Evidence of 'Modified Gravity' In 150 Galaxies Strengthens Dark Matter Alternative 98
A team of astronomers has discovered evidence in over 150 galaxies for a long-standing alternative model of "modified gravity." New Atlas reports: [R]esearchers on the new study say they've observed the [external field effect] (EFE) in action in 153 different galaxies. The team was studying the rotation curve of the galaxies, which plots the orbital speed of stars and gas against their distance from the center of the galaxy. The researchers discovered that galaxies in strong external fields slowed down much more frequently than galaxies in weaker external fields did. That's a prediction made only by [Modified Newtonian dynamics] MOND, and the discovery surprised even the astronomers themselves.
"The external field effect on rotation curves is expected to be very tiny," says Federico Lelli, co-author of the study. "We spent months checking various systematics. In the end, it became clear we had a real, solid detection." It's an intriguing result, and it may lend some weight to the MOND hypothesis for further study. But it's important to keep in mind that so far the bulk of the evidence still points towards dark matter, and it'll take much more work to topple that hypothesis entirely. The research was published in the Astrophysical Journal.
"The external field effect on rotation curves is expected to be very tiny," says Federico Lelli, co-author of the study. "We spent months checking various systematics. In the end, it became clear we had a real, solid detection." It's an intriguing result, and it may lend some weight to the MOND hypothesis for further study. But it's important to keep in mind that so far the bulk of the evidence still points towards dark matter, and it'll take much more work to topple that hypothesis entirely. The research was published in the Astrophysical Journal.
Mass.. (Score:2)
Re: (Score:2, Interesting)
No.
Origin is not identity [Re:Mass..] (Score:4, Informative)
So where does gravity come from?
Gravity comes from mass. So mass = gravity.
No.
"No" is correct.
So where do babies come from? Babies come from hospitals. So babies=hospitals.
So where does coffee come from? Coffee comes from Ethiopia. So coffee=Ethiopia
So where does bread come from? Bread comes from ovens. So bread=ovens.
The fact that x originates from y does not mean x and y are the same.
Re: Origin is not identity [Re:Mass..] (Score:1)
Re: Origin is not identity [Re:Mass..] (Score:1)
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Correct, Einstein said gravity is energy
Einstein said that the source term for the gravitational field was the stress-energy tensor, if that's what you're saying.
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More or less. But not in the sense of some kind of 'friction'. Imagine a ball with a certain energy and its mass equivalent. The gravity or inertia does not car how this energy is made up inside the ball. It does not matter if inside the ball is one heavy brick just sitting there or very light particles moving about very very fast as long as the total energy cones out the same. So if you have an atom and an electron is rotating near the kernel or it is rotating as far away from the kernel as possible witho
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Photons and gluons have no mass. Photons energy is computed with the Plank formula: p = h omega where h is Plank's constant and omega is the frequency.
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I should have added that nothing going the speed of light can have mass. To have mass means the particle can be used as a clock, therefore time for photons stands still.
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Photons and gluons have no mass.
Nitpicking here: IIRC from school, photons have no mass at rest, they always move at Vmax (of the medium).
But since they have/are energy they have mass and their mass “has” gravity.
I may be wrong and I’d love to learn.
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Yes, it's a tricky thing because the word "mass" is used in several different meanings. Usually physicists use the word "mass" as shorthand for "rest mass," which is, mass as measured in the rest frame of a particle. But photons don't have a rest mass.
In general relativity, the source for gravity is not actually mass, but is the "stress energy tensor", where the "energy" part is that Einstein thing, where mass and energy are related by the square of the speed of light. (But since it's a tensor, it has bo
Re: Mass.. (Score:2)
Photons don't have a rest mass because you can't have a stationary photon. They either don't exist or are travelling at c_medium
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It's a fun idea. You should do an experiment to see if it's true or not.
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Im pretty skeptical of modified gravity claims, but my understanding is they propose a different set of equasions governing the mass to gravity relationship, rather than an usneen mass.. The evidence still points very strongly to a dark matter explaination, but we really are in the "We have no frigging idea" stage of the science, so. . .. maybe?
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Citation needed.
