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Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter
- heartag 2y agoHey, look, it's my alma mater. Back in the news for wonky gravity physics research. Gotta love it. https://huntsvillebusinessjournal.com/news/2023/07/30/solving-the-mystery-of-huntsvilles-brilliant-scientist-disappearing/ https://huntsvillebusinessjournal.com/news/2023/07/30/solvin...
- throwup238 2y agoAt least it wasn't University of Mississippi!
- selimthegrim 2y agoThey actually have some really good faculty in gravitational wave stuff and general relativity.
- jfengel 2y agoI know UAH for its production of the Global Temperature Report, which produces primary data clearly showing climate change, and run by a bunch of climate change deniers. (Generally, not Stage 1 denialists, but various later stages of "it's not so bad" or "it's not our fault". At least one is also a creationist.)
- zephraph 2y agoHa, mine too! 2014
- bawolff 2y agoIm not a physicist. But it doesn't sound that convincing to replace dark matter due to lack of direct evidence, with something even more exotic which also has no direct evidence
- ItCouldBeWorse 2y agoWhen space expands it produces gravity? Like a groaning ship ripped apart, something snaps, when nothing is produced and becomes a place, producing a small background ripple. Concentric from the big bang outwards, like growth rings, dragging apart lights and things. Its not a valid concept, but its a new idea, something to test, anything is better, then collecting data and watching the model drift away every day like a ghost in the night.
- datavirtue 2y agoIt's like an LLM ate a whole bag of 2:1 gummies.
- simne 2y agoExists at least one example (to be exact there are few, but this one is overwhelming when looking carefully), which could be explained by topological defect - in 2023 made photo of two galaxies, which looking exactly same, but mirrored with invisible mirror. Sure, this could be just coincidence of very similar galaxies, need more observations.
- simne 2y agohttps://www.sciencealert.com/we-may-have-just-found-evidence-of-a-cosmic-string-a-crease-in-the-universe https://www.sciencealert.com/we-may-have-just-found-evidence...
- PartiallyTyped 2y agoNit: the title in the article is kinda wrong; Dark Matter is a set of observations for which we do not have a proper theory that explains it. It's not an "answer" or a "solution". We say it's "matter" because it interacts gravitationally.
- ijidak 2y agoSo, I'm confused by why we say it's matter when mass and energy are equivalent. Why have we concluded that it is matter and not dark energy. Let's momentarily ignore the fact that the name dark energy was already taken for the force causing the universe to expand. But can't both be attractive force and expansionary energy be different types of dark energy?
- PartiallyTyped 2y agoWe consider it matter because of the scaling of its energy density. If say the universe expands by a factor, the energy density of matter ρ is ρ ∝ 1/a^3, for radiation it is ρ ∝ 1/a^4. The cosmological constant is actually a constant. Radiation redshifts as the universe expands, but "matter" "just" "spreads".
- MaxikCZ 2y agoIsn't redshifting decrease in wavelength? The way even a mesh can reflect radio waves I always accounted to "the wave is so big it can't fit trough the holes of the mesh", so in that sense the radiation redshift equals to it spreading (even tho on interaction it manifests in a single point.
- PartiallyTyped 2y agoRedshift is an increase in wavelengths and a decrease in frequency. As an object moves further away from a reference point, all waves emitted from that object have an increased wavelength. Imagine a basketball player bouncing a ball up and down at a fix frequency. The wavelength is inversely proportional to the frequency. The wave here is the ball bouncing up and down. Now imagine the moment the ball hits the ground they start moving away from you at a fixed speed. Because they have accelerated, light now needs to travel some additional distance since the ball at the top is further away from you than the ball at the bottom was. But their new frequency remains the same because the displacement is now accounted for in the wavelength. If they stop moving, opposite happens and it blueshifts. If they keep accelerating, the distance increases and so does the redshifting.
- NoMoreNicksLeft 2y agoIf there is distinct "negative mass" out there, does that mean that we can built FTL devices after all? Or do we also need negative energy?
- MaxikCZ 2y agoThere's no evidence, physical or theoretical, of negative mass. (Yet.) But yes. If there's a negative mass we learn to control, possibility of FTL drive goes from "Absolutely not" to "Umm, maybe?".
- krapp 2y agoThe caveat being the Fermi Paradox. If FTL were possible, someone else should have figured it out by now and colonized the galaxy, and so we should see evidence of warp drives and galaxy-scale civilization everywhere. Since we don't see evidence of anything of the sort, FTL in any form probably isn't possible. Negative mass either doesn't exist or isn't useful.
- NoMoreNicksLeft 2y agoUnlike you, I have faith in intelligence's ability to screw things up so thoroughly that entire species just accidentally stumble down the stairs and break their own necks. FTl could easily be possible, but no one survives long enough to get their driver's license.
- est 2y ago> The shells in my paper consist of a thin inner layer of positive mass and a thin outer layer of negative mass; the total mass of both layers—which is all one could measure, mass-wise—is exactly zero, but when a star lies on this shell it experiences a large gravitational force pulling it towards the center of the shell Is "negative mass" a real thing in Physics or just some wild theory?
- T-A 2y agoVery much the latter: https://en.wikipedia.org/wiki/Negative_mass https://en.wikipedia.org/wiki/Negative_mass
- suzzer99 2y agoHere's something I've wondered. If the universe is made up of 85% dark matter, does that mean we can assume black holes are also made up of the same ratio of dark matter to regular matter (or at least when it went into the black hole)?
