|
 |
|
|
Feed: SCIENCE FORUMS BLOGS
Free science blogs from ScienceForums.net, the world's leading online science discussion forums.
DJBruce: A New Era
28-Jul-10
So it seems like I have not updated my blog in well... Lets just say a long time. In hindsight I realize I hoped to post often, and well I seemed to procrastinate and eventually forgot about it all together. So I have now updated the look of my blog, and even given a spiffy new name (let me know what you think about it). Hopefully this will mark the start of a more prominent era for my blog; as I am planning on trying to update at least once a week. Hopefully more.
ajb: Is "three" the new "two"?
27-Jul-10
The number “two” may appear to be very special in theoretical physics, but maybe it has had it's day...
By this we mean that much of physics is described in terms of “binary objects”: Lie brackets, commutators, metrics, rank two curvature tensors, quadratic Lagrangians, two dimensional world sheets of strings, Poisson structures, symplectic two forms, Laplacians and I am sure the list goes on. However, it has become increasingly clear in recent years that “higher objects” play an important role in theoretical physics as well as modern geometry.
For example, it has become increasingly clear that n-aray generalisations of Lie algebras play a role in physics. The Sh Lie algebras of Stasheff and the (not completely unrelated) n-Lie algebras of Filipov are great examples here. In one form or another, they can be found behind the BV-antifield formalism, Zwiebach’s closed string field theory, Kontsevich’s deformation quantisation of Poisson manifolds, Nambu's generalised mechanics and the Bagger–Lambert–Gustavsson (BLG) description of multiple
stacked M2 branes.
The last one has been of interest to me lately.
So, M-theory was introduced by Witten in 1995 as a non-perturbative unification of the various superstring theories. Here, the fundamental objects are not strings but extended membranes of dimension 2 and 5, the so called M2 and M5 branes. Since then progress has been slow. No-one really knows what M-theory is and there is no proper understanding of the dynamics of interacting branes.
Then in Bagger & Lambert [2] in 2006 and independently Gustavsson [3] in 2007 construct and effective action for the low energy description of a stack of two M2 branes. The novel feature here is that 3-Lie algebras play a role here. A 3-Lie algebra should be thought of as a "Lie algebra" but with a tribracket not a bibracket. Details should not worry us.
The theory has the fields take their values in a 3-Lie algebra and their is a novel gauge symmetry. However, the original BLG-model can be recast as a conventional gauge theory, the ABJM theory [1]. So it starts to look that maybe 3-Lie algebras are some weird artificial artefact of M2 branes.
(There are many, many papers on the arXiv dealing with modifying the original BLG model. This usually can be understood in terms of 3-Lie algebra. I won't say any more right now.)
But then very recently, Lambert & Papageorgakis [4] provided evidence that the effective description on M5 branes would also require 3-Lie algebras. However, they have not yet produced an action, which would be essential if the more or less standard methods of quantisation were to be applied.
This is fascinating. M-theory seems to be deeply tied to the theory of n-aray algebras, and in particular 3-aray algebras. There are may open questions here, both from a physics and mathematics point of view. In all it looks like n-aray algebra are here to stay.
-------------------
REFERENCES
[1] Ofer Aharony, Oren Bergman, Daniel Louis Jafferis, and Juan Maldacena. N=6 superconformal Chern-Simons-matter theories, M2-branes and their gravity duals. JHEP, 10:091, 2008.
[2] Jonathan Bagger and Neil Lambert. Modeling multiple M2’s. Phys. Rev., D75:045020, 2007.
[3] Andreas Gustavsson. Algebraic structures on parallel M2-branes. Nucl. Phys., B811:66–76, 2009.
[4] Neil Lambert and Constantinos Papageorgakis. Nonabelian (2,0) Tensor Multiplets and 3-algebras. 2010,
arXiv:1007.2982 [hep-th].
UC: Doublefark
27-Jul-10
Well, the title of the blog isn't quite so accurate anymore. I'm not a student, unless I go to grad school (which is looking like a no at the moment). I have a B.Sc. in Chemistry which is real nice and all, but I don't have a job that uses it. I don't even have a job. I'm not even looking. Frankly, I just don't care about much of anything anymore and I haven't for a while. It's a miracle that I graduated- probably only due to guilt about wasting money and the vast amounts of caffeine that I had running through me at all times. I haven't had more than a can of cola in months.
Some days I sit around the house and do nothing.
Others, I go geocaching by myself, or with friends when I can convince them to- but mostly by myself.
I don't know what I want out of my life right now.
buttacup: EnTAngleD: on SFN
27-Jul-10
I plan to post my thought process on the many projects I have worked so long to begin and hope to document their development into reality.
eg.
- Cryo-COIL propulsion unit
- Homemade Inverted Microscope
- Scientific Computing Engine
- The Worlds Highest Fidelity G-Type Power Supply
etc.
There may be posts detailing my ongoing attempts in modeling all mathematically .... as it goes for many on the forum .....
I may also randomly rant about my progress towards entering into University at my not as young as many age of 31 ..... as I wish to one day be a forerunner in the research of Cell and Tissue Engineering. But now I go to bed ......
Klaplunk: Hello world!
