When I was in China, Joe Silk told me about an interesting paper he was just finishing, and one of his collaborators, Bo Qin, from Beijing University, gave a nice talk about the work. The paper has now appeared, and has been discussed in a recent Nature news item.
I’ve written before on the basic idea of large extra dimensions, and some variants on which I’ve worked. I won’t repeat the motivations for considering them here, but will repeat the main idea.
You can imagine the strength of gravity as being a bit like the force due to a steady stream of water emerging from the nozzle of a hosepipe. Suppose that the water is confined, by some fancy nozzle, say, to emerge in a stream that is essentially one dimensional – a very fine stream. If you’ve ever fitted a tight nozzle to a hosepipe, then you’ll know that such a stream is very powerful, and the force it exerts on you, if pointed your way, is very high.
Now imagine that, instead, the water is spread out to emerge in a plane (OK, that would require one fancy nozzle, but I’m sure you can imagine it). In this case, if your body is in the way of the water in some direction (the same distance from the nozzle as in the first case), it will still exert a force on you, but less than when you were being hit by the one-dimensional stream. This is because you’re not being hit by all the water, but instead by a portion of it – there are other directions available for the rest of the water to go.
If we now fit a nozzle that allows the water to spread out in a spherically-symmetric three-dimensional pattern, then the force on your body will be yet weaker because there are still further directions for the water to spread.
The analogy I’m drawing here is with lines of gravitational flux, the density of which, in Newtonian gravity, describes the strength of gravity. The more directions (think dimensions) available for the water (think gravitational flux) to spread, the weaker is the force experienced.
Silk, Qin and their collaborator, Ue-Li Pen, from the Canadian Institute for Theoretical Astrophysics (CITA), suggested that this change in the behavior of gravity due to large extra dimensions (three, in fact) might explain why the dark matter cores of large galactic clusters are smaller than those expected from current theoretical models.
It’s a fun idea, albeit a speculative one, and it’s refreshing that they aren’t over-hyping the paper, as you can see from
Silk himself acknowledges that the proposal is “extremely speculative”.
and
There are other ways of explaining the puzzling dark-matter distributions, admits Silk’s colleague Ue-Li Pen of the University of Toronto in Canada. For example, one could assume that the rate at which stars explode, as supernovae, was quite different in the past.
“Personally, I think changing the supernovae rate is more conservative than changing the number of spatial dimensions,” Pen confesses. But he thinks that invoking extra dimensions is such an exciting idea that it is worth investigating, “even if it is a long shot”.
I can’t say I think it’s likely that this is how the universe works. Nevertheless, this paper caught my eye partly because I’d discussed it with Joe, but also because it is the kind of particle physics/cosmology idea that I find most attractive – namely one that takes a model (large extra dimensions) that was developed to address an existing particle physics problem (the hierarchy problem) and derives interesting cosmological implications (in this case involving dark matter).
Take a look at the brief description in Nature if you’d like to learn more, or if you’re up to it, dive right into the paper.
September 6th, 2005 at 12:02 am
Isn’t this a fine example of how science works?
You propose an idea because it fits at least some of the data you have. It is analyzed and tested by the scientific community. If it’s wrong, fine, now we know. If you treat it like the speculation that it is, it won’t even ruin your career.
This scientific attitude is a world away from that of proponents of certain other probably-wrong ‘theories’.
September 6th, 2005 at 10:24 am
I appreciate the visualization as a layman.
Now can you show how those extra dimensions can be reduced into the three diensional picture in a geometrical way?:)
If the basis of your approach is euclidean orientated, then the “dynamical realization” has not yet been introduced?
Although, from such coordinates currently given, do not give a good indication of why “gravity can be strong, (fine steam?)” when xtra dimensions are reduced to planck length in the same space you had just given to a rotation around each respective x,y,z direction.
As a museum orator of science in these halls of higher learning, can it be this simple?
September 6th, 2005 at 10:38 am
Plato. Sorry, but I’m not understanding the question. Can you have another try please, and I’ll try to give an answer? Thanks.
September 6th, 2005 at 1:01 pm
“it’s refreshing that they aren’t over-hyping the paper”
I agree that the Nature article doesn’t overhype the paper, with Silk calling it “extremely speculative” and his co-author Pen saying it is a “long shot” and that he thinks another explanation is more likely. Lisa Randall also avoids overhyping, calling it “an overstatement to use these observations as evidence of extra dimensions.”
