Friday, June 18, 2010

Six Minutes to Midnight - Part 3

Enhanced Greenhouse Effect

So as described in the previous section the greenhouse cycle is a finely balanced mechanism for the transfer of heat from the sun to the atmosphere and the ground here on Earth. What effect, if any, does human activity have on this cycle?

In the debate of climate change the key issue is whether human activity, such as the burning of fossil fuels which adds to the greenhouse gases, enhances this greenhouse effect. The effect of greenhouse gases is clearly understood but what is not understood is what affect adding to these gases will have on the climate. Will the climate act in a linear fashion or is there a threshold limit where we can trigger a runaway greenhouse effect?

There is clear evidence that industrial activity has added considerably to the concentration of greenhouse gases in our atmosphere.  The main change in these gases is the amount of carbon dioxide; current estimates put it at a 40% increase over the natural level since the pre-industrial era.

There is also the consideration of the feedback effect. An increase in global temperatures due to carbon dioxide increases ocean temperature, which in turn increases surface evaporation. This increase in evaporation leads to more water vapour which itself increases temperatures. This is an example of a positive feedback. These feedback effects can come in two forms:
  •   Positive feedback – drives global warming
  •   Negative feedback – reduces global temperatures

This makes the prediction of the average global temperature trend very difficult. To help illustrate this problem let’s take three simple scenarios:
  •  No change
  •  Double carbon dioxide levels
  • Double carbon dioxide + feedback effects

In the no change scenario the amount of solar energy incoming is balanced by the amount radiated back into space global average temperature remains at 15 oC.  If we double just the carbon dioxide we expect a global increase in the region of 1.2 oC. Now, using the same scenario, we add in the possible feedbacks and their net effect, causing an estimated increase of over 3 oC above the global average. This last scenario should cause great concern. A change such as this can lead to large scale changes to the environment and climate mechanics.

What is not clear from all the current climate models is whether we are reaching a tipping point or have we already passed it. The question of what is the lifetime of the current levels of the greenhouse gases in our atmosphere are, is one of the most important points of debate currently.  If we were to stop right now putting excess greenhouse gases into the atmosphere, how long would recovery take? The short answer is we don’t know. There are many feedback mechanisms in affect here, some of which we don’t fully understand and others which may be about to enter the fray.

The one undeniable fact is that carbon dioxide is very much linked with global temperatures; this link will be further explored in the next section where we return to ancient climates and see how changes in greenhouse gases are linked to changes in the climate. 

Past Climates

There is very clear evidence that the average global temperature has seen a rising trend over the last 100 years as the figure below illustrates.

Figure 3

Figure 3 represents the changes in average global temperature over the preceding 130 years. The zero on the scale represents the average temperature over the period of 1961-1990. There is a very obvious trend in the data presented here. However, as any good scientist knows, data can be misleading unless it is put in proper context. A good argument against such a set of data could be that we just may be in a current natural warming period. To counter such an argument, it is necessary to look at the climate over a far greater scale; to see the current climate in terms of a geological time scale.

To look back at previous climates in the time period of tens of thousands of years ago we can’t rely on direct measures like we have for the data in figure 3. A valuable source of evidence for past climates is the record which has being maintained by the ice. The ice which resides in Greenland and Antarctica provides scientists with a snapshot of previous climates. As the snow fell it trapped within it small pockets of air. As more snow fell it compacted into ice, and as more layers of ice were added it became compacted and formed ice sheets kilometres thick. Ice cores drilled into these ice sheets can reveal past climates. In one such recent ice core sample, data dating back almost 500,000 years was recovered. From the air trapped in these cores, scientists are able to extrapolate the carbon dioxide concentrations in the past climate. Also, from the isotopes of hydrogen and oxygen present, an estimate for the temperature can be calculated. These isotopes are very sensitive to small changes in temperature so can be used as a valid indicator of past global temperatures. 

Figure 4

As can be seen in figure 4, there is a very good correlation between carbon dioxide levels and temperatures in Antarctica. From the data the first obvious thing which pops out is the cyclic nature of the graph. There is a major cooling trend which appears to have a period of about 100,000 years. To account for this variation we have look beyond the terrestrial and examine our place in the solar system and more specifically our orbit around the sun.

The Earth’s orbit is elliptical by nature and this orbit varies periodically every 100,000 years. This variation manifests itself in the eccentricity of the orbit. The eccentricity of the orbit relates to the ratio of the maximum orbital distance compared to the minimum.  This precession of the orbit can account for this variation in the data. We can be quite confident in this proclamation, as we can be almost certain that the average solar radiation over this period was more or less constant. 



There are of course other disturbances in the data which we can also attribute to other periodic changes in the Earth’s orbit (see figure 5). The Earth's axis of rotation is tilted with respect to its orbital axis. This angle of tilt varies periodically at a rate of 41,000 years. This cyclic event can be seen in the data as a perturbation in between the major peaks.  There is also a smaller periodic shift in the Earth’s closest approach to the Sun (perihelion), the period of this event is about 23,000 years. 

