Dream bubbles are celestial objects found in the Furthest Ring, glubbed into being by Horrorterrors. The Horrorterrors were convinced by Feferi to set up special bubbles for our protagonists to use, including the Pre-Scratch Trolls. She was capable of negotiating with them due to her previous experiences with her Lusus, G'lbgolyb (Emissary to the Horrorterrors and possibly one herself), having gotten her used to the nature of the Horrorterrors, as well as a possible method of directly contacting them (as Feferi's dream self was cut in half and her original body later had a hole blown through the chest, she is probably rather glad that she set the system up).
The bubbles allow the players of Sburb/Sgrub who have lost a life to continue dreaming. The reality constructed in the bubbles is a combination of the memories of everyone inside the bubble accessible to any who has learned the bubble's nature. According to Aradia, it would be quite difficult to exit a bubble to get into a new one, however someone inside a bubble can travel to another one through common points in memory, taking their own memories with them to be integrated into the new bubble. These memories mix and combine, but in general no new memories are created.
Additionally, the bubbles store the consciousness of a player who has lost their dream selves and their original selves, making them double as a form of afterlife; the player is then capable of accessing the memory of anyone else who has gained access to the bubbles. Living players, who have lost or became their dream self, appear in the dream bubbles when they are asleep. It is in this fashion that the bubbles can be used as meeting places between the dead and the living; even those from alternate universes and doomed timelines can be found in a bubble.
The bubbles can be physically entered as well, as Aradia was capable of pushing herself through a bubble's skin to observe the battle with Bec Noir. Time and space are unstable in the Furthest Ring and mastery of at least one is required to navigate it, making it difficult to actively seek out dream bubbles. Roxy has been shown to enter a bubble with ease, subconsciously navigating the Furthest Ring due to her Hero of Void powers.
Rose was able to accomplish a similar feat by piloting the severed moon of Derse into a bubble, although the program used to navigate was created by Dave, a hero of Time. The trolls' ectobiology lab meteor has also passed through multiple dream bubbles that happened to be on their course through the Furthest Ring.
While it is possible to physically enter and exit dream bubbles the actual inhabitants of a bubble (i.e. dead and dreaming minds) are usually not capable of leaving it. This was demonstrated when Dirk's dreaming consciousness was unable to leave a bubble while the physically present Roxy and Serenity could. Aradia also remarked on this when Sollux was actually able to leave his bubble, a feat she previously considered impossible. It is unknown if memory objects can leave the bubbles, but John was shown to leave the dream bubble . (see Speculation).
Apparently, items found in dream bubbles can be taken back to the physical plane. Kurloz gave Gamzee a codpiece in a dream bubble and he was later (from Gamzee's chronology) seen wearing it on LOCAH. Additionally, it appears that dead characters present in the dream bubbles can have lasting effects on the characters who are physically passing through the bubbles, such as when .
Dream Bubbles can be destroyed, as demonstrated by Lrd English. He also was able to permanently kill all of its inhabitants. It is unclear if the former is required for the later and also if Lord English is the only one able to perform these feats, though several characters speculate that it probably is a power exclusive to him.
It seems that Dream Bubbles can be put to more unusual purposes. Smaller, miniature bubbles can be used to store memories. Dave has used these as a replacement for the Internet, creating a parody of Twitter spambot that he calls dave_ebubbles. It regurgitates everything he's said over the course of the adventure. There is a real equivalent on Twitter, which can be visited here. Similar bubbles are also used as switches that alter the surounding area by releasing the memory inside. They can only be used by the owner of said memory.
The very first dream bubble seen was included in Feferi would to set up a series of stable dream bubbles.It was very unstable and, at points, nightmarish. Later on,
In one bubble (colored blue) an entire planet was seen, populated with alternate-timeline dead trolls and visited by God Tier Rose and Dave, as well as a sleepwalking Dream Roxy. The planet itself has features of Earth, Alternia, Skaia, all four planets of the B1 kids, and some of the A2 trolls' planets (LOQAM, LOPAH, LOLCAT, LOTAF, and LOCAS). This bubble and apparently all its inhabitants were destroyed by Lrd English. (The meteor travelers' memories made up some of the landscape, but they escaped the destruction of the bubble.)
Another bubble (this one pink) features extensively starting in Act 6.2. This bubble is where the Pre-Scratch Trolls now reside after their demise. It was first discovered when Jake blacked out and saw Aranea, and again when Roxy got trapped between two Fenestrated Planes and was attacked by Meenah.
The dream bubble seemed to largely feature the pink moon of Alternia, but was later shown to have aspects of other areas as well, including Prospit, Derse, areas that resembled LOMAT (likely Aranea's planet), LOBAF (possibly Mituna's planet), and more (including Karkat's neigborhood and Terezi's forest). It is where the Act 6 Intermission 3 walkarounds take place.
A third, colored pale blue, was Jack Noir was searching for a place to hide from PM and rest. He entered this bubble, which took on his memories of the death and destruction he caused in the A2 and B1 sessions. John and Rose gained access to this bubble through their shared memories with Jack, it is later revealed to be the bubble inhabited by alpha-timeline Tavros and Vriska which is later revealed to be the same one as the one Openbound takes place, or to have merged or be intersecting with it, or for Vriska, Tavros and John to have switched from their bubble to the Openbound bubble.when
Several dream bubble seen so far has had a planet at their center. This may be true for all dream bubbles, but that is unknown as only a few have had their interiors shown zoomed out enough.
Memory objects in dream bubbles have so far shown little to no difference with their real counterparts. The memory version of the Pop-a-matic Vrillyhoo Hammer worked exactly the same as the real hammer likely would. A hat created by a roll of that hammer left the bubble temporarily, but may have fallen back into the bubble because it is tied to the bubble. The reason is still uncertain, and probably irrelevant.
Given that The Felt's jujus, a bowl of black licorice scottie dogs, and the bent horse hitcher have appeared in Openbound, Spades Slick may have access to the dream bubbles while he sleeps, though these objects may be memories of Andrew just as well. Jack Noir also affected a dreambubble, but he physically entered it rather than dreaming in it. If carapacians indeed dream in the bubbles, this could explain how Vriska could enter WV's dream by taking a nap.