# Half the universe’s missing matter found



## Brian G Turner (Oct 9, 2017)

Two separate studies discover that massive clouds of gas that form filaments between galaxies can account for 50% of the supposed missing matter in the universe:

Half the universe’s missing matter has just been finally found

Note that the article refers to "hot gas". So who wants to wager that much of the other half will be found to comprise of "cold" gas and dust, much of it within galaxies themselves?

Honestly, "dark matter" and "dark energy" have always seemed two of the daftest ideas to emerge from modern science. I thought it would be a matter of common sense that the universe must be filled with gas and dust we cannot observe directly. Coming up with convoluted and exotic ideas of what this "missing matter" might be always seemed ridiculous.

As did the observed dimming of Type 1a supernova being blamed  - not on gas or dust clouds, which might be a common sense approach - but instead by the inexplicable invention of a completely new and inexplicable force in physics.

Hopefully a little sanity can now return to the world of astrophysics - and lessons learned.


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## tinkerdan (Oct 10, 2017)

Yet at the bottom of the article you are invited to a link to this article::
*Read more:* Galaxies in filaments spaced like pearls on a necklace
::That includes both dark matter and dark energy in its explanation
 ...winding filaments of dark matter that guide the growth of galaxies and galaxy clusters
...Dark energy, a strange substance that opposes gravity, also affects the galaxy growth process and may serve to help keep galaxies apart.


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## J Riff (Oct 10, 2017)

Our universe is due to be vacuumed.


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## Vertigo (Oct 10, 2017)

But this doesn't explain one of the observations that inspired dark matter in the first place which is the anomalous rotation of galaxies.

It also has no bearing on dark energy which has nothing to do with missing matter but rather the missing energy that is still accelerating the expansion of the universe.


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## Brian G Turner (Oct 10, 2017)

Vertigo said:


> But this doesn't explain one of the observations that inspired dark matter in the first place which is the anomalous rotation of galaxies.



That's why I mentioned the study relates only to "hot" gas. It would be interesting to see what happens if we were able to account for "cold" gas and dust, too. 



Vertigo said:


> It also has no bearing on dark energy which has nothing to do with missing matter but rather the missing energy that is still accelerating the expansion of the universe.



Which mainly came about from presuming that Type 1a supernova should all have the same brightness. But when it was found this was not true, rather than give real consideration to the idea of gas or dust clouds obscuring observations, instead a completely new force of "dark energy" was promoted. 

When this originally appeared in _New Scientist_ I just couldn't understand why simpler explanations were ignored, and the fixation of inventing a new property of the universe that, to this day, appears to have no more scientific description or validity than the "ether" of the Victorian age.

2c.


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## Vertigo (Oct 10, 2017)

Brian G Turner said:


> That's why I mentioned the study relates only to "hot" gas. It would be interesting to see what happens if we were able to account for "cold" gas and dust, too.
> 
> 
> 
> ...


Agree on the first but for dark energy I would agree if that was the only evidence for this mysterious dark energy, but type 1a supernovas are only one piece of several pieces of evidence pointing to something (that we've labelled dark energy). There is also evidence coming from the cosmic microwave background and from the observational Hubble constant data (measure from cosmological redshift). So the several different legs supporting it mean that there's a little more to it than just brightness of supernovas and I don't think they've found a simpler explanation that could explain all of that evidence. If you check out the Wiki article Dark energy - Wikipedia it discusses these and a couple of other bits of evidence.

I must admit the details are all a little bit beyond me and I din't know about that particular one (the supernovas), the one I first heard about was the redshift evidence.


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## reiver33 (Oct 10, 2017)

Well, _that_ doesn't work for me! I've just used up the missing dark energy taking the Universe back 30 years in a story of disgruntled B-list scientists, bitter at all their past mistakes and missed opportunities; physical time travel is possible, it's just a question of scale...


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## Ursa major (Oct 10, 2017)

reiver33 said:


> Well, _that_ doesn't work for me!


You'll be all right...


...as long as your books have dust covers....


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## Mirannan (Oct 10, 2017)

I'm by no means an expert; but as I understand it there is a limit on baryonic dark matter (i.e. matter made out of the stuff we already know) which is fairly low. The reason is that if there was significantly more ordinary matter then the universe would be much more clumpy than it is observed to be.


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## mosaix (Oct 12, 2017)

More info on the Guardian website.

Astronomers find half of the missing matter in the universe


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## LordOfWizards (Oct 18, 2017)

Brian G Turner said:


> When this originally appeared in _New Scientist_ I just couldn't understand why simpler explanations were ignored, and the fixation of inventing a new property of the universe that, to this day, appears to have no more scientific description or validity than the "ether" of the Victorian age.



Thanks Brian, you have given a voice to that vexing thought I've had for years about the Dark Matter/DarkEnergy proposals coming out of the science world. It would seem as if they were 'playing it safe?' or something by not suggesting any simpler explanations, especially with Dark Matter. (You should hear me railing at the TV (The Science Channel here in the US) when yet another scientist states that there must be some magical ingredient making galaxies heavier.)  They say we can only account for 4.9% of the mass, and then say that it is based on that which is observable via electromagnetic signals. In other words, when we watch Andromeda spin, and it's moving too fast of all of the mass that we can detect with our various telescopes (Visible light, Radio waves), so there must be some "exotic" matter out there. Can we possibly estimate the amount of colder mass, as in billions of burnt out suns, hundred of thousands of light years wide scatterings of Hydrogen, Helium, and just plain dust and rocks? 

