8 ms·
It reminds of the alternative to dark matter that is MOND, stating that the law of gravity behaves as 1/r at large distances (as opposed to 1/r2 at our scale) [
by isolli 4y ago
It reminds of the alternative to dark matter that is MOND, stating that the law of gravity behaves as 1/r at large distances (as opposed to 1/r2 at our scale) [0]. I personally like it because it seems less ad hoc than to posit the existence of invisible matter, and similar in my mind to the special relativity adjustment. (Do not take this endorsement too seriously, of course.)
However: "The most serious problem facing Milgrom's law is that it cannot eliminate the need for dark matter in all astrophysical systems: galaxy clusters show a residual mass discrepancy even when analyzed using MOND. The fact that some form of unseen mass must exist in these systems detracts from the adequacy of MOND as a solution to the missing mass problem, although the amount of extra mass required is a fifth that of a Newtonian analysis, and there is no requirement that the missing mass be non-baryonic." [0]
[0] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
- entrep 4y agoAs gravity is a signed integer it overflows when it gets big enough and turns into a negative number.
- KingOfCoders 4y agoWhat is NaN+1?
- Drakim 4y agoNaN1
- bitcharmer 4y agohow would NaN apply to signed integers?
- withinboredom 4y agoThen you have a signed NaN and instead of eating them at your local indian food restaurant, you put it in a collection.
- xvilka 4y agoTransfinite[1] number. [1] https://en.m.wikipedia.org/wiki/Transfinite_number https://en.m.wikipedia.org/wiki/Transfinite_number
- fahadkhan 4y agoWatman! (Reference https://www.destroyallsoftware.com/talks/wat https://www.destroyallsoftware.com/talks/wat)
- sph 4y agoWhat ever happened to Gary Bernhardt? I miss his funny insight and those fantastic screencasts of his, they've shaped my way of thinking about code architecture
- CoastalCoder 4y agoYou're thinking of temperature.
- deleted 4y ago[deleted]
- mhh__ 4y agoMost physicists who can be bothered to comment do seem to think MOND is extremely ad hoc, in a sense.
- abnry 4y agoMy understanding is the 1/r^2 behavior comes from solving for Green's function of a PDE. Gravity is similar to Gauss's law (i.e. 1/r^2 behavior of charged particles) in the underlying PDE. So something in that equation would have to change.
- HarHarVeryFunny 4y agoApparently it makes very accurate predictions though, so it's not just a matter of ad hoc tweaking some law to fit reality... It does seem to capture some regularity/mechanics of nature.
- audunw 4y agoMy pet theory for gravity / general relativity (which is probably completely wrong, but fun to think about), is that space itself is created through particle interaction. Space will thus be denser and create a gravitational effect in places with lots of matter. That means space also has to decay. And unless you want space to become non-existent far away from matter, the rate of decay must also fall off somehow as you get further away from matter. I wonder if you could get such a space creation/decay process to match a curve that's 1/r2 at short distances and 1/r at long distances...
- MaxikCZ 4y agoInteresting idea. Although, if particle interaction creates space, shouldnt it counteract gravity? If the Earth, full of interacting particles, is hurling space outwards, stuff around Earth should fling into infinity, not fall towards it, or what am I missing?
- MAMAMassakali 4y agoBut aren't particles emergent property of space wave function collapse?
- bil7 4y agowave function does not have to collapse for particles to exist. Particles and wavefunctions are just different lenses for which to make sense of excitations in quantum fields
- dvh 4y agoMy pet theory is that let's say particles are the excitation of the field, imagine you come to a lake in a quest to understand water. The surface is field. You throw in a rock and the splashback is particle, you analyze the particle, you throw other things and analyze the other particles. Then you form a water theory based on these particles and you find out that boats shouldn't float at all. It's because particles are exceptional things, not the normal, calm field they come from. If you base your theory on those exceptional thing it will be non representative or outright wrong. That's why quantum physics is giving us weird results, because particles are exceptions, not the common state of the field.
- JumpCrisscross 4y agoIsn’t the bullet cluster the bullet in the head for MOND being a simple solution?
