Classically, particles are described by mass, spin, and charge.

Can we consider then that particles are bundles of properties? For all particles which have the same value for these properties describe same kind of particle; for example - one cannot distinguish between one electron and another.

One could argue, additionally, that particles possess angular and linear momentum; and of position in space and in time; for no particle is found in the void - itself and nothing else.

But given that these values can vary; are they better expressed as extrinsic (or accidental) properties; and the former as intrinsic properties - properties that characterise the particle?


It's probably worth making clear that I'm considering electrons as bundles of properties as nothing to do with QM itself, or that they're beyond direct perception; but because there is a small number of definite intrinsic properties that picks out an electron - and all electrons thus picked out are indistinguishable; whereas humans can be picked out say by describing their biological nature we wouldn't then say one human is indistinguishable from another; the same goes for mugs, rocks and radios.

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    "real" particle (if they even exist) are certainly not properties. Now, you're always free to consider that your abstract description of them is just a bundle of characterizing property, thus defining an electron as an object that respects some properties (in the same manner that a product in category theory is some object satisfying a universal property). You shouldn't mix the "reality" with the abstraction tho.
    – sure
    Commented Sep 5, 2015 at 15:27
  • @sure: I'd agree with you; there's two main descriptions of properties - bundles as mentioned; and inhering in some substance; the latter I think is the one you're alluding to; the characterisation through 'universal properties' is interesting in that objects that are all isomorphic are selected Commented Sep 5, 2015 at 17:51
  • It's possible to align the two, if existence is also seen as a property; but this is controversial; notably in category theory existence isn't a property. Commented Sep 5, 2015 at 17:56

4 Answers 4


Any object in a scientific model is a bundle of properties. The necessary circularity in scientific vocabulary always has to reduce to a chosen set of axioms that constitute the form of the definition to be used.

But that is just a side-effect of the choice to use mathematics as the language of science. We have devolved, in modern mathematics, on the understanding that that is just the way definitions work. There are so many different ways of capturing a behavior, many of which are so close to being alike, without truly being isomorphic, that we have to corral the behavior into the right sized box with a set of rules before we can proceed.

But those models are models of something. So, insofar as an electron is being handled by a theory, it is only a bundle of properties.

But then so is a species, or a personality or a biological niche. And no one would seriously contend that those things are made up of their properties in more than a formalistic way. The formalism captures observed behavior of something more real, if less definite.


In quantum theory we face the problem that the objects of our study are not mesocosmic objects. Objects like electrons are not already known to us from our daily experience. Quantum mechanics does not deal with objects familiar to us from simply viewing.

In general, microcosmic objects are strange to us and incomparable to familiar mesocosmic objects.

Science starts with a working definition of the objects in question, e.g. an electron is a particle with a negative electric charge, a mass small compared to the mass of an atomic nucleus, and it is found in the atomic shell.

Later the characteristics are refined and the object can be captured in a formal way: Electrons are described by the Dirac equation, the interaction of electrons with light is described by quantum electrodynamics.

These equations need some parameters as input, in the case of an electron: rest mass, electrical charge. Later one finds other parameters from the theory: spin, lepton number. In addition there are some free parameters like position, momentum. I understand what you mean when naming the former intrinsic and the latter extrinsic properties. But I would avoid such concepts from tradition because with quantum mechanics we are entering a totally new domain. You give an example when alluding to the fact, that in scattering experiments one has to abolish any concept of "conservation of individuality".

Coming back to your original question: We do not know whether an electron is a substance with accidental properties, or whether an electron is just a bundle of properties. I prefer a pragmatic and - temporary - working definition:

An electron is what is described by quantum electrodynamics.

Note. I assume that philosophers do not feel happy with my answer :-)


Jobermark's answer makes correct points, and I am not really qualified to talk about the properties of electrons, but a lack of qualification has never stopped me in the past, so here goes :

As you have pointed out in stating your question, the apparent fact that all electrons share the same fundamental properties makes it problematic to distinguish between two electrons based on their fundamental properties alone.

Another problem with identifying electrons with their fundamental properties is the possibility that these properties may vary over time. For example, according to astronomical measurement and the Standard Model, the proton-to-electron mass ratio has held the same value for "at least" half the age of the universe - implying that the Standard Model allows for the possibility of a change in electron mass over time.

This brings us to the more logical-philosophical issue of identity, properties, and change (over time). Am I the same person when I am wearing reading glasses as when I am not? I'd like to think so. Consider Heraclitus famous declaration : No man ever steps into the same river twice.

Arguments like these have often appeared in the history of philosophy, but it is now generally agreed by logicians that they are mistaken and rest on a simple ambiguity.

We must distinguish between an object and its properties.

What properties does identity have? First, it is a relation. Most importantly, it is a very special relation. It is the relation that relates every object to itself and to nothing else. At first glance, this appears to make identity a rather uninteresting relation. But this is not so. It actually contains a lot of significant information about how different names can identify the same object. Equally importantly, it allows us to make inferences via Leibniz's Law.

Thus, it is not correct to identify an object, such as an electron, with its properties.


In terms of what we know about fundamental particles, everything about them can be summed up by their properties and probabilities. We really have no way of knowing anything else about them. They could be thoughts in the mind of God, or numbers in a giant spreadsheet being calculated by some cosmic computer just as easily as they could be the typical conception of them as little submicroscopic balls zipping around the universe. As far as we know, one of those underlying schemes could be substituted for another without us being able to perceive the difference. It also means that --again, as far as we know --that one electron could be substituted for another indistinguishably.

That doesn't mean that they don't have a reality beyond those numbers, it just means that we don't (and potentially can't) know if they do or not. (In the case that we can't know anything else about them, whether or not you believe they have reality beyond what we know depends on whether or not you are a realist about noumenal properties.)

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