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Comment Re:Maybe (Score 1) 293

" I'd still quibble a bit here - you seem to be conflating "observational evidence" with "experimental evidence"."

To some degree I probably am, yes. Even so, if we have a dinosaur bone in front of us, we have that bone. We can poke it, we can hit our colleague with it, and we can scrape bits off and drop them in each other's tea. If we're excruciatingly lucky, we can dig out traces of organic material inside it and piss off a generation of paleontologists in the process. (So far as I'm aware, that's been done - not enough to do much with it, alas, but still organic.) The difference here is we can't do that with dark matter. The only evidence we have is far more indirect, and can be explained through a wide variety of mechanisms, few or none of which are amenable to direct testing, meaning something we ourselves can actively do. In the dinosaur case, we can at least dig up more bones, or find previous bones, scrape bits off those, and drop them in someone else's tea.

I think there is a very big distinction between these, though I do see your point.

"I haven't heard of a "gravity is different" theory that made accurate quantitative predictions of the CMBR data, where the dark matter theory did. Maybe I just didn't hear about it?"

Probably. If nothing else, you can get the CMB without too much issue from Brans-Dicke, from f(R) (no surprise there; it's effectively Brans-Dicke with a weird parameter), and if you play enough absurd games with an absurd theory you can even get things out of TeVeS which is a contrived relativistic form of MOND. If you write down a vaguely sensible bimetric theory -- and TeVeS is not really very sensible, but others are -- it seems likely we can get the CMB out of those, too. Braneworld theories give it happily, and Turok and Steinhardt's somewhat... eccentric ekpyrotic universe where two branes repeatedly slam together like cymbals with each slam kicking off a big bang, can also do it.

On a weaker scale, you can take GR but change the metric. Cosmology is built on the (Friedman-Lemaitre-)Robertson-Walker geometry, which is the second-most simple solution of GR there is. The simplest is Euclidean space. An FLRW geometry is a whole bunch of 3D Euclidean spaces stacked one on top of the other. It's slightly more complicated than that, since you can get closed FLRW (effectively a bunch of concentric, ultra-smooth spheres) and open FLRW (basically a load of saddles piled one on top of the other). There is good observational support for FLRW, but the same support can be given to a variety of particularly Bianchi universes, which are like an FLRW but slightly anisotropic. Control that anisotropy, and you've got a perfectly valid universe, with a slight directionality (which, intriguingly, Planck has seen in the sky -- though the form of anisotropy is actually not that easy to reconcile with simple Bianchi models). Until recently you could play games with Lemaitre-Tolman-Bondi metrics, which are like FLRW but lack the homogeneity, so that while around Earth everything looks spherical, away from us it is distinctly less so. In reality you still can use LTB models, but you have to be careful, and their main use (the observable effects of dark energy without having to introduce a physical dark energy or accelerating the universe) has been pretty comprehensively rubbished. (It's still not certain, since we haven't yet finished working out the perturbation theory properly, and without it any claims to be genuinely looking at the CMB and the oscillations in the large-scale structure should be taken with a bit of salt but, realistically... it's a very small bit of salt.)

And then we can assume gravity is the same but the problem is simply coming because even on galactic scales we're working with averaged motions (or, more concretely, a statistical mechanical system). On cosmological scales we can view things in three ways: a spatial average, an average across observations (these are distinct; one is the average of, say, the angular distance to objects of equivalent types, while the other is a straight spatial average), or statistical mechanics. Of these, unfortunately, we can't do the spatial average or the statistical mechanics -- so these are obvious, and necessary, directions for study. There has been a lot of work on the spatial average, none of it particularly convincing but some of it quite suggestive, and there is work on the statistical mechanical average, but that's hampered by the extreme difficulty of working with general relativistic statistical mechanics. Which is tough.

