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" able to look as far back as the cosmic events that followed the Big Bang.
A huge international project is under way 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 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.
"It should be able to see all the way back to when the first galaxies were formed after the Big Bang, basically as far as it is possible to see," said John Richer, a Cambridge University astronomer who represents Britain's interests in the 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 is 5,100 metres high, somewhere between sea level and space, about half the cruising height of a jumbo jet and just a whisker below the Everest base camp in Nepal.
The Atacama desert is the driest place on Earth; 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. Water is the one substance that could seriously interfere with the faint radiation signals emanating from deep space that the telescope is designed to capture.
The drawback for the construction workers 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. Although it is possible to work for limited periods at 5,000 metres, it is not an altitude at which people can live permanently.
Even acclimatised construction workers - mainly drawn from indigenous groups - 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 Atacama Large Millimetre Array (Alma), the name given to the network of telescope dishes that will open a new window on to the early universe.
Dr Tarenghi was speaking from the lower construction site of the future Alma control centre five kilometres from Chajnantor at a more comfortable altitude of 2,900 metres, 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 metres 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 block light at optical wavelengths.
Millimetre wave radiation can pass through something as thick as a 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 project is a truly international one, involving 14 countries from four continents but it is being run from Europe by the European Southern Observatory, a club of countries that has included Britain since 2002 - the UK pays its subscriptions through the Particle Physics and Astronomy Research Council.
The health of the scientists and construction workers 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, 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 to when the mountains and volcanoes of the high Andes were considered sacred.
While 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 in which 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 was a way to recognise the unique beauty and spirituality of the landscape. Mr Eschwey, a 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 from their dreams - one that will let them analyse objects they have yet to discover.
Dr Richer said that, in addition to seeing through dust clouds, millimetre-wave astronomy was finely tuned to study "cool" objects, the many 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.
'The doctor was hesitant, but I wasn't going to let a little high blood pressure stop me getting to the top'
By Steve Connor
The doctor taking my blood pressure looked as nervous as I felt. It was the second time he had done it in 10 minutes and the result was not much better than the first time around.
I was having the obligatory medical before making the final ascent to Chajnantor, the Andean plateau some 5,100 metres above sea level, and for some reason my blood pressure was not what it should be.
What made it worse was getting nervous about the possibility of failing the check-up. Being told to wait for a second test just added to the anxiety.
The doctor, who did not speak much English, looked into my eyes as if to give me the bad news. He was met with the determined stare of someone who had just travelled the best part of three days from the other side of the world. I would not easily be told now that the journey was going to end prematurely in a medical room.
I told him that high blood pressure was normal for British journalists and that I had been given the thumbs-up in London.
Eventually, he seemed to accept my story and having signed the necessary disclaimer about health hazards and the risk of possible death, I was on my way.
On the slow and bumpy ride up the dirt road in a 4X4, I took frequent sniffs on the oxygen canister supplied by the European Southern Observatory, which is building the Alma telescope at Chajnantor.
The sky is porcelain blue in the Andes but as you get higher the blue turns to a vibrant cobalt. The extreme brightness of the Sun becomes even more intense as the solar rays meet little resistance from the thin atmosphere at 5,100 metres.
When the truck approached our final destination, the landscape flattened out into a wide, featureless plateau surrounded by impressive mountains and snow-capped volcanoes. The tallness of the surrounding landscape did not make the plateau of Chajnantor feel particularly high. Yet this was the altitude of Everest Base Camp, and most people who get to that height have already spent a week or two trying to acclimatise -- whereas I had flown up from sea level.
As I stepped out of the truck, a bitterly cold wind punched my face and robbed me of what little breath I had left. A few puffs on the oxygen and I felt revived. A few more and I felt surprisingly jolly.
Walking just short distances at this altitude is exhausting, even with the help of oxygen supplies. At one point, my hat blew away and I remembered the advice not to run after it - people who do so tend to collapse.
Our party was followed by an ambulance and the same doctor who checked my blood pressure kept a nervous eye on me. At one point, he asked me whether I felt all right when he saw me grinning inanely for no obvious reason - clearly the temporary effects of too many sniffs on the oxygen.
An hour or so after arriving at Chajnantor, I had had enough and was ready for the descent. All I wanted to do now was lie down somewhere warm and sleep - a common feeling among people suffering mild oxygen deprivation.
Three hours later, I was back at 2,900 metres and almost fully revived. I was only glad that I was not one of the construction workers on the Alma telescope who have to spend an arduous day at an altitude that is so unforgiving.Reuse content