What is Dark Matter?

a reply to: darkorange

Okay, but the 'quark surplus' in the formation of the early universe is precisely what gave rise to (ordinary) matter. Both quarks and antiquarks were formed, and proceeded to annihilate one another. But there were some few quarks left over, and they combined to form matter.

Is a lone quark possible? at Physics Forums.

But wait! There's hope yet!

Elusive quark created in the laboratory

a reply to: Astyanax

Thanks again.

I do not insist it is quark. I am not a scientist. You probably are.

It just seemed to me from my lay tower that unused 'building blocks' are left to give universe its hefty weight albeit unseen coz they did not turn into something tangible like matter.

To detect building blocks is a full time job for decades for many.






DO.

wow extremely late for this one, but thanks Arbitrageur for the several shouts. I am still alive and well, and the good news is that we are buttoning up the finishing touches to the worlds first (hopefully if we switch on before a competing experiment) Multi-tonne scale dark matter detector.

The great thing about science is the following, we have multiple ways to view everything. We can get a measure of the matter out there in space floating around by looking at 21cm hydrogen, We can point our radio arrays these days and map out the amount of hydrogen in the night sky and get an estimate to how much stuff there is there, in the vacuum and those corrections go into the models. turns out those corrections are not enormous. 1-2 atoms per meter cube is fairly typical, and that basically means you need 10^23 ish cubic meters to get 1 - 2 grams of extra material. It just isn't enough.

Rogue planets / dark stars, could be a reasonable contribution, but thus far our searches have turned up way less than we would expect should dark matte be of this form. Why? well the smaller the object, the more you need... we have very good handles on the masses of white dwarfs, neutron stars and black holes. if this is what dark matter is, they should be spread everywhere, so thickly that generally the stars should twinkle because of objects passing in front of them much much much more often than we observe. Science has observed microlensing, but it just doesnt occur enough.

On SUSY and the LHC, the arguments motivating the none existence of SUSY are known as Naturalness. I personally think these arguments are extremely weak. It basically states that what ever is higher up, should be high mass, and those masses must not be fine tuned with couplings that trickle down to the Standard model. Its like, you can have couplings, but they must not require massive amounts of convoluted interplay. Why do i think this is weak? Well it bias itself in favour of mathematical elegance and beauty when in reality there doesn't need to be any. The standard model is already fine tuned, so why must SUSY not be?

SUSY is fine, even the lowest parameter models are fine, just the energy for creating the lightest super symmetric particle goes up by about 2 to 10 times and probably out of reach of the LHC.

That isn't to say that we should stop looking, we still have many questions about the Higgs and looking at Higgs production can yield hints of new physics. We are also looking for Dark Matter in beam dump experiments, that is, in a high energy beam if dark matter is created you wont see it and such events in a detector would have missing energy and missing momentum. Thus far, no beam dump experiment has observed this.

The interesting part of this is that trying to create it requires very model dependant physics, and if those models are wrong, then, we simply wont see anything. Thus you will hear lots of high energy physicists tell you that the Direct detection guys (IE people like me) are idiots because they will find it easily. Truth is, they assume that there is a coupling and a path in which you can create the dark matter at energies we can achieve. There doesn't need to be a coupling capable of doing that at energies we can achieve. So they might also be looking in the wrong place.

Either way, it is an exciting and vibrant field, and I can say that, for those who want to say we do it for the money, or we are a waste of money time and effort... Lets just say these experiments cost less than what a single NBA star gets a year... only, other than living a celebrity lifestyle upon retirement... we generally work 18+ hours a day, have to go down into dusty mine each day and basically figure out how to built insanely clean experiments... Then get told we have no clue what we are doing

a reply to: Arbitrageur

ErosA433 admits there's some chance dark matter may not be detectable directly by any experiment, if it doesn't interact with ordinary matter, and the gravitational effects may be all we can observe. Whether dark matter will be detected in such an experiment is unknown. But if we don't do the experiment, it's certain we won't learn anything. Whether they detect dark matter or get a null result, we will know more than we do now either way.

Great information from someone engaged in the business. Best statement: "But if we don't do the experiment, it's certain we won't learn anything."

It's too bad that some of these great posts get lost. Thanks for bringing it up.

a reply to: Phantom423

Like the project director for the new NASA 'flying saucer' atmospheric decelerator said: 'My boss told me that if this test of the device works and everything goes according to plan and we get good data out of it, I get an A. But if it doesn't work out and something goes wrong and we learn something, I get an A plus.'

originally posted by: ErosA433
Thus you will hear lots of high energy physicists tell you that the Direct detection guys (IE people like me) are idiots because they will find it easily.

Thanks, I was hoping you'd find this thread and add your thoughts to the topic.

I think if they were going to find it "easily", they would have done so already, though they might have a chance with the LHC upgrade they didn't have before.

There was a question in another thread that I didn't know the answer to about dark matter, or the lack thereof, on our own solar system. I read a paper claiming that it put upper limits on the amount of dark matter in our solar system:

Constraints on Dark Matter in the Solar System

We have searched for and estimated the possible gravitational influence of dark matter in the Solar system based on the EPM2011 planetary ephemerides using about 677 thousand positional observations of planets and spacecraft. Most of the observations belong to present-day ranging measurements. Our estimates of the dark matter density and mass at various distances from the Sun are generally overridden by their errors (σ). This suggests that the density of dark matter ρ dm, if present, is very low and is much less than the currently achieved error of these parameters.

If there's 8 times as much dark matter as baryonic matter, I would have expected a paper like this to report maybe at least twice as much dark matter as baryonic matter, with the understanding that the distribution of dark matter is only roughly correlated with baryonic matter, with notable exceptions in the bullet cluster etc. Any thoughts on whether this analysis could be correct, and does it challenge our assumptions about how dark matter is distributed?

On the LHC, depending ont he model, they have a great opportunity to observe new physics if it is there. Be it Higgs excitations, multiple Higgs, a Light SUSY particle, CP violation, lots of stuff. It is a very exciting time.


Iv not read the paper in question though questions came up at a conference recently regarding the same topic. Now, it is interesting to do these studies, but it is also true that the measurements are very tricky and depend upon a lot of factors. A quick glance at the papers are trying to fine perturbations in orbital mechanics. The estimated mass contained within a sphere out to the orbit of Saturn estimated to be 10^-10 Solar masses, comes out at about 1-2x10^20 kg

That is a lot admittedly! Except when you think that the Moon has a mass of 7x10^22 kg, So the mass of the dark matter in that sphere (if i read it correctly) so then I take a step back and think... hmmmmm, if you exclude the sun's mass as like a background gravitational force, then the amount of force you are trying to account for at the orbit of saturn (as an example) is

something like 2x10^20 against a background of 1.91x10^27 (From the other objects inside that volume we know of, excuding the sun and the asteroid belt. This is a measurement accuracy of 1 in 10million, which is EXTREMELY hard to do. So it is not to say it is impossible, but I agree with the statement made, the error is so huge, its hard to say more than a ball park estimate.

Now, it can also be said that this doesn't bode well right? since as you said you would expect 8 times more mass! but i actually dont think its a huge issue, mainly because even at high dark matter to baryonic matter ratios, the volume of space we are talking about is far far larger than that sampled here. The volume of the sample is about 10^-12 compared to a sphere of radius 1 lightyear... thats quite ALOT and remember that most of the baryonic matter we know of has settled into the disk, it kind of means that the sample here is actually more of a slice through that sphere, and not the whole sphere... Dark Matter on the other hand should be distributed within the sphere. So it then begs a question of if this study is sampling a very small volume slice through a thin disk, rather than a full spherical volume. Its problematic mainly because mass included above and below that sphere would count almost zero to the corrections, and so would not be observed really unless you had an orbital object moving in a polar orbit and another in a normal orbit.

at least thats how my mind sees it, i could be completely wrong though. My point really is this, It looks like the study says there is dark matter, but i think the study is extremely narrow, despite it being narrow, it is also extremely hard to do.


There are other theoretical predictions that place the local dark matter density as being very very low, however these predictions have many assumptions, many more assumptions than other models, and so, while not ignoring these, it is safer to test the other models first that have a bit more firm standing. There have been other measurements looking at certain classes of stars in the milky way as test particles. however when i read these papers, I could see that they where sampling in a certain way to reduce the local groups rotational noise from the data... however... with the short range of the search, it was also clear that you could sample a very biased sample that would not necessarily be fair use as test particles. Example being selecting dull red stars you think are part of a cluster that is passing through the disk... except then only having radial velocity measurements and not transverse velocity measurements which allows plotting of actual movement... but assuming still that all of your sample ARE without any doubt, part of the cluster. Im sure they know far better than me at what they are doing, but the way it was written had me not so convinced it was an unbiased sample or test.

