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[时事新闻] 我在本站质疑多年暗物质,新闻说宇宙失踪质量的一半被找到

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发表于 2017-10-11 09:55:59 | 显示全部楼层 |阅读模式

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本帖最后由 yuxin 于 2017-10-13 13:26 编辑

bar-2.jpeg

我在本站质疑: http://www.cfluid.com/forum.php?mod=viewthread&tid=113131
我昨天微博说“...觉得暗物质暗能量不可思议,所以想着另一种解释”: http://weibo.com/2735814533/FpKn ... botime&type=comment
一个小时后新闻:
宇宙失踪质量的一半被找到:不是暗物质 http://tech.163.com/17/1010/19/D0DK39LD00097U81.html

宇宙失踪质量的一半被找到:不是暗物质
2017-10-10 19:11:26 来源: 网易科技报道

宇宙失踪质量的一半被找到:不是暗物质
网易科技讯10月10日消息,据《新科学家》杂志报道,科学家终于发现星系与星系之间起到连接作用的物质。这次发现意义重大,因为这是我们第一次发现了占宇宙中大约一半的正常物质,而之前对恒星、星系和太空中其他明亮物体的观测存在的疑虑得到了解释。
计算机模拟呈现出一大块“宇宙网”,从这张图中我们可以看到纠缠的丝状物将宇宙的星系连接在一起,而这种纠缠状物就是由重子组成的。
重子是由三夸克组成的亚原子粒子。在现代粒子物理学的标准模型理论中,重子这一名词是指由三个夸克(或者三个反夸克组成反重子)组成的复合粒子。在这理论中它是强子的一类。值得注意的是,因为重子属于复合粒子,所以不是基本粒子。最常见的重子有组成日常物质原子核的质子和中子,与反质子、反中子合称为核子。此前天文学家发现了许多缕高温、呈散射状的“气体”,正是这些“气体”将宇宙的星系连接在一起,但是他们并不知道这些“气体”中有什么物质,而现在的发现解决了天文学家的疑惑。
因为这些呈丝状的“气体”温度虽高还不够高,因此不会释放出太多的能量,所以用X射线望远镜很难观测到这些物质。但是研究人员通过一种被称为“运动学SZ(sunyaev-zel'dovich)效应”的现象证实了这些物质的存在,这种效应描述了从大爆炸中遗留下来的光穿过热气体时状态。
你或许听说过暗物质的搜寻,所谓暗物质,是一种被认为在宇宙中弥漫的神秘物质,而我们可以通过引力来间接观测到这种神秘物质产生的影响。做个形象的解释,比如说根据目前所观察到的,某处有1个单位的普通物质,但是我们这次计算机模拟的宇宙模型却观测到了2个单位的普通物质,因此这多出的一倍“消失的物质”就是研究发现的关键。
两个独立的研究小组发现的“消失的物质”——由称为重子的粒子构成的,并不是暗物质。连接星系的丝状物弥散气体就是由重子组成的。法国空间天体物理学研究所Hideki Tanimura的团队堆叠了260000个双星系数据,英国爱丁堡大学的Anna de Graaff的研究小组使用超过一百万双星系数据。两队发现了确凿的证据证明星系之间的气体细丝。Tanimura的团队发现气体细丝几乎是预测的正常宇宙物质的三倍密度,Graaff的团队发现是六倍正常宇宙物质密度——证实了这些区域的气体足够浓密形成细丝。
“显然我们两个团队的观测结果存在差异,这一点我们在观测前就预想到了,因为我们观测的距离不同,所以造成了结果上的不同,”Tanimura说。“如果克服这个因素,我们的观测结果会和另一小组非常一致。”
两个团队都从斯隆数字巡天项目选择了双星系进行研究,双星系被认为是由重子链连接。他们堆叠两星系区域之间的普朗克信号,使得微弱的重子链可探测到。
“每个人都知道它的存在,但现在,我们两个不同的团队明确的发现了这种物质,”马萨诸塞州哈佛史密森天体物理学中心的拉尔夫·克拉夫特说道,“重子的观测很好地证明了我们关于我们关于星系如何形成以及宇宙的历史等许多观点都是正确的。”
2015年,普朗克卫星在可观测宇宙微波辐射背景地图。因为星系之间气体如此弥散,他们造成的暗斑点太弱以至于在普朗克地图上不能直接看到。
以下为《新科学家》杂志原文:
Half the universe’s missing matter has just been finally found
Discoveries seem to back up many of our ideas about how the universe got its large-scale structure
Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University). Visualisation by Andrey Kravtsov
By Leah Crane
The missing links between galaxies have finally been 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.
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.
Two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas.
“The missing baryon problem is solved,” says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.
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.
“There’s no sweet spot – no sweet instrument that we’ve invented yet that can directly observe this gas,” says Richard Ellis at University College London. “It’s been purely speculation until now.”
So the two groups had to find another way to definitively show that these threads of gas are really there.
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. As the light travels, some of it scatters off the electrons in the gas, leaving a dim patch in the cosmic microwave background – our snapshot of the remnants from the birth of the cosmos.
Stack ‘em up
In 2015, the Planck satellite created a map of this effect throughout the observable universe. Because the tendrils of gas between galaxies are so diffuse, the dim blotches they cause are far too slight to be seen directly on Planck’s map.
Both teams selected pairs of galaxies from the Sloan Digital Sky Survey that were expected to be connected by a strand of baryons. They stacked the Planck signals for the areas between the galaxies, making the individually faint strands detectable en masse.
Tanimura’s team stacked data on 260,000 pairs of galaxies, and de Graaff’s group used over a million pairs. Both teams found definitive evidence of gas filaments between the galaxies. Tanimura’s group found they were almost three times denser than the mean for normal matter in the universe, and de Graaf’s group found they were six times denser – confirmation that the gas in these areas is dense enough to form filaments.
“We expect some differences because we are looking at filaments at different distances,” says Tanimura. “If this factor is included, our findings are very consistent with the other group.”
Finally finding the extra baryons that have been predicted by decades of simulations validates some of our assumptions about the universe.
“Everybody sort of knows that it has to be there, but this is the first time that somebody – two different groups, no less – has come up with a definitive detection,” says Ralph Kraft at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.
“This goes a long way toward showing that many of our ideas of how galaxies form and how structures form over the history of the universe are pretty much correct,” he says.
Journal references: arXiv, 1709.05024 and 1709.10378v1







