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The Webb Telescope further deepens the Hubble tension controversy in cosmology

340 points by nsoonhui 2y ago

parkaboy 2y ago
Naive question: why should the expansion rate need to be uniform or constant everywhere? 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)
- BossingAround 2y ago
  That's the first thing that occurred to me too. It could also not be constant even at the same place, i.e. could it not be speeding up and slowing down as the universe expands?
- isolli 2y ago
  Indeed. Some researchers have proposed quintessence, a time-varying form of dark energy [0]. > 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. [0] https://en.wikipedia.org/wiki/Quintessence_(physics) https://en.wikipedia.org/wiki/Quintessence_(physics)
- itishappy 2y ago
  It's not constant (the early universe inflated quite quickly), and it doesn't need to be uniform, but it sure does appear to be. We measure it via redshift, pulsar timing arrays, and the temperature fluctuations of the CMB, and it looks pretty much the same in all directions.
- AnimalMuppet 2y ago
  The issue here is that it's not constant depending on the type of star we use to measure it. It's not a discrepancy in location in space. Or at least that's how I read the article.
- chongli 2y ago
  The controversy is that we get 2 different numbers depending on which method (cosmic microwave background vs cosmic distance ladder) we use to calculate the present rate of expansion. These numbers used to have their error bars overlapping, so we assumed they would eventually converge to the true value. But as we get more data the opposite is happening: the numbers are diverging and their error bars are shrinking such that they no longer overlap. 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.
  - detourdog 2y ago
    Thank you for this explanation. I would like to emphasize that our model being wrong and not our numbers sounds like progress. It also sound like progress that we seem to have 2 “scales” to play with to try to develop a consistently measurable distance.
  - api 2y ago
    Distance ladder seems much more error prone than the CMB.
    - artemonster 2y ago
      there is no "seems" with provable error bars
      - feoren 2y ago
        ehh ... everything we measure relies on our understanding of the universe in some way. It's perfectly reasonable that our distance measurements could rely on a shakier foundation of assumptions than our understanding of the CMB. I don't know enough to say one way or the other, but GP's comment is not unreasonable on its face. Whereas talking about "provable" in cosmology, and certainly in this case, does seem unreasonable -- especially with error bars, which by definition have a small chance of not including the real value. Normally I'd say that we can generally refine our assumptions to be extremely good, and just take more measurements, and keep narrowing that error bar, until we hit a level of certainty that anyone reasonable would call "proven", but the entire point of TFA is that this isn't happening in this case. We seem on our way to "proving" two inconsistent things.
- JumpCrisscross 2y ago
  > what should the expansion rate need the be uniform or constant everywhere? 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. [1] https://en.wikipedia.org/wiki/Dark_energy https://en.wikipedia.org/wiki/Dark_energy
  - tzs 2y ago
    There has been some interesting recent work that may get rid of the need for dark energy. 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. [1] https://www.youtube.com/watch?v=WWqmccgf78w https://www.youtube.com/watch?v=WWqmccgf78w
- xhkkffbf 2y ago
  Certainly when I look at convection currents in the ocean or the atmosphere, I see plenty of variation. Shoot, the earth's atmosphere constantly produces moving blobs of relatively high and low pressure.
- diob 2y ago
  So a lot of astronomy is based on the principle that we are not in a special pocket of the universe. See https://en.wikipedia.org/wiki/Cosmological_principle https://en.wikipedia.org/wiki/Cosmological_principle Basically, if this weren't to hold true, a lot of astronomy would fall over, even physics.
  - XorNot 2y ago
    Though it is worth noting if this were the case you would expect to see boundaries: if the laws of physics change due to spatial position, the discontinuity should produce an effect of some sort where matter and light transitions between regions.
    - mcswell 2y ago
      I suppose there could be a gradual change over distance, i.e. the first derivative of this change never varies.
  - deleted 2y ago
    [deleted]
  - hindsightbias 2y ago
    Sophon is amused: https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology) https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology)
  - eikenberry 2y ago
    Seems there are 2 ideas at odds. One is that the universe is infinite, in which case this is all localized and has no bearing on the universe outside of our small observable region. The other is that we are seeing enough of a bounded universe where the observations we make are of a significant enough chunk to make theories about it.
  - beltsazar 2y ago
    Yes, cosmological principle is probably the most fundamental assumption in astronomy. 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.
- photochemsyn 2y ago
  Spacetime is apparently extremely rigid as it supports the transmission of gravitational waves originating billions of light-years away, as detected by the LIGO experiments. This suggests smooth and gradual uniform expansion, at least spatially. Temporal variation (speeding up and slowing down uniformly at all points) might be possible but seems hard to explain.
- Jeff_Brown 2y ago
  Seems perfectly possible. General relativity, after all, was precisely the discovery that the curvature of space, well spacetime, is not uniform.
seanhunter 2y ago
Some cool background about the Hubble constant here, including a nice explanation involving blueberry muffins https://news.uchicago.edu/explainer/hubble-constant-explained https://news.uchicago.edu/explainer/hubble-constant-explaine...
- mcswell 2y ago
  I just finished off a blueberry bagel, the taste is still in my mouth. Maybe the universe is torus-shaped?
readthenotes1 2y ago
"This extrapolation predicts that the cosmos should currently be expanding at a rate of 67.4 km/s/Mpc, with an uncertainty that’s less than 1%." I can't measure my own weight with an uncertainty that's less than 1%. I wonder what these peeps are on...
- uncivilized 2y ago
  Their wallets are much bigger than yours.
  - readthenotes1 2y ago
    As is what they are trying to measure. I don't believe 1% measurement error in any universal element except perhaps the speed of light...
    - aidenn0 2y ago
