What is the difference between coasting and static cosmology?by Lino Tags: coasting, cosmology, difference, static 

#1
Feb1413, 02:13 PM

P: 259

Is the key difference between coasting and static cosmology models the presence of a linear acceleration, or are there other major differences?
Regards, Noel. 



#2
Feb1413, 04:50 PM

Sci Advisor
PF Gold
P: 3,273

As gravitational forces from objects in the universe would cause it to contract there has to be another force counteracting these, a dark energy. Einstein found that the cosmological constant could provide such a force and included it in his model. However it was soon shown that the model is unstable, and the slightest perturbation, a tendency to expansion or contraction, would grow into full blown expansion or contraction. Hubble's observations soon proved that the universe is in fact expanding. The coasting model expands linearly, with no deceleration or acceleration. This would happen in an empty universe (the original Milne model) with no gravitational fields , or if not empty (obviously as in the real universe) something would have to counteract the gravity forces. A dark energy with an equation of state [itex] \rho = \frac{1}{3}p[/itex] would achieve this (Kolb's model A coasting cosmology ). Or, if antimatter repels matter gravitationally then the universe could be split up into regions of matter and antimatter with overall gravitational forces cancelling would also achieve this. (The DiracMilne universe) Garth 



#3
Feb1413, 04:57 PM

P: 259

Thanks Garth. Guess I'll have to keep reading.
Regards, Noel. 



#4
Feb1513, 09:08 AM

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P: 4,721

What is the difference between coasting and static cosmology? 



#5
Feb1513, 10:07 AM

P: 259

Thanks Chalnoth. Could you recommend any search words or links that are critical of a coasting cosmology (everything I read seems to be very positive)?
Regards, Noel. 



#6
Feb1513, 11:56 AM

Sci Advisor
PF Gold
P: 3,273

The coasting model with matter requires dark energy such that the total equation of state is [itex] \rho_T = \frac{1}{3}p_T[/itex]. If the dark energy itself had an eos of [itex] \rho = p[/itex], as with the cosmological constant, then [itex] \rho_\Lambda = \frac{1}{3}\rho_M[/itex]. Such an eos is suggested in Self Creation Cosmology (page722) Whether the theory can fit other observational constraints is another question. Garth 



#7
Feb1513, 12:11 PM

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P: 4,721

http://lambda.gsfc.nasa.gov/product/..._act_snls3.cfm This is the list of parameters where they have taken the standard dark matter cosmology, but allowed the equation of state parameter [itex]w[/itex] to vary. This is model could easily include the coasting cosmology if [itex]w \approx 1/3[/itex]. The data used in this fit include WMAP (9year data), SPT, ACT, and SNLS3. The estimate of the equation of state parameter with this combination of CMB and supernova data becomes: [tex]w = 1.059 \pm 0.069[/tex] This is consistent with a cosmological constant ([itex]w = 1[/itex]). So a coasting cosmology is completely ruled out, unless you can come up with a reason to believe that the other parameters used in the model are completely wrong (e.g. there really isn't any dark matter, though it's really really hard to fit the available evidence without dark matter), but even then you have to do the hard work to fit the new model with the available data, which is copious. 



#8
Feb1513, 12:18 PM

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#9
Feb1513, 12:23 PM

PF Gold
P: 1,526

Here is one investigated paper of a Linear coasting model
http://arxiv.org/pdf/astroph/0306448v1.pdf Classical Cosmology tests Kolb[12] was probably first to demonstrate that data on Galaxy number counts as a function of redshift as well as data on angular diameter distance as a function of redshift do not rule out a linearly coasting cosmology. Unfortunately, these two tests are marred by effects such as galaxy mergers and galactic evolution. For these reasons these tests have fallen into disfavour as reliable indicators of a viable model. The variation of apparent luminosity of a “standard candle” as a function of redshift is referred to as the Hubble test. With the discovery of Supernovae type Ia [SNe Ia] as reliable standard candles, the status of Hubble test has been elevated to that of a precision measurement. Recent measurements by the supernovae cosmology project [13] eliminated the “minimal inflationary” Later researches as Chalnoth mentioned completely ruled out coasting models as far as i know. Leastwise I've never seen or heard of any recent articles on Coasting models 



#10
Feb1513, 12:34 PM

P: 259

Thanks all for the references and links.
Regareds, Noel. 


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