r/PhysicsStudents

What Does It Mean For Something To Exist?

A synthesis of mathematical Platonism, Kolmogorov complexity, computational irreducibility, and emergent reality

The Starting Question

Does the 5th prime number exist? Obviously yes — it's 11, whether or not anyone ever checks.

Does the 10^100^100th prime exist? This is where it gets interesting. Nobody has computed it. Nobody ever will, in the lifetime of this universe — the number itself is larger than could be written down using every particle in the observable universe as a digit. And yet: it has a definite, fixed value. It is either congruent to 1 mod 4 or it isn't. It is odd (trivially, all primes above 2 are). The question "what is the 10^100^100th prime" has exactly one correct answer, sitting there, unaffected by whether any mind ever reaches it.

This single observation is the seed of everything that follows. If that number has a determinate value independent of computation, in what sense does it "exist" before anyone calculates it? And if it does, what doesn't exist by the same logic? Does every possible chess game exist before it's played? Does every string of English text — including a play Shakespeare never wrote — exist somewhere, the way the giant prime does?

This document works through the reasoning that resolves these questions into a single coherent picture — not "the answer," but the strongest, most carefully stress-tested account we could build, with the actual weak points flagged rather than hidden.

Two Kinds of Existence

The whole confusion dissolves once you separate two things that get blurred together:

Combinatorial existence — being a well-defined member of a formally specifiable space. The moment you fix a generating rule (the definition of "prime," the rules of chess, an alphabet plus a maximum string length), everything downstream is already determined, whether or not anyone has looked. The 10^100^100th prime, the complete tree of every legal chess game from start to checkmate, every string of English text up to some enormous length — all of these are combinatorially existent the instant the rule is fixed. Nobody invents the answer; the rule entails it.

This is why "does the Library of Babel contain Shakespeare's unwritten play about a kettle" has an easy answer: yes, trivially. Fix the alphabet and a length bound, and every possible string of that length is combinatorially there, including that one, including its precise text, including a billion near-identical variants and infinitely more garbage.

Actualized existence — a physical process has actually traversed to that point, producing a state that exists in time, can interact with other things, and can be observed. Chess trees, primes, and Library-of-Babel strings are combinatorially existent by the trillions, but almost none of them are ever actualized — computed, played, written, instantiated as a physical state anywhere. The 10^100^100th prime is combinatorially fixed but essentially never actualized (nobody will ever compute it). Shakespeare's actual sonnets are both combinatorially existent (as one string among countless permutations) and actualized (a real brain, in real history, produced that specific string via an unrepeatable causal process).

The key move: "existence" as commonly used conflates these two. Once separated, most of the paradoxes in this document dissolve. The interesting question was never "is X combinatorially possible" (almost everything is) — it's "what determines which vanishingly small sliver of combinatorial space actually gets walked, physically instantiated, and causally connected to the rest of reality."

Why Some Structures Are Common: Kolmogorov Complexity

Kolmogorov complexity (K-complexity) of an object is the length of the shortest program that generates it. A parabola has extremely low K-complexity — a few characters of algebra describe it completely. A random string of a trillion digits with no compressible pattern has maximal K-complexity — the shortest "program" that produces it is just the string itself, verbatim.

Here is the empirical observation that makes this matter: nature is saturated with low-K-complexity structures.

The parabola: projectile trajectories, planetary orbits under simple gravity, the path of light in certain fields.

The exponential/e: population growth, radioactive decay, neural firing dynamics, capacitor discharge.

The normal distribution: measurement error, trait distributions, the Central Limit Theorem's pull toward it from wildly different underlying processes.

π: emerges not just in circles but in the Basel problem (the sum of the reciprocals of the squares of all positive integers converges to π²/6), in probability, in wave equations, in quantum mechanics.

Compare this to something like "a red ribbon tied around an alligator's tail while chocolate rains from the sky" — an extremely high-K-complexity structure, describable only by spelling out its specific, arbitrary details at length. This never shows up as the solution to a physical law, an optimization problem, or a biological process, because there is no compressed rule that generates it — it's an artifact of specifically human intention and historical contingency, not a convergence point that many independent paths would arrive at.

