Physicists have been known to occupy their time asking silly questions and seeking answers to those questions. One question currently on their minds is "why does space exist?" Lee Smolin, professor of physics at Penn State University, wrote in his book Three roads to quantum gravity: "So, in the end, the most improbable and hence the most puzzling aspect of space is its very existence. ... If you look around at the world seeking mystery, you may reflect that one of the biggest mysteries is that we live in a world in which it is possible to look around, and see as far as we like."

We may find it strange, even amusing, that there are presumably sane people spending their lives seeking an explanation for the existence of space. Yet Isaac Newton's question as to why an apple falls from the tree does not sound so silly today. When the answer is found it would seem to be a natural question for people to ask.

The universe can't stand still

In 1917, Einstein realised that, according to his general theory of relativity, the universe could not remain static. It must either expand or shrink. Yet even he refused to believe in such a universe. The general belief was that the universe had existed from the infinite past, and that it would continue to exist indefinitely. There was no beginning: there would be no ending. This was the static or steady state universe concept.

The astronomers then also did not know the structure of the universe. Our sun is just one of the billions of stars out there. The star that is nearest from earth other than the sun is Alpha Centauri, 4.2 light years away. That is the distance light travels in that time at the speed of 299,792 km/sec. (it's not per hour). Light from the sun takes about eight minutes to reach the earth.

It was not until the 1930s that the origins of the universe became a hot topic for the world's scientists. By then, astronomers had started to realise that our neighbouring Andromeda galaxy, which is 2.2 million light years away, and other galaxies seen in the night sky were not part of our galaxy. They were separate galaxies. Our own Milky Way galaxy is just one among billions of galaxies in the universe. An average galaxy contains hundreds of billions of stars.

Ironically, in order to understand properly what took place on a cosmic scale, scientists had to refer to studies that were concerned with the subatomic world, such as Einstein's special and general relativity theories as well as quantum physics. As a result, the old view of a steady state universe was put aside, to be replaced by a universe that could not stand still.

Lawyer takes on natures laws

In 1929 Edwin Hubble (the Hubble Space Telescope was named after him) discovered that the universe was expanding. Hubble actually graduated in law from Oxford but gave up after practising for just one year. He then took up PhD study in astronomy at the University of Chicago.

There must be something that made him lose interest in man-made laws and turned to studying the laws of nature. Could it be his realisation that the laws of man are good only on earth while the laws of physics are valid in all corners of the universe? History has proved that he made the right choice. He went on to discover an important law in astrophysics now known to us as Hubble's law. This is probably the only time a lawyer has written a law which applies to the whole universe.

Hubble made his important discovery when he noticed that, in tune with the Doppler effect, the wavelengths of spectral lines from distant galaxies were red-shifted. Since the degree of redness is influenced by the distance of the galaxies — the further the galaxies the redder the spectral lines — it seems that other galaxies must be moving away from us. (In sound, the Doppler effect tells us whether an ambulance is moving towards us or away from us when we listen to the pitch of its siren.) This means that the universe is expanding. If the universe is expanding there must be a moment in the distant past when the universe began and started to expand.

More convincing evidence came when Arno Penzias and Robert Wilson discovered the cosmic microwave background (CMB) radiation in 1965. We can actually see this CMB radiation in our living room. When there is an interruption of TV transmission due to some fault, the screen will display the familiar annoying black/white spots and lines, sort of like someone throwing sand from the inside of the glass screen. Part of this signal is the CMB picked up by the aerial when the broadcasting station goes down. We will see how the CMB provides evidence on the birth of the universe.

The Big Bang

From astronomical observations including Hubble's, physicists developed the Big-Bang model of the universe. In this, the universe began in a state of rapid expansion from a condition of near infinite density and temperature. The primordial plasma, the stuff the infant universe was composed of, was mainly energy in the form of radiation. It also consisted of particles such as neutrinos, electrons, positrons, neutrons, protons, and photons. According to Einstein's E=mc ², energy and matter particles are interconvertible. Photon is light of all wavelengths, or more accurately energy in the form of electromagnetic radiation.

Today some 14 billion years later, the temperature of the photons is about 2.7K (about -270 °C). The photons are the CMB we see on our TV screen. By studying the CMB astrophysicists are able to derive information about the nature of the universe at the early time when the photons first appeared. On June 30, 2001 Nasa launched the MAP (Microwave Anisotropy Probe) satellite into space. This latest effort was designed to study the CMB in order to get a more detailed picture of the early universe.

And the stars are born

The universe expands and cools. At some stage conditions became right for the particles to form elements. The first element to appear was the simplest form of matter which is H1 hydrogen formed from a proton combining with an electron. The balance of about 25 percent is He4 (helium) which is formed by the "joining up" of the hydrogen.

The H1 and He4 gases in the universe began to condense giving rise to unevenness in the matter density. This is like mist and fog condensing into dew and water droplets on cold nights. About one billion years after the Big Bang stars start to form by the process of gravitational collapse. This is due to gravitational attraction between the gas matter molecules in the interstellar cloud.

Stars shine by the nuclear fusion reaction of the hydrogen that makes up their initial bulk. The atoms "fuse" or "join up" to form larger atoms and in the process releases energy. This is the same reaction that makes the hydrogen bomb. The reaction uses up hydrogen producing larger atoms like carbon, oxygen and the rest of the elements.

