In that article, perhaps none. But on his website you can find that he has a doctorate in theoretical physics from Caltech, has been an astronomy professor and research scientist at Harvard, and is now a professor at MIT in the science writing program.
Dark matter is thought to make up >80% of the matter (slow-moving stuff which clumps under the influence of gravity) in the universe. There are lots of reasons for thinking that this stuff is out there:
galaxy rotation curves (you're right that this alone doesn't tell us about the universe's energy budget, just that of galaxies)
gravitational lensing (a surprisingly independent measure of the stuff in galaxies and galaxy clusters)
structure formation (you need more matter than the visible amount for the structure we see to form quickly enough)
the cosmic microwave background (the shape of the first two peaks of its spectrum tells us about matter and dark matter densities)
Dark energy seems to make up the remaining 70% (25% dark matter, 5% ordinary matter). The evidence for this comes from the acceleration of the universe's expansion, which is a fairly amazing thing.
You don't actually need to assume that Omega=1 (the universe is flat), because these different lines of evidence pick out a unique consistent solution. There's a great plot at LBL showing this. We don't need an ad-hoc assumption that Omega=1 anymore!
IAAP, and while I see where you're coming from I'd actually make the argument in the opposite direction.
A previous poster has already noted a paper (astro-ph/0508377) which quickly followed this one and refuted its conclusions (I have seen other physicists describe the same point elsewhere). It seems (though I have not yet checked the math myself) that the authors made an honest error, and they weren't modeling the situation they thought they were. In addition to the self-gravitating cloud of gas they were trying to model, the metric also includes a disk-shaped "singularity" - essentially a very thin, very heavy disk in the plane of the galaxy. It is this unphysical disk which is responsible for the effect they observe.
It's also worth noting that dark matter has MANY independent lines of evidence pointing to it (rotation curves, gravitational lensing, the cosmic microwave background, large scale structure, element abundances... see
here). Galactic rotation curves were the first such evidence, but arguably they are the weakest today. I'm still more than willing to believe that the dark matter paradigm could be wrong, and this result would be VERY interesting if true, but there would still be lots left to explain. This is how science works, of course - idea gets put forward, it gets checked by others, the community works out what to think of it.
This also makes me think of the current controversy over intelligent design, but in the opposite way to the previous poster. Look at the Slashdot thread around us. Hundreds of people are posting to say how relieved they are that dark matter doesn't exist, since they always thought it was too weird and that those pointy-headed physicists were out of touch with their own good common sense. They feel very confident doing this, even though (1) they admit that they don't understand the evidence and reasoning they are talking about (even as some of them chastise physicists for the "basic error" they were making), and (2) the reasoning itself was later shown to be flawed. Several posters have tried to make follow-up postings showing that this reasoning has been refuted, but they can't hit every discussion thread (and it's not clear it would do any good if they did). As with the anti-evolution "controversy", people latch on to sensational headlines of flaws in basic science and simplistic errors by scientists to believe whatever they felt most comfortable believing to begin with. From there, it's an uphill battle to get the truth out there.
As another poster (here)has already pointed out, other physicists have since worked through the algebra of this paper and found it lacking.
I'm told there is a mistake in the general relativistic metric used in the paper. Basically, a small error left them modeling the wrong situation. The situation they actually studied was one with an axially symmetric cloud of self-gravitating gas (the galaxy) AND a thin, heavy disk. The thin, heavy disk screws things up and produces the effect they observe.
Sigh... OK, so this article is complete crap, as a cursory read will show (another poster has pointed out a nonsense passage about neutrinos, for example).
It is true, however, that a lot of the ideas we commonly attribute to Einstein were thought of by others. Poincare and Lorentz, for example, did think a lot about the synchronization of moving clocks and come up with ideas later used in relativity (e.g. Lorentz transforms). Einstein did not attribute all of these sources in his paper, and I believe there was some debate over to what extent he was aware of that work (or of the result of the Michelson-Morley experiment which cast doubt on the idea of the ether). Einstein might even be in some trouble today if he published a paper without references to such things.
Einstein's original contribution was to some extent his way of looking at these problems. Earlier thinkers had noticed practical problems of clock synchronization, but by and large they believed that these were just experimental issues (due to the wind of the ether, for example) that you needed to correct for to obtain the true, absolute time. It was Einstein who declared that different people's clocks actually run differently, and that there is no absolute time (or ether)! His radical idea was that space and time were not absolutes that every observer could agree upon, not that clock synchronization was hard.
I recommend Galison's book "Einstein's Clocks, Poincare's Maps" for a discussion of the lead-up to these sorts of ideas.
There's actually a lot of evidence that the missing dark "stuff" is different than any stuff we've ever encountered before.
Dark Matter: Most of the dark matter isn't ordinary matter (less than 1/5 of it can be, if I remember the numbers right). There's very strong evidence from primordial chemical element abundances and from studies of the cosmic microwave background that, whatever it is, it's not made up of protons/neutrons/electrons the way ordinary matter is. It's true that there's some ordinary matter leftover that we haven't observed or accounted for, but when people talk about the mysteries of dark matter they're usually talking about the weird stuff. Best guess is some new kind of elementary particle (or some modification to gravity), which is certainly interesting.
Dark Energy: This isn't just ordinary energy/matter. Ordinary energy and matter slow down the universe's expansion by their gravitational attraction. Whatever this stuff is, its main attribute is that it's causing the expansion of the universe to speed up! This is also certainly interesting.
Yes, it is stuff we've never seen, and yes we're far from omniscient. But there's definitely no "just" about it!
I think the point of confusion here is: What does it mean to be "moving" if it doesn't somehow involve the time dimension? The strangenesses that you point to all seem to amount to this same idea. I'm not sure what it would mean to say that the time dimension moves with respect to the spatial ones, or that "The null vector, which represents a vector of zero length in space-time, can only imply zero movement through space-time. " You have to be careful what you mean by motion if you take time out of the picture.
