonant mass gravity wave detectors?
The experiment compares the gravitational attraction of a horizontal light beam against that of a solid apparatus. I do not think LISA will comply, the gravitational bending of light being equal in GR and SCC.
[Such deviation being of two components, one due to the 'free fall' of the photon the other due to the curvature of space - in GR these two contribute 1/2 + 1/2 respectively to the total deviation; in SCC they contribute 3/4 + 1/4 respectively of the same total deviation 1.75".]
- Garth

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Quote by Garth
On possible non-GR outcome of GPB experiment:
Quote by Nereid
Indeed! It should be an exciting time, should it not?
 Quote by Garth The question how would a non-GR outcome of the experiment be interpreted should it occur?
If such an outcome should occur do you think they will devise another epicycle?
It's pure physics, so lots of  will be found to do a bigger and better GPB; ten thousand new 'GR-killer' theories will flow from the word processors of theorists; ten creative ideas to test the new theories will be published, involving little more than what can be found in a leading university lab; three hundred extensive data-mining projects will be commenced, using BOINC (the new grid computing platform on which Seti@Home now runs); ... and key insight for 'the answer' will come from the mind of a bright young PhD student in China (or India).

 Good discussion here. I used to deride Dark matter as a makeshift idea to plug the emerging holes in GR, or newtonian at least. I guess what turned me around is string theory. For once Ican see how DM could exist. I don't think dark matter is one long brane covering the universe, though that is possible. But perhaps it has to do with the frequency of the wave nature of particles. For example, photons are considered a string just as baryons are, only at a higher vibration. Light happens to be at the upper vibratory limit of what our expanded dimensions can swallow. But does that mean there's no strings that vibrate faster than light? If there were, wouldn't we not see them at all, nor be able to detect them? Would that be, 'dark matter'? It's something I've thought about and perhaps Tachyons(sp?) are an offshoot of that dea, I don't know much about them though. Anyone like to comment?

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