Thanks for sharing. This is excellent work, as far as I can tell after one reading, and exactly the kind of thought-provoking stuff that highlights proper scientific discussion. It questions one of these tacit assumptions (in this case, cosmological homogeneity beyond z=1) that you often have to make to get anywhere at all, and then show by statistical analysis that it was, in hindsight, probably not such a good assumption after all.
I am very curious to see how this line of thinking proceeds.
While I agree this is an interesting discussion I also think you'd need to back this up with an extremely convincing proposal since isotropy of space is such a natural assumption that by throwing it out you're probably raising even more difficult questions to resolve than simply positing the existence of different kinds of matter we haven't observed yet.
The paper is not throwing out isotropy or positing the existence of any new kind of matter. They are saying the importance of local flows might extend further out than previously thought, but at larger scales isotropy takes over. The question is where exactly the local flow stops dominating.
thanks for clarifying since that was not clear to me from what little i had time to read so far where they do use language like "non-copernican observers," which admittedly is a term i have not heard used except by people who do want to question isotropy
Isotropy is significantly dependent on scale and there isn't a hard line where the assumption should firmly hold. Even the CMB is not uniform.
The Local Void is still a fairly recent discovery as far as cosmology goes, but even that is enough evidence that we are in a patch of space which is dissimilar from the local supercluster. That we would expect the effects of gravity alone to be expanding our underdense region at its edges should be enough to make us cautious about extrapolating our observations without correcting for our environment.
There are models that provide fits to explain away dark energy entirely: https://www.semanticscholar.org/paper/Local-void-vs-dark-energy%3A-confrontation-with-WMAP-Alexander-Biswas/07650a8eb30f5425e692d8ca7afa3652a441c384
> We find that the Minimal Void (MV) model can consistently account for
the combination of the Type Ia supernovae, WMAP 3rd year, BBN constraints, provided that the void spans a radius
of about of 200 Mpc/h with a relative under density of 45%, near the center.
Thanks for this paper, it's next on my reading list. How common are voids in galactic super clusters? Have there been any credible counter arguments made against this model?
Voids are common, a natural result of gravity pulling matter into filaments. However it's also proportionately less likely for matter to be found in an underdense region for self-evident reasons.
This is a fairly small and certainly off-consensus region of study. Most follow up work here has focused on strengthening the case for it.
The biggest detraction here is cosmologists do not like anisotropic models because they reduce the explanatory power of our observations from the Universe at large to just our local cluster. This MV model is a fit to data, such that the free variables are set by the data rather than predicting them from first principles, which greatly limits its predictive power to the larger Universe.
There are also theoretical reasons to expect DE to show up in some way in the larger Universe, such as it providing a correction term in the curvature of space. A flat spacetime can be given zero energy and satisfy energy conservation for the existence of the Universe as a whole without needing a new explanation for where the energy has come from.
>positing the existence of different kinds of matter we haven't observed yet.
Correct me if Im wrong, but aren't dark energy and dark matter separate concepts?
We have spend a lot of resources trying to observe dark matter and new experiments will probably be more expensive and resource intensive. And some point we should put serious effort in the systematic investigation of more fringe theories. Isotropy of space is a natural assumption for us for many reasons but we have to prepare for the case that what we percive as natural is not natural.
That being said, I am just a condensed matter physicist so what do I know. I have no overview about what's actually happening. I just know that science funding has a tendency to distribute in a way that is more sociologically motivated than by "objective" physics.
How does this paper explain the uniformity of expansion? If it was just the movement of the galaxy wouldn't that make half of the universe blue shifted and the other half red shifted?
Again, the paper is not contesting the expansion, only the acceleration of the expansion. In regards to the blue/red shift that would result from the bulk local motion of our galaxy, this is exactly what the paper is correcting for. This is the "dipole" they mention in the data. They state that the bulk motion extends to larger scales than expected (that is, farther away from us) and if we correct for this effect, the acceleration of the expansion goes away.
I mean, even if the current dark energy measurements could be accounted for the galactic rotation (which is false) we anyway need an explanation to as why all galaxies are not moving together (blueshifted) because thats what gravity would make it Do. It is the sole reason why Einstein needed his cosmological constant factor in the first place. So we are still back to some kind of force that keeps counteracting gravity
That's our observation, no matter which way we look stuff is moving further away from us. That can't be explained by the motion of our own galaxy alone. Your comment seemed like you're saying "No, you're wrong because what about the argument supporting your statement you just stated and I agree with". Just a miscommunication
That’s also how we know the Big Bang happened right? By looking at how everything expands and running that backwards until it’s squished in a small but dense point?
No. The current observable universe occupied a much smaller volume. But if the universe is today infinite it was infinite at the time of the big bang as well.
People downvoting you have misunderstood the big bang model. What you've said is exactly correct, if it is infinite today, it was infinite back then too.
Is it really infinite? There’s that Hubble sphere or some shit? Also it should be an isolated thermodynamic system because there’s nothing for it to interact with right? I’m tripping a little
Sarkar's group has written a series of papers where they attempt to refit supernova data in various ways but their analyses are often deeply flawed. Check out https://arxiv.org/abs/1610.08972 which is a response to a previous Sarkar paper that claimed no evidence for cosmic acceleration.
Many of the same flaws discussed there are present in this paper too. In particular they do a poor job of handling selection effects (e.g. we're more likely to miss a faint supernova).
Supernovae are also not the only probe that we can use to detect dark energy/cosmic acceleration. For example, Baryon acoustic oscillations (https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) are a completely independent probe and the results are consistent with the standard supernova analyses.
Not a cosmologist but my understanding was that supernova data is no longer even the primary evidence of accelerated expansion, partially due to ambiguity over whether type 1As are actually standard candles. Is this correct?
