Science -- Your Future, Scotland's Future
SCI-FUN's Christmas Card
Amazing Facts
Click here to read more about the amazing facts on the card, and to find out whether or not you guessed the answers to the questions. (If you tried, of course :-)
Amazing Facts
Did you work out what each of the "snowflakes" represented? Click here to get the answers...
Scientific "Snowflakes"
Holly and Berries #1
The images on the top-left of the page are the particle physics decorations: the berries are a collection of subatomic particles, and the 'holly' is represented by a variety of particle collisions and decays (see later).
Note: many of the links on this page are to articles in the Wikipedia, the free online encylopaedia, a collective net enterprise. Wikipedia has many excellent articles, carefully written, with extensive links to other sites. (As a barely-controlled anarchy, however, it's not without its quirks, which tend to show up in controversial subject areas.)
The proton and neutron are the constituent parts of all atomic nuclei in the universe. Until the middle of the last century it was believed that they were fundamental particles (although it was known that free neutrons decayed into a proton and electron), but gradually we began to suspect that there was an underlying structure to these (and many other) particles.

Current models suppose that the proton and neutron are made up of three quarks, which come in a variety of different types, as illustrated in the diagrams below. [The Wikipedia articles on quarks and particles are worth reading.] A third particle is shown: a pi meson (or pion), one of the products of the collision of cosmic rays with the atmosphere. (See below.)

The Proton
The Neutron
The positive Pi meson
The Proton:
up up down
The Neutron:
up down down
A pion (π+):
up anti-down
It's now suspected that the proton may not be completely stable, although current estimates are that it takes on average over 1032 years for a proton to decay, which is about 10,000,000,000,000,000,000,000 times longer than the lifetime of the universe...

(Interestingly, we can be sure that the proton's lifetime has to be greater than 1017 years: you have around 1027 protons in your body, and if the proton lifetime were this short you'd be highly radioactive...)

A watch dial painter in the early twentieth century (when radium-based paints were used for glowing numerals, and the painters licked the brushes to point the tips) turned out to be so radioactive through ingestion of radium that doctors were able to expose a radiograph of her body on film using only her own radioactivity, and her breath caused phosphor screens to glow brightly... (She didn't survive for long, in the company of many of her co-workers.)

Holly 1 – The Higgs Boson

The Higgs boson is the particle which (if it exists) gives other particles their mass, and whose existence was predicted by Professor Peter Higgs, formerly of Edinburgh University. The Higgs boson has not been experimentally confirmed... yet.

Creating a Higgs boson in the LHC
The image opposite (one of the sprigs of physics holly) is a Feynman diagram, a graphical method of describing the ways in which particles are created, interact, and decay. The diagram shows one of the ways in which a Higgs boson may be created in CERN's Large Hadron Collider (LHC), due to begin operation in 2007.

A brief (and somewhat clumsy :-) description.

[The following should be read with an accompanying soundtrack of creaking thin ice...]

When two protons from the opposing LHC streams are forced to pass close enough to each other (the protons effectively collide and overlap), an interaction takes place between the constituent parts of each particle.

In particular, two gluons (the carriers of the colour force, which binds the quarks tightly together inside the proton), represented by the spring symbols above, interact by fusing, creating a temporary virtual fermion loop, in which a top quark (the heaviest of six quark types) can be thought of as circling around the trianglular path. We never detect the quark directly: it's an intermediate state in the production of the Higgs particle.

We can think of the arrow for the anti-top quark as being a top quark pointing in the other direction, so that the loop could be redrawn to show a t in anti-clockwise circulation (created out of the energy of the gluon fusion). Writing the anti-top as above does, however, make it clearer (!!) that the virtual loop ceases with the production of a neutral Higgs boson, by the annihilation of the top and anti-top quarks, the resulting energy being great enough to cause the boson to be created, which itself then rapidly decays.

It's the decay products of the boson that we will look for in the collision data from the CMS and ATLAS experiments at CERN.

The PP4SS page will soon have more information and images from our recent trip to CERN, where we visited some of the LHC experiments, currently under construction.

Holly 2 – A Shower of Muons
A cosmic ray shower
The downward-pointing holly branch is based upon the picture shown opposite, illustrating the shower of particles produced when an energetic object from space (a high-energy proton or atomic nucleus, for example – loosely called a cosmic ray) strikes atoms in the upper atmosphere, and causes the production of a variety of different particles.

