Is Dark Energy Weakening? (bbc.com) 67
An anonymous reader shared this report from the BBC:
There is growing controversy over recent evidence suggesting that a mysterious force known as dark energy might be changing in a way that challenges our current understanding of time and space. An analysis by a South Korean team has hinted that, rather than the Universe continuing to expand, galaxies could be pulled back together by gravity, ending in what astronomers call a "Big Crunch".
The scientists involved believe that they may be on the verge of one of the biggest discoveries in astronomy for a generation. Other astronomers have questioned these findings, but these critics have not been able to completely dismiss the South Korean team's assertions...
The controversy began in March with unexpected results from an instrument on a telescope in the Arizona desert called the Dark Energy Spectroscopic Instrument (Desi)... The data hinted that acceleration of the galaxies had changed over time, something not in line with the standard picture, according to Prof Ofer Lehav of University College London, who is involved with the Desi project. "Now with this changing dark energy going up and then down, again, we need a new mechanism. And this could be a shake up for the whole of physics," he says. Then in November the Royal Astronomical Society (RAS) published research from a South Korean team that seems to back the view that the weirdness of dark energy is weirder still.
Prof Young Wook Lee of Yonsei University in Seoul and his team went back to the kind of supernova data that first revealed dark energy 27 years ago. Instead of treating these stellar explosions as having one standard brightness, they adjusted for the ages of the galaxies they came from and worked out how bright the supernovas really were. This adjustment showed that not only had dark energy changed over time, but, shockingly, that the acceleration was slowing down... If, as Prof Lee's results suggest, the force that is pushing galaxies away from each other — dark energy — is weakening, then one possibility is that it becomes so weak that gravity begins to pull the galaxies back together.
The scientists involved believe that they may be on the verge of one of the biggest discoveries in astronomy for a generation. Other astronomers have questioned these findings, but these critics have not been able to completely dismiss the South Korean team's assertions...
The controversy began in March with unexpected results from an instrument on a telescope in the Arizona desert called the Dark Energy Spectroscopic Instrument (Desi)... The data hinted that acceleration of the galaxies had changed over time, something not in line with the standard picture, according to Prof Ofer Lehav of University College London, who is involved with the Desi project. "Now with this changing dark energy going up and then down, again, we need a new mechanism. And this could be a shake up for the whole of physics," he says. Then in November the Royal Astronomical Society (RAS) published research from a South Korean team that seems to back the view that the weirdness of dark energy is weirder still.
Prof Young Wook Lee of Yonsei University in Seoul and his team went back to the kind of supernova data that first revealed dark energy 27 years ago. Instead of treating these stellar explosions as having one standard brightness, they adjusted for the ages of the galaxies they came from and worked out how bright the supernovas really were. This adjustment showed that not only had dark energy changed over time, but, shockingly, that the acceleration was slowing down... If, as Prof Lee's results suggest, the force that is pushing galaxies away from each other — dark energy — is weakening, then one possibility is that it becomes so weak that gravity begins to pull the galaxies back together.
Dark energy doesn't exist (Score:2)
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Nobody's asking him to. The challenge was for him to prove his own theory.
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it's not *his* theory, he didn't come up with it. he's just describing some theories that are out there.
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Nobody's claiming otherwise, you're just arguing for the sake of arguing here.
"His theory" in this context is very clearly the theory he just espoused.
Stop defending this clown.
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"there are theories out there that say X" is just stating a fucking fact, dork
Re:Dark energy doesn't exist (Score:5, Funny)
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that's the longest sig i've yet seen on /., M'sieu Fermat
Re: Dark energy doesn't exist (Score:2)
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Everyone and their uncle's dog has a universe model. One should be careful not to mistake mathematical structure and morphisms for actual physics.
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In some higher dimensional or âoebrane worldâ models, our 3D universe is treated as a hypersurface (a brane) embedded in a higherdimensional bulk spacetime, and what we call dark energy arises from geometric properties of that embedding rather than from a fundamental vacuum fluid. for the rotation of galaxies effectively mimicking a darkmatter halo in 4D space.
Apparently the solution to everything is more layers of indirection.
No such thing as dark energy (Score:1)
I hope alternative models of explaining the supernova measurements would get more attention, so that some day we could admit that this geocentric..., sorry, this dark energy model was wrong after all.
