In the context of physics where we usually have phrases like the "state of a system" or the "state of a particle" what exactly do we mean by the word "state" ? To begin, states seem to be associated with the properties of an object but what is the precise nature of this property ? For example if we talked about a potato, then it has a property called weight (possessing a property called weight) and a property of weighing exactly 100 grams. For which of the two cases is it then appropriate to use the term "state" ? Is the property of "having weight" different from the property of "weighing 100 grams" ? I am not sure but i have come across properties being either determinate or determinable, is that what's happening here ? So is the "state" in the general context or in that of physics a determinate or determinable ? To be honest i feel confused with the distinction between determinates and determinables, i mean how is it possible to be aware of weight without simultaneously being aware of the quantity of weight ? Doesn't the latter precede/lead to the former ?

1 Answer 1


"State" means different things in different situations. When you model the physical world for doing physics, engineering, or other things, you can't possibly model everything about the world, there is far too much to model. Furthermore, most of what is in the real world is not relevant to your purposes. So you only keep track of a few relevant variables, called the state of the system.

For example, if you are studying thermodynamics, then the temperature of your system is crucial, but if it's on a wobbly table that moves around a little, that doesn't matter; you don't include the motion in your state variables because it is not relevant to your purposes. The state includes temperature and other variables like pressure and volume (depending on what thermodynamic system you are modeling), but it doesn't include velocity.

By contrast, if you are studying the behavior of spheres in collisions, then the temperature is irrelevant over a broad range of conditions, and the relevant state variables are (for example) the diameter, mass, position, and velocity of each of the masses.

When modeling the orbits of the planets, the diameter become irrelevant and you leave that out of your state, so now it's just the mass, position, and velocity of each of the planets.

The state of a system is the collection of values of all of the variables that are relevant to whatever you are doing.

  • "The state of a system is the collection of values of all of the variables that are relevant to whatever you are doing." So that means that it wouldn't be sensible to say the state of a system has changed if the variables of relevance has changed, right ? Commented Jan 4, 2022 at 23:04
  • @Examination12345 -- If we assume the system is physical while the model is abstract, then the system and its state are independent of our focus or interest, unless our selection or measurement physically changes the system.
    – Michael
    Commented Jan 4, 2022 at 23:25
  • 2
    @Examination12345 the state changes when any of the variables change. The state is the values of the variables, not just a list of the variables. Commented Jan 4, 2022 at 23:25
  • 'A change of state' of a material, eg liquid to gas, will likely involve a change in what you keep track of. See en.wikipedia.org/wiki/State_variable
    – CriglCragl
    Commented Jan 5, 2022 at 10:09
  • @CriglCragl what you are calling a "change of state" is usually called a "phase change" these days, specifically to avoid the ambiguity over what "state" means. Today, "state" generally means what I described, and the word "phase" is used for the other meaning (liquid, gas, solid). Commented Jan 5, 2022 at 14:02

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .