Category Archives: Physics

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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BB #80: Gravity Waves

Being retired, along with doing all my TV watching via streaming services, has the consequence of almost completely disconnecting me from the weekly rhythm. Weekends mean nothing when every day is Saturday. To create some structure, I follow a simple schedule. For instance, Mondays I do laundry and Thursdays I buy groceries.

More to the point here, Monday (and sometimes Tuesday) evenings are for YouTube videos, many of which are science related. Last night I watched Jim Baggott give two talks at the Royal Institution, one about mass, the other about loop quantum gravity (LQG).

In the latter, Baggott mentioned gravity waves and that generated a Brain Bubble.

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Smolin: Einstein’s Unfinished Revolution

Earlier this month I posted about Quantum Reality (2020), Jim Baggott’s recent book about quantum realism. Now I’ve finished another book with a very similar focus, Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum (2019), by Lee Smolin.

One difference between the books is that Smolin is a working theorist, so he offers his own realist theory. As with his theory of cosmic selection via black holes (see his 1997 book, The Life of the Cosmos), I’m not terribly persuaded by his theory of “nads” (named after Leibniz’s monads). I do appreciate that Smolin himself sees the theory as a bit of a wild guess.

There were also some apparent errors that raised my eyebrows.

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Baggott: Quantum Reality

I recently read, and very much enjoyed, Quantum Reality (2020) by Jim Baggot, an author (and speaker) I’ve come to like a lot. I respect his grounded approach to physics, and we share that we’re both committed to metaphysical realism. Almost two years ago, I posted about his 2014 book Farewell to Reality: How Modern Physics Has Betrayed the Search for Scientific Truth, which I also very much enjoyed.

This book is one of a whole handful of related books I bought recently now that I’m biting one more bullet and buying Kindle books from Amazon (the price being a huge draw; science books tend to be pricy in physical form).

The thread that runs through them is that each author is committed to realism, and each is disturbed about where modern physics has gone. Me, too!

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Entropy 102

Last time I began explaining my “CD collection” analogy for entropy; here I’ll pick up where I left off (and hopefully finish — I seem to be writing a lot of trilogies these days). There’s more to say about macro-states, and I want also to get into the idea of indexing.

I make no claims for creativity with this analogy. It’s just a concrete instance of the mathematical abstraction of a totally sorted list (with no duplicates). A box of numbered index cards would work just as well. There are myriad parallel examples.

One goal here is to link the abstraction with reality.

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Entropy 101

Entropy is a big topic, both in science and in the popular gestalt. I wrote about it in one of my very first blog posts here, back in 2011. I’ve written about it a number of other times since. Yet, despite mentioning it in posts and comments, I’ve never laid out the CD collection analogy from that 2011 post in full detail.

Recent discussions suggest I should. When I mentioned entropy in a post most recently, I made the observation that its definition has itself suffered entropy. It has become more diffuse. There are many views of what entropy means, and some, I feel, get away from the fundamentals.

The CD collection analogy, though, focuses on only the fundamentals.

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