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Tim Thompson
2008-Dec-27, 07:40 PM
There have been several discussions over the interpretation of the expansion of space, whether or not we can say that space in physically, really expanding, or that it is only a coordinate system effect. I post this note only to draw the attention of anyone interested in the topic to the following recently posted paper:

Eppur si muove
Michał Chodorowski
arXiv: http://arxiv.org/abs/0812.3972
ADS: http://adsabs.harvard.edu/abs/2008arXiv0812.3972C

Abstract: In two recent papers, Abramowicz et al. claim that the expansion of the Universe can be interpreted only as the expansion of space. In fact, what they really prove is that the cosmological expansion cannot be described in terms of real motions in Minkowski spacetime. However, there is no controversy about this issue. Abramowicz et al. show that in general, the cosmological redshift is not a Doppler shift and they consider this fact as a proof that space expands. Again, nobody believes (perhaps except Milne) that for non-empty universes the origin of the redshift is purely Dopplerian. From the Principle of Equivalence it follows that there must be also a gravitational shift in presence of matter. Indeed, it is well known in cosmology that for small redshifts, the cosmological redshift can be decomposed into a Doppler component and a gravitational component. In a forthcoming paper, we shall perform such a decomposition for arbitrarily large values of the redshift.

The arXiv link leads to the abstract & a downloadable PDF preprint of the full paper. The ADS link allows access to references cited in the paper and to any papers which eventually cite this one, as well as including the arXiv link. It is interesting to me that the topic remains a matter of some controversy in the "real world", by which I mean the world of science outside the strange world of discussion boards.

trinitree88
2008-Dec-28, 10:59 PM
There have been several discussions over the interpretation of the expansion of space, whether or not we can say that space in physically, really expanding, or that it is only a coordinate system effect. I post this note only to draw the attention of anyone interested in the topic to the following recently posted paper:

Eppur si muove
Michał Chodorowski
arXiv: http://arxiv.org/abs/0812.3972
ADS: http://adsabs.harvard.edu/abs/2008arXiv0812.3972C

Abstract: In two recent papers, Abramowicz et al. claim that the expansion of the Universe can be interpreted only as the expansion of space. In fact, what they really prove is that the cosmological expansion cannot be described in terms of real motions in Minkowski spacetime. However, there is no controversy about this issue. Abramowicz et al. show that in general, the cosmological redshift is not a Doppler shift and they consider this fact as a proof that space expands. Again, nobody believes (perhaps except Milne) that for non-empty universes the origin of the redshift is purely Dopplerian. From the Principle of Equivalence it follows that there must be also a gravitational shift in presence of matter. Indeed, it is well known in cosmology that for small redshifts, the cosmological redshift can be decomposed into a Doppler component and a gravitational component. In a forthcoming paper, we shall perform such a decomposition for arbitrarily large values of the redshift.

The arXiv link leads to the abstract & a downloadable PDF preprint of the full paper. The ADS link allows access to references cited in the paper and to any papers which eventually cite this one, as well as including the arXiv link. It is interesting to me that the topic remains a matter of some controversy in the "real world", by which I mean the world of science outside the strange world of discussion boards.

Tim. I'll find the discussion interesting. thanks pete

Cougar
2008-Dec-29, 03:13 AM
Eppur si muove
Michał Chodorowski
arXiv: http://arxiv.org/abs/0812.3972

A very catchy title! But does Chodorowski think all the redshifts are doppler and so all the galaxies are moving through space? Apparently he prepublished the Abstract and Introduction before finalizing the rest of the paper, so I'm not exactly sure where he's going with this.

As I understand it, we don't know whether space physically "expands" like a balloon with dots on it or not; what we know is that distant objects are apparently in different frames of reference from us, the extent of the difference being quantifiable in proportion to apparent distance....

Spaceman Spiff
2008-Dec-29, 04:26 PM
For your convenience, here is a linked listing of the recent, related papers (all since 2006):

Eppur si espande (http://arxiv.org/PS_cache/astro-ph/pdf/0612/0612155v3.pdf)
Marek A. Abramowicz, et al.

A direct consequence of the expansion of space? (http://arxiv.org/PS_cache/astro-ph/pdf/0610/0610590v3.pdf)
M. Chodorowski

Is space really expanding? A counterexample (http://arxiv.org/PS_cache/astro-ph/pdf/0601/0601171v2.pdf)
M. Chodorowski

Expanding Space: the Root of all Evil? (http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.0380v1.pdf)
M.J. Francis et al.
(my personal favorite -- gotta love that title)

The kinematic origin of the cosmological redshift (http://arxiv.org/PS_cache/arxiv/pdf/0808/0808.1081v1.pdf)
E. Bunn & D. Hogg

A diatribe on expanding space (http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.4573v1.pdf)
J.A. Peacock

A short answer to critics of our article “Eppur si espande” (http://arxiv.org/PS_cache/arxiv/pdf/0812/0812.3266v1.pdf)
Marek A. Abramowicz, et al.

the last of which led to the paper that is the topic of this thread (thank you, Tim Thompson):

Eppur si muove (http://arxiv.org/PS_cache/arxiv/pdf/0812/0812.3972v1.pdf)
M. Chodorowski

This is a hot topic. I think this debate is a fine representation of some important elements of science: in addition to the intellectual exchange of supported ideas, on display (and largely stripped of the underlying complex maths) is one of our grandest models of nature and a discussion of how best to interpret it, which takes us to that question of the human mind which asks -- what is nature "really doing"?

Spaceman Spiff
2008-Dec-29, 04:30 PM
A very catchy title! But does Chodorowski think all the redshifts are doppler and so all the galaxies are moving through space?

No, that is not his position. See some of his previous papers on the topic that I linked to, above. You might want to have a look at the Francis et al. paper, which commented on both of these papers.

I look forward to seeing Chodorowski's next paper.

Tensor
2008-Dec-29, 11:55 PM
Thanks Tim (and Spaceman) for the references. Also for your references on QLG and QL Cosmology. I've used both posts to direct others to the papers.

Cougar
2008-Dec-30, 02:47 AM
No, that is not his position. See some of his previous papers on the topic that I linked to, above.

Ah, yes:



"The cosmological redshift can be thus thought of as a result of relative motions of the Fundamental Observers along the photon’s trajectory."

Cougar
2008-Dec-30, 03:07 AM
Ah, and then Abramowicz counters....



"In this paper we show that such interpretation is not possible." :hand:

(Well, he didn't include "the hand.") :)