Remember - even the modified gravity bods (Milgrom and allies) publish through conventional channels, which for this field mostly means the papers are on Arxiv.
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There is a well-known technique of proof in maths called "reductio ad absurdam [wikipedia.org], and this is a variant of it. Take the claims of [whatever] and follow them to logical extremes until you find something that is clearly untrue. Then, if the chain of logic is solid, that is evidence against the validity of the proposition you are testing.
It's not necessarily the strongest demolit
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You're forgetting supergravity, which contends that gravity doesn't come from mass but merely interacts with it.
External Field Effect (Score:5, Funny)
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Eddies in the space time continuum. Jump on the couch.
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MOND hypothesis? (Score:5, Insightful)
MOND hypothesis
?
For what i understood, MOND is 'just' trying to model gravity on galactic scales. It's not a theory about the cause of that, it's just a model, like how we try to model the weather.
Which makes me think that 'hypothesis' is a totally inappropriate word, since there's no underlying theory. Please correct me if i'm wrong.
Re:MOND hypothesis? (Score:5, Interesting)
Well, to some degree it's semantics. The universe works according to a set of axiomatic rules, which are not themselves based on a deeper set of rules; that much is tautological. Our intuition is that those rules should be simple and elegant, for some definitions of "simple" and "elegant". But maybe human intuition isn't perfect, and one of the rules of the universe is "there's a force called gravity, and its strength is complicated and full of particular extra constants, for no deeper reason". What would we do, refuse to accept reality?
Re: MOND hypothesis? (Score:2)
But maybe human intuition isn't perfect, and one of the rules of the universe is "there's a force called gravity, and its strength is complicated and full of particular extra constants, for no deeper reason". What would we do, refuse to accept reality?
Who's we... an intelligent person would keep looking.
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I'm not sure I agree with the breadth of your assertion, but I do agree that intelligent people would keep hoping to find a deeper, more elegant truth. But what if there weren't one? "This cannot be the basic law of the universe, because I don't like it" is not something a rational person should say.
Physics, like Maths, is probably broken (Score:2)
Godel broke maths. We thought we could prove all theories starting with a simple and elegant set of axioms. Turns out, however many axioms you have, you always need more.
Physics started to look clean around 1900. Electrons, Protons (and Nuclear Electrons). But then it all went downhill. Today we have an ever growing zoo of particles. Time and space are all twisted up. And the more we look the stranger it gets.
God played a joke on us. There is no underlying single formula that describes the universe.
DOGDIDIT (Score:5, Funny)
[briefly considers the 17 churches in this small town of ~3300] ...that seems to be a not unusual course of action.
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If God had a choice, why would she make the gravity rules all goofy? I suppose she got tired of refactoring her little "ant farm" to have clean rules, and just patched it with layers of tweaks. After all, it's only a hobby. (It's all screwed up anyhow, so throw in an obnoxious orange ant for the fun of it.)
Re: DOGDIDIT (Score:2)
Because she already had a mostly working implementation and found that a simpler gravity would require a major refactor of the rest of creation, so she put a bunch of arcane cosmology into the gravity function, added a TODO, and flicked the switch, deeming the solution good enough for v1.
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Our intuition is that those rules should be simple and elegant, for some definitions of "simple" and "elegant". But maybe human intuition isn't perfect, and one of the rules of the universe is "there's a force called gravity, and its strength is complicated and full of particular extra constants, for no deeper reason". What would we do, refuse to accept reality?
Maybe everything is the way it is because an invisible creature from the 6th dimension likes it that way and there is no deeper reason.
Re:MOND hypothesis? (Score:5, Informative)
Nope - it slightly changes the equations on how gravity works.
from wikipedia:
Milgrom noted that this discrepancy could be resolved if the gravitational force experienced by a star in the outer regions of a galaxy was proportional to the square of its centripetal acceleration (as opposed to the centripetal acceleration itself, as in Newton's second law), or alternatively if gravitational force came to vary inversely with radius (as opposed to the inverse square of the radius, as in Newton's law of gravity)
Re:MOND hypothesis? (Score:5, Informative)
To be fair, the proposed MOND operates in a range where the GR corrections to Newtonian gravity are so trivial that they cannot possibly be detected. GR corrections matter at high fields; MOND comes into play only at very very very low fields.
