Does the accelerated Expansion add credibility to Steady State Cosmology?by Herbascious J Tags: accelerated, cosmology, credibility, expansion, state, steady 

#1
Jun2008, 06:22 PM

P: 77

Recently the expansion of the Universe has been found to accelerate. When studying Hoyle, Gold and Bondi's Steady State Cosmology, it clearly predicts an acceleration like this. I realize that this theory has been 'put to bed', and abolished, and all the other colorful language people like to use, but I'm still surprised about the slience behind this. The Big Bang has holes as well, weak points in the arguement (like predicting a 2.7 degree CMBR, and large scale structure, etc.) but people still enthusiastically support it, with all kinds of justifications. I am not saying that the Big Bang is wrong, or that Hoyle's cosmology is as credible, but I still don't understand why NOONE is at least referencing the fact that their hypothesis clearly predicted this find (I also understand that there are lines of arguement that claim this acceleration is not wellmatched with SSC, but the arguements are not facts they are interpretive). In a proper scientific field, especially like cosmology where it is chalk full of speculation and interpretation, should not all ideas be given their proper consideration. I don't think it's valid to dismiss one theory outright, when at least it made one very special prediction. Although we won't suddenly embrace SSC, should't it at least have credit? Thougt's anyone?
(I also want to point out that the australian deep field studies don't find the same radio count that the british did. In fact their finds did not contradict SSC. Beyond this the CMBR is too low for Big Bang. The CMBR is nothing more than the fusion radiation from the helium abundance, which leaves no room what so ever for a 'seathing and dense hot sea' of radiation for years after the first moment of Ex Nihilo.) 



#2
Jun2008, 07:58 PM

Mentor
P: 8,287

Are you talking about the steady state model, or some adaptation of the steady state model to account for the acceleration of the universe? It would really help if you had a link to a paper which gave a discussion of the claims you make.




#3
Jun2008, 08:14 PM

P: 77





#4
Jun2008, 09:19 PM

P: 3,967

Does the accelerated Expansion add credibility to Steady State Cosmology? 



#5
Jun2108, 04:10 AM

P: 684





#6
Jun2108, 07:15 AM

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P: 1,253

Steady State Cosmology, in which H is constant for all time is simply a terrible model given current data. Indeed, there have been a number of studies that have sought to avoid assuming any model for dark energy and have simply fit the data (supernovae results being the more important) by some function H(z) (z=redshift). The data overwhelmingly demonstrates that H(z) most definitely changes over time. That is before you go into how SSC can explain the observed evolution of structure (i.e. the structure in the Universe is observed to change as a function of redshift), the evolution of the galaxies luminosity function etc etc, the list could go on for some time.
I've made a couple of plots to show how bad the fit is for SSC. The first one shows three curves for H(z). The black line is for the standard LCDM model, although the paramters of this LCDM shown are not the exact best fits, I just put in 0.3,0.7 the best values are similar to this. The red line is for a matter only universe, so no decceleration. The green line is SSC, in which H(z) is always unity. Note that what is plotted is actually H(z)/H(0). Clearly the green line looks very different to the white, which is the one we know fits the data. To demonstrate the fit to data, I've plotted the distance modulus [tex]\mu[/tex] for these models against some of the supernovae data as a function of redshift (the data are the blue crosses). The data is a little old, there are many more points and points at higher redshift known now but I had these older ones in a data file already. Adding the newer data doesn't change this demonstration. As can be seen, a universe with no acceleration (red line) poorly fits the data. The black line is a good fit while the green line is also clearly a bad fit. The reason we don't talk about SSC much these days is simply because is performs very poorly at explaining the data. It was a good model when it was developed, since there was less data, but even Hoyle, the champion of the model, accepted that it had been ruled out by the data late in his life. That was data that was much less precise than we have today, that continues to make this model a poorer and poorer fit. 



