tag:blogger.com,1999:blog-3145618750613855559.post1507037218752864642..comments2017-03-18T22:47:47.438-07:00Comments on Eddie Current’s Blog: Dark Energy: Too Big To FailEdward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.comBlogger41125tag:blogger.com,1999:blog-3145618750613855559.post-83757539348385516822015-11-19T14:48:34.899-08:002015-11-19T14:48:34.899-08:00This comment has been removed by the author.tonyonhttp://www.blogger.com/profile/08253501266473243514noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-79610233907959798932015-11-19T14:48:22.964-08:002015-11-19T14:48:22.964-08:00This comment has been removed by the author.tonyonhttp://www.blogger.com/profile/08253501266473243514noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-38804188967414081782015-11-19T09:01:50.749-08:002015-11-19T09:01:50.749-08:00This comment has been removed by the author.tonyonhttp://www.blogger.com/profile/08253501266473243514noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-60127491019311384512015-03-13T12:43:23.834-07:002015-03-13T12:43:23.834-07:00This comment has been removed by the author.tonyonhttp://www.blogger.com/profile/08253501266473243514noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-66939348741243137172013-10-10T05:33:32.081-07:002013-10-10T05:33:32.081-07:00We will make a new approach for an effect known as...We will make a new approach for an effect known as “Dark Energy” by an effect on gravitational field.<br /><br />In an accelerated rocket, the dimensions of space towards movement due to ‘Lorentz Contraction’ are on continuous reduction.<br /><br />Using the equivalence principle, we presume that in the gravitational field, the same thing would happen.<br /><br />In this implicates in ‘dark energy effect’. The calculi show that in a 7%-contraction for each billion years would explain our observation of galaxies in accelerated separation.<br /><br /> <br /><br /> <br /><br />Lorentz Contraction<br /><br /> <br /><br />If we suppose that gravitational field contracts the space around it (including everything within), we can explain the accelerated separation from galaxy through this contraction without postulating ‘dark energy’. <br /><br />The contraction of space made by gravity would cause a kind of ‘illusion of optic’, seem like, as presented below, that galaxies depart fastly.<br /><br /> <br /><br />The contraction of space would be equivalent to relativistic effect which occurs in a special nave in high-speed L.M.: With regard to an observer in an inertial referential stopped compared to a nave, the observer and everything is on it, including own nave, has its dimension contracted towards to movement of nave compared to a stopped observer (Lorentz Contraction).<br /><br />This means that the ‘rule’ (measuring instruments) within the nave is smaller than the observer outside of moving nave.<br /><br />The consequence is, with this ‘reduced rule’, this moving observer would measure things bigger than the observer would measure out of nave.<br /><br /><br /><br /> <br /><br />An accelerated rocket and its continuous contraction<br /><br /> <br /><br />In the same way, if we think of an accelerated increasing speed rocket, its length towards movement – compared to an inertial reference - will be smaller, and 'rule' within the nave will decrease continuously compared to this observer.<br /><br /> <br /><br />We would think of 'equivalence principle' to justify that gravitational field would have the same effect on 'rules' (measuring instruments) as an accelerated rocket would do within the nave, but, now, towards all gravitational field and not, in the case of rocket, only at acceleration speed.<br /><br /> <br /><br />I.e., the gravitational field would make that all rules within this field would be continuously smaller regarded to an observer outside of gravitational field and this would make, as we can see, these observers see things out of field be away fastly.<br /><br /><br /> <br /><br />The “dark energy” through gravitational contraction:<br /><br /> <br /><br />Let’s think what would happen if a light emitted by a star from a distant galaxy would arrive into our planet:<br /><br /> <br /><br />Our galaxy, as well as distant galaxies, would be in continuous contraction, as seen before, due to gravity.<br /><br />A photon emitted by a star from this distant galaxy, after living its galaxy, would go through by an “empty” big space, without so much gravitational influence, until finally arrives into our galaxy and, lastly, to our planet.<br /><br /> <br /><br />During this long coursed way (sometimes billion years), this photon would suffer few gravitational effect and its wavelength would be little affected.<br /><br />However, during this period, our system (our rules) would still decreasing due to gravitational field, and when this photon finally arrives here, we would measure its wavelength with a reduced ‘rule’ compared to what we had had at the moment when this photon was emitted from galaxy.