After a (well-deserved) break of three weeks, it is time to restart the year with some physics. I discuss today a scientific article that I have recently read, addressing dark matter. By the way, for those interested about the places I visited during my vacation, please check my travel blog @lesmouths-travel which will be updated in the next few days.
[image credits: RedHeadsRule (CC0)]
Although I have already written many times about dark matter, I will today present a novel idea explaining why it has not been directly observed up to now.
The cornerstone here is that dark matter only exists under a form of dark blobs with properties allowing it to escape detection.
But before entering the topic, let me first briefly sketch well-known generalities about dark matter and its potential detection, in order to make this post self-consistent.
DARK MATTER 101
Dark matter is one key concept in particle and astroparticle physics, and for a very good reason. All cosmological data, taken together with the Standard Model of cosmology, points to its existence.
Dark matter was originally introduced by Zwicky in 1930, in a scientific article in which he studied the motion of stars in galaxies.
[image credits: NASA (public domain)]
Taking Newtonian physics (or classical mechanics) alone, the circular motion of the various stars could not be explained.
Putting classical mechanics to the bin is however something that is unwanted (although some try to generalize it), and the alternative solution was to postulate the existence of some invisible matter.
This is exactly what dark matter is: it is invisible and thus dark (and actually very weakly interacting with matter), and it obeys to the laws of gravity like normal matter.
The presence of this extra invisible mass then yields an agreement between theoretical predictions and data.
In the following 80 years, many additional indirect proofs of the existence of dark matter have been unravelled, like the properties of the cosmic microwave background, of large structures in the universe and gravitational lensing, etc.
There is only one caveat. There is a bunch of experiments on Earth trying to directly observe dark matter, and they have all failed so far.
DARK MATTER DIRECT DETECTION
As said above, dark matter is dark (no kidding…) and very weakly interacting with normal matter. This means that it interacts with the visible world (‘very weakly’ is superior to ‘not at all’), so that there are ways to design experiments targeting its direct detection.
[image credits: LUX]
There are many of those experiments. They rely on a huge detector in which one tries to observe the interaction of dark matter with the detector material.
The probability of getting such an interaction is tiny, but it is non zero. Therefore, having a huge detector, recording data during a long time and relying on the fact that there is a constant flow of dark matter going through Earth is sufficient to get the chance to observe something.
In general, dark matter just goes through the detector unperturbed. Once in a while, it however hits an atomic nucleus from the detector material and makes it recoiling. Such a recoil can be observed through the detector electronics, which provides the way to detect dark matter directly.
As no dark matter particle has been observed so far, all models featuring dark particles turn to be more and more constrained. The rate at which dark matter interacts with normal matter has indeed to be small enough to guarantee the non-observation of any signal in the numerous direct detection experiments.
But the idea of dark matter is still far from being excluded by data. Dark matter can after all just be more bizarre than initially thought of.
DARK BLOBS AS DARK MATTER
For instance, one cool idea could be that instead of having a large density of point-like dark matter particles pervading our universe, dark matter could exist under the form of a small density of large composite blobs.
[image credits: Maxwell Hamilton (CC BY 2.0)]
Theoretically, this can be easily designed by enforcing dark matter to self-interact very strongly, which guarantees it to form composite state.
This may seem to contradict what I said above about dark matter being very weakly interacting, but dark matter must only be weakly interacting with normal matter.
Nothing was said concerning its self-interactions.
There exist experimental constraints on such an option, but those can be easily evaded when dark matter coalesces to form very large composite states known as dark blobs. And since those guys are large, one does not need many of them to accommodate the observed density of dark matter.
Moreover, provided the typical mass of the dark blobs is smaller than 1000 tons, the dark matter density is such that at least one blob passes through Earth each year. There are thus ways to detect it.
Again, dark and normal matter are very weakly interacting with each other. But we have here a huge blob of dark matter and a huge detector made of normal matter. It is thus very likely at at least some of their respective constituents will interact with each other.
In the scientific article I am talking about, the authors have shown that such interactions can be detected by current and planned experiments. We have thus means to discover dark matter if it exists under the form of blobs.
As there is no sign of a dark blob today, this class of model is already constrained by data, but it is at the same time far from being fully excluded. The future will hopefully tell us more about this.
TAKE-HOME MESSAGE
Dark matter is still one of the best idea to explain cosmological data. All the proofs we have today are however indirect, and we are missing a direct observation of dark matter. In this recent article, the fact that dark matter has not been directly observed has been connected to non-conventional properties.
