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First detection of the missing half of normal matter in our universe

lacksconfidence 9y ago
https://www.reddit.com/r/space/comments/75944s/half_the_universes_missing_matter_has_just_been/do4mfjx/ https://www.reddit.com/r/space/comments/75944s/half_the_univ... > The approximate distribution in the Universe is 5% regular matter, 25% Dark Matter, and 70% Dark Energy. Half of that 5% was missing, and now found. > Regular matter makes stars and visible galaxies, so it is "bright". Dark Matter is so named because it does not make things we can see with telescopes directly - it is "dark". We can see the effects it makes with gravity, such as the rotation curves of galaxies, and gravitational lensing. So we know something is there, just not what it is made of. Dark Energy was invented to solve a couple of mysteries. One is the geometrical "flatness" of the Universe, and the other is the apparent acceleration of the Universe's expansion. Like Dark Matter, we don't yet know what it is. But something is causing the flatness and acceleration, so we gave it a name as a place-holder for theories. > A similar situation happened a century ago, with the precession (shift) of Mercury's orbit with time. We thought it was caused by a planet inside of Mercury's orbit that we hadn't found yet. It was named Vulcan, after the Roman god of fire (not Spock's home planet). It turns out relativity was the right answer - the Suns gravity bends space near it, and causes the orbit to shift. Vulcan was just "a name we gave to whatever causes the observed effect". > Dark Matter and Dark Energy could turn out to be something entirely different than types of matter and energy, but in the mean time it gives them names we can attach theories about them to.
- ithilglin909 9y ago
  "...it gives them names we can attach theories about them to." Sometimes I think this gets lost in conversations about scientific topics. It's easy to be flippant about what we know in relation to scientists of the past, and miss out on an appropriate sense of awe about how much in the universe there is to discover.
- everdev 9y ago
  Thank you! 2.5% of the universe's missing matter has been found.
  - phinnaeus 9y ago
    Not 2.5% of the missing matter. 2.5% of the matter.
    - astrobe_ 9y ago
      I have a real trouble figuring out how they could say 2.5% was missing when 95% of all things in the universe is just a theory, according to those figures.
kpil 9y ago
Stacking a hundred thousand scans in order to find something made me think of the dead salmon study that won the igNobel prize.
vorg 9y ago
> Half the universe’s missing matter has just been finally found The first paragraph clarifies that this headline means "The missing (regular) matter comprising half the (regular matter in the) Universe has been finally found" rather than "Half of the missing (regular) matter in the Universe has just been found (and where could the other half be?)".
nur0n 9y ago
The best visualization I could find is on pg 14 of the pdf on this page: https://arxiv.org/abs/1709.10378v1 https://arxiv.org/abs/1709.10378v1
deleted 9y ago
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lifeisstillgood 9y ago
Can I just check - my understanding is that we can only see 5% of the expected mass in the universe - so we have just found another 5%? meaning dark matter needs to account for 90%? plus, how awesomely beautiful is the idea of tendrils of has connecting the galaxies through space.
- Meegul 9y ago
  Like many of us, I'm no astrophysicist, but one of the linked papers [1] references that we've thus far been able to locate 10% of baryon content, with this discovery bringing this number up to 30%. Assuming I'm interpreting this correctly, this means that there's still around 70% of expected baryonic matter unaccounted for. 1: https://arxiv.org/abs/1709.10378v1 https://arxiv.org/abs/1709.10378v1
- mrpopo 9y ago
  > You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far. My understanding is that, up until now, we could only observe half of the 5% expected mass, e.g. 2.5%, and we can now see the rest of it. The rest of the universe is still made up of 25% dark matter and 70% dark energy.
- subroutine 9y ago
  I too love the idea of there being filaments of matter connecting distant galaxies. I can only imagine the artistic renderings will make the universe look like a neural network. Can anyone clarify how these filaments remain “hot”?
  - posterboy 9y ago
    >things in motion tend to stay in motion comes to mind
    - subroutine 9y ago
nielsbot 9y ago
I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?
- brianyu8 9y ago
  I was also confused about this. However the article states that half of the normal matter (not dark matter) thought to exist has been detected. Basically we just found the missing normal matter and have not yet found dark matter.
- mcbutterbunz 9y ago
  No, this is just the half of the 5% of regular matter that was "missing".
- warent 9y ago
  I think it's actually saying that we discovered missing matter that isn't dark matter. So now all that's remaining unaccounted-for is dark matter (and dark energy) Disclaimer: also not an astrophysicist
- JohnBooty 9y ago
  EDIT: My understanding is incorrect. See the replies to the post for a correction. No. They're saying that 50% of the "dark matter" isn't dark, it's just regular matter that we weren't able to see. The density of this stuff (filaments of gas stretching between galaxies) is so low that it is really, really, really hard to detect. "Dark matter" theories posit that the missing matter isn't just regular matter that's hard to see; they posit that this dark matter is a fundamentally different... something. I don't believe this announcement addresses some of the other oddities (possibly) explained by dark matter, such as the rotation of galaxies: https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve
  - timthorn 9y ago
    > They're saying that 50% of the "dark matter" isn't dark, it's just regular matter that we weren't able to see. No, the dark matter proportion hasn't changed. There was missing "regular" matter that has now been accounted for.
mirimir 9y ago
> At the largest size, Google image search tells me that it looks exactly like foam rubber. Foam rubber is created by combining a chemical agent that glomps together through the wonder of polymerization with another chemical agent that delivers lots of gas bubbles to make space between the polymers. Universes are created by rapidly expanding a superdense plasma that glomps together through the wonders of gravity, while lots of expanding vacuum makes space between the galaxy clusters. https://palmstroem.blogspot.de/2016/01/no-universe-is-not-brain.html https://palmstroem.blogspot.de/2016/01/no-universe-is-not-br... Edit: This explains, in a light-hearted way, why there are filaments between galaxies and galaxy clusters.
- dotancohen 9y ago
  Why should vacuum expand? Is it due to gravity of the filament molecules pulling those molecules together into larger 'strings' or 'planes' which leave 'holes'? Or some other mechanism?
  - kijin 9y ago
    The universe expands. Things bound by gravity tend not to expand that much. As a result, most of the space that expands is vacuum.
    - dotancohen 9y ago
      Makes sense now, thank you!
    - divs1210 9y ago
      'The universe expands' in what? I thought everything was the universe, as meant by the term 'universal'.
      - logfromblammo 9y ago
