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What is Schrödinger's Cat?

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  • Written By: Michael Pollick
  • Edited By: Bronwyn Harris
  • Last Modified Date: 14 September 2014
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It is important to note that no actual cats, real or superpositioned, were harmed during the creation of this wiseGEEK article. (Inside joke for physics majors).

Erwin Schrödinger was a contemporary of other eminent physicists such as Albert Einstein and Neils Bohr, although he was more interested in a relatively new field called quantum physics. Quantum physics in general went against much of what Einstein and Bohr considered to be scientific fact, which led to a number of high-level debates between Schrödinger and Einstein. One of those arguments contained a paradoxical thought experiment we now know as Schrödinger's Cat, although the cat was never more than theoretical.

One of the inherent problems with subatomic systems is the difficulty of human observation. One can assume that subatomic particles behave in a certain way, but introducing a microscope or a camera to observe them in action can negatively affect the natural behavior of the subatomic system. This would be the equivalent of a classroom of students changing their behavior once they discovered a documentary film camera crew in the room. The same thing happens when physicists try to observe very small objects.

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"Schrödinger's Cat" is essentially an object lesson on the problems of relying on observation alone when dealing with subatomic systems. Schrödinger suggested an experiment in which a living cat would be placed in a cage on one side of a metal tube. Near the cat would be a vial containing poisonous gas and a trigger mechanism. A scientist would place a very small amount of a radioactive substance on the other end of the tube. This radioactive material would decay at a rate of one atom per hour, but the chances of that occurring are fifty-fifty. If an atom were indeed released, it would cause the vial of poisonous gas to break and the cat would die. No atomic decay would mean the cat lives.

Once this theoretical tube was sealed, no outside observation would be possible. No one would be able to check in on "Schrödinger's Cat" for an entire hour. After 60 minutes have elapsed, the question for the experimenter would be "Is Schrödinger's cat alive or dead?". Under Einstein's theories, the cat would either be dead or alive, with no middle ground. Only when the tube was opened and the status of the cat became observable could a definitive answer be found. Einstein would either see a dead or living cat, since God doesn't play dice with the universe.

Under Schrödinger's theory of quantum physics, however, the cat is actually in two different states at the same time. One version of the cat is dead, but another is still alive. This is the way subatomic systems would have to work as well, which sets up the paradox. A cat lives in a macroscopic system, in which objects either live or they don't. There is no middle ground, such as half a living cat. In quantum physics, however, the theoretical Schrödinger's cat could exist in various states, from completely alive to dead and all stages in-between. All of these states, known as superposition are possible outcomes from the experiment, although only one could be observed as true when the scientist examined the cat.

Schrödinger himself later expressed regret that he used a cat as the potential victim of a paradoxical thought experiment. His original point was to illustrate some of the problems of observing subatomic systems and drawing conclusions when the act of observation could skew the results. By taking the paradox out of the smaller subatomic world and moving it into the larger macroscopic world, Schrödinger did indeed prove his point to Einstein and others, but his theoretical object lesson would forever be known as "Schrödinger's Cat".

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anon344738
Post 18

First of all, we all know the cat kills himself because no cat is just going to sit there when there is something else in his space to play with.

It is so obvious Schrodinger made fools out of us all with this "theory" which makes no sense. And he got a Nobel Prize for pulling the most legs in scientific history.

The bottom line, which is the explanation for all things is, we do not know the outcome until we look. Schrodinger's cat is the state our minds are in -- what we are thinking.

It is so obvious, it is confusing because no one gets why he even brought it up in the first place.

anon166930
Post 16

@anon90628: can something be both a particle and a wave? Actually, the answer to that is yes. Light has both particle and wave like properties, and it is things like this that brought about the concept of quantum mechanics, because light can't act as a particle if it's a wave, and it can't act like a wave if it's a particle, but the reality is that it does, and no one knows why.

another interesting experiment that demonstrates the beauty of quantum mechanics is Young's double slit experiment, worth googling.

anon159967
Post 15

From what did Schrodinger derive such a conclusion?

anon143912
Post 14

All instances of this cat that may or may not have actually been sealed in a box since 1936 are dead.

anon114846
Post 13

My brain struggles with the concept of the cat being both alive and dead. Relative to the experimenter, the cat is both alive and dead.

However, relative to the cat, the cat must be definitively either alive or dead.

Is this thought experiment only to be considered through the point of view of an outside observer?

anon114230
Post 12

Rooferman, it has already been said that the experiment was purely for thought and was never actually conducted.

anon107230
Post 11

that's totally wrong as Schrödinger never went against Einstein. Like Einstein, he tried to prove that quantum physics doesn't answer the questions of the real world.

anon90628
Post 10

'the cat is not "both" alive and dead at any one give time. Death itself is a process that generally takes some amount of time, but once your dead, your dead.

The cat will either be alive or dead as a result of the experiment. Making an assumption that the cat is "both" alive and dead at the same time is both illogical and unnecessary.

Can something be both hot and cold at the same time? Can something be wet and dry at the same time? Can something be fast and slow at the same time?

What would we call a being that is alive and dead at the same time, a zombie?

In the real world, you are either alive or dead. In a "thought" experiment, you can be whatever you want. --John'

You, sir are failing to understand the concept of a parallel universe.

anon87526
Post 9

The cat is not "both" alive and dead at any one give time. Death itself is a process that generally takes some amount of time, but once your dead, your dead.

The cat will either be alive or dead as a result of the experiment. Making an assumption that the cat is "both" alive and dead at the same time is both illogical and unnecessary.

Can something be both hot and cold at the same time? Can something be wet and dry at the same time? Can something be fast and slow at the same time?

What would we call a being that is alive and dead at the same time, a zombie?

In the real world, you are either alive or dead. In a "thought" experiment, you can be whatever you want. --John

anon54201
Post 8

Great article. Thanks!

areyoujoking
Post 5

I cannot stress enough how much it does not matter about the cat.

anon28096
Post 4

What would happen if the cage was of plexiglass? Would that not make it so that the observer could observe the experiment without actually interfering? Or is it that the experiment is not being interfered when the observer opens the cage and looks into it to uncover the results, but instead in the act of knowing and observing the experiment?

Rooferman
Post 3

I kinda figured that, but it had me really curious about what happened. Thanks for taking the time to answer.

michaelp
Post 2

Rest assured, no actual cats were harmed in the Schrodinger's Cat experiment. It's all theoretical. The idea would be that IF someone set up the experiment in real life, there would be no way of knowing whether or not the "cat" died until the box was opened an hour later.

Since the release of the poison would be completely random, or not even happen at all during that hour, the experimenter would have to believe the cat was both alive and dead at any point in time during the experiment. The absolute truth would only be known once the box was opened.

It's not exactly the nicest experiment in the world to set up for an explanation of quantum physics, but I don't believe Schroedinger himself ever thought someone would ever set it up in real life.

Rooferman
Post 1

So, this may seem irrelevant to you smart folks, but here goes.

What ever happened with the cat? Did anyone actually open the box? Was this something they actually tried? Thanks.

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