Suppose there is a magical kingdom that is hidden somewhere over the rainbow and can never be reached by anything, most people would say that such a place might as well not exist.

However, the same people will probably say that distant galaxies that will retreat beyond the observable universe does exist.

What is the difference? Sure, distant galaxies has left traces of starlight, but one can also argue that the tale of magical kingdoms also originated from fact, before it is magically sealed away.

Would Occam's razor be the only reason why we should believe in distant galaxies and not magical kingdoms? (because starlight coming from distant galaxies and legends made up by drunks are easier to believe than perfectly projected light-shows by alien and magic?)

  • Believe whatever you want. There is, however, a vast epistemic difference between what can be believed and what can be empirically verified.
    – MmmHmm
    Commented Nov 23, 2016 at 22:45
  • Can you say what "interact" means? You can't interact with your reflection in a mirror, but it exists. Likewise your shadow. Reflections and shadows are physical phenomena that you can't physically interact with.
    – user4894
    Commented Nov 24, 2016 at 0:16
  • 2
    @user4894 You certainly >>can<< interact with your reflection in a mirror, whereby, yes, it certainly exists. But the "existence", e.g., of objects beyond our event horizon, like the op opined, is a more open question. As the famous philosopher Bill Clinton observed, "It all depends on what the meaning of 'is' is." In our case, it would mean a theory that predicts many directly measurable phenomena, but also requires the accompanying existence of something not measurable. For example, the phase of the wavefunction "exists" in Schrodinger's theory, but isn't directly measurable.
    – user19423
    Commented Nov 24, 2016 at 11:50
  • Absent your definition of 'interact' I'm afraid I don't follow your reasoning. I don't see how you can interact with you reflection in a mirror.
    – user4894
    Commented Nov 24, 2016 at 18:31
  • @user4894: you can look at it.
    – user20153
    Commented Nov 24, 2016 at 21:21

8 Answers 8


I think I am saying the same thing as the others here, but I want to avoid pointless distinctions and nuance.

Put less sarcastically, such a kingdom has existed in the minds of many literally-minded Fundamentalist Christians now and in the past. It is part of the description of heaven, which is miraculous rather than magical, but beyond the sky and not directly accessible to us until we die. Try telling them that it 'might as well not exist'. Likewise, if your Vedanta Hindu friend tells you that the computer you are reading this from does not really exist, he is likely to be serious in some sense.

I would suggest that it is pointless to pursue any given definition of existence. Any statement of existence is a belief. It is, therefore, modal: fictional, artificial or theoretical. It is tied to some rule, desire or theory under which it is true, and outside of that context or an adequately similar one, it is not true.

The theory that what you see exists, is, in fact, a theory. It is one that all but the most bizarre skeptics, the most refined religions, and the most abstruse sciences adopt, but it cannot be proven true. It can only be proven useful, and 'useful' depends upon your context.

To frame it from a Kantian (or modulo vocabulary, Vedanta) point of view, the only non-modal existence that would not be theoretical or fictional at some level is "noumenal" reality. But that is not accessible to us except by its effects upon us, which are not the actual things doing the affecting, and do not necessarily represent it authentically. So we cannot reliably say anything meaningful about it, setting aside mystical revelation and the impossibly perfect guess. So in a practical sense, noumenal reality itself might just as well not exist. Reducing us to exactly zero things that don't fall into the category of what "might as well not exist" in one sense or another.

Being incapable of interaction removes most uses. So theories that presuppose the existence of things with that property have little point other than inspiration or logical cohesion. But inspiration and the need for logical completeness are powerful forces. So they are pretty common. The three examples above (heaven, non-maya and noumena) have many parallels.

