Talk:Dark matter

If all the light energy photons in transit from the 100,000,000,000 stars added together would equal to what?

Essay archived.
The following discussion has been closed. Please do not modify it.
Light cannot go round corners it is straight, a star looks like a dot in the sky but the light is emitted all around but cannot be seem from the side of the star only when looking direct we see the light. if we could see light from the side the night sky would be lit up as the light travels out from every star an crosses the universal plains. The universe is connected through mass ropes of light that can't be seen. What is the universal mass equation of all the light in transit? If all the masses plus the light that is in constant transit since the dawn of time from 100,000,000,000 plus stars. Would it equal the missing matter e.g.: if a star was spaced atom by atom in a straight line how far would it go before it was invisible to the eye meaning mass can appear missing when it is right under your nose. And as the visible universe is 92billion light years across and some say its bigger to the point that 92 billion light years is an atom size to its real size. That is a lot of light rays in transit, a lot, and this may add to filling in those numbers, and if it does. I will write some extra notes, Law of force every action is a reaction, The impact of light upon all other celestial bodies push everything away so creating and adding to a forever expanding universe. So who has worked out does light have a force when hitting matter, even if infinity small would it move an object with zero resistance? photons light described as rope in the shape that appears to be a series of very small multiple magnetic fields each one the size of the frequency that pulse another ant link maybe like coil induction effect to connect from A to B then even an X particle runs, pushed or pulled to its destination. —Preceding unsigned comment added by 77.99.29.196 (talk) 06:42, 9 March 2011 (UTC)

This is not the place to present your own views on how photons and dark matter work.

It's also very easy to place an upper bound on the mass of the photons stars emit over their lifetimes: Less than about 1% of the rest mass of the stars, as it's derived from fusion of the stars' fuel. The mass of dark matter is vastly greater than this, per the article. --Christopher Thomas (talk) 07:02, 9 March 2011 (UTC)

Remind you that according to the current standard model of particle physics photons are massless, that's why they travel at the speed of light, otherwise, according to general relativity, it would be necessary a lot more than a quanta pack of energy to move at that speed.Wcris (talk) 18:08, 25 June 2011 (UTC)

Role of Dark Matter/Energy in the Kuhnian development of physics

My strong sense is that dark matter/energy are a reification of fundamental problems in modern physics, i.e. gravity + the Standard Model. As I've put on Higgs Boson and it's never been challenged, dark matter/energy is not (except as a metonym for the observed discrepancy between that theory and observation) a part of any accepted (or FTM, SFAIK proposed) theory of physics, although there are various conjectures and speculations which fall short of same. This aspect doesn't seem to be fully enough developed in the article as it stands now nor do I see commentary in the talk archives about same but may have missed something. Lycurgus (talk) 16:08, 6 May 2011 (UTC)

Look up lightest supersymmetric particle. We have strong reasons for believing supersymmetry happens, and it predicts that there will be at least one new stable massive particle. That's a prediction of dark matter.

Also look up big bang nucleosynthesis. The fact that the element ratios come out right if and only if there's a lot of non-baryonic matter around also predicts the existence of dark matter.

You can make a stronger argument for dark energy being a label for an unknown rather than a specific thing, but dark matter - the subject of this article - is much better-understood. --Christopher Thomas (talk) 17:14, 6 May 2011 (UTC)

Yes, thanks for illustrating the issue, pieces parts that don't add up to anything. My point is that the article should show, more than it currently does, the thing for what it is and not commit the fallacy of assuming that it describes a physical reality rather than an artifact leading to a more complete understanding of nature in which it might or might not continue to be so regarded as for example in the classic cases such as phlogiston, the subliminiferous ether, etc.. Lycurgus (talk) 20:39, 6 May 2011 (UTC)

Most scientists consider the evidence for dark matter persuasive (and specific enough to greatly narrow down what it is). Alternatives are already noted in the article. Giving them more prominence would violate WP:UNDUE, as the vast majority of textbooks and scientific literature assumes a) that it exists and b) that it has certain properties (usually that it's massive particles that interact via the Weak force, sometimes that it's massive non-interacting particles). --Christopher Thomas (talk) 03:56, 7 May 2011 (UTC)

