In Part 1, the measurement of cosmological distances using standard candles was introduced. In Part 2 a couple of types of standard candles, Cepheids and SN Type 1a were described. Part 3 brought that together with a primer on measuring velocity, and how that implies a distance in an expanding universe. With two independent ways of measuring ‘distance’ – Hubble flow and the SNe Ia standard candles, one compares the two and finds that the SN Ia distances are larger than those derived from the Hubble flow – the so called Hubble Residual (HR). Since the later depend on the model of the universe, in this case uniform expansion, the former implies that the Universe is not only expanding, but accelerating. Since we don’t know how that can happen, we invented dark energy to explain it. In this final installment, I’ll look at some challenges to that conclusion; I don’t intend to prove or disprove it – if I could do that, I’d be off claiming my Nobel Prize – but rather maybe illustrate the scientific method – the SCIENCE is never settled.
With that: given the implication/significance of an accelerating universe, there’s been a fair amount of work, even in the discovery papers, trying to find alternative hypotheses.
One possibility, that I’ll sort of dismiss out of hand, not because it’s not necessarily believable but because it has no predictive power, is that physical laws and/or constants are not constants. In that case physics may be different and identical initial conditions generating a Type 1a SNe but at cosmological distances might have systematically different behavior. In addition to the fact that there are no ‘easy’ testable predictions, the SNe used in the discovery of acceleration, while distant, are not that distant cosmologically speaking and therefore we are not looking too far back in time – (remember that owing to the finite speed of light, distance is directly proportional to how far back in time we are looking) and there is no evidence for any change in physics or constants over that “short” period of time. So almost everyone is comfortable assuming that physical laws and constants don’t change in any way that’s important to this problem. This is really a consensus in the true sense of the word.
It’s sand. And Smoke.
One other possibility is the affect of dust. Dust, mostly in the form of carbon and various forms of silicate materials is ubiquitous and complicates the interpretation of most astronomical observations. Dust interacts with light by scattering and absorbing it. Therefore, any dust along the line of sight to any particular SNe would have the affect of making it appear dimmer, and so is a natural, systematic (always makes them dimmer, never brighter) bias that, while mundane, could explain for the observations. Unfortunately, there are two major reasons to fairly confidently dismiss this possibility. First, dust absorption and scattering change the frequency distribution of light, the relative amount of energy transmitted at short wavelengths vs long wavelengths.
Think of a sunset 
– the reason a sunset appears red, pink, orange is that the path through the atmosphere that sun light must traverse is much longer at the horizon than at zenith. The dust in the atmosphere preferentially scatters and absorbs blue light (also why the sky “is” blue), leaving only the reds and oranges to make it to your eye-hole. Astronomical dust has many of the same properties and hence light from the SNe passing through a long path length of dust to get to our telescopes will preferentially have more blue light removed, changing the relative brightness different wavelengths. This particular effect is not observed in the SNe data; the brightness seems to be uniformly suppressed. “Exotic” dust that doesn’t have this wavelength dependent effect (so-called “gray” dust) but only reduces the brightness has been proposed. Realistic astronomical dust models (different composition and shapes) can produce this sort of behavior. But in order to have a 20% affect, very large quantities would be required – far beyond what would have significant effects in other observational data, effects that are not seen. Additionally, one requires a very large quantity of things like iron to be present in this sort of dust, more than is realistically available to make dust. So there’s a lot of detail there, but the upshot is that it is pretty well established at this point that dust is an unrealistic explanation. Probably real consensus here too!
The final thing we’ll look at here, and the subject of the papers that lead to this whole fiasco of a series, is a change in the intrinsic light curve corrected brightness of Type 1a SNe – while we dismissed this affect as following from a change in fundamental physics, that’s not the only way such a change could happen in the distant (old) universe. Type 1a SNe don’t happen in isolation. They occur in a galaxy and their properties are dependent on the stellar population from which they emerge. The ages of stellar populations, their initial composition, the density of the environment from which the form, etc. are all factors that can have subtle and systematic effects on the exact behavior of the eruption. Therefore is not only plausible, but expected, that, if galactic stellar populations (galaxy structure) change with time, Type 1a SNe ‘intrinsic’ brightness will most certainly also evolve. Up to here, nothing controversial – it is well accepted, a scientific consensus even, that this sort of luminosity evolution is not only possible, but actually observed. Indeed, there is an observed correlation between the age of the stellar population and the HR. The original discovery paper (and many follow-ups) looked into luminosity evolution of Type 1a SNe and concluded that is could not be used to explain the observations; there was no evidence for luminosity evolution in the data they used. Follow-up papers have claimed that the age ranges in the sample used to ‘discover’ the acceleration are insufficient to explain the size of the effect. Of course, that conclusion depends on both accurate age dating of the sample as well as accurate calibration of the relationship.