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发表于 2017-10-11 15:27:10 | 显示全部楼层
暗能量也可能不存在,下面是去年10月我们发的一篇新闻,新的实验证据表明宇宙并没有处于加速膨胀状态,因此暗能量的假设随之崩塌:

http://www.cfluid.com/article-28089-1.html
 楼主| 发表于 2017-10-11 18:11:22 | 显示全部楼层
宇宙加速膨胀应该不会搞错吧

点评

新闻说是观测错误,最新数据表明宇宙并没有加速膨胀。谁知道呢?说不定过几天剧情还会翻转  详情 回复 发表于 2017-10-12 09:30
发表于 2017-10-12 09:30:24 | 显示全部楼层
yuxin 发表于 2017-10-11 18:11
宇宙加速膨胀应该不会搞错吧

新闻说是观测错误,最新数据表明宇宙并没有加速膨胀。谁知道呢?说不定过几天剧情还会翻转
 楼主| 发表于 2017-10-13 13:17:24 | 显示全部楼层
http://scienceblogs.com/startswi ... rk-matter-synopsis/

Missing Matter Found, But Doesn’t Dent Dark Matter (Synopsis)
Posted by Ethan on October 10, 2017
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A nearly uniform Universe, expanding over time and under the influence of gravity, will create a cosmic web of structure. The web contains both dark and normal matter. Image credit: Western Washington University.
A nearly uniform Universe, expanding over time and under the influence of gravity, will create a cosmic web of structure. The web contains both dark and normal matter. Image credit: Western Washington University.
“There are stars leaving the Milky Way, and immense gas clouds falling into it. There are turbulent plasmas writhing with X- and gamma-rays and mighty stellar explosions. There are, perhaps, places which are outside our universe. The universe is vast and awesome, and for the first time we are becoming a part of it.” -Carl Sagan

It’s no secret that if we look at the matter we see in the Universe, the story doesn’t add up. On all scales, from individual galaxies to pairs, groups and clusters of galaxies, all the way up to the large-scale structure of the Universe, the matter we see is insufficient to explain the structures we get. There has to be more matter, both normal (atom-based) matter and dark (non-interacting) matter, to make our theory and predictions match.

