Dark Matter. Its existence is still not 100% certain, but if it exists, it is exceedingly dark, both in the usual sense — it doesn’t emit light or reflect light or scatter light — and in a more general sense — it doesn’t interact much, in any way, with ordinary stuff, like tables or floors or planets or humans. So not only is it invisible (air is too, after all, so that’s not so remarkable), it’s actually extremely difficult to detect, even with the best scientific instruments. How difficult? We don’t even know, but certainly more difficult than neutrinos, the most elusive of the known particles. The only way we’ve been able to detect dark matter so far is through the pull it exerts via gravity, which is big only because there’s so much dark matter out there, and because it has slow but inexorable and remarkable effects on things that we can see, such as stars, interstellar gas, and even light itself.
About a week ago, the mainstream press was reporting, inaccurately, that the leading aim of the Large Hadron Collider [LHC], after its two-year upgrade, is to discover dark matter. [By the way, on Friday the LHC operators made the first beams with energy-per-proton of 6.5 TeV, a new record and a major milestone in the LHC’s restart.] There are many problems with such a statement, as I commented in my last post, but let’s leave all that aside today… because it is true that the LHC can look for dark matter. How?
When people suggest that the LHC can discover dark matter, they are implicitly assuming
- that dark matter exists (very likely, but perhaps still with some loopholes),
- that dark matter is made from particles (which isn’t established yet) and
- that dark matter particles can be commonly produced by the LHC’s proton-proton collisions (which need not be the case).
You can question these assumptions, but let’s accept them for now. The question for today is this: since dark matter barely interacts with ordinary matter, how can scientists at an LHC experiment like ATLAS or CMS, which is made from ordinary matter of course, have any hope of figuring out that they’ve made dark matter particles? What would have to happen before we could see a BBC or New York Times headline that reads, “Large Hadron Collider Scientists Claim Discovery of Dark Matter”?
Well, to address this issue, I’m writing an article in three stages. Each stage answers one of the following questions:
- How can scientists working at ATLAS or CMS be confident that an LHC proton-proton collision has produced an undetected particle — whether this be simply a neutrino or something unfamiliar?
- How can ATLAS or CMS scientists tell whether they are making something new and Nobel-Prizeworthy, such as dark matter particles, as opposed to making neutrinos, which they do every day, many times a second?
- How can we be sure, if ATLAS or CMS discovers they are making undetected particles through a new and unknown process, that they are actually making dark matter particles?
My answer to the first question is finished; you can read it now if you like. The second and third answers will be posted later during the week.
But if you’re impatient, here are highly compressed versions of the answers, in a form which is accurate, but admittedly not very clear or precise.
- Dark matter particles, like neutrinos, would not be observed directly. Instead their presence would be indirectly inferred, by observing the behavior of other particles that are produced alongside them.
- It is impossible to directly distinguish dark matter particles from neutrinos or from any other new, equally undetectable particle. But the equations used to describe the known elementary particles (the “Standard Model”) predict how often neutrinos are produced at the LHC. If the number of neutrino-like objects is larger that the predictions, that will mean something new is being produced.
- To confirm that dark matter is made from LHC’s new undetectable particles will require many steps and possibly many decades. Detailed study of LHC data can allow properties of the new particles to be inferred. Then, if other types of experiments (e.g. LUX or COGENT or Fermi) detect dark matter itself, they can check whether it shares the same properties as LHC’s new particles. Only then can we know if LHC discovered dark matter.
I realize these brief answers are cryptic at best, so if you want to learn more, please check out my new article.
79 Responses
I know this is shot in the dark (no pun intended) but could there be 2 kinds of matter: a) one that has a dualist wave-and-particle-nature and b) one that (all but) never gets localized and thus never or seldom bumps into other particles.
Like electrons can diffract in a double slit and yet hit the surface of paper behind it. Maybe it is more difficult (or impossible) for the dark matter to get localized?
No?
This suggestion is just another way of stating that dark matter interacts weakly with normal matter. What does it mean to ‘get localized’? Well that’s just being ‘measured.’ Being measured is basically interacting with something. So ‘having problems getting localized’ just means the particles don’t interact strongly with stuff.
