How will the world end

A.� The Big Bang, which happened around 15 billion years ago, is generally accepted as the point at which our universe began, but will it ever end and if so, how Here The AnswerBank looks at some of the possible scenarios.

�

Q.� Scenarios Is there more than one way for the universe to end

A.� Yes, currently there are three possible endings depending on how the universe carries on growing.

�

Q.� And the first one is

A.� Known as the Big Freeze, this theory predicts that if our universe carries on expanding it will be ripped apart by the resultant frozen wasteland of black holes and dying stars.

�

Q.� Number two theory is

A.� At some point space will stop expanding and go into reverse, springing back towards its centre, causing galaxies to smash into each other in the process, until the biggest black hole of all times is formed. This theory is aptly termed the Big Crunch.

�

Q.� It's looking pretty grim so far, no chance of a happy ending

A.� Well the third scenario still has an unhappy ending; it just takes a little longer to turn up. The universe stops expanding slowly, eventually grinding to a halt. However the universe would eventually suffer the end envisaged for the first theory, the Big Freeze.

�

Q.� Why does the universe have to end

A.� Because of two opposing forces that are battling it out all the time: the inward pull of gravity and the outward push of expansion.

�

Q.� Which of the three theories is the most likely

A.� As stated above there are two opposing forces determining the fate of our universe. Scientists are trying to work out how much gravitational pull our universe has, to do this they need to know the mass, or density, of the universe. The general rule is that the bigger the object, the greater its gravitational pull.

�

In astronomy, density is measured in Omegas, which is the last letter of the Greek alphabet, just to underline the finality aspect. The amount of mass needed to stop the universe expanding is 1 Omega, otherwise known as the critical density.

If the critical density is greater than 1 then it's the Big Crunch for us as the universe's gravitational pull snaps everything back inwards. If it's less than 1 then the Big Freeze is the more likely scenario as the universe carries on expanding.

�

Only if the critical density measures 1 can we look forward to the slightly more pleasant third outcome.

�

Q.� Any calculations on what the universes critical density is

A.� At the moment the latest calculation is 0.3, which means we're heading for the Big Freeze.

�

Do you want to quiz The AnswerBank about a cosmic theory

�

by Lisa Cardy