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Gordon Freeman in City 17 rubble in 202-
- "Time, Dr. Freeman? Is it really that time again? It seems as if you only just arrived."
- ―The G-Man
The timeline of the Half-Life and Portal universe spans from the 1940s to the first decades of the 21st century. That timespan saw the rise and fall of rival scientific research corporations Black Mesa and Aperture Science, the invasion of Earth by the Combine, an alien intergalactic organization, in the aftermath of the Black Mesa Incident, and the uprising of humanity against them.
This timeline has been built by gathering every known date, with the known events and chronological facts organized around them. Several retcons have been made since the release of the first game; they have been applied here, with a mention of the changed dates.
Valve currently have no plans on issuing a complete official Half-Life / Portal series timeline, since they fear it would limit their creativity for possible future games, with always a risk of contradicting themselves. The story is still being written as of today (2013), and there is always a chance that facts will be altered in a future game. It was indeed shown with the ApertureScience.com timeline, strongly altered in Portal 2, that they have no interest in respecting previously established dates, leaving to the community the task of keeping the timeline as up-to-date and accurate as possible.
Cave Johnson receives the Shower Curtain Salesman award within Aperture Fixtures.
Cave Johnson appears in the UP Pioneer Press headlines for buying a salt mine in Upper Michigan, which is later reconstructed as the Aperture Science Innovators facility.
Between 1945 and 1954
Richard Keller is born. According to the Half-Life PlayStation 2 manual, he is said to be 55 in Decay, set in 200-.
Aperture Science receives the award for Best New Science Company from the Science and Business Institute of America.
Aperture Science is rated #2 among the Top 100 Applied Science Companies by the Mechanical Engineering World Journal (likely behind Black Mesa).
It is during this decade that the Black Mesa facilities are probably built, before being purchased and refurbished later by Black Mesa (several Half-Life texture files names contain the word "fifties", suggesting the facility is as old as from the 1950s). It is also possible the company existed in the 1940s, as evidenced by Aperture Science ranking second among scientific companies in 1949.
Aperture Science is the Runner Up for the US Department of Defense's Contractor of the Year award, likely losing to Black Mesa. By now, Aperture Science has begun testing Repulsion Gel. Test Shaft 09's Entrance Way, Lobby and Testing Lounge are built.
Aperture Science constructs Pump Station Alpha and at least Test Shaft 09 Chambers 01 and 02.
Aperture also goes public this year.
Aperture Science is the Runner Up for the US Department of Defense's Contractor of the Year award again, likely losing to Black Mesa.
Aperture Science receives the Spirit of Idaho National Potato Board award for the promotion of Potato Science.
- The Eisenhower administration signs a contract with Aperture Science to manufacture shower curtains to all branches of the US Military, except the Navy.
- Pump Station Alpha (which pumps Repulsion Gel) is in active use by now.
Aperture Science constructs at least Test Shaft 09 Chamber 26.
From 1957 to 1973
Aperture Science produces mostly shower curtains, eventually making Cave Johnson a billionaire.
Aperture Science constructs Test Shaft 09 Chambers 27 and 28.
Aperture Science's Test Shaft 09 "Zulu Bunsen" is condemned and sealed off.
Between 1963 and 1972
Colette Green is born. 
Aperture Science is involved in US Senate hearings regarding "missing astronauts". By now, Aperture Science has gone bankrupt.
Between 1969 and 1978
Gina Cross is born. She is said to be 31 in Decay, set in 200-.
Apollo spacecraft land on the Moon.
- Aperture Science re-opens Test Shaft 09 for testing. The lower sections appear to remain unused.
- Aperture constructs Pump Station Beta and begins Propulsion Gel testing.
Aperture Science constructs at least Chambers 01 and 02 of the Propulsion Gel Testing Facility.
Between 1973 and 1982
Gordon Freeman is born. He is said to be 27 in Half-Life, set in 200-.
- Aperture Science ceases producing only shower curtains.
- This date is also the earliest known use of a bulletin board system by Aperture Science.
Aperture Science constructs at least Chamber 05 of the Propulsion Gel Testing Facility.
- Aperture Science constructs the elevator out of the Propulsion Gel Testing Facility.
