Dark matter (Full Version)

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JasonM -> Dark matter (Oct. 26 2017 17:40:29)

For the nerds, it seems like they have a high confidence now that the elusive dark matter is baryons, or atoms stripped of electrons. No invisible parallel universes as far as we know.


kitarist -> RE: Dark matter (Oct. 26 2017 18:13:17)



For the nerds, it seems like they have a high confidence now that the elusive dark matter is baryons, or atoms stripped of electrons. No invisible parallel universes as far as we know.


From what you linked to, this seems to be about the non-dark matter/energy (i.e. about the baryonic matter which is what we can interact with). The problem is, of that 5% detectable matter we only see 10% of it (of the 5%), as inferred by other means. So the new research is about finding more of that non-dark , or baryonic, or ordinary, matter.

Dark matter is an entirely different beast. We still think it is 95% of all mass-energy content of the universe.

Ricardo -> RE: Dark matter (Oct. 26 2017 21:33:17)

Yes Jason, this is not THE missing matter, it's the "missing matter" we already knew about but had not yet litterally acounted for it yet. In other words they always have said we know what 20% of the normal matter in the universe is (the stuff in the standard model)....however they only actually saw 10% of it until now. Now they can see what it is....and it's just hydrogen and helium gas filaments ....the heavy nuclei add up (baryons, protons and neutrons in other words), the electrons barely count for s h i t. Remember hydrogen is just one proton, and helium is 2protons and 2 neutrons. (4 baryons). There is some other interesting combos of baryons such as deuterium etc, but they already acounted for that stuff. So nothing really big news going on here.

When summing total matter (mass that bends space or shows gravity doing stuff) and energy of the universe (driving the expansion), you got 25% dark matter (nothing in the standard model of particle physics), plus your 5% (finally) visible matter (all the stuff made by the standard model stuff), and the other 70% is dark energy.

One more thing to think on....antimatter and matter (both standard model particle stuff) constantly appear and cancel out each other (in the vacuum). Yet something happened after the Big Bang expansion event that allowed that tiny 5% of matter to not get cancelled out (inflation?), and therefore we see suff. What happened to that 5% antimatter that should be out there somewhere?

timoteo -> RE: Dark matter (Oct. 27 2017 3:35:01)


What happened to that 5% antimatter that should be out there somewhere?

The generally accepted explanation is that this is due to CP violation (https://en.wikipedia.org/wiki/CP_violation). In short, the laws of physics are *different* for particles and anti-particles. So while matter and anti-matter were both produced in equal amounts in the big bang, interactions among particles subsequent to that quickly resulted in the elimination of most anti-particles.

Ruphus -> RE: Dark matter (Oct. 28 2017 7:22:03)


From what I remember dark matter is supposed to present 95%

Dark matter PLUS dark energy....I understand it as 25%+70% more or less. Empty space (expanding voids) would have more of the dark energy, and filled space having the dark matter halos that normal visible matter aligns itself with (so yes as you said it).

As a layman I feel this elusive "dark stuff"is pointing to a 4th dimensional (spatial not the confused for time dimension which is already part of 3D space-time) large hyperspace influencing our 3D visible realm...the 5% we observe and test just being the tip of the iceberg of the universe at large. I know there is no experimental evidence for this idea and is counter to the "curled up tiny"higher dimensional space of string theory models. But works for me!. Also could explain for quantum jumping, entanglement, etc.

"Dark matter PLUS dark energy....". Yes, I have been inexact. The more as the two present very different subjects.

Regarding quantum jumping (futures unhackable and immediate means of correspondence over any distance) and further dimension (which clueless as I am, spontaneously triggers an association similar to a kind of cohesion, which however based on electrical values shouldn´t adhere to dark matter, I suppose) these being white plains to me.

In respect of space and incident, I am still much too blown away by the thought of multiverse. Imagening that any of countless choices to any existing bits move would each produce another parallel universe of its own incident and again to realized choices and universes ...

Phew, as if the milky way hadn´t been challenging enough, in times before there was discovered that another galaxy existed, and then another one, and then tens and thousands and billions ... All contained in just one single universe as we "knew" it.