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Like physicists are not trying to provide evidence for or disprove the dark energy model. Anyone, or more likely an international team, that does might get Nobel Prize. One experiment or analysis is not enough. One plausible theory is that dark energy is simply not constant, the constant value is an assumption, but only that.
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Like physicists are not trying to provide evidence for or disprove the dark energy model.
Actually, no, they are not. Meaning that dark energy is now mainstream physics, and if you dare to think otherwise, you are sidelined - very difficult to get funding for studies, or publications in peer reviewed journals. Hence, the only ones trying to prove otherwise are considered crackpots.
One plausible theory is that dark energy is simply not constant, the constant value is an assumption, but only that.
Again, epicycles.... Instead of trying to create a mathematical model for dark energy, one can explain the supernova observations themselves with e.g. variable light speed theory (i.e. in the past light travelled slowe
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The summary has not one but two examples of groups critically studying dark energy.
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The summary has not one but two examples of groups critically studying dark energy.
Yes, but they still are starting from the hypothesis that there IS dark energy and it has been accerating expansion. From TFA: "This adjustment showed that not only had dark energy changed over time...". I.e. they are trying to FIX dark energy calculations with adjustments.
Read my original post. In very similar way, the science tried to fix geocentric model with epicycles end deferents, resulting in REALLY odd orbits. And somehow those still seemed to fit observations. It required a more radical shift t
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Dark energy is a line on a graph that has a slope that's not zero. The one group has been measuring points on that graph. The other group has been speculating about how the points on the graph could be biased. Both of them find, to ever greater accuracy, that the slope of that line is not zero.
They're not "starting from dark energy" or "trying to fix dark energy."
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Re: I'm not worried (Score:2, Offtopic)
New? (Score:5, Interesting)
Isn't this what was always predicted, the cycle of the big bang to collapse and repeating?
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Certainly seems to fit with what I was taught in school. But, then there were news stories saying that the universe would expand forever. Some said the expansion was accelerating. Others say that the expansion is slowing.
I think it will expand for a long-ass time, and then it will contract for a long-ass time, and then singularity and then boom.
We simply need to observe it for the next 60-90 billion years and we'll have proof.
Re: New? (Score:2)
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Sounds like the version Cheech and Chong envisaged after taking a big bong rip.
Re: New? (Score:3)
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Not really in the popular science. Over the years there have been some doozies in the public square. Hawking surveys a few in his works. His final paper featured a smooth exit from cosmic inflation resulting in heat death in a long tail.
One problem with Big Crunch/string of pearls theories is that gravity propagates at the speed of light. As any fool kno, our light cone is on a massive diet as mass exits relevance by being on the far side of so much expanding space that it can never come back or influence u
God is Czech (Score:2)
I remember the rough consensus before the late 90's was that it would collapse, but most were noncommittal, saying, "we don't have enough info to answer".
My theory is God plays accordion with the universe: the repulsive force of dark energy oscillates back and forth.
Clues to what it is (Score:4, Interesting)
Each observation, like ones that appear to show "dark energy" weakening, give astronomers clues that may eventually reveal exactly what "dark energy" is. Dark energy is an unknown factor, something that doesn't quite fit our current mathematical models. When you make a mathematical model, and it turns out not to exactly match physical observations, the most logical conclusion is that the mathematical model is missing something, not that there is some mystical "dark" thing out there that can't be observed. We just have to figure out what that "dark" thing is!
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Not really unfortunate. Because the term was coined to describe something that doesn't interact with light (electromagnetic radiation). Making it difficult to observe.
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You are referring to dark *matter* while the article here is talking about dark *energy*. But the principles are the same.
Astronomers *theorize* that "dark matter" doesn't interact with light. It could also be that the models aren't quite right, or that there's a whole lot of unexpected dust out there, or rogue plants, or some other thing or things we haven't accounted for.
Re: Clues to what it is (Score:2)
Well it's not so much of a theory today dark matter doesn't interact with light: we literally cannot do it using any of the optical instruments we have.
Therefore if it exists we know for certain it interacts very weakly with em radiation. However the "if" is doing quite a lot of heavy lifting.
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dark matter doesn't interact with light
We haven't actually proven this. We just haven't seen such interaction. There's a whole lot we haven't seen, so I think it's arrogant of us to say that because we haven't seen it, it must not interact with light.