Image credit: Amanullah, et al., Ap. J. (2010).
Constraints on dark energy from three independent sources: supernovae, the CMB and BAO. Note that even without supernovae, we’d need dark energy, and that only 1/6th of the matter found can be normal matter; the rest must be dark matter. Image credit: Amanullah, et al., Ap. J. (2010).

In a wonderful new pair of papers, two independent teams have detected the warm-hot intergalactic medium along the large-scale structure filaments in the Universe. With six times the normal matter density, this accounts for a significant fraction of the missing normal matter in the Universe! It’s estimated that 50-90% of the baryons in the Universe are part of the WHIM, and this could be the first step towards detecting them. But it doesn’t touch or change the dark matter at all; we still need it and still don’t have it.


The warm-hot intergalactic medium (WHIM) has been seen before, but only along incredibly overdense regions, like the Sculptor wall, illustrated above. Image credit: Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang. Illustration: CXC/M. Weiss.

What’s the full story on the discovery of the missing matter? Find out over at Starts With A Bang on Forbes!

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Comments

#1
Frank

Omaha,NE
October 10, 2017
“Neutral atoms formed when the Universe was a mere 380,000 years old; after hundreds of millions of years, the hot, ultraviolet light from those early stars hits those intergalactic atoms. When it does, those photons get absorbed, kicking the electrons out of their atoms entirely, and creating an intergalactic plasma: the warm-hot intergalactic medium (WHIM).”

So the UV light from earliest stars keeping the intergalactic gas hot (and does it perfectly for all gas atoms somehow).

But how it is possible that UV light photons stayed same after billions of years of expansion of universe?

I have a really crazy idea on this WHIM which maybe a better explanation though:
What if WHIM is no ordinary gas?
What if WHIM is an effect similar to Hawking Radiation?

#2
Frank

Omaha,NE
October 10, 2017
What if spacetime is created by virtual particles as an emergent property?

What if Gravitational Fields are polarization of spacetime?
(Where positive curvature indicates probabilities of positive energy/mass virtual particles are higher in that region and negative curvature indicates probabilities of negative energy/mass virtual particles are higher in that region.)

#3
Frank

Omaha,NE
October 10, 2017
In case of WHIM, imagine Dark Matter particles increase probabilities of positive energy/mass virtual particles and we observe it as hot gas.

#4
Frank

Omaha,NE
October 10, 2017
Imagine any (+/-) unbalanced probabilities for virtual particles, on the path of light rays, act like different gas mediums that change the local refractive index, so the light rays bend.

#5
Frank

Omaha,NE
October 10, 2017
And in case of BHs, imagine probabilities of positive energy/mass virtual particles increase so much nearby, some of those particles turn real, that we could observe as Hawking Radiation.

#6
Patrice Ayme

October 10, 2017
missing mass problem for Dark Matter, or Dark Energy. I suggest both arise from a (Sub-)Quantum Effect, a prediction from a theory more general than Quantum Physics as we know it today. The basic idea is that there is something one should know as the “Quantum Interaction”, and it proceeds at a finite speed.

The “Quantum Interaction” would be the Entanglement speed and the Collapse speed. Over cosmological distances, it leaves remnants: Dark Matter. It also weakens gravitation over cosmic distances, accelerating the universe.

Some will scoff. However, basic ideas in physics can be simple.
https://patriceayme.wordpress.com/

#7
Frank

Omaha,NE
October 10, 2017
I just realized if my ideas about true nature of spacetime and gravitational fields (stated above) are correct then it would mean Casimir Force actually can be thought as creating artificial gravity, like in Star Trek for example. 🙂

#8
Michael Mooney

October 10, 2017
A generic comment on “what if” ‘science’:
What if pigs could fly? It would be one of infinitely “possible” “universes.’ (Excuse my excessive quotes. It’s all imaginary except that the Universe is “one verse.”)

Ducking pig shit or having a good umbrella would be ordinary reality in that “universe.”
But scientifically speaking…. just kidding.

