"Beware of the Physicist."

December 12, 2008 5:33 AM

What might |000> + |111> mean, on a garden gate?

This morning on the way to work, I passed a house where the garden gate bore a sign reading: |000> + |111>. (This isn't too surprising in Cambridge. My other favourite signs include "Silence" in Latin, Ancient Greek and Babylonian and "Don't lean bicycles here" in Latin and Ancient Greek.)

I'm at work now staring at a database, and it's been a few years since my last physics or pure maths courses. Can anyone suggest what the houseowners meant by their sign?

posted by daisyk to science & nature (13 answers total)

It's Bra-ket notation I think, but what the numbers are about I couldn't say. What is the house number?
posted by fvw at 5:45 AM on December 12, 2008

I was on the bus so didn't get a chance to check the house number, but I will try to tonight.
posted by daisyk at 5:57 AM on December 12, 2008

I think they're just trying to say something simple like "Superposition" or "Entanglement"

In bra-ket notation those are simply two (orthonormal) eigenstates (the kets) and the +/- denotes superposition. It would be cleaner if they had added a coefficient such as 1/sqrt(2) to actually have a normalized vector. In this case, it just says, "Some three particle/independent-state system is in a superposition of these two base states - 000 and 111"
posted by vacapinta at 6:20 AM on December 12, 2008

Background: Individual kets (e.g. |000> and |111>) define unique quantum states. Each digit in the ket represents the value of some quantum number. For example, if we were talking about a hydrogen atom, the digits would be written |E l m> where E is the energy, l is the total angular momentum, and m is the z-component of the angular momentum. If I had a state |2 1 0> and measured the energy, I would get 2 from this state. If I measured the z-component of angular momentum, I would get 0, etc...

When quantum states are superimposed, then the above changes. If I measure the energy on |000> + |111>, I can get either 0 or 1. I won't get 0.3 or 0.5 or anything else in the middle, though.

I would interpret this sign as a bad joke that the gate could be either open or closed, but it can't be in between.
posted by dsword at 6:31 AM on December 12, 2008 [8 favorites]

definitely bra-ket notation (likely enough in cambridge ma or cambridge uk)... but absent the formalism for quantum mechanics it's just a funny way of writing vectors

111 = 1 + 2 + 4 = 7 in binary...

so, with some poetic license, as a coordinate vector this would [1,7]

could the house number be 17?

(this doesn't actually make sense, since it really should be [0,7] under this licensing scheme. other schemes get you [1,1] or [0,7] or [7,0])

coudl the house number be 70? or 11?

however, think like a physicist and you need some way to collapse the state vector in order to measure the house number (if it is that) so you need to figure out what the house number operator is...
posted by geos at 6:48 AM on December 12, 2008

Following on from dsword's explanation, it's probably a physicist's way of saying "please close the gate". Obviously, if the gate were always in the closed state, it couldn't be used as a gate.
posted by scruss at 6:48 AM on December 12, 2008 [1 favorite]

Damn, I was hoping for hobo signs. Are there no hobos in Cambridge?
posted by filthy light thief at 6:49 AM on December 12, 2008

Are there no hobos in Cambridge?

If there are, they're probably like this.
posted by Optimus Chyme at 6:51 AM on December 12, 2008

"Then, a few days ago, he was out there waving his tin-foil wand at random strangers, and I heard him yell, 'I demand that you buy me an ice-cream cone! My third-favorite flavor is strange! My second-favorite is top! My favorite flavor is anti-charmed!' Suddenly, I realized the guy was talking about quarks."

I bet quarks are delicious.

Thanks, Optimus Chyme! At first I didn't realize it was an Onion story (it's early and I started reading).
posted by filthy light thief at 6:53 AM on December 12, 2008

I was hoping for hobo signs. Are there no hobos in Cambridge?

Very well-educated hobos.
posted by rokusan at 7:44 AM on December 12, 2008 [2 favorites]

This AskMe needs photos!
posted by pharm at 8:10 AM on December 12, 2008

"Open or close the gate" is clever, but why the three positions? Also, unless they have a big problem with the gate being left half-open... And then there's the intermediate state thing... Not convinced. Definitely needs pics. And probably the original poster going up to the house and asking what's up with that. It's not like the kind of person who does that wouldn't love the chance to tell people how clever it undoubtedly is. You'll be lucky if you get away with just the one two-hour physics lecture.
posted by fvw at 10:18 AM on December 12, 2008

Thanks for all the responses, everyone! I think fvw is right - I'm going to try taking a picture on Monday, and if I get a chance in the week I'll knock and ask them about the gate. I'll update here if I get anything useful.

Special thanks to Optimus Chyme for the Onion story too :).
posted by daisyk at 7:38 AM on December 13, 2008