However, you are right in the sense that the originally proposed MOND was not consistent with General Relativity. However, MOND has been modified since then (maybe we should call it MMOND) to create a hypothesis that is consistent with a suitably-adjusted GR.
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Hi Geoffrey,
It seems to me that all discussion revolves around the passage of time being constant from the innermost regions of the galaxy to the outermost region.
If I measure 2 billion years from the point of view of the Earth, would a person living near the center of the galaxy and another from the galaxy edge both agree that two billion years had passed? If not, what would this look like from the point of view of someone on the Earth? Faster than expected Newtonian motion?
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Good question. Let's see if I can make a quick order-of-magnitude approximation
From the Schwarzschild metric, gravitational time dilation is SQRT(1-2phi/c^2), where phi is the gravitational potential, GM/r. For a quick order of magnitude, if we assume that the galaxy can be approximated by a Schwartzschild metric we're probably not off by more than a factor of two or so. Phi is escape velocity squared. For a 1/r^2 gravitational field, the virial theorem says that gravitational potential energy is (negativ
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First, thank you for responding.
As you have probably guessed, I am not an astrophysicist. If I am understanding you correctly, what you are saying in the first part is that regardless of time dilation, there is still not enough gravity to hold that amount of mass in orbit.
In the second part, it seems you are telling me that there is not much of a time difference anyways, so ignoring it safe.
Did I parse your answer correctly (if primitively)?
If not, I apologize for wasting your time. I try to understand as I
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First, thank you for responding. As you have probably guessed, I am not an astrophysicist. If I am understanding you correctly, what you are saying in the first part is that regardless of time dilation, there is still not enough gravity to hold that amount of mass in orbit.
Well, the observation that there is not enough (observed) mass to hold the outer stars in their orbits around the center of the galaxy is the observation that the theory is attempting to explain. The answer is either there is more mass that we don't see, or else our understanding of gravity needs to be modified.
In the second part, it seems you are telling me that there is not much of a time difference anyways, so ignoring it safe.
Right.
Did I parse your answer correctly (if primitively)? If not, I apologize for wasting your time. I try to understand as I don't know everything (not even close). Side question, are you the guy I saw on a Discovery Channel special?
Possibly. Not sure what programs are currently airing on the Discovery channel, but I've been on a few here and there.
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Possibly. Not sure what programs are currently airing on the Discovery channel, but I've been on a few here and there.
It is an older one, not current. I am guessing it was you because when I saw the name on the screen, I remembered your name on Slashdot. I didn't want to actually bother you when I first noticed, but since I am talking with you now, I figured I would ask. I think that is pretty cool that you were on a segment. :)
But anyways, back to the discussion:
With the GPS satellites, time corrections need to be made. I understand that the changes are quite small. When scaled out from the center of the black hole to the
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Yes-- but the GPS correction due to General Relativity is only 45 microseconds per day. Even if the gravitational potential of the galaxy is a lot larger (and it definitely is)... the correction is still pretty small.
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I apologize. I don't think I represented myself very well there.
My reason for mentioning GPS satellites is that they represent the idea that the rate of time changes in relation to the density of mass and the distance to said mass.
Since there is significantly less mass at the edge of the galaxy, I would imagine that there would be a correspondingly significant difference in the rate of time.
Merry Christmas. :)
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It's not that it doesn't teach you anything, but it's similar to curve fitting.
https://www.youtube.com/watch?... [youtube.com]
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ALL scientific theories are similar to curve fitting. First you fit the curve, and then you check in other areas to see if it fits there, too. If it does you think you have a useful theory. The curve fitting part is the "hypothesis". Once you check it against other areas, and it matches, it becomes a theory.
This "external field effect" is part of "checking against other areas". IIUC, the version being tested has been modified from the original MOND to be consistent with General Relativity....but it sti
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Curve fitting means you add parameters until you find a way you can use empirical data to decide on the values of the parameters.
guessing the nature of the curve family is a hypothesis . Requireing few parameters is a measure of the quality of the hypothesis. Von Neumann's quote goes "give me 4 parameters and i can fit an elephant". It is mentioned.
multivariant analysis is the opposite of a hypothesis.
