Relativity and Cosmology Blog

# Relativity and Cosmology

This is a Blog on relativity and cosmology for engineers and the like. My website "Relativity-4-Engineers" has more in-depth stuff.

Comments/questions of a general nature should preferably be posted to the FAQ section of this Blog (http://cr4.globalspec.com/blogentry/316/Relativity-Cosmology-FAQ).

A complete index to the Relativity and Cosmology Blog can be viewed here: http://cr4.globalspec.com/blog/browse/22/Relativity-and-Cosmology"

Regards, Jorrie

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# Cosmology Equations

Posted October 15, 2006 1:50 AM by Jorrie

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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#1

### Re: Cosmology Equations

10/16/2006 7:52 AM

An interesting graph. I however have a question about the tear drop. Before the sides of the tear drop reach vertical dose it mean that you would be unable to see the background radiation of the big bang as we can now and wouldn't this make it a dark universe.

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#2

### Re: Cosmology Equations

10/16/2006 10:57 AM

Hi Masu, I think many people will have this question: "Before the sides of the tear drop reach vertical does it mean that you would be unable to see the background radiation of the big bang as we can now and wouldn't this make it a dark universe."

Remember I said that initially the photons were being dragged away from us despite them moving at the speed of light towards us. This vicious expansion rate did eventually drop down under the mutual pull of gravity caused by the energy of the universe. Then those same photons started to make headway and eventually reached us!

I actually plotted that teardrop curve by modeling the movement of a photon over the expanding space. This does perhaps say more than all the waffling before!

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#3

### Re: Cosmology Equations

10/24/2006 2:44 PM

Despite the quite understandable waffling, may I assume your answer is yes?

Or maybe?

Bill Morrow

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#4

### Re: Cosmology Equations

10/24/2006 3:32 PM

Hi Bill, yep, it's a (hopefully) understandable "yes"!

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#5

### Re: Cosmology Equations

07/09/2007 7:00 AM

Presently Cosmology is undergoing REVISION and BIG-BANG,
Dark Matter,DARK ENERGY and Black-holes are all under question.

Philosophy of Science : Plasmas, Electro-magnetic fields and Cosmology

Search:http://cosmologyvedas.blogspot.com/

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#6

### Re: Cosmology Equations

07/13/2007 5:23 PM

Guest-

I went to the link you gave and read the page. I have one response:

"Uh... what?"

Bill

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