Galaxy Without Any Dark Matter Baffles Astronomers (arstechnica.com) 200
A distant galaxy that appears completely devoid of dark matter has baffled astronomers and deepened the mystery of the universe's most elusive substance. The Guardian reports: The absence of dark matter from a small patch of sky might appear to be a non-problem, given that astronomers have never directly observed dark matter anywhere. However, most current theories of the universe suggest that everywhere that ordinary matter is found, dark matter ought to be lurking too, making the newly observed galaxy an odd exception. Dark matter's existence is inferred from its gravitational influence on visible objects, which suggests it dominates over ordinary matter by a ratio of 5:1. Some of the clearest evidence comes from tracking stars in the outer regions of galaxies, which consistently appear to be orbiting faster than their escape velocity, the threshold speed at which they ought to break free of the gravitational binds holding them in place and slingshot into space. This suggests there is unseen, but substantial, mass holding stars in orbit. In the Milky Way there is about 30 times more dark matter than normal matter. The latest observations focused on an ultra-diffuse galaxy -- ghostly galaxies that are large but have hardly any stars -- called NGC 1052-DF2. The team tracked the motions of 10 bright star clusters and found that they were traveling way below the velocities expected. The velocities gave an upper estimate for the galactic mass of 400 times lower than expected. The researchers described their discovery in the journal Nature.
Except rotation speeds have already been explained (Score:5, Insightful)
... in other ways. I remember reading a paper that explained exactly that away very nicely. I can't find it anymore, but I know it was mentioned in the Scientific American, many years ago.
Our math still does not fit reality, especially energy-wise, but not because of the rotation of galaxies.
It's just that in pop-sci, "dark matter/energy" is commonly presented as if our theories were right and it was just our observations of the universe that are wrong, when in reality, "dark matter/energy" is merely a convenient identifier for the discrepancy and is merely saying "we don't know yet". Implying that, obviously, it's our theories that are still wrong.
So saying "without any dark matter" is already highly questionable. Rather, this galaxy might help us fix our silly theories, to match the cold hard reality that we simply observe. Not the other way around.
Re:Except rotation speeds have already been explai (Score:5, Insightful)
You are wrong. Dark matter and dark energy are used as they are the only things that help explain our observations of nature.
Yes our theories are still wrong. They will be until we can describe everything - something not likely to ever happen. That's science. What you are doing is hand waving without understanding the basics.
Re: (Score:3, Insightful)
I'm more surprised this hasn't happened before. To me I believe it's simple. And YES a BELIEF. Gravity spans dimensions. I am more surprised it hasn't been observed before. My question has always been what does that neutrino look like from a different angle.... It's taken us this long simply to detect them. It is really so hard to postulate particles in other dimensions which we can detect through gravity. It it really so hard to believe that Plato couldn't have been partially right?
Re: (Score:2)
But for science we need a theory that predicts the results, and belief has no place in that.
I believe everything I know. I don't know everything I believe. Look up "believe".
Science vs Religion (Score:5, Insightful)
I am not GP, but:
"Dark matter and dark energy are used as they are the only things"
That statement is completely false. "Only" isn't a science word (it requires you disprove all other theories, even theories you haven't had yet), and neither of those claims is proven or even likely, given they don't address even currently understood data.
"hand waving without understanding the basics"
i.e. to paraphrase you make the claim that "dark matter and dark energy" are the basics of science, and that they are set in stone, and deeper understand requires knownledge/acceptance of these basics.
Again this is not science. You will likely have to throw away a lot of theories built on false logic (e.g. QM, standard model, mass/gravity) if the current understanding of these hit a dead end. You cannot say "this theory is broken, yet must form the basis of better theories", because that's nonsense logic. A broken theory is broken, it must be wrong.
"You are wrong"
And acceptance of mistakes is necessary for science, i.e. you might be wrong.
Really the danger to science is people like you. You learn things as though they're true, you build your careers based on this, and when experiments point to faults, you gloss over the failure and defend the broken model. It's more religion than science.
Re:Science vs Religion (Score:5, Interesting)
You may be correct that dark matter and dark energy may not be the only possible explaination, but the point Megol made still stands. OP claims that that science lays them out as fact and says our observations are wrong, which is complete nonsense. Dark matter/energy are modern equivalents of "here be dragons", we know something is going on but we are unsure of the exact nature of that something. Continuing observation is used to narrow down the possibilities. The article was about finding a galaxy that is extraordinary in that we can understand everything that is happening, the first time we can say that out of the approx. 400000000000 galaxies in the observable universe.
Re:Science vs Religion (Score:5, Insightful)
That statement is completely false. "Only" isn't a science word (it requires you disprove all other theories, even theories you haven't had yet), and neither of those claims is proven or even likely, given they don't address even currently understood data.