Anyway, yeah, you can get the CMB - and, more, the baryon acoustic oscillations which were formed about 12 billion years after the CMB but in the standard big bang model are intimately related - from modifications. The only problem is that those modifications do have to end up resembling FLRW so closely that the observations are practically indistinguishable, even if the underlying model bears no resemblance. That's tricky, and it's a major reason Lambda CDM holds as much support as it does.

Comment Re:Maybe (Score 1) 293

Not necessarily. I just posted a reply to someone else addressing a similar question. This kind of system - the Bullet Cluster is the most famous example - was originally touted as a "proof" of dark matter. It isn't, though it is another sign that if you want to beat dark matter (for whatever that means) you have to be able to predict what that model does. Basically, a modification to general relativity will almost certainly change the reaction of the Newtonian potential (which pops up in weak fields as the time-time perturbation to the metric) and the scalar spatial curvature (ditto, on the space-space component) to the presence of matter, and can do so in surprising ways. One of those surprises is that if you're reasonably careful how you choose your modified theory of gravity, you can get peaks in the lensing potential quite displaced from your matter distribution, without introducing any exotic forms of matter. (The cost is an exotic form of gravity, of course... but we actually know more about the fundmental nature of matter than we do about the form of gravity on supergalactic scales, so as daft as it may sound I'm a lot more comfortable this way.)

Of course, it makes the model look a bit more contrived, particularly compared with dark matter which has effectively three assumptions: there is a non-interacting species, with a density roughly five times high than standard-model matter, and it is pressureless. However, to do calcualtions you have to make a vast array of other assumptions on the form of the distribution, which introduce a wide number of parameters and arbitrary functions, which makes the whole thing a lot less clean than it initially appears.

Even so, yes, interacting galaxies form a powerful testbed for this kind of theory. But they're not the killer they were originally touted to be - merely a strong discriminant. (Which is excellent, we need that. This isn't -- or shouldn't be, but I know people who've made it into one -- an ego game. It's meant to be about finding better explanations for things, in a field where I think increasingly people are going to realise they're not going to be able to link all the way back to fundamental physics. Or they will if the education level stays up, but I'm concerned about that when I see cosmologists coming in who at most have been taught a bit of GR, enough to do cosmology, and nothing more. That is a bit alarming; there is a breed of modern cosmologist who doesn't seem to know, or care, about what underpins the theory, and for whom Robertson-Walker metrics are the be-all and end-all. Worse, *linear* Robertson-Walker. Even people I respect hugely -- naming no names though -- have published papers ascribing effects to "modified gravity" that are far more easily, and physically, explained through, err, physics, by looking at second-order perturbations. But that's a different topic...)

Comment Re:Maybe (Score 1) 293

"Correct, they only detected gravity, which we currently assume is only caused by the mass of matter."

Well, to be pedantic, they didn't detect gravity at all. A Nobel prize waits for that one, too. The assumption that it is "only" caused by mass is one of GR, certainly, but there are a plethora of theories in which this isn't the case, such as Brans-Dicke theories, generalised Brans-Dicke, f(R), f(G), scalar-vector-tensor, bimetric, etc. etc. etc.

"They've recently tested relativistic gravity by measuring red shifts and have some to the conclusion that gravity at galactic scale is working the same as solar-system scale."

Really? Could you provide a link to that one?

"And why does everyone keep bringing up only the rations of galaxies, what about gravitational lensing in dust-less gas-less empty space?"

A good question. Proponents of particulate dark matter theories have enjoyed bringing up gravitational lensing for some time now - and rightly so. They've enjoyed even more bringing up the Bullet Cluster, in which the gravitational lensing (presumably tracing the dominant mass) is in a very different location to the X-ray emission -- and rightly so. The thing is that you can actually get very similar results with, say, a bimetric theory. Even TeVeS can fit the Bullet Cluster if you're really careful about the massive neutrinos you add in. Massive neutrinos are not at all controversial, and sterile neutrinos aren't particularly so either, and a blend of those two can fit the Bullet Cluster with no problem -- and no vast quantities of dark matter.

