Tree of the Beyondfrontier ideas on energy, spacetime and mind

Real basis

• Casimir effect: In 1948 Casimir predicted that two uncharged metal plates placed very close together in a vacuum would attract each other, because fewer quantum fluctuations fit between the plates than outside. In 1997 Lamoreaux measured the force with a torsion balance, within about 5% of theory. The energy density between the plates is lower than that of empty vacuum, the only “negative energy density” ever confirmed in an experiment.

• Helium-3 fusion: Most of the energy released by deuterium–helium-3 fusion is carried by charged particles, which can be converted directly into electricity, with far less neutron radiation. The price is a temperature several times higher than deuterium–tritium fusion needs. Lunar soil holds helium-3 implanted by the solar wind, at only a few parts per billion.

• Bussard ramjet: In 1960 Bussard proposed collecting interstellar hydrogen as fuel with a huge magnetic funnel: the faster you fly, the more you collect. Later calculations found that the magnetic drag on interstellar plasma is often greater than the thrust fusion provides, so it works more like a drag chute. That turned out to be a good way to brake a starship.

• Stellar engine: In 1987 Shkadov imagined a giant curved mirror placed on one side of a star, reflecting half its light back. The imbalance in radiation pressure would make the star carry its whole planetary system along. For a Sun-like star, the speed after 1 million years would be about 20 m/s, after 1 billion years about 20 km/s, with a total displacement of about 34,000 light-years.

• Black hole jet power: In 1977 Blandford and Znajek calculated that magnetic field lines threading a rotating black hole can extract its rotational energy, driving a jet that shoots out at nearly the speed of light. This is thought to power quasar jets; the center of galaxy M87 has such a jet about 5,000 light-years long.

• Kugelblitz: In theory, focusing enough light into a single point would create a black hole directly. But a 2024 calculation showed that before the light gets that intense, it “knocks” electron–positron pairs out of the vacuum and carries the energy away (the Schwinger effect). Quantum effects block this route.

• Black hole engine: In 2009 Crane and Westmoreland calculated that an artificial black hole of about 600,000 tonnes and a radius under 1 attometer could output about 1.6×10¹⁷ W through Hawking radiation, with a lifetime of about 3.5 years, and in the ideal case accelerate a ship to 10% of light speed in 20 days. The hard part is building it: they imagined a giant gamma-ray laser, but the previous node showed that route is blocked, so another way of compressing matter is needed.

• Degenerate era: In 1997 Adams and Laughlin divided the universe's future into several eras: after about 10¹⁴ years the last red dwarfs go out, leaving only white dwarfs, neutron stars and black holes. After that, energy can only come from dark matter annihilation, collisions of stellar remnants, and perhaps proton decay.

• Cosmic factory: In 1987 Farhi and Guth studied whether a new universe could be made in a lab. General relativity allows a small blob of false vacuum to expand into a “baby universe” causally cut off from ours, but in classical physics the starting point must be a singularity. In 1990 they and Guven proposed that quantum tunneling might get around this.

• Relativistic flight: The closer you get to light speed, the slower time runs on board: at 0.99 c, one year passes on the ship and about 7 years outside. In 1971 Hafele and Keating flew atomic clocks around the world on commercial airliners and measured time differences matching relativity's prediction.

• Neutrino communication: Neutrinos pass through almost anything; even the whole Earth cannot stop them. In 2012 Fermilab sent the word “neutrino” through 240 m of rock using a neutrino beam, at about 0.1 bit per second. Sending takes a particle accelerator; receiving takes a detector weighing hundreds of tonnes.

• Gravitational-wave broadcast: Gravitational waves are barely absorbed by matter. But emitting detectable ones takes astronomical masses: the first signal LIGO received in 2015 came from two black holes of about 30 solar masses merging, releasing about 3 solar masses of energy in roughly 0.2 seconds.

• Horizon mapping: The universe is expanding at an accelerating rate, so light emitted today by galaxies beyond the event horizon can never reach us. About 94% of the galaxies in the observable universe are already beyond the horizon, and each year about 160 billion more stars cross that line. If you want to talk to distant civilizations, sooner is better.

• Traversable wormhole: In 1988 Morris and Thorne showed that general relativity allows wormholes a person could pass through, provided the throat is held open by negative-energy “exotic matter”. It began when Sagan asked Thorne for help with his novel Contact. In 1996 Ford and Roman's quantum inequalities added that negative energy can exist only in an extremely thin layer or for an extremely short moment.

• Sublight warp bubble: Alcubierre's 1994 faster-than-light warp solution needs negative energy; a 2009 calculation also found that the front wall of the bubble keeps accumulating Hawking radiation and eventually destroys itself. In 2021 Bobrick and Martire showed that a warp bubble using only positive energy is possible, but it can only be slower than light. Warp drives can exist; faster than light cannot.