The standard point of view is that in some sense, everything in the universe is actually "stationary". A particle is represented by some world-line in spacetime, a curve in 4D which traces out its position as a function of time. Different reference frames are simply different choices of coordinate axes in this 4D space - the worldline is still geometrically "the same", I just describe it differently than you do. My axes might be spatially rotated with respect to yours, or have a different origin for the time/space coordinates. Furthermore, I might be moving at a different velocity, which turns out to correspond to a rotation that involves the time axis - my time axis might have spatial components in your reference frame. This latter bit gives rise to all the cute effects of special relativity - time dilation, lorentz contraction, etc. I have to do a coordinate transformation to match my measurements to yours - a Lorentz transformation.
General relativity throws in the complication of gravity - spacetime has curvature, and so you can't choose a global inertial frame (a single coordinate system over all spacetime with all the technical properties that you'd like it to have, in which particles move in straight worldlines). You'll have leftover accelerations and strange effects in the presence of gravitating mass (or energy). The expansion of the universe (a GR effect) is a statement that the "scaling" of the spatial axes with respect to the time axis is not constant, but changes as you move along the time axis - none of these axes need to "move" in some other way.
Anyway, that's the cleanest point of view I know of. I'll be the first to admit that I may not understand what you're saying, but I don't think there is any need in basic relativity for the concept of dimensional motion.
There is definitely a certain amount of what you describe. Particle theorists need something to do, and string theory is the best game in town. It has essentially no testable predictions currently, and it was motivated originally by hadron physics (which the current implementations have nothing to do with).
I think the thing that really got people excited about string theory was the fact that it's a quantum theory of gravity that works at all. That's pretty powerful, since people had been trying crazy tricks for decades to get particle physics and gravity to go together. This time they had come up with a particle physics theory via an entirely different road and later noticed that it happened to solve the gravity problem! This framework also has lots of attractive features. I believe it was the first framework for quantum gravity that was renormalizable (free of the "bad" infinities that screw up quantum gravity), and I think some current implementations are thought to be finite (no infinities at all!). It necessarily contains supersymmetry, a proposed symmetry of nature that helps with many issues of particle physics (i.e. the stability of the mass of the Higgs boson). It also has a very mathematically rich structure - even if it had no relation to the real world, mathematicians would still love to study its intricacies. It hasn't produced any testable real-world predictions, but it has been used for a few useful calculations - in particular, it has been used to account for the details of Hawking radiation and black hole entropy.
I think that string theory is a bit too popular, and that the general public and funding agencies have the idea that it just has to be right. It's very attractive, but still very speculative and far-removed from the real world. There are far too many posts on the slashdot boards, say, to the effect of "Q: What does this recent physics experiment say about string theory? A: Nothing."
You're right that we've never observed a graviton. However, most physicists would say that this is hardly a surprise. There's no trouble explaining why - any effects of quantum gravity (any behavior where you'd have to know about gravitons and not just about general relativity) probably shouldn't kick in until the Planck energy scale (the energy scale associated with the observed strength of the gravitational force), which is something like 10^16 times greater than any energy ever achieved in an accelerator. Some theorists have come up with ways in which quantum gravity effects become manifest at lower energies (such as the extra-dimension theories the experiments in this post are designed to test), but your naive guess would be that we shouldn't have seen quantum gravity yet.
What you describe (gravity as pseudoforce) is actually something like the way gravity works in general relativity. In that theory, mass warps the fabric of spacetime. Objects travel in the straightest lines they can in this curved space, and we perceive the bends in those paths as being because of a "force" between masses. This theory has been extremely successful in explaining all sorts of large-scale phenomena (not to mention the fact that it is very theoretically beautiful).
The problem is that general relativity and quantum field theory (the theoretical framework of "particles" being exchanged that works so well for the other forces) seem to be fundamentally incompatible. General relativity is fundamentally a theory of the way the geometry of spacetime changes. Field theory is formulated on a pre-existing, static background spacetime. You get into mathematical trouble however you try to get these together.
You can continue in (at least) two ways. Particle physicists are usually more inclined to think that the field theory point of view is fundamental, and that whole geometry thing is just the way things look on large scales. This leads to string theory and the usual discussion of gravitons. If you treat the geometric point of view as more fundamental, you try quantizing spacetime and get loop quantum gravity. String theory is more popular, but no one knows what the right answer is (both may even be different points of view on the same thing!).
There's a big difference between knowledge and dogma. Certain fields (i.e. many scientific fields) incorporate a lot of experimental facts, a lot of successful ideas, and a lot of failed ideas. You need to know a great deal of this stuff in order to make progress in the field - even geniuses don't just sit in a room and realize how the real world "must" be without knowing a great deal about how it actually is (Einstein studied for his Ph.D. before he came up with relativity). Too many people think they have the next "theory of everything", for example, when in fact they just don't know enough about experimental results and mathematics to see why it doesn't work.
There is, of course, a danger of becoming too dogmatic about things and stifling creativity. My feeling, however, is that great innovations come about through a combination of (1) very creative individuals with knowledge of what has come before, and (2) happy accidents, encountered by open-minded and methodical people.
This is correct, if you take "Relativistic Physics" to mean "general relativity". Special relativity and quantum mechanics have been consistent since the 1950s - that's what quantum field theory is. In fact, quantum electrodynamics (the relativistic theory of electromagnetism) is the most precise theory in science, predicting certain numbers correctly to something like a dozen decimal places.
The problem is general relativity, the profound extension of special relativity to produce a relativistic theory of gravity. This has serious problems meshing with quantum mechanics, and this is what string theory is supposed to address.
The "big accelerator in Europe" (the CERN Large Hadron Collider) will probably NOT be able to test string theory. In fact, no experiment currently conceived will be able to do so (the experiment described in the article is intended to produce macroscopic phenomena that are analogous to what happens in string theory, not to observe actual superstrings). String theory (if it's true) involves phenomena that are believed to operate on the Planck scale, many orders of magnitude smaller than anything CERN can probe.
