Illimitable ocean without bound
Without dimension where length, breadth and height
And time and place are lost”
Wrote Milton in his immortal poem perhaps, as some people would like to think, subconsciously referring to the vastness of space.
About eight decades ago it was not only not unusual but also fashionable for astronomers to refer frequently in their articles to what has now come to be known as “empty space”. The idea behind this concept was that as soon as one escaped the Earth’s atmosphere a few tens of miles above the surface of the planet, there was absolutely nothing out there. In other words, there was a total vacuum there with not even a single atom in sight. Thus, according to this theory, there was a complete void like the one that Milton had described in his “Paradise Lost” in several places. In his fascinating book ” Life itself” Nobel Laureate Crick has given a fantastic description of the vast emptiness of space by describing what an astronaut or a passenger would see from a space ship which goes into empty space, at the speed nearing the speed of light from the Earth. He would not see even a speck of dust
Although the idea of “empty space” had been disputed long before, the real credit for this has to go to a German astronomer who in 1904 first challenged the concept. He had been looking at the spectrum of the star Mintaka in Orion’s belt, when he noticed something very curious that previous Astronomers had overlooked.
Before we analyse the concept of “empty space” we may first have to get a correct picture about stellar spectra themselves. Just as a telescope gathers light, a spectroscope does the reverse, “splitting” it up. When the light of the normal star is refracted through the spectroscope, it is split into bands of colour that are separated by dark lines. A spectrum formed by the light of the star carries the distinctive trademarks of the chemical elements that make up the star. Therefore when an astronomer sees true bright yellow lines close together in a characteristic position, he usually concludes that the stars contain the element ‘sodium’.
Let us now come to the Doppler effect named in honour of Christian Doppler the Austrian scientist who first gave the concept to the world in 1842. If a star is moving away from us, the wavelength of its light is slightly lengthened. All the lines in the spectrum are shifted over to the red or long wavelength’s region of the rainbow. However, if the star is moving towards us the shift is in the reverse direction to the blue i.e. the shortwave end. Another example would be the change in the pitch of the horn in a moving car. The pitch produced by the horn in a car moving away from us would be lower than it would be in a car moving towards us.
The German astronomer examined closely the dark lines in the spectrum of Mintaka and found that some of them did not exhibit the Doppler shift of the overall spectrum. The reason was obvious. The immovable lines did not belong to the star at all. Instead, they were caused by the clouds of the material in the space between the star and the Earth that absorbed some of the stellar light.
He, of course, proved to be quite right and the study of interstellar material began in right earnest. As more sophisticated methods of investigation were developed, it became possible to identify some of the interstellar substances. Hydrogen proved to be particularly plentiful and it became obvious that hydrogen is the most abundant substance in the universe as had long been suspected by astronomers. It is this fact which has made many astronomers in search of extra terrestrial life to transmit messages in the hydrogen frequency in the belief that any alien civilisation also can be expected to transmit messages in that frequency.
There have recently been new discoveries. Between the stars we find not only single atoms but also simple molecules. Then came the revelation that even organic molecules are present out there in the space. This discovery came as a real surprise to many astronomers but the results left no room for doubt.
One of these interstellar molecules is a chemical which every college student is familiar with, ethyl alcohol. Astronomers surveyed an inconspicuous star cloud in the Constellation Sagittarius near the centre of the galaxy and estimated that it contained enough ethyl alcohol to make more whisky than man has distilled throughout recorded history. This finding may naturally tempt connoisseurs of liquor into believing that they have found another reason for going into space and setting up colonies! They would be inclined to say that it would be really exciting to go into space, and scoop parts of the interstellar cloud and regale themselves with whisky throughout the journey. Unfortunately, nothing could be farther from the truth. The interstellar clouds are unbelievably tenuous, less dense than the most perfect laboratory vacuum we can produce. This is true even of the thicker nebulas such as Messier 42 in the sword of Orion. If you could take a bucket and plough through the Orion nebula scooping in material steadily, the amount collected would weigh less than a billiard ball does.
Tenuous as they are, these interstellar clouds are of fundamental importance to astronomers. Visible nebulae are places in which new stars are being born. Invisible clouds probably contain a large part of the mass of the universe.
Some scientists like Hoyle England’s preeminent astronomer have suggested that life began not on the Earth at all but out there in space, then brought here either by a meteorite or by a comet. Indeed if Hoyle is to believed, materials as complex as cellulose form spontaneously in interstellar space. To most people, however this hypothesis raises more difficulties than it solves, but it cannot be ruled out. The presence of organic molecules between the stars makes the possibility of life having evolved in outer space seem less farfetched than it would otherwise be.
Research is still going on energetically and new interstellar molecules are being discovered with amazing rapidity. The discovery of Ethyl Alcohol in space is particularly fascinating. Some astronomers speculate that this interstellar material will hold the answer to the question as to whether this universe will continue to expand for ever or will collapse.