You're not getting my point which I've explained above. Wait for someone else to comment and respond to them (or not as you please). Lycurgus (talk) 08:06, 7 May 2011 (UTC)

The problem here is that your Kuhnian philosophy is considered crackpot stuff by others. Regardless of whether you are right or wrong, you need to find some published source that expresses the view, and then propose text that describe your view in terms of whoever is on the record with that view. Roger (talk) 17:38, 7 May 2011 (UTC)

One might think that you were Phyllis' son :) In any case the sociology of science established by Kuhn and others is the current received and mainstream, and more or less sole academically accepted approach to the subject. Lycurgus (talk) 23:57, 10 May 2011 (UTC)

Did you find any Kuhnian sources for your dark matter ideas? Yes, Kuhn has a following among academic non-scientists but a lot of astrophysicists think that he was a crackpot. Roger (talk) 21:10, 13 June 2011 (UTC)

Alteranative theory on the composition of dark matter

Since I worked out this theory myself I could not add it to the main page

Another theory states that dark matter could be normal matter stripped of all its electrons due to interaction with positrons. This would mean that dark matter would not be able to interact with photons. This theory states that dark matter could be 'cold plasma', similar to normal plasma in that it has lost its electrons but dissimilar in the way it has lost its electrons and that normal plasma is energised with radiation and constant re-interaction with electrons. This theory further states that because dark matter has no electrons it cannot form bonds and exists as individual atoms.

Date 16/5/11 —Preceding unsigned comment added by Kishanparekh (talk • contribs) 13:27, 17 May 2011 (UTC)

This violates OR as noted in the talkheader. The place for this is in your userspace. There's no dearth of conjectures about the subject. That the observed universe is inside something and that the "dark matter" could be gravitation or other forces from that containing universe, although sourcable, isn't in either. Also it's false that matter stripped of electrons wouldn't interact with photons. Threads like this one are just exceptions to not touching talk space edits of others. Lycurgus (talk) 20:00, 18 May 2011 (UTC)

Sorry about that but I am just a 'slightly' over-average inteligence Fourteen year old, and I did watch a documentary about the origins of the universe wich said that the early universe had such high temperatures that atoms and electrons hadn't joined so the universe was a dark place because of that, I also read about plasma and about electrons forming bonds in atoms, so I used my common sense to put two and two together and got this theory. but I have put a copy on my userspace Kishanparekh (talk) 18:49, 22 May 2011 (UTC)

Normal matter stripped of electrons would be protons+neutrons which would strongly interact with photons. There is also the additional complication of where did these positrons come from and why positrons alone not positrons+protons. Mtpaley (talk) 01:27, 3 November 2011 (UTC)

Lack of evidence for WIMPs

The weakly interacting massive particles article is replete with various failures to detect any evidence of the WIMPs, which involve a certain amount of wishful thinking about supersymmetry that might not be all that compatible with Occam's Razor. But Frampton says primordial intermediate mass black holes are consistent with halo rotation, isotope ratios, microlensing, and wide binary observations, and at least two of them have been detected so far. Would anyone object to listing the black holes before the WIMPs for the top two theories in the introduction? 99.39.5.103 (talk) 11:38, 18 May 2011 (UTC)

Yes, I would object, because despite the lack of evidence, WIMPS are still the favorite candidate. That's not something we can overrule here, no matter how good the argument against WIMPS is. Also, I remember reading some criticisms of Frampton's idea, so it's not that you have a DM candidate without problems here. Count Iblis (talk) 14:42, 18 May 2011 (UTC)

I'd be very interested in reading those criticisms. The idea that dark matter is black holes is not unique to Frampton (e.g. the NASA source about them doesn't mention him at all) he's just been taking the lead in pointing out that all observations are consistent with them. WIMPs, on the other hand, currently have exactly zero observational evidence. Just because a lot of people are looking for them doesn't necessarily mean they are anyone's favorites. 99.39.5.103 (talk) 16:28, 19 May 2011 (UTC)