The article that Mosaix linked to says that scientists calculated the 4.9% mass figure based on "measurements of radiation left over from the Big Bang, which allowed them to calculate how much matter there is in the universe and what form it takes". But in the past the science shows have said it was because of the rotational inertia of other galaxies like Andromeda. Can someone clear this up for me? I would love to see those Big Bang calculations and what "observable radiation" they were basing it on. I've had enough education in math and science to follow these calculations and suppositions.


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## Brian G Turner (Sep 28, 2018)

Still looks as though we're finding more gas and dust, but struggling to count it all up - for the moment:
Extended emission filaments found in the galaxy Markarian 6
Cosmic 'dustpedias' could reveal new types of galaxy


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## LordOfWizards (Oct 2, 2018)

Getting scientists to properly name their theories appears to be a very _Dark Matter._


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## Brian G Turner (Oct 3, 2018)

Good to see this come up again, as an article this week shows that galaxies are surrounded by even bigger clouds of gas than originally believed: MUSE spectrograph reveals that nearly the entire sky in the early Universe is glowing with Lyman-alpha emission

I think we may be on the way to finally putting "Dark Matter" to rest.


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## Joshua Jones (Oct 6, 2018)

Good to meet another skeptic of dark matter. It is just such an ad hoc explanation which magically has all the properties it may need, including some which make is sound like The Force, to explain whatever mysteries it is invoked to solve... It is a good stand in for what is unknown in astrophysics, but as an actual theory...


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## RJM Corbet (Oct 6, 2018)

As far as I understand this is about missing _ordinary_ matter; it's not about finding dark matter.

Until I became aware of this 'hot filaments' thing, I didn't know that half to 90% of the _ordinary_ matter in the universe is still hidden. It's a misleading headline, imo.

This is not about finding dark matter at all?

Half the universe’s missing matter has just been finally found

... This is the first detection of the roughly half of the *normal* *matter* in our universe – protons, neutrons and electrons – unaccounted for by previous observations of stars, galaxies and other bright objects in space...

(From first para of above link)

The actual paper is linked here, for anyone who can understand it, lol:

[1709.05024] A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red   Galaxies


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## RJM Corbet (Oct 6, 2018)

mosaix said:


> More info on the Guardian website.
> 
> Astronomers find half of the missing matter in the universe



Astronomers find half of the missing matter in the universe

Last sentence of above article:

...Cosmologists are also still yet to discover the nature of dark matter, which makes up even more of the universe...

ie: Even after this discovery they'll still be looking for a whole lot more hidden *ordinary* matter?


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## Graymalkin (Oct 6, 2018)

Mystery solved. It's under my stairs!


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## RJM Corbet (Oct 6, 2018)

Joshua Jones said:


> Good to meet another skeptic of dark matter. It is just such an ad hoc explanation which magically has all the properties it may need, including some which make is sound like The Force, to explain whatever mysteries it is invoked to solve... It is a good stand in for what is unknown in astrophysics, but as an actual theory...


Dark Matter is just a term for the unknown force that is generating most of the gravity in the universe. It is not composed of matter or even of anti-matter. It's not composed of atoms or particles. It's just some force there. No-one knows what it is. The name 'dark matter' means nothing. Dark matter isn't really _matter_ at all?

EDIT: Dark Energy, as @Vertigo observes, is the _anti_-gravity force causing the universe to expand.


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## Joshua Jones (Oct 6, 2018)

RJM Corbet said:


> Dark Matter is just a term for the unknown force that is generating most of the gravity in the universe. It is not composed of matter or even of anti-matter. It's not composed of atoms or particles. It's just there. No-one knows what it is. The name 'dark matter' means nothing. Dark matter isn't really _matter_ at all?


If that is the case, my concern is that they are ascribing properties to a lack of knowledge, rather than a "something". There is a problem with our cosmological model, and rather than just admitting ignorance on the subject, they name their ignorance "dark matter" and "dark energy". I wish I had thought of "dark algebra" in primary school! 

I guess I would have more respect for someone who says, "we expect that we will make future discoveries which will explain this mystery, but at the moment, we don't know why..." rather than someone who says, "Dark matter explains it," knowing full well that dark matter is a stand in for a lack of knowledge. The argument takes the same form as a "God of the gaps" hypothesis, and I am reasonably certain those who theorize this would critique a Creationist who used such an argument. Physician (or physicist, in this case), heal thyself! 

I apologize if this is a rant, but I like my science to be based on evidence and intellectual honesty, rather than speculation, and I haven't seen anything remotely persuasive in favor of dark matter beyond a description of the problem. And, at least for me, a description of a problem does not a theory make.


