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 PROPERTY of EM radiation. One of many.