<br /><br /> <br /><br />So, in our measurement would verify if this photon had suffered Redshift because, with reduced rule, we would measure a wavelength longer than those was measured. The traditional explanation is “Shift for Red” happened due to Doppler Effect compared to galaxy separation speed!<br /><br /><br /><br /> <br />JOCAXhttp://www.blogger.com/profile/13731308994877058298noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-53367278493155899122013-02-27T23:08:47.275-08:002013-02-27T23:08:47.275-08:00I am not a physicist, but I do have real interest ...I am not a physicist, but I do have real interest in this topic. I am wondering how David Wiltshire's timescape cosmology deals with the Integrated Sachs Wolfe Effect. I would add that the concept of "dark energy" has bothered me from the time I first heard about it, as it seems very messy and a violation of Occam's Razor. In contrast, a universe perfectly balanced between eternal expansion and eventual contraction seems elegant.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-83112323049806722362013-02-13T22:13:10.179-08:002013-02-13T22:13:10.179-08:00I thank you for taking the time to respond David. ...I thank you for taking the time to respond David. It appears I was too quick to judge your idea. Based on previous experience with void models, I assumed your idea (which, after skimming through a couple of your papers, looked vaguely similar at first) was going to run into similar problems.<br /><br />I'll read your papers more closely. At the moment I'm still of the opinion that the ΛCDM seems right, but perhaps that will change.<br /><br />Thanks again for the knowledgeable response.elfmotathttp://www.scienceforums.netnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-39741669423716682112013-02-07T16:17:06.347-08:002013-02-07T16:17:06.347-08:00They didn't seem too upset -- I've seen a ...They didn't seem too upset -- I've seen a lot worse! I love the physicsforums as a resource. Whenever I have a question about established mainstream physics, and I want the established explanation for something or I want to learn the mainstream perspective, I go to the physicsforums. But it's a terrible place to challenge conventional wisdom or to float an original hypothesis. As eager as the regulars are to help someone with an honest question, they're just as eager to jump on someone who seems to have an agenda or an anti-science bent. Humility, I've learned, serves you well there. Thanks for the comment.Edward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-56812250150552720292013-02-05T23:51:06.793-08:002013-02-05T23:51:06.793-08:00I don't understand the attack on Eddie or Wilt...I don't understand the attack on Eddie or Wiltshire. I personally don't think anything is to big to fail in science, but there might be some ideas that may take more time to let go of. I'm all for new discoveries and explanations and wish anyone searching for truth good luck! Even if Wiltshire can not confirm his idea, it is possible that something else might get discovered by looking at the universe from a different perspective. Thanks kneejerkhttp://www.blogger.com/profile/11841116319767200741noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-7177405047906291862013-02-04T17:03:56.728-08:002013-02-04T17:03:56.728-08:00Very interesting discussion. I am not a researcher...Very interesting discussion. I am not a researcher in physics but still based on my previous knowledge reached the conclusion the dark energy is hocus-pocus. Yesterday I had posted a thread in physics forum and some people got upset: <br /><br />http://www.physicsforums.com/showthread.php?t=669099Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-9856230445667411022013-01-31T02:11:55.193-08:002013-01-31T02:11:55.193-08:00I am taking the gamble because I am convinced that...I am taking the gamble because I am convinced that the mystery of dark energy (and perhaps even dark matter too) does demand really new physics which was not in the toolbox of tricks that we had invented by the end of the 20th century. And as a relativist I know Einstein never finished the job. I am abandoning the idea that spacetime is a single geometry with a prescribed matter field. Instead I think cosmological spacetime describes a statistical ensemble of geometries, within which the notions of gravitational energy and entropy have to be better defined. It involves new symmetry principles (which I have tried to encapsulate with a "cosmological equivalence principle"). Such symmetry is no doubt related to the initial conditions of the universe and all those thorny questions about quantum gravity. But rather than trying to tackle those problems head on with purely mathematical ingenuity, I think we have to be guided by observations - which often means sorting out very prosaic astrophysical issues to get to the bottom of things.<br /><br />Physicists who talk about "modified gravity" have generally proceeded from a point of view in which all modifications come about from changing the action, while keeping the geometry simple. Indeed a lot of present day thinking in cosmology is really still Newtonian (actions and forces), with a simple Euclidean space lurking in the background. (From my point of view distances on cosmological scales - the 30/h or 100/h Mpc - are a convention adapted to one particular geometry. In a statistical description, when spatial curvature varies greatly and there is no one fixed metric - there are different equivalent metric descriptions. It is all about relative calibration of rulers and clocks.) So while the program I am pursuing is not "modified gravity" in the way it has traditionally been done, i.e., it does not change general relativity on the scale of bound systems on which it is tested, I would be happy to call it "modified geometry".<br /><br />This is new and uncharted territory. But if "dark energy" is the fundamental mystery that everyone says it is then any real lasting solution is going to be new uncharted territory at some point. You cannot have it both ways. It is entirely reasonable of my colleagues to "wait and see", since I might be wrong. But I am of the view that being a theoretical physicist is not about necessarily being right or wrong, but rather about having the courage to go right back to the conceptual foundations when the observations demand it, and to rigorously ask questions that have never been asked before.David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-13725629879720827292013-01-31T02:10:18.192-08:002013-01-31T02:10:18.192-08:004. SOCIOLOGY OF SCIENCE IN CHALLENGING A STANDARD ...4. SOCIOLOGY OF SCIENCE IN CHALLENGING A STANDARD MODEL<br /><br />"Anonymous" is very correct to point out that alternatives to dark energy are seriously considered in the community, and that your portrayal - based largely on the popular account - is simplistic. However, the issue of acceptance of new ideas by the scientific community is a complex one, so the possibility of something being "too big to fail" (sociological inertia) deserves further discussion. The "too big to fail" standard here is not dark energy itself, but the Friedmann-Lemaitre models which have been around since the 1920s and upon which a huge superstructure has been built absorbing many decades of many people's careers. That is a lot to challenge; and not something you do lightly.<br /><br />The timescape model is testable, and it actually fits the current data so well that the differences between timescape and Lambda CDM will require years of careful analysis to resolve. But the pace of doing this work is not only limited by the time it takes to do observations. There is also the fact that I and my students are the only ones working on developing the theoretical ideas and analytic tools to enable the timescape cosmology to be better tested. My work is certainly cited, but just because people find it interesting not because they are working on it. The attitude of my colleagues is most often: "that's an interesting idea, we'll wait and see". Of course there are those who simply do not believe me as well.<br /><br />Most scientists generally only read in depth those papers which are going to help them write their next paper. Our careers are built on producing papers to pass peer review. To do something totally new requires a big investment of time, and most people want to be convinced that something is going to work before they make that investment.<br /><br />In theoretical physics, researchers will quickly take to a new topic if they can adapt their existing tools, and produce papers quickly. The reason that large voids and other LTB models are the most well-studied inhomogeneous models, with many many papers written despite being extremely unlikely as physical models of the whole universe, is that they are exact solutions of Einstein's field equations to which existing techniques can be applied. It requires no hard conceptual thinking to produce new papers; just an ability to solve differential equations and a familiarity with the tools of general relativity.<br /><br />Anything which involves truly new physics is hard to sell, since there are always a lot of ideas on the market. In my case I am going to the fundamentals of hard problems that troubled Einstein and many mathematical relativists since. I am thinking conceptually and using observations as a guide to new physical principles. In reality, the "shut up and calculate" school still dominates. A lot of theoretical physicists shy away from conceptual thought; and like to solve hard mathematical problems within the confines of an accepted theoretical framework. I have given an invited lecture at a big conference and had a famous relativist come up to me afterward with the comment "congratulations, this is the true spirit of relativity" or on another occasion "this is the way that physics should be done". But very few people actually dare to do physics this way; it's too much of a gamble.