Moon, Asimov, superconductivity etc

I have been reading ‘the very error of the moon’ by Asimov. It is an essay on how moon came to be. But it is written in late eighties. What are the current ideas around moon’s formation?

Great question! A lot has changed since Asimov wrote that essay. Here's where the science stands today:

The Giant Impact Hypothesis — the dominant theory

The leading idea is that around 4.5 billion years ago, a Mars-sized protoplanet (now called Theia) slammed into the young Earth. The debris from this catastrophic collision eventually coalesced into the Moon. This wasn't even the consensus when Asimov was writing — it only gained wide acceptance after a landmark 1984 conference in Kona, Hawaii, where planetary scientists reviewed Apollo mission rock samples. The Apollo evidence was key: the age of the rock samples indicated the Moon formed around 60 million years after the solar system began to form, and the samples showed the Moon had been molten during its formation, covered with a deep magma ocean for tens of millions to hundreds of millions of years — consistent with an intensely energetic impact. NASA Science

The composition puzzle

One big challenge for the theory is that the Moon's rocks are isotopically very similar to Earth's — much more so than you'd expect if Theia were a body from a different part of the solar system. The lunar samples scientists have studied show very similar isotopic signatures to rocks from Earth, unlike rocks from Mars or elsewhere in the solar system. NASA If most of the Moon came from Theia, why does it look so much like Earth? This remains an active debate.

New twists: how fast did the Moon form?

The classical model imagined debris slowly accumulating in a disk over months or years. But a NASA and Durham University simulation suggests the Moon may have formed in a matter of hours, when material from Earth and Theia was launched directly into orbit after the impact. NASA This "fast formation" idea is exciting because it could better explain the Moon's Earth-like composition and its tilted orbit.

The Synestia model

Another variant proposes that the collision was so energetic it created a synestia — a vast, donut-shaped cloud of vaporized rock enveloping both bodies — and the Moon coalesced inside this structure, which would explain why it inherited so much of Earth's isotopic signature. However, this model arguably struggles to explain the Moon's current orbit. NASA

Alternative: binary-exchange capture

A 2024 paper by Penn State researchers proposed another possibility: that the Moon was captured during a close encounter between a young Earth and a terrestrial binary — the Moon and another rocky object. One lingering problem with the impact theory is that a moon formed from debris should orbit above Earth's equator, but our Moon orbits in a different plane, more aligned with the Sun. Penn State University

Recent dating refinement

In 2023, analysis of rock samples from Apollo 17 suggested the Moon's surface is about 40 million years older than previously thought, and a related study suggested the post-formation cooling period lasted about 20 million years rather than the 100 million previously estimated. EBSCO

The bottom line

The giant impact by Theia is still the consensus, but scientists are actively debating the details — how violent the collision was, how quickly the Moon assembled, and why it looks so chemically similar to Earth. Asimov would have found the current debates fascinating, since the field has moved from "did an impact happen?" to much more nuanced questions about the mechanics of how exactly it played out.

He presents some amazing facts about moon. That how it is so unlikely. For the planet of our size to have such a large satellite. And with high mass of Earth too. Has the study of planets and satellites outside of solar system revealed more such Earth- moon kind of unlikely combinations? Also, the tides by moon, I assume they are not as strong anywhere else… as in the pull of the satellite on the planet’s gas or liquid? Also, there seems to be water or ice on one of Jupiters satellite, but no tides? How do tides allow for life?

These are really rich questions — let me take them one by one.

Are Earth-Moon-like systems rare elsewhere?

Yes, strikingly so, at least as far as we can tell. Detecting exomoons — moons orbiting planets outside our solar system — is extraordinarily difficult. We've had a couple of tantalizing candidates (notably around Kepler-1625b and Kepler-1708b), but nothing confirmed. What we can say from exoplanet surveys is that Earth-sized rocky planets are common, but a companion as large as our Moon relative to its host planet appears to be genuinely unusual. Most large moons in our own solar system orbit gas giants — Jupiter's and Saturn's moons are large in absolute terms but tiny relative to their massive hosts. Our Moon is about 1/81st of Earth's mass, which is an extraordinarily high ratio. No other planet-moon pair in the solar system comes close to that ratio. So Asimov's instinct was right, and modern astronomy has only deepened that sense of strangeness.

