Chinmaya IAS Academy – Current Affairs Chinmaya IAS Academy – Current Affairs
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GS 3 science and technology
Dark Matter
- Dark matter is a hypothetical form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter.
Key Characteristics
- Invisible: It does not interact with electromagnetic radiation.
- Massive: Accounts for about 27% of the universe’s total mass-energy content.
- Interacts Gravitationally: Influences the motion of galaxies and the bending of light (gravitational lensing).
- Non-Baryonic: Composed of particles that are not part of the standard atomic structure (not made of protons, neutrons, and electrons).
Evidence for Dark Matter
- Galaxy Rotation Curves: Stars on the outskirts of galaxies rotate faster than expected based on visible mass alone.
- Gravitational Lensing: Light bending around massive galaxy clusters indicates the presence of unseen mass.
- Cosmic Microwave Background (CMB): Patterns in the CMB suggest more mass than visible matter can account for.
- Large-Scale Structure: The formation of galaxies and clusters requires more mass than visible matter provides.
Hypothesized Constituents
- WIMPs: Weakly Interacting Massive Particles, a leading candidate.
- Axions: Hypothetical ultra-light particles.
- Sterile Neutrinos: A heavier form of neutrino.
Challenges
- No direct detection of dark matter particles has been made despite extensive searches using particle detectors and experiments like LUX-ZEPLIN and AMS-02.
Dark Energy
Definition
- Dark energy is a mysterious force causing the accelerated expansion of the universe. It constitutes approximately 68% of the universe’s total mass-energy content.
Key Characteristics
- Repulsive Force: Works against gravity, driving galaxies apart.
- Uniform Distribution: Unlike dark matter, it does not clump and appears uniformly distributed in space.
- Dominant Component: Became dominant after the universe expanded sufficiently for gravity to weaken its pull.
Evidence for Dark Energy
- Supernova Observations: Type Ia supernovae show that the universe’s expansion is accelerating.
- Cosmic Microwave Background: Indicates an energy density consistent with a flat universe dominated by dark energy.
- Large-Scale Structure: Observations suggest an accelerating expansion over time.
Challenges
- The nature and origin of dark energy remain unknown, and its effects are observed only indirectly.
Difference Between Dark Matter and Dark Energy
| Aspect | Dark Matter | Dark Energy |
| Nature | Invisible, interacts via gravity | A repulsive force accelerating expansion |
| Function | Adds mass to the universe, explains galaxy rotation curves | Drives the accelerated expansion of the universe |
| Percentage of Universe | ~27% | ~68% |
| Interaction | Clumps around galaxies | Uniformly distributed |
Hubble Tension
The Hubble Tension refers to the discrepancy between the value of the Hubble Constant (H0H_0H0), which represents the current rate of expansion of the universe, as measured through different methods.
- The Hubble Constant is a critical parameter in cosmology, used to determine the age and size of the universe.
