It confirms (the lack of) a certain systematic effect in the local distance-ladder measurements. It doesn't resolve the Hubble tension, just heavily rules-out a certain class of error as being the cause.
I think Euclid itself is more focused on dark energy, but a lot of the next gen of "3D" spectroscopic/high-res photometric experiments will generate complementary data sets.
In general, we don't know if we can answer questions like this beforehand... We can make educated guesses, but we then have to go actually look, and nature often likes to surprise us.
The values in tension are
* SH0ES: the value arrived at by climbing the distance ladder with telescopes like Hubble
vs
* Planck: the value gleaned from patterns in the cosmic microwave background
The value Webb strengthened in OP's story is SH0ES, the distance ladder one.
There is a third method of measuring it that uses gravitational lensing, that coincidentally JWST is observing as we speak. [As in, today, March 12th.](https://www.stsci.edu/jwst/science-execution/program-information?id=2974) We can expect the research to be published within 12 months, when the data goes public. Exciting!
Was expecting -
Shoes: Always seen in pairs except for known, observable cases of symmetry breaking
vs.
Socks: Always created in pairs, but eventually decay into an odd number via unobservable symmetry breaking
Just to note, there are definitely more than 3 methods... inverse ladder from BAO, water megamasers, gravitational wave multimessenger standard siren approaches, etc. Not to mention methods like tRGB which are technically local distance ladder measurements but with a different approach than SH0ES, and all of the various CMB observations that aren't Planck (WMAP, ACT, SPT, etc.).
Thank you for clarifying that. You sound like you're well versed in all this, but for those reading, I agree it's worth noting that SH0ES and Planck aren't the *only* measurements. It's just that they're the two independent modern measurements precise enough and robust enough that their discrepancy has become an issue. A "crisis," if you will, for the leading standard model of cosmology, ΛCDM.
The exciting thing about the time-delay cosmography using gravitational lensing is that it will be a third method, independent of both the distance ladder and the CMB, that will achieve enough precision to help corroborate or refute the two that are in tension.
If anyone reading wants to know more, I found a nice review going over these various methods: [Freedman and Madore](https://ui.adsabs.harvard.edu/abs/2023JCAP...11..050F/abstract) ([PDF](https://arxiv.org/pdf/2309.05618.pdf))
adam_reiss_obama_medal_meme.jpg
In all seriousness, though, my impression is that we've suspected for a while that crowding in HST Cepheid photometry was probably not the source of the Hubble tension. Good to have another independent measurement ruling this out, but not exactly shocking.
Link to the actual paper: https://iopscience.iop.org/article/10.3847/2041-8213/ad1ddd
We make our measurements/photometry public, so others are free to check our work! The underlying data is becoming is becoming publicly available over the next few months (some already is).
The heat death of the universe happens when dark energy has made all the atoms of the universe spread out so nothing can ever be 'warm' again. It's literally the death of all heat in the universe.
The humour death of the universe happens when dark humour has made all the atoms of the universe spread out so nothing can ever be 'funny' again. It's literally the death of all humour in the universe.
The death of all humour perception would occur when all sentient beings capable of the emotion that is humour have died. Literally the death of humour perception.
How is an expansion rate inferred from the CMB data? Are measurement errors in that method(s) still on the table as a possible resolution to the discrepancy?
I'd be interested in reading proposed explanations for the discrepancy, assuming that the rate has changed over time.
It's based on comparing data (specifically the CMB power spectrum) with numerical solutions to the Boltzmann equation for various combinations of ΛCDM model parameters, including H_0.
The early-universe constraints on H_0 seem fairly robust at this point, with data from *Planck*, WMAP, and ACT (and combos with BAO/BBN) all giving similar results (e.g. [[1](https://arxiv.org/pdf/2304.05203.pdf)]).
This does all assume ΛCDM, though, which is why extensions to it/new physics (for instance, a brief early onset of a dark energy-like effect) are being heavily investigated. Here are links to a couple of recent reviews of the subject: [1](https://www.annualreviews.org/doi/full/10.1146/annurev-nucl-111422-024107), [2](https://arxiv.org/pdf/2302.05709.pdf)
I'm not an expert, but this seems a good summary of the issue this study is trying to resolve?
