<P> Olivia is held in Walternate's laboratories in the parallel universe, and given drugs and conditioning to make her believe she is Fauxlivia, and subsequently a willing test subject for Walternate's tests of the powers of Cortexiphan . Olivia slowly breaks this conditioning, and on one trial, is able to cross over to the prime universe to relay a warning to Peter about Fauxilivia . Her identity exposed, Fauxilivia is extracted back to the parallel universe by Walternate's shapeshifters, while Olivia gets help from Broyles to cross back to the prime universe . Olivia is distraught after her return, knowing about Peter's relationship with Fauxilivia . However, after some time, the two reconcile and admit they have feelings for each other . </P> <P> In the prime universe, the Fringe team learn more of the Wave Sink Device from Sam Weiss, understanding it was created by a long - advanced race known as the First People, with the power to destroy or create universes, but is only powered by Peter's biology . The two devices in both universes are quantumly entangled, allows one to alter the other universe . Walter surmises that Walternate wants to engage the device to destroy the prime universe in hopes of healing the parallel universe damaged by his crossing in 1985 . In the parallel universe, Walternate discovers Fauxilivia is pregnant with Peter's child and discreetly accelerates the pregnancy, as to obtain a sample of the child's blood to activate the Device . The effects on the prime universe are numerous but the parallel universe shows no sign of healing . Walter directs teams to move the prime universe Device to Liberty Island, the same location where the parallel device, as to minimize the affected areas, and then instructs Peter to use the device to counteract the parallel version . Instead, when Peter enters the device, he witnesses a future where the parallel universe was destroyed and the prime universe on verge of the same collapse, and finds that Walter would set a plan in motion to send the Device back into the far past via a wormhole (creating the First People myth), and having it trigger this memory when Peter uses it . After this experience, Peter uses the device to link the two together, fusing the two rooms from the prime and parallel universe into a bridge, allowing the two sides to meet one another . However, shortly after this, Peter disappears to the apparent obliviousness of both Fringe teams; the Observers, looking on, assert that Peter has erased himself from the timeline to let this event happen . </P> <Table> <Tr> <Th> No . overall </Th> <Th> No. in season </Th> <Th> Title </Th> <Th> Directed by </Th> <Th> Written by </Th> <Th> Original air date </Th> <Th> Prod . code </Th> <Th> U.S. viewers (millions) </Th> </Tr> <Tr> <Th> 44 </Th> <Td> </Td> <Td> "Olivia" </Td> <Td> Joe Chappelle </Td> <Td> J.H. Wyman & Jeff Pinkner </Td> <Td> September 23, 2010 (2010 - 09 - 23) </Td> <Td> 3X6101 </Td> <Td> 5.83 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, Olivia manages to escape "Walternate" 's clutches and takes taxi driver Henry (Andre Royo) hostage to get around New York . Throughout Olivia's attempted escape, it is revealed that the experiment was an attempt to replace her memories with those of her alternate counterpart . Olivia remembers a safe house and decides to go there . It turns out to be the home of her counterpart's mother, Marilyn, (Amy Madigan); Olivia's real mother died years ago . Marilyn convinces Olivia that she suffered a mental breakdown as the treatment takes full effect . Now that the experiment has succeeded, she "returns" to Fringe Division . Meanwhile in the prime universe, Walter and Peter prepare to move on with their lives, with neither seeming to suspect that the Olivia with them is in fact her alternate counterpart in disguise . </Td> </Tr> <Tr> <Th> 45 </Th> <Td> </Td> <Td> "The Box" </Td> <Td> Jeffrey Hunt </Td> <Td> Josh Singer & Graham Roland </Td> <Td> September 30, 2010 (2010 - 09 - 30) </Td> <Td> 3X6102 </Td> <Td> 5.24 </Td> </Tr> <Tr> <Td_colspan="8"> In the prime universe, Thomas Jerome Newton sends men to recover a box buried in the basement of a residence, which is part of Walternate's doomsday device . However, when the men open the box, everyone in the house except a deaf man in the group