What CERN can do, however, is look for the signature of supersymmetry. Supersymmetry must be there in order for string theory to work. The idea is that there are two kinds of particles in the world - fermions (like electrons) and bosons (like photons). Supersymmetry is a symmetry relating these classes of particles. String theory more or less only works with bosons - the only way for it to be consistent with the fermions we observe in our world is for there to be supersymmetry. Discovering supersymmetry does not, of course, mean that string theory must be true - it's a necessary condition, but not a sufficient one.
This is a good point - it's quite possible we don't understand gravity (especially in the case of dark energy!). However, there turns out to be a lot of evidence for dark matter (galaxy rotation curves, gravitational lensing, structure formation, the microwave background, etc.), and it turns out that it's hard to come up with a model without dark matter that explains all of these observations. Dark matter is, in a very real sense, the simplest interpretation of this data. There are some earlier posts of mine (and otheres) that talk about this evidence in more detail.
This observation, if confirmed, could be one of the best evidences yet that dark matter is real, physical "stuff". Visible galaxies and clusters form in the middle of large dark matter halos, which act as "seeds". Cosmologists have always predicted that there should be some population of these halos that never accumulate enough visible stuff to be visible. The discovery of such a "dark halo" is a fairly impressive confirmation of the theory. It's possible to believe that gravity can be modified to change rotation velocities in a galaxy, but it's hard to imagine such a modification producing effects where no real matter exists!
I'm not sure what you mean by "quanta of alpha helix". The term "alpha helix" comes up in biomolecular applications, but I don't see any connection with that...
Detecting gravitational waves isn't the same as detecting the pull of gravity (that we've been doing for a long time). There is an analogy to electromagnetism - the attractive or repulsive force between electric charges is like gravity's pull, but light (electromagnetic waves) are analogous to gravity waves.
General relativity predicts that accelerating mass can generate ripples in spacetime (gravity waves) that can carry away energy. There's a good bit of evidence that says the ripples are there (for instance, binary pulsars seem to spiral toward one another at just the rate that would be explained by the loss of energy to gravity waves), but the waves themselves have never been detected.
Detecting gravity waves would be an excellent test of general relativity, for one. It could also give us new ways of looking at events in the cosmos, similar to the way in which radio astronomy revolutionized the study of the universe.
Probably not, but then again some theorist out there probably has a model in which it does.
The basic issue is that zero-point energy (the energy associated with the ground state of a quantum field, i.e. the "energy of the vacuum") shouldn't vary in density from place to place in the way dark matter seems to. One of the only things we think we know about dark matter is that it seems to "clump" - local overdensities of dark matter surround visible galaxies and galaxy clusters and form the seeds around which they form. Vacuum energy shouldn't behave in this way - the same amount of energy density should be associated with any given part of space. Vacuum energy can't be gravitationally moved around in the same way that matter can, since it's in some sense a property of space itself.
It turns out, however, that vacuum energy is a semi-reasonable candidate for dark energy. A constant energy density like that is just the sort of thing that can give you a negative pressure (in the cosmological sense) and accelerate the expansion of the universe. Unfortunately, the amount of vacuum energy needed to explain the observed expansion is about 10^120 times smaller than the amount of zero-point energy we might expect there to be. We just don't know much about dark energy...
Dark matter is indeed "matter we can't find". It can't, however, be comprised entirely of, for example, gas or planets or tiny stars that we haven't discovered. From various lines of evidence, one can deduce that the vast majority of the missing matter cannot be made up of ordinary matter (stuff made up of protons, electrons, atoms). The best guess is that the dark matter is some kind of stuff that doesn't interact with light, but that outweighs all the visible matter in the universe by a factor of ~7. It's not just stuff we haven't seen, it's stuff we can't see (at least not in ordinary ways). This weird stuff is also required by current models to explain how structure forms in the universe.
Dark energy is also "energy we can't find", but it's a lot more than that. "Dark energy" is the name given to whatever phenomenon is causing the expansion of the universe to accelerate (as noticed by the research in this article, as well as earlier work studying distant supernovae). It has an anti-gravity-like behavior, which is weird (to say the least).
So on the one hand, dark energy and dark matter are just the "missing" stuff we need to throw in to get our estimates of the amount of visible matter and the amount of total matter to jibe. Both components do have very strange properties which affect the way the universe is today, however, so whatever stuff they are made of is very unusual!
Mathematics isn't really like a science in the usual sense. It's often classified with science because it involves the same kind of analytical thinking (and so tends to attract the same kinds of people) and the techniques developed in mathematics tend to prove useful in science (and scientific motivation often leads to new mathematical ideas, e.g. calculus).
Mathematics is, in a sense, the use of analytical thought to learn about the properties of a made-up world - the abstract world of mathematical axioms and theorems. In a sense, a mathematician defines what he/she means by concepts like "natural number", "prime number", "straight line", etc., makes a few axiomatic assumptions (e.g. "parallel lines coincide in at most one point"), and then uses a set of rules to produce other statements which are consistent with these definitions and axioms. One and one will always equal two, but in a deep sense that's because we DEFINED "one" and "two" in this manner!
In the sciences, we have only one world to play around in - the physical world we've been presented. Scientists use similar methods, but in some sense they are trying to figure out the axioms. Science can thus never be fully deductive - you have to make leaps of intuition to come up with new axioms. This limitation makes science, in a way, much harder and more frustrating. Scientists are always sort of feeling around in the dark, and that's just the way it has to be.
I'm not quite clear on what you mean by "the other aspect of this matter is gravity which is the negative quantity..." etc. Inflation isn't all that useful for telling us why there is matter to begin with. Quantum field theory tells us that there should be matter and antimatter springing into existence all the time in the hot early universe of the big bang model - the problem is why the matter and antimatter don't appear in equal amounts and annihilate each other. There are theories which can explain this, but they aren't aspects of inflation per se.
What inflation is good for is telling us why the universe is the way we see it today - ridiculously homogenous on large scales (scales so large that light doesn't seem to have had time to cross the intervening distance) but not perfectly homogeneous (otherwise we wouldn't have any lumpy things like galaxies or planets). The quantum fluctuations you describe naturally give rise to the slight "lumps" in the universe, while the rapid early expansion of inflation smooths out any big inhomogeneities in the early universe. This all turns out to work out really well and solve a lot of problems.
