Now we have detected something. Now we are in the realm of real and existent. At this point, only time will tell. We obviously can't assume anything and state it as definitive. As this is a hypothetical, once detected, what properties are expresses? Once you begin to accumulate empirical data, you can start to build an explanation of what it may be.
How do we distinguish between real and imaginary? We detect it.
There are other means of detecting something other than observing it solely by reflected electromagnetic radiation in the visual spectrum (light). If it has spatiotemporal extension and mass-energy, it has the potential to be detected.
Now, here again, an observation reported by an individual would not meet the original criteria of the OP, but, if confirmed would be an observation of something that exists, is real. The caveat here is that the human observer is a flawed and fallible observer, and effort must be made to verify and corroborate a reported observation. But now we have something to work with. All possible causalities must be explored, and either confirmed as the likely source/explanation, or else eliminated.
To date, and to the best of my knowledge, there are no corroborated observations that provide empirical evidence of an entity that exhibits the properties that have been commonly associated/attributed to the conceptualized entities labeled 'god'. As a matter of fact, the label 'god', used frequently in this thread is quite ambiguous as the label is applied to a large number of definitions. There are no definitions of the term, that I am aware of, that apply to anything that is real and existent.
