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Are physical quantites, such as mass, invented?

Use this forum to discuss the philosophy of science. Philosophy of science deals with the assumptions, foundations, and implications of science.
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Steve3007
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Are physical quantites, such as mass, invented?

Post by Steve3007 » January 9th, 2020, 5:37 am

The following analysis is intended to demonstrate the sense in which the physical quantity that we call "mass" is, like all such physical quantities, part of a mathematical model that we create to describe and predict our observations. I propose that this is actually the only way to create an unambiguous definition of such quantities.

We can describe a whole class of repeatable experiments/observations that could be performed. We could then point out the patterns in those observations and describe those patterns in the form of simple mathematical equations. We can then define mass as a specific term that appears in those equations.

Very simple example:

It is observed in various experiments conducted close to the surface of the Earth that various measurements related to the set of observations that we collectively refer to as an "object" fit this pattern:

mgh = 1/2mv2

Note: we don't have to think of any of the terms in this equation as representing anything other than the measured results of an observation or a constant. We don't have to care what the constants represent. We don't have to speculate as to what the dependant variables represent.

The measured quantities represented by the letters 'h' and 'v' in the above can be made to vary by changing the height and velocity of the object. However we vary them, if the quantity represented by 'g' is some constant (doesn't matter what it represents at this stage), then it is found that the above equation works if the quantity represented by 'm' also remains constant, for a given object. And it is found that different objects have different values for 'm' which satisfy the above equation. We can conclude this without having first made any decisions as to what we think 'm' represents. It's simply part of a pattern that we've noticed in our observations, expressed in precise, unambiguous mathematical terms. All we need to know about it is that, in equations like the one above and many others, it appears to remain constant for a given object however that object moves around, so long as we don't slice bits off it or stick bits onto it.

But if we like, we can call the quantity represented by 'm' "mass" and we can hypothesise that this "mass" concept is a property of the object which appears to be different for different objects but seems to remain constant for any given object. That seems a useful thing to propose.

We can take it from there, doing more experiments to gradually fill out this property that we've invented and called "mass". We can gradually forget that we invented it to describe and predict patterns in our observations and start thinking of it as something that "really exists" (whatever that means) if we want to. But we don't have to do that. Our ability to describe and predict our observations is entirely unaffected by that metaphysical decision. We can simply think of 'm' as a quantity in an equation which describes various aspects of our observations.

In a different context, this approach was once famously summarised by the phrase: "shut up and calculate!".

I'm happy to "unpack"/expand on the above further if necessary.

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Re: Are physical quantites, such as mass, invented?

Post by Schaps » January 9th, 2020, 6:28 am

This is an interesting question. As a ‘scientist’- physician, my current view of all science is that sciences, including the questions raised by the op, are indeed another form of art, cult-like norms to which certain societies are attracted. Many cultures and civilizations do and have functioned without needing to resort to “scientific “ studies. Therefore, properties such as “mass “are indeed invented by the human mind. Other animals function more effectively than the human animal without having to resort to any invention such as “mass”.

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Re: Are physical quantites, such as mass, invented?

Post by Terrapin Station » January 9th, 2020, 8:22 am

If physical properties are invented, what are we observing?

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Re: Are physical quantites, such as mass, invented?

Post by Pantagruel » January 9th, 2020, 8:54 am

Popper is careful to point out that mass is a relational property.

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Re: Are physical quantites, such as mass, invented?

Post by Steve3007 » January 9th, 2020, 12:49 pm

Schaps wrote:This is an interesting question. As a ‘scientist’- physician, my current view of all science is that sciences, including the questions raised by the op, are indeed another form of art, cult-like norms to which certain societies are attracted. Many cultures and civilizations do and have functioned without needing to resort to “scientific “ studies. Therefore, properties such as “mass “are indeed invented by the human mind. Other animals function more effectively than the human animal without having to resort to any invention such as “mass”.
Also, it's conceivable that an alien civilisation might have a whole load of different terms in their mathematical equations that they regard as "real" physical properties, but that aren't the same as ours. As long as their equations are logically compatible with ours there would be nothing to say that one of the two systems is the correct one, in any absolute sense.
Terrapin Station wrote:If physical properties are invented, what are we observing?
Good question. Two possible responses might be:

1. We have various sensations. They contain patterns/regularities/similarities. We label those sensations as observations and, in so doing, we postulate "objects" as useful models to help us to predict future sensations. By the same process we postulate those objects to have various properties, such as mass. That has worked so far. But there is no absolute sense in which we are observing anything. It's just useful to think that we are. Useful for making those predictions.

