Voyager Interstellar Message

In the annals of exploration, the achievements of the two Voyager spacecraft are unprecedented. The piddling journeys of Columbus and Magellan spanned a few tens of thousands of miles on the watery surface of one small world. Voyagers 1 and 2 have traveled billions of miles through the ocean of space, exploring dozens of new worlds along the way and revolutionizing our knowledge of the solar system in which we live. And as a gift of the brilliant mission design, these robot ships are no longer bound by the Sun's gravity. They have passed the outermost planets and are on their way to the cold, dark near-vacuum that constitutes interstellar space. Nothing can stop them. Their radio transmitters are unlikely to work beyond the year 2020. Thereafter, they will wander silently and forever in the realm of the stars.

Who knows who's out there? Perhaps the rest of the Milky Way Galaxy is populated by desolate, wasteland worlds circling a hundred billion stars. Or maybe the Galaxy is rich in life forms and intelligence and technology much further beyond our reach than the Voyagers are beyond the reach of Columbus and Magellan. Someday - maybe millions of years in the future - one of these ghostly, derelict ships may be detected and captured by the representatives of some devastatingly advanced interstellar culture. They will wonder about the shipbuilders.

If you could send a long message to such extraterrestrial beings - words, pictures, sounds, music - what would you say? How would you describe us? What would you leave out? Could you communicate intelligibly to very different beings with a wholly independent evolution? In 1977, at NASA's behest, a few of us had a remarkable opportunity to attempt such a (one-way) communication. Frank Drake suggested not a plaque, but a phonograph record. As described in the book, Murmurs of Earth, we designed and prepared the record to carry a rich message to the stars - 116 pictures and diagrams about our global civilization and our species, greetings, samples of the world's great music, the brain waves of a young woman in love and much else.

The Voyager mission has already become the stuff of myth, the premise for many works of science fiction. Brief excerpts from the Voyager record have been heard in films, television and radio. But the record itself has never before been available to the public, because of corporate rivalries and copyright restrictions. Warner New Media has broken through the logjam. Those of us who created the interstellar record - well-aware that different people would have made different selections - are delighted to help bring this message to you, essentially complete, as carried by Voyager. This is what the extraterrestrials will learn about us, should the spacecraft - now the fastest and farthest machines ever launched by the human species - one day encounter someone else in the depths of space.

A billion years from now, when everything on Earth we've ever made has crumbled into dust, when the continents are changed beyond recognition and our species is unimaginably altered or extinct, the Voyager record will still speak for us.

- Carl Sagan and Ann Druyan

Coming Full Circle

The Lord set the earth on its foundations; it can never be moved. (Psalm 104:5)

 Claudius Ptolemy

Whilst the subject of this article may be familiar to most readers, the logic behind the ideas may not be as obvious.  Our modern conceit ensures ‘we know’ how the universe is structured and are confident in our summation because our technology and scientific know-how support our theories beyond a shadow of doubt. 

Singh, pp 20, describes how our ancestors studied the sky by night and day to determine changes in weather patterns, measure time, and confirm directions.  The ground on which they stood stayed firm under feet, and the heavens passed overhead in an endless and ‘fairly predictable’ procession; consequently, they assumed the Earth was the centre of the ‘known universe’, and the heavens revolved around it and them.

Notwithstanding these early, Earth-centred assumptions, there were a few early thinkers who quite accurately proposed a heliocentric (sun-centred) ‘universe’.  Whilst the idea of our solar system as just a tiny part of the greater universe was still a long way off, these early heliocentric proposals were uncannily correct.  

Here we can observe yet another perfect example of human knowledge and ideas being built upon – handed down – and developed over several generations.   The earliest recognition for presenting a ‘true’ heliocentric model goes to Aristarchus of Samos (310 BC-230 BC); however, it is acknowledged that his proposals were based on the ideas of those who had gone before him. 

Philolaus of Croton (approx 470 BC–385 BC) a pupil of the Pythagorean school, in the fifth century BC, was possibly the first to suggest the Earth orbited the Sun.  In the following century, Heraclides of Pontus (approx 387 BC-312 BC) developed these ideas even further.  For his efforts, he was publically ridiculed, labelled crazy, and given the nickname of Paradoxolog – ‘the maker of paradoxes’. 

