26.02.2009 21:47

As you probabely know the idea of there being more than 4 dimensions is a very persistent one in speculative physics. Most prominently there is string theory which needs 11 dimensions, but there are many other fancyful ideas. (Which are a bit more economical in the number of dimensions they need). Me myself I work on such a model for my PhD.
Normally, the dimensions d > 4 are discussed away from every day experience by claiming that they are compact and small and hence we cannot walk into them. They only unfold for a very high energetic probe.
At least in popular books these ideas are illustrated with a picture like this: That is people tell you that you should imagine a small circle or (something more complicated as in the picture) attached at each point in your 4d space. That is you think of some lattice like in the picture, attach your circles and then take a continuum limit, ie let the circles move closer and closer together. Not so difficult is it? But this is blatantly wrong. Because according to this picture you have a compactified space at each point on the plane, but once you move into this plane, you get detached from the surface holding it. Whereas in reality at each point in the compact manifold there also extends the extended plane again. And from there it continues until you get mad. That is to say the above picture is very different from the one of a infinite cylinder of radius R: In the cylinder, which is extended in 1 dimension and compact along another, when you move along the circle at every point you have a inifinite line. Staying whith this two dimensions the above picture would correspond to a straight inifinite line, where there are circles attached at each point. So at every point in the line you are free to move into the circle or to continue along the line, but once you have left the line and entered a circle, there is really only one direction open to you until you have walked all along the circle.
Or take a torus (donut) which is 2 dimensional and compact in both directions. Each point is the intersection of two circles. The thing above isn't such.
Honestly, I can imagine 3 dimensions because that's the space I live in, and then I am fine with the fourth, because I know what time is, but all the other things I have no intuitive grasp.
J'ai pris l'image de ce site.Merci

20.02.2009 09:34

Vielleicht hilft's ja irgendwann...

18.02.2009 09:57

Eigentlich bin ich ja Bahn Grosskunde, da ich aus oekologischen Gruenden Bahnfahren dem Fliegen vorziehe. Aber zur Zeit bin ich mir nicht so sicher, ob man nicht einfach die Bahn boykottieren sollte bis die ihren Saustall aufgeraeumt haben und den lieben Herrn Mehdorn in die Wueste geschickt. Am Schluss ist dass alles nur eine Bereicherungsanstalt fuer Gutbetuchte auf dem Ruecken der Bahnfahrer, einfachen Bahnangestellten und Steuerzahler. Wahrscheinlich hat die Bahn einfach noch Glueck, dass grad alle damit beschaeftigt sind mit dem Finger auf die Banken zu zeigen. Wenn man schnell und koordiniert alle Reisenden einen Monat lang auf Alternativen umsteigen, dann ist Herr Mehdorn weg in Null Komma nix. Und warum auch nicht mit einer solchen Drohung diesen idiotischen Boersengang auch gleich noch vom Tisch wischen? Die deutschen Bahnfahrer wollen ihn ja nicht, dass hinreichend bekannt. Und fuer ne Bahn mit der keiner mehr faehrt zahlt auch keiner was an der Boerse.

06.02.2009 23:00

I have students version of Matlab (release 2007a) running on my laptop. It is actually the only piece of non-free software that I run. And indeed, I find their licence/company policy embarrassing. And it's plain expensive, only those students licences are cheap (ca. 70 Euros...) But still so it's a bad deal, because they are normally out-of-date releases and quite buggy. In my case I had no way to get certain frequently used characters like "^" (exponentiation) and "~" (negation) printed unless I switched to an American keyboard layout. But me, I don't now by heart where all the special characters are. So using the American layout worked but caused a lot of typos and wild character binding guessing. Not very comfortable. And then whenever I tried to edit certain features in the preferences the whole thing crashed. Until I noticed from the lots of JAVA exceptions that Matlab uses its own JRE. So I changed it to my newer Java version.
Now it works beautifully, I can browse the prefs without crashes, and I even get the "^"s and "~"s where they should be. But hey, if you ship a JRE with your program, why don't you check it's together working beforehand? It's a bit embarrassing, no?
So here is what I did:

