God's Word reveals there's only two dimensions of existence, this earthly one, and the heavenly one.
We also know from God's Word that angels have appeared on earth to flesh people (the two angels at Sodom and Gomorrah for example; the sodomites saw them as young men).
So if one believes God's Word as written, then that also means admitting the possibility of angels of the heavenly dimension being able to appear on earth.
Now whether those angels change form to appear on earth, we're not told, and I doubt it. But we also know that our Lord Jesus compared the resurrection to manifest like the angels (Matt.22:30). And we know our Lord Jesus in His Resurrection body was able to appear on earth, even build a fire, cook fish for His Apostles, and sit down and eat fish and honeycomb. We also know He was able to suddenly appear in a closed room to His disciples, not coming in through the door like a flesh person. Apostle Paul even said that flesh and blood cannot inherit the kingdom of God, neither does corruption inherit incorruption.
And, IF... the resurrected spiritual body can do all that on this earth, and... it is the type body the saints will have for God's Eternity, then which existence is the more REAL? This earthly flesh existence, or the one of the heavenly dimension? Selah.
A type body that can live upon this earth, yet won't get sick, will never die, feel no heat or cold, but still eat fish and fruit, then how does that relate to the type bodies of the fallen angels of Genesis 6 that once came to earth and co-habitated with the daughters of men?
Is it possible then, that the manifestation of the heavenly realm is of a higher frequency that separates it from our earthly realm? We know there exists all sorts of rays vibrating at higher frequencies that require special instruments just to detect their presence around us. What if the heavenly is of a frequency so fine man can't detect it? Is it probable that's why a glorious light appeared along with Moses and Elijah being seen upon a mount as witnessed by Christ's disciples, with Christ being temporarily transfigured then too? (Matt.17). That's something I often wonder about, that other dimension of the heavenly and how it actually relates to this earthly.
If there's anything to that, then I think of the possibility that the angels are around us now, and have always been, only that we can't see them. It would be like there's another layer over this earth we can't see today. But those in that other dimension can see us, and appear to us, and then disappear again.
In that sense, this earthly dimension we see is only one part of the 'story', and not even the authentic part, since Apostles Paul and Peter both revealed that material matter did not create itself (Heb.11:3; Rom.1:20). And science well knows that material matter cannot be created nor destroyed, but only change its state.
I know this is a grand mystery, and especially difficult for some to even consider, it being such an abstract-like thought. But it would account for the so-called UFO phenomenon. The next question from that point would be, if those who claim to have seen UFO's, were they seeing a 'vision' into the heavenly dimension, or... were they actually seeing the objects appearing in our own earthly dimension?
In Rev.12:7 forward, we're told when the dragon (Satan) and his angels are cast to the earth, neither was their place found any more in heaven. Which dimension does that reveal they are cast to? To me, that means in this earthly dimension we see. Is that not the same type of event shown in Genesis 6 with the "sons of God" coming to earth to co-habitate with flesh man?
For this reason, I believe some are actually seeing heavenly dimension objects popping in and out between our dimension and the heavenly dimension, given as a warning and as a sign for their coming like in the days of Noah. Maybe that's also why there seems to be a proposed agenda of portrayal of alien likeness with forms and shapes other than the image of man, just to get people's minds off the truth of the real appearance of the angels with the heavenly image of man.