Astronomical 'time machine' planned for Andes

A short walk in the vast, dry plateau of Chajnantor in the high Andes of Chile is an arduous and light-headed experience.

Here the air is so thin that day trippers have to carry oxygen canisters to avoid the debilitating symptoms of altitude sickness.

Chajnantor does not invite strenuous activity and yet this is the site of the most ambitious high-altitude construction project in the world.

By 2012 the plateau will be home to an astronomical "time machine" that will be able to look back to the cosmic events that followed the Big Bang.

A huge international project is underway at Chajnantor to build a $1bn telescope made up of 64 individual dishes or antennas each of which will be the size of a two-storey suburban house.

The entire array will act in unison to peer through the dense dust clouds of deep space, so permitting astronomers to gather ancient relic radiation from the earliest stars and galaxies that formed some 13 billion years ago.

The project is called the Atacama Large Millimetre Array, nicknamed Alma, the name given to the network of telescope dishes that will open a new window onto the early Universe.

"Alma should be able to see all the way back to when the first galaxies were formed after the Big Bang, so basically as far as it is possible to see," said John Richer, a Cambridge University astronomer who represents Britain's interests in the international telescope.

The bleak plateau where the time machine is being built nestles between a chain of snow-capped volcanoes.

Most importantly for the astronomers, Chajnantor lies 5,100 metres above sea level, about half the cruising height of a jumbo jet and just a whisker below Everest Base Camp.

At this altitude the air is almost devoid of any water, the one substance that can seriously interfere with the type of radiation that the telescope is designed to capture.

But the drawback is that the air here is also short of oxygen.

Atmospheric pressure at Chajnantor is less than half of what it is at sea level which means that every intake of breath contains something like 50 per cent fewer oxygen molecules than the human body is optimally designed for.

Even acclimatised construction workers - mainly drawn from local indigenous people - have been known to perform strange and potentially dangerous manoeuvres at this altitude, unaware that their brains are being slowly starved of oxygen.

"People up there don't think straight. That's why all orders are issued from down here," said Massimo Tarenghi, the director of the Alma project.

Dr Tarenghi was speaking from the lower construction site of the future Alma control centre some 5 kilometres from Chajnantor and situated at a more comfortable altitude of 2,900 meters, more than twice the height of Ben Nevis, Britain's tallest mountain.

"Up to 4,000 metres people behave pretty normally but something happens between 4,000 and 5,000 metres.This is when people do things they wouldn't normally do, and often they don't know why they are doing them," Dr Tarenghi said.

Each of Alma's 64 antennas, which measure 12 meters across, will be positioned in an array that will cover a distance of 14 kilometres (10 miles) at its widest point on the Chajnantor plateau.

Alma is designed to capture radiation that is in the millimetre-wave band of the electromagnetic spectrum.

Unlike optical light, this radiation can penetrate matter such as interstellar dust clouds which blocks light at optical wavelengths.

Millimetre wave radiation can pass through something as thick as a London telephone directory, which is why Alma will be able to see roughly twice as many stars and galaxies as the Hubble Space Telescope.

When Alma is finished in 2012 it will be the highest terrestrial telescope and the biggest and most expensive millimetre-wave telescope on the planet.

The reason why scientists have chosen Chajnantor as the site of such a complex scientific instrument is that it lies somewhere between sea level and space, which means that there are few water molecules in the atmosphere to interfere with the faint radiation signals emanating from deep space.

The Atacama desert is the driest place on Earth and at this altitude the air can hold next to no water vapour - humidity is about 3 or 4 per cent, which is about as dry as it can get without being in orbit.

But the downside for the Alma construction workers is the lack of oxygen.

Although it is possible to work for limited periods at 5,000 metres, it is not an altitude that people can live at permanently.

The project is a truly international one involving 14 countries from four different continents but it is being run from Europe by the European Southern Observatory, a club of countries.

The health of the scientists and construction workers operating at the Chajnantor site is carefully monitored and an ambulance is on hand at all times in case of emergencies.

Normally people do not stay overnight at the high site of Chajnantor but if they have to then special bedrooms are available that can be enriched with oxygen.

Drivers in charge of the 28-wheeled vehicles that will eventually carry each 120-ton antenna to the plateau will also work in oxygen-enriched cabins.

The site lies on ancient Inca trading routes and archaeologists have found evidence of human activity that goes back many hundreds of years when the mountains and volcanoes of the high Andes were considered sacred.

Just as the Inca went to the top of mountains to commune with their gods, scientists are venturing there to gain a better understanding of man's place in the wider cosmos.

The scientists recognise the local sensitivities of building on once sacred ground and each time construction begins at a new site a local elder is invited to conduct a "pachamama" ceremony when prayers are said and cups of wine and cocoa leaves are thrown into the air.

Jorg Eschwey, the site development manager, explained that conducting a pachamama is a way of recognising the unique beauty of a landscape that can have an almost spiritual effect on anyone fortunate enough to experience it first hand.

Mr Eschwey, an veteran builder of big telescopes for the European Southern Observatory, does not however get too carried away by the scale of the task at hand - a job that involves transporting 12,000 tons of concrete to an altitude of 5,100 metres.

"Logistics are complex, transport is a nightmare," he said.

But the real excitement over Alma comes from the astronomers who get to play with an instrument of their dreams - one that can analyse objects the researchers have yet to discover.

John Richer of Cambridge University said that in addition to seeing through dust clouds, millimetre-wave astronomy if finely tuned to study the many "cool" objects, stars and galaxies that do not emit the sort of radiation picked up by ordinary optical telescopes.

"Every time we observe a new piece of sky with Alma, every three minutes we will detect new galaxies that have never been seen before - just wherever you point the telescope you will see new galaxies," Dr Richer said.

"Here we're trying to open a really new view on the Universe with this magical wavelength of one millimetre and below. Alma's going to be the first major telescope that allows us to capture high quality images at these wavelengths," he said.

- INDEPENDENT