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## Vertigo (Oct 6, 2018)

Joshua Jones said:


> If that is the case, my concern is that they are ascribing properties to a lack of knowledge, rather than a "something". There is a problem with our cosmological model, and rather than just admitting ignorance on the subject, they name their ignorance "dark matter" and "dark energy". I wish I had thought of "dark algebra" in primary school!
> 
> I guess I would have more respect for someone who says, "we expect that we will make future discoveries which will explain this mystery, but at the moment, we don't know why..." rather than someone who says, "Dark matter explains it," knowing full well that dark matter is a stand in for a lack of knowledge. The argument takes the same form as a "God of the gaps" hypothesis, and I am reasonably certain those who theorize this would critique a Creationist who used such an argument. Physician (or physicist, in this case), heal thyself!
> 
> I apologize if this is a rant, but I like my science to be based on evidence and intellectual honesty, rather than speculation, and I haven't seen anything remotely persuasive in favor of dark matter beyond a description of the problem. And, at least for me, a description of a problem does not a theory make.


I confess I've never heard a scientist say 'Dark Matter explains it'. What I've heard from scientists is that Dark Matter is simply a label for the stuff they don't yet understand. And they tend to get, on the one hand, very frustrated by this stuff they don't understand and, on the other hand, quite excited about how much they've yet to discover.

I think you may be conflating the sensationalist reporting by 'science' journalists who love to talk up a good mystery with what the actual scientists are really saying. Every scientist I have heard talking about dark matter is anything but glib about it. In my experience every one I've heard has been very honestly baffled by it. Effectively what they are saying is, here's a bunch of phenomenon we can't explain so for the time being we will attribute it to an as yet unknown property of the universe and give that property a name as that makes it much easier to discuss. So of course they know dark matter is "a stand in for lack of knowledge" that's the whole point! And they're doing all they can to fill that gap in their knowledge. And do doubt if/when they do they'll find other stuff they don't understand. No one has claimed that dark matter is a tangible solution to these unknowns.

It's really no different to phlogiston, the name given to an unknown 'substance' to which they could attribute all the properties of fire, or, indeed, the ether that was thought to fill space at one time because waves 'needed' a medium to propagate in. There will always be such things in science until we actually  know everything and it seems unlikely that will ever happen.


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## Joshua Jones (Oct 6, 2018)

Vertigo said:


> I confess I've never heard a scientist say 'Dark Matter explains it'. What I've heard from scientists is that Dark Matter is simply a label for the stuff they don't yet understand. And they tend to get, on the one hand, very frustrated by this stuff they don't understand and, on the other hand, quite excited about how much they've yet to discover.
> 
> I think you may be conflating the sensationalist reporting by 'science' journalists who love to talk up a good mystery with what the actual scientists are really saying. Every scientist I have heard talking about dark matter is anything but glib about it. In my experience every one I've heard has been very honestly baffled by it. Effectively what they are saying is, here's a bunch of phenomenon we can't explain so for the time being we will attribute it to an as yet unknown property of the universe and give that property a name as that makes it much easier to discuss. So of course they know dark matter is "a stand in for lack of knowledge" that's the whole point! And they're doing all they can to fill that gap in their knowledge. And do doubt if/when they do they'll find other stuff they don't understand. No one has claimed that dark matter is a tangible solution to these unknowns.
> 
> It's really no different to phlogiston, the name given to an unknown 'substance' to which they could attribute all the properties of fire, or, indeed, the ether that was thought to fill space at one time because waves 'needed' a medium to propagate in. There will always be such things in science until we actually  know everything and it seems unlikely that will ever happen.


I understand all that, and to an extent, I can understand why they do it. On the other hand, using a term like "dark matter" implies that it is actually some sort of existence with properties, when it could actually be, say, 18 different things or a problem with the cosmological model we are using. The term has too many connotations to it, and it would be just as easy to discuss the problem as a problem rather than as a theoretical explanation. They could call it the Unexplained Galactic Gravitational Occurrence (UGGO) or Problem of Unexplained Gravity (PUG) just as easily and with less confusion by the populous. 

I think my issue is that naming a theory problem something which, at bare minimum  implies a specific physical solution is at best a poor choice of terms, at worst an attempt to appear as though one is closer to an explanation than one actually is or an exercise in speculation and arbitrarily assigning characteristics to an unknown. Nothing in this possible range strikes me as good or intellectually honest science.


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## RJM Corbet (Oct 6, 2018)

Joshua Jones said:


> I understand all that, and to an extent, I can understand why they do it. On the other hand, using a term like "dark matter" implies that it is actually some sort of existence with properties, when it could actually be, say, 18 different things or a problem with the cosmological model we are using. The term has too many connotations to it, and it would be just as easy to discuss the problem as a problem rather than as a theoretical explanation. They could call it the Unexplained Galactic Gravitational Occurrence (UGGO) or Problem of Unexplained Gravity (PUG) just as easily and with less confusion by the populous.
> 
> I think my issue is that naming a theory problem something which, at bare minimum  implies a specific physical solution is at best a poor choice of terms, at worst an attempt to appear as though one is closer to an explanation than one actually is or an exercise in speculation and arbitrarily assigning characteristics to an unknown. Nothing in this possible range strikes me as good or intellectually honest science.



Oh no, I don't think there is any implication of dishonesty or even carelessness. It's just a term that stuck. Scientists themselves understand quite clearly what it means.

In a way 'dark matter' does explain something invisible that nevertheless exhibits the gravitational effect of visible matter.

But it may be misunderstood by non-scientists as an actual form of matter. Which I believe it isn't, really? Magazines and newspapers cause further misunderstanding with misleading headlines.