No, not THAT Korean group!
That brings us to the meat of why I started this. There has been a series of papers over the last couple of years that address both these issues. They have been largely from a well respected (as far as I can tell) Korean group. There have been responses and the details have been argued back and forth. I’ll avoid too much detail here as one can very rapidly get underwater. Briefly, the Korean researches initially got very accurate spectroscopy (see Part 3) of a large sample of galaxies that allowed them to very accurately age date them. Then they looked the HR vs age in this sample and found a steeper relationship than previously found. In a series of back-and-forth papers, they claim that the luminosity evolution of SN Ia is significant enough, given the age ranges and the steeper relationship, to explain all of the HR and hence negate the need to acceleration and dark energy. There has been push back of course, including an analysis claiming to show that relation was very shallow and unable to explain the full HR. The responses reviewed the techniques and data sample used in Rose et al 2020 and found that the sample they used was not of high enough quality to get good age estimates of the galaxies in SN Ia samples; when they cross matched with their higher quality data, the found significant over estimates of the ages of the host galaxies thus biasing the aga-HR correlation low. Further, the statistical techniques used have well known biases that were not accounted for. They reanalyzed the exact same data as Rose et al 2020 and confirmed their earlier results. Their results are summarized in this plot: They can easily reproduce the observed Hubble Residual without invoking any esoteric physics like Dark Energy.
In the top plot, the blue points are individual measurements of the Hubble Residual of SN Ia. The systematic rise above the dashed 0 line (no acceleration universe) is the observation that “requires” dark energy. The solid black line is a model of the universe with acceleration, while the green line represents the authors model of luminosity evolution due to progenitor age. As you can see, there’s no need to invoke exotic physics if the authors are right.
Sure he can be a jack-ass, just ask Mrs. “Monkey” Garrison. But this is a good quote.
Conclusion – is the universe accelerating? Is their such a thing as dark energy? Maybe not. There are much more mundane explanations embedded in the minutiae and details of doing science – the boring stuff – whether or not this particular line of reasoning about luminosity evolution is correct or not. Short of it – accelerating universe is not a ‘fact’ as of yet. There’s a lot of room for the observations that drive it to be wrong, or more precisely the interpretation of those observations to be missing essential context. I can’t say I know the answer, though I suspect the Korean group is correct but that’s partly my contrarian nature. But a lot of science/scientist like to focus on “big” things and can lose sight of the assumptions that underlie the big ideas; no intention necessary – they just become ingrained in our understanding. I’m sometimes amazed how we can sometimes take as established truth things that rely on a single off-hand or unsupported statement from years ago.
Unfortunately, dark energy is sort of accepted as the default baseline paradigm and it’s presented as more of a consensus in the popular press than it really is. It’s hard for practitioners in the field to argue with the cache of a Nobel prize winner, let alone the general public. While scientific consensus is real and valuable if it is true consensus, I personally look at the consensus of dark energy as drifting into consensus of experts or social pressure, at least in the public presentation, but on the professional side as well perhaps. The cynic might observer that there’s lots of funding for experiments to “find the dark energy” – Scientists love them some funding! On the positive side, the scientific process continues. People are looking very carefully at the data and looking at the very basis of the argument for dark energy with a skeptical eye. And with some success. They are publishing in the mainstream journals and are able to present the evidence freely and, even though there is always some pressure to accept the baseline of knowledge (and that’s healthy for well established principles as long as the rare brilliant iconoclast can question and flourish to some degree) in any field, they are not ostracized, censored, don’t have their PhD’s or licenses revoked. Would that this was true in some other fields of scientific endeavor.