You're confused. Dark matter and dark energy aren't concrete things. They're placeholders for the remainders that don't fit the currently understood data. They are the X and the Y in an equation we haven't yet solved. X and Y are in fact the "only" solutions to the equation, because that's a tautology. The solution to the equation is the solution to the equation. But because we don't know what they are they could turn out to be almost anything, or a combination of things. There are a lot of theories as to what they might be, but none of them is definite, and none will be until we gather more data.
You cannot say "this theory is broken, yet must form the basis of better theories", because that's nonsense logic. A broken theory is broken, it must be wrong.
All of science is based on "broken" theories. Copernicus' ideas were wrong, but they led to Galileo. Galieo's ideas were wrong but they led to Newton. Newton's ideas were wrong, but they led to Einstein. Einstein is probably also wrong, and we're not quote sure what the next wrong theory will be. And yet those and the many other wrong theories have led to better things. Improved theories and actual engineering improvements.
Satellites can be launched into orbit using only Newton's "broken" theories, but it's Einstein's "broken" theories that allow accurate GPS using those satellites. The computer you are using to post to this site was built based on "broken" theories that nevertheless provided a stepping stone to new and better things.
Re: (Score:3)
You're confused. Dark matter and dark energy aren't concrete things. They're placeholders for the remainders that don't fit the currently understood data. They are the X and the Y in an equation we haven't yet solved. X and Y are in fact the "only" solutions to the equation, because that's a tautology. The solution to the equation is the solution to the equation. But because we don't know what they are they could turn out to be almost anything, or a combination of things. There are a lot of theories as to what they might be, but none of them is definite, and none will be until we gather more data.
But you can say that for anything outside your own head. Everything in the entire universe is just a placeholder to fit a set of observations. At some point we decide the the observations are detailed and consistent enough that we'll stop worrying about this and talk as if the object really exists. If you look at recent data, dark matter has reached that point. Multiple approaches give a pretty consistent idea of where it is, how much of it there is, and some aspects of how it behaves. Dark energy not so mu
Re: (Score:2)
Re: (Score:2)
People made observations that are inconsistent with what we understood at the time. These observations are things like galactic rotation, gravitational lensing, etc. Then physicists tried making up theories to explain what was going on. Dark Matter was such a theory, and it's been a successful one. It explains many more observations with a relatively simply hypothesis than competing theories, and so it's become accepted. Someone could certainly come along with another theory that works better, but at
Re:Except rotation speeds have already been explai (Score:5, Insightful)
Not "the only things that help explain our observations of nature", but rather, "the best things physicists have currently considered that help explain our observations of nature". The OP is right, it's not proven by direct evidence, so it's basically a placeholder for "we don't know, here's a guess of a possibility". The more we do know, the less likely it looks as an explanation, it's just that no better explanation has caught on yet. But in terms of evidence, it's certainly at the gods granted fire to mortals level of explanation. At best, you can say it might be possible. Just because we don't have a better explanation currently, doesn't make dark matter a good explanation. It's not competing with a whole lot. :)
Re: (Score:2)
I think your use of "wrong" is a pretty strong word.
As I understand it, our current theories don't explain the amount of mass of various very large bodies in the universe. To counter this folks have come up with "dark matter" and "dark energy" to explain it away as something we cannot yet observe. I myself thought it silly that there was a report of something missing this. What is interesting is that there is a discrepancy. I wonder how closely it meets our current understanding, in that it's mass is about
Re:Except rotation speeds have already been explai (Score:5, Informative)
There are enough unrelated discrepancies in our observations, that can all be explained by dark matter or dark energy (making up a consistent fraction of the universe in all cases), that I think it's safe to say there's probably something to it. Especially when we know the Standard Model in particle physics is flawed, and many extensions happen to contain viable dark matter candidates.
For dark matter specifically, I would say the smoking gun is the aptly named Bullet Cluster [wikipedia.org]. Two galaxies colliding, ordinary matter interacts and gets slowed, dark matter doesn't interact and gets separated from the ordinary matter, and then the dark matter and ordinary matter components can be observed separately (ordinary matter from ordinary photons, dark matter from its gravitational lensing effect on photons coming from galaxies behind the cluster).
Re: (Score:2)
Re: Except rotation speeds have already been expla (Score:4, Interesting)
Within it's tested limits the standard model is highly accurate. However given that this has been achieved by doing lots of experiments and using them to find some 20 odd constants, so that the model fits the experimental data then that's hardly surprising.
However step outside the tested limits and it's anyone's guess as to whether it's correct or not. Then add in that gravity is absent from the model and clearly at best it is incomplete and incomplete is also "flawed".
