The second plank of evidence: nucleosynthesis

The second plank of evidence for the Big Bang model lies in the area of nucleosynthesis. In English, this means that the abundance of the elements seen in the universe at large matches what one would expect in a universe that began in a state that was almost infinitely hot and infinitely dense.

The great Russian theoretician George Gamow was one of the first to take Lemaitre’s prediction of an early universe the size of an atom seriously (see post below). However, Gamow went even further. A specialist in nuclear physics, he calculated that the temperatures in the early universe would have been too high for atoms to form. Instead, matter would have existed as elementary particles, only gradually forming atoms as the universe expanded and cooled in the first few minutes.

Applying simple mathematics to the expanding universe led to a surprising result – that the matter of our universe should be composed almost entirely of the simplest two elements, Hydrogen and Helium (specifically, about 75% H and about 25% He). This prediction turned out to be correct – all the other elements of the Periodic Table account for about 0.1% of the matter of the universe!

The irrepressible George Gamow

This was an impressive early victory for the Big Bang model – however, it failed to explain where the other elements came from (Gamow’s own belief that the other elements are also made in the Big Bang was soon shown to be false, as the universe cools too quickly). It was later shown that all the other elements are ‘cooked in the stars’.

Essentially, what happens is this: a young star burns Hydrogen as fuel, fusing it into Helium, a process that balances the intense inward gravitational force on the star. As the star ages, it runs out of fuel to burn, becomes denser and the temperature increases. Helium then fuses into Lithium, Lithium into the next element, and so on. This process continues right down to Iron. At this point, some stars lose the battle with gravity, turning into neutron stars or even black holes.

Others have a different fate. By a process of accretion of a nearby star, they go supernova -  a cataclsmic process at extreme temperatures during which all the heavy elements of the Periodic Table are fused in turn, and then all spat out in one great explosion…

And that’s where you and I, and all the little children and everything we see about us comes from….stardust!

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Note: an interesting sidenote is that the formation of carbon in the fusion chain of stars was long a stumbling block. The puzzle was eventually solved by the British astrophysicist Fred Hoyle, by postulating the existence of a new, unkown isotope of carbon. He badgered an American experimental group to look for this isotope and they soon found it. The riddle of the formation of heavier elements was solved….but Hoyle was to become a controversial figure despite this great success. He was bitterly opposed to the Big Bang model on philosophical grounds – as the evidence mounted, he concocted ever more convoluted alternative models, refusing to concede defeat right up until his death. More on this later…

Note 2: the above is a simplified version of Big Bang nucleosynthesis. In fact, traces of Lithium and Berellium were also formed in the Bang, you can read the details here

The first plank of evidence: Hubble’s law

This week, our 1st years finally get to the first plank of evidence for the Big Bang in their introductory course in cosmology. Having covered the work of Kepler, Galileo, Newton and Einstein, and the theoretical debate between Einstein’s static universe and Friedmann’s dynamic one, they have reached the point where it’s time to introduce the first piece of experimental evidence in modern cosmology – Hubble’s law.

As every schoolgirl knows, Hubble discovered that distant galaxies are moving away from us (or any other point) with a velocity that is proportional to their distance. This is the crux of the evidence for the expanding universe and a major piece of the evidence for the Big Bang.

The law arose from Hubble’s observation of distant galaxies and is usually written as

v = Hd

where v is the recessional velocity of a galaxy, d is the displacement of the galaxy from us and H is the Hubble ‘constant’, or the slope of the graph.

The velocity of a galaxy is measured as a Doppler redshift of the light it emits and is relatively easy to measure. However, the measurement of the distance of a given galaxy is trickier (it is done using stars known as Cepheid variables.). In fact, Hubble had a major systematic error in his distance calculations, an error that was not corrected for decades.

