There isn't a lot of gravitational lensing — it's only significant when light passes near dense collections of matter. The net effect is that some images of distant stars or galaxies are sometimes displaced a bit from where they "should" be. Usually the light doesn't get lensed multiple times on its way to us, simply because it's rare for several lensing objects to exist on a line between us and the source. Most objects we see are not lensed at all, and those that are, aren't usually lensed much.
Anyway, to be kind of facetious, the universe with lensing is what the universe "really looks like".
Yes, but is there any corroboration of dark matter that doesn't involve gravitational theories? No. It's possible there never will be, if we're unlucky and have dark matter that only interacts gravitationally (e.g., massive sterile neutrinos). Hopefully there will.
But it's still not constrained in the way it would be if there were some other way of observing it, independent of gravitational inference. IOW, my point stands. IOW, your point doesn't stand. Certainly we would be able to infer more about dark matter if we could get some non-gravitational evidence. But the gravitational constraints alone mean that we can't get "whatever result we want" with dark matter, contrary to your claim.
What I'm saying is that we're currently comparing dark matter to a possible theory of gravity we don't have. Obviously dark matter currently wins that contest, just as competing versions of epicycles were once the winning theory of solar system orbits. Once again, epicycles were never a theory of anything, because they were entirely non-predictive. This is not the case with dark matter. Furthermore, the reason why we don't have a competing theory of gravity is because modified gravity is not very good at reproducing the successes of dark matter. It's possible that someone will come up with such a theory, but right now it looks like the dynamics will have to be so complex and contrived that it makes dark matter look appealing by comparison. This is on the basis of the many gravitational theories that have been tried.
Yes, but the reason that this is a weak position is that you're relying for the completion of the theory on a range of possible postulated entities. That's a catch-all response which basically amounts to "we don't know". You will recall that your original claim was that dark matter was invented "just to make the theory work", by which you mean gravitational dynamics in astrophysical phenomena. My point is that dark matter is not "just" there to make theory work; there are other, non-astrophysical reasons to believe that dark matter particles may well exist.
Incidentally, this characterization as a fudge to maintain "existing theory" is rather silly. Dark matter is a new theory, just like modified gravity theories are. Both of them replace our previous notion of astrophysics.
I'm pointing out that there's a lot of uncertainty here, and a lack of independent corroboration, and that responsible scientists shouldn't blind themselves to possible alternatives by according too much weight to intrinsically weak theories Dark matter is not an intrinsically weak theory. By now it has passed dozens of independent observational tests. And nobody is blinding themselves to possible alternatives. That's another silly characterization of what's going on. Dark matter was resisted for decades, and even today there are still alternatives like modified gravity being worked on. It's just that there is less and less room for them, as new evidence has disagreed with alternatives and continued to agree with dark matter.
Galaxys clump more than they should or even form never mind keep their distinctive shape given the current theory of gravitation. Rather than update Newton they invent dark matter. They tried updating Newton, in the form of the MOND theory you mention. It worked for galactic rotation curves, true, but failed at a lot of other things like clusters and cosmology. That's why dark matter is still the leading candidate. Even MOND advocates are now admitting that at least some dark matter seems necessary. Modified gravity theories are still looked at, but they haven't lived up to the promise.
There is also the case of that probe that is leaving the solar system faster that it should. The Pioneer anomaly.
Does dark matter account for that too. No. Why should it?
i.e. without dark matter (and dark energy), gravity doesn't predict much. That is an absurd statement. See, for instance, this review article for a truly extensive list of successful predictions of general relativity.
My take: If the theory doesn't work witht the data, it's because the theory is wrong--you don't go invent something just to satisfy the theory. You don't "invent something to satisfy the [wrong] theory". You invent a new theory. Dark matter is one such theory.
(Incidentally, sometimes the data is wrong, or the interpretation of the data.)
There are various takes on the evidence for dark matter, but altogether my understanding is that it's virtually undetectable (no E&M interaction)--so it can't be disproven It interacts gravitationally, and can be disproven that way. In fact, a number of specific dark matter proposals have already been disproven that way. (e.g., we know that the dark matter is not mostly made up of compact astrophysical bodies, and we know that it's not made up of light particles.) Future observations could potentially rule out the remaining dark matter proposals, but so far they have not.