Figure 5


All of these changes in axis orientation does not vary the amount of solar radiation incident on the Earth, but rather changes its distribution. For example, if the Earth’s Polar Regions are tilted further away from the Sun's rays, we can potentially enter an ice age, whereas if the Polar Regions are tilted towards the Sun, we enter a period of increased global temperatures. This effect is due to the seasonal variation we get. For example if the poles are tilted further away than the norm, the winter ice formed can spread much further south than normal. This further extension of the ice sheet can reduce global temperatures; the ice reflects more of the incoming rays so further reduces global temperatures.  This is an example of a feedback effect. This connection and subsequent theory relating to this phenomenon was developed by Yugoslavian climatologist Milutin Milankovitch in 1920.

An obvious question to ask now is: If we do enter an ice age what causes it to end? The natural cycles of the precession of Earth’s axis alone cannot undo a potential massive ice age. The Earth experiences smaller ice ages but these can be overcome as the Earth warms due to the natural cycle. As mentioned earlier ice is a very good reflector so even with the poles tilted towards the sun the incoming rays would increase melting by only a small amount. To find an answer to this almost paradoxical question we must again return to the greenhouse gases. As written earlier these gases act as a blanket around Earth. But the question arises where do these gases originate from?

These gases have a variety of sources such as; the animal life which continually takes in oxygen and breaths out carbon dioxide and the death of vegetation which releases carbon dioxide into the atmosphere, but these contributions are very small and do not account for the gas we see.  The Earth is highly geologically active with several active volcanoes at any one time. These volcanoes emit large quantities of these greenhouse gases and aerosols into the upper atmosphere.

A recent eruption in June 1991 of Mount Pinatubo released vast quantities of sulphur dioxide into the air, which in turn triggered a worldwide global cooling of about 0.5 K. This eruption did indeed cause a global cooling but under the right circumstances it can have the opposite effect. Such an event was believed to be the factor in bringing the Earth out of a major ice age which occurred around 700 million years ago. This ice age is referred to as the “Snowball Earth” theory, a paper first published in 1992 by Joseph Kirschvink. In his paper he was analysing the biology of this time period (Proterozoic Era). There was a mass extinction of the world’s species at this time and data from the geological recordings hinted that there was extensive ice covering the Earth’s surface which extended to the Equator.

The trigger for this event is unclear, it could be the culmination of the perturbation of the Earth axis relative to its orbit and a lower than normal concentration of natural greenhouse gases in the atmosphere. As the ice gathered it would reflect more sun light back and as a result we had a runaway cooling affect. So what triggered our release from this icy tomb?

It is believed that a major volcanic eruption triggered a series of events which released us from this icy tomb. The volcano that erupted released vast amounts of carbon dioxide and other greenhouse gases into the air. This massive release blanketed Earth and in doing so greatly increased the heat retention of the Earth. This in turn heated up the atmosphere which started to melt the ice sheets and liberated vast quantities of water. This water was loaded with rich nutrients which triggered a massive growth in the algae present in the world’s ocean at that time. This algae, which was now free to flourish at an unprecedented scale, released oxygen which aided new life and vegetation to grow. This positive feedback pulled the Earth from this ice age.

So as we can see there is a natural cycle of ice ages and warming periods which can happen in extremes. Understanding these past climates can help us understand how changes in greenhouse gases can effect climate change.

As can be seen in figure 4 there have also been eras where the global temperatures have been higher than they are now but what should be noted is the levels of carbon dioxide present as those times and compare those levels to what we have now. In the last interglacial period about 125,000 years ago global temperature were about 3-4 K higher than averages now but the carbon dioxide concentration was less than 300 parts per million (ppm), todays figure is about 385 ppm.

This figure should be a very worrying value. This value is outside the range of previous records so we have no recorded levels to compare this value to. This makes any prediction about future global climate trends very difficult to make. We could potentially see a runway greenhouse effect which could have drastic consequences for not only our civilisation but all life.

A possible indicator of what may happen is to look beyond our planet and out into the rest of the solar system. Our two neighbours are our best indicators of possible futures, both Venus and Mars have atmospheres which display similar greenhouse effects.

Our nearest neighbour Venus which is similar in size to the Earth has a thick atmosphere rich in carbon dioxide which accounts for about 96% of its composition. Its atmosphere is almost completely opaque to an observer on its surface. This thick blanket absorbs and retains far more heat than our own atmosphere. This thick atmosphere results in Venus having a surface temperature in excess of 500 oC. This high temperature means that water could never have existed as it does here on Earth. Water plays a key role in acting as a moderator, it has the ability to act as a sink for carbon dioxide and so can absorb excess carbon dioxide.

Mars is the polar opposite to Venus, Mars has a similar atmospheric composition but its atmosphere is far less thick. Due to its distance from the Sun it receives far less solar radiation and due to its thin atmosphere it retains far less heat. This means although Mars has a greenhouse effect in operation it can’t retain enough heat for the surface temperature to allow liquid water. This may not have been the case in its geological past; Mars lacks a magnetic shield such as the one which protects the Earth from the harsh solar wind. Mars’ core is no longer active so no magnetosphere is created, without this protection the solar wind can strip away gas from the planet. So with this lower temperature water could exist so it could help halt any over powering effects of the greenhouse cycle.  