Of course, no one knows exactly what caused this rapid expansion, but there are lots of good models that can do the job (which just don't have enough evidence to decide which particular one might be right). One model (eternal inflation) suggests that an eternal universe (the details of any initial Big Bang don't matter) would have occasional quantum fluctuations which expand outward in just the manner our universe seems to. The Big Bang could, in some sense, be just a local phenomena that happens every now and then in the bigger "universe".
Mythos inside and outside physics...
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100 Years of Einstein
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· Score: 4, Insightful
First off, I'm a physics grad student with nothing but the utmost respect for Einstein's work, and I make use of it's consequences frequently. He did some of the most beautiful stuff in the history of physics. Nonetheless, I think that his mythos may have arguably had a detrimental effect on theoretical physics and its public perception.
When asked what he would have thought if solar eclipse had not confirmed general relativity, Einstein famously responded something like he "would have been sorry for the dear Lord - the theory is correct!". The general picture people have is that Einstein sat in a room, thought really hard, and figured out how the world was supposed to be without ever needing to go out and LOOK at it. This idea has inspired generations of young physicists to think that the "real" route to truth about the world is mathematical insight. Over the ensuing century, however, this has essentially never been the case - the biggest breakthroughs generally come when an experiment sees something weird (i.e. discovers new particles or behaviors) and a theorist comes up with a mathematical picture that makes all the weird observations fit together. Experiments are still important - it's not just Plato sitting in his cave imagining how the world ought to be. Beautiful mathematical models of fundamental physics very frequently turn out to be experimentally wrong!
Outside of physics, the public image of Einstein has arguably breathed life into the legions of crackpots who think they know the theory of everything, claim that quantum mechanics is "obviously" wrong, etc. Everyone learns in school that Einstein was terrible at mathematics growing up and that he did his best work as a patent clerk, not at a university. Many people are encouraged by this, thinking that the best work comes from "outside the system" and need not involve a thorough understanding of the details of current science.
Unfortunately, this is not true. Einstein was quite good at mathematics (had he been a bit more versed in fancy Reimannian geometry, however, general relativity might have happened faster). He had a Ph.D. from one of the world's most prestigious grad schools. He was working as a patent clerk to pay the bills simply because he hadn't yet gotten a teaching job (they were scarce, and even in later years Einstein never did much teaching).
The point is that he knew his stuff (experimental results and current theory). Too many people think they can walk in off the street with no substantial knowledge of physics or mathematics and give a "common sense" alternative to modern physics that doesn't involve any of the "hard stuff". It usually turns out that their work contradicts some experimental result that they never bothered to learn about. I often see e-mails about such ideas that cite Einstein as an example of how an outsider with no knowledge can change a field. In principle, a gifted outsider with a new insight can change any field. In practice (as Einstein shows), it's good to know what others know first.
Several posters want to say that the success of Linux validates the approach of Wikipedia. I see three major differences:
(1) Who does the writing? Linux is made by a bunch of programmers (often programming experts) who have pooled their skill to produce a product. Experts are doing work in their field of expertise.
Wikipedia is the general public getting together to write specialized encyclopedia articles. Non-experts are contributing to various articles in their spare time. The thing that makes Wikipedia work pretty well, of course, is that there are lots of VERY devoted experts who maintain various articles. The method as a whole, however, cannot ensure this and is a bit unstable without these Herculean few.
(2) What's released? Open-source software releases stable versions every now and then to the general public, not the nightly CVS build.
Wikipedia, essentially, is always presenting its nightly build to those members of the public who don't religiously follow the change log.
(3) How do you know if it's right? Code can be run to see if it works. There can be all kinds of nasty, subtle bugs, but to first order you know if it works (though perhaps not how to fix it if it doesn't).
There is no such straightforward verification of encyclopedia material. Subtle inconsistencies or flaws can just sit there unless someone is VERY careful.
I'm all for eliminating bias through wide editing, but there is something to be said for the authority of people of "education". Too many ignorant people think they know all about a subject and are willing to exposit on it in detail. A couple examples:
(1) My physics department is often spammed by people without a science education who think they have solved the mysteries of the universe. Their conclusions are generally based on warped common sense and a lack of knowledge of the experimental facts. Nonetheless, they wish to spread them to the world (some manage to publish books) and decry any objection as being a result of the "biased scientific establishment".
(2) Many schools in America are embroiled in "controversies" about the teaching of evolution. Zealots spread misinformation to an ignorant public and try (with some success) to put nonsense alongside truth from schools. Again, we're told there is a "biased scientific establishment".
I don't bring these up to claim that Wikipedia would publish such people's work (it has decent controls, and it is supported by a vast community of expert contributors) or that it's wrong to take things you hear from authority (or anyone) with a grain of salt.
I do, however, take a bit of issue with the anti-intellectual form of populism that says that the "educated elite" are never to be trusted. The public doesn't always define its own truth. If you want to learn something, it helps to ask people who know something about the subject.
"The Elegant Universe" is a very good book, and I recommend it. It's worth noting, however, that the Nobel Prize award just given has nothing to do with string theory at all.
It's pretty much just a resolution issue. This sort of simulation is like looking at the universe through very blurry glasses - you can study the big features, but not the small ones. In this case, "small-scale" features include planets, stars, or even the inner structure of galaxies. These simulations can, however, tell us fairly reliably about the formation of large galaxies, galaxy clusters, and superclusters - the really big stuff in our universe.
One other interesting approximating simulations like this often make is to completely neglect ordinary matter (gas, dust, stars, etc.) and study only the behavior of dark matter. The dark matter outweighs the ordinary matter by so much that this is a reasonable thing to do. The structure of galaxies themselves, however, depend a great deal on the behavior of this ordinary matter, so such simulations are unable to study this very well anyway.
That's probably not the first thing they'll do, but not because it's not interesting. In most theories, the energies needed to directly explore quantum gravity (string theory, M-theory, etc.) in this way are more than 15 orders of magnitude higher than this accelerator can achieve. The first order of business is to look for physics at the TeV energy scale, such as the Higgs boson and supersymmetry.