  • well, other than the labels, another "magical kingdom that is hidden somewhere over the rainbow and can never be reached by anything" would be universes other than our own in the multiverse. no mortal beings in our universe will ever interact with them. do these other universes exist? Commented Jan 5, 2017 at 7:09
  • @robertbristow-johnson So, according to a theory that requires them, yes, according to other theories, no. Their existence would only matter if the theory that requires them has some use or other logical value. Does it? I am unconvinced that it does. What would you deduce from a multiverse theory other than multiple universes, that makes it a better theory?
    – user9166
    Commented Jan 5, 2017 at 19:47
  • job, you probably remember that i am a theist that also knows the difference between what is science and what is not science and what is theology and what is not. i think that reality in its entirety would include other universes if they exist. but we'll never know. i seem to sense that a multiverse concept is needed for materialists to explain fine-tuning and, like theism or deism, a measure of faith is needed for the materialists to rely on that. otherwise they do not have a statistical population to point to selection bias and anthropic reasoning to explain fine-tuning. Commented Jan 6, 2017 at 1:03
  • but i have no need for a multiverse axiom. in my opinion, a multiverse axiom is an unnecessary complication to make sense of things and is just as much a matter of faith as my belief in God. (and it cannot be anything other than an axiom, there will never be empirical evidence for other universes, and it's epistemological value is about the same as my belief in God.) Commented Jan 6, 2017 at 1:07
  • @robertbristow-johnson This is just a case example of exactly what the post says. There is no shared definition of 'exists', and we should stop forcing other people to answer existential questions they think are meaningless unless there is a good reason. You fail to give any good reason. So, why are you trying to make me answer an existential question that I consider meaningless? Are you just being contrary, or do you have a point?
    – user9166
    Commented Jan 6, 2017 at 20:28

There does not seem to be a necessary link between existence and capable-of-being-interacted-with-ness. This is to say that the sets of things that exist and things that can be interacted with need not be coextensive. Some people would take non-naturalist properties such as moral properties to be intuited, and some would take abstract objects (propositions, sets, mathematical objects) to be intuited, so we interact with them in such a way that we are affected by them, but by no means do we change-as-such these putative existents; though this is a charge often leveled at Plato, why suppose that something that only affects you rather than you affecting it changes? If it does not itself will something, but rather is passive, there does not seem to be change in any salient way, discounting equivocal rejoinders. Also, Lewisian possible worlds cannot be interacted with if they are not indexically actual. In other words, Lewisian possible worlds are concrete, independently existing, causally isolated, spatiotemporal wholes that we by definition cannot interact with, but still exist (though modal equivocation can make it seem otherwise, but even Lewis admits that his possible worlds at least tautologically actually exist). I am a neo-Meinongian, however, though I reject subsistence. I don't think abstract objects exist, and I couldn't immediately name anything I think that exists and yet can't be interacted with.



I do not think it is that difficult, if we separate in two cases:

  • Outside of a scentific approach: we are dealing in that case with opinions, speculation, with faith, etc. There is nothing we can say scientifically about the fact. A priori, it does not imply anything "good" or "bad" about the statement. As you say, it may or may not exist.

  • Within a scientific approach: it is rather frequent that a scientific theory that has been demonstrated by experiment to be highly workable is predicting phenomena that experience has not measured yet. This has happened many times in the past (in chemistry, in physics, etc.: e.g. some new elements or "black holes") that those predictions have been confirmed. Apparently, quantum mechanics is full of those enlightened guesses which are surprisingly helpful in doing predictions. Sometimes they haven't, of course, and experiment turned out something different.

Perception and Prediction

Actually, prediction is at the core of the scientific method, because it is a very important criterion in determining whether a theory is valid or not. If researchers, scientists or engineers (when working on the drawing board) could not indulge in the highly productive activity of prediction because 'it does not exist', then this would slow down the progress of science and techniques. In particular, it would oblige researchers to do very costly experiments upfront to measure everything, instead of calculations (simulations) that could give an indication whether it is worth continuing in a stated direction. And apparently, quantum mechanics is full of enlightened guesses which are surprisingly helpful to make calculations and predictions.

More broadly, if we considered that what is not observable does not exist by the mere fact it is not observable, we would live in a very flimsy reality indeed. First of all, what do we mean exactly by observable? In astronomy, many planets that are considered to exist have never been observed but have been "calculated into existence" because they seem the best explanation in the variations in observational data. The same applies to black holes, which are not observable by definition because they emit no light; what is observable is indirect effects.

Difficulties of prediction

The traditional mecanical world (Newtonian) could perhaps have open and shut discussions about this ("I believe only what I see or touch"); but with the onslaught of new phenomena which are far too big for our senses to perceive or sometimes even to grasp for our mind, or conversely too small, the notion of what we call reality had to be relativized.

