The Origin of Sound: A Symphony from Cosmic Vibrations to Human Language

I. Physics Perspective: The Cosmic Law of Vibrations and Waves

  1. Physical Definition of Sound Waves

    • Sound is fundamentally a mechanical longitudinal wave generated by vibrating objects, relying on a medium (gas, liquid, or solid) to propagate energy.

    • Mathematical Description: The acoustic wave equation (∇2�=1�2∂2�∂�2) reveals the relationship between sound speed � and medium density.

  2. Vibrations from Micro to Macro Scales

    • Molecular Motion: Collisions between air molecules transfer energy, creating alternating regions of compression and rarefaction (illustrated through animations).

    • Sound in Extreme Environments:

      • Deep Sea: Whales communicate over thousands of kilometers using infrasound (<20 Hz).

      • Solid Media: Seismic waves, including P-waves (longitudinal) and S-waves (transverse), reveal Earth’s internal structure.

  3. Boundaries of Sound: Vacuum and Relativity

    • 99% of the universe’s space cannot transmit sound, but spacetime ripples (gravitational waves) from merging black holes can be considered a "generalized form of sound."

II. Biological Evolution: How Sound Shaped Life

  1. Origin of Hearing: From Jellyfish to Vertebrates

    • Primitive Perception: Jellyfish detect water vibrations via statocysts (500 million years ago).

    • Vertebrate Breakthrough: Synergistic evolution of the lateral line system in fish and vestibular organs in the inner ear.

  2. Revolution in Sound-Producing Organs

    • Insects: Crickets stridulate wings, cicadas vibrate tymbals (up to 120 dB).

    • Birds and Mammals: Precise control of the syrinx (birds) and vocal folds (mammals) enables complex behaviors like mating calls and territorial warnings.

  3. The Biological Miracle of Human Language

    • Laryngeal Descent Theory: Around 200,000 years ago, Homo sapiens’ throat structure evolved, enabling vowel differentiation and laying the foundation for language.

    • Auditory-Brain Synergy: The temporal lobe’s auditory cortex rapidly decodes speech (e.g., the "cocktail party effect").

III. "Sound" in the Cosmos: Density Ripples from the Dawn of Creation

  1. Echoes of the Big Bang: Fossilized Sound Waves in the Cosmic Microwave Background

    • Baryon Acoustic Oscillations (BAO): Density waves in the early universe’s plasma remain observable 13.8 billion years later, serving as a ruler for cosmic expansion.

    • Data: The Sloan Digital Sky Survey (SDSS) confirmed BAO through galaxy distribution patterns.

  2. Black Holes and Neutron Stars "Sounding Off"

    • Gravitational Wave Event GW170817: The merger of neutron stars emitted gravitational waves and electromagnetic signals (kilonova), ushering in the era of "multi-messenger astronomy."

IV. Civilization and Philosophy: Sound as a Vessel of Meaning

  1. Myth and Ritual

    • Ancient Egypt: The god Ptah created the world through speech; spells in the Book of the Dead guided souls.

    • Australian Aboriginal Culture: The didgeridoo’s drone mimics the "breath of the Earth."

  2. Technological Revolution: From Phonographs to the Metaverse

    • 1877 Edison Wax Cylinder: First physical imprint of sound.

    • Digital Acoustics: How MP3 compression (psychoacoustic models) removes "inaudible" frequencies.

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