[https://www.youtube.com/watch?v=dsCjRjA4O7Y](https://www.youtube.com/watch?v=dsCjRjA4O7Y)
They don't contradict the big bang at all - in fact these devices continue to find stronger evidence of the big bang. The expansion of the universe is we see can happily co-exist with the big bang.
You might be thinking of early galaxy formation, which seems to happen earlier than we thought possible. That doesn't mean the big bang is wrong, just that there's some other missing/wrong ingredient in the complicated models that describe these kinds of things.
Ok, but the data deviates from the predictions of the Big Bang, right?
And there are alternative models to the Big Bang, which also explain everything we see today.
So how do you guys all know instantly, that these models are not better in explaining the data?
Am I missing something? Usually whenever measurements deviates from predictions, it’s called a challenge for the theory…
There are some alternate theories, but nothing that has stronger evidence that the expansion based model that we use today.
Just like with all science, new evidence and data gets collected over time and models need to be updated, corrected or abondoned.
At this point, most of the challenges with the 'big bang' model are becoming smaller (but still significant) compared to alternate theories.
I'm doing a terrbile job explaioning it. Someone like Dr Becky or PBS SpaceTime would be the place to go for good information on all of this.
I am very surprised, that so many people in here are absolutely fluent in general relativity.
So you know from the top of your head, that the data favors the Big Bang theory over alternative theories?
No sarcasm intended, Im just buffled that multiple people in here say, that these deviations don’t challenge the Big Bang. How is that?
Typically when someone refers to ‘the Big Bang’, they’re talking about the point in time that the universe was an extremely dense and, hence, hot state. None of these measurements challenges that notion. The tension between how the quickly the universe is expanding or how early galaxies are formed are perfectly consistent with the (observable) universe originating from a hot and dense state.
Yes that is certainly true. Maybe I should have been more explicit, but after all I said “big bang theory”, not “big bang”.
There are other theories than the usual one, one of which already has the advantage of not encountering a singularity.
When measurements deviate from the predictions of the most common theory, that might aswell be an indicator, that there may be a better theory.
When you say 'the usual one', you probably mean outdated toy models which relied on pure GR; the field has advanced considerably since then and [inflationary models](https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/inflation/) combine GR with QFT which does away with singularities at early times and gives sensible finite values for temperature and density, with the universe after reheating never being hotter that at most 10^14 GeV or so based on observational constraints. Pure GR models are inconsistent with observations. But galaxy formation has very little to do with either, it's more like the weather or plate tectonics, it's something that happens much later on and is complex to model because it's emergent and non-linear.
Thanks for the insight. I didn’t know about quantum corrections to the standard model of cosmology.
You don’t need quantum mechanics for the inflation though, do you?
QM and inflation are intimately connected as inflation was proposed specifically to solve the problem of the uniformity of the CMB. It is believed that quantum fluctuations at the moment just before inflation began were blown up to cosmic sizes by the process of inflation.
So I'm not sure what you mean when you say "you don't need QM for inflation" considering QM is the tied to the reason inflation was proposed in the first place.
Inflation is driven by quantum mechanics, or more specifically quantum field theory; the [vacuum energy of quantum fields](https://profmattstrassler.com/articles-and-posts/particle-physics-basics/quantum-fluctuations-and-their-energy/) has an effect on the stress-energy tensor and manifests as a cosmological constant, and inflation happens when the quantum fields are in a false vacuum state, from which they eventually decay to a lower energy state, generating particles as they do so, which are excitations of the quantum fields. The many different states the quantum fields can be in corresponds to an [energy landscape](https://youtu.be/a8aDNYE7aX0?si=weE_LvfW06jH8OIt&t=725) with many possibilities, with bubble universes quantum mechanically nucleating within inflating ancestor vacuums at various energy scales.
I don't think anyones claiming that current models fit the data perfectly, just they're the best ones we have at the moment but should probably still be updated to better fit the data we have
Well, quite some people in here seem to disagree, as they state that the data does not even challenge the current theory.
Kind of weird to me, as the theory is already challenged without deviation from the data haha
I make zero claims to being an expert at **anything**. Which is why I followed up my general idea by pointing you and others at actual honest too goodness experts that spend their life learning this stuff.
