Communicating the immense numbers used in astronomy, whether in distance or in time, is always a challenge when talking to public audiences. The concept of "powers of ten" is useful for making "big" numbers manageable, but their `immensity' tends to get lost. One idea I have exploited to bridge this gap is to use a roll of toilet paper as a timeline, changing the scale as needed to cover various time frames of interest. Here is one example of how this can be done.
I like to use "1000 sheet" rolls of TP because of its nice tie-in to powers of ten. Let's say I've just described how the dinosaurs died away 65 million years ago, and I want to put this into perspective. I pull out a roll of TP where scaling has been marked at 10,000 years per sheet. (I usually mark out to, say, 1 million years, which is 100 sheets in--a bit of a pain, but it adds to the effect.)
Now I just unroll 10 sheets or so and describe how everything we really know about in recorded history is one the first sheet. (Even the pyramids of Egypt are only a half sheet back, at, say, 2000-3000 BC.) I usually highlight the cave paintings in France, dated at 20,000 years ago or so, as representing "cave men" (e.g. when Fred Flintstone lived, if the audience is young enough!). For more sophisticated audiences, I may pause at 100,000 years or so and highlight the emergence of Cro Magnon man (basically, the arrival of modern homo sapiens on the scene. Then I start unwinding to find the dinosaurs at 65 million years.
The clever reader will have already figured out, however, that, at 1000 sheets per role, my whole roll of TP will only get be back 10 million years. It will take 6.5 rolls of TP to get me back to when the dinosaurs disappeared. (Obviously I don't have to unroll the whole roll of TP to make the point...) It is immediately realized by everyone involved how ridiculous it is that Fred Flintstone had a dinosaur for a pet!
The scaling aspects can now be used to advantage to get to times meaningful for many astronomical purposes, like the "billions" of years back to the birth of the solar system, or even back to the Big Bang. Take out a second roll of TP, marked with 10 million years per sheet. Thus each sheet on this roll corresponds to an entire roll of TP in the previous example! To keep a long story short (so to speak), the solar system formed 500 sheets back (half a roll) on this second TP roll, and the entire roll only gets back 10 billion years, or only about 3/4ths of the way back to the Big Bang.
I hope this gives some inkling of how to use this idea. Of course, one can work many variations on this theme depending on the subject being discussed. It is very flexible, depending on the time scale per sheet to be used and the subjects one wants to work in after using this as an introductory demonstration.
If you find this document useful, or if you have suggestions for improving it, please let me know through one of the following channels:
Telephone: 410-516-8447 Fax: 410-516-8260 E-mail: wpb@pha.jhu.edu Snail mail: Dept. of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686William P. Blair