But the hype level in the paper itself is a bit much. There’s nothing in there about the idea being “extremely speculative” or a “long shot”, or about alternate explanations being more plausible. And nine invocations of string theory in a three page paper? Isn’t that a bit out of control, especially since the ADD scenario is only tangentially related to string theory anyway? A well-known string theorist interprets the paper as saying: “Silk et al. explain that they may thus be capable to almost prove string theory by hardcore data”. OK, maybe he’s joking, always hard to tell what’s a joke and what’s serious with him…..
September 6th, 2005 at 3:32 pm
I have no problem with people making any speculative ideas, but it is wrong to claim such crackpot ideas as “Observational Evidence for Extra Dimentions..” as by the title of the paper. “Observational Evidence” is two heavy a phrase to use on such purely speculative ideas with no experimental support whatsoever.
But there is strong observational evidence that the authors have not learned Quantum Mechanics, I quote these two numbers from the paper:
(3) The size of the large extra dimensions was found
to be of order R = 10^-7cm, below which gravity deviates from Newton’s inverse square law and varies as r−5.
(4) The mass of dark matter particles was constrained to be mx = 3 × 10^-16 proton mass, falling into roughly the mass range of the axion which has been proposed as a dark matter candidate (see e.g. [32]).
Clearly, these two numbers are incompatible with the uncertainty principle. The mass scale gives a confinement of time scale no less than a certain quantity, which translates to a distance scale no smaller than a certain quantity, That quantity far exceeds the 10^-7 cm by many orders of magnitude!
Quantoken
September 6th, 2005 at 4:18 pm
To silly ole me, this thing actually looks pretty desperate.
Remember why dark matter was dreamed up in the first place? Flat galaxy rotation curves. They didn’t fit the visible matter distribution, unless you accepted that GR wasn’t working correctly at large scales. In spite of GR lacking independent observational support at those scales, rather than accepting its failure it was deemed more appropriate to assume the existence of some mysterious “dark matter”, never seen in any other observational or experimental setting. Great thinking, that: you have a theory with very limited experimental support, you finally get some data, it contradicts the theory – so of course you dream up a whole new matter sector rather than modify the theory…
(The scratching sound you may hear at this point is caused by Occam applying the famous razor to his bony wrists in a futile gesture of disgust.)
But, ironically, it turns out that even the fabled and ever-mysterious dark matter isn’t capable of fixing GR. Now it’s galaxy clusters that don’t work correctly, even if you endow galaxies with gravitating dark matter. So do we finally give up now and accept that GR needs to be modified at large scales?
Of course not; continuing in the great tradition of elves and trolls, we now add large extra dimensions to the dark matter mix. Needless to say, every bit as unseen as dark matter.
(Don’t worry about the swirling sound, that’s just the rotation of poor Occam’s earthly remains approaching the speed of sound.)
The whole thing would perhaps make some sense if there were no alternatives, but it’s not exactly a new idea that a quantum theory of gravity should feature a running G, and the formal similarities between YM and GR strongly suggest that the running should be of the asymptotically free kind, making G larger at larger scales.
So why don’t we talk a bit more about serious stuff like
http://arxiv.org/abs/hep-th/0410119
and a little bit less about elves and trolls?
September 6th, 2005 at 4:51 pm
Dissident, be careful what you say in a public forum. If you let people know that solar-system tests, the binary pulsar, Big-Bang nucleosynthesis, the power spectrum of large-scale structure, anisotropies in the cosmic microwave background, and gravitational lensing are really “very limited experimental support,” everyone will know that the Emperor has no clothes!
It’s common knowledge, whispered furtively to sympathetic fellow-travelers, that modifying general relativity in the infrared is child’s play, and it’s the work of a moment to write down simple models that explain all of the data. People like Mark and I would love to write papers and give talks exploring this idea, but we’re in no position to speak truth to power. You see, the cosmological Establishment still lives in fear of the ghost of Fritz Zwicky, and they insist that we stick to the established doctrine that there’s no reason to think every source of energy in the universe should interact strongly with electromagnetic radiation. I’m telling you, the Man is keeping us down — and he’ll come to get you, if you’re not careful.
Expect a knock at your door any night now.
September 6th, 2005 at 4:54 pm
Mark,
Sorry it’s very difficut to explain this
Dissident’s article is a case in point.
