What is matter?

[Demiurge]

From the point of view of quantum physics... Could physicists agree what matter is?

We see it, we describe it yet it resists intuitive understanding.

Is matter really just energy and measurement, decoherence, splitting, whatever process that brings out single outcomes aka "matter"?

 

[PeterDonis]

From the point of view of quantum physics... Could physicists agree what matter is?

"Matter" is a word. Physics is not done in words. It's done in math. So what the word "matter" means depends on what thing in the math you use that word to refer to.

 

[DaveC426913]

I think we've explored this before in another thread.

I offered the rough-n-ready description that - with a few notable exceptions* - matter encompasses the gamut of fermionic particles - the particles that obey the Pauli Exclusion Principle, and as a result "takes up room", in the way that, say, light does not. (You can fill a box with electrons until it's full, but you cannot "fill up" the same box with light.)

* Helium-3 is one of those notable exceptions that is matter, yet apparently does not seem to obey PEP.

That may not suit everyone, but I think it's a pretty good starting point.

 

[weirdoguy]

Is matter really just energy

Whatever "matter" means, for sure energy is a property of matter, not matter itself.

 

[Roberto Pavani]

Undergraduate answer to an undergraduate question: matter is anything that has inertial mass, i.e.,
anything that resists acceleration: $m = F/a$.
If you push it and it pushes back, it's matter.

 

[PhyEnthusiast]

I would have said: matter is simply condensed energy.

You might run into minor problems with this defintion because of energy-mass equivalence (most of an atom's mass comes from the binding energy of its constituents, after all). But the adjective 'condensed' captures quite well that it's something that now exists in reality, something you can somehow touch, and something that stays there without just disappearing again.

 

[PeterDonis]

Helium-3 is one of those notable exceptions that is matter, yet apparently does not seem to obey PEP.

He-3 does "take up room"; the fact that it is superfluid at low enough temperatures does not prevent it from occupying volume. "Superfluid" is not the same thing as "acts like light". (And note that He-3 is actually a fermion, not a boson, so "superfluid" is not even the same thing as "boson", although they are not unrelated. He-4 is the bosonic He isotope, and it becomes superfluid at a temperature about three orders of magnitude higher than He-3. But He-4 also occupies volume even when it is a superfluid.)

 

[DaveC426913]

He-3 does "take up room"; the fact that it is superfluid at low enough temperatures does not prevent it from occupying volume. "Superfluid" is not the same thing as "acts like light". (And note that He-3 is actually a fermion, not a boson, so "superfluid" is not even the same thing as "boson", although they are not unrelated. He-4 is the bosonic He isotope, and it becomes superfluid at a temperature about three orders of magnitude higher than He-3. But He-4 also occupies volume even when it is a superfluid.)

Right. That's why I originally proposed it in the older thread before being corrected.

Still, is it safe to say that - with some exceptions, anything fermionic can be described as matter because of its predilection for taking up room?

 

[PeroK]

I would have said: matter is simply condensed energy.

You might run into minor problems with this defintion because of energy-mass equivalence (most of an atom's mass comes from the binding energy of its constituents, after all). But the adjective 'condensed' captures quite well that it's something that now exists in reality, something you can somehow touch, and something that stays there without just disappearing again.

Mass and energy are properties of matter (and of antimatter). Matter also has charge, spin and other properties, like colour charge etc.

 

[Demiurge]

Whatever "matter" means, for sure energy is a property of matter, not matter itself.

Mass and energy are properties of matter (and of antimatter). Matter also has charge, spin and other properties, like colour charge etc.

Before a measurement though, what is energy a property of?

 

[weirdoguy]

for sure energy is a property of matter

Or the fields in general.

 

[Demiurge]

Electromagnetic radiation is energy. And is not a property of matter. Whatever matter is, calling energy a property of matter might be too narrow of an angle.

 

[weirdoguy]

Electromagnetic radiation is energy

No! It's not energy. Energy is a PROPERTY of EM radiation. One of many. Energy is property of things, not thing itself. @PhyEnthusiast it's for you also.

 

[Demiurge]

No! It's not energy. Energy is a PROPERTY of EM radiation. One of many. Energy is property of things, not thing itself. @PhyEnthusiast it's for you also.

Yes, I know this classical perspective. I think everyone agrees with it.

If someone were to ask what is more fundamental, things would be less ideal as quantum physics doesn't list matter as one of its preconceived notions.

 

[weirdoguy]

Yes, I know this classical perspective.

It's not classical. It's the only perspective in physics, both in quantum and classical.

