Tuesday, December 28, 2004

Supermarket math, supermodel, and a shorter day

I don't know what about you, but my policy is to count the total price of the goods that I buy in the shops - with the error not exceeding 3 percent.

I just returned from my usual shopping in the Massachusetts Shaw's Supersymmetric Market (MSSM). The cashier had some problems to scan the barcode of the two DANNON (for fellow Europeans: DANONE) yoghurts with fruit at the bottom. Incidentally, do you know that yoghurt with added fruit marmelade was invented in Prague in 1933, originally to protect yoghurt from decay?

OK, so she tried to scan the barcode, on her "PC". And it was like beep beep beep beep beep beep. And then she said "40 dollars". Half of that amount was true. And I was like Huh? It devoured my money. It was a very good amount of money.

Because of the counting policy, I did not have to look confused anymore and trust the "expert". Instead, I could have immediately said
  • That's nonsense. This is a $21.30 shopping.

And she had to count it again and she had to do it fast, so the total amount wasn't as good for her: $21.57. It's kind of ... a bummer.

I'm not Ellen Feiss, and I'm not a student, but this story is true! Of course, her error is that she counted the yoghurt 23 times. :-)

Petra Němcová survives tsunami

Petra is not only my countrymate, but she has also a very similar profession. Many of us study supersymmetric models, and she's a supermodel herself! I believe that her story is, so far, the most scary but especially most captivating among the stories of all people from the West who had to become witnesses of the very sad event in Asia that killed roughly 100,000 people. She had to grab a palm, while her pelvis was broken, and hold it for eight hours, while she listened to the screaming children that suddenly became quiet - and she had to watch her boyfriend, the British photographer Simon Atlee, who was dragged away by the stream and who is still missing. See the other articles here.

Did Earth's rotation become faster?

As Sean Carroll pointed out, some people believe that a large earthquake may speed up the frequency of Earth's rotation - i.e. shorten the day. Correct me if I'm wrong, but the explanation is that the size of Earth shrinks a little bit - it rearranges its mass in a more compact form - which reduces its moment of inertia. Because the angular momentum is kind of conserved, the angular frequency must increase. Am I right? A calculation leads to an estimate that can possibly be as large as 3 microseconds. Do you believe it? This change would not be measurable 40 years ago, but today the accuracy is 100 times better. Does it seem like a lot to you? Well, you still need 300,000 days i.e. roughly 1000 years to be allowed to remove one leap second; or add one? I'm not sure right now.

It's also estimated that some islands were moved by as much as 20 meters.


  1. Dear Lubos,

    I understand there have been 22 leap second adjustments since 1972.

    That is somewhat more frequent than the 300,000 days required for a 1 second adjustment. How do you explain that ?

    Also how do you reconcile a 4.5 billion year age for the earth if there is such a deceleration in earth's rotation ?

    It should have stopped completely by now, right ?