There will, of course, also be people sifting through the data looking for the things you describe - low-energy effects of quantum gravity, evidence for extra dimensions, and so forth. People are already looking for such things in Tevatron data.
Slashdot Mirror
In that article, perhaps none. But on his website you can find that he has a doctorate in theoretical physics from Caltech, has been an astronomy professor and research scientist at Harvard, and is now a professor at MIT in the science writing program.
Dark energy seems to make up the remaining 70% (25% dark matter, 5% ordinary matter). The evidence for this comes from the acceleration of the universe's expansion, which is a fairly amazing thing.
You don't actually need to assume that Omega=1 (the universe is flat), because these different lines of evidence pick out a unique consistent solution. There's a great plot at LBL showing this. We don't need an ad-hoc assumption that Omega=1 anymore!
IAAP, and while I see where you're coming from I'd actually make the argument in the opposite direction.
A previous poster has already noted a paper (astro-ph/0508377) which quickly followed this one and refuted its conclusions (I have seen other physicists describe the same point elsewhere). It seems (though I have not yet checked the math myself) that the authors made an honest error, and they weren't modeling the situation they thought they were. In addition to the self-gravitating cloud of gas they were trying to model, the metric also includes a disk-shaped "singularity" - essentially a very thin, very heavy disk in the plane of the galaxy. It is this unphysical disk which is responsible for the effect they observe.
It's also worth noting that dark matter has MANY independent lines of evidence pointing to it (rotation curves, gravitational lensing, the cosmic microwave background, large scale structure, element abundances... see here). Galactic rotation curves were the first such evidence, but arguably they are the weakest today. I'm still more than willing to believe that the dark matter paradigm could be wrong, and this result would be VERY interesting if true, but there would still be lots left to explain. This is how science works, of course - idea gets put forward, it gets checked by others, the community works out what to think of it.
This also makes me think of the current controversy over intelligent design, but in the opposite way to the previous poster. Look at the Slashdot thread around us. Hundreds of people are posting to say how relieved they are that dark matter doesn't exist, since they always thought it was too weird and that those pointy-headed physicists were out of touch with their own good common sense. They feel very confident doing this, even though (1) they admit that they don't understand the evidence and reasoning they are talking about (even as some of them chastise physicists for the "basic error" they were making), and (2) the reasoning itself was later shown to be flawed. Several posters have tried to make follow-up postings showing that this reasoning has been refuted, but they can't hit every discussion thread (and it's not clear it would do any good if they did). As with the anti-evolution "controversy", people latch on to sensational headlines of flaws in basic science and simplistic errors by scientists to believe whatever they felt most comfortable believing to begin with. From there, it's an uphill battle to get the truth out there.
As another poster (here)has already pointed out, other physicists have since worked through the algebra of this paper and found it lacking.
I'm told there is a mistake in the general relativistic metric used in the paper. Basically, a small error left them modeling the wrong situation. The situation they actually studied was one with an axially symmetric cloud of self-gravitating gas (the galaxy) AND a thin, heavy disk. The thin, heavy disk screws things up and produces the effect they observe.
Sigh... OK, so this article is complete crap, as a cursory read will show (another poster has pointed out a nonsense passage about neutrinos, for example).
It is true, however, that a lot of the ideas we commonly attribute to Einstein were thought of by others. Poincare and Lorentz, for example, did think a lot about the synchronization of moving clocks and come up with ideas later used in relativity (e.g. Lorentz transforms). Einstein did not attribute all of these sources in his paper, and I believe there was some debate over to what extent he was aware of that work (or of the result of the Michelson-Morley experiment which cast doubt on the idea of the ether). Einstein might even be in some trouble today if he published a paper without references to such things.
Einstein's original contribution was to some extent his way of looking at these problems. Earlier thinkers had noticed practical problems of clock synchronization, but by and large they believed that these were just experimental issues (due to the wind of the ether, for example) that you needed to correct for to obtain the true, absolute time. It was Einstein who declared that different people's clocks actually run differently, and that there is no absolute time (or ether)! His radical idea was that space and time were not absolutes that every observer could agree upon, not that clock synchronization was hard.
I recommend Galison's book "Einstein's Clocks, Poincare's Maps" for a discussion of the lead-up to these sorts of ideas.
There's actually a lot of evidence that the missing dark "stuff" is different than any stuff we've ever encountered before.
Dark Matter: Most of the dark matter isn't ordinary matter (less than 1/5 of it can be, if I remember the numbers right). There's very strong evidence from primordial chemical element abundances and from studies of the cosmic microwave background that, whatever it is, it's not made up of protons/neutrons/electrons the way ordinary matter is. It's true that there's some ordinary matter leftover that we haven't observed or accounted for, but when people talk about the mysteries of dark matter they're usually talking about the weird stuff. Best guess is some new kind of elementary particle (or some modification to gravity), which is certainly interesting.
Dark Energy: This isn't just ordinary energy/matter. Ordinary energy and matter slow down the universe's expansion by their gravitational attraction. Whatever this stuff is, its main attribute is that it's causing the expansion of the universe to speed up! This is also certainly interesting.
Yes, it is stuff we've never seen, and yes we're far from omniscient. But there's definitely no "just" about it!
I think the point of confusion here is: What does it mean to be "moving" if it doesn't somehow involve the time dimension? The strangenesses that you point to all seem to amount to this same idea. I'm not sure what it would mean to say that the time dimension moves with respect to the spatial ones, or that "The null vector, which represents a vector of zero length in space-time, can only imply zero movement through space-time. " You have to be careful what you mean by motion if you take time out of the picture.
The standard point of view is that in some sense, everything in the universe is actually "stationary". A particle is represented by some world-line in spacetime, a curve in 4D which traces out its position as a function of time. Different reference frames are simply different choices of coordinate axes in this 4D space - the worldline is still geometrically "the same", I just describe it differently than you do. My axes might be spatially rotated with respect to yours, or have a different origin for the time/space coordinates. Furthermore, I might be moving at a different velocity, which turns out to correspond to a rotation that involves the time axis - my time axis might have spatial components in your reference frame. This latter bit gives rise to all the cute effects of special relativity - time dilation, lorentz contraction, etc. I have to do a coordinate transformation to match my measurements to yours - a Lorentz transformation.
