WHEN Elisha Otis stood on a platform at the 1854 World Fair in New York  and ordered an axeman to cut the rope used to hoist him aloft, he  changed cityscapes for ever. To the amazement of the crowd his new  safety lift dropped only a few inches before being held by an automatic  braking system. This gave people the confidence to use what Americans  insist on calling elevators. That confidence allowed buildings to rise  higher and higher.

They could soon go higher still, as a result of another breakthrough in  lift technology. This week Kone, a Finnish liftmaker, announced that  after a decade of development at its laboratory in Lohja, which sits  above a 333-metre-deep mineshaft which the firm uses as a test bed, it  has devised a system that should be able to raise an elevator a  kilometre (3,300 feet) or more. This is twice as far as the things can  go at present. Since the effectiveness of lifts is one of the main  constraints on the height of buildings, Kone’s technology—which replaces  the steel cables from which lift cars are currently suspended with ones  made of carbon fibres—could result in buildings truly worthy of the  name “skyscraper”.

The problem with steel cables (or “ropes” as they are known in the  trade) is that they are heavy. Any given bit of rope has to pull up not  only the car and the flexible travelling cables that take electricity  and communications to it, but also all the rope beneath it. The job is  made easier by counterweights. But even so in a lift 500 metres tall  (the maximum effective height at the moment) steel ropes account for up  to three-quarters of the moving mass of the machine. Shifting this mass  takes energy, so taller lifts are more expensive to run. And adding to  the mass, by making the ropes longer, would soon come uncomfortably  close to the point where the steel would snap under the load. Kone says  it is able to reduce the weight of lift ropes by around 90% with its  carbon-fibre replacement, dubbed UltraRope.

Carbon fibres are both stronger and lighter than steel. In particular,  they have great tensile strength, meaning they are hard to break when  their ends are pulled. That strength comes from the chemical bonds  between carbon atoms: the same sort that give strength to diamonds. Kone  embeds tubes made of carbon fibres in epoxy, and covers the result in a  tough coating to resist wear and tear.

According to Johannes de Jong, Kone’s head of technology for large  projects, the steel ropes in a 400-metre-high lift weigh about 18,650kg.  An UltraRope for such a lift would weigh 1,170kg. Altogether, the lift  using the UltraRope would weigh 45% less than the one with the steel  rope.

Besides reducing power consumption, lighter ropes make braking a car  easier should something go wrong. Carbon-fibre ropes should also,  according to Mr de Jong, cut maintenance bills, because they will last  twice as long as steel ones. Moreover, carbon fibre resonates at a  different frequency to other building materials, which means it sways  less as skyscrapers move in high winds—which is what tall buildings are  designed to do. At the moment a high wind can cause a building’s lifts  to be shut down. Carbon-fibre ropes would mean that happened less often.

All of which is worthy and important. But what really excites architects  and developers is the fact that carbon-fibre ropes will let buildings  rise higher—a lot higher.

Lighter, stronger ropes mean the main limiting factor in constructing  higher skyscrapers would become the cost, says Antony Wood, an architect  at the Illinois Institute of Technology, in Chicago. Dr Wood is also  executive director of the Council on Tall Buildings and Urban Habitat,  which, among other things, lists the official heights of skyscrapers. At  present the tallest is the Burj Khalifa in Dubai, which was completed  in 2010 and, at 828 metres, shot past the previous record-holder, the  508-metre Taipei 101 tower. The Mecca Royal Clock Tower in Saudi Arabia,  completed in 2012, is now, at 601 metres, the second-tallest. The  Freedom Tower in lower Manhattan, built near the site of the World Trade  Centre’s twin towers (417 metres and 415 metres) that were destroyed by  al-Qaeda in 2001, had its spire added in May to reach 541 metres. But  work has now started on the Kingdom Tower in Jeddah, Saudi Arabia. Its  exact proposed height is still a secret, but it will be at least a  kilometre.

With a big enough budget it would, says Dr Wood, now be possible to  build a mile-high (1,600-metre) skyscraper. Even with carbon-fibre ropes  few of such a building’s lifts would go all the way from the entrance  lobby to the observation deck. Most would debouch into intermediate sky  lobbies, where passengers could change lifts (not least because a  mile-high lift which seemed to stop on every other floor would not be  popular; it would be unutterably tedious and might force the poor souls  on board to make eye contact).

Such an arrangement is already familiar. Many skyscrapers are more like  three-stage rockets, with different buildings stacked one on top of  another—offices, a hotel and apartments. Sky lobbies mark the frontiers  between these uses. But carbon-fibre ropes will allow each of these  stages to be taller, too.

Nor need carbon-fibre lift-cables be confined to buildings. They could  eventually make an idea from science fiction a reality too. Space lifts,  dreamed up in the late 1950s, are a way of getting into orbit without  using a rocket. Building one would mean lowering a cable from a  satellite in a geosynchronous orbit above the Earth’s equator while  deploying a counterbalancing cable out into space. The cable from Earth  to the satellite would not be a classic lift rope because it would not,  itself, move. But it would perform a similar function of support as  robotic cars crawled up and down it, ferrying people and equipment to  and from the satellite—whence they could depart into the cosmos.

There are, of course, many obstacles to building such a lift. But the  answer to one—finding a material that is light and strong enough for the  cable—might just have emerged from that mineshaft in Finland.