A newly published analysis of Type Ia supernovae calls into question the accelerating expansion of the universe and the existence of dark energy:
Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace. Their conclusions were based on analysis of Type Ia supernovae – the spectacular thermonuclear explosions of dying stars – picked up by the Hubble space telescope and large ground-based telescopes. It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named 'dark energy' that drives this accelerating expansion.
Now, a team of scientists led by Professor Subir Sarkar of Oxford University's Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set – a catalogue of 740 Type Ia supernovae, more than ten times the original sample size – the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.
Marginal evidence for cosmic acceleration from Type Ia supernovae (open, DOI: 10.1038/srep35596) (DX)
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Last month, a team of scientists led by Stacy McGaugh at Case Western Reserve University determined from observations of 153 galaxies that the dynamics of galaxy rotation seems to depend solely on the normal, visible matter in it (SN coverage here). It was a strong argument that rather than hypothesising dark matter to explain the oddities in galactic rotation, it may instead be necessary to modify the laws of gravity.
However, two scientists from McMaster University, Ben Keller and James Wadsley, have just recently examined the results of a detailed simulation of dark matter in galaxy formation previously done known as the McMaster Unbiased Galaxy Simulations 2 (MUGS2). The simulation was a sophisticated one that took into account various other factors such as gas dynamics, star formation, and stellar feedback, but incorporated no new physics beyond that of the standard Lambda-Cold Dark Matter (ΛCDM) cosmological model. They found that the relation that McGaugh et. al. discovered from observations of real galaxies was reproduced just about exactly by the simulation. Their paper is here. Their abstract states:
Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond ΛCDM. In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 ΛCDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.
So now it seems that the earlier troubles with dark matter were actually the result of too naïve a simulation, and by taking into account additional known, relevant physics, the troubles disappear.
Further coverage and commentary by astrophysicist Ethan Siegel here (archive.is).
Related: Study Casts Doubt on Cosmic Acceleration and Dark Energy
A physicist is using a theory he advanced to explain how EmDrive could work to explain how dwarf galaxies can be held together without the requirement of dark matter:
British physicist Dr Mike McCulloch, who previously used quantised inertia to explain how the controversial electromagnetic space propulsion technology EmDrive works, says that he has new evidence showing his theory can also explain galaxy rotation, which is one of physics' biggest mysteries. McCulloch, a lecturer in geomatics at Plymouth University's school of marine science and engineering, says he now has even more evidence that his "new physics theory" about quantised inertia works, and that it makes it possible to explain why galaxies are not ripped apart without using theory of dark matter.
[...] There are 20 dwarf galaxies in existence from Segue-1 (the smallest) to Canes Venatici-1 (the largest), and dark matter is only meant to work by spreading out across a wide distance, but it is still used to explain dwarf galaxies, even though this requires dark matter to be concentrated within these systems, which is implausible. Instead, McCulloch asserts that quantised inertia can be used to explain how galaxies rotate without using dark matter, and he has written a paper that has been accepted by the bi-monthly peer reviewed journal Astrophysics and Space Science.
Reprint of the IBT link here.
From the abstract of Low-acceleration dwarf galaxies as tests of quantised inertia (DOI not yet published):
Dwarf satellite galaxies of the Milky Way appear to be gravitationally bound, but their stars' orbital motion seems too fast to allow this given their visible mass. This is akin to the larger-scale galaxy rotation problem. In this paper, a modification of inertia called quantised inertia or MiHsC (Modied inertia due to a Hubble-scale Casimir effect) which correctly predicts larger galaxy rotations without dark matter is tested on eleven dwarf satellite galaxies of the Milky Way, for which mass and velocity data are available. Quantised inertia slightly outperforms MoND (Modied Newtonian Dynamics) in predicting the velocity dispersion of these systems, and has the fundamental advantage over MoND that it does not need an adjustable parameter.
Previously: Study Casts Doubt on Cosmic Acceleration and Dark Energy
Dark Matter Beats its Latest Challenge
Emergent Gravity and the Dark Universe
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Milky Way is Not Only Being Pulled—It's Also "Pushed" by a Void
(Score: 2) by Gaaark on Thursday October 27 2016, @02:08AM
Dark *blah* don't exist, mon.
