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This week, Collected Wisdom, the column we hope is always illuminating, tries to shed some light on the speed of light.
THE QUESTION: Toronto's Jackie Phillips writes: "You're driving your car at 100 kilometres an hour. You switch on the headlights. Is the light from your headlights now travelling 100 km/h faster than the speed of light?"
THE ANSWER: Okay, we can make this easy or we can make this difficult. What's it to be? Easy, eh? Thought so.
The answer, says Bob Orr of the department of physics at the University of Toronto, is no.
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"The speed of light is a constant for all observers. The light from your headlights is travelling at the same speed as if your car were stationary, or if it were travelling at the speed of light."
The constancy of the speed, he says, is basic to Einstein's theory of special relativity. "It has been tested to enormous precision in innumerable experiments."
Now, here's Alan Donald of Vancouver with a somewhat more complex take on the matter.
He says that from the point of view of a bystander, the velocity of light from the headlights is — to use a round figure — 300,000 kilometres a second. It's exactly the same for the driver. The light is not going any faster. How can this be?
"As the special theory of relativity shows, time passes slightly more slowly if you are moving, and this compensates for the velocity of the car. We don't notice this effect at speeds we routinely encounter. But we would if we were to travel at a substantial fraction of the speed of light, an objective many drivers on the Trans-Canada Highway seemed determined to reach."
FURTHER NOTICE
Some background, now, in response to our discussion last week about the most efficient highway speed for modern cars.
"As the federal public servant responsible for introducing a 100 km/h speed-limit policy during the 1974-75 energy crisis, I can assure you that actual car efficiency was not considered in choosing 100 km/h," writes Ian E. Efford of Crofton, B.C., former director-general of conservation and renewable energy at what was then the Department of Energy, Mines and Resources.
He says the 100 km/h upper speed limit did result in a lowering of other speed limits and a significant reduction in fuel consumption. But the number was chosen because it was easy to understand and "not so drastic that provincial politicians would reject it outright. I should note that the minister of energy for one province said that its citizens were simply unable to drive that slowly!"
HELP WANTED
Derek Wilson of Port Moody, B.C., wants to know if any "bird nerds" know the difference between a spotted bird and a speckled bird.
"I wonder why people say they 'lucked out' when they win something rather than saying they 'lucked in,' as it would appear to me they are in, not out of, luck," writes Carol McLean of Oakville, Ont.
And apologies to Erin Orsztynowicz of Collingwood, Ont., who asked last week why grocery stores never seem to have fruit flies raiding their produce. Erin is a she, not a he. We're still open for answers on this one, by the way.
Send answers (and questions) to wisdom@globeandmail.com. Include your name, location and a daytime phone number.
