# Dark Matter/Dark Energy **URL:** \ **Category:** Factual Questions\ **Created:** [April 5, 2011, 7:02pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306 "2011-04-05T19:02:08Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 25, 2011, 3:28am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/21 "2011-04-25T03:28:38Z")
Eh, dark matter isn’t all that fudgy. All you need is some particle (or particles) which doesn’t interact via the electromagnetic force, and there are plenty of candidates for those. Heck, there are a few that we already know exist. It wouldn’t really upset anything to discover a few more. I don’t think you’ll find any physicists who’ll argue with the notion that dark energy is a fudge, though. It’s just that we don’t yet know of anything better to replace it. Inflation is on a little firmer footing, but it’s likely to be related to dark energy (whatever it is), so it’s still not all _that_ firm. ---
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [April 30, 2011, 6:04pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/22 "2011-04-30T18:04:59Z")
(No bump intended)…Thanks all, for your responses. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [April 30, 2011, 8:10pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/23 "2011-04-30T20:10:32Z")
One question about dark energy has always bothered me. It’s claimed that it composes 70% of the stuff in the universe. But 70% of what? I assume they mean energy content using energy mass equivalence. But if dark energy has mass equivalence why doesn’t it also cause gravity? I’ve seen it described as pressure with a negative energy equivalence. So are we saying 70% of the sum of the absolute values of the energy in the universe is dark energy? But does this even make sense as virtual particle pairs are constantly coming into existence and annihilating? ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 1, 2011, 5:00pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/24 "2011-05-01T17:00:18Z")
The neutrino started out as a fudge to save conservation of momentum. Sometimes fudges work. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [May 1, 2011, 6:29pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/25 "2011-05-01T18:29:40Z")
I don’t know. I suppose that the neutrino was accepted when it became part of the Standard Model of Particle Physics: > **[Standard Model](https://en.wikipedia.org/wiki/Standard_Model)** > > The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions – excluding gravity) in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, proo But the Standard Model doesn’t account for neutrino oscillations or non-zero mass. It also has no explanation for dark energy or dark matter. It requires a separate theory for General Relativity. Supposedly there are some anomalies: > **[Anomaly (physics)](https://en.wikipedia.org/wiki/Anomaly_(physics))** > > In quantum physics an anomaly or quantum anomaly is the failure of a symmetry of a theory's classical action to be a symmetry of any regularization of the full quantum theory. > In classical physics, a classical anomaly is the failure of a symmetry to be restored in the limit in which the symmetry-breaking parameter goes to zero. Perhaps the first known anomaly was the dissipative anomaly in turbulence: time-reversibility remains broken (and energy dissipation rate finite) at the limit o In qua... Modern-day physics looks messy to me. I expect someone to eventually fit everything together into a more neat-looking theory. Or maybe the world really is this messy. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 2, 2011, 7:32pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/26 "2011-05-02T19:32:03Z")
> [@](#): > > One question about dark energy has always bothered me. It’s claimed that it composes 70% of the stuff in the universe. But 70% of what? I assume they mean energy content using energy mass equivalence. But if dark energy has mass equivalence why doesn’t it also cause gravity? It does cause gravity, according to exactly the same rules that anything else does. It’s just its weird composition that leads to its gravity being repulsive, rather than attractive. To explain further: Most people think of gravity as being caused by mass, and in our everyday experience, that’s an excellent approximation. But it’s only an approximation: The energy density (which corresponds to mass) is only one of 16 components (10 of which are independent) of a thing called the stress-energy tensor. The whole stress-energy tensor can be represented as so ```auto T[sub]00[/sub] T[sub]01[/sub] T[sub]02[/sub] T[sub]03[/sub] T[sub]10[/sub] T[sub]11[/sub] T[sub]12[/sub] T[sub]13[/sub] T[sub]20[/sub] T[sub]21[/sub] T[sub]22[/sub] T[sub]23[/sub] T[sub]30[/sub] T[sub]31[/sub] T[sub]32[/sub] T[sub]33[/sub] ``` where T[sub]00[/sub] is the energy density, T[sub]0j[/sub] and T[sub]i0[/sub] represent fluxes of momentum, and the remaining components represent various stresses (pressure and so on). An ideal fluid (i.e., with no viscosity) will have all the off-diagonal elements zero, and the 11, 22, and 33 components all the same value (this value being the pressure). Now, for something like a glass of water, the energy density is going to be far, far greater than the pressure, so we can ignore the pressure and just consider the energy density. For dark energy, though, the magnitude of the pressure is the same as the magnitude of the energy density, but negative. And since there are three pressure components but only one energy density component, the negative pressure turns out to be more significant than the positive energy density. Quoth **Wendell Wagner** : > [@](#): > > But the Standard Model doesn’t account for neutrino oscillations or non-zero mass. At the time neutrino oscillation was discovered, it wasn’t part of the Standard Model, but really, that’s true by definition. Now, though, it’s so well-supported experimentally that I expect all particle physicists would consider it standard. The Standard Model isn’t a single monolithic thing, but rather more of a snapshot of the current state of the art at any given moment. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [May 2, 2011, 9:09pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/27 "2011-05-02T21:09:24Z")
