The Extraterrestrial Sangha.
In the Pali canon it is said that there has been 28 Buddhas other than Siddhartha Gautama who is the Buddha for this age on Earth. This means that there must be other worlds out there and other beings that benefit from a Buddha (I can't and won't speak for others but this is my belief). These worlds help explain where all the beings that continue to increase the population on Earth come from. Another answer to the population increase is that some animals and insects are being reborn here as human beings. It has been estimated by science that insects outnumber humans by 200 billion!!
The Buddha Gautama once held up a glass of water and said that there were thousands upon thousands of life forms within, which was proven with the invention of the microscope. So if microscopic organisms can exist in a small drop of water then is it so difficult to imagine other worlds populated with other sentient beings? In other words, our world is but one of those tiny organisms in that glass of water (universe). So I was meditating and thinking about this all today and I am reconsidering my belief that the six realms are purely states of being in this world and that bodhisattvas are not real.
I still don't know but I'm not absolutely denying the possibility as I had before. I guess right now I'm agnostic about it all. As of right now though I still find it more beneficial to see the effects of the six realms in the present moment and to live in a way that best avoids those effects. Now, like I said I've come to a place where I'm not denying that they are also places but seeing it that way right now isn't as helpful for me as seeing it the other way. Perhaps that will change though as my practice deepens over the years but it may not either. I guess I'm just saying here that I'm not ruling anything out.
However, I still feel that it is more important to take care of the present moment right here and now than spend hours upon hours trying to understand the metaphysical. Though meditating upon the metaphysical can have its benefits. My concern is upon the present moment and making sure that my actions/thoughts, etc comport with the Eight-Fold Path. I find it more helpful to be skillful and to do my best to follow the Eight-Fold Path out of understanding of how my actions/thoughts, etc. effect others (and myself) than out of fear.
I have found personally that doing something out of fear doesn't stand the test of time. I begin to resent things when I do them out of fear but not so if I understand why an action/thought, etc. is less skillful and harmful to others. Avoiding certain actions out of compassion creates better results for me than from doing it out of fear or doing it because everyone says so. I have discovered that doing something to "fit in" or because everyone says so doesn't work either because I feel like I'm just faking it and going through the motions. When this is my motivation I eventually get tired of playing the game and give up.