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What is interesting that since MOND has been proposed, it also fits information that we didn't have at the time.
Which, despite its flaws, makes me think there may be something there.
So to use the example of Von Neumann, it's like taking four parameters, fitting an elephant, then finding that the same equation works for almost every other animal.
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#BlackMatterLives ?
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The MOND hypothesis is that gravity does not follow a simple inverse square relationship, like Newtonian dynamics (and our observations to date) says it does. From this hypothesis, you can then build a model that you hope explains galactic and cosmological dynamics without requiring the presence of dark matter. Spoile alert: it doesn't work very well.
MOND vs. dark matter (Score:4, Informative)
Disclaimer up front: I'm no astrophysicist.
From what I've read and watched about MOND is that there appears to be evidence against it -- mainly because of two observations:
1. While observations of the rotation speed of individual galaxies can be used to fit a parameter in a modified equation of motion for large-scale objects, the fit parameter differs widely from galaxy to galaxy and thus does not appear to be universal.
2. There are some observations where MOND completely breaks down, most notably the Bullet Cluster [wikipedia.org].
I've skimmed the paper, and what the authors claim is that existing dark matter models don't align with the observations they analyze in their paper (though they only mention CDM in their model, and while that's the most prominent candidate dark matter model a the moment, it's not the only one). From my very short skim of the paper it appears that their methodology is sound at least on a surface-level inspection -- but let's say their analysis holds even under a lot of scrutiny: to me this paper is not actual evidence in favor of MOND, it's rather evidence against existing dark matter models (though not necessarily dark matter itself), because they don't account for the observation made here. The paper does poke a hole in these dark matter models, and it's going to be very interesting how or whether scientists will be able to find better dark matter models because of this, or whether they'll come up with something completely different. But as long as the problems MOND has with various other cosmic observations (see above) aren't accounted for, I just can't see MOND as a viable hypothesis.
(As a side note: I think the paper is overstating the claim that they've found evidence of the strong equivalence principle (SEP) being violated: what they've actually found is that the SEP appears to be violated under the assumption that dark matter is distributed according to predictions by existing dark matter models, but that doesn't mean that the dark matter distribution couldn't be different to result in those curves, and we simply don't have the right predictive model for its distribution. Not saying that's definitely the case, I have no idea, but I'm always careful with claims that something so fundamental as the SEP is violated -- you need a lot more evidence for that.)
A good introduction to the astronomical evidence for dark matter can be found in this video by an astrophysicist [youtube.com].
Re:MOND vs. dark matter (Score:4, Insightful)
Do note that Dark Matter allows astronomers to place an arbitrary amount of it at an arbitrary location in space in order to explain a phenomenon. It gives them 4 variables to freely chose from to eliminate discrepancies in the current models, and astronomers have gone as far as using variable distributions of Dark Matter in space, thus basically stretching it to a near infinite amount of freedom. It makes Dark Matter not only a well working theory, but it carries a great burden of proof on its shoulder. It has so far not been detected and all so called proofs of its existence are self-fulfilling at this point.
MOND and other alternative models choose smaller degrees of freedom to explain the observable universe, and so these fail intentionally more easily, to allow for corrections sooner. With Dark Matter hinges everything on the detection of a particle, and with every failed Dark Matter experiment is it getting more difficult and costly to prove its existence.
In short, comparing MOND to Dark Matter is not as simple as comparing apples to apples.
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"There are some observations where MOND completely breaks down, most notably the Bullet Cluster."
MOND does not "completely break down" here, because there are plausible explanations for the lensing which do not require DM, according to Moti Milgrom, who created the MOND theory in 1982.
http://astroweb.case.edu/ssm/m... [case.edu]
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The problem is that, whilst all your objections are true, the same objections hold for dark matter. There's no model that works in all situations, which is a serious problem.
