No Galaxy Acceleration from Surpernova Data?

[CraigS]

Interesting papers, relatively recent, quite readable, by the same person (Southampton University), and using SN1A data (see attachments, if interested):

"Alternative cosmology fits supernovae redshifts with no dark energy" - March 2009.

His conclusion:
"Supernovae and radio galaxy redshift data are fitted in an alternative cosmology. The galaxies are assumed to recede with unchanging velocities in a static Robertson-Walker metric with a(t) = 1. An exact fit is obtained with no adjustable parameters. There is no indication that the recession velocities are changing with time, so no call for ”dark energy”."

Second paper:
"Does gravity operate between galaxies? Observational evidence re-examined" - May 2010.
His conclusion:
"On the largest scale, the net force accelerating or decelerating the galaxies is apparently zero. Each recedes with unchanging velocity following Newton’s first law."

Please note I'm not trying to push any particular personal views or opinions here (there's always more scientific debate for and against - and it seems this one isn't fully settled), but I thought it was interesting because the conclusion seems to differ from other papers based on Supernova Type 1a data.

In his words:
"This model may be incompatible with other cosmological data, such as the cosmic microwave back-ground and the distribution of galaxies. Most phenomena, however, depend on the distribution and movement of matter, not on the expansion of space itself. These questions remain to be examined."

Interesting.
Cheers.
PS: He's also saying that Martin Rees' (& others) provided comments during the study.

[renormalised (Carl)]

I'll have to read these...sounds interesting

If he's saying what I think he is, then there'll be no acceleration or contraction and the Universe will just coast along on into infinity. Pretty much in line with previous expectations and values derived for matter and energy density within the universe. That means no CC...that'll make a lot of physicists happy

Hmmm...what needs to be done is the SNIA model needs to be refined and more observations of the supernovae need to be done. Going to need a dedicated, worldwide supernova search program with both small and large scopes to figure out what's happening. In order to tie down the theory from the obs, they'll need to find 20-50 Type IA Sn's every year till they get a large enough sample to make this, at least, relative statistically significant...iron out any selection bias.

You watch what will be said by you know who

[bojan]

Interesting..

So, he is saying that distant galaxies are there where they are simply because their velocity (after BB explosion?) was highest.
I think this was one of the first simple explanations offered, after expansion was detected (by redshift).

[renormalised (Carl)]

Yes, but that explanation would imply a zero point in spacetime...i.e. a point of origin which would be observable. Given our point of reference, it would mean that the Earth (or where the Earth is in relation to the rest of the universe) would be the centre. That would make the geocentrists and the creationists extremely happy

That would also mean the CMB would appear to have a different temp at different positions within the universe....something we don't see from observation. Despite our position, the anisotropy would be detectable in the light coming from these distant objects, which it isn't.

[Steffen]

Originally Posted by renormalised

Given our point of reference, it would mean that the Earth (or where the Earth is in relation to the rest of the universe) would be the centre.

Or more precisely, St Peter's Basilica in Rome.


Cheers
Steffen.

[sjastro]

It also makes a mess of Hubbles Law. The recession velocity of the galaxies will be same for all observers (in the line of sight) irrespective of the distance between observer and galaxy.

Steven

[bojan]

Originally Posted by sjastro

It also makes a mess of Hubbles Law. The recession velocity of the galaxies will be same for all observers (in the line of sight) irrespective of the distance between observer and galaxy.

Steven

How is that?

[xelasnave]

Would not all the galaxies be in more or less the same place now as they were after the initial inflation period...(that short period of say up to 30 seconds that is attributed to inflation when the universe grew from the size of a basket ball to near all it is today) ... and really after inflation how far have galaxies really moved if you dont take into account inflation or "current" expansion... very little I expect when compared to the great distances created by the inflation period.

I dont think galaxies can be thought of as accelerating due to some explosive force as some may imagine the big bang may produce.

Galaxy movement in relation to each other and not in relation to the inflation would be relatively insignificant and any movement to or away from each other will be mere fractions of c.

alex

[sjastro]

Hubbles law states that in a metrically expanding Universe, the recession velocity is proportional to the distance between the observer and the object. So doubling the distance doubles the recession velocity.