        Imagine you have a meter-stick. It has uniform graduation markings to show you centimeters and millimeters. Now imagine that it is getting longer. No matter how hard you look at it, the stick is still one meter long. That's what the markings on it say, anyway. It's actually getting longer at the same rate as all the other meter-sticks. That's the expansion of the universe. Now imagine you balanced two marbles on the stick. They bow the stick ever so slightly, and roll together at the 50 cm mark. They are not expanding--or at least not expanding like the meter-stick expands. But they will continue to roll together. They are detectable masses acting under the effect of gravity. If you look closely, they appear to be shrinking. But it's actually the meter-stick expanding. When you expand this out to galaxy scale, two galaxies that are not moving with respect to each other are getting further apart. The mass in the galaxies have enough intra-galactic gravitational attraction to keep themselves from flying apart along with the vacuum, but not enough the keep their neighbor galaxies close. The inter-galactic gravitation doesn't pull hard enough to overcome the expansion. So they surf away from each other, becoming further apart. At least, that's how I understand it. I could be wrong.
wheresmyusern 9y ago
im confused about baryons. they say that it is a particle (presumably like an electron or photon or other particle) but then they go on to say that its a gas, not a particle. very confusing.
- nitrogen 9y ago
  Isn't a gas just a swarm of particles?
  - brianpan 9y ago
    We like to say flock of particles. Source: I am a smientist.
- Meegul 9y ago
  A baryon is a subatomic particle that is composed of three quarks, such as a proton or a neutron. An electron would be categorized as a lepton, rather than a baryon as it is not made of multiple quarks and is rather an elementary particle, for reference. Here's a good reference for subatomic elementary particles, where you can see some familiar names like electron and photon: https://en.wikipedia.org/wiki/Baryon#/media/File:Standard_Model_of_Elementary_Particles.svg https://en.wikipedia.org/wiki/Baryon#/media/File:Standard_Mo...
  - deleted 9y ago
    [deleted]
- colechristensen 9y ago
  gasses are made of particles neutrons and protons are baryons (each made of 3 quarks) electrons are leptons photons are bosons There are more things in those categories that are much less a part of the human experience.
- nikdaheratik 9y ago
  Baryons are types of subatomic particles. They include protons and neutrons as well as other kinds that only exist briefly in an atom smasher. In this case, they are using a generic term because they have no way of knowing whether it's primarily protons/neutrons or what else it could be made of. A gas in this sense is really a very loose collection of light particles, mainly hydrogen/helium or just empty separate protons and neutrons. As opposed to heavier atoms that are the product of stellar fusion and form more solid matter. If you think about this in terms of cosmology, the universe was originally a solid uniform blob of high energy particles. As it cooled, some of those particles grouped together to form stars and galaxies. However, there are parts in between galaxies that clumped together a bit but didn't really have enough mass to form anything. So it's really just made of tendrils of basic atomic building blocks.
iheartmemcache 9y ago
Dang I read the first paragraph of the article and immediately went searching for the real papers since I didn't expect any media outlet to include them at the bottom, but here they are for anyone who made the same mistake I did! https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.10378 https://arxiv.org/abs/1709.10378 Not a cosmologist but here's my go at the de Graff paper. (Let's get this out of the way, the title is click-bait and the paper/researchers makes no such claims as to anything near 50%. New Scientist is trolling for hits with the word "half" or the journalist is fundamentally misunderstanding the work.) In de Graff, et al, they claim 30% of "90% of the missing baryonic matter [that composes the ~25% of our total universe observable from within our light cone]" has been found in the CMB structured as filaments between galaxies. They claim there's effectively a planar network layered on top of Minkowski space composed this baryonic matter. The temperature was at this "Goldilocks" midrange no one had previously analyzed (ranging from 10^5-10^7K). This wasn't previously found because people were searching "only the lower and higher temperature end of the warm-hot baryons, leaving the majority of the baryons still unobserved(9)". [See "Warm-hot baryons comprise 5-10 percent of filaments in the cosmic web.", Nature, Eckert et al for more about baryons of this composition.] Additionally, these baryons have 10x the density of what we observe (so this could potentially be evidence for the first stable baryonic matter composed of second generation quarks, or more likely the binding energies are different from our standard uud/udd nucleon quarks) permeating the universe, and where the roads in the network meet ("dark matter haloes"), you have embedded galaxies and galaxy clusters. They continue with their analytic methods of the CMASS data, and claim within the framework 30% of the total baryonic content (which, again, all analytical methods put this into no more than ~25%) is composed of this form of this matter. I skimmed their methods and it seemed to at least logically hold -- they are using the appropriate data (SDSS 12) and didn't cherry-pick their galaxy pairs (so, no p-hacking here!).
- DiabloD3 9y ago
  From what I can tell, this basically also proves that large scale plasma exists between all bodies at any scale (planetary to systems to galaxies to clusters), and universe sized Birkeland currents exist; which is something cosmologists have been trying to prove/disprove for awhile. So, not only did they find some of the missing matter, they found some of the missing energy, too. This does, however, screw some of the more classical cosmologists.
epigramx 9y ago
The title is effectively click-bait because of: https://www.reddit.com/r/space/comments/75944s/half_the_universes_missing_matter_has_just_been/do4mfjx/ https://www.reddit.com/r/space/comments/75944s/half_the_univ...
- jl6 9y ago
  Also the lesser clickbait offense of using the word “just”.
- kwelstr 9y ago
  We should assume by default that every headline is clickbait now, unfortunately this is the business model of the internet. It's not good for accuracy and most articles are just a headline and some inane filler up words. I hope we'll smart up and find a better model for news soon. :/
  - 24gttghh 9y ago
    We could pay for it like we did for the hundreds of years prior to the internet, but they'll still make-up eye-grabbing headlines.
    - xenophonf 9y ago
      We're still paying for it. It's just that the currency's changed.
- virgil_disgr4ce 9y ago
  This is an excellent description of the situation--one that I thought was more common knowledge than it appears to be. :/
- dang 9y ago
  Ok, we've debaited it.
dushyantk 9y ago
Duped by https://news.ycombinator.com/item?id=15439321 https://news.ycombinator.com/item?id=15439321
yCloser 9y ago
finally, dark matter has been a really embarassing theory, I'm so happy they proved it wrong
- jug 9y ago
  First, this has nothing to do with dark matter. * 5% "ordinary", baryonic matter <-- all now accounted for * 27% dark matter * 68% dark energy Second, I don't think it's embarassing. I think the other explanations if it does _not_ exist are even more convoluted. At least the dark matter idea is only saying there is stuff that interacts poorly with other matter. That doesn't sound all too crazy as explanations like "despite all extremely precise evidence, theory of gravity must still be somehow wrong on larger scales!!" to me (math is not exactly known for sudden special cases), or having to create all new specific theories on why something else must be at play on a cosmic scale than simply (yes, simply) a dumb weakly interacting particle.
