# The Naked Scientists Forum

### Author Topic: How do scientists calculate how far back in time events occurred?  (Read 1040 times)

#### thedoc

• Sr. Member
• Posts: 508
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##### How do scientists calculate how far back in time events occurred?
« on: 01/05/2013 13:30:01 »
Tom Brown  asked the Naked Scientists:

As the objects in the universe that we can observe only give us information about the past, and the distance in the past depends upon the distance that objects are from us.

How do scientists compensate for this when they generate equations to define the universe as it is at a given moment ?

Regards
Tom

What do you think?
« Last Edit: 01/05/2013 13:30:01 by _system »

#### Chonardo

• First timers
• Posts: 1
##### Re: How do scientists calculate how far back in time events occurred?
« Reply #1 on: 01/05/2013 14:58:36 »
This newbielink:http://ncse.com/evolution/science/age-universe-measuring-cosmic-time [nonactive] provides a very vivid explanation on measuring cosmic-time. Hope it helps!

#### Pmb

• Neilep Level Member
• Posts: 1838
• Physicist
##### Re: How do scientists calculate how far back in time events occurred?
« Reply #2 on: 02/05/2013 02:47:08 »
Tom Brown  asked the Naked Scientists:

As the objects in the universe that we can observe only give us information about the past, and the distance in the past depends upon the distance that objects are from us.

How do scientists compensate for this when they generate equations to define the universe as it is at a given moment ?

Regards
Tom

What do you think?
There are formulas from cosmology which are calculated using general relativity to determine this. One measures the redshift of a galaxy and from that one calculates how long ago the light left it. It's pretty complicated. Especially if you don't know general relativity.

The details can be found in Exploring Black Holes - Second Edition which is online at
http://exploringblackholes.com/

I'm not sure what chapter its in. You'll have to do a bit of work to find it. I can understand the derivations and use them but I forget them soon after so I'd have to be knee deep in it to give details and my mind has been on other things lately, namely differential geometry and exterior derivatives etc.

#### The Naked Scientists Forum

##### Re: How do scientists calculate how far back in time events occurred?
« Reply #2 on: 02/05/2013 02:47:08 »