# Is force the unique possible relation between particles? [closed]

Is force the unique possible relation between particles?

It was requested to further specify my question. The followings paragraphs contain some of my thoughts and confusions.

Historical motivation:

• Since Aristotle the notion of force (dunamis, energeia) was intrinsic to the substance itself. The driving force was that the which caused movement (kinesis). Change from A to B is movement. The cause of this movement is force. However, Aristotle considered motion in a much broader sense than contemporary physics does. For example, he considered the transition between seeing and not-seeing, or sickness and health, as a kind of motion. Since the 17th century the concept of motion was restricted to spatio-temporal movement. Accordingly, the notion of force was changed into that which causes modifications of interrelated moving particles embodied in space-time. So, whereas the notion of force began as something intrinsic to a substance, it became something extrinsic, dependent on the structure of space, relating different particles and their properties.

To go back to my original question:

• The nature of the formula $F_G = G \frac{m_1 m_2}{r^2}$ contains the spatial distance between the two particles, as well some intrinsic properties of the particles (i.e. their mass). The formula of $F_C = k \frac{Q_1 Q_2}{r^2}$ has a similar form, and also captures some intrinsic properties of the two particles (i.e. their charge). But not only does force "captures" spatio-temporal relationships and some properties of particles, it also expresses the reason of their modification. Let's look at the formula: $F=m \cdot a$. Even though this is a mathematical identity, the equation can be interpreted as a physical difference. On the left-hand-side $F$ can be read as a "cause," whereas $m \cdot a$ on the right-hand-side can be read as an "effect." Force is the cause which brings out an effect (i.e. acceleration). I am aware that this notion of "cause" may be be outdated and that Newton's action-at-distance has been replaced by the notion of a field. But the nature of a field is even more ambiguous to me. Is it merely a mathematical construct? Does it have physical meaning?

• When I look carefully at the fundamental formulas of physics, they all seem to express relations between particles and their respective states. Force is in this sense a relational concept. Moreover, whatever a particle (or a system of particles) undergoes (motion, acceleration, etc.): there was a force which caused this change. However, it's not obvious for me how particles are able to inter-act and can in-fluence each other. My first guess was that forces were responsible for establishing this inter-connection. Forces "mediate" "between" particles. Be aware that I don't understand the words "mediate" and "between" here.

## closed as unclear what you're asking by John Rennie, tpg2114♦, Brandon Enright, David Z♦Feb 18 '14 at 18:55

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• Well, the question was closed and here is what I would have answered: Force is a concept coming from classical mechanics and classical electrodynamics. It can be extended in the special relativity case too. "Particle" is a concept specific to the microworld where it is Quantum mechanics that is relevant and particles generally interact with the exchange of other particles. There exist continuity conditions, which smoothly join the two domains, micro and macro, but , as the answer you have gotten before closure, in quantu mechanics what will emerge as "force" macroscopically – anna v Feb 18 '14 at 19:02
• continued: is not always an interaction with the exchange of particles. Quantum numbers force relationships between particles, the electrons and nucleons in a stable state forming atoms are also an example of greater complexity than the classical depiction of "force". – anna v Feb 18 '14 at 19:04
• We need just one more reopen vote to reopen this question! Anyone? – Abhimanyu Pallavi Sudhir Feb 19 '14 at 4:31