- bulatb 4y agoThat's the fascinating thing to me: it doesn't matter! MOND is a successful pseudoskeptical meme despite not being a successful physical theory. The narrative of MOND-the-meme is totally wrong but extremely compelling. That's enough to give it outsized fitness in its niche, and then that general compellingness (which comes from being really good at tricking us) is misinterpreted as scientific merit. Even by those who say they're interested in truth, not stories. It's an excellent test-case for critical thinking because everything about it as a meme should set off alarm bells, but often it doesn't.
- dtgriscom 4y agoIn the same vein, I miss cold fusion. It was such a lovely idea, and had such great promise. A shame that reality intruded...
- throwawaymaths 4y agoWait how is it pseudoskeptical? It's made independent predictions which have subsequently been confirmed, like a slope of 4 in the tully-fisher relationship and the EFE (among others). That's the definition of science. The EFE is particularly compelling because it was originally posited as a criticism of MOND but then the data came in.
- bulatb 4y agoI'm trying hard to be precise, but I could always do better. MOND the physical hypothesis is perfectly good science, whether it turns out to match reality or not. My issue is with MOND the meme, the complex of beliefs among non-physicists (like me) that MOND explains "dark matter"[0] without matter which is dark, whose fitness isn't really based on the success of MOND-the-model. I say MOND-the-meme is pseudoskeptical because it a) manufactures disbelief by misrepresenting a subject and then b) provides a "skeptical" alternative in order to appeal to skeptics which c) does not itself stand up to skepticism because (a) was a strawman and (b) was motivated reasoning. It survives because it makes you feel smart, not because it's sound or valid or the MOND hypothesis is true. Accepting MOND-the-meme would still be problematic even if the MOND hypothesis was overwhelmingly confirmed tomorrow. [0] Taking full advantage of the ambiguity between "dark matter" as the name for observations, one hypothesis explaining them, and an overall cosmological model.
- ncmncm 4y agoThe problem with dark matter is not that it is ad hoc. It is that it feels un-parsimonious to resolve a discrepancy in rotation curves by inventing five times more stuff than you had, all undetectable, and distributed just right to make all your curves come out right. It turns out that the mass of neutrinos produced so far adds up to as much mass as all the rest of particulate matter. I guess neutrinos must be distributed about evenly throughout the universe. If we could not ever detect neutrinos, that would be awkward. I have not heard of a mechanism by which these dark matter particles can cool and condense to clumps to seed galaxies. By contrast, baryonic matter gets to emit photons to give up kinetic energy.
- ChrisLomont 4y agoParticle physics has a pretty good track record of inventing undetected particles to solve missing item problems, then finding that particle later. I'd guess we're up to hundreds of such particles like this so far, with really big finds being positrons (and all anti-partickes, needed when adding relativity to spin), neutrinos (needed to account for missing mass), all the quarks (needed for certain symmetries, among others), and the Higgs bison itself (needed to explain masses). So don't discount adding currently undetected things as explanations for surprising measurements. It's been extremely fruitful.
- beeforpork 4y agoI want a Higgs bison steak, please! :-) Medium rare!
- ncmncm 4y agoGot no objections to inventing particles to take up and carry off whatever bit of stuff has to conserved: neutrinos, virtual particles, gluons, what-have-you. I don't really even object to inventing five times the mass of the known universe. It just feels, as I said, un-parsimonious. It feels quite a lot like inventing God to patch a "missing link" in your evolutionary succession. Maybe you'll find God there somewhere, but it doesn't seem like the first thing to try. So, maybe dark matter really will turn out to be an ordinary axion or something detectable only if you manage to squint just right, and God just loved those so much that almost everything is them, and we are all made out of just leftover scraps. Maybe there are dozens of elementary axions, with relationships and exciting interactions we can never figure out because we can't touch them in any way but gravitationally. But I still want to know how they cool.