How to change Matlabs Java version

By default Matlab ships with its one JRE, which is in (for linux 32bit)
$MATLABHOME/sys/java/jre/glnx86/jre_xx
where $MATLABHOME is your installation directory and xx stands for the Java version. In my case (release 2007a) it's Java 5. I created a link in this directory
$ cd $MATLABHOME/sys/java/jre/glnx86
$ ln -x /usr/lib/jvm/java-6-sun/jre jre1.6
Then I edited the file jre.cfg in the same directory to contain this link instead of the old version. But this is not enough. You have to set the environment variable MATLAB_JAVA. So I added the line
export MATLAB_JAVA=/usr/lib/jvm/java-6-sun/jre
in my .bashrc then open a new shell and start Matlab from it. Note that for me java-6-openjdk did not it crashed right after startup.

You might ask why I you have this "evil" software in the first place? Right. I know there is Octave to replace it, and I use that as well. The reason why I still have Matlab is that we teach courses in the Master's programme in Matlab. Oh, well this is even worse. We hook the student on to it... I totally agree, we should migrate all the material to Octave or even C (which the students are more at ease with anyway, they normally don't manage to get into the matrix/vector programming model of Octave/Matlab), but that is out of my hands.
I even had to buy the student licence for my laptop because there was no other way that I could show the programs in class.
(No, there is no University owned laptop that I could use. And no, the computers in the lab cannot be used with a projector, and no I could not login to a remote computer and run it there, because there was no network plug with a DHCP service in the computer lab at that time. I have tried it all. Uff, you are free to imagine by yourself, what I my opinion is about all this...)

06.02.2009 12:33

On the back of my notepad there is the schedule of a workshop. (I must have picked it up in the printer room or so, not that I know what workshop it was) One of the talks is entitled

How the wind created strangely shaped rocks in Turkey by computer simulation

I'd really like to get to know this wind. Seems to be a smart guy, maybe it could do my simulations once it is done with the rocks.

23.01.2009 16:44

I finally finished reading Lee Smolins the trouble with physics. It is one of the two "string bashing" books (the other one being Peter Woit's Not even wrong)which were widely discussed two years ago. (At least in the American physics blogosphere, see f. ex. old posts on Back reaction, Cosmic Variance and Asymptotia)
I enjoyed the book a lot. It raises many legitimate questions about the way physics is done nowadays and about the influence that the entire accademic world and organisation has on science. Smolin's main point is that there remain many major fundamental problems in physics unsolved and they remain unsolved despite many years of effort of many people. Why is this? Is not because we are not smart enough says Smolin, it is because we do it in the wrong way. People are encouraged to become hard working but unimaginative technicians rather than explore fundamental questions and question the premises. And then on top of this, over the last 20 years there has been a predominant theory, a theory which has claimed a solution to all problems and which was very successful in advertising that it will provide the final answer, but indeed it has failed to do so. This theory comes, and Smolin is right about this, with a special kind of culture: an arrogance which is unjustified by its results. This theory happens to be string theory. And it is for this reason that Smolin critisizes it. Every other theory which had played that role: being dominant over 20 years, monopolizing resources at the expense of other ideas and still not meeting up to the promises, would have to face the same critisim. So there is a lot about string theory in the book, but it is wrong to pin it down to "string bashing", that is what the discussion for instance on Cosmic Variance is mostly missing.
Rather I would say a similar critism applies also to many High energy phenomenologists and lattices gauge theorists: we too confine ourselves to mindlessly doing loop calculations to yet another order or waste more and more computing power to calculate low energy constants and hadron masses. We are but engineers. We know our technology well, but that is not the way we learn more about nature. And still we have the pretense to claim (when we compare ourselves to physicists in other fields, like solid states, etc) that we do fundamental physics.
Maybe the book is not so interesting for non-physicists, but I haven't read a better physics book in months. And this, where I claim to be a working physicist. That is sad...
A German translation is about to appear by April this year.