Still, the fact is that about 25% of the universe consists of this 'dark matter', another 71% or so of 'dark energy' and only the remaining 4% is the 'known universe' of 'ordinary' matter.

The interesting thing to me about this 'hot filaments' discovery is it reveals that 50% to 90% of even this 'ordinary' matter covered by the _standard_ _model_ is concealed in mysterious ways?


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## Joshua Jones (Oct 6, 2018)

RJM Corbet said:


> Oh no, I don't think there is any implication of dishonesty or even carelessness. It's just a term that stuck. Scientists themselves understand quite clearly what it means.
> 
> In a way 'dark matter' does explain something invisible that nevertheless exhibits the gravitational effect of visible matter.
> 
> ...


Let me back my argument up a bit. What is agreed upon is that there is not enough detected matter to produce about 5/6ths of the gravitation we observe. This is a significant problem in the current cosmological model, and there must be an explanation out there somewhere. The problem, though, arises when we make statements like "25% of the universe consists of this 'dark matter'" (which is not intended as a criticism of you, as NASA's website uses similar verbiage). I am not a cunning linguist, but to say the universe consists of 25% of anything is to give priority to a theory of weakly interacting massive particles over, say, the possibility that our theory of gravity is inadequate. For it to be expressed neutrally, one would have to say "We have no current explanation for a large percentage of the gravity we seem to observe." To put it another way, an absence of knowledge itself has no mass, and therefore cannot be the explanation of the problem. If the problem is elsewhere, then the universe is not 4-5% regular matter, but more like 30%. So, the phrasing requires a solution where there actually is something accounting for that mass, and that something has specific properties (cold, almost never interacts with regular matter or itself, etc.). Until or unless actual evidence of this is discovered, it should not be preferred.

That is the point I am really trying to make here. Instead of making up something which explains every mystery, why not just admit ignorance and study the possible answers? In my opinion, in the absence of evidence, we ought to be silent on scientific matters, but that is not the case with dark matter, as I have sought to demonstrate above.


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## RJM Corbet (Oct 6, 2018)

Joshua Jones said:


> Let me back my argument up a bit. What is agreed upon is that there is not enough detected matter to produce about 5/6ths of the gravitation we observe. This is a significant problem in the current cosmological model, and there must be an explanation out there somewhere. The problem, though, arises when we make statements like "25% of the universe consists of this 'dark matter'" (which is not intended as a criticism of you, as NASA's website uses similar verbiage). I am not a cunning linguist, but to say the universe consists of 25% of anything is to give priority to a theory of weakly interacting massive particles over, say, the possibility that our theory of gravity is inadequate. For it to be expressed neutrally, one would have to say "We have no current explanation for a large percentage of the gravity we seem to observe." To put it another way, an absence of knowledge itself has no mass, and therefore cannot be the explanation of the problem. If the problem is elsewhere, then the universe is not 4-5% regular matter, but more like 30%. So, the phrasing requires a solution where there actually is something accounting for that mass, and that something has specific properties (cold, almost never interacts with regular matter or itself, etc.). Until or unless actual evidence of this is discovered, it should not be preferred.
> 
> That is the point I am really trying to make here. Instead of making up something which explains every mystery, why not just admit ignorance and study the possible answers? In my opinion, in the absence of evidence, we ought to be silent on scientific matters, but that is not the case with dark matter, as I have sought to demonstrate above.


I'm quickly out of my depth with this stuff. But I do think that the standard model, wonderful as it is in predicting and explaining so much, sometimes overplays its hand. There's a lot of weird stuff out there that human science may never be able to know more than a small fraction about?

I would like to know a bit more about why so much of the (_ordinary/standard)_ matter is in fact apparently hidden away?

Any answers?


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## Joshua Jones (Oct 6, 2018)

RJM Corbet said:


> I'm quickly out of my depth with this stuff. But I do think that the standard model, wonderful as it is in predicting and explaining so much, sometimes overplays its hand. There's a lot of weird stuff out there that human science may never be able to know more than a small fraction about?
> 
> I would like to know a bit more about why so much of the (_ordinary/standard)_ matter is in fact apparently hidden away?
> 
> Any answers?


To be honest, I haven't done nearly enough digging into why ordinary matter may be hidden to speak intelligently on the matter (no pun intended, of course!). Anyone else here dug into it?


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## Venusian Broon (Oct 6, 2018)

Joshua Jones said:


> In my opinion, in the absence of evidence, we ought to be silent on scientific matters, but that is not the case with dark matter, as I have sought to demonstrate above.



Erm, this is evidence of _something. _For example Galaxy rotation curves, observations of Galaxy clusters, Gravitational lensing and a whole host of other results from quite a wide variety of observations.

So many in fact that it makes modified Newtonian dynamics or modified General Relativity unlikely candidates, as they can be modified to fit one case, but struggle to then fit the rest. Not impossible, but on the unlikely side of things. (Although to be fair, I do think General Relativity will need to change anyway, but that's because it lost to QM )

So, many scientists on the forefront of these areas of study _believe _that it is more likely that there is some dark matter element out there, as such a concept fits these observations better. 