What's more, if you take the physics to a genuine level (rather than one-dimensional, linearised systems) and start considering three-dimensional distributions of, say, a scalar/tensor theory, you find some extremely interesting interactions going on -- such as domain walls between areas where the scalar field is negative and areas where it is positive, followed by a sudden collapse and a dramatic ringing of oscillations through the universe. In this type of model, gravitational lensing is... different. It may not account for the entire lensing, it may not account for any, or it may account for the lot - I don't know, and to be honest neither does anyone else.

(I'd also like to point out that if we're talking properly, lensing does not actually trace mass. Except very near to a black hole or neutron star where the description breaks down, lensing traces the sum of the Newtonian potential and the scalar spatial curvature. In vanilla GR that "lensing potential" is certainly set by mass. In a slightly different theory, it can be set by a wide variety of things. The simplest, by a long way, is massive particles, and that's one reason dark matter is currently the most favoured explanation, but it is not the only way.)

I'm not wanting to argue, as such -- dark matter is by far the most accepted model, for a good reason. It explains the vast bulk of the observations more simply than any other model. Same with dark energy. Any replacement model has to replicate observations predicted by a dark energy/dark matter model, practically perfectly. But there are fewer fundamental reasons to believe it is literally true, particularly in the form currently presented, than is often believed (even by professionals).

Comment Re:Maybe (Score 1) 293

"They use a model of a galaxy as if the mass was in the center like the star in a solar system, and wonder why it then doesn't match"

That's because there's a theory in Newtonian gravity that the force you experience is the same as if it were all concentrated at the centre of mass. For *spherical* systems a similar theory holds in general relativity. It wasn't ad-hoc, it was people applying Newtonian gravity to galaxies, and other than a few oddballs like me, most people do not question that relativistic effects in galaxies are entirely subdominant and that we may as well just use Newtonian theory. And hell, they may very well be right; this is a totally open question.

Comment Re:Maybe (Score 1) 293

I think a lot of the issue here is actually your "they" vs "we" position. This isn't the case! All we really have -- and I speak as basically an insider -- is a "educated" vs "layman". I'm honestly, honestly not wanting to sound offensive or smug when I say that, just that the directions that physics goes in might seem nonsensical but there is almost always a very good reason to do it. If nothing else, it's starting from a theory that the researchers know is probably phenomenological (meaning "not fundamentally true", "grounded in observation and nothing more") but is at least self-consistent, coherent, complete, capable of taking in a situation and making concrete predictions, and then it's pushing that theory a bit further. There is absolutely no reluctance to introducing different theories, no matter what the popular conception is. My own field is cosmology, and I stopped bothering counting the endless variations on gravity, or the entirely different approaches to cosmology, or the weird shit coming in from the high-energy physicists, or the ways of producing inflatons or dark energy from different (reasonably well-motivated or batshit insane) multidimensional theories. Every single one of them was introduced for a solid, concrete reason, and I don't think *anyone* has ever attempted to state that this or that is fundamental reality, unless they had a very clear reason for doing so.

At the heart of everything is the knowledge that one is working from a theory -- a particular set of equations, true on a certain scale or in a certain energy range. I wouldn't try and use general relativity when describing gluons; it really doesn't work. I would try and use quantum chromodynamics when describing the orbits of galaxies in clusters; that would be ridiclous. I wouldn't even use GR for calculations within the solar system, for the most part, because it's way too complicated and the errors in using Newtonian gravity in that situation are so small.

The planet thing -- yes, true. But any explanation anyone comes up with has to fit with known physics, or challenge it in ways that leads, quantitatively, to further predictions that are then borne out by observation. If it can't do that, or if a suggestion fails on some fatal grounds (such as predicting planets orbiting close to stars, but failing to account for distant gas giants, or what have you) then it will definitely die. If something explains things perfectly but is controversial, it's probably already been written down and published by a professional astronomer...