Whilst there is some disparity about the dates given from various sources, it is clear that Aristarchus was born about the time of Heraclides’ passing.  Naturally, any of the aforementioned characters are worth further investigation if the reader is so inclined.  It goes without saying; their lives were a rich mosaic of mathematical and philosophical thought.  Truly – no man is an island!

Having established a viable and reasonably accurate model of a heliocentric ‘universe’ what happened to change that model?  Why did this ‘accurate proposal’ quite plainly disappear for the next fifteen hundred years, until resurrected in the early 1500s by Nicolaus Copernicus – and later, in the face of severe religious persecution, brought to the fore by Galileo Galilei?

Change doesn’t occur easily in the human intellect – egocentrism rules – and the majority, especially if supported by religious or mystical factions in society, tends to hold sway against even the most persuasive scientific arguments.  It appears our old companion – common sense – was partly to blame initially; the very idea of the Sun being at the centre of the universe just ‘seemed ridiculous’ to most people.  Add to this, the ‘fact’ that the heliocentric model did not stand up to rudimentary scientific analysis – and did not appear to reflect reality.  Three very specific criticisms appear to have been levelled:

1.     The Greeks reasoned that if the Earth moved rapidly through space – they would feel a great continuous wind pressure blowing against them.  The Earth, they concluded must be motionless!   This decision was obviously taken on a windless day!  However, far be it for me to interject

. 

2.     The Greeks inability to appreciate the effects of gravity in the sense that – to them – everything naturally moved towards the centre of the universe.  Apples fell from trees – stars were seen to ‘fall’ from the sky – and so – as everything ‘fell to earth’ – then Earth MUST be the centre of the universe.  If the Sun were at the centre of the universe – it was fairly obvious to the ancient Greeks – that everything would ‘fly up’ and off in the direction of the Sun.

3.     The third reason given is more understandable in that a lack of instrumentation or technology rather hindered the Greek ability to identify any shift in the positions of the stars.  The stellar parallax – as it is more familiarly now understood - indeed could not be detected with the naked eye, simply because of the vast distances involved.

(See: http://onlinedictionary.datasegment.com/word/stellar+parallax)

There were however, five celestial bodies that seemed to defy the observations at point 3 above – and these, as we now know, were the five known planets:  Mercury, Venus, Mars, Jupiter and Saturn.  For those who love trivia - the word ‘planet’ – originated from the Greek – planetes­ – meaning, ‘wanderer’. 

These five non-compliant bodies would present problems that would eventually be overcome by sheer human resourcefulness – or determination to appear correct at any price!  Quite simply, one of the core issues in the heliocentric debate was – if the heavens orbit in circles around the Sun – then it followed that there would be an obvious predictability in the patterns produced in the cosmos.  The patterns did not appear to concur with the hypothesis.

Over the course of several centuries many astronomers and mathematicians contemplated this conundrum!   Slowly but surely, a complex answer began to evolve.  The final solution to this problem became associated with the astronomer, Claudius Ptolemy (AD 90-c. AD 168). 

Ptolemy’s, astronomical paper on the intricate movements of the stars and planetary paths – the Almagest – is known as one of the most significant scientific documents in human history.  So powerful was Ptolemy’s argument, it held sway from its origins in Hellenistic Alexandria, into the Byzantine and Islamic cultures and on into Western Europe through the Middle-Ages and early Renaissance up until the time of Copernicus! 

One glance at a model of the Ptolemaic system reveals a system so complex as to be almost unbelievable.  Part of the problem that had to be overcome was caused by Mars and the outer planets – which, to observers on Earth, appeared to move sometimes ahead – at other times stop completely – and yet again at other times – to move backwards.  This apparent anomaly was simply a result of Earth’s position within the solar system and our respective orbits around the Sun.  However, to make the ‘mathematical facts’ fit the geocentric model; Ptolemy devised a complex, but workable solution, known as the epicycle!   (See: http://www.thefreedictionary.com/epicycle)

The analogy provided for this model compares to a wild fairground waltzer ride, in which the passenger is locked into a cradle joined to a long arm. Whilst the cradled passenger follows a small ‘circular orbit’ – the longer arm at the same time describes its own much larger ‘orbit’.  This complex arrangement complied with the demands created by the Earth-centred model and satisfied both science and religion at that time.

