tag:blogger.com,1999:blog-6976071487922527618.post5822345114345418916..comments2024-09-04T13:33:11.904+02:00Comments on Blank On The Map: Does the multiverse explain the cosmological constant?Sesh Nadathurhttp://www.blogger.com/profile/07155102110438904961noreply@blogger.comBlogger27125tag:blogger.com,1999:blog-6976071487922527618.post-24075400728336681322014-12-09T10:44:41.823+01:002014-12-09T10:44:41.823+01:00Do you know of some way in which the value of the ...Do you know of some way in which the value of the dark energy density is related to the CMB quadrupole (independent of the other multipoles)? Otherwise I'm not sure your observation amounts to much more than numerology.<br /><br />Also the point made by Raphael Bousso above is a good one: it's not the value relative to the prediction (0.1-1%) that counts, it is the number of standard deviations away from the prediction, i.e. how far they are in the tail. In the case of the low-l CMB multipoles, this is not very much.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-10686134673882179792014-12-07T20:21:47.263+01:002014-12-07T20:21:47.263+01:00But that Weinberg's prediction fails in a stri...But that Weinberg's prediction fails in a stringy multiverse doesn't mean that it fails as an interesting observation and possibly as an anthropic prediction. Instead, we already know our universe is atypical (largest l pole in Planck's CMB spectra). So we could expect Weinberg's prediction to be off there too, in the 1 - 0.1 % range.<br /><br />Is it testable? Not to the usual quality criteria. <br /><br />But again, what can we say on atypical objects more than that they belong to the tail? Maybe the usual criteria doesn't belong to such objects.Torbjörn Larssonhttps://www.blogger.com/profile/13304729731231255545noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-1274909838497431912014-04-18T00:21:34.649+02:002014-04-18T00:21:34.649+02:00Please read with a degree of levity :)
""...Please read with a degree of levity :)<br />"" Many very smart people have tried many ingenious ways of solving it, but it turns out to be a very hard problem indeed""<br /><br />I see. <br />Well..let me take a crack it......<br /><br />Nope...I got nothin<br /><br />Oh Wait. The long standing company line in the past was "The world only """appears""" designed...we're sure the parameters are wide to get to the complexity we see with our eyes"<br /><br />Ok............and the results are In...............and.......TaDa<br /><br />The Math is Infinitely worse than what we can see.<br /><br />In fact, its so mind blowing that it makes former claims of the "appearance of design" look childish. Our Universe is Impossible.<br />If only there were more universes...but wait, there's a problem with that..<br /><br />.....that's more than there are.<br /><br />Maybe we're in computer simulation? Maybe if we get some adhesive and patch all the loopholes together, we can glue it all together, and prop it up with string like a talking puppet. It would be embarrassing but aren't we already there?<br /><br />When is somebody gonna have the courage to just state the obvious. A magical everything maker machine that just happens to pop out exactly what you need doesn't solve problems ...it defines the real problem.<br /><br />Has it ever occurred to you that there would be another You that witnesses the same data and the only difference in that world is You(he) completely disagrees with you. There would be an infinite amount of them, robbing your conclusion of any claim to Reason. What I'm saying is I hear people treating the issue as if it can dismissed by a loophole using probability, but it introduces a reality where probability becomes meaningless. I think if people would spend a few days running through all the absurdities and contradictions that would exists if everything existed, they'd see ... not only is the price too high but the disease is worse than the cure.John Burgerhttps://www.blogger.com/profile/06021462296956618398noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-50526828171951963932014-02-18T17:39:19.224+01:002014-02-18T17:39:19.224+01:00And incidentally, I was also referring to f(R) gra...And incidentally, I was also referring to f(R) gravity models in my comment above: these theories do not solve the cosmological constant problem.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-85636302043527106582014-02-18T17:37:14.261+01:002014-02-18T17:37:14.261+01:00If you read Phil Gibbs' essay carefully you wi...If you read Phil Gibbs' essay carefully you will see that his argument reinforces Sean's point and mine. In order to show that energy is "conserved", he has had to introduce an extra term in his definition of "energy" to account for "the energy of the gravitational field". Now Sean's argument is that such a modification of the definition is not useful, but we don't even need to get into that discussion. The definition of energy you are using to claim that energy conservation means the vacuum energy density has to vary with time is not this modified definition. So either way you are wrong.