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Aerogel can be up to 99.98 percent empty space, yet a sheet of it will shield a flower from a blowtorch and a two-gram piece will hold up a two-and-a-half kilogram brick. This episode starts in 1931, when Samuel Stephens Kistler accepted a bet from his colleague Charles Learned: remove all the liquid from a jelly and replace it with gas without letting the solid structure shrink. Kistler won with supercritical drying, pushing the liquid past its critical point so that surface tension vanished and the fragile framework survived.

From there the episode explains why the material behaves so strangely. Rayleigh scattering gives silica aerogel its smoky blue tint, fractal chains of particles two to five nanometers wide spread loads like billions of tiny arches, and pores under 100 nanometers trap air so tightly that the Knudsen effect makes the solid a better insulator than the gas inside it. The same architecture can be built from carbon, metal oxides, seaweed, cellulose, and graphene, each with its own uses.

• Bare silica aerogel is so hygroscopic that handling it without gloves pulls water out of your skin and leaves dry, brittle patches.
• Carbon aerogels, developed in the late 1980s, are pitch black, conduct electricity, and are used in supercapacitors.
• NASA's Stardust mission used blocks of silica aerogel to stop hypervelocity comet dust intact, each grain resting at the end of a cone-shaped track.
• Chalcogels made from sulfur and selenium bind mercury, lead, and cadmium, filtering heavy metals out of contaminated water.
• An aerogel built from whey protein fibrils, a cheese industry byproduct, can pull gold ions out of dissolved electronic waste.

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On October 29th, 1969, a student programmer at UCLA tried to send the first message across a new network to the Stanford Research Institute, more than 300 miles away. He typed L, then O, and the system crashed before the G of login arrived. This episode traces the ARPANET from that stuttering start back to its real origins: the waste of circuit switching, the packet switching ideas of Paul Baran and Donald Davies, J.C.R. Licklider's memos on an intergalactic computer network, and Bob Taylor's annoyance at needing three separate terminals in his Pentagon office.

The story then moves to the hardware and the people. Universities refused to spend mainframe cycles on networking, so Wesley Clark proposed refrigerator-sized Interface Message Processors, built by Bolt, Beranek and Newman after AT&T dismissed the whole idea. Email soon swallowed the traffic, rule breaking followed, and Bob Kahn and Vint Cerf wrote TCP/IP to join separate networks together. The episode also settles the nuclear survival debate and follows the network to its formal shutdown in 1990.

• The first four nodes went live in late 1969 at UCLA, the Stanford Research Institute, UC Santa Barbara, and the University of Utah.
• Ray Tomlinson invented network email in 1971, and within a year it made up three quarters of all ARPANET traffic.
• In 1978 Gary Thuerk of Digital Equipment Corporation pitched computers to about 400 users at once, the first spam, and claimed $13 million in sales.
• On Flag Day at the start of 1983, the entire network switched from NCP to TCP/IP, turning it into the backbone of a network of networks.
• ARPA director Charles Herzfeld denied the nuclear origin story, yet Baran's packet switching research was explicitly designed to survive a nuclear war.

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AOL Instant Messenger, released in 1997, was never designed as a consumer hit. It grew out of an internal messaging feature written in the PL/1 language and running on a fault-tolerant Stratus mainframe, built only to move text reliably. Teenagers and college students took it over. By 2006 AIM held 52 percent of the North American instant messaging market, and its away message had turned the family computer into a broadcast tower for song lyrics, inside jokes, and party plans.

This episode covers the rise, the fights, and the fall. Starting around 1999, Microsoft reverse engineered AOL's closed OSCAR protocol so MSN Messenger users could reach AIM users, and the two companies traded overnight lockouts and patches. AOL then piled on features: chatbots like SmarterChild, AIM Pages, internet phone calls. The software grew bloated, its privacy design let strangers watch users unseen, and text messaging and smartphones finished the job.

• Anyone could add a screen name to a buddy list without approval, then see when that person was online and read their away messages without their knowledge.
• Links beginning with the aim prefix could open a chat window or change an away message straight from a web page, a deep hook that hackers later exploited.
• The Electronic Frontier Foundation's 2014 secure messaging scorecard gave AIM one point out of seven, for encrypting data in transit.
• By June 2011 AIM's share of installed apps had fallen to 0.73 percent. AOL laid off most of the development staff in March 2012.
• The servers were shut down on December 15th, 2017. Fans have since revived the service on a nonprofit server called AIM Phoenix.

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In a study spanning 2025 and 2026, judges chatting through a text window identified an AI model as human 73 percent of the time, a higher rate than the real people in the same experiment achieved. This episode asks how that happened by going back to 1950, when Alan Turing, working at the University of Manchester, published Computing Machinery and Intelligence. He thought the question of whether machines can think was too vague to answer, so he replaced it with a parlor game.

