Archive for category Science
50 years of the PS
Last month marked the first collisions in the largest man made particle physics experiment ever conducted, the LHC. In a remarkably short time, considering the drawbacks the experiment has suffered in the past, the LHC has gotten from very rough first collisions, to prolonged, stable beams and finishing up a few days ago with the highest energy collisions in any particle physics experiment to date.
This milestone comes just in time for the 50th birthday celebrations of another important particle accelerator; the Proton Synchrotron.
This machine was the first big circular particle accelerator at CERN, and was the beam source for such experiments as the Gargamelle bubble chamber, which first discovered neutral currents in the 70’s.
On the 3rd and 4th of this month at CERN, several Nobel Laureates arrived at CERN to reminisce about the success of the PS and the development of particle physics since. Many of the talks were focussed at discussing the experiments at the PS, SPS, LEP and then the LHC, with a few talks focussing mainly on theory.
The event was a fascinating insight into the minds of some of the greatest contributors to particle physics in the last half century. It definitely left me inspired.
As testament to the Proton Synchrotron’s success, it is still used as the second stage accelerator for the protons injected into the LHC today.
COLLISIONS!
Posted by Tom in Physics, Science, Technology on November 24th, 2009
So as you may well be aware, the LHC started up again this weekend after a good 14 months off.
September 10th last year was the date penned for the long overdue startup of the Large Hadron Collider – the worlds biggest (and best) particle accelerator. Unfortunately a problem with the cooling system caused a leak of liquid helium and a saftey mechanism called a quench kicked it. It basically ruined a few magnets so the whole thing had to be shut down to be fixed.
Well, it was fixed, and this weekend saw the grand reopening. On Friday evening, the various LHC control rooms were full of physicists and excitement as the beams were reinjected into the machine. First one way around, then the other. The plan, as us postgrads understood it, was that collisions (ie, two beams in the LHC going in opposite directions and brought to a focus at the detectors) were not due until early December.
Well, we were wrong. Today (the 23rd November), the LHC injected beam 1 into the LHC, then injected beam 2 and started ‘beam synchronization’. I don’t fully understand what that means, but I know that there was one bunch per beam (about a metre in length worth of protons), and my best guess at ‘beam synchronization’ is that the two bunches were brought close together.
Obviously the beams weren’t focussed and we weren’t running at anything close to design luminosity, but a few collisions occured in all 4 detectors. An exciting moment for everyone involved with the LHC, indeed.
The CERN Press Release of the weekend’s events and a summary of the collisions explains a bit further what the goings on were this weekend, and what the plans for the LHCs immediate future are.
The coming months should be an exciting time for particle physics, and the coming years will hopefully shed some light on the darker corners of the Standard Model and beyond…
Feynman Diagrams that look like animals
In Particle Physics, there is a special tool that is used to help understand, visualise and calculate certain aspects of a particle interaction. This is the Feynman Diagram.
A lot of Feynman Diagrams are fairly dull, monotonous affairs, essentially consisting of two particles scattering off each other, like so:
However, there are some Feynman Diagrams which can, with the help of a little imagination, be made more exciting!
Recently, I discovered that, if I stare too long at Feynman Diagrams, I start to see the diagram in a different way, much like how you can often see faces while staring at a plastered ceiling, or see shapes in the clouds.
I see animals in Feynman Diagrams.
Here’s a few to get you started.
Now, any High Energy Physicist will tell you that this has already been done, in the form of the Penguin Diagram.
Which, if you squint a bit, can look a bit like a penguin. (The animal, not the chocolate bar)
The Penguin Diagram originated when a bet between Physicists was made, the loser of which had to include the word ‘Penguin’ in their next paper. So it’s all a bit artificial really…
Next, the deer diagram. It’s fairly self explanatory, the gluon emitted by the up quark represents the antlers, the rest follows from that…
The fish diagram. This one takes a little bit of thinking, but not too much. Obviously the top quark pair production vertex is the ‘nose’ of the fish, the bottom and anti-bottom quarks are the main fins of the fish and the quark antiquark/lepton antilepton pairs are the tail fins.
The lobster. This one, I’ll admit, is a bit contrived. But bear with me. The quark antiquark/lepton antilepton pairs at the very right are obviously the claws. Where the quark and anti-bottom lines form a diamond with the top anti top pair is the head, the gluon is the body (albeit a very skinny body considering the size of the head), and the protons at the left are the tail.
Well, it’s either a lobster or Edward Scissorhands on his side with his arms upstretched…
Wow, COOL!