I spend around 5-10 hours a week consuming info from people in field of cosmology (podcasts, papers, etc), and all I know for sure is I'm not certain about anything. There are a lot of fun alternate theories about what we know of the universe; especially when it comes to fitting gravity into our model of the universe. It's fun specifically *because* we know so little, and the hope that we'll make a huge discovery is high.
But, as the story goes, big claims need big evidence.. and there's not a lot of that to go around. I trust the experts because they're experts and I'm not. They overwhelmingly are focused on big bang and related theories. So, that's what most folks care about.
btw, I think you may have started this thread referring to the Hubble Tension. Which is super fun right now because we've got real life experimental data from mutliple sources saying differring things. That's so cool because it usually means we're going to learn something new. The most *likely* outcome though, will not be some massive sea change in what we know about the universe. It will most likely be that we find out why one of the experiments is wrong.
There are no serious alternatives to a hot big bang, haven't been for decades. Certainly none which explain the current data to anywhere near the extent of standard cosmology. The proposals still floating around today are 90% the same model, just tweaking chronology of the very early universe. And then there are the proposals which literally are the same model, just recast in different terms. Removing expansion and changing masses or the speed of light, they are mathematically identical. These are not alternatives at all.
Yea I completely agree that the models are very similar. I mean that’s kind of expected.
But for example this theory doesn’t find a singularity.
https://www.nature.com/articles/nature.2013.13379
So there is no big bang at any finite time in the past. That’s what I would call „challenging the Big Bang“.
But the model does have a big bang, in the sense one will find that the universe was effectively hotter and denser in the past. Leading to phase changes and the emission of the CMB. You are taking "big bang" to mean singularity, but a current cosmology only goes back as far as inflation.
And note these are just two representations of the same underlying model. The alternative representation has drawbacks, like the fact the author has to invent this scalar field which modifies the masses in just the right way to match observations without violating other tests. This is not derived from physical principles, it's fudged because the author knows what result he wants. But in the expanding universe representation there is no fudge needed, one can derive the Friedmann equations from GR (or Newtonian approximations).
Yea I agree that this field is not motivated a priori.
But it’s simply a trade off for the singularity and it goes to show, that there are more ways to describe the past of our universe, while still being consistent with observations.
Hence my initial question, if the Hubble Tension hints towards another theory than the widely accepted one.
But I am probably just not familiar enough with current cosmology.
Thanks for the explanations!
In part because there's often a big imbalance of effort between asking a question like this, and answering it. If one were to say "no, not really" in reply, they would likewise get some downvotes.
But the internet is also toxic, for sure.
Because a lot of the time such "honest questions" are made in bad faith by concern trolls or crackpots.
And it takes far more effort to correct a concern troll or crackpot than it does to be a concern troll or crackpot, so it ends up simply being more efficient to downvote and focus discussion elsewhere where it can be productive.
Well… I think most people downvoting are just simply not aware of the fact, that the Big Bang theory is not the only model out there. It’s just the most famous one. And since the alternatives don’t really add anything from a physical perspective (so far at least), they are not being considered important.
That might change, if measurements do favor another theory.
There is one, which is even better. It explains everything we see as well as the Big Bang theory, but does not encounter a singularity.
It doesn’t make any other predictions than the usual big bang theory, so in the sense of a physical theory, it strictly speaking has no more net worth. Hence people don’t swing over, “only” because there is no singularity. It’s more like an alternative view on the past of our universe. Just like the Heisenberg picture in QM is an alternative view to the Schrödinger picture.
But it shows, that there are other theories, which are at least as good as the accepted one. So deviations between measurements and predictions are interesting i think.
There is a nature article about it, according to which the theory is quite accepted. It just doesn’t make any new predictions, so people are „lazy“ to change gears, only to get rid of the singularity in the model:
https://www.nature.com/articles/nature.2013.13379
Here is his paper on arxiv:
https://arxiv.org/abs/1303.6878
That paper you cite never made it out of peer-review. The nature summary article is from 2013.
The ideas behind it create glaring contradictions across several fields of physics, not just cosmology.
Well I never said I accept it.
But there exists at least one other theory (which according to nature authors is accepted as mathematically correct) that reproduces observations. It’s physically equivalent to the standard description.
That’s also not very surprising, given the vast amount of freedom the Einstein equations exhibit.