In the original imitation game, a man tries to convince a judge by typewritten notes that he is a woman. Turing swapped the man for a computer. The episode connects that premise to Turing's own life as a gay man forced to pass in mid-century Britain, then follows the test through ELIZA, PARRY, John Searle's Chinese room, and the Loebner Prize, where programs won by faking typos. It ends with researchers who now see the test as a trap that rewards replacing people.

• Joseph Weizenbaum's 1966 program ELIZA imitated a psychotherapist by turning keywords into questions, and he was disturbed by how readily people confided in it.
• Kenneth Colby's 1972 program PARRY played a paranoid schizophrenic. Psychiatrists shown transcripts could tell it from real patients only about 52 percent of the time.
• Searle's 1980 Chinese room argues that following rules to shuffle symbols is not understanding. The systems reply says the room as a whole does understand.
• Eugene Goostman, a 2001 chatbot posing as a 13-year-old boy from Odessa, Ukraine, fooled a third of the judges in a major competition.
• CAPTCHA stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart: a reverse test in which the machine interrogates the person.

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In Tunisia before the 2011 revolution, people saw the page not found screen on so many dissident websites that they gave it a name: Ammar 404, the invisible censor. That story frames this episode on the HTTP 404 status code, a three-digit reply built for machines. The first digit, 4, means the client asked for something the server cannot find. The system was borrowed from older protocols such as FTP, and better codes exist, like 301 for moved permanently and 410 for gone, but few webmasters bother to use them.

From there the episode moves through the odd afterlife of an error message. Servers lie with soft 404s that report success, a problem formalized in a 2004 paper by Ziv Bar-Yossef. Internet Explorer once replaced small error pages with its own, which pushed developers to fake their status codes. Governments and internet providers learned to disguise blocking as a missing page. Designers, political parties, and charities for missing children have all claimed the empty space for their own purposes.

• A DNS error means the house is not there at all. A 404 means the house is there and the door was answered, but the person you wanted is not home.
• In 2004 the British provider BT Group launched Cleanfeed, which returned a 404 for blocked pages instead of the 403 forbidden code.
• Internet Explorer and Chrome would swap in their own error page if a site's custom 404 was smaller than 512 bytes.
• During the 2015 UK general election, parties turned their 404 pages into attack ads, while the NotFound project lets any site show a missing child poster on its error page.
• Standard link crawlers miss roughly 83 percent of real 404 errors because most broken links come from outside a site. Server log analysis catches them.

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In 1965 the trade magazine Electronics asked Gordon Moore, then director of research and development at Fairchild Semiconductor, to predict the next ten years of semiconductor components. Working from a handful of data points, the chemist noticed that the number of components on a chip at the lowest cost per component was doubling every year. He extended the line and estimated that by 1975 engineers would fit 65,000 components on a single piece of silicon.

This episode explains why that guess held, how it was revised, and how it turned into a schedule the whole industry felt obliged to meet. In 1975 Moore slowed the pace to a doubling every two years, and Caltech professor Carver Mead gave the idea its name. The story then turns to the costs: fabrication plants priced at upwards of $20 billion, the end of Dennard scaling around 2005, electrons tunneling through barriers a few nanometers thick, and the search for what comes after silicon.

• The 1982 Osborne Executive opens the episode. A smartphone from 2007 weighed about 100 times less, cost about a tenth as much after inflation, and ran roughly 100 times faster.
• The popular 18-month figure came from Intel executive David House, who combined Moore's two-year doubling with Robert Dennard's finding that smaller transistors run faster.
• Rock's law, named for venture capitalist Arthur Rock, holds that the cost of a chip fabrication plant rises exponentially over time.
• Eroom's law, Moore spelled backward, describes drug development, where the cost of a new medicine roughly doubles every nine years.
• In 2022 Nvidia chief executive Jensen Huang declared Moore's law dead, while chipmakers turned to multi-core processors, 3D stacking, and FinFET transistors.

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Steve Jobs does not fit the usual picture of a tech chief executive. Put up for a closed adoption in 1955 and raised by a machinist who gave him a corner of the garage workbench, he grew up in Cupertino, dropped out of Reed College after one semester, and stayed on campus anyway, sleeping on floors, eating free meals at a Hare Krishna temple, and auditing a calligraphy class. He traveled to India, studied Zen, and considered becoming a monk.

This episode follows the tension between that seeker and the man who wanted control over everything he touched. It covers the Atari bonus he hid from his engineer friend, the illegal blue box that taught him two kids could outwit a giant phone network, and the company he co-founded in 1976. Then come the ouster of 1985, the exile years at NeXT and Pixar, and the 1997 return, when he cut a failing product line down to four machines and went on to remake the music player and the phone.

