## Earliest Pornography!?May 16, 2009

Posted by keithkchan in fun stuffs.

Sometimes it is appropriate to talk about porn. Here is one of the occasion. You can find porn easily today. But it is interesting to ask how early people have explicit interest in porn. The article, whose title is the Earliest Pornography? sheds new light to this question. A group in Germany unearthed a female statuette, dated back to more than 35000 years by carbon dating, in Germany. Wow, 35000 years is really old. The size of the statuette is pretty small, 6 centimeters tall and 3.4 centimeters wide. The statuette, made of mammoth ivory, shows enlarged breast and vulva. Although the definition of porn is a little bit subjective, maybe rather sensitive to your imagination, this one is not so controversial. They probably used it as some sort of decoration.

## Planck has lifted offMay 14, 2009

Posted by keithkchan in fun stuffs.

I am still alive. Of course I am not going to shut up forever. I think it is time for me to start bullshitting again.

Finally Planck has successfully launched. (Together with another satellite Herschel, I have no idea what it is, and probably nobody cares what it is.)

As you know Planck is the next generation CMB experiment, conducted by ESO. Now WMAP measures CMB temperature up to $l \sim 1000$ or so, and E-polarization is about a few hundred or so; Planck is expected to take us further afield, maybe temperature maybe $l \sim 2500$ and E-polarization to about 1500. It may also measure B-mode polarization, which can be due to the gravitational waves from inflation. The WMAP data seems to suggest that the amount of non-gaussianity is larger than simple inflation model, hopefully Planck will be able to give us a more definite answer. And many other possibilities. Maybe it will confirm string theory, but I don’t know know. Then Lubos Motl will be very happy. (Of course I will also be happy about that.)

## Horava-Lifshitz GravityApril 28, 2009

Posted by keithkchan in Journal club.

Recently, there are a lot of papers on the a new quantum gravity model, now dubbed Horava-Lifshitz gravity. It has been published in Physical Review. This model appears to be very exciting since it claims to be renormalizable. Many authors have immediately started calculating various things: inflation in this model, bouncing model, Schwarzschild solution, non-Gaussianity, blah, blah, blah.

Beside being renormalizable, another thing that is particularly exciting is that this model seems to be able to generate scale invariant spectrum without inflation. That sounds very cool!

Because of these seemingly attractive features in this model, in last week’s journal club, people in another journal club tried to read this paper. Since the model is novel and complicated, the smart people in our centre failed to understand the model. Gruzinov was very excited, and asked Kleban to talk about it in next week. He even criticized that the high energy people in our centre for their ignoring this interesting model.

So this week, Kleban presented this model. Before the start of the talk, Gruzinov asked Porrati for his comments. It turns out Porrati often makes funny comments. He said that I haven’t really read it, but if it was right, I would change my career to study swine flu. I find his comment very funny.

After all these prelude, I now briefly describe the model. Frankly speaking, I don’t really understand it, so I am not going to comment on it. The model is motivated by the Lifshitz point, which is used to model the triple point in condensed matter physics. By the way, this is another example that ideas in high energy physics originate from condensed matter physics. In this model there is critical exponent z, if it is 1, we get relativistic dispersion relation. This model is z=3 in the UV, and it becomes z=1 in the IR, and Lorentz symmetry is recovered as an accidental symmetry. The model is power counting renormalizable. In this model, space and time scales in differently, so that the the theory is rendered power counting renormalizable. Note that power counting renormalizable is just a first test of renormalizability. One really needs to check in details if it is indeed renormalizable. During the talk, some of the audience, in particular Gruzinov was increasingly impatient as the Lagrangian introduced was rather ad hoc. I don’t really understand it so I am not going to comment on that, just to say that the terms added are mostly spatial, and of high derivatives. Needly to say, it is very different from the usual GR and field theory. Gruzinov even said that life was short, why do we spend time on such a theory. Kleban reminded him that he should blame himself for asking him to present the paper. People were worried about about a parameter introduced in the theory, which start as 1/3 in UV, it has to flow to 1 in order to agree with GR in the IR regime. After browsing the whole paper, Horava did not say (or know ) how to realize this flow. Porrati said that it was almost impossible for any perturbative effect drive the parameter to flow from 1/3 to 1. At the end, nobody was happy about this paper. Gruzinov seemed to be pissed off. I personally find the talk rather amusing. The comments by various people, in particular Porrati and Gruzinov very interesting and illuminating.