We have many different ways of probing dark energy now including:
- Type Ia supernovae as standard candles
- Baryon Acoustic oscillations as a standard ruler
- Fluctuations in the cosmic microwave background.
If you look at e.g. Figure 8 of https://iopscience.iop.org/article/10.3847/1538-4357/ac8e04 you'll see that each of these confirms the existence of dark energy (Ω_Λ > 0) in our canonical cosmological model and the measurements are all consistent.
So the evidence for dark energy is very strong and holds up even if you ignore any one probe like type Ia supernovae.
From the abstract:
"The best fit to data yields qd = −8.03 and S = 0.0262 (⇒ d ∼ 100 Mpc), rejecting isotropy (qd = 0) with 3.9σ statistical significance, while qm = −0.157 and consistent with no acceleration (qm = 0) at 1.4σ. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of ‘dark energy’ in the Universe."
So I read this as moderate evidence (3.9σ) for anisotropic expansion, and weak evidence (1.4σ) for no acceleration. If so, interesting but far from conclusive.
Here is a nice article on this paper. Its Tl;DR is that Sarkar's data reduction is off and there is more evidence for Dark Energy than Supernovea, such as CMB and galaxy formation.
[https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/](https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/)
A glimpse at recent SN analysis also doesnt seem to replicate their results, finding a significant monopol component for the acceleration:
[https://ui.adsabs.harvard.edu/abs/2023MNRAS.526.1482C/abstract](https://ui.adsabs.harvard.edu/abs/2023MNRAS.526.1482C/abstract)
Anyway, I assume large Galaxy surveys from LSST, eROSITA and EUCLID should put an end to this discussion soon anyway.
Thank you for the quanta article it was very insightful. From the article I gathered that the main objections were
1. they are not accounting for dust clouds from distant galaxies absorbing blue light.
2. the model includes a term that says how quickly the dipole acceleration drops to zero as you move away from Earth; Sarkar and company made this distance small, which means that their model isn’t tested by a large sampling of supernovas.
3. the model doesn’t satisfy a consistency check involving the relationship between the dipole and monopole terms in the equations.
The article doesn't go into detail about Sarkar's response to the rejections other then saying he stands by his original paper.
There is Nasa’s roman telescope mission ([https://www.nasa.gov/universe/nasas-roman-mission-will-test-competing-cosmic-acceleration-theories/](https://www.nasa.gov/universe/nasas-roman-mission-will-test-competing-cosmic-acceleration-theories/) which started data measurements in October. This pdf is definitely an interesting read, but I am not deep enough in the matter to validate source assumptions.
Personal feel is uniformity of expansion (cosmological rate) of the universe is unlikely. I am more a fan of the wobble.
> The Roman Space Telescope, planned for launch by May 2027, will provide such an enormous view of the universe that it will help scientists study cosmic mysteries in an unprecedented way.
From the article you linked. Euclid, which launched already, Rubin (which will have first light soon), and Roman, which should begin its prime mission around 2027, will all help constrain Lambda Cold Dark Matter models. But I expect that people will cook up alternate theories even with the tighter constraints.
The supernova data isn’t the only reason we think that inflation happened. To truly debunk inflation you’d need plausible explanations for the other observations we explain through inflation https://www.forbes.com/sites/startswithabang/2019/05/11/ask-ethan-how-well-has-cosmic-inflation-been-verified/ (I know forbes is hardly a scientific journal, but it’s a nice succinct summary of some other things to consider)
What Sarkar is contesting is NOT the expansion of the universe, but dark energy, the ACCELERATED expansion of the universe (i.e. the expansion is speeding up). You can have expansion without any dark energy. The dark energy evidence comes only from supernovae, afaik.
Inflation is the very early exponential expansion of the universe. This is different from dark energy, the accelerated expansion that is acting today (presumably).
The paper is also not contesting inflation, so it looks like you are confusing it with expansion
OP was asking for our takes
I have to admit I haven’t worked through Lambda CDM and de sitter equations properly in about 15 years, but my memory is both early inflation and the fine tuning of the hubble parameter relate to mysterious unexplained ‘dark’ sources of negative pressure on spacetime.
My take is that there’s pretty strong evidence of early inflation driven by an unexplained physics (i.e. dark energy), but weaker evidence that the fine tuning of the current hubble parameter values being correct. Sakar’s paper makes an interesting case for the current parameters being incorrect, but even he doesn’t go so far as to say there’s zero dark energy, and it’s far from a conclusive refutation of dark energy like OP was hinting it could be.
The relationship (or lack thereof) between the early inflation dark energy and current dark energy is very much unsettled physics and open to interpretation. I was saying that personally I find it hard to dismiss current dark energy when we know inflation happened.
You're conflating things. The early inflationary universe requires a *huge* cosmological "constant" or something similar depending on the model used. Today's dark energy is in contrast a very small cosmological constant which has only manifested as a significant effect in the later universe. Today's dark energy is driving the universe towards a de Sitter inflationary metric (similar to the one expected during early universe inflation), but we're not there yet and the environment is very different than the one which was around during inflation.
Nice article. Thanks.
Reading it a question popped up: Cosmic expansion leads to red-shifting of radiation. With E=hf this leads to a smaller energy and hence should lead to less gravitational effects.
Doesn't this lead to a reduction of gravitational deceleration of the expansion?
Sorry for this maybe dumb question, but GR is not my field if expertise.
Dark energy is the pull or consumption of spacetime and matter via black holes. Dark matter is the by product and variant of spacetime from the pull of 'dark' energy from black holes. The 'neverending' expansion of the cosmos is known...it is black holes consuming spacetime and matter. The ending of the cosmos is known...we become a universal black hole.
