This living hypertext is a systematic summary of the knowledge attained by human civilization. For each subdivision of human knowledge, the text identifies its fundamental concepts, principles, mysteries, and misunderstandings.
These are some of the questions that this text is intended to address. Many of these questions are included because of their importance, while others serve more as invitations to their respective areas of knowledge.
+ Why is there something rather than nothing?
+ What exists beyond the human senses?
+ What exists after human death?
+ Is the future already decided?
+ What is being?
+ What is time?
+ Does God exist?
+ Which religion is correct?
+ Is the Bible true?
+ What is faith?
+ Which paranormal phenomena are real?
+ Might the world be an illusion or dream?
+ What can we know with absolute certainty?
+ What is truth?
+ What is meaning?
+ What is consciousness?
+ What would super-intelligence be like?
+ What are the limits of intelligence?
+ Could a machine think?
+ What is intelligence?
+ What is knowledge?
+ Does free will exist?
+ Does science involve faith?
+ Can science be getting any closer to truth if it is constantly correcting itself?
+ What is the meaning of life?
+ What do our choices matter if the future is already decided or if all possible worlds exist?
+ What is right and wrong?
+ What is wisdom? What is happiness?
+ Why do evil and misfortune exist? Is the world good or evil? Are humans good or evil?
+ Is blissful illusion better than reality?
+ Can there be an objective rational basis for values?
+ What would an omnipotent omniscience value?
+ What are rights? What entities should have what rights?
+ What is a person? Should any entity have more rights than a person?
+ What should be the rights of children and fetuses? animals and plants? machines?
+ Should private property be allowed?
+ Should private ownership of resources or ideas be allowed?
+ What is justice? liberty? equality? aggression? virtue?
+ What should be the duties and powers of the state?
+ What political system best protects rights and promotes prosperity?
+ What is love? How does one find and recognize it? What if one cannot?
+ How important is it to be liked? How can one be likable? What if one is not liked?
+ How should one face misfortune, fear, and danger?
+ How should one treat one's parents, siblings, spouse, or children?
+ How should one address one's creative and material needs? How should one treat the indigent?
+ How should one handle sex, drugs, and gambling?
+ What is beauty? What is humor?
+ Is beauty subjective or objective?
+ Could non-human intellects have different aesthetic faculties or preferences?
+ Why does mathematics describe the universe so well?
+ Is "this sentence is false" true or false?
+ What can be proved?
+ What are the limits of logic?
+ If one sand grain is not a heap and adding one grain cannot make a not-heap into a heap, how can any number of grains be a heap?
o Set Theory
+ What is infinity + infinity? ¥ - ¥? ¥ ´ ¥? ¥ ¸ ¥?
+ What are the unprovable axioms from which mathematics derives?
+ What is 0/0? What is 0-1? What is 00?
+ What is the difference between rational and irrational numbers?
+ What is the difference between real and imaginary numbers?
+ Riemann Hypothesis: are prime numbers really distributed according to the solutions of Riemann's zeta function?
+ What are the unprovable axioms of Euclidean geometry?
+ Why is a manhole cover round?
+ How many turns does it take for a circle to roll around the circumference of an identical circle?
+ What is the densest way to stack spheres?
+ Poincare Conjecture: is a 4-sphere simply connected (like a 3-sphere) or not (like a doughnut)?
+ Is 1 equal to 0.99999...?
+ How can a runner reach the finish if beforehand she must get halfway, and before that she must get halfway to halfway, ad infinitum?
+ Which is more likely, heads-heads-heads or heads-heads-tails?
+ How can you get a fair (50-50) odds from an unfair (e.g. 60-40) coin?
+ If Monty Hall reveals as empty one of the two prize boxes you didn't pick, should you switch your pick to the other unopened box?
+ How few colors can color the countries of any map?
o Applied Mathematics
+ How is information defined and measured?
+ What is the most basic computing device that is equivalent to any other?
+ What is the fastest possible way to sort a collection?