• Moving a wormhole mouth: The two mouths of a wormhole start out together, and one must be carried to its destination by a ship traveling below light speed. So a wormhole cannot reach places no probe has been, let alone beyond the cosmological horizon. Once a mouth is in place, travel between the two ends is instant.

• Wormhole time machine: In 1988 Morris, Thorne and Yurtsever pointed out that if one mouth of a wormhole makes a high-speed round trip, time dilation opens a time difference between the two mouths, and going through takes you into the past. In 1992 Hawking proposed the “chronology protection conjecture”: at the moment a time machine forms, vacuum fluctuations are amplified without limit and destroy it.

• Backward-in-time messaging: If a time machine exists, you can send messages to the past. In 1991 Deutsch showed that in the quantum-mechanical version of closed timelike curves, the grandfather paradox does not occur and the outcome converges automatically to a self-consistent state. The strangest one left is the bootstrap paradox: a message with no author, simply going around in a loop through time.

• Message to the start: Send a message to before the first second of this universe. By Deutsch's self-consistency condition, it can only be a message that has already been received.

• Through the wormhole: The wormhole mouth has been carried to the farthest probe, and the throat is about to open. Sagan wrote a similar scene in Contact, but a real wormhole can only connect to places your ship has been.

• Whole-brain connectome: In 2024 the FlyWire consortium published the whole-brain connectome of an adult fruit fly: nearly 140,000 neurons and over 50 million synapses. The human brain has about 86 billion neurons, over 600,000 times as many.

• Brain–brain interface: In 2019 the University of Washington's BrainNet let three people cooperate on a Tetris-like game using only brain signals: two sent “rotate” or “don't rotate” by EEG, and the third received it as flashes of light produced by magnetic stimulation of the visual cortex. The average success rate was 81%.

• Mind acceleration: An uploaded mind can run much faster than a biological brain, but the price is that the universe feels bigger: for a mind a million times faster, a message once around the Earth (about 0.13 seconds) takes a day and a half of subjective time. From this Sandberg concluded in 1999 that superminds would be trapped by the speed of light in a very small region.

• Distributed mind: An octopus has about 500 million neurons, two thirds of them in its eight arms, and a severed arm can still make grasping movements in response to stimuli. A mind does not have to be concentrated in one brain.

• Digital immortality: After a complete mind is copied, which one is you, the original or the copy? The philosopher Parfit pressed this with the “teleporter”: if a machine scans you, builds an identical you on Mars and destroys the original, did you travel to Mars, or die?

• Collective consciousness: When a honeybee colony swarms, scout bees “vote” for candidate nest sites with waggle dances, and once enough of them agree, the decision is made, with no central command. Human brain-to-brain interfaces are only just getting started.

• Jupiter brain: In 1999 Sandberg estimated the limits of a planet-sized computer: its size is bounded by heat dissipation and light-speed delay. If the brain is too big, the left half has to wait a long time to learn what the right half is thinking.

• Planetary mind: Lovelock's Gaia hypothesis treats Earth's life and environment as one self-regulating whole. In 2015 scientists found that Bacillus subtilis biofilms coordinate the growth of the whole colony with waves of potassium ions, “firing” like neurons.

• Cosmic mind: Link the minds of many planets together. At light speed, a thought spanning a galaxy takes 100,000 years to cross it, so it would be the slowest and also the largest thought in the universe.

• Moving into the device: Landauer's principle: at room temperature, erasing 1 bit of information dissipates at least about 3×10⁻²¹ J of heat. In theory, the energy in one phone battery could power an unimaginable amount of thinking; real chips are still very far from this limit.

• Quantum error correction: Qubits are extremely error-prone. In 2024 Google's Willow chip showed for the first time that encoding more physical qubits into one logical qubit makes the error rate go down, crossing the threshold for quantum error correction.

• Cosmic language: In 1960 the mathematician Freudenthal designed Lincos (a cosmic language), teaching from scratch using only mathematics and logic. The 1974 Arecibo message is 1,679 bits long, exactly the product of the primes 23 and 73, hinting to the recipient to arrange it as a picture 73 rows by 23 columns.

• Technosignature search: Besides radio, you can look for a civilization's waste heat. The 2015 Ĝ survey found no Type III civilization among 100,000 galaxies; the 2024 Project Hephaistos screened about 5 million sources down to 7 suspicious red dwarfs, and follow-up studies concluded they may be distant galaxies in the background, hidden by dust.

• Active messaging: The 1974 Arecibo message and the 1999 and 2003 “Cosmic Calls” all sent messages to the stars on purpose. Whether we should has long been debated; in 2010 Hawking warned that whoever answers us may not be friendly.

• Bekenstein bound: The amount of information a region can hold has an upper limit, and it is proportional to its surface area, not its volume. Bekenstein gave this bound in 1981, and it later grew into the holographic principle. By this bound, a sphere with a radius of 1 m can hold at most about 10⁷⁰ bits.