Figure 6

From figure 6 we can see how water can act as a moderator of global temperatures. Venus was too hot so its greenhouse effect entered what is referred to as a runaway state. This is not possible on the Earth. While on Mars the greenhouse is halted as water can exist in its solid form ice. We are highly fortunate on the Earth that we habit a zone in the solar system where water can exist in a liquid form. This enables the Earth to enjoy a temperature climate which is favourable to the formation of complex life forms.


Thursday, May 27, 2010

Six Minutes to Midnight - Part 2

Natural Greenhouse Effect

For mankind to inhabit this planet a stable temperature is required. The Earth’s atmosphere provides a mechanism which helps regulate this temperature, called the greenhouse effect. In essence there must be a balance between the heat that we get from the sun and the heat we radiate back into space.

The sun emits electromagnetic radiation across a range of wavelengths, the most obvious to us here on Earth is the visible spectrum that makes up all that we see. Of the EM radiation which arrives to Earth, we are bathed in the visible spectrum and the ultra violet spectrum. Of all the energy that reaches Earth, one third is reflected back into space. This reflection is due to the sun rays reflecting off of clouds and aerosols in the atmosphere and the ice sheets which cover the polar and higher elevation regions around the Earth. The remainder of this incident radiation is absorbed by gases in the atmosphere or by the surface.

The gases which absorb this radiation play a key role in this greenhouse effect; hence we refer to them as greenhouse gases. The most common of these gases are water vapour, carbon dioxide, methane, ozone, sulphur dioxide and nitrous oxide. A point I wish to clear up here before I continue is the common misnomer in both the media and many scientific publications: the term "carbon emissions". This term is widely banded about in discussions on climate mechanics, it of course refers to all the greenhouse gases not just the carbon based ones. The greenhouse gases absorb some of this solar radiation and as a result heat up, they then re-emit this heat as a longer wavelength em radiation which we know as infra-red radiation. These gases act as a blanket and keep the temperature of the Earth about 33 K higher than it would otherwise be.

Figure 1


The remainder of the solar energy on the Earth is used to evaporate water which in turn drives the cloud system. The heat released provides thermal differences which support the winds which aids the transportation of heat around the globe. This system is summarized in figure 1. This natural cycle is very finely balanced. Too little heat absorbed and we get a global cooling and too little radiated back into space we get a global warming.

This cycle which we call the natural greenhouse effect was first theorized by a French mathematician Jean-Baptiste Fourier. He compared how a greenhouse acted similarly to how the Earth maintains its temperature. In a greenhouse, the glass allows the light from the sun to pass unimpeded. This light is in turn absorbed by the plants which re-emit this light as heat. The glass acts as a barrier to this heat and it becomes trapped, heating up the greenhouse. In essence the glass plays the same role as the gases in our atmosphere.

You may now be asking the question what is so important about these gases that make them so important to this cycle. The atmosphere is made up of several different gases in various concentrations, the most abundant of these is nitrogen followed by oxygen. These two gases alone account for almost 99% of the atmosphere. In the remaining 1% of the atmospheric gases, the greenhouse gases can be found. What differentiates these greenhouse gases from the main atmospheric gases? The simple answer is oxygen and nitrogen are monatomic gases and as such their bonding structure does not vibrate with incident infrared radiation so they don’t readily absorb heat. However the greenhouse gases are a combination of two elements and the bonding structure in these configurations absorb infrared radiation easily. This phenomenon was known since the mid 1800’s due to the work of Irish physicist John Tyndall. From Tyndall’s experiment he was able to deduce the mechanism for why the Earth is able to maintain its temperature. The absorption characteristics of these gases are key to understanding the mechanism of the greenhouse effect.


  
Figure 2     

In the above diagram it shows the absorption of em radiation at certain wavelengths for the following gases, oxygen + ozone, carbon dioxide and water vapour. As can be seen from figure 2 oxygen/ozone is a very strong absorber in the ultra violet and a very narrow band in the infrared range. The key feature to pick up from this figure is the absorption of infrared radiation in water vapour and carbon dioxide. 

Six Minutes to Midnight - Part 1

"Don’t go around saying the world owes you a living.
The world owes you nothing. It was here first”
-  Mark Twain

Prologue

The issue of global warming is a topic which has invaded the consciousness of people all around the world. As a species we have faced many threats to our way of life such as disease, famine and war. Global warming now takes its place in this category.
Since 1947 a symbolic clock has been maintained, it represents the level of imminent threat to human civilisation. It was originally intended to reflect the threat of nuclear arms build-up and the cold war standoff between the two world superpowers of USA and the Soviet Union. The distance the clock was to midnight represented this threat. Throughout the intervening years since its inception it has moved closer or further away to reflect changes in global stability. Since 2007 it has been changed to now represent the threat of global warming, and as of May 2010, we stand at six minutes to midnight.


In this series of blog posts I will give a brief overview of the main topics of what is the greenhouse effect and how human activity affected this natural cycle. I will show how the climate has changed over the years preceding industrialisation. Finally I will introduce the scientists who have revealed this global threat.

Tuesday, May 11, 2010

Dumbed Down


Was a little bored of studying yesterday so got a bit distracted with watching some television. I was flicking through the channels when I came across “Mythbusters”. I have seen a good lot of their earlier seasons but I soon gave up on them. The so called “science” in their show was intolerable. For those of you don’t watch it or know of its existence, it is a show where a group of people test urban legends. Each week they have a bunch of legends/myths to test, they carry out “scientific” tests of these legends/myths and then declare them “busted”, “plausible” or “confirmed”.