<br /><br />Your attitude really annoys me, actually. What the hell are your qualifications, since you are so happy to cast ignorant aspersions on everyone else's? Your patronizing tone is a bit rich given your own obvious lack of knowledge of physics and even general reading comprehension. <br /><br />I'm happy to host genuine questions here from people who don't understand something and would like to learn more about it - if it is beyond my expertise I will say so - but comments combining ignorance and arrogance will be simply deleted.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-81510406412291492062014-02-18T16:26:10.650+01:002014-02-18T16:26:10.650+01:00Sean's a nice guy, but he's a cosmologist,...Sean's a nice guy, but he's a cosmologist, and a "senior research associate". He's no expert on relativity. Energy IS conserved in general relativity. Direct a 511keV photon into a black hole, and the black hole mass increases by 511keV/c². Lift a brick and you do work on it. Its mass increases. Drop it and some of that mass-energy, that which we call potential energy, is converted into kinetic energy. Discard that kinetic energy, and the mass of the brick is reduced. Ergo the mass defect. The same applies to you and your measuring equipment, hence a downward photon appears to have gained energy. Even though it hasn't. You know this, because when you direct a 511keV photon into a black hole, the black hole mass increases by 511keV/c². See Phil Gibbs’ essay at: http://vixra.org/abs/1305.0034. <br />There are other issues like this wherein people who promote themselves as the experts get things hopelessly wrong, and end up talking about the multiverse, or the evil twin universe, or some other speculative nonsense that has absolutely no evidential support. And some have a bad habit of grandstanding with “problems”, such that when somebody points out a problem with their problem, or a potential solution, they react badly. Sometimes they say “that can’t be right because we didn’t think of it”. Look again at what I said Sesh. Don’t forget the bag model. Ask yourself where the strong force goes in low-energy proton-antiproton annihilation to gamma photons. And note that I’m no advocate of MOND. Milgrom was referring to f(r) gravity, that’s all. <br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-91754687124750285592014-02-18T13:42:10.128+01:002014-02-18T13:42:10.128+01:00For further reading about the conservation of ener...For further reading about the conservation of energy, go to <a href="http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/" rel="nofollow">Sean Carroll</a>. His post also nicely conveys the sense of frustration cosmologists feel with people who think they've discovered the "simple mistake" we've all been making for so many years.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-77512791924744591962014-02-18T13:29:55.590+01:002014-02-18T13:29:55.590+01:00If only physics were so simple, and we could solve...If only physics were so simple, and we could solve all problems just by thinking of analogies with bubblegum and balloons and watching the Discovery channel! Unfortunately it isn't. A lot of people don't seem to realise that the "explanations" of physics that pop-science sources such as the Discovery channel provide are just <i>analogies</i>, they're not the real physics. Often they're not even good analogies, and completely fail as soon as they are examined in even the tiniest bit more detail.<br /><br />Another thing that many people curiously don't seem to realise is that professional physicists are not only very smart people, they also often have to study for something like 10 years before they even get a PhD, not to mention spending a lifetime studying these issues after that. So if you think, based on reasoning from Discovery channel analogies, that you have found a very simple solution to a problem that all professional physicists acknowledge is a serious one, it is overwhelmingly more likely that your "solution" and your analogies are wrong than that all physicists are wrong.<br /><br />I haven't the time to write a whole lot about this now, but here are some things you should consider. "Energy conservation" in general relativity is a subtle concept; energy is not "conserved" according to the definition of conservation you seem to be thinking of. In particular, the vacuum energy density most definitely does not vary with time; it remains constant even as the universe expands ("expansion creates more vacuum" is one way to think about it). Then the expanding balloon, which is just an awful analogy, gets almost everything about cosmology wrong (see comments <a href="http://www.preposterousuniverse.com/blog/2007/03/12/catholic-priest-proposes-new-model-for-creation/" rel="nofollow">here</a>). Then the statement that pressure is energy divided by volume is wrong - if anything, pressure would be p=-dE/dV, which is why a vacuum energy density that remains constant does correspond to a negative pressure. Also, thinking about "tensile strength" and negative pressure as "tension" is completely counter-productive and wrong (if negative pressure were tension, why would negative pressure cause accelerated expansion?).