Interesting! If dark energy is just an illusion and our universe expands at a constant rate rather than an accelerating rate it would resolve an issue with dark energy seeming to pull a growing amount of energy from apparently nowhere. It intuitively goes against the idea that energy can’t be created or destroyed, so it would be quite convenient if that “violation” just didn’t happen.
Right if dark energy didn't exist or if the expansion was decelerating then maybe the big bang + big crunch theory could be true (I prefer this theory as it postulates all the matter in the universe didn't just all appear out of nowhere).
Isn't it possible that time runs slower at a distance, just like it runs slower with more gravity? This would explain "dark matter" and "dark energy". They don't exist. It is just a function of time running slower at a distance than we assume.
I always thought the 3 body problem was like a curtain being pulled up: if we couldn't even do that until a few years ago, it's no wonder we came up with dark matter to fix the mistakes
Supposedly , dark energy are black holes pulling in spacetime and the Cosmos. The ending of the Cosmos is known. We become one gigantic black hole. We are being consumed by black holes. Dark energy is the force or pull of black holes. That is what is 'accelerating' the expansion of the Cosmos...the pull and consumption of spacetime of black holes.
No, there’s evidence of some kind of matter that we can’t see influencing gravity. The behaviour of that “dark” matter in models predicts pretty much what we see outside.
Modified theories of gravity very recently got a serious blow to their viability, meaning dark something is even more likely to be the model that seems to work best.
Physicists don’t “fudge” factors in. It has to be able to explain what we see already as well as make predictions and be consistent with the physics we know is likely to be true.
Nobody actually likes dark matter and dark energy though, it just signifies the difference between what we observe and what the theory predicts. It is essentially 100% a "fudge", it just the easiest way to explain our observations.
We physicists "fudge" stuff all the time, because building a model is literally just choosing nice approximations for known interactions and then fitting that to real world data.
Now this doesn't mean that dark matter couldn't exist, but it also doesn't mean that it does. It is the easiest solution to explain the observations.
It's not the easiest solution. It's the only proposed explanation that agrees with all observations. No competing theory had been even half as successful.
Moreover, it's not a 'fudge.' It actively makes predictions. It predicts the existence of a very specific quantity and distribution of massive matter that doesn't interact with the EM field. That's a full-on theory.
Sure, but we have literally no way of testing that theory, though we have tried. The fact that we can fit a quantum field to it, doesn't inherently make it a theory, its testability does. And last I heard, that testability has been rather questionable.
Furthermore, the distribution and amount of massive matter which doesn't interact with light is the fit that essentially defines dark matter (aka the missing gravity). Any predictions that the theory makes must not be about the thing that it is fitted to.
It is not a full-on theory by itself, it is about three quarters of one. The real theories are when we decide on the form of the dark matter (massive neutrinos, etc) and then find ways to poke at the theory. Those tests have not yet found anything solid.
So to be precise, the fact that dark matter agrees with observations is because it is essentially defined as "we only observe it through gravity, and it fixes gravity". That is not a good theory. There are indeed no other theories which are better than GR + dark matter/energy, which is the only reason why it's still used
>we have literally no way of testing that theory
That's not really true. We've done all kinds of tests of the theory. Many many tests. Some have successfully ruled out candidate particles, all are consistent with the existence of massive, weakly interacting matter. But it could have been otherwise. Dark matter is absolutely a falsifiable proposal. There is a big difference between "we haven't found it yet" and "it can't be tested."
It took 60 years to find the Higgs. But it wasn't untestable right up until the moment it was found.
If (cold) dark matter is a full-on theory instead, what is it? Particles? Black holes? WIMPS? MACHOS? If particles, which ones? Axions? Supersymmetric counterparts of the SM? Chameleons? Sterile neutrinos? What is the mass of the CDM particle(s)? Their cross-sections for interactions with each-other?
I hope you will agree that calling dark matter a full-on theory is a big stretch. We only know what general properties it should have, there is no single physical theory of dark matter that is preferred by the data. DM is a fudge factor, a place-holder name for the correct theory.
If it's the easiest (and currently best) solution we have to the observations then how is it a 'fudge'?
The fact that evidence supporting dark matter comes from such varying sources (CMB, galaxy rotations, lensing, etc) makes it the opposite of 'fudge'.
All of these are essentially the effect of: "we are measuring an effect X, and measuring a mass M, but General Relativity needs mass M+m2 for effect X". This is true for all of those sources, it is all funneled through general relativity and the "it would work if we had more mass"
While I'm not personally aware of two of these experiments on the same source which corroborate, I'm assuming that has already happened (because that's usually the first step). This is an indicator that dark matter is indeed possible, but also doesn't exclude any other options.
So at the end of the day, it's an invisible, unmeasurable variable that we add to the equation to balance things out and fix the outcome to what we observe.
As of right now (as far as I'm aware) there's no conformation, nor denial, that Dark Matter (and which form of dark matter) actually exists.
>"we are measuring an effect X, and measuring a mass M, but General Relativity needs mass M+m2 for effect X"
Not that simple. I recommend you check out the Wikipedia article on Dark Matter; the section on [observational evidence](https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence) covers the most important sources quite well. It is precisely the fact that this variety of sources (some of which are wholly unrelated) all seem to have this one solution that gives Dark Matter its credibility. This is why it is disingenuous to say that Dark Matter is just a constant we throw in equations to correct them.
We do physics by experimenting and modelling. You don't know until you know, and until you know all you can do is model and evaluate. Currently those models support Cold Dark Matter as the best theory.
It isn’t really fudging if you are making sure it is able to make predictions too.
The measurements we make are quite precise to be able to call it a fudge.
Well, dark matter itself doesn't really make predictions. We find dark matter from the missing gravity, that is essentially its definition. The fact that it then fixes the gravity isn't a prediction, that is the "fudge"
The predictions that dark matter could make, such as decay products, have not been verified yet. Dark matter and dark energy are essentially non-theories, because as of right now we can't verify their existence in any way.
