
#1
Jan2512, 11:24 AM

P: 84

Does the cosmological constant support MOND?
The equation for critical density is as follows (in terms of mass rather than density): Critical density (90.4 x e54 gm) = matter (4.1 x e54 gm) + dark matter (20.6 x e54 gm) + dark energy/cosmological constant (65.7 x e54 gm). Most estimates for matter are in the range of e55 gm (or more) which is close to the total for matter and dark matter (2.64 x e55 gm). Thus, dark matter may not exist and MOND may be a correct theory. Comments? 



#2
Jan2512, 03:01 PM

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P: 2,194

At any rate, MOND is, in almost all physicists' minds, a completely dead theory due to its inability to cope with the myriad of successes dark matter has had since its initial inception in galactic rotation curves (see, for example, the bullet cluster). As a simple idea, MOND was OK and plausible, but it has gotten egregiously complicated to attempt to deal with all these new phenomenon, and trying to save it reminds me of adding more epicycles to account for the motion of planets. 



#3
Jan2512, 03:18 PM

P: 84

I agree MOND seems rather lifeless but the numbers in the equation raised a question about the amount of dak matter. Below are the assumptions which allow for dark matter,but the assumption for mass (based on 5 x e10 stars/galaxy each .6 x sun's mass)may be considerably low as my original post states.
Assumptions for critical density: Hubble constant (H) = 72 km/sec/Mpc or 2.34 x e18/sec; volume of universe = 9.22 x e84 cm3; cosmological constant = 7.12 x e30 (from Brian Greene’s Hidden Reality, page 337); and ratio of matter (baryonic) to dark matter is 1 to 5. majority of baryonic matter exists as stars. Calculation of mass based on critical density : critical density = 3 x H2/(8 x pie x G) = 9.81 x e30 gm/cm3; density of matter and dark matter = 2.69 x e30 gm/cm3 (9.81 x e30 minus 7.12 x e30); density of matter = .45 x e30 gm/cm3 (ratio of 1 to 5); mass of both matter and dark matter = 2.47 x e55gm (volume x density); mass of dark matter = 20.6 x e54 gm; and mass of matter = 4.1 x e54 gm. Assumptions for number of stars: number of galaxies = e11; number of stars per galaxy = 5 x e10; average mass of star = .6 x e33 gm (.3 x sun’s mass). Calculation of matter based on number of stars: matter = 5.4 x e54 gm. Thus, using these assumptions the results are reasonably close, 4.1 to 5.4 x e54 gm for matter. When dark matter is included, 2.47 x e55 gm, the result is also close to the e55 gm, which is based on CMB splotches size (stated in Hidden Reality, page 275). 



#4
Jan2612, 02:24 AM

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P: 4,721

cosmological constant supports MOND
There is no estimate for baryonic matter alone that comes remotely close to the total matter in the universe.




#5
Jan2612, 09:27 AM

P: 84

Chalnoth, if matter and dark matter is 24.6 x e54 gm, I think there are estimates for matter ony in this range. However, in my calculation the volume is based on 13.7 lightyears for the radius. One could use 13. parsec which would give an answer 34.6 times larger for all the mass values.
In a calculation like this, which volume is logical? Thanks 



#6
Jan2612, 09:31 AM

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P: 4,721

And our best estimates of the density of normal matter place it at about 4.5% of the total energy density of our universe. 



#7
Jan2612, 10:14 AM

P: 84

Thanks, for some reason I did not comprehend that the total mass was directly related to volume. My objective was to show that the total mass (matter and dark matter) was about e55 gm and then reconciled this with different estimates of mass based on the number of stars. Now, I could not find a reliable source on the distribution of matter between gas and stars so the assumption is all stars and no gas. But to compute a mass from critical density, a volume is required. Anyway, using the radius of 13.7 x e9 light years, gives 4.1 x e54g gm for matter (4.5% of total). Dark matter was 20.6 x e54 gm (22.8% of total). Now for sake of argument, assume e11 galaxies each with e11 stars with an average mass of the sun 2 x e33gm. This gives 2 x e55 gm, a number close to the sum of matter and dark matter. Thus, I thought about MOND which would explain the situation.
Based on minimal response to the post, I am wondering if there any value to my objective. 



#8
Jan2612, 01:57 PM

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#9
Jan2612, 05:02 PM

P: 84

Chalnoth, thanks for your response, I know this is not as interesting as the multi universe topic. Ok, only density will be used. The equation is: Critical Density (9.81 x e30 gm/cm3) = matter (.45 x e30 gm/cm3) + dark matter (2.24 x e30 gm/cm3) + dark energy/cosmological constant (7.12 x e30 gm/cm3). For matter, the source is Hubble Space Telescope’s average stellar density of e9 stars/ly3 or 1.18 x e63 star/cm3. So the key variable is the average mass of a star. If it is the sun’s mass, matter density is 2.35 x e30 gm/cm3 and the argument for MOND has support. If the average is 30% of the sun’s mass, matter density is .7 x e30 gm/cm3 which is higher but closer to the .45 x e30 gm/cm3 above. Does this approach sound logical?




#10
Jan2612, 07:36 PM

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MOND would need to do some footwork of its own, rather than simply discrediting other theories, to gain support. 



#11
Jan2712, 02:35 AM

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The 'bullet cluster' was basically an execution style head shot for MOND. There have been some weak efforts to revive MOND since that time, but, the head wound still looks fatal. I am particularly amused by the idea of MOND allowing for some amount of dark matter. 'Pa, the dang dog drug up another sasquatch bone on the porch ...'.




#12
Jan2712, 03:01 PM

P: 84

[QUOTE=Nabeshin;3729610] Even if it were the case that the observed visual matter were able to account for the majority of the baryonic mass of the universe (which, as it has been pointed out, by almost all estimates cannot)
Do not understand this comment. The analysis showed that depending on the selected value of mass for a star, dark matter could be zero since matter would then exceed the total for both. What am I missing? 



#13
Jan2712, 03:11 PM

P: 84

[QUOTE=Chronos; I am particularly amused by the idea of MOND allowing for some amount of dark matter.
I do not see the relationship of this statement to my analysis. The density equation has nothing to do with MOND, it stands alone. My linking it to MOND was speculation based on a mass density with a high, but possible, value for the mass of an average star. This then allowed for no dark matter in the equation and MOND saya no dark matter. 



#14
Jan2712, 04:17 PM

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#15
Jan2712, 07:45 PM

P: 84

I do have references for the distribution of star classes, M 73%, K 14%... Using this information and the mass of each class the average mass is .5 x mass of sun. This results in a density 2 and1/2 times what was in the density equation for mass (again using an H of 72 and the other assumptions).One other thing I noticed was that the Hubble stellar density is based on volume. I am going to rerun the numbers with a range of mass assumptions.




#16
Jan2812, 11:45 AM

P: 84

There are two assumptions that are wrong in the analysis contained in my original and subsequent posts.
First, to account for space expansion, the volume of universe should be 4.4 x e28 cm3. Using the critical density equation, this gives a mass for matter of 1.6 x e56 gm (rather than the .45 x e56 gm). Second, a better estimate of the number of stars is e23 each with a mass of e33 gm (1/2 the sun). This gives a mass of e56 gm, a value close to what the critical density equation predicts. Thus, dark matter is accounted for and the cosmological constant does not support MOND. 



#17
Jan2812, 03:03 PM

P: 476

http://scholar.google.com/scholar?hl...us+matter+MOND 



#18
Jan2812, 04:54 PM

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