- Due to financial difficulties and possible legal problems arising from testing prominent citizens, Aperture Sciensce begins using homeless people as Test Subjects.
- The object of testing and experimentation at this time is Propulsion Gel.
- Complementing the Propulsion Gel testing, Aperture Science also begins experimenting with human deconstrucion, enhacement, and reconstruction procedures.
Between 1978 and 1987
Adrian Shephard is born. 
Cave Johnson receives the answer to a confidential letter titled "Human Enrichment & Testing Initiative, Resource Acquisitions", describing the four types of Test Subjects and their behavior.
- Aperture Science constructs the Conversion Gel Testing Facility's enrichment center, and now performs tests on its own employees. By now, Cave Johnson has spent $70 million on moon rocks to grind up and turn into Conversion Gel, and as a result of exposure has himself become gravely ill and addicted to pain medication.
- Aperture engineers complete the Heimlich Counter-Maneuver and Take-A-Wish Foundation initiatives. The company announces products related to the research in a televised ceremony. These products become immediately wildly unpopular. After a string of very public choking and despondent sick child disasters, senior company officials are summoned before a Senate investigative committee. During these proceedings, an engineer mentions that some progress has been made on Tier 3, the "man-sized ad hoc quantum tunnel through physical space with possible applications as a shower curtain." The committee is quickly permanently recessed, and Aperture is granted an open-ended contract to secretly continue research on the 'Portal' and Heimlich Counter-Maneuver projects.
September page of "The girls of Aperture Science" 1983 calendar, with a girl posing in bikini on an elevator or Unstationary Scaffold
platform, as seen in one of Ratman
For this year, a calendar named "The girls of Aperture Science" is issued by Aperture Science. It is unknown if it was issued each year.
From 1983 to 1985
Work progresses on the "Portal" project. Several high ranking Fatah personell choke to death on lamb chunks despite the intervention of their bodyguards.
The Aperture Image Format is created.
- The Conversion Gel Testing Facility is updated with an additional wall.
- Word reaches Aperture Science management that Black Mesa is working on a similar portal technology. In response to this news, Aperture Science begins developing GLaDOS, although the name was already in use in 1982.
This is the most recent date for the Aperture Image Format. At that time, it is maintained by Doug Rattmann.
While visiting the University of Innsbruck, Gordon Freeman observes a series of seminal teleportation experiments conducted by the Institute for Experimental Physics. Practical applications for teleportation become his obsession.
After a decade spent bringing the Disk Operating System parts of GLaDOS to a state of more or less basic functionality, work begins on the Genetic Lifeform component. During that time, the Aperture Science Red Phone plan is implemented in case GLaDOS appears to become sentient and godlike, requiring an employee to sit by a red phone on a desk in GLaDOS chamber's entrance hall.
At that time, GLaDOS's version is 3.11. This is also the latest known date of Aperture Science using a bulletin board system.
Aperture Science releases several testing elements, such as the Excursion Funnel, a tractor beam-like funnel made of liquid asbestos, the Thermal Discouragement Beam, a laser to be used with a Weighted Pivot Cube to destroy Sentry Guns and activate some buttons, the Aerial Faith Plate, a catapult plate flinging into the air Test Subjects or any other object upon contact, and the Pneumatic Diversity Vent, a variant of the Vital Apparatus Vent used for distributing objects to Test Chambers.
Gordon Freeman graduates from MIT with a Ph.D. in theoretical physics. Soon after, he starts working at Black Mesa.
Soon after Gordon Freeman's employment, he is instructed by Gina Cross' hologram counterpart for an HEV Suit Training Exercise in Sector A's Training Facility. This is Half-Life's Hazard Course.
Marc Laidlaw's brainstorm note from Raising the Bar
The December calendar (click on the image for more info).
This is the "year" during which the Black Mesa Incident occurs. Deliberately kept vague by the Half-Life team, it could be any date from 2000 to 2009.
Deduction points at "May 16, 200-" for the precise date of the incident. What follows are the different facts and clues leading to that choice:
- The year "200-", first appearing in the Half-Life instruction manual, is given in every official source from the Half-Life story arc era.
