Accelerated expansion

Definition

Accelerated expansion refers to the phenomenon where the universe is expanding at an increasing rate over time, a discovery primarily attributed to dark energy. This implies that galaxies are moving away from each other faster as time progresses, challenging previous understandings of cosmic dynamics and influencing theories about the fate of the universe.

5 Must Know Facts For Your Next Test

1. The discovery of accelerated expansion came from observations of distant supernovae in the late 1990s, which revealed they were dimmer than expected due to their increased distance and speed.
2. Dark energy constitutes about 68% of the total energy density of the universe, significantly affecting its large-scale structure and evolution.
3. Accelerated expansion suggests that the fate of the universe could lead to a 'Big Freeze,' where galaxies drift further apart and stars exhaust their nuclear fuel over billions of years.
4. The cosmological constant problem highlights a major discrepancy between theoretical predictions and observed values regarding dark energy, leading to ongoing debates in cosmology.
5. Current models propose that as the universe expands, the effects of dark energy will dominate, ultimately accelerating this expansion even further.

Review Questions

• How does the discovery of accelerated expansion challenge previous notions about the dynamics of the universe?
  • Before the discovery of accelerated expansion, it was generally believed that gravity would slow down the rate of cosmic expansion over time. However, observations of distant supernovae revealed that not only is the universe expanding, but it is doing so at an increasing rate. This unexpected behavior has led to significant revisions in cosmological models and theories, particularly concerning the role of dark energy in influencing this accelerated motion.
• Discuss the implications of dark energy on our understanding of the universe's fate in light of accelerated expansion.
  • Dark energy plays a crucial role in shaping the future of our universe by driving its accelerated expansion. As dark energy continues to exert its influence, it is believed that galaxies will move increasingly further apart, leading towards scenarios like the 'Big Freeze' where the universe becomes cold and empty. This has profound implications for our understanding of cosmic evolution, as it suggests a universe that may never collapse back into a singularity or stabilize into a static state.
• Evaluate how the cosmological constant problem is related to the concept of accelerated expansion and what it signifies for modern cosmology.
  • The cosmological constant problem arises from the stark difference between theoretical predictions for vacuum energy density and the observed effects attributed to dark energy leading to accelerated expansion. This discrepancy highlights significant gaps in our understanding of fundamental physics, especially in reconciling quantum field theory with general relativity. Addressing this problem is critical for modern cosmology as it could unlock deeper insights into both dark energy and the overall fabric and fate of our universe.

Related terms

Dark Energy: A mysterious form of energy that permeates space and is believed to be responsible for the accelerated expansion of the universe.

Cosmological Constant: A constant term introduced by Einstein in his equations of general relativity, representing the energy density of empty space that contributes to the universe's accelerated expansion.

Friedmann-Lemaître-Robertson-Walker Metric: A solution to Einstein's field equations of general relativity that describes a homogeneous and isotropic expanding universe, used to model cosmic expansion.