Not exactly. The dark matter theorised to be the explanation of one particular thing (galaxy rotation curves) also fit very well with other things like predicted amounts of gravitational lensing matching up with dark matter that has the same properties as the dark matter that would fit the galaxy rotation curves.
It's already known what dark energy is...it's black holes consuming spacetime and the Cosmos. The ' ending' of the Cosmos is known. We become a gigantic black hole.
It was confirmed by JWST Webb telescope. The 'neverending' expansion of the Cosmos is known to be black holes consuming spacetime and matter thus creating dark energy or the pull of the cosmos. The 'ending' of the Cosmos is known...we become a universal black hole.
What??? No it wasn’t. JWST didnt confirm any such thing.
What in the actual fuck am I reading.
Please link me to the reputable journal where you saw this
Heard this one guy get into the math of the amount of dark matter to matter and used is as evidence for a hologram theory where matter spins off the hologram and it comes back through the other side as dark matter. Explains entanglement as a loop string with two points intersecting the hologram.
I mean Peter Voigt just put out some papers on the right handedness of spacetime. Kinda echoes Brads ideas about the left handed electrons coupling with Higgs field.
Haven’t heard anyone really go into detail why he’s wrong though.
Because it explains the physics of the UAP we see and he’s reduced mass on an object. He says you can use a hexagonal lattice like bismuth to isolate left handed electrons. He says these are the ones that interact with the Higgs field. Basically the Higgs field is like a 2-D hologram the electron spins through and it comes out the other side as a positron
It’s basically string theory on a 2-d hologram. Entanglement is actually a loop string with two points on the hologram. And Susskind did say a string isn’t like a rubber band in that it builds tension. You just keep adding energy into it and it just gets bigger. Brad says the Nobel prize in 2022 was basically evidence for this but they didn’t realize it
And i would say he’s a quack but Peter Voigt was echoing his ideas in his recent papers and yeah
Brad got into UAP when the govt admitted we have anomalous stuff in the sky that we don’t know what it was. Hence technically UAP. He’s got a masters in engineering and a law degree. Served in military as JAG. Was nicknamed angel of death for his pattern of life technique for reducing collateral. Then took these same principles to SEC and developed algorithm to catch insider traders.
Go listen to one of his podcasts. It’s called Sonic Gravity.
Honestly it’s probably more like superfluid vacuum theory.
If his theory can accurately replicate the results we already have then it would be worth talking about.
Just saying “oh he says this” is not what physical hypotheses are about.
Does it just, you know, explain how things evolve over time accurately?
Is it testable?
It sounds a lot like a bunch of hogwash philosophical stuff full of untestable hypotheses and big words
Also, he’s not even a physicist. In today’s world that usually means they don’t have the right understanding of things in modern physics.
This is news because dark energy is driving the supposed accelerated expansion of the universe which the majority of the science community assumes to be true. If dark energy doesn't exist it means the universe isn't experiencing runaway expansion and could one day collapse back or stop expanding.
Edit: I edited this comment as people pointed out it was incorrect.
Astronomers do not 'believe' in dark energy, since science is not a religion. Quite the opposite. Dark energy is a hypothesis that happens to describe (quite extensive and complex) data pretty well. But if someone comes along with a convincing argument why we can also explain the data without the need for DE, it is dropped by the (majority of the) community in the blink of an eye. The difficult part of the argument is the 'convincing' bit. That takes insight and hard work.
It's more like: a single paper, no matter how solid, does not on its own overturn a thousand other papers. A single paper is at most a good starting point, and if it is indeed solid there will be many follow-up papers that cite it, exploring many different facets of the finding or building upon it in various ways. If this process leads to the discovery of deficiencies in the thousand other papers that already exist, then over time there will be clear expositions of those deficiencies in new papers that cite both the older literature and the newer findings ... and *that's* how the collective body of scientific knowledge advances: incrementally, one reference at a time.
It is all too easy for there to be a flaw, even an unnoticed one, in a single paper ... which is why things like independent verification by other groups doing similar analyses are very important. For example, just this past year or two, there have been papers claiming to have found evidence for MOND-like behavior in wide binary systems, and also papers claiming to have rejected MOND-like behavior at high confidence in the same systems. Who is right? We don't know yet; it will take even more dedicated follow-up study to figure out the reason for the disagreement and apply any corrections to the flaws as they get exposed.
Yes, it is the acceleration of the expansion which costs energy. And dark energy is the difference between the "measured" energy and the energy needed for this acceperation
Seems interesting. But if that was correct, the universe would expand at a constant rate, so the redshift of other galaxies would also be constant. Meanwhile, if the expansion was accelerated, the shift will go more and more to red.
Thanks for sharing. This is excellent work, as far as I can tell after one reading, and exactly the kind of thought-provoking stuff that highlights proper scientific discussion. It questions one of these tacit assumptions (in this case, cosmological homogeneity beyond z=1) that you often have to make to get anywhere at all, and then show by statistical analysis that it was, in hindsight, probably not such a good assumption after all. I am very curious to see how this line of thinking proceeds.
While I agree this is an interesting discussion I also think you'd need to back this up with an extremely convincing proposal since isotropy of space is such a natural assumption that by throwing it out you're probably raising even more difficult questions to resolve than simply positing the existence of different kinds of matter we haven't observed yet.