<br /><br />And finally, please stop with the postings about MOND. If what you meant was that the observed acceleration can be explained by modifying gravity at very large scales, there are better-motivated theories that try to do this. But these are theories trying to generate a mechanism for getting some acceleration rather than no acceleration. They don't explain the cosmological constant problem, which is why the acceleration is not huge.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-57122705273271777542014-02-17T18:59:56.461+01:002014-02-17T18:59:56.461+01:00Are you there Sesh? I think there’s a need to go b...Are you there Sesh? I think there’s a need to go back to basics with the vacuum catastrophe. Start with Einstein’s stress-energy tensor. It’s got an energy-pressure diagonal. And see page 185 of the Doc 30 Foundation of the General Theory of Relativity: <i>“the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy”</i>. Vacuum energy density varies in a gravitational field. And conservation of energy ought to tell you that in an expanding universe, it varies over time. IMHO people miss the trick here. It’s like they don’t know about the bag model, or the shear stress term in the stress-energy-tensor. <br /><br />The universe expands like the balloon analogy we’ve all seen on the Discovery Channel. And a balloon is the size it is because the internal pressure is counterbalanced by the tension in the skin. Now, how do you make that balloon bigger? You can blow some more air into it. That’s like adding more energy, increasing the pressure. But when it comes to the universe, that’s creation ex nihilo. It drives a coach and horses through conservation of energy. Plus dark energy is described as negative pressure, but space has a positive energy density and a positive volume, and pressure is energy divided by volume. So the pressure can’t <i>be</i> negative. That sucks. But there is another way to make that balloon bigger: reduce the tensile strength of the skin. Think bubblegum. Tension is negative pressure and when you reduce the tension the balloon gets bigger until the internal pressure is reduced and balances the tension again. But the balloon got bigger so the skin is now thinner so the tensile strength is reduced again, so the balloon gets bigger again. <br /><br />And so it goes, the universe expands, and that expansion doesn’t stop, because as space expands the “strength of space” reduces. I’m no advocate of MOND, but see page 5 of http://arxiv.org/abs/0912.2678 where Milgrom mentions elasticity and strength. <br /><br />IMHO looking at it in this simple mundane way makes all talk of a multiverse sound bizarre. <br /><br />John Duffield<br /><br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-82148041540265565772014-02-09T11:13:49.917+01:002014-02-09T11:13:49.917+01:00"Both theory and observation have moved away ..."Both theory and observation have moved away from the anthropic multiverse." IMO cleverly contrived D-brane adjustments can make the string landscape, SUSY, and eternal cosmological inflation correspond to any empirical observations — whether for good or ill is unclear.David Brownhttps://www.blogger.com/profile/10537922851243581921noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-86593120684294985072014-02-09T00:38:21.423+01:002014-02-09T00:38:21.423+01:00Apparently I can't spell my own name correctly...Apparently I can't spell my own name correctly! (I wondered why it wasn't auto-completing)Shaun Hotchkisshttp://trenchesofdiscovery.blogspot.comnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-27898435988297488112014-02-09T00:36:47.998+01:002014-02-09T00:36:47.998+01:00Hi Raphael, I'm kind of being a bit of a poach...Hi Raphael, I'm kind of being a bit of a poacher here, but if you were interested in writing a guest post about this at our blog (i.e <a href="http://trenchesofdiscovery.blogspot.co.uk/" rel="nofollow">here</a>), we would be super-keen to host you. It would only need to be, basically, exactly what you've written above, but in ever-so-slightly less technical language (though not too much less technical). Though you could also add a little bit more detail, if you wished.<br /><br />Of course, because you wrote your comment here, at Sesh's blog, and not at Trenches, if you do want to write a guest post and Sesh would prefer to host it, I would definitely back-off and look forward to reading it at Blank on the Map.<br /><br />However, either way, I do think this perspective deserves to be aired at a higher level than a comment, written almost a week after the original post. So, you should definitely write a guest post about this *somewhere*!Shuan Hotchkisshttp://trenchesofdiscovery.blogspot.comnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-65679170368172279232014-02-08T23:09:49.018+01:002014-02-08T23:09:49.018+01:00(... continued from above)
