The rotation of the halos is certainly taken into account in the hydrodynamical simulations Daniele mentions in the talk, and which his model is able to fit. So, to the extent that coherent rotation of the halos is a relevant effect it should be already taken into account in the modelling. There is no evidence that the entire observable universe has any net rotation.

@@CosmologyTalks Agreed! The universe, in my model, is in a non rotating but expanding shell configuration. But spiral galaxies are ACCRETION disks in coherently spinning DM halos. The DM halos continue to "pressure" the baryonic matter to the disk, spurring new star formation, on going into the future, until its disrupted by a merger event. Thats why spiral galaxies are so active!

The oscillations in the primordial hydrogen plasma that become what we see in the galaxy correlation function don't just "travel at the speed of sound" they quite literally are sound waves in this primordial plasma. The speed of sound is defined to be the speed they travel!

@ but the speed of sound varies with the medium. In water the speed of sound is 4 times that in air. Wouldn’t this too be medium dependent? Thx!

Ah, yeah, absolutely. When we say they travel "at the speed of sound" it is the speed of sound in the primordial hydrogen plasma, not e.g.the speed of sound in air, or water, on Earth. This will change over time as the universe expands and the relative contribution of radiation and matter changes (though not by much - see section 4 of iopscience.iop.org/article/10.1088/1742-6596/118/1/012007/pdf). It won't change over space because the early universe was so homogeneous.

When the CMB forms, and the universe becomes neutral, there are no sound waves anymore - so any evolution in "sound speed" from then onward isn't relevant. What we observe today and call BAO are the imprints of the waves that existed until that moment.

@@CosmologyTalks yes understood, but the speed the pressure waves moved at before that. Is that the speed of sound in air, or is that the speed of sound in a baryonic plasma, a speed i would imagine be quite different?

They do both magnify and demagnify. Paul shows a few plots in the talk where "delta m" (i.e. the change in magnitude) is both positive and negative (including the one I used in the thumbnail). I guess the phrase "weak lensing magnification" is supposed to imply both signs, demagnification is just "negative" magnification, in a sense.

@@CosmologyTalks Thanks!

If enough primordial blackholes of just the right mass existed we would have seen them via microlensing, for sure. For those mass ranges microlensing provides one of the best constraints on their existence. The very low mass ones described here by Ana and Valentin would be too small for that though, they would appear more like a fluid than as isolated masses.

@@CosmologyTalks thanks for that Shaun.

The oscillations in the primordial hydrogen plasma that become what we see in the galaxy correlation function don't just "travel at the speed of sound" they quite literally are sound waves in this primordial plasma. The speed of sound is defined to be the speed they travel!

They wouldn't experience time dilation themselves, it is us who see their clocks go more slowly. They would still have to correctly describe what we measure of course, but they would interpret that as due to our motion, not theirs.

@@CosmologyTalksThanks for your reply!! It seems the "time dilation" is strictly a manifestation of the redshift due to universal expansion. In their local frame there is no relativistic speed thus no special imprinting on the SNe to distinguish them from each other so i still fail to see how they would help calibrate the local Sen from each other!

Thanks for the nice words! :-)

@ it was amazing how harmoniously they supported, and clarified each other. Top notch both of them, as are your summaries of what they said. You’re lucky to have had them!

Hope you like it 🙂

😳 Thanks for the kind words.

Yeah, I'm inclined to agree that there are more natural dark matter candidates than primordial blackholes and that they can very naturally have masses that would mean they have not yet been observed (and might not without our lifetimes). Dark matter might even turn out to be many different particles, like the visible matter is. You probably saw that I did also push back on the claim that PBHs don't require any new physics. In my opinion, the inflation models that produce them are not the best motivated ones. However, there might be other ways that we're currently unaware of to produce these low mass ones, so the research is still interesting to me.

Thanks, yeah I've noticed that myself sometimes. I need to remember to boost the volume before uploading.

The most striking is 52±2 in 1990ApJ...365....1S An earlier work by the same team gave 50.3±4.3 (1976ApJ...210....7S) Differences between each of these and many current measurements around 70 are of very high significance if we accept both the central value and the uncertainty estimate (from Sandage & Tammann 1990 or even 1976). This should be explained! Perhaps some error source was underestimated, or the central value was biased?

