Daily Five civilization and thought experiment questionsanswers

Real basis

• When did the earliest human writing appear? Answer: about 5,200 years ago. Cuneiform in Mesopotamia, first used for bookkeeping.

• What was the oracle bone script mainly carved on? Answer: turtle shells and animal bones. They are divination records from the Shang dynasty. They were only recognized around 1899, and were first sold as the traditional medicine “dragon bones”.

• Where was “zero” first used systematically as a real number? Answer: ancient India. In the 7th century Brahmagupta wrote down the rules for calculating with zero. The Maya also invented zero independently.

• How much did ENIAC, the first general-purpose electronic computer, weigh? Answer: about 27 tonnes. It used about 18,000 vacuum tubes and filled a large room. A phone today has hundreds of millions of times its computing power.

• In what year did humans first land on the Moon? Answer: 1969. Apollo 11, on July 20, 1969. In 1961 Gagarin became the first person in space.

• Who was the first person in space? Answer: Yuri Gagarin. On April 12, 1961, Gagarin orbited the Earth once aboard Vostok 1, in about 108 minutes.

• On the Kardashev scale, roughly what level is human civilization at today? Answer: about 0.73. By Sagan's formula K = (lg P − 6) / 10, humanity's total power is about 2×10¹³ watts, which gives about 0.73.

• How was penicillin discovered? Answer: mold accidentally grew on a petri dish. In 1928 Fleming came back from vacation and found a dish contaminated by mold, with the bacteria around the mold dead.

• Who invented the World Wide Web? Answer: Tim Berners-Lee. He proposed the idea in 1989 at CERN, and did not patent it.

• Where did agriculture first appear? Answer: independently in several regions. The Fertile Crescent, China, Mesoamerica, the Andes, New Guinea and other places each domesticated crops on their own.

• Why is the Rosetta Stone so important? Answer: it wrote the same text in three scripts, which helped people read Egyptian hieroglyphs. The scripts are hieroglyphic, Demotic and ancient Greek. In 1822 Champollion used it to decipher the hieroglyphs.

• Where was the 1974 Arecibo message sent? Answer: the globular cluster M13. M13 is about 25,000 light-years away, so even if someone replied, the answer would take at least about 50,000 years to arrive.

• Where did the 1977 “Wow!” signal come from? Answer: a strong signal recorded by a radio telescope. Ohio State University's Big Ear telescope recorded a narrowband signal lasting about 72 seconds. An astronomer circled it on the printout and wrote “Wow!”. It has never appeared again.

• How far have human radio signals spread from Earth? Answer: about 100 light-years. High-power broadcasting began about a hundred years ago. But most signals are weak, and are drowned in noise not far beyond the solar system.

• Who invented movable-type printing? Answer: Bi Sheng. In the Northern Song dynasty, Bi Sheng made movable type from clay, about 400 years before Gutenberg's metal type. Cai Lun improved papermaking, not printing.

• The Ship of Theseus: the planks of a ship are replaced one by one. When all of them are replaced, is it still the original ship? What if the old planks are put together into another ship? This question has been argued since ancient Greece, and it is no longer only philosophy: if the neurons in your brain were replaced one by one with chips, would you still be you?

• The Chinese Room: a person who knows no Chinese sits in a room, processing Chinese notes by following a rule book, and the people outside think someone inside understands Chinese. Does the room “understand” Chinese? Searle proposed it in 1980, to challenge the idea that “being able to compute is the same as being able to think”. Today's large language models have made the question concrete again.

• The trolley problem: a runaway trolley is heading for five people, and you can pull a lever to divert it onto another track with only one person. Would you pull it? The philosopher Philippa Foot proposed it in 1967. Most people would pull the lever; but if you had to push a person off a bridge with your own hands to stop the trolley, most people would refuse. The outcome is the same, but it feels different.

• The Fermi paradox: the universe is so big and so old, so why have we not seen any alien civilization? What do you think is the most likely reason? Each answer corresponds to a kind of future: if the “Great Filter” is behind us, we are lucky; if it is ahead of us, we need to be careful.

• Brain in a vat: if your brain floated in nutrient fluid and all your senses were simulated by a computer, could you tell? Putnam proposed this version in 1981. It is a modern form of Descartes' “demon” argument, and a forerunner of the simulation argument.

• Mary's room: a scientist who grew up in a black-and-white room knows all the physics there is to know about color. When she steps out of the room and sees red for the first time, does she learn something new? Frank Jackson proposed it in 1982, to discuss whether subjective experience can be fully described by physical knowledge. He later changed his own view.

• The teleporter: a machine scans you, builds an exact copy of you on Mars, and destroys the original. Would you use it? The philosopher Derek Parfit argued that what really matters is not whether it is the same person, but the continuity of memory and character.

• If you could send a message to yourself from before the universe began, what would you write? By physicist David Deutsch's self-consistency condition, what you write can only be a message that was already received long ago. Perhaps you have already read it.

• The Dark Forest: if you discovered an alien civilization that had not yet discovered you, would you greet them first? Since the 1974 Arecibo message was sent, some scientists have opposed deliberately sending signals, and Hawking was cautious too.

• Laplace's demon: if a being knew the position and velocity of every particle in the universe right now, could it calculate the whole future? Laplace imagined this in 1814. Quantum randomness and the extreme sensitivity of chaotic systems to initial conditions lead most physicists to think it could not.

• Suppose your civilization could choose: stay around its home star forever, or send half its people off to the stars and lose contact with those who stay behind. Which would you choose? The speed of light means interstellar colonies are bound to drift away from the home world. The real history of human migration also shows that isolated groups diverge in language and genes.