      That's an absurd statement. For example, planck's constant is known to better than 1%, as is the mass of various particles. Heck, the Earth, which is sufficiently non-spherical for it to matter only differs in radius (between polar and equatorial) by 0.3%!
    - munchler 2y ago
      I suggest you take a look at this list of physical constants, paying special attention to the "uncertainty" column, and then get back to us on why you don't accept any of them except the speed of light. https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants
    - bloak 2y ago
      Here's a nice list: https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants G (the gravitational constant) is an interesting one: the value is only known to about 5 significant figures, but GM (the gravitational constant multiplied by the mass of the Earth) is known a lot more accurately, unsurprisingly, considering how well GPS works. Some of those constants seem to be known to about 12 significant figures.
ck2 2y ago
If you really want to overload your mind thinking about this, imagine this universe is only a bubble crowded into a group of other bubbles, like a kid blowing soap bubbles. So the pressure around our bubble is not uniform, there are more bubbles on one side than another, other bubbles are much larger and some are very tiny causing tiny "lumps" of pressure in various places on our bubble. Decades ago I really liked the "big collapse" theory that has now been abandoned, it was so "simple" in comparison to a universe that keeps expanding and not uniformly at that.
- turndown 2y ago
  Just because we are natives of this universe does not mean its behavior or characteristics will be naturally sensible to us. There is no “real” reason it should be something “simple” or reasonable to us. The universe simply is; us as well.
fartsucker69 2y ago
when did it start that the storytelling around every piece of physics news was framed as a controversy? I know it's been a while, but I feel like it wasn't this way 20 years ago...
- stevenhuang 2y ago
  The framing is not as contrived as you make it seem; the Hubble tension specifically is a genuine mystery and it is unknown why the indirect and direct methods don't corroborate when our theories otherwise indicate they should.
ajross 2y ago
Frustrating that all the comments seem to be jumping in to talk about dark energy and quintessence and multiverse pontification, when the actual contention in the linked article is that all of this may turn out to be a measurement error and that the Hubble tension may not actually exist after all.
sdenton4 2y ago
"researchers started using Cepheids to calibrate the distances to bright supernovas, enabling more accurate measurements of H0." It seems like if there were some error in the luminosity measurement for cepheids, it would propagate to the measurements with supernovas... I would expect that stacking measurement techniques (as is common with cosmology, where distances are vast and certainty is rare) would also stack error, like summing the variance in gaussians...
- FredPret 2y ago
  It'd be cool if we launched several space telescopes on Voyager-like trajectories. In 50-100 years they'd get a much better angular fix on stars that are too distant for Earth-orbit-sized angular measurements. https://en.wikipedia.org/wiki/Stellar_parallax https://en.wikipedia.org/wiki/Stellar_parallax
  - AprilArcus 2y ago
    They'd need some very big RTGs to last that long, and I don't think we manufacture plutonium at the necessary volumes for that anymore.
    - KennyBlanken 2y ago
      Last I remember, RTG manufacturing was very constrained, period. And that was before Russia took a massive shit in Ukraine and got themselves embargo'd by most of the rest of the developed world.
    - ars 2y ago
      I would use Americium-241 instead, longer half life and much more availability. Lower power, but a telescope like this does not need constant power, so some kind of short term power storage (capacitor I would assume, or some kind of ultra long life battery) could handle that.
      - fsckboy 2y ago
        in terms of the potential plutonium shortage, wikipedia: Americium-241 is not synthesized directly from uranium – the most common reactor material – but from the plutonium isotope 239. The latter needs to be produced first
z3t4 2y ago
Did I read it wrong, or does the universe expand at 10% of speed of light!? Could that possible be why the measurements are off? A close object vs an object very far away might look like they are in different places relatively.
- mr_mitm 2y ago
  Rest assured, this has been taken into account. The scientists who spend their life working on this topic have had the same thoughts you had within minutes of learning about the problem. It's extremely basic stuff actually.
  - z3t4 2y ago
    If it's extremely basic stuff and they've spent their entire life working on it, why did the two teams find different results? Thinking of objects moving 10% of light speed, or even two times the speed of light away from you, is not intuitive to a layman, and I can't imagine the Math.
    - mr_mitm 2y ago
      Because the problem lies somewhere else which is not extremely basic. Relativistic effects are not the issue here.
- feoren 2y ago
  The observable universe has a radius of about 14 Gigaparsecs. If H0 is 67.4 km/s/Mpc, then a naive calculation puts the edge of the observable universe expanding at 943,600 km/s, or about 3 times the speed of light. Of course we still observe this as merely "close to" the speed of light, but the point is that most of the universe is shooting away from us so fast that we will never see them as they are "now", even if we wait billions of years. We have no way of ever interacting with most of the "modern" universe, even theoretically. They might as well be in different universes. All we will ever see is their images from billions of years ago, even if we wait billions of years from now.
- evanb 2y ago
eisvogel 2y ago
The opening sentence of this article is 100% wrong. Hubble was a good scientist and correctly made no assumptions regarding his observations that objects that are further away by parallax are more red shifted. The assumption that these observations indicated an expanding universe was delivered to us by LeMaitre; if you believe in an expanding universe with a finite age, then give credit where it is due...
acyou 2y ago