dies . Walter discovers they were killed by ultrasonic sound waves, putting those in the vicinity into a trance before the box fatally "cooks" their brain . Walter and Nina attend the reading of the last will and testament of William Bell . Walter receives a note urging him "Don't be afraid to cross the line" along with a key to a safety deposit box . In the safety deposit box, Walter finds certificate of stock of Massive Dynamic, making him the sole shareholder . At the end of the episode, Peter tinkers with the disarmed box while Fauxlivia communicates with the parallel universe, saying "Peter is engaged" and receiving instructions to work on Walter . </Td> </Tr> <Tr> <Th> 46 </Th> <Td> </Td> <Td> "The Plateau" </Td> <Td> Brad Anderson </Td> <Td> Alison Schapker & Monica Owusu - Breen </Td> <Td> October 7, 2010 (2010 - 10 - 07) </Td> <Td> 3X6103 </Td> <Td> 5.19 </Td> </Tr> <Tr> <Td_colspan="8"> Back in the parallel universe, Olivia, Charlie, and Lincoln find after multiple accidents that the cause is Milo Stanfield (Michael Eklund), a man who suffered from low - functioning autism, but since underwent treatment with nootropic drugs, developing an incredible ability to calculate cause and effect to set off chain reactions that he uses to precipitate statistically impossible deaths . As Walternate perfects an experiment to determine how Olivia crosses universes, a Peter hallucination appears and informs her that she is not "from this world" and kisses her to remind her of who she is, leaving her anxious and worried . </Td> </Tr> <Tr> <Th> 47 </Th> <Td> </Td> <Td> "Do Shapeshifters Dream of Electric Sheep?" </Td> <Td> Ken Fink </Td> <Td> David Wilcox & Matthew Pitts </Td> <Td> October 14, 2010 (2010 - 10 - 14) </Td> <Td> 3X6104 </Td> <Td> 5.22 </Td> </Tr> <Tr> <Td_colspan="8"> In the prime universe, U.S. senator James Van Horn (Gerard Plunkett) is hospitalised following a car accident . After Newton arrives and shoots him in the face, Broyles discovers Van Horn was in fact a shapeshifter who collected data on Fringe Division . Walter discovers that Van Horn is still alive to some degree and has another "brain" in his back . Later, Fauxlivia and Peter capture Newton following a car chase . Knowing it may blow her cover, Fauxlivia visits him and gives him a suicide pill that causes him to bleed out mercury . In the end, Fauxlivia invites Peter to her home and sleeps with him in an attempt to draw his attention away from his growing suspicion that something is not right with her . </Td> </Tr> <Tr> <Th> 48 </Th> <Td> 5 </Td> <Td> "Amber 31422" </Td> <Td> David Straiton </Td> <Td> Josh Singer & Ethan Gross </Td> <Td> November 4, 2010 (2010 - 11 - 04) </Td> <Td> 3X6105 </Td> <Td> 4.80 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, a twin frees his brother from amber . Walternate reveals that those who are trapped in amber aren't dead, but in suspended animation and those who are released will compromise its structural integrity . However, if someone was to reveal this, it could be damaging, so the Fringe Department is tasked to capture those responsible . Throughout the episode, it is revealed that one of the twins is a serial bank robber, and when the innocent brother was ambered, he posed as him . In the end, the bank robbing twin gets ambered . Meanwhile, Walternate experiments on Olivia by taking her to a sensory deprivation tank . Olivia succeeds in traversing universes temporarily . In the end, a hallucination of Peter convinces her who she really is . </Td> </Tr> <Tr> <Th> 49 </Th> <Td> 6 </Td> <Td> "6955 kHz" </Td> <Td> Joe Chappelle </Td> <Td> Robert Chiappetta & Glen Whitman </Td> <Td> November 11, 2010 (2010 - 11 - 11) </Td> <Td> 3X6106 </Td> <Td> 4.82 </Td> </Tr> <Tr> <Td_colspan="8"> In the prime universe, Walter is dismayed to learn that Peter is continuing to study the blueprints from the doomsday device . Meanwhile, fifteen people suffer retrograde amnesia after listening to number stations . The team discovers that there is a hidden signal buried in the radio transmission, leading them to a strange cube - like device which is assumed to be the cause; the device is revealed to be from the parallel universe, and the shapeshifter controlling them is using them to wipe the memories should the listeners solve the numbers in the station . Walter