My understanding is that black holes were ruled out as dark matter candidates by gravitational microlensing searches (along with most forms of massive compact halo object). Furthermore, Big Bang nucleosynthesis only produces the observed distribution of elements if you have quite a lot of dark matter that doesn't interact strongly with normal matter. Black holes, on the other hand, would interact with normal matter, so they don't address the BBNS problem. The fact that the amount of matter needed for nucleosynthesis to match observations is also very close to the amount needed to make galactic rotation curves and struture formation work is strong circumstantial evidence in favour of WIMPs or completely sterile particles as dark matter. --Christopher Thomas (talk) 00:29, 27 May 2011 (UTC)

Paul Frampton says microlensing observations are consistent with IMBHs, and if they are primordial then that addresses the BBNS deuterium-lithium ratio issue. Why would post-big bang interactions affect the nucleosynthesis ratios? I'm not sure that black holes aren't sterile, since they are equal opportunity gravitational attractors. I think we should start with the microlensing data. Where are the various scenario predictions compared with observations in the literature? 12.238.13.194 (talk) 01:51, 28 May 2011 (UTC)

I am referring to primordial black holes. Non-primordial holes would be composed of baryonic matter (not the non-interacting dark matter BBNS needs in order to work), and so don't address that part of the dark matter problem. During the BBNS, primordial black holes would act as strongly-interacting particles (large scattering cross-section if nothing else, and probably a substantial absorption cross-section), and the whole point of dark matter in BBNS is that some of the universe's energy density goes into matter that does not participate in BBNS interactions (not even by scattering).

With regards to microlensing, feel free to do your own literature search, as it's not a field I follow (I'd just seen the results of a couple of searches many years ago with statements about what they ruled out). The acid test of whether Frampton's view is considered plausible is the number of unrelated researchers citing his work (as with most other research). It's probably worth looking at those papers as well during your search, as some of them will be written by people who disagree with his assumptions or calculations. --Christopher Thomas (talk) 02:09, 28 May 2011 (UTC)

This article is worth reading Count Iblis (talk) 23:45, 21 June 2011 (UTC)

It makes serveral strong claims, but I don't see how it addresses the Big Bang nucleosynthesis requirement for dark matter. Claiming a critical density of stellar mass black holes really should have resulted in very obvious effects, too - that's about a hundred black holes for every star, and they'd be expected to follow the same distribution in galaxies as normal stars do! Particle-based dark matter, by contrast, isn't expected to clump on scales smaller than a galaxy, explaining why it's distributed as a more-or-less uniform halo rather than mingling with the disc. The halo distribution is important, as it's needed to solve the galaxy rotation problem; more star-like objects in the disc doesn't do it.

Long story short, I'd want to see other articles supporting this one before considering it evidence of a change in the prevailing view of the scientific community. By all means add it to the primordial black hole section, though. --Christopher Thomas (talk) 06:37, 22 June 2011 (UTC)

Hawkins (2011) discusses microlensing in great detail (and passed peer review so that cite is better than arxiv's). Is there any support for the idea that primordial black holes would influence nucleosynthesis ratios? My understanding is that they would not, which is why dark matter must be mostly primordial black holes if it is mostly black holes. Frampton et al (2010) agrees with you, contrary to Hawkins' assertion of entirely stellar mass black holes, with regard to the galaxy rotation problem, in that there was probably a uniform distribution of primordial black holes, the most massive of which formed galatic cores, and the majority of which are intermediate mass. Since Frampton also passed peer review I intend to replace your deletion, with black holes first, replacing his conference proceedings cite. 76.254.22.47 (talk) 20:29, 24 June 2011 (UTC)

Get agreement from other editors here before replacing it, as - both here and elsewhere - you seem to be the only editor pushing Frampton's work, with objections from others (here and at Talk:Gamma-ray burst). For the record, I do not feel such a change would be wise, as - from what I can tell - the vast majority of the scientific community considers new particles to be the most plausible explanation, with black holes already given sufficient weight as a hypothesis. --Christopher Thomas (talk) 20:53, 24 June 2011 (UTC)

On what sources do you base your opinion? All of the WIMP researchers say in all of their reports that they have no evidence for the new particles that they are looking for. Perhaps I am the only editor who has read Frampton and his distinguished co-authors' work. If you assert that the "vast majority" of scientists believe something, the burden is on you to provide sources supporting that assertion. 76.254.22.47 (talk) 23:18, 24 June 2011 (UTC)

