I'm likely misinterpreting the article, but it seems to frame things in a way that first assumes expansion should be constant and it's a question of what the right constant value is between the measured/theoretical discrepancies.
(*yeesh, editing all those spelling errors from typing on my phone)
This tells us that either our model of the universe is wrong (therefore the cosmic microwave background method is giving us an incorrect answer) or that something is wrong with how we're calculating the distances along the cosmic distance ladder. The latter was originally the assumption that should be proven true with more and better data from newer telescopes. This is now turning out not to be the case: our cosmic distance ladder calculations seem to have been very good, so it now seems more likely that our model of the universe is wrong.
It also sound like progress that we seem to have 2 “scales” to play with to try to develop a consistently measurable distance.
I personally wouldn't trust the CMB calculation at all until the dark matter issue is resolved.
There is an equivalent boatload of evidence for modified gravity that can't be explained by particle dark matter [1], but one set of observations is hand waved away as a minor inconvenience while the other set is taken as definitive proof.
If gravity doesn't work the way we expect, then lensing in galaxy collisions isn't necessarily telling us what we think it is.
But setting that aside, if we take even the most naive modified gravity, MOND, then lensing does require a form of particle dark matter, like sterile neutrinos, but the total amount of dark matter required to explain the evidence is only double the amount of visible matter, rather than almost 10x the amount of visible matter as in LCDM. This has significant implications for calculating the Hubble constant from the CMB [2].
[1] https://tritonstation.com/2024/06/18/rotation-curves-still-f...
[2] TeVeS is wrong, but it shows that modified gravity significantly effects the H0 calculation, https://arxiv.org/abs/1204.6359
Whenever a scientist says that it's not possible that the model is wrong, then I just roll my eyes. Of course models can be wrong - and isn't that exciting? Good on them for making sure that there are no errors in the measurements - that's incredibly valuable and absolutely necessary - but I'm really excited to see creative models being thought up that are drastically different. My personal hell is the universe being consistent and boring.
But no one said that. Im fact, scientists are known to say things like: all models are wrong, but some are useful.
> That the three methods disagree “is not telling us about fundamental physics,” Freedman said. “That’s telling us there’s some systematic [error] in one or more of the distance methods.”
Freedman is saying that the model is not wrong.
To argue that the physics is wrong, you are likely to be arguing that very well tested theories like general relativity, special relativity or electromagnetism are off in some way. That's a much higher bar than just the measurements of either the ladder or CMB being wrong in some way.
It's easy to think up ways that your sensor could be 5-10% off. It's very difficult to come up with an entirely new theory of gravity that explains everything we observe about the world, but also makes gravity a few percent weaker in this one case.
You shouldn't really roll your eyes at that. They're ultimately doing all the work which will prove it right or wrong. They might wind up not liking the answer they get, but the conviction is necessary to get them there because human emotions are weird.
Conversely, the hypothesis that LambdaCDM is wrong does nothing to explain why the distance ladder methods disagree.
She clearly isn't saying that any model is infallible, she's just saying that clear flaws with one set of models throw into question some specific accusations that a different model is wrong.
You actually need to pay attention to the details; the physicists certainly are. Glib contrarianism isn't very useful here.
I'm sure scientists have to deal with people jumping on them about their model being wrong, but this part is clearly exaggeration.
I no longer engage with these people for sport, but about 15-10 years ago I had two scientific creationists that I kept around as virtual pets. one was Hindu and one was from the religion of peace. neither was very stable and both were prone to getting a bit emotional about it.
each time, they would pick one piece of settled science, but they didn't have the mathematical machinery to understand the model itself, so they would rely on the layman cartoon versions and misunderstand something crucial there. for example, the existence of error bars on the concordance plot of radioactive dating. from this they could throw doubt on the whole chronology of the formation of the solar system and the evolution of man. for one of them, a technological civilisation from Hindu mythology existed millions of years ago. for the other, their very peaceful god created everything personally in one go, and evolution by natural selection didn't happen.
It's exciting to see how the question drives many new discoveries.
[1] https://en.wikipedia.org/wiki/Great_Attractor
I'll try to paraphrase what it meant: measuring H0 comes down to measuring the relative velocity of galaxies around us. The great attractor was a relatively recent discovery that the "closer" galaxies, the ones we can use in the distance ladder, all have a common component in their velocities which we've recently begun to understand better.
Not according to at least one research group described in the article: the Freedman group, which is only getting the higher answer using Cepheids, but gets a lower answer, one consistent with the CMBR calculations, by two other methods. Which raises the possibility that it's the Cepheid part of the cosmic distance ladder that's the problem.
Perhaps we need some outside groups to take a look at this to see if either group is making systematic errors in their analyses.
I agree this would be a good thing.
https://youtube.com/playlist?list=PLnU8XK0C8oTDaiwe8Us_YNl4K...
