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Rob Knoops | CERN / University of Leuven | Belgium

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April fool’s lands on CERN

Wednesday, April 2nd, 2014

Apart from the usual jokes on Quantum Diaries (See for example the blog posts of Kyle, Byron, Aidan, Alexey), this year’s April fool’s had quite some remarkable ‘fish’ worth mentioning:

On the official website CERN announced they were going to switch to comic sans, featuring a video of ATLAS spokesperson Fabiola Gianotti. The use of comic sans in the slides of the Higgs discovery in 2012 caused quite a commotion.

Also on the CERN website, it was announced that new parking rules will be enforced at all entrance gates, allowing only cars whose digits on the number plate is odd (even) on odd (even) days, respectively. With these new rules it seems to be more advantageous to have an ‘odd’ licence plate (Some months end on 31 which is odd, followed by the first day of the next month, which is odd again).

There is a vacant position for Director General of CERN coming up, you can apply here. In fact, I am not even completely sure whether this is an April fool’s joke or not, is it?

Then there was google, launching an app to catch wild pokemon. Of course, CERN is indicated as a pokelab on the map.

My friend Andri seemed to have written a paper together with Peter Higgs. I wonder how I could have ever overlooked the paper with A. Turing in the references.

Finally, building 27 seemed to have suffered some damage and the coffee will be more expensive as of April 1st (which unfortunately seems not to be a April fool’s joke).

Have I missed any? Please put them in the comments or tweet to @KnoopsRob.

CERN as a pokelab on google's pokemon app

CERN as a pokelab on google’s pokemon app

The coffee will be more expensive as of April 1st (note a joke), thanks to Alex Brown for pointing this out.

The coffee will be more expensive as of April 1st (not a joke), thanks to Alex Brown for pointing this out.

April fool's arrives in Building 27

April fool’s arrives in Building 27


CERN Christmas Play

Tuesday, December 24th, 2013


Note on the door separating the recently renewed HR department and the theory department.

Note on the door separating the recently renewed HR department and the theory department.

It’s that time of the year again, the time for CERN’s theory group’s yearly christmas play.
If’ you’d wander around in CERN’s corridors and happen to pass the theory department, you can notice the remarkably high concentration of jokes flying around in the corridor. See for example the note on the door separating the (recently renewed) HR department and the (still looking like a lab in the 60s) theory department.

Of course I am not the first one to blog about the CERN christmas play, see for example here or here. In fact, this silly play has a tradition that goes 30 years back. I could find some records of it on the cern document server going back to 1984. I didn’t have the time to check them all out, but let me know if you can spot any famous physicists in their young days, I am sure there are a lot!


Invitation for the 'Theory christmas party', hinting this year's theme as a quest for the holy grail and a reference to CERN's official 'thank you  drinks' called 'Bosons & more'.

Invitation for the ‘Theory christmas party’, hinting this year’s theme as the quest for the holy grail and a reference to CERN’s official ‘thank you drinks’ called ‘Bosons & more’. The king’s head has been replaced by the head of our director general, and the knights by the spokespersons of the biggest experiments.



Anyway, back to this year’s play. Each year, a group of theorists gathers together during their lunch breaks for about a week to practice their script, written and directed by John Ellis, to perform after the christmas dinner, on an improvised stage, set up in the main cafeteria.

The theme of the play varies every year (see last year’s Bond themed one), and this year there was chosen a Monty Python parody (I love Monty Python) on a quest for the (un)holy grail.

I will post the video here as soon as it is available (which may take until after the christmas break). In the meanwhile, here are some of the highlights (picture credits go to Mike Struik):

The scene shifters practiced a different silly walk for each scene shift. It was amazing to see how good they got at this.

The scene shifters practiced a different silly walk for each scene shift. It was amazing to see how good they got at this. Note the -not so representative- version of the LHC in the back.



Referencing the oppressed peasant sketch . The theorists/peasants have no idea that something like a DG (director general) exists. CERN’s DG, Rolf Heuer has become quite a public figure in the last years.

Epic appearance of Professor Ellis as God, explaining 'Rolfur', king (DG) of the CERNois, to look for the unholy grail of particle physics, namely 'dark matter'

Epic appearance of Professor Ellis as God.