Another important point to consider from Lacki and Beacom (2010) is that postulated WIMPs would gravitate towards and collect inside black holes, even if black holes were very rare. So, you can either believe there are black holes at the centers of galaxies, or more than a few percent of dark matter is composed of WIMPs, but not both. In hindsight it seems so simple, but a generation of cosmologists got hung up on a fanciful interpretation of a single data point from the very ambiguous bullet cluster. 76.254.22.47 (talk) 17:23, 25 June 2011 (UTC)

Im certian someone's thought of this but i dont know where to look.

So, Im not a scientist. At all, in any sense of the word. But I was wondering if this effect could be compensated for, by surrounding the universe with void (which must fill) that pulls thigns in all directions, so gravity would increase toward the void at all times, because of how much matter would be shot continually into it, until heat death occurs.

I am almost definetly wrong and would be kinda astounded if I had any part of that even vaguely correct. So dont worry too much about that. What im really wondering is if theres any...simpler way to explain the effects of dark matter, that wouldnt be too abstract. It makes sense as a not-totally-correct way to visualize things for me, but I think others would have better views.

Additionally however, if someone HAS postulated my idea, id love to read about it. whether serious or mostly-disproven (cant disprove anything :( ) its still very interesting. Sorry for bringing this up here but I cant even figure out where to start googling for this sort of thing. 74.128.56.194 (talk) 20:09, 13 June 2011 (UTC)

Oh, Edit: I tend to take information, and compile it into a way that will have nothing to do really with the actual idea, but will still vaguely fit together. So feel free to criticize, as I cant always tell when when ive fallen off the deep end. The crazy pills are labelled poorly. 74.128.56.194 (talk) 20:13, 13 June 2011 (UTC) 74.128.56.194 (talk) 20:09, 13 June 2011 (UTC)

Dark vs transparent

section 2.0--"from background galaxies since Dark Matter has the ability to deflect light."

on the other hand we have in the introduction: "The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent." This seems contradictory or at least needs explaining.24.7.28.186 (talk) 04:59, 21 June 2011 (UTC)

"Dark" in this case means "not emitting light", rather than absorbing light. I've updated the introduction to clarify this. As for deflecting light, that refers to gravitational lensing - bending of light by the gravity of a large amount of dark matter - rather than scattering events. I've attempted to make that text clearer, too. --Christopher Thomas (talk) 06:38, 21 June 2011 (UTC)

Don´t emit light? Do you mean visible light? Because this article says Dark Matter is believed to emit gama rays at specific frequencies, although elusive to detection so far. So, not to be confused with black holes darkness, derived form light being pulled to its event horizon due to the enormous gravitational field. Wcris (talk) 18:20, 25 June 2011 (UTC)

matter and antimatter as a source

From quantum mechanics we know that a perfect vacuum can not exist; particles and their anti versions popup into reality all the time and annihilate each when colliding. I dont know the frequency of this, but could it be enough on a grand scale to have a mass presence ?

All particles have mass even those particles that live shortly, on the large scale of light years together they could represent a large mass

Reason why posting this question here is because one should also ask how empty is empty; if space cannt be empty would that be enough for dark energy/mass, or is more mass needed ? (in an article like this the nature of empty space sohuld also be discused) 84.107.182.108 (talk) 21:43, 4 September 2011 (UTC)

What you are referring to is called vacuum energy, which can be thought of as the energy density of virtual particles in empty space. Because vacuum energy is tied to space itself, it doesn't move or clump the way dark matter does, and so cannot be dark matter. Vacuum energy is one of the possible explanations for dark energy, but bear in mind that the idea of virtual particles appearing and disappearing doesn't necessarily reflect what's actually happening - it's a mathematical artifact of perturbation theory. So it's possible to draw misleading conclusions from that idea.

Further questions about this should go to the science reference desk. This page is for discussing specific changes to the article, not general questions. --Christopher Thomas (talk) 22:23, 4 September 2011 (UTC)

baryonic?