Tides elsewhere — do they compare?

This is fascinating. Tidal forces absolutely exist elsewhere, but they work very differently depending on context. Jupiter's moon Io is the most dramatic example — it is so violently squeezed by Jupiter's tidal pull (and resonance with Europa and Ganymede) that it is the most volcanically active body in the solar system. The tides there aren't ocean tides, they are solid body tides — the entire rocky surface of Io flexes by tens of meters. Europa similarly experiences tidal flexing, which is thought to generate enough heat to maintain a liquid ocean beneath its icy crust.

But here's the key distinction: those are moons being pulled by a giant planet. The Moon pulling on Earth is the reverse geometry — a relatively small body pulling on a much larger one — and it's this that creates our familiar ocean tides. In our solar system, no other planet has a large moon pulling on liquid oceans in quite the same way. Mars has two tiny moons, Phobos and Deimos, which create almost no tidal effect at all. Venus has no moon. So Earth's ocean tides are, as far as we know, a fairly unique situation in the solar system.

Europa's water and tides

Europa is a great example here. It does experience tides — just not ocean tides in the earthly sense. The tidal flexing of its ice shell generates heat, and that heat is what keeps a liquid water ocean (perhaps 100 km deep) beneath the ice. So tides are actually central to Europa's potential habitability, just in a completely different mechanism than Earth's. The liquid water isn't on the surface being sloshed around — it's buried under kilometers of ice, kept warm by tidal heating. Whether that's enough for life is one of the biggest open questions in astrobiology right now.

How do tides help life on Earth?

This is where it gets philosophically rich. The proposed connections are several:

First, tidal pools. The rhythmic flooding and draining of coastal zones creates highly dynamic environments with concentrated nutrients, temperature variation, and chemical gradients. Many evolutionary biologists think these intertidal zones were crucial nurseries for the emergence of complex life and the eventual transition to land. Organisms in tidal pools had to adapt to dramatic swings in conditions — a powerful evolutionary pressure.

Second, the Moon stabilizes Earth's axial tilt. This is perhaps even more important than the tides themselves. Without the Moon's gravitational steadying influence, Earth's axial tilt would wobble chaotically over millions of years — potentially swinging between near-zero and very high values — which would cause catastrophic climate swings. The Moon keeps us locked at a relatively stable 23.5 degrees, which gives us our predictable seasons and a relatively stable long-term climate. Mars, which has no large moon, does wobble dramatically on geological timescales.

Third, the Moon has been gradually slowing Earth's rotation since its formation. Early in Earth's history, a day was only about 6 hours long. The Moon's tidal braking has slowed that to 24 hours. Some researchers argue that the current day length is in a kind of "sweet spot" for photosynthesis and biochemical cycles — though this is more speculative.

Fourth, tidal mixing in the oceans drives nutrient circulation, bringing cold, mineral-rich deep water up toward the surface and distributing heat across the globe. Without strong tides, the oceans would stratify much more, potentially making them far less biologically productive.

The honest answer is that we don't know that life requires all of this — life might find a way on a tidally quiet world. But Earth's Moon seems to have provided a remarkable package of stabilizing and dynamically enriching influences that together made our planet's story possible. Whether that package is necessary or just one fortunate path among many is one of the deepest open questions in the study of life in the universe.

Thanks. Are there any other writings like Asimov’s accessible and rich essay which refer to the above discussion or tangents from it?

Great taste — Asimov had a rare gift for making science feel like wonder rather than work. Here are some writers and books that hit a similar register, roughly grouped by theme:

In the spirit of Asimov's essay-style science writing

Bill Bryson's A Short History of Nearly Everything is probably the closest modern equivalent in tone — wide-ranging, self-deprecating, genuinely awed, and extremely accessible. It covers planetary formation, the history of life, and a lot of the "how unlikely is all of this?" territory that Asimov loved.

Richard Feynman's essays, particularly in The Pleasure of Finding Things Out and What Do You Care What Other People Think?, have that same quality of a brilliant mind sharing genuine delight. Not specifically about moons, but the sensibility is very Asimovian.

Directly on the Moon, planets, and the themes you've been exploring

The Story of Earth by Robert Hazen traces Earth's history from its formation through the emergence of life, and the Moon's role in stabilizing the planet features prominently. It's narrative and readable rather than textbook-like.

Rare Earth by Peter Ward and Joe Brownlee (2000) is perhaps the most direct modern parallel to Asimov's essay. It makes exactly the argument you and Asimov were circling — that the specific conditions of Earth, including our unusually large Moon, our position in the galaxy, our plate tectonics, and our Jupiter acting as a cosmic shield, are so improbable that complex life may be extraordinarily rare in the universe. It sparked enormous debate and is genuinely gripping.

The Ends of the World by Peter Brannen is more recent and covers mass extinctions, but the writing has that same quality of making deep time feel visceral and real.

On moons, oceans, and life elsewhere

The Moons of Jupiter — interestingly, Alice Munro has a short story collection by that title, but the book you'd want here is Alien Oceans by Kevin Peter Hand, a NASA astrobiologist who works on Europa. It's accessible, recent, and deals directly with the question of tidal heating and life in subsurface oceans. Hand writes with genuine passion and it reads almost like a detective story.

On the bigger "how unlikely is Earth" question

Cosmos by Carl Sagan remains a touchstone — Sagan and Asimov were contemporaries and shared a similar gift, though Sagan is more lyrical where Asimov was more conversational. The TV series is equally worth watching if you haven't.

The Zoomable Universe by Caleb Scharf and Ron Miller is a more recent, visually rich journey from the largest scales of the cosmos down to the quantum, and Scharf's other book The Copernicus Complex tackles the "are we special?" question head-on with excellent up-to-date science.

If I had to pick just one to start with given what you've been reading, I'd say Rare Earth — it will feel like a direct and passionate continuation of the conversation you've been having with Asimov's essay, and it will push back on some of his assumptions in productive ways while sharing his sense of cosmic amazement.

When people say motion is negligible at absolute zero, what scale of motion are they referring to? Do electrons stop buzzing around?

Great question, and there's a really important distinction to unpack here.

What "stops" at absolute zero

When physicists say motion becomes negligible at absolute zero, they're primarily referring to thermal motion — the random kinetic energy of atoms and molecules jostling, vibrating, and moving around due to heat. Temperature, at its core, is a measure of this thermal agitation. So at absolute zero (0 Kelvin, -273.15°C), you're removing all of that thermally-driven random motion. Atoms in a solid, for instance, stop vibrating around their lattice positions.

But electrons absolutely do not stop

This is where quantum mechanics intervenes decisively, and it's one of the most beautiful results in physics. Electrons keep doing what they do — orbiting nuclei, occupying their energy levels — completely independently of temperature. Their motion is governed by quantum mechanics, not thermodynamics. The Heisenberg uncertainty principle actually forbids electrons from being perfectly still, because if you knew both their position and momentum precisely (as "stopped" would require), you'd violate the uncertainty principle. So electrons at absolute zero are still fully "buzzing," as you put it.

In fact this extends beyond electrons. Even atoms themselves retain what's called zero-point energy at absolute zero — a residual quantum mechanical motion that cannot be removed no matter how cold you get. Liquid helium famously refuses to freeze even at absolute zero under normal pressure, because its zero-point motion is energetic enough to prevent the atoms locking into a solid lattice. You have to apply pressure to freeze it.

Two completely different kinds of "motion"

It helps to think of it as two largely separate regimes:

Thermal motion is classical (or semi-classical) — it's the motion you can extract energy from, that drives heat engines, that makes gases expand, that we experience as warmth. This is what temperature measures and what absolute zero eliminates.

Quantum motion — electrons in orbitals, zero-point fluctuations — is a fundamentally different beast. It's not "motion" in the sense of a particle tracing a path. It's better thought of as the inherent quantum mechanical nature of the particle existing in a probabilistic state. It doesn't contribute to temperature, you can't extract it as heat, and it persists regardless of how cold things get.

One more wrinkle — what about superconductivity?

Near absolute zero something strange happens to electrons in certain materials — they pair up (called Cooper pairs) and flow through the material with zero resistance. This is superconductivity. So electrons aren't just still buzzing at near-absolute zero, they're in some materials doing something even more organised and extraordinary than at room temperature. Cold doesn't subdue electrons — it sometimes frees them from the disorder that normally impedes them.

