Understanding the accelerating expansion of the universe based on redshift

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Discussion Overview

The discussion revolves around the concept of the universe's expansion, specifically whether this expansion is accelerating or decelerating, as inferred from redshift measurements. Participants explore various observations and studies related to cosmic expansion, including historical context and current data.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion over conflicting claims regarding the acceleration of the universe's expansion, citing a video lecture that suggests deceleration.
  • Another participant references the Perlmutter supernova legacy study as evidence supporting the notion of expansion.
  • A different participant notes that while the early universe experienced deceleration, it has been accelerating for the past few billion years, indicating that the epoch considered is crucial to the discussion.
  • It is mentioned that current evidence from numerous supernovae, galaxy surveys, and cosmic microwave background observations supports the acceleration claim, suggesting that isolated observations of individual galaxies may not significantly impact the broader understanding.
  • A post includes references to NASA's resources on the Big Bang and redshift, implying that these are foundational to understanding cosmic expansion.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are multiple competing views regarding the nature of the universe's expansion and the interpretation of redshift data.

Contextual Notes

The discussion highlights the importance of considering different epochs in cosmic history when discussing expansion rates, as well as the limitations of relying on a small number of observations to draw broader conclusions.

Laconic99
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Understanding the accelerating/decelerating expansion of universe based on redshift..

I am trying to understand how the expansion of the universe is accelerating, if indeed it is. It's confusing, as some people say that the expansion is accelerating, whereas I have a video lecture where the professor says that the expansion is decelerating. My question is how do you conclude that expansion is accelerating/decelerating based on these numbers, given that the more distant galaxy is seen as it was much longer ago than the closer one?

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Circinus Galaxy.

Distance from earth: 1.23x10^20 km (13 million ly)

speed: 426 km/sIOK-1 galaxy.

Distance from earth: 1.23x10^23 km (13 billion ly)

speed: 290 477 km/s

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Space news on Phys.org
The Perlmutter supernova legacy study confirmed expansion.
 
In the early universe, the expansion was decelerating. It's only within the last few billion years that it's been accelerating. So I guess it depends upon what epoch you're looking at.

But in any case today we have hundreds of supernovae, as well as large galaxy surveys and cosmic microwave background observations that all confirm the same story. Two individual galaxy observations aren't going to overturn this (or even add much to it, because two single galaxies are just two small data points among thousands).
 
Tests of Big Bang: Expansion from NASA by Official: Dr. Gary F. Hinshaw,
Updated: Friday, 04-16-2010
http://map.gsfc.nasa.gov/universe/bb_tests_exp.html

Universe is Expanding - "Red Shift" is Proof of Einstein's General Theory from "Cosmic Times is a product of the Imagine the Universe! website. Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan P. Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center. . .
Last Updated: Tuesday, 05-Jan-2010 16:34:49 EST"
Best to review the contents online from the link (url) below:
http://cosmictimes.gsfc.nasa.gov/online_edition/1929Cosmic/expanding.html
 
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