Webb telescope helps refine Hubble constant
phys.org98 points by pseudolus 6 days ago
98 points by pseudolus 6 days ago
I've always thought as a layman that the weakest link in all of this is our cosmic distance ladder, seems like the most likely place that errors would stack up and lead us to some wrong conclusions. So may places for things to go wrong, we make a lot of assumptions about type 1a supernovas actually being a constant brightness, dust obscuring our view of them, plus all of the assumptions we've made about even measuring the distance between the ones we've measured. And its not like cosmologists havent acknowledged this, but I think a lot of the hubble tension might be solved once we figure out how to measure these distances more accurately.
The error bars on those distances have been shrinking for decades. Slow steady progress.
... And for completeness, the shrinking actually made the tension worse.
Until now with a far better telescope able to significantly improve the sample size, that is.
Ugh, this is so frustrating. We know our current theories cannot be complete but the LHC has mostly just confirmed assumptions, and now this. Everything seems to well contained.
Which is exactly how systematic error would manifest
It would have to be a pretty robust error to survive 30 years of continuous study.
Or a common unchallenged assumption. Orthodox errors are always only obvious in hindsight
The various candles are not independent yardsticks, nor are they just assumed to be true. Wherever possible they are compared against each other. And there are people who spend entire careers debating how dust absorbs light in order to best compensate for such things.
If measurements point to some sort of incongruity, questioning the accuracy of one's ruler is a fools trap. Altering the rulers to remove incongruities results in a spiral of compromises, internal debates that don't result in progress. If one suspects that the rulers are wrong, the answer is to build a better ruler. Not to arbitrarily chop bits off until the difficult observations go away.
I totally agree, hope my comment didnt come off to the contrary. As a layman, I consume most of my information through popsci sources (though I try to go more for the Dr. Beckys than the meatless or sensational stuff), and its generally described as something that we just take for granted - "we just found the oldest galaxy ever observed, only a few hundred million years after the big bang - and its too bright and has way more 'metals' than expected" - but we measured that with redshift, which makes a bunch of assumptions that of course they cant talk about in every video, but we dont talk about anyone questioning them.
I have no doubt that there are great scientist spending their entire careers trying to improve these rulers and measurements, but I also know that there are great scientists spending their entire careers basing everything on the best rulers they have...
> Freedman's latest calculation, which incorporates data from both the Hubble Telescope and the James Webb Space Telescope, finds a value of 70.4 kilometers per second per megaparsec, plus or minus 3%.
> That brings her value into statistical agreement with recent measurements from the cosmic microwave background, which is 67.4, plus or minus 0.7%.
Does it? As a lay person who can do basic arithmetic, this seems incorrect? Maybe there is some rounding or truncation, since I didn't check the source paper, or maybe I don't understand how confidence intervals work.
`70.4 × 0.97 = 68.288` and `67.4 × 1.007 = 67.8718`
These numbers are certainly close, but to my naive interpretation, the ranges don't overlap?
> These numbers are certainly close, but to my naive interpretation, the ranges don't overlap?
As is typical, the tolerances given are sigma values for an assumed normal distribution, not the width of a uniform distribution. The disagreement is less than five sigma, so (in the domain of physics) the disagreement is not considered significant enough to be a high-confidence indicator of new physics.
This wins some kind of award for most useful information packed into two sentences on HN. This is exactly what I've been wondering since this came out.
This is a big source of confusion when it comes to errors. I think most people think intuitively in terms of a 'peak-to-peak' specification of errors, i.e. range of X means that all possible values are within that range. But that's not really how statisticians think, and they tend to think in terms of standard deviation. Even if you soften the 'intuitive' view to 95% confidence range, that's about a 6x difference in terms of what the number means (assuming, optimistically, a gaussian distribution).
It looks like "statistical agreement" is doing a lot of work in that statement.
Not really. You can calculate the statistical significance of the difference of these measurements, which I’ve done here: https://www.mycompiler.io/view/4LA310YXZHO
For a null hypothesis of “their differences are consistent with zero”, the p-value is 17%, equivalent to a 1.4 sigma difference. That’s pretty far from a reasonable rejection criterion for the null hypothesis. I think most people would agree that that means these measurements are plausibly consistent.
it is "c" divided by the age of Universe for pretty obvious reasons. Now we just have to precisely determine the age of the Universe :)
Nothing about this is obvious. The age of the universe is related to the integral over the inverse Hubble parameter. The age of the universe is founded by measuring the Hubble constant among other things, not the other way round.
Amazing timing considering that Atlantic article that made the rounds here yesterday https://www.theatlantic.com/science/archive/2025/05/adam-rie...
I can’t read the rest of the article, but is the JWT contradicting his conclusion?