The errorbars on the 100 side seem to have been more modest (10), e.g. 95±10 in 1982Obs...102..178D and 100±10 in 1979ApJ...233..433D This makes them less inconsistent with the current measurements (≈2 sigma is not extraordinary). P.S. I had some troubles posting these details, because KZbin doesn't seem to like ADS links for some reason, and Authors (YYYY) format is ambiguous for the papers in question.

KZbin can be weird about external links. It isn't even within my power to approve such comments, YT just hides them and doesn't even put them in the "review" tab. I *think* if someone posts a number of comments on a channel over time without the channel owner marking the comments as spam then eventually external links are allowed, but the process is very vague/unclear. That's a good question. I don't know what was wrong with the Sandage measurements and all review articles of the history just kind of imply that they became obsolete, without explaining why (e.g. this one arxiv.org/abs/2305.11950 is really good, but like most others just accepts that the Key Project won). I had a quick look through the literature, in particular Sandage's own papers to see if he ever explained what *he* thought was going wrong. I didn't find any explanation, but in his later papers (e.g. this one from 2006 ui.adsabs.harvard.edu/abs/2006ApJ...653..843S/abstract) he was claiming 62.3 +-1.3+-5 which would be consistent, within 2 sigma, with SH0ES. And this one from 2010 (ui.adsabs.harvard.edu/abs/2010ASSP...15..289T/abstract) has the following claim in the abstract "The basis of this value has been weakened because the period-luminosity relation of Cepheids is not universal, but depends on their metallicity and possibly other parameters.", which might be part of the reason? It is a bit scary how people could be so confident earlier on though with results that in 2024 appear to have been wrong, and one hopes that the community is not making similar mistakes (and even if astrophysics is the Hubble tension resolution that it is something newly understood not just under-estimations of things we already know of).

I realized after posting that these are NOT like supernovae and not bright enough to be seen individually at 13GLY so that is an unfair application. However in mid range (like cepheids) color is still a function of distance. Seems like spectroscopy makes them a "safer" standard candlr where cepheids don't need a "color check".

Yeah, as I'm sure you noticed, I did bring this up in the video as my naive thought was also that one would be better able to isolate the galaxies with spectroscopy. *My* thought was that it would be easier to isolate the carbon stars if one could see there was actually lots of carbon there. However their point that one can do this all empirically and just isolate the stars in the blue band of the figure in the thumbnail of this video and work with that population of stars defined in that way does seem persuasive to me. One doesn't need to understand the feature in order to use it, so long as one is confident it won't change with time. Your concern that the colour itself will redshift is true. I'm not sure by how much one expects the x-axis to shift though for the velocities that are relevant (as you point out in your clarification reply, we're only considering things ~10-50 Mpc away, not Giga Lightyears). The x-axis is called the "colour", but it isn't a measurement that is proportional to the wavelength/frequency of the light, it is the difference in measured magnitude between two photometric bands. So what is relevant is how much one expects the magnitude in each band to change when the light is redshifted, not how much one expects the wavelength of light to shift. I am very very far from an expert on this so I'll just have to speculate that this is small for the bands considered (if the luminosity as a function of wavelength in the wavelengths within the band is relatively constant this is indeed what I would expect because as some light is redshifted out of the band, other light is redshifted in). This stack exchange Q&A claims that the effect is indeed small (0.01 mag, which will bring very few galaxies in/out of the blue band): astronomy.stackexchange.com/questions/43581/hr-diagram-x-axis-color-and-redshift

@@CosmologyTalks Thanks for the thoughtful response. Abby did mention that because of JAGB brightness and abundance that they could be used much further out than cepheids which raised the concern over photometric versus spectral identification. The ability to make photometric narrow band filters with various transmission bands could be used to tease out these stars for galaxies beyond cepheid capabilities is intriguing. Best I could tell from other sources (en.wikipedia.org/wiki/Carbon_star), the carbon star "red" is due to blue absorption by the 3rd dredge up and not by distinctive (sharp in spectroscopy) emission spectra from the carbon thus spectroscopy might not be conclusive anyways? No need to answer, wonderful that this exciting new work is underway.