• Black hole computer: In 2000 Lloyd calculated the “ultimate laptop”: 1 kg of matter can perform at most about 5×10⁵⁰ operations per second; compressed into a black hole, it reaches the limits of both storage and speed at once.

• Universe simulation: In 2003 Bostrom proposed the simulation argument: if civilizations can and are willing to simulate conscious beings, then the vast majority of conscious beings live inside simulations. In 2012 physicists proposed a test: if the universe is computed on a lattice, the arrival directions of the highest-energy cosmic rays would show traces of the lattice.

• Observer's telescope: A 2019 photon experiment tested “Wigner's friend”: two observers can reach contradictory records of the same quantum event. Observers may not be objective bystanders after all.

• Recursion: A civilization inside a simulation can run simulations too. Bostrom noted that simulations can be nested layer within layer, with computing power discounted at each layer.

• Seeing the Observer: The telescope is pointed not at any one star, but at the one deviation that cannot be removed from all the observation records.

• Permanent silence: Turn off all radio stations, bring your waste heat down to ambient temperature, and make your star look like any other. In a universe with relativistic kinetic weapons, “not being found” is the most reliable survival strategy: a 1-tonne object hitting at 0.1 c carries energy equal to about 100 million tonnes of TNT.

• Direct dark matter detection: In 2024 the LZ experiment, about 1.5 km underground in the USA, used 7 tonnes of liquid xenon to wait for dark matter particles to hit atomic nuclei. It saw no signal, setting the strictest limits so far. Dark matter has so far been “seen” only through gravity.

• Proton decay search: Grand unified theories predict that protons decay. The Super-Kamiokande detector watched 50,000 tonnes of pure water for over twenty years and never saw one, which means the proton lifetime exceeds 10³⁴ years. The next-generation Hyper-Kamiokande will use about 260,000 tonnes of water.

• Vacuum stability: Taking the Higgs boson's mass of about 125 GeV together with the top quark's mass, our vacuum may be only “metastable”: a lower-energy state exists. A 2018 calculation gave its expected lifetime as about 10¹³⁹ years, vastly longer than the age of the universe.

• Echoes of dark matter: Gravitational lensing can “photograph” dark matter: after the Bullet Cluster collided, the hot gas stayed in the middle while the center of gravity moved off to the two sides.

• Is dark energy changing?: In 2025 DESI measured the history of cosmic expansion using over 14 million galaxies and quasars, and combined with the cosmic microwave background and supernovae, favors “dark energy weakening over time” at 2.8 to 4.2 standard deviations. If it keeps weakening until it turns negative, the universe will one day contract again.

• Hoyle resonance: In 1953 Hoyle inferred that carbon-12 must have an excited state at about 7.65 MeV, or stars could not make enough carbon, and there would be no us. Experiments soon found it. Many of the universe's parameters look as precisely set as if tuned, which is the starting point of the “fine-tuning” debate.

• Black hole evaporation: In 1974 Hawking showed that black holes radiate and slowly evaporate. A one-solar-mass black hole takes about 10⁶⁷ years to evaporate completely, and the largest supermassive black holes about 10¹⁰⁰ years.

• Vacuum engineering: If you could change the vacuum state of a small patch of space, you might get a different set of physics. The danger: once a lower-energy vacuum bubble forms, it expands at nearly the speed of light and rewrites all the physics inside. Coleman and De Luccia studied this kind of decay in 1980.

• Watching the proton: If protons decay, then at some point after 10³⁴ years all ordinary matter in the universe will vanish, leaving only photons, electrons, positrons and neutrinos.

• Big Crunch: If dark energy turns negative, expansion will stop and then reverse. The cosmic microwave background will heat up again, galaxies will move closer together, and in the end everything returns to a single point.

• Triggering the vacuum: A new vacuum bubble smaller than an atom, expanding at nearly the speed of light. You cannot see it before it arrives.

• The last proton: Choose to keep watch at the end of the universe and see the last proton decay.

• Talking to dark matter: Put all the evidence about dark matter together and listen to that string of low-energy events.

Related research

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

• Inflationary universe: Guth proposed that the early universe underwent exponential expansion, explaining in one stroke why it is so flat and why temperatures are almost the same everywhere.

  Source: Guth, Physical Review D 1981, "Inflationary universe: A possible solution to the horizon and flatness problems"

• Accelerating expansion: Using distant supernovae as “standard candles,” they found the expansion of the universe is accelerating. Dark energy entered the picture, and the work won the 2011 Nobel Prize.

  Source: Riess et al., The Astronomical Journal 1998, "Observational evidence from supernovae for an accelerating universe and a cosmological constant"

• 42 supernovae: Another team independently reached the same conclusion: some energy in the universe is driving the accelerating expansion.

  Source: Perlmutter et al., The Astrophysical Journal 1999, "Measurements of Omega and Lambda from 42 high-redshift supernovae"

• 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"

• 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"