After the ’slight setback’ last year, that pushed the schedule back by about a year, the LHC is back to being one of the coolest places on Earth.
The magnets of the LHC, during operation, must be cooled to around 1.9 Kelvin, which is around -271.25 Celcius. COOL!
Now that the whole collider is cooled and the new quench system installed (a failsafe mechanism), the first beams can be brought back into the LHC.
At first, the energy of each proton beam will only be a fraction of their design intensity, around 450GeV.
The first collisions should happen in late November, followed by a step up in energy to a few TeV, where the next lot of collisions will happen. This is still less than half of the design intensity, but at this energy, there may still be some new physics to do. It breaks Tevatron’s record of the highest energy particle accelerator lab at least.
At the moment, it’s looking like the LHC will stay with collisions at this lower energy for quite some time, before the final push towards 7 TeV per beam.
After all, it broke once, why risk doing it again when you can get perfectly good data first!?
ANTLERS – A Note on parTicLE physics acRonymS
Since starting my PhD with the ATLAS project, I’ve learned about various acronyms used to name detectors, software, and other related projects in the particle physics community. A simple example would be LHC – Large Hadron Collider. Nothing funny going on there, it does exactly what it says on the tin. It collides hadrons (protons and lead ions in this case) and it is rather large.
Not all acronyms are quite as nice and to the point, however. I will list just a few of the more contrived ones (throughout, bold type is used to denote the letters used in the acronym).
Firstly ATLAS – A Toroidal LHC ApparatuS.
Since when did the final letters of a word count to appear in an acronym? Fair enough if you take the first two or three letters of a word, but taking the first and last letters. Come on! At least think of another word beginning with S!
Second, DEGREE – Dissemination and Exploitation of GRids in Earth sciencE.
Now we are just being stupid. Taking the last letter and not even the first letter. Of the word SCIENCE, no less.
GENIUS – Grid Enabled web eNvironment for site Independent User job Submission.
This one leaves whole words out. Important words like web and job. Which are pretty much the point of the environment. To submit jobs through the web… I can ALMOST forgive the use of ‘N for environment’, but not when you omit such crucial words!
BaBar – B-Bbar detector. Now this is just adding letters to make it sound like cartoon elephants!
Finally, ATLANTIS – ATLAS eveNT dISplay.
Do I need to say anymore?
In the world of High Energy Physics, there is definately a trend of ‘pick your acronym first’ going on. What words the represent is entirely arbitrary as long as the Acronym sounds nice. If the words have relevence to the project, it’s just a bonus.
HONOURABLE MENTIONS (for comedy value):
GIGGLE – GIGascale Global Location Engine.
LEMON – LHC Era MONitoring.
PASTA – Processors, memory, Architectures, STorage and TApes.
and for the Twin Peaks fans:
DIANE – DIstributed ANalysis Environment.
Derren Brown
Let us for a moment take a look at the explanations Derren Brown gave during his ‘how to win the lottery’ show. This is an issue that really bugged me since the show aired, and I thought I’d clear stuff up, purely as a rant on my part. Surely if you believed anything he said, you wouldn’t be on this page.
The experiment involving a group of people and apparatus involving equally spaced pins and plastic balls. The balls are dropped into the top and fall haphazardly to the bottom of the box, hitting several pins on the way and landing at a seemingly random place at the bottom. The experiment goes like this: the people in the room willed the balls to fall on a specific side of the chamber and, lo and behold, they did!
“Wow, how impressive!”, I hear you say. Well, not really. A coincidence, yes, but scientific proof of the psychic power of crowds, hardly. For one experiment to show one positive result means nothing, as any scientist knows. For the result to be significant, it must be repeatable. Nowhere did Derren Brown mention that the balls fell to that side of the box for 17 experiments out of 20 for example.
Even then I’d be dubious if there were no real theory to go with it and I’d just think that the box had some manufacturing flaw that caused the balls to prefer one side.
So, psychic power of crowds? No.
Next he tried to explain that he could predict the numbers by using the ‘wisdom of crowds’ method.
Ok, this is an interesting concept that suggests that many people taking an educated guess at some measurable but unknown quantity can estimate said quantity with surprising accuracy when everyones guess is averaged.
The key here being the educated guess at a measurable quantity. The lottery is an inherently random event and there is no way to predict in advance such a random event, where each ball has an equal probability to occur.
It is not the same thing as guessing the number of beans in a jar or the weight of an ox. The whole phenomena works on the premise that the quantities being guessed at can be successfully guessed by a single person.
