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Air thins on high, black holes trap light, canary holds smallest egg record

Q: Why does the air get thinner at high altitude? Katie, Oregon, Wisconsin

Ultra long duration balloon flies where the air is thin — above 99 % of Earth’s atmosphere. [NASA]

A: Air seems nebulous but is massive. Earth’s gravity pulls air molecules down, squeezing them together.

Air languishing at Earth’s surface has 200 miles of atmosphere above and a weight of 14.7 pounds (6.67 kg) on each square inch (6 square centimeters). At 18,000 feet high, the weight above halves and the air is twice as thin.

Further Reading:

The Weather Book by Jack Williams

Black holes trap light

Q: I was taught in school that gravity is a force between two masses. And that the speed of light is the fastest something can travel, because light has no mass. So why can light not escape from a black hole? If it has no mass, how can it be under the influence of gravity? Leland, Lakenheath, England

How gravity bends light. The actual star is depicted in red. It appears to be in the position of the yellow star. The bent curve (solid line) shows how light travels from the actual (red) star to an observer on Earth. [Rod Nave, Georgia State University]

A: Much of what you were taught is valid even under the terrible constraints of a black hole. The speed of light is, indeed, the fastest any object can go. Gravity is an interaction between two masses. Photons (light particles) are massless. Then, how does a black hole’s gravity trap light or, more generally, how can gravity influence light?

"This is deep water," says Rod Nave, physicist at Georgia State University but suggests thinking about how gravity bends light.

We first tested Einstein’s General Theory of Relativity with this effect. His theory predicted that a massive object, like the Sun, would bend light. Sure enough, during the solar eclipse of 1919, we observed the light from a star behind our Sun only because the Sun’s gravity field bent the star’s light. Otherwise, the Sun would have blocked the starlight. So, we have observed gravity influencing light.

The reason behind gravity’s ability to bend light is something called the principle of equivalence. Einstein stated we can’t tell the difference between the effects of gravity and those of a reference frame (like an elevator) that’s smoothly accelerating with the same acceleration as gravity.

A ball released in an elevator rising with 1G (32 feet/sec/sec or 9.8 m/sec/sec) acceleration will look exactly like it’s falling from a person’s hand in a stationary room. The ball will get closer and closer to the rising elevator floor until it hits.

Thus, the released ball in the rising elevator has an "inertial mass", which is exactly equivalent to its "gravitational mass" when it falls to the ground.

Moreover, photons have inertial mass (similar to that of air particles moving in the wind). Photons, for example, bop against a solar sail. The sail moves away from the bounced photon like a struck punching bag.

Since photons have inertial mass, they have an equivalent gravitational mass. Gravity influences light (for instance, bending it) via the photon’s gravitational mass.

Inside a black hole, gravity is so extreme it can bend light back down into the black hole. "It’s like the trajectory of a tossed baseball that has no chance of escaping Earth," says Nave.

Further Surfing:

WonderQuest: Black holes die, but it takes a while

HyperPhysics by Rod Nave: Black holes

Canary holds smallest egg record

Q: What’s the record for the smallest bird egg? Someone, World

A Yorkshire canary [Sid Golding, artist; Brian Keenan, Yorkshire Canary Club, © 1988, used with permission.]

Guinness World Records says the smallest bird egg was laid on Oct. 5, 1998 by a posture canary. It was a piddling 0.275 inches (7 mm) long and 0.2 inches (5.25 mm) in diameter — about the size of a pea.

Q: Is there a record for the world’s smallest chicken egg? Chelsea, Tippecanoe, Ohio

A: I can’t find it if there is. About the closest I can come is Farm Life talk: "I found a brown egg the size of an acorn in the coop," says Tim R. Lambert, Maine farmer, about the smallest chicken egg his bantam and Barred Rock hens ever laid. (Related figure: Tim’s egg).

This just in:  We went out to the coop and found a fully formed brown egg that is 1 1/4" x 7/8" and weighs 12 grams (0.4 oz). It is smaller than the egg on your website, and it came from full-sized (not bantam) chickens.  Amy, Mequon, Wisconsin

Further Surfing:

Yorkshire Canary Club

Canary Classics: The border fancy canary (a Victorian-times posture canary)

(Answered Feb. 6, 2004, updated:  June 15, 2007)