Here is a “simple comparison” of this “vast distance” equals, the type of space and information, in the here and now. This space now can contain all that type of information.
If one did not hold the reductionist principle in view, how would this space have ever made sense, considering the vast amount of information contained in this x,y,z,t direction. From those “extra dimensions” to now.
It’s very hard to conceptualize and put into words what we might see at the beginning of the universe, can exist in this space we occupy.
How would visualize this? Is this view wrong?
September 6th, 2005 at 6:15 pm
Dear Sean, going down your list you mention:
1) Solar-system tests and the binary pulsar – NOT on galactic scales. And in fact, even the little old solar system has been presenting us with the well known Pioneer anomaly for quite some time now.
2) Big-Bang nucleosynthesis – not a test of GR at all, just of a kitchen-sink cosmological model which could easily swallow a modified theory of gravity (or things like large extra dimensions and dark energy would be equally ruled out by it).
3) The power spectrum of large-scale structure – attributed to inflation, at least if you happen to believe that magnifying quantum fluctuations will give you a smooth metric [which is an interesting assumption to say the least if you know the measure of classical-looking, smooth trajectories to Feynman path integrals (zero) and, conversely, what the dominating contributions look like (think Rocky Mountains, just worse)] and of course in the existence of yet another troll (or is it an elf?) never seen by anyone in any experiment, the scalar field(s) which we are told drove inflation. You may want to clarify how any of this constitutes empirical verification of GR at galactic scales…
3) Anisotropies in the cosmic microwave background – which in fact do not seem to fit expectations from inflation (Axis of Evil). Not that their doing so would constitute empirical verification of GR at galactic scales, either.
4) Gravitational lensing – verified with precision (i.e. the mass is well known) only within the solar system. Galactic scales, remember?
While I appreciate the irony of the statement that “It’s common knowledge, whispered furtively to sympathetic fellow-travelers, that modifying general relativity in the infrared is child’s play”, it’s not like I’m asking for the moon. I’m pointing to existing work, which takes its starting point from GR, recognizing it for what it is – a classical theory which MUST be expected to be modified by quantization – and makes a serious attempt to work out those radiative corrections based on well established QFT methods (RG flow analysis).
It may be less glamorous and fun than inventing new scalars, dark matter candidates and extra dimnesion left, right and center, but it sure looks a lot more like serious physics. Why not have a look?
http://arxiv.org/abs/hep-th/0410119
September 6th, 2005 at 7:35 pm
Sean:
It is worthy noting that virtually every astronomy observation instruments we invented do nothing but collecting and detecting photons that directly falls onto the instruments. So it is wrong to conclude that whatever we see (through photons) are all that exist in the universe, consider that there may be plenty of matter, even the regular types, that could exist, but whose existence can not be directly infered from the photons.
For example, if there’s very dilute space dusts which is in equilibrium to absorb and emit equal amount of microwaves at CMB temperature, you would NOT be able to detect their existance. You can only find out that they exist by flying a spaceship and actually collecting them. NASA did just that, and it turns out space dusts are several order of magnitude more dense than originally believed! If you do some calculation, it could well explain away any need of exotic “dark matter particles”.
We are not even sure of the correct composition of the Sun, because we can not see the core of it. It is widely believed that the Sun and all the planets form from the same one cloud of dusts and gases. If that is the case, don’t you expect that the more heavy elements would be more likely condensed and sink to the center of the solar system, and lighter elements are more likely to be concentrated on the outside.
Doesn’t it seem ODD that the lightest elements, hydrogen, all condense and sink to the center to form the Sun, while much heavier elements, like iron and silicon, floats and boyants to form outer planets like the earth. And even odd is Jupiter and Saturn, which is mostly hydrogen, though they are neither too close nor too far away from the center.
Doesn’t it make you wonder the text book may be wrong in assuming what we see at the surface of planets and stars are all there is, while ignoring the fact that what we can not see below the surface, could be a completely different picture?
http://web.umr.edu/~om/
Quantoken
September 6th, 2005 at 10:44 pm
Dissident, it just so happens I have been recently reading all the papers of M. Reuter and co-authors and their approach to renormalisation group improved Einstein Equations and improved black hole solutions, and galaxy rotation curves without the need for dark matter. For a generally spatially dependent Newton constant G(x) they also seem to treat it as a scalar field carrying gravitating 4-momentum, with an associated energy-momentum source. They consider a modified Einstein-Hilbert Lagrangian L_{EH}=R/[16 pi G(x)]. The spatial dependence of G(x) leads to an induced pressure and energy density in the vacuum too depending on the derivatives of G(x), or G’( r),G”( r) in spherically symmetric spacetimes. It is different from Brans-Dicke theory with the BD scalar phi(x)=1/G(x) but they can match their theory to it when you take the singular limit of BD theory.
