Sunday, May 24, 2009

770 jerusalem

In the Ramat Shlomo neighborhood of northern Jerusalem, there is a duplicate copy of "770" - the central Chabad shrine in Crown Heights.

The building's location was very carefully chosen. It is on "Lubavitcher Rebbe St." and the house number is 36 - double chai. Surely neither street name nor number is a coincidence.

Thursday, May 21, 2009

Gemara is kefira?

"There are three types who deny [kofer] the Torah: 1) One who says the Torah is not from God - even one verse, even one word, if he said that Moshe said it of his own volition [amro mipi atzmo], behold he denies the Torah..."
(Rambam, Hilchot Teshuva 3:8)

"These [the curses in Vayikra 26] are written in plural language and Moshe repeated God's words [mipi hagevurah amran]; while these [the curses in Devarim 28] are written in singular language and Moshe said them of his own volition [mipi atzmo amran]."
(Gemara, Megillah 31b)

Though it is more likely that the Rambam is choosing one gemara (Sanhedrin 79) over another, or else that "mipi atzmo" means different things in Rambam and gemara, the idea that the Rambam considered the gemara to be heresy is slightly amusing. At least to me.

Monday, May 18, 2009

Cross pollination

"Do you search for what is highest and greatest? Every plant can teach it to you."
-Schiller (1759-1805)

"Know that each and every plant has its own song... How beautiful and pleasant it is when we hear their song. It is very good to pray between them and to happily serve God."
-R' Nachman of Breslov (1772-1810)

Thursday, May 14, 2009

John Jacob Jingleheimer Schmidt

When I was in preschool, in between my digging tunnels to China, they taught me the song "John Jacob Jingleheimer Schmidt". Only much later did I realize that this is basically a racist song making fun of German names and the German language in general.

To get a sense of how times have changed (or how the sensitivities of some ethnic groups matter more than those of others) let's change the name in the song to something more appropriate for a a 21st-century immigrant.

"Ching Chi Po Foo, that's my name too!
Whenever I go out, people always shout: Long live Ching Chi Po Foo! Dadadadadadada!"

Imagine the outcry if they started teaching that song to kids.

Monday, May 11, 2009

A tunnel to China

Like every other little kid in the US, I once tried to dig a hole to China. Not having a globe and assuming at China was on the exact opposite side of the world, I tried to dig straight down through the center of the earth to China. Of course, recess always ended before I got more than a foot or two underground.

At a later age, I realized how incredibly useful such a hole would be if it could actually be built. Rather than flying or sailing around the world, you could just step into the hole and start falling. You would continuously accelerate until reaching the center of the earth, at which point you would decelerate until reaching a halt right at the surface of China. (Then you'd have to leave the hole quickly, lest you fall back down to America again.) Thus, there would be very quick transportation between the US and China, expending no energy whatsoever. Also, a hole like this would not have to go through the exact center of the earth. You could dig a hole from New York to Los Angeles and put train tracks in it. The train would accelerate "downhill" for 2000 miles, then decelerate "uphill" until stopping automatically at its destination. All extremely fast and totally free once the tunnel was built.

I wondered how long exactly it would take to make such a trip. But it took many years until I learned how to do this calculation. Since the acceleration of gravity varies with depth, the solution requires the use of calculus and differential equations. Not until my sophomore year of college did I learn how to solve the problem. And not until last night did I fully solve it, including the case when the tunnel does not go through the earth's center. I assumed of course that the earth is perfectly spherical, with uniform density, and that there's no friction.

It turns out that it takes 42 minutes to make the trip through such a tunnel. Amazingly, if my calculations are right, this time does not depend on the tunnel's path. Falling through the earth's center to China, or tunneling on a diagonal from NY to LA, or simply digging a perfectly horizontal and frictionless tunnel through the hill you live next to - no matter what tunnel you build, it will take 42 minutes for gravity to pull you from one end to the other.

Obviously you will fall faster when going to China. You will reach a speed of 18000 miles per hour at the center of the earth, while as for the hill next door, the 42 minutes spend sliding through that short frictionless tunnel would pass agonizingly slowly. If there was a slight breeze, it would overcome gravity and push you in the opposite direction.

Of course, the center of the earth is hot enough to melt rocks, not to mention metal, making a tunnel to China very short lasting even if it could somehow be built. And it's hard to imagine a vehicle surviving a trip at 18000mph. If you collided with someone at the center of the earth, both of you would instantly be vaporized. So really, this tunnel idea is totally impractical. But if it could somehow be built... well, the idea has given me something to think about now for roughly 20 years and counting.

[Technical note: 42min = pi*sqrt(g/R), 18000mph = sqrt(g*R). Equation of motion: X=R*cos(t*sqrt(g/R)). For tunnel not through the earth's center, replace the first R with half the tunnel length. R=earth's radius, g=acceleration at earth's surface. ]

Thursday, May 07, 2009

Reactions to terrorism

Likud: How dare they kill our children!
Yisrael Beitenu: Let's [bleep bleep] them for killing our children.
Kadima: How dare they kill our children! But what can we do about it, since international opinion says there's nothing wrong with it?
Labor: The positive side of our children dying is that it demonstrates our commitment to a two-state-solution and goodwill towards the PA chairman.
Ichud Leumi: How dare they kill our children! Only we have the right to kill children!
Meretz: How dare we kill our children!

Sunday, May 03, 2009


Imagine you were walking peacefully down the street, when suddenly a man burst out of his house and ran up to the border of his property while waving a weapon and yelling nasty threats at you. What would you do?

After getting the hell out of there, you would likely call the police and have the man arrested for assault, or at least for disturbing the peace.

So why is it perfectly legal and OK when a dog behaves the same way towards you?

Recently I set out to try and do something about this situation. I purchased an ultrasound device that people cannot hear but which is supposedly unbearable to dogs. The idea is that whenever they bark at me I'll give them a quick dose of ultrasound and they'll quickly learn that it's in their interest to remain quiet. Results have been mixed. The first dog I tried it on, a large German shepherd, immediately froze and dropped to the floor as if electrocuted. Another couple incidents like that and I'm sure the neighbors would never hear it again. But today I tried the ultrasound on two small dogs and it barely made them flinch.

Therefore a different strategy is needed for next time. I now want to purchase some kind of tear gas which, while potentially causing problems at security checks, will be an effective dog deterrent whenever needed.

Go ahead and accuse me of cruelty to animals. But I like to think that not only dogs, but humans possess rights as well. And I intend to exercise mine.

P.S. I am not anti-dog. Some of my best friends are dogs. It is just the dogs that bark at me I don't like. Oh yeah, and the ones that use the sidewalk as their bathroom, but that is more a deficiency in the owner than in the animal.

Friday, May 01, 2009


In almost every nature reserve in northern Israel there are herds of cows walking around and grazing.

I used to think how nice it would be to be one of those cows, living all your life in such beautiful and interesting surroundings. (Bear with my anthropomorphism for the moment.)

But then I realized why it is better to be human. The cow spends its entire life in one beautiful location. I, as a person, can eventually see every such location.