The universe this morning

A report from the frontiers of uncertainty by Tom Wilkie and Charles Arthur
Click to follow
The Independent Culture
Archimedes famously claimed he could move the Earth, given a fulcrum and a sufficiently long lever. The attention of modern astronomers, however, is focused on something vastly larger than our own planet: the entire universe. But their ambitions are more modest: rather than moving it, they simply want to "weigh" it.

In a cramped office on the top floor of the physics department at Glasgow University, Dr John Simmons spends his time counting galaxies and looking for patterns in their arrangement in the sky. In the rather more commodious premises of the Space Telescope Science Institute at Johns Hopkins University in Baltimore, Maryland, Dr Mario Livio worries that the most recent spectacular pictures taken by the Hubble Space Telescope may be missing nine-tenths of the "stuff" of which the universe is made. For 35 nights over a period of four years on top of a mountain in the Chilean High Andes, Dr Peter Katgert of the Netherlands' Leiden Observatory and his team of astronomers painstakingly employed the European Southern Observatory's 3.6-metre optical telescope to measure the speeds at which more than 5,600 galaxies are moving away from us. The measurements were published earlier this month.

Around the world, thousands of men and women are engaged on this enterprise of modern astronomy, whose scale appears almost an act of hubris. Our own solar system may seem vast to our earthbound perspective, barely explored by space probes built to the limits of our technology. Yet, in cosmic terms, it is but the attic of a terraced house in Cricklewood compared to the London of our own galaxy, the Milky Way. The sun is a dull little star in an insignificant location, one of perhaps 100,000 million in the galaxy, most of them clumped together to form a flat wheel or disc. Although, according to Einstein's theory of relativity, light is the fastest moving thing in the universe, it would take a beam of light at least 100,000 years to cross the Milky Way from one side to the other - longer than the whole history on this earth of anatomically modern humans.

But the Milky Way is far from being everything there is, and in its turn is a rather insignificant galaxy among many others. The broadening of astronomers' horizons came in 1924 when, after five years of observations and measurements, the American astronomer Edwin Hubble proved that the faint smudges - nebulae - seen by the largest telescopes were actually other galaxies far beyond the confines of our own. Five years later, he claimed that the universe itself was expanding and the galaxies receding from us at a speed proportional to their distance.

Appropriately, the Hubble Space Telescope in its turn hugely expanded astronomers' ideas of the number of galaxies in the universe. The "deep field" pictures taken by the telescope revealed far more galaxies than astronomers had expected. As a result, they quadrupled their estimate of the total number in the universe - from 50 billion to 200 billion galaxies.

In the face of such numbers, any attempt to measure the amount of stuff which the universe contains may appear an act of folly. But the prize is immense, for in "weighing" the universe - strictly, measuring its total mass - lies both its history and its future: the books of Genesis and Revelations contained in a single number.

Dr Katgert's study of 5,600 galaxies in the southern skies, which was started in 1989 but only reported this month, indicates that there may not be enough mass in the universe for its gravitational attraction to halt the current expansion. We may therefore be living in an open universe which will expand for ever.

Dr Livio, however, believes that "beauty" requires a universe containing a critical mass, such that the expansion will halt - even though he concedes that observations can find only 10 to 20 per cent of this mass. To resolve this issue, he has decided to look to the beginning of time.

Dr Livio told last month's meeting of the American Association for the Advancement of Science that the universe suffered a gigantic bout of cosmic "inflation" just after the Big Bang which started everything off 15 billion years ago. Less than one millionth of a millionth of a millionth of a millionth of a millionth of a second after the moment of creation, it underwent a rapid and tremendous increase - separate and different from the Big Bang - expanding more than a billion billion billion billion billion times almost instantaneously.

A central problem for Dr Livio is to understand why the mass of the universe has clumped together to form galaxies and clusters of galaxies. The Big Bang would have scattered everything uniformly in all directions, so how did such irregularities as galaxies and galactic clusters arise? Dr Livio hopes that quantum mechanics will come to his rescue - perhaps "during the inflation, random quantum fluctuations are expanded to a cosmic scale". Thereafter, "regions of higher density will attract each other and become denser and then collapse under their own gravity," he continued.

But the Hubble Space Telescope has pictured galaxies or pre-galactic fragments from times when the universe was less than a billion years old, so there was not enough time - according to current theories of galactic formation - for ordinary matter to produce the structures that astronomers can see. The economic metaphor extends here, as Dr Livio seeks an "invisible hand" to bring these things together. Many astronomers believe the sources of attraction must come from material that they cannot see, because it is "dark matter" - that is, it does not emit radiation which our telescopes and instruments can detect. But this dark matter can betray its presence by its gravitational pull on the stars and galaxies which we can see, thus accounting not only for the clustering but also for the dynamics of the movement of the galaxies. And the neat payoff is that the dark matter which clusters the galaxies could provide sufficient mass to "close" the universe and bring its expansion to a halt.

For Dr Simmons, however, "the link-up with inflation and high-energy physics - that's speculative. But as for the later history and evolution of the universe, the structures exist and the amount of observational data is huge, and growing all the time."

Dr Livio concedes too that while "the basic assumptions of the Big Bang appear extremely good - there was a hot, big bang - inflation and dark matter appear vulnerable."

Certainty about the very beginning derives not from recent pictures taken by optical telescopes like the Hubble but from a series of observations culminating, in 1965, with the detection of radio signals from empty space. This "cosmic microwave background" showed that even intergalactic space was not completely cold and the only way of accounting for it was to assume it was the relic of a phase when the entire universe was very hot. Two American physicists, Arno Penzias and Robert Wilson, received the Nobel Prize for hearing, in effect, the echo of the Big Bang. As the antiquarian and scholar of ancient religious texts, NK Sandars, remarked at the time of the discovery, it recalls the creation myth in the book of Job:

His breath made the heaven luminous,

His hand transfixed the fleeing serpent

All this but skirts the way he treads

A whispered echo is all we hear of him

But who could comprehend the thunder

of his power?

Sandars noted, "To us the 'whispered echo' of the next to last line may have a very modern sound, recalling the background 'whisper' picked up from interstellar space and believed by adherents of the Big Bang theory of cosmic beginnings to be the last ripple of that event."

Until the mass of the universe is fixed, endings are rather less clear. There are three possibilities: the open (ever-expanding) version; the closed one, where the total mass will eventually, after billions of years of expansion, fall back on itself in a "Big Crunch": present theory suggests this will happen if the mean density of the universe is more than three atoms per cubic metre. The third option, and the one many astronomers favour on aesthetic grounds, is that the expansion of the universe will one day stop, yet its total mass is insufficient to drag it back together. This is known as the "critical" universe.

But it is not clear that, from a human perspective, this holds any attractions. Over immense periods of time, even stars die. The likely fate of our own sun is that it will swell up into a red giant - so bloated that it will swallow up the Earth itself - before collapsing into a white dwarf, cold and sterile, with its nuclear fires extinguished for ever. Some stars, more massive than our own sun, undergo violent convulsions throwing off the outer layer in a supernova explosion - becoming bright enough for a few weeks to outshine even the galaxy in which they are situated. But then the inevitable inward collapse either to a dead neutron star or to extinction as black holes. Ultimately, after a period a billion times longer than the universe has yet existed, quantum mechanics may allow even the neutron stars and other matter to collapse into tiny black holes, which fizzle out by giving up their energy as radiation. This may be the ultimate end of the material world, frozen into unchanging stasis like the innermost circle of Dante's Inferno

Overleaf: The universal history

Comments