Re: (Score:2)
You hear that energy cannot be created nor destroyed, and then in the next sentence say the universe is expanding which means more space, but we know space has vacuum energy, so which is it
Both. The total energy in the Universe is ~0. We assume perfectly zero, but we only know to some decimal place of precision. Everything we see is both something and nothing at the same time. Energy in an of itself is nothing. It's the potential of the energy that allows something to exist or work to be done. Vacuum energy cannot be tapped as an energy source because there is no gradient.
The expansion of space is removing net energy. It's creating more total energy, but that energy is useless. At some poin
Re: (Score:2)
You could say the same thing about quarks and leptons. They're things scientists made up to explain things. Apparently, we can never see a quark in isolation.
"God did it" is crap science, in that it closes off investigation. "We don't currently know how it works" is scientific, and invites further investigation. So far, no reformulation of equations explains what black matter explains. Physicists have tried all sorts of theories, and dark matter is clearly the most promising.
Re: (Score:2)
Re: (Score:2)
For the tl;dr crowd, this is a proposal that we discard all of non-quantum physics for roughly the past century, and reformulate everything on the basis of single experiments with the luminiferous aether. For the record, I fail to see why this approach is promising.
Re: (Score:2)
Okay, let's see aether theory on galactic rotation curves, gravitational lensing, time flow like on GPS satellites, observed expansion of the Universe, etc. I assume it can explain all of those. If not, it hasn't contradicted an observation because it hasn't been tested.
Special and General Relativity have been very well tested over the years. Any replacement theory has to agree with them almost precisely over a very large range of conditions, much like relativity relates to Newtonian mechanics.
Dark
Re: (Score:2)
Einstein is responsible for Special Relativity, not the mathematics of it. He made the mental leap so daring that it was controversial for decades afterwards, despite the evidence. Had Poincare realized what the math was telling him, it would have been Poincare's Theory of Relativity, and it isn't.
So, how do the scalar components account for galactic rotation, movement of galaxies in clusters, mass distribution in a galactic collision, the gravitational lensing observed in various places, the cosmic m
Re: (Score:2)
[Luminiferous] Aether theory has never been disproven
What? I'm Petty sure it was decapitated when the speed of light was shown to be the same in all direction as the Earth orbits the Sun. One of the predictions of Luminiferous Aether is a universal frame of reference for light, making it slower or faster depending on which direction you're moving, fundamentally incompatible with Relativity. Seems quantum vacuum is classified as a form of "Aether", but is definitely not Luminiferous Aether.
Re: (Score:2)
I'm surprised your GPS in your cellphone works in spite of your bad science.
Comment removed (Score:5, Insightful)
Re: (Score:3)
That was the point ... ... how to chissle a stone of several tonns, transport it, erect it, make big structures from it. They had boats, fishing tools etc.
But you somehow twisted it.
People in the stone age already had science
Re: (Score:3)
Please, note that there is are some very powerful distinctions between practical engineering and the predictive power of science.
Re: (Score:2)
Onviously.
In science earth gravity is something like 9.8 at the poles and 9.7 at the equator.
In engineering you simple use a 10.
Oh, that was in meter / sec * sec.
Engineering is a subset of science - sort of (Score:5, Interesting)
Please, note that there is are some very powerful distinctions between practical engineering and the predictive power of science.
There are but literally every bit of engineering is based on scientific evidence. Whether or not the person doing the engineering fully and properly understands that science does not make it less true. Engineering doesn't work unless it is based on the ability of science to make predictions. There is science independent of engineering but not the other way around.
People sometimes call engineering "applied science". I think that definition is incomplete. I think it is "applied science with economic and temporal constraints". Engineering is science applied to practical tasks within the constraints of a budget and with a deadline.
Re: (Score:3)
Engineering has worked despite nobody in the world knowing the underlying science. You can make a bridge by trial and error, and that's pretty much how engineering worked for most of its existence.
Engineering follows the scientific method (Score:2)
Engineering has worked despite nobody in the world knowing the underlying science.
What is your point? Even pure science doesn't have a perfect grasp of the world so I'm not really sure where you are going with your argument. Science is at its core a method of investigation rather than a body of knowledge. The body of knowledge that results is a second order effect of the process. Engineering IS a branch of science because it follows the scientific method. It would not work if it did not. One does not have to have a conscious awareness of what the scientific method is to follow the
Re: (Score:3)
I think you're changing the definition of "science" past the useful point. Science is a method of study that's centuries old, not millennia, and postdates engineering. It is characterized by predictions. Make some observations, come up with a theory, make predictions from the theory, test them, get new observations, etc. Trial and error by itself does not predict anything. If you've come up with a few bridge designs that work, and what you know is that they work, you're not doing science. If you make
Thought experiments are not engineering (Score:2)
Engineering is the art of applying science.