> [@Chronos](#): > > At the time neutrino oscillation was discovered, it wasn’t part of the Standard Model, but really, that’s true by definition. Now, though, it’s so well-supported experimentally that I expect all particle physicists would consider it standard. The Standard Model isn’t a single monolithic thing, but rather more of a snapshot of the current state of the art at any given moment. All particle physicists would certainly acknowledge neutrino mass and mixing, but many (probably the majority) still consider the Standard Model to be a very specific SU(3)xSU(2)xU(1) partially spontaneously broken gauge symmetric theory that has massless left-handed neutrinos and (among other things) no lepton flavor violation. You regularly see neutrino oscillations labeled as being the first confirmed evidence of “physics beyond the Standard Model”. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [May 3, 2011, 2:02am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/28 "2011-05-03T02:02:43Z")
Thanks, Chronos. One more question then. When they say dark energy makes up 70% of the universe, do they mean its total T[sub]00[/sub] is 70% of the sum of T[sub]00[/sub] of ordinary matter, dark matter, and dark energy or are they measuring something else? ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [May 3, 2011, 8:12pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/29 "2011-05-03T20:12:19Z")
> [@OldGuy](#): > > Thanks, Chronos. > > One more question then. When they say dark energy makes up 70% of the universe, do they mean its total T[sub]00[/sub] is 70% of the sum of T[sub]00[/sub] of ordinary matter, dark matter, and dark energy or are they measuring something else? In general relaqtvity for a general spacetime the total energy density is totally subjective as it’s entirely dependent on how you choose to ‘sum’ it. Really what is meant is that, assuming the universe is totally homogenous and isotropic, in FLRW (Friedmann-Lemaitre-Robertson-Walker) cooridinates (which will define which space-like hypersurface in spacetime corresponds spatially to the universe at a given time, t) at the current value for t what the contribution of dark energy is to T[sub]00[/sub] for any event in the current universe is (T[sub]00[/sub] is cooridnate dependent). I hope that’s not too confusing. Basically speaking it’s not the percentage of the sum, it’s the current percentage at every point in the universe, assuming it’s the same at every point. Further that’s also assuming a certain ‘preferred’ frame of reference. ---
**Author:** ![BACI](https://avatars.discourse-cdn.com/v4/letter/b/ce73a5/32.png) [@BACI](https://boards.straightdope.com/u/BACI)\ **Post date:** [May 26, 2011, 11:32pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/30 "2011-05-26T23:32:31Z")
According to this article it looks like we don’t need the concept of dark matter anymore: > **[Amelia's summer job: finding part of the universe](https://www.theage.com.au/technology/amelias-summer-job-finding-part-of-the-universe-20110526-1f6h5.html)** > > A SUMMER internship to learn more about astrophysics turned into a stunning coup for a Monash undergraduate, Amelia Fraser-McKelvie, when she helped solve one of the big mysteries of science. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [May 27, 2011, 1:50am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/31 "2011-05-27T01:50:44Z")
I’m really suspicious of that article. Do a search on the three researchers names. You’ll find quite a few citations, but they’re all from the past few days. It’s also rather strange that all the articles lead off with talking about this undergraduate student, not the two Ph.D.'s who are surely the senior researchers on the team. I suspect that the following has happened: These three reseachers have come up with a possible solution to the dark matter problem. They have gotten a paper about their solution accepted in a scientific journal. The student (or the two older researchers) have told the public relations department at University of Monash (where she is a student) about this paper. The PR department has written up a clever release with lots of information about the student and some vague information about their theory. They have sent copies of this release to every scientific news service in the world. Until we hear about what the general opinion of scientists on this idea is, take all this with a grain of salt. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 27, 2011, 7:28am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/32 "2011-05-27T07:28:30Z")
What that article actually says is not that she’s found a replacement for the concept of dark matter, but rather that she (and the group she works with) has found some filaments of dark matter between galaxies. OK, that’s believable enough: Anyone with a telescope can find some of those. That tells us _where_ it is (at least, some of it), but doesn’t tell us anything about _what_ it is. It’s not the solution to the mystery, but part of the mystery itself. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [May 27, 2011, 1:50pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/33 "2011-05-27T13:50:13Z")