+ Can a polynomial-time solution for NP-complete problems be found, or proved not to exist?
+ How accurate are opinion polls?
+ What is a standard deviation?
* Natural Science
+ Why does science work so well?
+ What is the origin of the universe?
+ What is the mechanism of the universe?
+ What is the fate of the universe?
+ What is the origin of life?
+ What is the mechanism of life?
+ What is the fate of life?
+ What is the origin of mind?
+ What is the mechanism of mind?
+ What is the fate of mind?
# What is the difference between force, momentum, energy, and power?
# What is the difference between mass and weight?
# What is the difference between speed, velocity, and acceleration?
# Do the conservation of linear and angular momentum entail each other?
# Why don't humans notice the earth spinning?
# Why is a moving bicycle easier to balance?
# How is the sound barrier different from the light barrier?
# Why is there no sound in space?
# Why does helium raise the pitch of the human voice?
# What is the Doppler Effect?
# Why are solids, liquids, and gases different?
# How long can a straw be and still work?
# What is friction?
# How does a siphon work?
# Why do helium and hot-air balloons rise?
# Why are bubbles round?
# What is the difference between heat and temperature?
# Why is there a lowest possible temperature but no highest possible temperature?
# What is entropy?
# If not for the Uncertainty Principle, could Maxwell's Demon violate energy conservation?
# Why does liquid evaporate?
# Why does liquid condense on cold things?
# Why does a tile floor feel colder than a carpet at the same temperature?
# What is light? What is color?
# What makes primary colors primary?
# Why are glass and air transparent?
# Why do mirrors reflect?
# Why do mirrors reflect left-right but not up-down?
# Why is the sky blue? Why are sunsets red? Why is blood red? Why are clouds white? Why are plants green?
# What causes rainbows?
# What causes mirages?
# How does depth perception work?
# What is electricity?
# What is magnetism?
# How are electricity and magnetism related?
# What stops one solid object from going through another?
# Why does a magnet attract metal but not wood?
# Why do parts of magnets repel each other?
# Why don't birds on power lines get electrocuted?
# What is Relativity?
# What is space-time?
# What causes gravity?
# How fast does gravitational influence propagate?
# What if the speed of light were infinite?
# What if the speed of light were not constant for all observers?
# What is meant by E=mc2? How is it derived from the postulates of special relativity?
# If a car approached light speed, what would happen to its headlight beams?
# Can anything go faster than light?
# Does light have mass or exert pressure?
# Is time travel possible?
# What are black holes? What are wormholes?
# How do charged black holes interact if photons cannot escape them?
# Why is the vacuum energy density so close to zero and so far from theoretical expectations?
# What is the cosmological constant?
# Why are there 3 dimensions of space and 1 of time?
+ Quantum Theory
# What is a quantum?
# What is the Uncertainty Principle?
# How can a particle behave like a wave?
# What is the smallest particle? What are virtual particles?
# What is antimatter? Why is antimatter so rare?
# What is radioactivity?
# What is the difference between fission and fusion?
# What is the lifetime of the proton?
# Do conservation of linear and angular momentum entail each other? What are conservation of parity and pseudovectors?
# What is gauge symmetry?
# Is there really supersymmetry between fermions and bosons?
# Can quark non-confinement and massless strong particles be excluded purely from the Yang-Mills equations of QCD?
# What property or charge does the weak force act on? Does the weak force attract, repel, or what?
# Is M theory true?
# What if radiation were not quantized? What if Planck's constant were a different value? What if there were no quantum indeterminacy?
# If there were no quantum indeterminacy, couldn't an arbitrarily small space contain an arbitrary amount of information?
# How did the universe begin?
# What happened before the beginning of the universe?
# How will the universe end?
# Does the universe have an edge?
# How big is the universe?
# Where is the center of the universe?
# What is the universe expanding into?
# How old is the universe?
# How do scientists know how old the universe is?
# Why does the universe's expansion appear to be accelerating?
# How did galaxies and galaxy clusters emerge from the early smooth universe?
# What is the universe made of?
# What is the global topology of the universe?
+ What is the fate of the Earth?
