Expansion of the Universe: Distinguishing No.1 & No.2

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Discussion Overview

The discussion revolves around the concept of the expansion of the universe, specifically distinguishing between two types of expansion: one associated with the Big Bang and inflation (referred to as Expansion No.1) and another linked to the current accelerated expansion attributed to dark energy (Expansion No.2). Participants explore the implications of cosmological redshifts and the evidence supporting these expansions.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes Expansion No.1 as the initial rapid expansion due to the Big Bang, which decelerated over time, evidenced by cosmological redshifts observed in distant galaxies.
  • The same participant argues that cosmological redshifts are often misinterpreted as evidence for the current expansion (Expansion No.2) rather than a reflection of the earlier deceleration of Expansion No.1.
  • Another participant contends that there is only one expansion but acknowledges that it can be divided into distinct epochs, providing a timeline of the universe's expansion history.
  • This participant describes the transition from inflation to normal expansion and the eventual dominance of dark energy, which leads to accelerated expansion.
  • One participant expresses doubts about the interpretation of redshifts, suggesting that decreasing redshifts in more recent observations indicate a deceleration of expansion rather than acceleration.
  • Another participant provides a link to external resources as evidence for the accelerating universe, though the validity of this evidence is not universally accepted in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the universe's expansion. There are competing views regarding the interpretation of cosmological redshifts and whether they support the existence of two distinct expansions or a single expansion with varying rates.

Contextual Notes

Participants reference specific redshift values and timelines, but there is uncertainty regarding the implications of these observations on the nature of expansion. The discussion highlights the complexity of interpreting cosmological data and the assumptions underlying different models of the universe's expansion.

krrazypassion
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Expansion of the universe: Aren't there 2 distinct expansions we are talking about?

Expansion No.1: This is caused due to Big Bang. Singularity expanded with huge acceleration. Also called inflation. With time, this expansion decelerated. It is observed in the cosmological redshifts. The deeper we look in space, the deeper into past we are looking. So, as we look deeper, we witness a younger universe. A universe as was sooner after big bang. Here, we see matter with large cosmological redshifts,up to 1089 in case of the Cosmic Microwave Background, which happened around 378000 years after Big Bang. The cosmological redshifts in case of very distant galaxies(currently received light from these has traveled 13.1 billion years) are 8, and this happened 652 million years after Big Bang. Closer galaxies(currently received light from these has traveled 11.5 billion years) show cosmological redshift of 3.

Expansion No.2: This is the reason why we are talking about increasingly expanding universe. And that leads to dark energy.

However, we are often given explanations of presently expanding universe due to Expansion No. 2 with the irrelevant examples of cosmological redshifts which are observed to be increasing as we look deeper, while these examples actually indicate only the fact that there was a big bang and inflation, and this expansion no.1 decelerated with time. Right?(read the first paragraph again if you didn't grasp the point I'm trying to make about expansion no.1 and cosmological redshifts)

Also, what are the relevant examples and evidences for expansion no.2 then?
 
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1) go to http://www.wolframalpha.com/
2) Enter “redshift”
3) You will see an entry with a note saying “Assuming Doppler redshift ”...Next to it there is a more drop-down. It gives 4 options. Select the cosmological redshift from the more drop-down.

4) Now you will get, by default, a redshift of 0.001 and results about it.
Change this value to 1089, 8, 4 and see the results every time. Especially Observe the big bang “timeline” and “time since big bang” row.

Getting what I mean to say about cosmological redshift and expansion no.1 now?
 


Umm, no, there is only one expansion... It makes sense to separate it into distinct epochs, perhaps, but I don't understand your question.

Here's the brief expansion history:
t=10^-43s: Planck era. Start here, take as initial conditions some matter densities, curvatures, and initial expansion rate.
t=10^-35s: GUT eta. Inflation happens. Period of very rapid expansion. Change in scale factor by about 10^30.
t=10^-28s (roughly): Expansion stops. Universe resumes its normal expansion. That is to say, there was the introduction at t=10^-35s of some scalar field which produced an extremely large negative pressure, thus acting as a cosmological constant to create accelerated expansion. But by 10^-28s, the particle decayed and the constituents of the universe are the normal matter, radiation, and dark energy (dominated completely, during this epoch, by radiation).
t~10000yr: Energy density of matter/radiation equal. Universe is decelerating at this point (but still expanding!)
t~7Gyr: Matter/Dark energy equal. At this point, universe begins accelerating.
t=14Gyr: Now!
(Note, numbers are only order of magnitude, don't mean to look them up right now)

One can label a redshift at any point along this timeline, by knowing how the scale factor was evolving as a function of time. So I don't understand why you think your "two expansions" (which don't even make sense to me) are meaningful.

Hopefully I've cleared up the question?
 


I still have doubts:
1)The red shift has been decreasing as we observe more recent universe. So this indicates deceleration of expansion rate as time has progressed. (as already illustrated in my question: "we see matter with large cosmological redshifts,up to 1089 in case of the Cosmic Microwave Background, which happened around 378000 years after Big Bang. The cosmological redshifts in case of very distant galaxies(currently received light from these has traveled 13.1 billion years) are 8, and this happened 652 million years after Big Bang. Closer galaxies(currently received light from these has traveled 11.5 billion years) show cosmological redshift of 3. " In fact, the cosmological red shift around 7Gyr is 0.76 and around 9Gyr is 0.45. So, its decreasing all the time! The cosmological redshift evidence only tells that universal expansion is decreasing!

So, what evidence do we have that universal expansion accelerated at 7Gyr as you stated?
 


Thanks! :)
 

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