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New Gravity Theory Dispenses with Dark Matter
Darkness Matters writes "According to New Scientist, a theory of modified gravity, which has no need of dark matter, has just explained why the Pioneer 10 probe is 400,000 miles off its expected course as it leaves the solar system. It sounds pretty convincing, although in dispensing with dark matter, they've had to utilize the theoretical particle, called a graviton, which appears from the vacuum of space wherever stars are densely packed, making gravity stronger."
"See I told you guys it wasn't flying monkeys! Turns out it's flying Unicorns!"
Behold the riant ape! Beware, his crooked thumbs!
you're telling me dark matter doesn't matter?
GRAVITRON! http://en.wikipedia.org/wiki/Gravitron Damn that was a horrible ride.
You know as a child I made up invisible things to blame and was told that was a bad thing to do. Only now I find out I was really a budding scientist...
This has been around for years. If a hypothesis involving gravitons is explained by experimental evidence, then this hypothesis could be elevated to theory.
Besides, didn't we use to shoot gravitons at that loud squiggly thing in Yar's Revenge?
There exists no way of exchanging information without making judgments. --Bene Gesserit Axiom
Man, I hope this is real so much. I've always hated dark matter. You know what dark matter reminds me of? Aether. The whole idea of dark matter reminds me of a stupid hack -- which I suppose you have to deal with when it comes to topics like physics now and then.. its not like we can just go and look so readily ;P
:)
:D
Anyway, these "Gavitons".. I think I've had them in computer games for a while now, its about time we 'discovered' them. Aethe-- I mean Dark Matter was such a cranks idea anyway... anything has to be better then "OOoooh! There must be... some.. uh, invisible undetectable matter.. that uh, has mass. But you can't see it, because.. its dark! yeah thats the ticket." Given an unlimited choice of possibilities I could have came up with something better, and it probably would have been about as scientifically valid too.
Hurray for gavitons! Prepare the graviton pulse cannons!
--SD
"Computers will never truly be free until the last windows user is strangled with the entrails of the last mac user."
Oh...graviton.
Prove it.
Its funny how easy it is to explain something when you get to come up with your own theoretical items.
Lets see...how 'bout its off course cause the Universe has shifted due to a USABLE poll on Slashdot...
Well, at least we don't have to worry about Dark Matter critters lurking in deep space.
http://www.schlockmercenary.com/d/20040311.html
Plain wrong : From TFA "critics point out that MOND cannot explain the observed masses of clusters of galaxies without invoking dark matter"
The new theory is STVG, not MOND. MOND is ANOTHER alternate theory, which is being compared to STVG. Maybe instead of trying to rush to prove the submitter wrong and post early so you can get modded up, you should... I dunno, read the fucking article?
Couldn't they make up their mind?
Sheesh, evil *and* a jerk. -- Jade
While the graviton has never been observered, it's not as wildly unlikely as that article seems to suggest. Of the four fundemental forces (strong/weak nuclear forces, E/M and gravity) only gravity hasn't had a "force mediator" particle (one which "carries" the force, for example photons for electricity and magnetism) observed in lab experiments. However, as gravity is the weakest force (by an order of I believe around 10^-28 times, or similar), this is not unlikely. However, it is extremely unlikely there ISN'T a particle which mediates gravity, ergo the (pretty reasonable) assumption of the existance of the graviton. Assuming it exists, further things can be predicted about it from other laws of Physics, hence we have a particle we've never seen but are pretty sure exists, with certain properties.
Nearly right : The theory posits that gravitons are created by all (massive) matter, it's just that near densely packed stars the effect is more significant.
Actually, no. The point the atricle is making is that the effect increases near large concentrations of mass at a rate greater the simple total mass would predict.From TFA: Plain wrong : From TFA "critics point out that MOND cannot explain the observed masses of clusters of galaxies without invoking dark matter"
The article isn't about MOND, it's about the scalar-tensor-vector gravity (STVG) theory. MOND was just mentioned as a competing theory...a theory that couldn't adequately explain the behavior of galatic clusters or the Pioneer spacecraft.