+ How many stars are there? How many visible stars are there?
+ How do scientists know how far away stars are?
+ Why causes spiral galaxies to have arms?
+ Why do stars twinkle?
+ Why do stars appear to the eye to have diameter?
+ What powers the Sun?
+ How cold would it get, and how soon, if the Sun turned off?
+ Why is the night sky dark?
+ Is the dark side of the moon dark?
+ Why does Earth always see the same face of the moon?
+ Why do the planets go the same direction around the Sun?
+ What is fire?
+ Makes a substance reflective, transparent, or opaquely colored?
+ What is acid?
+ Why does metal rust?
+ What causes the seasons?
+ Why does a compass point north?
+ What causes earthquakes?
+ What is lightning?
+ What causes wind?
+ Why is the earth's interior hot?
+ What is the difference between true north and magnetic north?
+ What are the Northern Lights?
+ What causes rain?
+ What causes waves and tides?
+ Why are no two snowflakes alike?
+ Why is air thinner at higher altitudes?
+ Why does air temperature change with altitude?
+ What is life?
+ How did life arise?
+ How can the complexity of living things be explained?
+ Is there life and intelligence beyond earth?
+ How improbable was the genesis of life on an earth?
+ How improbable was the evolution of intelligence on earth?
+ How improbable was the evolution of humans on earth?
+ What is DNA?
+ What is evolution?
+ What is a virus? Are viruses alive?
+ How does amino acid sequence determine protein structure?
+ What makes a seed alive or not?
+ Why does food last longer in a refrigerator or freezer?
+ Why don't dry foods spoil?
+ How do drugs work?
+ Why is oxygen poisonous to many kinds of organisms?
+ Why do animals get old and die?
+ Why do animals yawn or sleep?
+ How did sex evolve?
+ How did flight evolve?
+ Why are insects attracted to lights?
+ How do insects walk on water or ceilings?
+ How does memory work?
# Are humans good or evil?
# How did language evolve?
# Is humanity still evolving?
# Are humans naturally meat eaters?
# Why are humans relatively hairless?
# Why are there more right-handers than left-handers?
# Why do males have nipples?
# Are facial expressions innate or learned?
# Why are men more promiscuous than women?
# Why do humans make and enjoy music and humor?
# Why do human babies cry so much?
+ How does a computer work?
+ How fast and small can computers get?
+ How does a plane fly?
+ How does a satellite stay up in the sky?
+ How does a battery work?
+ How does a refrigerator work?
+ How does a microwave oven work?
+ How does a radio work?
+ How does an antenna work?
+ How does a TV work?
+ How does a light bulb work?
+ How does a camera work?
+ Why does an air conditioner need to be in a window?
+ What are plastic and steel made of?
+ How are diamonds cut?
+ Why do spaceships have to speed up to get to a higher (slower) orbit?
+ What is the difference between a twin and a clone?
+ How are new drugs invented and tested?
+ How does one calculate the net present value of a project or investment?
o Industrial Technology
+ What is the future of telecommunications?
+ What is the future of energy production?
+ What is the future of transportation?
+ What is the future of education?
* Social Science
+ What is wealth? How is wealth created?
+ What is money? What causes inflation? What determines prices?
+ How can productivity, utility, value, and quality be measured?
+ What determines wages and standard of living?
+ What causes recessions and depressions?
+ What determines interest rates?
+ Why are free markets more efficient than controlled economies?
+ What is the social utility of speculation?
+ What are the limitations of free markets?
+ What is a natural monopoly?
+ What is the difference between debt and deficit?
+ Are the rich getting richer and the poor poorer?
+ Does labor-saving technology increase unemployment?
+ Do imports take away domestic jobs?
o Political Science
+ Why are there corporations?
+ What is discrimination?
+ How unjust is current wealth distribution?
