Is the Expanding Universe Slowing Down According to Age?

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Discussion Overview

The discussion revolves around the concept of the expanding universe and whether the observed expansion suggests that the universe is slowing down with age. Participants explore the implications of distance and age on the perceived speed of galaxies, as well as the relationship between the expansion rate and the Hubble constant.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that farther objects are observed as moving away faster than closer objects, raising the question of whether this implies the universe is slowing down due to the age of these objects.
  • Another participant clarifies that the perception of older objects is due to the finite speed of light, and that all objects at a similar distance from a chosen origin recede at the same rate, as defined by the Hubble constant.
  • A subsequent reply asserts that the universe's expansion is actually accelerating, suggesting that ancient galaxies are observed from a time when the universe was expanding at a slower rate.
  • Another participant proposes that if older images of galaxies correspond to faster movement, it could imply an inverse relationship between a galaxy's age and its speed, suggesting a potential slowing down of expansion over time.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the observed expansion of the universe. While some agree on the mechanics of the Hubble constant and the nature of light travel time, there remains contention regarding the interpretation of age and speed relationships, leaving the discussion unresolved.

Contextual Notes

Participants discuss the implications of the finite speed of light and the assumptions involved in interpreting the expansion of the universe, but do not resolve the mathematical or conceptual complexities involved.

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i've seen many documentaries. most recently nova had one on the expanding universe which prompted me to send them (nova@wgbh.org) the following:

based on the nova shows I've seen, they suggest the universe is expanding.
farther objects are observed as moving away faster than closer objects.
but the farther objects are also older, so according to age, wouldn't that mean that the universe is slowing down?
also, are all objects at a similar distance moving away at a similar speed?
===
they sent a response that said they forwarded to their producers, but in the meanwhile, i thought i'd look elsewhere...

thanks in advance for any responses.
 
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Farther objects are older to US because we can only observe them as they were in the past depending on how long light from that object took to get to us. But if you take a constant slice of time at any instant and analyze the observable universe (this is all mathematically) all objects, and I mean at the large where isotropy and homogeneity are preserved, are of course the same distance in time from t = 0. The rate at which objects recede from whatever you pick to be the origin (since you do have that freedom) is directly proportional to the distance between the object and your chosen origin. Objects all at the same distance from "the origin" will recede at the same rate.
 
The answer to your last question is yes. The Hubble constant which is used to measure the expansion of the universe is based on an expansion speed per distance from us.

So, picture the universe expanding uniformly in all directions. So, the further away a particular object (e.g., galaxy) is, the more expanding space there is between you and it. So it appears to be moving away faster than something which is closer.

And due to the finite speed of light, the older it appears to us (not actually older...it's just that we're seeing it's past because light from its present state has not reached us yet).

So, the ancient galaxies we're seeing at great distances are not causing the universe to slow down. But since the universe expansion is actually accelerating, I suppose we're seeing those ancient galaxies from a time when the universe was expanding at a slower rate.

Clear as mud?
 
Phobos said:
But since the universe expansion is actually accelerating, I suppose we're seeing those ancient galaxies from a time when the universe was expanding at a slower rate.
Clear as mud?

but since we are seeing the galaxies as they were a long time ago - the further away, the further back into the past - and the older the image, the faster it is moving...
that would imply to me that the galaxy's age is inversely proportionate to it's speed.
the newer the image, the slower it is moving. wouldn't that mean that things are slowing down as time goes on?
 
Last edited:
thanks for answering the other quetion, btw
 

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