Engineering IS science. It is the practical application of the scientific method [wikipedia.org] to a real world problem resulting in a product or process. Calling it an "art" really doesn't accurately describe what is going on because the term "art" is so vague as to be effectively meaningless in this context.
As thought, it can be independent of resource constraints (money and time).
If it is just a thought experiment then it isn't engineering. Engineering always results in a tangible product or process. Thought experiments are just theoretical physics or math. It doesn't become engineering
GPS not proof of dark matter (Score:1)
You cannot cite the GPS system as proof of the dark matter postulate, its design and implementation did not involve dark matter theory, and he's free to question the validity of dark matter theories while still using Google maps.
The defense of dark matter theory is to show how it explains the new observation already not pretend criticism is luddite stone age thinking.
Re: (Score:1)
You are not getting it.
GPS accounts for gravitation as well as Einstein's common relativity effects.
Which as OP stated were wrong (hence we have invented "dark energy").
Re: (Score:1, Informative)
Except rotation speeds have already been explained ... in other ways.
But you don't just have to explain rotation curves: you also need to explain the velocity dispersion of elliptical galaxies, mass estimates of galaxies clusters, gravitational lensing patterns, etc. All told, there are at least eleven [wikipedia.org] pieces of evidence for dark matter, of which the galaxy in this story is one: if our theories of gravity, for example, are wrong, and rotation curves should actually look as they do, then why is this galaxy an exception?
"dark matter/energy" is merely a convenient identifier for the discrepancy and is merely saying "we don't know yet"
This is completely correct! But we do know a few things
Re: (Score:2)
... in other ways. I remember reading a paper that explained exactly that away very nicely.
You are wrong and a troll. At best, those that are attempting a modified theory of gravity have come up with a theory to explain galactic roate in 2D, not 3, and completely misses any other observations such as gravitational lensing.
So saying "without any dark matter" is already highly questionable. Rather, this galaxy might help us fix our silly theories, to match the cold hard reality that we simply observe. Not the other way around.
From TFA: "It turns out that a galaxy without dark matter is incompatible with models that replace it using modified gravity. Since there's some normal matter here, any version of modified gravity would have that matter produce dark-matter-like effects. We don't see any indicati
Re: (Score:2)
Rotational speeds have been explained rather nicely by other theories, but dark matter/energy has become astronomical doctrine so those better-fitting yet alternate theories get scoffed at.
Can you give a RECENT example of another theory that explains rotational speeds and doesn't contradict any other observations?
Does it also explain ANY of the other things that Dark Matter explains?
Re: (Score:2)
The other theories to explain rotational speeds don't account for other things dark matter does. It was first hypothesized as a solution to galactic rotation, as I remember, but there's been plenty of other confirmation coming in. Something we can't detect by other means is creating gravitational fields.
How far away is it (Score:1)
Didn't see that coming. (Score:2)
Dark matter is a kludge (Score:5, Insightful)
Dark matter has always struck me as a kludge. It amounts to "we don't know WTF is going on, so here's our fudge factor". There is no evidence that dark matter exists, other than the fact that gravity on large scales doesn't behave the way cosmologists expect. Two other possibilities receive too little attention:
- Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
- Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
So now they've discovered a galaxy where the kludge factor of dark matter is not needed. Maybe this will prompt more cosmologist to consider the alternatives...
Re: (Score:2, Interesting)
The thing is, our theory of gravity (general relativity) makes a lot of other predictions on scales of the same order, and they seem to work fine. There are also cases like the Bullet Cluster [wikipedia.org] where the dark matter and ordinary matter components of two galaxies get separated from eachother, and the dark matter component can be seen by its gravitational lensing effect.
There's also the issues with particle physics. The Standard Model is incomplete (there are observations it can't account for), and when extendi
Re: (Score:3, Interesting)
The name "dark matter" itself is indicative of it being known unknown. It's not named something vaguely Greek or Latin like the lots of the pedestrian forms of matter because we don't know with confidence what it is yet, and haven't had direct evidence as it's particular nature as "matter", and the phenomena might possibly not even be due to matter at all. The evide
Re: (Score:2)
...nothing more than a theory...
This is the point form which no one will take you seriously.
Re: (Score:2)
We can't start with the Solar System and use that to research the Universe. It's far too small. General Relativity expresses itself best on a much larger scale. Nor do comets and asteroids provide arguments against it. As far as we can tell, they obey the laws of relativity very nicely. There may be other things we don't understand about them, but it's possible to know more about one thing than another, and the fact that we can't explain everything doesn't mean we're completely ignorant.
Model error cannot be dismissed (yet) (Score:4, Insightful)
The thing is, our theory of gravity (general relativity) makes a lot of other predictions on scales of the same order, and they seem to work fine.
