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Zombie physics: Baffling results that won't die
- pavel_lishin 11y agoHypothetically, if there are sentient critters composed of dark matter, would black holes be a total mystery to them? Since we only really interact with dark matter gravitationally, would they just see inexplicable gravitational point-masses with absolutely nothing there to cause them?
- anon4 11y agoAre there no dark matter black holes?
- jerf 11y agoTheoretically, any sufficient concentration of mass-energy creates a black hole. Theoretically, even light alone can create a black hole: https://en.wikipedia.org/wiki/Kugelblitz_%28astrophysics%29 https://en.wikipedia.org/wiki/Kugelblitz_%28astrophysics%29 Realistically, without the interaction of electromagnetism to create enough drag for gravity to be able to cause large clumps, it seems as unlikely that dark matter formed a black hole as light did.
- Udo 11y agoSince we have no idea what dark matter is, it's unknown how it interacts with black holes. If it is really a form of actual matter, it can become part of a black hole like anything else in the universe. Whatever its nature, a sufficient point-like concentration of dark matter will certainly create an object with the properties of a black hole, but it's unclear at this time whether dark matter even comes in the shape of point sources, or if there is anything "there" to fall into an existing black hole. We just don't know. Most physicists believe dark matter is just a type of particle, and if that turns out to be correct, its interaction with black holes will be exactly like with any other particle.
- jerf 11y agoWell... isn't that what black holes look like to us, too? We don't "see" anything there to cause them either.
- pavel_lishin 11y agoBut we can infer that there used to be a star there, and we can infer what the mechanism is that creates them; we also "see" immense electric fields sometimes, and we see accretion disks and other things. The dark-matter-critters would see literally none of that; they'd only realize anything was amiss if they saw gravitational lensing of their stars (if they even have light) or felt tides when someone happened to pass near one.
- yk 11y agoAs much as they are for us. Dark matter is matter that only reacts to us via gravity, so the effect of a black hole which also only acts via gravity^1 is the same for them as for us. ^1 I am ignoring charged black holes here, because astronomical black holes should be basically uncharged and my intuition is, that if there is some kind of dark charge, then the black hole could also be charged under that force.
- biswaroop 11y agoThey would still 'see' gravitationally active stars turning into black holes. They would infer a form of anomalous radiation from seeing the stars collapsing, and they would guess that there are other fields that interact with this other form of matter.
- pavel_lishin 11y agoThat's assuming that there are DM stars in the same place that our stars are (which is probably a safe assumption to make, if DM stars exist at all.)
- biswaroop 11y agoNo, I'm referring to real matter stars. DM critters would see the gravitation from real stars, and would watch them implode into black holes.
- ars 11y agoA particle that interacts only with gravity can not make a star.
- pavel_lishin 11y agoI'm hypothesizing that dark matter can interact with itself, just as our matter can interact with itself.
- ars 11y agoIt's more complicated than that. Think about it from an energy point of view - if it interacts with something it makes (transforms) energy. Where does that energy go? Normal particles get hot and make blackbody radiation, i.e. photons. Dark matter can't. Does it have a temperature? Can temperature flow between the particles? Without blackbody radiation you are going to have some violations of the laws of thermodynamics. Unless dark matter has some other particle to act as an equivalent. So you are hypothesizing an entire family of dark matter particles, and a whole set of new forces. Two entire universes each with entire sets of particles, that only interact via gravity. We could have a second sun and a second earth, that overlap us and never know it, we would just think that the gravitational constant is different (because our perceived mass is higher). Sounds like a wonderful setting for a science fiction/horror story.
- Udo 11y agoEverything about the universe as we see it would be a mystery to them, because the only way of them interacting with our universe is through gravity. But if you see it from our side, to us dark matter is just an incomprehensible field of gravity with no known source as well. So their perception could be absolutely identical to ours. This opens up a wild but entertaining hypothesis. Assume we have two universes, one of which is ours, and both are located very "close" to one another (whatever that means, maybe it's the next Brane over or something). Our dark matter could just be gravitation leaking out from that other universe. It would certainly explain why there is no other interaction. It would also explain why gravity is such a weak force (because it's leaking out). And our gravitational hotspots would in turn have the same effect on their matter.
- SolarNet 11y agoIt would also explain the amounts of normal matter and dark matter (4.9% normal, 26.8% dark), there could be a couple of universes that are close to a given universe (like ours). I'd be curious what sort of geometric configurations (along with equations) would lead to ~5.47 universes worth of gravity to leak through to each universe.
- gizmo686 11y agoAssuming the leaking hypothesis, the exact amount that is leaking into our universe wouldn't have any particularly meaningfull reason, in the same way that we now understand that their is no particular reason behind the distance between the Earth and the Sun.
- pavel_lishin 11y agoBut can't we infer a lot about the formation of the Solar System from the masses of the planets and their current orbits? One could argue that the particular reason we're here is because Jupiter swept the Solar System of most of its dangerous asteroids.
- ars 11y ago> Hypothetically, if there are sentient critters composed of dark matter You can't. Particles that interact only via gravity can't "do" anything. Unless you theorize there is some other force that only affects dark matter. If the only force is gravity then dark matter particles can "overlap" without interacting, so you would have huge clouds of particles orbiting and passing through each other for eternity since they have no friction they have no ability to transform velocity into other forms of energy. Since they are eternally in free fall they can detect nothing whatsoever. Occasionally some ordinary mass would go by and move their orbits and they would not be able to tell since you can not feel gravity when in free fall. > would they just see inexplicable gravitational point-masses with absolutely nothing there to cause them? You can not see gravity directionally, so you can not see points with more, or less, gravity. You can't even detect the sum total of gravity affecting you since it will just make you accelerate, which you can not detect if over things nearby are also accelerating. You can only detect gravity that is countered by some other force. All the gravitational detection we do is by detecting particles via light, not via gravity.
