Ciamar a tha thu?

In honour of languages day, here's another highlight of my trip to Scotland. This village is the only place in the UK to have a chemical element named after it - strontium. The element was discovered nearby about 200 years ago. It is of interest to physicists because the fallout from nuclear explosions contains a lot of the radioactive isotope strontium-90. This is a problem because the body prefers to take this in place of calcium for bones. It has a half life of about 28 years so it's not good for health. It was a major problem after the Chernobyl accident.

All place names in the Highlands are anglicised versions of Gaelic names. I've been trying to learn to pronounce Gaelic. The title of this piece means "How are you?" You can reply "Tha gu math, tapadh leat" - Fine thank you.

Why do some physicists get really annoyed about string theory?

Last week my network had some bitter emails on from physics teachers complaining about string theory. What makes them so angry?

String theory comes from this idea: If a room has 3-dimensions, a flat piece of paper has two dimensions and a line has one dimension, then a point (a spot) will have no dimensions. This makes the maths difficult when we start dealing with atoms and other particles, which are modelled as being points. Inverse proportionality doesn't work because 1/0 comes out as infinity. In black hole, the problem is called a singularity.

So someone suggested that if we said that particles were really one-dimensional vibrating strings, then it would all be all right (except that it would mean that the Universe would be in 11-dimensions). This is all good except that for a theory to be accepted in physics, it has to make predictions that can be tested by experiment. This is difficult for string theory. My email correspondents are angry because a lot of research money is spent on string theory and yet it might not even be real physics. However, some of the greatest brains in modern physics are on board. One of them, Brian Greene, wrote an excellent book on string theory. It's in the school library.

Why is the sky blue?

When rays from The Sun enter the atmosphere, the light is a mixture of all the colours of the spectrum. Particles in the air scatter certain colours sideways. The smaller the wavelength, the greater the scattering, so blue is scattered most. Having been knocked sideways, it is this light that gives the sky its colour.

At sunset, when the light comes in at an angle, the light has to pass more particles to reach us. Thus more colours are scattered, leaving orange and red to reach us.

I did an experiment to show this using a projector and a bowl of milk. I introduced milk in small amounts to represent the scattering particles. The photograph shows what happened.

The search for a sun dog

What you're looking at in these two photographs is the layer of thin, high cloud. It's called cirrus if it is small, wispy cloud, and cirrostratus if it coalesces to form a layer.

At certain times, you can get a circular rainbow around The Sun as its light is refracted through ice particles in these high clouds. Sometimes you get part of it like an upside down rainbow. I'll put a newspaper photo of this up on the wall in C11.

However, sometimes, the effect is so intense that you get two fake suns, one on each side of The Sun. These are called sun dogs. I've never seen one but it is supposed to happen up to once a week in these lattitudes. Apparently the best conditions are when The Sun is low in the sky. The hunt is on.

Go to http://en.wikipedia.org/wiki/Sun_dog for details and photos.

The book has arrived!

Sustainable Energy: Without the hot air by David J C MacKay is now in the school library. You really ought to read it!

See earlier post for why this book is so important.

A kid asked a question at Jodrell Bank

I was stood looking through the fence at the telescope when a child turned up with his dad. He asked his dad "How do they make it turn round?". His dad said "It's got wheels." The child said "I can see that, but how do they get the wheels to turn on something so heavy?"

My problem as a physicist is that I take to many things forgranted. I hadn't thought about the technical problem of producing a mechanism to turn such a heavy piece of equipment. It's obvious that it turns, because it does! I tend to get stuck in "It's like that, and that's the way it is" thinking. The best physics don't ignore it because it works. They ask howit works and why it works.

Jodrell Bank

In August, we went to Jodrell Bank. It is a radio telescope connected to Manchester University. If you are headed south on the M6, it is worth a visit - about 5 miles off the motorway just past Manchester. It only cost £2 to get in. There's a lot to see, but I'd advise a nice day because a lot of it is outside.

The idea is that stars produce waves across the whole electromagnetic spectrum, and that what we can actually see is only the tip of the ice berg. Many types of electromagnetic wave cannot get through the atmosphere, but radio waves can.

The opportunity to work at Jodrell Bank would be a good reason to look at physics at Manchester University.

You can read more about their research at http://www.jodrellbank.manchester.ac.uk/research/

You must read this book

It sounds boring, but Sustainable Energy: Without the Hot Air by David J C MacKay is a must-read. In it, he assesses various possible futures for energy supply in the UK after fossil fuels have finished. The key thing that makes this book stand out is that he uses simple methods to calculate the available energy resources in each sector.

So whether you think nuclear or wind is the future, he comes up with the numbers.

He is a Professor in the Physics Department at Cambridge University. He tries not to state his preferred future option, but I think you may detect slight bias in places!

I ordered a copy from Wigton Library (they had to get a copy sent up from Kendal!) but it will be in the school library soon. However, if you want it for free, you can download it from www.withouthotair.com

It will make you a better physicist.

Schiehallion

The other important sighting from the top of Ben Nevis was a cone shaped mountain to the south east called Schiehallion. In some ways, it is the holy mountain of physics.

In 1774, the Astronomer Royal Nevil Maskelyne travelled to Scotland and used Schiehallion in an experiment to find the mass of the Earth.

What he did was to hang a pendulum. The Earth attracts the pendulum downwards but the mountain attracts the pendulum sideways.

By measuring the angle of dangle, he was able to use Newton's Law of Gravitation to calculate the mass of the Earth, providing he knew the mass of the mountain.

That's why he chose Schiehallion. As you can see, it has a very regular shape meaning its volume is easily calculated. It is isolated so other mountains have little effect. Using the density of the rocks and the volume, he could calculate the mass.

My two unanswered questions are these:

• The angle of dangle was very small, much less than a degree. How did he measure it?


• How did he know which direction was vertical? You usually hang a pendulum (plumb line) to work that out.