- PartiallyTyped 2y agoIANAP (physicist) The only the matter portion of the universe is 85% dark matter (26.8% of mass-energy content of the universe). As for the question; I don't think it's right to assume that dark matter really is exotic matter. It's just a set of observations. It's something that behaves like matter (with respect to density scaling) but only seems to interact gravitationally. Some theories posit that it's some unknown particles, others that they are primordial black holes, and some that gravity just behaves differently (MOND). I really enjoyed Dr Angela's videos on Dark Matter [1,2] [1] https://www.youtube.com/watch?v=qS34oV-jv_A https://www.youtube.com/watch?v=qS34oV-jv_A [2] https://www.youtube.com/watch?v=PbmJkMhmrVI https://www.youtube.com/watch?v=PbmJkMhmrVI
- andrewflnr 2y ago> It's just a set of observations. I've never heard anyone but Collier put forward this perspective on "dark matter", and I can't recall any other physicist using the term in a way consistent with that perspective. Frankly I think she was off base. Her videos are fun but her takes on terminology are often pretty bad.
- PartiallyTyped 2y agoCould you elaborate? It’s a set of observations about “something” that behaves like matter[1], and interacts only gravitationally. There are many theories proposed but none has any real answers or solutions. The following is taken from Cern[2]: > Many theories say the dark matter particles would be light enough to be produced at the LHC. If they were created at the LHC, they would escape through the detectors unnoticed. However, they would carry away energy and momentum, so physicists could infer their existence from the amount of energy and momentum “missing” after a collision. Dark matter candidates arise frequently in theories that suggest physics beyond the Standard Model, such as supersymmetry and extra dimensions. One theory suggests the existence of a “Hidden Valley”, a parallel world made of dark matter having very little in common with matter we know. If one of these theories proved to be true, it could help scientists gain a better understanding of the composition of our universe and, in particular, how galaxies hold together. And thus at least whoever wrote this and the people who approved that publication agree with the notion that it is observations for which no concrete theory exists that explains them. [1] i used “behaves like matter” in the sense that follows this definition: > In standard cosmological calculations, "matter" means any constituent of the universe whose energy density scales with the inverse cube of the scale factor, i.e., ρ ∝ a−3 . This is in contrast to "radiation", which scales as the inverse fourth power of the scale factor ρ ∝ a−4 , and a cosmological constant, which does not change with respect to a (ρ ∝ a0). The different scaling factors for matter and radiation are a consequence of radiation redshift: For example, after gradually doubling the diameter of the observable Universe via cosmic expansion of General Relativity, the scale, a, has doubled. The energy of the cosmic microwave background radiation has been halved (because the wavelength of each photon has doubled);[51] the energy of ultra-relativistic particles, such as early-era standard-model neutrinos, is similarly halved.[d] The cosmological constant, as an intrinsic property of space, has a constant energy density regardless of the volume under consideration.[52][e] In principle, "dark matter" means all components of the universe which are not visible but still obey ρ ∝ a−3 . In practice, the term "dark matter" is often used to mean only the non-baryonic component of dark matter, i.e., excluding "missing baryons". Context will usually indicate which meaning is intended. https://en.m.wikipedia.org/wiki/Dark_matter https://en.m.wikipedia.org/wiki/Dark_matter [2] https://home.cern/science/physics/dark-matter https://home.cern/science/physics/dark-matter
- saddat 2y agoI wonder what Sabine Hossenfelder’s opinion on this would be .
- defrost 2y agoI wonder what David Blair, Kip Thorne, Jerome Gauntlett, and a host of others might think. There's a suprisingly large number of people in theoretical physics dabbling about with gravity, quantuum gravity, dark matter, et al. Not all of them have a uTube channel.
- rthnbgrredf 2y agoI think the simplest explanation for dark matter is that it consists of something we already know exists and behaves exactly like dark matter: black holes. To fit this explanation, we would need a vast number of black holes, each relatively small, approximately the size of a tennis ball. These black holes would be large enough to have persisted since the early universe, avoiding conversion into Hawking radiation. The remaining question is how such a multitude of primordial black holes could have formed in the early universe. The most likley answer to this question is density fluctuations. During the very early moments after the Big Bang, slight variations in density could have caused regions of space to collapse under their own gravity, forming black holes. If the density contrast was large enough, these regions would collapse directly into black holes.
- matthewdgreen 2y agoWouldn’t these black holes radiate some Hawking radiation, making them potentially detectable? And how long would they exist for? Also what keeps these black holes from interacting with normal matter and clumping in the center of galaxies?
- rthnbgrredf 2y agoYou ask very good questions. > Wouldn’t these black holes radiate some Hawking radiation, making them potentially detectable? Yes, according to widely accepted theory, they do. However, Hawking radiation is incredibly weak. With current technology, we are not able to detect such a faint signal. > And how long would they exist for? This depends on the size of the black hole. They will last much longer than our solar system, many billions of years, until they eventually evaporate. > Also, what keeps these black holes from interacting with normal matter and clumping in the center of galaxies? They do interact with normal matter via gravitation. If primordial black holes exist, many of them would fall into the supermassive black hole at the center of our galaxy and other galaxies. However, there are also those that orbit around the center. The problem is that our telescopes currently cannot detect a tennis ball-sized black object with the mass of a few Earths, it is an incredible tiny black dot in front of a black background. Hence, they are literally dark matter.