stem cells
One case involving stem cells occurred in the past year with Haruko Obokata, a young cell biologist at the Riken research institute in Japan
It is in the nature of scientists to argue over the evidence for or against any important breakthrough. Sometimes announcements made in good faith do not stand up to detailed scrutiny, namely the replication of the research by other experts.

On other occasions, scientists can be duped by the misconduct of their own colleagues prepared to cherry-pick favourable data to suit their conclusions, or, even worse, to fabricate data and commit outright scientific fraud - the most heinous crime in science.

One of the best examples of fraudulent research in recent years was the work on the cloning of human embryos by the South Korean researcher Hwang Woo-Suk of Seoul National University who announced in two scientific studies published in 2004 and 2005 that he had isolated human embryonic stem cells.

It turned out that he had faked many of the results and that he had engaged in dubious ethical practices in obtaining the human eggs needed for the research. He was eventually charged and found guilty of embezzlement and bioethical violations.

Another case involving stem cells occurred in the past year with Haruko Obokata, a young cell biologist at the Riken research institute in Japan. Dr Obokata claimed, with her Japanese and American colleagues, to have created stem cells by bathing ordinary blood or skin cells in a weak acid solution.

She called the technique "stimulus-triggered acquisition of pluripotency" (STAP) and it promised to revolutionise medicine as it offered the hope of creating therapeutic stem cells from a patient's own skin or blood with a simple, cheap technique that could be performed in any well-equipped lab.

Unfortunately, it was shown that the scientific research paper contained errors and other scientists were unable to replicate the findings, leading to a complete retraction of the research. Dr Obokata, however, continues to believe that the technique works and is still trying to replicate here own findings.

Replication is of course at the heart of science. When chemists Stanley Pons and Martin Fleischmann announced in 1989 that they had achieved nuclear fusion at room temperatures - so-called "cold fusion" - physicists everywhere wanted to reproduce the findings. Nuclear fusion, which powers the Sun, was only thought to occur at extremely high temperatures. If it could occur at room temperatures it would open the door to cheap, unlimited and clean energy.

It was too good to be true because it turned out not to be true. No-one has been able to demonstrate cold fusion as described by Pons and Fleischmann

Sometimes a scientific announcement is made that chimes with a bigger philosophical significance. In 1996, for instance, Nasa announced that it had found evidence of fossilised mini-microbes in a piece of a meteorite from Mars, which fell to Earth 13,000 years ago and was discovered in Antarctica in 1984.

The clear implication was that life had existed on Mars and that we on Earth were "not alone" in the Universe. "If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered," said President Bill Clinton on the day of the announcement on 7 August 1996.

The trouble, once again, was that the discovery could not be confirmed by other researchers. It may have been a bad day for the idea of extra-terrestrial life, but it was a triumph for the scientific method.