If someone were to ask what is more fundamental, things would be less ideal as quantum physics doesn't list matter as one of its preconceived notions.

I don't know what you mean, but it's not physics, it's philosophy at best.

 

[PeroK]

Electromagnetic radiation is energy. And is not a property of matter. Whatever matter is, calling energy a property of matter might be too narrow of an angle.

Colour is a property of paint. But colour is a property of other things as well.

Energy is not exclusively a property of matter. It can be a property of other things as well. E.g It might also be a property of the vacuum (dark energy).

In any case, the main point is that matter is not "condensed energy".

 

[Demiurge]

It's not classical. It's the only perspective in physics, both in quantum and classical.



I don't know what you mean, but it's not physics, it's philosophy at best.

Kind of. It is interpretation of physics.

 

[weirdoguy]

It is interpretation of physics.

This subforum is about QM interpretations, and it does not mean what you think it means. Philosophy is in general forbidden topic here on PF.

 

[Demiurge]

This subforum is about QM interpretations, and it does not mean what you think it means. Philosophy is in general forbidden topic here on PF.

You were replying to this, which concerns interpretative issues of quantum physics:

Is matter really just energy and measurement, decoherence, splitting, whatever process that brings out single outcomes aka "matter"?

 

[Demiurge]

Colour is a property of paint. But colour is a property of other things as well.

Energy is not exclusively a property of matter. It can be a property of other things as well. E.g It might also be a property of the vacuum (dark energy).

In any case, the main point is that matter is not "condensed energy".

I also have this uneasy feeling calling matter a form of energy or condensed energy.

It is not terribly too far off though. Intuitively. If we were ever allowed to picture what is going on...
Because if we were to skip this part, we'd have to stick to PeterDonis' method and just use the equations.

 

[weirdoguy]

It is not terribly too far off though.

It is VERY far off, and one need only very basic understanding of physics to see that. Energy has a very specific definition (do you know that definition?) and is a NUMBER. Matter is not number.

 

[weirdoguy]

which concerns interpretative issues of quantum physics:

It does not, not in the sense "interpretation of QM" is understood here.

 

[Demiurge]

It is VERY far off, and one need only very basic understanding of physics to see that. Energy has a very specific definition (do you know that definition?) and is a NUMBER. Matter is not number.

Energy is not the ability to do work in quantum physics but the property to change how states change over time.

Measurement gives energy to outcomes.
Before measurement, a quantum system can exist in a superposition of energy states.

The central issue is the quantum physics doesn't even talk about matter. The apparatus is not geared for it. It is left to the imagination of the student.
A lot of the top names in the field don't even know what quantum physics is about. Other worlds, minds, bits, ultra exotic setups and scenarios.
Matter is not fundamental in quantum physics and this is the core issue. And if matter is not fundamental, then energy as you define it as a property of matter, shouldn't even exist between measrements. And it does. There is zero point energy and space is never truly enpty.
You may need a broader definition of energy. And by employing one, you would, maybe, be tempted to look at it the way I framed it in the OP

 

[Demiurge]

Quantum physics raises measurement as central. And possibly fundamental.
Not "matter"(whatever it is). Or energy.

They come later.

 

[weirdoguy]

Energy is not the ability to do work in quantum physics

Energy is a conserved quantity associated with time-translation invariance of action (certain integral of lagrangian). That's general definition, applicable to both quantum and classical physics. "Abilit to do work" is from elementary school physics.

in quantum physics but the property to change how states change over time.

Nonsense. What you meant is that hamiltonian governs the time evolution of the system.

You may need a broader definition of energy. And by employing one, you would, maybe, be tempted to look at it the way I framed it in the OP

I think that you should learn more physics before you start talking anything about it's interpretations.

 

[PeterDonis]

is it safe to say that - with some exceptions, anything fermionic can be described as matter because of its predilection for taking up room?

If that's how you want to define "matter", sure. As I said in post #2, "matter" is a word. There is no one single thing in the actual physics that that word refers to.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

Measurement gives energy to outcomes.

This is personal speculation and is off limits here.

Thread will remain closed.

 

[Dale]

@Demiurge by way of brief explanation, the QM interpretations sub-forum is for discussing the published interpretations found in the professional scientific literature.

 

[bhobba]

Using my magical mentor powers at the lay level, matter is a disturbance in quantum fields that permeate all space.

Adding interpretation into the mix, as well as explaining what is meant by disturbances in a quantum field, I highly recommend reading the book by Art Hobson:
https://www.amazon.com.au/Fields-Their-Quanta-Quantum-Foundations-ebook/dp/B0DLNLLG7Y

Thanks
Bill