To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past.
The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of the spectrum: redshift. (Think of the wavelength of a wavy line drawn on a piece of rubber that's then stretched out.) We've known for nearly 100 years that the universe is expanding. (Edit: not just that the objects in it are moving apart but that space itself is expanding.)
The evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do. That means they were moving away from us slower in the past, so something must be accelerating them.
We use the brightness of Type Ia supernovae to measure distance. Even though supernovae aren't identically bright, their brightness follows a curve which lets us calculate their peak brightness (they are standardizable).
This paper argues that the calculations cosmologists use to standardize supernovae brightness fail to take into account the age of the progenitor stars, as far as I can tell. If true, this means our distance measurements are inaccurate and these stars are actually closer than we thought, enough to restore to linear relationship between distance and redshift that one would expect in a universe expanding at a constant rate.
In other words, their redshift is lower not because the expansion rate of space was lower in the past, but because they're not as far away as we thought they were.
Speaking from the pov as a former astrophysicist, that definition of redshift is not quite accurate.
While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity.
The Universe is expanding at every known point at the same time at the same rate. However, this is only an observable effect over > 10 Mpc of distance (e.g. extra-galactic distances). This is far too large to effect a point particle like a photon no matter how far it travels so I'm afraid your analogy of a rubber sheet is incorrect.
The lengthening of said photon's wavelength comes instead from doppler expansion due to the nature of differing relativistic reference frames.
According to our local reference frame, doppler effects of nearby stars and galaxies are only due to local motion such as Andromeda being blue shifted as it approaches us for our eventual merger. However, as you go further and further out from our galaxy the metric expansion of spacetime begins to dominate the relative motion of all bodies, leading to observing progressively redder and redder light curves. A galaxy billions of light years away is perceived to be moving away from our reference frame at a significant percentage of the speed of light!
However, if you were to change our relativistic reference frame to match a distance galaxy's you would not see its photons "stretched out" but in fact they would look completely unshifted despite having traversed nearly all of spacetime, expanding as it went.
If I am reading this correctly, in plain English what it seems like they are suggesting is that old Type Ia supernovae worked differently from newer supernovae; e.g. that a Type Ia supernova 5 billion years ago had a different brightness curve than a Type Ia supernova from 50 million years ago.
On its face this seems like an extraordinary claim; I can’t think of how to square it with the (fundamental) assumption that the laws of the universe have not changed during its lifetime.
Thanks for the explanation, but I'm stuck on the last sentence of this part:
>evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do.
I think what you mean is "than we'd expect them to."
I'm not an astronomer, but "tired light" makes more intuitive sense to me to explain the redshift. In effect, we already know that matter can affect light through gravitational interaction. Since light is travelling so fast and far it seems intuitive thst interstellar matter, as fleeting as it is, could act to slow light down over these great spacetime distances.
It is hard to overstate how important the resolution of this question is to physics, and in particular to theoretical physics. The “cosmological constant problem”, that is the problem explaining the cosmological acceleration (if it exists), is arguably the most important and hardest question in high energy theoretical physics. Many theoreticians have spent significant effort studying this question, working under the assumption that the empirical evidence is solid. If this is not the case, it changes the landscape of cutting edge physics research.
There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration).
Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.
Do you know if these measurements were possible in the past, and no one thought of doing them? Or are they only recently possible, enabled by new technology?
What's more mind-boggling to me is all these thousands of scientists running around looking at the extreme oddity of multi-dimensional string theory, and nobody bothered to check if the cosmological constant is actually real.
It seems like physics is really being held back by perverse incentives.
And of course my pocket view that string theory will turn out to be the single largest waste of brilliant human minds in history.
Good. Science is meant to be a honest search for facts: data, knowledge and wisdom. Being wrong is a feature. "I don't know" is an acceptable starting point with no shame attached. Being certain means a mountain of data to back it up. Being allowed to be wrong is a requirement. Anyone saying a scientist can't ever be wrong is likely placing oddball limits on progress that will only damage and limit the future[1]. How can you experiment if you can never be wrong?
It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain.
Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example.
Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed.
* not me.
[1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that.
[2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.
Dark matter is definitely not a rounding error [0]. There are multiple evidence for strong gravity effects where we just don't see the required matter the explain the observed phenomenons [1][2]
> Taken at face values, the luminosity evolution of SN is significant enough to question the very existence of dark energy. When the luminosity evolution of SN is properly taken into account, the team found that the evidence for the existence of dark energy simply goes away
Cosmology is great because there's still so much in flux. There are so many fundamental things that are still in active research. I find it all very exciting.