hoodoof 9y ago
They probably looked under the cushions on the couch. Anything you lose is always there.
andrewaylett 9y ago
"made of particles called baryons rather than dark matter" That's clumsily worded, as it makes it sound like it's still something exotic. _We're_ made of baryons: this is just normal matter.
- vanderZwan 9y ago
  As a former physics student, I see your point but disagree. Apologies for the wall of text about just this one choice of wording, but discussing why science communication is a very difficult trade-off takes a bit of space. One reason to stick to "baryons" is that it is the term used by the researchers in their papers. So it is more true to the research that is being summarised. The start of the article (unlike its title...) mentions that this research is about normal matter quite clearly, so this should give enough context to avoid confusion: > 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. You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far. Baryons are subatomic particles[0][1], not atoms, which is what most people think of when discussing "matter". If we say "normal matter", some people will think we're talking about chunks of dirt floating between galaxies. I'm not joking, have you ever been to a public physics lecture? And mistakes like this are not the audience's fault - it's the expert's fault for assuming non-experts know what they know. For people with the right background (chemists, physicists, astronomers, etc) it is clear this is "just normal matter". For everyone else - so most people - "normal matter" means matter in earth-typical circumstances of pressure and temperature, in a solid/liquid/vapour phase. The papers describe intergalactic plasma filaments with a temperature between 10⁴ to 10⁵ K. That is pretty exotic by normal-people standards. And yes, fire is a plasma, but for most people fire is just very hot gas, and the article even builds on that: > Because the gas is so tenuous and not quite hot enough for X-ray telescopes to pick up, nobody had been able to see it before. So the other reason reason to stick to "baryons" is that this is exotic matter from the point of view of non-experts. When describing research you have to start from their model of the physical world, and build your way back to the research. I think the choice in wording appropriate here. The other paragraphs make it clear this is about normal matter, while this sentence makes it clear it's not normal matter in Earth-circumstances, which is how the average human thinks about it if not corrected. [0] https://en.wikipedia.org/wiki/Baryon https://en.wikipedia.org/wiki/Baryon [1] https://simple.wikipedia.org/wiki/Baryon https://simple.wikipedia.org/wiki/Baryon (the Simple English wiki is probably more useful to us non-cosmologists here)
pokemongoaway 9y ago
Oh where would we be without these geniuses!?
- dang 9y ago
  Would you please not post unsubstantive comments like this? https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newswelcome.html https://news.ycombinator.com/newswelcome.html
macca321 9y ago
Does this mean the universe is more weird or less weird than we thought?
- ecshafer 9y ago
  Less weird. A large amount of the missing matter, but not all lot it, has been observed where it was theorized. The issue was we've not had reliable ways to measure that specific matter in the area it is
Robotbeat 9y ago
Missing /regular/ matter. Doesn't count dark matter. Shame on New Scientist for incorrect headline.
skj 9y ago
"Both teams took advantage of a phenomenon called the Sunyaev-Zel’dovich effect that occurs when light left over from the big bang passes through hot gas." That just seems unreal to me. Edit: To clarify, I'm not accusing it of being made up. I just think it's amazing.
- icegreentea2 9y ago
  Just as a heads up, if you ever read stuff about the 'Cosmic Microwave Background' or 'Cosmic Background Radiation', that's the 'light left over from the big bang' bit.
- vanderZwan 9y ago
  They can tell that the big bang is the light source because of Hubble's Law[0]. In short, the universe itself (so space itself) expands[1], and it does so fast enough to create a Doppler effect in light, causing redshift[2]. When we look further out into space, we effectively look "back" into time because of the limit of the speed of light. The older the light, the more it has redshifted because the more space has expanded while it was travelling. So this redshift increases very predictably the further we look out into space and back into time. As a result, when observing space we can say when light is left-over from the big bang, because we can tell the age of the light by how much its spectral lines have redshifted. [0] https://en.wikipedia.org/wiki/Hubble%27s_law https://en.wikipedia.org/wiki/Hubble%27s_law [1] https://www.youtube.com/watch?v=_llA2q1rlSg https://www.youtube.com/watch?v=_llA2q1rlSg [2] https://en.wikipedia.org/wiki/Redshift https://en.wikipedia.org/wiki/Redshift
- terryf 9y ago
  Yeah, totally. The other mindblowing thing is that since photons are moving at the speed of light, thus time for them pretty much stands still. Thus, if a photon was created at the moment of the big bang and happens to "bump" into something else today then from the standpoint of the photon, it only "lived" for an instant. (based on my level of physics understanding, so please do correct me if I'm wrong, thanks)
numbsafari 9y ago
So on the eve of the seventh day, god swept half the matter under a rug and then went out to play. I guess we really are created in his image...
chewbacha 9y ago
Ok, it seems like a lot of people here think dark matter is a “thing” but it’s not. Dark matter is simply unaccounted for mass in the universe. When we discover mass that we didn’t know about before, the amount of “dark” matter decreases. The word “dark” here merely means “known unknown” because we observe the effect but not the cause. This discovery has unveiled some of the dark matter as baryon particles in a plasma. So some of that dark matter is now known.
- mikebridgman 9y ago
  If you read vanderZwan's analysis in another comment thread, it seems this discovery did not involve dark matter. It was well below 50%, and the baryon particles were always predicted to be there, they were just finally observed directly.
- BeetleB 9y ago
  >This discovery has unveiled some of the dark matter as baryon particles in a plasma. So some of that dark matter is now known. The article clearly points out that this is not the case. The amount of dark matter is still the same. >Dark matter is simply unaccounted for mass in the universe. The article clearly points out that this is not the case.
  - chewbacha 9y ago
    You are correct, i misread one of the first paragraphs.
squozzer 9y ago
It was all misrouted luggage at the world's airports.
- dang 9y ago
  Please don't do this here.
ZenoArrow 9y ago
Is it just me, or does anyone else get put off by hyperbolic scientific news coverage? Even if the result is interesting, the framing of one result as representative of all unknown normal matter makes me not want to bother reading the article, it's hard enough splitting out facts from bullshit when you have a decent grounding in a subject, it's even harder when your knowledge is almost nonexistent.
greggarious 9y ago
Well, I wouldn't exactly say I've been missing it OP.

