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10 Theories About What Exists in the 4th Dimension

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Science and Nature

Scientific concepts, discoveries, and nature phenomena (by segment)

Number 10: The tesseract (4D geometry)

  • Dimensional shadow principle (Flatland logic): Observers confined to fewer dimensions perceive only the cross-section/shadow of higher-dimensional objects.
  • 4D analogue of a cube: A tesseract (four-dimensional hypercube) has a defined higher-dimensional structure:
    • Cube: 6 faces, 12 edges, 8 corners
    • Tesseract: 8 cubic cells, 24 square faces, 32 edges, 16 vertices
  • Visualization limits: Humans can model 3D projections (e.g., Schlegel diagrams), but cannot truly “see” the full 4D object.
  • Art reference: Salvador Dalí’s Corpus Hypercubus illustrates an unfolded/projection view of a tesseract.

Number 9: Time as the fourth dimension

  • Special relativity (1905): Space and time are interwoven, not separate; described as a unified 4D spacetime.
  • Minkowski spacetime (1908): Spacetime geometry treats time as a mathematical coordinate.
  • Time dilation in practice:
    • GPS: Requires relativistic corrections to avoid large daily errors (about 10 km/day claimed in the subtitles).
    • Hafele–Keating experiment (1971): Airborne atomic clocks measured time dilation consistent with Einstein’s equations.
  • General relativity and gravitational waves (2015):
    • LIGO detection (Sept 14, 2015): Gravitational waves from two black holes merging ~1.3 billion light-years away.
    • Interpreted as distortions in spacetime geometry propagating at the speed of light.
  • Block universe idea (early setup for #1): Past and future are treated as coordinate locations in a fixed spacetime geometry (noted as an open interpretive question).

Number 8: Higher-dimensional beings

  • Cross-section again: A 4D object passing through 3D space would appear as a 3D “slice” that grows, changes, and disappears.
  • 4D hypersphere intersection behavior: Would look like a sphere appearing from a point, expanding, then shrinking back to a point and vanishing.
  • Speculative frameworks tied to physics:
    • String theory’s higher-dimensional branes and bulk
    • Claim: anomalies/supernatural-like effects could (in principle) arise from motion/intersection in extra dimensions.
  • Parallel “bulk” direction: Higher-dimensional objects could exist in spatial directions we cannot directly observe.

Number 7: Kaluza–Klein theory and hidden dimensions

  • Unified geometry idea (Kaluza):
    • Adding a 5th spatial dimension to general relativity yields a unification where gravity and electromagnetism emerge from the same geometric structure.
  • Compactification (Klein):
    • The extra dimension is curled up to an extremely small scale (~10⁻³³ cm, Planck length).
  • Extra dimensions in string/M-theory:
    • String theory: 10 spatial dimensions total (as stated)
    • M-theory: 11 dimensions
    • Extra dimensions are compactified similarly.
  • Experimental searches:
    • Large Hadron Collider (CERN): Looking for signatures such as microscopic black holes from gravitational “leakage” (no confirmed signal).
    • Gravity tested down to ~50 micrometers for deviations (none found, but not definitive exclusion).

Number 6: Dark matter as a fourth-dimensional phenomenon

  • Galaxy rotation discrepancy (Rubin & Ford, 1970s):
    • Spiral galaxy outer stars orbit too fast for visible matter under known gravity.
  • Dark matter properties (as described):
    • ~27% of the universe’s energy content (as stated)
    • Invisible electromagnetically; does not emit/absorb/reflect light
    • No confirmed direct detection as of 2025 (as framed in the subtitles)
  • Brane-world reinterpretation (Randall–Sundrum, 1999):
    • Dark matter could be ordinary matter on a parallel brane in the higher-dimensional bulk.
    • Only gravity couples between branes; other forces remain confined to “our” brane.

Number 5: Quantum realm and higher-dimensional probability

  • Quantum wavefunction and Hilbert space:
    • No definite particle properties until measurement; described by probability waves.
    • Wavefunction dimensionality grows with particle number:
      • 1 particle: needs 3 dimensions
      • N particles: wavefunction lives in 3N dimensions (Hilbert space)
  • Many-worlds interpretation (Everett, 1957):
    • All possible outcomes occur, with reality branching into physically coexisting branches.
  • Entanglement evidence (Aspect et al., 1982):
    • Experimental confirmation of entanglement consistent with nonlocal correlations (“spooky action”).
  • Holographic principle (’t Hooft 1993; Susskind 1995):
    • Maximum information in a region scales with surface area, not volume.
    • Suggested link to higher-dimensional encoding/projection: the 3D world as a projection from a 2D boundary.