So in short: absolute zero silences the thermal chaos of atoms, but the quantum world underneath carries on completely undisturbed, as lively as ever, just by different rules.

What you mention towards the end about super conductivity. Tell me more please. Is it the quiet halls of the otherwise chaotic moving atoms electrons find themselves open gateways? Which elements or compounds present this?

Your metaphor is actually remarkably apt — the "quiet halls" image captures something real about what's happening. Let me build this up properly because it's a genuinely strange and beautiful story.

Why electrons normally face resistance

In an ordinary metal at room temperature, electrons moving through the lattice of atoms are constantly being scattered — bumping into thermally vibrating atoms, impurities, and defects in the crystal structure. This scattering is electrical resistance. The hotter the material, the more violently the atoms vibrate, the more the electrons get deflected, and the higher the resistance. Your metaphor works well here — it's like trying to walk through a crowd of people who are all randomly lurching about.

Cool the material down and the atomic vibrations settle. The crowd calms. Resistance drops. For most metals this just continues gradually — copper gets slightly more conductive as you cool it. But in superconductors, something qualitatively different happens at a critical temperature. Resistance doesn't just drop — it vanishes entirely. Not "very low." Exactly zero.

The Cooper pair — the strange heart of it

Here is where it gets wonderfully counterintuitive. You might expect that at low temperatures electrons, being negatively charged and therefore repelling each other, would just move independently through those quieter halls. But something else happens. An electron moving through the lattice very slightly attracts the positive ions around it — pulling them fractionally inward, leaving a tiny wake of slightly higher positive charge density. A second electron, coming along a moment later, is weakly attracted to that positive wake. The net effect is that the two electrons become loosely correlated — a Cooper pair — bound together by this indirect, lattice-mediated attraction, despite their mutual electrostatic repulsion.

The binding energy is tiny — these pairs would be ripped apart by the thermal jostling at room temperature. But below the critical temperature, thermal energy is low enough that the pairs survive.

Now here's the quantum mechanical magic. Individual electrons are fermions — particles that obey the Pauli exclusion principle, meaning no two can occupy the same quantum state. This is actually why electrons stack up in different energy levels in atoms. But Cooper pairs have integer spin, which makes them bosons, and bosons don't obey the exclusion principle. They can all pile into the same quantum state. Below the critical temperature, essentially all the Cooper pairs condense into a single collective quantum state — a phenomenon called Bose-Einstein condensation. The entire ensemble of conducting electrons moves as one coherent quantum wave through the material.

This is your "open gateway." The electrons are no longer individual particles scattering off imperfections. They move as a single quantum entity, and scattering off individual atoms simply cannot disrupt a collective quantum wave the way it disrupts individual particles. The wave flows around imperfections rather than deflecting. Hence zero resistance.

Which materials do this?

The story here is surprisingly rich and still unfolding.

Simple elemental superconductors — many ordinary metals become superconducting at very low temperatures. Mercury was the first discovered, by Heike Kamerlingh Onnes in 1911, at about 4 Kelvin. Lead, tin, aluminium, niobium all do it. Niobium has the highest critical temperature among pure elements at about 9 Kelvin. These are well understood by the Cooper pair theory (called BCS theory after Bardeen, Cooper and Schrieffer, who won the Nobel Prize for it in 1972).

Low-temperature alloys and compounds — niobium-titanium alloys are the workhorses of practical superconductivity, used in MRI machines and particle accelerators like the LHC at CERN. The electromagnets in the LHC are kept at 1.9 Kelvin — colder than outer space — and carry enormous currents with zero resistance.

High-temperature superconductors — in 1986 something shocking happened. Georg Bednorz and Alex Müller discovered superconductivity in a copper oxide ceramic at around 35 Kelvin, far higher than anyone thought possible with conventional theory. Within a year, other researchers pushed this above 77 Kelvin — the boiling point of liquid nitrogen, which is cheap and abundant compared to liquid helium. This was revolutionary practically, but also deeply theoretically troubling because BCS theory couldn't explain it. These cuprate superconductors remain only partially understood after nearly four decades of intense study. They're among the most studied materials in all of condensed matter physics and the mechanism is still genuinely debated.

The current record for ambient-pressure superconductivity is around 138 Kelvin in mercury-based cuprates — still cold by everyday standards (-135°C) but remarkable by the old benchmarks.