<br /><br /><br /><br />David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-72995278634212657772013-01-31T02:08:05.778-08:002013-01-31T02:08:05.778-08:00It boils down to empirical questions such as "...It boils down to empirical questions such as "is the reddening by dust in other galaxies similar to that of the Milky Way?". I find that it should be in order for timescape to come out better, and indeed independent measurements in other galaxies confirm that the Milky Way value reddening parameter R_v=3.1 is within a standard deviation of the mean R_v=2.8. Yet some supernova fits to the standard cosmology give R_v=1.7, which is way off. It is these sorts of nitty gritty issues that crop up again and again when you try to do any observational cosmology. Astrophysics is basically a dirty empirical subject where you cannot control the conditions of the lab. To distinguish two competing models on many independent tests therefore requires years of work. Some of the most definitive tests I discuss in arxiv:0909.0749, such as the redshift-time drift test, which actually take decades to do.<br /><br />The tension in the value of the dressed Hubble constant is actually interesting because in the timescape model one expects a natural variance of up to 17-22% in the nearby Hubble flow below the scale of statistical homogeneity. This may also impact on the assumptions made in normalizing the distance ladder, which is crucial to determining H0. So there are important systematic astrophysical issues to be resolved. The most interesting tests are in fact nearby, below the scale of statistical homogeneity, where the universe is most inhomogeneous. We have begun looking at this.<br /><br />Indeed in arXiv:1201.5371 we do a model-independent test, with a finding that is very much at odds with the assumptions in the standard model. The spherically averaged Hubble flow appears to be significantly more uniform in the rest frame of the local group, rather than the assumed rest frame of the CMB. The only way to understand this as far as I can see is that there appears to be a significant non-kinematic component to the CMB dipole due to foreground density gradients from the differential expansion of space; indeed we find a dipole whose strength is correlated with structures at the same scales that generate the spherical (monopole) variation in the Local Group frame. Such a finding supports the timescape model but does not prove it. On the other hand, some astronomers are beginning to collect data for far more ambitious tests of the timescape model: see arXiv:1211.1926.<br /><br />In short, observational tests are being undertaken. It just takes time.<br />David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-6543113788412295002013-01-31T02:06:11.220-08:002013-01-31T02:06:11.220-08:003. OBSERVATIONAL TESTS, ANOMALIES AND TENSIONS
&q...3. OBSERVATIONAL TESTS, ANOMALIES AND TENSIONS<br /><br />"Anonymous" very correctly says that alternatives such as mine are taken seriously, and what matters are observational tests. I have detailed several observational tests in Phys. Rev. D90 (2009) 123512 = arXiv:0909.0749. Some of these involve things which are already tensions for the standard model.<br /><br />"Elfmotat" mentions that I have pointed out a tension between my dressed Hubble<br />constant, and the current value of Riess et al; I can live with something in<br />the range up to 68 km/s/Mpc (or down to 58 km/s/Mpc) but 72 km/s/Mpc would<br />be too high. I should point out, however, that there are also many observations which provide tensions, or indeed outright anomalies, for the standard Lambda CDM cosmology.<br /><br />In cosmology it is sometimes said that any model which fits all of the data at any one time is almost certainly wrong because some of the data is going to change. For example, the standard model has the primordial lithium abundance anomaly, which has existed since the first release of WMAP data in 2003 and which has not gone away. This one is actually very interesting for me, since when I put the numbers in it is very likely that the timescape model can deal with the lithium abundance anomaly. (This happens because the ratio of baryons to dark matter is naturally increased for given baryon-to-photon ratio.) For the standard model the lithium abundance anomaly is statistically much more significant than the Hubble constant tension in my case - which is the difference between a "tension" and an "anomaly".<br /><br />The standard model is accepted despite some outright anomalies, and various other tensions, simply because it fits so many independent pieces of data. Of course, the standard model has been developed over decades with thousands of people working on it, and so it can be subject to many more tests than any other cosmological model. To claim better than standard model on the primordial lithium abundance anomaly, for example, I have to be able to fit all of the Doppler peaks in the CMB anisotropy spectrum to more tightly constrain the baryon-to-photon ratio.<br /><br />Thus far with the CMB I have only fit the overall angular scale of the Doppler peaks (which itself is a major test). To do the rest is hard because one cannot simply use existing numerical codes written for the standard model, developed over a decade by many people. One has to revisit the whole problem from first principles. That sort of thing takes time. Similarly, techniques used to analyse galaxy clustering statistics are very much based on the standard model; so again to do the tests rigorously requires revisiting the whole observational methodology.