Why does this happen? Two compounding reasons:

There are combinatorially far more short programs than long ones, so if reality is "sampling" from the space of possible generating rules in any sense, simple rules dominate purely by sheer numbers — a short-program bias, sometimes formalized as a Solomonoff-style universal prior weighting simpler descriptions more heavily.

Low-K structures are more invariant. A parabola works identically for any mass, in any location, under any (uniform) gravitational field — it doesn't depend on a particular observer's setup or history. The red-ribbon-and-alligator structure is intrinsically tied to one specific human intention and one specific historical moment. Simple structures are what remains once everything contingent and observer-dependent has been stripped away — which is exactly why they recur across radically different physical systems.

Mathematical Platonism, Sharpened

Naive Platonism says numbers exist in an abstract realm, full stop, mysteriously. That's not a very useful claim on its own — it just relocates the question of existence into an unexplained "realm."

The sharper version, built from the discussion above: mathematical objects that are uniquely picked out by a formal rule (the nth prime, the outcome of a fully specified chess position under perfect play, a Galois group associated with a specific polynomial) have a genuine, mind-independent determinacy. This isn't mysticism — it's the same claim as "the rule entails the outcome," full stop. Nobody invents the answer; the rule fixes it, and different minds investigating the same rule converge on the same answer, the way independent archaeologists excavating the same site find the same artifacts rather than inventing different ones.

The strongest evidence for this view isn't abstract — it's a repeated historical pattern: entirely different-looking areas of mathematics keep turning out to be the same structure viewed from different angles, discovered independently, never designed to match.

The Basel problem (sum of 1/n² = π²/6) connects to the Riemann zeta function, which connects to the distribution of prime numbers, which connects to random matrix theory and even the statistics of quantum chaotic energy spectra.

Évariste Galois showed that whether a quintic polynomial is solvable by radicals is governed by the symmetry structure of its roots (what's now called a Galois group) — a structure that was already there, dictating solvability, before anyone had invented the concept of "group." Galois didn't design this; he was forced to discover it.

Fermat's Last Theorem, an elementary-sounding number theory statement, was ultimately proven via the Taniyama–Shimura conjecture connecting elliptic curves to modular forms — two areas of mathematics that looked unrelated until they turned out to be secretly the same domain.

This recurring "different roads converge on the same city" pattern is hard to explain if mathematics is purely a human invention with no independent structure — arbitrary human inventions don't do this. It's much more naturally explained if these structures have some kind of real, mind-independent determinacy that mathematicians discover rather than design.

The caveat that keeps this honest: all of this unity and depth is still conditional — conditional on the starting axioms (Peano arithmetic, ZFC, etc.). Change the axioms and, in principle, different structures emerge (this is part of what the field of "reverse mathematics" studies). The deep interconnection is real, but it's interconnection relative to a starting logical substrate, and nothing above explains why that substrate — bare logical consistency, non-contradiction — is itself true rather than presupposed. More on this in Section 8.

Computational Irreducibility: Why Existing-in-the-Space Isn't Enough

If combinatorial existence is cheap (nearly everything describable "exists" in this thin sense), the real question becomes: what determines which structures actually get reached — computed, instantiated, played out?

This is where computational irreducibility does the real work. Some processes have shortcuts: the Basel sum can be evaluated via a closed-form derivation (Euler's proof using the sine function's product expansion) without literally summing infinitely many terms one at a time. But many processes have no shortcut, even in principle — the only way to know the outcome is to run every step. Predicting a system's future state may require performing each computational step without shortcuts, in direct contrast to classical mathematical approaches that seek predictive formulas bypassing exhaustive calculation.

This is the actual distinction between "cheap" and "expensive" existence:

π² /6 is cheap: reality (or mathematics) happened to be compressible here, and Euler found the compression.