So do Newtonian mechanics but that was proven to be a useful but incomplete model. Likewise it's hardly inconceivable that there are aspects of gravity not adequately described by general relativity. That doesn't mean general relativity is wrong or useless just like Newtonian mechanics are still useful.
Now obviously it very well could be some sort of matter and there is evidence to suggest that is a reasonable proposition. But until we get more evidence the possibility of it being an error in our mathematical models remains non-zero. I think this fact tends to get dismissed because it's a lot less glamorous than to imagine some sort of exotic matter or new particles. But we've seen it happen before where we invoked fanciful solutions (epicyles [wikipedia.org] anyone?) to explain something that was better explained with an improved model.
The Standard Model is incomplete (there are observations it can't account for), and when extending the standard model in ways to account for those observations, many models wind up including particles that would behave consistently with dark matter.
Exactly. The Standard Model is amazing and highly predictive but we still haven't reconciled it with gravity and we know for a fact that it is incomplete. Therefore it's not at all a stretch to imagine that dark matter is evidence of what the Standard Model is still missing. And that is an exciting prospect. I hope we figure out this mystery during my lifetime.
Re: (Score:2)
The mathematics of Special Relativity were mostly or completely derived by others. Einstein appears to be the first person to look at the math and realize what it was saying. Poincare did good work, but he never by himself arrived at the conclusion that there is no absolute reference frame, absolute space, or absolute time.
Re:Dark matter is a kludge (Score:5, Interesting)
There is a very promising theory by a Dutch theoretician (paper here) [arxiv.org], which can explain the observations without the need for dark energy / matter. I have seen the presentation of his work, and, as far as my understanding, it is based on idea that gravity is an emergent force, so-called entropic gravity Drupal [wikipedia.org].
Re: (Score:2)
Our goal is to give a theoretical explanation for why the emergent laws of gravity differ from those of general relativity precisely when the inequality (1.4) is obeyed.
from page 6 this cluster obeys 1.4 but is inconsistent with the theory. So in essence this observation, if correct, is evidence against the proposed theory as it provides no mechanism I am aware of that would yield a rotation consistent with standard model like this observation does.
Re: (Score:3)
gravity is an emergent force?
That implies galaxies are slowly becoming into existence. That is despite we can see them out to 13 billion light years. Hardly emergent.
No, I think you misunderstand the word "emergent": it means that gravity is not a fundamental force, but is a product of a more basic force, which is entropy. Hence entropic gravity.
For example, when people say (rightly or wrongly) that intelligence is simply an emergent result of sufficient brain complexity, they don't mean that intelligence doesn't exist, only that it is not a separate, magically created thing in itself.
Re:Dark matter is a kludge (Score:4, Insightful)
From Wikipedia [wikipedia.org]:
Dark matter's properties are inferred from observations in gravitational lensing, from the cosmic microwave background, which shows the structure of the universe early in its history, from astronomical observations of the observable universe's current structure, and from evidence about the formation and evolution of galaxies, from mass location during galactic collisions, and from the motion of stars within galaxies, and of galaxies within galactic clusters.
That is way more than a kludge. That is many observations explainable by a simple hypothesis - that is, a scientific theory.
Re: (Score:2)
That is way more than a kludge. That is many observations explainable by a simple hypothesis - that is, a scientific theory.
Unfortunately, it's not a testable hypothesis, so it's not a scientific theory. It's just an idea, like the string idea (which is also erroneously referred to as string theory).
Re: (Score:2)
Why isn't it testable? We've made predictions based on the assumption of dark matter and verified them. That makes it a testable hypothesis.
We've got something similar to dark matter: neutrinos. Dark matter as we perceive it isn't neutrinos, but it shares some of the properties. It's a reasonable extension from something we already know.
Re: (Score:2)
Re: (Score:3)
What makes it even more kludgy is that this dark matter is supposed to make up a significant percentage of the universe. Except there is *NONE* in our solar system or it's immediate vicinity. If there was any dark matter locally then General Relativity would not explain the planets orbits around the Sun with such precision because it's does so using only visible matter.
This is a huge problem for dark matter because it presumes that our solar system is somehow very special, which is frankly too fantastical.
This is just wrong. This paper: https://arxiv.org/pdf/1404.193... [arxiv.org] (which also has a lot of interesting background) collects estimates of the density of dark matter in this part of the galaxy, most of which are around 0.01 solar masses/ cubic parsec (around 10^-21 kilograms/m^3). So even if the solar system was pervaded by dark matter of this density it would make no measurable difference to anything. For example the entire sphere up to Earth's distance from the Sun would contain about a billion tons of da
Re: (Score:2)
That's no better. You are still claiming that the part of the universe that we inhabit is magically devoid of the main source of matter in the Universe that also happens to magically be invisible. That IMHO is an epic Occam's razor failure. It's in the realms of junk science.
