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In this 'mini-series', I will describe the workings of some of the most used basic cosmology equations. As an introduction, something about the space-time of the observable universe, which is represented by the parabola and the "teardrop" shape in this figure from Relativity 4 Engineers:
The parabola is what happened to the extremes (observable horizon) of our observable universe since the Big Bang (BB), located at the origin. The teardrop shape represents the paths of photons that started out toward us shortly after the BB and have just reached us (basically the cosmic microwave background radiation).
During the extreme spatial expansion at the beginning of time, these photons were carried away from us for some time, despite traveling towards us at the speed of light across their local space. When the expansion rate decreased sufficiently due to gravitational attraction, the photons started to get nearer to us and could eventually reach us.
Note that we (the observers) are still at the space coordinate of the BB, but separated from it by some 13.5 Gy in the time coordinate. This is however only so because we were free to choose a coordinate system centered on ourselves. Possible observer in other galaxies could have done the same and could have come up with the same diagram.
In the next mini-article, some relevant equations from Relativity 4 Engineers will be discussed.
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Re: Cosmology Equations