https://www.reddit.com/r/space/comments/75944s/half_the_universes_missing_matter_has_just_been/do4mfjx/ https://www.reddit.com/r/space/comments/75944s/half_the_univ... > The approximate distribution in the Universe is 5% regular matter, 25% Dark Matter, and 70% Dark Energy. Half of that 5% was missing, and now found. > Regular matter makes stars and visible galaxies, so it is "bright". Dark Matter is so named because it does not make things we can see with telescopes directly - it is "dark". We can see the effects it makes with gravity, such as the rotation curves of galaxies, and gravitational lensing. So we know something is there, just not what it is made of. Dark Energy was invented to solve a couple of mysteries. One is the geometrical "flatness" of the Universe, and the other is the apparent acceleration of the Universe's expansion. Like Dark Matter, we don't yet know what it is. But something is causing the flatness and acceleration, so we gave it a name as a place-holder for theories. > A similar situation happened a century ago, with the precession (shift) of Mercury's orbit with time. We thought it was caused by a planet inside of Mercury's orbit that we hadn't found yet. It was named Vulcan, after the Roman god of fire (not Spock's home planet). It turns out relativity was the right answer - the Suns gravity bends space near it, and causes the orbit to shift. Vulcan was just "a name we gave to whatever causes the observed effect". > Dark Matter and Dark Energy could turn out to be something entirely different than types of matter and energy, but in the mean time it gives them names we can attach theories about them to.