I agree with you that a running G could be a feature of quantum gravity or any extention of GR not just in the infrared but in the ultraviolet too. The mathematical and physical similarities between Yang Mills and GR are well known too. YM equations and Einstein equations are nonlinear for example, so both gluons and gravitons are self-interacting. Gravity could ultimately prove to be “antiscreening” like QCD with G(x) growing large at large scales but also getting smaller at microcopic scales. If G starts to run in the ultraviolet at some critical point so that if G( r)->0 sufficiently fast as r–>0, then with this ‘asymptotic freedom’ one might tame the singularities of associated with black holes, gravitational collapse and cosmology.
However, if string theory really is a UV completion to GR can it say anything concrete about this idea?
September 6th, 2005 at 11:08 pm
I am not an expert in these matters Quantoken but I would assume you should take into account mixing, diffusion and convection within the sun or any star. (Off topic so I will be brief.) Also, when the sun formed from a gas/dust cloud (still mostly hydrogen) and nuclear reactions began in the core “switching on” the sun the resulting radiation pressure would push out the material left over, with the lighter stuff being pushed much farther out and the heavier elements staying closer to the parent star. Jupiter-like planets have been observed in close orbits around their parent stars but the prevailing theory is that these form farther out then spiral inwards. Our system may be an exception.
September 7th, 2005 at 3:15 am
Steve, thank you for the QEG/RG summary. Regarding the closing question, “if string theory really is a UV completion to GR can it say anything concrete about this idea?”, my uneducated guess is no. For string theory to contribute something new to the IR regime, I’d expect the full, non-perturbative – and still very much missing – M theory to be needed. But I’d love to see what Clifford, Lubos and other stringers think about this.
September 7th, 2005 at 2:13 pm
Steve:
That’s exactly the point I made, it should be expected that heavier elements sinks and lighter elements boyants. The mass segretion can be calculated easily in thermodynamics. The accepted solar model, which considers the sun to be mostly hydrogen and helium, and very little heavy elements, contradicts the conventional knowledge, and can not be right. The sun could well have an iron core and we can’t see it because it’s shielded from the lighter elements segreted on the surface. If the earth and the sun were formed from the same dust cloud, and the earth has an iron core, how could it be possible that the iron doesn’t sink to the center and form an iron core of the sun as well?
And there is no need to invent any crackpot theory of extra dimentions to explain the “dark matter”, either. The “dark matter” is simply regular matter that is transparent and hence invisible to light. Namely, it’s just molecular hydrogen.
It’s a known fact that all the meterites and grainy space dusts in the space are mainly iron and other heavy elements. Those material of heavy elements constantly crash down to form stars and planets and sink to their cores, mean while, once the astronomical bodies become heavy enough, their gravity fields would be able to attract and accumulate hydrogen from surrounding space, and start the nuclear process that allow them to shine. I believe the sun has a core that’s mainly iron and it actively and continuously sucks up the hydrogen from the surrounding space to provide the fuel for thermo nuclear reactions. It’s an ongoing process that can be going on indefinitely.
This also explains the fact that virtually all stars we observe, young or old, have very similar hydrogen/helium composition, and such composition has no apparent age dependency, despite of the fact that hydrogen is depleted and helium is continuously generated. That’s because there’s an active process of material exchange with the surrounding “dark matter”, and hydrogen is constantly replenished and extra helium is ejected.
Of course that means we have to re-evalate the matter and element compositions of the universe, and the big bang nuclear synthesis hypothesis will have to be turned upside down.
A blind person touches an elephant and says the elephant is but just a piece of skin. Astronomers, with all the modern instruments, are not any wiser than a blind man, if they believe what they see by the instruments are all there are in the universe!
Quantoken
September 24th, 2005 at 12:28 pm
Update: new interesting paper out on astro-ph,
“Galaxy Rotation Curves Without Non-Baryonic Dark Matter”
http://arxiv.org/abs/astro-ph/0509630
September 24th, 2005 at 12:29 pm
Drat! Wrong URL. Should be
http://arxiv.org/abs/astro-ph/0506370
September 24th, 2005 at 6:44 pm
Thanks Dissident!