and Astrid solve the numbers; they are a series of coordinates throughout the world . When they arrive at a location in New Jersey, the team discover the coordinates lead to parts of the doomsday device . In the parallel universe, Olivia attempts to arrange another test, but a hallucination of Peter tells her she has to return home . </Td> </Tr> <Tr> <Th> 50 </Th> <Td> 7 </Td> <Td> "The Abducted" </Td> <Td> Chuck Russell </Td> <Td> David Wilcox & Graham Roland </Td> <Td> November 18, 2010 (2010 - 11 - 18) </Td> <Td> 3X6107 </Td> <Td> 4.85 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, Olivia has to deal with a serial kidnapper known as the "Candyman", who kidnaps children then releases them a few days later, but released with severe health problems after draining the hormones from their pituitary glands, which the Candyman uses to maintain his youth . With the help of Broyles' son, who was a victim, Olivia ultimately finds a kidnapped child and kills the Candyman, while Broyles kills a former physician - turned - priest who is in league with the Candyman, after he returns to kill his son . Broyles later discovers that Olivia has recovered her identity, but lets her go after realizing Walternate intends to kill her . Olivia enlists the help of Henry to send her to Liberty Island then break into the facility . Olivia is able to return back to her universe, but is later pulled back by Walternate . However, Olivia returned long enough to tell a cleaning lady to warn Peter she is trapped in the parallel universe . </Td> </Tr> <Tr> <Th> 51 </Th> <Td> 8 </Td> <Td> "Entrada" </Td> <Td> Brad Anderson </Td> <Td> Jeff Pinkner & J.H. Wyman </Td> <Td> December 2, 2010 (2010 - 12 - 02) </Td> <Td> 3X6108 </Td> <Td> 5.13 </Td> </Tr> <Tr> <Td_colspan="8"> Realising she has been exposed, Fauxlivia drugs Peter and escapes . The next morning, the team find the typewriter (a "quantum entanglement" device) used to contact the parallel universe in a typewriter store . Peter discovers the location where Fauxlivia is going to return to her universe . The team arrive at the station and Fauxlivia is arrested . Meanwhile in the parallel universe, doctors prepare to kill Olivia and use her to help Fauxlivia return . Broyles manages to break her out . The two go to Walternate's old lab in Harvard . She lies in the isolation in time before Broyles is arrested . Olivia successfully crosses over back to the Prime universe, while Fauxlivia returns to hers, leaving behind the mutilated body of "Alternate - Broyles" to make up for her mass . While Peter and Olivia reunite at a hospital, the typewriter store owner trades a man a piece of the doomsday device in exchange for the restoration of his paralyzed legs . </Td> </Tr> <Tr> <Th> 52 </Th> <Td> 9 </Td> <Td> "Marionette" </Td> <Td> Joe Chappelle </Td> <Td> Monica Owusu - Breen & Alison Schapker </Td> <Td> December 9, 2010 (2010 - 12 - 09) </Td> <Td> 3X6109 </Td> <Td> 4.74 </Td> </Tr> <Tr> <Td_colspan="8"> The Fringe team tracks down cases of people having had donated organs removed . They come to learn the organs all belong to the same person, Amanda, a young ballerina that committed suicide . They identify the culprit, Roland Barrett, a man that met Amanda at a suicide counseling clinic and became enraptured with her . Having reassembled her body from the corpse and donated organs, Barrett is able to bring her back to life but, when he looks at her, realizes that it isn't really Amanda he brought back . The resurrected girl later dies again . Meanwhile, Olivia attempts to adjust to life back in her world, and finds it emotionally difficult to cope with how Fauxlivia integrated herself into Olivia's life, particularly her relationship with Peter . She breaks down at the end of the episode, reprimanding Peter for how he couldn't tell it wasn't Olivia that he was sleeping with . Peter is unable to answer her . As Walter and Peter later go out for a milkshake, the Observer is seen watching them, and he reports on his phone that "He is still alive". </Td> </Tr> <Tr> <Th> 53 </Th> <Td> 10 </Td> <Td> "The Firefly" </Td> <Td> Charles Beeson </Td> <Td> J.H. Wyman & Jeff Pinkner </Td> <Td> January 21, 2011 (2011 - 01 - 21) </Td> <Td> 3X6110 </Td> <Td> 4.87 </Td> </Tr> <Tr> <Td_colspan="8"> A series of events leads Walter to befriending