#7
Jun2208, 09:45 PM

P: 77

Just to clarify, this thread is not intended to bring doubt to the Big Bang model. The BB is a very elegant and well developed theory, which I personally believe to be the best currently available. My only commentary is the unusual silence regarding the SSC theory, which I have always liked as well. It just seems that there are all kinds of esoteric theories about cosmology, which get plenty of discussion, even though these alternate theories have zero observational support (strings, dark matter, etc.). I'm not expecting people to drop BB for SSC, BUT I do expect the community to have some kind of acknowledgement when we suddenly find the universe to be accelerating, which IS a central component to an SSC universe like Hoyle's.
Beyond this, I understand that SSC has dropped out of favor because of observation (it has the unusual advantage that it is directly testable, and therefore may be disproven), but complete abandonment of any theory, especially in cosmology is simply unscientific. For example, when this new accelerating data became available, everybody started talking about Einstein's Lambda again, refering to his 'greatest blunder' and how it might now have some validity. All I'm getting at is, why doesn't the community say "Wow, Hoyle predicted that with his very popular SSC model. Maybe we can look back and examine how he was able to make such a prediction and see if there is anything to draw from it?" This is not an attack on the Big Bang, I'm simply pointing to an unusual resistance to a once popular theory, in a field of research that is very speculative and interpretive. 



#8
Jun2208, 10:01 PM

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#9
Jun2208, 10:02 PM

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P: 1,253

You are mixing fields here. Let me get this straight, observational cosmology is not a speculative field and has established, from observations, a model for the expansion of the Universe that is remarkably consistent with a wide range of independent data sets. When we observed that the Universe was accelerating, it was also seen that this acceleration was no where near the function form (i.e. q(z) ) of SSC. That is why this model wasn't dug up, because it didn't fit the data. Not for any other reason. Einsteins \Lambda did appear to fit (and still does with newer data) so that is why that was the old theory that was dug up and not Hoyle's.
Now, as for the speculative side of things, string theory etc are in no way connected to observational cosmology. It is hoped that such a theory may one day explain why the Universe started accelerating, but we don't need to consider the 'why' in order to simply try and understand what is happening. The what looks nothing like Hoyle's model. This is why it is good science to not actively consider this model, because it doesn't predict anything correctly. You seem to think it is 'unscientific' to hold onto a theory even if it doesn't fit available data? I don't understand how this makes sense. Don't confuse the speculative fields of theoretical physics like string theory and LQG (or LQC) with observational cosmology which can in no way be described as speculative. There is no good reason based on current evidence to think that a steady state model is a good model at this point. This is always a transient statement dependent entirely on new data and new ideas, but Hoyle's model predicts no data set correctly and hence is a very bad model to start playing around with at the current time. 



#10
Jun2208, 10:09 PM

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P: 1,253

The curve may seem close to each individual point but the key thing is that we must consider all points. If they all lie on one side of a curve that curve can't be a good model. Edit: Oh and yes, newer data is important. Note that the curves separate more and more at high redshifts. Much of the new data is at a higher redshift than what I have shown, so make the differences between models more stark. This is particularly true for SSC since in that model there is only acceleration, wheares what we find is that SN above about z~1 show that the Universe was decelerating then, followed by the more recent acceleration. SSC doesn't predict this so would perform very poorly for the high redshift data. Note also the SN are just one observation (although very important admittedly) and the other bits of evidence also suggest deceleration followed by acceleration. 