____
~ |rip/\/\aster /\/\onkey
The way the post is worded, I think there is some misunderstanding what a "graviton" is. The graviton is the force-carrying particle of gravity, in a similar way to the photon being the force-carrying particle for electromagnetic phenomena. Although the graviton has not yet been directly observed, there is little doubt among physicists that it does exist. The current best theories we have (standard model of particle physics, etc.) strongly suggest that it exists.
The post makes it sound like suggesting that gravitons exist is outlandish... but this is rather accepted. Instead, it seems that their theory is a particular attempt to quantize gravity (there have been many attempts over time, with all ultimately being unsatisfactory). Whether or not their new theory is useful remains to be seen.
Also, in TFA, they say: "In this case, a hypothetical particle called a graviton - which mediates gravity - appears in large numbers out of the vacuum of space in regions crowded with massive objects such as stars." Again, it is generally accepted that in any reasonable theory of quantum gravity, gravitons will be the force-carrying particle for gravity. Where there is a large gravitational field, virtual gravitons will be exchanged to mediate the force (more info on virtual particles). This is nothing new. And in particle physics, virtual particles can always appear and disappear from the vacuum.
So again, I think we can't coment much on this theory without reading the actual paper (anyone have a link?). I would like to understand what is actually novel about their formulation. Also, they are not the first to try and reformulate the basic laws of gravity to get rid of the "dark matter anomaly" and none have been found to be consistent with all the experimental data.
If gravity isn't quite what it seems to be in terms of strength versus distance, then studies of planetary systems should show the effect. The relationship between orbital radii and orbital periods (and orbital path) would not be quite consistent with the 1/r^2 rule for Newtonian gravity. Admittedly the distance and mass scales of a our planetary system are far smaller than the galactic scales discussed in the theory, but our ability to make extremely precise measurements of planetary distances and orbits should compensate for that.
Two wrongs don't make a right, but three lefts do.
Scientists have actually calculated that Dark Matter is, in actuality, Chuck Norris. He recently flew to the west coast, and this threw off the Pioneer 10 probe by 400,000 miles.
Scientists have also not yet revealed the real reason behind the ban on human cloning. The real reason human cloning is outlawed is because scientists fear Chuck Norris being cloned. They theorize that two simultaneous Chuck Norris roundhouse kicks could possibly destroy the universe....
"All great things are simple & expressed in a single word: freedom, justice, honor, duty, mercy, hope." --Churchill
If there's no dark matter, what's that stuff coming out of Nibbler?
Now we're going to see the inevitable parade of, "See, I knew dark matter was a stupid idea all along".
First off, dark matter, even if it ultimately turns out to be wrong, is not a stupid idea; it explains a wide variety of independent phenomena (and contrary to the eternal "it's just epicycles" cry among Slashdotters, it is testable, falsifiable, and predictive).
Second, this new work is, well, new. Only one of the three papers (other two: here, here) has passed peer review so far. When a theory like dark matter has amassed evidence in its favor over a period of decades, it takes a lot to overturn it.
Even if their STV theory does ultimately pan out (and there have been many alternate proposals in the past that have ended up failing), it will take years to be hashed out in the literature and subjected to far more tests; so far they have only passed a few of the observational tests that dark matter does, even assuming that their papers are correct, which no one has checked — there are no followup studies by other authors at this point.
Basic lesson: for every revolutionary new theory that works, there are a hundred that don't, and it can take a long time to decide which is which. New Scientist is not doing anyone a service by jumping on the latest unpublished preprint of the month and hyping it as the revolution of the century, as they tend to do.
This is the problem when you read dumbed-down explanations of science. It really does sound like fantasy and BS. However, we have not moved into "the fantasy realm". According to our current best theories of particle physics (the standard model, etc.), virtual particles can indeed appear in the vacuum, exist for a short time, then disappear. All of this comes out of a quantum treatemnt of fields (quantum field theory, etc.), where Heisenberg indeterminacy (also called the Heisenberg uncertainty principle) leads to these quantum fluctuations on small scales.