<br /><br />The interesting thing about the timescape cosmology is that quantities such as the luminosity distance are so close to those of the standard model that the differences are at the level of systematic errors. Supernova distances are the test we have studied most, as they are the simplest. Even in this simple case the fact that supernovae are not purely standard candles but standardizable candles means that the systematics have to be sorted out before one can say whether Lambda CDM or timescape is better (see arXiv:1009.5855). There are two main methods of data reduction - SALT/SALT-II and MLCS2k2 - if you use the first method you would say Lambda CDM fits better, and if you use the other then you would say timescape fits better.<br /><br /><br /><br />David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-59700073847119653902013-01-31T02:03:58.390-08:002013-01-31T02:03:58.390-08:00What I do is fundamentally different, in that I be...What I do is fundamentally different, in that I begin from an approaches pioneered by Thomas Buchert, in which one considers the statistical properties of a truly inhomogeneous matter distribution with regions of varying density and varying expansion rates in the fully nonlinear regime. So I do not solve Einstein's field equations directly, but rather Buchert's equations which describe the average evolution of a statistical ensemble of voids and wall regions. Rather than postulating a hypothetical single large void to have a simple exact solution of Einstein's equations, I am dealing with an approach which accounts for the actual observed inhomogeneity in a statistical sense within general relativity.<br /><br />2. NEW PHYSICS IN THE TIMESCAPE COSMOLOGY<br /><br />Going from a statistical description of cosmology to one which refers to our own observations requires additional input. It's like having the ideal gas law on one hand, and then having to use that law to explain physics from the point of view of a molecule of gas. So I certainly add new physics; the crucial physics relates to the relative calibration of rulers and clocks of observers in regions of different density which have decelerated by different amounts.<br /><br />General relativity is actually not a complete theory. On account of the equivalence principle, gravitational energy is not localizable, and a conserved energy cannot be defined in general. The best one can do is "quasilocal energy"; but the nature of quasilocal energy expressions is something that Einstein struggled with, and many mathematical relativists since, with no general consensus as there are no unique conservation laws. Since the universe is so remarkably simple despite the complex cosmic web of different densities, I think it likely that there are nonetheless simple principles to be found which shed light on this fundamental, but unsolved, part of general relativity. I proceed on that basis.<br /><br />I do not have time/space to describe my from-first-principles reasoning here. I wrote an FQXi essay a while ago which describes the ideas qualitatively, also available as arXiv:0912.4563. In particular, I treat the relative deceleration of regions of different density - which impacts on the relative kinetic energy of the expansion of space - as a physical degree of freedom in the calibration of clocks. So while the idea that "clocks run slower in denser regions" is familiar in solar system physics or near black holes, what I am dealing with is not the familiar relative position of observers in a static potential but something intrinsically different. It's a new effect.<br /><br />Since I am proposing a new effect, it's not a case of this being something obvious in general relativity that we just forgot to account for. If that was the case this would be much more readily accepted by theoretical physicists. Rather I am extending the basic physical ideas of relativity to a new regime - the complex many body problem of cosmological averages - where we know there are unsolved problems.<br /><br />The gravitational energy gradient / clock effect is essential for my solution to the problem of dark energy; when you put the numbers in it would not work otherwise. That is the reason why after toying with different names I chose to call it the "timescape cosmology" to highlight the essential new physics and distinguish my work from other approaches to inhomogeneity, such as large void models.David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-11268390833681519462013-01-31T02:02:34.279-08:002013-01-31T02:02:34.279-08:001. DISTINCTION OF STATISTICAL AVERAGING FROM NON-C...1. DISTINCTION OF STATISTICAL AVERAGING FROM NON-COPERNICAN VOID MODELS<br /><br />Your correspondent Elfmotat has confused my model with non-Copernican large void models criticized by Moss, Zibin and Scott, Phys. Rev. D83 (2011) 103515 = arXiv:1007.3725. The timescape model is not such a model, is not subject to the criticisms made in this paper, and is not ruled out by any other observations.