Cosmic acceleration

Definition

Cosmic acceleration refers to the observed phenomenon in which the expansion of the universe is speeding up over time, contrary to the earlier assumption that gravity would slow it down. This acceleration suggests that a mysterious force, termed dark energy, is dominating the universe's energy content and driving this accelerated expansion. Understanding cosmic acceleration is crucial for grasping the ultimate fate of the universe and the nature of its composition.

5 Must Know Facts For Your Next Test

1. Cosmic acceleration was first strongly indicated by observations of distant Type Ia supernovae in the late 1990s, which appeared dimmer than expected, suggesting an expanding universe that is accelerating.
2. The discovery of cosmic acceleration led to a significant shift in cosmological models, moving from a decelerating universe to one where dark energy dominates and influences its future evolution.
3. Cosmic acceleration suggests that galaxies are moving away from each other at increasing speeds, impacting our understanding of gravity and the large-scale structure of the universe.
4. Researchers estimate that about 73% of the total energy density of the universe is in the form of dark energy responsible for cosmic acceleration, while only about 27% is ordinary matter and dark matter combined.
5. The precise nature of dark energy remains one of the biggest mysteries in modern cosmology, with theories ranging from a cosmological constant to dynamic fields like quintessence.

Review Questions

• How does cosmic acceleration challenge previous assumptions about the expansion of the universe?
  • Cosmic acceleration challenges previous assumptions by indicating that instead of slowing down due to gravitational forces, the universe's expansion is actually speeding up. This was not anticipated since gravity should naturally pull matter together, slowing expansion. The realization that a significant force like dark energy could counteract gravity fundamentally altered our understanding of cosmic dynamics and led to new theories regarding the fate of the universe.
• Discuss how observations of distant supernovae contributed to our understanding of cosmic acceleration.
  • Observations of distant Type Ia supernovae were crucial in revealing cosmic acceleration because these supernovae act as 'standard candles' for measuring distances in the universe. When astronomers found that these supernovae appeared dimmer than expected, it implied they were farther away than predicted, indicating that the expansion rate was not only continuing but accelerating. This evidence prompted researchers to propose dark energy as a driving force behind this unexpected behavior in the expansion of the universe.
• Evaluate the implications of cosmic acceleration on future cosmological models and theories about dark energy.
  • The implications of cosmic acceleration are profound for future cosmological models, as they suggest that dark energy will continue to dominate over gravitational forces, leading to an ever-accelerating expansion. This challenges existing models and compels scientists to explore new theoretical frameworks. The unresolved nature of dark energy also invites ongoing research into its properties and potential variations over time or across space, potentially reshaping fundamental theories about gravity, spacetime, and even the overall fate of the universe.

Related terms

Dark Energy: A form of energy that permeates all of space and tends to accelerate the expansion of the universe, making up about 68% of the total energy content.

Big Bang: The leading explanation for the origin of the universe, stating that it began as a singularity approximately 13.8 billion years ago and has been expanding ever since.

Cosmological Constant: A term introduced by Einstein in his equations of General Relativity, representing a constant energy density filling space homogeneously and associated with dark energy.