The current scientific consensus is actually pretty good - the consensus being that standard theory, quantum theory, big bang theory, particle theory, universe expansion model all have as good a likelihood as not of going down in history the same way as miasma theory, phlogiston theory and Newtonian classical mechanics, given the apparent and vast shortcomings of basic science around our universe's constitution, composition and origins. It's a mature and constructive recognition of our limitations and where we can improve. One of the proximate causes around our failure to progress in this and other areas is the funding model of publish or perish. Many researchers are trying to carve out a career, but not necessarily to contribute to progress or advancement. An examination of the funding structure and incentives for universities and researchers appears to be in order. One suggestion would be to limit grants for private universities and colleges. Another would be to cap compensation for university and college staff. Yet another would be to add funding or tax breaks for technology scale up and application development in the private sector. And another would be cutting funding to masters', PhD and post-doc levels, and increasing funding for 1-, 2- and 4- year career oriented and skill development programs. Yet another suggestion would be limiting loan eligibility to 1-, 2- and 4- year degree or lower programs. Another would be tying university and college funding to the success of attached technology scale up and application development programs. Another would be requiring undergraduate and lower grants and tuition revenue to be spent directly on those programs and facilities, and research funds to be kept and spent separately. I would like to know some examples of how recent, publicly funded PhD, masters degree and postdoc work or research has materially advanced or will advance our world's knowledge and progress and has resulted in material benefits to society, and not just unreproducible studies on paper and unviable technologies and products.
grishka 2y ago
What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenomenon that occurs to spacetime or electromagnetic waves? How can we be so sure it's space that's expanding, not time? The more I read about this, the more it feels like phlogiston theory[1]. Works great for describing observations at first, but as more observations are made, some contradict the theory, so exceptions are made for these cases (phlogiston must have negative mass sometimes/there must be extra matter or energy for galaxies to spin as fast as they do), and then finally someone discovers something (oxygen/???) that explains all observations much simpler and requires no weird exceptions. [1] https://en.wikipedia.org/wiki/Phlogiston_theory https://en.wikipedia.org/wiki/Phlogiston_theory
- dotnet00 2y ago
  We can create and observe doppler shift by making things move towards/away from us. Thus it is proven that if something is moving away from us, it will produce a redshift. In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. As an obvious example, doppler shift often needs to be accounted for to communicate with spacecraft.
  - nilkn 2y ago
    X causes Y does not mean that Y implies X. It’s reasonable to suspect X given Y and an absence of other such causal relations, but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level.
    - deleted 2y ago
      [deleted]
    - ko27 2y ago
      You are not a making insightful point at all. Nothing in the world can guarantee you that "Y implies X", after all, we can be living in a simulation. Does that mean we should shutdown all scientific discussions by repeating what you stated? Of course not.
inciampati 2y ago
Does quanta magazine manage to reach this level of detail in other fields?
refibrillator 2y ago
If you’re interested in learning more about the rich human history and ingenuity underpinning the Hubble “constant”, please do yourself a favor and scroll through The Cosmic Distance Ladder by Terence Tao of UCLA: https://terrytao.wordpress.com/wp-content/uploads/2010/10/cosmic-distance-ladder.pdf https://terrytao.wordpress.com/wp-content/uploads/2010/10/co... The slides are delightfully visual and comprehensive yet terse, walking you up the rungs of the cosmic ladder from the Earth through the moon, sun, and beyond. I can almost guarantee you’ll learn something new and fascinating.
- deleted 2y ago
  [deleted]
- okokwhatever 2y ago
  Delightful, thanks
- aquafox 2y ago
  There's also the video of this talk: https://www.youtube.com/watch?v=7ne0GArfeMs https://www.youtube.com/watch?v=7ne0GArfeMs
  - iNic 2y ago
    He is a really good speaker! I also recommend his recent talk on AI in math research.
- Certified 2y ago
  I really like all the caveats and the time taken to explain things in the first part of that document, but later it starts to rush and gloss over important details and caveats. On page 151 of that link, when it starts talking about using parallax to measure the distance to nearby stars, it says "However, if one takes measurements six months apart, one gets a distance separation of 2AU." This is obviously incorrect because the whole solar system is orbiting around the galactic core, which itself is moving with respect to the CMB rest frame. I did a quick calc based on the 552.2 km/s galactic velocity value from Milky Way wiki [1] and found that it moves an additional 0.97AU in 6 months. I am assuming that this has been accounted for by scientists, and is being simplified to make it more digestible for the reader, but it hides a rather large dependency for every higher rung on the cosmic distance ladder. A cosmic velocity ladder that seems to be based off of Doppler CMB measurements [2]. If we are indeed using measurements many months apart and under or overestimating our velocity through the universe, even a little bit, every higher rung of the ladder would be affected wouldn't it? In the process of writing this, I thought "Surely we have launched a satellite pair that can take parallax measurements at similar times in different places!" They could range off of each other with Time of Flight, be positioned much further apart than a few AU, and take parallax star measurements at more or less the same time without atmospheric distortion, but it doesn't seem like we have. Both Hipparcos and Gaia were satellites that were deployed to measure parallax, but not as a pair. My reading suggests they used multi-epoch astrometric observations (speed ladder dependent) to generate their parallax measurements and it seems our current parallax and star catalogues are based on the measurements taken by these two satellites. New Horizons got the most distant parallax measurements by comparing simultaneous* earth observations, but it was limited to Proxima Centauri and Wolf 359, far from a full star catalogue. I would love if someone more knowledgeable can steer me towards a paper or technique that has been used to mitigate the cosmic distance ladder's dependency on this cosmic speed ladder. Regardless of how certain we think we are of our velocity through the universe, it seems to me that sidestepping that dependency through simultaneous* observations would be worthwhile considering how dependency laden the cosmic distance ladder already is. [1] https://en.wikipedia.org/wiki/Milky_Way https://en.wikipedia.org/wiki/Milky_Way [2] https://arxiv.org/pdf/astro-ph/9312056 https://arxiv.org/pdf/astro-ph/9312056 * Insert relativity caveat here for the use of "simultaneous". What I mean in this context is more simultaneous than waiting months between measurements.