Often on the show they jump to conclusions, preform flawed experiments and from them claim to derive meaningful results. Yes I know the show is designed to be entertaining but at the same time this show has a large catchment and so can influence a great number of people. Is this what people who work in science every day, want to be seen educating the general public about science?

This isn’t the only piece on television where the science takes a back seat on a science show. The British television show “Brainiac” is guilty of such acts. A lot of the science in the show is set at the level of a two year old. Why is it we are stuck with shows like this on television?

The once great documentary series Horizon has not escaped the dumbing down effect seen on scientific television shows. During the 80’s and early 90’s this show provided excellent documentaries on current events in science. Yet now we constantly get shows where the science takes the back seat as the presenter on the show has to pander to what they must perceive is a complete idiot who watches it. The entire science content of these one hour documentaries could be easily condensed into a 10 minute slot.

Yes I realise I am ranting a bit here but this is a serious matter. Is this the type of television that we want fostering a new generation of scientists? When I was growing up I watched Carl Sagan’s great television series Cosmos and every Christmas watched the Royal Institution Christmas Lectures. The national geographic documentary series were a great source of wonder for me also. Shows like this inspired me to take up science.


I also recently began to see this trend in the printed media too. I enjoy a lot of reading, I mostly contain myself to science books across all the topics. In many books published today I see no theories explained in all their full glory and mathematical equations are avoided at all costs. I recently read a book which suggested to the reader to skip over the next chapter as it contained some mathematical equations and it would not hinder their enjoyment of any of the upcoming chapters. Has it really gotten to that stage where writers who wish to publish a popular scientific book have to try and remove any mathematical equations in them?

This apparent fear of adding complexity to scientific books I think stems from the growing culture of dumbing down on television. My fear is will this dumbing down extend to the education system. I was looking over the recent changes to the leaving certificate maths paper in Ireland. This new course dubbed “Project Maths” is nothing but a watered down version of what we have. I found myself rechecking the course title on the leaving cert paper as I was dismayed at how simplistic it is, I thought I had clicked on the junior cert paper by mistake.

Recent scandals in the media highlighting third-level grade inflation only adds to this view. This scandal may lead to several high profile companies moving elsewhere, as many critics see this happening under the guise of keeping these companies happy. Grades have been deliberately keep high so as to attract prospective employers here. Ireland is underperforming in many areas of science and maths subjects in schools. Changes such as Project Maths don’t help alleviate the situation. Unfortunately there is no easy solution to this problem. I think of first port of call to this problem is why are people so fearful of equations? Is it it’s inherently abstract nature or is it down to out-dated teaching methods?

A recent report into the countries’ maths teachers was startling. It reported that only 48% of our countries’ current maths teachers were qualified to teach the subject. How can a core subject like maths be left reach such a poor state? Ireland is not alone in this predicament. The main reason for this occurring in my opinion is that teachers who didn’t do maths as the primary trust of their teaching degree or post graduate qualification are not barred from teaching it at secondary school.

Whatever the cause and outcome of this dumbing down of science in the media the end result will not be good for not only the economy but also science in general.

Monday, May 10, 2010

Jocelyn Bell Burnell

On November 28 1967, a young postgraduate student named Jocelyn Bell Burnell and her thesis supervisor Antony Hewish made one of the great discoveries of 20th century astronomy. This great discovery won Hewish and his research partner Martin Ryle the 1974 Nobel prize. The awarding of the Nobel prize to just Hewish and Ryle has being seen by many as controversial but unfortunately Jocelyn was no stranger to adversity in her career.

Born July 15th 1943 in Belfast, Jocelyn Bell Burnell didn't have a typical girls up bringing. Her father was an architect for the Armagh Observatory. From a young age this exposure to this observatory and its library fuelled an interest in astronomy. She was granted the opportunity to pursue a science stream in school. This was unusual for the period as most girls her age were generally put in classes where stitching and home economics were the norm. Not all was went well for young Jocelyn, she failed her eleven plus exams. With this set back she was sent to a local boarding school, it was here that she found a love of physics. When she finished school she went to Glasgow University to earn a degree in physics which she completed in 1965.

With her degree completed she went to Murray Edwards College in the University of Cambridge. It was here while doing research work into quasars using a radio telescope that she made that faithful discovery. While analysing data which she had gathered, a regular repeating signal was observed. This discovery was totally unexpected and it took several more years for it to be correctly identified. She had discovered the first example of a pulsar. A pulsar is a rapidly rotating neutron star.



This discovery would give Hewish and his research partner Ryle the first ever Nobel prize for physics for an astronomer. She was overlooked for this award and even to this day it is still not clear why. There are several possible reasons, firstly she was a woman working in  male dominated field and secondly she was at that time a Ph. D student. Whatever the reason she was wrongfully denied the Nobel prize.

She completed her Ph. D in 1969, and moved to Southampton to take up a post in the University of Southampton. She also held various other posts at University College London and the Royal Observatory in Edinburgh. In addition to these posts she worked as tutor, lecturer and examiner for Open University. It was here that she was appointed the head of physics in 1991. She retired from active academic work in 2004. She currently holds the position of president of the Institute of Physics and is the Visiting Professor of Astrophysics at the University of Oxford.