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I mean kinda, but not really. I did clarify later that it must interact weakly rather than not at all, but either way, we have cameras capable of counting individual positions at optical frequencies which are now readily available at small science lab (individual PI) levels of funding.
Bear in mind that neutrino observation while expensive is now somewhat routine.
That's not too say dark matter of it exists has absolutely zero interaction with light, though that, like neutrinos is possible, but if it does we
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The existence of dark matter is theorized mainly because our mathematical model of the universe, doesn't match observations of the actual universe. When a model doesn't match reality, it's almost certainly that the model is wrong or missing something, not that there is some mysterious "dark" something that we can't see or interact with. See Occam's razor.
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Eugh please don't make me defend dark matter.
The motion of galaxies doesn't match the amount of observed mass according to Newton's laws (it's not relativistic). The two primary hypotheses are that Newton's laws aren't quite right (MOND--modified Newtonian dynamics) or that the amount of observed mass isn't right. The latter being dark matter because it interacts so weakly with light that we can't observe it (hence, dark).
MOND fits the motions really pretty badly so it isn't a mainstream theory by any stret
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If by "dark" you mean dark as in "unlighted" like rogue planets, asteroids, and dust clouds, sure, I can buy that. We can't easily see them because our telescopes are mainly good at seeing bright objects like stars.
But if you mean "dark" as in some kind of exotic thing that can't be seen and doesn't interact with light, that's pretty exotic and certainly is not the first choice in light of Occam's razor.
Or maybe...our observations are otherwise wrong. We are sitting on a speck of dust in one lonely corner o
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If by "dark" you mean dark as in "unlighted" like rogue planets, asteroids, and dust clouds, sure, I can buy that. We can't easily see them because our telescopes are mainly good at seeing bright objects like stars.
Dust clouds we can see because they block light from behind them. One of the candidates for dark matter is indeed MACHOs which are compact baryonic objects like brown dwarfs, rogue planets and primordial black holes (ones from the big bang, so they don't need to be stellar mass or anything).
Excep
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You say on one hand that this is one of the biggest unanswered questions in physics. At the same time, you (or at least many) insist that "dark matter" is a mysterious kind of matter that doesn't interact with light or other electromagnetic radiation. Is the question unanswered? Or do we know what this dark matter is? We can't have it both ways. Sure, we can have opinions and beliefs about which are more likely. But until we are able to *test* and confirm our hypotheses, we have nothing more than conjecture
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You say on one hand that this is one of the biggest unanswered questions in physics.
Yep.
At the same time, you (or at least many) insist
Woah there buddy! I'm not insisting! I do know people who insist that the problem of motion is solved by missing mass, and now all we have to do is find the new exotic particle. I don't count that as solved, personally.
is a mysterious kind of matter that doesn't interact with light or other electromagnetic radiation.
Yes: if the motion of galaxies is caused by mass we're not
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if the motion of galaxies is caused by mass we're not observing then it probably does have to be some kind of exotic matter, since normal matter doesn't fit with the things that have been observed.
"Mass we're not observing" is doing a lot of work here.
We did not observe an exoplanet until 1992. That's not very long ago. And even now, we can only observe exoplanets when they happen to be lined up between us and the star they orbit, such that they darken the light of that star as the planet passes "in front" of it. This means that our ability to observe exoplanets is very, very limited. In any systems whose orbital plane is not in line with our perspective, exoplanets would be entirely invisible to us.
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Yeah it's doing a fair bit of work for sure.
But it's not like this point isn't somewhat obvious, right? Physicists haven't collectively decided to ignore something obvious here too give some young buck a chance to make a name for themselves by overturning the field. Anyone would overturn it and grab the Nobel prize if they could.
Things is planets are very low mass.
If there were lots more of them by mass then they'd have more gravitational effects we could observe, and maybe even start to accreate.
The things
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Perhaps my hypothesis doesn't match the observations. But I'd argue that the very concept of dark matter, indicates that the standard model *also* doesn't match observations. That's kind of what "dark matter" *is*. Literally no one has a model that accurately describes what we see. So where does that leave us? Humble.
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Your hypothesis doesn't match observations.
You are right that this is all beyond the standard model and/or general relativity.