causality0 2y ago
Everyone expected the sharp vision of the James Webb Space Telescope to bring the answer into focus. I think people forget that, due to the longer wavelengths to which it's sensitive, Webb actually has a poorer angular resolution than Hubble.
trhway 2y ago
Not an astronomer by any means. Just can't see it as a mere coincidence that the stars at the distance of the "age of universe" light years run away with about "c". I.e. "c" / "age of Universe" = Hubble constant (i.e. "c"/13.7 billions ly / 3.26 ly per pc = 71.3 km/s per mpc.)
mmmBacon 2y ago
One thing that’s not mentioned is what error there is in the theoretical calculation and what is the measurement error. From the theoretical POV I’d expect the theory to have an upper and lower limit based on values from initial assumptions. Getting the theory to 8% of the actual value is a pretty big achievement. It’s pretty difficult to predict much simpler, real systems to within 8% let alone something as complex as the expansion of the universe.
spamjavalin 2y ago
What a wonderful read - thank you
Danmctree 2y ago
Is there a good place to find redshift data and distance estimates for many galaxies?
zombot 2y ago
Fuck, now they've got animated nags that are autoplaying and don't get filtered out by uBlock Origin. One more site that uses dark patterns too chase away visitors.
jakeogh 2y ago
Mold: a sci-fi short story[1] that connects this with the recent estimate[2] on the signature from a failed (or not) warp drive. [1] https://www.youtube.com/watch?v=8URdhSigzjs https://www.youtube.com/watch?v=8URdhSigzjs [2] https://news.ycombinator.com/item?id=41101144 https://news.ycombinator.com/item?id=41101144
mr_world 2y ago
I love this controversy. I swear it's the most exciting thing in modern physics. The thought that there's something fundamentally wrong with the cosmic distance ladder and the way that we measure the expansion of the universe. I'm no mathematician or physicist, but this stuff just fascinates me. I interpret it something like: The further one looks, the faster objects in the universe are expanding. However, when one looks out at the universe, they are looking backwards in time, to a time when the universe was expanding at a more rapid pace. Right? Close to the big bang? Because there was a period of rapid expansion after the big bang, so the universe had to have moved faster in the earlier universe? So the only part of space that actually appears to be static would be around our local space, the stars we can see? Often the universe is depicted as a giant bubble, expanding outwards in all directions. It is how the human mind is built to think, a classic blunder dating back to the days of Ptolemy, where Earth was the center of everything. At the edge of our observable universe is the beginning of it all. We can fast forward then through time to see the most modern picture of our universe, the reference frame that is our own galaxy. We are not at rest in a static galaxy, so why should the laws of relativity and dilation not apply to massive objects Everywhere else we look is in the past, and the cosmic background is visible from every direction. So once expanded in 3D space, and accounting for time, all of space would appear to be accelerating towards the cosmic background and point of the big bang? “[...]But in 1929 astronomer Edwin Hubble measured the speed of many galaxies and found, to his surprise, that all were moving away from us-- in fact, the further away the galaxy, the faster it was going. His measurements showed that space is expanding everywhere, and no matter where you look, it will seem as if all galaxies are receding because the distance between everything is constantly growing. Faced with this news, Einstein decided to remove the cosmological constant from his equations.” -some scientific American article It’s not moving away from us, it’s moving towards the beginning of time at a faster and faster rate, but only because we’re looking backwards through time. In reality, due to our reference frame, and other subsequent frames of observed bodies, we are the only point in the observable universe that is in the “present”. To that effect, when everything appears to be moving away from us at a faster and faster rate, it is moving away from the origin (big bang) at a slower and slower rate. Galaxies are not moving away, they are showing an accelerating speed due to the time difference, and the slightly higher cosmological constant several hundred million years in the past, a constant that scales with time and its relation to distance according to metric expansion and the speed of light. It is the higher constant with relation to distance that gives the illusion of a universe whose expansion is accelerating. It can be assumed then, that as you move between vast points in space, the universe will update; showing that astronomical objects aren’t accelerating away, but are not in fact moving at all. If not moving towards each other and closer together. So no matter where you travel, it is likely that the bubble of the observable universe travels with you, you do not accelerate away faster the closer you get to the galaxies that appear from Earth or other reference points from Earth to be expanding faster away. If you look at the night sky from a planet in one of these far away galaxies, the overall structure of the universe would be very similar if not the same to the structure as it appears from Earth. With all galaxies appearing to be accelerating away from each other at a faster and faster rate. Sorry im high on shrooms
openasocket 2y ago
One of the frustrating aspects of cosmology is how difficult it is to actually apply the scientific method to it. You can't make a couple stars in a lab and see how they behave, the same way you can for particle physics. Fundamentally, most of cosmology comes down to observation, not true experimentation, where the experimenter is directly acting and comparing that to a control group. There are some experiments that can be done, but there are just some fundamental limitations. This is also the case in the so-called "soft sciences" like economics and psychology. But it's even true in some corners of the "hard sciences" like evolutionary biology.
alberth 2y ago
I have a simple mind ... and I can't wrap my head around how they compensate for the huge lens flare from JWST. https://www.youtube.com/watch?v=Y7ieVkK-Cz0 https://www.youtube.com/watch?v=Y7ieVkK-Cz0