This is not the same thing as winning the lottery, that’s just pure luck.
No matter what numbers come out of the ‘prediction’, they are still equally as likely to come out as another set of 6 numbers. That probability being 1 in 14 million, or thereabouts.
If there was anything special going on, it’s not ‘deep maths’, it’s some sort of psychic phenomena inherent in groups of around 24 people. Something which was completely overlooked by Derren.
In conclusion, Derren Brown is a clever man, a good illusionist and he successfully captivated many people into believing his trick. However, his ‘explanation’ of the trick was itself another trick and again fooled many people.
But please, let’s stop pretending that maths has some sort of special power to predict the lottery. There is no pattern. It is random.
And before anyone calls me a hypocrite for liking the movie Pi, at least that doesn’t pretend to be real. 
A bit of shameless scaremongering
The media loves to grab onto any new technology or experiment that has even the tiniest whiff of controversy about it and whip up some fanciful scare stories about how it will (not if, will) end the world and we all have to sign a petition and protest. Fair enough, with big experiments there is always going to be a small risk involved. The potential benefits to science and progress always far outweigh the potential risks, however, as if they didn’t the experiment just wouldn’t be feasible.
A recent example is the LHC. Everyone got into a huge panic shortly before the first beam last September when the idea came to light that a micro black hole might be formed. People immediately hear the words ‘black hole’ and ‘new experiment’ and ‘expensive’ and immediately assume a group of geurilla scientists are trying to take over the world. These people should not be allowed to leave the house.
The purpose of this post is not to address these trivial issues though. It is infact to address a much more serious and much more likely issue. That a nearby supernova will wipe out all life on Earth.
A supernova is what happens when a massive star begins to collapse under its own gravity, then, not being able to take the immense pressures and forces involved, suddenly begins rapid nuclear fusion and catastrophically explodes, expelling a vast amount of energy and leaving behind a neutron star or black hole.
One of the most famous supernovae is SN1987A, which is the first supernova to occur in 1987. It was highly luminous and even visible to the naked eye for a while. But even then, 1987A was a distant supernova.
A supernova closer to home, say, within a kiloparsec, has a high chance of ending a lot of life.
Some calculations:
Assumptions:
1. The stars in the Milky Way are spherically distributed.
2. The mass of the Milky Way is entirely composed of stellar objects.
3. All stars in the Milky Way are roughly as massive as the Sun.
Taking these assumptions into consideration, we will most likely come out with an underestimate of the stellar number density of the Milky Way, purely based on assumption number 1.
Mass of the Milky Way: ~ 6×10^11 Solar Masses (1.42×10^42 kg)
Radius of the Milky Way: ~ 50,000 Light Years (4.7×10^20 m)
Average Density of the Milky Way: ~ 3.2×10^-21 kg/m^3
Now assumption number 4, the stars are uniformly distributed throughout the Milky Way.
Density within a radius of 1kpc: ~4×10^38 kg
Stars within a radius of 1kpc (using assumptions 2 and 3): ~200,000,000
So if we make an underestimate that 1% of the stars in the Milky Way are large enough to produce enough energy in a supernova to kill us all, that makes close to 2 million high mass stars that are close enough to wipe out all life on Earth.
In fact, it’s been proposed that the reason for one of the mass extinctions in the Earth’s history was caused by a nearby supernova.
The reason we aren’t all kicking up a fuss about it? Well, for one, there’s absolutely nothing we can do about it. There’s no way to predict when a supernova will happen (aside from observe the stars for evidence of their evolutionary stage) and there’s definately no way to stop one. The second reason is that a supernova is a relatively rare event. The Milky Way has around 100 billion stars. The average rate of supernovae in our galaxy is around 5 per century. So the probability of a single star in the Milky Way going supernova is around 3×10^-14. This means that we can expect a nearby (within 1kpc) star to go supernova around once every 1,000,000 years.
A mass extinction caused by a nearby supernova has, literally, a one in a million chance of happening.
Stargazing
One of my favourite things to do on a clear night is stargaze. It is one of the most common aspects of our lives, yet never fails to be fascinating.
On any given night, given a good clear sky and a location free of too much light pollution, one can easily find the band of the Milky Way, stretching all the way across the sky, our neighbour galaxy Andromeda (or M31), various meteorites, Saturn, Jupiter, Mars, Venus (only around dusk/dawn), and of course the Moon. Occasionally it is even possible to see Mercury, although its postion as nearest planet to the Sun makes it only visible close to Sunrise/Sunset, and succeptible to being drowned out by the light of the Sun.
