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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4 comments

Pleasure to Promote CR4

Posted September 16, 2006 3:39 PM by Jorrie

This new-look CR4 is so good that I am giving it some prominence in the next issue of my newsletter (Relativity 4 Engineers Monthly). Thanks guys!

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The Feature Creep

Join Date: Feb 2005
Location: Boston, MA
Posts: 1055
#1

Re: Pleasure to Promote CR4

09/18/2006 1:25 PM

Thanks, we can use all the good press we can get

Its users like you that every community needs and we hope that other people will share this site with friends and coworkers. We've put a lot of blood, sweat and tears into the new site design and were glad to see it get such a warm reception.

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Guru
Engineering Fields - Aerospace Engineering - Retired South Africa - Member - The Rainbow-nation Engineering Fields - Engineering Physics - Relativity & Cosmology Popular Science - Cosmology - The Big Picture!

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#2
In reply to #1

Contents of Last Relativity 4 Engineers Newsletter

09/19/2006 3:02 PM

Equinox Special

In this issue:

1. Relativity 4 Engineers eBook Special

2. Applauding CR4 - The Engineer's Place



1) Relativity 4 Engineers eBook Special

One of the great forums for engineers and the like, CR4 (see the next topic), has just upgraded to a new look and feel. To applaud their excellent efforts, we decided to offer the eBook on that forum for a seriously discounted price of just USD 20.00, valid until October 5, 2006.

Obviously, you, as valued subscriber of the Relativity 4 Engineers Newsletter, are also eligible for a special price - even better than the CR4 price - you can have it at half the release price: USD 17.50!

To take advantage of the limited offer, please click on this link (only available to subscribers):

Relativity 4 Engineers eBook Special

or

Subscribe to Relativity 4 Engineers Newsletter


2) Applauding CR4 - The Engineer's Place

CR4, part of Globalspec, a highly rated engineering search engine, is a discussion forum for engineers and other technical trades. CR4 is an acronym for Conference Room 4, the place where engineers like to gather for engineering talk and other related (or unrelated) matters. My spouse suggested that CR4 might just as well mean Coffee Room 4!

Click on the following links to visit the CR4 forum and the Globalspec site - if you don't already know them, you may be pleasantly surprised.

CR4 - The engineer's place

Globalspec engineering search engine


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Active Contributor

Join Date: Oct 2006
Posts: 14
#3
In reply to #2

Re: Contents of Last Relativity 4 Engineers Newsletter

10/09/2006 5:44 PM

1. Relativity 4 Engineers eBook Special

Thank's for your ebook I downloaded a coupple days ago. I tried to read but outside of tensor's algebra that I don't master, something else is bathering me: time.

In every day life, as well on my oscilloscope (2 GHz bandwith & 10 Ms/s) time is allways going forward. Then physical time NEVER goes backward: the arrow of time.

When using a mathematical model for space time with four coordinates x,y,z & t, the variable t is given the same nature as the three other spatial coordinates. The mathematical time can go backward??? The physical time does not?

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Guru
Engineering Fields - Aerospace Engineering - Retired South Africa - Member - The Rainbow-nation Engineering Fields - Engineering Physics - Relativity & Cosmology Popular Science - Cosmology - The Big Picture!

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Location: 34.02S, 22.82E
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#4
In reply to #3

Re: Contents of Last Relativity 4 Engineers Newsletter

10/10/2006 2:09 AM

Quote: "When using a mathematical model for space time with four coordinates x,y,z & t, the variable t is given the same nature as the three other spatial coordinates. The mathematical time can go backward??? The physical time does not?"

Firstly, there is very little use of tensors in the eBook - mainly just good old engineering-like sums!

Your question: yep, in math and models we can run time backwards and get valid results. Physical time just doesn't want to go backwards as far as we know. Time travel is possible, but only in the forward direction. If we could go back in time, all sorts of paradoxes might arise - you know some, I'm sure.

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