Mr. Peterson and other users in this forum said that Field IS NOT Locus as electric field or magnetic one.
But, we are dealing with particulars that cannot observe by human eye. So, is the place in our solar system that call Oort cloud can be treated as locus because it can be observe?
And, I want to ask again why physical field isn't Locus?
Apparently you are referring to this post in an old thread:
https://www.freemathhelp.com/forum/threads/physical-geometric-places.120366/#post-482325
A locus (which, as you indicated then, is Latin for "place") is defined as a set of points that satisfy some condition, such as an equation; it is often thought of as the "locus of a point", the region visited by a point that can move under some constraint. A classic example is that a circle is the locus of points a fixed distance from a fixed point, the center. I often give as an example the path that will be trampled by a dog chained to a stake, which will spend (most of) its time at the end of the chain, as far from the stake as possible. The locus consists of all the places where the dog will be found.
You can think of the Oort cloud as a locus, in the sense that it is the region that may be occupied by certain objects (though technically, I would say that the cloud is those objects, not the places where they go). Also, I'm not sure whether it has clearly defined edges, so it may be more fuzzily defined than a locus properly should be. But it is at least very similar to my dog-on-a-chain example, as is the orbit of a planet.
The reason a field, such as an electric field, is not a locus is that it is
more than just a set of points. It can be thought of as an assignment of some property (such as electric field strength or vector) to
each point in
all of space. That is, it is a function from space to either real numbers (voltage) or vectors.
The issue is not whether something can be observed, however. My dog locus would still exist if there were no marks on the ground.
Addendum: I just searched for "electric field" in Google and its dictionary entry said, "a
region around a charged particle or object within which a force would be exerted on other charged particles or objects." That may explain your thinking. It is, however, nonsense in terms of physics!
