Schrodinger's Cat -- The Beginning
As the study of quantum physics developed in the early 20th century, some
of the bazaar discoveries triggered much head scratching. One of the
most difficult to grasp features of the quantum world is that things appear to
operate in probabilistic ways rather than in deterministic ways. In fact,
speaking of the state of some quantum particle when not being observed
proves to be meaningless.
Unlike a macro object, like a ball, quantum objects behave quite differently.
You can put a ball on a table, go into another room, and assume correctly that the ball is sitting there all the while that you are away. Return, and you'll
see the ball as you left it.
If you roll another ball at the first, you can predict quite precisely what
will happen when the rolling ball hits the stationary ball, if you know their
respective masses, the velocity of the rolling ball, and the angle of collision.
The Nature Of Quantum Weirdness
Schrodingers Cat Limerick
But the quantum world seems to be a kind of shadow world, with things not
specifically in one state or another until they are observed. If a ball
behaved in the quantum way, you'd have no idea what state the ball would be in
once you left the room, and would not know what state it would be in when you
Well, that's overstating it a bit. It's not that you could have no
idea, but you could only compute a distribution of possibilities, and the ball
may be in anyone of them when next observed. If you had such a quantum ball and
performed the experiment thousands of times, you'd be able to see that the
observed states matched up in frequency with the predicted probabilities.
So in the weird quantum world, one doesn't compute the next state of a
particle, for instance. Instead one computes the next distribution of
probabilities, and will witness one of those possible outcomes when making
an observation. It's like things exist in a dream world in all possible
states at the same time, and only settle on one when an observation is made.
Erwin Schrodinger was an early pioneer in the development of quantum
physics, and he developed what's known as the Schrodinger Wave Equation as a way of
managing these quantum probabilities. With the equation, an object's
wave function could be calculated, which has since been interpreted as a distribution of possible states. Everything has a wave function, but the weirdness
only seems to crop up in the atomic world.
Enter Schrodinger's Cat
In an effort to help conceptualize
the strange quantum world, Schrodinger introduced a thought experiment
called Schrodinger's Cat. In this experiment, Schrodinger designed a thought experiment that
placed a familiar macro-world cat in a position that put its existence
into a quantum situation.
As the experiment goes, the cat is placed in a box with a vial of poison.
The vial is setup so that it will be broken, releasing the poison, if and
when some quantum event occurs. Of course, the release of the poison would
kill the cat.
But the quantum process that will trigger the release of the poison has no
specific state of existence, being in a sense in all possible states at once.
One cannot compute when the quantum event might take place, only compute the
distribution of possibilities.
Since the cat is in the box, and its fate is now part of the quasi-state of
the quantum process, its existence is also in a quasi-state. The math that must
be used to compute the cat's fate is that which computes the quantum process.
So it suggests that while in the box and unseen, the cat's state of existence
is that of being both alive and dead, with some probability function being the
only quantitative statement that can be made. Schrodinger referred to this
coupling of the cat's state of existence and the quasi-state of the quantum
process as entanglement, meaning that the cat's wave function and the
quantum process wave function are entangled.
It turns out that all objects have a wave equation description, but it
degenerates to a classical physics description for macro objects. However,
when the cat is in the box with a quantum process, the wave functions for
the cat and the quantum process become entangled, and must be solved together.
My Schrodinger's Cat Limerick
The Schrodinger's cat thought experiment is introduced to all students of
physics at some point, and is also oft lampooned because of its confusing
implications. Just for fun, I've put the enigmatic story of Schrodinger's cat
into a witty limerick, as follows:
Said Schrodinger's Cat With A Smile
I'll Be In The Box With A Vial.
With The Poison I'll Be
Quantum Tangled You See,
Thus Alive And Dead Both All The While.
I put a Schrodinger's Cat theme on a couple of different t-shirt designs
with some illustrations. You can get either design on a wide variety of
t-shirts or sweatshirts, or on coffee mug by clicking you the respective
But The Tale Doesn't End There
One of the uncomfortable interpretations of quantum strangeness is that
somehow existence depends upon we humans observing it; that without
some intelligence making an observation, it would seem that a specific
quantum state doesn't exist, or as a physicist would say, the wave function
Immediately some began to ask the obvious question, "What if a camera or
some recording device was there to watch the state of a quantum process?
Would that make the wave function collapse?"
To treat this idea, another physicist by the name of Eugene Wigner proposed
another thought experiment, known as Wigner's Friend. In
this thought experiment, Wigner's friend is placed in a room to watch over the
Schrodinger's cat experiment, while Wigner goes elsewhere. Wigner goes on to
explain that once out of the room, all that happens is that his friend also has
his wave function entangled with the quantum process that controls the
fate of the cat.
The math would thus suggest that when Wigner is outside the room, the
solution for inside the room is his friend simultaneously existing in all
possible states, such as both witnessing a live cat and a dead cat. When
Wigner opens the door, the composite wave function would collapse, yielding his
friend reporting on the now determined state of the cat.
Sound confusing? Albert Einstein and Niels Bohr went round and round on
these weird predictions, with Bohr seemingly winning them all.
Maybe this will help or maybe this will only add to the confusing, but
the limerick I wrote about the Wigner's friend experiment will at least
add some humor to the quandary.
My Wigner's Friend Limerick
With pen in hand and tongue in cheek, I put together this clever
limerick to describe the Wigner's friend thought experiment:
Said Wigner About His Friend Lyle,
He Sat With The Cat All The While.
But Entanglement Came
For Him Just The Same
As The Cat In The Box With The Vial
Wigners Friend Limerick
Again, by clicking on the image you can purchase the design on a wide
variety of light and dark colored t-shirts and sweatshirts, as well as on
a coffee mug. Notice that the image of the cat appears like a multiple
exposure, suggesting the quasi-state of the cat. I took poetic license in
my limerick to give the hypothetical friend the name Lyle.