- pavel_lishin 11y ago> You can't. Particles that interact only via gravity can't "do" anything. Unless you theorize there is some other force that only affects dark matter. There was a story here not too long ago about the possibility of a Dark QCD - meaning that it's possible that Dark Matter interacts among itself just fine, in ways similar to the way that we do. (Meaning that it's not just one type of invisible garbage mass out there.) > All the gravitational detection we do is by detecting particles via light, not via gravity. Yup; I meant that if there is a Dark QCD, which means some sort of Dark Matter chemistry (and probably a Dark Matter light), they'd be able to observe the effects of gravity in the same ways that we do - by seeing gravitational lensing (of Dark Light), or by observing orbits, or by observing tides from fly-bys.
- biswaroop 11y agoCan someone explain why the CMB map in the first image is so suggestively annotated? The original looks far more isotropic: http://bit.ly/1MBURTA http://bit.ly/1MBURTA
- rubidium 11y agoTo demonstrate the strange fluctuations. They just used a different colormap than "the original" (which, by the way, is just one more popular colormap chosen to represent the data). Don't worry though, this isn't just an artifact of the colormap. There's been work done to show that the hot and cold spots are statistically anomalous, thus this Nature article.
- biswaroop 11y agoHmm. The official source says "In this image the anomalous regions have been enhanced with red and blue shading to make them more clearly visible." (http://bit.ly/1MBXXHg http://bit.ly/1MBXXHg) That sounds a bit more than a different colormap :) Also, can't we explain the dipolar variation with some motion in some direction we haven't accounted for (in our local cluster for instance)? I imagine that quadrupole and octopole variations are harder to explain through motion.
- contravariant 11y ago>Also, can't we explain the dipolar variation with some motion in some direction we haven't accounted for (in our local cluster for instance)? I imagine that quadrupole and octopole variations are harder to explain through motion. As far as I know that shouldn't be the case. There's no standard frame of reference with respect to which you can move, so for nearly all intents and purposes the earth might as well be standing still. There's also not really any way to 'move' with respect to the CMB; it's always the same time (i.e. distance) away. And at the time of it's creation particles were (presumably) moving in random directions at random speed, with no specific average (or if you want to be precise, with a Lorentz invariant speed distribution). Searching for 'CMB Lorentz violation' does turn up a few results, but most of those seem to be pure conjecture, I couldn't find any experimental evidence either way.
- gepoch 11y agoI was relieved to find nature.com and real physics here. My immediate assumption was that this was going to be clickbait about perpetual motion and such.
- rubidium 11y agoOne not on the list: possible influence of solar neutrinos on nuclear decay rates. I'm not sure of the current state of this research, but last I heard 4 years ago it was still an un-resolved question. http://news.stanford.edu/news/2010/august/sun-082310.html http://news.stanford.edu/news/2010/august/sun-082310.html
- _rpd 11y agoHere's a recent summary ... > Concerning the variability of beta-decay measurements > (Submitted on 20 Oct 2015) > Many experiments have been carried out to study the beta-decay rates of a variety of nuclides, and many - but not all - of these experiments yield evidence of variability of these rates. While there is as yet no accepted theory to explain patterns in the results, a number of conjectures have been proposed. We discuss three prominent conjectures (which are not mutually exclusive) - that variability of beta-decay rates may be due to (a) environmental influences, (b) solar neutrinos, and (c) cosmic neutrinos. We find evidence in support of each of these conjectures. http://arxiv.org/abs/1510.05996 http://arxiv.org/abs/1510.05996
- beamatronic 11y agoWe are seven billion intelligent beings, with significant resources, intelligence, and motivation, and we still don't fully understand "reality". That is just humbling.
- cozzyd 11y agoTo be fair, not that many of us are working on physics...
- api 11y agoWhy should it be easy for us to understand the system that (we assume) gave rise to us? In fact, there are numerous arguments via things like Godel's theorem that it should be hard by definition to understand one's "container."
- Lambdanaut 11y agoI'm curious to hear about those arguments. My intuition tells me that what makes it hard is that if you are part of the system trying to understand the full system, you must change the system in order to observe it. In effect, you can never have a perfect model of the system because the system will always be affected by the model you build.
- api 11y agoI'd suggest googling Godel's incompleteness theorem for starters. It proves that within any given system of rules there exist valid theorems that cannot be reached by only logical 'graph traversal' of the state space represented by that system. All systems of rules have 'islands of unreachable truth' within them. (My attempt at a summary.) A lot of people maybe read too much into it, but it's a very interesting and profound theorem. Among other things it more or less proved that attempts to logically deduce all possible theorems of mathematics from axioms -- which were popular at the time -- are futile because this is impossible. It's related in some ways to the Church-Turing thesis, which also proved such efforts impossible by showing that the halting problem is not solvable... you could never enumerate all the theorems of mathematics because it's impossible to tell if you're done.
- cozzyd 11y agoI remain pretty convinced by the argument in http://arxiv.org/abs/1210.5501 http://arxiv.org/abs/1210.5501 that DAMA is not seeing dark matter.