-cvj
September 24th, 2005 at 6:45 pm
Dissident,
Do you have any thoughts about that paper you’d like to share?
-cvj
September 24th, 2005 at 11:57 pm
I’ll have to wash my typing hands thoroughly afterwards, but if you follow the references and look at Bekenstein’s TeVeS it does look braney, doesn’t it? You have a GR-style metric, a time-like vector field and a scalar field which all combine to give the modified metric which actually couples to matter: so, in turn, gravity in the bulk, the brane’s normal vector and the brane’s oscillations?
Then there are the *good* ideas… but I’d better let those mature before sharing them. The brane thing you can kill all you want though.
Gak!
September 25th, 2005 at 8:38 am
We study the dynamical equations for extra-dimensional dependence of a warp factor and a bulk scalar in 5d brane world scenarios with induced brane metric of constant curvature
I couldn’t help notice the brane comment.
Is it because it just a theory that it is rejected? Or that it rubs the existance of Dark energy the wrong way? I was thinking of Gia Dvali as the fifth speaker
September 25th, 2005 at 8:58 am
Warped Geometry of Brane World Gary N. Felder, Andrei Frolov, Lev Kofman
We study the dynamical equations for extra-dimensional dependence of a warp factor and a bulk scalar in 5d brane world scenarios with induced brane metric of constant curvature
http://arxiv.org/abs/hep-th/0112165
Sorry linked phrase did not come up.
September 26th, 2005 at 8:07 am
Thank you for the link, Plato! It’s interesting to note that it predates TeVeS by several years.
As for it being “rejected”, I wouldn’t know about that. After all, it did get published. As always, I only speak for myself, so I can only tell you my general attitude towards bold new extensions of the existing theoretical framework, be they extra dimensions, supersymmetry, strings, dark matter sectors or even just a bunch of new scalars to achieve inflation, dark energy or conveniently large amounts of CP violation for baryogenesis: this game is easy to play, often much too easy. Constraints from experiment and observaton are few and far between, and in many cases that situation can not be expected to improve within the foreseable future, so just about anyone can come up with a whole bunch of extended models which all achieve the one or two goals for which they were created, while conveniently evading the need to actually predict anything which we can hope to verify independently. Is it still science then? Or is it just a spinning of tall tales, science fiction minus the literary talent?
As I wrote way up there, if they were the only alternative, such extensions would perhaps make sense after all. But the current situation is such that we do not even remotely have a good handle on existing theories. We don’t need to get into quantum gravity and how GR may be modified upon quantisation (as in the RG work by Reuter et.al.) to see that; it’s enough to consider how little we know about the non-perturbative sector of good old Yang-Mills theories. Even a first-principle calculation of the spectrum of relativistic bound states is too hard for us. It may not have been if a fraction of the brainpower which has been poured into superstrings over the last two decades had gone into QFT, but perhaps that was too much like real work. So we have the ineresting situation that we lack the mathematical tools necessary to build realistic parton models of elementary particles and compute their spectra, so we don’t, so we say such models don’t exist, so we look to supersymmetry and superstring and super-whatever instead, so we keep not developing the necessary mathematical tools to handle parton models. All the while ignoring the fact that so far, every new layer uncovered in the composition of matter has been of the parton kind; molecules made of atoms made of electrons and nucleons made of quarks.
The stringers would have us believe that the parton chain stops here; from now on it’s all different. Remarkably, nature is supposed to have changed working model right here, at the very point where technological, political and economic constraints make it hard (impossible?) to keep probing matter at shorter distance scales. The same “reasoning” underlies the hope to somehow miraculously find large extra dimensions at the LHC, which may very well prove to be the last large collider to be built in generations, if ever. But this point, this energy scale, is special only to humans. It’s still ridiculously far removed from the Planck scale. So why on earth should nature choose to change its ways right here, so human physicists could come up with something so interesting that politicians and the general public just might be convinced to keep playing the funding game a little bit longer?
Sure, it’s possible. But there’s no reason to expect it. Meanwhile, there is real, hard work to be done on understanding the theories which we already have, and which have been verified to a splendid level of precision in the regimes where we have learned to apply them.
