Accelerating expansion

Definition

Accelerating expansion refers to the phenomenon where the universe is expanding at an increasing rate over time. This behavior is driven by a mysterious force known as dark energy, which counteracts the attractive force of gravity and affects the dynamics of cosmic expansion.

5 Must Know Facts For Your Next Test

1. The discovery of accelerating expansion came from observations of distant supernovae, which appeared dimmer than expected, indicating that they were farther away due to the accelerated rate of expansion.
2. Dark energy accounts for approximately 68% of the total energy density of the universe, significantly influencing its overall geometry and fate.
3. The cosmological constant, introduced by Einstein, is one possible form of dark energy that leads to a uniform repulsive effect throughout space.
4. Current models suggest that if the acceleration continues indefinitely, the universe could ultimately end in a scenario known as the 'Big Freeze' where galaxies drift apart and stars burn out.
5. Observations of large-scale structures and the cosmic microwave background radiation support the existence of dark energy and its role in accelerating cosmic expansion.

Review Questions

• How does dark energy contribute to the phenomenon of accelerating expansion in the universe?
  • Dark energy acts as a repulsive force that counteracts gravitational attraction on cosmic scales. This leads to an increase in the rate at which galaxies are moving away from each other. As space expands, dark energy becomes more dominant compared to matter, which causes the acceleration in cosmic expansion to occur over time.
• In what ways do observations of distant supernovae support the concept of accelerating expansion?
  • Observations of distant supernovae have shown that they are dimmer than expected under a static universe model. This suggests that these supernovae are farther away due to an accelerated expansion, indicating that the universe's rate of expansion is increasing rather than slowing down. These findings provided some of the first strong evidence for dark energy's influence on cosmic dynamics.
• Evaluate how the concept of accelerating expansion affects our understanding of possible scenarios for the end of the universe.
  • The idea of accelerating expansion reshapes our understanding of potential scenarios for the end of the universe. If this acceleration continues indefinitely, theories like the 'Big Freeze' become more plausible, where galaxies move apart so quickly that they become isolated and stars gradually exhaust their nuclear fuel. This contrasts with scenarios like a 'Big Crunch', where gravity would eventually halt expansion and reverse it, leading to a collapse. The prevailing evidence for accelerating expansion suggests that a cold and dark future is more likely.

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 its total energy density.

Cosmic microwave background radiation: The afterglow radiation from the Big Bang, which provides key evidence for the universe's early conditions and supports models of cosmic expansion.

Friedmann equations: A set of equations derived from Einstein's general relativity that describe the expansion of the universe and how it evolves over time, incorporating various forms of matter and energy.