However dark matter has another property; it cannot lose thermal energy (cool down.) Dark matter *has* to be ‘localizable’ by gravity or it wouldn’t clump as it does. But it can’t emit energy or it would clump into ‘dark matter stars’ or other such condensed bodies.
Protons were already burnt out, cannot cool down. Gluons was said to be massless. Classical physics was started in electromagnetic field with photons as masless. Higgs mechanism was intended to gluons.
Only massive higgs can decay to photons (EM radiation). But momentum energy (some gravity mechanism) + very short planck scale time interval, decays to dark matter ? …
The Higgs mechanism was intended to explain why many (but not all) particles have mass. The electron say and W boson. We understand pretty well how protons get their mass, the strong force.
Massless particles cannot decay at all, to anything, to do so would break the speed of light. As for dark matter we’re not sure what could decay into it, if anything.
Matt, let me rephrase my question–what physical substance might dark matter be composed of if not particles? What else is available for making matter?
Thank you for inquiring about my work. The best example is probably a paper submitted to the International Journal of Theoretical Physics.
http://vixra.org/pdf/1209.0004v1.pdf
It was motivated by the discovery that the gravity model I’d been working on—whose premises differ greatly from Einstein’s, nevertheless—predicts a maximum force of the same value as that derived from GR.
[Abridged by host to remove inappropriate material.]
It seems to me that your reasoning for the experiment you propose is premature. Do you have evidence that measurements of precisely timed satellites (such as gravity probe B), moving in the gravitational field of the Earth and the Moon INSIDE the Earth-Moon system, would not have an altered result? In other words, you should be able to say what the fields are when you are in the interior of a *system*, not just the interior of a solid body, and check that existing satellite orbits are consistent with these formulas.
If you are unable to do this because you only have equations for spherically symmetrical bodies, then I think you have a very weak argument. It’s not clear you have sensible equations that, for instance, conserve energy and momentum.
Independently of this, I have no objection to someone doing a motion-in-interior experiment, and would support a proposal to perform it as long as (a) it is very inexpensive, and/or (b) there is at least one other thing for which it is useful and for which there is a stronger argument than the one you give. If you want someone to do an expensive experiment, such as one that involves a satellite, you need to prove, beyond doubt, that you have a consistent set of equations, and that no existing experiment already rules it out.
As your opening premises imply, the validity of modern cosmology—which has come to include large quantities of exotic dark matter—depends on the validity of GR.
The large physical domain of GR encompassed by the interior solution has not been tested with regard to gravity-induced motion. Static and seismological measurements have been made, yes. But nobody has ever seen one body fall through the center of another body due to the gravity of only those two bodies.
The latter observation could be made by doing the experiment that Galileo proposed, with laboratory-sized bodies, of course. This is the experiment whose apparatus I have called a Small Low-Energy Non-Collider and that Larry Smalley has reviewed in the NASA Technical Memorandum linked here:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750014902.pdf
I have never proposed drilling a hole through the Earth. That the host would suggest that I have indicates just one of the many ways that he has misunderstood and underestimated my work..
What “work“? Show me the work, and we can discuss. The paper you linked to here is a scientific paper by somebody else, proposed to measure something else. And if you don’t want people to think you a crackpot, then stop acting like one, and also, stop calling this experiment a “Small Low-Energy Non-Collider”. Almost every experiment in my physics department is a small, low-energy, non-collider experiment.
p.s. and I recommend you not send cutesy little advertisements of your “work” to physics departments. [Can you imagine Einstein doing that?!] Your reputation was destroyed by that action. (I should be clear — your sense of humor was appreciated. But your scientific reputation? Trashed.)
Anything associated with NASA is trash in my opinion. And I have 20 years of work to back me up.
I don’t know, is the Curiosity rover trash? Say what you like but NASA’s done some solid science and engineering.
In order to form a disk under the influence of gravity particles must be able to ‘bump into’ each other and emit energy. When normal matter ‘cools’ it initially is a cloud shape, a sphere. Bits of it are moving in all directions around the center. As they bump together they start cancelling out their movements; bits moving up cancel bits moving down, left bits cancel right bits and so on. The cancelling is done by the emission of EM radiation (Light, IR, radio waves…) This tends to move all the matter to the center.