• The calligraphy class he audited after dropping out is why he later insisted that computer fonts be beautiful and proportionally spaced.
• At Atari he was promised a bonus for reducing the chips in the game Breakout. His friend did the engineering, and he lied about the size of the payout.
• The blue box produced a 2600 hertz tone that tricked the telephone network into handing over its trunk lines, allowing free long distance calls.
• He recruited a Pepsi executive by asking whether he wanted to sell sweetened water for the rest of his life or change the world. By 1985 the board had sided with that executive and pushed the founder out.
• NeXT never sold in volume, but its modular software became the foundation of his old company's products after it bought the startup and brought him back.

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The View-Master is remembered as a red plastic toy, but its history runs through a Portland drugstore, a player piano workshop, and the War Department. Edwin Eugene Mayer, a pharmacist, bought into a photo finishing business called Sawyer's in 1919 and built it into the nation's largest producer of scenic postcards. In 1938 he met William Gruber, a piano mechanic and photography obsessive who had mounted 16 millimeter Kodachrome film in the sturdy paper stock he knew from piano rolls.

This episode traces what the two built after their viewer debuted at the 1939 New York World's Fair. Between 1942 and 1945 the US military bought 100,000 viewers and nearly six million reels to teach range estimation and aircraft identification. After the war Sawyer's bought rival Tru-Vue for its Disney license and moved into children's entertainment. Later chapters cover GAF, Tyco, and Mattel, a contaminated factory well, and a failed virtual reality revival with Google.

• Each reel holds 14 images in seven pairs, shot with lenses about two and a half inches apart to match the spacing of human eyes.
• Gruber disliked the name View-Master because he thought it sounded like a kitchen appliance, in the vein of Toastmaster or Mixmaster.
• Every reel ever made works in every viewer ever built, so a 1939 Grand Canyon reel fits a red plastic model from the 1990s.
• The EPA found the solvent trichloroethylene in groundwater at the old Oregon factory, and the plant closed for good in 2001.
• Anatomist David L. Bassett worked with Gruber on a 25-volume stereoscopic atlas of human anatomy, and over 1.5 billion reels have been produced in all.

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On June 1st, 1990, KIIS-FM in Los Angeles promised a Porsche 944 S2 to its 102nd caller. Kevin Poulsen, known online as Dark Dante, did not dial fast. He took over Pacific Bell's central office switches, seized the station's 25 phone lines, blocked every other caller in the city, and counted his way to number 102. He had been at this since his teens in Pasadena, when he broke into the ARPANET at 17 using a TRS-80.

This episode follows Poulsen from fugitive to reporter. The FBI found his trail after he failed to pay rent on a storage shed full of equipment, and when Unsolved Mysteries profiled him, its tip lines went dead. Arrested in April 1991, he was sentenced to 51 months and then barred from computers for three years. He came back as a journalist at SecurityFocus and Wired, broke the Chelsea Manning chat logs story, and helped design SecureDrop, the tool newsrooms use to protect whistleblowers.

• Poulsen never attacked the radio station itself. He controlled the telephone company's switches and dropped every incoming call but his own.
• He was the first American released from prison under a court order banning him from computers and the internet, a ban the episode compares to confiscating a burglar's lockpicks.
• In October 2006 he wrote a script that cross-referenced MySpace profiles with sex offender registries, finding 744 matches and leading to the arrest of Andrew Lubrano.
• SecureDrop, first called DeadDrop, was designed with James Dolan and Aaron Swartz. It routes submissions through Tor and has journalists read them on air-gapped machines.
• The first official SecureDrop instance launched at The New Yorker in May 2013, and the project later passed to the Freedom of the Press Foundation.

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In June 2003, more than 130 people gathered around one expensive rug on the ninth floor of Macy's in Manhattan. Each told the confused salesperson the same story: they lived together in a warehouse on the outskirts of New York and were shopping for a love rug. Then they left. It was the first successful flash mob, and its architect was Bill Wasik, a senior editor at Harper's Magazine who wanted to see whether downtown trend chasers would show up for something meaningless if it felt exclusive.

This episode follows the idea from that cynical experiment to its darker afterlife. Wasik's first attempt failed when the target store was tipped off, so he staged participants in four Manhattan bars and handed out the real location on slips of paper. The craze spread worldwide, drew pushback from police and city officials, and by around 2011 had mutated into flash robs, with groups of teenagers overwhelming stores. A 1973 Larry Niven story had predicted nearly all of it.

• Sociologists separate a flash mob, which is deliberately pointless, from a smart mob, a term Howard Rheingold coined in 2002 for gatherings with a political or practical goal.
• Other early Wasik events included 200 people applauding for exactly 15 seconds in a Hyatt Hotel lobby and a crowd posing as lost bus tourists in a SoHo shoe boutique.
• Larry Niven's story Flash Crowd imagined cheap teleportation letting thousands of people appear at a minor incident and turn it into a riot.
• The phrase flash mob was also used in 19th century Tasmania for a subculture of female prisoners, a coincidence with no link to Wasik.
• Duke psychologist Mark Leary ties flash robs to deindividuation, the anonymity of a crowd that lets people do what they would never do alone.