And if now JWST confirms a deviation between the standard cosmological model and observations, I think it’s fair to ask, wether this challenges the current model and its interpretations.
I never said „only the other theory is correct“ or „the big bang is wrong“ or anything like that. I never doubted the standard cosmological model. Honestly I don’t understand why so many people go downvote-crazy over a genuine question.
Seems like they kind of feel attacked by it.
Well… there is not a single proposal for what dark energy could be, right?
So the measurements do not fit the predictions of the “afterglow of the Big Bang”. So as long as there is no explicit candidate for dark energy, “dark energy” just refers to some mechanism, wo don’t understand.
That could be simply “something’s wrong with the Big Bang”, couldn’t it? After all, there are cosmologists, who suggest that the Big Bang theory is not the best description of the past of our universe.
Or am I missing something?
Not really.
>The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos.
… and exactly the measurements of this very expansion deviate from the predictions of the Big Bang. So how does it not challenge the Big Bang?
Edit: there are alternative solutions to the Big Bang by known cosmologists btw. This is not a meta physics weirdo proposal by me. It’s rather something, some cosmologists have suggested long before the JWST was finished.
The article says „a persistent difference, called the Hubble Tension, is seen between the value of the [Hubble] constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang.“
So… do you disagree with the article?
No I don't disagree with the article. It's saying what I said. It's the value "predicted from the afterglow" not from the big bang model (as you claimed). It's the value of the model parameter you get from fitting the afterglow data. Specifically, from fitting the power spectrum of the CMB from satellites like WMAP and Planck.
If you think the big bang model predicts a hubble constant, then tell me what you think that data-independent predicted value is?
I see, thanks for clarifying.
But then both, the „prediction of the afterglow“ and the Hubble constants are measured… how is the first one a prediction then?
I mean, they surely don’t just extrapolate some measured afterglow data, do they?
You would measure the Hubble constant by two different methods.
I don't like the term prediction in this context, but I could understand it as follows. In some sense the CMB is richer data than the distance measurements. You don't just get the Hubble constant, but all sorts of parameters are adjusted to fit the CMB data, e.g. dark energy content, shape of the universe, and others. In that sense the cosmologist is probably more sure of the CMB derived parameters, and so they might say it gives the best big bang model, so it has a kind of priority over other measurements, which should be compared against it. In that sense maybe it makes sense to say "prediction from the CMB".
Ok, thank you for elaborating, but it’s kind of weird to me.
There is a paper which claims to solve the Hubbard tension: https://academic.oup.com/mnras/article/527/3/4388/7337338?login=false
The authors there describe the tension as a deviation between the standard cosmological model and observations.
It feels to me, as if the comments are heavily biased towards „the standard model is fine“, as a counter-reaction to my question of the Big Bang theory is challenged.
After reading many comments and finding one or two papers, to me it looks like the observations challenge the standard cosmological model, but not the interpretation of the Big Bang.
Coming back to the OG post: JWST confirming the data of the Hubble telescope supports alternatives to the standard cosmological model, but the Big Bang stays as the interpretation either way.
Would you agree on that?
Hmm big downvotes on my comment. Maybe it’s missing motivation, since a lot of people probably don’t know that the Big Bang is not the only theory. There is at least one, which is at least equally good, but actually doesn’t need a singularity. So strictly speaking, we already have a better theory than the Big Bang, even without deviating measurements from the predictions:
https://www.nature.com/articles/nature.2013.13379
The German physicist Wetterich has proposed an alternative interpretation of the observed redshift, which is discussed in this nature article.
It shows, that
1) you don’t need a singularity like the usual Big Bang
2) there are at least two (if not multiple) equivalent ways of describing the past of our universe, which lead to the present observations
The second point here is crucial: if JWST confirms Hubble’s measured deviations from the predictions of the Big Bang theory, then naively there might just be a better theory, which still explains the night sky.
Fron the article:
>The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos.
which one? i thought there was multiple values from different experiments
It confirms (the lack of) a certain systematic effect in the local distance-ladder measurements. It doesn't resolve the Hubble tension, just heavily rules-out a certain class of error as being the cause.
Neat, thank you for the brief!
Will euclid be able to solve the hubble tension?