In addition of being very weakly interacting with the normal world, dark matter was assumed to be very strongly interacting with itself. As a consequence, it exists under the form of a small density of dark blobs. Such blobs can in principle regularly pass through Earth, and the nice feature is that current and future experiments have a potential to observe them.
If the future is dark, it is thus very exciting and potentially blobby!
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glad to have you back on the frontier, sensei :p
Moreover, provided the typical mass of the dark blobs is smaller than 1000 tons, the dark matter density is such that at least one blob passes through Earth each year. There are thus ways to detect it.
in theory, that is ... but from all i read (you know i have about zero formal education other than basic algebra, lol) its more than highly unlikely since , if neutrinos can shoot through a lightyear of matter ( lead in specific ) and dark matter should (in theory) be more elusive since it hasnt been actually observed yet then a detector the size of the earth would STILL have a near to zero chance on a cosmic scale ?
Then again if it accounts for 96% of everything it should be everywhere so that might up the chances again .
And from all i read the data on the matter does not completely corellate with the observations on the matter either so i still don't understand why its considered more likely than alternating gravity (maybe it's easier /grin i dont know )
you know my logic comes without numbers here but as far as i know so does the rest because it hasnt been proven, which makes all numbers hypothetical, doesn't it.
Seeing as, if i understand correctly , it's assumed for the sake of hypothesis that there's alternating interaction then even more so i dont understand why alternating gravity would be frowned upon like that.
Then again, i'm not the physicist ofcourse, i come to learn, not to discern but it sometimes makes no sense to me and it hasnt been proven yet i fear its sometimes wishful thinking to selffulfilling prophecy. Im not being negative here, im just being straight about the drive of the human mind.
It's slightly strange how the amount of dark matter corellates with the amount of "invisible internet too", i think that's also 94-96% ... all nodes "below the surface" no standard user will ever get to see so maybe its all back to fibonacci hahah, sorry there i go again mixing it up in my metaverse.
What i WANTED to ask before i got lost in my head : since dark matter packs in these blobs there should be more mass to observe, and if it interacts with its own kind but not with standard matter AND is subject to gravity it also stands to reason (in my head) that these blobs would act like everything acted in the beginning, they would meld together and become more massive over time (at least thats my simplified view of the origin of the cosmos here) so the more time passes as they stick together more and more, driven by the fact they're subject to gravity, you would have bigger blobs that become more massive so over time they would have to be easier to detect since
... mass bends light ? right ? i mean the presence of it, that's Einsteins representation of spacetime , its specifically about fotons and pathways where massive objects lead to dents and bends,
which can be observed so
what places would be more likely to find more massive blobs or superblobs (lol) of dark matter then ?
would it be more likely to find them closer "to the point of origin" where all started from that marble sized dot or would it be more likely to find more condensed/bigger blobs (over time as we are a few billion years later now) on the outskirts as it keeps expanding (i do believe i'm right in my assumption dark matter is similar to everything that did not condense into the current/light matter in the first 10-20 minutes of the universe, no?) but if its blobs and if its subject to gravity, even if only interacting with itself, it should condense from small blob to bigger blobs over the course of billions of years ? (do correct me if my gedanken go out of line here, lol) so there must be areas where its more likely to find bigger blobs, even if current methods of detection might not have the resolution it takes to detect a shift that small due to the severe lack of mass over volume it might be able to theorize where its more likely ?
(yea thats a question mark, lol) so i think i need to do some housechore stuff ... sadly the gnomes are still on strike :p
i hope i'm making sense, i know i split myself over the course of several paragraphs into a few different people usually
and as always , thanks for the post, much appreciated
Thanks for the nice and detailed comment, as usual. Yes I am finally back :)
Neutrinos form a background in such experiments. We however have not excluded the fact that dark matter interaction rates are larger than the neutrino ones. As long a this option is still viable, we have a long way to go.
They coalesces by virtue of the dark matter self-interactions. Gravity is still too weak at that scale (we are talking ab out tons and not solar masses).
and
how close am i to the theory ? :p
hm , something odd with the markdown numbering system 1) 2)
No, this means that dark matter may interact more, just because the interaction strength is stronger.