Dark matter is a crutch of a theory with so many problems they had to invent an imaginary substance to explain them. The history of science is filled with examples of new particles that were predicted — and discovered — on the basis of experimental discrepancies. You're going to have to do better than that.
The term "dark matter" originally referred to normal matter that we couldn't see because it wasn't lit up. Once this idea was proven inadequate, dark matter became something new and its definition was shaped solely by what the theorists needed it to be. You say that like it's a bad thing. Theories that don't work are replaced by theories that do.
But even with these inventions, they are routinely surprised by what they find in the universe. So? Nobody has claimed that we know everything about the universe. Dark matter and dark energy are features of our universe, but they don't explain everything about it.
Physicists and cosmologists searching for a "unifying theory" of the universe are, in my assessment, searching for the exact same thing as people who believe in God. For religious people, their god is their unifying theory. Dark matter, and dark energy, are their latest fictional creations to justify their obsessive need to find certainty. Dark matter and dark energy have little to do with unification. And unified theories don't have anything to do with "finding certainty", either. A unified field theory would be no more nor less certain than a non-unified theory. Dark matter and dark energy don't have anything to do with "finding certainty" either; they are no different from any other scientific endeavor: to provide explanations for unexplained natural phenomena. Nothing in science is certain.
This Hubble "map" is a CONSTRUCTION. It's not actual evidence; it proves nothing. It is a visualization of the observational data that has been measured, and it is evidence for dark matter insofar as it is a confirmation of the predictions of that theory.
I just love how the "anomalies" are discussed so dismissively, as if they aren't the crack in the dike threatening to bring the whole house of cards down. You have a naive view of science. People like to paint a revolutionary picture of science, but in reality, 99% of the time, anomalies don't actually revolutionize anything; they are resolved as mundane instrumental errors, systematic model approximation errors, etc. Yes, it's possible that dark matter can be torn down, but there is now enough evidence in its favor that there has to be a correspondingly large amount of evidence against it. That was not always the case, but it is today.
MOND does do very well for galaxies. In some respects, it does better than dark matter (although dark matter is not wrong for galaxies). However, MOND runs into serious problems explaining other phenomena, and in light of that, it is more plausible that dark matter is in galaxies after all. See this post for more discussion.
Is there any chance that there's two classes of graviton? Like the electromagnetic force has attract opposite, repel like. Could the gravitational force which has some similarities to the electromagnetic force have attract like, repel opposite. That would require a vector theory of gravity. General relativity is a tensor theory. There are combined tensor-vector theories that have features of both, as you suggest. But there is no observational evidence in their favor right now.
And while I'm at it, is it possible stuff escapes black holes because passing matter causes small changes in the gravitational field hence shifting the event horizon and causing the photons that are orbiting near the event horizon to escape orbit. No. An event horizon, by definition, is a region from which nothing can ever escape. The horizon of a black hole can distort, and something near a black hole can be perturbed away from it, but anything that escapes a black hole was never within the event horizon to begin with — by definition.
Your theory has been proposed, but nobody has been able to come up with new laws of physics that can explain the observations without dark matter, and it's not for lack of trying.
Has everyone forgotten we're looking at light which is millions, even billions of years old? No.
The fact that we're inventing "dark matter" to explain inaccuracies in light which has moved billions of AU through billions of years.. it's just bloody stupid. "Inaccuracies in light"? It gets redshifted, some of it gets scattered or adsorbed, but that doesn't prevent us from measuring the gravitational dynamics of distant galaxies.
he phenomena which dark matter tries to explain only really says that something has happened to the light while traveling through space, probably some kind of expansion or change in the time/space continuum The expansion of space redshifts light, but that doesn't have much to do with dark matter, and is irrelevant for nearby galaxies.
I think you are extremely confused about what dark matter is and what evidence supports it.
See this post for links about the status of MOND vs. dark matter. In short: not looking good for pure MOND, although MOND + dark matter might be possible — but that kind of defeats the purpose of MOND.
"Dark Matter" always struck me as a kind of dodge. We discover that the universe doesn't have enough mass to account for the current pet theories in physics, and so rather than question the theories themselves, we invent a mysterious new "dark matter" that we can't actually see (but which MUST be there because the theories can't POSSIBLY just be wrong). This doesn't have anything to do with "pet theories", it has to do with the very basic fact that bodies in space aren't behaving gravitationally in the way we think they should. There are really only two possibilities: there are sources of gravity other than what we can see, or the laws of gravity are different from what we think. Both possibilities have been considered, and the first is the one that has stood up best to observational tests.