Of course, such blatant manipulation of reality is not the sole province of the ancients; in more modern times, Einstein’s cosmological constant was an equally blatant mathematical mirage designed to suit the ‘required populist truth’.  Luckily for Einstein, he got to make amends for his moment of weakness in his rush to comply with the wishes of the ill-informed majority.  

(Of course - there's more to that story as well)

As for the Ptolemaic system, the only tweak required to commit it to the garbage bin of magnificent human mirages was a slight adjustment to orbital physics. 

The most basic mistake made in the first place by those who anticipated the heliocentric model, was to base their assumptions on perfect 360° ‘divine circles’.  In doing this, those heavenly bodies that wandered the night skies – and should have had predictable orbits – were not where they were supposed to be at the appointed season! 

In fact, if the orbits are based upon the true elliptical paths taken by the planets in our solar system, then we know with certainty, that those objects will unfailingly appear at the predicted times.

Refs:

Encyclopedia, W. T. F. (2011, March 1). Almagest. Retrieved April 4, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Almagest.

Encyclopedia, W. T. F. (2011). Aristarchus of samos. Retrieved April 5, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Aristarchus_of_Samos.

Encyclopedia, W. T. F. (2011, March 1). Ptolomy. Retrieved April 4, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Ptolemy.

Singh, S. (2005). Big bang. London: Harper Perennial.

Stamatellos, G. (1997). Philolaus of croton. Retrieved April 5, 2011, from philosophy.gr: http://www.philosophy.gr/presocratics/philolaus.htm.

“Physics of the Future” – Michio Kaku pp – 6/7

Journalist Mark Sullivan asks us to imagine someone reading a newspaper in the year 1900:

In his newspaper of Jan 1^st 1900, the American found no such words as radio, for that was yet twenty years in coming; nor ‘movie’, for that too was mainly in the future; nor chauffeur, for the automobile was only just emerging and had been called ‘horseless carriage’...There was no such word as aviator...Farmers had not heard of tractors, nor bankers of the Federal Reserve System.

Merchants had not heard of ‘chain-stores nor self-service’; nor sea-men of oil-burning engines...Ox-teams could still be seen on country roads...Horses or mules for trucks were practically universal...

The blacksmith beneath the spreading chest-nut tree was a reality.

Physics of the Future - The Inventions That Will Transform Our Lives - by Professor Michio Kaku

Deep Space Pioneers

Where were you on the 2^nd March 1972 (some refs state 3^rd of March) – the day Pioneer 10 (AKA Pioneer F) was launched into space on its epic journey to Jupiter and its search for alien life? 

Thirty-seven years – is a lifetime away.  Imagine the crudity of the ‘ancient technology’!  Big – clunky – cutting edge in the broadest sense of the word!  Then consider the mathematical beauty of the successes achieved – and how it was so painstakingly accomplished.  As has been said many times – today, we have more computing power in a home PC than was available to such complex cosmic endeavours. 

Launched atop an Atlas/Centaur/TE364-4 three-stage launch vehicle; Pioneer 10 carried only eleven instruments – as follows:  1. Plasma Analyzer (P/L) 2. Charged Particle Instrument 3. Cosmic Ray Telescope 4. Geiger Tube Telescope 5. Trapped Radiation Detector (P/L) 6. Meteoroid Detector (ENC) (F) 7. Asteroid-Meteoroid Experiment (ENC)(F) 8. Ultraviolet Photometer 9. Imaging Photopolarimeter (ENC) (P/L) 10.  Infrared Radiometer (F) and 11. A Helium Vector Magnetometer. 

This very limited and specific collection of instruments sent back more useful information in its working lifetime than could of ever been hoped for; leading the way for all future deep space exploration.

For the record – the third stage booster was required to gain a speed of 51,810 kph to enable the unit to complete its flight to Jupiter.  At the time, this made Pioneer 10 the fastest man-made body to leave Earth – at a speed that would take it past the Moon in just eleven hours; traversing 80 million kilometres of space and crossing the orbit of Mars in only twelve weeks.  

Measuring just 2.9 metres in length, and 2.7 metres at its widest point, Pioneer 10 weighed in at just 258 kgs.  Electrical power was supplied by four radioisotope thermoelectric generators (RTGs), each providing just 155 watts of power at launch – decaying to 140w in transit to Jupiter.  The spacecraft required just 100w to power all systems. 

