451–460 of 547 posts
Articles like these make me want to stop doing everything and isolate in the basement for several months to study physics. Then I realize I have a family to feed and elderly parents to take care for. Sigh, so many beautiful mysteries in the world, and only one life. edit: A friend told me germans have the word "Sehnsucht" to describe such a feeling. So I guess it might be somewhat universal.
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If MOND completely described observable phenomenon it would supplant dark matter, but it doesn't. MOND still requires dark matter, just less of it. Or, to quote Milgrom, "some standard matter in some form that has not been detected"[1]. Which, IMHO, is nearly isomorphic to DM as far as statements go. So until we figure out what the missing mass is, MOND is widely viewed as an unnecessary complication. There is missin…
Problem that I see with dark matter is that it is unfalsifiable. If you can have arbitrary amounts of dark matter in arbitrary positions - how can you falsify that?
The exact spatial DM distribution is not a parameter of the cosmological standard model. Instead, you assume an initial condition (pretty much a smooth distribution with only quantum fluctuations, which are parameterized by one or two parameters), apply the laws of physics to evolve this state some 14 billion years and compare the statistics of the theoretical and observed distribution.
In fact, DM suffers from the dwarf galaxy problem. Our theory predicts more than we observe. It's a bit of a challenge for DM, and considering how fuzzy our knowledge of galaxy formation is and how much other evidence for DM there is, it's not falsifying it yet. But if this is cemented by future observations it might very well be a blow to DM.
Besides, DM was hypothesized after measuring the famous rotation curves of galaxies. DM could have been easily falsified if we made gravitational lensing measurements afterwards and didn't see any DM. But we saw DM. Same thing with baryionic accoustic oscillations in the cosmic microwave background angular power spectrum. We looked there after we already thought that DM should be there, and the power spectrum looks just like if there is DM. It could have easily falsified DM, but didn't. The list goes on. DM could have been falsified may times, but passed almost all tests so far. Well, except for the ones in the lab, unfortunately.
Articles like these make me want to stop doing everything and isolate in the basement for several months to study physics. Then I realize I have a family to feed and elderly parents to take care for. Sigh, so many beautiful mysteries in the world, and only one life. edit: A friend told me germans have the word "Sehnsucht" to describe such a feeling. So I guess it might be somewhat universal.
Earlier quoted context omitted.
>cosmologists have consistently, over decades, insisted, in public, that they knew more than they did Exactly, and each time the theories are proven wrong, it's explained as a never-ending series of "oddities", yet the theories are never altered in any meaningful way other than ad-hoc additions to explain each "oddity". At some point there needs to be a reckoning that, for instance, the current theories of star forma…
This is exactly what pushed me away from pursuing cosmology. One of the most important 'discoveries' in cosmology was that of cosmic inflation [1]. The issue is that if you model the big bang, what it creates is nothing like what we see. Regions of space that wouldn't have had time to have become causally connected (nothing could have gotten between them even traveling at the speed of light since the time of the big…
That's just called science. What else do you propose? Give up because you didn't get it right the first time?
Earlier quoted context omitted.
If MOND completely described observable phenomenon it would supplant dark matter, but it doesn't. MOND still requires dark matter, just less of it. Or, to quote Milgrom, "some standard matter in some form that has not been detected"[1]. Which, IMHO, is nearly isomorphic to DM as far as statements go. So until we figure out what the missing mass is, MOND is widely viewed as an unnecessary complication. There is missin…
The explanatory power of dark matter is so weak though. With the right clumping of LCDM you could probably also explain various reports of poltergeists around the world. Then you could claim that reports of poltergeists are evidence of LCDM over MOND because it's another phenomenon that MOND can't explain.
The distribution of dark matter being uneven is evidence that something functioning like dark matter has to exist as MOND doesn't easily replicate that. Colliding galaxy clusters show a distribution of matter that differs from the distribution of visible matter, so the simplest explanation is that there is invisible matter that reacts gravitationally.
Sorry for an likely ignorant question, but can someone ELI5 why we are confident that evereything in universe is less than 13 billion years old or whatnot, and not just redshifted beyond recognition?
Not only that, but the CMB's properties, like its frequency spectrum or its tiny anisotropies match what you would expect to an astonishing degree.
Articles like these make me want to stop doing everything and isolate in the basement for several months to study physics. Then I realize I have a family to feed and elderly parents to take care for. Sigh, so many beautiful mysteries in the world, and only one life. edit: A friend told me germans have the word "Sehnsucht" to describe such a feeling. So I guess it might be somewhat universal.
Now I'm convinced we can understand really fundamental things about our reality, and that is so so interesting.
I'm dreaming of going back, getting a math master's, then a physics PhD ... Maybe
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Any straight line you draw from earth to any direction in the sky will then reach a star.
Which is insanely far away and all light coming from there will have diminished in energy enough to be barely visible? Inadequate explanation. Even if the universe was a closed box with perfectly reflecting borders, what you would actually see in the sky is something like an average brightness of the entire universe with some fluctuations.
This was predicted by astronomer Stacy McGaugh on his super interesting blog as a natural consequence of modified Newtonian dynamics ( https://tritonstation.com/2022/01/03/what-jwst-will-see/ ). McGaugh came to support MOND over dark matter reluctantly for just such reasons—MOND routinely predicts things in advance that dark matter struggles to justify ex post facto, usually by adding additional moving parts to the m…
I've been out of the loop for a while. Can MOND satisfactorily explain gravitational lensing?
"Yan found 87 distant galaxies behind the galaxy cluster SMACS 0723" --> this is not true. They found 87 galaxy candidates. To be fair to the article, they do note that these await spectroscopic confirmation but experts only believe those with spectroscopic confirmation. Everything else is tentative and we don't yet have good numbers on confirmation rates. Finally, the Yan et al candidates are wildly inconsistent with almost every other estimate of high-redshift galaxy samples. You can see a comparison in Table 4 here: https://arxiv.org/pdf/2212.06683.pdf. They claim more than double the number of high-redshift sources compared to everyone else. JWST data is still very new and hard to both reduce and analyze. One particular problem is correlated hot pixels which can appear as very high-redshift sources. I don't know if this impacts the Yan et al paper but just an example of something that is not 100% straightforward to deal with. I highly recommend people take this with a healthy amount of skepticism until everything has a spectrum.