#9
Frank

Omaha,NE
October 10, 2017
I am guessing if positive spacetime curvature slows down time then negative should speed it up. Then if Casimir Force is creating spacetime curvature, and since we can make it negative in the lab, then we can make time move faster, and it maybe measurable in the lab.

#10
Michael Mooney

October 10, 2017
“Missing Matter Found, But Doesn’t Dent Dark Matter”

Translation into scientific realism:
We found more normal matter but we still have no idea what else we can not yet detect which might generate gravitational force to explain our astronomical observations.

Might be that it’s normal (baryonic) matter that our excellent equipment is still not able to detect. (Instrumentalists would hate to admit that.)

#11
CFT

October 10, 2017
@michael Mooney #10,
I was thinking along similar lines. If the stats were off before, and every time they improve instrumentation they discover more things, (in the early 20th century they thought the size of the universe pretty much was our galaxy) what compels some to keep making definitive statements of certainty and creating models based on such very limited information? I’d think some would start saying, ‘save your breath until the fat lady sings.’ While I can understand people want to understand the proportional make up of the universe, I keep asking “how do you know how much of it you are looking at to base your proportions on?” Unless you know big something is, saying 50%, 20% etc, is meaningless. Until that is known, all guesses, and they are just guesses, should be tempered with prudence. I would suggest blatantly keeping all estimations always within only what has been measured, and be very clear about what that encompasses at the time the calculation is made. This would then start to provide a precise time lapse record of how much scientific estimations change with new data.

#12
Frank

Omaha,NE
October 10, 2017
I wonder if we could use sheets of Graphene like Casimir Plates and stack them as countless layers to create a multiplied Casimir Force generator. Then we could also add a strong electric and/or magnetic field to amplify that force.
Would a device like that could create human weight level strong artificial gravity field?

And of course “What if pigs could fly?”
Thanks for reminding us this big question MM.
I don’t think I know the right answer.
I think you always bring joy to this website and keep it alive.
I apologize if I ever hurt your feelings.
I always indicate when I am just kidding.

#13
CFT

October 10, 2017
@Frank #12,
Pretend you get what you want, I call this the god game. Give yourself whatever you want, but afterwards roll with the punches of consequences that follow. If you could produce a machine that generated gravity in a small localized area, what else do you think might happen?
.
If the gravity was generated at small location, everything would be drawn to this small location, not very suitable for walking around, unless your ship was built like an onion, layers within layers. If the field could somehow be put into the flooring, this would created a problem too, as unless the field was very small, people on the deck below would be pulled upwards into their ‘ceiling’. If you put the same effect on each deck, you would be pulled upwards and downwards at the same time….this doesn’t sound very practical for normal human movement either. Also, gravity has the effect of pulling something down towards the source, but would this not cause all kinds of stresses on your space ship structure as well? You might be much better off just using centrifugal force in large spinning sections, and magnet shoes in areas where that wasn’t practical, it might save an awful lot of engineering headaches.

#14
Frank

Omaha,NE
October 11, 2017
@CFT #13,
Imagine you made bricks of artificial gravity generators.
Imagine a spaceship (or spacestation) with a single floor of those bricks. Imagine the crew walks on top and bottom of that single floor (upside-down to each other). So you have a kind of symmetric (up-down) 2 floor internal spaceship design.

#15
Frank

Omaha,NE
October 11, 2017
Also what if those brick can also create artificial anti-gravity?
(Wikipedia says we can generate both attracting or repelling Casimir Force.)

If that is possible, imagine each floor of spaceship is 2 layer of bricks. Top layer generates gravity, bottom layer generates anti-gravity. People on top feels downward force of gravity but people on the lower floor does not feel upward force of gravity, because the anti-gravity layer (which they are closest) cancels out total gravity to zero for them.

#16
Frank

Omaha,NE
October 11, 2017
I wonder what would happen if we somehow created artificial gravity in front of a spaceship and artificial anti gravity in the back? Could that cause the spaceship to move forward faster and faster, like keep falling in a gravity well?

#17
CFT

October 11, 2017
@Frank #15,
Interesting concept, but I’m not sure you even can have something that is only gravitational on one side (I know of no examples in reality), that sounds more like electro magnetism than gravity.
.
At the risk of bursting your balloon, trying to make spaceships and stations like horizontal office buildings may just not be in the cards of possibility.