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Is it? All that says to me is that it means that human ingenuity and inventiveness is less than what is necessary to accurately describe the universe. Outside the arts and fiction writers, I've never heard anyone seriously propose that human ingenuity and inventiveness is actually infinite - which would put it in a class of two with human stupidity (cited in evidence : Slashdot comments, which puts a high minimum bound on the quantity
Newton was right. (Score:2, Funny)
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Naah. The missing mass in the Universe resides in jars of Cheez Whiz and similar products. They are "Cheesily Interacting Massive Particles" or ChIMPS.
squirrel! [Re:Newton was right.] (Score:4, Funny)
What they call dark matter is actually just apples. The only reason astronomers haven't realized it yet is that there aren't any observatories near orchards.
The leading hypothesis seems to be that it might be squirrels.
https://xkcd.com/2186/ [xkcd.com]
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Anything help (Score:3)
MOND has always hypothesised that Newton's Laws could need adjusting on the galactic scale. When the math behind MOND shows to hold true beyond the galactic scale and leads to new findings consistent with new observations, then it's already paying off.
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Just a reminder, from the 1950s...
Neutrinos are a 100% made up, fantasy filler particle to balance a math equation based on calculations that we suspect are wrong because we don't actually know how electricity and magnetism works. They have never, ever, ever been detected in any way. They are more likely not to exist because we're more likely to be calculating momentum conservation incorrectly than an object with zero charge and zero proof of existing that we literally made up, assuming at the time that it
Re:Just a reminder (Score:4, Insightful)
Of course, the general point should be that along with those theories that were proven correct, there are plenty of examples of theories proven wrong.
Now I think the parent poster went a bit overboard in proclaiming that dark matter is the unlikely result, we simply do not have data to make such a supposition. It is worth keeping in mind we shouldn't get too attached to any specific theory and 'know' it to be true, as seems to be the case often in popular science coverage in dark matter (which further tends to imagine dark matter is *one* specific material when in reality if it is as-yet unseen matter, could be multiple forms of material rather than a singular thing).
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After all, it's just a theory... a
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Nepture *was* dark matter once.
The thing is, every time an article like this comes out a complete ignoramus like the OP proclaims all this nonsense. We know quite a bit about dark matter - we know its equation of state, we know it interacts gravitationally, we know it causes lensing as a result...
And I'm not going to argue with every shitty journalists' version of things - of course there could be an entire dark sector, with an entire dark Lagrangian. The point is, we should be pretty damned confident that
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And don’t forget that black hole was also thought to be just a theoretical curiosity and would never actually exist.
Then there was also the ridiculous idea that you could create some propagating wave through vacuum by shaking a magnet, when wave solution was found from the Maxwell Equations.
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Just a reminder, from the 1890s...
Luminiferous aether is 100% made up, fantasy filler... blah blah blah. No really, it was because a bunch of very smart people who really thought they were right were absolutely wrong based on preconceived notions. This could go either way, not sure where you were going with this.
Funny you should mention Neptune. Did they ever find the planet Vulcan? You know, the one said to exist by the same guy who "discovered" Vulcan because they didn't understand the differences in Newt
Re:Just a reminder (Score:5, Insightful)
Oh for fuck's sake. This happens with every article on dark matter, someone crowing about epicycles and acting like they just invented Occam's Razor, denouncing The Scientific Establishment for smugly taking the easy way out rather than reconsidering their theories.
Wanna know a secret? Cosmologists hate the idea of dark matter. Even the ones who study it, who made their careers around it, hate it. It made sense for Poincare to hypothesize "dark stars" which the optical telescopes of the time would miss, but as we got more of a handle on "what's out there" nobody's been happy with an arbitrary extra balancing factor that shows up in galaxies but not in asteroids. So people keep trying to throw out dark matter, to come up with a more elegant and complete theory. And meanwhile, we get more and better observations, which have the nasty habit of matching the predictions made by the dark matter theory. The continued prominence of the dark matter theory is a triumph of science over irrationality: We don't want it to be true, but as rational beings we are forced to believe what the data is telling us.
Scientists just 1: like grant money and 2: don't like admitting they're wrong nor don't know the answer to something.
Scientists don't like being wrong, but they love proving everybody else wrong. Do you honestly think that if someone came up with a reasonable, observations-matching, elegant alternative to dark matter, the world wouldn't beat a pathway to their door? That would be grant money eternal. This idea of the whole scientific community propping up an unworthy scientific consensus rather than "admitting they're wrong" is absurd to anybody who's seen the long-term machinery of academia. It's a deeply flawed system, yes. But it isn't even slightly flawed in that way.