It might help if rather than throwing our hands up and inventing magic matter when we model galactic rotation using Newtonian dynamics which we know to be an incomplete theory of gravity, that astronomers got off their lazy backsides an
Re: (Score:2)
Re: (Score:2)
Except there is *NONE* in our solar system or it's immediate vicinity.
Wrong. [berkeley.edu]
The average density of dark matter near the solar system is approximately 1 proton-mass for every 3 cubic centimeters, which is roughly 6x10-28 kg/cm3. The actual density might be a little lower or higher, but this is the right order of magnitude.
Based on this number, we can work out the total mass of dark matter within the radius of Earth's orbit around the sun: for an orbital radius of 100 million km, we get a total of 2.3x1012 kg of dark matter within the Earth's orbit. This sounds like a lot, but the sun's mass is 2x1030 kg. All of that dark matter only weighs 10-18 as much as the sun does, so we cannot detect the tiny pull of dark matter upon the Earth's orbit. The same story is true all over the solar system: the gravitational pulls of the sun and planets are always much larger than that of the dark matter.
Re:Dark matter is a kludge (Score:5, Insightful)
Dark matter has always struck me as a kludge.
Astrophysicist (but not a cosmologist) here: this is true! In its favour, though, this makes "dark matter" an umbrella term that covers any phenomenon that fits the data. It might be stray, undetected, planet-sized objects; it might be some exotic neutrino variant; it might be little clumps of antiquarks; it might be one of any number of things. All these possibilities are referred to under the term "dark matter".
On the particular possibilities you mention:
Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
This is certainly possible, and some theorists work on it. My understanding, though, is that these approaches postulate energy (with an equivalent mass) resulting from large-scale gravitational fields; that is, you can think of this as a form of dark matter that arises from the gravitational field itself.
This sort of approach has trouble explaining the formation of small-scale dark-matter halos, which depend on some kind of dark-matter self-interaction. It's also incompatible with the example in this article: if "dark matter" results directly from gravitational fields, how can you have a galaxy without it?
Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
If this were the case, we'd expect the rotation curves of nearby galaxies to be well-behaved, while more distant galaxies would show gradually increasing evidence for the influence of "dark matter". We don't see that. There are theories that fundamental constants do change over time - I've seen some interesting tests for the speed of light changing based on gamma-ray absorption spectra - but they don't work as an alternative explanation to dark matter.
Re: (Score:2, Insightful)
There's reason to believe that known types of matter can't account for all, or even most, of dark matter. All this means is that there's another type of matter which doesn't emit light, which we don't know about. Given that neutrinos were only discovered in 1970, and yet they're h
Re: (Score:3)
Dark matter is the sexy name for matter we haven't seen yet. It could be emitting no radiation, or it could be no one has looked for the right emissions. As happened not so long ago when huge amounts of cool galactic gas were found, nicely visible when someone finally looked at the right frequencies.
It's surprisingly easy to 'not see' quite obvious (in hindsight) signals when observing resources are limited and careers are best served by looking for the expected over random observation because that usually
Re: (Score:2)
Dark matter is matter that can't be detected by electromagnetic means. I'm not dark matter, since if you come over to me and shine a light on me you can see me with photons, which are electromagnetic. Non-luminous normal matter does interact electronically, and we can see it by its effects. It can block light, or diffuse light. We know how to detect matter like that, and so we know that dark matter isn't like that.
Re: (Score:2)
Re: (Score:2)
We generally can detect stuff at the mass required to do some of what dark matter explains. If there were enough non-luminous planets in the Galaxy to outweigh all the visible matter by a factor of five, we'd notice it.
Re: (Score:2)
If there were enough non-luminous planets in the Galaxy to outweigh all the visible matter by a factor of five, we'd notice it.
This is not true, these things are basically invisible to us - until recently it was believed that brown dwarves were way more common than they now appear to be, but it is none the less true that baryonic dark matter can not account for all (or even a large portion) of the dark matter in the universe. That's why I said above that known types of matter can't account for all, or even most, of dark matter.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
- Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
This hypothesis is quite easy to test. Just observe the dark matter of various galaxies and plot them as a function of distance. A pattern would emerge.
Although I think it's unlikely, part of me finds this hypothesis fun. We have to remember that we don't really understand why most physical constants are the values that they are. They are subject to change without notice. However, this has never been observed.