- Several entries from Adrian Shephard's diary are given in the Opposing Force instruction manual, written by Gearbox writers. March is used, corroborating the Raising the Bar date. Shephard says in his last diary entry, written on March 15, "We were told today to be ready in case it happens tomorrow.", suggesting that the incident occurs on March 16. It seems that the Gearbox writers replaced May by March: in the Half-Life instruction manual, Freeman is said to start working at Black Mesa on May 15 (later retconned to an unknown, earlier date), he is also said in the Half-Life PlayStation 2 instruction manual to attend the Hazard Course on May 16 at 7:30 (in a Hazard Course schedule with dates all set in May), and Barney is said to start his duty on May 16 at 9:00. Therefore May 16 appears to be the best day for the incident, and consequently March from Shephard's diary should be replaced by May, for consistency.
- A calendar with the "Blue Marble" photo is also seen in the Half-Life chapter Office Complex, in the Opposing Force chapter Welcome to Black Mesa, in the Blue Shift chapters Insecurity and Captive Freight and in the Decay chapter Domestic Violence, always using the same texture file showing the December page. While the table was not made with much precision, December 8 and 15 start on a Monday, suggesting the calendar is for the year 2003 or 2008.
- While "200-" could refer to any date from 2000 to 2009, a note by series' writer Marc Laidlaw seen in Raising the Bar features "March 31, 2003", and a time, "4:33 p.m.". Although it has not been confirmed by Valve, it is possible that the Half-Life events originally were to start on March 31, 2003.
- On March 24, 2010, an updated and expanded Aperture Science timeline originally given on ApertureScience.com in 2006 and submitted by Erik Wolpaw was published on Game Informer. Several dates were changed, and the last paragraph was expanded with facts suggesting that the Black Mesa Incident had occurred in 1998, the same date as that of Half-Life's release, instead of the original "200-". However Marc Laidlaw dismissed "1998" as the date for the Black Mesa Incident, as the date "200-" given when the first Half-Life was released is the only correct one. It is unknown why Erik Wolpaw made that mistake, and if it was intended or not. For convenience and consistency, that "1998" will always be replaced by "200-" on the wiki, even with the dates pertaining to Aperture Science.
Several days before May 16
The untested AI of GLaDOS is activated for the first time as one of the planned activities on Aperture's first annual bring-your-daughter-to-work day. Upon being activated, she almost instantly becomes self-aware, takes control of the Enrichment Center, locks everyone inside, and floods the Enrichment Center with a deadly neurotoxin, but is partially halted when she is quickly fitted with a Morality Core. She then begins a permanent cycle of testing, aimed at beating Black Mesa in the race to develop functioning portal technology.
From Shephard's diary entries (originally March; see above): "Another typically hellish day at base camp... I'll be glad when this is over and I can get assigned a mission. There has been this really weird civie spotted at the base. Rumor is he's from some government branch looking to recruit; others say he's with some secret research group. I would jump at the chance to join. It would be cool just for the change and the adventure."
Freeman's letter of acceptance to Black Mesa, as it appears in the instruction manual of the PlayStation 2 version of Half-Life
Gordon Freeman receives a letter from the Black Mesa Office of the Administrator's LM confirming he is hired.
From Shephard's diary entries (originally March; see above): "I finally saw the government guy today. I am not sure he is a g-man, but he was wearing a really uptight suit and carrying a briefcase. He looked more like a lawyer or insurance agent to me. I did notice him checking me out. Several times throughout the day I spotted him just watching me during training. I wonder what he's up to..."
- From Shephard's diary entries (originally March; see above): "For weeks our drills have been the same crap day after day. Today we assemble for the morning run and our drill instructor tells us we have one week to become experts at indoor strategic combat. We will be spending every day this week at the combat simulation facility. As far as I know this a specialized training not taught in boot camp. What I want to know is if this is to test our ability to adapt or if we are being readied for a specific mission? Time will tell..."
Colette Green receives a letter from the Black Mesa Office of the Administrator's LM saying that sample GG-3883 will replace sample EP-0021.
Before May 12
Barney Calhoun is performing a retinal scan and has his salary increased. His two-day Security Guard Training is scheduled.
From Shephard's diary entries (originally March; see above): "The rumors have been flying since our indoor combat training began. Most of my peers are convinced that we are being primed for a mission. No one can agree on what the mission is. I have heard the name Black Mesa Facility thrown around a lot, but I have no information about the place. The rumors are that some top-secret research is going on there. Doesn't sound too exciting to me..."