You accuse astrophysicists of making up crap to fit new things into broken theories. OK, in some cases, fair enough - but my point is that some of that made up crap (such as braneworlds; what a load of bullshit) was introduced for very specific reasons, to answer very specific, and very pertinent questions. I've got a lot of contempt for braneworlds, but those theories were not introduced to stroke someone's ego or to give someone something to do; they were introduced as a way of examining the gross cosmological features one would expect to see in a world described by string theories. Braneworld theories themselves were pretty specious things, but that was the point, and so far as that goes, all power to them. My opposition comes entirely from the undue attention (and money) thrown at them, not for their introduction, and not for the reasons for their introduction, and not for the fact that the universe is obviously not a 3+1D brane suspended in a 4+1D universe. Because it isn't, such a suggestion has never seriously been made.

In the case of dark matter and dark energy, there have been alternatives, and plenty of them. I've gone on record - on Slashdot as well as in publications - stating that the "answer" to the dark matter problem is very likely to be an ugly mixture of every solution we have yet proposed: massive neutrinos (they are massive, but extremely warm), sterile neutrinos (likely cold), a lightest supersymmetric particle or two, unforeseen effects of general relativity in cylindrical metrics, a change in the behaviour of gravity on large scales, the effects of averaging observations across a very large area, the fact that a galaxy is effectively a confined gas of 10^9 hot bodies, and probably more. But we can't analyse it like that (although any professional worth their salt would acknowledge that "a single" dark matter is likely to be a simplfication... note, unfortunately, that I expect at least some professionals not to be worth their salt and to loudly trumpet that "the" dark matter has been found :( ) because it would be useless. We'd lose all predictive power altogether -- the data is far too noisy to support a vast array of parameters. Instead you extract the gross feature of the bulk of these -- "w=0" -- and constraint that. When data improves you can add to it.

Unfortunate? Yes, but also inevitable. And please believe me, people never cease looking for a "better theory". That's the entire point of research in astrophysics; if we thought that it was all done we could all go home and earn more money in different jobs. Instead, we have a constant stream of theories someone hops is better, is promising enough to yield two, three or ten papers, and is then smashed, or turns out to be grossly disfavoured compared to the tedious, and unsatisfactory, standard model(s).

Comment Re:Maybe (Score 1) 293

"This is the Electro-Gravitic theory of space and provides a clear explanation for dark matter, dark energy without resorting to anything we have not already proven experimentally or incredibly complex math that defies human understanding."

That's the kind of comment that always makes me extremely wary, particularly as practically the only place I've ever seen it is following a wall of text that builds -- on relatively specious assumptions and assertions -- without any actual concrete theory. The problem is entirely that, no matter what philosophy we can dig out of it, physics is about algorithms. We *have* to have numbers we can put into our algorithms, which typify the scenario we wish to consider, and we *have* to have numbers out, which are what, according to this theory, we expect to see coming out.

The problem with the theories I've seen where people promise "clear explanations" for dark matter, dark energy, and frequently cheap or free energy, is that they fail the first step -- they do not provide a robust and self-consistent mathematical framework.

Anyway, with that little rant out of the way, I'd be cautious. What Einstein demonstrated is that a theory of gravity that is both far simpler and frankly better experimentally supported than Newtonian gravity is general relativity. In Newtonian gravity, the gravitational field is a three-dimensional field, instantaneously sourced by two or more objects of positive gravitational charge. (This is commonly dubbed "mass", and in this context is normally called "gravitational mass" in modern physics.) One enormous issue with this concept is that if you take Newton's law of acceleration (F=ma) and equate it with Newton's law of gravitation (F=GMm/r^2), you cancel the ms and get a=GM/r^2. OK, brilliant. Nothing there... except that Newton's law of acceleration has sweet FA to do with gravity. That mass is an "intertial mass"; it describes the response of a body to a force, and there is no a priori reason to link it with a gravitational mass at all. I don't think -- though I may be very wrong, of course -- that Newton was aware of this subtlety, but by the early 20th century it was very well known, and things like Eotvos experiments were set up to try and tell whether these masses were actually different at all.