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That claim is in stark disagreement with Max Planck's observation [wikipedia.org] that new ideas aren't accepted until the old generation dies out.
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No, it's not in disagreement. Whether scientific consensus moves a paper at a time or a generation at a time, it moves. (Eppur si muove!)
Anyways, from what I've personally seen, Planck's far too pessimistic. Grad students who came to believe in oxygen instead of phlogiston learned about it from someone else, and they learned it from an establishment populated by more than just other grad students, so clearly someone's changing their mind mid-career.
Planck's observation makes the most sense in the context of
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No, it's not in disagreement. Whether scientific consensus moves a paper at a time or a generation at a time, it moves. (Eppur si muove!)
Anyways, from what I've personally seen, Planck's far too pessimistic....
Quite. Let us all remember that Max Planck was making a sociological observation about a particular group of people up to a particular time in history.
Assuming Planck's observation holds true beyond that time is an exercise in extrapolation, and is especially speculative because his very writings altered scientists' understanding of the process, and hence their behavior. Academia has changed considerably since Planck.
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The reason why Dark Matter works so well is because it is beyond our understanding, and so indistinguishable from magic. Whenever our math is off do we sprinkle Dark Matter onto it in just the right amount and all is well again in our universe. And each time we do this does it also become proof of its existence. Of course we hate it. Einstein would probably call Dark Matter and Dark Energy the greatest blunder of our time.
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No, Dark Matter isn't a new mathematical model. It's a particle we assume exists. It uses the old model in hope we don't have to create a new math.
Dark Matter allow us to freely choose an amount as well as location to compensate for unexplained phenomenona. This gives us 4 variables to play with. You see something that cannot be explained with our current model!? Just sprinkle some Dark Matter pockets into space here and there, and in the right amounts, and you might have a working explanation. Having the a
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All in all, wi
Consistent with expansion measurements? (Score:2)
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Thinking they have either noticed a glaring problem with current theory or have superior explanation, that is the Dense Matter between slashdotters' ears.
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2 different phenomenon are associated with 'Dark' in astronomy but are unrelated.
* Dark Matter is a model of a source of mass that has no electromagnetic interaction and is distributed between stars and galaxies. At a scale of about 10k ly it becomes easily detectable with gravitational lensing in areas that are unexpected from the visible matter and the orbital velocities of stars in galaxies.
* Dark Energy is a model that shows a very weak apparent acceleration of space itself with no input of known energy
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Old lesson not learned? (Score:1)
It's an argument over where to stick the extra layers of epicycles to make the numbers match. With all this fudging, I strongly suspect we are just not spotting a simpler explanation. This includes throwing dimensions at string theory.
Then again, maybe the Universe(s) is indeed some kind of giant regression engine, where natural selection and/or the anthropic principle reshuffles each universe instance and "tunes" each layer, like some kind of parametric DNA.
Rigged! (Score:1, Insightful)
"Gravity is rigged, believe me! It's was tweaked in a Wuhan lab to make Americans fall harder to give Jiihna a factory worker advantage. I'm the one chosen to fix it, but am being blocked by rigged voting machines and fake news, who won't let my family hunt lions, tigers, and bears. Dem Dorothy is NOT going to stop me this time; Chloroquine made me water-proof. I'm going to declare Martian Law and confiscate all the Diebold machines to get to the bottom of this terrible terrible scam, AND find Hillary's ema
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(And I say that in full awareness of the way that dictators normally get into power by being elected.)
If.... (Score:1)
Seems like there's an awful lot of (gravity - via energy), in galaxies.
I wonder why ... (Score:2)
I was going through my daily listing of new Arxiv papers a couple of hours ago, and briefly (about 3 seconds) considered reading the latest missive from Milgrom trying to get MOND to work. It didn't interest me then, and it still doesn't, and the coincidence is hardly significant (Milgrom publishes several times a year, and the last time I did the numbers, on average there is a paper on MOND published about every fortn