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Old Jun 30th 2018, 01:04 AM   #1
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Lightbulb Defining substance

Iím fairly new to the world of physics but am extremely intrigued by many of its various fields. Most recently I have been struggling to find a clear answer as to what determines if something has substance. My novice assumption would be that substance can be defined by its interaction with anything containing a measurable value. Another idea I was thinking was about whether somethingís interaction with the material world can be observed, even if the subject itself cannot be. Can someone please confirm if either of these is true or where I may be able to look for answers? Thank you!
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Old Jun 30th 2018, 06:04 PM   #2
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Hello JM and welcome.

There are several things you need to know before trying to answer your questions.

Physics doesn't really address issues of 'reality' , 'existence', 'truth' or proof.


Consideration of these really lies in the province of what is called metaphysics, which is part of philosophy. Metaphysics by the way does not refer to something magical and mystic, it is simply a posh word meaning 'beyond physics'


There are several reasons for this, the important ones here being

That 'theories' in Physics are really models of something and necessarily incomplete. The only perfect model of something is the thing itself.

That many (important) words used in Physics have more than one 'definition' depending upon the model or use.

Both these mean that any discussion or consideration must take place in context (of what the Physics is for).


So you will need to supply more detail of your intended application to serve this contextual purpose.


For instance consider the question, "Does light have substance ?"


Well you or I don't feel any hammer like blows when it fall upon us.

But Physics tells us that if enough photons hit us they could knock us over.

Yet it also tells us that if we weighed a photon on the most sensitive scale in the universe we would find it has no mass.


So tell us more
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Old Jun 30th 2018, 09:24 PM   #3
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Despite what a search turns up.... "Substance " is not a term used in Physics ...

We have enough problems defining the terms we have Mass ....Charge .... Length ....Time .... Force etc ...

A man of substance is one with good character.
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Old Jul 1st 2018, 11:11 AM   #4
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Substance is something one only has in there own mind and not scientific at all unless one can demonstrate the something with experiments and formulas to convince others minds that the something has substance.

Most believe the earth has substance in there own minds but really is mostly a void between nuclei and electrons. In physicist minds the earth has very little substance.

Substance is usually a word used by people who detect something only with there 5 senses and ego. Science attempts to go beyond that but still gets influenced greatly by the senses, false education, profit and ego.
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Old Jul 2nd 2018, 03:32 AM   #5
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Substance/Existence

Iím trying to determine how or why we can say that dark matter ďexistsĒ at all, when I have so far found nothing to confirm a way to quantify it. If our only way of confirmation is based upon quantification or measurement of the matter around it or itís interaction with such matter, I would hypothesize that thought itself could be counted as existing based upon the same logic of interaction. If I choose to lift my hand, the thought tells my brain to make it happen. If Newtonís third law tells us that every action causes a reaction, our thought is the first piece of the equation.
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Old Jul 2nd 2018, 03:44 AM   #6
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Whenever the word substance is used by physicists in the literature, it usually refers to the name of a material or an element. So, in a mug, the substance is "ceramic" or the substance in a container might be "air" or "hydrogen" gas.

Substances in this context are then just a mixture (or not) of atoms and/or molecules of different kinds. Substances have a phase (e.g. gas, liquid, solid or plasma) and their properties are a mixture of material properties (density, conductivity, etc.) and behavioural properties (e.g. Newtonian/non-newtonian fluid, monotamoic/diatomic gas, mixture, etc.). Chemists deal with substances a lot!

Metaphysics, as Studiot explains, is the main fields that discusses substances in the context of whether something fundamental, like photons or electrons, can be said to be "stuff".

Personally I think most of the debates about this are kind of redundant. We already have names for *things* at those small scales and the theories developed to describe them do a well enough job without needing to redefine what substances are.

As for dark matter... remember that it is just the name for a discrepancy between the rotation profiles of Seyfert galaxies and what we would expect from galactic dynamics theory. Therefore, because the discrepancy exists, "dark matter" exists. However, whether the solution for dark matter is indeed additional matter (which is presumably what you care about) or whether it is some other dynamics effect, like Modified Newtonian Dynamics (MOND) is still be to be resolved.

As you say, dark matter is verified by exploring the interactions of objects with their neighbours or via gravitational lensing. In astrophysics, gravity is king, so if there's any motion, gravity is the cause. Therefore, dark matter can be quantified by the amount of mass required to rectify the discrepancy between the measured luminous mass and the motion using standard Newtonian gravity.

As for thoughts? Well, in physics, thoughts are just a name for certain brain activity, which is the set of electronic signals propagated by neurons. Those electronic signals are responsible for causing a muscle fibre to contract or relax. It has nothing to do with the dark matter problem. That's probably not going to be a satisfactory response for you though!
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Old Jul 2nd 2018, 06:15 AM   #7
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As indicated in the previous posts
Physics is actually rather poor at telling us what things are
Rather Physics tells us what things do.

Regarding "Dark Matter",
An anomaly has been detected where cosmological observations are failing to match the existing models.
One way of fixing this anomaly is to add some additional "dark matter" which only interacts with "normal matter" via gravity.
There are other options, but dark matter is (currently) the favoured theory.

Regarding Thoughts,
There is a serious amount of consideration around "Information" being the fundamental feature from which "existence" is formed.
This concept could seem to imply the possibility of a substantial interaction with thought.
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Old Jul 2nd 2018, 01:02 PM   #8
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Thank you all for your feedback. It gives me much to consider. Although most of what I’m hearing is leading me to believe that physics does not prove that anything exists, based solely upon interaction. (I thought that was the pure basis of physics.) To sum up my understanding of all the wonderful feedback, if the laws of physics does not in its purest essence at least provide a valid theory about thought, then physics technically proves very little. Please don’t take offense to my observation, as I still believe that physics will one day be the school of science to one day quantify and enable us to interact with thought itself.
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Old Jul 2nd 2018, 01:43 PM   #9
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Originally Posted by JMRiordan View Post
Thank you all for your feedback. It gives me much to consider. Although most of what I’m hearing is leading me to believe that physics does not prove that anything exists, based solely upon interaction. (I thought that was the pure basis of physics.) To sum up my understanding of all the wonderful feedback, if the laws of physics does not in its purest essence at least provide a valid theory about thought, then physics technically proves very little. Please don’t take offense to my observation, as I still believe that physics will one day be the school of science to one day quantify and enable us to interact with thought itself.

You still haven't told us what you understand by 'substance', and pretty well every respondent had queried this in one way or another.

Now I will add a second question to this since you raised the subject.

What does it mean to say that something does or does not exist?

Does, for instance James Bond, exist?

In some senses he does indeed.

Yet he is a perfectly acceptable abstract noun in the English Language and appears in many books and films.

How about does a hole exist?
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Last edited by studiot; Jul 2nd 2018 at 02:21 PM. Reason: spelling
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Old Jul 2nd 2018, 01:46 PM   #10
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As Studiot indicated You are probably looking for "metaphysics"
This is a more philosophical subject looking for the fundamentals of existence

The Scientific method demands an observable, testable, repeatable, processes
against which an idea can be challenged and found to fit the observations, or not.
If the idea does not fit the observations, then it is simply wrong and has to be discarded.
If it does fit then it can be presented as a theory.

A good theory not only correctly fits all current observations,
but also suggests fruitful directions for possible future observations.

The ideas of the mind and thought and consciousness etc. are still quite nebulous.
As these ideas start to firm up (and become theories) and as physics continues to expand its horizons, perhaps a link up will be possible.

But Not Today.
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