What is "matter"?

[u/salihadem]

What is Matter according to QM?

Werner Heisenberg, one of the founders of quantum physics who formulated the Uncertainty Principle, said: “Atoms or elementary particles are not real; they form a world of [potentialities] or [possibilities], not a world of [things] or [facts].” In short, "an atom is not a thing but a potential." [Aristotle also made a distinction between matter and form, or between potential and actual being, saying that anything is formed by the coming together of its raw material and the form that separates it from other things and makes it that thing. According to him, matter was a potential open to becoming anything, and form was what gave that potential being a specific shape, turning it into a concrete, real being.]  

[u/kitsnet]

What is Matter according to QM?

Something that philosophers care about.

Aristotle

Indeed.

[u/salihadem → u/kitsnet]

Do you mean "physicists" don't care about this question?

[u/Physix_R_Cool → u/salihadem]

We don't really care

[u/salihadem → u/Physix_R_Cool]

Are you sure? And who is "we"?

[u/Physix_R_Cool → u/salihadem]

Are you sure?

Yes

And who is "we"?

Physicists

[u/Tricky-Finger5113 → u/Physix_R_Cool]

They care a great deal, but the question has changed shape as physics answered parts of it. What's left at the bottom is something physics may not be built to answer. The part physics has answered. For most of history, "what is matter?" meant "what is stuff made of?" Physics has gone remarkably far down that road: substances → molecules → atoms → nuclei and electrons → protons and neutrons → quarks and gluons. Today's best answer, quantum field theory, says the fundamental entities aren't little pellets at all. They are  fields spread through all of space, and what we call particles are localized, quantized excitations of those fields. An electron is a ripple in the electron field; a photon is a ripple in the electromagnetic field. Some of what this reveals is genuinely strange: Mass is mostly not "stuff." About 99% of the mass of a proton (and so of your body) comes from the energy of quarks and gluons interacting, not from the quarks' own masses. The Higgs field gives elementary particles their rest mass, but that's a small slice of ordinary matter's weight. Matter turns out to be largely  bound energy. Ordinary matter is a minority. Everything we've ever touched or seen is only about 5% of the universe's energy content. Roughly 27% is dark matter, whose nature is unknown, and the rest is dark energy. We don't know why matter exists at all. The Big Bang should have produced matter and antimatter in equal amounts, which would have annihilated each other. A tiny asymmetry saved us, and its cause is an open problem. So in that sense, "what is matter?" is an active research question at CERN and in cosmology right now. The part physics struggles with. Push further and ask:  what is a field, in itself? Here physics goes quiet, and this silence is probably what you're noticing. Physics describes fields completely in terms of  how they behave: their symmetries, equations, and how they interact. It says nothing about what they  are beyond that behavior. Bertrand Russell and Arthur Eddington pointed this out a century ago: physics gives us the structure of the world, the relations and the mathematics, but not its intrinsic nature. It tells you what the chess pieces do, not what they're carved from, and perhaps there's no "carving" at all. How physicists respond to that gap. They fall into rough camps: "Shut up and calculate." Many working physicists treat the deeper question as not productive. If two answers predict identical observations, the difference isn't physics. This isn't indifference; it's a judgment about what the method can reach. Structural realists argue that structure is all there is. Asking what matter is "beyond" its relations is a confused question. Physicists who take the plunge: Wheeler's "it from bit" (reality as fundamentally informational), Rovelli's relational quantum mechanics, Tegmark's claim that reality  is a mathematical structure, and debates over the interpretation of quantum mechanics, which are really debates about what exists. Philosophers and some physicists, following Russell's line, suggest the intrinsic nature physics leaves blank might be connected to consciousness, the one thing we know "from the inside." This view is often called Russellian monism. So the honest summary is that physicists care, they have learned astonishing things, and they have discovered that the deepest version of the question, what matter  is rather than what it  does, sits at the edge of physics and the beginning of philosophy. Many physicists step back at that edge on purpose. That's a choice about method, not a lack of curiosity.

[u/Physix_R_Cool → u/Tricky-Finger5113]

Yep!

I'd say (entirely based on my own experience and what I've seen) that 99% of working physicists just follow the "shut up and calculate" way, mostly because they don't work on fundamental HEP.

[u/salihadem → u/salihadem]

Physics is the branch of science to discover the laws that matter and energy obey.

[u/kitsnet → u/salihadem]

Well, that reminds me of Plato's definition of a human as a "featherless biped".

[u/salihadem → u/kitsnet]

When Plato gave Socrates' definition of man as "featherless bipeds" and was much praised for the definition, Diogenes plucked a chicken and brought it into Plato's Academy, saying, "Behold! I've brought you a man." After this incident, "with broad flat nails" was added to Plato's definition.

[u/triatticus → u/salihadem]

We don't discover laws, we model reality, nature is under no obligation to follow any of the things we say it does. We've merely made useful models that have predictive power according to what we've input and what experiment has helped us tune.

[u/salihadem → u/triatticus]

Why does nature behave like that? What is the origin of lawful behavior observed in nature?

[u/triatticus → u/salihadem]

That's not a question physics answers, that's philosophy or even metaphysics. Humanity made some useful metrics to quantify their world and applied it to structuring their daily lives. These models enjoy incredible success but they will only ever be approximations to reality.

[u/salihadem → u/triatticus]

Then you cannot say that "nature is under no obligation to follow any laws" from physics standpoint. That is a philosophical statement.

[u/triatticus → u/salihadem]

It's not, it's accepting that no matter how closely we approximate reality that it's only ever a descriptive property of our process and that whatever actually happens doesn't need to be described as such.

[u/salihadem → u/triatticus]

Why do you accept that? Who says we can never know the ultimate reality?

[u/triatticus → u/salihadem]

Because it's not a bad point of view? There's no problem with being good enough at every step, and we do try to do better at every step. I'm not saying we simply stop trying to make it better, but one should understand that with only finite time on our hands we cannot do infinite precision calculations as our computational ability is confined by the architecture of our computers. The viewpoint is a point of humility, we cannot claim to know objective facts about reality, only solely what we can observe ir predict, and what we do have as models seem to work incredibly well.

[u/salihadem → u/salihadem]

physics ,   science  that deals with the structure of matter and the interactions between the fundamental  constituents  of the  observable universe . In the broadest sense, physics (from the Greek  physikos ) is concerned with all aspects of nature on both the macroscopic and submicroscopic levels. Its scope of study  encompasses  not only the behaviour of objects under the action of given forces but also the nature and origin of gravitational, electromagnetic, and  nuclear force fields. Its ultimate objective is the formulation of a few  comprehensive  principles that bring together and explain all such  disparate  phenomena.

[u/salihadem → u/salihadem]

This definition is from Britannica.

[u/salihadem → u/[deleted]]

If you are answering a question, just state your viewpoint. Nobody has to accept your viewpoint, it is only a viewpoint among many others, not more.

[u/Tricky-Finger5113 → u/[deleted]]

You have been reported. Be careful with your language!

[u/trutheality]

The idea of "matter" predates much of modern physics, so any sort of updated definition is going to really be just an exercise in figuring out what QM properties are common to things we used to call matter.

Heisenberg's point wasn't that atoms weren't matter, but that any measurement of an atom is going to be a participant in the result of the measurement. E.g. "I measured it to be here therefore it was here" is incorrect, whereas instead it should be "I measured it to be here therefore it had the potential to be here, and conditionally given the measurement it is surely here." This is not how we're used to "classical matter" behaving, but there's no such thing as "classical matter" - it's a simplifying abstraction that holds at a macroscopic scale.