I'm seriously considering going to this colloquium today :

Clifford M. Will (McDonnell Center for the Space Sciences,

Washington University, St. Louis, USA)

Title: "The Confrontation between General Relativity and Experiment"

Abstract : " We review the experimental evidence for Einstein's general relativity. Tests of the Einstein Equivalence Principle support the postulates of curved spacetime, while solar-system experiments strongly confirm weak-field general relativity. We describe the status of the recently concluded Gravity Probe B gyroscope experiment. Binary pulsars provide tests of gravitational-wave damping and of strong-field general relativity. Recently operational laser interferometric gravitational-wave observatories, and a future space interferometer, may provide new tests via the properties of gravitational waves."

I've often wondered what Gravity Probe B will tell us about gravitation. If you want an introduction to the experiment, you can find it at Stanford's site at http://einstein.stanford.edu/

If I actually get there, I'll let you know how it went.

-Dimi

UPDATE : The talk was very good, an rather interesting too. Appartently the gravitational community has been comparing general relativity with experiment since the 60's, and has been ruling out many alternate theories as a consequence. A very good review can been found here.

In addition, the gravity probe B results will be unveiled mid january. The speaker is part of a NASA advisory board, so he already has an idea, but as he put it "if I tell you now, I'd have to kill you".

## Tuesday, December 5, 2006

## Tuesday, November 28, 2006

### The next couple of days

If you're wondering what I'm up to the next few days...

I'm leaving the house in a few minutes to meet up with a few people at party. The theme for tonight is that the special "Duvel" beer will be available at only €1. People who know their Belgian beers will realise that this is very good news indeed :-)

Tomorrow I'm having a meeting with the other TA's about one of my classes to check on our progress. A friend of mine (and the TA for my freshman physics course long, long ago...) is defending his PhD thesis, and I'll be trying to attend. I'm not sure what it's about yet, but I vaguely remember it's something about using B-tagging to detect heavy higgses at the LHC. Should be fun.

I was wondering to wear shorts tonight. Its still 16°C here, and we're almost december...

Tata,

D.

I'm leaving the house in a few minutes to meet up with a few people at party. The theme for tonight is that the special "Duvel" beer will be available at only €1. People who know their Belgian beers will realise that this is very good news indeed :-)

Tomorrow I'm having a meeting with the other TA's about one of my classes to check on our progress. A friend of mine (and the TA for my freshman physics course long, long ago...) is defending his PhD thesis, and I'll be trying to attend. I'm not sure what it's about yet, but I vaguely remember it's something about using B-tagging to detect heavy higgses at the LHC. Should be fun.

I was wondering to wear shorts tonight. Its still 16°C here, and we're almost december...

Tata,

D.

## Sunday, November 26, 2006

### Progress report

Greetings,

This week there was some progress on the research front. Arjan, a post-doc at my lab was kind enough to show me a little trick to figure out what all the Lorentz-invariant contractions of the Riemann-tensor are for a given order. I basically reduces the problem to solving a kind of Sudoko puzzle, not unlike the Cartan root system for Lie algebra's.

Remember my search for good differential geometry tests? The Cambridge lecture notes were very helpful, but there's always more isn't there. A math professor at my university suggested the following book (no, I haven't taken over Lubos' obsession with Amazon adds, it's just the only place I could find it).

http://www.amazon.com/Geometry-Physics-Introduction-Second/dp/0521539277

The aforementioned math professor is studying it himself. It's good to see people from the math department taking an interest in the link between mathematics and physics, something that's rather close to my heart. I think I'll ask my dad to bring it with him when he gets back to Belgium, since it appears to be alot cheaper and more easily available in the States.

-Dimi

This week there was some progress on the research front. Arjan, a post-doc at my lab was kind enough to show me a little trick to figure out what all the Lorentz-invariant contractions of the Riemann-tensor are for a given order. I basically reduces the problem to solving a kind of Sudoko puzzle, not unlike the Cartan root system for Lie algebra's.

