Dude, good question! I have no idea... playing in Deception, I figured they were just different worlds. Like Earth, but not different planets? Ha-ha.

I doubt it. I would think of them as completely alternate universes. The netherealm may not even reside on a planet. Our perception of earth and our universe require any sort of life to be on a planet. Its very possible that this varies in other realms.

Netherealm to me, is a perception of what religious believers look at as hell. A timeless palceless area of death, flames and pain.

Edenia seems to have waterfalls tha tjust lead nowhere. It also looks much like earth. I doubt it actually has a body of space that we know as "outer space" tho.

Chaosreal is clearly something of its own. the red nucleus shooting upwards and downwards mean there is no solid planet really. This universe revolves around that middle object.

Orderrealm seems to be floating. But I would also not be surprised if it were on supports and high above a body of mass. Very interesting.

Outworld seems to be very planet-like. I would not be surprised if it was an alternate universe with the similar structure of ours.

Other realms like Zetarra(spelling), Nitaras realm and Quan Chi's realm, remain a big mystery. I would love to know more.

Thoughtful reply, Casselman! You bring up very good points about my/our biased perception of what a 'realm' must be - that idea of Netherrealm being timeless and placeless is interesting. Does that mean that it's infinite, too?

I think part of it, also, is that the MKD 'realms' were so small. Seido looked like a city floating on a planet to me - well, I was reminded of Sonic the Hedgehog's Floating Island, at least. :D We could take Earthrealm as a guide: Earthrealm in MKD was just one village.

Why don't we figure this out guise?! Even if it's not canon!

One could argue the sizes of each individual realm varies from the size of a planet each to a size of the Known universe in each one. from Deception's perspective, we're lead to believe the former, but considering the word "realm" is used to describe an alternate dimension. the Latter is applicable as well

I think they are weird alternate universes.

Orderrealm floats in the sky, Chaosrealm is the most bizarre place you could think of. Edenia looks like earth minus the atmosphere ruining cars(I hate seeing big technology in beautiful places lol) and waterfalls leading water to nowhere. Netherrealm is definately MK version of hell so it's an alternate dimension. Outworld looks like a planet but again, from an alternate dimension.

Anyway, I don't think those realms are from a one and only universe. I never heard of MK characters going in a space trip to planet outworld.

I like to the think of the realms a different planets that each exist within the same universe, and that the "portals" that connect them, whether natural or man-made, are folds in space/time that allow travel thoughout said universe. Also, similarly to what was said above, Heaven and Hell are timeless spaces with in the universe, each seemingly infinite in size, which can't or don't produce natural life (at least life as seen within the the "lesser" realms).

I often think of this very question, and through the many creation stories I've hypothysized, this is the most logical conclusion that I've been able to come up with.