In fact, science did not even need quantum mechanics to get to that conclusion:

It is usually thought that this indeterminacy, that we cannot predict the future, is a quantum-mechanical thing, and this is said to explain the behaviour of the mind, feelings of free will, etc. But if the world were classical -- if the laws of mechanics were classical -- it is not quite obvious that the mind would not feel more or less the same. (...) Speaking more precisely, given an arbitrary accuracy, no matter how precise, one can find a time long enough that we cannot make predictions valid for that long a time." - Richard Feynman

Science versus philosophy

In any case, by pursuing existence in science, we could get into particularly convoluted paradoxes: for most people, the workings of computers, astronomy, quantum mechanics, even a car engine are a matter of faith. They have never looked into a CPU or a piston, they have only been told about it. Does it exist for them, since they never perceived it? It depends on the definitions.

Even in the daily life of this automated workd, quite a lot of things that we assume (or "predict") are there, we never get to experience directly. But we do assume they are "real" because it fits, it works and we are so rarely disappointed about them that we hardly give them a second thought. When book an airline ticket via the Web, we take an enormous amount of things on faith (a money transaction, an airline, an airplane, a seat, a crew, an airport etc.) and the only thing we have is a confirmation. How do we know, at that time, that they really exist?

To avoid such quandaries, one solution for scientists is to stay away from philosophical questions of ontology: to content oneself with (direct or indirect) perception and prediction, and to admit that (scientific) reality is some kind of enlightened social consensus about how things (are supposed to) work.


You're really talking about the difference between an empiricist epistemology and an empiricist ontology, or in other words, between whether we characterize our knowledge as being bounded by our experiences or our reality itself as being so bounded.

There's not really an objective answer here, we can either take the standpoint that anything at all might exist outside the boundaries of what we can experience, or we can assert that anything we can't interact with is functionally non-existent.

As to what might lie beyond, it may make sense to extrapolate from what we know, but it isn't decisive. Before the Americas were discovered, Europeans might have guessed that a land mass with trees, animals and people could exist on the opposite side the world, but it's unlikely they would have pictured the existence of the Grand Canyon.


Whether things you can't interact with can exist depends on your definition of existence. If existence depends on perception, as debated here: Debate.Org: Is existence based upon perception?, then the tumbling dust and possible magical kingdoms outside the observable universe exist, for you, only as probable, unknown somethings beyond the observable universe. If a magical elf lives there in a magical kingdom, then the elf's perception discriminates a kingdom from the inevitable space dust, (which is effectively nothingness).

That discrimination, differentiation, perception makes existence is illustrated in the tale of The Prince & The Pauper, where pauper thinks the prince's seal is a nutcracker. Perception and interaction with an object at-hand combine to turn an abstract concept (essentia) into an actual nutcracker, not that the prince would agree that the correct concept has been reified.

From Heidegger: The Thomistic doctrine of the distinctio realis between essentia and existentia in ente creato (The Basic Problems of Phenomenology, page 91)

Existere is something other than essence; it has its being on the basis of being caused by another. "Omne quod est directe in praedicamento substantiae, compositum est saltem ex esse et quod est" (De veritate, q.27); each ens, therefore as ens creatum is a compositum "ex esse et quod est", of existing and of whatness. This compositum is what it is, compositio realis; that is to say, correspondingly: the distinctio between essentia and existentia is a distinctio realis. Esse, or existere, is conceived of also, in distinction from quod est or esse quod, as esse quo or ens quo. The actuality of an actual being is something else of such a sort that it itself amounts to a res on its own account.

If we compare it with the Kantian thesis, the Thomistic thesis says — indeed, in agreement with Kant — that existence, there-being, actuality, is not a real predicate; it does not belong to the res of a thing but is nevertheless a res that is added on to the essentia. By means of his interpretation, on the other hand, Kant wishes to avoid conceiving of actuality, existence, itself as a res; he does this by interpreting existence as relation to the cognitive faculty, hence treating perception as position.

The difference between things that can't be interacted with, such as space dust beyond the observable universe, and things that don't exist, is that you can reason that there is space dust beyond the observable universe. You can perceive there is matter there because the limit of observable light has nothing to do with matter.

As for things like "future inventions" or "unknown things", which you supposedly can't interact with. Well they exist for you as members of the set of future inventions, or unknown things, and you have interacted with them on this minimal cognitive level.