His thinking is based on the assumption that the Hubble tension can't be reconciled with the standard model.
> "Using its infrared detectors, we can see through dust that has historically plagued accurate measurement of distances, and we can measure with much greater accuracy the brightnesses of stars," added co-author Barry Madore, of the Carnegie Institution for Science.
It's amazing just rich the electromagnetic spectrum is for analyzing the universe, from radio to X-rays, and how complementary the pictures are. Though we get visually pleasing pictures in the visible spectrum, most of the really intellectually pleasing stuff of the past century has been outside the visible range.
Having waited half my life to see Webb finally launch, it's amazing to see how much we're discovering through it. Seems like every other day there's another insight found.
Further away galaxies are receding faster. Light from further away galaxies is older. Does it therefore not follow that the expansion of the universe is slowing down?
I have a total n00b question. Why would this be a “constant”? Wouldn’t different galaxies and different matter in the universe expand at different rates, and be an acceleration/deceleration, where one observation is the derivative or velocity of that one entity being observed?
A natural follow-up to your question might be: "If everything is expanding, then wouldn't the ruler itself be expanding, so the expansion becomes unobservable?"
I'm not a physicist, but from my understanding, the situation is a bit more complicated than the phrasing in your question suggests.
Observation #1: The light from far-away galaxies is redshifted (spectral lines are a bit off from where we'd expect them to be). This suggests that these galaxies are moving away from us. The farther away the galaxy, the more it is redshifted. This suggests that the farther away the galaxy, the faster it is moving. Observations indicate that the recession speed is directly proportional to distance.
This observation is consistent with general relativity, which suggests an expanding universe with homogeneous mass.
But on a smaller scale, gravitational binding somehow takes over, and on even smaller scale, things like electromagnetic and nuclear interactions start having a greater impact, and that's why the Milky Way isn't itself expanding. For that matter, even Andromeda (0.8 Mpc) is too close to be affected by Hubble-style expansion, which only becomes observable at the multi-megaparsec scale.
Hubble found that the recessional velocity of a galaxy is proportional to its distance. The proportionality constant is called the Hubble constant.
It's a bit of a misnomer though, because it's only constant through space, not time. At the time of discovery it was assumed to be constant in time, too.
The irony of course being that Hubble's original data is, at least in modern scientific analysis, very well compatible with "no expansion". There is _a lot_ of community flavour involved in how we talk about measurement results
Thanks that makes sense. Strange why pop science articles don’t explain this critical point. I probably should have looked it up.
Dumb question: why did we need to see far-away galaxys moving away faster than near galaxies to conclude that the universe was expanding? Wouldn’t just the fact that everything is moving away from us lead to the same conclusion?
> why did we need to see far-away galaxys moving away faster than near galaxies to conclude that the universe was expanding? Wouldn’t just the fact that everything is moving away from us lead to the same conclusion?
Imagine inflating a balloon onto which you've painted dots. All the dots move apart. But the ones furthest apart move apart faster than those close together. This is how you know the dots aren't just moving in their local environment, the entire space is expanding (everywhere).
(If you want a 1D representation, move your fingers apart at a constant rate. Consider how much further apart your pinky and index finger are compared with your middle and ring finger. That wouldn't happen if you just make a Spock hand.)
If we see farther away galaxies moving away at the same speed as nearby galaxies that means that all the expansion of the universe happens between us and the nearby galaxies (since the farther away galaxies wouldn't be moving away from the nearby galaxies). So we would have some kind of local expansion of space around our galaxy. This is if we see a redshift in all directions, if we see a redshift in one direction and a blueshift in the opposite direction, that just means that our galaxy is moving relative to the observed galaxies (also, such a dipole can be seen in the microwave background).
That is not a fact; there are stars that are moving closer to us, and the Andromeda Galaxy is expected to "collide" with the Milky Way at some future point.
Webb was well worth the extended wait
This article is about another paper suggesting a resolution.
It is not an article about a resolution having been confirmed.
If you think scientific discoveries like this are important, _please_ contact your congressperson and indicate that you oppose the catastrophic cuts proposed to NASA astrophysics in the President's Budget Request: https://www.planetary.org/press-releases/the-planetary-socie...
I appreciate that, and science should be saved.
But the cuts go far beyond that, to things that are less showy but with more direct effects on the lives of people. Tens of thousands of jobs have been lost, with microscopic effects on the bottom line, but with myriad small effects on our parks, our roads, even national security.
Space is the "charismatic mega fauna" of the budget, but the whole "ecosystem" is ravaged. It must be saved, but take it as an indicator of just how much damage has been done. Spare a thought and a word for the NIH, the Fish and Wildlife Service, and the Social Security administrators whose jobs are not glamorous but nonetheless critical to people who depend on them.