Room-temperature superconductivity — this is the holy grail. In recent years there have been dramatic claims of superconductivity near or above room temperature in hydrogen-rich compounds under extreme pressure — hundreds of gigapascals, the kind of pressure found deep inside planets. Carbonaceous sulfur hydride was reported in 2020 at around 288 Kelvin (just above room temperature) under pressure. These results have been controversial, with some retracted or disputed, but the underlying physics seems real even if specific claims need scrutiny. Achieving room temperature superconductivity at ambient pressure would be one of the most transformative technological discoveries in history — essentially free electrical transmission, revolutionary computing, energy storage, transportation.

What would room-temperature superconductivity mean?

Power grids currently lose roughly 5-10% of electricity to resistance during transmission. Superconducting power lines would eliminate that entirely. Superconducting motors and generators would be far lighter and more efficient. Magnetic levitation trains (maglev) already use superconducting magnets. Quantum computers depend on superconducting circuits. And medical MRI machines — which require expensive liquid helium cooling today — could become dramatically cheaper and more widespread.

The quiet halls you imagined are real, and humanity has been trying for over a century to figure out how to build them at room temperature. We're tantalizingly close, and the physics along the way has been some of the strangest and most beautiful in all of science.

How science or the physical world changes dimensions and the rules change completely. Infinities within and infinities without and after each scale change, or a few scale changes, a new set of reality rules seem to apply. This, superconductivity is about the edge of the quantum and the physical world as we know it. A switching rule, if you may. Affected by both temperature in this world and quantum rules in its world. Time stops as temperature drops to absolute zero? If there is no motion, there is no heat, there is no direction? Also, time is not a scale in the quantum world, right?

You're touching something profound here, and the way you're framing it — scale changes bringing entirely new rule sets, switching boundaries — is actually quite close to how physicists themselves think about it, under the formal name of emergence. Let me follow your thread carefully because each part deserves its own treatment.

The scale-change idea — emergence

This is one of the deepest ideas in all of science. Philip Anderson, a Nobel laureate in condensed matter physics, wrote a famous 1972 essay called More is Different which argues exactly what you're intuiting — that at each level of scale and complexity, genuinely new laws emerge that cannot be simply derived from or reduced to the laws below. Superconductivity is a perfect example. Nothing about a single electron tells you that a trillion of them, under the right conditions, will spontaneously organise into a single quantum wave that flows without resistance. The collective behaviour is irreducibly new. Similarly, wetness is not a property of a single water molecule. Life is not a property of a single amino acid. Consciousness is not a property of a single neuron. At each threshold, something genuinely unprecedented appears. The universe seems to be structured as nested layers of reality, each with its own grammar.

Your "switching rule" framing is elegant — superconductivity really is exactly that. It sits precisely at the boundary where quantum coherence scales up into the macroscopic world. Normally quantum effects are confined to the microscopic because thermal noise destroys the delicate phase relationships between particles almost instantly at any appreciable temperature. Superconductivity is one of the rare cases where a quantum phenomenon — coherent collective behaviour — survives at a scale we can hold in our hands, run current through, and build machines with. It is quantum mechanics refusing to stay microscopic.

Time at absolute zero

This is where it gets philosophically vertiginous. Your instinct is pointing at something real. If temperature is fundamentally about the rate of change — atomic vibrations, molecular collisions, energy exchanging between states — then as temperature drops toward absolute zero, the rate at which the thermal world changes approaches zero. In a very meaningful sense, a system at absolute zero has reached its lowest energy state and has nowhere thermodynamically to go. No spontaneous transitions, no heat flow, no entropy increase. The thermal arrow of time — the direction defined by entropy always increasing, disorder always growing — simply has no work to do.

The physicist's way of saying this is that at absolute zero a perfect crystal has zero entropy — there is only one possible arrangement of the system, no disorder, no multiplicity of states. And since the arrow of time we experience is deeply tied to entropy increase, a system at absolute zero is in a sense outside of thermodynamic time. Not frozen in time exactly, but no longer participating in it.

But — and this is crucial — the quantum zero-point motion continues. And quantum mechanics has its own relationship with time that is deeply strange.