• If a monkey hit a typewriter at random for an infinite amount of time, could it type out a complete Dream of the Red Chamber? Answer: almost surely yes. Mathematically the probability is 1, but the time required is far longer than the age of the universe. This is the same point made by Cloud of Poems and The Library of Babel: the value of information lies not in its existence, but in its being found.

• If there had never been any observer in the universe, would it still “exist”? Physicists disagree widely on this. Wheeler proposed the “participatory universe”: observers take part, in some way, in bringing the universe into being.

• The sorites paradox: one grain of sand is not a heap, and adding one more grain still does not make a heap… at which grain does it become a heap? It is a chain paradox from ancient Greece. The “species” in biology has the same trouble: evolution is continuous, and the boundaries between species are drawn by people.

• If your memories were copied in full into another body, and both people said they were you, who would be right? This is the core question of Permutation City. For mind uploading, it is already more than a thought experiment.

Related research

These studies relate to this topic but are not direct proof of this page.

• The origin of rice: Comparing over a thousand rice genomes showed that cultivated rice originated from wild rice in the Pearl River basin of China.

  Source: Huang et al., Nature 2012, "A map of rice genome variation reveals the origin of cultivated rice"

• Farmers and languages: The expansion of farming populations carried their languages to new places and shaped today's distribution of language families.

  Source: Diamond & Bellwood, Science 2003, "Farmers and their languages: the first expansions"

• Radiocarbon dating: Libby invented a way to measure the age of ancient objects with carbon-14, giving archaeology a “clock.” Nobel Prize 1960.

  Source: Arnold & Libby, Science 1949, "Age determinations by radiocarbon content: checks with samples of known age"

• Electromagnetic field theory: Maxwell unified electricity and magnetism and calculated that the speed of electromagnetic waves equals the speed of light: light is an electromagnetic wave.

  Source: Maxwell, Philosophical Transactions of the Royal Society 1865, "A dynamical theory of the electromagnetic field"

• Special relativity: Time and space are not absolute. A junior clerk at a patent office published four physics-changing papers in a single year.

  Source: Einstein, Annalen der Physik 1905, "Zur Elektrodynamik bewegter Körper"

• Penicillin: Mold that grew by accident in a petri dish killed the bacteria around it, and the antibiotic age began.

  Source: Fleming, British Journal of Experimental Pathology 1929, "On the antibacterial action of cultures of a penicillium"

• Computability: Turing imagined an abstract machine that defined what “computation” is, laying the theoretical basis of modern computers.

  Source: Turing, Proceedings of the London Mathematical Society 1936, "On computable numbers, with an application to the Entscheidungsproblem"

• Information theory: Shannon turned “information” into a measurable quantity, and the bit was born.

  Source: Shannon, Bell System Technical Journal 1948, "A mathematical theory of communication"

• The transistor: One piece of semiconductor can amplify a signal. It replaced vacuum tubes and shrank computers from room-sized to pocket-sized.

  Source: Bardeen & Brattain, Physical Review 1948, "The transistor, a semi-conductor triode"

• The World Wide Web: An internal proposal, which the boss annotated “vague but exciting.” It later became the World Wide Web.

  Source: Berners-Lee, CERN 1989, "Information management: A proposal"

• Searching for interstellar signals: Two physicists suggested listening for alien signals with radio telescopes near hydrogen's 21 cm frequency, launching SETI.

  Source: Cocconi & Morrison, Nature 1959, "Searching for interstellar communications"

• Dyson sphere: A sufficiently advanced civilization might wrap its star, and we could find it through anomalous infrared radiation.

  Source: Dyson, Science 1960, "Search for artificial stellar sources of infrared radiation"

• Scale of civilizations: Sorts civilizations into three types by the energy they can use: planetary, stellar and galactic.

  Source: Kardashev, Soviet Astronomy 1964, "Transmission of information by extraterrestrial civilizations"

• Black holes evaporate: Quantum effects make black holes radiate energy slowly. Black holes are not eternal and will eventually evaporate.

  Source: Hawking, Nature 1974, "Black hole explosions?"

• Warp drive: General relativity allows a “warp bubble” that compresses space ahead and stretches it behind, but it needs negative energy that may not exist in reality.

  Source: Alcubierre, Classical and Quantum Gravity 1994, "The warp drive: hyper-fast travel within general relativity"

• Light sails to the stars: Pushing ultralight light sails with a ground-based laser array could accelerate probes to one fifth the speed of light.

  Source: Lubin, Journal of the British Interplanetary Society 2016, "A roadmap to interstellar flight"

• Where are they?: If alien civilizations were common, they should already fill the galaxy. From this Hart argued that we may be the first.

  Source: Hart, Quarterly Journal of the Royal Astronomical Society 1975, "An explanation for the absence of extraterrestrials on Earth"

• The last chapter of the universe: Worked out the fate of the universe over trillions of years and beyond: stars go out, protons perhaps decay, and black holes finally evaporate.

  Source: Adams & Laughlin, Reviews of Modern Physics 1997, "A dying universe: the long-term fate and evolution of astrophysical objects"

• Leaving the heliosphere: Particle changes measured by Voyager 1 show it has left the realm of the solar wind and entered interstellar space.

  Source: Stone et al., Science 2013, "Voyager 1 observes low-energy galactic cosmic rays in a region depleted of heliospheric ions"

• Seven tons of liquid xenon: About 1.5 km underground, 7 tonnes of liquid xenon waited for dark matter particles and saw no signal, setting the strictest limits so far. What dark matter is remains unknown.

  Source: LZ Collaboration, Physical Review Letters 2025, "Dark matter search results from 4.2 tonne-years of exposure of the LUX-ZEPLIN (LZ) experiment"