ithilglin909 9y ago
"...it gives them names we can attach theories about them to." Sometimes I think this gets lost in conversations about scientific topics. It's easy to be flippant about what we know in relation to scientists of the past, and miss out on an appropriate sense of awe about how much in the universe there is to discover.
everdev 9y ago
Thank you! 2.5% of the universe's missing matter has been found.
- phinnaeus 9y ago
  Not 2.5% of the missing matter. 2.5% of the matter.
  - astrobe_ 9y ago
    I have a real trouble figuring out how they could say 2.5% was missing when 95% of all things in the universe is just a theory, according to those figures.

kpil 9y ago

Stacking a hundred thousand scans in order to find something made me think of the dead salmon study that won the igNobel prize.

vorg 9y ago

> Half the universe’s missing matter has just been finally found The first paragraph clarifies that this headline means "The missing (regular) matter comprising half the (regular matter in the) Universe has been finally found" rather than "Half of the missing (regular) matter in the Universe has just been found (and where could the other half be?)".

nur0n 9y ago

The best visualization I could find is on pg 14 of the pdf on this page: https://arxiv.org/abs/1709.10378v1 https://arxiv.org/abs/1709.10378v1

deleted 9y ago

[deleted]

lifeisstillgood 9y ago

Can I just check - my understanding is that we can only see 5% of the expected mass in the universe - so we have just found another 5%? meaning dark matter needs to account for 90%? plus, how awesomely beautiful is the idea of tendrils of has connecting the galaxies through space.

Meegul 9y ago
Like many of us, I'm no astrophysicist, but one of the linked papers [1] references that we've thus far been able to locate 10% of baryon content, with this discovery bringing this number up to 30%. Assuming I'm interpreting this correctly, this means that there's still around 70% of expected baryonic matter unaccounted for. 1: https://arxiv.org/abs/1709.10378v1 https://arxiv.org/abs/1709.10378v1
mrpopo 9y ago
> You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far. My understanding is that, up until now, we could only observe half of the 5% expected mass, e.g. 2.5%, and we can now see the rest of it. The rest of the universe is still made up of 25% dark matter and 70% dark energy.
subroutine 9y ago
I too love the idea of there being filaments of matter connecting distant galaxies. I can only imagine the artistic renderings will make the universe look like a neural network. Can anyone clarify how these filaments remain “hot”?
- posterboy 9y ago
  >things in motion tend to stay in motion comes to mind
  - subroutine 9y ago

nielsbot 9y ago

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

brianyu8 9y ago
I was also confused about this. However the article states that half of the normal matter (not dark matter) thought to exist has been detected. Basically we just found the missing normal matter and have not yet found dark matter.
mcbutterbunz 9y ago
No, this is just the half of the 5% of regular matter that was "missing".
warent 9y ago
I think it's actually saying that we discovered missing matter that isn't dark matter. So now all that's remaining unaccounted-for is dark matter (and dark energy) Disclaimer: also not an astrophysicist
JohnBooty 9y ago
EDIT: My understanding is incorrect. See the replies to the post for a correction. No. They're saying that 50% of the "dark matter" isn't dark, it's just regular matter that we weren't able to see. The density of this stuff (filaments of gas stretching between galaxies) is so low that it is really, really, really hard to detect. "Dark matter" theories posit that the missing matter isn't just regular matter that's hard to see; they posit that this dark matter is a fundamentally different... something. I don't believe this announcement addresses some of the other oddities (possibly) explained by dark matter, such as the rotation of galaxies: https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve
- timthorn 9y ago
  > They're saying that 50% of the "dark matter" isn't dark, it's just regular matter that we weren't able to see. No, the dark matter proportion hasn't changed. There was missing "regular" matter that has now been accounted for.