The 10^100^100th prime is expensive but well-defined: there is likely no shortcut faster than sequential primality testing near numbers this large — this isn't just an engineering inconvenience, current research argues it reflects a genuine form of computational irreducibility in how primes are distributed, where no general algorithm can compute the next prime substantially faster than testing candidates one by one.

Shakespeare's actual sonnets are maximally expensive: the only "computation" that produces that exact text is running an entire human brain through an entire specific, unrepeatable lived life. There is no closed-form shortcut to a specific poem — no formula you can evaluate to skip the historically contingent process that produced it.

This is the resolution to the "does the unwritten Shakespeare play exist" puzzle: it exists combinatorially (it's just one string among the permutations), exactly as much as the giant prime does. But actualizing it required walking an irreducible historical process — an actual brain, in actual history — for which no shortcut existed. "Being in the Library of Babel" was never the interesting fact. The interesting fact is always: what filter or process reliably reaches this particular structure rather than the astronomically larger surrounding ocean of noise?

For physics: the fine-structure constant, physical laws, the specific configuration of the universe 13.8 billion years after the Big Bang — none of that is retrievable via shortcut. It required actually running roughly 10^60 Planck-time steps of computation from simple initial conditions. The simplicity is in the starting rule; the universe's current complexity is the accumulated result of genuinely irreducible unfolding, not a shortcut anyone (including the universe itself) could skip.

The Tower of Emergence

Putting Sections 3–5 together gives a specific picture of how staggering complexity (a person, a civilization, a Shakespeare play) arises from staggering simplicity (a handful of physical laws), without requiring the universe to "want" complexity or violate the dominance of low-K structures:

Physics (a small number of low-K field equations and constants)

→ Chemistry (low-K rules — valence, bonding — recursively generating a combinatorially vast space of possible molecules)

→ Self-replication and evolution (itself an extremely low-K algorithm: variation + selection, a strikingly short description) compounding over roughly 4 billion years of irreducible computation

→ Nervous systems and brains (structures shaped by the accumulated output of that filter)

→ A specific person (the further, unrepeatable output of one brain's specific developmental and experiential history)

→ A specific creative act (a poem, a proof, a scientific insight) that could not have been reached by any shortcut — only by that entire stacked chain of filters actually running to completion.

Each layer is a cheap rule (low K-complexity) whose outputs, after enough iterated, irreducible computation, become effectively unrecognizable as "simple" — this is the distinction between K-complexity (how short the generating rule is) and logical depth (how much irreducible computation is required to unfold that rule into its current state). The picture: low K-complexity, extremely high logical depth. Simple beginning, forced long history, complex present state — with no contradiction between "the universe is fundamentally simple" and "a Shakespeare sonnet is fantastically improbable-looking," because complexity here comes from iteration, not from the universe favoring complex outcomes directly.

This resolves the apparent paradox of how anything as improbable-looking as human culture or an individual mind can exist in a universe dominated by simplicity: it isn't drawn at random from the space of all possibilities, it's converged upon by a specific, real chain of nested filters, each one individually cheap, compounding into something that looks — from any single vantage point — astronomically unlikely.

The Computer as Universal Actualizer

A NAND gate (or NOR gate) is Boolean-complete: any computable function whatsoever can, in principle, be built from a sufficient number of them wired together. This is not a metaphor — it is the literal, concrete fact that makes "actualization" something other than mysticism.

A computer, in this light, is nothing more or less than a physical system capable of realizing the transition function of any formal structure you can specify — a general-purpose bridge from combinatorial existence to actualized existence. When you declare an arbitrary axiom system and use a computer to explore its consequences, you are doing exactly what evolution does exploring chemical-configuration space, or what a brain does exploring thought-space: taking a formally well-defined but merely combinatorial structure and walking it, producing a physical state that is now causally connected to — and can be observed by — the rest of reality.