(caveat that this is all just my own understanding I'm not a niche-subject expert on this...) The three methods JAGB, cepheids and TRGB) aren't entirely independent as they all need to use the same supernovae and the same local geometric calibrator. They do, however, more or less independently provide the link between those two distances. The JAGB method is to take the mode (i.e. peak value) of the histogram of the luminosities of the galaxies in the blue band of this video's thumbnail. This absolute luminosity shouldn't change over time, so the actual measured luminosity will get brighter/dimmer as a galaxy gets closer/father away, thus it provides a distance indicator (calibrated on a nearby galaxy where we know from geometric means how close it is). The cepheids and TRGB methods use different stars and features in the colour-magnitude diagram and so are independent methods to go from geometric distances to SN distances. CCHP can isolate stars within that blue band in any galaxy and, as far as I understand, the amount the x-axis value it should redshift is negligible over the distances being considered so they use the same band in all galaxies. The mode makes sense to me as the best measure because both median and mean will be affected by stars in the tails of the distribution, whereas the mode will not. It might have a larger scatter than median/mode but will be less likely to be biased. Re: your aside, yes I replied to your comment in the other video saying I brought this up 😅

I have to start with a pedantic comment, but it is important so we make sure we're taking about the same things. H0 can't depend on redshift, no matter what new physics there might be. This is because its definition is "the value of the Hubble parameter at z=0". Note, the Hubble parameter itself does depend on redshift, in every model, and this is taken into account when people quote an "H0" value by looking at objects not at z=0. But I think what you mean by "H0 is not a constant but depends on redshift" is "the value we would infer for H0, by studying objects at a specific redshift and assuming ΛCDM, might depend on that redshift" (correct me if I'm wrong). This is true, and important to note, yeah. In fact, if the Hubble tension is not due to astrophysics, then almost certainly the value we get for H0 when we assume ΛCDM *will* depend on the redshift we observe at, because we're evolving it to z=0 with the wrong model. The problem is that it is really hard to get a model that can fix this without breaking other observations. You mention that 10, or even 42, galaxies aren't enough to see how things change with redshift. That's true, but a few things should be clarified. The 10, or 42, galaxies are all *very* close to us. So close that we don't expect them to be moving with the Hubble flow. These are just the galaxies where supernovae have gone off close enough that we can calibrate the supernovae to things like cepheids, TRGB and JAGB. The full SN data sets then used from Pantheon+ and the Carnegie Supernva Program to measure the expansion rate in the Hubble flow have many more SN and extend much further away (100s in CSP and 1000s in Pantheon+). So the redshift dependence of the Hubble parameter itself can be more accurately mapped out than one could with just 42 SN. In fact, this is the problem, and why it is so hard to fix the Hubble tension with some modification of the universe's expansion history. The data is too good and too constraining, rather than not informative enough. The even bigger problem comes from when supernovae are calibrated via the BAO. The recent Dark Energy Survey catalogue of around 1800 supernovae is the most constraining here. If one calibrates the DES SN via the BAO scale, and then look at the DES SN near z=0, the measured expansion rate is very tightly constrained to be close to the ~67 CMB value (+- 1, or even less). The number of supernovae involved make it very hard to fix the Hubble tension with anything cosmological between the redshifts where BAO are measured and z=0, so it requires something happening before the BAO observations in order to modify the BAO scale itself (or something wrong in the supernova calibration due to astrophysics, but if SN calibration is going wrong then the Hubble tension evaporates too). (see the recent Cosmology Talk on this: kzbin.info/www/bejne/oau3YaeNjMyaiNE) The DES SN+BAO inverse distance ladder is so constraining though that there *would* be enough statistical power to break the SN into redshift bins and ask "what H0 value do we infer from SN in this redshift range" (as you suggest). I'm unaware of anyone having done that, but it would be cool to see, yeah! (the dataset itself is very new - maybe someone is doing it already?)