What's wrong with putting out what you think is the likeliest hypothesis, even if it's all a bit hazy? It's be best we've got at the moment. You've got to start with something. Others can try and design experiments to narrow down what this 'dark matter' may be and how it's actually interacting with the rest of the universe. 

Perhaps in 50 years we'll all look back and laugh at this, because the one crucial experiment proved that dark matter was a mirage, a bit like the ether. So what? That's how science works.


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## RJM Corbet (Oct 6, 2018)

[


Venusian Broon said:


> Erm, this is evidence of _something. _For example Galaxy rotation curves, observations of Galaxy clusters, Gravitational lensing and a whole host of other results from quite a wide variety of observations.
> 
> So many in fact that it makes modified Newtonian dynamics or modified General Relativity unlikely candidates, as they can be modified to fit one case, but struggle to then fit the rest. Not impossible, but on the unlikely side of things. (Although to be fair, I do think General Relativity will need to change anyway, but that's because it lost to QM )
> 
> ...



Right. Thanks VB.
Can you enlighten more about this missing 'normal matter' -- such as located in these hot filaments?


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## Brian G Turner (Oct 7, 2018)

RJM Corbet said:


> why so much of the (_ordinary/standard)_ matter is in fact apparently hidden away?



We struggle to calculate the actual size and mass of galaxies, and especially struggle to measure the amount/mass of gas and dust within and around galaxies - something the news items I've posted in this thread especially highlight.

This is important - ideas about "missing mass", aka, "dark matter" presume we actually have accurate information about all of the above, which is absolutely not true - we haven't even begun to properly figure them out.


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## TheEndIsNigh (Oct 7, 2018)

What's the surprise. Dark matter is dark. Some has been found so it wasn't dark after all. Just hiding in the cupboard as it were.

I do wonder about the weight of all those particles that have been spewing out across the universe for the billions of years it has existed. Our sun apparently loses 4 billion tons per second. Ok some of that explains the energy production but a sizeable part of it is given out in the form of particles photons, neutrinos and the like.

Even if we assume a mere 10,000 tons of actual matter per second for five billion years, that amounts to a large chunk of change. Multiply that by the number of suns knocking about and we have a fair dollop of something to account for.

In addition, all those particles have been whisking off away from our local visible universe out into the wild frontier of emptiness at the speed of light. No doubt they'll be having a gravitational pull, back on us in our small bubble.

What amazes me is the theoretical physicists churn out a lot of nonsense to* not* explain the initial expansion of the local bubble universe (balloons and the like that puts their favoured speed of light in the slow lane, as far as being the fastest thing around) and then because they know even less about what happened after that, they come up with equally theoretical nonsense about dark energy.

My personal take on the expansion is that if a bang can happen, it can happen twice or a million times.

Imagine a million bubbles of matter out there (why not an infinite number)  - Too far away for the nearest to be seen (cos not enough time has passed). That wouldn't prevent the gravitation pull effects of such far distant matter. How much matter - Well, how much would it take. Maybe we could theorise about it and get it just right.

All this pales into insignificance of course when compared to the true facts.

Seven days and then down the pub.


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## Joshua Jones (Oct 7, 2018)

Venusian Broon said:


> Erm, this is evidence of _something. _For example Galaxy rotation curves, observations of Galaxy clusters, Gravitational lensing and a whole host of other results from quite a wide variety of observations.
> 
> So many in fact that it makes modified Newtonian dynamics or modified General Relativity unlikely candidates, as they can be modified to fit one case, but struggle to then fit the rest. Not impossible, but on the unlikely side of things. (Although to be fair, I do think General Relativity will need to change anyway, but that's because it lost to QM )
> 
> ...


I agree with you that it is evidence of something. The problem I have with the dark matter theory is twofold. First, it is discussed as fact ("the universe is 25% dark matter" rather than "we think the universe is 25% dark matter"), so the general populous thinks there are particles out there which don't interact with regular matter but have gravity, despite the fact that there is not one shred of evidence for it. Second, the argument takes the form of the "God of the Gaps" argument, which is logically unsound. The only difference is that is it a "particle of the gaps", and the properties ascribed to the gap don't include conciousness. But, the nature of the properties is insignificant to the logical issues with the argument. It is kinda like being here in a puzzle...





...and expecting to find one piece to complete it. We don't even know the scope of the possible answers at this point or how big the puzzle may be. We don't know if it is an issue of detection, mass, or theory. So, all I am suggesting is that scientists look into all these possibilities, and if they are, be honest and transparent about the unsettled nature of the research. And, I don't believe calling the problem dark matter is conducive to that transparency.


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## RJM Corbet (Oct 7, 2018)

Brian G Turner said:


> We struggle to calculate the actual size and mass of galaxies, and especially struggle to measure the amount/mass of gas and dust within and around galaxies - something the news items I've posted in this thread especially highlight.
> 
> This is important - ideas about "missing mass", aka, "dark matter" presume we actually have accurate information about all of the above, which is absolutely not true - we haven't even begun to properly figure them out.


So the more _ordinary_ (baryonic) matter that's discovered hidden away in things like these hot filaments, the less dark matter that needs to be substituted to account for the extra gravity?

Which does seem obvious. Which is why I wondered why the articles stated that the discovery of this missing matter did not affect the search for dark matter.

Sorry, I'm not being argumentative. Genuinely trying to learn.