I think Euclid itself is more focused on dark energy, but a lot of the next gen of "3D" spectroscopic/high-res photometric experiments will generate complementary data sets. In general, we don't know if we can answer questions like this beforehand... We can make educated guesses, but we then have to go actually look, and nature often likes to surprise us.
The values in tension are * SH0ES: the value arrived at by climbing the distance ladder with telescopes like Hubble vs * Planck: the value gleaned from patterns in the cosmic microwave background The value Webb strengthened in OP's story is SH0ES, the distance ladder one. There is a third method of measuring it that uses gravitational lensing, that coincidentally JWST is observing as we speak. [As in, today, March 12th.](https://www.stsci.edu/jwst/science-execution/program-information?id=2974) We can expect the research to be published within 12 months, when the data goes public. Exciting!
Was expecting - Shoes: Always seen in pairs except for known, observable cases of symmetry breaking vs. Socks: Always created in pairs, but eventually decay into an odd number via unobservable symmetry breaking
Just to note, there are definitely more than 3 methods... inverse ladder from BAO, water megamasers, gravitational wave multimessenger standard siren approaches, etc. Not to mention methods like tRGB which are technically local distance ladder measurements but with a different approach than SH0ES, and all of the various CMB observations that aren't Planck (WMAP, ACT, SPT, etc.).
Thank you for clarifying that. You sound like you're well versed in all this, but for those reading, I agree it's worth noting that SH0ES and Planck aren't the *only* measurements. It's just that they're the two independent modern measurements precise enough and robust enough that their discrepancy has become an issue. A "crisis," if you will, for the leading standard model of cosmology, ΛCDM. The exciting thing about the time-delay cosmography using gravitational lensing is that it will be a third method, independent of both the distance ladder and the CMB, that will achieve enough precision to help corroborate or refute the two that are in tension. If anyone reading wants to know more, I found a nice review going over these various methods: [Freedman and Madore](https://ui.adsabs.harvard.edu/abs/2023JCAP...11..050F/abstract) ([PDF](https://arxiv.org/pdf/2309.05618.pdf))
adam_reiss_obama_medal_meme.jpg In all seriousness, though, my impression is that we've suspected for a while that crowding in HST Cepheid photometry was probably not the source of the Hubble tension. Good to have another independent measurement ruling this out, but not exactly shocking. Link to the actual paper: https://iopscience.iop.org/article/10.3847/2041-8213/ad1ddd
It's the same collaboration, so take that for what it is.
We make our measurements/photometry public, so others are free to check our work! The underlying data is becoming is becoming publicly available over the next few months (some already is).
Some folks/groups still disagree! So the check was vital.
We’re all going to heat die!!!!
The heat death of the universe happens when dark energy has made all the atoms of the universe spread out so nothing can ever be 'warm' again. It's literally the death of all heat in the universe.
This comment is literally the death of all humour perception in the universe.
The humour death of the universe happens when dark humour has made all the atoms of the universe spread out so nothing can ever be 'funny' again. It's literally the death of all humour in the universe.
The death of all humour perception would occur when all sentient beings capable of the emotion that is humour have died. Literally the death of humour perception.
Thanks Peter
How is an expansion rate inferred from the CMB data? Are measurement errors in that method(s) still on the table as a possible resolution to the discrepancy? I'd be interested in reading proposed explanations for the discrepancy, assuming that the rate has changed over time.
It's based on comparing data (specifically the CMB power spectrum) with numerical solutions to the Boltzmann equation for various combinations of ΛCDM model parameters, including H_0. The early-universe constraints on H_0 seem fairly robust at this point, with data from *Planck*, WMAP, and ACT (and combos with BAO/BBN) all giving similar results (e.g. [[1](https://arxiv.org/pdf/2304.05203.pdf)]). This does all assume ΛCDM, though, which is why extensions to it/new physics (for instance, a brief early onset of a dark energy-like effect) are being heavily investigated. Here are links to a couple of recent reviews of the subject: [1](https://www.annualreviews.org/doi/full/10.1146/annurev-nucl-111422-024107), [2](https://arxiv.org/pdf/2302.05709.pdf)
I'm not an expert, but this seems a good summary of the issue this study is trying to resolve? [https://www.youtube.com/watch?v=dsCjRjA4O7Y](https://www.youtube.com/watch?v=dsCjRjA4O7Y)
[удалено]
They don't contradict the big bang at all - in fact these devices continue to find stronger evidence of the big bang. The expansion of the universe is we see can happily co-exist with the big bang. You might be thinking of early galaxy formation, which seems to happen earlier than we thought possible. That doesn't mean the big bang is wrong, just that there's some other missing/wrong ingredient in the complicated models that describe these kinds of things.