Excellent. Thanks.
Good write up, Thanks!
Denying Dark Energy and Dark Matter is racist.
But yes. A good write up. Thank you.
Dark Matter Lives
I really enjoyed this series. Thank you.
The universe is subservient to the Great Firster. It’s existence is merely an ephemeral illusion that masks the Great Truth of Firsting. It will all come crashing down, collapsing in upon itself with The Firstening. Why study such a thing?
Why study such a thing?
Well, it gives us something to do during this interminable wait for the Great First. Just ask the Israelites – keep making grandiose promises that you don’t follow through with on a reasonable timescale, and people will start worshiping false idols out in the desert.
I study the firsting like a proctologist studies ass cancer. It’s not because they like it or want to see it, but it needs to be dealt with.
Great article. What is the function of ‘dark energy’ as in, how does it theoretically cause the acceleration?
The. Droplets.
Gee whiz/hypey explanation (but with math!) https://www.youtube.com/playlist?list=PLsPUh22kYmNA6WUmOsEEi32zi_RdSUF4i
Antihypey: https://www.youtube.com/watch?v=ytS7u8mCxEY
That’s all sort of hand-wavy and, in large part, beyond the scope. Remember that means “I don’t know”! There some explanation here, by someone for whom it may not be “beyond the scope”.
Why do they keep saying negative pressure? In normal parlance negative pressure is also called ‘suction’, what they’re really describing is positive pressure, which tends to push everything away. Unless in their concept the negative pressure is outside/on the edge of the universe pulling everything to it?
I studied physics at the University of Lawsonomy. Suction and pressure, baby, that explains every thing I know.
Suction and pressure leads to a baby. Checks out.
Did you just explain the “birds and the bees” to the “Lorax of the bees”?
I think that’s why Carroll decries it’s use in the first half of the linked article. What is really comes down to is that, as proposed, dark energy is a property of space-time. Therefore, as the universe expands, its density will not go down, unlike normal matter we see. So with a constant density of dark energy, through the Friedman equations (see “the Math” in the linked article), imply the acceleration. Again, this doesn’t explain WHAT dark energy is, just how such a thing would lead to the ‘acceleration’. I think Carroll’s explanation is a pretty good one.
Preface: I am just a simple country engineer, so I like my physics Newtonian and my effects to be expected based on personal experience. Negative Poisson ratio materials were already a bit of a mindfuck for me.
I think the problem with using ‘pressure’ is that pressure will dissipate as you expand/contract the space, whereas we’re keeping this acceleration constant.
I think it ends up getting called negative because it is negative in the equation, but what Carrol explains regarding balloons/rubber bands is exactly the opposite of the physics. Most people are going to think of the balloon as the universe and the dark energy is like the air expanding the universe, against the tension in the balloon (gravity) that would make it contract.
That is my problem. It seems to be being described as a universal constant similar to gravity, but that is not dependent on distance (which allows for the constant acceleration). If you really think about it, I’m not really sure why gravity would arise (spacetime bending, sure, totally get it…), so this is about as plausible, except that I can directly observe gravity’s effects whereas this is a mystery to me and is apparently unobservable at local scales.
Here is another for you: why would the acceleration be constant? Shouldn’t the weakening of gravitational forces cause the acceleration to increase with time?
“Shouldn’t the weakening of gravitational forces cause the acceleration to increase with time?”
If I understand the question, no. Unless you’re putting energy into the system you can’t increase acceleration – that requires application of a force. If you expand and therefore the matter density decreases (normal matter, no dark energy, etc), every object will feel a smaller and smaller gravitational force. But that won’t cause it to accelerate, no matter what. Depending on how much matter there is and what the initial impulse for the expansion was, it will either decelerate and collapse back on itself (that would be a cyclical ‘big bang’ sort of theory), asymptotically approach a state of rest, or simply continue expanding forever. These are the simple open, flat, closed universe models that cosmologists started out with early on once the expansion was recognized. I may be mis-understanding though?
I think the real question is whether the laws of physics as we know them are consistent across all of space (and time) or do they vary not only with relative velocity but also position.