mirimir 9y ago

> At the largest size, Google image search tells me that it looks exactly like foam rubber. Foam rubber is created by combining a chemical agent that glomps together through the wonder of polymerization with another chemical agent that delivers lots of gas bubbles to make space between the polymers. Universes are created by rapidly expanding a superdense plasma that glomps together through the wonders of gravity, while lots of expanding vacuum makes space between the galaxy clusters. https://palmstroem.blogspot.de/2016/01/no-universe-is-not-brain.html https://palmstroem.blogspot.de/2016/01/no-universe-is-not-br... Edit: This explains, in a light-hearted way, why there are filaments between galaxies and galaxy clusters.

dotancohen 9y ago
Why should vacuum expand? Is it due to gravity of the filament molecules pulling those molecules together into larger 'strings' or 'planes' which leave 'holes'? Or some other mechanism?
- kijin 9y ago
  The universe expands. Things bound by gravity tend not to expand that much. As a result, most of the space that expands is vacuum.
  - dotancohen 9y ago
    Makes sense now, thank you!
  - divs1210 9y ago
    'The universe expands' in what? I thought everything was the universe, as meant by the term 'universal'.
    - logfromblammo 9y ago
      Imagine you have a meter-stick. It has uniform graduation markings to show you centimeters and millimeters. Now imagine that it is getting longer. No matter how hard you look at it, the stick is still one meter long. That's what the markings on it say, anyway. It's actually getting longer at the same rate as all the other meter-sticks. That's the expansion of the universe. Now imagine you balanced two marbles on the stick. They bow the stick ever so slightly, and roll together at the 50 cm mark. They are not expanding--or at least not expanding like the meter-stick expands. But they will continue to roll together. They are detectable masses acting under the effect of gravity. If you look closely, they appear to be shrinking. But it's actually the meter-stick expanding. When you expand this out to galaxy scale, two galaxies that are not moving with respect to each other are getting further apart. The mass in the galaxies have enough intra-galactic gravitational attraction to keep themselves from flying apart along with the vacuum, but not enough the keep their neighbor galaxies close. The inter-galactic gravitation doesn't pull hard enough to overcome the expansion. So they surf away from each other, becoming further apart. At least, that's how I understand it. I could be wrong.

wheresmyusern 9y ago

im confused about baryons. they say that it is a particle (presumably like an electron or photon or other particle) but then they go on to say that its a gas, not a particle. very confusing.

nitrogen 9y ago
Isn't a gas just a swarm of particles?
- brianpan 9y ago
  We like to say flock of particles. Source: I am a smientist.
Meegul 9y ago
A baryon is a subatomic particle that is composed of three quarks, such as a proton or a neutron. An electron would be categorized as a lepton, rather than a baryon as it is not made of multiple quarks and is rather an elementary particle, for reference. Here's a good reference for subatomic elementary particles, where you can see some familiar names like electron and photon: https://en.wikipedia.org/wiki/Baryon#/media/File:Standard_Model_of_Elementary_Particles.svg https://en.wikipedia.org/wiki/Baryon#/media/File:Standard_Mo...
- deleted 9y ago
  [deleted]
colechristensen 9y ago
gasses are made of particles neutrons and protons are baryons (each made of 3 quarks) electrons are leptons photons are bosons There are more things in those categories that are much less a part of the human experience.
nikdaheratik 9y ago
Baryons are types of subatomic particles. They include protons and neutrons as well as other kinds that only exist briefly in an atom smasher. In this case, they are using a generic term because they have no way of knowing whether it's primarily protons/neutrons or what else it could be made of. A gas in this sense is really a very loose collection of light particles, mainly hydrogen/helium or just empty separate protons and neutrons. As opposed to heavier atoms that are the product of stellar fusion and form more solid matter. If you think about this in terms of cosmology, the universe was originally a solid uniform blob of high energy particles. As it cooled, some of those particles grouped together to form stars and galaxies. However, there are parts in between galaxies that clumped together a bit but didn't really have enough mass to form anything. So it's really just made of tendrils of basic atomic building blocks.