The article is very vague about what exactly the research team has found or discovered. It doesn’t explain whether the team has found some sort of solution to what dark matter is or just some examples of it or whatever. That’s why I think this came from a release from a university PR office. This is clearly written by a non-scientist trying to explain a scientific discovery that they didn’t really understand. It’s by someone who doesn’t know much about science but who knows how to write a clever article by emphasizing the human angle. **Really** , do a search on the three researchers’ names and look at the several dozen articles that you’ll find. They are all from the past few days. All of them are vague on the scientific details. This is nothing except an announcement of a future publication which hardly any scientists other than the three researchers have had time to think about. ---
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [May 28, 2011, 4:03am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/34 "2011-05-28T04:03:31Z")
> [@Chronos](#): > > What that article actually says is not that she’s found a replacement for the concept of dark matter, but rather that she (and the group she works with) has found some filaments of dark matter between galaxies. OK, that’s believable enough: Anyone with a telescope can find some of those. That tells us _where_ it is (at least, some of it), but doesn’t tell us anything about _what_ it is. It’s not the solution to the mystery, but part of the mystery itself. So what are these filaments they’re talking about? Is that something we’ve known about for some time? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [May 28, 2011, 11:35am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/35 "2011-05-28T11:35:46Z")
[Galaxy filament](http://en.wikipedia.org/wiki/Galaxy_filament). It has a list of galaxy filaments and galaxy walls. The first of each was found in the 1980s. ETA: that top picture in the link is a simulation designed to match measurements, but not a measurement itself. Toward the bottom, the 2dF survey map is a map drawn just from measurements. ---
**Author:** ![mla1](https://avatars.discourse-cdn.com/v4/letter/m/c0e974/32.png) [@mla1](https://boards.straightdope.com/u/mla1)\ **Post date:** [May 28, 2011, 11:39am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/36 "2011-05-28T11:39:05Z")
Dark energy is effectively anti-gravity. dark matter is what holds complex systems e.g. galxies, solar systems. When you se a shadow and not the person you know they are there by the way the light appears. That is how we detect it the affect it has on light. Dark energy is purely theoretical and is believed to expand the univers. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 28, 2011, 7:03pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/37 "2011-05-28T19:03:54Z")
Dark matter is irrelevant on a scale as small as a solar system. There’s more dark matter than normal matter overall in the Universe, but the normal matter is much more clumped, and when you’re very near one of those clumps (like a star), it’s locally more important than the diffuse dark matter. ---
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [May 28, 2011, 8:18pm UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/38 "2011-05-28T20:18:32Z")
> [@ZenBeam](#): > > [Galaxy filament](http://en.wikipedia.org/wiki/Galaxy_filament). It has a list of galaxy filaments and galaxy walls. The first of each was found in the 1980s. > > ETA: that top picture in the link is a simulation designed to match measurements, but not a measurement itself. Toward the bottom, the 2dF survey map is a map drawn just from measurements. Thank you. I’m still not clear on this though. These great walls or supercluster complexes are simply galaxies and superclusters, except instead of forming in spots around the universe, they form a sort of messy cobweb structure, with superclusters clumped at the joints. Whew, that’s large-scale! How does that speak to dark matter, other than DM hangs around galaxies (or vice versa?)? Is this a discovery of more galaxies than we thought, along with their associated dark matter? How much of the universe’s missing mass does this account for? Or, is this not so much a discovery of galaxies as a discovery of a way to see the galaxies we already knew were there? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 29, 2011, 1:20am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/39 "2011-05-29T01:20:19Z")
The filaments of galaxy superclusters form around filaments of dark matter. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [June 16, 2011, 7:26am UTC](https://boards.straightdope.com/t/dark-matter-dark-energy/577306/40 "2011-06-16T07:26:20Z")
It appears to me that, contrary to the claim in post #33, the discoveries of Fraser-McKelvie, Pimbblet, and Lazendic-Galloway do not show that there is no dark matter. It appears to me that it shows that the usual claim that most of the mass of the universe is dark energy, with a smaller amount of dark matter and a still smaller amount of ordinary matter, is true or at least is consistent with their observations: [http://en.wikipedia.org/wiki/Amelia\_Fraser-McKelvie](http://en.wikipedia.org/wiki/Amelia_Fraser-McKelvie) [Previous page](https://boards.straightdope.com/t/dark-matter-dark-energy/577306.md?page=1) [Next page](https://boards.straightdope.com/t/dark-matter-dark-energy/577306.md?page=3)