Cosmic acceleration

Definition

Cosmic acceleration refers to the phenomenon where the expansion rate of the universe is increasing over time, suggesting that distant galaxies are moving away from us at an accelerating pace. This unexpected behavior challenges traditional views of cosmic evolution and raises questions about the underlying forces driving this acceleration, linking it to modified gravity theories and the eventual fate of the universe.

5 Must Know Facts For Your Next Test

1. Cosmic acceleration was first discovered in the late 1990s through observations of distant supernovae, which appeared dimmer than expected, indicating an accelerated expansion.
2. The nature of dark energy, which accounts for about 68% of the universe, remains one of the biggest mysteries in modern astrophysics.
3. Modified gravity theories attempt to explain cosmic acceleration by altering Einstein's general relativity, providing alternative explanations for the observed phenomena without invoking dark energy.
4. The discovery of cosmic acceleration has significant implications for our understanding of the universe's long-term future, affecting predictions about its ultimate fate.
5. Current observational data supports cosmic acceleration, but ongoing research is necessary to refine our understanding and explore potential new physics beyond the standard model.

Review Questions

• How does cosmic acceleration challenge existing theories of cosmology?
  • Cosmic acceleration challenges existing theories by contradicting the expectation that gravity should decelerate the expansion of the universe over time. Traditional models based on matter and radiation alone suggested that as the universe expanded, gravitational attraction would slow down this expansion. However, observations indicating an accelerated rate require a reevaluation of these models, leading to new concepts like dark energy or modified gravity theories to account for this unexpected behavior.
• What role does dark energy play in cosmic acceleration and how might modified gravity theories provide alternative explanations?
  • Dark energy is theorized to be a driving force behind cosmic acceleration, causing galaxies to move away from each other at an increasing rate. It constitutes a significant portion of the universe's total energy density. Modified gravity theories offer alternative explanations by suggesting that alterations in our understanding of gravity itself could account for the observed acceleration without invoking dark energy. These theories propose variations to Einstein's equations or new forces acting on cosmic scales.
• Evaluate how understanding cosmic acceleration influences predictions about the future of the universe.
  • Understanding cosmic acceleration significantly impacts predictions about the future state of the universe. If current observations hold true, they suggest scenarios like the Big Freeze, where the universe continues to expand indefinitely and galaxies drift apart. This has profound implications for cosmology, including how we view time and space on grand scales. Insights into cosmic acceleration may lead us to rethink fundamental questions about the ultimate fate of all matter and energy in existence.

Related terms

Dark Energy: A mysterious form of energy that permeates all of space and is thought to be responsible for the observed acceleration of the universe's expansion.

Friedmann-Lemaître-Robertson-Walker (FLRW) Metric: A solution to Einstein's field equations in general relativity that describes a homogeneous and isotropic expanding or contracting universe.

Big Freeze: A potential fate of the universe where it continues to expand forever, leading to a state of low energy density and isolation among galaxies.