Laying Schrödinger’s Cat to rest

Dec 11

Physics David 4 Comments
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We’re talking about Quantum Physics today, and how one of the most difficult to understand concepts is made twice as confusing as is necessary by one of the most poular popular-science gedankenexperiments (that’s German for “thought experiment”). If you don’t know about Schrödinger’s Cat, then this post probably isn’t for you. Although if you are a fan of physics or popular science (for which I applaud you), then read on.

Firstly, I’m going to outline what the “Schrödinger’s Cat” gedankenexperiment is actually meant to demonstrate, then once we understand that, I’ll look at what’s wrong with how the gedankenexperiment is presented to the public.

The weirdness of elementary quantum theory

In quantum mechanics, we find that particles (which are on the quantum-size scale) seem to be able to be in two places at once (position being just one example). Certainly this is WEIRD and counter intuitive. Don’t feel dim for wondering how this can possibly happen, never feel dim. In fact, everyone from the physicists who came up with all this, to the best minds we have today, still don’t understand the mechanism by which this happens.

The important thing to keep in mind, and to some this may be intellectually unfullfilling, is that as scientists we come up with a theory and then check to see that it agrees with nature (i.e. experimental observations). We can never truly know if our theories are telling the real truth about nature, all we can know is that our theories describe the behaviour of nature, within the limits of our technology and ability to test that theory.

In quantum mechanics we have a terminology, in which we say a particle is in a “superposition of states”. This simply means that we think of the particle having more than one physical state superimposed upon it. This could be more than one position, or more than one energy, etc. Again, this is strange, weird, counter-intuitive. However, we find that we must accept it, because there are experiments that test for this very behaviour and they all come back positive. I’d love to explain the experiments, but then this post would end up being three times as long as intended!

What causes this superposition of states to collapse into a single state is interaction with another physical object (whether it be another particle or some measurement apparatus, it’s all the same). Therefore, a particle in a superposition of states could spontaneously collapse due to collision with a cosmic ray, or it could be collapsed purposefully by someone interacting with it, by means of measurement.

The many flaws of the Schrödinger’s Cat gedankenexperiment

Before I continue, I am going to assume you are familiar with Schrödinger’s Cat. If you are not, please read this.

In the simplest of terms, the objective of the Schrödinger’s Cat gedankenexperiment is to demonstrate two things to the lay person:

  1. That quantum systems can exist in a superposition of states.
  2. That measurement of a quantum system actually changes the system.

However, it is my opinion that the Schrödinger’s Cat gedankenexperiment only serves to confuse an already abstract and confusing concept, all the while distracting and misdirecting your attention with the plight of a cute kitty!

In my opinion, the following is all that is wrong with the the Schrödinger’s Cat gedankenexperiment:

  1. Leads the reader to think that the act of measurement is more meaningful than it really is.
    • Some people create the impression that the act of measuring, i.e. looking at, a quantum system is somehow a profound act, and that only by measurement can a superposition of states be collapsed. The reality is that measurement is simply introducing an external system to the object of our interest. Just because something is being introduced for means of measurement does not give it any special status in the theory. A photon emitted from a laser for purposes of measurement is no different than a photon of daylight. In the the Schrödinger’s Cat example, by opening the box and observing the contents we are lead to believe that simply looking into the box causes the superposition to collapse. Not at all! If anything, it is the daylight flooding in, interacting with the radioactive sample, that causes the collapse. Although, the sample could have already been forced to decay, or not, by cosmic rays entering the box, or infra-red photons (from the cat’s body heat), before we opened it!
  2. Misleads the reader into thinking that an effect only observed at the quantum level can apply to a macroscopic object, such as a living creature.
    • To the casual reader/listener, there is a very firm impression given that cat is alive and dead at the same time; this is an unforgivable error when trying to educate people about such an important subject. Such large, complex, objects cannot, exist in a superposition of states.

I think I shall leave it there now, but it is for these reasons that I would hope a better gedankenexperiment is thought up to educate the public about the strangeness of superposition of quantum states. I have yet to hear any TV/radio science pundit use Schrödinger’s Cat without totally confusing the issue.

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The boundaries of language

Nov 5

Physics David No Comments
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This is a reply to a blog post called “Is astro-physics hindered by our language?” by Nate Lanxon. It is indeed an intriguing question, and it is certainly not limited to astrophysics.

The following scenario came into my head that lead to this thought. Let’s say an English speaker heads to Japan and wants to tell a Japanese speaker, for whatever reason, that he is happy. Saying “I am happy,” means nothing to a Japanese speaker, just as saying “Shiawase da naa,” would mean nothing to our English speaker.

So instead, he simply smiles widely. The emotion is conveyed and, more importantly, it’s understood. And without uing the languages we’ve developed for ourselves.

To stretch the point even further, I’d argue that the smile would be meaningless to a being from another world. The point here though, is that language and facial expressions are the same in that they are subjective reference terms.

I would go on to say that the only truly objective language that could be shared across the universe is mathematics. Any sentient being must have the ability to count. Even if you have two beings that are completely alien to each other, they should be able to agree how to count. From counting, the whole of mathematics then flows, the only hurdle would be the notation.

I think of the word ‘infinity’. To me, infinity isn’t a thing; it’s not a tangible object. Rather, it’s a word we’ve slapped on something that doesn’t exist, so we have a way of talking about it as if it did. Now I don’t believe in physical infinities. I don’t like to think the singularities at the centres of black holes have an infinitely huge gravitational pull. I’m not suggesting the gravitational pulls are not there — obviously — or that they don’t function exactly as they appear to function, but that we’ve slapped a word around them that’s blurring our understanding.

Some physicists do believe in “singularities“, they accept the infinities in our theories. I’m not one of them, I side with Dirac who I believe is to have said: “if you have singularities in your theory, then your theory is wrong“. However, by virtue of the mathematical language we have, infinities do exist, in the abstract and in logic. In fact, there are many proved theorems that wouldn’t exist without the idea of infinity (e.g. the number Pi is defined as an infinite sum, and Pi is very much involved in real world objects). There are observations of nature that agree with mathematical theorems, which in turn rely on infinity.

That means one of two things; either the concept of infinity does have some presence in nature, or that the language we’ve formed which encompasss that idea is merely a good representation of nature.

There are so many potential explanations for how black holes work, but I wonder if one of the things we’re causing problems for ourselves by using, is terminology and language. ‘Infinity’, ‘dimensions’, ‘wave-particle duality’… all terms we’ve wrapped around ideas or observations. What if our understanding of these words and the concepts and scenarios they represent, are standing in the way of us better understanding the actual, non-tangible, ‘things’ themselves?

Wave-Particle duality is indeed another intriguing example. This is a phenomenon that came out of the mathematics, we had no physical intuition for wave-particle duality, the physicists of the time, simply followed where the mathematics took them (something of an intellectual relay race). Although once the mathematics yielded a testable result, the theory was indeed confirmed to agree with observations of nature.

The newest breakthroughs of mathematical physics: Quantum Theory and String/Brane theory, really give me impression that we’ve hit the limit of what we can understand with the mental language we have. By “mental languge”, I don’t just mean our spoken languages, I mean our physical intuitions of the world around us.

There have been geniuses in maths and physics who have leapt beyond logic and come up with a new law (or two) that we now depend on. It would be interesting to be able to understand the cognitive abilities that lead them to those revelations. Indeed, all academics I know often solve a problem when they stop thinking about it and let their subconscious do the work.

Also, perhaps this question of language is a case of different tools for different jobs. There will be different ways of thinking and communicating that are best for particular types of problems.

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