Tag Archives: measurement problem

Objective Collapse

In the last four posts (Quantum Measurement, Wavefunction Collapse, Quantum Decoherence, and Measurement Specifics), I’ve explored the conundrum of measurement in quantum mechanics. As always, you should read those before you read this.

Those posts covered a lot of ground, so here I want to summarize and wrap things up. The bottom line is that we use objects with classical properties to observe objects with quantum properties. Our (classical) detectors are like mousetraps with hair-triggers, using stored energy to amplify a quantum interaction to classical levels.

Also, I never got around to objective collapse. Or spin experiments.

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Measurement Specifics

In the last three posts (Quantum Measurement, Wavefunction Collapse, and Quantum Decoherence), I’ve explored one of the key conundrums of quantum mechanics, the problem of measurement. If you haven’t read those posts, I recommend doing so now.

I’ve found that, when trying to understand something, it’s very useful to think about concrete real-world examples. Much of my puzzling over measurement involves trying to figure out specific situations and here I’d like to explore some of those.

Starting with Mr. Schrödinger’s infamous cat.

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Quantum Decoherence

In the last two posts (Quantum Measurement and Wavefunction Collapse), I’ve been exploring the notorious problem of measurement in quantum mechanics. This post picks up where I left off, so if you missed those first two, you should go read them now.

Here I’m going to venture into what we mean by quantum coherence and the Yin to its Yang, quantum decoherence. I’ll start by trying to explain what they are and then what the latter has to do with the measurement problem.

The punchline: Not very much. (But not exactly nothing, either.)

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Wavefunction Collapse

The previous post began an exploration of a key conundrum in quantum physics, the question of measurement and the deeper mystery of the divide between quantum and classical mechanics. This post continues the journey, so if you missed that post, you should go read it now.

Last time, I introduced the notion that “measurement” of a quantum system causes “wavefunction collapse”. In this post I’ll dig more deeply into what that is and why it’s perceived as so disturbing to the theory.

Caveat lector: This post contains a tiny bit of simple geometry.

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Quantum Measurement

Over the last handful of years, fueled by many dozens of books, lectures, videos, and papers, I’ve been pondering one of the biggest conundrums in quantum physics: What is measurement? It’s the keystone of an even deeper quantum mystery: Why is quantum mechanics so strangely different from classical mechanics?

I’ll say up front that I don’t have an answer. No one does. The greatest minds in science have chewed on the problem for almost 100 years, and all they’ve come up with are guesses — some of them pretty wild.

This post begins an exploration of the conundrum of measurement and the deeper mystery of quantum versus classical mechanics.

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Many Worlds Insanity

I was surprised to discover I’ve never posted about the Many Worlds Interpretation (MWI) of quantum physics — I would have sworn I had. I’ve mentioned it a few times, and I know I’ve discussed it in comment sections, but it seems I never tackled the subject explicitly for the record.

It’s been on my mind lately because others have talked about it. Sean Carroll’s book promoting it generated a wave of discussion. The final push for me was Jim Baggott’s Farewell to Reality, which consigns MWI to the “fairy tale physics” heap.

Since I quite agree, this seems a good followup to yesterday’s post.

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