"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption.""
Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?
The question is moot: it's precisely because we have evidence of things not currently explained (observation does not fit theory) that we must postulate that our theory is wrong, or that there is more to discover, or both.
"Dark energy" is a conventional term to describe some energy of unknown source that has the effect of accelerating space expansion with time. We call "dark energy" the thing that explains this observation, whatever that thing might be (we just assume it's some form of energy since it produces motion, acceleration, in a way seemingly opposed to, and stronger than gravity, but for all we knew it could be fluffy creatures from the 7th dimension, "energy" is just an educated guess).
If you remove the observational discrepancy, then you remove the need for "dark energy" to exist in the first place.
The article precisely suggests that:
- there was no such observational discrepancy, rather errors in calculations following observation
- reality is thus shown to conform to our current equations; it's our interpretation of the pretty pictures we took that was wrong all along; this is now corrected.
If true, it's the end of dark energy as a cause because the consequence is gone.
At no point (before or after it's proven or disproven) does "dark energy" imply a postulate on "what it actually is" — and chances are, when we explain previously unknown phenomena, the finders come up with a new theory and ad hoc terminology. Rarely the word sticks when it's just too good an intuition — e.g. the "atom".
Note that "dark matter" is exactly the same, it's a conventional term to denote some matter-like unknown object that has the effect of giving galaxies their characteristic shapes and interactions forming much larger patterns (structure about as big to individual galaxies as galaxies are to individual stars).
It is my impression that dark energy is generally accepted in cosmology. Whether that counts as "proceeding as if dark energy is well evidenced" is perhaps a different question. If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there. That something should be evidence. Is it enough to count as "well evidenced"? Perhaps not, especially if this new study is correct that one piece of the evidence does not actually support dark energy.
This doesn't really address your point, but the 2011 physics Nobel [1] said that "What is known is that dark energy constitutes about three quarters of the Universe."
Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least.
>> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?
As a non-cosmologist just reading HN I would say yes. Not quite as extensively as Dark matter though. I personally think that's a mistake too based on my limited research on the topic. If these are both overturned it will be a huge blow to "scientists" credibility in the eyes of the public. That's how invested they are.
Do I understand correctly that this is actually saying that accelerating expansion of the universe may be in error? That there is, instead, no accelerating at all, but merely constant expansion?
Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.
There are very few ways to modify Einstein's Equations and still have them make sense. An easy one is to add a constant term. Such a term is known as the Cosmological Constant, and a positive value for it would result in a constant repulsive force between masses regardless of distance. This results in an accelerating expansion of the entire universe, but, with a supremely small value it only becomes noticeable at large scales, where it starts to dominate attractive gravity. This appears to model what we're observed happening with galaxy clusters.
Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. However, the article refers to observational evidence measuring the expansion of the universe, not dark energy. There is no evidence for dark energy as such, and if you listen to colloquia on cosmology, you will hear about the cosmological constant, not dark energy. It is not necessary to hypothesize the existence of negative energy particles to model what we've observed, and you'll only really hear the term used in the popular press because it sounds sexy.
There is a standard cosmological model called LCDM model, Lambda Cold Dark Matter model, which is basically the minimal thing you can use to fit cosmological observations, it contains a cosmological constant and cold dark matter, that is dark matter that is heavy enough that it is cold in the present universe. From the cosmic microwave background and Baryon Acoustic Oscillations (BAO), that is basically the distribution of galaxies, you can measure values for your favorite cosmological model. There are additionally for the dark matter density galactic rotation curves and for the cosmological constant super nova data.
Now dark energy is basically another name for the cosmological constant. (In general relativity the cosmological constant gives you the curvature of empty space, and dark energy is the same term moved to the right hand side.) However, the philosophical difference is, that sufficiently funny particles, like for example the Higgs, can easily mimic the effect of an cosmological constant. So there is an industry of people who calculate the effects of different extensions of the standard model on LCDM cosmology.
Now, above I said that CMB, BAO and SN data all agree in cosmological observations on the value of the cosmological constant. So for it to be wrong, it needs to either evolve, or several different measurements need to conspire to mask the effect of an constant. So my assumption is, either their non standard evolution is compatible with LCDM cosmology, or there is something wrong with the analysis.
Amusingly, this video is about entirely different work that also calls into question the basis for claims about dark energy.
Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.
So these guys criticize SN-!a as standard candles, and then rely on other results criticizing BAO and CMB measurements also indicating accelerating expansions. However, why all these measurement would err in the wrong direction is not clear. I'm not convinced yet.
Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable.
In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but there is no reason to assume it is the only one. We just don't get to study any young-universe stars that haven't blown up.
Did anybody even discuss metallicity and possible effects on brightness of t1a sn's, when DE was first proclaimed? If not, why not?
One or two years from now I invite you to take a look back at this comment and see if you still feel so smug. This is a relatively recent paper, give it some time to be chewed up and spit out by the cosmological community before hailing it as the deathknell of a decades old tricky problem.
Even if this paper is correct, there is still overwhelming evidence for dark energy provided by other observations, in particular those of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO). This article provides some details on why Dark Energy is in no danger of being called in question: https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...
As far as I can tell, Quanta Magazine article does mention the original post findings. Additionally, the Quanta article and the findings preprint were published just a week apart. Not enough time to formulate a good response:
* Quanta Magazine article: 17 Dec 2019
* Arxiv preprint: 10 Dec 2019 [1]
CMB and BAO are mentioned in the original post too:
> Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely.
I know they are proposing different mechanisms for the error in calculation but it gives a sense of a 'moment' shifting against dark energy. Coincidence?
Spatial expansion is a great heuristic explanation, but it can be misleading: Locally, the cosmological constant will manifest as just another pseudo-force, easily overcome by nuclear and electromagnetic forces holding us together.
When dark energy was first accepted, it seemed to me, as an outsider, that it happened very quickly, without, apparently, any time as a possibly-contentious, 'could this be so?' hypothesis in the way that, for example, dark matter did (and, to some extent, still is.) That surprised me because, up to that point, there seemed to be a problem with the cosmological distance ladder, with different methods getting different results, and with there being stars that seemed older than the universe supposedly was.
In comparison, when superluminal neutrinos were tentatively announced a few years ago, there was a lot of justified skepticism about there being experimental error (admittedly, overthrowing special relativity is an even more extraordinary claim than dark energy.)
Are galaxies in old universe more densely packed than in our neighbourhood?
Can expansion be seen not in redshift but in angular distances of galaxies? I'm asking in general not in relationship to the article. It wouldn't help for the problem raised by this article.
Do you know any good source where I could follow through the whole argument that universe is expanding and the expansion accelerates? Without handweaving.
I thought there was little reason to expect a big rip, because it requires assumptions about an increasing cosmological constant, which there’s no evidence for.
radiation spreads and matter clumps. in this universe matter was allowed to form but radiation dominates. island chains swallowed up by a rising ocean.
if you look at the magnetic soup we call matter, or maybe electromagnetism is a better term, is dark matter / dark energy / anti-matter (&anti energy??) just the same thing of a higher frequency
say if matter / observables go from 0hz - 30+ Zhz.. is dark energy from 30+Zhz to ???Zhz and perhaps anti matter / energy from ???Zhz to ???????Zhz? (more question marks being higher ? :D )
Electromagnetism is only one of a number of fundamental forces [1]. See [0] if you are curious about EM radiation at different frequencies. Radio and microwaves, infrared and visible light, ultraviolet light up to x-rays and gammarays are all part of the EM spectrum.
[+] [-] flashman|6 years ago|reply
The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of the spectrum: redshift. (Think of the wavelength of a wavy line drawn on a piece of rubber that's then stretched out.) We've known for nearly 100 years that the universe is expanding. (Edit: not just that the objects in it are moving apart but that space itself is expanding.)
The evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do. That means they were moving away from us slower in the past, so something must be accelerating them.
We use the brightness of Type Ia supernovae to measure distance. Even though supernovae aren't identically bright, their brightness follows a curve which lets us calculate their peak brightness (they are standardizable).
This paper argues that the calculations cosmologists use to standardize supernovae brightness fail to take into account the age of the progenitor stars, as far as I can tell. If true, this means our distance measurements are inaccurate and these stars are actually closer than we thought, enough to restore to linear relationship between distance and redshift that one would expect in a universe expanding at a constant rate.
In other words, their redshift is lower not because the expansion rate of space was lower in the past, but because they're not as far away as we thought they were.
[+] [-] bananabreakfast|6 years ago|reply
While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity.