Number 4: Multiverse and parallel brains (brane collision cosmology)

  • M-theory (Witten, 1995):
    • Five string theories unify into M-theory requiring 11 dimensions.
    • Branes (“brains”): Our universe as a 3D membrane in a higher-dimensional bulk.
  • Ekpyrotic universe (Steinhardt & Turok, 2001; Science paper):
    • Big Bang arises from a collision of two parallel 3D branes separated in an extra dimension.
    • The “event” is not creation from nothing but energy transfer at collision.
    • Possibility of cyclic collisions (repeated “births”).
  • Separation distance claim:
    • Some formulations allow separation as small as millimeter scale in the extra dimension—without crossing by standard-model forces.
  • Gravity-only coupling to the bulk:
    • Electromagnetic/strong/weak forces confined to the brane; gravity propagates in bulk.
  • Hawking & Hertog (2018, JHEP):
    • A final paper proposes a smooth multiverse mechanism constrained by higher-dimensional physics after a quantum Big Bang.

Number 3: The holographic universe

  • AdS/CFT-inspired claim (Maldacena, 1997):
    • Equivalence between:
      • gravity in a 3D region and
      • a quantum theory without gravity on the 2D boundary.
    • The two are said to be identical descriptions, not approximations.
  • Historical foundation:
    • Bekenstein (1972): black hole entropy proportional to horizon area (not volume).
    • ’t Hooft (1993): holographic principle formalized.
    • Susskind (1995): extension/popularization.
  • Evidence/experiments mentioned:
    • 2017 (Southampton): claim that CMB statistics support holographic description comparably to inflation.
    • Holometer at Fermilab (2012–2016): looked for quantum holographic noise (no definitive detection; constraints improved).
  • Interpretive geometry:
    • 3D space emerges from information on a 2D surface; “depth” is a projection direction into the bulk.

Number 2: Wormholes and fourth-dimensional shortcuts

  • Einstein–Rosen bridge (1935):
    • General relativity yields equations that can contain a “bridge”/connection between spacetime regions (initially treated as a nonphysical curiosity).
  • Wheeler (1957): the term “wormholes.”
  • Traversable wormholes analysis (Thorne et al., 1988):
    • Not ruled out, but would require exotic matter with negative energy density.
  • Casimir effect (experiment first observed 1997 as stated):
    • Demonstrates negative energy density is physically possible in limited amounts.
  • 4D geometric shortcut model:
    • Wormhole described as a fold in spacetime, connecting distant points via the fourth dimension (not by normal 3D travel).
    • Traveling could take no time from the traveler’s perspective (as claimed in the subtitles).
  • Quantum simulation (Caltech, Nature paper, Nov 2022):
    • Google Sycamore simulated an Einstein–Rosen bridge using 9 qubits.
    • Interpreted as dynamics matching wormhole traversal physics (simulation, not a literal traversable wormhole).

Number 1: “You already exist in four dimensions” (block universe / eternalism)

  • Relativity of simultaneity (special relativity):
    • Observers can disagree about what “now” means.
  • Minkowski (1908) reframing:
    • The universe as a static 4D spacetime object, with time as a coordinate; perceived “flow” is argued to be an illusion.
  • Julian Barbour (1999):
    • The universe does not “evolve”; it “is” as a complete 4D structure containing all moments.
  • Block universe consequences:
    • Past and future are fixed within spacetime; present moment depends on observer trajectory.
    • Free will (classical sense) may be geometrically incompatible with fixed spacetime (as presented).
  • Philosophical label: eternalism (with “everything exists” interpretation).
  • Named proponents: Roger Penrose, Brian Greene, Julian Barbour.
  • Core claim: All moments of an individual’s life are simultaneously real as spacetime coordinates.

Researchers / sources featured (named in subtitles)

  • Edwin Abbott Abbott (Flatland)
  • Charles Hinton (Era of Thought)
  • Salvador Dalí (Corpus Hypercubus)
  • Albert Einstein
  • Hermann Minkowski
  • Vera Rubin
  • Kent Ford
  • Werner Heisenberg
  • Hugh Everett
  • Alain Aspect (and team)
  • Gerard ’t Hooft
  • Leonard Susskind
  • Edward Witten
  • Paul Steinhardt
  • Neil Turok
  • Lisa Randall
  • Raman Sundrum
  • Roger Penrose
  • Brian Greene
  • Julian Barbour
  • Jacob Bekenstein
  • Theodor Kaluza
  • Oskar Klein
  • Thomas Hertog (with Stephen Hawking)
  • Stephen Hawking
  • John Wheeler
  • Kip Thorne (Caltech)
  • Google (Sycamore processor)
  • LIGO
  • Fermilab (Holometer)
  • CERN (Large Hadron Collider)
  • Charles Howard Hinton (as named in subtitles; same person as “Charles Hinton” context)

Original video