The point here is that if the intertial and gravitational masses are the same, every object reacts to a gravitational force with the same acceleration. Try and think of the last time you saw that. I would put a vast amount of money on it being the last time you were in a vehicle that was turning a corner. (If you think slightly more subtly, it was the last time you wondered why weather patterns on Earth run the way they do.) It is well known that centrifugal and coriolis forces are artificial ("fake") forces, caused by observing in an accelerating frame of reference, such as a car going round a corner, or on the surface of a spinning planet. However, they feel very real to the objects that are in those frames, as anyone going round a corner, or being flung from a roundabout, can verify. The hallmark of a fictional force is that every object experiencing them moves with the same acceleration. In this context this is obvious: the "force" is entirely due to the acceleration of the frame of reference, so it's bloody obvious that the force felt is going to be the same acceleration by every body. The thing is that there is no "natural" force that does this: any force where all bodies feel the same acceleration is probably fictional, and that "probably" is only there in case someone cooks up a bizarre theory where they can get this any other way.

That's the soul of GR, and as soon as you try and work through from there (known as the "weak equivalence principle": that the intertial and gravitational masses *are* equivalent, not merely that they're close to it) you're lead straight to a four-dimensional theory of gravity. It also leads to issues of causality, of the propagation of gravitational radiation at what we link with the speed of light (certainly at a finite velocity), and all the fun shit about black holes and worm holes and Alcubierre solutions.

The theory you're discussing seems to me to drop us back to a three-dimensional gravity. I'm not a fan of doing so without a very good reason; if nothing else, you would have to ensure that you introduced no observable violations of the equivalence principle, and you would have to match GR's predictions within the solar system. If that can be done, excellent, but in all honesty I doubt it.

On the other hand, the type of thing you're talking about might be saved by looking at more concrete models. If you phrase electromagnetism in the language of general relativity, you bundle electric and magnetic fields together into the Faraday tensor, which obeys certain rules. If you take the "Weyl tensor" (which is set, one way or another, by the curvature of space in GR) you can split it into "electric" and "magnetic" parts that act for all the world like versions of the electric and magnetic fields that happen to be matrices (well, that's a lie; tensors of rank 2, but think of them as matrices) instead of vectors. This is where "gravitomagnetism" comes from and it's a pretty profoundly interesting way of viewing gravity.

What's more, Einstein himself -- along with others, such as the celebrated Kaluza and Klein -- attempted to unify electromagnetism with general relativity. If you add an extra dimension onto the normal four, you get something similar to Kaluza-Klein theory. In this theory, you not only have a geometric theory of gravity, but you get, practically for free, a geometric theory of electromagnetism, too. Excellent! Unfortunately you also get a dilaton, which rather fucks things up, but the point is still there - there are interesting links between electromagnetism and gravity. Even more interestingly, electromagnetism is a genuine force, unlike gravity. (Maybe that accounts for the dilaton appearing? But that's true speculation again.)

Comment Re:Blogspot :( (Score 1) 358

I'm probably a borderline Google apologist, but FFS, Google, stop posting "real" information on Blogspot - where dozes of workplace content filtering software block access to out of the box.

Why? They own it, it's their official blog platform, after all.

Just because it's mostly misused by a bunch of emo teens wanking off doesn't make it any less legit of a site. Especially one that Google owns directly.

You might as well complain as to why Google is still serving pop ups, pop unders and all that other nasty stuff ads.

Comment Re:SNOWDEN !! DOUBLE-AGENT ?? (Score 1, Informative) 328

'Traitor' and 'whistleblower' are not contradictory concepts. Snowden committed treason to reveal illegal behavior in the NSA. I am in favor of using his information to force the NSA to follow the law, *and* in favor of putting him in jail for treason.

