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Main positions:Director, High Performance Computing Platform, PKU
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School/Department:Institute of Theoretical Physics

Lei Yian

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Education Level: Postgraduate (Doctoral)

Administrative Position: Associate Professor

Alma Mater: Peking University

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The Problem of the Spectral Picture: Magnetism Missing
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Introduction: A Fundamental Oversight

In the grand edifice of physics, quantum mechanics is celebrated as one of the greatest intellectual achievements of the twentieth century. It successfully predicted atomic spectra, explained the nature of chemical bonds, and catalyzed the semiconductor revolution. Yet behind this brilliance lies a little-known but profoundly significant issue: quantum mechanics has omitted magnetic energy from its theoretical framework.

This is not a minor technical oversight but a conceptual flaw that strikes at the very foundation of quantum theory. A careful examination of the mathematical structure of quantum mechanics reveals that this so-called "complete" theory cannot naturally express one of the most basic concepts in classical physics—the energy stored in magnetic fields. To conceal this deficiency, theoretical physicists have constructed an elaborate conceptual scaffolding: spin, fermions, exchange interactions, and so on. These seemingly profound quantum notions are, in essence, theoretical patches designed to compensate for the missing magnetic energy.

Chapter 1: The Classical Picture of Magnetic Energy

What is magnetic energy?
In classical electromagnetism, magnetic energy is both simple and profound. When electric current flows through a wire, a magnetic field is established in the surrounding space, and this field stores energy. The magnetic energy density is given by the elegant formula:

u = B^2 / (2 mu_0)

where B is the magnetic field strength and mu_0 is the vacuum permeability. This formula tells us that stronger fields store more energy, and this energy is physically present throughout space.

Consider a simple experiment: when two like magnetic poles are brought close together, work must be done against the repulsive force. Where does this work go? It is converted into magnetic field energy stored in the space between the magnets. Upon release, the magnets fly apart, converting that stored energy back into kinetic energy. Throughout this process, energy conservation holds perfectly.

Spatial distribution of magnetic energy
The defining feature of magnetic energy is its spatial distribution. Unlike kinetic energy (associated with particles) or potential energy (associated with positions), magnetic energy permeates all of space. One can compute the energy density at any point and integrate over any volume to obtain the total magnetic energy. This continuous spatial distribution is intrinsic to magnetic phenomena.

Take a current-carrying loop as an example. The magnetic field it generates extends not only inside the loop but throughout the surrounding space, decaying with distance but theoretically reaching to infinity. This nonlocal energy distribution is perfectly described in classical physics by Maxwell’s equations.

Interaction between magnetic dipoles
The interaction energy between two magnetic dipoles can be precisely calculated:

U = -(mu_1 · mu_2) / r^3 + 3 (mu_1 · r_hat) (mu_2 · r_hat) / r^3

This expression not only gives the strength of the interaction but also its directional dependence. Parallel alignment yields the lowest energy (attraction), while antiparallel alignment yields the highest (repulsion). This interaction is mediated by the magnetic field in space, providing a clear physical picture.

Chapter 2: The Spectral Nature of Quantum Mechanics

From time domain to frequency domain
The revolutionary aspect of quantum mechanics lies in its adoption of a new descriptive framework: spectral representation. The Schrödinger equation essentially solves for the eigenfrequencies and eigenmodes of a system. When we solve it for the hydrogen atom, we obtain a set of discrete energy levels—these are the system’s resonant frequencies.

This approach is analogous to analyzing the sound of a musical instrument. The sound of a violin can be decomposed into a fundamental frequency and various overtones, each with specific amplitude and phase. Quantum mechanics does precisely this for atoms: it decomposes electron motion into different "vibrational modes" in frequency space.

Advantages and costs of spectral representation
The spectral method is extremely powerful for periodic phenomena. Atomic spectra, selection rules for transitions, and chemical bonding all become transparent in this picture. However, this representation comes at a cost.

Lost information includes:

  • Instantaneous position: only probability distributions remain

  • Orbital trajectories: replaced by probability clouds

  • Spatial energy density: reduced to abstract expectation values

  • Most critically—the spatial distribution of magnetic fields

When a classical system is transformed into the frequency domain, all local spatial information is "smeared out." Just as a Fourier transform of an image yields frequency components but erases object positions and shapes, so too does quantum mechanics lose the spatial structure of fields.

Wave function: probability or physical reality?
Quantum mechanics describes a system by a wave function Psi, with |Psi|^2 interpreted as a probability density. However, Psi is complex-valued, and its phase carries essential physical information. Crucially, the wave function cannot directly represent magnetic fields. Magnetic fields are vector fields with direction and magnitude, whereas the wave function is a scalar (for spinless particles) or a spinor (for particles with spin).