340 points by nsoonhui 2y ago

Naive question: why should the expansion rate need to be uniform or constant everywhere? 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)

BossingAround 2y ago
That's the first thing that occurred to me too. It could also not be constant even at the same place, i.e. could it not be speeding up and slowing down as the universe expands?
isolli 2y ago
Indeed. Some researchers have proposed quintessence, a time-varying form of dark energy [0]. > 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. [0] https://en.wikipedia.org/wiki/Quintessence_(physics) https://en.wikipedia.org/wiki/Quintessence_(physics)
itishappy 2y ago
It's not constant (the early universe inflated quite quickly), and it doesn't need to be uniform, but it sure does appear to be. We measure it via redshift, pulsar timing arrays, and the temperature fluctuations of the CMB, and it looks pretty much the same in all directions.
AnimalMuppet 2y ago
The issue here is that it's not constant depending on the type of star we use to measure it. It's not a discrepancy in location in space. Or at least that's how I read the article.
chongli 2y ago
The controversy is that we get 2 different numbers depending on which method (cosmic microwave background vs cosmic distance ladder) we use to calculate the present rate of expansion. These numbers used to have their error bars overlapping, so we assumed they would eventually converge to the true value. But as we get more data the opposite is happening: the numbers are diverging and their error bars are shrinking such that they no longer overlap. 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.
- detourdog 2y ago
  Thank you for this explanation. I would like to emphasize that our model being wrong and not our numbers sounds like progress. It also sound like progress that we seem to have 2 “scales” to play with to try to develop a consistently measurable distance.
- api 2y ago
  Distance ladder seems much more error prone than the CMB.
  - artemonster 2y ago
    there is no "seems" with provable error bars
    - feoren 2y ago
      ehh ... everything we measure relies on our understanding of the universe in some way. It's perfectly reasonable that our distance measurements could rely on a shakier foundation of assumptions than our understanding of the CMB. I don't know enough to say one way or the other, but GP's comment is not unreasonable on its face. Whereas talking about "provable" in cosmology, and certainly in this case, does seem unreasonable -- especially with error bars, which by definition have a small chance of not including the real value. Normally I'd say that we can generally refine our assumptions to be extremely good, and just take more measurements, and keep narrowing that error bar, until we hit a level of certainty that anyone reasonable would call "proven", but the entire point of TFA is that this isn't happening in this case. We seem on our way to "proving" two inconsistent things.
JumpCrisscross 2y ago
> what should the expansion rate need the be uniform or constant everywhere? 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. [1] https://en.wikipedia.org/wiki/Dark_energy https://en.wikipedia.org/wiki/Dark_energy
- tzs 2y ago
  There has been some interesting recent work that may get rid of the need for dark energy. 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. [1] https://www.youtube.com/watch?v=WWqmccgf78w https://www.youtube.com/watch?v=WWqmccgf78w
xhkkffbf 2y ago
Certainly when I look at convection currents in the ocean or the atmosphere, I see plenty of variation. Shoot, the earth's atmosphere constantly produces moving blobs of relatively high and low pressure.
diob 2y ago
So a lot of astronomy is based on the principle that we are not in a special pocket of the universe. See https://en.wikipedia.org/wiki/Cosmological_principle https://en.wikipedia.org/wiki/Cosmological_principle Basically, if this weren't to hold true, a lot of astronomy would fall over, even physics.
- XorNot 2y ago
  Though it is worth noting if this were the case you would expect to see boundaries: if the laws of physics change due to spatial position, the discontinuity should produce an effect of some sort where matter and light transitions between regions.
  - mcswell 2y ago
    I suppose there could be a gradual change over distance, i.e. the first derivative of this change never varies.
- deleted 2y ago
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- hindsightbias 2y ago
  Sophon is amused: https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology) https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology)
- eikenberry 2y ago
  Seems there are 2 ideas at odds. One is that the universe is infinite, in which case this is all localized and has no bearing on the universe outside of our small observable region. The other is that we are seeing enough of a bounded universe where the observations we make are of a significant enough chunk to make theories about it.
- beltsazar 2y ago
  Yes, cosmological principle is probably the most fundamental assumption in astronomy. 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.
photochemsyn 2y ago
Spacetime is apparently extremely rigid as it supports the transmission of gravitational waves originating billions of light-years away, as detected by the LIGO experiments. This suggests smooth and gradual uniform expansion, at least spatially. Temporal variation (speeding up and slowing down uniformly at all points) might be possible but seems hard to explain.
Jeff_Brown 2y ago
Seems perfectly possible. General relativity, after all, was precisely the discovery that the curvature of space, well spacetime, is not uniform.

seanhunter 2y ago

Some cool background about the Hubble constant here, including a nice explanation involving blueberry muffins https://news.uchicago.edu/explainer/hubble-constant-explained https://news.uchicago.edu/explainer/hubble-constant-explaine...

mcswell 2y ago
I just finished off a blueberry bagel, the taste is still in my mouth. Maybe the universe is torus-shaped?

readthenotes1 2y ago

"This extrapolation predicts that the cosmos should currently be expanding at a rate of 67.4 km/s/Mpc, with an uncertainty that’s less than 1%." I can't measure my own weight with an uncertainty that's less than 1%. I wonder what these peeps are on...