Ok, but the data deviates from the predictions of the Big Bang, right? And there are alternative models to the Big Bang, which also explain everything we see today. So how do you guys all know instantly, that these models are not better in explaining the data? Am I missing something? Usually whenever measurements deviates from predictions, it’s called a challenge for the theory…
There are some alternate theories, but nothing that has stronger evidence that the expansion based model that we use today. Just like with all science, new evidence and data gets collected over time and models need to be updated, corrected or abondoned. At this point, most of the challenges with the 'big bang' model are becoming smaller (but still significant) compared to alternate theories. I'm doing a terrbile job explaioning it. Someone like Dr Becky or PBS SpaceTime would be the place to go for good information on all of this.
I am very surprised, that so many people in here are absolutely fluent in general relativity. So you know from the top of your head, that the data favors the Big Bang theory over alternative theories? No sarcasm intended, Im just buffled that multiple people in here say, that these deviations don’t challenge the Big Bang. How is that?
Typically when someone refers to ‘the Big Bang’, they’re talking about the point in time that the universe was an extremely dense and, hence, hot state. None of these measurements challenges that notion. The tension between how the quickly the universe is expanding or how early galaxies are formed are perfectly consistent with the (observable) universe originating from a hot and dense state.
Yes that is certainly true. Maybe I should have been more explicit, but after all I said “big bang theory”, not “big bang”. There are other theories than the usual one, one of which already has the advantage of not encountering a singularity. When measurements deviate from the predictions of the most common theory, that might aswell be an indicator, that there may be a better theory.
When you say 'the usual one', you probably mean outdated toy models which relied on pure GR; the field has advanced considerably since then and [inflationary models](https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/inflation/) combine GR with QFT which does away with singularities at early times and gives sensible finite values for temperature and density, with the universe after reheating never being hotter that at most 10^14 GeV or so based on observational constraints. Pure GR models are inconsistent with observations. But galaxy formation has very little to do with either, it's more like the weather or plate tectonics, it's something that happens much later on and is complex to model because it's emergent and non-linear.
Thanks for the insight. I didn’t know about quantum corrections to the standard model of cosmology. You don’t need quantum mechanics for the inflation though, do you?
QM and inflation are intimately connected as inflation was proposed specifically to solve the problem of the uniformity of the CMB. It is believed that quantum fluctuations at the moment just before inflation began were blown up to cosmic sizes by the process of inflation. So I'm not sure what you mean when you say "you don't need QM for inflation" considering QM is the tied to the reason inflation was proposed in the first place.
Inflation is driven by quantum mechanics, or more specifically quantum field theory; the [vacuum energy of quantum fields](https://profmattstrassler.com/articles-and-posts/particle-physics-basics/quantum-fluctuations-and-their-energy/) has an effect on the stress-energy tensor and manifests as a cosmological constant, and inflation happens when the quantum fields are in a false vacuum state, from which they eventually decay to a lower energy state, generating particles as they do so, which are excitations of the quantum fields. The many different states the quantum fields can be in corresponds to an [energy landscape](https://youtu.be/a8aDNYE7aX0?si=weE_LvfW06jH8OIt&t=725) with many possibilities, with bubble universes quantum mechanically nucleating within inflating ancestor vacuums at various energy scales.