Not yet even remotely having come to picking up the fragments of my exploded little mind, now the megalo yesterday turning out to having been just an atom in the toenail of what ought to be the giant, and again, still could just be particle of the actual whole.

Life likes to demo us how presumptuous we tiny beings and minds are. Always topping our current overview endless of times over.

And already in mere times of the sole milky way, did the hasty philosophers on entry level conclude that vis-á-vis 20 billion years of time and 100 billion of suns, fate and history on earth shouldn´t matter more than a soap bubble.

Meanwhile even lesser as planets are being detected ...

Yet, a laissez-fair conclusion being prematurely careless in same ways as superstition. Not just because of comparable evolution within this universe staying rare like hen´s teeth. But simply just for the windings, strivings and sufferings that let to terrestrial status quo. Which again we have exterminated largely already and are about to desert very soon. Only just for mental disease of degenerated civilization.

From there relevant appearing: A rendering of energy source to state of no-brainer, a nano tech replicating any desired material object for all and sundry / hopefully stranding pharaos and their lever to destructive regime, and medical micro tech allowing people to enjoy the final relief from exploitation, witnessing democracy and humane surrounding in good health (and if wanted in chosen state of biological age), vertical farming, algae, artificial meat ... all to then let go what´s left of fellow creature and environment at that point in time and to free them from abrahamic subjection.

No matter how unfathomable and infinite the giant and eventual lushness we may be seeing out there: Past and contemporary havoc of ours stays just as pity as if the earth was the one and only planet that provided consistent enough conditions and past for advanced form of life.

To me presently looking up to the stars and possibly beyond is like wiping one´s diving goggles while piranhas eating your feet. Or like looking through a telescope while standing on a rock needle that´s left from a global erosion.

To my understanding, we need all the focus for halting the insanity.

jalalkun -> RE: Dark matter (Oct. 31 2017 0:18:50)


What happened to that 5% antimatter that should be out there somewhere?

Neil DeGrasse Tyson explains it this way: at the beginning photons spontaneously separated into pairs of matter and anti-matter particles which annihilated each other immediately after, and for unknown reasons there were photons that split into two matter particles. for each 1 billion anti-matter particles there were 1 billion and 1 matter particles, which means for each billion of particle pairs annihilating each other there was one excess matter particle.

timoteo -> RE: Dark matter (Oct. 31 2017 3:49:50)

Tyson is great, really. But did he say that? Conceptually he's correct, in that certain processes favor production of matter over antimatter, and that the asymmetry is very very small. But his use of pair production from photons as an example isn't strictly correct as far as I know.

The only processes which have been experimentally detected to exhibit CP violation are K0 and B0 decay. And perhaps there's a hint of violation in neutrino oscillations - some suggestive results were published earlier this year. CP violation is a strictly weak interaction process, and electromagnetic interactions like low(ish) energy gamma decay have never been observed to violate CP. Of course, in the extremely high energy range such as existed in the first fraction of a fraction of a second of the big bang, the weak and electromagnetic forces were unified, so this distinction doesn't matter if we're talking about that super-early period.

Gamma decay to two identical leptons would violate conservation of lepton number, and decay to two identical baryons would violate conservation of baryon number. Which is why we always see e.g. gamma -> electron + positron (specifically lepton + antilepton, or in general particle + antiparticle). The particle and antiparticle cancel each other out so combined they have the same net properties as the photon. And conservation laws of all sorts are thus maintained and all is well in the world.

The problem with attributing all of the matter/antimatter difference to CP violation is that the measured CP violation that we currently know about is too small to account for the entire difference. But we're still looking...

I am vaguely aware of several theories that propose additional mechanisms for matter/antimatter asymmetry, but they are all strictly theoretical with no experimental evidence to back them.