You have a simplistic characterization of the situation which has nothing to do with the reality. The astrophysics community didn't say around and insist, "Duh, we must be right about everything — except the sources of matter — and therefore dark matter has to exist." Dark matter was resisted for decades. Heavily. It's just that it has continued to work, and pass new tests, and the alternatives haven't.
It strikes me as a wishful-thinking fiction more than a testable, observable phenomenon. Despite the numerous independent observational tests it has passed, and alternative theories have failed. Curious.
They are affected by gravity, so the quantum theory of gravity would say that they must be able to exchange gravitons and hence self-gravitate. Yes, photons do self-gravitate, for the reason you gave. This is true even in classical general relativity; you don't need to bring quantum mechanics into it.
Fact is that Dark Matter and Dark Energy are not falsifiable theories. Of course they are. You can't explain any arbitrary set of independent phenomena using dark matter. (And I would like to hear your reason why "dark matter" is not falsifiable, but "modified gravity" is.)
There is no dispute on the success of MOND to fit Galaxies. The fact that it is not widely accepted is because it is ad-hoc, and it is not an effective theory But mostly because it fails other observational tests that dark matter passes. MOND does great on galaxies, as you say, but that's no good if it's wrong!
But now with TeVeS it is now an effective theory. Now, it can also fit gravitational lensing and WMAP data. The existence of TeVeS doesn't make MOND suddenly able to explain results, such as the Bullet Cluster, that MOND currently gets wrong.
It is good that you agree that MOND people accept their failings. I only wish that the scientific establishment did the same with their own theories and accepted the short comings of Dark Matter and Dark Energy. Sigh. I doubt you know anything about what the "scientific establishment" thinks about dark matter.
All the other 3 forces are defined by a type of Conformal field thoery, except for Gravity. That's wrong. The Standard Model is not a conformal field theory. It can't be in any theory with massive particles.
It seems obvious to me that ultimately Gravity will also be defined by a type of Conformal Field theory. [...] It will also resolve all the numerous problems of Cosmology, flatness problem Dark Matter Dark Energy etc. That's a lot of faith in a theory that has shown no ability to actually solve any of those problems, let alone all of them.
AFAIK, the Standard Model doesn't call for 70% of the mass of the universe to reside in neutrinos, or even 10%. No, it doesn't.
Does the standard model describe the majority of mass as non-electromagnetic? We have not discovered any dark matter candidates, if that's what you're asking. The Standard Model can be argued to contain the axion, although that's more of a solution to a fine tuning problem than a logical requirement of the model. The axion is a dark matter candidate. There are also extensions to the Standard Model (such as supersymmetry) which contain other dark matter candidates.
Photons aren't energy, they're matter with an energy equivalence proportional to their frequency. Photons are massless bosons and as such are generally not considered "matter".
Maybe the descriptions of "dark energy" are inaccurate - they're describing dark matter at high energy. Dark energy has nothing to do with dark matter. Dark energy could be modified gravity (the cosmological constant) or a new kind of particle (probably scalar, and therefore not "matter" as we know it).
It just seems strange that we've never directly experienced dark matter/energy on or near Earth, when it's the large majority. It's not strange, if it's both massive and weakly interacting (which are precisely the properties needed to make it work as dark matter). Massive means that we may not be able to produce it in particle accelerators, and weakly interacting means it's very hard to detect. It's actually possible that dark matter interacts only by gravity, which essentially means that we can never directly detect it. We hope that's not the case.
Not that we should have it on our unique planet (in Feynman's terms - because we're on it, it's unique) - but can't we synthesize it, to study it? Especially if it's got nearly magical properties of undetectability and/or antigravity. There is no reason why every particle in the universe has to be easy for humans to detect and produce, and there are certainly plenty of particles hypothesized to solve one problem or another which are neither. It's possible that some particles can be detected only, or most readily, by their gravitational influence on astrophysical scales. There is certainly evidence in favor of that scenario.
Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed. No one has actually succeeded in producing a modified gravity theory that can mimic the effects of dark matter. It is not true a priori that this can be done; there are a lot of constraints on both the possibilities for dark matter and the possibilities for a gravitational theory, and they don't necessarily intersect.
There are pretty strong parallels between dark matter and the infamous epicycles. Dark matter is not like epicycles. Epicycles are essentially a Fourier expansion of any orbital motion, and as such, they are totally non-predictive and unfalsifiable. Dark matter theories do make predictions, and it is not possible to explain away all gravitational anomalies we see using dark matter. It's capable of being falsified, and a number of specific proposals for dark matter have been falsified.
The real problem is that there are no checks and balances here: by adjusting the mass distribution of dark matter, we can get whatever result we want, and there's nothing to either prove or disprove the proposed distribution. This is false. If you take any one phenomenon, such as galactic rotation curves, you can explain it by postulating a particular distribution and type of dark matter. But there's no reason why that same distribution and type should also account for other, independent phenomena — which it does. We can't get "whatever result we want" by fudging the dark matter distribution. If we fudge it one way, it can disagree with other observations. The fact that it doesn't is the reason why dark matter has become a mainstream theory.
In the absence of independent evidence of dark matter, it would be more elegant if laws of gravity were discovered which explained the observations well without dark matter. I say they're equally elegant, regardless of whether we detect dark matter. Either way, we have to alter the laws of physics (to alter gravity or to include new particles). Saying that one is better than the other is just prejudice. The true measure is which idea works better.
That's a pretty weak position. It certainly doesn't do anything to counter the accusation that objects are being invented just to make the theory work. That's also wrong. Particles like axions, neutralinos, etc. were hypothesized for reasons completely independent of the justifications for dark matter. However, they easily could be dark matter. Once again, there's no reason a priori why a new type of particle introduced to solve the strong-CP problem in QCD or the hierarchy problem or grand unification in the Standard Model should also happen to solve astrophysical anomalies, but they can, if they exist (depending on their masses, which we can't predict yet).
I think you need to learn a lot more about dark matter theories and the evidence for them before you so casually dismiss them.
But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science. Dark matter is a solidly established theoretical construct. It hasn't risen to the level of "proven" (insofar as anything can be "proven" in science), but there is a hell of a lot of evidence in its favor.
For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives. There are alternatives to dark matter. They're not faring too well compared to dark matter when it comes to explanatory power, but they exist. I know you'd like to play amateur psychologist to the astrophysics community, but alternatives are considered. It's just becoming harder and harder to come up with alternatives that work, since observations have excluded so many of them. That's the reason why dark matter has become the mainstream explanation. Not because of "blinkered imagination", but because it works and the alternatives just don't. Alternatives that have at least some success do get attention, in proportion to the number of tests they pass.
For another, it tends to make some laymen skeptical about *any* claims of science. Possibly because said layman are unaware of the decades of extensive testing the theory has undergone and all of the alternatives that have failed to measure up.
Oops, you were referring to dark energy, not dark matter. Dark energy may not be a "substance" at all; the best current explanation of dark energy (the cosmological constant) is a modification of the laws of gravity, not a new kind of particle.
70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations?? Why should it, if it's weakly interacting and massive? (Which are precisely the properties it needs to explain the astrophysical observations, by the way.)
I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment. The difference is that dark matter keeps on passing new and independent observational tests.
Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess, You act as if having a bunch of observational evidence for dark matter is unimportant.
the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect, Would dark matter be more palatable to you if it only made up 5% of the universe? Why does it suddenly become more implausible if it makes up most of the universe. It's because it makes up most of the universe that we can even tell it's there.
can't do experiments on, That remains to be seen; we may be able to create such particles in accelerators, and we may also be able to detect them in the Sun, in cosmic ray experiments, etc.
That being said, even if we can't do experiments on dark matter, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that all matter must be easily producible and manipulable by humans?
doesn't exist locally, That's false. It surely does exist locally.
That being said, even if it didn't exist locally, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that everything interesting or important in the universe has to exist nearby?
and is completely different from the universe we do observe and interact with It's not that different. Ordinary neutrinos have most of the properties needed to be dark matter; they're just not massive enough.
On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model. Aether theories didn't make any predictions that correctly explained any new observations. Dark matter does.
Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form. The cosmological constant is a modification of the laws of gravitation, not anything like what was historically referred to as the aether.
Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality. This point is well taken. However,
Recall that special relativity is based on Einstein's assertion that equations should be symmetric. That wasn't Einstein's motivation for introducing special relativity. (On the other hand, the complete form of Maxwell's equations of electromagnetism were based on Maxwell's assertion that the equations should be symmetric.)
And, for the record, we must also admit that there is no evidence for a particle of magnetic or gravitation force. The electromagnetic force is mediated by the photon, for which there is abundance evidence. Gravitons, as you say, currently have no experimental evidence in their favor.
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There isn't a lot of gravitational lensing — it's only significant when light passes near dense collections of matter. The net effect is that some images of distant stars or galaxies are sometimes displaced a bit from where they "should" be. Usually the light doesn't get lensed multiple times on its way to us, simply because it's rare for several lensing objects to exist on a line between us and the source. Most objects we see are not lensed at all, and those that are, aren't usually lensed much.
Anyway, to be kind of facetious, the universe with lensing is what the universe "really looks like".
Incidentally, this characterization as a fudge to maintain "existing theory" is rather silly. Dark matter is a new theory, just like modified gravity theories are. Both of them replace our previous notion of astrophysics. I'm pointing out that there's a lot of uncertainty here, and a lack of independent corroboration, and that responsible scientists shouldn't blind themselves to possible alternatives by according too much weight to intrinsically weak theories Dark matter is not an intrinsically weak theory. By now it has passed dozens of independent observational tests. And nobody is blinding themselves to possible alternatives. That's another silly characterization of what's going on. Dark matter was resisted for decades, and even today there are still alternatives like modified gravity being worked on. It's just that there is less and less room for them, as new evidence has disagreed with alternatives and continued to agree with dark matter.
We have observed new species evolving. And evolution certainly can be disproved; it makes plenty of concrete predictions.
(Incidentally, sometimes the data is wrong, or the interpretation of the data.) There are various takes on the evidence for dark matter, but altogether my understanding is that it's virtually undetectable (no E&M interaction)--so it can't be disproven It interacts gravitationally, and can be disproven that way. In fact, a number of specific dark matter proposals have already been disproven that way. (e.g., we know that the dark matter is not mostly made up of compact astrophysical bodies, and we know that it's not made up of light particles.) Future observations could potentially rule out the remaining dark matter proposals, but so far they have not.
MOND does do very well for galaxies. In some respects, it does better than dark matter (although dark matter is not wrong for galaxies). However, MOND runs into serious problems explaining other phenomena, and in light of that, it is more plausible that dark matter is in galaxies after all. See this post for more discussion.
Your theory has been proposed, but nobody has been able to come up with new laws of physics that can explain the observations without dark matter, and it's not for lack of trying.
I think you are extremely confused about what dark matter is and what evidence supports it.
See this post for links about the status of MOND vs. dark matter. In short: not looking good for pure MOND, although MOND + dark matter might be possible — but that kind of defeats the purpose of MOND.
You have a simplistic characterization of the situation which has nothing to do with the reality. The astrophysics community didn't say around and insist, "Duh, we must be right about everything — except the sources of matter — and therefore dark matter has to exist." Dark matter was resisted for decades. Heavily. It's just that it has continued to work, and pass new tests, and the alternatives haven't. It strikes me as a wishful-thinking fiction more than a testable, observable phenomenon. Despite the numerous independent observational tests it has passed, and alternative theories have failed. Curious.
I think you need to learn a lot more about dark matter theories and the evidence for them before you so casually dismiss them.
No. Neutrinos aren't massive enough to be (most of the) dark matter. See here for a brief but more detailed discussion.
Oops, you were referring to dark energy, not dark matter. Dark energy may not be a "substance" at all; the best current explanation of dark energy (the cosmological constant) is a modification of the laws of gravity, not a new kind of particle.
That being said, even if we can't do experiments on dark matter, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that all matter must be easily producible and manipulable by humans? doesn't exist locally, That's false. It surely does exist locally.
That being said, even if it didn't exist locally, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that everything interesting or important in the universe has to exist nearby? and is completely different from the universe we do observe and interact with It's not that different. Ordinary neutrinos have most of the properties needed to be dark matter; they're just not massive enough.
That being said,
Seconded.