First day of Barney Calhoun's Security Guard Training under Miller's Holographic Instructor counterpart, in Sector A Training Facility. This is the Blue Shift Hazard Course.
Second day of Barney Calhoun's Security Guard Training.
Colette Green's letter about sample GG-3883 and Gina Cross' Hazard Course Training schedule.
Walter Bennet is being instructed by Gina Cross for an Anti-Mass Spectrometer Overload Simulation.
Colette Green was to be instructed by Isaac Kleiner for an Anomalous Materials Handling, but it was postponed to June.
- Barney Calhoun is assigned to a 09:00 - 22:00 Blue Shift assignment until August 15 and reports at Area 3 Medium Security Facilities at 09:00. Other unknown security guards are assigned to Red, Orange, Yellow, Green and Indigo Shifts in specific areas of Sector A, B, and C. For that timespan, the Violet Shift is on standby.
- From Shephard's diary entries (originally March; see above): "The rumor has been confirmed. We are being trained for a mission at the Black Mesa Facility. All I know is that the place is being used by scientists who are doing some kind of new research. I can't imagine what we would be needed for. We were told today to be ready in case it happens tomorrow. I don't know what "it" is, but the whole thing is a little strange. I kind of hope it doesn't happen; the mission doesn't seem to have much excitement potential. I'd rather hold out for something with more likelihood of combat."
- This day was originally Gordon Freeman's first day of work at Black Mesa, but it was retconned in Half-Life 2 and its episodes, where it is implied that Gordon was already working for some time at Black Mesa before the incident: Barney tells Gordon he owes him a beer and reminds him who he is when first meeting in the City 17 Trainstation, and Alyx tells in the City 17 Underground that Gordon and Barney would compete in air ducts to get into Kleiner's office whenever he got himself locked out, among others.
Gina Cross is being instructed by Richard Keller for a Mark V HEV Suit Prototype Testing.
Gordon Freeman is being instructed by Gina Cross' hologram counterpart for an HEV Suit Training in Sector A's Training Facility. This is Half-Life's Hazard Course.
Several system crashes occur around Black Mesa (the security guard in the Sector C lobby states he has had a system crash "about 20 minutes ago").
Barney Calhoun starts his tram ride from the Area 8 Topside Dormitories at Black Mesa, to start his second Blue Shift day at Area 3 Medium Security Facilities in Sector C. He arrives there some time before 9:00.
After his HEV Suit Training, Gordon Freeman starts his tram ride from Level 3 Dormitories at Black Mesa. He is 30 minutes late.
Remainder of the day
- Freeman, Calhoun, Green and Cross fight their way through the facility.
- Overnight, Freeman successfully launches the rocket.
As heard during the tram ride at the start of Half-Life, the Black Mesa Hazard Course Decathlon was to start in the Level 3 facility. This never happened due to the incident.
Otis Laurey was to be instructed by the Miller's holographic instructor counterpart for a Security Guard Training at 16:30, but he was apparently unable to attend and Cross suggests to Green to ask Barney to replace him. This never happened due to the incident.
- Early in the morning, Gina Cross and Colette Green are able to perform a resonance reversal. Their fate, along with Keller's, are unknown.
- Barney Calhoun successfully escapes Black Mesa with Rosenberg, Simmons and Walter Bennet.
- Adrian Shephard and his squad are attacked by Alien Crafts and their Osprey crashes. As Gordon Freeman fights his way across the surface towards the Lambda Complex, Shephard is left behind (this matches the message addressed to Cooper). Race X creatures appear sometime later.
- Black Mesa is destroyed by an atomic bomb. Shephard is also placed in stasis by the G-Man.
- As the Black Mesa facility is destroyed, GLaDOS's race against Black Mesa is stopped.
Colette Green was to conduct a Public Relations Tour. This never happened due to the incident.
Colette Green was to be instructed by Isaac Kleiner for an Anomalous Materials Handling on May 14, which was postponed to June. It never happened due to the incident.
Barney Calhoun's Blue Shift was to end on that day. It ended earlier due to the incident.
