Merry Christmas
Today, December 25, is Christmas Day, celebrated by many, often with family and friends. (Well, some, like me, actually follow the tradition of celebrating on the 24th, not the 25th.)
The English word Christmas invokes a Christian tradition, but other languages, like my native Czech, are much less precise in attributing the ownership of the tradition.
Christmas is really a holiday that historically spans cultures and religions. It is a continuation of a very old custom to celebrate the time around the winter solstice. Ancient Egyptians celebrated Horus and the resurrection of Osiris,
Nordic countries celebrated the time of Yule, Germanic ones, the god Odin.
Persians had their Yalda (where "Yule" probably comes from),
Romans had their Saturnalia
and it was only when Pope Julius I declared the 25th to be the official birthday of Jesus (partly to counter the hedonism of Saturnalia) that the modern concept of Christmas was created.
Despite that, some Christians, such as the New England Puritans, still saw so much association of Christmas with the old pagan rituals that they actually banned celebrating it for a part of the 17th century. (Since then, the feelings about Christmas seem to have shifted). No matter, it seems likely to me that it will still be with us for another good 3-4 thousand years.
So Merry Christmas!
By the way, have you ever wondered as a child who is delivering all those Christmas presents? Well, I didn't - I knew right away that it was my parents. Having a stranger sneaking into your house just to mess with our Christmas would definitely be odd and a bit scary - I was not OK with that idea. (But I did have some knives and bats, even as a child, so I was moderately confident that I could scare them off.)
But I digress ... so, I decided to play along (at least while I was really young and my parents still had the illusion that the brain in my child-like body had also child-like thoughts). In Czech culture, the presents are delivered by Ježíšek - baby Jesus (sometimes called Christkind.)
Some cultures employ Father Chrismas, others Grandpa Frost, or directly St.Nicholas. Some even use a gnome or a goat.
Note: St.Nicholas is the main European source of the tradition of gift giving.
The original story of St.Nicholas states that he did not like the idea of one poor father in the neighborhood forcing his daughters into prostitution so that they could pay the dowry they apparently needed to get married and out of the house. Various stories about this exist, all converging on the idea that the saint ended up financially helping the women to avoid said prostitution.
It does strike me as a sign of a not very good society when you have to rely on a saint to save you from prostitution. It is also not a great custom to ask women to pay men to marry them. And, I put it to you, forcing your daughters into prostitution is really a very, very bad way to solve one's financial difficulties. I'm glad I don't live in such a place.
Later on, Martin
Luther and others purists were uneasy about so much attention
being given to the saint - a mere mortal, not God - so they pushed and pushed,
until the tradition of gift giving has shifted from the St.Nicholas Day (December 5-6) to Christmas (December 24-25) when people were supposed to celebrate God and not the saint.
Whatever the reasons and whatever the time to do it, giving presents to bring out a little happiness is still OK, I'd say.
Today, on Christmas Day, humanity will get its special present: the James Webb Space Telescope will be launched to space. The telescope will help us answer questions about the physics of the beginning of the Universe, which will contribute to the physics we need to secure our survival on the planet. So, may I introduce here two "fun" Christmas trivia questions for you:
- What do the James Webb Space Telescope and Trojans have in common?
- What does it have to do with the metric system being decimal and not duodecimal (base-10 and not base-12)?
What does James Webb Space Telescope and Trojans have in common?
Their location. It is/will be in one of the 5 Lagrange points where the gravitational pulls of 2 celestial bodies (Earth-Sun in the case JWST) are at equilibrium. The telescope will use L2, the Trojans are at L5.
"Trojans" is the name given to asteroids that are captured by a planet's gravity and then permanently orbit the Sun in a fixed relative position to the planet. Earth has a couple of such (natural) Trojans, Jupiter has many thousands, perhaps millions. Note: in the cases of L4 and L5, one point is positioned "in front" of the planet and one is positioned "behind". In that case, the asteroids at the "front" point, L4, are called "Greeks", while the ones left behind, at L5, are "Trojans". (But these days people tend to call "Trojans" asteroids at both L5 and L4.)
One of the first Trojans discovered around Jupiter was named Achilles.
Note: Achilles was the Greek warrior hero who stayed behind, with a few others, hidden in a wooden horse, when the Greeks left the field at end of the Trojan war. The Trojans thought that they had won and pulled the horse as a trophy inside their city and celebrated. But then the Greeks hidden inside the horse got out and secured victory for themselves instead.
An object used in this kind of ruse is now often called a Trojan Horse. Sometimes such tricks are used, e.g. by computer malware. Achilles was half-god and was almost immortal, but died nevertheless in that struggle after being shot in the only part of his body that was vulnerable: a tendon in his heel, now called the Achilles Tendon.
Note: Achilles was shot by Paris, the lustful prince of Troy who caused the war by abducting Helen, the wife of a Greek king, because of her physical beauty. Paris got to that position because it was promised to him in exchange for a favourable judgement by one of the three goddesses trying to decide which one of them was the sexiest (Aphrodite won).
That itself was a ruse orchestrated on them by the goddess of discord, Eris. She was angry for not being invited to a wedding, while others were.
Note: a separate space probe is being sent to examine Jupiter's trojans. This is relevant, because some of those objects were captured by Jupiter's gravity at the very beginning of our Solar system, 4.5 billions years ago, and have remained there untouched since then. We can learn a thing of two by examining them.
Note: the new telescope is replacing the famous and very accomplished Hubble Space Telescope. Among Hubble's accomplishments was the determination of the age of the Universe (13.8 billion years), the rate of Universe's expansion (the Hubble constant: 73.3 km/s/Mpc), establishing the presence of a black hole at a center of every major galaxy, and the creation of a 3D map of dark matter. (Well, the expansion rate is a bit messy, because for the past 5 billion years, dark energy was speeding things up).
Note: the purpose of the new space telescope is to see the first stars & galaxies after the Big Bang, see planets and exoplanets in greater detail, etc. Since it will work in infrared and not visible light, it is far better suited to study more distant objects that are speeding away faster and have a greater "red shift" in their spectrum.
The telescope has a mirror coated in pure gold and has a 5-layer heat shield ("sunshade"), with a 300°C temperature difference between the two sides, which allows the telescope to further be cooled down from 50K to 7K to make observations. The shield material is a "miracle material" from DuPont called Kapton, which is extremely stable over a huge range of temperatures.
What does it have to do with metric system being decimal and not duodecimal (base-10 and not base-12)?
Joseph-Louis Lagrange (who calculated those "Lagrange Points") was also an important member of the small committee of French scientists that designed the metric system. The committee wanted to use a base-12 (duodecimal) system, but Lagrange convinced them to use a base-10 (decimal) system, because 10 is less divisible than 12. He even considered using a base-11 (undecimal) system. (I would argue the exact opposite, for the same reasons. Using the duodecimal system would have been wonderful - I'm a big fan.)
Thomas Jefferson knew about the metric system and wanted it to be adopted in America, too. However, the ship carrying the sample kilogram to America was intercepted by British pirates.
The scientist who carried the sample died while being held ransom and the sample made it to America only much later, when it did not matter any more. America stayed with feet and pounds, and different, older ratios between units.
Note: Lagrange was a very consequential mathematician and physicist. Some of the methods he developed are now the cornerstone of modern optimization techniques. His "Lagrangian" is the precursor of modern "Hamiltonian", which was used to formulate the well-known Schrödinger Equation.
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