However in any clump that wasn’t perfectly made by god himself there’s going to be an ‘excess’ of movement in one spinning direction. (Also in a ‘line’ direction which means the cloud will not be sitting still but moving.) Some movement won’t get cancelled out and so the cloud won’t be able to squash down in one 2D ‘spin thing’. This is how we get disks in galaxies and stars. (In 4 dimensions you end up with TWO disks, 6 you get 3…)
With dark matter particles can’t cool. Gravity keeps trying to pull it towards the center but the motion can’t get cancelled out. DM stays all puffy like a cloud of steam.
Concerning the reasons given for deletion of a link in my previous comment, I should respond as follows:
a) My “individual idea” coincides, essentially, with Galileo’s. Having been accused of advertising that idea, I stand guilty as charged.
[The host deleted the previous post because it was far too long and directed purely at self-defense, and not of interest to anyone except the writer. Since the writer persists, the host will give him another chance to consider proper etiquette, but will not allow a long discussion by someone who has proven himself a crackpot of the highest order.]
The host may imagine the result of Galileo’s experiment as “self-evident,” even without direct empirical support. I’d guess that Galileo would have preferred to let Nature testify on the matter.
Your position is indefensible and there’s no hope of saving it. (a) You’ve shown you have no sense, or physics understanding; it is impossible to build a tunnel through the earth, due to the immense geological forces and heat inside the earth, and even if you could it would cost more than you can fathom — it is as silly an idea as building a bridge to the moon. (b) Crackpots never know the difference between a wordy commentary and a true scientific paper. They learn from a few famous papers that were wordier than some — guess what! those are the ones they read! since the technical ones are too hard — so they imitate them without understanding that it is the small technical details in the famous papers are what made them famous. For example, read this Nobel-Prize-winning paper by Penzias and Wilson, http://adsabs.harvard.edu/full/1965ApJ…142..419P(c) pages 419-421; it’s all words, no equations! Well, wait, and look closely. There are crisp statements, one after another, each one packed with information about the experiment. There’s a reference to a longer paper that describes the experiment, too. And there are numbers, with uncertainties. This is a scientific paper par excellence. It’s not just a set of ideas; it is a set of results. (c) Crackpots usually reach back to and appeal to someone very famous without regard for the fact that there’s been a lot of work done by other people in the interim. They don’t bother to read the work of those other people; they just don’t have the time. Well, a lot has been learned in the last few centuries, and Galileo’s idea is now known to be completely impractical, even though he did not know that. And more is known about gravity — empirically — than you realize. (d) Specifically, crackpots never consider carefully the full range of data that scientists have available, and never check what can be done with existing or easy-to-obtain data. I am an empiricist and do not take answers to physical questions as self-evident, so I always think about the data. There are in fact tests of gravity inside a body. For instance, our understanding of the sun is remarkably good, as evidenced by helioseismology and solar neutrino emission, which probe the interior of the sun; our understanding assumes standard gravity, and therefore tests it. I believe that you would also learn something from the seismology of the earth, though probably less than from the sun. Also, we exist OUTSIDE the sun, but INSIDE the earth-moon-sun system, and INSIDE the galaxy, so we do know something about gravity inside objects from that score. Now if you want to propose a hugely expensive and impractical experiment, it’s *your* job to prove that other, cheaper methods haven’t done, or can’t do, a pretty good job. For instance, did you consider what you could learn from a neutrino beam sent through the earth? Maybe you would not learn much, but at least that’s an experiment people could do someday, with a neutrino factory, for finite cost — so you should check. But oh, I know, that’s too hard. Let’s just listen to Galileo, because we’re not smart enough to think for ourselves.
Insofar as the prevailing ideas about dark matter assume that General Relativity (GR) is right, and that our proper concern is “equations whose predictions agree with data,” it is pertinent to point out a rather large gap in GR’s confrontation with data.