It's also wrong to suggest that whistleblowers should receive automatic pardons. There were ways to reveal this information without committing treason; Snowden chose not to take that route. He's a traitor *and* a hero, and ideally his actions would cause positive change in the world while he's rotting in jail.

Comment Re:No media server support upsets me (Score 1) 312

I find it interesting they are sustaining the physical disk format as it seems to lend its self to being ripped, while a purely digital format could possibly have "better" drm?

Well, Blu-ray has several protections for that embedded in the disc itself, including identifying marks (what type - factory, BD-R, BD-RE, etc, including ID codes for factory pressed discs identifying the factory and timestamps).

And the last time digital only was suggested, everyone was up in arms, despite several advantages to the physical-assisted digital only stream (e.g., It offered the ability to actually sell used digital copies, even those purchased completely online without a physical disc. As a unintended benefit, nothing was ever out of print - you could simply torrent a copy and pay the digital license fee to get the game). The disc in that case was purely used only to aid you if you can't download 25/50GB of data.

But of course, everyone bitched and moaned, and we're back to the old style of game distribution - discs you can resell used, online "digital" purchases you can't.

Heck, Sony even mocked it.

As for ripping and all that - expect it after it's hacked. Both next-gens are really like the original Xbox - and likely there are going to be plenty of holes to exploit.

Then again, Microsoft discovered making it easy to homebrew on the Xbox360 made it less vulnerable to hacking (it was modded to play pirated games, but those had severe limitations), while Sony discovered that while homebrewers were happy on the PS3, the moment they took it away, they started breaking its rather weak security.

Comment Re:What problem are they solving? (Score 1) 195

Even with PGP, the SMPT headers are unencrypted. This allows an attacker to build a graph of who talks to who. The central weakness of traditional email is that messages are passed around through multiple untrusted servers before they reach their destination.

It's a central problem if you want two arbitrary people to talk to each other. Or if you just want to do a "blind broadcast".

Which makes those hacks to AIS and ADS-B really uninteresting because encrypting and authenticating the transfers is impossible - if everyone needs the key to decrypt the message, well that's pointless to the extreme since none of the parties has a way to fetch additional keys (so you can't verify the transmission anyhow - by the time you can do it, it's useless information). Sure, you could mandate PKI, but then everyone needs the same encrypting key so everyone else can decrypt it, and a hacker can easily get at the key. If you sign it, again, how do you verify it without the key? In this case, you might as well send it in the clear because encrypting it just means you'll have to get at a well known key and adds an unnecessary step.

And yes, as long as two random parties have to communicate, it's always vulnerable to metadata analysis.

This system depends on creating an encrypted link (presumably with tor-like indirection) and only passing messages direct from sender to receiver. The downside is that both parties have to be online to effect the transfer. The instant messaging aspect is used to notify a sender's server when a receiver is available to accept new (possibly cached) messages.

This cannot work because there are times when you'll be online and the recipient not, so you'll end up playing very fancy games of phone tag.

And even if encrypted, most protocols have sufficient "leakiness" that one can guess at what's going on.

And direct connections are subject to metadata analysis as well.

You're far better off encrypting the message and doing something like Tor to move it between machines - not only does this spread out the connections, but each node can only see the next node in line, and cannot be sure if the next node is the destination or relay.

Of course, the problem with that is it requires knowing the entire routing table in advance, and for reliability you probably want to send the same message through different paths and you need a way to identify when duplicates arrive.

Comment Re:Hollywood has helped before (Score 1) 101

Despite some of the roles he has played, he's not an idiot. He's still probably more of a publicity hire than anything else, but I wouldn't rush to judge him before you see any actual work of his.

Of course it's a publicity hire. Think of it - Lenovo just hired Steve Jobs! (Well, the actor who played him in the awful biopic...)

I guess Lenovo might revive the whole "I'm a PC. I'm a Mac" ads...

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