The universe’s biggest mystery

Cosmic Composition Breakdown

• Normal matter (atoms, molecules, stars, planets) comprises only 5% of the universe.
• The remaining 95% consists of two undiscovered components: dark matter and dark energy.
• Both dark matter and dark energy are invisible as they neither absorb nor emit light, rendering them undetectable by standard electromagnetic instruments.

Dark Matter: Evidence and Hypotheses

• Discovery and Mechanism:
  • Existence inferred in 1933 by astronomer Fritz Zwicky via gravitational anomalies.
  • Observations showed outer galaxies in clusters moving too fast to be held by visible mass, implying "missing mass" acting as gravitational glue.
• Detection Methods:
  • Primary detection relies on observing gravitational effects rather than direct electromagnetic radiation.
  • Current searches utilize:
    • The Large Hadron Collider (CERN) to identify particle candidates, with over a decade of search yielding no results.
    • Gravitational wave detectors to identify spacetime ripples potentially caused by massive dark matter clumps.
• Candidate Particles:
  • MACHOs (Massive Astrophysical Compact Halo Objects): Includes neutron stars and brown dwarfs; currently considered unlikely to account for the majority of dark matter.
  • WIMPs (Weakly Interacting Massive Particles): Leading hypothetical particle candidates currently under investigation alongside other undiscovered particles.

Dark Energy: Acceleration and Theories

• Discovery of Acceleration:
  • Late 1990s findings revealed the universe's expansion is accelerating, contradicting the prior assumption that gravity would slow it down.
• Nature and Properties:
  • Functions as a repulsive force opposite to gravity, pushing galaxies apart.
  • Accounts for the majority of the universe's energy, though its specific nature remains unknown.
  • Scientific consensus lacks a unified theory; it may be a particle, fluid, force, or intrinsic property of space.
• Leading Theoretical Models:
  • Cosmological Constant: Re-evaluation of Einstein's discarded term, originally added to prevent universal collapse, now seen as a potential match for dark energy's behavior.
  • Quintessence: A dynamic fluid theory filling space, distinct from a static constant.

Future Cosmological Scenarios

• The Big Freeze: If dark energy continues pushing galaxies apart, stars will cease shining, leading to a cold, empty universe.
• The Big Rip: A scenario where dark energy eventually overcomes all gravitational forces, tearing the universe apart.
• Understanding the strength and nature of dark energy is critical for predicting these long-term cosmic fates and comprehending the initial conditions of the Big Bang.