+ Why are criminals freed on technicalities?
+ What is the difference between a liberal and a conservative?
+ What is the difference between a leftist and a rightist?
+ What is the difference between a libertarian and an anarchist?
+ What is the difference between a socialist and a fascist?
+ Is human population too high?
+ Are human societies naturally warlike?
+ Why do humans love and hate?
+ Why do humans laugh and smile and cry?
+ Why do humans dream?
+ Why do humans enjoy music?
+ How and why do men and women behave differently?
+ Why do the sun and moon seem bigger when low on the horizon?
+ Why are there different languages?
+ What do all languages have in common?
+ Did all languages descend from a common ancestor?
+ Do animals have languages?
+ Is linguistic ability innate?
+ How did humans first grow crops?
+ How did humans first domesticate animals?
+ When did humans first control and create fire?
+ When did humans invent the wheel?
+ When did humans first create watercraft?
+ Why has European civilization been so successful?
+ What have been the most important advances in human history?
+ What caused the fall of the Roman Empire? Mayan Empire? Soviet Union?
+ What caused World War I? The Great Depression? World War II?
+ Will humanity suffer social decay? economic crash? tyranny? resource depletion? overpopulation? runaway pollution? asteroid impact? nuclear catastrophe? microbial epidemic? nanotech plague?
+ Will humanity enjoy divine salvation or loss of faith? paranormal abilities? alien contact? time travel? warp travel? machine or human superintelligence? immortality?
+ Will it ever be possible to transplant a human mind into a machine?
+ Will it ever be possible to reanimate dead people or frozen brains?
2010 Automatic translators allow monolingual humans to converse with any speaker of any major human language.
2015 Bandwidth has increased enormously due to fiber optics and spread-spectrum radio.
2020 Almost all overt tyranny has been eliminated.
Physicists have confirmed that the fate of the universe is asymptotic expansion.
Most text, images, audio, and video is produced and consumed digitally. Unauthorized reproduction and distribution of such media is routine.
1st Martian sample return has revealed no conclusive fossil evidence of life.
2030 20% of former fideists have become mystics.
Radio astronomers have discovered signals from extraterrestrial intelligence.
Computer display technology plateaus with cheap flat panels and retinal projectors.
2040 Physicists have completed a quantum unification theory.
Personal bodily flight has become commercialized.
Transonic flight still serves just a few intercontinental routes.
2050 Molecular biologists have detailed description of how life on Earth began.
Computing is limited not by processing, storage, or bandwidth but by heat, latency, and batteries.
Fresh water availability is now limited only by energy costs of transportation and desalinization.
Automated vehicle/traffic control gives rail-like traffic flow to roads.
Privacy is curtailed by commercial availability of mobile remote-controlled microsensors.
2075 Physicists have reached limits of knowing why fundamental physical laws are as they are.
Hydrogen fuel cells are replacing internal combustion of fossil fuels.
VTOL aircraft are as widely owned as RVs in 2000.
2100 Expected and maximum human longevity have increased by 30 years.
Humans are able to record and archive all they ever see, hear, and say.
Most of humanity is using a common currency descended from the American dollar.
Unmanned radio observatory has been established on far side of moon.
2150 Remaining fideisms have diluted into agnostic mysticism; true fideists dwindle.
Fusion provides major parts of humanity's power.
Most psychotropic drugs are legal; addiction is prevented neurochemically.
2200 Permanent manned space stations in Earth orbit have been established.
1st artifactual life and artificial intelligence systems have been created and enfranchised.
Obesity and other nutritional diseases are curable.
2300 1st Von Neumann probes have been dispatched from Earth.
Most genetic, infectious, immunological, and cancerous disease is preventable or curable.
Most of humanity enjoys Western standards of living and productivity.
Earth's population has stabilized at around 20 billion.
The workweek has stabilized at around 20 hours.
2400 Extropian positivism has displaced most other belief systems.
2500 Heat pollution has become the last significant environmental problem.
A truly global federal government exists.
