What is the universe made of?

Cosmic Composition Breakdown

• Normal (baryonic) matter constitutes only approximately 5% of the universe.
• Dark matter accounts for roughly 27% of the universe's mass-energy content.
• Dark energy comprises the remaining estimated 68% of the universe.

Dark Matter Characteristics and Detection

• Dark matter does not reflect, emit, or absorb light, nor does it interact via electromagnetic forces (it is not made of atoms or charged particles).
• Its existence is inferred from gravitational effects that exceed the mass visible in ordinary matter.
• Galactic Rotation Anomalies: Galaxies rotate at speeds that would cause them to fly apart if only visible matter's gravity were acting as the binding force.
• Gravitational Lensing: Massive dark matter structures bend the fabric of spacetime, causing light from background objects to curve even where no visible mass is present.
• Dark matter forms a cosmic web of "halos" around galaxies and is considered essential to the formation of large-scale structures like stars and solar systems.
• Gravity from dark matter acted as the "master builder" for the first 10 billion years of the universe.

Dark Matter Hypotheses and Experiments

• Current theories suggest dark matter consists of undiscovered stable particles, potentially remnants from the Big Bang.
• Direct detection experiments searching for dark matter particles bumping into normal matter have yielded no success to date.
• The Large Hadron Collider (LHC) in Switzerland attempts to create dark matter particles through high-energy proton collisions.

Dark Energy Origins and Properties

• Dark energy was identified in the late 1990s by astronomers observing distant supernovae, revealing that the universe's expansion is accelerating rather than slowing down.
• The term "dark energy" was coined by Michael Turner.
• Unlike dark matter, dark energy does not clump; it is uniformly distributed throughout space.
• It is not composed of particles but is theorized to be a property of space itself, specifically "vacuum energy" or "zero-point energy."
• Albert Einstein's "cosmological constant," originally inserted to maintain a static universe model, may mathematically account for dark energy.

Future Scenarios and Evolutionary Shifts

• As the universe expands, the total amount of dark energy increases, maintaining its density while the influence of matter dilutes.
• Big Rip Scenario: If dark energy's acceleration increases, it could eventually tear apart galaxy clusters, individual galaxies, solar systems, and planets.
• Big Crunch Scenario: If dark matter's influence were to dominate again, the universe could collapse back upon itself.
• Indefinite Expansion: If the ratio between the two forces remains stable, the universe may continue to expand outward indefinitely.
• The dominance of these forces has shifted over time: dark matter drove structure formation in the early universe, while dark energy has become dominant more recently.