musical icon Roscoe Joyce (Christopher Lloyd), keyboardist of Walter's favorite band, Violet Sedan Chair . Walter learns through the Observer September that bringing Peter from the parallel universe ultimately, through a long chain of events, led to the end of the band due to the death of Joyce's son . The Fringe team is unaware that September has engineered events in the present to test Walter's resolve to let go of Peter when the time is right . </Td> </Tr> <Tr> <Th> 54 </Th> <Td> 11 </Td> <Td> "Reciprocity" </Td> <Td> Jeannot Szwarc </Td> <Td> Josh Singer </Td> <Td> January 28, 2011 (2011 - 01 - 28) </Td> <Td> 3X6111 </Td> <Td> 4.53 </Td> </Tr> <Tr> <Td_colspan="8"> The Fringe team and Massive Dynamic have assembled the buried components of the doomsday device, speculated to be an artifact of the "First People", a lost civilization that supposedly existed until the "mother of all mass extinctions". The device reacts to Peter's presence, but they are unable to identify what triggered this . When several shapeshifters are assassinated, Fringe and Massive Dynamic attempt to locate a mole from the parallel universe using Fauxlivia's computer files to identify the shapeshifters . Walter happens across the same files in Peter's room, and finds that Peter has been the assassin . Though Peter claims he killed the shapeshifters as he refuses to remain reactive to the events, Walter fears that the device has "weaponized" him for some purpose . </Td> </Tr> <Tr> <Th> 55 </Th> <Td> 12 </Td> <Td> "Concentrate and Ask Again" </Td> <Td> Dennis Smith </Td> <Td> Graham Roland & Matthew Pitts </Td> <Td> February 4, 2011 (2011 - 02 - 04) </Td> <Td> 3X6112 </Td> <Td> 4.26 </Td> </Tr> <Tr> <Td_colspan="8"> A biological attack leaves a man dead, with no bones in his body . Fearing the start of a larger incident, the Fringe team track one culprit but he is hit by a car and falls into a coma . Walter suggests using Simon, an undocumented Cortexiphan patient with uncontrollable telepathic abilities, to read his mind to identify other targets . Olivia is able to coax Simon to help when he discovers he cannot read her mind as a fellow Cortexiphan patient . Simon helps to track down and stop two other ex-enlisted men who were part of "Project Jellyfish", which involved being exposed to a biological agent that would disintegrate skeletons; though the men were immune, their children were stillborn due to the agent . The men are seeking revenge . After completing the case, Simon gives Olivia a note revealing Peter's thoughts are still with Fauxlivia . Meanwhile, Nina Sharp has discovered that Sam Weiss is the author of several books of the First People . Sam tells Nina that Peter's disposition towards Olivia or Fauxlivia will determine which universe will survive when the machine is activated . </Td> </Tr> <Tr> <Th> 56 </Th> <Td> 13 </Td> <Td> "Immortality" </Td> <Td> Brad Anderson </Td> <Td> David Wilcox & Ethan Gross </Td> <Td> February 11, 2011 (2011 - 02 - 11) </Td> <Td> 3X6113 </Td> <Td> 3.74 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, the Fringe team investigates the deaths of two people, killed by the apparently extinct "skelter beetle". With Fauxlivia's boyfriend Frank's help, they track the cases to Dr. Silva who had been trying to develop a cure for the avian flu prior to the extinction of the sheep, the only known hosts for the skelter beetles . Fauxlivia is caught by Dr. Silva when she and Lincoln locate him, and believes Dr. Silva has selected her for the final host to gestate the queen beetle sustaining the species . When the rest of the Fringe team arrives, Dr. Silva reveals he was the final host, and dies after extracting the queen . Frank finds that Fauxlivia was exhibiting early pains due to being pregnant, but realizes it cannot be his child, and leaves her . Walternate, knowing that Peter is the father, provides Fauxlivia with his full support, believing that this is another way for Peter to voluntarily return to the parallel universe . </Td> </Tr> <Tr> <Th> 57 </Th> <Td> 14 </Td> <Td> "6B" </Td> <Td> Thomas Yatsko </Td> <Td> Glen Whitman & Robert Chiappetta </Td> <Td> February 18, 2011 (2011 - 02 - 18) </Td> <Td> 3X6114 </Td> <Td> 4.02 </Td> </Tr> <Tr> <Td_colspan="8"> Strange physical behavior, including the deaths of six partygoers, in an apartment building