I thought I recognised your username so I looked through past comments and see now that you commented on the inverse distance ladder video I linked above, so you've obviously already watched it! As you pointed out in that comment, the highly constraining nature of the inverse distance ladder does assume the FLRW metric (i.e. homogeneity and isotropy). So, if homogeneity and/or isotropy was sufficiently violated that we need to go beyond that metric then that might be a path to resolve the Hubble tension without astrophysics, yes! Given how constraining the CMB is in the early universe and the inverse distance ladder is in the late universe I might even go as far as to say that beyond FLRW is one of the most compelling directions to look in. Calculating anything without assuming the FLRW metric is notoriously difficult though, and no numerical relativity codes have shown (in my opinion) a convincing need to go beyond FLRW in a statistically isotropic universe. But neither has anyone (in my opinion) conclusively proven that we definitely don't need to either. People are actively looking into this, but, yeah, it is notoriously difficult to calculate beyond FLRW so progress is slower than progress within FLRW.

​@@CosmologyTalks Yeah, when I mean by "H0 might vary by redshift" in the original comment is that "the value we would infer for H0, by studying objects at a specific redshift and assuming ΛCDM, might depend on that redshift".

@@CosmologyTalks I also commented on the Jenny Wagner talk on the case against the cosmological principle about an year ago, asking her about alternative metrics to FLRW. The first time I took seriously the idea of moving beyond FLRW for a solution to the Hubble tension was when it was mentioned as an option in section VII.H in the Snowmass 2021 paper titled "Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies". At the time it was more appealing to me than many of the more mainstream approaches like early dark energy which tried to resolve the Hubble tension but was running into problems with the S8 tension, and moving beyond FLRW would at the same time also potentially resolve the various cosmic dipole anomalies discussed in section VIII.F of the Snowmass paper.

Thanks! Yeah, the SH0ES paper came out after recording, though not before I published the video - I actually re-recorded my intro after noticing that SH0ES had their own JAGB paper earlier this year. It is hard as a bystander, absolutely - things are so nuanced! Hopefully the data eventually makes it very clear what the local Hubble value actually is. There have been various re-analyses of each other's data over the years - and as far as I understand, the SH0ES paper from yesterday didn't take issue with the measured values of any of the three CCHP+JWST results. Instead (again as far as they understand) they claim it is what is expected! Their claim appears to be that these analyses use a subset of the full set of local galaxies with supernovae, and this particular subset has a random scatter which, even with old HST data, pushes H0 down in all three methods. With JWST measurements in other galaxies they say one gets larger H0 values and the full combined H0 of all data in all three methods favours an H0 in tension with LCDM+CMB. (I think CCHP would argue that this subset actually contains the most trustworthy galaxies and the deviation between this sample and the full one might be systematic not random scatter.) So, essentially, the claim is that this result is correct, but within an accepted range of statistical fluctuations if H0 actually was ~72-73-ish. They do also claim that the combined H0 value in the CCHP "status report" doesn't take into account that the three methods use the same supernova data (and thus aren't independent of each other). So, even if SH0ES take the individual measurements at face value and aren't surprised, they do challenge the combination of the data. I thought I asked Wendy and Barry about this in the video last week and they said they did take that covariance into account, but perhaps my question wasn't clear, or perhaps SH0ES are wrong and CCHP did combine the data sets correctly.

Naively, yes. However, SH0ES had a paper out yesterday essentially claiming that these results are expected, given what we know from HST data about the galaxies used (and the supernovae within them): arxiv.org/abs/2408.11770 If I understand correctly, the SH0ES claim is that these lower values of H0 are expected because these galaxies/supernovae already gave lower H0 values with HST data, and therefore a full analysis of all galaxies with local supernovae, using JWST, will still give a large H0 in all three methods (and they do have their own JWST measurements in some other galaxies to back this up). SH0ES claim that the CCHP measurements are correct, but not unexpected within statistical fluctuations. I *think* (though I may be wrong) that CCHP would claim that the galaxies they used are the most trustworthy ones and that the different H0 values in these ones vs other ones might therefore be more to do with systematics. (It is a bit weird to me that CCHP and SH0ES seem to be choosing to point JWST at galaxies that will give low/high H0 values respectively. Telescope time is expensive so they do need to pick and choose which to look at, but why these specific subsets?) So, honestly, I don't know how one should update one's belief about whether the tension is/isn't caused by astrophysical systematics. On balance, I've probably updated my belief that the resolution comes from new fundamental physics marginally downwards. However my belief was already quite low because of how hard it is to come up with believable models that *can* fix it, without breaking anything else (vs the chances of their being some unknown thing, or even things, happening in galaxies and/or supernovae).