General relativity throws in the complication of gravity - spacetime has curvature, and so you can't choose a global inertial frame (a single coordinate system over all spacetime with all the technical properties that you'd like it to have, in which particles move in straight worldlines). You'll have leftover accelerations and strange effects in the presence of gravitating mass (or energy). The expansion of the universe (a GR effect) is a statement that the "scaling" of the spatial axes with respect to the time axis is not constant, but changes as you move along the time axis - none of these axes need to "move" in some other way.
Anyway, that's the cleanest point of view I know of. I'll be the first to admit that I may not understand what you're saying, but I don't think there is any need in basic relativity for the concept of dimensional motion.
There is definitely a certain amount of what you describe. Particle theorists need something to do, and string theory is the best game in town. It has essentially no testable predictions currently, and it was motivated originally by hadron physics (which the current implementations have nothing to do with).
I think the thing that really got people excited about string theory was the fact that it's a quantum theory of gravity that works at all. That's pretty powerful, since people had been trying crazy tricks for decades to get particle physics and gravity to go together. This time they had come up with a particle physics theory via an entirely different road and later noticed that it happened to solve the gravity problem! This framework also has lots of attractive features. I believe it was the first framework for quantum gravity that was renormalizable (free of the "bad" infinities that screw up quantum gravity), and I think some current implementations are thought to be finite (no infinities at all!). It necessarily contains supersymmetry, a proposed symmetry of nature that helps with many issues of particle physics (i.e. the stability of the mass of the Higgs boson). It also has a very mathematically rich structure - even if it had no relation to the real world, mathematicians would still love to study its intricacies. It hasn't produced any testable real-world predictions, but it has been used for a few useful calculations - in particular, it has been used to account for the details of Hawking radiation and black hole entropy.
I think that string theory is a bit too popular, and that the general public and funding agencies have the idea that it just has to be right. It's very attractive, but still very speculative and far-removed from the real world. There are far too many posts on the slashdot boards, say, to the effect of "Q: What does this recent physics experiment say about string theory? A: Nothing."
You're right that we've never observed a graviton. However, most physicists would say that this is hardly a surprise. There's no trouble explaining why - any effects of quantum gravity (any behavior where you'd have to know about gravitons and not just about general relativity) probably shouldn't kick in until the Planck energy scale (the energy scale associated with the observed strength of the gravitational force), which is something like 10^16 times greater than any energy ever achieved in an accelerator. Some theorists have come up with ways in which quantum gravity effects become manifest at lower energies (such as the extra-dimension theories the experiments in this post are designed to test), but your naive guess would be that we shouldn't have seen quantum gravity yet.
What you describe (gravity as pseudoforce) is actually something like the way gravity works in general relativity. In that theory, mass warps the fabric of spacetime. Objects travel in the straightest lines they can in this curved space, and we perceive the bends in those paths as being because of a "force" between masses. This theory has been extremely successful in explaining all sorts of large-scale phenomena (not to mention the fact that it is very theoretically beautiful).
The problem is that general relativity and quantum field theory (the theoretical framework of "particles" being exchanged that works so well for the other forces) seem to be fundamentally incompatible. General relativity is fundamentally a theory of the way the geometry of spacetime changes. Field theory is formulated on a pre-existing, static background spacetime. You get into mathematical trouble however you try to get these together.
You can continue in (at least) two ways. Particle physicists are usually more inclined to think that the field theory point of view is fundamental, and that whole geometry thing is just the way things look on large scales. This leads to string theory and the usual discussion of gravitons. If you treat the geometric point of view as more fundamental, you try quantizing spacetime and get loop quantum gravity. String theory is more popular, but no one knows what the right answer is (both may even be different points of view on the same thing!).
There's a big difference between knowledge and dogma. Certain fields (i.e. many scientific fields) incorporate a lot of experimental facts, a lot of successful ideas, and a lot of failed ideas. You need to know a great deal of this stuff in order to make progress in the field - even geniuses don't just sit in a room and realize how the real world "must" be without knowing a great deal about how it actually is (Einstein studied for his Ph.D. before he came up with relativity). Too many people think they have the next "theory of everything", for example, when in fact they just don't know enough about experimental results and mathematics to see why it doesn't work.
There is, of course, a danger of becoming too dogmatic about things and stifling creativity. My feeling, however, is that great innovations come about through a combination of (1) very creative individuals with knowledge of what has come before, and (2) happy accidents, encountered by open-minded and methodical people.
This is correct, if you take "Relativistic Physics" to mean "general relativity". Special relativity and quantum mechanics have been consistent since the 1950s - that's what quantum field theory is. In fact, quantum electrodynamics (the relativistic theory of electromagnetism) is the most precise theory in science, predicting certain numbers correctly to something like a dozen decimal places.
The problem is general relativity, the profound extension of special relativity to produce a relativistic theory of gravity. This has serious problems meshing with quantum mechanics, and this is what string theory is supposed to address.
I agree with the post, just trying to clarify!
The "big accelerator in Europe" (the CERN Large Hadron Collider) will probably NOT be able to test string theory. In fact, no experiment currently conceived will be able to do so (the experiment described in the article is intended to produce macroscopic phenomena that are analogous to what happens in string theory, not to observe actual superstrings). String theory (if it's true) involves phenomena that are believed to operate on the Planck scale, many orders of magnitude smaller than anything CERN can probe.
What CERN can do, however, is look for the signature of supersymmetry. Supersymmetry must be there in order for string theory to work. The idea is that there are two kinds of particles in the world - fermions (like electrons) and bosons (like photons). Supersymmetry is a symmetry relating these classes of particles. String theory more or less only works with bosons - the only way for it to be consistent with the fermions we observe in our world is for there to be supersymmetry. Discovering supersymmetry does not, of course, mean that string theory must be true - it's a necessary condition, but not a sufficient one.