<br /><br />I am certainly not the first person to suggest that inhomogeneities rather than dark energy may be at the root of what appears as apparent cosmic acceleration (just the exact mechanism by which this is achieved is very different to anyone else - see next section). Elfmotat mentions Rocky Kolb who with collaborators generated publicity and controversy in 2005, with an argument based on perturbation theory about a homogeneous cosmology. But in fact people like Marie-Noelle Celerier and Kenji Tomita had already suggested inhomogeneities as an alternative to dark energy, using non-Copernican void models in 2000.<br /><br />The large void models are the most well studied in this field, because there is a simple exact solution for the Einstein equations with any spherically symmetric pressureless dust source, which goes back to Lemaitre and Tolman in 1933. The Lemaitre-Tolman (or Lemaitre-Tolman-Bondi LTB) models are of course unlikely philosophically, as well as observationally, since they require us to be near the centre of a universe with a very peculiar spherically inhomogeneous density profile - generally with us near the centre of a large void (though not necessarily, see arXiv:0906.0905) - thereby violating the Copernican principle. Furthermore, the void (or other spherical inhomogeneity) has to be much larger than the typical structures we observe.<br /><br />What we actually observe is not a single large void but a complex cosmic web of structures, with particular characteristic scales to the inhomogeneity which are much smaller than the toy model large LTB voids that that Moss, Zibin and Scott discredit. Surveys show that about 40% of the volume of the late epoch universe is in voids of 30/h Megaparsecs (where H0= 100 h km/s/Mpc is the Hubble constant). A similar fraction is in smaller voids, while clusters of galaxies are contained in filaments that thread the voids and walls that surround them in a cosmic web. The universe is homogeneous in some statistical sense when one averages on scales larger than about 100/h Mpc. These are observed facts which almost everybody agrees on.<br /><br />The actual inhomogeneity is far too complex to be solved in Einstein's equations, even on a computer. In the standard model one assumes that the universe evolves as if were a completely homogeneous uniform fluid with Newtonian gravity perturbations added on top. Since the 30/h Mpc voids are in the "nonlinear regime" (smaller than the statistical homogeneity scale) as far as perturbation theory is concerned, the only way to understand them in the standard model is to run computer simulations with Newtonian gravity + dark matter + dark energy + the uniformly expanding background. Full general relativity is not used; that problem is in the too-hard basket. It's not just a question of computing power - there are fundamental ambiguities about splitting space and time in general relativity which impact on the numerical problem. People have recently learned how to do the two body problem (e.g. 2 black holes) in numerical relativity; the cosmological problem is far more complex.<br /><br />David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-10382140542931619112013-01-31T02:00:40.108-08:002013-01-31T02:00:40.108-08:00Dear Eddie Current,
Thanks for your email bringin...Dear Eddie Current,<br /><br />Thanks for your email bringing my attention to this discussion, and for your clearly written piece. While I do not have a lot of time to discuss every point, I am happy to make some comments. I will do this under the following headings. I have to break it up as the software does not allow me more than 4096 characters<br /><br />1. Distinction of timescape from non-Copernican "void" models<br />2. New physics in the timescape cosmology<br />3. Observational tests, anomalies and tensions<br />4. Sociology of science in challenging a standard model<br /><br />David Wiltshirehttp://www2.phys.canterbury.ac.nz/~dlw24/noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-51975283361188960302013-01-28T20:24:36.975-08:002013-01-28T20:24:36.975-08:00Sorry, I'm not sufficiently knowledgeable on t...Sorry, I'm not sufficiently knowledgeable on that topic, but yes, if I did understand my prof way back correctly, then GR and QFT don't really work together. I'm not really surprised, though: GR describes gigantic masses and astronomical length scales, whereas quantum field theory describes the smallest of all length scales. The problem is that to make sense of field theories, one has to introduce certain energy cut-offs to prevent certain integrals from diverging. Depending on where you set this cut-off, you get wildly disagreeing predictions...<br /><br />I'd expect that mistakes happen when extrapolating one of QFT or QR into the realm of the other, just as classical mechanics fails at high velocities. When attempting to unify them, at least one of them will have to be modified. In that case, I'd place my bet that quantum mechanics will survive relatively unscathed.