Ricardo -> RE: Dark matter (Nov. 3 2017 14:52:24)

Curious if the asymmetry is thought to have occurred before after or during the "inflationary period" in early moments of the Big Bang? It would make sense to me that in the moments space expanded faster than light, solving the current horizon problem puzzle, that certain virtual and other "destined for annihilation" pairs would have been denied their destiny accounting for a perceived imbalance of one or the other in our quadrant of observable space.

timoteo -> RE: Dark matter (Nov. 4 2017 3:33:25)

My post from a few days ago got lost with the foro troubles. In short, I did some research and found out there are actually three things required for matter / antimatter asymmetry. (Interestingly, this is attributed to A.D. Sakharov, Sov. Phys. JETP Lett. 5, 24 (1967)).

CP violation is just one of the required conditions. A baryon number violating process (not yet known, remains the stuff of theory) is another. Then "a departure from thermal equilibrium". I don't know what that refers to.

Anyway, this can all be found at http://pdg.lbl.gov/2017/reviews/contents_sports.html - scroll down to the section labelled "Astrophysics and Cosmology" and click on http://pdg.lbl.gov/2017/reviews/rpp2016-rev-bbang-cosmology.pdf
You want to start reading on page 17, section 22.3.6 "Baryogenesis".

Read about the Review of Particle Physics here: http://cerncourier.com/cws/article/cern/70136

The Review of Particle Physics publication on the PDG website is THE reference for things like this. It's published every other year and contains peer-reviewed summaries of the current state of all things in particle physics, with extensive references. It's available as an 1800 page PDF, or as individual smaller PDFs for each section (this is what I linked to above). Or if you're a real geek you can get the print version for free.

The matter / antimatter asymmetry arose "long" after inflation ended. By that, I mean inflation ended at about 10^-32 seconds after the big bang and antimatter didn't start to go away until about 10^-12 seconds after the big bang. The universe had to get cool enough for symmetry breaking (the differentiation of the four fundamental forces), then once that happened CP violation could occur in the weak force. There won't be any Niven-esque anti-matter star lurking anywhere in the universe though - inflation assures that the physical laws are the same all over, so the symmetry breaking and disappearance of antimatter took place everywhere simultaneously.

Ricardo -> RE: Dark matter (Nov. 4 2017 15:14:04)


The matter / antimatter asymmetry arose "long" after inflation ended. By that, I mean inflation ended at about 10^-32 seconds after the big bang and antimatter didn't start to go away until about 10^-12 seconds after the big bang. The universe had to get cool enough for symmetry breaking (the differentiation of the four fundamental forces), then once that happened CP violation could occur in the weak force. There won't be any Niven-esque anti-matter star lurking anywhere in the universe though - inflation assures that the physical laws are the same all over, so the symmetry breaking and disappearance of antimatter took place everywhere simultaneously.

Ah ok, got it thanks.

Last year I read about a "protophobic boson" that repeated experiments confirmed to be 17Mev implying a short ranged "5th nuclear force", but never heard more about it. Any news on that weirdness? Searches turn up same news as last year.

timoteo -> RE: Dark matter (Nov. 6 2017 8:02:06)

I hadn't read about that one. So I searched and found the preprint at https://arxiv.org/abs/1504.01527

A preprint is a paper that hasn't been published yet, but is made available to others so they can see details of results quickly without having to wait 6 months or more until after the peer review and publication. So the caveat is that this is not the exact paper that was published - there could have been corrections or additions in response to the peer review or editors' feedback. Sometimes preprints never make it to publication, if for example the authors withdraw the paper for some reason or peer review finds significant problems that can't be corrected.

I read the preprint. They seem to have a significant signal. Five standard deviations means that this is almost certainly NOT a statistical fluctuation. Everyone publishes signals of five sigma - it's the two-three sigma signals that get you in trouble by being wrong more than you expect :-) The size of the signal raises issues because this sort of experiment has been done thousands of times - even when it's not the subject of a paper, experimentalists will do things like measure the angular correlation of decay products just to see if there are problems with their detectors. You measure everything you can, especially well-known quantities, then you check and recheck, to give you confidence that you have accounted for all the systematic errors inherent in measurement. Only then do you have some confidence that anything new you find is real. That's why it's odd that a signal of this magnitude hasn't been seen before.

Even then, experiments find "new" stuff all the time. Every experimentalist has a story about someone who got burned by publishing or almost publishing a wrong result. But that's getting less likely these days with larger experiments and everyone acting as a check on everyone else's enthusiasm to rush to publication. Back when experiments were three guys at a particle accelerator, things were different.

