I'm John Ellis. I am a theoretical physicist
What is my favourite theory?
I'm going to have to say... string theory.
 Of course the Standard Model is fantastic 
and that describes all the visible matter in the universe
but we need something else
There are lots of other puzzles  that we don't know the answers to
I think, eventually, we are going to want to make a quantum theory of gravity
and for that, I think, string theory is the only possible candidate
It is and incredibly beautiful, incredibly powerful theory and... That is my favourite.
If I could choose a superpower, what would it be?
I would just like to think more clearly...
Is it possible to erase a white/ blackboard without permission?
You bet!
Here in Switzerland, at CERN, if we want to preserve our blackboard or whiteboard
we have to write L.S.V.P. up in the corner. Otherwise, when you come back the following day
it may have disappeared...
Fortunately, the writing on my blackboard never seems to disappear
It just gets more and more layers of it as time goes on
What is my favourite animal?
Well... as you can tell from my pullover
the answer has to be a penguin
which is the name I used to describe a certain type of diagram a long, long time ago
What is my favourite particle?
That is an easy one! 
It has to be the Higgs boson
What have I learned working here?
I've learned to work with and appreciate people from many different countries
 who maybe think in many very different ways
and that, actually, help us do science together
If I was made of dark matter, how could I contact you?
That would be very very difficult
Well... one way I could contact you is by exchanging gravitational force
The evidence that we have for dark matter comes from its gravitational effects
so... perhaps I could figure it out a way of using those
But it maybe that dark matter has other forces, other interactions
which might be stronger than gravity
which would make the job easier
Although I still think it would be very very difficult
It's dark matter black? If not, why is it called dark?
Let me start with the second question, why is it called dark?
It's called dark because it doesn't emit any light that we can see
The only evidence we have for its existence is its gravitational effect 
It's possible that even though it doesn't emit light that we can see, or that we've seen so far,
it is possible that it might emit a very very small amount of light
So, it's possible that it might have other interactions
And we are looking for that in our experiments here at CERN and also in deep-underground laboratories
So... It might not be completely black but it certainly is dark
Broken symmetry or supersymmetry
You know... the universe would be a very boring place if symmetries were not broken
For example, we have weak interactions, which are responsible for forms of radioactivity
and we know that they are related, via symmetry, to electricity and magnetism
But, what would happen if that symmetry was not broken?
Then, radioactivity would be as important in the universe as light
and life would be impossible 
The universe would be completely different
I think we should be very very glad that symmetries are broken
What is supersymmetry?
Supersymmetry... that is a beautiful theory
that tries to relate particles that spin at different rates
I should explain...
All particles, except the Higgs boson, are rotating around an axis
They spin at different speeds
The electron spins relatively slowly, the photon, that also spins, but at a higher speed
We have theories that can relate different particles that spin at the same rate
For example, we relate the electron to the neutrino
but, supersymmetry is the only theory that we have that is capable of relating particles
that spin at different speeds
That is interesting in itself but, you can do all sorts of wonderful things, theoretically
Like... it could help us to understand why the Higgs boson has the weight, the mass that it does
It can help us to unify the fundamental interactions
It is an esencial ingredient in string theory
and, my favourite, it could also provide the dark matter that fills the universe
So... It's a wonderful theory
If only we could find some evidence for it...
Thank you very much for all your interesting questions
I hope you liked the answers
This is a fairly heavily trafficked corridor