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## Brian G Turner (Oct 7, 2018)

You're not being argumentative, and that's precisely my take on it - but there are all sorts of theories out there about what may constitute this "missing matter", some of which are quite exotic. 

And my opinion isn't necessarily right - I just think I'm stating the obvious.


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## RJM Corbet (Oct 7, 2018)

TheEndIsNigh said:


> ...I do wonder about the weight of all those particles that have been spewing out across the universe for the billions of years it has existed. Our sun apparently loses 4 billion tons per second. Ok some of that explains the energy production but a sizeable part of it is given out in the form of particles photons, neutrinos and the like.
> 
> Even if we assume a mere 10,000 tons of actual matter per second for five billion years, that amounts to a large chunk of change. Multiply that by the number of suns knocking about and we have a fair dollop of something to account for.
> 
> In addition, all those particles have been whisking off away from our local visible universe out into the wild frontier of emptiness at the speed of light. No doubt they'll be having a gravitational pull, back on us in our small bubble...



But surely the physicists have taken this into their calculation of all the (ordinary/baryonic) matter in the universe? I mean how does someone set-out to calculate the mass of all the matter in the universe anyway? Mind boggling ...


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## RJM Corbet (Oct 7, 2018)

Brian G Turner said:


> You're not being argumentative, and that's precisely my take on it - but there are all sorts of theories out there about what may constitute this "missing matter", some of which are quite exotic.
> 
> And my opinion isn't necessarily right - I just think I'm stating the obvious.


Sure. But if these filaments really accounted for half the dark matter in the universe, surely it would say so? It would be _momentous_? Huge. Instead it's tucked away accompanied by the careful qualification that the search for dark matter is unchanged by the discovery of these filaments?


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## Brian G Turner (Oct 7, 2018)

RJM Corbet said:


> But if these filaments really accounted for half the dark matter in the universe, surely it would say so?



The headline says "half" - so although the problem isn't solved, IMO it's a indicator of how we might solve it in the near future - certainly if we've generally underestimated the mass of dust and gas in the galactic disk, though it would help if we could be sure how big that disk is in the first place.


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## RJM Corbet (Oct 7, 2018)

Brian G Turner said:


> The headline says "half" - so although the problem isn't solved, IMO it's a indicator of how we might solve it in the near future - certainly if we've generally underestimated the mass of dust and gas in the galactic disk, though it would help if we could be sure how big that disk is in the first place.


In a nutshell then: half the missing gravity once ascribed to dark matter has now been accounted for? By these filaments?


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## Brian G Turner (Oct 7, 2018)

RJM Corbet said:


> In a nutshell then: half the missing gravity once ascribed to dark matter has now been accounted for? By these filaments?



In theory - but as with all things in astrophysics, it remains to be seen how well this is applied and modified.


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## RJM Corbet (Oct 8, 2018)

Just did some checking on that. It seems not to be the case:

Astronomers Have Found the Universe's Missing Matter

... ASTRONOMERS HAVE FINALLY found the last of the missing universe. It’s been hiding since the mid-1990s, when researchers decided to inventory all the “ordinary” matter in the cosmos—stars and planets and gas, anything made out of atomic parts. (This isn’t “dark matter,” which remains a wholly separate enigma.) They had a pretty good idea of how much should be out there, based on theoretical studies of how matter was created during the Big Bang. Studies of the cosmic microwave background...

https://www.forbes.com/sites/starts...erse-and-still-need-dark-matter/#5a93df3b4fb1

... By examining stars, dust, and gas in galaxies and clusters, scientists had found only 18% of the normal matter. But by surveying intergalactic space, including along filaments and in cosmic voids, scientists found not only gas, but ionized plasmas of all temperatures, that lead us to 100% of what’s expected. There is no more; and therefore, dark matter is still absolutely necessary.ESA ...


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## Vertigo (Oct 8, 2018)

RJM Corbet said:


> Just did some checking on that. It seems not to be the case:
> 
> Astronomers Have Found the Universe's Missing Matter
> 
> ...


Yes this was my understanding that this discovery is only picking up the missing _normal_ matter but it goes no closer to accounting for the behaviour for which the label dark matter was created. Though I may be wrong; this whole area seem to be becoming something of an understanding minefield for the lay observer!


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## mosaix (Oct 8, 2018)

I don’t see a problem in any of this.  What’s in a name? Scientists have to start somewhere even if they know there going to end up somewhere completely different. 

I remember Jeremy Clarkson (spit) on QI saying ‘Why do people always have to label things?’  He was referring to medical complaints. The reason is so that there’s a simple common language that we can use instead of becoming long winded about it every time we want to have a discussion about something.  You know Jeremy, so that we don’t have to say ‘that thing that we depress with our left foot that temporarily disconects the gearbox from the drive shaft so that we can change gear’ - it a clutch BTW for those with an automatic gearbox.


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## Vertigo (Oct 8, 2018)

mosaix said:


> I don’t see a problem in any of this.  What’s in a name? Scientists have to start somewhere even if they know there going to end up somewhere completely different.
> 
> I remember Jeremy Clarkson (spit) on QI saying ‘Why do people always have to label things?’  He was referring to medical complaints. The reason is so that there’s a simple common language that we can use instead of becoming long winded about it every time we want to have a discussion about something.  You know Jeremy, so that we don’t have to say ‘that thing that we depress with our left foot that temporarily disconects the gearbox from the drive shaft so that we can change gear’ - it a clutch BTW for those with an automatic gearbox.