Re: (Score:2)
Dark matter has always struck me as a kludge. It amounts to "we don't know WTF is going on, so here's our fudge factor". There is no evidence that dark matter exists, other than the fact that gravity on large scales doesn't behave the way cosmologists expect. Two other possibilities receive too little attention:
- Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
- Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
So now they've discovered a galaxy where the kludge factor of dark matter is not needed. Maybe this will prompt more cosmologist to consider the alternatives...
Actually this evidence supports Dark Matter and contradicts those two theories quite nicely. They both describe universal phenomena -- if the laws of gravity are different, or physical laws are changing the every distant galaxy should show the same anomalous motion. On the other hand if the usual anomalous motion is due to "stuff" (dark matter) then it's not very surprising that some rare event (like a collision) could have separated this galaxy from its original dark matter.
Re: (Score:2)
Dark matter has always struck me as a kludge. It amounts to "we don't know WTF is going on, so here's our fudge factor". There is no evidence that dark matter exists, other than the fact that gravity on large scales doesn't behave the way cosmologists expect. Two other possibilities receive too little attention:
- Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
Which is pretty much the importance of the galaxy we are speaking of. Let's ignore the fact that any modified theory of gravity would be so weird that nobody can even come up with a possible example that would demonstrate what we are seeing, and thus be a much, much more complicated and weirder explanation than a dark matter model. That they found a galaxy, can determine the mass of it, and yet it is acting in a behavior that is not consistent with other galaxies, pretty much shows that a modified theory of
Re: (Score:2)
Our current theory of gravity does not apply on the scales we are observing, i.e., the theory is incomplete.
Already tested. Gravity works perfectly as expected over large distance. Even the inverse has been shown true, that if any other value was being used, we should not see what we're seeing. So not just affirmation of what we know, but affirmation that what we don't know will not affect what we do know by any significant amount for what we care.
Physical laws are not constant. e are looking at very distant objects, and seeing them in the distant past. Perhaps universal constants are not, in fact, constant across large spans of space and/or time.
Already tested. Changes to gravity in the past would have affected at least the CMB, among many other things. And even our local region of space is affected, as in our
Re: (Score:2)
I totally agree with your assessment and your first point. No idea about the 2nd.
To me what seems to be the crux of it is the scales of observation. At small scales (relatively) things it seems make sense, it is only at the truly vast scales, that things start to get wonky.
To me that points to the issue being one of two things;
1) our methods of observation at such distances having themselves issues
2) the scales involved introduce additional factors hereto unforeen
The sizes for this kind of stuff always make
Maybe Stars are escaping (Score:3)
I wonder, did scientists account that perhaps the stars in the outer galaxy are not actually orbiting, but escaping? Wouldn't this also explain the spiral form of the galaxy?
They probably did, using some strange scientific tricks that are beyond me.
Re: (Score:2)
Two problems: (1) we can measure the rotational velocities (2) The galaxies are old enough to have rotated 50 or so times and the spiral structure is still there.
Interesting (Score:5, Informative)
While it's true we don't know if dark matter is an effect, or an actual stuff like wimps (weakly interacting massive particles), the evidence of uniform dispersion from gravitational lensing to kinematics while the uniformity still clumps in a gravitational way is starting to be convincing. A great example is the bullet cluster [wikipedia.org] where the friction of the colliding gasses slowed the normal matter but the dark matter was virtually unaffected, the gravitational attraction was too weak and the dark matter stripped from the baryonic matter. But further, computational models consistent with measurement rely on dark matter to have a cooling effect which wouldn't work (or it's not at all clear anyhow) if it wasn't particle like. If I was a betting man, I'd put my money on a weakly interacting particle.
Re: (Score:2)
This is all fairly straightforward to me and I am actively working on proving it.
Long story short, mass causes the existence of spacetime. The further from a mass you get, the faster time flows (look at GPS satellite corrections for proof).
Time moving faster explains the galactic rotation curve directly "Time is moving faster therefore the apparent speed of the outer edge of the disc moves faster than it should in respect to a non-relative observer."
BAM! Dark Matter is relegated to explaining other unanswer
Maybe they just can't see it? (Score:2)
*Tadum* *Crash* *Thud* ...
Thank you, thank you, I'm here all week. Tip your waitor and try the fish.
Captain pedantic here (Score:5, Informative)
This suggests there is unseen, but substantial, mass holding stars in orbit. In the Milky Way there is about 30 times more dark matter than normal matter.
This is an improper statement of what we actually know. It's like saying a UFO must be an alien from another planet while forgetting what the U stands for. We have close to NO IDEA what the phenomena we call dark matter actually is so saying there is 30X as much of it is a nonsensical statement. It could be some sort of matter but we are not at all certain of that. You could say that our current models of gravitation due to matter only explain a few percent of what we see and that would be an accurate statement of what we know. It's possible that the 30X statement is correct but we don't know that yet. If "dark matter" ultimately turns out to be some flaw in the model of general relativity or the like then saying there is 30X as much dark matter as "normal" matter will sound idiotic. If we want to talk in terms of force then fine - saying there is 30X as much gravitational force makes perfect sense.