Her remarkable story is all the more amazing when you see it from the viewpoint of a woman in science in the early 1960's. In several interviews she gave recently about her time in university studying for her degree she remarked how difficult it was. She recalled that being the only woman in a class of fifty was a very daunting experience. On a daily basis she faced ridicule  and disdain. She was a pioneer from many women in science and this may be her greatest contribution to the field.

Sunday, May 9, 2010

Ernest T.S. Walton


Ireland has produced several Nobel prize winners but only one of them for a science discipline. Ernest Thomas Sinton Walton was born in Dungarvan, Co. Waterford on the 6th of October 1903. From an early age Ernest displayed an aptitude in mathematics and science. This great talent earned him a scholarship to Trinity College, Dublin in 1922. By 1927 he had received a masters degree in physics and mathematics. In 1927 he was awarded a scholarship to attend Trinity College, Cambridge. There he worked as a research student under the great experimentalist Ernest Rutherford.

Ernest had arrived at physics as it had entered its golden age of discovery. It was the beginning of the adventure to probe the inner structure of the atom and within find the building blocks of all the matter we see around us. Walton was tasked with the design and building of an apparatus to aid this work. In 1929 Walton was joined by fellow student John Cockcroft. Together they developed a particle accelerator which could accelerate protons towards a target.

L-R: Cockcroft, Rutherford, Walton


Using this accelerator they bombarded a lithium sample with high energy protons. In April 1932 during one of these bombardments of a lithium target two alpha particles were detected. This was the first time a transmutation of an element was done under human control.


Here for the first time was experimental evidence for what would be the most famous equation in science E=mc2. In Einstein's mass-energy equivalence it stated that mass, m, times the speed of light, c, squared was equal to energy, E, in joules. This incredible simple equation would have a profound impact on the world in the years to come. In the Walton-Cockcroft experiment when the masses of the proton and lithium nucleus were compared to the masses of the two resulting alpha particles (helium nuclei) there was some mass 'missing'. The energy released in this transmutation when analyzed was found to be equivalent to the mass missing. For their work on this Walton and Cockcroft earned the Nobel prize in physics in 1951






By 1934 Walton had returned to Ireland as a fellow in Trinity College Dublin. In 1946 he was appointed to the prestigious position of Erasmus Smith's Professor of Natural and Experimental Philosophy. He continued to lecturer as the head of the physics department at Trinity until his retirement in 1974. He is held in high regard for his elegant approach to teaching. It was said of him that he could make the most complex theories easily approachable for his students. Although retired he still frequented the corridors of Trinity for many years after. 


He was the recipient of several awards and honours during his career with the Nobel prize being the jewel in the crown. At the age of 91 Ernest Walton passed away on June 25th 1995. With his passing Waterford Insititude of Technology named its new state of the art IT building in his honour. 


I do not wish to put any negative comments in this piece about such a great man but I feel it is a great shame that we do not do more to honour more individuals such as Walton. For me he is one of the greatest Irish people and deserves all the admiration and more that he received.

Saturday, May 8, 2010

Irish Scientists

Just recently Irish national broadcaster RTE decided to conduct a poll for the 40 greatest Irish people. I must admit I was very shocked by some of the people who made it into the final 40. We are a nation who prides itself on our national heritage and history, yet in the so called 40 greatest Irish people we find the likes of Stephen Gately, Ronan Keating, Louise Walsh, Roy Keane, Liam Neeson, Daniel O Donnell, Colin Farrell, Bono etc. Seriously is this the best we could come up with?

Where are some of great scientists that were born here? We are a small nation but we have produced some very fine scientists. So starting this week I will write a piece on a few of these people who have graced us with their presence. Each week I will add another. I have chosen a few that I have a good knowledge of, if there is any you think that I should add please feel free to comment and I will try to put together a piece on them. The list I am going to work off is as follows;

There are several great contributors I have missed out on and time permitting I will try and return to them and give them the recognition they deserve. First thing from this list I have complied here is the lack of women. It may have to do with the lifestyle in years gone by that women were not encouraged more to do science as a possible career but the two women on this list have made significant contributions to their respective fields.

I decided to start with Ernest Walton as he was born only a few miles from I live. He is our only ever Noble prize winner in science. I still feel Jocelyn Bell Burnell should be our second but controversially she was over looked while her associates received the Noble prize.

What is a physicist?

Okay this sounds like a strange question but stick with me for a moment. What is the first thing that pops into your head when you here the word physicist?

Is it a pair of glasses, a lab coat and a social awkward person?


Where did this stereotype stem from and is it justified? I will admit some of it is justified from my experience, physicist due tend to be a little odd at times but that is true of many sciences. I suppose the view in the public of the appearance of a physicist comes a lot from the media. The media tends to only report sensationalist news especially regarding science. For example do you think you would see this headline on the front on a newspaper "Strange Quark Mass Weights In" or are you more likely to see "LHC will Implode the Moon". It has to said that the reporting of black holes at the LHC in Cern seems to have died off. If only people realized that there is far more energetic collisions happening just a few miles above your head.

Another point is that in a lot of movies physicists are very much portrayed as crazy individuals who haven't seen the outside world in years.