Thanks for both the positive and critical feedback, both are valuable! And yep, that's the correct spelling of my name 🙂. I had similar thoughts while editing. We probably should have had that plot, with the posterior probabilities for H0 from each method, presented within the first few minutes, so viewers know what the details are then building back towards (like we did with the DESI talk). Otherwise all we have is the vague claim of "not seeing extraordinary evidence", without it being clear what that precisely means until much later. Yeah, the table probably isn't something one should show to undergraduate students if encouraging them to quote the "right" number of significant figures 😅 - "you marked me down, but even Freedman et al. did it!" The table being on the screen for long was a bit of an accident, I think. My hunch is that Wendy only intended to show it for 10 seconds or so to briefly comment on, and then to spend most of the time talking about the figures. Unfortunately, I didn't wait with my questions and then we had a long-ish discussion before Wendy had introduced the figure. I couldn't jump ahead with the slides before the figure was introduced because it would be a distraction. Maybe I should have moved to fullscreen speakers though instead?

I gave you a shout out in the JAGB talk when they quoted their H0 values again (i.e. mentioning your observation about the number of significant figures in the reported values 😅).

While watching the talk, I also remembered the more recent claim by the SH0ES team that crowding can not explain the Hubble tension based on JWST data (arXiv:2401.04773). But towards the end (1:03:27) Wendy says that the furthest galaxy they checked was only ~40 Mpc away, and the crowding may still be a significant problem at larger distances. And this counter-argument actually applies to the 2024 paper (I checked the list of target galaxies). That might be a little unclear from the video, because only Adam Riess's talk from 2020 was mentioned specifically by Shaun, and it couldn't have relied on JWST observations.

At school we did indeed have a rule to leave one significant figure in the uncertainty. However, there was an exception: leave two if the first digit is 1 (I guess because rounding is particularly crude then). In scientific materials, two significant figures in the uncertainties seem more common overall. Maybe three significant figures in the table arise from the combination of these two considerations.

Also, I remember some of the SH0ES people arguing that the TRGB detection in a color-magnitude diagram is not so clean and definite as Wendy and Barry claim, there are allegedly arbitrary choices affecting the results. IIRC, the slope of the boundary is not understood too well, and/or it is often blurred so that one can draw a sharp line in different ways. In a few papers (e.g. arXiv:2304.06693 or arXiv:1908.00993) they used TRGB as the middle rung of the distance ladder and get values consistent with Cepheids. On the other hand, even the later work seems pre-JWST. Moreover, I haven't seen/heard such objections regarding JAGB yet.

Wow, I bet there are some cool stories from those days. It must be wonderful for Wendy and Barry to look back on those days and think about how far things have come.

@@CosmologyTalks I think you remove the brackets and question mark 🙂 . Actually, much of Wendy's own thesis work involved photographic plates, but it was Bob McLaren's lab which introduced Wendy and Barry and several other faculty and students to the infrared for observing Cepheids. The development of large low-noise CCDs for the HST came just as Wendy finished her thesis, and "the rest is history"...

Brackets and question mark removed! 😁

Indeed! I expect SH0ES still disagree though and Wendy does also say later in the video that their results are at least consistent with there being a tension. So this is far from a smoking gun that there is no new physics and something is definitely wrong with our understanding of cepheids. We'll all have to wait and see where the *dust* eventually settles.

You are right that if there is time dilation this would also necessitate redshift. However, within known physics, there is no reason why a static universe would have time dilation of the magnitude observed here. Even if one postulated some new physics that caused the time dilation, we would then have a very unstable universe that would either start to expand or collapse due to known gravity. With expansion, one gets both time dilation and redshift immediately.

@@CosmologyTalks thank you for not ridiculing me. By the way, the expansion rate following physics as today, requires vast amount of dark energy. I think scientific community could do their exercise, and try to build a model around an unexplained cosmological time dilation, and check the compatibility with all effects as we observe today.

