GENEVA (Reuters) -- A 100-ton wheel, the last piece of an ambitious experiment that scientists hope will help unlock the secrets of the universe, was successfully lowered into an underground cavern on Friday.

It is the final major element in the ATLAS particle detector, the largest of four detectors being hooked up to the world's most powerful particle accelerator which the European Organization for Nuclear Research (CERN) hopes to start up around the middle of 2008.
""This last piece completes this gigantic puzzle,"" CERN said in a statement.
The wheel was lowered down a 100-metre shaft and aligned within a millimeter of other detectors at CERN, the world's leading center for particle research located at a sprawling complex along the Swiss-French border.
The ATLAS detector will measure particles called muons expected to be produced in particle collisions in the accelerator, known as the Large Hadron Collider (LHC).
The LHC will recreate conditions just after the Big Bang, which many scientists believe gave birth to the universe, by colliding two beams of particles at close to the speed of light.