How the Greeks Knew the Earth was a Sphere

‘As long ago as 340 BC the Greek philosopher Aristotle, in his book On the Heavens,
was able to put forward two good arguments for believing that the earth was a round sphere rather than a Hat plate. First, he realized that eclipses of the moon were caused by the earth coming between the sun and the moon. The earth’s shadow on the moon was always round, which would be true only if the earth was spherical. If the earth had been a flat disk, the shadow would have been elongated and elliptical, unless the eclipse always occurred at a time when the sun was directly under the center of the disk. Second, the Greeks knew from their travels that the North Star appeared lower in the sky when viewed in the south than it did in more northerly regions. (Since the North Star lies over the North Pole, it appears to be directly above an observer at the North Pole, but to someone looking from the equator, it appears to lie just at the horizon. From the difference in the apparent position of the North Star in Egypt and Greece, Aristotle even quoted an estimate that the distance around the earth was 400,000 stadia. It is not known exactly what length a stadium was, but it may have been about 200 yards, which would make Aristotle’s estimate about twice the currently accepted figure. The Greeks even had a third argument that the earth must be round, for why else does one first see the sails of a ship coming over the horizon, and only later see the hull?’

– Hawking. S. (1998) A Brief History of Time New York, United States: Bantam Books p. 2

Boiling Myth?

“Adding salt to water makes it boil more quickly.”

Mostly false. Depends on the nature of the salt.

Merely adding some salt to regular water will only make a difference in large quantities. However, it is true that salt water boils more quickly than regular water. If you look at the heat capacity of salt water, you will find that it is less than pure water. In other words, it takes less energy to raise the temperature of salt water 1°C than pure water. This means that salt water heats up faster and eventually gets to its boiling point first.

See other: Mythconceptions?

Atomic Theory

‘[…] when atomic theory was first proposed, it sounded pretty crazy. And yes, we call it ‘Atomic Theory’, using the scientific definition of theory, which is “a well-tested set of ideas that explains many disparate observations”, not the colloquial definition of theory, which is “a guess.” But luckily there’s no-one running around any more saying “atoms are just a theory.”

But it wasn’t that long ago that people were running around saying that. You want to know who settled it for good? Einstein! Atoms had been postulated for a long time by the 20th century, but it wasn’t until Einstein mathematically proved the existence of atoms and molecules in 1905 that the matter was truly settled. And you thought Einstein was all about relativity and E=mc2, he also proved atoms exist! Continue reading

On Relativity

“When you sit with a nice girl for two hours, you think it’s only a minute. But when you sit on a hot stove for a minute, you think it’s two hours. That’s relativity.”

– Albert Einstein

On the Closed Universe

“The universe is like a safe to which there is a combination, but the combination is locked in the safe.”

– Peter de Vries