Hubble’s graph was an important advance, for it settled the debate between a static and expanding universe (leading Einstein to label his cosmological constant, introduced to the equations of GR to force a static universe, ‘his greatest blunder’). The graph also immediately hinted at a universe that might once have been very much smaller – perhaps even as small as an atom, as first suggested by the mathematician Georges Lemaitre. (To see this, trace your finger down the slope of the graph towards the origin). This is the model now known as the Big Bang model of the origin of the universe.

However, one problem with the new model immediately emerged. It is easily shown that the age of such a universe can be calculated as the inverse of the slope of the Hubble graph (1/H): unfortunately this calculation gave an answer that was far younger (not older) than the known age of some stars! This observation severely weakened the Big Bang hypothesis and it was only years later that it was discovered that the error lay in Hubble’s estimation of stellar distances (the x-axis). Nowadays, estimates of the age of the universe from updated and expanded Hubble graphs agree exactly with the age calculated from several independent phenomena.

Hubble’s graph contains many subtleties so here are a few other points:

1. Of course the galaxies aren’t really moving at all. General relativity predicts that it’s really space that’s expanding and the galaxies ride the wave.

2. A question arises when Hubble’s law is applied to one galaxy only – surely any object that has a velocity that is proportional to its displacement it must be accelerating? (since its displacement is changing). I wrote a post on this very question a while ago, and got some very interesting answers…see post on Hubble Puzzle

3. Not all galaxies are moving away from one another – for example, our nearest galaxy is approaching us, due to local gravitation effects. Woody Allen has a famous skit on this in the film ‘Annie Hall’, you can see the clip on YouTube here (thanks Dave!)

Off-piste or piste off?

Yesterday, I was travelling through the snow in beautiful Switzerland once more, returning from the ski resort of Verbier to Geneva airport. The snow was so heavy that some regional trains weren’t working for once, but the pragmatic Swiss laid on extra buses so tourists could make connections with the Intercity trains.

Travelling through Switzerland in the snow

It’s a tale of two holidays. I spent the weekend 13-16th in the lovely Swiss town of Martigny with the Frankfurt International Ski Club. We were bussed into Verbier for skiing every day, but as ever it was the social aspect of the club that stood out (see previous post below). It’s hard to beat staying in a posh hotel with thirty friends from Germany, Britain, the US and other countries, with multiple languages over dinner & drinks every evening. Best of all, the hotel bar happened to be the town hotspot, so we  got to meet plenty of the local Swiss French …

Tooling up before the downhill

The rest of the club returned to Frankfurt on Monday, while yours truly decamped to Verbier village (this week is the midterm holiday for teachers). What a contrast! Verbier is picture postcard pretty but almost entirely anglicised. A huge number of British tourists, and nothing but English spoken in the bars and restaurants. Quite a disappointing village socially, full of young Brits on the piss…

Choclate box -pretty Verbier village

On the other hand, the skiing was fabulous. The Ski Club of Great Britain have a ski rep in Verbier, a service that is very useful for dedicated skiers. Essentially, members are guided around the mountain by an advanced skier who knows the resort well, both in terms of challenging runs and where best to have lunch! It’s also a great way of meeting other skiers of the same level. All week, we got a superb tour of the mountain – plenty of difficult skiing, mostly slightly off-piste, but never too far from the main lifts and pistes…

The only snag was the day we took a tour with a mountain guide. As so often, the guide justified the expense by doing a bit more than we really needed (I sometimes think these guys are so incredibly fit they can’t relate to the rest of us). I’ll ski most things, but I get fed up trudging up steep ridges at high altitude with skis, transciever, probe and shovel on my back, gasping for oxygen at 3000m – all for a few minutes of deep powder. I just don’t have the fitness any more. Basically, I end up more piste off than off-piste!

All in all, it was a great trip in one of my favourite countries. Now it’s back to rainy, monolingual Ireland and endless meetings about cutbacks in college. Sigh. Maybe I should look for a job in CERN…

The human physics laboratory

Another great lecture at WIT this week was a public lecture on the physics of the human body. (The lecture was presented as the annual Tyndall lecture of the Institute of Physics and also as part of Engineering Week at WIT by CALMAST, see post below).