An RTG is a nuclear electrical generator that draws its power from the process of radioactive decay!  Heat released by the decay process is converted into electricity via the Seebeck effect (an explanation of which would take us down the murky road to the magic world of semiconductors).  Put simply, an RTG is a form of battery; a power source long associated with space probes, satellites and even terrestrial unmanned scientific facilities.  The most obvious drawback to their use is the requirement to safely contain the radioisotopes long after the useful ‘battery life’ has been expended.

By July 15^th 1972, Pioneer 10 entered the Asteroid Belt – an area 280 million kms wide and 80 million kms thick – located approximately between the orbits of Mars and Jupiter.  The thinly spaced objects within the Asteroid Belt travel at speeds estimated to be 20 km/sec and the objects within, vary in size from mere dust particles to rocks the size of the state of Queensland!  Whilst other spacecraft have since negotiated this area of space, at the time scientist were unsure if Pioneer 10 would be able to safely navigate its way across this possibly terminal minefield.

By the 4^th of December, 1973, Pioneer 10 made its first fly-by of the gas giant, Jupiter, achieving a dream first approved in February 1969.  The earliest mission objectives had been outlined as follows: explore the interplanetary medium beyond the orbit of Mars – investigate the environment within the Asteroid Belt and assess the belt’s potential hazards to future outer planet missions – explore the locality around Jupiter – and make a close approach Jupiter to gather information on the possible effects of Jovian radiation on spacecraft instrumentation.

In just twenty-one months the textbook mission had been completed beyond all expectations – but the story continued for the tiny probe well beyond this point as for many years a weak signal continued to be traced by the Deep Space Network.  Right up to 1997 and onward, the probe was employed to train flight controllers on how to obtain radio signals from space!  The final successful telemetry – the technology that allows remote measurement and reporting – from Pioneer 10, was on April 27^th 2002.

Amazingly, on the 23^rd of January 2003, what is recognised as the very last extremely weak signal was received from the still operating probe.  At that time Pioneer 10 was estimated to be 12 billion kilometres from Earth (80 au).  A further contact effort was made on February 7^th 2003 – but this attempt was unsuccessful. 

On March 4th, 2006 – the last time the probe’s antenna would be acceptably aligned with Earth – yet one last attempt at contact was made.  No response from Pioneer 10 was forthcoming.  It is thought that sheer distance and lack of power were the reasons for the eventual loss of contact, rather than the destruction of the probe.  It should also be noted that the probe must first be contacted by NASA before it will respond and send back data.

When its last position was recorded, Pioneer 10 was headed in the general direction of Aldebaran, in the constellation of Taurus.  At an estimated speed of 2.6 au per year – assuming Aldebaran has relative zero speed – Pioneer 10 should reach this distant destination in approximately 2 million years.

Pioneer 10 and its twin, Pioneer 11 (AKA Pioneer G), may yet possibly achieve one last duty if they are ever intercepted by ‘alien life’.  Both vehicles carry the famous gold anodized aluminum plaques - suitably shielded from erosion and cosmic dust - which depict the human race in all its naked glory.  Further information – should the extraterrestrials be adventurous or interested enough – and have technology well in advance of that presented to them in the shape of the defunct Pioneer probes – provides the exact location of our ‘Blue Island’ world.

Refs:

Encyclopedia, W. T. F. (2010). Radioisotope thermoelectric generator. Retrieved January 1, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator.

Encyclopedia, W. T. F. (2010). Thermoelectric effect. Retrieved January 1, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Seebeck_effect#Seebeck_effect.

Hamilton, C. J. (N/A). Pioneer 10 & 11. Retrieved December 31, 2010, from NASA Houston TX 77058: http://www.solarviews.com/eng/pn10-11.htm.

Lakdawalla, E. (2006). The final attempt to contact pioneer. Retrieved January 3, 2011, from The Planatary Society: http://www.planetary.org/blog/article/00000477/.

NASA. (2010, April 1). Pioneer 10 & 11. Retrieved December 31, 2010, from NASA  Science Missions: http://science.nasa.gov/missions/pioneer-10-11/.

Stenger, R. (2002, December 1). A distant pioneer whispers to earth. Retrieved January 3, 2011, from CNN - Science and Space: http://edition.cnn.com/2002/TECH/space/12/18/pioneer.contact/index.html.