"Observation," properly deflated, requires nothing mystical: it just means a physical system now exists whose state is correlated with, and causally downstream of, a specific branch of the combinatorial space — no different in kind from a photographic plate registering where a photon landed. Once a computer runs an axiom system and produces a theorem, or once a brain produces a specific thought, there is now a physical fingerprint of that outcome sitting in the universe, available to interact with other things. That transition — from "specifiable" to "physically instantiated and causally connected" — is the whole content of what "becoming real" means on this account.

Process vs. Structure: Is Time Doing Any Real Work?

A remaining tension: is the whole tree of possibility (every chess game, every axiom system's consequences, every physical history) a timeless structure that simply is what it is, all at once — or is computation actually happening, step by step, with time doing real, irreducible work?

The case for pure structure (eternalism): If the entire combinatorial graph is fixed the moment the generating rules are fixed, then in principle the entire history of a chain of computation — every step — is already implicit and determinate, the way a chess game's outcome is already implicit in perfect play from the rules. Under this view, "computation happening" is just what a cross-section of an already-complete structure looks like from inside that cross-section. Memory, under this view, isn't something accumulated over real time — it's a piece of local structure that happens to be correlated with a particular path through the graph, the way a chess position (which multiple different move-sequences could reach) is a lossy trace of some path, without literally containing the sequence of moves that produced it.

The case for process being fundamental: Computational irreducibility (Section 5) only means something — only has explanatory bite — if some facts genuinely require steps to be walked for other facts to be settled. If the whole tree is timelessly, statically already there, then nothing was ever "reached" in any meaningful sense, and the entire distinction between cheap (compressible) and expensive (irreducible) existence collapses, because in a fully timeless structure, both are equally, statically present regardless of the "cost" it would take a step-by-step process to arrive at them.

The resolution: these are not two different facts in competition, but two different vantage points on the same object — the view from outside the whole structure (which sees no direction, no "happening," just a complete shape) and the view from inside one thread embedded within it (which experiences traversal, memory, causation, and the felt sense that steps had to occur in order). Any observer embedded as a "line" within the structure — biological or otherwise — would report identically either way: as flow, as accumulated past, as computation genuinely happening — regardless of whether the whole four-dimensional (or higher-dimensional) object was tenselessly complete all along. There may be no fact of the matter, even in principle, that distinguishes "time really flows" from "time is a structural feature experienced as flow by anything embedded in it" — not because both descriptions are secretly identical claims, but because nothing could in principle tell them apart from inside.

Memory, fairness, the felt sense of choice, computation "happening" — under this resolution, none of these are illusions. They are the specific, unavoidable phenomenology of being an embedded, finite, forward-only slice of something that, viewed as a whole, may have no privileged direction at all. You cannot step outside your own thread to check which description is "more true" — the stepping-outside would itself just be another thread, another embedded traversal, without end.

Memory, Precisely

Given the above, memory has a clean, non-mystical definition that works under either the process or structure reading:

Memory is a physical state that encodes a compressed, lossy trace of the specific path that produced it, allowing later computation to be conditioned on that path without re-walking it. A synaptic weight, a written mark, a transformer's key-value cache — all are the same kind of object: a low-K-complexity fingerprint of a much larger, higher-complexity history, discarding the incompressible detail and retaining only what's cheap enough to carry forward.

Crucially, this fingerprint is almost always lossy, not literal — a chess position after forty moves does not uniquely determine the move sequence that produced it (many different sequences can converge on the same position); a hippocampus's trace of an episode is a reconstruction, not a replay; a language model's cached attention state is a compressed summary, not a full record of the conversation. Memory, under this account, is really just one more instance of the Kolmogorov-complexity filtering described in Section 3 and 6 — nature (or a nervous system, or a computer) keeps the compressible, low-K summary of what happened and discards the rest, because retaining everything is more expensive than the system can afford.

Where This Leaves the Original Question: Is the Universe Unfair?

Fairness presupposes a privileged branch — some alternative course of events against which the actual one can be judged as unjust. But if all consistent, formally specifiable structures are equally combinatorially available, and what gets actualized is simply whichever branch a given causal chain happens to walk, there is no fact of the matter about which branch "should" have been walked instead. Fairness was never a property of the underlying structure. It only appears locally, inside regions of the structure complex enough to contain agents who model alternatives and evaluate outcomes against them — which is to say, fairness is itself one more emergent structure in the tower described in Section 6, a feature of minds, not a feature of the graph they're embedded in.