No worries, you've been very polite so I see no reason to not be polite in return :-) The precise expansion rate does require dark energy, which is indeed difficult to fit into fundamental physics models, but that is different to expansion itself. If the observable universe wasn't expanding or contracting, it would be unstable and would soon do one or the other, depending on its overall density compared to its surroundings. Therefore any model that posited a new time dilation effect to replace redshift wouldneed to explain what that effect is, but then would also have to fix the unstable universe problem of a universe that *isn't* expanding (i.e. it is harder to have a universe not expand than it is to have it expand). This specific video was about time dilation, but the most statistically powerful evidence of an expanding universe is still the temperature and polarisation anisotropies in the cosmic microwave background (CMB). If the universe is expanding, then in the past it was much hotter, which means that the neutral hydrogen in the universe would once have been ionised. At that time there would be a hydrogen plasma and any fluctuations in the plasma's density would act like sound waves. Running the clock forwards, at some point that plasma cools enough that neutral hydrogen forms. At that point of time the universe becomes transparent and the light emitted streams more or less freely until we see it today as microwave radiation. However, if that radiation came from a primordial hydrogen plasma it should have fluctuations in its temperature and polarisation that look like they came from the sound waves in the plasma. They do look just like that (you can see all the harmonics of the wave). Any alternative model would need to explain where the CMB came from and why it looks like so much like it came from a primordial hydrogen plasma. It is interesting to speculate on alternative theories, but at some point the accumulated weight of evidence pointing towards one model becomes so overwhelming that it isn't worth the time to look for alternatives anymore, there are just too many hoops it would need to jump through compared to the original model. The expansion of the universe is in that state (there is more than *just* time dilation, redshift and the CMB), but the ΛCDM model (especially the dark energy part of it) certainly isn't, which is why cosmologists consider all sorts of alternatives to it.

@@CosmologyTalks nice! When I say to do their exercise, I mean to find alternative explanation to CMB origin. Necessity of a parameter as dark energy , and short age universe are according to my understanding big problems. Do not need to spend more time with me 😇. I know very well that time dilation as carefully analysed for 1500 supernovae, is absolutely compatible with current model. Again thank you!

@@CosmologyTalks 1965, one year after my birth, Hoyle accepted that he was wrong... I have to go back and see the discussions during this period..

Yeah, I think that's true. Within general relativity the gravitational redshift on light from distant galaxies would be negligible though, and wouldn't increase with distance. Even outside of general relativity, to have a gravitational redshift increase with distance would require us to be at the centre of a peak in the gravitational potential (an enormous under-density the size of the observable universe). No other galaxy would therefore see redshift in *every* direction of the sky. For example, if they look at the direction of our galaxy the light would be blueshifted. We actually know this isn't the case because we see the CMB scattered of distant galaxies (via the kSZ effect) and it was redshifted there too. This would also be very unstable and would immediately *start* expanding due to the same gravitational gradient causing the redshift.

Or at least (if not the same), it possibly shares similar nature, and does not necesserily signify any expansion. I am usually bullied when I Express this view.

​@@CosmologyTalksI am convinced that cosmological time dilation is a separate effect, which is not gravity, but is the cause if cosmological red shift. Not the other way round. It is not necessary to correlate it with any expansion.

It might have been, I don't remember. It certainly seems like it when watching it back now, 12 months later. I'm surprised nobody mentioned it for 12 months though and now two people have within a few weeks of each other. It could also just be that I had too much caffeine before recording and spoke too fast?

I wouldn't quite frame it as the dark walls "solving" either dark matter or dark energy. Instead, they would be evidence of the existence of a "dark sector". By "dark sector" I mean some collection of fields that exist but don't interact much with the visible fields. There are well motivated models of dark sectors where their interaction strength with the visible fields is stronger in low density (i.e. vacuum) environments. These are the ones that would have domain walls that get trapped in an experiment like this. The detected dark sector itself could be either dark matter, dark energy, or something entirely different, depending on its density and pressure.

@@CosmologyTalks ohh i see, very interesting, i hope they can put forward this research as soon as posible, maybe they can find an "axionic" filed or something like that, thank you for your answer 🤙

It is quite fast, isn't it. Oops, ah well. Some of the more recent talks might be at a better pace?

If it's too fast or slow, you can adjust the speed yourself, as workaround -- that's the best thing when watching video recordings, at least in my opinion.

Yeah, that's true!

I don't know if it is independently measurable with high confidence, but they certainly do correct for it when analysing GW detection events and would get tensions with understood physics if they didn't.

Haha, yeah. Congrats on your piece of history! 😁

Glad you like them!

Very exciting!