Today, S. (2003). The pioneers are way out there after 30 years. Retrieved December 31, 2010, from Space Today Online: http://www.spacetoday.org/SolSys/ThePioneers.html.

Ward, M. (2001, April 30). Distant probe phones home. Retrieved January 1, 2011, from BBC News: http://news.bbc.co.uk/2/hi/science/nature/1305068.stm.

 

Comprehending the Incomprehensible

The most incomprehensible thing about the universe is that it is comprehensible. A. Einstein

                                                           

Last month, I made a vain attempt to define energy; as an adjunct to that article I felt it worthwhile exploring human scientific thought and development generally. The human pursuit of understanding the natural world and all that surrounds us culminates with the ultimate answers to the ultimate questions: ‘Where did it all come from’?  And - ‘what the heck is it all about’?

During an Astronomy, Forum, Prof. Fed Watson mentioned in passing the recent advances in technology that allows never before dreamed of results in the areas of amateur and professional astronomy and cosmology.  It seems difficult to believe that for thousands of years, the human race had such an extremely unrealistic view of the universe, and our place in it.  Yet, without the historically flawed models, the assumptions, and wildly mythological structures, much of what we take for granted today, might remain cloaked in mystery.  It is this human ability to build upon accumulated knowledge – sometimes renewed after a lengthy hiatus – or even transferred across racially differing societies – that facilitates genuine scientific progress.

Human curiosity is not culturally exclusive; from the earliest times, every culture, worldwide, has had some form of mythical version of the creation story.  Each ‘creation story’ mirrored the situation and society from which it originated; and each story symbolised the ‘supreme truth’ within its own society.  Scientific progress would not truly begin until many of these ancient traditions, bound up in folklore, superstition  and myth, started to decline. 

In trying to make some sense of order in the various models that have impacted the most on today’s perception of the universe, I think one of the earliest notable hypotheses is the ‘Mesopotamian Model’.  This model was developed by the inhabitants of the Nile and Tigris-Euphrates valleys.  The Earth was depicted as flat, and surrounded by lofty mountains.  The sky was a solid dome upon which the stars were placed, and water canopies emptied their rainfall.  The planets, the Sun and the Moon, were all imagined to be relatively small, and guided by celestial forces.  Interestingly perhaps, aspects of this model are offered in the Bible (Joshua 10 & Psalm 19). 

Whilst still containing strong mystical overtones, over time the Mesopotamian Model was adopted and modified by other civilizations.  Around the 6^th century BC early theorists such as Anaximander (possibly also the founder of evolutionary theory) and Xenophanes appeared on the scene, and whilst their explanations of the natural world were still far removed from modern ideas, they nevertheless did develop theories that didn’t rely on supernatural elements for support.  These ancient philosophers are recognised as the first true cosmologists, by virtue of the fact that they were genuinely concerned with the scientific study of the physical universe and its genesis.  The ancient Greek word – kosmeo – from which our modern word – cosmology – is derived, literally translates into - to order or to organise.

Every authentic scientific premise must make a prediction about the universe that can be measured and observed; history recognises Pythagoras as the man who made such scientific enterprise possible through mathematics.  His successors developed and enhanced his ideas, allowing science to become a sophisticated and authoritative discipline capable of some amazing early achievements.  Amongst these early achievements – without which later developments would have been impossible – were the measuring of the dimensions of the Earth – the Moon – and the Sun; and the distances between them.  To quote the author, Simon Singh: “these measurements were a milestone in the history of astronomy, representing as they do the first tentative steps on the road to understanding the entire universe.”

At this point it is worth taking a closer look at how some of these early measurements were achieved, and the human logic that lay behind such discoveries.  Aristotle (384 BC-322 BC) is acknowledged as being the first to write down a complete set of rules for logical analysis.  Whilst earlier philosophers had merely suspected the Earth was a globe – by drawing on their observations of the Sun and the Moon; Aristotle established these assumptions as fact.

  

He observed many eclipses, and obviously recorded his observations over time.  He noticed that during a lunar eclipse, the shadow of the Earth on the Moon was circular.  Naturally, a flat round object may also cast such a shadow.  However, Aristotle noted the shadow remained circular no matter in which direction the eclipse took place – in Aries, Capricorn, Gemini or Sagittarius.  It followed; the only object capable of casting a circular shadow from all directions is a sphere!   Thus, based on his empirical research, Aristotle affirmed the Earth was indeed spherical. 