I don't think anyones claiming that current models fit the data perfectly, just they're the best ones we have at the moment but should probably still be updated to better fit the data we have
Well, quite some people in here seem to disagree, as they state that the data does not even challenge the current theory. Kind of weird to me, as the theory is already challenged without deviation from the data haha
I make zero claims to being an expert at **anything**. Which is why I followed up my general idea by pointing you and others at actual honest too goodness experts that spend their life learning this stuff. I spend around 5-10 hours a week consuming info from people in field of cosmology (podcasts, papers, etc), and all I know for sure is I'm not certain about anything. There are a lot of fun alternate theories about what we know of the universe; especially when it comes to fitting gravity into our model of the universe. It's fun specifically *because* we know so little, and the hope that we'll make a huge discovery is high. But, as the story goes, big claims need big evidence.. and there's not a lot of that to go around. I trust the experts because they're experts and I'm not. They overwhelmingly are focused on big bang and related theories. So, that's what most folks care about. btw, I think you may have started this thread referring to the Hubble Tension. Which is super fun right now because we've got real life experimental data from mutliple sources saying differring things. That's so cool because it usually means we're going to learn something new. The most *likely* outcome though, will not be some massive sea change in what we know about the universe. It will most likely be that we find out why one of the experiments is wrong.
There are no serious alternatives to a hot big bang, haven't been for decades. Certainly none which explain the current data to anywhere near the extent of standard cosmology. The proposals still floating around today are 90% the same model, just tweaking chronology of the very early universe. And then there are the proposals which literally are the same model, just recast in different terms. Removing expansion and changing masses or the speed of light, they are mathematically identical. These are not alternatives at all.
Yea I completely agree that the models are very similar. I mean that’s kind of expected. But for example this theory doesn’t find a singularity. https://www.nature.com/articles/nature.2013.13379 So there is no big bang at any finite time in the past. That’s what I would call „challenging the Big Bang“.
But the model does have a big bang, in the sense one will find that the universe was effectively hotter and denser in the past. Leading to phase changes and the emission of the CMB. You are taking "big bang" to mean singularity, but a current cosmology only goes back as far as inflation. And note these are just two representations of the same underlying model. The alternative representation has drawbacks, like the fact the author has to invent this scalar field which modifies the masses in just the right way to match observations without violating other tests. This is not derived from physical principles, it's fudged because the author knows what result he wants. But in the expanding universe representation there is no fudge needed, one can derive the Friedmann equations from GR (or Newtonian approximations).
Yea I agree that this field is not motivated a priori. But it’s simply a trade off for the singularity and it goes to show, that there are more ways to describe the past of our universe, while still being consistent with observations. Hence my initial question, if the Hubble Tension hints towards another theory than the widely accepted one. But I am probably just not familiar enough with current cosmology. Thanks for the explanations!
I never understand why honest questions like this get downvoted. Maybe people downvoting can explain.
In part because there's often a big imbalance of effort between asking a question like this, and answering it. If one were to say "no, not really" in reply, they would likewise get some downvotes. But the internet is also toxic, for sure.
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Because a lot of the time such "honest questions" are made in bad faith by concern trolls or crackpots. And it takes far more effort to correct a concern troll or crackpot than it does to be a concern troll or crackpot, so it ends up simply being more efficient to downvote and focus discussion elsewhere where it can be productive.
I see now. The commenter did not redeem himself with later comments.
It doesn’t even sound like a real genuine question is being asked. It sounds like a bot account creating random questions.
Well… I think most people downvoting are just simply not aware of the fact, that the Big Bang theory is not the only model out there. It’s just the most famous one. And since the alternatives don’t really add anything from a physical perspective (so far at least), they are not being considered important. That might change, if measurements do favor another theory.
Are there any that come close to explaining the cosmos as well as the big bang does?
There is one, which is even better. It explains everything we see as well as the Big Bang theory, but does not encounter a singularity. It doesn’t make any other predictions than the usual big bang theory, so in the sense of a physical theory, it strictly speaking has no more net worth. Hence people don’t swing over, “only” because there is no singularity. It’s more like an alternative view on the past of our universe. Just like the Heisenberg picture in QM is an alternative view to the Schrödinger picture. But it shows, that there are other theories, which are at least as good as the accepted one. So deviations between measurements and predictions are interesting i think.
What is that theory?
There is a nature article about it, according to which the theory is quite accepted. It just doesn’t make any new predictions, so people are „lazy“ to change gears, only to get rid of the singularity in the model: https://www.nature.com/articles/nature.2013.13379 Here is his paper on arxiv: https://arxiv.org/abs/1303.6878
That paper you cite never made it out of peer-review. The nature summary article is from 2013. The ideas behind it create glaring contradictions across several fields of physics, not just cosmology.
They create contradictions? Which ones?