That virtual particles appear and disappear from a vacuum is actually well established. It gives rise, for instance, to Hawking radiation, and one can even measure Casimir forces.
This new theory is clearly speculative, but that whole "particles appearing out of the vacuum" thing is not the new and interesting part. That is a plainly accepted aspect of all modern quantum theories.
Because that's the noodle-string theory.
The Tao of math: The numbers you can count are not the real numbers.
The real problem with this article is that it was published in NewScientist, which, as I discovered as an undergrad, is often full of incredibly exciting ideas supported by very little evidence and frequently go nowhere.
The Higg's Boson (or God Particle) mediates the Higg's Field, the Graviton mediates the gravitational field - they are different things, although are related.
The Higg's Boson creates mass and the graviton turns mass into gravity, or something like that - it's not my area...
Sorry to reply to my own post, but here are, possibly, the scientific papers in question. Doing a search on arXiv for the names of the authors (Joel Brownstein John Moffat) provides a paper entitled "Gravitational solution to the Pioneer 10/11 anomaly" (warning: PDF).
I'm not an expert in gravitational theory, so I would appreciate others correcting any mistakes I make. The abstract to the paper says: "The theory allows for a variation with distance scales of the gravitational constant G, the fifth force skew symmetric field coupling strength (omega) and the mass of the skew symmetric field = 1/(lambda)."
I think this is quite a departure from what is conventional accepted about gravity. The gravitational constant, G, sets the scale for the force of interaction of gravity. It is normally assumed that this value is constant throughout the entire universe. They seem to be allowing that this value changes with distance, so that the interaction of gravity is different at small and large length-scales. That they are able to come up with a fit to actual experimental data is quite amazing... although so many bits of astronomical data have been computed assuming a particular (and constant) value of G, so to compare with "established facts" they will have to reconsider all of these previous calculations.
I highly suggest you read up on it if you like physics.
Slashdot's rate-of-post filter: Preventing you from posting too many great ideas at once.
To exerimentally verify this go and buy one copy of New Scientist and one copy of Scientific America. Compare.
Can't. Quit reading SA after they started publishing thinly vieled political hacks instead of science articles.
... and then there's the crouton, which mediates salads.
Intron: the portion of DNA which expresses nothing useful.
From Wikipedia:
Detecting a graviton, if it exists, would prove rather problematic. Because the gravitational force is so incredibly weak, as of today, physicists are not even able to directly verify the existence of gravitational waves, as predicted by general relativity.
Yoda: Hard to see, the dark side is.
He who knows best knows how little he knows. - Thomas Jefferson
It's only a theory folks. We shouldn't be teaching it because it hasn't been proven. It's not a fact.
(For the humor impaired I'll give you a few moments to let the words sink in)
We will bankrupt ourselves in the vain search for absolute security. -- Dwight D. Eisenhower
I'm not an expert in particle physics either, but here's what I know:
Is not one of the big problems with "gravitons" that gravity appears to act more or less instantaneously at great distances? And isn't that a little troubling from the "Action at a Distance is Big No-No" point of view?
No, according to the theories gravitons would travel at the speed of light. In fact, bear in mind that the exchange of virtual particles is what prevents "action at a distance", if you like. Instead of gravity (or magnetism) having an effect "just because", the theory explains that it is because virtual particles are flying back and forth between the two objects in question. In the case of gravity, it is virtual gravitons, and in the case of magnetism, it is virtual photons. Both travel at the speed of light, which explains why force effects (like gravity and magnetic fields) are not instantaneous: they propagate at the speed of light (this has been measured and is not in dispute).
Pioneer 10 is pretty damned far out there at this point.
