htraE is presumably the name for the backwards universe counterpart version of Earth. Although not referred to as htraE, it can be assumed to be called so due to the nature of the backwards reality, since language is also reversed. In Last Human, htraE is referred to as Backwards World.
In the Series III episode "Backwards", Kryten and Arnold Rimmer enter a Time Hole in Starbug 2 and crash land on htraE. At first, they believe they have found home, until they find a sign reading "Nodnol, 871 Selim". Rimmer is confused as he has not heard of Nodnol, but Kryten says that the sign is reversed and translates it. After a strange incident where a box throws itself into a van, they get a lift. After "unhitching" a lift, they quickly discover that they are indeed on Earth but at a point where the Big Crunch is contracting the Universe, causing time to run backwards. In a small café in Retshcnam, they discover that the year is 1993 (or as the locals write it, 3991). After reading a newspaper and looking at the jobs page, they decide to work as a novelty act known as The Sensational Reverse Brothers as they can use their forwardness to great effect. The act became a regular hit at the Nogard dna Egroeg eht.
Three weeks later, Cat and Lister find the same time hole and land on htraE. After discovering Starbug 2 in a lake, Lister is surprised that he leaves the water dry. He also seems to have several injuries, including a black eye and a cracked rib. The two of them find the sign for Nodnol and Lister deduces that they must be in Bulgaria, as he believes himself to be excellent in Geography. After a bizarre incident "un-stealing" a tandem, they managed to "un-hitch" a lift to be taken to the pub where Rimmer and Kryten are performing (after finding a poster of the Reverse Brothers).
Lister and Cat are completely unimpressed by the Reverse Brothers act, as it involves mundane acts such as saying things like “welcome to the show“, and eating a boiled egg and drinking a glass of water. They are further bemused by how much the locals love the act (Lister believing that Bulgarians have simple tastes). Eventually they discover that they are actually in a backwards universe, after seeing the Pub manager "un drinking" a pint of bitter, and seeing that the menus are written backwards.
Backstage, Rimmer and Kryten decide that they want to stay in the reverse universe. On the first night, Kryten had £50 forced into his wallet at knife point. There is no disease or death, and events such as World War II would be considered great events, as millions would come back to life, and Hitler would bog off back to Austria. Lister is not so keen on staying, as he remarks that he will age backwards, until eventually becoming a sperm, saying that that's not how he imagined his retirement. He also believes St Francis of Assisi of this reality would be considered a sadist going around maiming small animals and Santa Claus would be a fat bastard who goes down chimneys stealing toys.
Suddenly they are confronted by the manager, who in an angry backwards tirade, blame the group for a fight, and sacks them. All are confused by this, as there hasn't been a fight. While Kryten and Rimmer have a word with the manager, Lister and the Cat decide to "un-eat" a pie, which upsets the man who has "un-bought" the pie. He attacks Lister which heals his rib and eye. Kryten realises that the fight they started is now about to start. Lister cries "Un-rumble" and a massive backwards brawl emerges, where tables and chairs are mended, Lister is reversed thrown through a window, which mends it, and "un-punches" a man, repairing his tooth. The Dwarfers decide to leave htraE for their own universe, finding this universe too weird and disgusting, especially when the Cat finds out to his horror how toilet breaks work in a backwards universe.
In the episode, htraE is at a point in time where the Big Crunch has occurred, where the contraction of the Universe has now caused time to move backwards, appearing like a reversed movie. The locals of the backwards reality seem to be aware that time once ran forward and construct their society now time is moving in reverse. Lettering and numbers are printed in reverse order, and sometimes mirrored. This confused Rimmer, who initially believed that the year was 3991. Lister and the Cat also believed that Nodnol was in Bulgaria, and that backwards English was Bulgarian. Forward English also sounds Bulgarian to the backwards natives. Presumably, people from the forward reality would appear to be moving in reverse from the perspective of the backward native. This would explain why Rimmer and Kryten were so popular as the Sensational Reverse Brothers, as their act would be considered miraculous in this reality. Rather than reporting stories before they happen, newspapers describe events and adverts as opposite concepts. For example Michael Ellis brought three people back to life and forced staff to accept £10,000 in a bank raid, whereas originally he would have stolen the money and killed three people. Job prospects include dish dirtying, and prospects of demotion in companies. Rimmer believes that the backwards reality made more sense than their own reality. Many years later, on a resurrected Red Dwarf, the alive Rimmer also shared this view, presumably speaking to Lister about the backwards reality.