Now, smoke up some more.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @03:07AM
The name of another network technology out of it.
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @03:28AM
and Nobel prizes usually require more than 3 sigma of confidence. I'm rooting for constant expansion.
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @05:11PM
The article suggested the original calculations were based on other assumptions that have not been thoroughly tested. It's like they habitually used to assume spherical cows, but new knowledge suggests that spherical cows are not significantly more likely than say cubical cows.
Do they take Nobels away for innocently wrong conclusions?
There's a trade-off. Constant expansion probably means the Universe will last longer, but it also means that bad guys from far off have a better chance of coming our way. An accelerating expansion would relatively quickly isolate civilizations, putting distant galactic systems beyond near-light-speed travel. Earth-bound encounters between different civilizations show that they are usually of unequal technological capability and of different philosophy, leading to mass slaughter and other problems. The more civilizations that can reach us, the more likely a bad and powerful group will slaughter us. Good "fences" make for good neighbors.
(Score: 2) by HiThere on Thursday October 27 2016, @07:36PM
Dark Energy driven expansion would have no affect on the "bad guys", as the local group (Milky Way, Andromeda, etc.) is gravitationally bound, and will hold together against cosmic expansion long enough for the sun to die.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 3, Funny) by Anonymous Coward on Thursday October 27 2016, @03:31AM
Fuck all you cosmic racists!
(Score: -1, Redundant) by Anonymous Coward on Thursday October 27 2016, @03:42AM
Have to admit dark energy/matter has been pretty convenient, much like aether, and has about as much backing evidence- it must be there otherwise how do you explain...
Anyway, it always struck me as poor hypothesizing, and while neutral about evidence to the contrary, hopefully it will get cosmologist to get their shit a little more together at explaining what is really happening.
(Score: 3, Touché) by Bogsnoticus on Thursday October 27 2016, @05:37AM
I was downvoted to oblivion in various forums for daring suggest that dark energy was just a modern name for aether.
Looks like i'm going to have to dig up those old posts, and accompany them with this more recent information, as well as a smug "I told you so" :)
Genius by birth. Evil by choice.
(Score: 3, Funny) by quintessence on Thursday October 27 2016, @09:45AM
That's okay. According to my mom and how often I call, my existence has always been called into question.
http://science.nationalgeographic.com/science/space/dark-matter/ [nationalgeographic.com]
https://en.wikipedia.org/wiki/Aether_(classical_element) [wikipedia.org]
Does seem reviving bad ideas from the past to explain though.
(Score: 3, Interesting) by fubari on Thursday October 27 2016, @05:44PM
Does seem reviving bad ideas from the past to explain though.
Actually they were awesome ideas. Just because in idea is wrong doesn't make it bad.
"Luminiferous aether" [wikipedia.org] was a sound, logical theory based on the physics of the day.
It was a great idea that just happened to be wrong, and that was a stepping stone to a new and better view of the universe.
(Excerpt from the wikipedia link, emphasis added.)
The point is, giving birth to relativity and quantum theory doesn't sound to shabby for a "bad idea".
(Score: 3, Insightful) by maxwell demon on Thursday October 27 2016, @05:45AM
The observational data seemed to indicate that there is something we don't know about the universe, which causes accelerated expansion. That was observational data, so no hypothesizing. Note that it was called "dark energy" exactly because we had no clue what it was. No trace of hypothesizing in that.
Of course given that fact (and yes, that was a fact, not a theory, hypothesis or conjecture) there were many speculations what this mysterious "dark energy" is. But nobody claimed any of this as fact; indeed, one of the candidates of "dark energy" was the cosmological constant, which isn't even a form of energy, but simply an additional term in Einstein's equation (which itself has no explanation; it was introduced by Einstein because he believed in a static universe, and without that term he couldn't get it; when the expansion of the universe was observed, Einstein called it his biggest blunder).
The only assumption that went in was that the observational data was conclusive. Well, it turns out that it wasn't. If there's a lesson in that, it's to put more distrust in the observations.
The Tao of math: The numbers you can count are not the real numbers.