I’ve been interested in the brane hypothesis where matter arises from the resulting collision of two higher dimensional branes bouncing off each other. An infinite regeneration of dissipating universes.
We already have a non-conforming point in the universe – where the laws of physics as we know them are useless – the Big Bang.
Maybe I’m still misunderstanding dark energy: I am viewing it as an acceleration that is pushing everything away from the center of the universe through some arcane power.
Right, so why does the smaller gravitational force not result in there being a higher acceleration.
Say I have a single particle, with nothing else around. It is hurtling at a good speed away from the center of the universe, and we also know it is accelerating away at a constant rate, per our observations. It is being pulled by a gravitational force, in towards the center of the universe. It is also being pushed by a constant force out (dark energy). From our observations, the dark energy ‘force’ is greater than the gravitational pull because we are observing the acceleration already.
As the particle moves further from the center of the universe, that force imbalance should continually increase as one remains constant (dark energy) and the other weakens (gravity). The particle should experience an impulse (change in acceleration)? But our observations are claiming a constant change in velocity?
Okay, rereading Carrol, assuming he is carefully wording this, the acceleration is not constant. “It’s accelerating away from us, exponentially.”
Which makes more sense, as much as it can anyway.
I think a large part of the confusion – certainly on my part – is visualizing the expansion as occurring in space, i.e. wrt to some fixed reference frame rather than as being part of the frame itself – i.e. the paragraph (in Carroll’s write-up) that lays out that the expansion rate is not a speed. So it’s not what we normally think about when we think about velocity and acceleration.
What helped me get that he meant there was impulse is just listing it like he describe din multiple times and recording the diameter of the universe if it was doubling every time and then calculating the average acceleration and velocity across that time difference.
t.1=1, d.1=1,
t.2=2, d.2=2, v.2=1
t.3=3, d.3=4, v.3=2, a.3=1
t.4=4, d.4=8, v.4=4, a.4=2
you see that between t=3 and t=4 that we have a change in acceleration
I’ll be hoping in and out (mostly out – unavoidable work deadlines and all) today, so I’ll apologize in advance for my predicted silence.
Let’s ask Dr. Fauci. He is science, after all.
No.
Thanks for this thoroughly enjoyable series. Somehow I find myself captivated by things I do not and never will understand.
SCIENCY from the morning links;
Area of Florida: 65758 mi^2
Area of the oceans of the Earth: 140,625,000 mi^2
Divide the area of florida by the oceans: 0.00046761 feet per foot of glacier above the water (below is already compensated for).
So if is glacier is 1000 ft high then the oceans will rise less than half a foot. Measurable but not catastrophic.
(Took me less than 5 minutes to look up the values and run the figures through a calculator. Much too hard for a simple reporter to handle.)
Good article, PM. Thanks for posting this.
They claim the glacier varies between 2900 and 3600 feet in ‘depth’ so, that would be fairly significant.
Only the current height above water matters.
Only the current height above Land matters.
The portion floating on the water is already displacing a lot of its volume.
*some floating portion may still induce raising level, but within the margins of error for measurements.
Maybe I’ve been thinking about it wrong. . I’ve been thinking of it like a normal glacier that forms in the mountains, and thus all of it is basically above sea level.
I’ve been assuming it is on solid ground, rather than say, resting on the ocean floor. If that is the case you need to discount a portion of the ice above sealevel as well, equal to about 10%* of the amount below sea level
*percentage subject to change based on density of seawater vs pure water?
Are we sure it sits on the seabed?
See the flickr link below…
Per Plisade, at least some portion of it? either way, not nearly as straight forward as you now need to start worrying about the bathymetry below the ice, not sure how accurate they can measure that though geophysical methods should get you close enough.
I don’t really understand the whole thing, but this looks cool…
https://www.flickr.com/photos/nercscience/39994470000/in/album-72157680410020281/
And this makes sense…
https://www.sciencenews.org/article/antarctica-thwaites-glacier-ice-shelf-collapse-climate-5-years
Why does the new $9B ship we paid for look like a rust-bucket? Is the LGBT Navy too privileged to paint?
https://www.thesun.co.uk/news/17021658/us-navy-stealth-destroyer-rusty-california/
It is a trick to make the enemy underestimate its capabilities.