leads Walter to believe that the same damage to the fabric of space - time occurring in the parallel universe is occurring in the prime one, and with Massive Dynamic's help, prepare a means to encase the building and surrounding area in the amber - like substance they had previously encountered . Olivia discovers that a widow, Alice, has an emotional quantum entanglement with the doppelganger of her deceased husband, Derek, that is keeping a crack between the universes open . With Olivia and Peter's help, Alice is able to recognize that the man she is seeing is not her husband, severing the ties between them and closing the crack just before a singularity developed . Olivia and Peter finally work through their relationship and spend the night together, while Walter worries that he was moments away from performing the same actions that Walternate had to do in the parallel universe to save it . </Td> </Tr> <Tr> <Th> 58 </Th> <Td> 15 </Td> <Td> "Subject 13" </Td> <Td> Frederick E.O. Toye </Td> <Td> Jeff Pinkner & J.H. Wyman & Akiva Goldsman </Td> <Td> February 25, 2011 (2011 - 02 - 25) </Td> <Td> 3X6115 </Td> <Td> 4.02 </Td> </Tr> <Tr> <Td_colspan="8"> Following from the second - season episode "Peter", this episode returns to 1985 to recount events after Peter's abduction . Elizabeth, worried that Peter will kill himself trying to return to what he believes is his home, takes him to Jacksonville, where Walter is conducting Cortexiphan trials on children . Walter finds young Olivia has been able to cross to the parallel universe, believed to be a result of fear of her abusive stepfather, and sees it as a way to return Peter . When one of Walter's tests causes Olivia to set the room ablaze by pyrokinesis, she runs away . Peter finds and meets her, and gives her confidence to trust Walter and face the fears of her stepfather . Olivia tearfully returns to Walter's office, giving him her sketchbook that shows her pictures of the parallel universe, her stepfather, and her and Peter together, but she soon finds that she inadvertently crossed to the parallel universe again . Walter warns off Olivia's stepfather, while Peter returns with Elizabeth to Reiden Lake and comes to call her "mom", a lie that eventually leads to her suicide . In the parallel universe, Walternate, having previously lost his resolve, gains new confidence, knowing through Olivia's sketchbook that Peter is in the prime universe . </Td> </Tr> <Tr> <Th> 59 </Th> <Td> 16 </Td> <Td> "Os" </Td> <Td> Brad Anderson </Td> <Td> Josh Singer & Graham Roland </Td> <Td> March 11, 2011 (2011 - 03 - 11) </Td> <Td> 3X6116 </Td> <Td> 3.64 </Td> </Tr> <Tr> <Td_colspan="8"> The Fringe team investigates a case of thieves stealing rare metals that appear to float from the ground . Walter identifies traces of the elements osmium and lutetium in their blood, the alloy inexplicably creating a material lighter than air . They discover the culprit, Dr. Crick, an aerospace engineer who discovered the alloy and saw to try to detoxify it as a means to allow his paraplegic son to walk again . Walter realizes the strange properties of the alloy are due to further weakening of the prime universe as a result of his crossing in 1985, and determines that he must seek advice from William Bell . Believing that Bell had prepared to be returned through the use of "soul magnets", he strikes the bell that Bell bequeathed to Nina Sharp in his will . Simultaneously, as Peter is showing Olivia the five data disks he collected from the dead shapeshifters, Olivia is possessed by the spirit of Bell . </Td> </Tr> <Tr> <Th> 60 </Th> <Td> 17 </Td> <Td> "Stowaway" </Td> <Td> Charles Beeson </Td> <Td> Story by: J.H. Wyman & Jeff Pinkner & Akiva Goldsman Teleplay by: Danielle Dispaltro </Td> <Td> March 18, 2011 (2011 - 03 - 18) </Td> <Td> 3X6117 </Td> <Td> 3.80 </Td> </Tr> <Tr> <Td_colspan="8"> Bell, in possession of Olivia's body, promises that no harm will come to her and he will leave it after finding a suitable host . The Fringe team tracks down an apparently immortal woman, Dana with the help of an FBI agent, Lincoln Lee . Walter and Bell believe the immortality may be due to Dana having been struck by lightning twice before . They find that Dana is attempting to connect to the souls of suicidal people, hoping that she can die with them