Cosmic expansion

Definition

Cosmic expansion refers to the observation that the universe is continuously stretching, causing galaxies to move away from each other over time. This phenomenon is primarily driven by the initial conditions of the Big Bang and has been observed through the redshift of light from distant galaxies, indicating that the universe is growing larger as it ages.

5 Must Know Facts For Your Next Test

1. Cosmic expansion was first discovered by Edwin Hubble in the 1920s when he observed that distant galaxies are receding from us, providing evidence for a dynamic universe.
2. The rate of cosmic expansion is quantified by Hubble's constant, which estimates how fast galaxies are moving away per unit distance.
3. As galaxies move apart due to cosmic expansion, their light shifts to longer wavelengths, resulting in redshift, which astronomers use to study the universe's rate of expansion.
4. The discovery of cosmic acceleration in the late 1990s led to the understanding that dark energy plays a significant role in driving this accelerated expansion.
5. Current observations indicate that the universe has been expanding since its inception about 13.8 billion years ago, with this expansion becoming faster over time.

Review Questions

• How does redshift provide evidence for cosmic expansion, and what does it indicate about the motion of distant galaxies?
  • Redshift is a critical observation that supports the idea of cosmic expansion by showing that light from distant galaxies shifts toward longer wavelengths. This shift indicates that these galaxies are moving away from us, confirming that the universe is not static but is instead continuously expanding. By measuring the degree of redshift, astronomers can determine how fast these galaxies are receding, providing vital insights into the dynamics of our universe.
• Discuss Hubble's Law and its significance in understanding cosmic expansion.
  • Hubble's Law states that there is a direct relationship between the distance of a galaxy and its recessional velocity, meaning that galaxies farther away are moving away faster. This law is significant as it provides a quantitative framework for measuring cosmic expansion and supports the Big Bang model of an ever-growing universe. By studying Hubble's Law, scientists can estimate distances to far-off galaxies and infer how quickly the universe has expanded since its formation.
• Evaluate the impact of dark energy on our understanding of cosmic expansion and its implications for the future of the universe.
  • Dark energy significantly impacts our understanding of cosmic expansion by suggesting that not only is the universe expanding, but this expansion is accelerating over time. This realization emerged from observations in the late 1990s and challenges previous notions that gravity would slow down this expansion. Understanding dark energy is crucial because it raises questions about the ultimate fate of the universe; if dark energy continues to dominate, it could lead to scenarios such as a 'Big Freeze,' where galaxies drift apart indefinitely.

Related terms

Redshift: A shift in the light spectrum of an object towards longer wavelengths, which occurs when an object is moving away from the observer, commonly used in astronomy to measure the speed of cosmic expansion.

Hubble's Law: A fundamental observation in cosmology that states the velocity at which a galaxy is receding from an observer is directly proportional to its distance from that observer.

Dark Energy: A mysterious form of energy that permeates space and accelerates the expansion of the universe, making up about 68% of the total energy content of the universe.