Myself in the middle as an ex-perimentalist, referring to the dead parrot sketch.

Myself in the middle as an ex-perimentalist, referring to the dead parrot sketch. We truly could not find a real experimentalist willing to play a role 😉

John Ellis made an epic appearance playing ‘God’, explaining ‘Rolfur’, king (DG) of the CERNois, to look for the unholy grail of particle physics, namely dark matter and dark energy.
Now the Higgs boson is found, it seems  that our DG tries to promote the search for dark matter as one of CERN’s most important tasks.
Unfortunately for CERN, we are not the only one looking for dark matter and there are many ways to search for it without the need of a particle accelerator. In fact, we would only be able to detect it here, if dark matter is made up of WIMPs (weakly interacting massive particles). A recent post that I particularly liked on this can be found here.

Sir LHC-alot being wooed by the damsels.

Sir LHC-alot being wooed by the damsels.


A French guy defending the bridge to stockholm, trying to prevent sir LHCalot to claim a Nobel Prize.

A French guy defending the bridge to stockholm, trying to prevent sir LHCalot from claim a Nobel Prize.

Video will appear soon!


Can String Theory predict stuff?

Tuesday, August 20th, 2013

What’s the deal with string theory? Why do people claim string theory is nonsense? Can we predict anything with it? As a theorist with too many experimental friends, these questions are thrown at me all the time. So today answering these will be my challenge.

Dislaimer: In the following I might have wiped too many ‘details’ under the doormat in order to keep everything readable. But feel free to post any comment if you would like me elaborate on specific parts.

Basically string theory says that the tiniest bits of matter are in fact little strings, in contrast to for example the Standard Model, where every particle is considered to be a point. This has a lot of interesting consequences, but I will only address the essential points that we will need along the way.
For this it is sufficient to believe that as soon one wants to quantize this string (with ‘to quantize’ I mean “to write a quantum mechanical theory of this string”), one quickly gets to the result that this theory we are talking about actually has to live in 10 dimensions (or 11 for M-theory, but let’s not talk about that).
I think the best way to look at this fact is to say ‘We need 10 dimensions to make the mathematics work out’. For people with a physics background: One way to look at it, is that we need 10 dimensions to make some anomalies vanish.

Anyway, we are now with a 10-dimensional theory. How should we look at these extra dimensions?
Mathematically it is simple: While you would usually work with (x,y,z) coordinates, we now instead work with (x1, x2, x3, … , x10 ) as coordinates. Physically it is more difficult, since the world as we observe it has only 4 dimensions (three spatial dimensions and we count ‘time’ as a dimension as well, adding up to 4). The question then arises: Where did the other six dimensions go? The theory should at least take into account why we can not see those six extra dimensions in our everyday live (or even in high energy experiments like the LHC at CERN until now).

The answer is that we think that these extra dimensions are ‘compactified’. So what does this mean?
Consider for example a circle. If I’d be walking along this circle long enough, I will end up at the same point again. Such a ‘rolled up’ direction we call a compactified dimension.
The reason why we can not see these extra dimensions in our everyday live and experiments, is that they are simply too small for us to notice.

Now, for our string theory, we need to compactify six dimensions. Stuff gets interesting when we are trying trying to compactify more than one dimension. For example, let’s roll up two dimensions. It is not hard to imagine that the surface of a sphere is an example of a compact two-dimensional object (we usually call these objects ‘manifolds’), but another option we have is to compactify the two dimensions in the form of a donut, or even a pretzel. It is already clear that we can make a huge amount of different objects, and the amount of choices we can make increases radically when we try to compactify six dimensions.
(The above is actually a bit oversimplified, string theorists for example like to compactify the extra dimensions on so-called ‘Calabi-Yau manifolds’)

Now the funny thing is, that for every different way you compactify the extra dimensions, the laws of Physics, as in the coupling constants, interactions and even the particle content in our four known dimensions will be different. Every such possibility we call a ‘vacuum’ of string theory.
The challenge is then, to compactify the extra dimensions in such a way that the theory we end up with would look like the Standard Model like we know it now ( + perhaps some extra particles that we have not discovered yet). People have actually found quite a lot of those configurations that look like our Standard Model.