<br /><br />But to get really thorough answers I can recommend the site physics.stackexchange.com where I know that a lot of really knowledgeable people post quite a lot, including top professors in the fields of cosmology. Lagerbaerhttp://physics.stackexchange.comnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-72803088432085816812013-01-28T16:18:12.755-08:002013-01-28T16:18:12.755-08:00It looks like we're done now. You didn't s...It looks like we're done now. You didn't show how Wiltshire's model requires Earth to be in a privileged position. You also never explained why the appearance of accelerated expansion <i>wouldn't</i> be a necessary observation from Earth if general relativity is correct. Instead you went from declaring the model falsified beyond consideration, to identifying one "tension" between the model and a recent calculation -- while shrugging off 107 orders of magnitude of disagreement between dark energy and a much better-supported theory, quantum field theory! The reasoning? Because we have some calculations from the CMB, which in turn are based on the same FLRW solution of homogeneous expansion that led to this mess in the first place. And, because dark energy "just looks right to me." Unwittingly, your comments exemplify what I mean by too big to fail. This thread is closed.Edward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-25472759101578477302013-01-28T13:35:17.718-08:002013-01-28T13:35:17.718-08:00Fair enough; thanks for the comment. Is it true th...Fair enough; thanks for the comment. Is it true that QFT disagrees with GR? Or just that gravity has not yet been successfully quantized? In the mid 1800s electricity and magnetism hadn't been unified, but the theories didn't necessarily disagree (as far as I know). QFT on the other hand makes a density-energy prediction that greatly disagrees with the notion of a small cosmological constant, which is dark energy all the way.Edward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-52625187727566465922013-01-28T13:07:41.396-08:002013-01-28T13:07:41.396-08:00It's safe to say that dark energy is not yet p...It's safe to say that dark energy is not yet proven beyond reasonable doubt, which is why alternative models are actively discussed in the community. However, by focusing on just this one paper and then claiming that it completely solves the issue is a bit too simplistic. A bit like homeopathy proponents who latch onto that single clinical study that somehow could be interpreted as lending credence to their claims. So now we have an alternative explanation. Good. What predictions does it make that distinguish it from the dark energy hypothesis? Can we test those?<br /><br />IMHO it is perfectly reasonable to postulate: "Suppose the extra expansion is caused by some extra energy. What properties would it need to have to do so" and then go from there to build testable hypotheses. <br /><br />Note that quantum field theory not only (seemingly?) disagrees with dark energy. It also disagrees with general relativity. This is to be expected, since one is developed to describe microscopic length scales while the other is responsible for astronomical length- and mass scales. One of them, QFT or GR, will have to be further modified to get them to agree. The problem is that to date we do NOT have a satisfying theory of quantum gravity, with or without dark energy.<br /><br />Proposing alternatives to dark energy for explaining the real or apparent acceleration of the universe's expansion are definitely not ignored by the scientific community.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-76541145254090699042013-01-27T17:20:57.437-08:002013-01-27T17:20:57.437-08:00His model produces a prediction for Hubble flow th...His model produces a prediction for Hubble flow that's in tension with observation, among other problems. As I mentioned above, Wiltshire himself has acknowledged this.elfmotathttp://www.scienceforums.netnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-78219598449789981492013-01-26T21:18:59.138-08:002013-01-26T21:18:59.138-08:00Then you still haven't explained why the model...Then you still haven't explained why the model is disproved by observation. The big arrows in my picture refer to other matter accelerating away, and voids beyond that. No privileged position is given for our location. If all of the voids are expanding faster than all of the bound regions, then we would appear to be in a Hubble bubble, would we not?Edward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-58455494294087270832013-01-26T21:02:20.280-08:002013-01-26T21:02:20.280-08:00I think you're just misunderstanding what &quo...I think you're just misunderstanding what "center of a void" means. It means that we lie in a privileged section of universe (our galaxy) surrounded by voids (the space between galaxies). Basically, refer to your image above (our galaxy surrounded by void).elfmotathttp://www.scienceforums.netnoreply@blogger.comtag:blogger.com,1999:blog-3145618750613855559.post-1277367150087221952013-01-26T20:34:19.848-08:002013-01-26T20:34:19.848-08:00My article is based on Wiltshire's webpages li...My article is based on Wiltshire's webpages linked above, which are based on this paper:<br />http://arxiv.org/abs/0809.1183<br /><br />Neither have anything to do with Earth being at the center of a void. I guess I must be either crazy or stupid.Edward Currenthttp://www.blogger.com/profile/06772053738612119871noreply@blogger.com