In the local Universe, virtually all we know about gravity-induced motion comes from observations of phenomena over the surfaces of large bodies such as the Earth or Sun. In other words, the Schwarzschild exterior solution has seemingly been well-tested.
But throughout the range of these tests—from mm to AU—Schwarzschild’s interior solution has never been tested. The most noteworthy feature of the interior field of a massive body is that—according to GR—the rate of a clock at its center is supposed to be a minimum. In terms of Newtonian gravity, this corresponds to the prediction that a test mass dropped into a hole through a larger body will oscillate between the hole’s extremities. Neither of these predictions has ever been tested.
Almost 400 years ago Galileo proposed such a test. The apparatus needed to carry it out may be called a Small Low-Energy Non-Collider. Such an apparatus could be operated in an Earth-based laboratory (modified Cavendish balance) or in an orbiting satellite.
Because the unexplored domain is so large (the most ponderous half of the gravitational Universe) and because the idea to explore it has been on the books for so very long, it is clearly in the interest of science to conduct Galileo’s experiment.
Furthermore, as suggested in:
[Link Deleted by Host. Why? (a) This is not an advertising site for individuals to promote their individual ideas. Submit papers to journals. (b) The host looked at the paper. It has not a single equation, calculation or simulation. It does not consider the possibility that properties of the Earth’s geology, obtained via seismology, or properties of the Sun, or of neutron stars, constrain the properties of gravity already, and it does not show that the proposed experiment (which is practically impossible anyway) could potentially give stronger constraints. In short, it is not a scientific paper and is not suitable for this site.]
at least one reason exists to suspect that the standard prediction may not be correct. If this turned out to be true, various cosmological assumptions would also have to be re-thought. But even independent of any such radical result, the fact that GR’s (Schwarzschild’s) interior solution has not been tested is surely reason enough to finally fill this gap in our empirical knowledge of gravity.
Interesting as the debris produced by the Large Hadron Collider may be, the spirit of Galileo, myself, and perhaps others eagerly await the building and operation of the device designed to probe the opposite extreme: a Small Low-Energy Non-Collider.
Mr. Strassler, thanks for the summary. I dont perceive it as cryptic at all, but as a concise abstract,
Matt, what could dark matter be if not particles?
Didn’t I answer this question? Check around… if not I’ll answer again. Maybe the answer disappeared.
I would like to wait for the establishment of the ILC (International Linear Collider) which will be constructed in Japan. I visited the proposed site. It is a good place. The ILC would collide electrons with positrons. So a great energy will be produced and many particles will appear clearly without remnants. Scientists are talking about the first work for the ICL which will be the precise study of the Higg’s particle.
Excepting climate change, I do not believe that there is a topic in the physical sciences that can elicit more denialist comment than dark matter.
I’d argue quantum mechanics does, especially when you factor in the New Age ‘quantum is magic’ viewpoints.
In my book (or at least one of several editions of my metaphysics,) I suggest dark matter is simply just space — that mass is simply condensed space, and that Gravity is the affect of influx of space INTO matter. If something like this were true, I don’t think it’s crazy to say that dark matter are simply special states of raw space ( remember Gravity is, put most simply, an affect of raw space ) — and that the real question might be : what are those conditions in deep space that allow for raw space to behave as it is being observed (as ‘dark matter’) ?
I mean, in summary conclusion, why couldn’t it simply just be space ?
Sent from my iPhone
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What are your equations? This is just talk. We got over “just talking” 400 years ago.
Prof, if there were no fermions, would space collapse down to a “point” of some maximum energy density?
No, there are already vast spaces where the density of fermions is simply abysmal. If space were that sensitive our universe would never have been able to settle into what it is now.
Is it possible in principle that DM does not behave according to GR and QM ?
Yes. In principle.
If Galaxies configurations needs DM as a template , then it is logical to ask : what is the template that configurated DM ?
OR any DM distribution can configurate galaxies ?
Any dark matter configuration that isn’t precisely smooth will collapse under gravity to form sheets and filaments and clumps. Gas collects around these regions and galaxies form there.
But to form clumps doesn’t the DM need to ‘cool down’? If so, how can it if it doesn’t interact with anything?