iheartmemcache 9y ago

Dang I read the first paragraph of the article and immediately went searching for the real papers since I didn't expect any media outlet to include them at the bottom, but here they are for anyone who made the same mistake I did! https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.10378 https://arxiv.org/abs/1709.10378 Not a cosmologist but here's my go at the de Graff paper. (Let's get this out of the way, the title is click-bait and the paper/researchers makes no such claims as to anything near 50%. New Scientist is trolling for hits with the word "half" or the journalist is fundamentally misunderstanding the work.) In de Graff, et al, they claim 30% of "90% of the missing baryonic matter [that composes the ~25% of our total universe observable from within our light cone]" has been found in the CMB structured as filaments between galaxies. They claim there's effectively a planar network layered on top of Minkowski space composed this baryonic matter. The temperature was at this "Goldilocks" midrange no one had previously analyzed (ranging from 10^5-10^7K). This wasn't previously found because people were searching "only the lower and higher temperature end of the warm-hot baryons, leaving the majority of the baryons still unobserved(9)". [See "Warm-hot baryons comprise 5-10 percent of filaments in the cosmic web.", Nature, Eckert et al for more about baryons of this composition.] Additionally, these baryons have 10x the density of what we observe (so this could potentially be evidence for the first stable baryonic matter composed of second generation quarks, or more likely the binding energies are different from our standard uud/udd nucleon quarks) permeating the universe, and where the roads in the network meet ("dark matter haloes"), you have embedded galaxies and galaxy clusters. They continue with their analytic methods of the CMASS data, and claim within the framework 30% of the total baryonic content (which, again, all analytical methods put this into no more than ~25%) is composed of this form of this matter. I skimmed their methods and it seemed to at least logically hold -- they are using the appropriate data (SDSS 12) and didn't cherry-pick their galaxy pairs (so, no p-hacking here!).

DiabloD3 9y ago
From what I can tell, this basically also proves that large scale plasma exists between all bodies at any scale (planetary to systems to galaxies to clusters), and universe sized Birkeland currents exist; which is something cosmologists have been trying to prove/disprove for awhile. So, not only did they find some of the missing matter, they found some of the missing energy, too. This does, however, screw some of the more classical cosmologists.

epigramx 9y ago

The title is effectively click-bait because of: https://www.reddit.com/r/space/comments/75944s/half_the_universes_missing_matter_has_just_been/do4mfjx/ https://www.reddit.com/r/space/comments/75944s/half_the_univ...

jl6 9y ago
Also the lesser clickbait offense of using the word “just”.
kwelstr 9y ago
We should assume by default that every headline is clickbait now, unfortunately this is the business model of the internet. It's not good for accuracy and most articles are just a headline and some inane filler up words. I hope we'll smart up and find a better model for news soon. :/
- 24gttghh 9y ago
  We could pay for it like we did for the hundreds of years prior to the internet, but they'll still make-up eye-grabbing headlines.
  - xenophonf 9y ago
    We're still paying for it. It's just that the currency's changed.
virgil_disgr4ce 9y ago
This is an excellent description of the situation--one that I thought was more common knowledge than it appears to be. :/
dang 9y ago
Ok, we've debaited it.

dushyantk 9y ago

Duped by https://news.ycombinator.com/item?id=15439321 https://news.ycombinator.com/item?id=15439321

yCloser 9y ago

finally, dark matter has been a really embarassing theory, I'm so happy they proved it wrong

jug 9y ago
First, this has nothing to do with dark matter. * 5% "ordinary", baryonic matter <-- all now accounted for * 27% dark matter * 68% dark energy Second, I don't think it's embarassing. I think the other explanations if it does _not_ exist are even more convoluted. At least the dark matter idea is only saying there is stuff that interacts poorly with other matter. That doesn't sound all too crazy as explanations like "despite all extremely precise evidence, theory of gravity must still be somehow wrong on larger scales!!" to me (math is not exactly known for sudden special cases), or having to create all new specific theories on why something else must be at play on a cosmic scale than simply (yes, simply) a dumb weakly interacting particle.

hoodoof 9y ago

They probably looked under the cushions on the couch. Anything you lose is always there.

andrewaylett 9y ago

"made of particles called baryons rather than dark matter" That's clumsily worded, as it makes it sound like it's still something exotic. _We're_ made of baryons: this is just normal matter.

vanderZwan 9y ago
As a former physics student, I see your point but disagree. Apologies for the wall of text about just this one choice of wording, but discussing why science communication is a very difficult trade-off takes a bit of space. One reason to stick to "baryons" is that it is the term used by the researchers in their papers. So it is more true to the research that is being summarised. The start of the article (unlike its title...) mentions that this research is about normal matter quite clearly, so this should give enough context to avoid confusion: > 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. You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far. Baryons are subatomic particles[0][1], not atoms, which is what most people think of when discussing "matter". If we say "normal matter", some people will think we're talking about chunks of dirt floating between galaxies. I'm not joking, have you ever been to a public physics lecture? And mistakes like this are not the audience's fault - it's the expert's fault for assuming non-experts know what they know. For people with the right background (chemists, physicists, astronomers, etc) it is clear this is "just normal matter". For everyone else - so most people - "normal matter" means matter in earth-typical circumstances of pressure and temperature, in a solid/liquid/vapour phase. The papers describe intergalactic plasma filaments with a temperature between 10⁴ to 10⁵ K. That is pretty exotic by normal-people standards. And yes, fire is a plasma, but for most people fire is just very hot gas, and the article even builds on that: > Because the gas is so tenuous and not quite hot enough for X-ray telescopes to pick up, nobody had been able to see it before. So the other reason reason to stick to "baryons" is that this is exotic matter from the point of view of non-experts. When describing research you have to start from their model of the physical world, and build your way back to the research. I think the choice in wording appropriate here. The other paragraphs make it clear this is about normal matter, while this sentence makes it clear it's not normal matter in Earth-circumstances, which is how the average human thinks about it if not corrected. [0] https://en.wikipedia.org/wiki/Baryon https://en.wikipedia.org/wiki/Baryon [1] https://simple.wikipedia.org/wiki/Baryon https://simple.wikipedia.org/wiki/Baryon (the Simple English wiki is probably more useful to us non-cosmologists here)

