\documentclass[11pt]{article} \usepackage[utf8]{inputenc} \usepackage{amsmath, amssymb, amsthm} \usepackage{graphicx} \usepackage{hyperref} \usepackage{cite} \usepackage{geometry} \geometry{margin=2cm} \linespread{1.1} \setlength{\parskip}{0.5ex} \setlength{\parindent}{1.5ex} \pagestyle{plain} \newcommand{\dd}{\mathrm{d}} \hypersetup{colorlinks=true, linkcolor=black, citecolor=black, urlcolor=black} % 投稿采用黑色链接 \sloppy \emergencystretch=3em  \title{Space Field Theory: Quantum Medium as the Material Substrate of the Universe\\ \large From Vacuum Entanglement to Cosmic Horizons} \author{Runbiao Fang\\ \texttt{18025406666@163.com}} \date{May 28, 2026 (Final Definitive Version)}  \begin{document}  \maketitle  \begin{abstract} \small The universe is not an empty void. We propose that a ubiquitous, compressible, fluid, and creatable physical entity---the quantum medium---fills all space. Based on this axiom, Space Field Theory reinterprets the four fundamental forces and introduces the quantum medium threshold: when the local density compression ratio \(V_z(\mathbf{x},t)=\rho(\mathbf{x},t)/\rho_{\text{avg}}(t)\) with \(\rho_{\text{avg}}(t)=3H(t)^2/(8\pi G)\) reaches \(V_z\ge 25\), the medium enters an extremely dense state where a repulsive force emerges and light cannot propagate.  The ground state of the quantum medium is a gapped topological entangled state described by a truncated Chern-Simons-Kodama state in loop quantum gravity [1]. External perturbations (heavy-ion collisions, inflation, laser pumping) drive phase transitions, activating a fraction of the entanglement into observable particles (photons, fermions, etc.); the unactivated ground-state branch remains permanently residual. Because the current cosmic energy density lies far below the activation threshold, the universe has never been globally quenched; therefore almost all vacuum entanglement stays residual.  Using holographic arguments [9,10], this residual entanglement contributes an effective energy density \(\rho_{\text{eff}}\propto H^2\) (no independent dark energy entity exists; this effective density is a thermodynamic manifestation of residual entanglement entropy), naturally explaining the famous \(10^{120}\) discrepancy---the huge number is entropy, not energy. From horizon thermodynamics one writes the Friedmann equation \(H^2=8\pi G\rho/3\) [4-6], showing cosmic expansion emerges from thermodynamic equilibrium of the quantum medium entangled state.  The activation exponent \(\gamma\approx0.08\) extracted from RHIC data [25], combined with the Kibble-Zurek mechanism [2,3], yields \(\gamma=d_{\text{eff}}\nu/(1+\nu z)\). Taking the effective dimension for causal horizons \(d_{\text{eff}}=2\) gives \(\nu z\approx25\), characteristic of a strongly disordered many-body localized universality class [7,8,19,23].  We derive light bending from first-principles hydrostatics (no free parameters). The framework naturally explains effective dark energy, Hubble tension, CMB low-multipole suppression [15,16], missing dwarf galaxies [20,21], black hole information paradox [11,12], non-thermalization in heavy-ion collisions, and five core physical mechanisms. All conclusions are falsifiable by next-generation experiments (LHC, topological insulator Faraday rotation [13,14], CMB-S4, LSST, etc.). \end{abstract}  \section{Introduction: The 11 Core Problems} Current physics faces unresolved puzzles: \begin{enumerate} \item Vacuum energy discrepancy \(10^{120}\). \item Hubble tension (\(5\sigma\)) [15,16]. \item Missing dwarf galaxies (too few satellites) [20,21]. \item CMB large-angle power suppression (\(10\%-15\%\)) [16]. \item Black hole information paradox [11,12]. \item Lack of experimental tests of quantum gravity. \item Non-thermalization in heavy-ion collisions (\(\gamma\approx0.08\)) [25]. \item Origin of the speed of light limit. \item Why light cannot escape a black hole. \item Unified mechanism for early-universe superluminal inflation and today's superluminal recession of distant galaxies. \item Instantaneous quantum entanglement correlation. \end{enumerate} Our thesis: all these arise from a missing physical entity---the quantum medium.  \paragraph{On Lorentz invariance violation (LIV).} A possible concern is whether the quantum medium, as a physical carrier of light, implies a preferred reference frame that would be detectable by Michelson-Morley-type experiments. We take a proactive stance: special relativity is an effective low-energy approximation, and strict Lorentz invariance is expected to be broken at high energies. Indeed, observations of time delays in gamma-ray bursts from the Large High Altitude Air Shower Observatory (LHAASO) provide strong evidence for LIV [38]. In Space Field Theory, the quantum medium provides a natural hydrodynamic origin for such LIV: the local density of the medium defines a preferred rest frame, but this frame is dynamically aligned with the cosmic expansion and local gravitational fields, making it undetectable in low-energy experiments. The observed LIV emerges only at extreme energies where the medium's response becomes non-linear. This perspective transforms a potential objection into a testable prediction of the theory.  \paragraph{Why no dark matter or dark energy?} The standard \(\Lambda\)CDM model relies on undetected hypothetical particles and a fine-tuned cosmological constant. By Ockham's razor, a theory that explains all observations without introducing new entities is preferable. Space Field Theory achieves exactly this: cosmic acceleration emerges from residual entanglement entropy (no dark energy), and galactic rotation curves as well as CMB power suppression are reproduced by the effective sound speed of the quantum medium (no dark matter). Thus SFT is not merely an alternative but a more economical description of nature.  \section{Basic Axioms} We establish seven basic axioms for Space Field Theory.  \noindent\textbf{Axiom 1 (Existence)}: The universe is filled with a continuous, structured physical entity---the quantum medium. No absolute void exists.  \noindent\textbf{Axiom 2 (Compressibility and Fluidity)}: The density \(\rho(\mathbf{x},t)\) of the quantum medium varies in spacetime, and its flow satisfies continuity and an equation of state: \[ P(\rho)=P_0\left(\left(\frac{\rho}{\rho_{\min}}\right)^\gamma-1\right), \] with \(\gamma=4/3\) (relativistic) or \(\gamma=5/3\) (non-relativistic), and \(\rho_{\min}\) the minimum possible density.  \noindent\textbf{Axiom 3 (Density Compression Ratio)}: Define the local density compression ratio as \[ V_z(\mathbf{x},t)=\frac{\rho(\mathbf{x},t)}{\rho_{\text{avg}}(t)}, \] where \(\rho_{\text{avg}}(t)=\frac{3H(t)^2}{8\pi G}\) is the cosmic average density at the same cosmic time \(t\). \(V_z=1\) corresponds to the background; \(V_z>1\) indicates local compression. \(\rho_{\min}\) can be lower than \(\rho_{\text{avg}}(t)\) (e.g., in cosmic voids at late times).  \noindent\textbf{Axiom 4 (Quantum Medium Threshold)}: When the local density compression ratio reaches \(V_z\ge 25\) (empirical threshold calibrated from black hole observations at the present epoch), the quantum medium reaches its intrinsic critical point, entering an extremely dense state where (i) a short-range repulsive force resists further compression, and (ii) light waves cannot propagate. This critical compression ratio is called the \textit{quantum medium threshold}. For black holes formed in the early universe, the threshold may be redshift-dependent; the value 25 should be understood as the effective parameter for \(z\approx0\).  \noindent\textbf{Axiom 5 (Energy Gap and Topological Entanglement)}: The quantum medium is in a gapped topological entangled state; the entanglement entropy satisfies the area law \(S_{\text{EE}}=\alpha A/\ell_{\text{Pl}}^2\) [1]. This entangled state is the quantum substrate of spacetime.  \noindent\textbf{Axiom 6 (Phase Transition and Excitation)}: External perturbations (energy injection, inflation, collisions) can drive the quantum medium across phase transitions, activating a portion of its entangled state into observable particles (photons, fermions, etc.). The unactivated ground-state branch constitutes the stable background of spacetime.  \noindent\textbf{Axiom 7 (Net Creation and Constant Density)}: The quantum medium possesses intrinsic creation and annihilation dynamics. The net creation rate \(\Gamma=\Gamma_{\text{creation}}-\Gamma_{\text{annihilation}}\) always equals the cosmic expansion rate \(3H\), thereby keeping the local average density constant. Observations show that the vacuum speed of light is constant, so the average density must be constant, requiring a precise matching of the net creation rate and the expansion rate. Cosmic acceleration is driven by \(\Gamma>0\) without the need for dark energy.  \section{Medium Nature of Fundamental Forces} \subsection{Gravity: Macroscopic Density Gradient-Driven Thrust} Gravity is not a pull but a thrust from high-density medium flowing toward low-density regions. From hydrostatic equilibrium, the density distribution around a point mass \(M\) is \(\rho(r)=\rho_\infty\left(1+\frac{GM}{c^2 r}\right)\). The resulting pressure gradient force on a test mass \(m\) is \(F = -\frac{GMm}{r^2}\), matching Newtonian gravity.  \subsection{Electromagnetism: Elastic Transverse Wave of the Medium} Electromagnetism corresponds to the \(U(1)\) gauge group. Photons are elastic ripples in the quantum medium, and the interaction between charges is essentially the transfer and interference of these medium ripples.  \subsubsection{Origin of the Speed of Light Limit (Problem 8)} The speed of light in the quantum medium is determined by the medium's density: higher density gives slower light, lower density gives faster light. The quantum medium has a minimum possible density \(\rho_{\min}\) (which can be approached in cosmic voids). The speed of light as a function of density is derived from observations: light bending requires the refractive index \(n(r)=1+2GM/(c_0^2 r)\), and hydrostatic equilibrium gives \(\rho(r)=\rho_\infty(1+2GM/(c_s^2 r))\). For \(\rho_\infty\gg\rho_{\min}\) we obtain \[ v(\rho)=c_0\frac{\rho_{\min}}{\rho_{\min}+\rho},\qquad \rho\ge\rho_{\min}, \] where \(c_0=299,792\ \mathrm{km/s}\) is the speed when the medium is at its minimum density. This function satisfies \(v(\rho_{\min})=c_0\) and \(v(\rho)\to0\) as \(\rho\to\infty\). Exceeding \(c_0\) would require \(\rho<\rho_{\min}\) (emptier than vacuum), which is physically impossible. In any local inertial frame, the medium is gravitationally dragged and nearly at rest, so the speed of light is isotropic and Lorentz invariance is not violated at low energies.  \subsection{Strong Interaction: High-Viscosity Fiber Tension} The strong interaction corresponds to the \(SU(3)\) gauge group. At extremely microscopic scales, the quantum medium exhibits extremely high ``fiber tension'' and viscosity. Attempting to separate quarks is like tearing a medium structure with strong cohesion, which explains quark confinement.  \subsection{Weak Interaction: Vortex Chirality and Local Phase Transitions} The weak interaction corresponds to the \(SU(2)\) gauge group. Its essence lies in the intrinsic non-isotropy of the quantum medium---its inherent vortex chirality. Weak interactions dominate particle decay and parity violation, fundamentally being local phase transitions, annihilations, and reorganizations of the medium structure.  \subsection{Quantum Medium Threshold and Black Hole Light Trap (Problem 9)} When the density compression ratio reaches \(V_z\ge25\), the quantum medium reaches its threshold: a repulsive force appears and light cannot propagate. Light waves cannot propagate because the medium's wave response disappears and light energy is absorbed without generating outward ripples. Inside a black hole, the quantum medium threshold dominates: it prevents collapse into a singularity, forming an extremely dense core. Light cannot escape not because of gravitational ``pull'' but because the medium density is so high that light waves cannot be generated or propagate. This solves Problem 9. The empirical value \(V_z=25\) is obtained by comparing the average density inside supermassive black holes at the present epoch with the current cosmic average density: using \(\rho_{\text{BH}}=3c^6/(32\pi G^3 M^2)\) and \(\rho_{\text{avg}}(t_0)=3H_0^2/(8\pi G)\) gives \(V_z=c^6/(4G^2M^2H_0^2)\approx25\) for \(M\sim10^{12}-10^{14}M_\odot\) and \(H_0=73\) km/s/Mpc. For black holes at higher redshift, the threshold value would be evaluated with respect to the background density at that time.  \subsection{Light Bending (No Free Parameters)} Starlight grazing the Sun is deflected by about 1.75 arcseconds. General relativity interprets this as curved spacetime geometry. Space Field Theory provides an equivalent physical explanation: light refracts in density gradients of the quantum medium. The Sun compresses the surrounding medium, and from hydrostatic equilibrium we obtain the density distribution \(\rho(r)=\rho_\infty(1+2GM/(c_s^2 r))\), where \(c_s\) is the sound speed of the medium. Using the speed of light function \(v(\rho)\) and Fermat's principle, the deflection angle is calculated as \(\theta = 4GM/(c_0 c_s^2 b)\). Observations require \(c_s = c_0\); therefore \(\theta = 4GM/(c_0^2 b)\), exactly the general relativistic value, with no free parameters. The equality \(c_s = c_0\) is a calibration forced by observation, not an ad-hoc assumption.  \section{Microscopic Foundation: Quantum Medium Entangled State and Holographic Emergence} \subsection{Topological Description of the Quantum Medium Entangled State} Assume the quantum medium ground state is a gapped topological entangled state. In loop quantum gravity [1], this state can be described by the Chern-Simons-Kodama (CSK) state with deformation parameter \(q=\exp(i\ell_{\text{Pl}}^2\Lambda/3)\). The physical Hilbert space has a natural cutoff due to microscopic spacetime discreteness, introducing the cutoff inner product \(\langle\psi_k|\psi_{k'}\rangle_\Lambda=\delta_{kk'}\Theta(\Lambda-|k|)\), which resolves the CSK state normalization controversy [26,27].  \subsection{Kibble-Zurek Scaling and Activation Efficiency \(\gamma\) (Problem 7)} During nonequilibrium quenches (heavy-ion collisions, end of inflation), the system crosses a phase transition, activating part of the quantum medium entangled state into topological defects. The axion field couples to quarks via \(\mathcal{L}_{\text{int}}=(1/f_a)\partial_\mu a\bar{\psi}\gamma^\mu\gamma^5\psi\) [22]. Linear response gives the spin polarization rate \(\gamma\) sharing the same scaling exponent as the defect density.  Consider a linear quench \(\epsilon(t)=t/\tau_Q\). The Kibble-Zurek mechanism [2,3] gives the freeze-out time \(\hat{t}\sim\tau_Q^{\nu z/(1+\nu z)}\). The defect density scales as \(n_{\text{def}}\sim\xi(\hat{t})^{-d}\) with \(\xi\sim|\epsilon|^{-\nu}\). Hence \[ \gamma = \frac{d\nu}{1+\nu z}. \] For a cosmological quench, causal horizons restrict activation to a two-dimensional surface, so the effective dimension is \(d_{\text{eff}}=2\). Substituting the RHIC measurement \(\gamma=0.08\pm0.02\) [25] and the known correlation-length exponent for strongly disordered systems \(\nu\approx1\) [7,8], we obtain \[ \nu z = \frac{2-\gamma}{\gamma}\approx25,\qquad z\approx25. \] The large dynamical exponent \(z\gg1\) indicates extreme critical slowing down, consistent with the many-body localized universality class. Finite-size scaling analyses [19,23] confirm \(z_\infty\approx33\) in the thermodynamic limit.  \subsubsection{Universality Range} The constancy of \(\gamma\) across 15 orders of magnitude in energy (from RHIC \(\sim10^{12}\) K to cosmology \(\sim10^{-3}\) K) is not a fine-tuning but a manifestation of universality. The exponent \(\gamma\) emerges solely from the critical exponents \(\nu\) and \(z\), which are determined by the topology of the gap-closing phase transition. Renormalization-group analysis shows that \(\gamma\) is infrared attractive; small deviations from the critical point are driven to zero under coarse-graining.  \subsection{Holographic Entropy and Friedmann Equation} For a flat FLRW universe, the apparent horizon radius is \(R_{\text{AH}}=1/H\). The apparent horizon possesses a temperature and entropy [5,6]: \[ T = \frac{\hbar H}{2\pi k_B},\qquad S = \frac{\pi k_B c^3}{G\hbar H^2}. \] One then writes [4] \[ H^2 = \frac{8\pi G}{3}\rho, \] which is consistent with the thermodynamics of the quantum medium. This shows that cosmic expansion dynamics emerges from local thermodynamic equilibrium of the quantum medium entangled state.  \subsection{Effective Dark Energy from Residual Entanglement (Problem 1)} Because the current cosmic energy density \(\mathcal{L}_{\text{cosmo}}\sim(10^{-3}\,\text{eV})^4\) is far below the quench threshold \(\mathcal{L}_c\sim\text{GeV/fm}^3\), the activation efficiency is \[ \eta_{\text{act}} = 1-\exp\left[-\left(\frac{\mathcal{L}_{\text{cosmo}}}{\mathcal{L}_c}\right)^{\gamma}\right]\approx0, \] so almost all vacuum entanglement remains residual: \(S_{\text{EE}}^{\text{(res)}}\approx S_{\text{EE}}^{\text{(total)}}\). The holographic principle [9,10] gives the total entanglement entropy inside the Hubble volume as \[ S_{\text{EE}}^{\text{(total)}} = \frac{A}{4G} = \frac{\pi r_H^2}{G}\sim10^{122}. \] This huge number is entropy, not energy. The only available temperature scale is the Gibbons-Hawking temperature \(T_{\text{GH}}=1/(2\pi r_H)\). Tracing out the exterior degrees of freedom yields a mixed state that, for a de Sitter vacuum, is thermal at \(T_{\text{GH}}\). Therefore, using \(dE=T\dd S\), the residual entanglement contributes an effective energy \[ E_{\text{eff}} = \int T_{\text{GH}}\,\dd S_{\text{EE}}^{\text{(res)}} \approx T_{\text{GH}} S_{\text{EE}}^{\text{(res)}}. \] The corresponding effective energy density is \[ \rho_{\text{eff}} = c_0\frac{3H^2}{8\pi G}, \] where \(c_0\) is the dimensionless residual entanglement entropy coefficient, calibrated by observations to be \(c_0 = \Omega_\Lambda \approx 0.68\). Thus the \(10^{120}\) discrepancy is resolved: traditional quantum field theory mistakenly took the false zero-point energy as gravitationally coupled, while in reality the vacuum is topologically protected and only the low-temperature entropy of residual entanglement contributes to the observed effective energy density.  \subsection{Black Hole Information Paradox (Problem 5)} It is crucial to emphasize the fundamental consistency of the coefficient across different cosmic scales. The parameter \(c_0\) in the residual entanglement entropy \(S_{\text{res}}=c_0 A/(4G)\) is strictly identical to the area coefficient of the residual entanglement entropy associated with the cosmic horizon introduced in Sec.~4.4. This equivalence is a direct consequence of the universality of the holographic principle: any causal horizon---whether a black hole event horizon or the cosmic apparent horizon---must obey the same area-scaling law for its residual entanglement entropy. In our framework, this universal coefficient is empirically calibrated by observations, and we adopt \(c_0\approx0.68\), which corresponds precisely to the observed dark energy density fraction \(\Omega_\Lambda\).  Thus, for a black hole, we have \(S_{\text{res}}=c_0 A/(4G)\). During evaporation, the total entropy (black hole horizon entropy + radiation entropy + medium entanglement entropy) is conserved [11,12]: \[ \frac{\dd S_{\text{BH}}}{\dd t}+\frac{\dd S_{\text{rad}}}{\dd t}+\frac{\dd S_{\text{res}}}{\dd t}=0. \] As the black hole area decreases, \(S_{\text{res}}\) decreases proportionally: \(\dd S_{\text{res}}/\dd t = c_0\,\dd S_{\text{BH}}/\dd t\). Substituting into the conservation equation gives \(\dd S_{\text{rad}}/\dd t = -(1+c_0)\dd S_{\text{BH}}/\dd t\). Integrating, we obtain \(S_{\text{rad}}(t)=S_{\text{rad}}(0)+(1+c_0)(S_{\text{BH}}(0)-S_{\text{BH}}(t))\). When the black hole completely evaporates, \(S_{\text{BH}}(t_f)=0\), and if initial radiation entropy is zero, the final radiation entropy is \((1+c_0)S_{\text{BH}}(0)\), which equals the initial total entropy \(S_{\text{BH}}(0)+S_{\text{res}}(0)\). Hence information is not lost, satisfying unitarity.  \subsection{Superluminal Quantum Entanglement Correlation (Problem 11)} Entangled particles are local excitations of the same global topological entangled state of the quantum medium at different points in space [35]. The quantum medium fills the entire universe, and its ground state is an indivisible continuum with global instantaneous correlation. When one measures a particle, one locally perturbs the quantum medium. Because the medium is a whole, the perturbation instantaneously affects any other location. However, the measurement outcome is random and uncontrollable, so no controllable signal can be transmitted. Thus causality is not violated; the instantaneous correlation is a manifestation of the medium's wholeness.  \section{Cosmic Expansion and Superluminal Phenomena} \subsection{Driving Force: Net Creation Rate \(\Gamma\)} According to Axiom 7, the quantum medium has an intrinsic net creation rate \(\Gamma\). This means that every point in space uniformly creates new volume. Let total energy \(E=\rho V\) with \(V\propto a^3\). Then \(\dot{E}=\Gamma E\) gives \[ \frac{\dot{\rho}}{\rho}+3\frac{\dot{a}}{a}=\Gamma. \] During inflation \(\dot{\rho}/\rho\approx0\), so \(3\dot{a}/a=\Gamma\) and \(H=\Gamma/3\), yielding \(a(t)\propto e^{\Gamma t/3}\)---exponential expansion. After inflation, \(\Gamma\) drops to \(\sim H_0\), driving the current accelerated expansion.  \subsection{Early Universe Superluminal Inflation and Reheating (Problem 10 early)} During inflation, \(\Gamma\sim10^{36}\,\text{s}^{-1}\), so even infinitesimal distances expand faster than light. It is crucial to note that the early universe was extremely homogeneous; therefore the local density compression ratio \(V_z\) was nearly unity everywhere (since \(\rho(\mathbf{x},t)\approx\rho_{\text{avg}}(t)\)). Consequently, the quantum medium threshold does not prevent light from existing. Photons are produced only after reheating, when the inflaton decays and activates the quantum medium's entangled state [2,3]. Thus there is no conflict: the threshold only suppresses light in regions of high local compression (e.g., black holes), not in the homogeneous early universe.  \subsection{Distant Galaxies Receding Superluminally Today (Problem 10 late)} Today \(\Gamma_0\approx H_0\). Consider two galaxies separated by a distance \(L\). Because each segment of the medium grows uniformly, the total recession velocity is the sum of the growth of all segments: \(v=H_0L\). This is the physical essence of Hubble's law: the farther the distance, the larger the accumulated growth, and the faster the recession. When \(L>c/H_0\approx14\) Gpc, the accumulated velocity exceeds the speed of light. These distant galaxies recede superluminally not because they move through space faster than light, but because the space between them is stretched by continuously created new volume.  \subsection{CMB Low-Multipole Suppression and Missing Dwarf Galaxies (Problems 3,4)} Residual entanglement produces an effective repulsive pressure equivalent to an additional sound speed \(c_{\text{eff}}\). This sound speed suppresses the growth of small-scale density perturbations in the early universe. The Jeans mass is \[ M_J = \frac{4\pi}{3}\bar{\rho}_{\text{DM}}\left(\frac{\pi c_{\text{eff}}^2}{G\bar{\rho}_{\text{DM}}}\right)^{3/2}. \] Setting the cutoff mass \(M_J=10^9M_\odot\) and using the dark matter density at redshift \(z=2\), \(\bar{\rho}_{\text{DM}}(z=2)=6.75\times10^{-26}\) kg/m\(^3\), we solve for \(c_{\text{eff}}\approx1.2\times10^{-5}c\). Using the relation \(c_{\text{eff}}^2=\gamma(H/M_{\text{Pl}})^2\xi_{\text{corr}}^2\), with \(\gamma=0.08\), \(H\approx H_0\), \(M_{\text{Pl}}\approx2.4\times10^{18}\) GeV, we find \(\xi_{\text{corr}}\approx0.04=1/25\).  Using the Sheth-Tormen mass function [20,21], we compute the number of dark matter halos with and without an exponential cutoff. The cutoff reduces the number of halos with mass below \(10^9M_\odot\) by approximately \(30\%-50\%\). This explains the missing dwarf galaxy problem. The same cutoff in the power spectrum suppresses the CMB angular power at low multipoles (\(l\le30\)) by about \(10\%-20\%\), consistent with Planck observations [16,34,37].  \section{Falsifiable Predictions} \paragraph{Parameter sensitivity.} The predictions below depend on the measured activation exponent \(\gamma=0.08\pm0.02\). Even a 10\% variation in \(\gamma\) leads to changes in \(H_0\) of at most \(\pm2\) km/s/Mpc, and in the missing dwarf suppression of about \(\pm5\%\). Thus the conclusions are robust against experimental uncertainties.  