This representational mismatch is the root cause of quantum mechanics’ inability to naturally incorporate magnetic energy. In classical theory, the electric field E and magnetic field B are equally fundamental components of the electromagnetic field tensor. In quantum mechanics, however, the scalar potential can be coupled into the Schrödinger equation via gauge coupling, while the magnetic field enters only indirectly through the vector potential A—and even then, it suffers from the arbitrariness of gauge choice.

Chapter 3: Spin—A Misunderstood Concept

The forced introduction of spin
The 1922 Stern–Gerlach experiment showed that a beam of silver atoms splits into two when passed through an inhomogeneous magnetic field. This could not be explained by orbital angular momentum, as the valence electron of silver resides in an s-orbital (L = 0). Physicists were thus compelled to introduce a new concept: spin.

But what is spin? Textbooks describe it as "intrinsic angular momentum" with no classical counterpart. This explanation is, in effect, an admission: we do not know the physical origin of spin; we can only describe its behavior with mathematical operators.

Spin and magnetic moment
Electron spin generates a magnetic moment:

mu = -g (e / 2m) S

where g ≈ 2 is the so-called g-factor. Why is it approximately 2? The standard answer is: "This is predicted by the Dirac equation." But deeper analysis reveals that this result arises from choosing a specific mathematical structure to fit experimental data.

If spin corresponded to actual physical rotation, classical electromagnetism would require g = 1. The fact that g ≈ 2 implies an "anomalous" magnetic moment—suggesting either an unusual charge distribution or an unconventional mode of motion. This hints that spin may correspond to some internal dynamics not yet understood.

The nature of spin: spectral feature or physical reality?
From a spectral perspective, spin-1/2 might simply be a frequency-domain signature of some underlying periodic motion. The Zitterbewegung ("trembling motion") predicted by the Dirac equation—oscillations at frequency 2mc^2 / hbar—offers a clue: the electron may undergo ultra-high-frequency oscillations. These are averaged out in macroscopic measurements, leaving only their spectral imprint—manifested as spin.

If this picture is correct, then spin is not fundamental but emergent. It is the spectral representation of internal electron dynamics (possibly involving magnetic fields). Because quantum mechanics sees only the spectrum, it must postulate spin as a primitive concept.

Chapter 4: Exchange Interaction—A Substitute for Magnetic Energy

The dilemma of the Heisenberg model
To explain ferromagnetism, Heisenberg proposed the exchange interaction model:

H = -J sum_{i,j} S_i · S_j

where J is the exchange integral. For J > 0, spins align parallel (ferromagnetism); for J < 0, they align antiparallel (antiferromagnetism).

But what is the physical meaning of J? The standard explanation is "it arises from the exchange symmetry of the wave function"—a purely quantum notion with no classical analog. Worse, J cannot be calculated from first principles; it must be fitted to experimental data.

Exchange interaction vs. magnetic dipole interaction

Classical magnetic dipole interaction Quantum exchange interaction
Clear physical picture (field-mediated) No intuitive image
Derivable from first principles Requires empirical fitting
Includes spatial dependence (1/r^3) Often limited to nearest neighbors
Direction-dependent Reduced to scalar coupling

Clearly, exchange interaction is a crude phenomenological model that obscures the true physical mechanism—magnetic field interaction.

Proliferation of "exchange" mechanisms
To account for diverse magnetic phenomena, physicists have invented an ever-growing list of exchange mechanisms:

  • Direct exchange: orbital overlap

  • Superexchange: via intermediary ions

  • Double exchange: electron hopping

  • RKKY interaction: via conduction electrons

  • Dzyaloshinskii–Moriya interaction: antisymmetric exchange

Each requires its own model and parameters. This "baroque" proliferation of theories suggests we may have strayed from the right path. In the classical picture, all these could be unified as manifestations of magnetic interactions under different conditions.

Chapter 5: Fermions—An Unnecessary Concept?

Introduction of Fermi statistics
To explain the Pauli exclusion principle, quantum mechanics introduced Fermi–Dirac statistics: particles with half-integer spin (fermions) must have antisymmetric wave functions. No two electrons can occupy the same quantum state, explaining atomic shell structure and the periodic table.

But why do such statistics exist? The standard answer—"It is a fundamental law of nature"—is no explanation at all.

