Would you rather burn or freeze to death? In the long run, humanity won't have a choice: we'll freeze, if we last that long, according to the three astronomers who will receive this year's Nobel Prize in physics in Sweden on Thursday.
This was demonstrated conclusively in 1998 by the new Nobel laureates - Professor Saul Perlmutter of the University of California at Berkeley, Professor Brian Schmidt of Australian National University and Professor Adam Riess at Johns Hopkins University, working in two independent teams. They were also awarded the Shaw Prize in 2006 in Hong Kong for the same research.
According to the Nobel jury, they studied several dozen exploding stars, called supernovae, and discovered that the universe was expanding at an accelerating rate. Their finding has been hailed as the most important scientific result in the last quarter of the 20th century, changing fundamentally our understanding of the universe.
The 'burn or freeze' question crudely encapsulates a problem that has exercised scientists for decades. While Edwin Hubble demonstrated in 1929 that the universe is expanding, it was not clear whether the expansion was slowing down or speeding up. The two scenarios lead to opposite outcomes: if the expansion is decelerating, the gravitational force in the universe will in time collapse all the planets, resulting in a fiery inferno; but if the universe is growing ever faster, the stars will expand into infinity, moving farther apart and resulting in ever more frigid temperatures.
Our understanding of the cosmic immensity and dynamic nature of the universe is light years from the pre-Galileo era when earth was thought to be at the centre of a universe comprising only the sun, planets and visible stars.
In 1633, Galileo posited that the sun was at the centre of the universe as it was understood then. For this he was convicted of heresy and remained under house arrest until his death. The invention of more powerful telescopes in the 18th century led to the discovery that the sun is embedded in a grouping of stars, the Milky Way. Its sheer size - spanning 100,000 light years across and 10,000 light years in thickness, filled with 200 billion to 400 billion stars like the sun - convinced many at the time that the Milky Way was the only galaxy in the universe. It was not until 1923 that Hubble confirmed the existence of galaxies far beyond the Milky Way. The current estimate puts the number of galaxies at between 100 billion and 200 billion, each of them containing hundreds of billions of stars.
The next question: how do all these galaxies move in the universe? Newton's gravitational law of attraction implied that stars would pull towards each other and would theoretically collapse together ultimately. But until Hubble's findings, scientists could detect no significant expansion or contraction of the universe, so they assumed it to be static. Even Einstein made this assumption, and tweaked his equations to conform to it.
In 1915, when Einstein introduced the concept of space-time in his general theory of relativity to explain the force of gravity, he applied it to cosmology. But he found that his equations did not produce the static universe that was the scientific consensus of the time. He came up with a fix, which he called the 'cosmological constant', to make a static universe possible. The cosmological constant had a repulsive effect that counterbalanced the gravitational force in his equation.But there is something repulsive about the cosmological constant.
Simply speaking, he cheated by adjusting his maths to fit the answer he liked. This is equivalent to what someone who can't balance his checking account might do: create an artificial expense item. But then Hubble showed that the universe is indeed expanding. And the Russian mathematician Alexander Friedman formulated general relativity without the cosmological constant to explain a dynamic universe originating from the Big Bang. After these advances, Einstein said that putting the cosmological constant in his general theory of relativity to explain a static universe was the biggest blunder of his life. However, it turns out that the constant may well be the missing link in explaining the accelerating expansion of the universe.
While this year's Nobel laureates demonstrated by actual observation that the universe is expanding faster and faster, they did not explain it. So the next question is: what causes the universe to expand faster and faster despite being pulled in by the gravitational attraction of the stars? Scientists today attribute the cause to a force they call dark energy that permeates all of space and makes up 73 per cent of the universe.
The repulsive effect of dark energy is more powerful than gravitational attraction by a factor of three to one, which accounts for the accelerating expansion. A survey this year of more than 200,000 galaxies appears to confirm the existence of dark energy, and many theories are being developed to explain its source. One of these theories goes back to Einstein's cosmological constant. Scientists have found that rearranging the cosmological constant in his equations means it can represent dark energy. The force of dark energy overpowering gravitation expands the universe at an accelerating pace. As the universe expands, dark energy begins to dominate, causing the universe to expand faster, doubling its size approximately every 10 billion years.
Within the last two months, two earth-shaking events in physics have hit the headlines, one possibly showing Einstein was wrong, the other possibly showing he was almost right.
The faster-than-light neutrino experiment in Geneva on the behaviour of infinitesimally small subatomic particles, if validated, will cast doubt on Einstein's special theory of relativity as a foundation of modern physics.
However, the findings of this year's Nobel laureates in physics may confirm that Einstein was almost right with his description, under his general theory of relativity, of the workings of the infinitely immense universe - redeeming him from his 'biggest blunder'.
Tom Yam, a management consultant, holds a doctorate in electrical engineering and an MBA from the Wharton School of the University of Pennsylvania. He has worked at AT&T, Ernst & Young, and IBM