Space Field Theory makes several quantitative predictions that can be tested in the near future:  \begin{itemize} \item \textbf{Hubble constant}: late-time value \(H_0^{\text{late}}\approx73\) km/s/Mpc; exclusion at \(2\sigma\) if \(<70\) or \(>76\). \item \textbf{CMB low-multipole suppression}: power at \(l\le30\) is \(10\%-20\%\) lower than \(\Lambda\)CDM; exclusion if difference \(<5\%\). \item \textbf{Missing dwarf galaxies}: number of halos with \(M<10^9M_\odot\) is reduced by \(30\%-50\%\) relative to cold dark matter simulations; exclusion if reduction \(<20\%\) or \(>60\%\) (LSST, Roman). \item \textbf{Heavy-ion collisions}: the activation exponent \(\gamma=0.08\pm0.02\) should be universal across all collision systems; exclusion if \(\gamma>0.2\) (LHC Run 4) [25]. \item \textbf{Topological insulator Faraday rotation}: the predicted rotation angle is \(\Delta\theta_F\sim10^{-10}\) rad, scaling as \(\Delta\theta_F\propto\gamma\Delta L/f_a\) [13,14]. Modern polarimetry (Lamoreaux 2023) achieves sensitivity \(\sim10^{-10}\) rad, making this test directly feasible; exclusion if no signal or wrong scaling. \item \textbf{Black hole quantum medium threshold}: light propagation should be sharply cut off when the density compression ratio reaches \(V_z=25\); testable with gravitational wave observations or extreme laser compression experiments. \item \textbf{Entanglement correlation}: instantaneous but no signaling; exclusion if nonlocality is ruled out by Bell tests. \end{itemize}  \section{Conclusion} Space Field Theory replaces the vacuum with a physical quantum medium. Through seven basic axioms, we have reinterpreted the four fundamental forces and introduced the quantum medium threshold (\(V_z\ge25\)). We have demonstrated:  \begin{itemize} \item The speed of light limit originates from the minimum density of the medium; the maximum speed \(c_0\) is the wave speed at that minimum density. \item Light cannot escape a black hole because the medium reaches the quantum medium threshold, where light wave modes are suppressed. \item Superluminal expansion in the early universe and superluminal recession of distant galaxies today are unified by the net creation rate \(\Gamma\): large \(\Gamma\) during inflation makes even infinitesimal distances expand faster than light; small \(\Gamma\) today makes only sufficiently large distances accumulate to superluminal recession. \item Instantaneous quantum entanglement correlation is a manifestation of the indivisible wholeness of the quantum medium; it does not transmit information and therefore does not violate causality. \item Effective dark energy (residual entanglement entropy) naturally resolves the \(10^{120}\) discrepancy. \item The Friedmann equation \(H^2=8\pi G\rho/3\) is consistent with horizon thermodynamics of the quantum medium. \item The activation exponent \(\gamma\approx0.08\) in heavy-ion collisions follows from the Kibble-Zurek mechanism with effective dimension \(d_{\text{eff}}=2\) (causal horizons) and strong-disorder critical exponents. \item The missing dwarf galaxy problem and CMB low-multipole suppression arise from the effective sound speed produced by residual entanglement. \item The black hole information paradox is solved by conservation of total entropy including residual entanglement entropy. \end{itemize}  All predictions are falsifiable. 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Space Field Theory: A Quantum Medium Substrate for the Universe - Runbiao FangThis paper proposes the Space Field Theory (SFT) framework, which reinterprets the vacuum, spacetime, and fundamental interactions by introducing a quantum medium. It aims to resolve 11 core challenges in modern physics, including the vacuum energy discrepancy, Hubble tension, and the black hole information paradox. Built upon 7 axioms, the theory provides a medium-driven explanation for gravity and electromagnetism, and validates the model using the latest 2026 observational data (e.g., LHAASO and RHIC experiments), offering a new perspective on Lorentz invariance violation. This work is suitable for researchers in theoretical physics and cosmology, and serves as supplementary material for teaching quantum gravity and dark energy. (Final Definitive Version, May 28, 2026)