uncivilized 2y ago
Their wallets are much bigger than yours.
- readthenotes1 2y ago
  As is what they are trying to measure. I don't believe 1% measurement error in any universal element except perhaps the speed of light...
  - aidenn0 2y ago
    That's an absurd statement. For example, planck's constant is known to better than 1%, as is the mass of various particles. Heck, the Earth, which is sufficiently non-spherical for it to matter only differs in radius (between polar and equatorial) by 0.3%!
  - munchler 2y ago
    I suggest you take a look at this list of physical constants, paying special attention to the "uncertainty" column, and then get back to us on why you don't accept any of them except the speed of light. https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants
  - bloak 2y ago
    Here's a nice list: https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants G (the gravitational constant) is an interesting one: the value is only known to about 5 significant figures, but GM (the gravitational constant multiplied by the mass of the Earth) is known a lot more accurately, unsurprisingly, considering how well GPS works. Some of those constants seem to be known to about 12 significant figures.

ck2 2y ago

If you really want to overload your mind thinking about this, imagine this universe is only a bubble crowded into a group of other bubbles, like a kid blowing soap bubbles. So the pressure around our bubble is not uniform, there are more bubbles on one side than another, other bubbles are much larger and some are very tiny causing tiny "lumps" of pressure in various places on our bubble. Decades ago I really liked the "big collapse" theory that has now been abandoned, it was so "simple" in comparison to a universe that keeps expanding and not uniformly at that.

turndown 2y ago
Just because we are natives of this universe does not mean its behavior or characteristics will be naturally sensible to us. There is no “real” reason it should be something “simple” or reasonable to us. The universe simply is; us as well.

fartsucker69 2y ago

when did it start that the storytelling around every piece of physics news was framed as a controversy? I know it's been a while, but I feel like it wasn't this way 20 years ago...

stevenhuang 2y ago
The framing is not as contrived as you make it seem; the Hubble tension specifically is a genuine mystery and it is unknown why the indirect and direct methods don't corroborate when our theories otherwise indicate they should.

ajross 2y ago

Frustrating that all the comments seem to be jumping in to talk about dark energy and quintessence and multiverse pontification, when the actual contention in the linked article is that all of this may turn out to be a measurement error and that the Hubble tension may not actually exist after all.

sdenton4 2y ago

"researchers started using Cepheids to calibrate the distances to bright supernovas, enabling more accurate measurements of H0." It seems like if there were some error in the luminosity measurement for cepheids, it would propagate to the measurements with supernovas... I would expect that stacking measurement techniques (as is common with cosmology, where distances are vast and certainty is rare) would also stack error, like summing the variance in gaussians...

FredPret 2y ago
It'd be cool if we launched several space telescopes on Voyager-like trajectories. In 50-100 years they'd get a much better angular fix on stars that are too distant for Earth-orbit-sized angular measurements. https://en.wikipedia.org/wiki/Stellar_parallax https://en.wikipedia.org/wiki/Stellar_parallax
- AprilArcus 2y ago
  They'd need some very big RTGs to last that long, and I don't think we manufacture plutonium at the necessary volumes for that anymore.
  - KennyBlanken 2y ago
    Last I remember, RTG manufacturing was very constrained, period. And that was before Russia took a massive shit in Ukraine and got themselves embargo'd by most of the rest of the developed world.
  - ars 2y ago
    I would use Americium-241 instead, longer half life and much more availability. Lower power, but a telescope like this does not need constant power, so some kind of short term power storage (capacitor I would assume, or some kind of ultra long life battery) could handle that.
    - fsckboy 2y ago
      in terms of the potential plutonium shortage, wikipedia: Americium-241 is not synthesized directly from uranium – the most common reactor material – but from the plutonium isotope 239. The latter needs to be produced first

z3t4 2y ago

Did I read it wrong, or does the universe expand at 10% of speed of light!? Could that possible be why the measurements are off? A close object vs an object very far away might look like they are in different places relatively.

mr_mitm 2y ago
Rest assured, this has been taken into account. The scientists who spend their life working on this topic have had the same thoughts you had within minutes of learning about the problem. It's extremely basic stuff actually.
- z3t4 2y ago
  If it's extremely basic stuff and they've spent their entire life working on it, why did the two teams find different results? Thinking of objects moving 10% of light speed, or even two times the speed of light away from you, is not intuitive to a layman, and I can't imagine the Math.
  - mr_mitm 2y ago
    Because the problem lies somewhere else which is not extremely basic. Relativistic effects are not the issue here.
feoren 2y ago
The observable universe has a radius of about 14 Gigaparsecs. If H0 is 67.4 km/s/Mpc, then a naive calculation puts the edge of the observable universe expanding at 943,600 km/s, or about 3 times the speed of light. Of course we still observe this as merely "close to" the speed of light, but the point is that most of the universe is shooting away from us so fast that we will never see them as they are "now", even if we wait billions of years. We have no way of ever interacting with most of the "modern" universe, even theoretically. They might as well be in different universes. All we will ever see is their images from billions of years ago, even if we wait billions of years from now.
evanb 2y ago

eisvogel 2y ago

The opening sentence of this article is 100% wrong. Hubble was a good scientist and correctly made no assumptions regarding his observations that objects that are further away by parallax are more red shifted. The assumption that these observations indicated an expanding universe was delivered to us by LeMaitre; if you believe in an expanding universe with a finite age, then give credit where it is due...