#18
Frank

Omaha,NE
October 11, 2017
If we can create artificial anti-gravity, I think it could be also useful as a shield in space, against space dust etc.

#19
Perry

October 11, 2017
There is evidence of the strongly interacting dark matter every time a double slit experiment is performed, as it is what waves.

#20
Sean T

October 11, 2017
Again, MM and CFT, you show your lack of understanding. The “missing matter” discussed in this post is normal matter. We know from real, actual observations of how things gravitate that we were not seeing all of the normal matter that exists. This WHIM is at least some of that missing normal matter.

We know also, again from real observations, that either one of two things must be true. Either there is matter out there that is not normal, baryonic matter, but rather must have certain properties and interactions — this is known as dark matter. The alternative is that our models of gravity are wrong, i.e. we need to come up with a modified version of the laws of gravity — this is known in the physics community as Modified Newtonian Dynamics, or MOND.

How do we determine which alternative is correct? Contrary to what you guys seem to think, it is NOT just assumed that our current theory of gravity is correct and that there must be dark matter. The various flavors of MOND have indeed been given careful consideration. In general, these were designed to account for galactic rotational anomalies, and it’s unsurprising that they do better than dark matter at explain galactic rotational speeds. However, these MOND models are atrocious at all other scales, whereas dark matter does very well at all other scales.

Does this mean that dark matter is right and MOND is wrong? Maybe, but not necessarily. If you still think MOND is the answer, then it’s incumbent on you to come up with a new version of MOND that accounts for observations on ALL scales better than dark matter can. If you (or anyone else) can do so, then MOND will supplant dark matter and we will reject the idea of dark matter. If not, then dark matter is the best idea currently available, and it is the model that most physicists will continue to investigate further.

#21
Perry

October 11, 2017
Dark matter fills ’empty’ space and is displaced by ordinary matter. What are mistaken for dark matter filaments is actually the state of displacement of the dark matter.

Galaxy clusters move through and displace the strongly interacting dark matter, analogous to a caravan of submarines moving through and displacing the water.

#22
Sinisa Lazarek

October 11, 2017
@ Frank re: cassimir effect vs gravity

Cassimir effect is not similar to gravity. There is no “attraction” between the plates. Instead (as understood) it is vacuum energy pushing the plates because the number of modes outside is greater then the number of modes between the plates. No matter how large of cassimir apparatus you build, it still doesn’t effect anything outside of plates themselves. Thus, bricks based on anything relating to cassimir effect would just contract themselves and nothing significant would happen.

For gravity. you need mass or energy. Super large amounts. In principle, if you could build a mega dynamo machine, that generates massive amounts of energy, that would cause it to bend spacetime and thus act as gravitational source to things nearby. Anti-gravity is a completely different beast, I don’t know how that would work… even in theory. A dark-energy powered machine maybe.

#23
Frank

Omaha,NE
October 11, 2017
What if Planck particle is the smallest and Dark Matter particle is the biggest size/energy particle of the Universe?

#24
Michael Mooney

October 11, 2017
More on Ethan’s “un-dented” dark matter, from Axil’s link on the “kill list” post.
From the New Scientist, Leah crane, Oct, ’17:
“Two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas.”

New Scientist, Sabine Hossenfelder and Naomi Lubic, ’15:
“Strangely familiar: Is dark matter normal stuff in disguise?…
***Dreaming up new particles to explain the universe’s missing mass has got us nowhere.*** Great clumps of quarks stuck together in weird ways could do the trick.” (My *** emphasis.)

#25
gahermit

October 11, 2017
@ cft #11 the same thought has occurred to me. i believe we are only seeing .000001% of the actual whole multi universe universe

#26
Michael Mooney

October 12, 2017
(Still here for now.)
@CFT #11:
” Unless you know (how) big something is, saying 50%, 20% etc, is meaningless.”
This point has always been obvious to me too. I wonder how such a simple, basic truth keeps eluding instrumentalist mathematicians like Ethan…. The pretense of knowing more than is known… and the math to “prove it.”