When Harnik, Kribs, Pe...(... continued from above)<br /><br />When Harnik, Kribs, Perez and I decided to apply this measure to the prediction of the cosmological constant, in <a href="http://arxiv.org/pdf/hep-th/0702115.pdf" rel="nofollow">hep-th/0702115</a>, we had no idea that it would so dramatically improve the prediction; nor, that it would permit us to drop the assumption that observers require galaxies. We set out by carefully modelling galaxy and star formation, writing mathematica codes, etc., only to discover that the only relevant time scale for Lambda, in the causal patch approach, is the time when the observers live. We realized this only after our postdiction for Lambda, produced by our code, turned out to be in perfect agreement with observation (in the sense that the observed value was within the central 1 sigma region). Only then did we understand that we had worked way too hard, and it wasn't even necessary to keep track of galaxies. Including traditional anthropic boundaries such as galaxy formation, etc., only further suppresses the distribution in a regime where it is already negligible. (The argument is quite simple, so in hindsight this should have been obvious, as is often the case.) <br /><br />It took a while to appreciate the generality of this result. It remains somewhat obscured by the discussion of entropy production in the Harnik et al. paper. Even in my 2007 review which you cite doesn't discuss it very clearly. The point is that with the causal patch, one primarily resolves the coincidence problem that Lambda dominates around the time when the chosen class of observers live. It depends on nothing else. It is robust, e.g., against variations of the initial density contrast, and it applies even to vacua with completely different low energy physics.<br /><br />For a brief and more up-to-date summary of this, see Sec. 3.7 of <a href="http://arxiv.org/pdf/1203.0307.pdf" rel="nofollow">1203.0307</a>. For a more speculative discussion of where the enormous scales in our universe may originate, see <a href="http://arxiv.org/pdf/1011.0714.pdf" rel="nofollow">1011.0714</a>.<br /><br />To summarize, you are right that in general, it is impossible to compute a probability distribution without specifying both a measure and the structure of the landscape. However, by asking the right questions it is possible to test measures independently of other vacua, using only the existence of our own vacuum. (It is also possible to rule out certain landscapes of vacua for all known measures, such as the Brown-Teitelboim landscape.) The causal patch measure has turned out to resolve serious problems with Weinberg's seminal argument, and to make more robust predictions. But this came as quite a surprise; it was certainly not designed for this purpose.Raphael Boussonoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-12295831719526660482014-02-08T23:03:32.480+01:002014-02-08T23:03:32.480+01:00Sesh, thanks for bringing up the important questio...Sesh, thanks for bringing up the important question of the interplay between the measure problem and Weinberg's argument. <br /><br />First, a technical point unrelated to the measure problem: even if we treated Weinberg's catastrophic boundary (galaxy formation) as sharp, it is just a theta function that multiplies the prior probability distribution, dP/d(log Lambda), which is proportional to Lambda. So the exponential growth of the probability density in log Lambda survives, up to Lambda of order 1/(galaxy formation time)^2, and the probability is zero for greater values. Thus, in this simplified treatment, the probability density is indeed highest right at the catastrophic boundary. But given a probability distribution, one never claims that the prediction is the value where the probability density is highest. Rather, we ask how many standard deviations the observed value is from the central value. If this is many sigma, we have falsified the prediction at that level of confidence. So it's not correct to say that Weinberg's argument predicts that we should find ourselves right at the catastrophic boundary. However, depending on the strength of the anthropic assumptions, one does find that the observed value is outside two or three sigma, so there is definitely some tension. Moreover, as you correctly note, this tension becomes catastrophic once we allow the initial density contrast to vary.<br /><br />Now concerning the measure. You are right that the measure is an important ingredient in how predictions are made in an eternally inflating universe. (This hasn't got much to do with the multiverse. Since the observed cosmological constant is positive, we have eternal inflation, and hence a measure problem, unless our own vacuum is tuned to decay in a few billion years.)