Apparently Pioneer 10 is 89 AU from the sun. 90 Astronomical Units is 12 light-hours. Still, your point is well-taken... gravity operates over distances of millions and even billions of light-years... so how can these "virtual gravitons" cover such distances? After all, supposedly virtual particles exist only for a short time!
My apologies to the hard-core particle physicists for this simplistic explanation, but here goes: When you look at the Heisenberg Indeterminacy Principle, you find that there is a relation between space and momentum. We all know the famous "the more accurately you localize a particle, the more spread out its velocity is"... it turns out that this implies a similar relation for energy and time. What it means is that high-energy particles can "pop into existence" for very short periods of time... but low-energy particles could exist for longer times. This is what allows virtual particles to do their thing. Very strong forces (nuclear forces and electromagnetic) involve high-energy virtual particles, which can only travel short distances before "disappearing"... that's why those forces operate over short distances.
But gravity is very very weak (by comparison). So that means that a virtual graviton can pop into existence, and travel for a long distance and time (millions of years) before disappearing. That's what, in fact, causes gravity to operate over such vast distances. So in fact the distance-scales and force intensities are intrinsicaly related in quantum treatments. So "a short time" means something different for EM-forces and gravity-forces.
I hope this (simplistic) explanation is somewhat useful to someone.
The "After all, if something couldn't come from nothing how did God come about?" question is not a valid one. For an indepth explanation please read augustine, aquinas, c.s. lewis, I think descartes version of the ontological argument even hits on this, but really any book on christian apologetics will help you out. A very rough sketch of the arguement is that God, by definition, needs to exist without being casued. Everything in this universe needs a cause, so what caused it? For Aristotle it was the unmoved mover, for creatonists it is the Christian God. That which necesarily exists without needing to be caused. That is one of the attributes of the creationist God (or really anybodys God). To say what caused God, ok say x caused God then what caused x? It goes on forever eventually something must exist that needs no cause. That something is God. While I and many other christians don't agree with the creationists attack on evolution, it is a logical fallacy to commute one wrong step with all of christianity being false. As I can't prove it in depth in a post on /. please refer to any apologist, c.s. Lewis is my favorite for a more conclusive step by step account.
your friendly neighborhood philosophy student
I know what you mean: First built by the Autobots, Graviton had such desire to conquer that he defected to the Decepticons, and eventually went solo, and is currently plotting to drag stars in to power his quest for power. Will Autobots and Decepticons form a temporarily alliance to stop him in this 3 part series: The Fall of Dark Matter, and the Rise of Graviton.
God spoke to me.
I read physics at university. An optional Third year course was 'General Relativity'. In the little booklet they gave us to help in choosing what courses to 'major' in (it was an english university), there was an asterisk next to 'General Relativity', as well as 'Cosmology' as a matter of fact. The asterisk denoted 'mathematically rigorous - to be considered only by students with particularly strong mathematical backgrounds'. My friends and I didn't take it - we did things like Computational Physics and Astrophysics instead. In fact, one afternoon, for a laugh (crazy guys that we were) we sat in on a General Relativity lecture to see if we could even keep up. It was a thirty minute lecture on 'Aphelion Procession Using the Scwarzchild Geodesic'. We didn't stand a chance - ball-breakingly tensor analysis. My point is, at that time I knew a hell of a lot more physics than your average guy in the street and I didn't have a clue what was going on in that General Relativity lecture. I read around, spoke to people smarter than I was, spent a fair bit of time trying to get my head around General Relativity I didn't even scratch the surface. And I was a straight-A student back then. I just don't think there exists such a thing as a layman explanation of our understanding of gravity. That other splendid bugger Dr Richard Feynman once said something like 'If a theory can't be reasonably well explained in a single undergraduate lecture then we don't really understand it at all.' It may be that we don't really understand the theory of General Relativity - maybe there is a far more elegant theory explaining gravity that could be explain gravity in simpler terms. For certain, though, that theory does not currently exist. It's a shame, because like you I was always frustrated by the absence of a simple answer to 'How does gravity work?', Why is it always attractive and never repulsive? Some things are just really, really difficult to model and the only models we have are 'mathematically rigorous'. In the words of JBS Haldane 'The universe is not only stranger than we imagine, it is stranger than we can imagine'. http://en.wikipedia.org/wiki/Richard_Feynman http://en.wikipedia.org/wiki/General_relativity http://en.wikipedia.org/wiki/Tensor_analysis
I thought Dark matter effectively functioned like negative gravity so as to account for the accelerated expanding universe? How does the graviton explain this phenomenon?
The existence of God is easily falsifiable. Just kill yourself and ask St Peter at the pearly gates yourself. If you don't want to perform this experiment then that's your problem. But it's certainly a lot easier than falsifying String Theory.
-- SIGFPE
1. God needs to exist without being caused (P, proposition)
2. Therefore, God exists without being caused (P, same proposition again)
You don't really even have an argument there, you're just making an arbitrary fact claim with no evidence, and no argument. You can expand this and make it more fancy, but it's always reducible to this fact claim. Arguably the greatest mistake is fact claim "Everything needs a cause." Which is either correct, or incorrect, if it is correct, then god can't be uncaused, and therefore, accordingly to your logic the universe can't exist (deus ex machina not being allowed in proper logic), if it is incorrect, then god isn't necessary for the universe to exist anyway. God may exist, but by Occam's razor, it is the simplest explanation that it does not.
That's wrong. It comes from a naive treatment of gravitons as classical particles that bounce off each other, rather than as virtual particles whose quantum phases superimpose after taking all possible paths to their destination. See here.
That's also wrong. Gravitons are affected by everything they interact with. However, their interaction is very weak.
Gravitons have absolutely no problem explaining this, just like the photon theory doesn't have any problem with explaining why the electric field isn't "cut off" when a charge passes in front of another charge.
Note: some of the replies to my posts have fixed mistakes I made in the explanations. For instance, it is more correct to specify that the maximum range over which a force acts has to do with the mass of the particle (which is related to particle energy, of course). Massless particles can operate over (in principle) infinite distances, so there is no upper bound to EM and gravity forces... however the "perceived distance" over which a force acts also has to do with how quickly it decays, and I believe this is related to what I was describing.
It's important to distinguish between virutal particles and real particles. Take E&M for a moment: an electric field exists because of the exchange of virtual particles between the (charged) objects in question. However, a beam of light (or radio waves etc.) is an E&M wave, and is carried by real photons. The terms 'real' and 'virtual' were used because you can directly measure real particles, whereas virtual particles are detected only indirectly (by their effect). So a beam of light is 'real' and its constituent particles will not "pop out of existence" ever (they may be absorbed or otherwise interact with other particles, mind you). So a beam of light will eventually reach the other end of the universe. However, the field "emanating" from an electrically charged stationary particle will be infinitely weak if you go infinitely far away (because only extremely low-energy virtual particles can reach out that far).
Similarly, the graviational field is made by exchanging virtual gravitons. In principle, an accelerating mass creates gravitational waves: REAL gravitons. Efforts are underway to detect these gravitational waves directly (LIGO).
No it would not. Just as photons don't have negative momentum just because they pull together oppositely charged objects.
One of the most significant pieces of evidence for dark matter is the rotation curve of galaxies. If the Universe functioned like we thought it did, the rotation curve of a galaxy should be a downward sloping curve - the further out a star is from the galactic center (where the mass of the galaxy is concentrated), the slower its orbit should be. This is what Kepler's Law tells us - that the orbital speed of an object decreases inversely with the square root of the orbital radius.
What we find, however, is that the rotation curves of galaxies are nearly flat, meaning that the mass distribution of galaxies must be nearly equal all the way through. This means there must be a large amount of matter that we don't see. There aren't enough dwarf stars, planets and other things like that to make up this mass. Of course we haven't counted or seen all of these, but if you do the math, there would have to be a ridiculous amount of these - more than is likely. Hence, we have dark matter.