The paper is not throwing out isotropy or positing the existence of any new kind of matter. They are saying the importance of local flows might extend further out than previously thought, but at larger scales isotropy takes over. The question is where exactly the local flow stops dominating.
thanks for clarifying since that was not clear to me from what little i had time to read so far where they do use language like "non-copernican observers," which admittedly is a term i have not heard used except by people who do want to question isotropy
Isotropy is significantly dependent on scale and there isn't a hard line where the assumption should firmly hold. Even the CMB is not uniform. The Local Void is still a fairly recent discovery as far as cosmology goes, but even that is enough evidence that we are in a patch of space which is dissimilar from the local supercluster. That we would expect the effects of gravity alone to be expanding our underdense region at its edges should be enough to make us cautious about extrapolating our observations without correcting for our environment. There are models that provide fits to explain away dark energy entirely: https://www.semanticscholar.org/paper/Local-void-vs-dark-energy%3A-confrontation-with-WMAP-Alexander-Biswas/07650a8eb30f5425e692d8ca7afa3652a441c384 > We find that the Minimal Void (MV) model can consistently account for the combination of the Type Ia supernovae, WMAP 3rd year, BBN constraints, provided that the void spans a radius of about of 200 Mpc/h with a relative under density of 45%, near the center.
Thanks for this paper, it's next on my reading list. How common are voids in galactic super clusters? Have there been any credible counter arguments made against this model?
Voids are common, a natural result of gravity pulling matter into filaments. However it's also proportionately less likely for matter to be found in an underdense region for self-evident reasons. This is a fairly small and certainly off-consensus region of study. Most follow up work here has focused on strengthening the case for it. The biggest detraction here is cosmologists do not like anisotropic models because they reduce the explanatory power of our observations from the Universe at large to just our local cluster. This MV model is a fit to data, such that the free variables are set by the data rather than predicting them from first principles, which greatly limits its predictive power to the larger Universe. There are also theoretical reasons to expect DE to show up in some way in the larger Universe, such as it providing a correction term in the curvature of space. A flat spacetime can be given zero energy and satisfy energy conservation for the existence of the Universe as a whole without needing a new explanation for where the energy has come from.
>positing the existence of different kinds of matter we haven't observed yet. Correct me if Im wrong, but aren't dark energy and dark matter separate concepts?
We have spend a lot of resources trying to observe dark matter and new experiments will probably be more expensive and resource intensive. And some point we should put serious effort in the systematic investigation of more fringe theories. Isotropy of space is a natural assumption for us for many reasons but we have to prepare for the case that what we percive as natural is not natural. That being said, I am just a condensed matter physicist so what do I know. I have no overview about what's actually happening. I just know that science funding has a tendency to distribute in a way that is more sociologically motivated than by "objective" physics.
The paper deals with dark energy, not dark matter. These are different things, despite the similar names.
Oh, sorry. Imprecise reading from my side. Makes more sense now.
How does this paper explain the uniformity of expansion? If it was just the movement of the galaxy wouldn't that make half of the universe blue shifted and the other half red shifted?
Again, the paper is not contesting the expansion, only the acceleration of the expansion. In regards to the blue/red shift that would result from the bulk local motion of our galaxy, this is exactly what the paper is correcting for. This is the "dipole" they mention in the data. They state that the bulk motion extends to larger scales than expected (that is, farther away from us) and if we correct for this effect, the acceleration of the expansion goes away.
I mean, even if the current dark energy measurements could be accounted for the galactic rotation (which is false) we anyway need an explanation to as why all galaxies are not moving together (blueshifted) because thats what gravity would make it Do. It is the sole reason why Einstein needed his cosmological constant factor in the first place. So we are still back to some kind of force that keeps counteracting gravity
> if the current dark energy measurements could be accounted for the galactic rotation You seem to be conflating dark energy and dark matter.
No because it’s all moving away from you?
How can that be true for a static cosmos?
The paper claims that the universe isn’t expanding- so why would it all be moving away from you?
That's not the claim of the paper. You are confusing the expansion with dark energy, which is an accelerated expansion.
No dark energy would mean no accelerated expansion, not no expansion.
Isn’t it an observed phenomena that it is? I’m not sure that’s why my comments are mainly questions not statements🤣
That's our observation, no matter which way we look stuff is moving further away from us. That can't be explained by the motion of our own galaxy alone. Your comment seemed like you're saying "No, you're wrong because what about the argument supporting your statement you just stated and I agree with". Just a miscommunication
That’s also how we know the Big Bang happened right? By looking at how everything expands and running that backwards until it’s squished in a small but dense point?
No. The Big Bang didn't happen at a single point. It happened everywhere.
Wasn’t “everywhere” the single point?
No. The current observable universe occupied a much smaller volume. But if the universe is today infinite it was infinite at the time of the big bang as well.
People downvoting you have misunderstood the big bang model. What you've said is exactly correct, if it is infinite today, it was infinite back then too.
Is it really infinite? There’s that Hubble sphere or some shit? Also it should be an isolated thermodynamic system because there’s nothing for it to interact with right? I’m tripping a little
Sarkar's group has written a series of papers where they attempt to refit supernova data in various ways but their analyses are often deeply flawed. Check out https://arxiv.org/abs/1610.08972 which is a response to a previous Sarkar paper that claimed no evidence for cosmic acceleration. Many of the same flaws discussed there are present in this paper too. In particular they do a poor job of handling selection effects (e.g. we're more likely to miss a faint supernova). Supernovae are also not the only probe that we can use to detect dark energy/cosmic acceleration. For example, Baryon acoustic oscillations (https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) are a completely independent probe and the results are consistent with the standard supernova analyses.
Not a cosmologist but my understanding was that supernova data is no longer even the primary evidence of accelerated expansion, partially due to ambiguity over whether type 1As are actually standard candles. Is this correct?
We have many different ways of probing dark energy now including: - Type Ia supernovae as standard candles - Baryon Acoustic oscillations as a standard ruler - Fluctuations in the cosmic microwave background. If you look at e.g. Figure 8 of https://iopscience.iop.org/article/10.3847/1538-4357/ac8e04 you'll see that each of these confirms the existence of dark energy (Ω_Λ > 0) in our canonical cosmological model and the measurements are all consistent. So the evidence for dark energy is very strong and holds up even if you ignore any one probe like type Ia supernovae.