In the section "Baryonic and nonbaryonic dark matter" the article refers to "primordial black holes". I dont see how a black hole could be classed either as either baryonic or not baryonic - a black hole is not composed of subatomic particles . To use a self referential justification the first sentence of baryonic in wikipedia is "A baryon is a composite particle made up of three quarks". Clearly this is not the case for a black hole, going beyond that I hit the wikipedia wall of justifying a claim that is so obvious that nobody writes it down.Mtpaley (talk) 20:45, 26 September 2011 (UTC)

I reworded it and removed "baryonic" Bhny (talk) 21:43, 26 September 2011 (UTC)

In this context, "baryonic dark matter" (which is arguably a misnomer) refers to matter that does participate in electromagnetic and strong force interactions, while "non-baryonic dark matter" refers to matter that only interacts via the weak force and gravity. I'd classify black holes as acting like baryonic dark matter in this context, but in practice it's best to just follow the conventions used by references that discuss them. --Christopher Thomas (talk) 23:49, 26 September 2011 (UTC)

There seems to be some variability in whether primordial black holes are considered to be baryonic or non-baryonic dark matter, depending on the context. They are non-baryonic in that they don't participate in Big Bang nucleosynthesis, but they may be included with baryonic dark matter for experimental / observational purposes because they are constrained by weak lensing like MACHOs. A quick search turns up at least one source Hawkins 1988 that classes them as non-baryonic, and one Bergstrom 2000 that classes them as baryonic. As Christopher Thomas correctly points out, the best thing is to follow the sources. In this case, the sources are at least somewhat mixed. It's not clear to me that there's a preponderance of usage one way or the other. --Amble (talk) 17:13, 28 September 2011 (UTC)

Molecular hydrogen as dark matter

I am not a cosmologist but I have a question that does not seem to be addressed in the article. The following two paragraphs are a preface to my question.

Hydrogen is the most common element in the universe. At the average temperature of 3K any hydrogen atoms which have interacted should end up as molecular hydrogen. Given an age of 14 billion years, most of the hydrogen in existence outside of stars and areas of intense radiation should have interacted and exist in the molecular form.

I understand that molecular hydrogen is very difficult to detect due to cancelling spins and a small or non-existent dipole moment. The seemingly obvious candidate for dark matter is large quantities of molecular hydrogen. This molecular hydrogen may reside in great quantities surrounding the luminous centers of galaxies and in intergalactic space and could well account for 95% of the matter in the universe.

Question: Why do cosmologists insist that the dark matter must be some unknown exotic form of matter that has never been directly detected instead of molecular hydrogen?

It seems to me that a very good reason is necessary to propose an exotic solution when molecular hydrogen seems to fill the requirements quite well. I think that ignoring this issue leaves the article incomplete. When discussing scientific matters, it is more important to understand why scientist believe what they do, than the fact itself that most scientist believe something.

I apologize if I have missed something that should be obvious. Carl Hitchon (talk) 16:36, 29 September 2011 (UTC)

This is already covered in the article. About 1% of the universe's mass is stars. About 4% is normal matter that is not stars. Most of that is primordial hydrogen and helium (the hydrogen may be atomic or molecular depending on whether it's dense enough to combine into molecules). The "Filaments" thread on this page describes the discovery of structures made of this.

The reasons why most dark matter (23% of the mass of the universe) cannot be normal matter are also outlined in the article. The big bang nucleosynthesis only gives the correct abundances of hydrogen, deuterium, helium, and lithium if some of the matter in the universe is an exotic, non-interacting type. Non-interacting dark matter also clumps differently than normal matter: normal matter in the galaxy is concentrated in the disc, whereas the dark matter halo has a more or less spherical distribution. Molecular hydrogen would follow the distribution of normal matter (the distribution happens because clouds of normal matter can collide with each other but dark matter passes through itself).

I hope this addresses your question. Further questions should probably go to the Reference Desk, as this page is mostly for requesting changes to the article itself. --Christopher Thomas (talk) 18:20, 29 September 2011 (UTC)

Thanks for your prompt response Christopher. I suspected that the BB theory's nuclear synthesis argument leads to the need for the exotic matter instead of ordinary cold hydrogen and you have confirmed that. This line of reasoning is not obvious in the article since molecular hydrogen is not mentioned, let alone the difficulty of detecting H2, if H2 is in fact the dark matter. It leaves the impression that we must look only for zebras without first eliminating the possibility of horses.