The Universe is expanding at every known point at the same time at the same rate. However, this is only an observable effect over > 10 Mpc of distance (e.g. extra-galactic distances). This is far too large to effect a point particle like a photon no matter how far it travels so I'm afraid your analogy of a rubber sheet is incorrect.
The lengthening of said photon's wavelength comes instead from doppler expansion due to the nature of differing relativistic reference frames.
According to our local reference frame, doppler effects of nearby stars and galaxies are only due to local motion such as Andromeda being blue shifted as it approaches us for our eventual merger. However, as you go further and further out from our galaxy the metric expansion of spacetime begins to dominate the relative motion of all bodies, leading to observing progressively redder and redder light curves. A galaxy billions of light years away is perceived to be moving away from our reference frame at a significant percentage of the speed of light!
However, if you were to change our relativistic reference frame to match a distance galaxy's you would not see its photons "stretched out" but in fact they would look completely unshifted despite having traversed nearly all of spacetime, expanding as it went.
[+] [-] snowwrestler|6 years ago|reply
On its face this seems like an extraordinary claim; I can’t think of how to square it with the (fundamental) assumption that the laws of the universe have not changed during its lifetime.
[+] [-] wallace_f|6 years ago|reply
>evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do.
I think what you mean is "than we'd expect them to."
[+] [-] mirimir|6 years ago|reply
But maybe there are other standardizable objects. The sense I got from TFA is that there aren't.
[+] [-] alex77456|6 years ago|reply
May be a stupid question but wouldn't this apply only if we knew that the universe is uniformly dense? And we only see a tiny portion of it.
[+] [-] brylie|6 years ago|reply
[+] [-] guygurari|6 years ago|reply
There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration).
Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.
[+] [-] RookyNumbas|6 years ago|reply
[+] [-] BoiledCabbage|6 years ago|reply
It seems like physics is really being held back by perverse incentives.
And of course my pocket view that string theory will turn out to be the single largest waste of brilliant human minds in history.
[+] [-] rs23296008n1|6 years ago|reply
It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain.
Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example.
Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed.
* not me.
[1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that.
[2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.
[+] [-] tiborsaas|6 years ago|reply
[0] https://www.forbes.com/sites/briankoberlein/2016/09/23/rotat...
[1] https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to...
[2] http://cosmology.berkeley.edu/Education/CosmologyEssays/Grav...
Briefly, dark matter is very real, it's our knowledge that is dark.
[+] [-] Pigo|6 years ago|reply
https://www.youtube.com/watch?v=ZcV25N37-C4
[+] [-] sparker72678|6 years ago|reply
Cosmology is great because there's still so much in flux. There are so many fundamental things that are still in active research. I find it all very exciting.
[+] [-] tomrod|6 years ago|reply
[+] [-] jshevek|6 years ago|reply
Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?
[+] [-] K0SM0S|6 years ago|reply
"Dark energy" is a conventional term to describe some energy of unknown source that has the effect of accelerating space expansion with time. We call "dark energy" the thing that explains this observation, whatever that thing might be (we just assume it's some form of energy since it produces motion, acceleration, in a way seemingly opposed to, and stronger than gravity, but for all we knew it could be fluffy creatures from the 7th dimension, "energy" is just an educated guess).
If you remove the observational discrepancy, then you remove the need for "dark energy" to exist in the first place.
The article precisely suggests that:
- there was no such observational discrepancy, rather errors in calculations following observation
- reality is thus shown to conform to our current equations; it's our interpretation of the pretty pictures we took that was wrong all along; this is now corrected.
If true, it's the end of dark energy as a cause because the consequence is gone.
At no point (before or after it's proven or disproven) does "dark energy" imply a postulate on "what it actually is" — and chances are, when we explain previously unknown phenomena, the finders come up with a new theory and ad hoc terminology. Rarely the word sticks when it's just too good an intuition — e.g. the "atom".
Note that "dark matter" is exactly the same, it's a conventional term to denote some matter-like unknown object that has the effect of giving galaxies their characteristic shapes and interactions forming much larger patterns (structure about as big to individual galaxies as galaxies are to individual stars).
[+] [-] AnimalMuppet|6 years ago|reply
[+] [-] dfischer|6 years ago|reply
[+] [-] awb|6 years ago|reply
I thought dark matter and dark energy are simply placeholders for a discrepancy we see between our models of the universe and our observations. No?
[+] [-] carbocation|6 years ago|reply
Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least.
1 = https://www.nobelprize.org/prizes/physics/2011/press-release...