Sidenote: One of the physical constants that varies from one vacuum to another, is the Cosmological constant, and I’m currently trying to find a way to make this one work out.

Now, the problem lies in the amount of vacua (or ‘different ways to compactify string theory down to four dimensions’) string theory has. Its exact number will depend on who you ask, but it is usually quoted as around 10500. That’s huge! This is more than there are particles in the universe. And every single one of those vacua will correspond to a different kind of universe, most of them that do not even look like the Standard Model at all! But then, what would it mean if we would find just one vacuum out of those 10500 that would correspond completely to the world and laws of nature we know? If we can just chose the one we like, how can the theory predict anything?

Honestly, at the moment, nobody knows. Some people have ideas: Perhaps there exists some dynamical principle that points to exactly the right vacuum of string theory in which we live, and the universe did not have a choice. Perhaps there is some anthropological principle going on: If the universe would have chosen to live in another vacuum of string theory, the laws of nature would be very different and would not allow for example for stars to be formed, so that we would not have been here to ask this question.

Instead of going all philosophic on this, let’s address the question: Why do you do string theory anyway? String theory has one big power, namely its mathematical machinery. In fact, string theory has taught us a lot about quantum field theories, like the Standard Model, in general. Also, it has shed light on the quantum mechanics (and entropy) of black holes. But perhaps the coolest thing that came out of string theory would be the AdS/CFT correspondence.

Very vaguely, the AdS/CFT correspondence states that there is a relation (‘duality’) between a theory of quantum gravity in some space, and a field theory (without gravity) that’s living only on the boundary of this same space. So, not only does it manage to relate a D-dimensional theory to a (D+1)-dimensional theory, but it relates also a theory with gravity to a theory without gravity. This idea, born in string theory, has been used to calculate stuff in a lot of other branches of physics, going from QCD in heavy ion collisions to superconducting materials. So even if it would turn out in the end that the elementary particles are not little strings, string theory already had its victories, purely by its mathematical machinery, what it has thought us about physics and how we can use this in other branches of physics.



Caves ouvertes

Wednesday, May 29th, 2013


Since I’m new on Quantum Diaries, let me first introduce myself. I’m Rob, a Belgian Ph.D. student at CERN. Unlike most other physicists here, I am doing purely theoretical workthe kind of work for which one doesn’t need CERN’s Large Hadron Collider or any other equipment, except perhaps for its blackboards. 

 The nice thing about being a theoretical physicist at CERN is that the experimental guys are never too far away, so you are quickly updated on their latest discoveries. For us theorists, that knowledge is like heaven. 
As a theorist surrounded by experimentalists, I hope to be able to give a slightly different view on any discoveries. But until then, let’s talk about life around CERN and Geneva. When arriving in Geneva as a foreigner, it is quite difficult to understand and adapt to the city’s quietness when it comes to nightlife. With all bars closing at 2am and nightclubs being overly expensive, young expats need to be creative to have a good time (read: home parties).
Although it can be difficult to find out about them (since the Swiss seem to be horrible at advertising), there are a few events that make Geneva absolutely worth it. Young people at CERN seem to have armed themselves against the lack of advertisements by exchanging useful weekend information on Facebook groups such as Young@CERN. This way, Geneva’s most awesome events usually have quite a high percentage of cernies attending them.

For example this weekend, the little villages on the Swiss side behind CERN (Satigny, Russin, Dardagny, etc) had their ‘caves ouvertes’, or open (wine) cellars in English. Basically, you go to one of these villages around noon, buy an empty wine glass for 5 Swiss Francs, and then pass as many winemakers as possible who will let you taste all of their wines for free. 
Whether you are interested in tasting a certain winemaker’s pinot noir or merlot, or you just want to walk around the vineyards carrying a glass of wine, it usually is a Saturday afternoon well spent. 
Or perhaps, like me, you are just wondering about the effect of wine on your fellow physicists..

See you next year at the caves ouvertes!
Mainly cernies here

Mainly cernies here

Here as well.

Here as well.