I’ll say it again. We’re forgetting fundamentals in this country.
Optimistic me wants to believe this, along with all the woke BS, even the apparent piss poor ship handling of late.
They don’t have time to teach and train navigation with every other critical bit of training the military has to do. I mean, doesn’t some computer just do all of that anyway?
Makes me wonder if the Marines still teach fixing and fighting with bayonets.
“The spirit of the bayonet is to kill” is what we learned in Army green in 1966. No idea of what is happening today.
My bayonet is a two-spirit.
Apparently so…
“Today, Marines wield the OKC-3S bayonets that are essentially KA-BARs with bayonet rings and locks. The Army’s M9 works as a large knife as well. As knives, they can be multipurpose tools for cutting, chopping, and even digging. A good knife goes a long way, even if it’s just opening MREs and breaking down cardboard boxes.”
https://www.sandboxx.us/blog/bayonets-in-2021-why-do-they-persist/
U.S. Army’s FM 23-25.
“The will to meet and destroy the enemy in hand-to-hand combat is the spirit of the bayonet.”
Yep, still there
dude, that’s the stealth coating!
Cussler’s “The Oregon Files”
They didn’t pay the dealer for rust coating.
I bet they skimped on the clear coat protection and interior treatments as well.
Putty couldn’t get them to pay for undercoating either.
High-Five!
I read this, and I am glad that I bailed out on physics after graduating and became an engineer.
Amen.
My opinions on dark energy and matter have always been that they are just stand-ins for a misunderstanding of the natural order.
Of course, some physicists latched onto those ideas and are loath to give them up. I think they resist giving them up because even though they worked on alternative theories, they were unable to find good ones and they’re envious of those who do.
Thanks for the series. It was a good refresher course and brought me up to speed on developments I was unaware of.
*glances at the Penrose tome on the shelf that taunts me and dares me to pick it up so it can humiliate me*
Well, they are loathe to give them up because they work better overall than anything else. Although as PM mentioned, people are looking for alternatives.
Penrose tome
“The Road to Reality”? I found that one rough. Especially when you see stuff like “and this becomes much more simple and obvious when viewed from the perspective of a hyperbolic manifold.” as i get a glassy expression and start to drool. And that’s a “popular” publication!
Yeah, that one.
I’m so out of practice on my math skills that I view it as a reeducation effort. I’d have to relearn everything just to get through it.
Which is why it just sits there, taunting me.
He’s got these cute little icons for questions – 3 of ’em, simple, hard, challenging. Looked at enough of the simple ones with a “WTF is this even asking” result to start to hate that smiling smug little face with his finger raised in triumph.
At least he starts with Pythagoras. I think I can get through that without too much despair.
Yeah, the physics of time is a subject I like to pound my head against like a brick wall. Time’s Arrow appears to be my version of Penrose.
What you can’t visualize a rotating tesseract moving through higher dimensions in your mind’s eye?
I’m surrounded by Neanderthals.
Nope. Just Irish.
Whats the difference? Invention of alcohol?
God invented whiskey to keep the Irish from ruling the world.
Obligatory
If time were a part of normal physics, it wouldn’t be mono directional which is the only way we experience/conceive it.
That has always bothered me. But, if you experienced backwards time, would you know it?
Normal may be and probably is just a subset of all existence.
*insert David Hume here*
I’m sometimes amazed how we can sometimes take as established truth things that rely on a single off-hand or unsupported statement from years ago.
Thank dog I’m not susceptible to such things!
I’ll be back in a bit, need to make sure I get my 10,000 steps.
https://healthblog.uofmhealth.org/womens-health/myth-busting-no-more-8-glasses-a-day
https://www.scientificamerican.com/article/its-time-to-end-the-war-on-salt/
I was aware of both of those – far too many are not.
My favorite: “eating fat makes you fat”.
From 2011. They were still respectable then, right?
Barely
It’s full of strings.
Actually what is the status of string theory?
G strings for the win!
The critiques I’ve read about string theory in recent years lead me to believe that it still does not have any testable hypotheses, which in my mind relegates it to “an interesting natural philosophy.” Others will probably disagree, YMMV, et cetera.