Classical explanation via magnetic repulsion
From a classical electromagnetic perspective, two electrons with aligned spins possess parallel magnetic moments. According to dipole–dipole interaction, such moments can repel in certain configurations. If electrons indeed undergo internal motion that generates magnetic moments, then magnetic repulsion could naturally prevent them from occupying the same spatial region.

In other words, the Pauli exclusion principle might be the quantum manifestation of magnetic repulsion. Fermi statistics may not be fundamental but rather the spectral representation of magnetic interactions.

Statistical rules vs. dynamical principles
Quantum mechanics replaces dynamical laws (forces and interactions) with statistical rules (Fermi/Bose statistics). This substitution appears elegant but conceals physical mechanisms:

Dynamical description Statistical description
Particles interact via fields Particles obey abstract statistics
Forces cause motion changes Symmetry dictates allowed states
Energy conservation determines stability Probability distributions determine outcomes

The former offers clear causality; the latter provides only formal rules. By accepting the concept of fermions, we effectively abandon the search for physical mechanisms.

Chapter 6: Quantum Electrodynamics as a Patch

The "success" and problems of QED
Quantum electrodynamics (QED) is hailed as the most precise theory in physics, predicting the electron’s magnetic moment to agreement with experiment at the level of 10^{-12}. But how is this precision achieved?

The answer is renormalization. QED calculations yield infinities, and physicists developed a procedure to remove them. While mathematically consistent, the physical meaning remains obscure. Even Feynman admitted: "Renormalization is suspect from a mathematical standpoint."

Vacuum fluctuations: fiction or reality?
QED attributes the deviation of g from 2 (the "anomalous magnetic moment") to vacuum fluctuations: the electron continuously emits and absorbs virtual photons and interacts with virtual particle–antiparticle pairs. These "quantum corrections" yield the observed tiny deviations.

But do virtual particles truly exist? They violate energy conservation (albeit within the bounds allowed by the uncertainty principle), cannot be directly observed, and are inferred only through their "effects." This resembles a computational trick rather than a description of physical reality.

The dilemma of field quantization
To incorporate magnetic fields into quantum theory, physicists developed quantum field theory (QFT). The electromagnetic field is quantized into photons, and magnetic interactions become photon exchanges. But this raises conceptual difficulties:

  • How to describe static magnetic fields with photons? Photons propagate at light speed, yet static fields are time-independent. The standard answer—"virtual photons"—reintroduces the problem of unobservable entities.

  • Coulomb vs. Lorentz gauge: Different gauge choices yield different physical pictures, revealing a lack of uniqueness in the theory.

  • Non-perturbative effects: Strong-field physics cannot be described by perturbation theory, limiting QED’s domain of validity.

Chapter 7: Reinterpreting Experimental Evidence

Stern–Gerlach experiment
Standard interpretation: Demonstrates quantization of spin.
Alternative interpretation: If the electron possesses an internal current loop, it would experience torque in an inhomogeneous field. Only two stable orientations (parallel or antiparallel to the field) would be energetically favored, splitting the beam into two—without invoking abstract spin.

Anomalous Zeeman effect
Standard interpretation: Fine structure due to spin–orbit coupling.
Alternative interpretation: Internal motion (generating magnetic moment) couples to orbital motion, analogous to classical magnetic gyroscope precession. Fine structure may reflect resonant frequencies of this coupling.

EPR correlation experiments
Standard interpretation: Quantum entanglement and nonlocality.
Alternative interpretation: If two particles are linked via magnetic fields (which extend throughout space), measuring one could influence the other through the field. In the spectral representation, this appears as instantaneous correlation, but in spacetime it may involve causal propagation.

Chapter 8: Directions for Theoretical Reconstruction

Attempts to restore magnetic energy
One possible path is to explicitly include magnetic energy in the quantum framework:

H = H_0 + integral (E^2 / 2 epsilon_0) d^3r + integral (B^2 / 2 mu_0) d^3r

This requires unified treatment of electromagnetic fields and particle wave functions. Some approaches include:

  • Schrödinger–Maxwell equations: Coupling Schrödinger and Maxwell equations, though self-consistency remains challenging.

  • Stochastic electrodynamics (SED): Assumes a classical zero-point electromagnetic field; explains some quantum phenomena but remains incomplete.

  • de Broglie–Bohm theory: Retains particle trajectories, allowing more natural inclusion of magnetic interactions.

Beyond spectral representation
Another direction is to develop frameworks that transcend pure spectral description:

  • Time–frequency hybrid representations: Preserve both temporal and spectral information (e.g., wavelet transforms), potentially retaining magnetic energy’s physical meaning while preserving quantum predictions.