and "stow away" with their soul to heaven to rejoin those of her family that were killed in a burglary attempt . They are able to prevent Dana from using a bomb set to destroy a commuter train . Instead, when she leaves the train with the bomb, the bomb explodes and she finally dies . As Bell discusses the potential theological implications with Peter, a church bell ringing nearby brings about Olivia's personality temporarily, and Bell realizes his possession of her body may be more difficult than he thought . </Td> </Tr> <Tr> <Th> 61 </Th> <Td> 18 </Td> <Td> "Bloodline" </Td> <Td> Dennis Smith </Td> <Td> Alison Schapker & Monica Owusu - Breen </Td> <Td> March 25, 2011 (2011 - 03 - 25) </Td> <Td> 3X6118 </Td> <Td> 3.84 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, Fauxlivia is kidnapped and given a procedure to accelerate the birth of her child . As the Fringe division searches for her captors, Lincoln and Charlie learn that Fauxlivia and Olivia of the prime universe had recently temporarily swapped places, and become distrustful of Walternate . Ultimately, Fauxlivia escapes, and the Fringe division finds her in time to safely give birth to her son . It is revealed the process was all initiated by Walternate, who obtains a sample of the child's blood after Fauxlivia is brought back safely . </Td> </Tr> <Tr> <Th> 62 </Th> <Td> 19 </Td> <Td> "Lysergic Acid Diethylamide" </Td> <Td> Joe Chappelle </Td> <Td> Story by: Jeff Pinkner & J.H. Wyman & Akiva Goldsman Teleplay by: J.H. Wyman & Jeff Pinkner </Td> <Td> April 15, 2011 (2011 - 04 - 15) </Td> <Td> 3X6119 </Td> <Td> 3.65 </Td> </Tr> <Tr> <Td_colspan="8"> Realizing that Olivia's soul is in danger of being lost due to her possession by William Bell, the team battles frantically to extract Bell's consciousness from Olivia's body . Peter and Walter enter into her mind, with their interactions will Bell being featured in animation . Peter is eventually able to extract him, though Bell's consciousness is unable to be saved . </Td> </Tr> <Tr> <Th> 63 </Th> <Td> 20 </Td> <Td> "6: 02 AM EST" </Td> <Td> Jeannot Szwarc </Td> <Td> David Wilcox & Josh Singer & Graham Roland </Td> <Td> April 22, 2011 (2011 - 04 - 22) </Td> <Td> 3X6120 </Td> <Td> 3.33 </Td> </Tr> <Tr> <Td_colspan="8"> In the parallel universe, Walternate activates his doomsday machine, triggering devastation in the prime universe . Peter realizes he has no choice but to enter the machine and try and break the circuit . However, the machine rejects him and knocks him unconscious . Meanwhile, Fauxlivia resolves to save both worlds by trying to bring Peter back to convince the Secretary to stop the machine . She is prevented from entering the prime universe and imprisoned . </Td> </Tr> <Tr> <Th> 64 </Th> <Td> 21 </Td> <Td> "The Last Sam Weiss" </Td> <Td> Thomas Yatsko </Td> <Td> Monica Owusu - Breen & Alison Schapker </Td> <Td> April 29, 2011 (2011 - 04 - 29) </Td> <Td> 3X6121 </Td> <Td> 3.52 </Td> </Tr> <Tr> <Td_colspan="8"> Following the continuing disintegration of the prime universe, the Fringe team races to prevent the destruction of their world . FBI agent Olivia Dunham recruits Sam Weiss for help while Peter recovers from touching the doomsday machine in the previous episode . Peter is eventually able to reinsert himself into the machine, causing him to wake up fifteen years in the future . </Td> </Tr> <Tr> <Th> 65 </Th> <Td> 22 </Td> <Td> "The Day We Died" </Td> <Td> Joe Chappelle </Td> <Td> Story by: Akiva Goldsman & J.H. Wyman & Jeff Pinkner Teleplay by: Jeff Pinkner & J.H. Wyman </Td> <Td> May 6, 2011 (2011 - 05 - 06) </Td> <Td> 3X6122 </Td> <Td> 3.29 </Td> </Tr> <Tr> <Td_colspan="8"> Peter, who has entered the prime version of the machine with Olivia's help, experiences a vision of the future where the parallel universe has been destroyed and the same threatens the prime one . He opts instead to merge the two machine rooms, creating a bridge where inhabitants of both universes can solve their dilemma, before disappearing and being forgotten by both Walters and Olivias . </Td> </Tr> </Table> <Tr> <Th> No . overall </Th> <Th> No. in season </Th> <Th> Title </Th> <Th> Directed by </Th> <Th> Written by </Th> <Th> Original air date </Th> <Th> Prod . code </Th> <Th> U.S. viewers (millions) </Th> </Tr>

When does olivia come back to her universe