The lecture was given by Dr Kevin McGuigan, Senior Lecturer in physics at the Royal College of Surgeons of Ireland. Kevin is well-known for his successful research into the solar disinfection of drinking water, but he clearly has a second talent as a natural communicator of science.

The theme of the talk was that if you consider almost any important principle in physics, you will find a great example of its application in the human body. There were dozens of intriuging examples of this, here are just a few:

- Discussing friction, Kevin described the role of saliva in overcoming friction in indigestion. The students weren’t particularly interested until he gave a superb demonstration of the effect by getting two hapless volunteers to stuff themselves quickly with cream crackers without water!

- On Newton’s second law, the speaker explained the concept of impulse, showing clips of the effect on the neck/head of the driver of a car brought to rest from high speed, or struck from behind. He then explained the importance of both the crumple zone and air bags.

- A quick overview of the physics of rotational motion in liquids led to a discussion of the role of fluid in the ear. Kevin then gave a demonstration of the role of this liquid in balance by rotating a hapless volunteer in a chair 10 times!

The human laboratory: IoP Tyndall lecture

The speaker also discussed Bernouille’s equation, discussing what happens during an aneurysm as example. However, I suspect the students enjoyed another example of Bernouille’s equation most – ‘The physics of farts’. Here Kevin gave each member of the audience two sheets of paper and got them to observe what happens when you place them close to the mouth and blow (it behaves like a shutter opening and closing due to the difference in air pressure on the sides of each sheet). He then explained this as the same process that happens as  boys (only boys?)  attempt to release compressed air from their posteriors without making a sound, usually with a resulting brmmmmmpt!!

Another fine example was a demonstration of how sweat cools the body, using the latent heat of vapourization.

All in all, this was a super example of an outreach lecture that got a fantastic reception from a packed auditorium of students and schoolkids. I had to leave early, but I found myself frantically taking note of examples for next year’s 1st science class!

ESA Mission to Mars

This week is Engineering Week in Ireland and it got off to a great start at WIT with a talk on space exploration at the European Space Agency (ESA) by Micheal McKay, the Belfast-born engineer who has acted as Flight Operations Director for ESA lunar and Mars missions. (The seminar was presented by CALMAST, the Centre for the Advancement of Learning of Mathematics, Science and Technology at WIT, see here for other science/engineering events this week).

Dr McKay started with a superb outline of space exploration in general and of the work of the European Space Agency in particular. He put great emphasis on practical applications such as:

- the monitoring of the earth’s climate via the ESA ERS satellites:

- the forthcoming ESA Galileo GPS network, an independent European satellite telecommuncations network, vital for air traffic contol and for air/sea rescue:

- the SOHO mission, a study of the interaction of solar output with the earth’s magnetic field with the ESA SOHO satellite:

- observations of the most distant galaxies using Far Object Cameras mounted on ESA satellities:

- the study of the atmosphere of Venus using an ESA satellite, gathering vital information on the greenhouse effect and its implications for the earth.

One of the ESA’s earth-monitoring satellites

A schematic of the ESA’s Galileo GPS system

McKay then went on to talk about the ESA’s greatest success – the Mars Express Orbiter. He gave a superb overview of the information got from the orbiter, despite the loss of the Beagle II Lander. Indeed, McKay spent a good deal of time on the Mars mission, explaining carefully that it was the Mars Express that established the first firm evidence for substantial ice/water at the south pole. At this point, the speaker described two great examples of the sort of thinking-outside-the box engineering solutions  necessary in his  job  – the slow rotation of the Mars orbiter into sunlight to free up a jammed hinge on one of the antennae, and a software ’sunglasses’ patch to protect a sensitive detector from excess sun…both successfully completed from hundreds of millions of miles away!