Time in the quantum world

You're right to sense that time is different there, though the full picture is subtle. In quantum mechanics, time is treated very differently from space. In special relativity, space and time are unified into spacetime and treated on similar footing. But in quantum mechanics, time is not an observable — you cannot write down a "time operator" the way you write down a position or momentum operator. Time in quantum mechanics is more like a parameter, a backdrop against which things evolve, rather than a thing that is measured or that participates in the physics. This is actually one of the deep tensions between quantum mechanics and general relativity — one of the reasons a unified theory is so hard. They treat time in fundamentally incompatible ways.

In quantum mechanics the Schrödinger equation governs how a quantum state evolves with time, and it is perfectly time-symmetric — it runs equally well forwards and backwards. There is no arrow of time baked into it. The arrow of time we experience — past is different from future, causes precede effects — has to be imported from thermodynamics, from the fact that entropy increases. Strip away thermal processes and the underlying quantum equations don't care which direction time runs.

There's an even deeper puzzle called the problem of time in quantum gravity. When you try to apply quantum mechanics to the universe as a whole using the Wheeler-DeWitt equation, time disappears entirely from the fundamental equation. The universe's wavefunction just... exists, timelessly. Time as we experience it may be an emergent property — something that arises at a certain scale or level of complexity — rather than a fundamental feature of reality at the deepest level. Julian Barbour, a physicist who has written beautifully and accessibly on this, argues that time is essentially an illusion generated by the existence of change, and that at the most fundamental level reality is a static landscape of possible configurations — what he calls Platonia — with no flow of time at all.

Pulling it together

So your intuition forms a coherent picture. At the thermal scale, time has direction because entropy increases and things change irreversibly. Cool a system down and you slow its participation in thermodynamic time. At absolute zero, thermal time effectively stops. But underneath, quantum time — which was never really a flowing river to begin with, more like a mathematical parameter — carries on, or perhaps was never really "time" in the sense we mean at all. And at the deepest level of quantum gravity, even that parameter may dissolve, and what we call time may turn out to be an emergent property of scale, complexity, and observation — something that crystallises out of a more fundamental, timeless substrate, the way wetness crystallises out of molecules that are not themselves wet.

The infinities within and without that you describe — the nested rule-sets, the switching thresholds — may be pointing at the possibility that time itself is one more emergent property, one more rule that applies at certain scales and dissolves at others, rather than the absolute stage on which everything plays out. That's a genuinely live possibility in contemporary physics, and one of the most disorienting ideas humans have ever seriously entertained.

Tell me more about the wheeler dewitt theory and the Barbour writing you mention.

Both are worth exploring carefully because they connect in a beautiful and unsettling way.

The Wheeler-DeWitt Equation

In the 1960s, John Archibald Wheeler and Bryce DeWitt were trying to do something that sounds straightforward but turns out to be almost paradoxical — apply quantum mechanics to the entire universe. In ordinary quantum mechanics you have a system (a particle, an atom) and you describe its quantum state evolving over time according to the Schrödinger equation. Time is the backdrop, the stage, against which the drama plays out.

But when you try to write a quantum equation for the whole universe, you run into an immediate problem. There is no "outside" of the universe. No external clock. No external observer watching it evolve. In general relativity, time is not a fixed backdrop — it is part of the fabric of spacetime itself, dynamic, curved by matter and energy, inseparable from the geometry of the universe. When you try to marry this to quantum mechanics, time gets swallowed.

The Wheeler-DeWitt equation is what you get when you apply the quantum mechanical constraint equations to the geometry of space itself — what's called quantum geometrodynamics. And the shocking result is that the equation contains no time variable at all. It looks schematically like:

H|Ψ⟩ = 0

Where H is the Hamiltonian (the energy operator, which in ordinary quantum mechanics drives time evolution) and |Ψ⟩ is the wavefunction of the universe. In ordinary quantum mechanics this equation would say the system has zero energy and doesn't evolve — a trivially static, dead equation. But here it's saying something more profound: the wavefunction of the universe simply is. It doesn't evolve in time because there is no external time for it to evolve in. The universe as a whole, at this fundamental level of description, is frozen. Timeless.

This is called the problem of time in quantum gravity and it's not a minor technical nuisance — it's a deep conceptual wound at the heart of physics. If the fundamental equation governing the universe contains no time, where does our vivid, irreversible, flowing experience of time come from?