Observing the planets requires a favourable position in both our and the planets orbit, but a lot of the time at least one planet is visible.
Taking this fascination with the night sky further, one can observe with a telescope (or a good pair of binoculars). This then allows an observer to see even more objects, various star clusters and nebulae are faintly visible, but definately there.
The best thing to do if you get the chance to stargaze with an instrument is to study the Moon. The Lunar surface is riddled with impact craters and vast mountain ranges, many of which are clearly visible, even with a small pair of binoculars. Just scanning over the Lunar surface can make hours of fascinating observation time.
More distant than the moon, the planets offer another fantastic observation opportunity. Venus waxes and wanes as it goes along its orbit, the rings of Saturn are distinguishable, and even the four moons of Jupiter, Galileo’s very own observation, are visible.
Another thing which immensely fascinates me is Astrophotography. For this to be done best, it requires a good digital SLR camera with a long exposure on a nice clear night. I, however, lack this equipment, so am forced into taking pictures of the Moon. Still, some very good pictures can still be taken, showing the detail on the surface of the Moon.
Here’s a picture I took of the Moon with my telescope and a standard digital camera.
For better pictures, head over to Astronomy Picture of the Day.
It’s Official
I received my unconditional offer to study for my PhD in Particle Physics at the University of Birmingham today. In addition, I also found a place to live and put down the deposit so all that’s left to do is fill in the forms and collect my keys!
It all feels like it’s falling into place now and I am quite excited about the prospect of moving to Birmingham.
Hopefully while I’m there, I’ll be part of an amazing Physics project (ATLAS); meet plenty of new friends; have plenty of visits from old friends; make a lot of new music drawing from brand new inspirations; actually get somewhere with it…
The last point is probably a bit ambitious, but one can hope!
Ah, the Perseids
It’s that time of year again. The Perseids reach their peak and everyone goes meteor shower crazy.
I will admit, spotting a meteorite just as it ‘flashes’ is a pretty spectacular event and it never gets old. I was just hanging out of my bedroom window trying to spot a few myself.
Reaching a peak at around 22:20pm (on the 12th August) and then again at around 3:20am, with just over 1 meteor per minute, it’s pretty easy to find a few just by staring at the constellation Perseus.
I find it pretty fascinating where they come from.
Everyone has heard of comets, right?
Well, comets orbit the Sun, and in their wake they leave a trail of ice and rock. As Earth continues on its own orbit, it intercepts some of these trails at certain points of the year. The meteorite trails you see in the sky are formed when the icy part of the trail melts and the rocks burn up as they enter the atmosphere.
Now, the Perseids shower originates from the debris from the comet Swift-Tuttle. Not a very well known comet, but nevertheless it has a funny name…
A more famous comet associated with a popular meteor shower is Halley’s comet. This gives rise to the Orionid meteor shower, so called because the meteors radiate from the constellation Orion. This shower occurs around mid October, and is a bit dimmer than the Perseid shower, but is so much cooler because it’s Halley’s comet.
Even better than that, however, are the Taurids.
Caused by a lesser known comet, comet Encke, they also produce a relatively dim shower. However it occurs close to Hallowe’en, which earns it some cool points. The debris stream of the comet has also been disrupted by the gravity of larger planets, like Jupiter, into two distinct streams, which can be seen as the Northern Taurids and Southern Taurids.
Even bettter than that, though, is the possible claim the Taurids can make.
They may be the cause of the Star of Bethlehem.
Now, a quick disclaimer. This doesn’t have to assume that the Christian religion is correct, or that a ‘God’ even exists. Just that Jesus Christ was born around the time we all know…
With that out of the way, the Taurids have a periodicity. This means that it has a peak in activity roughly every 3000 years. Astronomers have estimated that the next peak in activity will occur around 3000AD. Which makes the previous peak around 0AD. Jesus’ Birthday.
This is a kind of nice thought, and it has Astronomical credability, although a more likely scenario would be the triple conjunction of Jupiter and Saturn that also occured at that time. That event can also be placed at that time with a bit more accuracy.
The conjunction of two planets means that they ‘overlap’ each other on the sky. Now, they may not exactly overlap, and the light from the planets will add together to make a particularly bright point of light. If this happened around that time, it would have definately seemed like a ‘divine message’, it’s not everyday that you see a bright light appear in the sky three times in a row…
But then, this is all moot as we then have to assume that three ‘wise’ men would follow a strange bright star on a whim and that it would lead them to a newborn child in a barn…
Make of the mythology what you will, but the astronomy stands up 
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