The general idea of 19th century Empty Space was that as soon as one ventured beyond Earth's atmosphere, a few tens of miles over our heads, there was absolutely nothing there. It was a total vacuum, not an atom within range. A complete void was thought to exist above our heads.
Although the idea of empty space had been disputed long before, it was really disproved by the work of a German astronomer named Johannes Franz Hartmann in 1904. He was looking at the spectrum of the star Mintaka, in Orion's belt, when he noticed something very curious that his predecessors had overlooked.
Just as a telescope collects light, so a star spectroscope splits it up. When the light of a normal star is refracted through the astronomical spectroscope, it is split into bands of color that are separated by dark lines. The spectrum formed carries the distinctive trademarks of the chemical elements that make up the star. If you see two bright yellow lines close together in a characteristic position, you may be quite sure that the star contains the element sodium.
The Glass Universe by Dava Sobel
Plenty of Hydrogen
Hartmann looked carefully at 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. They were caused by clouds of material in space, between the star and Earth, that absorbed some of the stellar light.
Hartmann was, of course, quite right, and the study of interstellar material began in 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.
Alcohol in Space
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. This discovery came as a real surprise to many astronomers, but the results left no room for doubt.
One of these interstellar molecules is our old friend ethyl alcohol. Astronomers surveyed an inconspicuous star cloud in the constellation Sagittarius, near the center of the galaxy and estimated that it contained enough ethyl alcohol to make more whiskey than homo sapiens have distilled throughout the history of civilization.
Unfortunately it would be impossible to extract the ethyl alcohol from space. The interstellar clouds are unbelievably tenuous, less dense than the most perfect laboratory vacuum we can produce. This is true even of the thicker clouds like the bright nebulas, such as in the Sword of Orion. If you could take a bucket and plow 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 in astronomy. Visible nebulas are places in which new stars are being born. Invisible clouds probably contain a large part of the mass in the universe as a whole, much more than the stars themselves.
Life from a Meteorite
Some scientists have suggested that life began not on Earth at all but in space, then was brought here either by a meteorite or according to Sir Fred Hoyle, by a comet. Indeed, Hoyle and his colleague Chandra Wickramasinghe believed that materials as complex as cellulose form spontaneously in interstellar space. To most people, this hypothesis raises more difficulties than it solves, but we cannot rule it out. The presence of organic molecules between the stars makes it seem less farfetched than it would otherwise be.
Research is going on energetically and new interstellar molecules are being discovered with amazing rapidity. I think that the 20th century discovery of ethyl alcohol is particularly fascinating. Poets have often rhapsodized about "the spirit in space." Well, the spirit is there—even if not in quite the form that the poets meant. Many astronomers think this interstellar material indicates whether the universe will expand forever or will collapse, causing another big bang.