acyou 2y ago

The current scientific consensus is actually pretty good - the consensus being that standard theory, quantum theory, big bang theory, particle theory, universe expansion model all have as good a likelihood as not of going down in history the same way as miasma theory, phlogiston theory and Newtonian classical mechanics, given the apparent and vast shortcomings of basic science around our universe's constitution, composition and origins. It's a mature and constructive recognition of our limitations and where we can improve. One of the proximate causes around our failure to progress in this and other areas is the funding model of publish or perish. Many researchers are trying to carve out a career, but not necessarily to contribute to progress or advancement. An examination of the funding structure and incentives for universities and researchers appears to be in order. One suggestion would be to limit grants for private universities and colleges. Another would be to cap compensation for university and college staff. Yet another would be to add funding or tax breaks for technology scale up and application development in the private sector. And another would be cutting funding to masters', PhD and post-doc levels, and increasing funding for 1-, 2- and 4- year career oriented and skill development programs. Yet another suggestion would be limiting loan eligibility to 1-, 2- and 4- year degree or lower programs. Another would be tying university and college funding to the success of attached technology scale up and application development programs. Another would be requiring undergraduate and lower grants and tuition revenue to be spent directly on those programs and facilities, and research funds to be kept and spent separately. I would like to know some examples of how recent, publicly funded PhD, masters degree and postdoc work or research has materially advanced or will advance our world's knowledge and progress and has resulted in material benefits to society, and not just unreproducible studies on paper and unviable technologies and products.

grishka 2y ago

What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenomenon that occurs to spacetime or electromagnetic waves? How can we be so sure it's space that's expanding, not time? The more I read about this, the more it feels like phlogiston theory[1]. Works great for describing observations at first, but as more observations are made, some contradict the theory, so exceptions are made for these cases (phlogiston must have negative mass sometimes/there must be extra matter or energy for galaxies to spin as fast as they do), and then finally someone discovers something (oxygen/???) that explains all observations much simpler and requires no weird exceptions. [1] https://en.wikipedia.org/wiki/Phlogiston_theory https://en.wikipedia.org/wiki/Phlogiston_theory

dotnet00 2y ago
We can create and observe doppler shift by making things move towards/away from us. Thus it is proven that if something is moving away from us, it will produce a redshift. In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. As an obvious example, doppler shift often needs to be accounted for to communicate with spacecraft.
- nilkn 2y ago
  X causes Y does not mean that Y implies X. It’s reasonable to suspect X given Y and an absence of other such causal relations, but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level.
  - deleted 2y ago
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  - ko27 2y ago
    You are not a making insightful point at all. Nothing in the world can guarantee you that "Y implies X", after all, we can be living in a simulation. Does that mean we should shutdown all scientific discussions by repeating what you stated? Of course not.

inciampati 2y ago

Does quanta magazine manage to reach this level of detail in other fields?

refibrillator 2y ago

If you’re interested in learning more about the rich human history and ingenuity underpinning the Hubble “constant”, please do yourself a favor and scroll through The Cosmic Distance Ladder by Terence Tao of UCLA: https://terrytao.wordpress.com/wp-content/uploads/2010/10/cosmic-distance-ladder.pdf https://terrytao.wordpress.com/wp-content/uploads/2010/10/co... The slides are delightfully visual and comprehensive yet terse, walking you up the rungs of the cosmic ladder from the Earth through the moon, sun, and beyond. I can almost guarantee you’ll learn something new and fascinating.

deleted 2y ago
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okokwhatever 2y ago
Delightful, thanks
aquafox 2y ago
There's also the video of this talk: https://www.youtube.com/watch?v=7ne0GArfeMs https://www.youtube.com/watch?v=7ne0GArfeMs
- iNic 2y ago
  He is a really good speaker! I also recommend his recent talk on AI in math research.
Certified 2y ago
I really like all the caveats and the time taken to explain things in the first part of that document, but later it starts to rush and gloss over important details and caveats. On page 151 of that link, when it starts talking about using parallax to measure the distance to nearby stars, it says "However, if one takes measurements six months apart, one gets a distance separation of 2AU." This is obviously incorrect because the whole solar system is orbiting around the galactic core, which itself is moving with respect to the CMB rest frame. I did a quick calc based on the 552.2 km/s galactic velocity value from Milky Way wiki [1] and found that it moves an additional 0.97AU in 6 months. I am assuming that this has been accounted for by scientists, and is being simplified to make it more digestible for the reader, but it hides a rather large dependency for every higher rung on the cosmic distance ladder. A cosmic velocity ladder that seems to be based off of Doppler CMB measurements [2]. If we are indeed using measurements many months apart and under or overestimating our velocity through the universe, even a little bit, every higher rung of the ladder would be affected wouldn't it? In the process of writing this, I thought "Surely we have launched a satellite pair that can take parallax measurements at similar times in different places!" They could range off of each other with Time of Flight, be positioned much further apart than a few AU, and take parallax star measurements at more or less the same time without atmospheric distortion, but it doesn't seem like we have. Both Hipparcos and Gaia were satellites that were deployed to measure parallax, but not as a pair. My reading suggests they used multi-epoch astrometric observations (speed ladder dependent) to generate their parallax measurements and it seems our current parallax and star catalogues are based on the measurements taken by these two satellites. New Horizons got the most distant parallax measurements by comparing simultaneous* earth observations, but it was limited to Proxima Centauri and Wolf 359, far from a full star catalogue. I would love if someone more knowledgeable can steer me towards a paper or technique that has been used to mitigate the cosmic distance ladder's dependency on this cosmic speed ladder. Regardless of how certain we think we are of our velocity through the universe, it seems to me that sidestepping that dependency through simultaneous* observations would be worthwhile considering how dependency laden the cosmic distance ladder already is. [1] https://en.wikipedia.org/wiki/Milky_Way https://en.wikipedia.org/wiki/Milky_Way [2] https://arxiv.org/pdf/astro-ph/9312056 https://arxiv.org/pdf/astro-ph/9312056 * Insert relativity caveat here for the use of "simultaneous". What I mean in this context is more simultaneous than waiting months between measurements.