Does astroscience not deserve a spokesperson? We aren’t allowed to be passionate about this if other things are “more important”?
Those issues have their cheerleaders, so I see no reason to start with “that’s good, BUT”.
I really hate this trend of pretending people are supposed to care about A more than B and that, more than C. Let people champion the things they’re passionate about. Everyone is already suffering from compassion fatigue.
> Spare a thought and a word for the NIH, the Fish and Wildlife Service, and the Social Security administrators
Not sure framing this in terms of sympathy for jobless bureaucrats is as effective as considering the impact on babies who will die of diseases in cancelled pipelines, ecosystems and fisheries that will collapse due to negligence or proud grandmas who will go hungry because SSA fucked up their cheques.
NASA did take a 25% budget cut. Through a combination of OMB and NASA decisions this led to a 50% cut in the entire sciences budget which went from $7.3b to $3.9b; however, the line item budgets for both Webb and Hubble are not touched and both are expected to operate at full planned capacity.
The rest of the cuts are around propulsion systems and mars science missions. The administration and some parts of NASA see the commercial segment becoming more developed and more capable and are hoping they will be able to fill the gap. This also accelerates the plan to retire the ISS and move to commercial orbital platforms.
Interestingly this budget does allocate $646 million more to exploration in 2025 than it did in 2024. Showing a shift in priorities from Earth based science missions to full manned missions returning to the Moon and eventually to Mars.
If your congressperson is Republican. Only their votes matter for the current budget.
There are alternatives to taxation. With enough attention and disposable income, citizens can privately fund amazing things. Like the polio vaccine was.
Alternatives: https://en.m.wikipedia.org/wiki/List_of_non-profit_space_age...
Regardless of what funding mechanism you would prefer in its place, turning off the existing system with no transition plan is a huge mistake.
You mean the polio vaccine distributed by the World Health Organization, and developed with the assistance of the New York Public Health Department?
The Jonas Salk research and development of the first polio vaccine that saved many lives is what I am referring to. See quote and article below.
>There was very little government funding for any kind of biomedical research. The polio research was privately funded through the March of Dimes,” explained Randy Juhl, Dean Emeritus and Distinguished Service Professor Emeritus in the School of Pharmacy.
https://www.pittwire.pitt.edu/pittwire/features-articles/ann...
The same March of Dimes that was founded by Franklin Delano Roosevelt when he was President? Technically the money didn't come from government coffers, but it's very silly (and incorrect) to suggest that the effort was independent of the government.
The problem is that this totally unmoves the layman, same as an incremental change in a metaphysical system would unmove the layman. Just one costs a lot more than the other.
> problem is that this totally unmoves the layman
Which is why we live in a republic. (And since the Industrial Revolution and Battle of Jena, one twinned to a technocratic administrative state.)
NASA like all old orgs are extremely inefficient and overwhelmingly waste money. The solution is to create new orgs not hindered by old people that do the least work for the most pay.
> NASA like all old orgs are extremely inefficient and overwhelmingly waste money
The U.S. government just got red teamed by an extremely adversarial auditor in DOGE. They weren’t able to find almost any fraud (outside the DoD, which they didn’t touch). They found maybe tens of billions of spending they didn’t like out of a budget of trillions.
Also, we’re on a start-up board. Are you seriously arguing that every start-up, or even the median start-up, is less wasteful than the median century-old company?
NASA inefficiency is driven from the top down, by terrible goals and perverse incentives, mainly inflicted on the agency by lawmakers, but also due to getting stuck in a local optimum. It's not bottom up waste and fraud.
> NASA inefficiency is driven from the top down, by terrible goals and perverse incentives
To the extent there is documented inefficiency at NASA, it's in the way it manages its contractors for manned exploration. Its science budget is a paragon of institutional efficiency.
> It's not bottom up waste and fraud
Read the GAO report [1]. (Ctrl + F Bechtel.)
But for sake of argument, let's assume this is true. How does cutting the science budget while preserving SLS make sense?
So where's private businesses space telescope, if they're so efficient?
Efficiency != profitability, though I don’t agree with him either. Not sure there’s much money to be made while searching the cosmos
Not in the short term and not directly for the company doing it. This is more of a reason for government funding though, not less.
I don't know whether it's some HN auto-"fixing" thing in this case, but the title is garbled. At present it ends "suggesting resolution rate debate" but the original title is "... suggesting resolution to long-standing expansion rate debate". There is no "resolution rate debate", whatever that might be. The claim is that new data might help resolve a debate about the expansion rate of the universe.
It wasn't the HN software, the submitter was just trying to fit the title into the character limit. I've edited it to just include the first part of the article's title, verbatim.