Eratosthenes (276 BC-195 BC) is reportedly the first person to have used the word ‘geography’; he also ‘invented’ a system of latitude and longitude.  More impressively, he accurately measured the size of the Earth.  His measurement of about 39,250 km was accurate to 2% compared to modern measurements.  How he achieved this feat with the most basic tools available is testimony to human ingenuity. 

Whilst studying at a library, Eratosthenes learned of a water-well with extraordinary properties.  This well was situated near the township of Syene (near modern day Aswan).  Each year – at noon on the 21^st June – the day of the summer solstice - the Sun shone directly into the well, illuminating it right to the bottom.  Being an erudite chap, Eratosthenes realised for this to happen, the Sun must be directly overhead.  Eratosthenes, who resided in Alexandria, was aware that such an event didn’t happen in his locality.  Being aware of the Earth’s curvature, he reasoned that the Sun could not be overhead in Alexandria and Syene (several hundred km south) simultaneously; he decided to exploit his discovery in an attempt to establish the actual size of the Earth.  Today – we call this a ‘problem-solving approach’ – in which we take a problem and reduce it to simpler terms before making extrapolations to arrive at our final conclusions.

It is not within the scope of this article to explore too deeply how Eratosthenes arrived at his final results with little more than a stick and a brain; but by coordinating his readings to occur at the same time as the Sun was overhead and shining down the well in Syene, he placed a stick in the ground in Alexandria.  At the appropriate time, Eratosthenes recorded the angle of the shadow cast by the stick at mid-day.  Having established the size of the angle – 7.2° - the rest of the equation became academic.  Using the distance between the two towns, he extrapolated his results to estimate the distance around the Earth.  Having established the size of the Earth – it then became possible to estimate the size of both the Moon and the Sun – and their distances from Earth!

 

I can only reiterate this is: ‘a man – with a stick and a brain’!  Human resourcefulness leaves me quite flabbergasted – as does its frequent lapses in common sense!

In fairness to earlier philosophers, it was they who laid much of the foundations relating to the measurements mentioned above.  However, there was always one missing value – the size of the Earth.  Now this value was available, the remaining values were a matter of course.  Using Earth’s shadow cast on the Moon during a lunar eclipse, it didn’t take Eratosthenes long to estimate the Moon’s size as about one-quarter that of Earth.  Thus geometry, logic, and empirical research began to pave the way to genuine scientific discovery.  Measurements, sizes, distances, all relating to our own solar system became firmly established.  As indicated earlier, these measurements were remarkably accurate and have stood the test of time and advancing technology. 

Other suppositions being made about the universe at that time were not as accurate.  The influences of mythology and religion were, and still are, deeply entrenched in the human psyche.  These suppositions and the logic that lay behind them will be explored in later articles.

Refs:

Administrator, D. (2005, March 6). The ptolemaic system - a short history. Retrieved March 13, 2011, from The Flat Earth Society Forum: http://www.theflatearthsociety.org/forum/index.php?PHPSESSID=8c20b1a28c0eefa7dfb2f4a61e3326d5&topic=14.msg22#msg22.

Encyclopedia, W. T. F. (1999). Eratosthenes. Retrieved March 15, 2011, from Wikipedia: http://en.wikipedia.org/wiki/Eratosthenes.

JJ, O. E. A. (1999, January 1). Pythagoras of Samos. Retrieved March 14, 2011, from School of Mathematics University of St Andres Scotland: http://www-history.mcs.st-and.ac.uk/Biographies/Pythagoras.html.

Singh, S. (2005). Big bang. London: Harper Perennial.

Nuclear Fission v Nuclear Fusion

"Now I am become Death, the destroyer of worlds."  J. Robert Oppenheimer

David M Jones

A couple of years ago, I started to read a hefty, but very readable book entitled: ‘The Making of the Atomic Bomb’.  As I waded through page after page relating to the development of the science and physics that would eventually bring about the birth of the nuclear age, I marvelled at how difficult it was - and no doubt, still is - for mankind to create that which occurs naturally in nature.

The logistics of bringing about an environment in which a nuclear chain-reaction can begin seemed hardly feasible.  Many scientists considered the task might be physically impossible.  The conditions required for a nuclear chain-reaction to occur must be akin to those that exist only in the stars. 