The Mars Express Orbiter

McKay also spent some time explaining the next ESA Mars project, a  manned mission to Mars in 2030.  I won’t describe this part in detail, but you can find details of the Aurora mission here;

This ws a fine seminar and there were a few general themes  I liked a lot:

(i) ‘you too can do this’ – like so many at the top, the speaker continually emphasised to the students that they too had the potential for a great career in space exploration

(ii) the outstanding success of a relatively young European space agency (currently accounts for 40% of the global space market) and the fact that European citizens are not always aware of it

(iii) the spectacular benefits of European co-operation, and of the co-operation between ESA and NASA and other space agencies – nations seem to co-operate better in space than down here!

(iv) the importance of space exploration in its own terms for our knowlege of our universe, plus the beneficial spinoffs such as the ERS  earth observation missions

(v) the success of Ireland’s membership of ESA: not just in terms of commercial contracts gained, but the payback in terms of experience and knowledge brought back to Ireland, and the potential for fantastic careers in space exploration for the next generation of Irish science and engineering students

Interesting that many of these themes are precisely the advantages that I, and others, refer to as the potential benefits of Irish membership of CERN – see earlier post on CERN and Ireland.

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At question time, I asked the speaker the stock question – given the expense of building the space station necessary for manned expeditions to Mars, what can a manned mission discover that robotics cannot? He answered this in detail, carefully listing the problems of communication and contol of robots. It will be interesting to see what happens in the context of the current recession..

All in all, this was an inspiring seminar for our students given by a top expert in the field.  For me, the highlights were a music video showing the docking of the ESA vessel Columbus to the International Space Station, and the description of the solutions to engineering problems with the Mars Express orbiter – from a software patch to protect a detector from excess sun, to the rotation of the station into sunlight to free up a jammed hinge!

The first antimatter

Reading the post below on the spectrum of anti-hydrogen, it strikes me that I haven’t explained the concept of antimatter very well. AM has always been one of my favourite manifestations of the strange world of quantum physics (hence the blog title), so let’s have a proper post on it…

The idea of antimatter first emerged in 1928. In that year, Paul Dirac derived, from first principles of quantum theory, a wave equation for the electron that included the effects of special relativity. It was a stunning achievement and marked the beginning of modern quantum field theory. However, the Dirac equation had one very strange property – there were dual solutions for the equation, implying that positive and negative energy levels existed for the particle.

What was the physical meaning of a whole extra set of energies of opposite sign for the electron ? It couldn’t be that a repulsive electromagnetic force also existed, as the atom would fly apart. Dirac eventually decided that the only sensible answer was that the equation also described the energy of a particle of opposite sign to the electron.

This was an outlandish prediction of a brand new version of quantum theory and few scientists were convinced. However, in 1932 the experimentalist Carl Anderson discovered the decay track of an intriguing new particle in studies of cosmic rays – a particle that was of the same mass as the electron, but of opposite charge (the anti-electron or positron). It was a spectacular success for Dirac’s equation and marked a watershed in quantum theory. Long years later, other anti-particles were discovered in accelerator experiments, from the anti-proton to the anti-neutrino.

The discovery of the positron (1932): the particle was deflected by a magnetic field in the opposite direction to the electron, but was too light to be a proton

In the 1980s, accelerator physicists managed to create entire anti-atoms of hydrogen, by allowing positrons to be trapped by anti-protons. However, such ‘hot’ anti-atoms are hard to study and the next challenge was to create ‘cold’ anti-atoms so their properties could be studied in detail; this was achieved in the late 1990s.

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A fundamental problem

From the first, it was realised that antimatter and matter would annihilate on contact (from relativity), and this raised a new fundamental question in physics: Why do we live in a universe made almost entirely of matter? Why didn’t matter and anti-matter annihilate immediately after the Big Bang? This puzzle hints at a deep asymmetry in the decay of matter and antimatter and is known as the puzzle of baryogenesis, more on this later..