The systems theory is incomplete. I am one of many working on it. This is the proposal of my current writing: object systems exist for the subject systems they interact with. If a system is unable to interact with other, then it does not exist for the other. Therefore, existence is subjective. There is no such thing as absolute existence. If you can find where does a finger or a hurricane begin and end, that is the system... For you. Other people may disagree with you. Systems don't exist really in nature, there are only atoms interacting, and our brain create the limits.

Think which atoms belong to the finger, or the sea. It is absolutely subjective. What is the FBI as a system? Does it include the building? The water on the building? The subject determines the system existence depending on the needs. If I need to geolocalize the FBI office, then it is a dot for me.

Other example: does God exist? No, until you interact with him. Does the second moon of the earth exist? No until you are able to interact with it.

Update: did Einstein existed? We didn't interacted personally with him: yes, because we can interact with his ideas, and because we know they were created by a name named Einstein, and we believe in certain people. Some people is mathematically convinced that there were no "attack" nor planes on 9/11, because some calculations and proof don't admit a plane. Those planes "objectively" don't exist for them. Objectivity can be just a compromise and a fuzzy agreement. Those planes exist for some and don't exist for others.

About closed systems: ideal closed systems may exist (ex, the system black box without inputs and outputs), but physical closed systems don't have i/os by definition, therefore can't interact, therefore, don't exist.

Interaction is a very interesting subject few people has taken care of, you can read my draft of a theory of general interaction on ydor.org.

  • So you are saying no matter exists outside the observable universe? Or do you accept that you can reason that it does. Commented Nov 25, 2016 at 0:55
  • I understand it goes against traditional thinking: 1-out of observable not, out of interact-able yes, if we can calculate it exists, it does. 2-if we can calculate that matter exists on a far point of the universe, it exists. If we cant interact with it with our math, our reason (your comment), it does not. 3-we call it matter, because we touch matter, but it is nothing than fundamental particles (energy?) on interaction: "all mass is interaction" --Feynman
    – RodolfoAP
    Commented Nov 25, 2016 at 5:05
  • A big problem with existence is the anguish of knowledge. Do extraterrestrials exist? How can that tremendous fact be subjective? Removing anguish, we just don't know. They don't exist until proven. Also, if we all die, they stop existing: the concept of existence dies with us. Maybe atoms will continue to interact on the universe, because we interpolate its behaviour. But we will not be there to assess existence. That's good : how do you assess existence? Interacting. Will include it on my text.
    – RodolfoAP
    Commented Nov 26, 2016 at 5:40

To find the difference (if any), one must start by clearly defining "can't be interacted with" and "don't exist."

Can't be interacted with - Not humanly perceivable.
Don't exist - the "thing" has no (zero) amount of energy, mass, or matter.

With these definitions, it becomes clear that if something does not exist, then it is not humanly perceivable. But if something is not humanly perceivable, it does not mean that it does not exist! So, the difference is that they are not reversible.


Supposing such things is generally masturbatory without some kind of objective reason (evidence) to consider the thing possible in the first place. But I considered this something worthy of commenting upon because I often use a similar reasoning to address notions of 'faith-based' belief. In short:

"If something has no discernible, quantifiable or qualifiable effect upon reality, it is irrelevant to that reality."

My own personal philosophy tends to be objective in nature but deals strongly with relevance. (note, I use the word 'relevance' not 'relativity' for a strong and specific purpose) As thinking and curious beings we seek to expand our knowledge to include things it has not included before. But such necessarily requires that new knowledge extends in some way from things already at least partially known or understood. To do otherwise is what is called 'revelation' and constitutes mysticism. It bears no relevance to reality without evidence to support it, thus speculating about such things without at least some minor basis to 'know' (as opposed to merely 'believing) it exists is folly. It might serve well for a science fiction novel, but it is my opinion that even fantastic fiction still hinges from some known resemblance to the real and the known. Consider the following:

"Marjacam Rasbitt set out to harbilakt the shidickly mastinovi, but was djordblasted by his reduvinush rilo-batic when he tried to farfiz a wooshaning norg."

Without some notion of what the words in the places of nouns, verbs, adjectives and adverbs actually mean (epistemology) the sentence makes no sense what-so-ever. You can't even begin to guess. Folly. In fact, had I not attempted in some way to use existing (known) structure such as capitalizing a proper name and using suffixes similar to known nouns/verbs/adjectives/adverbs, the sentence would make even less sense.

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