The Presidential Address “Time the Essence”,19th September 2008

David Forshaw entertained us with an intriguing and thought provoking account of the mystery of time;. Commencing with an apt quotation from a book by G J Whitrow, “…Only time has this peculiar property which makes us feel intuitively that we understand it perfectly so long as we are not asked to explain what we mean by it…”

Some suggest time is like a fluid, others a series of linked atomic particles. Our sense of time is based entirely on our perception of it on this planet of ours.

The question :- “How long is a second?” was raised. Very short seconds were referred to , e.g. the nanosecond (0.000,000,000,1 second) and even the femto second , 10 to the power minus 24, a so called atom of time or “chronon” – the time it takes for light to cross the distance of a proton from an electron.

The audience was asked to take part in a little experiment, namely to count up to a minute in their heads giving a signal when in their estimate this had been reached. As expected some were very close to the correct time and there was a scatter of slower and faster results. Could the faster people be more impulsive? and the slower more contemplative? Experiments conducted with two men spending nearly five months in underground caves were found after two weeks to have greatly underestimated time’s passage.

Some birds only migrate at night. No particular stars appear to be involved in their direction finding ability, but only the general pattern of the night sky. In the daytime the elevation ofthe Sun, its position, and the length of daylight hours contribute to birds navigational skills.

Music and the length of a second were then discussed, mentioning how in some pieces of classical music with differing lengths of silences between chords, different sections of the orchestra could come in fractionally out of phase with others. Samples of Sibelius’ 5th symphony and a Beethoven string quartet were played to illustrate this.

The significance of 60 seconds in a minute and 60 minutes in an hour were discussed. The Babylonians responsible for this method of time division noted that 60 was the smallest number that was divisible by 2,3,4,5, and 6. Various other calendars were referred to including the Egyptian, Mayan, Sanscrit and Roman systems.

The length of the year was discussed with the interesting finding that it varies slightly in length depending on whether it is estimated from the equinoxes or solstices, the average being 365.24219 days this being the current average length of our tropical year. This is not the same as the sidereal year which is some 20 minutes longer due to precession. The equation of time was then explained as being the resultant of the Sun travelling along the ecliptic rather than the celestial equator, coupled with the eccentricity of the Earth’s orbit. To make things more complicated, as a result of tidal drag, the Earth was slowing down by degrees. Studies of growth bands on fossil corals suggest that 600 million years ago the day was 21 hours long. All these factors were contributing to the difficulty in estimating the length of a second.

Relativity was drawn into the equation “with some trepidation”
Time slows down for people travelling at close to the speed of light, and even jet airliners travelling at less than one millionth the speed of light experienced a slowing of time equal to 59 nanoseconds going east and 273 nanoseconds going west., the difference caused by the Earth’s rotation to the east.

Finally, whilst consuming a leisurely meal in a French rural setting, the various courses lovingly described by David, he observed hundreds of swifts chasing after insects and started to ponder over whether time scales for different species operated at different wavelengths to our own, Another short experiment, namely asking the audience to estimate a fraction of a minute (48 seconds) brought the proceedings to a close.
This interesting talk was very well received. It was followed by the cheese and wine reception during which the effort Chris and Tricia Banks had put into preparing this sumptuous repast was gratefully acknowledged.