I agree with you re the labeling but the problem I have is whether or not this particular discovery has any impact on the Dark Matter issue which I believe it may not.


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## Joshua Jones (Oct 8, 2018)

mosaix said:


> I don’t see a problem in any of this.  What’s in a name? Scientists have to start somewhere even if they know there going to end up somewhere completely different.
> 
> I remember Jeremy Clarkson (spit) on QI saying ‘Why do people always have to label things?’  He was referring to medical complaints. The reason is so that there’s a simple common language that we can use instead of becoming long winded about it every time we want to have a discussion about something.  You know Jeremy, so that we don’t have to say ‘that thing that we depress with our left foot that temporarily disconects the gearbox from the drive shaft so that we can change gear’ - it a clutch BTW for those with an automatic gearbox.


Yeah, I don't agree with Jeremy Clarkson on not using labels. In my field of study, we use shorthand labels all the time. My concern is when the label doesn't accurately represent the status of the research or gives preference to one possible solution over another. For example, when philosophers of my sort refer to the Problem of Evil, we are using a shorthand term for a complex philosophical argument including multiple forms of argumentation. This could be answered by granting that it is, indeed, a legitimate contradiction or probabilistic likelihood (depending on which aspect is being addressed), or answered by a defense, or a theodicy. But, if we call the Problem of Evil "Theodicy", we are giving a preference from the outset to one solution. 

In the case of dark matter, it is also the term used to refer to WIMPs, which is why this discussion has been so confusing. This is because the solution of missing mass is implied directly in the term for the problem, and WIMPs are the proposed solution to that missing mass. But, there are other possible solutions, and we may not even understand the scope of the possible solutions yet. So, my problem isn't with labeling this problem, but the priority given to one solution by the specific label chosen. And, as at least most of us in this discussion are writers, I think we understand the importance of words and how much power they can have. 

So yes, by all means, let researchers study WIMPs and whatever other hypothetical solutions exist. Just don't name the problem after a hypothesis, and don't make confident statements like "the universe is 25% dark matter" until the hypothesis is at least a theory.


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## Venusian Broon (Oct 8, 2018)

Vertigo said:


> Yes this was my understanding that this discovery is only picking up the missing _normal_ matter but it goes no closer to accounting for the behaviour for which the label dark matter was created. Though I may be wrong; this whole area seem to be becoming something of an understanding minefield for the lay observer!



Finding normal matter can be extremely difficult, astronomically speaking. 

Even things that like to shine, like stars, can be obscured, too far away and too puny to be ever picked up by any instrumentation on and around Earth. Hence the large variance in the estimate in the number of stars the Milky way has - ranging from 100-400+ billion at the moment, I believe. We just can't see the (probably) large population of red dwarfs that are likely to be present. 

Just to muddy figures these figures come more from other observations of the effective mass of the galaxy. And as RJM points out in one of the articles he brought up, how much of dark matter halo a galaxy might have could be highly variable too, so that adds further mass observation issues.


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## Venusian Broon (Oct 8, 2018)

Joshua Jones said:


> In the case of dark matter, it is also the term used to refer to WIMPs, which is why this discussion has been so confusing. This is because the solution of missing mass is implied directly in the term for the problem, and WIMPs are the proposed solution to that missing mass.



I'm not an astrophysicist, just did condensed matter physics as a PhD, but my understanding of this situation is that 'dark matter' refers to the whole gamut of theories and hypothesis's that exists. WIMPs is one of them, but it also refers to MACHOs, primordial black holes and will also include the modified gravitational theories. And everything else that might explain what's happening. 

Yes, perhaps those that have been studying it for years have decided, given the more detailed evidence and understanding they have, might have plumped for one or the other, such as WIMPs. But there are still advocates for the others. Therefore I've never heard of the term dark matter being exclusively tied to just WIMPs.

I do think when their results are being reported by journalist they tend to get lost in transaction, because of the journalist's drive to simplify what the scientists are communicating. Virtually all the time I actually hear a scientist talk/write about their work, they do _not _state confidentially things like 'the universe is 25% dark matter' (Something, I find, that a tag line on a news article tends to say) but, rather say: 'I/we believe that 25% of the universe could be dark matter', or prefix it with 'On our current understanding/observations the leading hypothesis is...' Usually if you read the article carefully these types of responses are usually buried near the end of the article.

So actually I think it's quite a good term. There are a bunch of observations that seem to imply that there's some mass there that we can't see. That's a good first guess.


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## Joshua Jones (Oct 8, 2018)

Venusian Broon said:


> I'm not an astrophysicist, just did condensed matter physics as a PhD, but my understanding of this situation is that 'dark matter' refers to the whole gamut of theories and hypothesis's that exists. WIMPs is one of them, but it also refers to MACHOs, primordial black holes and will also include the modified gravitational theories. And everything else that might explain what's happening.
> 
> Yes, perhaps those that have been studying it for years have decided, given the more detailed evidence and understanding they have, might have plumped for one or the other, such as WIMPs. But there are still advocates for the others. Therefore I've never heard of the term dark matter being exclusively tied to just WIMPs.
> 
> ...