So it was pretty funny that last week everybody was excited about this paper and this week everybody loses interest in it. We have to wait for another breakthrough…

Update: I would like to add a few comments on it. Nobody really knows how to come up a workable quantum theory of gravity. So anybody can take strong opinion in this regard. But anybody that asks the right question is much much more likely to succeed than others. So Porrati and Gruzinov think that Horava’s approach is not going to work. Fine.

But shouldn’t it be obvious that anything that is obvious is not going to work. Anything that is going to work is not going to be obvious. The reason that those smart people fail to come up with a sensible theory of quantum gravity maybe because they are too strongly biased. I defend this theory does not mean that I believe that this the right theory. But I certainly think that this is an interesting and novel idea. OK, Horava did not lay out the model in details. But I think he has set up a proposal that is interesting enough to pursue it further. One of the reason that so many people have jumped into this theory because they think that it is interesting and worth trying. So my philosophy to these kind of difficult open questions is that we should keep mind opened.

Up-update: Apparently, this post is controversial and stimulating. Lubos Motl has written a post about this post. And he tries to dissect each comments I said. So I should feel honored since nobody has taken my words so seriously before. But I am going to de-comment since I got much more publicity than I want. You check out his comments to see if it is justified.

I got so much publicity that I may need to put up a stupid disclaimer that the contents of this blog has nothing to do with NYU, don’t sue the director of graduate studies if you don’t like this post. OK, anyway I now shut up.

## Comments on the experimental requirementsApril 23, 2009

Posted by keithkchan in Philosophy.

I haven’t updated this blog for some time. Today I had some discussions with my Mr Payam and Mr Mincer. I feel that I have pretty strong opinion that I want to blog about.

In our department, we have a rather perversive requirement — students have to fulfill some experimental requirement by either taking the experiment courses or doing an experimental project with a faculty member. This requirement has caused a lot of trouble for some of us. This is particularly bad for the theoretical students since most theorists don’t like doing experiments. I think I am a theorist but not a highbrow one, so I think I can give “relatively balanced” opinion.

The argument for the existence of this experimental requirement is that the department expects the graduates to know how real experiments are done, and give the students a chance to discover their potential in doing experiments.

Everyone enters the graduate school have already known the importance of experiments of physics. After all physics is an experimental science. We agree. Doing good experiments are hard. Need a lot of creative designs and careful planing, and a lot of practical skills. We agree that experimentalists are not stupid. When we apply for graduate school most of us already have well defined field of interests, taking the experimental course is not going to change anything. OK, doing experimental project may be able to shift their interest. But then the whole idea of having this requirements is to let the experimentalists to have more students. After all the lab can take up a lot of students, many of the lab procedures are tedious and labour-intensive.

So far I have been suffering a lot from from this requirements. Due some misguided thoughts, I tried to do a project with some guy in astronomy. After some time, it became so technical, time-consuming and more importantly boring, I quited the project. From that experience, I guess the most important thing I learn is that astronomy is boring.

My friend Mr Payam took the experiment course. He spent a lot of time doing those experiments and writing lab report, so it messed up his research.

I think this requirements should not exist at all. I have complained about to some people, but they insist on keeping it. Apparently, I am not the only one have this opinion. According to Mr Mincer, some theorists hold the same viewpoint as mine. Unfortunately, experimentalists and theorists can only agree that they disagree.

I certainly agree the importance of experiment to physics, but I disagree that theorists should be afflicted with the pains that the experimentalists suffer.

