Space is not really empty. A perfect vacuum does not exist in nature. Space is filled by a thin gas –”interstellar gas” first detected in 1904 by Hartmann. The concentrations of gas and dust become much greater and denser in the neighbourhood of galaxies, which are surrounded by “fog”, mostly composed of atoms of hydrogen, ionised by radiation from the stars. Even this matter is not inert and lifeless, but is broken up into electrically-charged subatomic particles, subject to all kinds of movement, processes and change. These atoms occasionally collide and can change their energy state. Though an individual atom might only collide once every 11 million years, given the vast numbers involved, it is enough to give rise to a continuous and detectable emission, the “song of hydrogen”, first detected in 1951.
Almost all of this is hydrogen, but there is also deuterium, a more complex form of hydrogen, oxygen and helium. It might seem impossible that combination should occur, given the extremely sparse distribution of these elements in space. But occur it does, and to a remarkable degree of complexity. The water molecule (H2O), was found in space, as was that of ammonia (NH3), followed by formaldehyde (H2CO), and even more complex molecules, giving rise to a new science – astrochemistry. Finally, it has been proved that the basic molecules of life itself – amino acids – exist in space.
Kant (in 1755) and Laplace (in 1796) first advanced the nebular hypothesis of the formation of the solar system. According to this, the sun and planets were formed out of the condensation of an immense cloud of matter. This seemed to fit the facts, and, by the time Engels wrote The Dialectics of Nature, it was generally accepted. In 1900, however, Thomas C. Chamberlain and Forest Ray Moulton put forward an alternative theory – the planetesimal hypothesis. This was further developed by British scientists Sir James Hopwood Jeans and Sir Harold Jeffreys, who advanced the tidal hypothesis in 1918. This involved the idea that the solar system originated as a result of a collision of two stars. The problem with this theory is that, if it were true, planetary systems would be extremely rare phenomena. The vast distances separating stars mean that such collisions are 10,000 times less common than supernovae – themselves far from common occurrences. Once again, we see that, by attempting to solve a problem by resorting to an accidental external source like a stray star, we create more problems than we solve.
Eventually, the theory that was supposed to have displaced the Kant-Laplace model was shown to be mathematically unsound. Other attempts, like the “three-star collision” (Littleton) and Hoyle’s supernova theory, were also ruled out in 1939, when it was proved that the material drawn from the sun in such a way would be too hot to condense into planets. It would merely expand into a thin gas. Thus, the catastrophe-planetesimal theory was overthrown. The nebular hypothesis has been reinstated, but on a higher level than before. It is not merely a repetition of the ideas of Kant and Laplace. For instance, it is now understood that the clouds of dust and gas envisaged in the model would have to be much bigger than they thought. On such huge scales, the cloud would experience turbulence, creating vast eddies, which would then condense into separate systems. This perfectly dialectical model was developed in 1944 by the German astronomer Carl F. von Weizsäcker, and perfected by the Swedish astrophysicist, Hannes Alfvén.
Weizsäcker calculated that there would be sufficient matter in the largest eddies to create galaxies in the process of a turbulent contraction, giving rise to sub-eddies. Each of these could produce solar systems and planets. Hannes Alfvén made a special study of the magnetic field of the sun. In the early stages, the sun was spinning at a great speed, but was eventually slowed down by its magnetic field. This passed on angular momentum to the planets. The new version of the Kant-Laplace theory, as developed by Alfvén and Weizsäcker, is now generally accepted as the most likely version of the origins of the solar system.
The birth and death of stars constitute a further example of the dialectical workings of nature. Before it runs out of nuclear fuel, the star experiences a prolonged period of peaceful evolution lasting millions of years. But on reaching the critical point, it experiences a violent end, collapsing under its own weight in less than a second. In the process, it gives off a colossal amount of energy in the form of light, emitting more in a few months than the sun emits in a billion years. Yet this light represents only a small fraction of the total energy of a supernova. The kinetic energy of the explosion is ten times greater. Perhaps ten times more than the latter is carried away in the form of neutrinos, emitted in a split-second flash. Most of the star’s mass is scattered into space. Such a supernova explosion in the vicinity of the Milky Way hurled forth its mass, reduced to nuclear ashes, containing a large variety of elements. The earth and all that is in it, ourselves included, is entirely composed of this recycled stardust, the iron in our blood being a typical sample of recycled cosmic debris.
These cosmic revolutions, like the earthly variety, are rare events. In our own galaxy, only three supernovas have been recorded over the past 1000 years. The brightest of these, noted by Chinese observers in 1054, produced the Crab Nebula. Moreover, the classification of stars has led to the conclusion that there is no new kind of matter in the universe. The same matter exists everywhere. The main features of the spectra of all stars can be accounted for in terms of substances that exist on earth. The development of infrared astronomy provided the means of exploring the interior of dark interstellar clouds, which are probably where most new stars are formed. Radio astronomy has begun to reveal the composition of these clouds – mainly hydrogen and dust, but with an admixture of some surprisingly complex molecules, many of them organic.
And so the birth of our solar system some 4.6 billion years ago developed out of a cloud of shattered debris of a now extinct star. The present sun coalesced at the centre of the revolving flat cloud, whereas the planets developed at different points encircling the sun. It is believed that the outer planets – Jupiter, Saturn, Uranus and Pluto – are a sample of the original cloud: hydrogen, helium, methane, ammonia and water. The smaller inner planets – Mercury, Venus, Earth and Mars – are richer in heavier elements and poorer in gases like helium and neon, which were able to escape their weaker gravities.
Aristotle thought that everything on earth was perishable, but that the heavens themselves were changeless and immortal. Now we know differently. As we gaze with wonder at the immensity of the night sky, we know that every one of these heavenly bodies that light up the darkness will one day be extinguished. Not only mortal men and women, but the stars themselves that bear the names of Gods experience the agony and the ecstasy of change, birth and death. And, in some strange way, this knowledge brings us closer to the great universe of nature, from which we came and to which we must one day return. Our sun has at present enough hydrogen to last for billions of years in its present state. Eventually, however, it will increase its temperature to the point where life on earth will become impossible. All individual beings must perish, but the wonderful diversity of the material universe in all its myriad manifestations is eternal and indestructible. Life arises, passes away, and arises again and again. Thus it has been. Thus it will ever be.