This new theory says that the force of gravity should be stronger near the galactic core, where the stars are packed most densely. So the core is even more massive than we thought, meaning that the rotation curve of the galaxy should be even more skewed - far from flat. So either New Scientist seriously misrepresnted his theory, or it doesn't even deserve a cursory thought. MOND at least seems plausible.
"More of the 'uh... well, it went away when you came in. It's only around when you're not looking. And it knocks things over when I'm the only one in the room' variety..."
This sounds more like the work of a quantum physicist.
The strength plays the role of Newton's gravitational constant in GMm/r^2. The 1/r^2 is what matters the most in determining how quickly the force falls off, but the constant in front matters too. For a massive exchange particle, you get the Yukawa potential k exp(-r/R)/r where R is the "characteristic distance" determined by the mass, R = hbar/mc. (Larger masses mean shorter distances.) k is the strength of the interaction (actually the square of the coupling constant), but the overall function is dominated by how fast the exponential decays, which is governed by R (and thus m).
That's not true; the strength of an interaction determines how strongly two particles of a given energy influence each other, not how strong the particles themselves are. In fact, the strong nuclear force in quantum chromodynamics weakens at higher energies (leading to the phenomenon of asymptotic freedom and confinement).
That's true, but what governs their lifetime is not the strength of the interaction, but their mass(-energy), via a kind of energy-time uncertainty relation.
There is sort of a way like that to explain, say, the inverse square law: a sphere of radius r has an area that increases like r^2, explaining the 1/r^2 dropoff of the force: the virtual particles can go to more places and get "diluted". But the idea is that "fewer" virtual particles end up at any one spot, not that they "run out of gas" and can't travel that far. You sum over all virtual particle histories, of arbitrary lengths.
What's really going on is a million times weirder, of course.
If corporations are people, aren't stockholders guilty of slavery?
I think we all know that Dark Matter and Gravitons are just a hoax. What really holds those galaxies together is the gravitational effects of the substance which carries IEEE 802.3 packets: the ether.
A slashdotter who didn't build his own computer is like a Jedi who didn't build his own lightsaber.
The photons from your light beam are real, not virtual. There is no limit to how long they can exist.
For those who applaud the end of dark matter, this sort of law-modification theory should really be much more worrying. Dark matter at least has a plausible explanation, is predicted by various theories, makes predictions, and is somewhat intuitive. (come on, how likely is it that all the massive particles in the universe just happen to interact electromagnetically as well? We know from measurements that some, at least, do not - e.g. neutrinos.)
Altering the laws of physics so that they do not behave consistently (specifically, they just happen to do something different when far away from our local experiments) and giving no explanation why this should be so except to fit the previous data is really a terrible way to do things. And if new observations topple your carefully constructed modifications? What are you going to do - change your maths again?
The analogy is seeing a red ball, and declaring not that there is a red ball, but that there is a subtle effect with optics that creates circular red blobs in your vision from time to time.
Just read J Moffats paper, http://lanl.arxiv.org/abs/gr-qc/0506021, and so i'm not supprised he can
describe correctly the three problems: galaxies, galaxy clusters, and the pioneer anomally. With enough free parameters you can always fit a curve to a data, and STVG has got lots a parameters:
its got ordinary gravity as GR
plus a cosmological constant
plus a repulsive vector field
plus 3 scalar fields
The scale fields describing how the strength of each of the forces varies in space (and time). He then curve fits his new equations with different free parameters for each problem, which you have to do because the strength of the forces varies from place to place. With 3 problems and 3 free variables its not surprising he can fit a solution. This isn't to say STVG doesn't make sense, it does, and fits in well with string theory for example. The problem is with that many free parameters its easy to fit a solution to any problem, but hard to make acturate predictions or disproveable assertions.
Two downmods and the karma bonus on that post is gone, doesn't matter what other mods there are.
Justice is the sheep getting arrested while an impartial judge declares the vote void.