Yes, indeed. Except that with a few tons, you don't bend much so that this would not be noticeable.
okay, so i had question two right, does that mean i pass ? :) cos in most unis you dont pass on 50% , right ?
when i started OU for psychology i think the required score was about 70% or no bach lol
but part 1 leaves me hanging for a moment there
what exactly do you mean by interaction strenght ? i thought gravity pulled depending on mass, so a more massive object will be more subject to it ? thats why the moon revolves and a comet just slings by ?
or is there something else at work ? because right now variable interaction strength sounds to me a lot like variable gravity (ooh dont shoot me hhahah)
no really what i read is (please do correct me) the same amount of mass in a blob of dark matter or a zone of neutrinos will interact differently with the gravitational pull and therefor make a different "dent" in spacetime (thats regardless of volume ofcourse, that far i got already :)
When there is a dark sector, they may come with their own set of interactions that are different from the fundamental ones we know. Those interactions may have different strength. Not electromagnetic, not weak, not strong. Just a different one.
I hope this short answer clarifies.
yes, it actually does , thanks , its an unknown variable
Welcome back @lemouth and thank you for sharing your holiday diaries!
Dark matter is fascinating and one day a team of physicists will probably win the nobel prize for experimentally proving its existence.
I know that there are some theories about the production of dark matter through nuclear reaction between ordinary matter particles.
In that way, is it possible to prove indirectly the existence of dark matter by measuring expected mass or energy loss during collisions of normal matter particles in particle accelerators?
Cheers!
Thanks for welcoming back!
I am looking forward to see this day! hopefully I will still be alive (if not, that could also mean that dark matter should be more elusive and special than initially thought off :D ).
Most of them allows for that. As soon as dark matter interacts in one way or the other with normal matter, it can be produced from the scattering of ordinary particles. This is the point at the basis of the entire dark matter search program at the LHC for instance.
This would actually be a direct proof and not an indirect one, as direct would be directly produced in an accelerator. But what will be detected would be the presence of something missing, exactly as we discussed in the madanalysis project posts.
What is the consequence of the interaction between constituents of dark matters and normal matters. And what is the implication of this hypothetical form of data entering earth?
Welcome back once again @lemouth
I am not sure to get the question. Dark matter can interact with normal matter, making it recoiling. This recoil can be observed 9this is the main consequence). In terms of consequences on humans, if this is the question, there is none (like the interactions of neutrinos with humans, but at a much much much reduced pace). The same holds for Earth as the interactions are at the end of the day very local.
Thanks for welcoming me back :)
I wonder why we would only encounter a blob once a year? If dark matter acts gravitationally, then you would expect there to be a ring of the stuff in the orbit of most stars and planets, and by extension a little ring of blobs in the Earths orbit.
Very good question. Thanks for asking!
The point is that the density of dark matter is well measured. Therefore, the more massive a single blob is, the smaller number of blobs is required to get the right relic density of dark matter. Consequently, the blob flow going through Earth is smaller.
For blobs lighter than 1000 tons, we are guaranteed to have a flow sufficient for having at least one of them going through us each year.
Does it clarify?
Ha ha unfortunately no it doesnt. What is 'relic density', and why does density have any bearing on the orbit?
This is explained in details in this post. In short:
Now dark matter is spread all over the universe and dark matter particles can go through Earth. Those are the ones that one tries to detect.
Hopefully, now it will be slightly clearer ;)
While the dark matter hypothesis appears to be the most compatible with current cosmological models, there might not be dark matter. Two of the most popular alternatives to dark matter are the Modified Newtonian Dynamics (MOND) and some sort of electromagnetic coupling (Electric Universe Model).
MOND is simply adding an extra term in Newton's Gravity Equation, but the fit is not as good as originally appeared.
The Electric Universe Model holds a lot of promise and intrigue. Electromagnetic coupling between the sun and the planets is shown dramatically in the auroras found on Earth, Jupiter, Saturn and Uranus that are caused by electric Birkeland currents from the sun.
Well the unsolved mystery is stimulating developments in Theoretical and Experimental Physics. Have fun with that.
Wow! Glad to see you are back. it is a long time I have not read anything (post or comment) from you! Are you back?
MOND is indeed very alive and compatible with data (to a smaller extent than the dark matter paradigm, as you said). This is what I understood in the following sentence: "All cosmological data, taken together with the Standard Model of cosmology, points to its existence." The wording "Standard Model of cosmology" is important. Note that in many other posts I wrote on dark matter, I mention the modified gravity alternative (but I don't do it systematically; this depends on my mood ;) ).
Concerning the electric universe theory, I must disagree with you. To my knowledge, this theory has been debunked and proved wrong. After quickly googled five minutes ago, this is still the case.
Thanks for remembering me.
Something is causing additional cohesion on the stars in the outer rims of galaxies.