Short version. We don't know what it is so it's illogical to keep saying how much of it there is until we know what it is.
Re: (Score:2)
Re: (Score:2)
Short version. We don't know what it is so it's illogical to keep saying how much of it there is until we know what it is.
I'm not a physicist so I can't say for sure how much they are talking out their ass, but in principle you are incorrect.
I'm sure you're talking out of your ass.
People figured out how to do basic microbiology to make yogurt, ferment beverages, etc before they had a meaningful idea of what microbes were.
And this is why I'm sure. The two situations are not remotely comparable. The only way they would be is if people claimed that fermentation was caused by invisible demons, and further claimed that was science. The so-called theory of Dark Matter (which is not a scientific theory because it's not testable) does not claim to explain what dark matter is. It only claims that it exists, and it only offers as evidence some stuff we can't explain. There's no evidence given t
Dark yogurt (Score:2)
I'm not a physicist so I can't say for sure how much they are talking out their ass, but in principle you are incorrect.
Always possible but I very much doubt it in this case. What we are calling "dark matter" very plausibly might not actually be matter at all. Until we can actually prove that it is matter or something similar it is improper to say there is X quantity of it.
People figured out how to do basic microbiology to make yogurt, ferment beverages, etc before they had a meaningful idea of what microbes were.
Missing the point. They weren't making claims that it was some mysterious "dark yogurt". They simply shrugged and said they didn't know. "Dark matter" is a placeholder term we use to explain a phenomena in terms of something we think we do understand.
Re: (Score:2)
Applying names to things is a first step in understanding them. We have very strong evidence that something causes gravitational effects and doesn't interact in other ways we could detect. We call it dark matter, because it's more scientific-sounding than calling it Fred. It's got gravity, and that's characteristic of some form of matter. We really don't know much about it, but giving it a name means we can more easily list what we know and what we don't know, speculate on other properties it might hav
why did scifi have to can it was good (Score:2)
why did scifi have to can it was good
this fits with what I consider for dark matter (Score:2)
Dunno why, but I always thought the observable effects of what gave the creation of dark matter was always the near massless photons.
near zero mass over the shear size of the universe adds up.
Re: (Score:2)
Re: (Score:2)
Photons don't stay in one place, so they aren't the dark matter we've observed. Neutrinos aren't it, for the same reason.
Prior art for incomplete theories (Score:2)
Easily explained. (Score:2, Funny)
It's called White Giant Flight. Even stars want to get the hell away from the darkies. Don't blame them, I would want to raise my young stars in a galaxy full of black holes and brown dwarfs.
Re: Easily explained. (Score:2, Funny)
#DarkMatterMatters
Re: (Score:2)
The universe already has a pretty great wall. [wikipedia.org]
Re:Easily explained. (Score:4, Funny)
I would want to raise my young stars in a galaxy full of black holes and brown dwarfs.
I'm raising my kids on Red Dwarf. Much better.
Re: (Score:2)
A lot of Republicans care. Ever heard of the Southern Strategy? It was explicitly a plan to get racists to vote Republican.
Re: (Score:1, Insightful)
And prison guards alike
Yeah.
One wonders what Obama was thinking - "If I give the crazy mullahs in Iran a few hundred billion dollars, they'll STOP trying to build nukes!"
It's so much better to have an Obama-fueled nuclear arms race in the Middle East, right? Because once Iran gets nukes, Saudi Arabia and Egypt won't be far behind...
That'll work out well.
Maybe Obama should have just told the Iranians that there's a "red line" they can't cross....
Re: (Score:3, Informative)
$1.7 billion, to be precise. And we didn't even get all of our hostages back:
http://www.latimes.com/nation/... [latimes.com]
Re: (Score:2)
It was their fucking money, you idiots.
You'd think that the crowd that constantly yells about taxation being theft would be able to figure out that releasing someone's own money to them is not a "gift."
Re:President without any sense baffles historians (Score:4, Funny)
Aliens of the gaps. (Score:4, Insightful)
Re: (Score:2)
What's wrong with scientists being baffled? It's part of the process. If they never were baffled, it would mean they couldn't figure out anything new.
Re: (Score:2)
Re: (Score:2)
Unfortunately "baffles scientists" is a phrase I've come associate with people who use it as a strawman
I thought it referred to a scientist when they made an astounding discovery, often concerning supernatural events reported in World Weekly News. WaPo's John Carlson mentioned that the WWN quoted a "baffled scientist" so often that the writers "started joking about an institution called the Academy of Baffled Scientists."