Same with the possibility of a perpetually oscillating, “bang/crunch” universe. If the time scale of such a two phase cycle is beyond our ability to measure, the cosmology is discarded. (Hey, it’s still expanding at an accelerating rate!… so that one is impossible, they say.)
 楼主| 发表于 2017-10-13 13:23:20 | 显示全部楼层
https://www.forbes.com/sites/sta ... atter/#3582ff3ffaf7

Missing Matter Found, But Doesn't Dent Dark Matter

Starts With A Bang
The Universe is out there, waiting for you to discover it  
Opinions expressed by Forbes Contributors are their own.
Ethan Siegel Ethan Siegel , Contributor
Western Washington University
A nearly uniform Universe, expanding over time and under the influence of gravity, will create a cosmic web of structure. The web contains both dark and normal matter.
Look out at the Universe as deeply as possible, and everywhere you look, there they are: stars and galaxies, beautiful, distant, and in all directions. All told, there are some two trillion galaxies in the observable Universe, each one with hundreds of billions of stars, on average. But if we take all that light, even knowing how stars work, it only explains a tiny fraction of the Universe's mass. Looking within the galaxies themselves for gas, dust, black holes, nebulae, and more, we still don't get close to enough mass to make up our Universe. A recent new set of studies have revealed new "missing matter" in between the galaxies for the first time, inching us closer. But even so, over 80% is completely unknown. Until we find dark matter, this mystery won't be solved.

NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)
The full UV-visible-IR composite of the XDF; the greatest image ever released of the distant Universe. Note that these spectacular images only showcase the emitted light from the normal matter that's formed stars, but that doesn't account for the overwhelming majority of matter.
We know how much total matter there has to be in the Universe. The expansion rate is dependent on what's present in the Universe, so measuring the Hubble flow of variable stars, galaxies, supernovae, etc., tells us how much matter, radiation, and other forms of energy need to be present. We can also measure the large-scale structure of the Universe, and from the clustering of galaxies on a variety of scales, determine how much total matter, as well as how much is normal and how much is dark, there needs to be. And the fluctuations in the cosmic microwave background, the Big Bang's leftover glow, tell us a whole lot about not just the total amount of matter necessary to give the Universe, but how much is normal matter and how much is dark matter.

ESA and the Planck Collaboration
The fluctuations in the Cosmic Microwave Background were first measured accurately by COBE in the 1990s, then more accurately by WMAP in the 2000s and Planck (above) in the 2010s. This image encodes a huge amount of information about the early Universe, including its composition, age, and history.
Finally, looking at the light elements left over from the Big Bang offers a completely independent piece of data: the total amount of normal (i.e., atom-based) matter that must exist. From all the different lines of evidence, we see the same picture. The fact that about 5% of the Universe's energy is in normal matter, 27% is dark matter, and the other 68% is dark energy has been known for nearly 20 years now, but it remains as puzzling as ever. For instance:

We still don't know what dark energy is, or what causes it.
We know from a slew of observations that dark matter exists, and we know its generic properties, but we have yet to directly detect it or find the particle(s) responsible for it.
And even the normal matter — the stuff made of protons, neutrons, and electrons — isn't fully accounted for.
In fact, if we add up all the normal matter we know about, we're still missing the majority of it.

Supernova Cosmology Project, Amanullah, et al., Ap.J. (2010)
Constraints on dark energy from three independent sources: supernovae, the CMB and BAO. Note that even without supernovae, we’d need dark energy, and that only 1/6th of the matter found can be normal matter; the rest must be dark matter.
There are two ways to measure the Universe that are completely independent of one another: through the light that objects emit or absorb, and through the gravitational effects of matter. The earlier methods described — the expansion of the Universe, the large-scale structure, and the cosmic microwave background — all use gravity to make their measurements. But light plays a major role, too. Stars shine because of the internal physics that causes nuclear reactions inside them, and so measuring the light coming from all of them tells you how much mass there is. Measure the absorption and emission of other wavelengths of light, and you can calculate how much mass there is in not only stars, but gas, dust, nebulae, and black holes. Go to high energies, and you'll even be able to measure hot plasmas within galaxies. But we're still missing more than half, perhaps even up to 90%, of the total normal matter. In other words, of that 5%, we're missing most of it.