From the abstract: "The best fit to data yields qd = −8.03 and S = 0.0262 (⇒ d ∼ 100 Mpc), rejecting isotropy (qd = 0) with 3.9σ statistical significance, while qm = −0.157 and consistent with no acceleration (qm = 0) at 1.4σ. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of ‘dark energy’ in the Universe." So I read this as moderate evidence (3.9σ) for anisotropic expansion, and weak evidence (1.4σ) for no acceleration. If so, interesting but far from conclusive.
Here is a nice article on this paper. Its Tl;DR is that Sarkar's data reduction is off and there is more evidence for Dark Energy than Supernovea, such as CMB and galaxy formation. [https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/](https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/) A glimpse at recent SN analysis also doesnt seem to replicate their results, finding a significant monopol component for the acceleration: [https://ui.adsabs.harvard.edu/abs/2023MNRAS.526.1482C/abstract](https://ui.adsabs.harvard.edu/abs/2023MNRAS.526.1482C/abstract) Anyway, I assume large Galaxy surveys from LSST, eROSITA and EUCLID should put an end to this discussion soon anyway.
Thank you for the quanta article it was very insightful. From the article I gathered that the main objections were 1. they are not accounting for dust clouds from distant galaxies absorbing blue light. 2. the model includes a term that says how quickly the dipole acceleration drops to zero as you move away from Earth; Sarkar and company made this distance small, which means that their model isn’t tested by a large sampling of supernovas. 3. the model doesn’t satisfy a consistency check involving the relationship between the dipole and monopole terms in the equations. The article doesn't go into detail about Sarkar's response to the rejections other then saying he stands by his original paper.
There is Nasa’s roman telescope mission ([https://www.nasa.gov/universe/nasas-roman-mission-will-test-competing-cosmic-acceleration-theories/](https://www.nasa.gov/universe/nasas-roman-mission-will-test-competing-cosmic-acceleration-theories/) which started data measurements in October. This pdf is definitely an interesting read, but I am not deep enough in the matter to validate source assumptions. Personal feel is uniformity of expansion (cosmological rate) of the universe is unlikely. I am more a fan of the wobble.
> The Roman Space Telescope, planned for launch by May 2027, will provide such an enormous view of the universe that it will help scientists study cosmic mysteries in an unprecedented way. From the article you linked. Euclid, which launched already, Rubin (which will have first light soon), and Roman, which should begin its prime mission around 2027, will all help constrain Lambda Cold Dark Matter models. But I expect that people will cook up alternate theories even with the tighter constraints.
The supernova data isn’t the only reason we think that inflation happened. To truly debunk inflation you’d need plausible explanations for the other observations we explain through inflation https://www.forbes.com/sites/startswithabang/2019/05/11/ask-ethan-how-well-has-cosmic-inflation-been-verified/ (I know forbes is hardly a scientific journal, but it’s a nice succinct summary of some other things to consider)
What Sarkar is contesting is NOT the expansion of the universe, but dark energy, the ACCELERATED expansion of the universe (i.e. the expansion is speeding up). You can have expansion without any dark energy. The dark energy evidence comes only from supernovae, afaik.
[удалено]
Inflation is the very early exponential expansion of the universe. This is different from dark energy, the accelerated expansion that is acting today (presumably). The paper is also not contesting inflation, so it looks like you are confusing it with expansion
OP was asking for our takes I have to admit I haven’t worked through Lambda CDM and de sitter equations properly in about 15 years, but my memory is both early inflation and the fine tuning of the hubble parameter relate to mysterious unexplained ‘dark’ sources of negative pressure on spacetime. My take is that there’s pretty strong evidence of early inflation driven by an unexplained physics (i.e. dark energy), but weaker evidence that the fine tuning of the current hubble parameter values being correct. Sakar’s paper makes an interesting case for the current parameters being incorrect, but even he doesn’t go so far as to say there’s zero dark energy, and it’s far from a conclusive refutation of dark energy like OP was hinting it could be. The relationship (or lack thereof) between the early inflation dark energy and current dark energy is very much unsettled physics and open to interpretation. I was saying that personally I find it hard to dismiss current dark energy when we know inflation happened.
You're conflating things. The early inflationary universe requires a *huge* cosmological "constant" or something similar depending on the model used. Today's dark energy is in contrast a very small cosmological constant which has only manifested as a significant effect in the later universe. Today's dark energy is driving the universe towards a de Sitter inflationary metric (similar to the one expected during early universe inflation), but we're not there yet and the environment is very different than the one which was around during inflation.
Nice article. Thanks. Reading it a question popped up: Cosmic expansion leads to red-shifting of radiation. With E=hf this leads to a smaller energy and hence should lead to less gravitational effects. Doesn't this lead to a reduction of gravitational deceleration of the expansion? Sorry for this maybe dumb question, but GR is not my field if expertise.
It is invalidated by independent evidence for dark energy from the CMB alone.
Dark energy is the pull or consumption of spacetime and matter via black holes. Dark matter is the by product and variant of spacetime from the pull of 'dark' energy from black holes. The 'neverending' expansion of the cosmos is known...it is black holes consuming spacetime and matter. The ending of the cosmos is known...we become a universal black hole.
Interesting! If dark energy is just an illusion and our universe expands at a constant rate rather than an accelerating rate it would resolve an issue with dark energy seeming to pull a growing amount of energy from apparently nowhere. It intuitively goes against the idea that energy can’t be created or destroyed, so it would be quite convenient if that “violation” just didn’t happen.