I call this a "cold fusion" moment - that was also a big signal that was totally wrong - it couldn't be reproduced at all by anyone. I was there when the cold fusion paper was first presented at a conference (it was announced way beforehand, via press conference, not even a preprint - they wanted to be sure to secure the patent rights ...). At least one of my colleagues went out and bought stock in palladium (essential for the result), on speculation that it was a real result. He lost a lot of money ...

So on this one I'm saving my judgement until it's reproduced. I've seen hundreds and hundreds of tantalizing results. I've been on an experiment where we found "new" stuff that we didn't publish because it just wasn't a large enough signal or because we couldn't see the same thing in a completely different dataset. I've seen many papers that hint at the detection of supersymmetry, or at the detection of a fifth force, or at the discovery of a new particle, or all sorts of other things. If they're real, someone else will be able to measure the same thing, especially for an experiment like this where they don't need an extreme setup (for example, don't need a multi-million dollar experiment at the world's largest particle accelerator ...) Correlation of e+e- pairs from an essentially at-rest system is an experiment I did in one of my undergraduate physics lab courses. I'm not saying this experiment was at that level, just saying reproducing this result will not be hard to do if it's real.

Even if it's reproduced, there's really no theoretical interpretation yet. Sure, there are some preprints I found that suggest this signal could be caused by this or by that, but the problem with a lot of these theories is they can only *analyze* and say whether something is consistent or not, they are no good at *predicting* what the experiment should see. To me, they always read like artificial constructs needed to fit the fact, but not motivated by anything. (A totally made-up example would be "well, if there were 12 types of Higgs bosons, then we could conceivable see this sort of result.") A theory that interests me would have to provide some means of testing, not just analysis. It would say, if this theory is true, then it would explain the results AND you should also see xxx is a different experiment.

This experiment was set up to try to detect dark matter. They concluded that they had evidence for a light gauge boson, which is a force-carrying particle, hence evidence for a 5th force like you said. I'll be interested in seeing whether it can be confirmed. It's been a year, so either no one is trying (I doubt that, given the potential importance of the find) or they haven't managed to reproduce it yet and are still trying, checking and rechecking everything - you have to be a lot more careful when disproving something ...

Ricardo -> RE: Dark matter (Nov. 11 2022 19:20:09)

This guy has convinced me…though he admits Euclid evidence might prove him wrong or on the right path, but it certainly makes more sense than other stuff I have heard. The whole thing is interesting but for Dark matter answer check from 48:00 or so.

Also if anybody has seen the 2018 paper he references and any problems with this simple idea he does not address?

Ricardo -> RE: Dark matter (Nov. 16 2022 12:01:01)

Well, nobody cared much for that. I did find more explanation here starting from 15 min or so. It seems that we have to accept that RH massive neutrinos get mass “inherently” rather than via the Higg’s field like all other massive particles. He claims it is fine (see-saw??), but I would like to understand how other stable particles, if any, have mass from that method. At first I was thinking of “photon mass” which is from momentum but this is very different anyway. Also the cooper pair “boson like” phenomenon of electrons in superconductivity has weird things at low temp going on, but still don’t get how he is justifying this situation. Also, it is known that Neutrinos “change flavor” so to speak (almost invoking the “one electron” theory back into things) while moving, and he does not address that issue either. At least they can check masses for the light nuetrinos and eventually find out if one is massless or NOT.

One thing I was thinking about is the supposed “graviton”. So the forces exchange bosons, more or less of them shows relative strength. But for gravity the Higgs provides mass….however the mass of the Atom contains only some small percentage of what Higgs gives to the quarks. The rest of “Atomic mass” that warps space comes from Energy in the Atom…quarks moving around very fast, etc., so i think the guy questioning Turok about how the Neutrino could warp space if it did not get mass from the Higgs is relevant…but I think if atoms need some 90+% of graviton exchange (or whatever warps space due to the presence of mass/energy), then a similar thing can be said about these RH Neutrinos? Perhaps this is the point i am missing about this “large mass” that is not acquired from Higgs???

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