It’s still mathematical masturbation.
IMO, a clever mathematical construct. With absolutely no testable predictions (as of yet). So of value only insofar as one develops ideas and techniques and ways of thinking about things. As a model for physical reality? Not so useful.
I think the theoretical physics community is sort of zig-zagging their way towards that conclusion, but there’s still lots of smart people who’ve dedicated a significant portion of their careers to it, so…
Would that this was true in some other fields of scientific endeavor.
Kuhn pretty much laid bare the reality of science as a human endeavor.
I also like Feynman as well (from memory) science isn’t about keeping other people honest, it’s about keeping yourself honest.
Scientists love them some funding!
Pfoey. They’re angels.
On a serious note: Nice article.
The Corps has started booting out Marines who didn’t get the vax.
https://www.msn.com/en-us/news/us/more-than-100-marines-kicked-out-of-the-service-for-refusing-covid-vaccine/ar-AART0O7
The Krauts shutdown their nuke powerplants, now the French have to take some of theirs offline for repair. The Euros are going have to science really hars to stay warm this winter.
Maybe they should be nice to the Russians.
https://www.bloombergquint.com/technology/eu-power-markets-face-precarious-january-as-supply-risks-mount
Time to start drawing some new maps of Ukraine.
Damn your nimble fingers.
including their new province of Ukraine.?
I imagine the Germans fighting Russia in the Ukraine and it ends just like the “Battle of the Bulge” movie – Germans walking away from their out-of-gas Leopard tanks.
January power delivery in France at $715/MWh?
My big question when it comes to Big Bang cosmology is what to do with the “tired light” hypothesis. The settled science that c is an absolute, universal constant seems to be unprovable over the kind of enormous distances represented across the universe. What if light is slowing down in such tiny increments over such huge distances we can’t measure it using current methods? And since the distances to galaxies are themselves measured with redshift, which itself would be invalidated given tired light, it’s a self-licking ice cream cone. If tired light is, in fact, a thing, then distant quasars could potentially be a lot further away than distances derived from redshift measurements indicate.
TL;DR – Tired light fucks up our entire concept of the size and scope of the universe.
Tired light – proposed originally by one of those rare brilliant iconoclast Fred Zwicky – is pretty inconsistent with observations though. Not only because it fails to predict some cosmological observations, but because all the mechanisms proposed for it should have local observable effects that are not seen. Of course, that’s not to say there’s not some discovery waiting there, but it’s one of those things that is “fringe” simply because it doesn’t seem to work!
Pfft, here’s a true rare, brilliant iconoclast: https://www.masterbooks.com/starlight-and-time-paperback-single
Now that is intriguing. Almost tempted to take a look, if for no other reason than entertainment. Plus, the guy has a PhD behind is name. I’ve found people who like their titles to be nothing if not eminently trustworthy….
Jill Biden, EdD agrees.
Seriously, I can’t follow all the science, but I’ve enjoyed the series.
Once again,
lifeomicron comes at you fast:Pfft it’s not like they need 11 players on the pitch against Newcastle.
I’m cancelling meetings with people at a NY hospital (100% vaxxed) because a bunch of them have covid.
Unpossible.
Joe told me that the vaxxed won’t catch covid.
They can, but only from unvaccinated people. So the unvaxxed are to blame.
Really, we should simply execute all the filthy unvaxxed — it’s for the greater good!
I assume the hooligans of Liverpool are dealing with an outbreak?
I think you’re all missing the obvious answer – the expansion of the universe is accelerating because of Global Warming.
Maybe it’s expanding because all the other solar systems and galaxies want to get away from Trump.
Or they’re trying to avoid unvaxxed deplorables.
transphobia
I also struggle with the conservation of energy if everything is accelerating- but apparently that, and light being the limit to velocity are only local phenomena.
Maybe as the universe is expanding it’s stretching the nothing-fabric it came from and as that fabric stretches its pores are opening up and letting in something unknown into our dimension/universe and spreading us around kinda like a tsunami takes a town and spreads it around the countryside.
/just makin shit up
I find your ideas intriguing. Do you have a newsletter?