This is a good point - it's quite possible we don't understand gravity (especially in the case of dark energy!). However, there turns out to be a lot of evidence for dark matter (galaxy rotation curves, gravitational lensing, structure formation, the microwave background, etc.), and it turns out that it's hard to come up with a model without dark matter that explains all of these observations. Dark matter is, in a very real sense, the simplest interpretation of this data. There are some earlier posts of mine (and otheres) that talk about this evidence in more detail.
This observation, if confirmed, could be one of the best evidences yet that dark matter is real, physical "stuff". Visible galaxies and clusters form in the middle of large dark matter halos, which act as "seeds". Cosmologists have always predicted that there should be some population of these halos that never accumulate enough visible stuff to be visible. The discovery of such a "dark halo" is a fairly impressive confirmation of the theory. It's possible to believe that gravity can be modified to change rotation velocities in a galaxy, but it's hard to imagine such a modification producing effects where no real matter exists!
I'm not sure what you mean by "quanta of alpha helix". The term "alpha helix" comes up in biomolecular applications, but I don't see any connection with that...
Detecting gravitational waves isn't the same as detecting the pull of gravity (that we've been doing for a long time). There is an analogy to electromagnetism - the attractive or repulsive force between electric charges is like gravity's pull, but light (electromagnetic waves) are analogous to gravity waves. General relativity predicts that accelerating mass can generate ripples in spacetime (gravity waves) that can carry away energy. There's a good bit of evidence that says the ripples are there (for instance, binary pulsars seem to spiral toward one another at just the rate that would be explained by the loss of energy to gravity waves), but the waves themselves have never been detected. Detecting gravity waves would be an excellent test of general relativity, for one. It could also give us new ways of looking at events in the cosmos, similar to the way in which radio astronomy revolutionized the study of the universe.
Probably not, but then again some theorist out there probably has a model in which it does.
The basic issue is that zero-point energy (the energy associated with the ground state of a quantum field, i.e. the "energy of the vacuum") shouldn't vary in density from place to place in the way dark matter seems to. One of the only things we think we know about dark matter is that it seems to "clump" - local overdensities of dark matter surround visible galaxies and galaxy clusters and form the seeds around which they form. Vacuum energy shouldn't behave in this way - the same amount of energy density should be associated with any given part of space. Vacuum energy can't be gravitationally moved around in the same way that matter can, since it's in some sense a property of space itself.
It turns out, however, that vacuum energy is a semi-reasonable candidate for dark energy. A constant energy density like that is just the sort of thing that can give you a negative pressure (in the cosmological sense) and accelerate the expansion of the universe. Unfortunately, the amount of vacuum energy needed to explain the observed expansion is about 10^120 times smaller than the amount of zero-point energy we might expect there to be. We just don't know much about dark energy...
That's almost it, but not quite.
Dark matter is indeed "matter we can't find". It can't, however, be comprised entirely of, for example, gas or planets or tiny stars that we haven't discovered. From various lines of evidence, one can deduce that the vast majority of the missing matter cannot be made up of ordinary matter (stuff made up of protons, electrons, atoms). The best guess is that the dark matter is some kind of stuff that doesn't interact with light, but that outweighs all the visible matter in the universe by a factor of ~7. It's not just stuff we haven't seen, it's stuff we can't see (at least not in ordinary ways). This weird stuff is also required by current models to explain how structure forms in the universe.
Dark energy is also "energy we can't find", but it's a lot more than that. "Dark energy" is the name given to whatever phenomenon is causing the expansion of the universe to accelerate (as noticed by the research in this article, as well as earlier work studying distant supernovae). It has an anti-gravity-like behavior, which is weird (to say the least).
So on the one hand, dark energy and dark matter are just the "missing" stuff we need to throw in to get our estimates of the amount of visible matter and the amount of total matter to jibe. Both components do have very strange properties which affect the way the universe is today, however, so whatever stuff they are made of is very unusual!
Mathematics isn't really like a science in the usual sense. It's often classified with science because it involves the same kind of analytical thinking (and so tends to attract the same kinds of people) and the techniques developed in mathematics tend to prove useful in science (and scientific motivation often leads to new mathematical ideas, e.g. calculus).
Mathematics is, in a sense, the use of analytical thought to learn about the properties of a made-up world - the abstract world of mathematical axioms and theorems. In a sense, a mathematician defines what he/she means by concepts like "natural number", "prime number", "straight line", etc., makes a few axiomatic assumptions (e.g. "parallel lines coincide in at most one point"), and then uses a set of rules to produce other statements which are consistent with these definitions and axioms. One and one will always equal two, but in a deep sense that's because we DEFINED "one" and "two" in this manner!
In the sciences, we have only one world to play around in - the physical world we've been presented. Scientists use similar methods, but in some sense they are trying to figure out the axioms. Science can thus never be fully deductive - you have to make leaps of intuition to come up with new axioms. This limitation makes science, in a way, much harder and more frustrating. Scientists are always sort of feeling around in the dark, and that's just the way it has to be.
I'm not quite clear on what you mean by "the other aspect of this matter is gravity which is the negative quantity..." etc. Inflation isn't all that useful for telling us why there is matter to begin with. Quantum field theory tells us that there should be matter and antimatter springing into existence all the time in the hot early universe of the big bang model - the problem is why the matter and antimatter don't appear in equal amounts and annihilate each other. There are theories which can explain this, but they aren't aspects of inflation per se.
What inflation is good for is telling us why the universe is the way we see it today - ridiculously homogenous on large scales (scales so large that light doesn't seem to have had time to cross the intervening distance) but not perfectly homogeneous (otherwise we wouldn't have any lumpy things like galaxies or planets). The quantum fluctuations you describe naturally give rise to the slight "lumps" in the universe, while the rapid early expansion of inflation smooths out any big inhomogeneities in the early universe. This all turns out to work out really well and solve a lot of problems.