  • Geometric dynamics: Treat particles as excitations of spacetime geometry, with magnetic fields as geometric structures—possibly unifying quantum and gravitational physics.

  • Hydrodynamic analogies: Model quantum systems as "fluids," with spin as vorticity and magnetic fields as flow fields—offering intuitive physical pictures.

Suggestions for experimental tests
If quantum mechanics indeed omits magnetic energy, testable consequences should exist:

  • Energy anomalies in strong magnetic fields: Systematic deviations between quantum predictions and experiment may emerge.

  • Energy balance in magnetic materials: Precise calorimetry during magnetic phase transitions might reveal unaccounted energy.

  • Magnetic effects in mesoscopic systems: At scales between classical and quantum, phenomena unexplained by current theory may appear.

Chapter 9: Philosophical Reflections

Mathematical formalism vs. physical reality
Much of quantum mechanics’ success stems from its mathematical elegance. We possess precise computational rules that yield experimentally verified results. But what physical reality do these mathematical objects (wave functions, operators, state vectors) represent?

When we replace magnetic moments with spin operators, and magnetic forces with exchange interactions, are we describing nature—or constructing an elegant mathematical model? Predictive power does not guarantee ontological correctness.

Violation of the principle of simplicity
Occam’s razor demands theoretical parsimony. Yet quantum mechanics, to avoid magnetic energy, has introduced a host of auxiliary concepts:

  • Spin (instead of magnetic moment)

  • Fermions/bosons (instead of particles)

  • Exchange interaction (instead of magnetic force)

  • Virtual particles (instead of fields)

This conceptual inflation suggests we may have taken a wrong turn. A truly fundamental theory should be simpler and more unified.

Loss of intelligibility
As Feynman remarked: "Nobody understands quantum mechanics." This incomprehensibility may stem precisely from the omission of a key physical element—magnetic energy. When a theory drifts too far from physical intuition, it becomes a mere computational tool, losing its power to explain and understand nature.

Conclusion: The Necessity of a Paradigm Shift

The true limitation of quantum mechanics
The problem with quantum mechanics is not inaccuracy of predictions, but a fundamental flaw in its theoretical framework. As a spectral analysis tool, it is inherently incapable of representing spatially distributed magnetic energy. All "quantum magnetism" theories are patches built upon this foundational deficiency, not genuine solutions.

This realization compels us to reconsider:

  • Is quantum mechanics a final theory, or an approximation under specific conditions?

  • How much of "quantum behavior" is real, and how much is a mathematical artifact?

  • How can we construct a theory that preserves quantum successes while naturally incorporating magnetic energy?

The dialectics of scientific progress
History shows that major advances often arise from critical scrutiny of "successful" theories. Newtonian mechanics reigned for two centuries, yet relativity and quantum theory revealed it as an approximation. Similarly, quantum mechanics’ success should not deter us from probing its limits.

Recognizing that "quantum mechanics has lost magnetic energy" may be the seed of the next physics revolution. It reminds us to:

  • Avoid being mesmerized by mathematical formalism

  • Always seek physical essence

  • Maintain critical thinking

Future directions
Moving beyond quantum mechanics requires courage and imagination. Potential breakthroughs may come from:

Theoretical innovation:

  • Developing quantum theories that explicitly include magnetic energy

  • Unifying spacetime and spectral descriptions

  • Discovering more fundamental physical principles

Experimental exploration:

  • Testing quantum predictions under extreme conditions

  • Searching for evidence of "lost" magnetic energy

  • Developing novel measurement techniques

Conceptual revolution:

  • Re-examining foundational concepts

  • Questioning "sacred" assumptions

  • Returning to physical intuition

Final reflection
That quantum mechanics has lost magnetic energy reveals a profound paradox in human understanding of nature: we can construct astonishingly successful mathematical models while missing the most basic physical realities. This should instill humility—even our most successful theories may harbor fundamental blind spots.

The future of physics may not lie in refining the existing framework, but in identifying and correcting these deep conceptual flaws. By courageously acknowledging that "quantum mechanics has lost magnetic energy," we take a crucial step toward a deeper understanding of nature.

As Einstein said: "God does not play dice." Perhaps, once we recover the missing magnetic energy and understand the true nature of spin and fermions, we will find that the "probability" and "uncertainty" of the quantum world are merely artifacts of our spectral perspective—and that nature still obeys deterministic, intelligible laws, only more subtle and beautiful than we imagined.

This is the true wonder of science: every discovered problem may be the gateway to a deeper truth. That quantum mechanics has lost magnetic energy may well be the key that unlocks the door to a new physics.