If gravity causes the strange rotation of galaxies, then either there is more mass (dark matter) or gravity is a bit stronger at vast distances than predicted (MOND). Gravity is not the only force that acts over great distances, Electromagnetic forces can also.
Yes, but the electric universe theory does not agree with many data. If a theory does not reproduce data, well... Also, their supporters are now most on the conspiracy theory business than in science, at the moment.
I have a very ill-defined (and unimplementable) idea in my head now that takes advantage of this.
Imagine a device which emits a strong repulsive force sitting at the bottom of a large gravity well. Would this act as a sort of 'dark matter concentrator'?
Also, it's curious that dark matter appear to interact just fine with non-dark matter gravitationally. Is there some explanation for this, or am I missing something?
It depends whether dark matter interacts with the device at all. Why would it do it?
Gravitational interactions are fine, but negligible compared to the rest as the masses are way too small for what concern the scales of interest.
I worded it poorly and probably should draw a free body diagram. The point is exactly that the dark matter won't interact with our 'generically repulsive' device, but will be affected by the gravity well. So, you've got both types of matter 'falling' towards the device, but normal matter is getting spit out due to the repulsive force, so dark matter accumulates.
What I'm getting at is why does dark matter interact gravitationally?
There are theories in which dark matter can be captured, for instance, by neutron stars. This would be very similar to this device. For instance, see here.
This is the original reason behind dark matter: we need it to explain the galaxy rotation curves so that it must interact gravitationally. Otherwise, thus would just be other exotic stuff that would probably be called by another name.
Heh, the neutron star idea is sort of what I was working up to (I was thinking within jets from similar). So I'm sad at not being original, but happy that someone more well-versed though similarly.
As to the other topic, I'm aware that dark matter was proposed to explain galaxy rotation curves. Is there any idea as to why it interacts gravitationally, or is that still along the lines of 'because it does,b y definition'?
Well, you question may somehow be: how gravity works at the most fundamental level. And the answer is: "we don't know yet, but some are working on it" :)
With all these advances towards the discovery of dark matter, it still amazes me why it has escaped detection - well, even though dark matter is yet to be observed, their existence cannot be doubted.
I really found this piece highly educative sir
Welcome back
The fact that it escapes detection is not surprizing. Nature does not like to be too easy to discover, and there are still so many options allowed by data :)
Thanks for welcoming back! :)
Perhaps there are quite complex structures of dark matter in the universe, coalescing into pockets, or even large entities of dark matter. Maybe we are living in a dark matter vacuum in our local region, so we have little chance of detecting it. What are your thoughts on this @lemouth?
Assuming there is dark matter at all, there must be some of it in the Milky Way. As a consequence, there is a flux of dark matter going through Earth, potentially observable if large enough and interacting enough.
Greetings! very interesting, I use to read Physics articles in particular from Quantica, but this subject is truly fascinating. I have read about Friedmann density parameter, and some of the Einstein´s research.
I don't know quantica. Do you have the website by any chance, as I may give it a (very) quick look (I rarely follow physics communication platforms and prefer reading what interests me directly from the source :) ).
I read directly books. it´s very interesting and you realize everything is related, I´m reading right now about "The Observer effect" try with this: https://phys.org › Physics › Quantum Physics
Ah ok. I thought you were considering a website named quantica. I misunderstood you. I know phys.org and I don't really follow that, as for any science sites. I read directly the sources of any news, un-popularized (a least for what concerns physics) :)
Ok! any way try to check it! regards!
There is no way. I am wondering why I should do that? What would this bring me? As a scientist, I read directly the articles I am interested in, and I don't see the point reading the corresponding press releases, except for checking they are correct, maybe ;)
Welcome back :)
Let's ambush the dark blob the next time it shows it's dark mug on earth :D
Thanks! I guess one may need a bigger mug for that ;)
I'm in for whatever it takes to capture the elusive guy :)
So am I! ^^
Very interesting and really very good publication. I enjoy reading your posts @lemouth. I'll be waiting for more. My cordial greetings.
Thanks for passing by. I will write more, but you know my rhythm is not very fast. Too busy with many other things ;)
Hi @lemouth Sir! :)
Happy to see you back!! :)
The information provided above about the dark matter is really very informative as always!! I learnt few new facts here. Thank you for bringing up this article!!
Have a great day ahead Sir!! :)
I am also happy to be back! Thanks for passing by and still reading me :)
You are most welcome @lemouth Sir! I was and will always be a reader of your posts Sir, no matter what. :)
Thanks for your trust! :)
:)
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