The model presented here is that galaxies are moving in space at a constant velocity rather than space expanding. A galaxy moving away from an observer in space will travel at that velocity irrespective of how far the galaxy is from the observer.

Steven

[bojan]

Yes, but more distant galaxies had higher initial velocity (and still have), so they are further away at present.
So, something like Hubble law could still be observed...

[xelasnave]

Does the expansion of space mean that galaxies will have any velocity?
alex

[bojan]

I don't think the papers from Craig's post are talking about metrically expanding Universe.

[CraigS]

Originally Posted by bojan

I don't think the papers from Craig's post are talking about metrically expanding Universe.

These guys seem to be enquiring into the nature of "the metrically expanding universe" and I think they're saying that the observation data doesn't seem to support a "metrically accelerating universe".

The definition which Steven quotes seem to be critically dependent on the definition of "metrically expanding". In my naivity, I thought Hubble's Law was Earth-centric. There again, I guess there's nothing special about Earth's frame of reference ?

Cheers

[CraigS]

Originally Posted by xelasnave

Does the expansion of space mean that galaxies will have any velocity?
alex

G'Day Alex;
What caused the velocity is outside the scope of the paper's investigation area.
Cheers

[renormalised (Carl)]

Originally Posted by Steffen

Or more precisely, St Peter's Basilica in Rome.


Cheers
Steffen.

Well, if you want to be really precise

[CraigS]

Originally Posted by CraigS

These guys seem to be enquiring into the nature of "the metrically expanding universe" and I think they're saying that the observation data doesn't seem to support a "metrically accelerating universe".

The definition which Steven quotes seem to be critically dependent on the definition of "metrically expanding". In my naivity, I thought Hubble's Law was Earth-centric. There again, I guess there's nothing special about Earth's frame of reference ?

Cheers

Oh ... unless it's St Peter's Basilica in Rome !

[sjastro]

The paper uses terminology familiar to the concept of metric expansion.
For example Z is a cosmological redshift not a doppler shift.

Getting back to my original comment if two observers in different locations measure different velocities for an object moving away in space then acceleration (or deceleration) is occurring which contradicts the point of the article.

I find it difficult how one can fit Hubble's recession velocities into this picture for a doppler shift mechanism.

Even considering a "localized" version where the Z is interpreted as a Doppler shift in our patch of the Universe doesn't help either.

Steven

[renormalised (Carl)]

Originally Posted by CraigS

These guys seem to be enquiring into the nature of "the metrically expanding universe" and I think they're saying that the observation data doesn't seem to support a "metrically accelerating universe".

The definition which Steven quotes seem to be critically dependent on the definition of "metrically expanding". In my naivity, I thought Hubble's Law was Earth-centric. There again, I guess there's nothing special about Earth's frame of reference ?

Cheers

I still haven't read the paper yet, but I can gather that they think the universe, from their observation of the supernovae, seems to employ more of a constant expansion. They're saying that the galaxies are moving apart at a constant rate relative to their position in the initial expansion , no matter where or how far away you look. So, if a galaxy is 12 billion light years away and is moving away at 0.9c, then even after traveling a further 2 billion light years, it will still be traveling at 0.9c...and so forth. As Steven has reiterated, that throws redshift-distance determination right out the door, unless you can find a factor which when added to or multiplied by z, gives you the correct distance. That is, providing they're assumptions as to the metric for the expansion are correct to begin with.

[renormalised (Carl)]

These following pages should help to enlighten everyone...

http://www.jb.man.ac.uk/~jpl/cosmo/RW.html

http://en.wikipedia.org/wiki/Friedma...3Walker_metric

http://en.wikipedia.org/wiki/Scale_f...%28universe%29

http://en.wikipedia.org/wiki/Metric_expansion_of_space

[bojan]

Originally Posted by renormalised

That is, providing they're assumptions as to the metric for the expansion are correct to begin with.

OK, this makes sense..