Another question: Can the LHC produce and collide electron/positron pairs? Would that be helpful? It seems you would get higher collision speeds with a lower mass particle.
It doesn’t, no. Gravity is enough. These are very loose “clumps”, not like clods of earth… A galaxy has the shape of a ball (a halo made of dark matter) with a disk at its center (made of ordinary matter that has “cooled down”). Cooling makes the ordinary matter into a disk; lack of cooling keeps the dark matter more of a sphere or ellipsoid.
“… lack of cooling keeps the dark matter more of a sphere or ellipsoid.”
If dark matter is driven by gravity and there is “so much” of it, then why would it flatten out into a disk shape all around the visible galaxy?
You first said, “… it doesn’t interact much, in any way, with ordinary stuff, …” and then you went on and said, ” … The only way we’ve been able to detect dark matter so far is through the pull it exerts via gravity,”
“… in ANY way, ” The obvious question, which I think was also implied by Sue, above, is, to put it slightly differently, is gravity the only field that explains dark matter’s influence or is the another field which we do know of yet to links the two (all) configurations of matter?
Sorry Prof, I meant to say why dark matter would it NOT fatten out into a disk?
With the LHC the issue is not he speed, that is just a side effect of the energy involved. The idea is to get two particles of highest energy possible colliding then looking at what pops out.
Since the results depend on what you’re colliding electron-positron collisions could be useful in some circumstances, but not in a machine as specialized as the LHC. (In fact there are other machines that collide other particles from electrons to atomic nuclei. Each teaches us something different.)
A briefing paper by Prof Fowler (U of Virginia) for the benefit of his students, referred to matter creation, with specific reference to proton to proton collisions resulting in:
p+p -> p+p+p + p.bar
Is it feasible that rather than matter “creation”, a bonded proton-antiproton pair lurking invisibly in hyperspace was split apart in the p+p collision?
This alternative interpretaion would have no effect on the validity of the mass energy equation as far as I can tell.
What does it mean to lurk invisibly in hyperspace? Define lurk, invisible, and hyperspace, and give me the equations that describe it. By contrast, I know exactly what Fowler meant, with all the equations that go with it. It happens that these equations for protons are not so easy to solve… but if instead we talked about electron + electron –> electron + electron + electron + positron, I could calculate the rate for the process, as a function of the energies and momenta and angles of the produced particles, to better than 1%. I could do it laboriously by hand, but now the algebra can be done by a computer program such as MadGraph in about 1 minute or less. So I can’t compare the precise thing he meant with the vague notion that you propose. Fowler’s notion has been tested in experiments, not in some sort of vague way, but in precise ways; and simply checking that energy and momentum are conserved is not a high enough bar in particle physics.
There is evidence of dark matter every time a double slit experiment is performed; it’s what waves.
How mainstream physics is incapable of understanding de Broglie’s “subquantic medium” is the dark matter is beyond comprehension.
You have to be trying to not understand what occurs physically in nature to not understand de Broglie’s “subquantic medium” is the dark matter.
Why would dark matter, which is only noticable on the scale of galaxies because of its ultraweak interaction, suddenly affect a beam of photons on the distance of centimeters?? Your post doesn’t make any sense
If dark matter isn’t real, than what created, the scaffold upon which the galaxies were stretched upon across the Universe? Since dark matter doesn’t seem to interact with itself, or very little if at all, (wimps), what makes it clump, especially for the original scaffold? Is it first the stars than the dark matter attracted by the stars or other interstellar material? Just trying to get my little, very little, mind around this.
The reason I believe dark matter exists is that I don’t know a good answer to your first question.
Gravity makes dark matter clump. Note that these aren’t clumps like clods of dirt. These are just regions with more dark matter flying around than other regions.
According to simulations, dark matter clumps first, stars form later. We don’t have direct verification of this, but the simulations give a universe that looks like ours, so the circumstantial evidence is strong.
