Entries by Jorrie

LightCone7 Tutorial Part III – How Things are Computed

In Part I and Part II of this mini-series, we have briefly discussed the basic user interface and the use of charts to depict the LCDM cosmological model. In this final part of the tutorial, we will summarize the computational methods used for all the output values. This serves as reference material for the LightCone7 […]

LightCone7Combo Tutorial Part II – Charts

Part I dealt with the basic user interface of LightCone7Combo. This part of the tutorial is about potentially useful cosmological insights to be gained from LightCone7 charts. As a first example, we will find the answer to a common question: when did cosmic expansion changed over from decelerating to accelerating? We could have jumped into […]

LightCone7Combo Tutorial Part I

LightCone 7 Combo is a versatile tabulating/charting cosmological calculator, useful for understanding the expansion history of the universe (and even some future expansion), based upon the Lambda-Cold-Dark-Matter (LCDM) model. Part I of this mini-series gives a broad overview of the user interface and the main functions. Follow-on parts will highlight some specific uses and techniques. […]

Approximate LCDM Expansion in Simplified Math (Part 4)

  Part 4: Cosmic Recession Rates An astronomer, accompanied by his amateur relativist friend, aimed a telescope at a distant galaxy and measured its redshift. It came out at exactly z=2. The astronomer thought for a moment and then said: “The recession rate of this galaxy exceeds the speed of light by about 20%”. His […]

The LCDM Cosmological Model in Simplified Math (Part 3)

  Part 3: Important Cosmological Horizons and Distances A question that often comes up is: “how big is the observable universe?” The question can have more than one answer, depending on the context, so cosmologists have given it a technical name and a precise definition. It is called the ‘particle horizon’, here indicated by Dpar, […]

Approximate LCDM Expansion in Simplified Math (Part 2)

  Part 2: Time and Distance In Part 1 we have seen how one of the simplest ways of expressing the fractional expansion rate of the universe, i.e. the Hubble value H, is with this equation: 2.1 [itex]H = (0.44 S^3+1)^{0.5}[/itex] zeit-1 Here S is the ‘stretch factor’, which is the inverse of the scale […]

Approximate LCDM Expansion in Simplified Math

  If we restrict ourselves to a spatially flat LCDM universe model, the first Friedmann equation can be written in a very simple form. Marcus started several PF threads in a collaborative effort to develop this simplified approach.[1] It is still a work in process, but here I summarize the main insights so far, the […]