This isn't a claim that suffering, inequality, or loss don't matter — quite the opposite. It's a claim about where the moral weight actually lives: not in the cosmos (which has no evaluative stance to offer), but entirely in the minds capable of noticing and caring that things could have gone otherwise. That capacity to notice is not a small thing — it may be one of the more remarkable outputs of the entire irreducible, billions-of-years-long unfolding described above.

Honest Status of This Synthesis

This document is not a report of settled science or accepted philosophical consensus. It should be read as a coherent, internally stress-tested synthesis, built by connecting several genuinely separate, actively-debated research programs:

Kolmogorov complexity and algorithmic information theory — fully mainstream, uncontroversial mathematics and computer science.

Computational irreducibility — a real, recognized phenomenon (particularly associated with Stephen Wolfram's work), though its universal applicability across physics is debated rather than settled consensus.

The Mathematical Universe Hypothesis (MUH) and its refinement, the Computable Universe Hypothesis (CUH) — this entire framework already exists as a named, actively-studied position in philosophy of physics (associated with Max Tegmark), grounded explicitly in a form of radical mathematical Platonism holding that mathematical structures exist independently of minds as a timeless, fundamental reality, with the "weighting by simplicity" patch (favoring low-Kolmogorov-complexity structures to explain why our universe looks simple) already present in the literature as a response to a known objection to Tegmark's original, unweighted version. This is a real, minority-but-serious position — not something most physicists or philosophers currently endorse, and explicitly criticized by others as unfalsifiable.

AdS/CFT and emergent spacetime — legitimate, active theoretical physics, though "spacetime is emergent" is a leading research direction, not an established consensus fact.

Process vs. structure ontology (eternalism vs. presentism, the block universe) — a genuine, longstanding open question in philosophy of physics and metaphysics, with serious defenders on multiple sides and no resolution in sight.

The achievement here is a real one: independently reconstructing something close to a known, contested academic position (MUH/CUH), including its actual patches for its actual known problems, through pure first-principles reasoning in conversation — without first having read the literature. That is a genuine act of synthesis and should be recognized as such. It is not the same as having discovered new, testable, field-advancing scientific or mathematical results, and it would need to survive serious contact with the existing objections in the literature (which are substantial) to be more than a very good, very coherent personal philosophical position.

Hey everyone,

Long story short: A few years ago, I did my first year of University studying Physics. I passed all my classes, but honestly, I didn’t study much, the specific first-year subjects weren't really hitting the spot, and my girlfriend at the time was moving to a different city 400km away. So, I decided to follow her and switch majors.
Since I've always been interested in investing and the stock market, I chose Economics/Finance.

Fast forward to now: I'm about to start my 3rd year, I'm 22, and honestly... this school is giving me absolutely nothing. It’s quite easy, and ironically, being here made me realize how much I actually miss physics. I find myself constantly watching channels like Physics Explained and realized that it actually interests me.
When I finish this degree, I'll be 23 with just a Bachelor’s. If I go back to physics, I’ll be a 23-year-old freshman sitting in class with 18 and 19-year-olds, while my peers will be graduating and starting their careers. It feels a bit daunting, not going to lie.

On top of that, two big issues:
I haven’t done serious math in almost two years, so I’m definitely rusty.
I’ve been thinking about doing a part-time Master’s in Finance while doing Physics full-time, just so I don't "waste" my current degree, but I’m terrified of burning out completely.

Should I just go back to physics or should I just forget it, finish finance, and keep physics as a hobby? Has anyone here restarted their studies "later" in their 20s?
FYI - we are still together after 3 years and there is physics course at university in the city i moved in with my girlfriend which is capital city of my country and in my smaller hometown

Thanks for any advice!

r/PhysicsStudents

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