[+] [-] phkahler|6 years ago|reply
As a non-cosmologist just reading HN I would say yes. Not quite as extensively as Dark matter though. I personally think that's a mistake too based on my limited research on the topic. If these are both overturned it will be a huge blow to "scientists" credibility in the eyes of the public. That's how invested they are.
[+] [-] crazygringo|6 years ago|reply
Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.
[+] [-] philipov|6 years ago|reply
Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. However, the article refers to observational evidence measuring the expansion of the universe, not dark energy. There is no evidence for dark energy as such, and if you listen to colloquia on cosmology, you will hear about the cosmological constant, not dark energy. It is not necessary to hypothesize the existence of negative energy particles to model what we've observed, and you'll only really hear the term used in the popular press because it sounds sexy.
[+] [-] yk|6 years ago|reply
Now dark energy is basically another name for the cosmological constant. (In general relativity the cosmological constant gives you the curvature of empty space, and dark energy is the same term moved to the right hand side.) However, the philosophical difference is, that sufficiently funny particles, like for example the Higgs, can easily mimic the effect of an cosmological constant. So there is an industry of people who calculate the effects of different extensions of the standard model on LCDM cosmology.
Now, above I said that CMB, BAO and SN data all agree in cosmological observations on the value of the cosmological constant. So for it to be wrong, it needs to either evolve, or several different measurements need to conspire to mask the effect of an constant. So my assumption is, either their non standard evolution is compatible with LCDM cosmology, or there is something wrong with the analysis.
[+] [-] platz|6 years ago|reply
Dark Energy might not exist after all
https://youtu.be/oqgKXQM8FpU
[+] [-] ncmncm|6 years ago|reply
Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.
[+] [-] nxpnsv|6 years ago|reply
[+] [-] ncmncm|6 years ago|reply
Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable.
In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but there is no reason to assume it is the only one. We just don't get to study any young-universe stars that haven't blown up.
Did anybody even discuss metallicity and possible effects on brightness of t1a sn's, when DE was first proclaimed? If not, why not?
[+] [-] AnIdiotOnTheNet|6 years ago|reply
One or two years from now I invite you to take a look back at this comment and see if you still feel so smug. This is a relatively recent paper, give it some time to be chewed up and spit out by the cosmological community before hailing it as the deathknell of a decades old tricky problem.
[+] [-] dmix|6 years ago|reply
[+] [-] j-dr|6 years ago|reply
[+] [-] ash|6 years ago|reply
* Quanta Magazine article: 17 Dec 2019
* Arxiv preprint: 10 Dec 2019 [1]
CMB and BAO are mentioned in the original post too:
> Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely.
[1]: https://arxiv.org/abs/1912.04903
[+] [-] Hoagy|6 years ago|reply
I know they are proposing different mechanisms for the error in calculation but it gives a sense of a 'moment' shifting against dark energy. Coincidence?
[+] [-] SiempreViernes|6 years ago|reply
[+] [-] exabrial|6 years ago|reply
[+] [-] cygx|6 years ago|reply
[+] [-] osbertlancaster|6 years ago|reply
We are not expanding. Size of e.g. a hydrogen atom is not changing.
[+] [-] mannykannot|6 years ago|reply
In comparison, when superluminal neutrinos were tentatively announced a few years ago, there was a lot of justified skepticism about there being experimental error (admittedly, overthrowing special relativity is an even more extraordinary claim than dark energy.)
[+] [-] flick|6 years ago|reply
[1]: https://arxiv.org/abs/1912.02191
[2]: https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...
[+] [-] scotty79|6 years ago|reply
Can expansion be seen not in redshift but in angular distances of galaxies? I'm asking in general not in relationship to the article. It wouldn't help for the problem raised by this article.
[+] [-] scotty79|6 years ago|reply
[+] [-] layoutIfNeeded|6 years ago|reply
[+] [-] gbrown|6 years ago|reply
[+] [-] cerealbad|6 years ago|reply
[+] [-] vectorEQ|6 years ago|reply
say if matter / observables go from 0hz - 30+ Zhz.. is dark energy from 30+Zhz to ???Zhz and perhaps anti matter / energy from ???Zhz to ???????Zhz? (more question marks being higher ? :D )
or is this completely invalid and a dumb thought?
[+] [-] _Microft|6 years ago|reply
[0] https://en.wikipedia.org/wiki/Electromagnetic_spectrum [1] https://en.wikipedia.org/wiki/Standard_Model