- MatthiasPortzel 4y agoXKCD 1758 on the subject https://xkcd.com/1758/ https://xkcd.com/1758/
- withinboredom 4y agoI always wonder if this "missing mass" is just light. As in it is so close to zero mass to be undetectable at a normal scale, but at galaxy scale, it actually has mass.
- smeyer 4y agoHow do you square your idea with the other substantial implications of photons having mass?
- bl0rg 4y agoPhotons bend spacetime even without having mass.
- zeven7 4y agoBingo, does energy not affect spacetime the same as mass? I always assumed it did. My assumption was this was already worked into the calculations and not enough to account for dark matter.
- simiones 4y agoIf photons had a very small but non-0 mass, it would simply mean that they actually move slightly slower than c, but it wouldn't otherwise have any significant implications. There are in fact experiments that are trying to check whether photons have a mass we can detect. Also, just as a note, I'm using the term "mass" for what used to be called "rest mass" (as opposed to "relativistic mass"). Even if their "rest mass" is truly exactly 0, and their speed is exactly c, they still have energy and momentum, and thus they have mass in general relativity, but that is a different discussion.
- peterpost2 4y agoWouldn't that mean that light also has infinite energy?
- squeaky-clean 4y ago
- survirtual 4y agoIs it possible that the gravitational discrepancies can be explained with dyson spheres? Or dyson spheres collected into grids (with a dyson sphere scale tech you can prob move suns by making the dyson sphere a giant fusion engine). There is an advantage to arranging dyson spheres closer together in order to reduce latency between nodes. If your dyson spheres were optimized enough, could absorb all known spectrums and recycle them. Wouldn’t that appear completely dark save for gravity? I mean, isn’t it possible entire galaxies have been converted in this way? Seems like it could be a much simpler explanation within the confines of current understanding. But I’m sure this has been thought about and accounted for.
- badpun 4y agoMy layman understanding is that the dyson spheres would occlude objects behind them if they happen to be in line of sight to us. Given that things in the universe are not static, other (visible) bodies would move in and out of occlusion, allowing us to detect the DS.
- gbasin 4y agoNothing an LCD and some cameras can't solve
- growt 4y agoSure, but occams razor would probably prefer some gas cloud.
- throwawaymaths 4y agoThis is like saying that the existence of precession in mercury's orbit detracts from the adequacy of a Newtonian analysis and so there must be a dark matter blob pulling mercury's orbit around.
- dotnet00 4y agoThere's also the issue that some galaxies don't violate our pre-dark-matter models as much or do so in a different way. With dark matter that's easily explained as an abnormal dark matter halo (eg maybe displaced due to an ongoing interaction with another galaxy or absent for an unknown reason). When abnormalities like that are considered, dark matter becomes the elegant solution while theories that tweak gravity start to seem somewhat ad hoc.
- fartsucker69 4y agohuh? how is MOND less ad hoc? it introduces more parameters to fit its arbitrary conception about how gravity is supposed to scale. even worse, since basic MOND disagrees with a ton of basic evidence since it just doesn't work except for the few problems it was created for, the actual MOND derivatives that do try to make it work introduce even more parameters to fit.
- throwawaymaths 4y agoIt introduces ONE parameter. And TWO, for the relativistic version. To simplify, LCDM introduces at a minimum one parameter (relative dark matter:visible matter ratio) for each galaxy to get the rotation curves correct. That's at least a billion parameters. MOND has made successful predictions:. The EFE, for example (there are others). LCDM has not, as far as I can tell -- please correct me if I'm wrong [0] > work except for the few problems it was created for That's actually a poor heuristic. Suppose we hadn't discovered relativity yet (but had galactic rotation curves, which only depend on good telescopes and newton, and Doppler effect), and we observed mercury's precession. Would you then use precession as an argument for dark matter on the basis that there's a dark matter entity in our solar system pulling mercury around? I would think that would not be a good idea. [0] ok I looked it up and actually LCDM predicted no galaxies with redshift greater than 7... And thanks to jwst we now know there are galaxies with much much greater redshift, a feature explicitly predicted by MOND.
- throwawaymaths 4y ago[1] I forgot about cmb polarization, that is a successful prediction of LCDM