I’m having trouble comprehending/accepting that the ATLAS detector, which is having some 40 million proton-bunches slamming into each other–pretty much at the same axial location point as best I would understand– each second–within each bunch-crossing there being some 20- 25 collision-events taking place–it seems impossible (to this lay-person) that the debris from all these 20-25 events doesn’t get “totally smeared/consolidated” together in the detector elements so that the assignments of debris products back to a single one-proton whanging into a one-proton collision-companion event can be uniquely discriminated. Can you elaborate on this, for us? Thanks!
The particles that come flying out of the collision point, almost all of them traveling at nearly the speed of light, take about 25 billionths of a second to cross from the inside of ATLAS to the outside. In that brief moment, almost all exit the detector or are absorbed. So at some level, the detector is clear before the next collision arrives.
Meanwhile, the overlapping simultaneous collisions do create a challenge. Fortunately the 25 collision are spread out over a few centimeters. Particles that carry electric charge leave tracks, and those tracks can be traced back and uniquely assigned to a single proton-proton collision. So we can focus on one collision and forget the tracks that come from the other collisions. See for instance https://pbs.twimg.com/media/ArP6oBMCMAA3BLl.png:large .
Particles that don’t carry electric charge are another matter. With some interesting exceptions, they all get consolidated. But clever statistical subtraction allows the experimenters to do a pretty good job of accounting for this, allowing them to determine what happened in an interesting collision.
The full story is long and complex and the experimenters will have a more and more difficult challenge as the years go by and the collision rate increases.
re: the existence of dark matter. Thank you for your answer! Indeed, if dark energy can be equated with the Cosmological constant (which no one pretends to understand) perhaps dark energy could be another quirk of gravity. Something I had not considered!
Could dark matter be an array of particle types, and perhaps even more possibilities?
Yes, definitely. I simplified the discussion by suggesting it is only of one type, but sure, we have to consider that option (and people do.)
But Matt – light may not be able to move without it – or anything come to that ! I may be providing the space for physical operators.
One thing that’s pretty clear about dark matter is that it does not decay into ordinary matter, or transform into energy. If it did, the products of this transformation would give it away, given how much dark matter there is. So the creation of dark matter from collider energy would essentially be a one-way process. While the LHC is powerful, it’s certainly not generating an unprecedented amount of energy by the standards of the universe. So if it can transform familiar stuff into dark matter, so can many high-energy natural processes. And if the familiar-stuff-to-dark-matter transformation really is one-way, it should look like familiar stuff is gradually bleeding out of the universe. I wonder if there’s any cosmological way to look for this apparent failure of energy conservation around high-energy phenomena like supernovae.
LHC-like collisions, at such high center-of-mass energies, are rare in the universe. They do happen, but they are quite rare. The effect you mention does exist, but it would be far, far, far too small to observe.
This assumes of course that the conversion is only ‘one way’. If the conversion of dark and normal matter were in balance then we wouldn’t see any overall change. I do believe some people hold out hope that we can detect the decay of dark matter particles. If it was weak enough we wouldn’t see it easily at all. (Like the supposed decay of the proton.)
If dark matter were sterile neutrinos, how can the LHC experiments distinguish between dark matter and neutrinos? (I’ll be tuned).
Sterile neutrinos are not Standard Model neutrinos, and they would not be produced in the same way. Standard Model neutrinos are often produced along with electrons, muons and taus (the charged leptons). Sterile neutrinos that could be dark matter would not be produced in this way.
Some theories say the gravitation is so weak because some of it “leaks” to other dimensions or so. Could “dark matter” be actually gravitation that leaks into our universe from elsewhere? Maybe there was a multiversum that came about and the dark matter is a shadow from the gravitation from the other possible universa. No?
Dark matter must be “non-relativistic” (i.e. moving much slower than the speed of light) — otherwise it would not clump in galaxies, as we observe it to do. Gravitation is a long range force due to massless particles. HOWEVER, some types of Kaluza-Klein particles — massive particles arising because of extra dimensions, http://profmattstrassler.com/articles-and-posts/some-speculative-theoretical-ideas-for-the-lhc/extra-dimensions/how-to-look-for-signs-of-extra-dimensions/kaluza-klein-partners-why-step-1/ — can potentially be dark matter.