Of course, no one knows exactly what caused this rapid expansion, but there are lots of good models that can do the job (which just don't have enough evidence to decide which particular one might be right). One model (eternal inflation) suggests that an eternal universe (the details of any initial Big Bang don't matter) would have occasional quantum fluctuations which expand outward in just the manner our universe seems to. The Big Bang could, in some sense, be just a local phenomena that happens every now and then in the bigger "universe".
First off, I'm a physics grad student with nothing but the utmost respect for Einstein's work, and I make use of it's consequences frequently. He did some of the most beautiful stuff in the history of physics. Nonetheless, I think that his mythos may have arguably had a detrimental effect on theoretical physics and its public perception.
When asked what he would have thought if solar eclipse had not confirmed general relativity, Einstein famously responded something like he "would have been sorry for the dear Lord - the theory is correct!". The general picture people have is that Einstein sat in a room, thought really hard, and figured out how the world was supposed to be without ever needing to go out and LOOK at it. This idea has inspired generations of young physicists to think that the "real" route to truth about the world is mathematical insight. Over the ensuing century, however, this has essentially never been the case - the biggest breakthroughs generally come when an experiment sees something weird (i.e. discovers new particles or behaviors) and a theorist comes up with a mathematical picture that makes all the weird observations fit together. Experiments are still important - it's not just Plato sitting in his cave imagining how the world ought to be. Beautiful mathematical models of fundamental physics very frequently turn out to be experimentally wrong!
Outside of physics, the public image of Einstein has arguably breathed life into the legions of crackpots who think they know the theory of everything, claim that quantum mechanics is "obviously" wrong, etc. Everyone learns in school that Einstein was terrible at mathematics growing up and that he did his best work as a patent clerk, not at a university. Many people are encouraged by this, thinking that the best work comes from "outside the system" and need not involve a thorough understanding of the details of current science.
Unfortunately, this is not true. Einstein was quite good at mathematics (had he been a bit more versed in fancy Reimannian geometry, however, general relativity might have happened faster). He had a Ph.D. from one of the world's most prestigious grad schools. He was working as a patent clerk to pay the bills simply because he hadn't yet gotten a teaching job (they were scarce, and even in later years Einstein never did much teaching).
The point is that he knew his stuff (experimental results and current theory). Too many people think they can walk in off the street with no substantial knowledge of physics or mathematics and give a "common sense" alternative to modern physics that doesn't involve any of the "hard stuff". It usually turns out that their work contradicts some experimental result that they never bothered to learn about. I often see e-mails about such ideas that cite Einstein as an example of how an outsider with no knowledge can change a field. In principle, a gifted outsider with a new insight can change any field. In practice (as Einstein shows), it's good to know what others know first.
Several posters want to say that the success of Linux validates the approach of Wikipedia. I see three major differences:
(1) Who does the writing?
Linux is made by a bunch of programmers (often programming experts) who have pooled their skill to produce a product. Experts are doing work in their field of expertise.
Wikipedia is the general public getting together to write specialized encyclopedia articles. Non-experts are contributing to various articles in their spare time. The thing that makes Wikipedia work pretty well, of course, is that there are lots of VERY devoted experts who maintain various articles. The method as a whole, however, cannot ensure this and is a bit unstable without these Herculean few.
(2) What's released?
Open-source software releases stable versions every now and then to the general public, not the nightly CVS build.
Wikipedia, essentially, is always presenting its nightly build to those members of the public who don't religiously follow the change log.
(3) How do you know if it's right?
Code can be run to see if it works. There can be all kinds of nasty, subtle bugs, but to first order you know if it works (though perhaps not how to fix it if it doesn't).
There is no such straightforward verification of encyclopedia material. Subtle inconsistencies or flaws can just sit there unless someone is VERY careful.
I'm all for eliminating bias through wide editing, but there is something to be said for the authority of people of "education". Too many ignorant people think they know all about a subject and are willing to exposit on it in detail. A couple examples:
(1) My physics department is often spammed by people without a science education who think they have solved the mysteries of the universe. Their conclusions are generally based on warped common sense and a lack of knowledge of the experimental facts. Nonetheless, they wish to spread them to the world (some manage to publish books) and decry any objection as being a result of the "biased scientific establishment".
(2) Many schools in America are embroiled in "controversies" about the teaching of evolution. Zealots spread misinformation to an ignorant public and try (with some success) to put nonsense alongside truth from schools. Again, we're told there is a "biased scientific establishment".
I don't bring these up to claim that Wikipedia would publish such people's work (it has decent controls, and it is supported by a vast community of expert contributors) or that it's wrong to take things you hear from authority (or anyone) with a grain of salt.
I do, however, take a bit of issue with the anti-intellectual form of populism that says that the "educated elite" are never to be trusted. The public doesn't always define its own truth. If you want to learn something, it helps to ask people who know something about the subject.
"The Elegant Universe" is a very good book, and I recommend it. It's worth noting, however, that the Nobel Prize award just given has nothing to do with string theory at all.
It's pretty much just a resolution issue. This sort of simulation is like looking at the universe through very blurry glasses - you can study the big features, but not the small ones. In this case, "small-scale" features include planets, stars, or even the inner structure of galaxies. These simulations can, however, tell us fairly reliably about the formation of large galaxies, galaxy clusters, and superclusters - the really big stuff in our universe. One other interesting approximating simulations like this often make is to completely neglect ordinary matter (gas, dust, stars, etc.) and study only the behavior of dark matter. The dark matter outweighs the ordinary matter by so much that this is a reasonable thing to do. The structure of galaxies themselves, however, depend a great deal on the behavior of this ordinary matter, so such simulations are unable to study this very well anyway.
That's probably not the first thing they'll do, but not because it's not interesting. In most theories, the energies needed to directly explore quantum gravity (string theory, M-theory, etc.) in this way are more than 15 orders of magnitude higher than this accelerator can achieve. The first order of business is to look for physics at the TeV energy scale, such as the Higgs boson and supersymmetry.
There will, of course, also be people sifting through the data looking for the things you describe - low-energy effects of quantum gravity, evidence for extra dimensions, and so forth. People are already looking for such things in Tevatron data.