When scientists solve one puzzle of the universe, another crops up. John Von Radowitz looks at seven of the biggest questions that are exercising the cleverest minds

SCIENTISTS have answered all kinds of questions about the universe, but every solved puzzle creates even more mystery.

New Scientist magazine has identified seven of the biggest questions which are still baffling scientists.

What makes the universe tick?

Scientists cannot further our understanding of the universe until this problem is solved. Physics as we know it today is built on Einstein's theory of relativity and quantum mechanics. The former revolutionised the concept of space and time, while the latter confounded established notions when studying the behaviour of particles smaller than atoms.

What's the universe made of?

Physicists still don't know what's really out there. Astronomers can see stars, planets, gas and dust containing normal atoms. But for every gram of ordinary matter you can see, there are several grams of unseen ''dark'' matter, the nature of which is unknown.

Scientists know this because of the way stars move. Our galaxy, the Milky Way, spins too fast for the gravity of its visible material to hold it together. There must be something else, or the peripheral stars would be flung off into space.

Was Einstein's antigravity really a mistake?

Einstein himself questioned including the hypothesis of reducing or cancelling a gravitational field in his theories. But he may have been right to include a type of antigravity called the ''cosmological constant'' to his general theory of relativity. For this constant gives space a repulsive property, allowing it to expand faster and faster.

Einstein added this fudge factor because, when the cosmos was thought to be static, something was needed to balance the gravitational pull of matter and prevent it collapsing.

Why do we live in three dimensions?

Some scientists think space emerged from the Big Bang with three dimensions just by chance, and other regions of the universe may have a different number.

There are hints that our familiar three dimensions of length, breadth and height may be an illusion. According to some theories, space could have nine or even ten dimensions, but we are only aware of three of them.

Is time travel possible?

Enstein's theory of relativity predicts that an observer moving very fast relative to the Earth can leap into the Earth's future. This is because the fast-moving traveller's time slows down, as far as people on the Earth are concerned.

Are we living in a cosmic colander?

At the centre of every black hole there's something nasty called a singularity. At this point, gravity and the curvature of space-time become infinite.

No one really understands singularities. We don't know if they mark an end to space-time, or whether they merely signal a breakdown of our theory.

How can I ask these questions?

Put another way, where does consciousness come from? Quantum mechanics has been cited as a possible key to consciousness. But the principles governing information and complexity are still being worked out. At some level, it is thought, quantum mechanics must play a part in the story of life.

Since the rules for processing quantum information differ dramatically from those for classical systems, perhaps this will provide the key to the puzzle.