I'm surprised that nobody brought up this topic yet. But there is a dream realm (or plane as these places are called usually) and its existence is confirmed by Luna in "Do princesses dream of magic sheep", though she called it realm of sleep. It was never explained much with but some things were shown.

• It is an actual plane and entites which exist only on it can travel to the real world. Is it necessary to be some some sort of spirit to do it, remains unclear.
• There is some space outside of any particular dream and it is possible to invade dreams from it.
• If a pony dreams of other ponies, it is possible to travel directly from his dream to theirs.
• It is possible to magically create a shared dream but the more ponies share it, the harder is the task for the caster.
• Realm of dreams fully supports emotional eating thing with Tantabus getting magically stronger by creating nightmares.
• It is unclear if ponies are the only species with magical dreams.

So what are your thoughts? Did you know the dream realm exists? Have you created any details of its physics or explained canonical ones? I have and too much to write it down here and now, but if anyone would get interested, then I'll try. Though, the basis is simple: there is no physics.

7202940

It is unclear if ponies are the only species with magical dreams.

Spike partook in the Ponyville shared dream, at least - I think any creature which dreams at all can take part.

As it is, Princess Luna seems to be the only canonical adept of dream magic. Although it's not impossible others exist, her abilities are likely the cap. Since she seems to use horn magic, unicorns are good candidates for other dream mages, but given that all creatures are already connected to the dream realm there might be other ways. One plausible candidate might be batponies, in worlds where they exist.

Notably, Luna does her job during her own waking hours, which might suggest even she can't properly control dreams from the inside. (And the fact that she herself dreams during the daytime points to the somewhat spurious connection between dreams and night that her power is based on...)

7202940

• There is some space outside of any particular dream and it is possible to invade dreams from it.

In general, this area is also portrayed fairly consistently -- in "Bloom and Gloom", "For Whom the Sweetie Belle Tolls" and "A Royal Problem" -- as a space filled with dark blue clouds and starry lights.

7203139
Which brings to mind a certain pony's mane - so which came first, the chicken or the egg?

7203139
How about this? It's quite lighter but still looks similar.

7203153
Oh yeah divive princesses are divine praise and adore! Right?

7203237
Huh?

And that other plain might well be connected - although given that Twilight only appeared there after her body appeared to be vaporised, it's possible that it's somewhere beyond dreams.

(If it is a seperate plane, perhaps Celestia has power there which parallells Luna's in the dream realm?)

7203261
Why make it separate plane?

Huh?

Did you mean that Luna is the reason of dream realm's existance?

7203300
I think it was still there before - she didn't invent dreams - but we might see it like that because of her magic.

Of course, in that case the other place might be the same one, illuminated bi Celestia's magic... except that Celestia explicitly has no power in the dream realm. So it has to be separate.

7203304

I think it was still there before - she didn't invent dreams - but we might see it like that because of her magic.

It is divine level of power, to determine an entire plane's appearance. Or did you mean image?

Of course, in that case the other place might be the same one, illuminated bi Celestia's magic... except that Celestia explicitly has no power in the dream realm. So it has to be separate.

What "power" do you mean? Do you think it was she who made Twilight alicorn?

7203308
Image, yes.

And I think Twilight became an alicorn on her own, but Celestia might have helped guide the process - and she definite showed her images of the past, perhaps taken from her memories. So they can't have been in the dream realm, because Celestia's magic doesn't work there.

7203322
Then I prefer to think that Luna was wrong. Because I don't want to multiply planes because of this only phrase.

7203756
Is there a problem with what we saw in MMC not being the dream-realm?

7203237
I'll grant that it looks similar, but there's no particular indication in the show as to what that place actually is. Assuming it's somehow connected to the dream realm might not be a bad idea -- it's either that or Princess Celestia just happens to have an entire special dimension she uses just to make ponies into princesses, as I see it.

7203953

Assuming it's somehow connected to the dream realm might not be a bad idea

Yeah, especially if there are memories floating around which are the base for dreams (putting aside magic like Luna's invasions).

7203818

Princess Celestia just happens to have an entire special dimension she uses just to make ponies into princesses

That' what I was talking about.

7205129
Or uses for many purposes not shown on-screen? Or even just visits sometimes, because it doesn't actually belong to her?

7205131
And these are the questions with no answers which make this version unnecessarily complicated. Unless you manage to answer them, but then it would greatly increase your headcanon's caliber.

7205142
Do they need answers any more than if the show had never introduced the dream realm? I mean, there are a lot of places in the show we only saw once, but that's no reason to just go conflating them because they're a bit similar.

If I had to give it a name, I would call it the "astral plane" and relate it to the nature of magic. Or perhaps the edge of the afterlife.

Bump!

7202969
Luna said this:

here is nothing my sister can do. She has no power in the realm of sleep. Only I can move from dream to dream.

But later Tree of Harmony visited the student six's dreams to call for their help. Luna is wrong in this part so she can be wrong in the other or even lie because she doesn't want Celestia to know about this as she is already obsessed with guilt. But seriously, there are two places which look similar and allow to do similar things, but they are not one.

7225038
If they are not one, then there's no problem believing Celestia is really helpless in dreams. Luna not knowing about the Tree is understandable, since it's power is growing and evolving.

7225057
"Luna is wrong" is lesser assumption than "Two similar otherwordly places are actually two diferent dimensions" and makes worldbuilding more coherent.

7225101
Similar doesn't mean the same. And coherent doesn't mean unnecessarily reductive.