#11
Jun2308, 04:24 PM

P: 77





#12
Jun2408, 06:07 PM

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P: 1,253

Supernovae Type 1A are roughly, once you take several factors into account, standard candles. This means that there is a consistency to them, each explosion (when corrected by known factors) is about the same brightness, known to astronomers as the absolute magnitude [tex]M[/tex]. By observing how bright they appear to be, the apparent magnitude [tex]m[/tex] we can then determine how far away they were as a function of redshift, since more distant objects appear dimmer. We can't simply use the normal intensity dropping as 1/distance squared in an expanding general relativistic universe, but instead we need to determine the luminosity distance, [tex] d_L [/tex] which is function that depends on the particular cosmology. This luminosity distance for a given model predicts how the supernovae would appear to us as a function of redshift if they were perfect standard candles and there was no uncertainty in measurement.
What I plotted on the graphs is actually distance modulus [tex] \mu [/tex] which is defined as [tex] \mu = m  M = 25 + 5 log d_L [/tex] so for the blue crosses of the data, the difference between the absolute magnitude of SN type 1A and the observed magnitude gives us [tex]\mu[/tex] and then for the curves, the cosmology gives us [tex]d_L[/tex] which is converted to [tex]\mu[/tex] as shown. In particular [tex] d_L(z) = \frac{c(1+z)}{H_0} \int_0^z \frac{dz}{H(z)} [/tex] which is how you get from the graphs I gave of H(z) to the second one. Does that answer your question? Let me know if you need anything clarified, more info etc. Edit: Note the last formula for luminosity distance is valid only for a flat universe, open and closed universes have a somewhat more complex formula, but the principle is the same. 



#13
Jun2408, 06:31 PM

P: 77

Ok, I see. Mathematically, the relationship of luminosity vs. redshift should appear different given different assumptions about the nature of the expansion. Hence the lines on the graphs. Each makes there own prediction about the curve and we then plot observation against it. I'm not familiar with the equations (they are too advanced), but I think the general point is there. That is interesting. So what you are saying is that the nature of the curve reveals acceleration and/or deceleration.
My only other question would then be; how reliable is the standard candle approach? Are these supernovae events all as similar as this assumes? Perhaps, if they are not, are we using somekind of probability algorythm to 'average out' so to speak a general pattern? At this point, I am no longer refuting anything, I am genuinely trying to understand the reality of this. Thank you again. 



#14
Jun2408, 06:56 PM

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P: 1,253

The biggest nonstandard candleness of SN can be nicely removed by a process known as 'stretch correction'. This where there is a relationship between the SN peak brightness and the light curve width (how long in days it shines for). Once the light curves are corrected for redshift (redshift stretches the light curve out in the same way as it stretches the light wavelength) they look like the top plot in the attached figure. Note that the peak brightness of them is all quite different. However, once a simple scaling is applied to the the brightness as a function of light curve width, the bottom plot is achieved. These stretch corrected light curves are then remarkably standard. Note that this stretch correction is an empirical result. It appears to work even though we don't have a great idea of the physics behind why it works. This is a gap in knowledge that a lot of theoretical work and low redshift SN observations are working to solve. 



#15
Jun2608, 04:10 PM

P: 77

This is very cool. I understand that the redshift should also apply to the duration of the SN. I'm assuming that it is stretched in the same way a photon wavelength is stretched, hence redshift...




#16
Jun2608, 05:33 PM

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P: 1,253

This is starting to reach to the edges of what I am sure about, but I will answer the question as best I can, and hope I don't mislead you!
The stretch correction process certainly indicates that there is some physical mechanism in the Supernovae explosion that leads to this correlation. I believe there is some relationship between the stretch correction and properties of the SN spectra, in particular the strength of some metal lines, particularly Nickel. The strength of the line tells us how much of that metal is present in the SN progenitor (the thing that the SN is before it goes boom) and I think it is the different metal abundance that regulates the peak brightness and width. This is another reason to doubt that high redshift SN1A are different from low redshift ones, since we can observe these abundances in both cases. 



#17
Jun2608, 06:15 PM

P: 77

Fascinating. Thank you for the extensive feedback with all of this, Wallace. It's great to get straight feedback and insight regarding the technical side of these things. I will keep a close eye on Super Novae research from now on!
Cheers All. 



#18
Jun2608, 06:19 PM

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P: 1,253

No worries. There is a project underway at the moment dubbed 'the nearby supernovae factory' (or something like that) which is aiming the look in detail at hundreds (possibly thousands?) of SN1A in the low redshift Universe. Since they aren't looking at the distant stuff they can do it with a small telescope ( I think it is only ~1m) and get lots of observing time, since small telescopes aren't so sought after. You can't do much cosmology with these local SN, but they hope to get a much better understanding of them in order to better inform observations of the high redshift ones. And of course just to understand these SN in their own right!



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