What if the gravitons are not coming from particles in our own universe or even a higher dimension in our own universe, but from a separate universe or universes whose gravity bleeds into our own? If other universes exist on other membranes next to our own and gravity bleeds between universes, it seems possible that large celestial objects could be affected by the gravity of other massive celestial objects in other universes.
I would like to believe there is some sort of dark matter particle we have yet to discover, but all data so far suggests it’s something else. It would have to be a particle that doesn’t interact strongly with anything except gravity, but yet doesn’t seem to interact gravitationally with matter or even other dark matter particles (ie clump together to form dark matter stars, black holes, etc.) Perhaps there is an additional repulsive force that prevents dark matter from coalescing.
My money is on warped space-time geometry – perhaps due to forces external to our 3D universe such as multiverse gravitons or perhaps some unknown higher dimensional structure inherent to the expansion of the universe.
I really don’t like calling these “separate universes”. If the matter in that “universe” pulls via gravity on our matter, then we’re all part of the same universe. By definition. Because in that situation, you can in principle produce particles of the “other universe” by colliding particles in “our universe”, via high-energy collisions; and black holes can decay both to particles of “our universe” and particles of the “other universe”. Are we to say that black holes are in two universes at once? No… it’s one universe, with two types of matter.
No repulsive force is needed to keep dark matter from coalescing. The absence of a long-range attractive force other than gravity is sufficient.
Thank you for your very insightful reply. I will probably have to re-read it a few times to fully wrap my head around that idea. You have an intriguing perspective on the multiverse theory should there be interactions between such “universes”.
We still have much to learn about dark matter. The recent, seemingly contradictory observation that it may interact with itself when galaxies merge may open the door to new physics.
(A) It’s not contradictory. We only know dark matter interacts super-weakly with ordinary matter; we do not know it interacts super-weakly with itself. (B) The paper that claims dark-matter self interacts is far, far less convincing than the media has made it sound. I found it rather unimpressive. And the result is, at best, 2.5 Standard Deviations. We have seen several more impressive-sounding results go away in each of the years that I have been running this website.
Matt,
I am nit-picking here just a little. But you contradict yourself when saying: 1)Dark Matter. Its existence is still not 100% certain
and then you say:
2)The only way we’ve been able to detect dark matter so far is through the pull it exerts via gravity, which is big only because there’s so much dark matter out there. [imply that, yes, it does exist.]
re: 1) – did you mean that the existence of dark matter at a particle is not 100% certain?
You are admirably cautious in what you write which is why I’m asking this.
Your articles are always stimulating!
Best, Sue
If dark matter exists, then gravity is behaving as expected, and we have detected dark matter through its gravitational effects.
If it does not exist, then the effect we have detected is due to something about gravity that we don’t understand.
Those are the only two simple options, as far as I can see.
Thanks for the question.
Is dark matter (and probably dark energy, dark field(s), which most likely is(are) creating it) associated with how big is the universe, in the first place?
All the measurements and observations we have so far are relevant within the local region we are living in. By that I am implying that since space (and the expansion of space) is not bounded by the speed limit, c, in any theory thus far, then space can, indeed, change FTL. So, are observations are within the realm of what we can see via the EMF spectrum. We don’t know how large or shape the universe is all we can imply is that in our local region it is flat (open).
So, going back to dark matter, if it does exist, then could that imply that the universe could very be a very large shell (or a sphere of varying density from the centre to the “surface”, the boundaries of space. It seems to me, anyway, that if space is a continuum then bounded space can ONLY be spherical. So, we could indeed be living in the whitecaps of dark matter floating in an unimaginable spherical field of dark energy.
This is in fact pretty close to the ‘lower level’ type of multiverse theory. Our observable universe is quite large now, 90 billion odd light yeas across, but we’re pretty sure there’s more out there that we’ll never even see. It could be that our little patch is how it is by sheer chance but that tends not to be taken very seriously. In general physics sticks to the notion that we’re nothing special and that our patch of space is representative of the whole universe. (Otherwise the answer to any question could be turned into ‘That’s just how it randomly happened.’)