2880 Asteroid 1950DA (1km wide) has a 1/300 chance of hitting Earth March 16.
3000 Humans have created on the moon their 1st self-sustaining extraplanetary colony.
Earth has received 1st telemetry from unmanned probes to nearby stars.
Neurotechnologists have started to modify and augment natural human intelligence.
Genetic engineers have designed first artificially-created species.
English is the native language of 90% of humans.
Floating communities and estates have become increasingly popular.
4000 1st embarkation of mobile space habitat toward nearby star.
Humans culture animal tissue in bulk rather than raise animals en masse.
As the next ice age begins, Earth is about 0.5C cooler (relative to 2000CE) than it otherwise would have been.
10K 1st terraforming(of Mars or a Jovian moon) has started to show progress. Another 90Kyr-long ice age has begun, and Earth is about 3C cooler (relative to 2000CE) than it otherwise would have been.
16K The precession of Earth's axis has made Vega the northern pole star.
23K The 1679-bit 1974 Arecibo interstellar message finally covers the 21Kly distance to its target, the globular cluster M13 (300K stars).
100K A majority of persons descended from H. sapiens lives beyond Earth.
250K An object more than a kilometer wide will probably have struck Earth.
Earth's magnetic will by now probably have reversed, as it does every few hundred thousand years and as it last did 780Kya.
1M A majority of persons descended from H. sapiens lives beyond the Solar system.
The red dwarf Gliese 710, currently 63ly away, will pass within 0.5 ly of Sol and appear at 0.6 magnitude.
2M Pioneer 10 (launched in 1972, 68 ly away) passes near Aldebaran at 44 Mm/h.
50M Africa has collided with Europe (closing the Mediterranean), Australia has merged with SE Asia, and California has slid up the coast to Alaska. Mars' moon Phobos is destroyed as its orbit finishes decaying.
100M Earth has information from probes to the Andromeda galaxy.
226M Sol has completed one more orbit around the Milky Way's center.
250M The Americas merge with Afro-Eurasia, reducing the (formerly growing) Atlantic to an inland sea.
1B Earth has information from probes to every star system in the Milky Way.
2B Increased Solar output has extincted any remaining Earth life due to runaway greenhouse effect.
6B Sun ends its main-sequence life as a red giant large enough to engulf and possibly swallow Earth, and then cools into a white dwarf.
Milky Way and Andromeda galaxies collide.
10B Milky Way galaxy's intelligent population stabilizes at its maximum.
100B Living systems are huddled around red dwarfs for light and warmth.
The charred and frozen Earth-Moon system (if not already swallowed by Sol's red giant phase) has stabilized to a 47-day rotation/revolution at a distance of 560,000 km.
150B Due to the universe's accelerating expansion, the view of everything outside the gravitationally-bound Local Group of galaxies stops changing and fades away.
1014 Almost all stars stopped shining, having become brown or white dwarfs. Little or no life remains.
1015 Planets have been dislodged from their solar systems by stellar close encounters.
1020 The remaining stars (brown or white dwarfs) have all either been dislodged from their galaxies, or collapsed into central galactic black holes. Dwarf collisions cease, and the last few stars formed thereby stop shining.
1040 Proton decay has left the universe with only black holes and subatomic particles.
10100 The last black hole evaporates, emitting the cold dark universe's final flash of visible light.
Nanoplague. Self-replicating nanotechnology could in theory become a cancer to the Earth's biosphere, replacing all ribonucleic life with nanotech life. The primary limit on the expansion of such nanotech life would, as for all life, be the availability of usable energy and material. Since any organic material would presumably be usable, the primary limit on how nanocancer could consume organic life would be the availability of usable energy. Fossil fuels are not sufficiently omnipresent, and fusion is not sufficiently portable, so nanocancer would, like ribonucleic microorganisms, have to feed on sunlight or organic tissues. Ribonucleic photosynthesis captures a maximum of about 10% of incident solar energy, while nanocancer should be able to capture at least 50%. The only way to stop nanocancer would be to cut off its access to energy and material or interfere with its mechanisms for using them.