We have a pile of observations which don't match known physics and for which the current leading hypothesis is missing mass, yet we know the mass in that case can't entirely be ordinary matter, because it doesn't match that either. This is definitely the realm of new physics, without a doubt. Either there's some exotic new particle, or some other exotic new effect.
Whatever we have, s
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Your hypothesis doesn't match observations
If by "observations" you mean, "what we can see" (which is a pretty literal interpretation of the words), then yes, I agree. We can't see enough rogue planets or other matter floating through space, to confirm the ordinary matter hypothesis. That is not the same as saying that the observations contradict the ordinary matter hypothesis.
You talk about the pile of observations that don't match "known physics" and yet you and your physicist friends are still highly confident in your "dark matter" hypothesis. Ma
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We can't see enough rogue planets or other matter floating through space, to confirm the ordinary matter hypothesis
No it's stronger than that. You can work out things you ought to see if there are enough rogue planets and other baryonic matter floating through space. We don't see the predictions of that either which means it's not likely to be just unilluminated normal matter.
You talk about the pile of observations that don't match "known physics" and yet you and your physicist friends are still highly conf
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I literally said I wasn't that convinced by it. And you come back with that.
OK, I apologize for assuming that you were going along with the standard dark-matter hypothesis. It didn't sink in that you were using a hypothetical argument.
This is the definition of "standard model" that I'm using: https://en.wikipedia.org/wiki/... [wikipedia.org] It seems pretty relevant to our discussion.
The timing of inflation isn't important in regards to this discussion. If light took 12 billion years to arrive, that means that the galaxy itself became 22 billion light years farther away, in (as the theory goes) ba
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This is the definition of "standard model" that I'm using: https://en.wikipedia.org/wiki/ [wikipedia.org]... It seems pretty relevant to our discussion.
Oh the lambda-CDM model. I thought you were talking about the Standard Model https://en.wikipedia.org/wiki/... [wikipedia.org] which is also relevant.
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Well it's not so much of a theory today dark matter doesn't interact with light:
Transparent aluminum. It's solved.
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He's correct. The term was coined to describe something that doesn't interact with light (much) so is hard to observe. That something was dark matter. The term got reused for dark energy.
Rogue plants (and planets) and dust that are not hot enough to glow brighter than the background are dark. In the conventional sense even. They're also pretty strictly constrained as dark matter candidates because, shockingly I know, they were some of the first things astrophysicists thought of, and looked for. Well, maybe
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The article itself clearly is talking about dark energy, not dark matter.
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Nobody is disputing that.
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...or rogue plants...
For the last time, the Flying Spaghetti Monster is no plant!
Though I do rather like the idea of rogue plants wandering the cosmos, looking for stars to steal light from. That seems a ripe trajectory for a good sci-fi story.
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or rogue plants,
Feed me, Seymour!
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I don't think it's just an unfortunate (unlucky) word choice. There has been a lot of speculation that this dark matter and dark energy really are unobservable. This is not just due to vocabulary.
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no one understands quantum mechanics either
Re: Clues to what it is (Score:1)
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This.
Physicists and astronomers are often overly attached to their observations. Just try to lop a few significant figures off some measurement and watch them scream. And then someone finds a cable that wasn't plugged in properly.
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Each observation, like ones that appear to show "dark energy" weakening, give astronomers clues that may eventually reveal exactly what "dark energy" is. Dark energy is an unknown factor, something that doesn't quite fit our current mathematical models. When you make a mathematical model, and it turns out not to exactly match physical observations, the most logical conclusion is that the mathematical model is missing something, not that there is some mystical "dark" thing out there that can't be observed. We just have to figure out what that "dark" thing is!
Some observations made from the JWST in the past year have called into question whether our theoretical dark energy / dark matter models need massive refinement. We're beginning to suspect that time isn't a universally stable entity, and moves faster in some parts of the universe, and slower in others, giving us, in a bubble of time that isn't quite in sync with the surrounding area, some very confusing observational biases that we've attempted to compensate for with convoluted theories like dark matter and
Gib Gnab (Score:1)
Douglas Adams was right all that time
So stuff is moving away from it? (Score:2)
We have something we are assuming is pushing stuff away or in some other way continously expanding the universe. And it is slowing down, as if it is now further away, sounds like we now know it is 3D space and weakens over the distance it itself is creating.