Ars Technica’s series on quantum mechanics: How big is a particle?

A couple of weeks ago, I shared Ars Technica’s first article in a series on quantum mechanics that promised to be math and philosophy free. So far, the author, Miguel Morales, has stuck to that promise. Today he published the third installment.

This one focuses on the size of particle, and why that’s far from a straightforward idea. In the process, he describes the difference (or at least a difference) between fermions (matter) and bosons (force carriers). He also lays a little bit of groundwork on decoherence, although without using that term yet. And he covers a topic that sometimes comes up in our conversations: the uncertainty principle, and why it’s not just an epistemic problem.

All of this continues to be (mostly) handled in terms of concrete experiments, which I think is a very good approach.

Morales also continues to discuss the results in terms of waves. Talking about the dynamics in terms of particles inevitably makes the entire affair feel much more spooky. But as long as we’re talking about waves, things seem more grounded. That said, it’s still quantum mechanics, and ultimately when a quantum object hits something, it does so as a localized particle, and that remains the central inescapable mystery. But the dynamics prior to that point are waves, or at least wave-like.

Of course, you can still think of it all as just waves of probability, if you insist. 🙂

13 thoughts on “Ars Technica’s series on quantum mechanics: How big is a particle?

    1. It is for many interpretations. And in truth, it’s always related to probability of observed outcomes. But for the ones with quantum state realism, it’s more than that. (I should have put a “just” in that line.)


  1. “when a quantum object hits something, it does so as a localized particle, and that remains the central inescapable mystery” – I don’t claim to understand the detail, but my intuition is that the quantum object is actually interacting with another quantum object (the detector) and triggering enough energy to generate a new quantum phenomenon that we deem a detection. It’s all interacting probability waves in which the amplitude is something we kind of understand but the phase is always unknown to us and brings the mystery with it. Isn’t it always the particle view that is spurious?


    1. It depends on the interpretation. (There are several.) Many interpretations, such as Copenhagen, view the particle as the primary reality and the wavefunction as a mathematical contrivance, which leads to an epistemic wavefunction collapse when the particle hits. Others, such as GRW, see the wave existing until it objectively collapses into the particle. The deBroglie / Bohm pilot-wave, see both the particle and wave co-existing, with the wave guiding or piloting the particle. The Everett interpretation is pure wave mechanics with no collapse, but that results in many-worlds, with each outcome existing in its own world, a view many can’t abide.


  2. What I yearn for above all from science is “meaning” in the very broad context of the word. Or perhaps do I mean to go further? And to crave that I or we can use these exotic discoveries (or in most cases theories) to explain the anxieties which have plagued us from the very beginning. In a very deep sense while some of what we observe may be “true” or may “exist” it does not seem to tell us our place in it all.

    Most (?) scientists seem to believe we are a random by-product of physical processes. Others (Hawkins for instance) that we are robots with no free will.

    Perhaps we are not capable of seeing the big picture yet. Or there again perhaps there is no big picture to see.

    Liked by 1 person

    1. Meaning in that sense is a tough thing to look for in science. A lot of it tends to trample on the things we once found meaning in. Indeed, I think the reason the ideas of the Earth orbiting the sun, the geological age of the world, or evolution through natural selection, were initially resisted (and still are in many cases) is because of what they do to our sense of place in the universe.

      I suspect one reason so many people like quantum mechanics, is it seems to offer the possibility that we’re not all part of some machine inexorably winding down to heat death and maximum entropy. Maybe there’s room for surprises. And maybe our consciousness even has a role in those surprises.

      Of course, the other possibility is that we’re even more insignificant than we thought before, that reality renders our very sense of self and choice more irrelevant than we could have previously imagined. Many will hold out hope for the former, but the historical pattern favors the latter.

      All of which, to me, indicates that we shouldn’t look to reality for meaning. We have to resolve to make our own meaning, and figure out how to bend reality to it.

      Liked by 1 person

      1. I think that your conclusion may well be accurate. Unfortunately. Human happiness so very much depends on the lens through which one looks upon the world – whatever that word is and however we come to understand it. I believe that we will come to be able to alter our perceptions – to cure the terrible bleakness from which some of us suffer. And if you look upon whatever is out there through a different lens and accept it for what it is, then lo! You can indeed create your own sense, your own meaning.

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        1. Good point. It may be once we’re able to modify ourselves, we could end up going full Buddhist. Doing so today takes a lot of time, effort, and dedication, but if we can change our innate desires, then there’s no barrier to us reprogramming ourselves to be content with out lot. On the other hand, there’s also no barrier to altering ourselves to tirelessly push the boundaries either. Many paths might be taken.

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  3. “…we shouldn’t look to reality for meaning. We have to resolve to make our own meaning, and figure out how to bend reality to it.”

    Well stated Mike, this would make a great manifesto for subjective experience if not a literal definition.


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