26-Jul-10
Hello,
Welcome to my voyage; for the last six months I've been studying religious books attempting to decipher how they were understood years ago, before the dictionary and academa. This has become a hobby that I take more seriously than education. I have provided enough proof to myself to believe confidently God exists - I will update this daily with any new findings I discover.
swansont: All of Steve Jobs's Men
22-Jul-10
Those who visit the tech world are probably aware of the iPhone4 antenna issues and all the media hoopla surrounding it. I have no real dog in the fight, horse in this race or cliché in this idiom. I don't own an iPhone and I'm not shilling for Apple. But it pains me to see a bunch of tech-savvy people making crappy emotional arguments about something that should be quantifiable,and/or making crappy technical arguments because they don't look at what the data are (or aren't) telling them.
Apple had to respond, of course, and there are a number of articles out there explaining the business psychology of this; in some sense it's already too late — once the idea that Al Gore invented the internet is out there, actual facts will do very little to change things, so the undercurrent that the phone is a dud cannot truly be slain (the best you can do is a flesh wound). There is no Vorpal blade for persistent myths of the internet. Some people will believe that because they heard it, and others will repeat it because they love to hate Apple. But you have to try, and so a solution was proposed. Free bumpers for everyone. Feel free to discuss whether Steve Jobs was not apologetic enough to suit you, or whatever.
That's not my point.
My point is that people kept making this out as a technical problem, when all along it has been a PR problem, and a lot of people not employed by Apple kept insisting otherwise (except that perception is reality, hence the solution mentioned above). I've seen it called a design flaw and also called a defect. The latter is flat-out wrong — the problem is not with the phone itself being faulty, as if swapping it out for another phone would solve the issue. The problem is user-specific. Is it a design flaw? Yes and no. It is, in the sense that there is degradation in performance that can be avoided with a technical fix, but then you have to call any sub-optimal performance a design flaw. You have to insist that cheap technology suffers from a design flaw if it doesn't work as well as a more expensive technology, and I think that this is not what we mean by flaw. It is a trade-off, a natural and expected offshoot from optimizing on multiple variables, including price. You want better performance? Spend a few extra bucks. In what industries is that not the case?
The real metric for seeing if this is a "flaw" is to do a proper analysis of performance and the analysis, for the most part, was absolute crap. Most of it concentrated on how much the signal dropped when you held the phone the "wrong" way, and went no further. BFD. That's a science fair project. When you attenuate a signal, it goes down. When you short out an antenna (or at least change the capacitance or change the resistance of it, whatever was actually happening), you will lose signal. What the analyses lacked is any sort of context for these numbers, and while careful data-taking is important, the real tough part about science is in proper interpretation — figuring out what the data mean. And few of the stories did that. Diminished signal is not proper context, because all phones do that when you cover the antenna. All that these numbers show is that the phone works better when you don't cover the antenna. Confirming this is not going to get you to Sweden.
You can't compare it to a different phone on another network, because everyone knows AT&T sucks. Their network has made them infamous, like El Guapo. The real comparison of any validity would be to properly compare the phone to the one it replaced. Because the real question is this: Is the new one better? I haven't done any exhaustive cataloging of all the stories on the iphone4, but of the dozens I've read, I have seen just one technical analysis that addresses this (though there are undoubtedly others). The conclusion? The new phone holds calls at a lower signal strength than the old one.
The other bad comparison was the number of drpped calls form the iPhone 3GS and iPhone 4. The new phone drops more calls — that's bad, right? What if I told you that I did a survey and found 25 people liked a name brand of soft drink, but another one found that 100 people liked Crappa-Cola? Do those numbers mean anything? What if I had to survey 10,000 people to find the 100 who liked Crappa-Cola, but only 50 to get the result for the name brand? The numbers would be meaningless as a direct comparison — we have to normalize the responses. That's just basic science analysis. So a direct comparison of the numbers of dropped calls is just as meaningless without knowing that we are similarly normalizing the data.
When John Gruber of Daring Fireball reported those numbers, I sent an email to point this out to him. I had to mention that this isn't an Apples-to-Apples comparison (and, of course, I'm using the obvious pun, because that's what I do. It was low-hanging fruit. Damn, I did it again) I wrote, in part,
What is important is the comparison to the previous version of the phone: does the iPhone4 drop calls that the 3 or 3GS does not? And the answer that seems to be, for the most part, "no." It's hard to tell, because most of the Geekmedia aren't looking at it that way, and much of the remaining evidence is anecdotal.
In Antennagate Bottom Line, you mention the comparison of numbers of dropped calls, but I argue that this is not the right metric. What one needs to know is if the iPhone4 drops a call that would not be dropped by a 3GS. If the additional drops are in areas that the 3GS would have never connected in the first place, then the statistic isn't telling us what everyone claims it is. All that would mean is that there is a large drop rate in regions that were previously regarded as dead zones. That's an improvement, not a regression.
Without that information, one does not truly know how to interpret the statistic.
And not only did he made a post addressing that, he frikkin' quoted my email! (and this little ego-boost is the whole reason for finally writing this up. I've been quoted by Gruber and linked to by Kottke. In your face, world!)
|