2. I've changed my mind. The objects and their physical properties aren't invented. We're observing them.


There are various discoveries (i.e. various sensations) in Quantum Mechanics that lead to the idea that option 1 is the only one that fits with the patterns in our sensations.

But even in the absence of those discoveries, the way in which we decide that a physical property is a physical property (example given in the OP) illustrates, I think, that they are, in a sense, arbitrarily created. It's possible to imagine that others could have been created instead. This becomes more apparent when we consider increasingly abstract-seeming properties. For example, we could go on (using the same equation in the OP) to consider energy. Then we could consider more exotic properties like entropy, enthalpy, electric charge, charm, strangeness, etc.

The line between what we tend to think of as a concrete, physical property and what we tend to think of as a piece of abstract mathematics made up by a bunch of physicists is somewhat arbitrary.
Pantagruel wrote:Popper is careful to point out that mass is a relational property.
That's interesting. Could you expand on that?

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Re: Are physical quantites, such as mass, invented?

Post by Pantagruel » January 9th, 2020, 1:06 pm

Google Popper and relational properties and you'll get some relevant sections. Regurgitating Popper's propensity theory would be a bit of a chore, it's all I can do to get through it!

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Re: Are physical quantites, such as mass, invented?

Post by Thomyum2 » January 9th, 2020, 1:24 pm

Steve3007 wrote:
January 9th, 2020, 5:37 am
The following analysis is intended to demonstrate the sense in which the physical quantity that we call "mass" is, like all such physical quantities, part of a mathematical model that we create to describe and predict our observations. I propose that this is actually the only way to create an unambiguous definition of such quantities.
It's funny to see your post here because this very same thought occurred to me while I was composing my recent post regarding the definition of 'event' in the thread discussing whether or not time is 'just and idea'. To briefly recap what I had said there, the event is 'the fundamental entity of observed physical reality represented by a point designated by three coordinates of place and one of time in the space-time continuum', so all observations can be reduced to this - three spatial and one time 'point'. Which implies that any object is simply a spatial observation. This is not a new idea, and of course brings to mind Descartes' definition of matter: 'extension in length, breadth, and thickness constitutes the nature of corporeal substance.'

So I think you're entirely correct - matter is not a fundamental substance but is instead derived from observation, and the properties that we attribute to objects or matter - those of having 'mass' - are simply those that we construct based on our observations of the changes that the observed objects, and their relationships to other objects, undergo in space across time.

Of course, the other basic property that we construct to describe these changes is 'energy', which is also a function of observation of changes in space and time. And I think science now understands mass and energy to be equivalent.

On a related note, it's of interest to point out that the standard for measurement of mass, which used to be a comparison given 'amount' of mass (such as a cc of water to equal a gram) was in 2019 just revised to be defined in terms of the Planck constant. If understand it correctly, the implication of this is that the 'yardstick' to measure a unit of mass now is no longer even a given quantity of mass, but is energy, and is entirely reducible to relative measurements of observations of space and time.

Steve3007 wrote:
January 9th, 2020, 5:37 am
But if we like, we can call the quantity represented by 'm' "mass" and we can hypothesise that this "mass" concept is a property of the object which appears to be different for different objects but seems to remain constant for any given object. That seems a useful thing to propose.

We can take it from there, doing more experiments to gradually fill out this property that we've invented and called "mass".

We can gradually forget that we invented it to describe and predict patterns in our observations and start thinking of it as something that "really exists" (whatever that means) if we want to. But we don't have to do that. Our ability to describe and predict our observations is entirely unaffected by that metaphysical decision. We can simply think of 'm' as a quantity in an equation which describes various aspects of our observations.
Your pragmatist approach is showing through here! I agree, and think the arguments over what is 'real' or not, what 'exists' or not, are often rooted in language problems that ultimately make little practical difference, and as such have a lot of echoes of William James' story of the squirrel going around the tree.

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Re: Are physical quantites, such as mass, invented?

Post by Tamminen » January 9th, 2020, 4:02 pm

Thomyum2 wrote:
January 9th, 2020, 1:24 pm
On a related note, it's of interest to point out that the standard for measurement of mass, which used to be a comparison given 'amount' of mass (such as a cc of water to equal a gram) was in 2019 just revised to be defined in terms of the Planck constant. If understand it correctly, the implication of this is that the 'yardstick' to measure a unit of mass now is no longer even a given quantity of mass, but is energy, and is entirely reducible to relative measurements of observations of space and time.
And mass itself is now defined by field interactions, eg. the mass of electron can be calculated from how the Higgs field interacts with the electron field. And 99% of proton's mass consists of binding energy, and so on. So what is mass?

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Re: Are physical quantites, such as mass, invented?

Post by Atla » January 9th, 2020, 4:55 pm

Maybe I didn't understand the question. All human concepts are descriptive, and tend to be defined in relation to other concepts. Not just physical quantities.
What matters is how accurately our concepts describe, 'match' the observations.

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Re: Are physical quantites, such as mass, invented?

Post by Terrapin Station » January 9th, 2020, 7:26 pm

Steve3007 wrote:
January 9th, 2020, 12:49 pm

Good question. Two possible responses might be:

1. We have various sensations. They contain patterns/regularities/similarities. We label those sensations as observations and, in so doing, we postulate "objects" as useful models to help us to predict future sensations. By the same process we postulate those objects to have various properties, such as mass. That has worked so far. But there is no absolute sense in which we are observing anything. It's just useful to think that we are. Useful for making those predictions.

2. I've changed my mind. The objects and their physical properties aren't invented. We're observing them.
"Inventing" has a connotation of someone doing something intentionally. So re (1), just the standard idealist stance of "we can only know our own minds" still doesn't suggest that something is an invention.

I don't think the idealist approach is a very good approach, though.

But even in the absence of those discoveries, the way in which we decide that a physical property is a physical property
All properties (and thus all existents) are physical properties. The notion of a "nonphysical property" is incoherent. So there's no deciding to be done there.

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Re: Are physical quantites, such as mass, invented?

Post by h_k_s » January 9th, 2020, 11:12 pm

Steve3007 wrote:
January 9th, 2020, 5:37 am
The following analysis is intended to demonstrate the sense in which the physical quantity that we call "mass" is, like all such physical quantities, part of a mathematical model that we create to describe and predict our observations. I propose that this is actually the only way to create an unambiguous definition of such quantities.

We can describe a whole class of repeatable experiments/observations that could be performed. We could then point out the patterns in those observations and describe those patterns in the form of simple mathematical equations. We can then define mass as a specific term that appears in those equations.

Very simple example:

It is observed in various experiments conducted close to the surface of the Earth that various measurements related to the set of observations that we collectively refer to as an "object" fit this pattern:

mgh = 1/2mv2

Note: we don't have to think of any of the terms in this equation as representing anything other than the measured results of an observation or a constant. We don't have to care what the constants represent. We don't have to speculate as to what the dependant variables represent.

The measured quantities represented by the letters 'h' and 'v' in the above can be made to vary by changing the height and velocity of the object. However we vary them, if the quantity represented by 'g' is some constant (doesn't matter what it represents at this stage), then it is found that the above equation works if the quantity represented by 'm' also remains constant, for a given object. And it is found that different objects have different values for 'm' which satisfy the above equation. We can conclude this without having first made any decisions as to what we think 'm' represents. It's simply part of a pattern that we've noticed in our observations, expressed in precise, unambiguous mathematical terms. All we need to know about it is that, in equations like the one above and many others, it appears to remain constant for a given object however that object moves around, so long as we don't slice bits off it or stick bits onto it.

But if we like, we can call the quantity represented by 'm' "mass" and we can hypothesise that this "mass" concept is a property of the object which appears to be different for different objects but seems to remain constant for any given object. That seems a useful thing to propose.

We can take it from there, doing more experiments to gradually fill out this property that we've invented and called "mass". We can gradually forget that we invented it to describe and predict patterns in our observations and start thinking of it as something that "really exists" (whatever that means) if we want to. But we don't have to do that. Our ability to describe and predict our observations is entirely unaffected by that metaphysical decision. We can simply think of 'm' as a quantity in an equation which describes various aspects of our observations.

In a different context, this approach was once famously summarised by the phrase: "shut up and calculate!".

I'm happy to "unpack"/expand on the above further if necessary.
If I were you then I would start with a formal definition from Physics of what your terms mean, first.

It then becomes much more sound to proceed from what is known to what might be debated, rather than starting from the vague or unknown and stumbling forward into the completely foggy and unknown.

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Re: Are physical quantites, such as mass, invented?

Post by Felix » January 11th, 2020, 5:45 pm

Steve3007: But if we like, we can call the quantity represented by 'm' "mass" and we can hypothesise that this "mass" concept is a property of the object which appears to be different for different objects but seems to remain constant for any given object. That seems a useful thing to propose.
Not useful at all since mass is dependent upon weight and velocity. Are those properties invented?
"We do not see things as they are; we see things as we are." - Anaïs Nin

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Re: Are physical quantites, such as mass, invented?

Post by h_k_s » January 12th, 2020, 9:29 pm

Felix wrote:
January 11th, 2020, 5:45 pm
Steve3007: But if we like, we can call the quantity represented by 'm' "mass" and we can hypothesise that this "mass" concept is a property of the object which appears to be different for different objects but seems to remain constant for any given object. That seems a useful thing to propose.
Not useful at all since mass is dependent upon weight and velocity. Are those properties invented?
While the very earliest of philosophers assumed the existence of physical things and their mass, Descartes started with an examination of the existence of "mind" which is a topic that Aristotle simply assumes and calls it in Greek "soul" or "breath."

I believe we can logically debate whether mind, soul, or breath have mass.

But doubting that physical things and beings have mass is ludicrous. Only extreme Skepticism would venture to even attempt such nonsense.

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Re: Are physical quantites, such as mass, invented?

Post by Steve3007 » January 13th, 2020, 3:55 am

Thomyum2 wrote:It's funny to see your post here because this very same thought occurred to me while I was composing my recent post regarding the definition of 'event' in the thread discussing whether or not time is 'just and idea'.
Yes, I saw your post there and made some brief comments on it.
To briefly recap what I had said there, the event is 'the fundamental entity of observed physical reality represented by a point designated by three coordinates of place and one of time in the space-time continuum', so all observations can be reduced to this - three spatial and one time 'point'....
I'm not sure about the statement "all observations can be reduced to this". An event (in this context) is simply a 4 dimensional coordinate; a point in space-time.
...Which implies that any object is simply a spatial observation.
Fair enough, although I think it's more accurate to say that an object is the common factor in a set of related observations.
So I think you're entirely correct - matter is not a fundamental substance but is instead derived from observation, and the properties that we attribute to objects or matter - those of having 'mass' - are simply those that we construct based on our observations of the changes that the observed objects, and their relationships to other objects, undergo in space across time.
Yes, and that applies to other physical properties too. But it's perhaps harder to believe with the concept of mass because we have a visceral sense that we experience it directly. We feel we can pick up lumps of the stuff in our hands. We don't tend to think the same of physical properties like energy or entropy, despite them having the same status, in terms of their measurement, as mass.
Of course, the other basic property that we construct to describe these changes is 'energy', which is also a function of observation of changes in space and time. And I think science now understands mass and energy to be equivalent.
Yes, that's one other basic property in our particular set of models. But, at the end of the day, any quantity whose numerical value remains constant across a set of different descriptive equations, but which varies consistently when we vary one aspect of the experimental setup, and about which we can therefore invent a conservation law, can be regarded as a physical property. Electric charge (measured on Coulombs) is another one that springs to mind.
On a related note, it's of interest to point out that the standard for measurement of mass, which used to be a comparison given 'amount' of mass (such as a cc of water to equal a gram) was in 2019 just revised to be defined in terms of the Planck constant. If understand it correctly, the implication of this is that the 'yardstick' to measure a unit of mass now is no longer even a given quantity of mass, but is energy, and is entirely reducible to relative measurements of observations of space and time
That's an interesting change. Are you talking about the Planck mass? In SI units (kgs, metres, seconds) the Planck constant is of the order of 10-34, the speed of light is of the order of 108 and the universal gravitational constant is of the order of 10-11. The Planck mass is defined in terms of those fundamental constants.
Your pragmatist approach is showing through here! I agree, and think the arguments over what is 'real' or not, what 'exists' or not, are often rooted in language problems that ultimately make little practical difference, and as such have a lot of echoes of William James' story of the squirrel going around the tree.
I haven't read that story. I'll look it up.

Yes, I think a lot of debates in philosophy are either pure semantics or pure metaphysics. I have no objection to metaphysics in itself, but I think it's meaningless unless it is ultimately tied to that which can, in principle, be observed.

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Re: Are physical quantites, such as mass, invented?

Post by Steve3007 » January 13th, 2020, 4:01 am

Thomyum2 wrote:On a related note, it's of interest to point out that the standard for measurement of mass, which used to be a comparison given 'amount' of mass (such as a cc of water to equal a gram) was in 2019 just revised to be defined in terms of the Planck constant. ...
Steve3007 wrote:That's an interesting change. Are you talking about the Planck mass?...
After you mentioned that I looked it up. Thanks for pointing it out. Interesting. Here's a an article that I found in a brief search:
https://www.livescience.com/65522-new-kilogram.html

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