Remember my search for good differential geometry tests? The Cambridge lecture notes were very helpful, but there's always more isn't there. A math professor at my university suggested the following book (no, I haven't taken over Lubos' obsession with Amazon adds, it's just the only place I could find it).

http://www.amazon.com/Geometry-Physics-Introduction-Second/dp/0521539277

The aforementioned math professor is studying it himself. It's good to see people from the math department taking an interest in the link between mathematics and physics, something that's rather close to my heart. I think I'll ask my dad to bring it with him when he gets back to Belgium, since it appears to be alot cheaper and more easily available in the States.

-Dimi

## Saturday, November 18, 2006

### Looking for a soulmate? Start blogging!

An interesting thing has happened.

Sean Carrol, one of the bloggers at Cosmic Variance, is engaged to be married to Jennifer Ouellette of that other well-known blog, Cocktail Party Physics. You can read their respective stories on the linked blogs.

How strange this blogging thing can be. Not only has it unexpectedly transformed the way science is popularised or influenced tenureship, it is now becoming a major influence on the blogger's personal life. I wonder how common this phenomenon will become. As an aspiring scientist I firmly believe in the scientific method, so any charming ladies who are not put off by guys who know how to calculate the energy levels of a hydrogen atom are welcome to post their comments ;-)

Kidding aside, best wishes to the happy couple and may their marriage be a happy one!

Sean Carrol, one of the bloggers at Cosmic Variance, is engaged to be married to Jennifer Ouellette of that other well-known blog, Cocktail Party Physics. You can read their respective stories on the linked blogs.

How strange this blogging thing can be. Not only has it unexpectedly transformed the way science is popularised or influenced tenureship, it is now becoming a major influence on the blogger's personal life. I wonder how common this phenomenon will become. As an aspiring scientist I firmly believe in the scientific method, so any charming ladies who are not put off by guys who know how to calculate the energy levels of a hydrogen atom are welcome to post their comments ;-)

Kidding aside, best wishes to the happy couple and may their marriage be a happy one!

## Monday, November 13, 2006

### Sick

Not much to tell you really. I've been rather sick for the last week or so, but I had to go out last week to take care of some things. As a result it's gotten worse this weekend to the point that I had to cancel the recitations for today. So as you can imagine, there is not much interesting I can write is unless you're really interested in the contents of my hanckerchief...

## Sunday, October 29, 2006

### Needed : math

Hi all,

I was faced with a problem this week. Well, several problems. The start of it all (the meta-problem if you will) was te realisation that dawns on you constantly when you try to do anything in string theory, and any branch of theoretical physics for that matter; I don't know enough mathematics.

Fair enough, this is where we get some studying done. The plan for the coming weeks is to get a good grasp of differential geometry. It's pretty hard to find a good text that describes it at the level that I need. I don't need it to be too rigorous (my apologies to the mathematicians), but it needs to be rigorous enough. I think that my long search is over. Prof. Gary Gibbons from Cambridge was kind enough to post the following lecture notes on his website

Applications of Differential Geometry to Physics

The notes are from a Part III course in Cambridge, which seems to be exaclty what I need.

The main reason why I need this is that I want to understand more about vector bundles. Remember that I'm working on gravity in the string theory context? Well, gravity is described by General Relativity, who'se mathematical language is that of tensor calculus on manifolds. I'm trying to use methods found by my advisor to construct exact solutions that hopefully will shed some light on the high energy behaviour. These methods arised in the context of gauge theories, which are described mathematically by symmetry groups called Lie groups. Fibre bundles (at least to me) seem to be the natural bridge between the two. Apparently, gauge fields can be seen as connections on vector bundles. This is what I want to understand better.

-Dimi

I was faced with a problem this week. Well, several problems. The start of it all (the meta-problem if you will) was te realisation that dawns on you constantly when you try to do anything in string theory, and any branch of theoretical physics for that matter; I don't know enough mathematics.

Fair enough, this is where we get some studying done. The plan for the coming weeks is to get a good grasp of differential geometry. It's pretty hard to find a good text that describes it at the level that I need. I don't need it to be too rigorous (my apologies to the mathematicians), but it needs to be rigorous enough. I think that my long search is over. Prof. Gary Gibbons from Cambridge was kind enough to post the following lecture notes on his website

Applications of Differential Geometry to Physics

The notes are from a Part III course in Cambridge, which seems to be exaclty what I need.

The main reason why I need this is that I want to understand more about vector bundles. Remember that I'm working on gravity in the string theory context? Well, gravity is described by General Relativity, who'se mathematical language is that of tensor calculus on manifolds. I'm trying to use methods found by my advisor to construct exact solutions that hopefully will shed some light on the high energy behaviour. These methods arised in the context of gauge theories, which are described mathematically by symmetry groups called Lie groups. Fibre bundles (at least to me) seem to be the natural bridge between the two. Apparently, gauge fields can be seen as connections on vector bundles. This is what I want to understand better.

-Dimi

## Saturday, October 21, 2006

### Social and other gatherings

Yesterday was fun. A professor in my department decided to hold a little social gathering at his appartment in Brussels. The original pizza plan was foiled, due to the cook of his usual pizza place being abroad for the pizza world championships (no, I'm not making this up...), but in the end it all worked out and we had a nice meal.

So what happens when a bunch of string theorists get together with a few bottles of wine? A very interesting discussion erupted about the nature of mathematics and it's relation to physics. We also agreed the landscape was rubbish ;-)

The next few weeks will be very busy. I will be attending a graduate school about nonperturbative aspects of quantum field theory, supersymmetric QFT's, string theory and D-branes. Speakers will include Frank Ferrari, Ludwig Fadeev, Ben Craps, Carlo Maccaferri and Riccardo Argurio. Should be fun, but it will take up a lot of time. Wait, weren't the days of attending lectures all day over...?

In conclusion, some random pictures from various parties last week

So what happens when a bunch of string theorists get together with a few bottles of wine? A very interesting discussion erupted about the nature of mathematics and it's relation to physics. We also agreed the landscape was rubbish ;-)

The next few weeks will be very busy. I will be attending a graduate school about nonperturbative aspects of quantum field theory, supersymmetric QFT's, string theory and D-branes. Speakers will include Frank Ferrari, Ludwig Fadeev, Ben Craps, Carlo Maccaferri and Riccardo Argurio. Should be fun, but it will take up a lot of time. Wait, weren't the days of attending lectures all day over...?

In conclusion, some random pictures from various parties last week

## Thursday, October 12, 2006

### Colloquia en Lectures

Some news about that new aspect of my new life, qolloquia, symposia and the likes.

Next week I'm invited to the following :

Solvay Colloquium by Professor C.N. Yang

THEMATIC MELODIES OF TWENTIETH CENTURY PHYSICS: QUANTIZATION, SYMMETRY AND PHASE FACTOR

The Inaugural Lecture of the 2006 International Solvay Chair in Physics by Professor Ludwig Fadeev

THE MASS PROBLEM IN YANG-MILLS GAUGE THEORY

Sounds fun doesn't it? I'm going to attend, but I'll mentally prepare myself that I will be feeling rather stupid afterwards.

As for other news... all I can say is : curse Blackadder DVD's! I really ougth to have gotten more work done yesterday. No matter, I'll make up for it today.

Party tonight as well. I'll post op pictures if I don't forget my camera.

Next week I'm invited to the following :

Solvay Colloquium by Professor C.N. Yang

THEMATIC MELODIES OF TWENTIETH CENTURY PHYSICS: QUANTIZATION, SYMMETRY AND PHASE FACTOR

The Inaugural Lecture of the 2006 International Solvay Chair in Physics by Professor Ludwig Fadeev

THE MASS PROBLEM IN YANG-MILLS GAUGE THEORY

Sounds fun doesn't it? I'm going to attend, but I'll mentally prepare myself that I will be feeling rather stupid afterwards.

As for other news... all I can say is : curse Blackadder DVD's! I really ougth to have gotten more work done yesterday. No matter, I'll make up for it today.

Party tonight as well. I'll post op pictures if I don't forget my camera.

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