NASA, ESA, and A. Feild (STScI)
An illustration of a slice of the cosmic web, as viewed by Hubble. The missing matter we can detect through electromagnetic signals is the normal matter alone; the dark matter is unaffected.
So where should the rest of it be? Not in galaxies at all, but between them. Dark matter should clump and cluster together in large-scale filaments, but so should normal matter. When the high-energy radiation from the first stars passes through intergalactic space, the dark matter and light completely ignore each other, but the normal matter is vulnerable. Neutral atoms formed when the Universe was a mere 380,000 years old; after hundreds of millions of years, the hot, ultraviolet light from those early stars hits those intergalactic atoms. When it does, those photons get absorbed, kicking the electrons out of their atoms entirely, and creating an intergalactic plasma: the warm-hot intergalactic medium (WHIM).

Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang. Illustration: CXC/M. Weiss
The warm-hot intergalactic medium (WHIM) has been seen before, but only along incredibly overdense regions, like the Sculptor wall, illustrated above.
Up until now, the WHIM has been mostly theoretical, as our tools haven't been good enough to measure it except in a few rare locations. The WHIM should be very low in density, located along dark matter filaments, and at very high temperatures: between 100,000 K and 10,000,000 K. For the first time, now, there's a statistically significant signal that exceeds the 5σ statistical significance mark, thanks to research by two independent teams. One, led by Anna de Graaff, looked at the cosmic web; one, led by Hideki Tanimura looked at the space between luminous red galaxies. Both of them detected the WHIM to greater than 5σ significance, and both used the same method to do it: the Sunyaev-Zel'dovich effect.

J.E. Carlstrom, G.P. Holder and E.D. Reese, ARAA, 2002, V40
By scattering lower-energy photons to higher energies, ionized plasmas found throughout the Universe bump lower-energy light to higher energies, increasing their temperatures.
What is the Sunyaev-Zel'dovich effect? Imagine you're sending light uniformly, in all directions, throughout the Universe. As it travels, the expansion of the Universe stretches it, causing it to fall to lower wavelengths. But in some places, it will pass through a hot, ionized plasma. When photons pass through a plasma, there's a slight effect due to the electromagnetic, wave nature of light: the photons gets shifted to slightly higher energies, due to both the temperature and the motion of the plasma.

It was way back in 1969 that the Sunyaev-Zel'dovich paper predicting this effect came out, The interaction of matter and radiation in a hot-model universe, but it would be decades before the effect was first detected. In fact, the paper was written almost entirely by Sunyaev, with Zel'dovich merely adding in how difficult the effect would be to detect. Nearly 50 years later, we've used it to detect the missing normal matter in the Universe.

Ralf Kaehler, Oliver Hahn and Tom Abel (KIPAC)
The cosmic web is driven by dark matter, but the small structures along the filaments form by the collapse of normal, electromagnetically-interacting matter. For the first time, normal matter overdensities along the filaments without stars or galaxies has been detected.
But this doesn't eliminate the need for dark matter; it doesn't touch that undiscovered 27% of matter in the Universe, not in the slightest. It's another piece of that 5% that we know is out there, that we're struggling to put together. It's just protons, neutrons, and electrons, existing in about six times the abundance within these filaments as compared to the cosmic average. The fact that this filamentary structure contains normal matter at all is further evidence for dark matter, since without it there'd be no gravitationally overdense regions to hold the extra normal matter in place. In this case, the WHIM traces the dark matter, further confirming what we know must be out there.

The Millenium Simulation, V. Springel et al.
The cosmic web of dark matter and the large-scale structure it forms. Normal matter is present, but is only 1/6th of the total matter. The other 5/6ths is dark matter, and no amount of normal matter will get rid of that.
Yes, we've found some of the missing matter in the Universe, and that's incredible! But the missing matter we found was part of the normal matter — part of the 5% of the Universe that includes us — and leaves all of the dark matter untouched. The latest discovery suggests something incredible: that the missing baryon problem might be solved by looking to the great cosmic web that gave rise to everything we see. But that remaining 27% of the Universe must still be out there, and we still don't know what that is. We can see its effects, but no amount of missing normal matter is going to make a dent in the dark matter problem. We still need it, and no matter how much normal matter we find, even if we get all of it, we'll still only be 1/6th of the way to understanding all of the matter in our Universe.

Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang! His books, Treknology and Beyond The Galaxy, are available wherever books are sold.
 楼主| 发表于 2017-10-13 13:24:47 | 显示全部楼层


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