I think it's important for the public to understand the difference between inferences made from theory versus what is known more directly by observation. For example we can easily detect CO so it's existence cannot be denied but I don't think that is possible for H2. The chain of reasoning that leads to the requirement that dark matter is non-Byronic is complex and based on theory, not direct observation (as far as I know).

Does the BBNS-predicted abundance of lithium in fact match observation? I'm not trying to start a debate. I just believe the article could be a bit more upfront about it's suggestion that most of the matter in the universe is composed of mysterious non-interacting particles that have never been detected. It is a surprising proposal. Although the article does mention BB cosmology as a basis for the belief in a relatively small amount of ordinary matter, there are difficulties with that theory.

If there are observations that prove that the abundance of H2 is insignificant, then that material should be mentioned and referenced. Under "Alternative Theories" H2 is not mentioned. Does that mean it has been ruled out by observations? Other than this I think the article is fair in pointing out some of the problems with the exotic particle theory such as the "cuspy halo problem". Thanks again. Carl Hitchon (talk) 19:18, 30 September 2011 (UTC)

Molecular hydrogen, like neutral atomic hydrogen, can be detected from its absorption lines. Astronomers have been mapping the interstellar (and intergalactic) medium for quite some time, so the abundance is reasonably well known. Neither the big bang nucleosynthesis nor the galaxy rotation curve observations can be explained by normal matter, per above, and we already have direct observation of concentrations of non-interacting matter through gravitational lensing surveys.

The article as-written does not seem to mention BBNS arguments. This is very odd, as it's an important piece of evidence. It's described at Big Bang nucleosynthesis#Deuterium. If I have time, I'll add a sub-heading about it to the "observational evidence" section. Any of the other lurkers here are welcome to add it instead, as I'm rather busy at the moment. --Christopher Thomas (talk) 22:14, 30 September 2011 (UTC)

Can someone supply references which demonstrate that the abundance of H2 (particularly in halos) is reasonably well known through absorption line detection? Please exclude data derived from the CO proxy since it is based on complex assumptions. Carl Hitchon (talk) 15:44, 1 October 2011 (UTC)

You can check through the references at interstellar medium if you like, but the purpose of this page is to discuss improvements to the article, not to answer questions or to address your own conjectures about what dark matter is (per the banner at the top of this page). Questions normally go to the Reference Desk. --Christopher Thomas (talk) 18:48, 1 October 2011 (UTC)

The intro is way too long and the Composition section is way too short

According to WP:LEAD#Length we shouldn't have introductions over four paragraphs, and three should do fine for an article of this size. Why is the very brief Composition section all about WIMPs, sourced to a preprint, and doesn't mention the leading MACHO theories? Where is the mention that LHC has provided zero evidence of supersymmetry or WIMPs after almost two years now? Dualus (talk) 22:28, 24 October 2011 (UTC)

I created a new "Overview" section and moved most of the intro there. Bhny (talk) 16:53, 27 October 2011 (UTC)

(almost) incompatible

"though many scientists remain skeptical since negative results of other experiments are (almost) incompatible with the DAMA results if dark matter consists of neutralinos"

Someone want to explain just what the heck "almost incompatible" means? It's almost wrong (which means it's still right). Almost incompatible would still be compatible. Almost going fast means it's still going slow. Almost won means you still lost. So why is "almost incompatible" used as a reason to shoot something down? Sounds like the statement is almost right. — Preceding unsigned comment added by 220.248.48.66 (talk) 03:50, 29 October 2011 (UTC)

Contribution of Dark Matter to the mass of the Universe

In the first paragraph: "Dark matter is believed to constitute 83% of the matter in the universe.[2]"

This should read: "Dark matter is believed to constitute 23% of the matter in the universe.[2]" 130.88.173.52 (talk) 17:28, 21 November 2011 (UTC)

It's 23% of the mass, but 83% of the matter. Dark energy has mass, but does not count as matter. --Christopher Thomas (talk) 23:17, 21 November 2011 (UTC)

But the unicorns

Why? WHy?