What is truth? - continued.

For centuries the finest brains on the planet believed that the Earth stood still, and that the sun appeared in the east every morning, travelled across the sky and disappeared in the west at night. Where it went to in the interim was a matter of some conjecture, but what was clear to everyone was that we were stationary, and it was moving. We now look back on those people as ignorant savages, but given the information they had - which amounted to no more than observing the sun as it moved across the sky - it was a perfectly logical conclusion to come to, indeed it was the only possible conclusion they could have come to. It was only when more information came to light (Galileo and all that) that it became clear that there might be other explanations. The main idea underpinning Einstein's Special Theory of Relativity is that everything is in motion, and that therefore there is no "solid ground" from which you can make definitive observations and measurements - all you can do is make observations and measurements from your particular point of view ("frame of reference") and these may be different from those of other people observing or measuring from a different frame of reference. This can lead to some rather unsettling ideas, as we shall see later.