Schroedinger's Cat

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Main article: Quantum mechanic
Main article: Housecat

Schroedinger's Cat is the name of a housecat that is generated in the possession of a quantum mechanic. Quantum mechanics have a 5% chance of being generated with a special large box.[1] This box will contain a housecat that is either alive or dead; the state of the cat is not fixed until it is observed by opening the box. When the box is opened, there is a 50% chance the game will attempt to create a peaceful live housecat named "Schroedinger's Cat" as close as possible to the player; if a housecat is not created (if the 50% chance fails, housecats are genocided or the level has no square free for a monster), the box will contain a named housecat corpse instead.[2]

Except for its name and unusual origin, Schroedinger's Cat is just a normal housecat. You may tame it with food, kill it for experience, etc. You can even change its name with the call command. If Schroedinger's Cat is dead, you can reanimate its corpse using turn undead (it will be hostile).

Although the state of the cat should be fixed as soon as it is observed in any fashion, currently only opening the box is considered an observation. Before the box containing Schroedinger's Cat is opened, it is technically empty, although its weight is increased to account for the weight of the cat.[3] In particular, neither telepathy nor monster detection will show a live cat in the box, nor will food detection show its corpse. Probing will say that the box seems empty.

NetHack 3.4.3

In NetHack 3.4.3, probing will simply show the box as empty. This was bug C343-263.


Schrödinger's cat is a famous thought experiment in quantum mechanics involving imagining locking a cat in a box with a mechanism that has a 50% chance of killing the cat, depending upon the final state of a quantum system, for example whether an unstable nucleus has decayed within a certain time. The orthodox Copenhagen interpretation of quantum mechanics asserts that the cat in the box is in a superposition of possible outcomes, in half of which the cat is dead, and half of which it is alive. Only when the box is opened and "observed" does the quantum wavefunction collapse, and the fate of the cat become determined. Schrödinger asserted that this was absurd, and thus so was the Copenhagen interpretation. Physicists are still divided on this matter. Note that this was a thought experiment; no actual cats were killed, or even half-killed.


The housecat inside the box is still alive!
Schroedinger's Cat is alive - a housecat is generated in the square nearest to the large box.
You think something brushed your foot.
As above, but you cannot see the housecat.
The housecat inside the box is dead!
Schroedinger's Cat is dead - a housecat corpse is in the large box.
The large box seems empty.
You probed the large box.

Encyclopedia entry

Imagine a sealed container, so perfectly constructed that no
physical influence can pass either inwards or outwards across its
walls. Imagine that inside the container is a cat, and also a
device that can be triggered by some quantum event. If that event
takes place, then the device smashes a phial containing cyanide and
the cat is killed. If the event does not take place, the cat lives
on. In Schroedinger's original version, the quantum event was the
decay of a radioactive atom. ... To the outside observer, the cat
is indeed in a linear combination of being alive and dead, and only
when the container is finally opened would the cat's state vector
collapse into one or the other. On the other hand, to a (suitably
protected) observer inside the container, the cat's state-vector
would have collapsed much earlier, and the outside observer's
linear combination has no relevance.

[ The Emperor's New Mind, by Roger Penrose ]


  1. makemon.c in NetHack 3.6.0, line 680
  2. observe_quantum_cat in pickup.c
  3. mkobj.c in NetHack 3.6.0, line 1341: weight of special boxes is adjusted to include cat

This page may need to be updated for NetHack 3.6.0.

It may contain text specific to NetHack 3.4.3. Information on this page may be out of date.

Editors: After reviewing this page and making necessary edits, please change the {{nethack-343}} tag to {{nethack-360}} or {{noversion}} as appropriate.