After May 200-
During this period of around 20 years Gordon Freeman is in stasis. It starts at the aftermath of the Black Mesa Incident in May 200- and ends at Gordon's arrival in City 17 in 202-.
- Portal Storms rage on Earth while Xen creatures continue to be teleported. The governments and United Nations provide the protection centers located in major cities worldwide.
- The Aperture Science Enrichment Center remains in lockdown, with employees still trapped inside. The number of Aperture Science employees also likely diminishes, until there are only a few of them left.
- The Combine launches an assault on Earth. Earth governments and the United Nations enter into war against them. The Seven Hour War occurs. Earth surrenders to the Combine after seven hours, and Wallace Breen, former Black Mesa Administrator, is appointed Earth Administrator.
- This is the period during which Portal is set. It occurrs a short amount of time after the Combine invasion of Earth.
- In the Aperture Science computer-aided Enrichment Center, Chell is awoken by GLaDOS who makes her perform seemingly routine tests. However Chell soon learns that the Aperture employees are long dead or escaped, and that GLaDOS is seemingly the only being left in the decaying facility. After much promise of cake at the test's conclusion, Chell is met with an incinerator, which she narrowly escapes, and works her way through the maintenance areas, despite GLaDOS's protests. Eventually, Chell finds GLaDOS's control room, and manages to escape death by neurotoxin by detaching the GLaDOS's Personality Cores, and partially destroying her as a result. Chell is forced to the surface by GLaDOS's explosion, only to be dragged away from freedom and back into the facility by the Party Escort Bot. Unknown to Chell however, GLaDOS is still alive.
- Doug Rattmann, being the one of the last Aperture employees alive, witnesses GLaDOS' destruction. After the Party Escort Bot drags Chell back into the facility, Rattmann feels guilty for Chell's situation and reenters the facility to help her.
- At an unknown time before Gordon Freeman's awakening, Isaac Kleiner and Eli Vance each build in their respective labs a teleport not needing a Xen relay with the aid of Alyx Vance and Judith Mossman, among others. When tested on a cat, it kills it. They then continue working on it until Freeman's arrival.
One year before 202-
This is the last time Alyx Vance drives Highway 17, as said by her in the radio transmission at Shorepoint Base.
The destroyed Citadel in the second Episode Two
- Around 20 years after the Black Mesa Incident, Gordon Freeman is awakened by the G-Man after a long period of stasis. He explores City 17, encounters the Resistance and some of his former Black Mesa colleagues. Soon after he joins their cause in the war against the Combine and triggers the uprising of City 17 and his surroundings, becoming the primary target to the Combine. After destroying the Citadel's dark fusion reactor and defeating Breen, Gordon is called into stasis by the G-Man a second time.
- The Resistance reverses the Combine Superportal, inflicting a consequent blow to the Combine plans, but unfortunately Resistance leader Eli Vance is killed by an Advisor at White Forest.
GLaDOS' partial destruction is followed by a period of inactivity within the Enrichment Center, during which time maintenance systems and Personality Cores maintain its functions. The facility remains in disarray, having become overgrown and dilapidated.  Pre-recorded 'Emergency Test Protocols' can oversee test chambers in times cataclysmic system failure, "able to sustain themselves on a minimum 1.1 Volts". Chell spends this time in stasis until the events of Portal 2. For at least some of her stasis, Chell is under supervision by a remaining Aperture employee, Doug Rattmann.
The span of time between Portal and Portal 2 is not entirely clear. During Portal 2's opening sequence, an automated 'Courtesy Call' implies that Test Subjects in stasis are revived every 50 days. However, when the player is next woken, an autonomous P.A. system reports that the time elapsed is "99999...99...". It is unknown what unit of time it refers to. Of course, it may be that the system has completely broken down and is no longer capable of accurately tracking time.
Chell facing GLaDOS in the ruins of the Enrichment Center.
After an unknown, but abnormally long, period in stasis, Chell is awoken by Wheatley, a personality core. Wheatley insists he can secure an escape route out of the Aperture Laboratories, which instead results in the inadvertent reactivation of GLaDOS. As the story progresses, Chell finds herself traversing old condemned Enrichment Spheres originating from earlier than June 15, 1961, at which time Aperture Laboratories was under the direction of Cave Johnson.