He also has an alternative theory for stellar physics that might call into question the interpretation of Cepheids and SNs, tho I don't think he's done a major analysis there, at least afaik
Anyone with an ounce of sense should have concluded that LCDM was wrong long ago. Hopefully this will finally cause physicists to actually try something different.
Now the Euclid satellite has been launched, which I remember being the big hope that it will give us data that will finally enable us to tell which LCDM alternative could replace LCDM as the standard model of cosmology. You won't even get funding for such a mission unless you make a case for how it can improve our understanding of the universe. "We hope it will confirm our currently accepted view" will not get you one cent.
So I'm not sure where you get the confidence that nothing different is being tried and that professional scientists wouldn't have an ounce of sense. I find it a bit disrespectful actually.
I invite you to read the introduction (and introduction of part 1) of this review paper of the science behind the Euclid mission: https://arxiv.org/abs/1606.00180
It's understandable to laymen, co-authored by reputable, leading scientists in the field (disclaimer: I'm on the author list) and I hope that after reading it you would revise your opinion.
Here is a short excerpt:
> The simplest explanation, Einstein’s famous cosmological constant, is still currently acceptable from the observational point of view, but is not the only one, nor necessarily the most satisfying, as we will argue.
I think you mean, "nothing could be made to fit the data as well as LCDM". See below.
> When new data came in, and it pointed yet again at LCDM, it was considered a disappointment.
This is highly revisionist, and exemplifies the kind of cherry picking that has kept LCDM alive when it has outright failed numerous predictions and had to be adjusted after the fact to fit the data:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331
LCDM is a complete mixed bag when it comes to predictions, where MOND has a very slight edge. It's absolutely clear that MOND is not correct or complete either, but it is undeniable that it has had greater predictive success than anyone anticipated and with far fewer free parameters than LCDM, mostly in areas where LCDM is weak. If LCDM can't explain why MOND has been so successful, which it currently cannot, then it is incomplete at best.
Basically, the only good, almost definitive, evidence for particle dark matter is gravitational lensing, but if we're considering modified gravity anyway, then lensing isn't necessarily telling us what we think.
On the flip side, no possible cold dark matter halo is compatible with recent observations that rotation curves are flat past a million light years [1]. I can't wait to see what epicycles they add to LCDM to save it this time.
[1] https://tritonstation.com/2024/06/18/rotation-curves-still-f...
> So I'm not sure where you get the confidence that nothing different is being tried and that professional scientists wouldn't have an ounce of sense. I find it a bit disrespectful actually.
Try talking to a MOND proponent and you'll get a very different picture of how open scientists are to alternate approaches and questioning LCDM.
See https://en.wikipedia.org/wiki/Cosmological_principle
Basically, if this weren't to hold true, a lot of astronomy would fall over, even physics.
Most people don't realize that science—and even everything in life—has to start from some axioms/assumptions, just like math. I first realized this fact when I was reading the Relativity book written by Einstein himself, who challenges the assumptions in classical physics.
As time goes, some of the assumptions could be proved to be unnecessary or even wrong. There must be still some assumptions left, though—because without them, we can't talk about science, or anything, really.
> A group of researchers argued in 2021 that observations of the Hubble tension may imply that only quintessence models with a nonzero coupling constant are viable.
It doesn't.
"The simplest explanation for dark energy is that it is an intrinsic, fundamental energy of space" [1]. That's the cosmological constant.
Dark energy is a thing because we don't assume that to be the case. Irrespective of your dark energy model, however, there will be a predicted global average.
Briefly, recent large scale maps of the universe suggest that the universe might not be as uniform as we thought it was. In particular we appear to be in a large region (something like a couple billion light years across) of low density.
Dark energy is needed to make the solution to Einstein's field equations for the whole universe match observations. However that solution was derived based on a universe with matter distributed uniformly. At the time it was first derived that appeared to be the case--we thought the Milky Way was the whole universe.
When we learned that the Milky Way was just a small galaxy in a vastly larger universe than had thought we were in and that there were bazillions of other galaxies, those galaxies appeared to be distributed uniformly enough the the solution to the field equations still worked.
Later we found that there is some large scale structure in the distribution of galaxies, like superclusters, but those seemed uniform enough throughout the universe that things still worked.
If that couple of billion light year low density region turns out to exist (large scale mapping of the universe is hard enough that it may just be observational error) the universe may not actually be uniform enough to for the field equations based on uniform matter distribution to actually work.
Some researchers worked out the solutions to the field equations for a universe that has such large low density bubbles big enough to invalidate the uniform universe solution, and found that such a universe would have an expansion force without the need to invoke any kind of dark energy.
There was a recent PBS Space Time episode that covered this: "Can The Crisis in Cosmology be SOLVED With Cosmic Voids" [1]. The above is my summary of what I remember from that. See the episode for a better explanation and references to the research.