It is refreshing to see more coverage at least over here with the likes of Brian Cox speaking up for science. It is my opinion that an integral part of any science degree should be some form of presentation work. It is now of vital importance that science be portrayed with pubic in a more favorable light. With the current recession science funding has been hit hard. It should be the complete opposite, we should be putting more funding into research and science. Education is the key for pulling economies out of recession.

Physics needs more people like Richard Feynman. He was not your atypical physicist (ignoring his personal life), he was very outgoing and always wanted to help the public grasp the vibrant and exciting world of physics. His public lectures and books still amaze today. There is certainly an appetite in the public for more science related books. It is a shame that one of the most popular books on science, A Brief History of Time, was one of the least read books by people who purchased it. With the new age on internet 2.0 science in general has a great opportunity to reach so many people with a more engaging medium. One of my favourite things to do when I have so spare time is to watch some of the MIT lectures on physics given by Walter Lewin. He is such a great example for anyone wishing pursue education as a profession. It is a joy to watch the enthusiasm with which he enlightens his captive audience. So here I am trying to do a small part in helping to spread the good word of physics.






Friday, May 7, 2010

Divisible Part 4

The Invisible Man

The neutron was discovered very late on in this story as it has no charge so was very difficult at the time to observe. In 1920 Rutherford predicted the existence of a neutral particle of similar mass to the proton. He came to this conclusion because he knew that the alpha particle was just a helium ion which he knew to have two electrons and two protons. With two protons and two electrons the mass did not add up so he assumed that a chargeless particle was responsible for the missing mass. He was not the only person to reach this conclusion with American nuclear chemist William Harkins (1873-1951) even going so far as to name this invisible particle "neutron". In the early 1930’s German physicists Bothe and Becker were studying the effects of high energy alpha particles bombarding light elements. It was noted that an unusual radiation was being produced. It was very hard to observe any meaningful data from this result and thus proved difficult to formulate any concrete conclusion regarding this phenomenon.

This phenomenon was again noted in 1932 by two French physicists Irene Joliot-Curie (1897-1956) and Frederic Joliot (1900-1958). They bombarded hydrogen containing compounds and found that protons were ejected at high speed. They had assumed that they had noted a form of gamma or x-rays; however they did not realize the significance of this discovery.

It was not until James Chadwick (1891-1974) in the same year devised an experiment to eliminate the idea of gamma or x-rays. In his experiments he bombarded boron gas with alpha particles. The particles emitted from these collisions were allowed to collide with paraffin wax. Protons were knocked out of the paraffin. From this observation he concluded that the protons were in collision with some massive particle. From the energies involved he concluded that the new particle must be of similar mass to the proton and also have no charge as it made no track in the cloud chamber. Chadwick won the Nobel Prize for this discovery in 1935. With the discovery of the neutron several physicists believed we had now found the key to the physics within the nucleus. Werner Heisenberg (1901-1976) published several important papers on the subject in which he concluded that the nucleus was comprised of protons and neutrons held together by some unseen force.



The discovery of the neutron would solve many of the problems noted with atomic masses. It was known since the early 20th century that not all atoms of the same element were the same mass. Thompson observed this in several experiments on neon gas; in these experiments several tracks for neon were recorded. This should not have been the case if all neon atoms were the same. From this observation Thompson concluded that not all atoms of neon were identical and that they differed in terms of their mass. This apparent oddity could now be accounted for by changing the number of neutrons present in the atom.

Nuclear Models

Several models of the atom were proposed throughout the 19th century until the model we arrive at now in mid 1930’s. In the 19th century an idea was theorized by Dalton that the atom was a solid sphere but this has the obvious short coming of being unable to explain charge and electricity. This problem was tackled by the Thompson who theorized the ‘plum pudding’ model in which electrons were present in a mass of material whose charge was positive. This at least explained why atoms were electrically neutral.

The evidence for the existence of atoms themselves has a long history stretching back to the age of the Romans. In c. 60 BC a Roman poet records observations of dust particles in the air. In this poem he noted the apparent random motion of the dust. The author hinted that there may be some unseen particles so small we can’t see them and these are what are responsible for the motion. This motion is what we refer to as Brownian motion named in honour of Robert Brown (1773-1858). Brown was a botanist whose observations of pollen suspended on water gave rise to this phenomenon. He observed that the pollen grains appear to jostle about in an apparent random motion. He repeated this experiment with dust to eliminate any suggestion that the pollen was somehow alive, but could not give a satisfactory answer for this motion. It would take a brilliant young physicist to link this motion in pollen grains to the atom. In 1905 Albert Einstein (1879-1955) published a paper of his observations. In it he discussed the motion of the pollen was linked to the vibrations at the atomic level. This, he offered, was direct evidence for the existence of atoms and molecules.



The inner structure of the atom remained elusive until Rutherford and his scattering experiment. In this experiment he established that atoms were comprised of mostly empty space with a tightly packed positive nucleus at their core. In Rutherford’s model the electrons orbited the nucleus like planets orbiting the sun. This wasn’t without its problems as the model could not explain why the electrons do not collapse into the core. Niels Bohr (1885-1962) further expanded on this model in which the electrons could only have certain allowable orbits.



