Every new technology involves risk. Often the risk is known, or known to be smaller than some acceptable limit. The risk from lcd displays for example, is known to be small because they produce only visible light to which we are exposed all the time without suffering adverse consequences. Sometimes however, technology can introduce new risks. The best example is possible mobile phones. These emit and receive electromagnetic waves with wavelengths that put them in the microwave range. Many people have heard of microwaves because microwave ovens use electromagnetic waves to heat food. Some people may think this means that when you hold a mobile phone close to your head it will cook your brain – though the frequencies used to cook food are exactly those to heat water. The frequencies used by mobile phones are not the same - and in fact experiments conducted with rats show visible changes when brain scans are done before and after exposure to mobile phone signals.
The images may be misleading, because brain scans change according to the activity. Even if mobile phone signals are harmful, they are being reduced in strength all the time as processing technology improves so that weaker signals can be decoded.
The precautionary principle states that when the risk from an activity or technology is unknown, it is better to restrict the activity and regulate the technology or even stop them, or their use altogether. Many people though, will continue using their phones, whatever the rumours, until they are proven to be unsafe. This is in contrast to nuclear power, to which a lot of people are opposed even though the risks are well known and low.