causality0 2y ago

Everyone expected the sharp vision of the James Webb Space Telescope to bring the answer into focus. I think people forget that, due to the longer wavelengths to which it's sensitive, Webb actually has a poorer angular resolution than Hubble.

trhway 2y ago

Not an astronomer by any means. Just can't see it as a mere coincidence that the stars at the distance of the "age of universe" light years run away with about "c". I.e. "c" / "age of Universe" = Hubble constant (i.e. "c"/13.7 billions ly / 3.26 ly per pc = 71.3 km/s per mpc.)

mmmBacon 2y ago

One thing that’s not mentioned is what error there is in the theoretical calculation and what is the measurement error. From the theoretical POV I’d expect the theory to have an upper and lower limit based on values from initial assumptions. Getting the theory to 8% of the actual value is a pretty big achievement. It’s pretty difficult to predict much simpler, real systems to within 8% let alone something as complex as the expansion of the universe.

spamjavalin 2y ago

What a wonderful read - thank you

Danmctree 2y ago

Is there a good place to find redshift data and distance estimates for many galaxies?

zombot 2y ago

Fuck, now they've got animated nags that are autoplaying and don't get filtered out by uBlock Origin. One more site that uses dark patterns too chase away visitors.

jakeogh 2y ago

Mold: a sci-fi short story[1] that connects this with the recent estimate[2] on the signature from a failed (or not) warp drive. [1] https://www.youtube.com/watch?v=8URdhSigzjs https://www.youtube.com/watch?v=8URdhSigzjs [2] https://news.ycombinator.com/item?id=41101144 https://news.ycombinator.com/item?id=41101144

mr_world 2y ago

I love this controversy. I swear it's the most exciting thing in modern physics. The thought that there's something fundamentally wrong with the cosmic distance ladder and the way that we measure the expansion of the universe. I'm no mathematician or physicist, but this stuff just fascinates me. I interpret it something like: The further one looks, the faster objects in the universe are expanding. However, when one looks out at the universe, they are looking backwards in time, to a time when the universe was expanding at a more rapid pace. Right? Close to the big bang? Because there was a period of rapid expansion after the big bang, so the universe had to have moved faster in the earlier universe? So the only part of space that actually appears to be static would be around our local space, the stars we can see? Often the universe is depicted as a giant bubble, expanding outwards in all directions. It is how the human mind is built to think, a classic blunder dating back to the days of Ptolemy, where Earth was the center of everything. At the edge of our observable universe is the beginning of it all. We can fast forward then through time to see the most modern picture of our universe, the reference frame that is our own galaxy. We are not at rest in a static galaxy, so why should the laws of relativity and dilation not apply to massive objects Everywhere else we look is in the past, and the cosmic background is visible from every direction. So once expanded in 3D space, and accounting for time, all of space would appear to be accelerating towards the cosmic background and point of the big bang? “[...]But in 1929 astronomer Edwin Hubble measured the speed of many galaxies and found, to his surprise, that all were moving away from us-- in fact, the further away the galaxy, the faster it was going. His measurements showed that space is expanding everywhere, and no matter where you look, it will seem as if all galaxies are receding because the distance between everything is constantly growing. Faced with this news, Einstein decided to remove the cosmological constant from his equations.” -some scientific American article It’s not moving away from us, it’s moving towards the beginning of time at a faster and faster rate, but only because we’re looking backwards through time. In reality, due to our reference frame, and other subsequent frames of observed bodies, we are the only point in the observable universe that is in the “present”. To that effect, when everything appears to be moving away from us at a faster and faster rate, it is moving away from the origin (big bang) at a slower and slower rate. Galaxies are not moving away, they are showing an accelerating speed due to the time difference, and the slightly higher cosmological constant several hundred million years in the past, a constant that scales with time and its relation to distance according to metric expansion and the speed of light. It is the higher constant with relation to distance that gives the illusion of a universe whose expansion is accelerating. It can be assumed then, that as you move between vast points in space, the universe will update; showing that astronomical objects aren’t accelerating away, but are not in fact moving at all. If not moving towards each other and closer together. So no matter where you travel, it is likely that the bubble of the observable universe travels with you, you do not accelerate away faster the closer you get to the galaxies that appear from Earth or other reference points from Earth to be expanding faster away. If you look at the night sky from a planet in one of these far away galaxies, the overall structure of the universe would be very similar if not the same to the structure as it appears from Earth. With all galaxies appearing to be accelerating away from each other at a faster and faster rate. Sorry im high on shrooms

openasocket 2y ago

One of the frustrating aspects of cosmology is how difficult it is to actually apply the scientific method to it. You can't make a couple stars in a lab and see how they behave, the same way you can for particle physics. Fundamentally, most of cosmology comes down to observation, not true experimentation, where the experimenter is directly acting and comparing that to a control group. There are some experiments that can be done, but there are just some fundamental limitations. This is also the case in the so-called "soft sciences" like economics and psychology. But it's even true in some corners of the "hard sciences" like evolutionary biology.

alberth 2y ago

I have a simple mind ... and I can't wrap my head around how they compensate for the huge lens flare from JWST. https://www.youtube.com/watch?v=Y7ieVkK-Cz0 https://www.youtube.com/watch?v=Y7ieVkK-Cz0