a reply to: ErosA433
Thanks for the great reply. So there could be some measurement or assumption errors, but if not, then we would infer that the correlation between dark matter and baryonic matter is not that well correlated on the scale of our solar system. If we look at a somewhat larger scale for evidence of dark matter between the local stars near us, we would expect to find more. But this has been done too and the results were not what the researchers expected, so I'm really puzzled:

A lack of dark matter in the solar neighborhood

A detailed analysis reveals that a small amount of DM is allowed in the volume under study by the change of some input parameter or hypothesis, but not enough to match the expectations of the models, except under an exotic combination of non-standard assumptions. Identical results are obtained when repeating the calculation with kinematical measurements available in the literature. We demonstrate that a DM halo would be detected by our method, and therefore the results have no straightforward interpretation.

The authors are presumably at least somewhat experts in this area so if they don't know how to interpret their findings in a straightforward manner, it's no wonder I'm having a hard time making sense of their findings. As far as I can tell these researchers were expecting to find evidence to support dark matter models, and they were as surprised as anybody that they didn't, or as they put it it's unlikely to be consistent with the Lambda-CDM model:

Dark Matter Study

As team leader Christian Moni Bidin puts it:

"The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun. But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!"

I suppose in this case you can make a similar argument and say that again they need to look at an even larger scale to find the dark matter, beyond the local stars, to the galactic halo, where dark matter is thought to exist. However, since the authors say "We demonstrate that a DM halo would be detected by our method", they apparently think they should have observed such halo effects which they didn't to any significant degree.

I think there probably is some kind of dark matter that's not baryonic, but it seems difficult to figure out how it's distributed. Of course maybe both papers have some kind of flaws in assumptions or measurements and I don't know enough about their work to detect those.

Yep, these are very valid points, and it is very confusing. Interestingly the author or at least the first one listed is the same as the paper i had read on the subject a while ago

arxiv.org...

The one where I basically stated that I am not sure that picking 400 stars is extremely representative of the whole galaxy, and the selection they made is reasonable but again, questionable. And i correct myself here, they sampled Red Giants with proper motion and radial, but it still seems like an case of bias, though still highly interesting. So why not Red Dwarf stars? Why not GTypes? why not neutron stars, ? (yeah i know- distance and lack of proper motion data)

The paper was questioned by another group and your link is the second round of clashing of swords. In all, it is quite difficult to say what is happening here... but what is definitely happening is they are making observations of stars, taking a sample of just 400, from a pool of... well probably many many many thousands. The language is kind of interesting too since it does sound to me... delivered with a bit of arrogance (yes Scientists can be rather egotistical we all know) The author is listed on many astronomy papers so its safe to assume there is a good reason for the selections made.

Having a paper reply that, actually the numbers are fine within theoretical prediction, and then do a follow up with a similar outcome that comes no closer to considering the response (from how iv just read it) is also rather interesting and i am not sure anything totally firm can be said conclusively.

Despite the original being 3 years old now, im not sure it is really a conclusive study, and it is clear that it has a few problems.

That said, we do not know the actual 3d shape of the halo, we can look at other galaxies but its kind of up in the air as to the formation... it could be clumpy... which is what the paper might have discovered, but the paper simply says "NO DARK MATTER" which i dont think is so helpful to solving this riddle.

Going out of the box here and going to say dark matter is what is commonly known to us as black holes, or rifts in space time thus we are unable to comprehend it as it is considered the multiverse. It is the whole within the part and the part within the whole. Think fractals with the big bang in a multiversal type of thinking. . . .

Who really knows what it is, I am just guessing lol. . . . .

originally posted by: ErosA433

Rogue planets / dark stars, could be a reasonable contribution, but thus far our searches have turned up way less than we would expect should dark matte be of this form. Why? well the smaller the object, the more you need... we have very good handles on the masses of white dwarfs, neutron stars and black holes. if this is what dark matter is, they should be spread everywhere, so thickly that generally the stars should twinkle because of objects passing in front of them much much much more often than we observe. Science has observed microlensing, but it just doesnt occur enough.

On SUSY and the LHC, the arguments motivating the none existence of SUSY are known as Naturalness. I personally think these arguments are extremely weak. It basically states that what ever is higher up, should be high mass, and those masses must not be fine tuned with couplings that trickle down to the Standard model. Its like, you can have couplings, but they must not require massive amounts of convoluted interplay. Why do i think this is weak? Well it bias itself in favour of mathematical elegance and beauty when in reality there doesn't need to be any. The standard model is already fine tuned, so why must SUSY not be?