At some stage a star runs out of fuel and dies. Depending on its state it may explode as a supernova spilling debris over a region of space. Some of the dust will condense with more hydrogen and helium gas in space and form new stars and planets. Our solar system, including the earth, was formed from remnants of stars that lived before its time billions of years ago. Such processes are still going on in other parts of the universe.

Life eventually evolves on earth. The atoms and molecules in our bodies come from a rather similar process. God created humans but not out of sugar and spice and all things nice. All the matter in our bodies has its origin in the stars. This prompted Martin Rees, astrophysicist and professor of astronomy at Cambridge to comment, "If you are a romantic person, you can say we are made of stardust, otherwise we are just nuclear waste."

The fate of the universe

Today, our sun is about 4.5 billion years old. It is a relatively young star. Physicists calculate that it will die in about five billion years time when it runs out of the hydrogen that fuels its nuclear furnace. This is the fate of our sun. What then is the fate of the universe?

To see the future, physicists turn to Einstein. Einstein was a great believer in fate. In 1934 he said, "All of these endeavours are based on the belief that existence should have a completely harmonious structure. Today we have less ground than ever before for allowing ourselves to be forced away from this wonderful belief." To him and other relativists, the universe runs on a set of laws, nothing is left to chance. Perhaps his most famous dictum is "God does not play dice."

To most people, Einstein's most famous equation is E=mc2 but to astrophysicists and cosmologists his field equation is what they live by. In its original simplest form it is written as G=8piT. This equation has been described by physicists as beautiful, elegant and rich: No other equation in physics is more simple in form and none contains such a treasure of applications and consequences.

But be warned, beauty is only in the eye of the beholder. It is an acquired sense, much like the acquired taste for durians. A durian lover can say all he wants about his passion but to the uninitiated, it's plain yuk!

In the field equation G is Einstein curvature tensor and T the stress-energy tensor. A tensor is a mathematical entity depicting a complex quantity. The Einstein tensor is a second-rank tensor. Taking into account symmetries it has 10 independent components. This simple equation is actually 10 differential equations! To understand it we need to learn tensor calculus and differential geometry. Beauty can indeed be deceptive. Whoever says beauty is skin deep has certainly not seen the beauty of the universe which is embodied in Einstein's equation. Let's forget about the beauty part and see what the equation can do.

Space is curved

The equation tells us, in simple terms, how matter generates curvature in spacetime. The equation contains within itself, among other things, Newton's equations of motion. It governs the motion of the planets in the solar system, the deflection of light by the sun, the collapse of a star to form a black hole, the expansion and contraction of the universe, and much, much more.

In space light always travels in a "straight" line. However, when it's near to massive or "heavy" objects such as our sun, its path bends because the space there is curved by strong gravitational force. No wonder a massive body like Mike Tyson can deflect punches throw at him! While there is truth in Mike Tyson's case, the curvature produced here is so tiny that it can't even be measured by the most sensitive instrument. Still, it is possible to calculate such space curvatures with Einstein's equation.

Physicists can also calculate the future evolution of the universe using this equation. Solutions to the equation provide the link between the present state and the future of the universe. There are two possible scenarios. First, the universe may keep on expanding forever. The second possibility is that it will stop expanding at some point in the future and reverse into contraction, eventually collapsing back to a state of near infinite density call the "Big Crunch". This will happen if the gravitational force of all the matter in the universe is strong enough to overcome the expansion.

Which alternative it will follow depends on several factors which can be measured or observed in our present-day universe.

The universe is flat

One factor physicists can observe in the present universe is its radius of curvature. This can be determined from observation of the CMB radiation. The radius of curvature will tell us whether our universe has an "open", "closed" or "flat" geometry.

In 1519 Ferdinand Magellan sailed round the world without falling over the edge. This proved to us that the world is not flat.

Now almost 500 years later astrophysicists tell us that from the observed data our universe is flat. We can visualise a flat two-dimensional object like a sheet of paper but it is hard to grasp the concept of a flat three-dimensional universe. Curved space in a flat universe can make sense if you imagine drawing a curved line which has only one dimension on a flat sheet of paper which is two-dimensional.

Data obtained in 1998 by the astrophysicist Saul Perlmutter and his group at the Lawrence Berkeley National Laboratory in California also indicated that the universe would keep on expanding. On earth a collapsing universe with the stars crushing together must seem like the sky is falling down. So the findings of Perlmutter and company is good news indeed: The sky would not be falling down after all!

There are many other questions about the universe physicists are asking. One that is being hotly pursued today is what 'preceded' the initial state of the Big Bang. Einstein's relativity theory fails to provide the answer. However, many physicists are convinced that a new theory call quantum gravity — a theory combining relativity and quantum mechanics — will provide the answer. Physicists also think this new theory will explain the existence of space.

Nobody has yet explained in detail this new theory. Several approaches are being pursued, among which are loop quantum gravity and String/M-theory. Both are hot research subjects for theoretical physicists all over the world. The use of the M-theory cosmology to study the universe is fast becoming a 'sexy' research area attracting many bright young PhD students entering the world physics community.

For us lucky ordinary mortals, credit card bills and monthly instalments are things that keep us awake at night. But for these poor unfortunate souls, worries about the sky falling down and why space exists are giving them sleepless nights. They can't go to sleep at night because that is the time astrophysicists go to work in observatories to study the stars. Closed minds will not resolve whether the universe is open or closed. We need open minds to open up our world to comprehension, for Einstein said, "The most incomprehensible thing about the world is that it is comprehensible."

CY THAM earns his living doing physics at the Cavendish Laboratory, Cambridge.