Schrodinger's Bus
Peter Newman
A tale about cats and buses, and a question that has been nagging...
For me, the Schrodinger's Cat thought experiment has always seemed
reasonable (if only because cats act like they live in a different
dimension to us humans ;-). The idea of microscopic quantum uncertainty
involving the decay of a single atomic nucleus, hence releasing the poison
(or not) that kills the macroscopic cat (or not) is easy to accept. The
idea that this results in a superposition of states (live cat/dead cat)
until an observer opens the box is a little weird, but still looks nice
and 'experimental' to a lab rat like myself.
But then, one morning, a funny thing happened to me on the way to the
university...
I had to run to catch the bus. I jumped on, flashed my bus pass to the
driver, and went and sat upstairs (this is Britain where we take our buses
seriously). I then realised I didn't know which of two routes the bus was
going to take, because in my haste I had not seen the route number on the
front of the bus. Either it was a number 33, and would turn left at the
next set of traffic lights, or it was a 35, and would go straight on.
"Hang on", I thought, "does this means I am in a superposition of two
buses?" This was some months ago, and despite numerous head scratching
sessions, I still cannot decide if this was, or was not, a 'Schrodinger's
Bus' problem. At one level, it was "simply a lack of information" and
nothing to do with the deep philosophical problem Schrodinger was trying
to highlight. Everyone else on the bus knew which route it would take -
only I was in the dark. The bus was definitely a 33, or definitely a 35.
But at another level, the lack of information about whether or not a
particle has decayed seems to be exactly what superimposed a dead cat on a
live cat. In the Cat experiment, there is a finite period of uncertainty
between closing the box and opening it. While closed, the superimposed
cats coexist; once opened, reality collapsed to one observed state (or the
other).
As observer in the Bus experiment, I could argue that *from my point of
view* the same was true. As some time in the past, a route manager made
an arbitrary decision (because of a quantum event in their brain?) about
what times routes 33 and 35 would run, of which I had no knowledge. The
first time at which I could have knowledge was when the 'box was opened'
at the traffic lights. From my point of view, the other poeple on the
bus were as much a part of the experiment as the bus itself, and their
'in the box' observations did nothing to collapse what I saw as a
superposiion of states.
To quote Schrodinger (from the Measurement in Quantum Physics FAQ at
http://www.mtnmath.com/faq/meas-qm.html):
"It is typical of these cases that an indeterminacy originally restricted
to the atomic domain becomes transformed into macroscopic indeterminacy,
which can then be resolved by direct observation. That prevents us from so
naively accepting as valid a ``blurred model'' for representing reality.
In itself it would not embody anything unclear or contradictory. There is
a difference between a shaky or out-of-focus photograph and a snapshot of
clouds and fog banks."
But then, the extension of Schrodinger's Bus is that *everything* is a
Schrodinger's experiment, and from *everyone's* point of view, most of the
Universe is in superimposed states. This seems *really* weird!
So, my question is: was I in one bus, or a superposition of two? Or am I
suffering from a severe case of a little knowledge being a dangerous
thing (in which case, please give me references to read).
Meanwhile, it is time to go catch a bus home.
Cheers,
Pete Newman
P.S. Sure enough, we got to the traffic lights, the bus turned left, and
instantly collapsed into a number 33.
--
Email: p.r.n...@uclan.ac.uk
WWW : http://sa1.star.uclan.ac.uk/~prn
Paper: Centre for Astrophysics, University of Central Lancashire
Preston PR1 2HE, England
-------------------------------
Happy is he who has been able to learn the causes of things - Virgil
Fred McGalliard
Peter Newman wrote:
>
> But then, the extension of Schrodinger's Bus is that *everything* is a
> Schrodinger's experiment, and from *everyone's* point of view, most of the
> Universe is in superimposed states. This seems *really* weird!
Very good! I never liked talking about killing cats anyway. And this gets us
over that silly box thing. What is weird is taking this mathmatical construct
and trying to use it to model reality. It may work, just as you could
calculate the chance of being on one bus or the other as a superposition.
But in fact only one situation actually presents itself. However, if there is
really only one bus, how can a diffraction patern be formed? (obviously mixing
buses and much smaller objects). I think that this illustrates how inadequate our
macroscopic experience based models are for atomic scale objects.
Edward Green
Peter Newman <p.r.n...@uclan.ac.uk> wrote:
>A tale about cats and buses, and a question that has been nagging...
Peter, first of all a related fact about New York City subways.
Everyone who rides them on a regular basis knows that they behave just
like your bus. Until they enter the station and you observe them,
they are in an indeterminate state among all the trains that may run
on that line. Furthermore, if you, the observer, are waiting for
either an N train or an R train to reach the platform and you see
the lights approaching in the tunnel, you can cause the train to
collapse into the one you want by believing it is the one you are
waiting for! I have tried this, and can verify it works at least 50%
of the time, which makes it an important subway riding strategy. :-)
With regard to you question, or wonder, or musing, or whatever...
I merely note that an "indeterminate quantum superposition of states"
and imperfect information about the state of the world *are
operationally indistinguishable*, and therefore, being a good
wielder of Occam's razor, as I have been taught by those more savvy
than I, I conclude that the distinction is purely psychological.
There is only one truly classically unexpected prediction of quantum
mechanics, and that is the behavior encapsulated in Bell's Theorem.
Ed
Bruce C. Fielder
> Very good! I never liked talking about killing cats anyway.
I agree! Tell you what - if my cat jumps on me in the next two minutes,
I'll kill Schrodinger.
kra...@aol.com
Peter Newman:
|"Hang on", I thought, "does this means I am in a superposition of two
|buses?"
No. You might try looking at Omnes' book on the interpretation of
quantum physics; look in particular for a discussion of why the Moon
may be said to be in one particular place.
Also note that the bus has long since interacted with much of the
outside world, so that the distinction between the two types of bus
is really a distinction between two types of states of the world. It may
be (on one view of quantum physics) that the world as a whole is in a
superposition of states, some which are much like this one, but in which
you caught the other kind of bus. But if so, the "I" which is having this
experience and thinking these thoughts is not the same as that other
one; you will never meet.
Keith Ramsay
Pete
> Peter Newman:
> |"Hang on", I thought, "does this means I am in a superposition of two
> |buses?"
> No. You might try looking at Omnes' book on the interpretation of
> quantum physics; look in particular for a discussion of why the Moon
------8< snip 8<-------
> Keith Ramsay
Keith-- Are you still out there? I never thanked you for your answer!
24 years later, the TV show, "Some Boffins with Jokes" on the BBC, brought up my story again as I tried to explain it to my wife. And wow! Thanks, Google, for preserving Usenet history.
Meanwhile, happily retired now, I take great pleasure in appying my knowledge of (mostly non-quantum) physics to the design and flight of model aircraft. Much more fun than sitting on buses ;-)
--Pete