SUSY was the chosen one, said to destroy the anomalies, not join them!

She was to bring balance to the Forces, not break more symmetries in service to the Darkness.

SUSY is fine, even the lowest parameter models are fine, just the energy for creating the lightest super symmetric particle goes up by about 2 to 10 times and probably out of reach of the LHC.

You really think Susy's gonna show for that date tomorrow after standing you up over and over?

originally posted by: mbkennel

SUSY was the chosen one, said to destroy the anomalies, not join them!

You really think Susy's gonna show for that date tomorrow after standing you up over and over?

I got to satisfy SUSY,
SUSY sho' satisfies me.

a reply to: ErosA433
Thanks again for the thoughtful reply. You could be right about errors in assumptions of the papers and I find it hard to rule anything out until we have some good explanations. I may not know the answers but at least you've given me some good perspective to think about when considering the apparently conflicting observations, and I appreciate that.

originally posted by: FormOfTheLord
Going out of the box here and going to say dark matter is what is commonly known to us as black holes, or rifts in space time thus we are unable to comprehend it as it is considered the multiverse. It is the whole within the part and the part within the whole. Think fractals with the big bang in a multiversal type of thinking. . . .

Who really knows what it is, I am just guessing lol. . . . .

To suggest black holes as a potential source of dark matter is well within the "box", and thus the possibility has been meticulously researched, so I don't think you know where the "box" is. Gravitational microlensing observations tend to rule out a significant contribution of the missing mass from not only black holes but from any compact massive objects including planets with a mass larger than Earth.

originally posted by: mbkennel
You really think Susy's gonna show for that date tomorrow after standing you up over and over?

Eros could be right and Susy may show, but I tend to doubt it; I've lost faith in Susy.

a reply to: Astyanax
I like that quote!

a reply to: Parthin


(I plan to read the replies already made after my post)

if you think that orphaned planets and rogue stars, clouds of wispy matter, all outside the observable structures in the Galaxy and total Cosmos... is the answer to the 80% of excess gravity that is required to fit the mathematical models of the seen universe--- then you are pipe dreaming


perhaps the 'God Particle' and other Quarks, Leptons, & additional exotic Quanta are the 'Deep Waters' that fluxuate to create Gravity (which should not exist) but is accounted for by the theory of 'Dark Matter' universes

the flux of a God-Particle popping into existence and then disappearing into that pre-primal soup generates a gravitron as a spin-off of being temporary matter... but there is no constantly around, stable, 'invisible' matter that exerts that extrapolated 'dark matter'

a reply to: Arbitrageur

My overall gut feeling

a) rotation curves are still there

but whenever we REALLY look for Dark Matter

b) local Solar neighborhood
c) microlensing
d) CERN

it somehow always seems to slipslide away. And then who ordered Dark Energy? And quantum gravity and string theory are still a goose egg on goals. Something about that whole combination of evidence.

and then strange things like gravity, sometimes, maybe, changing during a solar eclipse? (and not at maximum totality but on entrance and exit)

www.physorg.com... [controversial and may be atmospheric fluid stuff but it's unclear]

and the flyby anomaly, (pioneer 10 seems to have been resolved)

journals.aps.org...

www.popsci.com...

Is a flyby anomaly different from an eclipse?

channelling Sherlock Holmes..... "when you have eliminated the impossible, whatever remains, however improbable, must be the truth"

maybe there's something about gravitation, maybe even classical gravitation, we have wrong

originally posted by: mbkennel
a reply to: Arbitrageur

My overall gut feeling

a) rotation curves are still there

but whenever we REALLY look for Dark Matter

b) local Solar neighborhood
c) microlensing
d) CERN

it somehow always seems to slipslide away.

That's about how it looks to me too.

and then strange things like gravity, sometimes, maybe, changing during a solar eclipse? (and not at maximum totality but on entrance and exit)

I'm not sure if it's related to gravity, or if it's got something to do with temperature, thermal stress, etc, but I certainly wouldn't rule out the latter:

Gravity Anomaly During the Mohe Total Solar Eclipse and New Constraint on Gravitational Shielding Parameter

This paper is intended to explain the observed anomaly by conducting the tilt experiment due to the thermal stress and temperature change in the solar eclipse.

www.physorg.com... [controversial and may be atmospheric fluid stuff but it's unclear]

404 Error - The Page Cannot be Found

and the flyby anomaly, (pioneer 10 seems to have been resolved)

journals.aps.org...