One proposed answer — developed by Don Page, William Wootters and others — is called the relational or conditional interpretation. The idea is that time emerges from correlations within the universe. You pick some subsystem — a clock — and ask: conditioned on the clock reading a certain value, what is the state of everything else? Time is not absolute, it is relational. It only exists as a relationship between parts of the universe. There is no master clock ticking away independently. Different observers with different clocks construct slightly different versions of time, and none of them is the "real" one. This has actually been tested in small quantum systems in recent years — a beautiful 2019 experiment by a group in Vienna demonstrated that from an "outside" perspective a quantum system is static, but from the perspective of an internal observer using an entangled clock, time flows normally. The universe may work the same way, just at an incomprehensibly larger scale.

Julian Barbour

Barbour is a fascinating figure — an independent physicist who for decades funded his research by translating Russian scientific papers, working largely outside of academia, and produced some of the most radical and carefully argued ideas about time in contemporary physics. His main book on this is The End of Time, published in 1999, and it is one of those rare books that is both genuinely scientifically serious and written with enough clarity and beauty that a non-specialist can follow the central argument.

His central claim is stark: time does not exist. Not in the sense of a flowing river, not as a dimension we move through, not as something that passes. What exists, he argues, is a vast landscape of possible instantaneous configurations of the universe — every possible arrangement of matter and geometry. He calls this landscape Platonia, borrowing Plato's sense of a realm of pure, timeless forms. Each point in Platonia is a Now — a complete, instantaneous snapshot of a possible universe. The Wheeler-DeWitt wavefunction assigns a probability amplitude to each of these Nows.

What we experience as the flow of time — the sense of moving from past to present to future — is, in Barbour's view, an illusion generated by the fact that certain Nows contain within them records and memories of other Nows. A particular configuration of the universe contains brains that hold memories of previous configurations. It contains fossils, photographs, written records. These are all just features of the current instantaneous Now — but they create an overwhelming internal impression of having come from somewhere, of being in the middle of a journey. We experience time because our present moment contains traces of other moments, not because we are actually moving through anything.

Think of it this way. Imagine a single frame of a film. If that frame contains an image of a blurred hand caught mid-swing, it creates the impression of motion even though it is a static image. Barbour's argument is that our universe is like an extraordinarily rich still frame — containing within it all the apparent evidence of a history — but there is no projector running. The film is not being played. Only this one frame exists, and it contains its own story written into it.

This sounds almost mystical but Barbour grounds it carefully in the mathematics of the Wheeler-DeWitt equation and general relativity. He's not making a metaphysical or spiritual argument — he's following the physics to what he thinks is its logical conclusion.

Where they connect and what remains unresolved

Both the Wheeler-DeWitt approach and Barbour are pointing at the same underlying strangeness — that time as a fundamental ingredient of reality may be like the caloric (the old notion of heat as a fluid) or the luminiferous ether. A useful fiction at the scale where we live, but not a real feature of the deepest level of physics. Something that emerges at a certain scale of complexity, just as temperature emerges from the statistics of many particles, or as your "switching rules" emerge at thresholds of complexity.

Lee Smolin, another physicist who writes accessibly, disagrees sharply with Barbour and argues in his book Time Reborn that time is the most fundamental thing there is — that the timeless picture is deeply wrong and that physical laws themselves evolve in time. It's a genuine, unresolved scientific and philosophical argument between serious thinkers.

Carlo Rovelli's The Order of Time is perhaps the most beautifully written recent treatment of all of this — he arrives at a view somewhat like Barbour's but approached from loop quantum gravity, and the book is almost literary in its quality. He argues that time as we experience it is made of three separate things — the directionality given by entropy, the "flow" given by our blurred thermal perception of the world, and the present moment — and that when you strip each of these away carefully, nothing remains that we would recognise as time. It dissolves. What remains is a network of events and relations between them, with no master clock, no universal now, no river moving in any direction.

Barbour's The End of Time and Rovelli's The Order of Time together would give you a profound and beautiful exploration of everything we've been discussing — and they sit very naturally alongside the Asimov essay sensibility you started with. Both are written for the curious non-specialist and both will genuinely alter how you think about what it means to exist in a moment.