## Cosmic TopologyApril 16, 2009

Posted by keithkchan in Cosmology.
1 comment so far

Thanks to my colleagues, in particular Mr David, who urged me to update this blog. So I decide not to watch Spiderman cartoon tonight, and write something on this blog. By the way, Spiderman is also a geek. Although he studied at an imaginary university (Empire State University) in Mahattan, we believe that the writer in fact imply NYU. Also he rests on the trademark of NYU, the characteristic NYU flag frequently. Of course, I like Spiderman before coming to NYU.

What do I want to talk about? Well let me write up the paper I presented in the journal club this week. The paper I chose is arXiv:astro-ph/0402324, whose title is Cosmic Topology: a Brief Overview. Well this sounds rather off the main stream of cosmology. Yes, that’s true. The main motivation for me to learn something about these stuffs is that I wonder if the current observed cosmic acceleration can arise from some nontrivial global topology of the universe. It turns out that this is rather unlikely (should I just say impossible?).

In standard cosmology, we usually assume that the spatial topology of the universe is either the Euclidean space $E^3$, 3-sphere ($S^3$), or a 3-hyperbolic space ($H^3$). However, as realized by Karl Scharzschild, in fact the spatial topology can be $M/\Gamma$, where $M$ is one of the homogeneous and isotropic space and $\Gamma$ is some symmetry transformation that leaves the metric invariant. For example, instead of the whole infinite Euclidean space, we may live in a cube with the opposite face identified, that is a 3-torus. The point is that general relativity is a local metrical theory, it does not allow us to determine the spatial topology. My goal to realize cosmic acceleration by nontrivial topology evaporates and my interest in this subject has dropped by a factor of 3. Incidentally, there are a few papers in the literature trying to argue that spatial topology is the cause of cosmic acceleration. I have read one, and my impression is that it is totally nonsense.

Then can we really tell the spatial topology of the universe by observations. Yes, it is possible. The most striking consequence of the nontrivial topology is that we can see multiple images of the same object in the sky. Unfortunately there are great difficulties in direct detection. The images of the object, such galaxies, are seen from different angles, at different stages of their life, and some of the images may be blocked by other objects. Thus it is almost impossible to tell by direct detection. Instead we can look for some signatures of nontrivial global topology in statistics. I am not going to the details of the statistics, but I just outline the main ideas. One of the way is to compute the distance between the galaxies in a catalogue, and plot the distribution as a function of their separations. Because the separation between the copies of the object is some characteristic length scale, it will show up as a sharp spike in the distribution. One can also look for identical circles in the CMB temperature map, which is so far the best way to probe nontrivial topology. It has ruled out the famous (or infamous) dodecahedral universe that some people proposed to explain the lower-than-expected power in the quadrupole and octopole in the CMB map. Incidentally many people made fun of this model.

Now I should point out that if the particle horizon is much smaller than some “periodic scale” of the universe, even if we live in a universe with nontrivial topology, we have no way to tell. So far, there is no observational evidence that the universe has nontrivial topology. So we can apply Occam’s razor to cut out the unnecessary complications and stick to the standard cosmology happily. On the other hand, we should be open-minded, exhausted all the possibilities, and don’t make fun of those people who have good reasons to do non-standard cosmology.

## Meat-for-sex theoryApril 13, 2009

Posted by keithkchan in fun stuffs.
1 comment so far

The frequent visitors of the Blackboard, if they exist at all, may notice that I haven’t actively updated this blog for some time. Well, life is complicated, I have been suffering from depression for some time for various reasons. Now I try to get over from it. One of the things I may want to do is to keep this blog afresh again.

OK. There is one news in Science, entitled chimps trade meat for chance of sex; I find very interesting. In particular, it may shed light on how to get lucky for us. Researchers have found that male chimps sometimes share meat that they hunt with female chimps. I am not sure if they do it just for fun or for pure comradeship. I think they have ultimate motive. Anyway, this in turn increases the chance that the male can have sex with females by a factor of two. This effect is also long term, a few months later, the females still remember it, and this still holds. That’s pretty good deal. People who are still in the category of losers may learn something useful from it. Get luck.