(Score: -1, Offtopic) by Anonymous Coward on Thursday October 27 2016, @01:09PM
You are claiming the observation of expansion requires no hypothesizing? The actual observations are of redshifted light, not expansion. Also whatever statistical model was used for the uncertainty surely included a number of questionable assumptions (eg each star is independent of the others, etc).
(Score: 1, Insightful) by Anonymous Coward on Thursday October 27 2016, @06:32AM
Dark energy and dark matter don't have much to do with each other except we call them both "dark".
Evidence for dark matter is very solid. We don't know what it is, but it's extremely unlikely that we'll just one day say "whoops, looks like it's not real, sorry about that." Personally, I think it's mostly microscopic primordial black holes.
And this is just one study. If the results are confirmed independently, and ideally backed up by other results obtained by a different method, then it's groundbreaking. Totally changes the cosmology game. But individual studies have a way of evaporating under stricter scrutiny.
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @09:37AM
Dark energy and dark matter don't have much to do with each other
Except for on the one hand, you have some undetectable mass that is supposedly the majority of the mass in the universe exerting a gravitational field, and on the other hand this field seemingly has no effect on the acceleration of the universe.
That's quantum mechanics level weird. And cosmologist throw up their hands and say "it must be" without bothering to explain how these two ideas interact with each other.
True enough that one study doesn't make a revolution, but even without it, the dark matter, dark energy view of the world didn't make much sense.
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @04:06PM
Did you read GP's statement that dark energy and dark matter have little to do with each other before writing about this "dark matter, dark energy view of the world?"
Also, if expansion is not accelerating, then why should dark matter have any bearing on this acceleration that we just supposed is not happening?
But nope! It's all politically correct garbage! The world is flat! I've never observed anything that would lead me to believe the earth is a ball!
(Score: 2) by The Mighty Buzzard on Thursday October 27 2016, @10:37AM
Last I heard, black holes with an event horizon that small would decay quickly enough that you couldn't measure their lifespan with a stopwatch.
My rights don't end where your fear begins.
(Score: 5, Interesting) by RedBear on Thursday October 27 2016, @06:39AM
I'm so far from being a theoretical physicist or astrophysicist it's not even funny. But of course like most people I like to ponder such things. Someone else pointed out this interesting blog [blogspot.com] by an actual physics professor(?) in the UK, Mike McCulloch, who espouses the idea of something called MiHsC or Quantum Inertia, wherein objects that come very close to achieving zero inertia end up getting pushed along at a certain minimum speed by encountering Unruh radiation waves with extremely long wavelengths. Like, the "horizon of the observable universe" long. If I'm understanding the gist of the theory correctly.
Anywho, seems like a universe that's plodding along pushing itself apart at a steady, constant pace would jive much better with his theory than a universe being pushed apart at a constantly accelerating pace due to "dark energy". Because according to the MiHsC theory objects simply can't come to a complete standstill, but the Unruh radiation only accelerates objects to a certain (very small) maximum velocity, which wouldn't seem to jive well with a constantly increasing rate of expansion. Again, that's if I'm understanding things in layman's terms correctly.
The blog is really interesting because he purports to explain something like 29 different unexplained cosmic and subatomic phenomena without the use of either dark energy or dark matter "fudging". All with what seems to be a remarkably simple equation. I'd love to see a few people here with more experience in the field weigh in on how rational the theory seems to be.
¯\_ʕ◔.◔ʔ_/¯ LOL. I dunno. I'm just a bear.
... Peace out. Got bear stuff to do. 彡ʕ⌐■.■ʔ
(Score: 3, Insightful) by Justin Case on Thursday October 27 2016, @01:46PM
objects that come very close to achieving zero inertia
So, nearly-massless objects?
objects simply can't come to a complete standstill
In relation to what?
objects to a certain (very small) maximum velocity
In relation to what? There isn't a zero-point in the universe against which all other positions and velocities can be measured.
What you're saying may be entirely correct, and my understanding of this stuff is pretty limited. But I'm not following your reasoning here.
(Score: 0) by Anonymous Coward on Thursday October 27 2016, @08:41PM
Not sayin', but just sayin'.
http://math.ucr.edu/home/baez/crackpot.html [ucr.edu]