In Bohr’s model electrons could only orbit within certain energy levels. This prevented the electrons from losing energy (rotating bodies radiate energy) and falling into the centre as they were restricted to a minimum energy. From this model the atomic spectrum of hydrogen was explained. However this model could not be extended to explain other elements as there spectra were far more complex.

With the discovery of the neutron in the early 1930’s it did appear then that the full picture of the atom was reviled. We now had a nucleus with neutrons and protons which in turn was orbited by electrons. Physics now had an explanation for the atomic structure and why we have isotopes. Also from this model radioactivity could be explained in a manner which resulted in charges within the atom either in the emission of energy from electrons changing orbits, electrons decaying from the atom, or alpha particles ejected from the nucleus.

There were still several problems with this model which could not be explained. At this time physicists had no explanation for why the protons could be in such close proximity in the nucleus. From classical physics they should be repelled from each other and the core of the atom should fly apart. But with the discovery of the neutron it hinted that this may be partly responsible for holding the nucleus together.  The atomic age brought about the end of classical physics and opened up the new age of quantum physics. 

Divisible Part 3

Are You Positive? 

With the discovery of the electron it was assumed that there must be some particle responsible for a positive charge as atoms were not ionized. In many texts the discovery of the proton is attributed to Ernest Rutherford (1871-1937), but it was discovered prior to his work by German physicist Eugen Goldstein (1850-1930). Goldstein began to study if there were ‘rays’ emitted by the anode in the discharge tube as most studies at the time had been concerned with the ‘rays’ emitted by the cathode. The charge/mass ratios of these emissions were also measured but the results differed greatly from the charge/mass of the electron. It was found that the charge/mass ratio depended on the gas in the tube and was much smaller than that of the electron. When the gas in the tube was hydrogen the charge/mass ratio was found to be greatest. This snag of the charge/mass being dependant on the gas put Goldstein off, what he actually was seeing was ions.

For the definitive discovery of what we now know as the proton it would take several years of work by Rutherford. In 1911 he experimented on a thin gold foil sheet which he bombarded with alpha particles (this experiment was carried out by two of his students Geiger and Marsden). The vast majority of these particles passed through the foil with no interference but several were deflected by varying amounts. It was found that the majority of the deflected particles were deflected by small angles while some were deflected by angles greater than 900 and some even ricocheting back along the path they came. From this he concluded that the gold atom contained within it a very small central mass which was positively charged (the alpha particles have a positive charge so it was assumed that they would be repelled by a like charge at the centre of the atom).
At the time the diameter of the atom was generally considered to be about 10-10 m but Rutherford found the nucleus to be of the order of 10-15 m effectively making the atom comprised of mostly empty space. So the model of the atom was now a densely packed central core of positively charge particles with electrons surrounding it. This model of the atom took over from the view put forward earlier by Thompson. There were several snags with this model but these will be discussed later in the essay.



Rutherford and his colleagues were bombarding nitrogen gas with alpha particles in 1918 and found that there was hydrogen present in the tube. This could only be possible if the nitrogen nuclei contained hydrogen nuclei. This led to a suggestion that the hydrogen atom was a fundamental particle. We now know that the hydrogen atom is a proton paired with an electron.

Divisible Part 2

Electron 

During the 19th century physicists developed a concept that electrical charge was an indivisible quantity. In 1874 this idea was championed by Irish physicist George Johnstone Stoney (1826-1911). However he incorrectly believed that these charges were always attached to the atom and could not be removed. Experimental work by William Crookes (1832-1919) in 1879 first demonstrated that these charge carriers were negatively charged. He believed that these charges were rays being emitted by the cathode of his discharge tube experiment. But in 1895, French physicist Jean Perrin (1870-1942) established that these 'rays' were in fact particles. He done this by adding a small wheel assembly to the Crookes' Experiment which moved upon bombardment of the cathode's stream.


Crookes Tube

The discovery of the electron as it became known was attributed to J. J. Thompson (1856-1940) but it was known for years that charge was carried in some form by a wave or particle. However Thompson with his colleagues did establish the charge to mass ratio for the electron.

Not only did Thompson establish the charge/mass ratio, he also demonstrated that electrons were emitted by radioactive, heated matter and illuminated matter. This was also independently verified through experimental work by Henri Becquerel (1852-1908), who showed that certain radiation emitted from substances could be deflected in the same manner as electrons and also have the same charge/mass ratio.

It was not until the early 20th century that the mass of the electron was found. In an experiment developed by American physicist Robert Millikan (1868-1953) in 1909, a charged droplet of oil was suspended in an electric field so that it remained stationary in the gravitational field. This was repeated for various charges and it was found that these were all integer multiplies of the same value. From this work the charge on the electron was established, which in turn gave rise to the value for the mass of the electron.



The mass of the electron was surprising, being only a small fraction of the mass of the lightest known element at the time, hydrogen. This was the first sign that the atom was not some solid piece of matter and gave rise to the view that electrons were some form of component of an atom.

Based on this discovery, Thompson put forward his model for the structure of the atom. In his model the atom was akin to a plum pudding. The electrons were scattered throughout the pudding whose charge was positive, therefore making it electrically neutral.