## Some Foolish StuffsApril 1, 2009

Posted by keithkchan in fun stuffs.
1 comment so far

Today I saw some foolish stuffs. Thanks to my colleagues, I realize that today is April Fools’ Day. Since I haven’t updated this blog for some time, I would like to share them here.

First, I saw a piece of news of Miss Universe in BBC’s web site. The title is Guantanamo ‘fun’ – Miss Universe. It was about a visit of the Miss Universe to Guantanamo Bay. They then wrote on the blog that it was so “soooo beautiful” that they did not want to go. Oh come on that was a prison, hundred of prisoners were suffering there. Do they have any sense? I have long suspected that many of the Miss Whatever does not have a brain. It seems to confirm my conjecture. Not surprising, other viewers are also pissed off by their stupid remarks, e.g. one said “”My God! Never underestimate the predictability of stupidity. This is horrendous.” (BTW, fortunately, although I often say stupid things here, nobody so far come and kick my S =) ). Unfortunately, the Miss Universe did it a few days before Fools’ day. No excuse.

Another  fun/stupid news is about a paper posted on the arXiv today 0903.5377 (Thanks to my colleague Mr Ben for drawing my attention to this horrendous paper).  They claim that they have found that some rare clusters, whose morphology was so weired that they look like letters, and they go on to claim that it was signals from extraterrestrial civilizations. Their interpretation is no different from that people think they see elephants, monkeys, bananas, human face in the clouds. Their interpretations also reveal they have no sense of how laws of physics limit what living organisms can do (Of course they are astronomers, I should not blame them for not knowing physics).  Later my colleagues remind me that today is stupid people’s day. They are free to do whatever they think that are right. Fine. They can do whatever they like today. But I do expect that they should put version 2 on the arXiv to replace the stupid version tomorrow.

That’s the end of my April Fools’ stuff.

## An impressive mechanical dogMarch 28, 2009

Posted by keithkchan in fun stuffs.

Well I just saw a video in Dmitry Poldolsky’s blog, I find it truely impressive. I used to think that robot move in a very rigid way. But this video may changed my view point. Notice that when the robot was kicked, it tried to maintain balance by some complicated maneuvers. The robot is more vigil than some people! Truely impressive, isn’t it? Sometimes engineers can do something that impress physicists.

## The Art of Asking “Stupid” QuestionsMarch 21, 2009

Posted by keithkchan in Philosophy, Whatever.

These few days we tried to verified the approximation used in some guys’ paper, who claimed to have done what we have done. In their paper they used the spherical approximation, instead of solving the equations exactly. When I showed my advisor the results, he immediately said that it must be wrong since in the large scales the nonlinear effects should not matter. I then spent a couple of days to check if there were stupid mistakes that I have made. Indeed I did, but it was not related to the major problem. Although the conventional wisdom was that the linear regime should not be affected by the nonlinear effects, the equation we solved were highly nonlinear, this was not obvious to me. I went to press him, and we finally realized that in the spherical approximation the nonlinear effect in the high k can indeed influence the scale physics. Incidentally, this partially suggests the answer to my previous question if quantity is more important than quality. Those guys write many papers, quality may fluctuate a bit.

I often ask questions most of them are probably stupid. I think the real good physicists certainly know the importance of asking questions. Sometimes, some concepts may be so “obvious” to them they did not even think about it. Like in the case of my advisor who is regarded as an expert in this field, but he could still miss something sometimes.

I believe that if I keep on asking questions I will be able to good questions sometime. The most important thing is not to stop asking questions, even if they are are stupid. After all, it is not clear if it is stupid a priori.

## Summer School TimeMarch 20, 2009

Posted by keithkchan in Anouncement.