This is not a trick question. Would you call a rainbow a "physical object"? If not, why not? What is the difference between a rainbow and what you would describe as a physical object? Just to make this really interesting, I'm going to allow the option of a contradictory answer to the main question.
Colloquially no. In everyday speech objects have edges that can manipulated physically. But even here a physical object can be something that we can detect with our senses... that's certainly true.
But philosophically, yes, because anything that can referenced at all is an object.
So it depends what kind of object you mean
...Exactly...
The question, like so many philosophy and metaphysics questions, is a piss poor and ambiguous question. The question here is not about the nature of rainbows at all but about what the hell the question is asking. The real, unasked question is what is the definition of "physical object". Once defined, the answer to the op is simple. My question would be why the hell the red herring of the rainbow.
Much of what I've said has addressed this. (I think)
Not everything is an object, even if some things while not objects in the narrow sense are objects in the broad sense.
A mental object is not an object in the narrow sense, yet it is an object in the broad sense, but an imaginary object is no more a type of object than is a toy car a type of car. It's a kind of toy. With an imaginary object, there is no presence of something. While an illusion is either a meteorological phenomenon or product of one, it's certainly not a physical object--even though there could be no illusions without any.
(I feel I'm flip flopping like a fish out of water)
Given the popularity of this kind of response, I feel that I need to address it, especially since it calls for a little linguistic analysis. I'll try to keep it as brief and nontechnical as possible, but lexical semantics (and lexicology) is one of my areas of special expertise. However, the question isn't just linguistic, because it has to do with how we model physical reality.
First of all, nobody is seriously questioning whether a rainbow is a physical phenomenon, but calling it an "object" biases the discussion in a subtle way. The word
object is a
count noun, as opposed to a mass noun. It is a countable thing. Mass nouns like
water need to be quantified before we can count them: "glass/bucket/tub of water". No concept is inherently countable, so some languages lack count nouns. Their nouns just refer to "substance" or "stuff", and they have special linguistic processes for adding countability when context requires it. What it means semantically for something to be a count noun is that it incorporates the unit of measurement in the meaning of the word. Hence, it sounds a bit odd to ask whether air or water is a "physical object", because those mass nouns are not inherently quantified on their own. Rainbows are countable, but they don't have to be. English just renders them that way. We are not interested in the semantics of count and mass nouns, but the semantic property of countability can get in the way of the metaphysical nature of rainbows. Lets just ignore countability.
Now we can look at other semantic properties that distinguish rainbows from other physical phenomena and objects. Rainbows are not
tangible. You cannot touch them. In fact, you cannot even approach them, because they are optical illusions caused by physical atmospheric conditions. So that makes them seem, at first blush, to be different from rocks and trees. We interact with them differently than we interact with rocks and trees, which are tangible objects. But are rocks and trees not also "optical illusions" in a sense? They have physical properties that rainbows do not, but we also interact with them as visual objects.
What I think is really important in this discussion is not the particular physical attributes of the objects that we interact with in our reality, but the manner in which we interact with them. Let's call the manner of interaction an
affordance, where manner of interaction is defined and limited by the sensory equipment (and cognitive processing) inherent in the human body. Word definitions do not always make reference to affordances, but they are an essential semantic component of all concepts, even abstract ones. Physical things--objects, substances, events--are especially defined in terms of how the peripheral nervous system interacts with them--vision, smell, taste, touch, sound, etc. In that sense, a rainbow is as much a physical object as anything else, but it has unique interactive properties--affordances--that distinguish it from other physical objects.
So here is a related question. When you sit down, you form a "lap". A baby can sit on your lap. Is your lap therefore a physical object? I think most people would be as troubled by that question as the one about rainbows, but rainbows aren't tangible. Laps are. OTOH, laps only come into existence when you sit, and they go out of existence when you straighten your body out. Like any physical object, their existence persists for a limited amount of time. They have a temporal beginning and an end. But their temporal lifespans are so much more limited than those of trees and rocks. How would that translate into the language of an alien civilization whose members could not form laps? They would have to know about human anatomy to even begin to know what one was, but they still wouldn't know of what use laps were to us. Nor would they necessarily have a sensory basis for understanding what a rainbow was.