Divisible Part 1

Prologue                                             

The question regarding the very nature of the matter comprising the universe is one which has challenged human thought for millennia. From the time of the earliest Greek philosophers to modern day particles physicists, mankind has sought to understand the underlying structure of nature.

The majority of science prior to the 19th century was concerned with the behaviour of the macroscopic world we live in and predicting events. It was chemists who first tackled this difficult question. From their observations it would appear that elements we have may not be as fundamental as once believed. 

Atomos

The concept of matter being comprised of small indivisible units has been around for millennia. The first account of this in western history arose from the writings of the Greek philosopher Democritus (c.350 BC). In his writings he asserted that matter is made up of small indivisible particles which he referred to as “atomos”. This was one of the first examples of the idea that matter was not continuous. However this idea did not receive widespread support and was disputed by most influential philosophers at the time, Plato and Aristotle. The Greeks were philosophers, not experimentalists, so without any evidence this idea of atoms fell by the wayside.

Democritus


This idea of matter being comprised of small indivisible units would remain dormant until the late 18th century when a chemist, Antoine Lavoisier (1734-1794), pioneered the theory of reaction stoichiometry. This theory relies on the conservation of mass during chemical reactions. This conservation hinted that there may be some underlining relationship between the different elements. This theory was furthered by John Dalton (1766-1844) in 1804 to develop the concept of atomic weight. From this concept the theory of atoms was revived. Dalton stated that all elements are made of small particles called atoms and that all atoms of a given element are identical. Noted French chemist Gay-Lussac (1774-1850) also arrived at a similar conclusion based on his theory of how substances react in discrete amounts. However all was not right with these theories. There was the snag that as measurements became more accurate the mass of elements was not consistent (this would not be solved until the idea of isotopes was theorized).

In the 18th and 19th centuries there was a great flourish of discoveries of new, exciting elements. The question of whether these elements related to one another in any way arose. At this time a Russian chemist, Dmitri Mendeleev (1834-1907), began trying to answer this question. He attempted to list out all of the known elements and classify them into groups according to their chemical properties. It was only when he began to group them by their atomic weight and similar chemical properties a pattern began to emerge. Noting several gaps in his new table, he predicted new elements which would have certain chemical properties. This became the familiar table known as the Periodic Table of Elements (1869). For the first time there was a hint that the elements may not be fundamental as had been believed. His work was vindicated when he predicted two new elements which were found in 1876 (Gallium) and in 1886 (Germanium). 

Mendeleev's Periodic Table

Ash-termath

For any of those who were travelling over the last few weeks you will know all too well how a volcano called Eyjafjallajokull can make for an unpleasant trip. Flights throughout Europe have seen cancellations since the eruption started back in March. Volcanoes can have a major impact on the climate, so how if any will this eruption have an effect on our climate?

When volcanoes erupt they eject ash and various gases into the atmosphere. The ash is comprised of pumice and crushed rock. The height that this ash gets thrown to can lead to aircraft being grounded. Current jet aircraft operate at an altitude of 9-15 km. The ash ejected can damage the turbine blades on a jet engine. The temperatures within a jet engine are hot enough to melt this ash and it can re-solidify on the internals in the engine which can lead to tragic consequences.

Volcanoes emit vast quantities of gases, these gas emissions are dependant on the type of eruption. Of these gases water vapor, carbon dioxide and sulphur dioxide are the most common. All these gases we commonly refer to as greenhouse gases. Of these gases sulphur dioxide poses the greatest risk. Not only does it readily convert into sulfuric acid which can fall back to earth as acid rain, it can also condense into sulfate aerosols in the upper atmosphere. These aerosols when present in the upper atmosphere act like a mirror reflecting the sun's rays back into space. This can reduce average global surface temperatures across the planet by up to 0.5K. This phenomena is referred to as a volcanic winter. The most recent of these winters occurred in 1991 when Mount Pinatubo erupted in massive explosion of gases and ash.


In this eruption 10 cubic kilometres of material was ejected into the atmosphere along with nearly 20 million tons of sulphur dioxide. When this sulphur dioxide condense in the stratosphere it triggered a global temperature drop of 0.5K.


Looking at the temperature trend during the 90's there is a very obvious bump due to the eruption of Pinatubo. There have being several other of these climate changing events in recorded human history. Several famines during the 18th and 19th centuries have been associated with volcanic eruptions. So what effect then will this newest eruption have on our delicate climatic system?

Initial reports from the Instituto Nazionale di Geofisica e Vulcanologia estimate that the Eyjafjallajokull volcano has ejected about 120-150 million cubic meters of material. This material reached a height of about 7km in the atmosphere hence the problem with flights. This amount of material is relatively small in comparison to some of the major events. It is the current thinking that this will only have a minor local effect on the atmosphere in and around Iceland. However it must be added that we have no idea how long this current eruption will last. When  Eyjafjallajokull last erupted in 1821 it continued to erupt for over 14 months. So we could see disruption to flights on going for months to come.

I will leave you with a sobering thought, as bad as this volcano is perceived to be be there is a far more dangerous threat lying in wait. Almost 70,000 years ago a volcano called Mount Toba erupted in vast explosion. This 'super-eruption' trigger a winter that last between 6-10 years globally and almost wiped out the human species. Current thinking among seismologists point to a similar event happening in the future in Yellowstone National Park, Wyoming, USA.