But where does the light come from? Super K is kept in complete darkness. The only light comes from charged particles travelling faster than light in the water.

Wait a minute.

Faster than the speed of light.

But I thought that nothing could travel faster than light.

This is true in empty space, a vacuum or air (which is a good approximation of empty space). Here light reaches the natural speed limit of the Universe, which we give the symbol c, equal to about 300,000 kilometres or 186,000 miles per second.

In water light is slowed down, so that it can actually only travel around 3/4 of the speed it does in air or empty space. This slowing of light can be seen in action by putting a straw in a glass of water or your favourite clear soda. You will notice that there seems to be kink in the straw where you go from the air to the liquid; this is because the speed of light, and therefore the fastest path for light to reach your eyes, is differnt in air and water. Because of this effect it is not against the laws of nature for use to produce thing travelling faster than light does in water, such as 0.8c (80% the speed of light in empty space).

When things with an electric charge (such as the electron which is being pumped around your computer or phone to power it right now) travels faster than light in water then we get a very interesting thing happens.

You may have heard of something called a sonic boom. This is a loud explosion of air that happens when anything travels faster than the speed of sound through air. Cutting it’s way through the sky, a jet fighter plane it is constantly pushing air out of it’s way at airs natural speed, the speed of sound. The problem comes as the jet reaches this same speed; the air cannot get out of the way of the plane fast enough and so begins to bunch up and build up in pressure (energy). As the plane crosses the sound barrier, and travels faster than the speed of sound in air, then this pressure (energy) build up is released as a huge explosion.

This “Sonic Boom” was the reason that Concorde, when flying it’s fast London/Paris to New York run, could only hit top speed when over the Atlantic. If it had done so over populated areas it would have wreaked havoc with windows below.

The same thing occurs when things with electric charge travel faster than light can. When I say a particle has a certain electric charge, take the negatively charged electron for example, all I am saying is that that something is constantly telling the world around it that “I exist and if you come in to contact with me you must treat me in this manner”. This information which is constantly streaming from anything with an electric charge tells other electrically charged things, as well as electric and magnetic fields, that if you come within the personal space then you should treat me like this: bend me this way in a magnetic field or repel me is you too have the same like charge.

Instead of air bunching up as it does with fighter jets it is this information, streaming out at the speed of light within water, that bunches up and builds up in energy (pressure). This energy is released as light, a visible (optical) version of the Sonic Boom. Instead of hearing it we see it, with our inverse light bulbs. This effect is called Cherenkov radiation.

The light comes out in a cone and casts great circles or rings on the side of Super K which can be recosntructed from the 1000′s of electronic eyes covering the walls.

Dr Ben Still

This vast space is filled with over 33 Olympic sized swimming pools worth (50,000 tonnes) of ultra pure water. The water is so pure in fact that if you were to put your hand in it you would lose all of the naturally occurring salts and oils in your skin leaving it bone dry. The reason for this is we require light to be able to travel the entire distance through the water to reach our electronics on the walls. Any impurities dissolved, like the stuff you see on the back of your bottle of mineral water, would scatter the light on it’s journey to the walls and reduce the amount we see.

So light from particles in this huge amount of ultra pure water enter our inverse light bulbs and is turned into electricity which we then channel to our computers to build up a picture of what is going on in Super K.

Dr Ben Still

Next Blog: Faster than light.

Once more to the boat, once more to the talk. Once more to tentative audiences hanging on my words, surprised and amazed with the booooum and the light. Once more I will miss my lunch, forget my hunger and push on through. Once more I will have the privilege to talk of ghosts, faster than light and the creation of it all.

Once more I will wear my white Tyvek suit. Come and join us before we are gone.

Dr Ben Still

We have had a brilliant team of volunteers helping us out and I would like to thank you all for your hard work, managing all the people visiting and joining in with boat and rope pulling duty. The photo attached to this blog was taken after our triumphant first day with just some of these volunteers alongside the scientists, technical crew and the design director Nelly.

I look forward to seeing and talking with many more people, answering questions and transporting them to Japan to talk about particle physics.

Dr Ben Still

From a girlfriend surprising their boyfriend to families on a day out, all seem enthralled by the sights, sounds, atmosphere and science of Super K Sonic Booooum. Wowed by the experience all seem to discover something new about the Universe in which they live. Maybe the fact that it is all made from just twelve building blocks or that light travels slower in water than in air. Whatever the message taken away I hope it raises questions, questions that were not there before.

Three more days and I hope many more questions and intrigued people to follow.

Dr Ben Still

Lunch time now and we have installed half of the balloons (PMTs) in the Super K Sonic Booooum tunnel! We string them together and then hang them on the wire support structure. We have a production chain Balloons – > Strings -> Tunnel and it is working like clock work, we hope to finish the tunnel by the end of the day.

It is looking so good and, as a famous particle physicist once sung, things can only get better.

Dr Ben Still

The water pool and boat rails were in place and the net tunnel constructed in three days of hard work and the technical talents of Andrea Salazar, Lee Jones and Hugo Sterk. After a quick video conference meeting I spent the rest of the afternoon with a group of brilliant volunteers who helped us blow up 800 balloons (PMTs ) today, thank you all!

The first 5 strands of balloons have been fixed to the net tunnel as the installation takes shape. We now wait on crucial supplies of tape before we continue with the hanging of the other balloons. Tomorrow promises to be very busy with 200 more balloons arriving and almost all 1000 to be strung and hung.

It is certainly a change to a day in the office programming at my desk.

Dr Ben Still

Jack, 23, London