September 26th, 2005 at 10:41 pm
The same “reasoning” underlies the hope to somehow miraculously find large extra dimensions at the LHC, which may very well prove to be the last large collider to be built in generations, if ever. But this point, this energy scale, is special only to humans. It’s still ridiculously far removed from the Planck scale. So why on earth should nature choose to change its ways right here, so human physicists could come up with something so interesting that politicians and the general public just might be convinced to keep playing the funding game a little bit longer?
Then I might be a victim as well?: )
But while this issue has gone on, I have become somewhat puzzled then. As a response for another, would any loss of energy value determinations of what you had before you started into particle reductionsism, should indicate, that energy valuation after the event, should be equal and accounted for? Indicate, that this energy had gone some where, if it’s not?
I am certainly not of the higher calibre of degree here but I am somewhat puzzled. If this were to be the case then, indeed, there is somewhat of an anomalie that needs to be dealt with.
Can you answer this?
September 27th, 2005 at 6:22 am
If you perform an experiment in which some of the energy you put in seems to disappear somewhere, unaccounted for, then yes, you have some explaining to do. Conservation of energy is not something we’d give up lightly; rewriting all those textbooks would be exhausting… but large extra dimensions would certainly not top the list of things to consider.
First of all, “missing energy” is a normal feature of collider experiments, since you can’t expect to catch all the stuff that comes out of them. You have two particle beams banging into each other inside a tunnel of finite width; any decay products flying off into the tunnel are lost. Around the collision point, you have detectors which, while huge and most impressive, also have blind angles and – most importantly – finite size.
The latter means that very weakly interacting particles can fly right through them without leaving any visible trace. There really isn’t much you can do about this; neutrinos go right through the planet all the time, so even an Earth-sized detector would not get them all. This is indeed how neutrinos were first discovered: back in the heroic days of quantum mechanics, late 20s to early 30s, there was a missing energy problem with nuclear beta decay. Pauli suggested that the missing energy was being carried away by a neutral particle, Fermi gave it a name and constructed a theory of weak interactions incorporating it, and they both ended up getting a well-deserved Nobel prize years before anyone had actually detected a single neutrino (see e.g. http://www.ps.uci.edu/physics/news/nuexpt.html).
So, even today experimentalists must routinely correct their data to account for naturally “missing” (really undetected) energy. They would start to worry only if there was a significant deviation between these corrections and the amount of energy actually missing. If this were to happen – and it must be underscored that it hasn’t, currently this is all speculation about what might be seen at the LHC when it starts taking data, hopefully in just 2-3 years – the first hypotheses to analyze would be
1) a new “neutrino”, i.e. very weakly interacting particle, being produced in the collisions and flying right through the detectors (this would be an obvious dark matter candidate, by the way);
2) a new interaction causing processes with a strong angular dependence, i.e. a large fraction of final products flying off into the tunnel, around the directions of the colliding particles.
These would be the natural assumptions for any honest high energy physicist. Ruling them out would take many years of hard work. Energy disappearing into large extra dimensions would be a last straw to be invoked only after all else has failed.
September 27th, 2005 at 10:23 pm
You have given me some things to think about.
One of those is as follows. The second was insight of Pierre Auger experiments and the issue of “microstate blackholes.” I’ll come to that later.
We were given some indications on this site about the state of affairs with Albrecht. Do you think this time span of proposed validation processes, were constructively and experimentally handled appropriately through it’s inception? As scientists would like to have seen all such processes handled in this respect?
Stanford’s Savas Dimopoulos: New Dimensions in Theoretical Physics
Our new picture is that the 3-D world is embedded in extra dimensions,” says Savas Dimopoulos of Stanford University. “This gives us a totally new perspective for addressing theoretical and experimental problems.
http://www.sciencewatch.com/may-june2001/sw_may-june2001_page3.htm
http://www.nature.com/nature/journal/v411/n6841/images/411986af.0.jpg
The angular movements needed to signal the presence of additional dimensions are incredibly small — just a millionth of a degree. In February, Adelberger and Heckel reported that they could find no evidence for extra dimensions over length scales down to 0.2 millimetres (ref. 11). But the quest goes on. The researchers are now designing an improved instrument to probe the existence of extra dimensions below 0.1 mm. Other physicists, such as John Price of the University of Colorado and Aharon Kapitulnik of Stanford University in California, are attempting to measure the gravitational influence on small test masses of tiny oscillating levers.
http://www.nature.com/nature/journal/v411/n6841/box/411986a0_bx1.html
And lastly,
Eric Adelberger on Aug 12th, 2005 at 2:37 pm Then we will replace our molybdenum detector ring with an aluminum one. This will reduce any signal from interactions coupled to mass, but will have little effect on subtle electromagnetic backgrounds. These experiments are tricky and measure very small forces. It takes time to get them right. We will not be able to say anything definite about the anomaly for several months at least.