And, I would add, at least from a procedural standpoint, we should start by examining the more simple answers before looking at the complex ones. And, I could completely support statements like "we believe that 25% of the universe could be dark matter" as you cited above. This is a statement of a hypothesis, and it is weighted correctly for that.

My issue comes with exerpts like this from NASA's website, "More is unknown than is known [regarding dark energy]. We know how much dark energy there is because we know how it affects the universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27% (Dark Energy, Dark Matter | Science Mission Directorate)." This seems to be the language of a theory, not a hypothesis. Now, this could be a case of Americans overstating their case (as we do on occasion), or it could be a desire to appear to the general public more settled on a matter than we actually are. I don't pretend to know which is the case or if it is something else altogether, but that exerpt makes it seem the matter is settled. And, for the record, I don't think you are wrong when you say that scientists don't typically make such claims when speaking to one another, and many likely are more cautious when speaking to the general public. There are, however, at least some who are not so cautious when communicating with the public, even in media they control. 

As this is, and will invariably be the case where individuals are concerned, I think it better to name the problem something which blocks this to an extent, so we can have a more informed populous (a pipe dream in the age of Twitter, I am sure!). If we want to go with something catchy like dark matter, I would think "dark gravity" may be better, as it puts the ambiguity on the gravity, rather than on the hypothesized cause of the gravity. 

I know I may be particular on this point, but I do believe words matter, and should be carefully weighed before issued. 

Does that make any sense, or am I just being unnecessarily particular?


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## RJM Corbet (Oct 8, 2018)

Venusian Broon said:


> Finding normal matter can be extremely difficult, astronomically speaking.
> 
> Even things that like to shine, like stars, can be obscured, too far away and too puny to be ever picked up by any instrumentation on and around Earth. Hence the large variance in the estimate in the number of stars the Milky way has - ranging from 100-400+ billion at the moment, I believe. We just can't see the (probably) large population of red dwarfs that are likely to be present.
> 
> Just to muddy figures these figures come more from other observations of the effective mass of the galaxy. And as RJM points out in one of the articles he brought up, how much of dark matter halo a galaxy might have could be highly variable too, so that adds further mass observation issues.


But it appears cosmology has already quite long ago calculated the total baryonic mass of the universe (from big bang data or whatever, I'm clueless) and the point is that the large part of this predicted baryonic mass could not be located until recently.

However the discovery first of these filaments, and then the MUSE discovery of primordial hydrogen clouds, has now completed the package of baryonic matter  predicted. They've now got it all. But it's _still_ only capable of generating about 5% of the gravity in the universe.

It seems there is not and can not be any more baryonic matter in existence. 5% of the universe is all its ever going to be.

The exact same 'amount' of dark matter is still out there, unaffected. No change at all. It still makes up about 25% of the universe.

@Joshua Jones: I apologise for restating the commonly used percentage figures here, for convenience. Dark Gravity would indeed probably be a far better label than dark matter, for non-physicists. But the physicists themselves are not confused by it?


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## Joshua Jones (Oct 8, 2018)

RJM Corbet said:


> But it appears cosmology has already quite long ago calculated the total baryonic mass of the universe (from big bang data or whatever, I'm clueless) and the point is that the large part of this baryonic mass was hidden until recently.
> 
> However the discovery first of these filaments, and then the MUSE discovery of primordial hydrogen clouds, has now completed the package of baryonic matter  predicted. But it's still only capable of generating about 5% of the gravity in the universe.
> 
> ...


It doesn't seem that there is much confusion for physicists on what is meant by the term, at least from my observations. The problem seems to come when it crosses over to the populous, and there doesn't seem to be much desire to clarify at this point. 

And no need to apologize; I understand what you mean, and it is much easier to discuss these things in those terms. I give lay people a pass on the terms they use. Professionals in the field and those who are hired to represent them, however...


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## mosaix (Oct 21, 2018)

Witches, goblins and the quest to solve the mystery of dark matter


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## RJM Corbet (Oct 21, 2018)

Dark matter - Wikipedia

... In the standard Lambda-CDM model of cosmology, the total mass–energy of the universe contains 4.9% ordinary matter and energy, 26.8% dark matter and 68.3% of an unknown form of energy known as dark energy.

Thus, dark matter constitutes 84.5% of total mass, while dark energy plus dark matter constitute 95.1% of total mass–energy content...


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## Ursa major (Oct 21, 2018)

mosaix said:


> ‘that thing that we depress with our left foot that temporarily disconects the gearbox from the drive shaft so that we can change gear’ - it a clutch BTW for those with an automatic gearbox.


Pedant Alert!

The thing that those with manual transmissions depress with their foot is the clutch pedal, not the clutch.
My car has an automatic transmission, but although it has no clutch pedal, it does have _two_ clutches.


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## Dave (Oct 21, 2018)

Clutch [kluhtch] noun

_Also called clutch bag, clutch purse. a woman's small purse that can be carried in the hand and usually has no handle or strap._

Is that it?


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## Ursa major (Oct 21, 2018)

Clutching is also associated with straws (though I don't know why or how).


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## RJM Corbet (Oct 23, 2018)

That seems to be the long and the short of it ...


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