I think that dark matter doesnt exist, although that the strong asymmetry between particles and amtiparticles, being tese henerated by the asymmetry of spacetime by the telativistics speeds in the transformations of energy into mass and viceversa.the transformations are not consetbed necause the increase of energy into mass is not uniform woth tje speed.then the totsion in the spacetime does appear as hidden matter.maybe the vortex of aether could bethesolution with the time with two dimension.have a superhyperbolicheometry and toplogy with 4 dimensional manifold not totally smooth
Makes no sense.
Is… is this a spambot trying to write physics?
The latest experience with accurate GPS measurements and satellites indicate contradictions in the interpretation of general relativity. It indicates that massive bodies hardly move with respect to the space in which they are embedded.
Instead that space is the dynamic factor.
This might indicate that also dark matter and dark energy must be reinterpreted.
Reference?
The question of today is : we observe gravitation effects , we infer that some gravitating something exists , but , is it possible that some unknown configurations of space itself is the cause of what we observe in the large scale with no such DM ???
N. B. : according to GR gravity assumed to be space configuration .
No one has proposed a theory — i.e., a set of consistent equations that makes detailed predictions and violates no known observations — where such an idea would make sense. If someone does, that would be very interesting.
Sorry ,but this is too easy. Such a theory is almost too simple. Where ever you need the force of gravity to be stronger , you increase the number tfo gravitons being exchanged over a give unit of time. To double the strength you double the number fo gravitons being exchanged. Should this be true it must apply to all massless bosons, and thats can be seen too. Now that doesn’t happen in the solar system much. So the other conditions is that the faster gravitons ,and all massless bosons only go faster if they go through the same space. That’s a long story why, but back to trying it out for gravity. So the slower one body moves off the line of sight in space the stronger the force. Results; between the centers of two galaxies a factor of 10, between a star and ihe center of a galaxy a factor of 2+ , in the bar of a galaxy up to 3 at the end of the bar, etc. Very close to what MOND and MOG state, only with a reason this time. Ever neutrinos do this, with mass, but only go faster than C in one direction, not both as is the case for massless particles. Two minor examples are Opera1 and Pioneer which now do not need some other made up story..
Makes no sense.
I don’t know if it is the same thing M. Many is asking but here goes …
We (think) we live in a 3D universe because that is the configuration of visible matter. I once touched on this in one of your other articles that perhaps the 3D configuration is a result of the 6 quarks in the proton. one of and maybe the most likely configurations of the 6 quarks would be a bipyramid creating the 3 axes which crystals also conform to.
Is there any way that dark matter is composed of more that 6 quarks in the “dark” proton hence “living” in a higher dimension and sharing the same universe we, 3D creatures, live in?
Is there any law in physics that rules out higher dimensions of matter?
There are in fact a number of theories that state gravity is so weak because it ‘leaks’ into other dimensions.
I am not entirely sure I get your theory but I’m assuming you’re saying that dark matter could be matter in other dimensions aside from the 3 we perceive. If this is so it cannot be able to pass from those dimensions into our own as gravity would cause it to eventually move into our dimensions in the same way gravity makes the rain above you fall until it meets your head. Theories that posit other massive universes (Such as Brane theories) have things like big bangs happening when two universes bump into each other.
Such ‘trapped’ particles would be problematic; what happens if you make one? Would it be stuck here? And why only be able to ‘communicate’ with these dimensions via gravity?
I recall watching a NOVA special (or some other such special) on quantum theories which proposed that perhaps gravitons bleed through our space-time into other dimensions – perhaps even a multiverse. The idea was that the reason gravity is so weak is because the force “leaks” into other dimensions and that it’s possible that dark matter is a result of gravitons bleeding into our universe from some other universe/multiverse. Perhaps massive objects in other universes/dimensions influence us through gravity.
Any thoughts on this proposal and whether there’s any hope to prove/disprove it given the only thing we’d likely be able to detect would be the gravity itself if true?
See the answer to your question below.
I think your comment represents very good speculation about what could be happening. I have had the same thoughts for sometime. I would love to discuss this with you further if you are interested: don@donwmurphy.com
Delighted too. And there are at least four errors but no way to edit. So to make more sense change “tfo” to of; “fo’ to of; thats” to that; “ever” to even. Thanks Don.