Measuring Redshift to Support Accelerating Universe

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Discussion Overview

The discussion centers around the measurements and implications of redshift in relation to the concept of an accelerating universe. Participants explore the relationship between redshift, distance, and the expansion rate of the universe, considering both observational evidence and theoretical interpretations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that an increasing redshift of distant stars or galaxies over time indicates that the universe is expanding at an increasing rate.
  • Another participant clarifies that redshift measurements are taken from numerous stars across various distances, implying that redshift alone does not confirm acceleration.
  • Some participants argue that while redshift indicates expansion, it does not necessarily imply that the rate of expansion is increasing, questioning the measurability of changes in redshift over short time frames.
  • There is a discussion about how redshift measurements correspond to different times in the universe's history, with one participant emphasizing that light from more distant galaxies reflects the state of the universe at earlier times.
  • Another participant raises a question about the nature of acceleration, suggesting that the appearance of acceleration might be a result of the expansion of space rather than objects moving away from each other.
  • Some participants mention the importance of multiple methods and evidence, including supernova data, to support the idea of an accelerating universe.
  • There is a mention of tools and articles that could aid in understanding the relationship between redshift and time, as well as the implications of cosmic expansion.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of redshift data and its implications for the acceleration of the universe. There is no consensus on whether the evidence supports the idea of an accelerating expansion or if it could be interpreted differently.

Contextual Notes

Some participants express uncertainty regarding the measurability of changes in redshift over time and the implications of distance on redshift measurements. There are also discussions about the limitations of relying solely on redshift as evidence for acceleration.

  • #31
Thank you for your detailed explanations. I can follow all of them.

I should have noticed that the definitions of all parameters, constants and columns are displayed when mouse pointer is held above the "blue question-marks". I tried to click on them and nothing happened. I use Opera as web browser and for example it will not display Chart when I change "Display as" to "Chart". Now I tired Internet explorer and it works fine even with "chart display".

Is it possible to calculate all this variables inside the table by explicit mathematical formulas, or numerical methods are needed?
 
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  • #32
azerbajdzan said:
Thank you for your detailed explanations. I can follow all of them.

I should have noticed that the definitions of all parameters, constants and columns are displayed when mouse pointer is held above the "blue question-marks". I tried to click on them and nothing happened. I use Opera as web browser and for example it will not display Chart when I change "Display as" to "Chart". Now I tired Internet explorer and it works fine even with "chart display".

Is it possible to calculate all this variables inside the table by explicit mathematical formulas, or numerical methods are needed?

I believe numerical integration is needed for some of the calculations. Some of the equations can not be solved explicitly in closed form. But PF member Jorrie designed and programmed the table-calculator and he would be the right person to ask about how it was implemented.

There are several other cosmology calculators online but they do not make TABLES showing the whole history over an interval of time. They are "one-shot" calculators. However I think all the calculators use essentially the same numerical methods and the same basic equations.

Several other PF members besides Jorrie could also tell you more about the mathematical and computational details of standard cosmic model, including for example George Jones and Brian Powell (nick = bpowell).
I suppose you could write PM (private message) to either of them or to Jorrie, if you have technical questions. Or look for their posts on the open forum.

Nobody here is REQUIRED to reply to questions, of course :biggrin: but if you do not become a nuisance and ask too many questions too rapidly then people are usually pretty nice. good luck finding out about the standard cosmic model! if that is what you want to do.
 
  • #33
The calculator uses JavaScript, you can look up how it works.

var N = 10000000; // Number of fine grain steps
It is a numerical calculation.

Some simplified cosmologic models can be evaluated analytically.
 
  • #34
azerbajdzan said:
Is it possible to calculate all this variables inside the table by explicit mathematical formulas, or numerical methods are needed?

A brief description of the equations and numerical integration used in the LightCone tabular calculator is available here: http://cosmocalc.wikidot.com/advanced-user.
 

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