Would you do away with extra dimensional attempts at comprehension, as crackpotism?
September 27th, 2005 at 10:34 pm
Link should read below:
Eric Adelberger on Aug 12th, 2005 at 2:37 pm
http://blogs.discovermagazine.com/cosmicvariance/2005/08/10/modifications-to-general-relativity/#comment-1310“>
September 28th, 2005 at 2:00 am
“albrecht” should read Adelberger
September 28th, 2005 at 7:35 pm
As far as I know, Adelberger et.al. have been emphasizing all along that there are many things that can go wrong and that they need to do a lot more double-checking and tweaking of the experiment before announcing anything. Rumors are just that, rumors.
And no, I wouldn’t call the extra-dimensional track crackpotism, unless propounded as established fact or as “the only way” or some similar nonsense. But it should be kept in mind that to date it’s just a highly speculative hypothesis, nothing more.
September 28th, 2005 at 10:46 pm
Dissident:I wouldn’t call the extra-dimensional track crackpotism
Ah, thank you.
Eric Adelberger:It is true that we are seeing an anomaly at shorter length scales but we have to show first that the anomaly is not some experimental artifact. Then, if it holds up, we have to check if the anomaly is due to new fundamental physics or to some subtle electromagnetic effect that penetrates our conducting shield. We are now checking for experimental artifacts by making a small change to our
http://blogs.discovermagazine.com/cosmicvariance/2005/08/10/modifications-to-general-relativity/#comment-1310
What anomaly would he being refer too. Could you define this better?
I am going to get very bold here. As a layman you must forgive me?:(
While the gaussian coordinates reveal, as well as the metric, variations in “distant measures,” why would geometric principals not be “more common” in perception and associative values?
Here, the older perspectives on the quark to quark measures, might have revealled a better understanding in the geometric developement along side of Aldebergers experiments.
How we see such a dynamcial avenues revealled in the understanding of gravitational differences assigned to the bulk perspective?
Would this be counterproductive, having concepts established in our thinking to this point?
While it is a simple idea to develope curvature parameters seen establish by the Friedman equations, such dynamics need something in which to assign not only the “fate of our universe” but some principle being talked about here, to couple to dynamics, not only in regards to cosmological principles, but quantum ones as well?
Do you find in this case of extra dimensions, compatibility in issues related to Omega, and critical density geometrically inclined? That it would need physics to apply such ideas we would all agree. I am thinking of Microstate blackholes and their dissipation, as a culmination of such geometrics.
Atlas comes to mind now in regards to “the trigger”. Is this not what Smolin is trying to accomplish seeing glast determination in the calorimetric bringing a greater depth to our perceptions of the universe?
September 28th, 2005 at 11:02 pm
To help further enlighten by developing perspective and position, as I look at scientists quests. Trying to make sense.
Sep 14th, 2005 at 12:40 pm
http://blogs.discovermagazine.com/cosmicvariance/2005/09/12/cosmic-violence/#comment-3389
October 14th, 2005 at 4:23 am
Wow! Just caught sight of
http://xxx.lanl.gov/abs/astro-ph/0507619
at
http://www.cerncourier.com/main/article/45/8/8
(in turn linked from
http://blog.olympus.het.brown.edu/science/archives/000386.php).
Now THIS is work to my liking! (I would also feel immensely stupid for having missed it, were it not for the fact that I was in full immersion mode and not looking at new stuff at all at the time.)
October 17th, 2005 at 10:44 am
While we see progressive features about the way Sean produces imagery one had to know indeed that such progression to algebraic geometry would have understood that spherical valuation can “exceed the surface” to bring into view, a global perspective about the consequernce of this elliptical scene.
So we change the color, and sometimes, the color lets us see how this global perspective encases the elliptical valuation? It did not just hold then to this “surface valuation” in a cosmic event but was ever unfolding to reveal dynamcial properties that GR helps us see. It is only part and parcel of a developing framwork? There had to be some geometrical consistancy, even taken to this level.
Oui, Non?
I am learning here, so be kind.