16.01.2009 22:04

Also einmal mehr nehm ich mir vor in Zukunft wieder häufiger zu bloggen. Ein Grund warum ich mein gegenwärtiges Leben satt hab, ist dass irgendwie nie Zeit für irgendwas bleibt. Nicht um über Dinge nach zu denken, geschweige denn um sie dann auch noch aufzuschreiben.

05.11.2008 21:26

The most interesting part of these statistics is the second tab. White men above 50 years voted McCain. But the young, the women, the non-white won the election. Do these statistics tell us that racism still is a issue, despite the result and all the nice words. Or is it more general, that everybody simply tends to vote for somebody who is most alike himself?

30.10.2008 20:04

aka Ubuntu 8.10 was released today. And even though I wanted to do a clean install on the weekend, I ran the update this afternoon. I was lucky, it took only one hour, so I still got my train to Munich. Up to now everything is fine, so I won't trouble my weekend with the new installation. It's nice to have a properly running distro again. After all this mess with Hardy, which I found a pretty disappointing release, especially for a long time support. For me the hardy kernel 2.6.24-xx did not even boot, I tried some things suggested here and there and then gave up and run the system with the old kernel from Gutsy. This had some other unfortunate consequences related to libgphoto2 which was not working properly with Gutsy's 2.6.22-xx kernel.
Phee, it's over, everything is running clean!

30.10.2008 19:26

Meisten kauf ich ja so Strassenzeitungen und les sie nicht wirklich, nicht so aber vor zwei Wochen in Berlin. Das Thema der Oktoberausgabe vom Strassenfeger war der öffentliche Verkehr, (immer wichtig) und besonders nett ist ein netter Artikel über die missglückten U-Bahn projekte Berlins. Jeder kennt die Geschichte der Kanzler U-bahn, die Verlängerung der U5 vom Alex bis zum Brandenburger Tor/Kanzleramt. Deren Bau war von Helmut Kohl angestossen worden, die Fertigstellung aber lange ungewiss, es gab einen Baustop und der halbfertige Tunnel wurde auf die übliche Berliner Art "zwischengenutzt" für Veranstaltungen aller Art.
Solcher Art Projekte sind in Berlin ja nix neues, erst wird gross angerichtet, dann geht das Geld aus und uebrig bleibt ein Gerippe. Auch bei den U Bahnen gabs die erste Todgeburt schon in den 20ern. Beim Moritzplatz gibt es einen verwaisten Bahnhof aus der Zeit, der fuer eine Schnellbahn ins Zentrum geplant war. Unter der Dresdener Strasse gibts n U Bahn Tunnel, doch dann hat man entschieden die Streckenführung der U8 zu ändern. Es existieren Kreuzungsbahnhöfe am Adenauerplatz und in Jungfernheide. Und zu Zeiten des kalten Kriegs sollte eine Linie (U 10) vom Potsdamer Platz nach Steglitz gebaut werden. Es blieb wohl bei mehreren Tunnelabschnitten, weil 1984 als es ernst wurde die S-Bahn in West Verantwortung ueberging und der U Bahn-Bau erstmal gestoppt wurde.
Schmuck das alles, da würde man doch glatt mal ne U-Bahn Führung im Verborgenen machen wollen.

29.10.2008 13:48

All these stupid pictures (here and here) in the news of men in suits staring at screens full of numbers of waving their hands in desperation and tiredness, because there was yet another (foreseeable) values fluctuation at the stockmarkets. Please, if you think there aren't more interesting headlines then at least spare us the picture. It has no content whatsoever, I stare at my screen everyday and wave my hands in desperation, because the numbers I get are wrong.

17.10.2008 10:01

In einer Demokratie vertreten Regierung und Parlament, den Souverän wie man bei uns so schön sagt. Der Staat sind wir und damit ist öffentliches Vermögen Volksvermögen. Ja klar, unsereiner der Steuerzahler hat es ja rangeschaffen und gehegt und in Schussgehalten. Wie kann es denn sein, dass die Regierung Vermögen veräussert, obwohl bekanntermassen fast 80% der Bürger dagegen sind?
Das ist eigentlich Veruntreuung fremden Eigentums, meine Herren.