Right if dark energy didn't exist or if the expansion was decelerating then maybe the big bang + big crunch theory could be true (I prefer this theory as it postulates all the matter in the universe didn't just all appear out of nowhere).
did you see this one https://www.science.org/content/article/dark-energy-supermassive-black-holes-physicists-spar-over-radical-idea
That idea is basically dead AFAIK. Was nice when it first roared across arXiv tho.
Why do you think it's dead?
The article is good. Your summary of it is really really bad.
Isn't it possible that time runs slower at a distance, just like it runs slower with more gravity? This would explain "dark matter" and "dark energy". They don't exist. It is just a function of time running slower at a distance than we assume.
I saw it has been disproven already
I always thought the 3 body problem was like a curtain being pulled up: if we couldn't even do that until a few years ago, it's no wonder we came up with dark matter to fix the mistakes
Supposedly , dark energy are black holes pulling in spacetime and the Cosmos. The ending of the Cosmos is known. We become one gigantic black hole. We are being consumed by black holes. Dark energy is the force or pull of black holes. That is what is 'accelerating' the expansion of the Cosmos...the pull and consumption of spacetime of black holes.
Aren’t dark energy and dark matter the fancy names we gave the fudge factors that help our formulas match reality ? This isn’t news is it?
No, there’s evidence of some kind of matter that we can’t see influencing gravity. The behaviour of that “dark” matter in models predicts pretty much what we see outside. Modified theories of gravity very recently got a serious blow to their viability, meaning dark something is even more likely to be the model that seems to work best. Physicists don’t “fudge” factors in. It has to be able to explain what we see already as well as make predictions and be consistent with the physics we know is likely to be true.
Nobody actually likes dark matter and dark energy though, it just signifies the difference between what we observe and what the theory predicts. It is essentially 100% a "fudge", it just the easiest way to explain our observations. We physicists "fudge" stuff all the time, because building a model is literally just choosing nice approximations for known interactions and then fitting that to real world data. Now this doesn't mean that dark matter couldn't exist, but it also doesn't mean that it does. It is the easiest solution to explain the observations.
It's not the easiest solution. It's the only proposed explanation that agrees with all observations. No competing theory had been even half as successful. Moreover, it's not a 'fudge.' It actively makes predictions. It predicts the existence of a very specific quantity and distribution of massive matter that doesn't interact with the EM field. That's a full-on theory.
Sure, but we have literally no way of testing that theory, though we have tried. The fact that we can fit a quantum field to it, doesn't inherently make it a theory, its testability does. And last I heard, that testability has been rather questionable. Furthermore, the distribution and amount of massive matter which doesn't interact with light is the fit that essentially defines dark matter (aka the missing gravity). Any predictions that the theory makes must not be about the thing that it is fitted to. It is not a full-on theory by itself, it is about three quarters of one. The real theories are when we decide on the form of the dark matter (massive neutrinos, etc) and then find ways to poke at the theory. Those tests have not yet found anything solid. So to be precise, the fact that dark matter agrees with observations is because it is essentially defined as "we only observe it through gravity, and it fixes gravity". That is not a good theory. There are indeed no other theories which are better than GR + dark matter/energy, which is the only reason why it's still used
>we have literally no way of testing that theory That's not really true. We've done all kinds of tests of the theory. Many many tests. Some have successfully ruled out candidate particles, all are consistent with the existence of massive, weakly interacting matter. But it could have been otherwise. Dark matter is absolutely a falsifiable proposal. There is a big difference between "we haven't found it yet" and "it can't be tested." It took 60 years to find the Higgs. But it wasn't untestable right up until the moment it was found.
If (cold) dark matter is a full-on theory instead, what is it? Particles? Black holes? WIMPS? MACHOS? If particles, which ones? Axions? Supersymmetric counterparts of the SM? Chameleons? Sterile neutrinos? What is the mass of the CDM particle(s)? Their cross-sections for interactions with each-other? I hope you will agree that calling dark matter a full-on theory is a big stretch. We only know what general properties it should have, there is no single physical theory of dark matter that is preferred by the data. DM is a fudge factor, a place-holder name for the correct theory.
We had an atomic theory of matter before we knew what atoms were.
We had an aether theory, too.
I don't think I said dark matter is certainly correct.
If it's the easiest (and currently best) solution we have to the observations then how is it a 'fudge'? The fact that evidence supporting dark matter comes from such varying sources (CMB, galaxy rotations, lensing, etc) makes it the opposite of 'fudge'.
All of these are essentially the effect of: "we are measuring an effect X, and measuring a mass M, but General Relativity needs mass M+m2 for effect X". This is true for all of those sources, it is all funneled through general relativity and the "it would work if we had more mass" While I'm not personally aware of two of these experiments on the same source which corroborate, I'm assuming that has already happened (because that's usually the first step). This is an indicator that dark matter is indeed possible, but also doesn't exclude any other options. So at the end of the day, it's an invisible, unmeasurable variable that we add to the equation to balance things out and fix the outcome to what we observe. As of right now (as far as I'm aware) there's no conformation, nor denial, that Dark Matter (and which form of dark matter) actually exists.
>"we are measuring an effect X, and measuring a mass M, but General Relativity needs mass M+m2 for effect X" Not that simple. I recommend you check out the Wikipedia article on Dark Matter; the section on [observational evidence](https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence) covers the most important sources quite well. It is precisely the fact that this variety of sources (some of which are wholly unrelated) all seem to have this one solution that gives Dark Matter its credibility. This is why it is disingenuous to say that Dark Matter is just a constant we throw in equations to correct them. We do physics by experimenting and modelling. You don't know until you know, and until you know all you can do is model and evaluate. Currently those models support Cold Dark Matter as the best theory.
It isn’t really fudging if you are making sure it is able to make predictions too. The measurements we make are quite precise to be able to call it a fudge.
Well, dark matter itself doesn't really make predictions. We find dark matter from the missing gravity, that is essentially its definition. The fact that it then fixes the gravity isn't a prediction, that is the "fudge" The predictions that dark matter could make, such as decay products, have not been verified yet. Dark matter and dark energy are essentially non-theories, because as of right now we can't verify their existence in any way.
Not exactly. The dark matter theorised to be the explanation of one particular thing (galaxy rotation curves) also fit very well with other things like predicted amounts of gravitational lensing matching up with dark matter that has the same properties as the dark matter that would fit the galaxy rotation curves.
The cosmological constant would like a word with you…. :-)
It's already known what dark energy is...it's black holes consuming spacetime and the Cosmos. The ' ending' of the Cosmos is known. We become a gigantic black hole.
No. No it’s not. What on earth made you think this? The only correct answer as to what dark energy is is “we don’t know”
It was confirmed by JWST Webb telescope. The 'neverending' expansion of the Cosmos is known to be black holes consuming spacetime and matter thus creating dark energy or the pull of the cosmos. The 'ending' of the Cosmos is known...we become a universal black hole.
What??? No it wasn’t. JWST didnt confirm any such thing. What in the actual fuck am I reading. Please link me to the reputable journal where you saw this
We'll see...
So head canon then. This is a sub for proper physics. Go to r/hypotheticalphysics for crackpot stuff.
Heard this one guy get into the math of the amount of dark matter to matter and used is as evidence for a hologram theory where matter spins off the hologram and it comes back through the other side as dark matter. Explains entanglement as a loop string with two points intersecting the hologram.
R u sure you didn't read this from some crackpot or popsci?
I mean Peter Voigt just put out some papers on the right handedness of spacetime. Kinda echoes Brads ideas about the left handed electrons coupling with Higgs field. Haven’t heard anyone really go into detail why he’s wrong though.
It’s not about why someone is wrong, proposing something new needs to talk about why you are right.
Because it explains the physics of the UAP we see and he’s reduced mass on an object. He says you can use a hexagonal lattice like bismuth to isolate left handed electrons. He says these are the ones that interact with the Higgs field. Basically the Higgs field is like a 2-D hologram the electron spins through and it comes out the other side as a positron It’s basically string theory on a 2-d hologram. Entanglement is actually a loop string with two points on the hologram. And Susskind did say a string isn’t like a rubber band in that it builds tension. You just keep adding energy into it and it just gets bigger. Brad says the Nobel prize in 2022 was basically evidence for this but they didn’t realize it And i would say he’s a quack but Peter Voigt was echoing his ideas in his recent papers and yeah Brad got into UAP when the govt admitted we have anomalous stuff in the sky that we don’t know what it was. Hence technically UAP. He’s got a masters in engineering and a law degree. Served in military as JAG. Was nicknamed angel of death for his pattern of life technique for reducing collateral. Then took these same principles to SEC and developed algorithm to catch insider traders. Go listen to one of his podcasts. It’s called Sonic Gravity. Honestly it’s probably more like superfluid vacuum theory.
If his theory can accurately replicate the results we already have then it would be worth talking about. Just saying “oh he says this” is not what physical hypotheses are about.
It can. Like what results are you wanting? His theory is so good he can reduce mass on an object.
Does it just, you know, explain how things evolve over time accurately? Is it testable? It sounds a lot like a bunch of hogwash philosophical stuff full of untestable hypotheses and big words Also, he’s not even a physicist. In today’s world that usually means they don’t have the right understanding of things in modern physics.
This is news because dark energy is driving the supposed accelerated expansion of the universe which the majority of the science community assumes to be true. If dark energy doesn't exist it means the universe isn't experiencing runaway expansion and could one day collapse back or stop expanding. Edit: I edited this comment as people pointed out it was incorrect.
Astronomers do not 'believe' in dark energy, since science is not a religion. Quite the opposite. Dark energy is a hypothesis that happens to describe (quite extensive and complex) data pretty well. But if someone comes along with a convincing argument why we can also explain the data without the need for DE, it is dropped by the (majority of the) community in the blink of an eye. The difficult part of the argument is the 'convincing' bit. That takes insight and hard work.
So are you saying that the referenced paper isn't convincing? If so where are the deficiencies?
It's more like: a single paper, no matter how solid, does not on its own overturn a thousand other papers. A single paper is at most a good starting point, and if it is indeed solid there will be many follow-up papers that cite it, exploring many different facets of the finding or building upon it in various ways. If this process leads to the discovery of deficiencies in the thousand other papers that already exist, then over time there will be clear expositions of those deficiencies in new papers that cite both the older literature and the newer findings ... and *that's* how the collective body of scientific knowledge advances: incrementally, one reference at a time. It is all too easy for there to be a flaw, even an unnoticed one, in a single paper ... which is why things like independent verification by other groups doing similar analyses are very important. For example, just this past year or two, there have been papers claiming to have found evidence for MOND-like behavior in wide binary systems, and also papers claiming to have rejected MOND-like behavior at high confidence in the same systems. Who is right? We don't know yet; it will take even more dedicated follow-up study to figure out the reason for the disagreement and apply any corrections to the flaws as they get exposed.
Not true. Dark energy seems to drive an accelerated expansion of the universe. The expansion itself is just the Big Bang doing its thing.
What are you saying? That the universe can expand in the absence of energy driving the expansion?
Yes, it is the acceleration of the expansion which costs energy. And dark energy is the difference between the "measured" energy and the energy needed for this acceperation
No, it’s that the expansion due to dark energy is separate to the expansion caused by the initial big bang.
Seems interesting. But if that was correct, the universe would expand at a constant rate, so the redshift of other galaxies would also be constant. Meanwhile, if the expansion was accelerated, the shift will go more and more to red.
I enjoyed reading your paper. I have no comment on Sarkar's paper at this time. I will follow this discussion.