Collected Wisdom Philip Jackman

# How fast are we all hurtling through space? Add to ...

This week, Collected Wisdom embarks on a voyage to the farthest reaches of the universe – so we're definitely going to take a substantial packed lunch.

THE QUESTION

Marke Slipp of Wolfville, N.S., wonders how fast we Earthlings are hurtling through space, considering the speed at which the Earth spins on its axis, the speed at which the Earth orbits the sun and how fast the universe is expanding.

We're travelling at 1,332,000 kilometres an hour, says Mike Hudson of the Department of Physics and Astronomy at the University of Waterloo.

How did he arrive at this figure? First of all, he explains, you have to have a point of reference. “Usually when we ask how fast something – such as a car – is moving, it is assumed to be relative to the surface of the Earth. In the case of our own Milky Way galaxy in the expanding universe, we might ask how fast we are moving compared with other galaxies.”

If the universe is expanding evenly, he says, each galaxy will see every other one moving away from it – observers on each galaxy will think they are at rest and the others are moving. However, the universe's expansion is not even, so some parts will appear to move faster than others.

“This greater velocity (compared with the average expansion) is something we can measure, and it's very fast,” he writes.” The sun is moving at 1,332,000 kilometres an hour compared with a distant horizon defined by the cosmic microwave background radiation.”

This speed is made up of three velocities – the sun's motion around the centre of the Milky Way galaxy (792,000 km/h), the Milky Way's speed while approaching our nearest neighbour, Andromeda (442,800 km/h), and the speed at which both the Milky Way and Andromeda galaxies are moving compared with the background radiation (2,160,000 km/h).

These three speeds don't add up to 1,332,000 km/h, however, because the velocities are heading in different directions. Some add, some partly add and some partly subtract. Meanwhile, the speed at which the Earth rotates on its axis (1,656 km/h at the equator) and the Earth's orbital velocity around the sun (108,000 km/h) are relatively small.

THE QUESTION

Why are beer cans 355 millilitres but beer bottles only 341 millilitres? Mike Maher of Montreal wants to know.

It's because 12 fluid ounces in the U.S. system is equivalent to 355 ml, while 12 fluid ounces in our imperial system is 341 ml, says George Ollerhead of London, Ont. He says the 355 ml format was adopted here to match the size of cans sold in the United States, where canned beer was initially more popular. Returnable bottles, however, stuck with the 341 ml format, in keeping with the imperial measure.

A.J. Schipper of Toronto adds: “Since neither is a normal metric size, we could solve this inconsistency by using the easy-to-understand size used in most countries, which is 330 ml, basically one-third of a litre.”

HELP WANTED

• How can dogs drink from dirty pools of water and not get sick? asks James R. Macready of Collingwood, Ont.
• Why, wonders Eric Mendelsohn of Toronto, do life-insurance policies offer a greater benefit if death is accidental?
• Why do so many double doors have one side locked? This puzzles Peter Ladner of Vancouver.
• Can you settle a bet between me and my partner? asks Bronwyn Whitaker of Victoria. Who is stronger, faster and has more ability: a hockey team of 15-year-old boys or the Canadian women's Olympic hockey team?

Let's hear from you: If you have the answer to one of these questions (or a question of your own) send an e-mail to wisdom@globeandmail.com. Please include your location and a daytime phone number.

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