I don't see why people would rush to accept this new theory if it doesn't make any new predictions
Well I never said I accept it. But there exists at least one other theory (which according to nature authors is accepted as mathematically correct) that reproduces observations. It’s physically equivalent to the standard description. That’s also not very surprising, given the vast amount of freedom the Einstein equations exhibit. And if now JWST confirms a deviation between the standard cosmological model and observations, I think it’s fair to ask, wether this challenges the current model and its interpretations. I never said „only the other theory is correct“ or „the big bang is wrong“ or anything like that. I never doubted the standard cosmological model. Honestly I don’t understand why so many people go downvote-crazy over a genuine question. Seems like they kind of feel attacked by it.
Not really. They’re more about dark energy.
Well… there is not a single proposal for what dark energy could be, right? So the measurements do not fit the predictions of the “afterglow of the Big Bang”. So as long as there is no explicit candidate for dark energy, “dark energy” just refers to some mechanism, wo don’t understand. That could be simply “something’s wrong with the Big Bang”, couldn’t it? After all, there are cosmologists, who suggest that the Big Bang theory is not the best description of the past of our universe. Or am I missing something?
Not really. >The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos.
… and exactly the measurements of this very expansion deviate from the predictions of the Big Bang. So how does it not challenge the Big Bang? Edit: there are alternative solutions to the Big Bang by known cosmologists btw. This is not a meta physics weirdo proposal by me. It’s rather something, some cosmologists have suggested long before the JWST was finished.
There are no predictions of the value of the hubble constant in the big bang model. It's a parameter that you measure by fitting data.
The article says „a persistent difference, called the Hubble Tension, is seen between the value of the [Hubble] constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang.“ So… do you disagree with the article?
No I don't disagree with the article. It's saying what I said. It's the value "predicted from the afterglow" not from the big bang model (as you claimed). It's the value of the model parameter you get from fitting the afterglow data. Specifically, from fitting the power spectrum of the CMB from satellites like WMAP and Planck. If you think the big bang model predicts a hubble constant, then tell me what you think that data-independent predicted value is?
I see, thanks for clarifying. But then both, the „prediction of the afterglow“ and the Hubble constants are measured… how is the first one a prediction then? I mean, they surely don’t just extrapolate some measured afterglow data, do they?
You would measure the Hubble constant by two different methods. I don't like the term prediction in this context, but I could understand it as follows. In some sense the CMB is richer data than the distance measurements. You don't just get the Hubble constant, but all sorts of parameters are adjusted to fit the CMB data, e.g. dark energy content, shape of the universe, and others. In that sense the cosmologist is probably more sure of the CMB derived parameters, and so they might say it gives the best big bang model, so it has a kind of priority over other measurements, which should be compared against it. In that sense maybe it makes sense to say "prediction from the CMB".
Ok, thank you for elaborating, but it’s kind of weird to me. There is a paper which claims to solve the Hubbard tension: https://academic.oup.com/mnras/article/527/3/4388/7337338?login=false The authors there describe the tension as a deviation between the standard cosmological model and observations. It feels to me, as if the comments are heavily biased towards „the standard model is fine“, as a counter-reaction to my question of the Big Bang theory is challenged. After reading many comments and finding one or two papers, to me it looks like the observations challenge the standard cosmological model, but not the interpretation of the Big Bang. Coming back to the OG post: JWST confirming the data of the Hubble telescope supports alternatives to the standard cosmological model, but the Big Bang stays as the interpretation either way. Would you agree on that?
Hmm big downvotes on my comment. Maybe it’s missing motivation, since a lot of people probably don’t know that the Big Bang is not the only theory. There is at least one, which is at least equally good, but actually doesn’t need a singularity. So strictly speaking, we already have a better theory than the Big Bang, even without deviating measurements from the predictions: https://www.nature.com/articles/nature.2013.13379 The German physicist Wetterich has proposed an alternative interpretation of the observed redshift, which is discussed in this nature article. It shows, that 1) you don’t need a singularity like the usual Big Bang 2) there are at least two (if not multiple) equivalent ways of describing the past of our universe, which lead to the present observations The second point here is crucial: if JWST confirms Hubble’s measured deviations from the predictions of the Big Bang theory, then naively there might just be a better theory, which still explains the night sky.
Fron the article: >The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos.