Mass and Inertia are NOT Actually Properties Of Matter

The great physicist Ernst Mach did not consider Mass to be a true property of matter.  He contended that what we label “Mass” does not exist for one object in isolation.  Mass is only created by the “mutual relationship” between two or more objects.  To speak of “Mass” is merely to speak of the changes in Velocity that each object generates in the other.

Said Mach:  “It is possible to give only one rational definition of Mass, and that is a purely dynamical definition.”

Relatedly, Mach considered the Law Of Inertia superfluous.  His reasoning was this…  If we know that a change in Velocity only occurs when one object is acted upon by another, than this already tells us that something unmolested will continue in a straight line and in uniform motion… no need for a separate “law of inertia” asserting this fact.

Now, we all know that heavier things are more difficult to move than lighter things.  The standard scientific line would have it that this is due to Inertia (heavier objects possess more of it).  However, this really just boils down to a tautology…  Something is more resistant to movement because it possesses more Inertia, and things which have more Inertia are more resistant to movement.

I feel that physicists have failed to provide any real scientific explanation for why “heavier” objects are harder to move than “lighter” ones—or really, what even makes one object “heavier” than another, fundamentally speaking.  I mean, yes, obviously, denser objects or larger objects with more mass are harder to move than less dense or lighter ones… but WHY?

Somewhat in opposition to his own dynamical theory of Mass, Mach, in his book The Science Of Mechanics, attempted to explain Inertia this way:  Inertia can be viewed as “an endeavor of the whole towards the center.”   But I’m left wondering…  if this endeavoring toward the center somehow accounts for Inertia, would not a circular object’s endeavorings cancel-each other out, producing a net-zero effect in regards to how much the object resists movement?  Still, perhaps the answer to the riddle of Mass is somehow related to this conceptualization of Inertia.

Actually, I’ve come to believe that the whole concept of “Inertia” is bogus.  We really do not know WHY more massy objects are more difficult to move.  My best guess is that it has something to do with Mach’s (now forgotten) dynamical interpretation of Mass.  But if Mach is right, then an object alone would have no mass (or– would the interactions of its component parts generate some?).  Generally speaking, I’m betting that Mach was correct and that Mass (that is, resistance to movement, a.k.a. Inertia) only manifests as some sort of unexplained interaction between objects.

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7 thoughts on “Mass and Inertia are NOT Actually Properties Of Matter”

1. Mr Proctor… I took the liberty of posting your thoughtful comments, with the slight edit of the deletion of the short last paragraph. I don’t allow ad hominem attacks. If you prefer I delete the entire comment, please just let me know. Thanks for taking the time to read and post… H.S.

1. Eric Proctor says:

I apologize for any negativity I conveyed, non was intended.

1. Thanks for the gracious response. Please comment/ correct again whenever you have the time and inclination. I don’t usually respond to comments unless someone has a question, but I think good comments can add to the value of a post. (Yeah, okay, maybe sometimes they’re the ONLY value in a post!)… H.S.

2. Thanks for the thoughtful comment! I’ll have some time to give it some real consideration this weekend, and may respond with either a concession or (more fun!) some non-bickering other angles to consider. Thanks again for taking the time to stop by! …H.S.

3. I found your inclusion of Friction and of Buoyancy in the consideration of Mass astute and intriguing. In a way, such considerations support Mach’s contention (and the one I was promoting in this post) that an object alone does not possess Mass. That is, Mass is not an intrinsic quality of an object, but a dynamic relationship of an object and its environment. Both Friction and Buoyancy are environmentally dependent characteristics.

When we say that a “more massive” object will have “greater mass” and thus will be harder to velocity-alter — isn’t this still relying on the assumption of Mass-a.k.a.-Inertia? That is, it sounds like that particular line of reasoning boils down to:
greater mass => greater inertia
…which is the very unhelpful “explanation” I was complaining about. Also, I may not be using the word “tautalogy” completely correctly here (?). I simply find that Mass and Inertia are used to define each other in non-elucidating ways.

The same goes for the idea that something with more “Energy” will have more “Mass.” “Energy” is a nebulous term– we might as well call it “Mojo” or “The Force,” if you get what I’m saying. We can, of course, write “E=mc^2”– but that’s really more about how much Energy is contained in Mass, not how much Mass is contained in Energy. At the moment– and I may be blanking– I can’t think of any example of someone or something turning pure Energy into Mass. Seems to go the other way.

Truthfully, I think my example of pushing an asteroid in a gravity-less field so unrealistic and hyper-hypothetical, that it probably hurts my philosophical contention (well, actually Mach’s) more than helps it. If I had it to do over again, Ithink I’d drop that part. It’s a pummel-worthy notion.

All that you said about Light is so true, and so amazing to me! I’ve never actually been convinced that Light, itself, contains “Heat”– but that it can generate Heat in the things it encounters. It’s almost like the tree falling in the forest thing– if there were no objects to feel the sun’s rays, would there be any Heat?

The connection you make between Velocity and Mass-a.k.a.-Inertia with the baseball-sized rock kinda circles back to the idea of Mach’s that Mass is only created by the mutual relationship between two or more objects– for Velocity is ultimately a RELATIVE concept, n’est-ce pas?

Again, I appreciate your thought-provoking and intelligent comments. It’s nice to think that maybe one of us may say something here that will inspire some brilliant mind reading these comments on to some great new idea in Physics! Best wishes… H.S.

4. You bring up an important distinction, Mr. Smith. By convention, we have defined “weight” as, basically, “a measurement of the force of gravity upon an object,” and “mass” as something along the lines of, “the amount of matter an object has.” “Weight” can vary… For example, a baseball will weigh differently on the moon than it does on Earth; on the other hand, it’s “mass,” by definition, is the amount of matter the baseball contains, and we assume that amount to remain constant.

And yet, the concept of “mass” still presents us problems… When we say mass is “the amount of matter” an object possess, we neglect the fact that not all “matters” are equal. There’s also the problem of defining this “amount” thing– is it surface area? volume?– It can’t be “density,” for density requires mass as an element in its definition. And according to modern theories, an object’s size can vary with its velocity, so that surface area and volume are not as straightforwardly useful as they may seem at first glance.

And when we try to pin mass down as the amount of “resistance” an object offers to a change in its velocity, we run-up against the problem of relative concepts (as we do with “weight”). Firstly, velocity is, itself, a relative concept, and secondly, experience has shown that a change in velocity can CHANGE an object’s mass.

Thanks for the reminder that, no matter how “far out” a discussion goes, we must remain grounded and ever-cognizant of fundamentals!

5. Very informative comment! This post is actually getting a fair amount of traffic, and I think lotsa people will be inspired by all these comments to THINK about Gravity (and perhaps other things) instead of just taking it for granted. Thanks for stopping by!