My own curiosity eventually took me off on a tangent and I started to do a little research.  Our earthly scientists sought how to split uranium atoms to bring about nuclear fission; I soon discovered this was not the process which occurs in the stars.  On the contrary, stars, including our sun, create energy as a by-product of nuclear fusion!   What was the difference I wondered?  A little more reading revealed that our atom bomb and its fission reaction is achieved through splitting uranium atoms by means of an implosion.  That implosion results in a central core of fissionable material being placed under tremendous pressure – squeezing the metal core to less than half its previous volume.  Under those conditions a fission chain-reaction is possible.  This, I assumed, must at least compare briefly to natural conditions occurring under massive gravitational pressures.

FUSION

For fusion to work, extremely high energies are needed to fuse the nuclei together. This is needed to overcome the electrical repulsion (known as the coulomb barrier) between two positively charged nuclei, so that they get close enough to have the strong nuclear force bind the nuclei. This nuclear force has an effective range of around 10^-15 meters, which is why fusion occurs most easily in stars, where a high density and temperature environment exists. The density and temperature are the primary factors in determining the probability of the nucleons fusing in the star... Most of the energy generated within the Sun is created from a sequence of reactions that "burns" hydrogen into helium, known as the proton-proton reaction. (Team Thinkquest, 1998)

The article goes on to describe how, in our sun, the reaction occurs in the innermost region, where density is increased to one-hundred times the density of water on Earth.  At this density, temperatures soar to approximately fifteen million K (27,000,000 degrees F).  Hydrogen atoms are stripped of their electrons – creating plasma of free electrons and protons, the nuclei of the hydrogen.  Under these conditions hydrogen is converted to helium.  The resulting helium amalgam is smaller in mass than the original (hydrogen) free matter – the excess of this process being given off as heat and light.  That description, I hasten to add, is a gross over-simplification on my part to meet the restrictions of this short article.

Fundamentals: the Sun as a Star

Our Sun is by far the largest object in our solar system, containing more than 99% of solar system’s total mass. Observations of other stars indicate that the Sun is fairly "normal": it has a mass, luminosity and temperature that is somewhere in the middle-to-low end of the observed spectrum. It is also one of about 100 billion similar objects in the Milky Way.  Its characteristics are hard to grasp by earthly values, with a mass of 2 x 10³⁰ kg, an atmospheric temperature of 5500 ^oC and a luminosity of 4x10²⁰ megawatts.

The Sun is mainly composed of hydrogen and helium (~75% and ~25% by mass, respectively), with traces of heavier elements synthesized by past generations of stars in the solar neighbourhood.  These heavier elements are the main constituents of the inner terrestrial planets in the solar system; the Jovian planets have compositions almost identical to the Sun itself.

The proximity of the Sun to the Earth allows scientists to study phenomena in the solar atmosphere that are too small or too faint to be observed in even the nearest star to our own.  (The Curious Team, 1997 - 2010)

Armed with the knowledge that fusion occurs naturally, and the process of fission was ‘accidentally discovered’ by radio-chemists Otto Hahn and Fritz Strassmann in 1938 – whilst in the course unrelated experiments - I wondered where fission might occur spontaneously in nature. 

Unbelievably, it appears that 1.5 billion years ago - here on Earth - a natural nuclear fission reaction took place.  The site of this natural reaction was discovered 1972, in Oklo, Gabon, Africa - the area pictured above.  Scientists estimate the fission reaction continued on-and-off for hundreds of thousands of years!  Whilst it was active, this natural process produced nuclear waste similar to the wastes produced by the man-made nuclear fission reactors of today

. 

References:

Cohen, G. A. (1976, July 1). A Natural Fission Reactor. Retrieved January 8, 2010, from Scientific American: http://www.ans.org/pi/np/oklo/.

Rhodes, R. (1986). The making of the atomic bomb. New York: Simon & Schuster.

Team, T. C. (1997 - 2010). Ask an astronomer web site. Retrieved January 8, 2010, from Cornell University: http://curious.astro.cornell.edu/sun.php#questions.

Team, T. 9. (1998). Atomic alchemy basic fusion. Retrieved January 7, 2010, from Thinkquest 98: http://library.thinkquest.org/17940/index.html.