3 ms·

I can't speak to the technical nature of the work, as I don't work in the field, but the last-named author, likely the advisor, seems to be a respectable resear

I can't speak to the technical nature of the work, as I don't work in the field, but the last-named author, likely the advisor, seems to be a respectable researcher. > I have served on the committee of the International Society on General Relativity and Gravitation 2017-2022, and am a past President of the Australasian Society for General Relativity and Gravitation and a past President of the New Zealand Institute of Physics. I served 8 years on the editorial board of Classical and Quantum Gravity, 2012-2019. http://www2.phys.canterbury.ac.nz/~dlw24/ http://www2.phys.canterbury.ac.nz/~dlw24/ So while your criticism may well be justified, you make it sound like this is a fringe paper, which I don't think is the case. So instead of opening a meta discussion about what physics papers get posted & upvoted on HN and why (which is hardly novel), I'd be much more interested in how big the issues you're mentioning are and whether the results of the paper could be salvageable. I at least do think that Wiltshire's research is interesting and he has made good points[0] about the challenges of coarse-graining spacetime structures and where & why the underlying assumptions of LCDM might fail to hold. [0]: See e.g. the lecture notes on https://arxiv.org/abs/1311.3787 https://arxiv.org/abs/1311.3787

astro-cosmo-q 2y ago
I am certainly not suggesting anything negative about the character or reputation of the authors of the work. I think that work on alternatives to the accepted concordance cosmology model (LCDM) should definitely be explored, and David Wiltshire et al. should pursue this if they deem it promising. As an aside: You may not find this compelling, which is understandable, but I will note that the vast majority of cosmologists (very conservatively 95%) do not question the FLRW aspect of the cosmological concordance model (which is what the paper here does away with in the alternative timescape cosmology), even if they question other parts of it (i.e. by considering dynamical dark energy, neutrino interactions, etc.). I agree that timescape is an interesting idea, but it seems like only a few people have been working on it for over a decade now - unless you have a very (and I think unfairly) dim view of professional cosmologists, if there was a strong case to be made for the timescape model based in data, the greater community would have adopted it by now. Finally, and independent of the sociological points above, an answer to your question about specifics aside from the types of statistical/modeling issues of the type I mentioned above. Again this is not exactly my area and I have not done the analysis myself, so I will refrain from strong opinions. However, my immediate reaction to this is that it is easy to fit one particular dataset (in this case part of the Pantheon+ supernovae sample) with a more complicated model than LCDM, but often these types of models fail when other cosmological datasets are included. Considering such joint constraints with multiple datasets is not an “extra ask” of alternatives to LCDM - to be taken seriously any alternative model should hold up in a joint analysis of precision cosmological datasets (see, for example, the tests of a more seriously considered alternative model in the community, early dark energy [0]). These days, this is often the combination of Cosmic Microwave Background (CMB) Anisotropies, galaxy Baryon Acoustic Oscillations (BAO), and one of several supernovae samples - see e.g. [1] for a somewhat pedagogical overview. The failure to fit several datasets is a common issue e.g. with many MOND papers. In this case, the authors do not try to fit data to anything but a single (modified) supernovae dataset. I would expect that if they included a fit to CMB/BAO data, there would be trouble with the timescape model, as this is exactly what was found in an analysis of the timescape model in another state-of-the-art supernova dataset [2] - there the timescape model could not accommodate the supernova data when combined with CMB/BAO data [2]. [0] https://arxiv.org/abs/2302.09032 https://arxiv.org/abs/2302.09032 [1] https://arxiv.org/pdf/2007.08991 https://arxiv.org/pdf/2007.08991 [2] https://arxiv.org/pdf/2406.05048 https://arxiv.org/pdf/2406.05048
- codethief 2y ago
  Thanks for elaborating! > However, my immediate reaction to this is that it is easy to fit one particular dataset (in this case part of the Pantheon+ supernovae sample) with a more complicated model than LCDM, but often these types of models fail when other cosmological datasets are included. This is what I was afraid of. Thanks for the links, in particular for [2]!

astro-cosmo-q 2y ago

I am certainly not suggesting anything negative about the character or reputation of the authors of the work. I think that work on alternatives to the accepted concordance cosmology model (LCDM) should definitely be explored, and David Wiltshire et al. should pursue this if they deem it promising. As an aside: You may not find this compelling, which is understandable, but I will note that the vast majority of cosmologists (very conservatively 95%) do not question the FLRW aspect of the cosmological concordance model (which is what the paper here does away with in the alternative timescape cosmology), even if they question other parts of it (i.e. by considering dynamical dark energy, neutrino interactions, etc.). I agree that timescape is an interesting idea, but it seems like only a few people have been working on it for over a decade now - unless you have a very (and I think unfairly) dim view of professional cosmologists, if there was a strong case to be made for the timescape model based in data, the greater community would have adopted it by now. Finally, and independent of the sociological points above, an answer to your question about specifics aside from the types of statistical/modeling issues of the type I mentioned above. Again this is not exactly my area and I have not done the analysis myself, so I will refrain from strong opinions. However, my immediate reaction to this is that it is easy to fit one particular dataset (in this case part of the Pantheon+ supernovae sample) with a more complicated model than LCDM, but often these types of models fail when other cosmological datasets are included. Considering such joint constraints with multiple datasets is not an “extra ask” of alternatives to LCDM - to be taken seriously any alternative model should hold up in a joint analysis of precision cosmological datasets (see, for example, the tests of a more seriously considered alternative model in the community, early dark energy [0]). These days, this is often the combination of Cosmic Microwave Background (CMB) Anisotropies, galaxy Baryon Acoustic Oscillations (BAO), and one of several supernovae samples - see e.g. [1] for a somewhat pedagogical overview. The failure to fit several datasets is a common issue e.g. with many MOND papers. In this case, the authors do not try to fit data to anything but a single (modified) supernovae dataset. I would expect that if they included a fit to CMB/BAO data, there would be trouble with the timescape model, as this is exactly what was found in an analysis of the timescape model in another state-of-the-art supernova dataset [2] - there the timescape model could not accommodate the supernova data when combined with CMB/BAO data [2]. [0] https://arxiv.org/abs/2302.09032 https://arxiv.org/abs/2302.09032 [1] https://arxiv.org/pdf/2007.08991 https://arxiv.org/pdf/2007.08991 [2] https://arxiv.org/pdf/2406.05048 https://arxiv.org/pdf/2406.05048

codethief 2y ago
Thanks for elaborating! > However, my immediate reaction to this is that it is easy to fit one particular dataset (in this case part of the Pantheon+ supernovae sample) with a more complicated model than LCDM, but often these types of models fail when other cosmological datasets are included. This is what I was afraid of. Thanks for the links, in particular for [2]!