Their empirical formula predicting the anomaly would be repeated on the second and third flyby or Rosetta failed, as there was no anomaly on the second flyby, and on the third flyby, there was practically no anomaly but the small anomaly measured was negative instead of positive like the others, so it's not a compelling case for any new physics.

Archive.org link which ATS can't handle, so you have to click "quote", then copy/paste the link below to a separate browser tab:
web.archive.org...://webservices.esa.int/blog/post/5/916
Mystery remains: Rosetta fails to observe swingby anomaly

Together with ESA colleague and orbital mechanics specialist Frank Budnik, Morley co-authored a scientific report in 2006 that studied the Rosetta anomaly during the 2005 swingby and listed possible causes. These range from tidal effects peculiar to the near-Earth environment, atmospheric drag, or the pressure of radiation emitted or reflected by the Earth

I'm not sure what tidal effects they mean, but I don't know if, or how accurately they have programmed these known gravitational anomalies into their predictions, but it seems like a difficult task at best:

Gravity of Earth

Earth's gravity measured by NASA's GRACE mission, showing deviations from the theoretical gravity of an idealized smooth Earth, the so-called earth ellipsoid.

If those anomalies are what they refer to as "tidal effects peculiar to the near-Earth environment" then that would be my first guess, and while I'm not opposed to the idea of new physics I see no compelling need for it with the data set related to these flybys, though admittedly based on limited knowledge of how well they've programmed the anomalies above found by the GRACE mission. Even if by some miracle they managed to program the GRACE mission data perfectly into their predicted flyby trajectory, how accurate is the GRACE mission data? Does it look any different at different altitudes? Maybe a mission with higher resolution measurements would reveal more detail of the anomalies.

channelling Sherlock Holmes..... "when you have eliminated the impossible, whatever remains, however improbable, must be the truth"

on a TV game show, where you know there are only three doors and you've eliminated door 1 and door 2, then you could use some logic along those lines to conclude it must be behind door #3. However I don't think the real world works like that. It may be impossible to even list all the possibilities, in order to determine what "whatever remains". There may be possibilities we didn't even think of so I don't see how we can make any conclusions about what remains.

maybe there's something about gravitation, maybe even classical gravitation, we have wrong

personally I haven't ruled that out, but I don't see how any modification of gravity theory by itself could solve all our observational conflicts like the bullet cluster which you said you're aware of. So even if there's something wrong with gravity theory, there's still something else, at least it appears that way.

originally posted by: mbkennel
a reply to: Arbitrageur

My overall gut feeling

a) rotation curves are still there

but whenever we REALLY look for Dark Matter

b) local Solar neighborhood
c) microlensing
d) CERN

it somehow always seems to slipslide away.

The only place that doesn't slipslide away is option e) Large scale gravitational lensing, which gives pretty good signals for the extra gravitation. BUT as far as doing it locally, yep its always a problem. oh yeah and you forgot f) Direct detection.

The other interesting thing that is being performed right now is in the field of searching for Axion like particles which allows a particle to interact with a magnetic field to produce photons. This although not as favoured as the WIMP model, is still a very active area of research.

SUSY... im not hugely compelled by it Arbitrageur, just like you. There doesn't have to be anything coupled higher up in the way SUSY theories propose. It could be something else completely. Right now, we don't have any hints during LHC run 1, but now that run 2 is starting, maybe we might get some hints. As stands right now, the search is pretty bare, but i think people where too quick in their dismissal for reasons that don't make consistent sense. Do I believe SUSY is the answer? I think its an elegant one, but it doesn't have to be the answer or mechanism for a WIMP like particle.

It would be interesting if new physics can be found at the LHC, but so far the searches have yield rather little. Could be anything on that picture you shared or... might be something not on that picture

originally posted by: [post=19410573]ErosA433 Either way, it is an exciting and vibrant field, and I can say that, for those who want to say we do it for the money, or we are a waste of money time and effort... Lets just say these experiments cost less than what a single NBA star gets a year... only, other than living a celebrity lifestyle upon retirement... we generally work 18+ hours a day, have to go down into dusty mine each day and basically figure out how to built insanely clean experiments... Then get told we have no clue what we are doing

Lol nice one.
Hmmm.... Dark Matter. Try dilating time of your instrument and you will detect dark matter. Guaranteed

a reply to: Nochzwei

sure, because... you know... storing nearly a 4 tonne target at cryogenic temperatures is easy right... so why not

a reply to: Bedlam

I think a Flying V with a Bigsby on it is an abomination. Bring torches! Bring torches!