pokemongoaway 9y ago

Oh where would we be without these geniuses!?

dang 9y ago
Would you please not post unsubstantive comments like this? https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newswelcome.html https://news.ycombinator.com/newswelcome.html

macca321 9y ago

Does this mean the universe is more weird or less weird than we thought?

ecshafer 9y ago
Less weird. A large amount of the missing matter, but not all lot it, has been observed where it was theorized. The issue was we've not had reliable ways to measure that specific matter in the area it is

Robotbeat 9y ago

Missing /regular/ matter. Doesn't count dark matter. Shame on New Scientist for incorrect headline.

skj 9y ago

"Both teams took advantage of a phenomenon called the Sunyaev-Zel’dovich effect that occurs when light left over from the big bang passes through hot gas." That just seems unreal to me. Edit: To clarify, I'm not accusing it of being made up. I just think it's amazing.

icegreentea2 9y ago
Just as a heads up, if you ever read stuff about the 'Cosmic Microwave Background' or 'Cosmic Background Radiation', that's the 'light left over from the big bang' bit.
vanderZwan 9y ago
They can tell that the big bang is the light source because of Hubble's Law[0]. In short, the universe itself (so space itself) expands[1], and it does so fast enough to create a Doppler effect in light, causing redshift[2]. When we look further out into space, we effectively look "back" into time because of the limit of the speed of light. The older the light, the more it has redshifted because the more space has expanded while it was travelling. So this redshift increases very predictably the further we look out into space and back into time. As a result, when observing space we can say when light is left-over from the big bang, because we can tell the age of the light by how much its spectral lines have redshifted. [0] https://en.wikipedia.org/wiki/Hubble%27s_law https://en.wikipedia.org/wiki/Hubble%27s_law [1] https://www.youtube.com/watch?v=_llA2q1rlSg https://www.youtube.com/watch?v=_llA2q1rlSg [2] https://en.wikipedia.org/wiki/Redshift https://en.wikipedia.org/wiki/Redshift
terryf 9y ago
Yeah, totally. The other mindblowing thing is that since photons are moving at the speed of light, thus time for them pretty much stands still. Thus, if a photon was created at the moment of the big bang and happens to "bump" into something else today then from the standpoint of the photon, it only "lived" for an instant. (based on my level of physics understanding, so please do correct me if I'm wrong, thanks)

numbsafari 9y ago

So on the eve of the seventh day, god swept half the matter under a rug and then went out to play. I guess we really are created in his image...

chewbacha 9y ago

Ok, it seems like a lot of people here think dark matter is a “thing” but it’s not. Dark matter is simply unaccounted for mass in the universe. When we discover mass that we didn’t know about before, the amount of “dark” matter decreases. The word “dark” here merely means “known unknown” because we observe the effect but not the cause. This discovery has unveiled some of the dark matter as baryon particles in a plasma. So some of that dark matter is now known.

mikebridgman 9y ago
If you read vanderZwan's analysis in another comment thread, it seems this discovery did not involve dark matter. It was well below 50%, and the baryon particles were always predicted to be there, they were just finally observed directly.
BeetleB 9y ago
>This discovery has unveiled some of the dark matter as baryon particles in a plasma. So some of that dark matter is now known. The article clearly points out that this is not the case. The amount of dark matter is still the same. >Dark matter is simply unaccounted for mass in the universe. The article clearly points out that this is not the case.
- chewbacha 9y ago
  You are correct, i misread one of the first paragraphs.

squozzer 9y ago

It was all misrouted luggage at the world's airports.

dang 9y ago
Please don't do this here.

ZenoArrow 9y ago

Is it just me, or does anyone else get put off by hyperbolic scientific news coverage? Even if the result is interesting, the framing of one result as representative of all unknown normal matter makes me not want to bother reading the article, it's hard enough splitting out facts from bullshit when you have a decent grounding in a subject, it's even harder when your knowledge is almost nonexistent.

greggarious 9y ago

Well, I wouldn't exactly say I've been missing it OP.