<br /><br />It turns out to be very difficult to write down proposals for measures that are both well-defined and not obviously ruled out. For example, until the causal patch measure was invented, known measures predicted that even the most basic observations are 10^dozens (!) of standard deviations from the mean. This devastating conclusion obtains independently of whether there are other vacua, so these measures are ruled out. Importantly, the measure Weinberg implicitly used (observers-per-baryon) is ruled out, roughly for this reason; see e.g. <a href="http://arxiv.org/pdf/hep-th/0610132.pdf" rel="nofollow">hep-th/0610132</a> . <br /><br />I proposed the causal patch measure in 2006. (Closely related measures were developed subsequently by Vilenkin, Guth, Linde and others.) I was not motivated (indeed, at the time, unaware) of the catastrophic problems with Weinberg's measure; nor by the phenomenology of the prediction for Lambda. My interest was entirely formal: it seemed to make sense to apply certain lessons from quantum black hole physics to cosmology, and this measure seemed like the most straightforward implementation. The idea is to average of all possible causally connected regions, so it's really quite simple and it certainly contained no knobs to dial, to yield some particular probability distribution for some observable. (In fact it would be very difficult to do this with any measure that is defined purely as a geometric cutoff, which all the leading proposals are.) Raphael Boussonoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-2515358982379433422014-02-05T15:53:31.573+01:002014-02-05T15:53:31.573+01:00Sorry, further irrelevant discussion about MOND wi...Sorry, further irrelevant discussion about MOND will be ruthlessly deleted. Comments that don't make a point but just regurgitate irrelevant quotes from elsewhere will also be deleted.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-49404070782274424382014-02-05T15:47:29.203+01:002014-02-05T15:47:29.203+01:00This comment has been removed by a blog administrator.David Brownhttps://www.blogger.com/profile/10537922851243581921noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-84808045900676564302014-02-05T15:15:12.884+01:002014-02-05T15:15:12.884+01:00Please don't view this page as the appropriate...Please don't view this page as the appropriate place for such nonsensical stream-of-consciousness comments.<br /><br />However, I thought it worth pointing out that clicking through from the first link you provide one sees Leonard Susskind <a href="http://www.edge.org/3rd_culture/susskind03/susskind_index.html" rel="nofollow">claiming</a> "there is a constant in nature called the cosmological constant, and it's a certain number. If that number differed by the tiniest amount from what it really is, the universe could not have been born with galaxies, stars, planets, and so forth". This is exactly the kind of hyperbole I was trying to refute above. Even making favourable assumptions that the landscape picture is currently unable to justify, the number could be <i>more than 1000 times bigger</i> than it is and galaxies, stars and planets would still be able to form.<br /><br />I just really annoys me when all arguments about the anthropic principle go on and on about how Weinberg correctly predicted the value of the cosmological constant. Weinberg himself was probably the first to admit that his argument does not give the correct value.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-79691055143443994782014-02-05T14:45:47.835+01:002014-02-05T14:45:47.835+01:00"... in the absence of any other observationa..."... in the absence of any other observational evidence for the multiverse ..." Does string theory with the finite nature hypothesis make 3 empirical predictions, based upon restriction of string vibrations to the Leech lattice? Is a complete infinity always either (1) a mathematical convenience or (2) a physical error?<br />"In the physics I have learned there were many examples of where the mathematics was giving infinite degenerate solutions to a certain problem (classical mechanics problems e.g.). There the problem was always a mistake in the physics assumptions. Infinity is mathematical not physical, as far as I know." — Maria Spiropulu, Caltech physics professor http://www.edge.org/discourse/landscape.html#spiropulu <br />If X’s law is to string theory as Kepler’s laws are to Newtonian mechanics, then who is X?<br />http://www.weizmann.ac.il/weizsites/milgrom/ Mordehai (Moti) Milgrom, Weizmann Institute of Science<br />Have string theorists stupidly ignored Milgrom for 30 years?<br />Google "space roar dark energy".David Brownhttps://www.blogger.com/profile/10537922851243581921noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-51452549363918414102014-02-03T22:11:57.113+01:002014-02-03T22:11:57.113+01:00Weinberg's opinion of his original argument is...Weinberg's opinion of his original argument is presumably the same as stated in his paper that you mention, i.e. that it doesn't work precisely because of the high-redshift galaxies. Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-21642649240710591062014-02-03T22:06:02.529+01:002014-02-03T22:06:02.529+01:00That's only one in 1000 if nothing except $\La...That's only one in 1000 <i>if</i> nothing except $\Lambda$ can vary.<br /><br />In my opinion the qualitative difference when it comes to the multiverse is that it may not be able to make any kind of predictions other than anthropic ones (I await correction on this if someone knows of some), and anthropic predictions are plagued by the measure problem. <br /><br />So it <i>may</i> turn out to be falsifiable, but that's a possibility that is rather less likely than for most other theories.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-6181496458192557852014-02-03T21:56:57.000+01:002014-02-03T21:56:57.000+01:00As you pointed out yourself in a comment above 1 i...As you pointed out yourself in a comment above 1 in 1000 is much better than 1 in 10^60. The retrofitting is only for the last three orders of magnitude.<br /><br />The multiverse might not be true, but I don't see the qualitative difference between it and any other scientific model in history.Shaun Hotchkisshttp://trenchesofdiscovery.blogspot.comnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-38735400220528184772014-02-03T21:42:02.014+01:002014-02-03T21:42:02.014+01:00The point I'm making is that the "predict...The point I'm making is that the "prediction" of the cosmological constant is not the simple victory for the multiverse that it is made out to be.<br /><br />A corollary point is that if one must retro-fit the measure to to get the right cosmological constant then the fact that one gets the right cosmological constant is not evidence that the multiverse exists.<br /><br />You'll notice that other than these two points I make no comment on whether the multiverse is in general falsifiable (perhaps there are all sorts of other possibilities I'm not expert enough to know about).Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-22910171469467650742014-02-03T21:37:03.730+01:002014-02-03T21:37:03.730+01:00Raphael Bousso's review I mentioned above ackn...Raphael Bousso's review I mentioned above acknowledges it (in a footnote), but argues that (a) a discrepancy of three orders of magnitude is better than one of 120 orders of magnitude, and that (b) with certain approaches to the measure problem one can eliminate the three orders of magnitude. But he doesn't deal with the problem of circularity of argument that then results.<br /><br />I haven't read the Martel et al paper as carefully as Weinberg's original. The value of the anthropic bound they get might be better, but they still fix the amplitude of the initial fluctuations to be the same as in our universe, which appears unlikely to be justified by theory.Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-12014018499645626682014-02-03T21:32:03.424+01:002014-02-03T21:32:03.424+01:00I don't understand the point you're trying...I don't understand the point you're trying to make. If it is that the multiverse is science, only it is difficult science, then I agree. Maybe I'm just overreacting to the "not even wrong" brigade when I assume that instead you're trying to claim that a multiverse has been tested and ruled out and all that is left is unscientific.<br /><br />But the point to me is just that it just isn't as simple as what Weinberg thought. Fine. The multiverse may be correct, it might not; we should continue testing and find out. It just so happens that those tests are hard. The measure problem means that in all likelihood one has to include one's choice of measure within one's model. Fine. After post-dicting one observation one can start predicting others.<br /><br />How is this one model for how the universe works any different to any others that have come in the past? It might be right, we should try to work out if it is, just like any other scientific model!Shaun Hotchkisshttp://trenchesofdiscovery.blogspot.comnoreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-40961344590625298462014-02-03T21:26:23.284+01:002014-02-03T21:26:23.284+01:00There are two problems I see with your suggestion....There are two problems I see with your suggestion. The first is that the effect of vacuum energy on inertial mass is confirmed by measurement of the Lamb shift and its effect on gravitational mass has been confirmed by free fall experiments (which test the equivalence principle). So we know that the vacuum gravitates. We know that the Standard Model of particle physics works very well up at least LHC energies. If particle physics is going to turn out to be wrong it's got to do so in some extraordinary fashion.<br /><br />The second problem – perhaps of more relevance to those of an astrophysical mindset – is that if the vacuum doesn't gravitate there can be no inflation, so what about the horizon problem, the initial seed fluctuations and so on?Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.com