This is a topic that I've briefly mentioned in some other thread years ago in this forum. Now it's been bouncing at the back of my head lately, and thought it deserves a thread of its own.
Just a context for the uninitiated; While we are all familiar with the phenomenon of inertia in everyday life, we still struggle to explain it in physics. It is usually simply viewed as "intrinsic property of matter", with no further explanation as to why or how the phenomenon occurs.
It seems to me that all attempts to describe an actual mechanism for inertia revolve around Mach's Principle
one way or another. Meaning, people tend focus on finding some kind of hypothetical interaction between a local body and the rest of the universe (Which also famously acted as an inspiration to General Relativity).
But I have never seen any hypothesis or investigation towards a much simpler possibility; inertia due to the finite-speed binding interaction between the microscopic elements of a massive body. In fact, the more I think about this, the more I struggle to explain how it would be possible for inertial effect to not happen.
Here's a hand-wavy version about the basic principle;
- Imagine a universe consisting exclusive of massless (inertialess) elements (no intrinsic inertia as "property of matter").
- Imagine that those elements can bind together to form composite objects.
- Imagine that information can propagate only at finite speeds (no action at a distance).
If we now imagine "pushing" a single inertialess particle, it would move out of the way with no resistance whatsoever (no inrinsic inertia).
But let's imagine a situation with two elementary particles, A and B, bound together. Being bound together implies there's a mechanism that makes those particles settle into specific spatial distance from one another. It does not matter what this mechanism is. What matters is that information between the particles propagates at finite speed.
When particle A is "pushed" towards B, there must be some small delay before information about the A being pushed reaches particle B. During this information delay, particle A must be pushing closer to B than its natural stable distance. It gets "uncomfortably close" if you will. Thus, A must feel this situation as resistance to acceleration (and consequently pass the effect back to the "pusher" by the same mechanism). This effect is completely identical to "inertia", even though the elements making up the composite object did not have "mass" as intrinsic property to themselves. Since the elements are bound together by some mechanism, "pulling" would yield identical effect (the particles will get too far apart, and will try to get closer together).
Follow this idea up to more particles, and you get a Newtonian billiard ball model, where inertia is fully local effect to the macroscopic objects. The effect appears when object starts to accelerate, and disappears when acceleration ceases. Nothing to do with interaction between distant stars and local bodies, everything to do with binding interactions that make up massive objects.
The apparent strength of "inertia" effect would be directly proportional to the number of (massless) elements bound together, the strength of the applied force (or the magnitude of acceleration - depends on perspective), the interaction propagation speeds, and the strength characteristics of the binding mechanism(s). Basically it would be exactly what we call "inertia" as these are circularly defined properties.
The single most important point I'm making is, when objects are bound together from smaller microscopic elements, it seems impossible to escape this type of "resistance to acceleration" effect. To escape this conclusion, you'd have to propose "action at a distance" between the microscopic elements of the body!
If you view macroscopic objects as "elementary particles settle into a stable configuration", then you can view inertia as the simple fact that the same configuration becomes unstable during any acceleration. It must become unstable because there's no "action at a distance within the object". It will return to a stable configuration as soon as acceleration ceases.
And yet another way to view the same thing is that all of the microscopic elements can only know where their neighbors were in the past (just like we look at stars only in the past but in much smaller scale). Thus, applying continuous force on any part of the macroscopic object must always push the bindings into a state where there's going to be a push back to the applied force.
Of course the most obvious implication of this is that it would not be correct to call massive "elementary particles" as truly "elementary" - their inertial effect would be a result of some binding interaction, or possibly in some cases a result of how they interact with a massive measurement device. Of course we know from particle accelerators that we can indeed break massive particles into smaller parts, that are not all stable by themselves (and lose total mass in the process).
Here's some more random conjecture related to the above. Take it for what it's worth (I think it's worth thinking about);
If mass arises due to binding interactions, instead of being intrinsic property, it would yield a circumstance where objects bound by stronger mechanisms would tend to "have more mass" when measured. This appears to be true in The Standard Model of particle physics. For example, neutrinos were long thought to have no mass. They interact very weakly with other objects. A weak interaction would yield very weak inertial effects -> very small apparent mass. Maybe this is not just a co-incident. (Remember to take a close look at how particle mass is actually measured)
Also in this view it is quite simple to intuitively understand Mass <-> Energy relationship. When an atom nucleus decays, it loses more "mass" than the sum of the parts that detached. It must, because it also lost some binding interaction(s) that were partially responsible for the inertial effects -> effective measured mass (Looking at this via conservation of energy of course yields the same result so long that you have properly defined the energy of the binding interactions themselves).
Since F = ma -> a = F/m, it implies that any force imparted on an unbound massless particle would experience instant acceleration to C. This sounds like a potential starting point for a model of photon - electron interactions... ...maybe.
Well, thoughts? Are you guys aware of any theories revolving around the above concept? Is it possible something this simple has been completely overlooked for this long? Wouldn't be the first time I guess.
What am I missing?
Edited by AnssiH, 30 June 2020 - 07:34 AM.