Some of the end-product particles are muons, which can be detected at sea-level, thanks to Einstein's Special Relativity theory, and the bizarre behaviour of objects travelling near the speed of light. Our PP4SS page will include a full description of this property, in our "muon lifetime" experiment... (more soon).

(Note: the π symbols in the diagram refer to pions, one of which (the π+) is one of the 'berries' above.

As you read this sentence, products of cosmic ray showers such as this are sleeting through your body, occasionally causing bits of cell damage, which are (mostly) repaired.

Find out more about the particle physics exhibits currently being designed by SCI-FUN at the following page:
PP4SS page: particle physics for scottish schools.
PP4SS: particle physics for scottish schools.
Holly and Berries #2
Magnetic holly
The magnetic holly leaf is produced by sprinkling iron filings around a carefully chosen series of magnets, with their poles pointing in opposite directions around the 'leaf'. The filings tend to orient themselves along the field lines, which can be thought of as extending out from the north pole of each magnet, terminating at a south pole. In the case of the pattern chosen, field lines arc between each pole. (And we only sprinkle filings at the 'right' places, of course!)

Click here to visit a web page with a fascinating Java applet *, which simulates in real time the interactions of magnetic and electric fields, and allows you to generate the holly pattern. Click on the image opposite to see one attempt to produce the field shape, using the program.

* The applet was written by Paul Falstad, a software developer in California. He has lots of other interesting science applets (and links to other pages) at his main website,

Question 1: I used many more magnets than necessary to produce the holly pattern. Can you work out how to make almost exactly the same pattern (with the same number of spikes, for example), but with far fewer magnets?
The Geomagnetic Field
The Earth's magnetic field
One of the 'berries' shows the Earth with its magnetic field, as a giant compass (opposite). We don't fully understand the ways in which the field is generated, but we know that the magnetohydrodynamic * properties of the liquid iron outer core are where the field is created and sustained.

Any mechanism for the field has to take into account its periodic reversals over time. More accurately, the dipole (bar-magnet) component dies away, leaving the non-dipole field (the wibbly-wobbly high-order spherical-harmonic type bits), then grows again with the opposite polarity. (What was North is now South...)

[Open University kipper tie mode ON:]
Best theories involve a self-exciting dynamo in the liquid outer core, thermally driven by core boundary iron crystallisation. (The self-exciting dynamo has the property that it can generate a field of either polarity for the same direction of spin, and coupled dynamos can also exhibit spontaneous field reversals.)
[Open University kipper tie mode OFF:]

And what happens when the field reverses? Execrable films such as The Core notwithstanding, the disappearance of the main dipole field won't lead to the end of the world. (There's no evidence that reversals are connected with previous extinctions, since the non-dipole field would still keep most external particles away, although a chaotic period of time would ensue (and some aspects of human society would be altered). Anyway, there are a few thousand years to go, at least...)

* "magnetohydrodynamics" is actually a word. (I was accused of making it up...) It's the study of fluids which carry a current (and can therefore sustain a magnetic field).

Question 2: If a compass points its North end towards the Earth's 'North' pole, what does this tell us about the polarity of the pole at the, er, North pole? (Don't confuse this North pole with the North pole where Santa used to be supposed to live; it's a different North pole. (Santa lives in Lapland now, where the post is better.))
Saturn and Titan
Looking for life on Titan
The other two berries are the planet Saturn and one of the most recent images of its large moon Titan's surface, taken during the first pass of the Cassini/Huygens spacecraft, currently orbiting the Saturnian system.

The Huygens probe was successfully detached from Cassini, and parachuted down to a safe landing on January 14th 2005! Click here to go to the ESA site, to see some of the extraordinary images returned by the spacecraft. during its descent and landing. An outstanding European success, and a wonderful example of scientific collaboration.

Running out of inspiration (and time), I eventually found a picture of a real Holly leaf. Er, and that's about it... apart from a tiny factoid: holly wood is particularly dense, with a compact texture. It's often stained black and used as a substitute for ebony when making black piano keys.

Remember to check out the Amazing Facts and "Snowflakes" pages