Hubble's Law

Definition

Hubble's Law states that the farther away a galaxy is, the faster it is moving away from us, which implies that the universe is expanding. This law was derived from observations made by Edwin Hubble in the 1920s, establishing a direct relationship between the distance of galaxies and their recessional velocity. Hubble's Law provides crucial evidence for the Big Bang theory, suggesting that the universe began from a singular point and has been expanding ever since.

5 Must Know Facts For Your Next Test

1. Hubble's Law can be mathematically expressed as $$v = H_0 imes d$$, where $$v$$ is the recessional velocity, $$H_0$$ is Hubble's constant, and $$d$$ is the distance to the galaxy.
2. Hubble's constant is currently estimated to be about 70 kilometers per second per megaparsec, meaning that for every megaparsec (approximately 3.26 million light-years) away, a galaxy moves away at an increasing speed.
3. The discovery of Hubble's Law was groundbreaking because it provided a measurable way to determine how quickly the universe was expanding and thus supported the Big Bang theory.
4. Observations supporting Hubble's Law have been instrumental in understanding not just the expansion of the universe, but also its age and overall structure.
5. The law also implies that if we could rewind time, all galaxies would converge to a single point, supporting the concept of a dynamic and evolving universe.

Review Questions

• How does Hubble's Law support the idea of an expanding universe?
  • Hubble's Law shows that galaxies farther away are moving away from us at greater speeds. This consistent pattern suggests that the universe is not static but rather expanding. By observing this redshift in distant galaxies, scientists infer that if we trace back their motion, they would converge at a single point in time, indicating a beginning or origin for the universe.
• Discuss how Hubble's Law relates to redshift and what this tells us about distant galaxies.
  • Hubble's Law is closely linked to redshift because as galaxies recede from us, their light shifts toward longer wavelengths. This redshift serves as a crucial observational tool; by measuring how much light shifts, astronomers can determine how fast a galaxy is moving away and consequently its distance from us. This relationship reinforces Hubble's findings and provides direct evidence of an expanding universe.
• Evaluate the implications of Hubble's Law for our understanding of cosmic evolution since the Big Bang.
  • Hubble's Law fundamentally alters our comprehension of cosmic evolution by indicating that the universe has been expanding since its inception during the Big Bang. It challenges previous notions of a static cosmos and leads to questions about what happens as this expansion continues. Understanding this expansion impacts theories regarding dark energy and offers insights into potential future scenarios for the fate of the universe.

Related terms

Redshift: The phenomenon where light from an object is shifted towards longer wavelengths as it moves away, indicating that the object is receding from the observer.

Cosmological Constant: A value introduced by Einstein in his equations of general relativity to account for the energy density of empty space, which can influence the expansion rate of the universe.

Cosmic Microwave Background Radiation: The thermal radiation filling the universe, a remnant from the Big Bang, which provides critical evidence for the early state of the universe.