One key issue for the Dwarfers is the concept of good and evil, since performing a moral action in their own time period would now be reversed. For example, Kryten and Rimmer believe that the backwards reality is better than their own. There is no crime, since a mugger "forced" £50 into Kryten's wallet, and the bank robber and triple killer Michael Ellis actually brought his victims to life. Diseases would make you better and there is no death. Lister counters these arguments by stating that St Francis of Assisi of this reality is a petty minded sadist who goes around maiming animals. Santa Claus would be a big fat git who goes down chimneys stealing toys.
It appears for the Dwarfers, the effects of the backwards reality doesn't quite have the same effect as it does for the natives. For example, Kryten and Rimmmer are hired for their novelty act, sacked for a fight, then the fight happens. Should they be locals to this reality, they would have been sacked, told off, then the fight breaking out, doing their act and then being hired. They also seem to be able to walk normally yet perform certain actions such as eating and drinking in reverse. The most notable of this being when the Cat went behind the bushes and found to his horror how toilet breaks worked on this planet. This is likely due to the fact that they are not natives to this time period and their presence causes inconsistent logical actions.
The reverse-time universe is explored in greater depth in the novel Backwards, after being briefly glimpsed in the novel Better Than Life. After being trapped on a desolate planet Earth while the rest of the crew were stuck in the event horizon of a black hole, Lister experienced a time dilation effect, with the result that the crew have only been away for a few weeks while he was trapped for thirty-four years. After returning to Red Dwarf, Lister suffers a fatal heart attack while fighting a Polymorph, which had removed his fear before it was restored to him in shock in the final assault. In order to bring him back to life, Holly (IQ elevated to 12,368, despite only having under thirty seconds of run-time left) presents the crew with a complex plan to take his remains to the reverse-time universe, along with the remains of Kristine Kochanski- treated with various unspecified forms of radiation on Holly's orders- so that Lister can return to his original age. Lister returned to life, after a backwards mugging and two heart attacks. He realised the nature of this universe after reading his license and finding his name was printed backwards, and was reunited with his wife, Kristine, when he returned to his home address.
In the novel Last Human, the crew return to pick Lister up as scheduled, and also depart with Kochanski, who has also been restored with her own memories and temporal perspective. Although he claims to be twenty five, there is a mention they leave the backward universe on Lister's twenty fourth birthday. It is mentioned that they had two boys Yelxeb and Mij (Jim and Bexley) who grew younger and younger, returning to their mother's womb. They ran what Kochanski called a "Food Collection Depot" which was essentially a backwards version of a restaurant.
In the novel Backwards, Kochanski stayed in the backwards universe, only able to remember the future. As soon as she met Lister, she forgot him, seemingly suggesting that she somehow belonged to this universe. Lister spent eight years in the backwards universe in prison for murder, even though Lister himself is unaware of whether he did it or not. Unable to 'remember' the future like everyone else, his study of newspaper records only reveals that he was found fleeing the crime scene in the company of a man that Lister identifies from descriptions as the Cat, with his inability to account for the Cat's presence counting against him at trial, resulting in him being sentenced to fifteen years in prison before being released early for good behaviour. From a brief description what appears to be the reverse destruction of the Berlin Wall, Lister was due to be picked up in 1989, meaning he arrived dead in the year 2025. Due to missing the time window to their Universe they spent another ten years on htraE, leaving in 1979.
After meeting up with the crew Lister eventually discovers that the 'murder' he was arrested for was actually 'committed' by Kryten, when Kryten discovered a hillbilly with an axe in his chest and pulled it out when the man started screaming. When attempting to take off, the crew discover that Starbug has suffered over a decade of decay, resulting in the realization that they are destined to spend the next decade trapped on the backwards Earth until they can repair the ship and conditions are suitable for their next attempt to return to their universe.
In the novel, htraE is located in Universe 3, one of the seven main Universes located at the Omnizone. This Universe is a mirror image of the Dwarfer's Universe, except of course time moves backwards. When the crew arrive in this Universe, their bodies adapt to the physical laws, and for the most part they are forced to obey the physics of this universe, with complications such as Kryten observing that the batteries for Rimmer's light bee might become overcharged. They can flout convention by consciously choosing to walk forwards and can still have the ability to speak forwards as well. In the case of Lister, who spent a total of 46 years of reverse living, a forward native person can learn the mechanics of backward language (which Lister called "back talk") and can still use forward logic and thought processes. This would explain why Lister was unaware if he had committed the crime which he was accused of. Unlike in the TV series, the novel universe goes to great lengths to explore how effect precedes cause, such as the Cat having sex and Rimmer defining the experience as the Cat having become a virgin, or the crew un-eating food and Kryten then having to put the animal back into its skin before leaving it in the trap that killed it. It also shows how the Dwarfers are properly affected by the backwards flow of time; by the time the crew depart htraE, Lister and the Cat have reverted to teenagers, with Rimmer musing that Lister now has "a mental age of 107, a physical age of 15, and an emotional age of two and a half".