Robot Aggression. Some humans fear that the combination of robotics and artificial intelligence will in effect create a new dominant species that will not tolerate human control or even resource competition. These fears are misplaced. Artificial intelligence will be developed gradually by about 2200, and will not evolve runaway super-intelligence. Even when AI is integrated with artifactual life by the early 2200s, the time and energy constraints on artifactual persons will render them no more capable of global domination than any particular variety of humans (i.e. natural persons). Similarly, humanity's first Von Neumann probes will be incapable of overwhelming Earth's defenses even if they tried. To be truly dangerous, VN probes would have to be of a species with both true intelligence and a significant military advantage over humanity. Such a species would be unlikely to engage in alien aggression.
von Neumann probes
Named after the Hungarian-born American mathematician John von Neumann who, among many other achievements, developed a theory of machines that can make exact copies of themselves. The potential advantages of using self-replicating robot spacecraft for galactic exploration was discussed by Chris Boyce in his book Extraterrestrial Encounter: A Personal Perspective (Chartwell Books, New York, pp. 113-124, 1979).1 Boyce, in turn, has said he got the idea from a chapter entitled "The Likelihood of the Evolution of Communicating Intelligences on Other Planets" (ch. 4) written by Michael A. Arbib in the 1974 Ponnamperuma-Cameron book Interstellar Communication: Scientific Perspectives (pp. 63-66). Arbib wrote an even earlier paper, in 1969, in which he discusses self-replicating automata (SRA) based on von Neumann and Burk's seminal paper published in 1966.
Boyce, in his book, envisaged the following scenario. Initially, a von Neumann probe, consisting of an interstellar propulsion system and a universal von Neumann replicator with human-level intelligence, would be launched from the home star toward a neighboring stellar system. Upon arrival it would seek out raw materials, from local sources such as asteroids, and use these to make several copies of itself (including its rocket engines). The copies would then be launched at the next set of neighboring stars. This process would be repeated, over and over again, so that increasing numbers of identical probes would be involved in penetrating ever more remote regions of the Galaxy. Having dispatched copies of itself, a probe would begin to explore the star system in which it found itself. It would conduct scientific research and transmit the results back to the point of origin. It could also be used as a means of colonization by constructing an artificial life-sustaining environment and then implanting this with synthesized fertile egg-cells bearing genomes transcribed from the probe's computer memory. Eiseley has suggested that the embryonic individuals of such a colony could be tended by robots, also built by the probe, until they were old enough to function independently. They would then be free to develop their own civilization around the host star. The great advantage of a von Neumann probe is that, being a universal machine, it can be used for any purpose at its target system depending on the instructions sent out to it from its ultimate creators. Consequently, as the creators made technological advances at home they could reprogram a remote von Neumann probe, for example, to build faster rocket engines for the next generation of probes or more sensitive sensing equipment with which to study its host stellar system. How rapidly the Galaxy could be completely explored and colonized in this way depends on several factors, including the interstellar transit times of the probes (see interstellar travel), the speed at which they reproduce and carry out other tasks within the host systems, and the specific strategy used for interstellar colonization.
Frank Tipler, writing after Boyce et al, and borrowing the idea of von Neumann probes from them, has used the concept as an argument against the existence of intelligence elsewhere in the Galaxy. He proposed a conservative value of 300 million years, or less than 5% of the present age of the Galaxy, for complete galactic colonization. He assumed the von Neumann probe approach to be so logical and economical that it would be commonly adopted by advanced civilizations. According to this view, there should be a significant and obvious presence of such devices within the solar system. Yet, no such presence has been detected. Tipler therefore draws the conclusion that we are the only intelligent race among the Galaxy's several hundred billion stars (Tipler's Argument). The validity of this conclusion has been questioned by, among others, Sagan and Newman (see Sagan's Response).