October 15, 2007 - I'M SITTING in a darkened hall listening to neuroscientist Anders Sandberg describe how to scan ultra-thin sections of brain. First, embed the brain in plastic, then use a camera combined with laser beam and diamond blade to capture images of the tissue as it is sliced.

The method is being developed (in mice, so far) to better understand the architecture of the brain. But Sandberg, who is based at the University of Oxford, has a rather more ambitious aim in mind. For him, this work is merely the first step towards uploading the contents of human brains - memories, emotions and all - onto a computer.

This is the opening session of the ninth annual meeting of the World Transhumanist Association (WTA) in Chicago. Sandberg and his fellow transhumanists plan to bypass death by using technologies such as artificial intelligence (AI), genetic engineering and nanotechnology to radically accelerate human evolution, eventually merging people with machines to make us immortal.

This may not be possible yet, the transhumanists reason, but as long as they live long enough - a few decades perhaps - the technology will surely catch up.

To many, these ideas sound seriously scary, and transhumanists have been attacked for jeopardising the future of humanity. What if they ended up creating a race of elite superhumans bent on enslaving the unmodified masses, or unwittingly programmed an army of self-replicating nanobots that would turn us all into grey goo? In 2004, political scientist Francis Fukuyama singled out transhumanism as the world's "most dangerous idea".

Now this small-scale movement aims to go mainstream. WTA membership has risen from 2000 to almost 5000 in the past seven years, and transhumanist student groups have sprung up at university campuses from California to Nairobi.

It has attracted a series of wealthy backers, including Peter Thiel, co-founder of PayPal, who recently donated $4 million to the cause, and music producer Charlie Kam, who paid for the Chicago conference. For the first time the organisation has recruited celebrity speakers, such as actor-environmentalist Ed Begley Jr and Star Trek veteran William Shatner.

Other well-known speakers are also on the roster, including AI developer Ben Goertzel, longevity biologist Aubrey de Grey and futurist Ray Kurzweil, the group's unofficial prophet. Kurzweil has recently caused a stir with his best-selling book The Singularity is Near, which explores what happens when our technologies become smarter than us. With transhumanists looking to woo the masses to their cause, I've come to Chicago to find out whether they deserve their dangerous reputation.