On 01/12/2010 5:13 PM, Le_Forgeron wrote:
> Some people will never get the relativity stuff correctly.

I supoce it depends on their viewpoint ;-)

-- 
Regards
     Stephen

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Stephen <mcavoys_at@aoldotcom> wrote:
> Nice but: ???These galaxies are rushing away from us, in some cases, 
> faster than the speed of light???.
> The images are awe inspiring but the words crap. IMO.

  And exactly what is wrong about that statement?

  Firstly, general relativity does not forbid the distance between two
points in space (and hence the distance between two particles, or two
galaxies) from growing faster than c. On the contrary, GR *predicts* this
to happen. What GR forbids is a particle *traveling* between two points
faster than c.

  The expansion of the universe causes galaxies which are sufficiently
far away from each other to recede from each other faster than c. This
does not contradict GR (but it is, in fact, a prediction of GR). In fact,
at the initial stages of the universe it is estimated that the expansion
rate was exponential, much much faster than it is today. Yet even today
there all parts of the universe which are farther away from us than a
certain distance are receding from us farther than c. This is the basis
for the concept of "cosmological horizon", which basically means that
the observable universe (ie. observable by us) is smaller than the entire
universe.

  The expansion of the universe is not the only situation where distances
growing faster than c is predicted to happen. Another situation is within
the so-called ergosphere of a rotating black hole (look it up). A particle
inside the ergosphere (but outside the event horizon) will be dragged to
a speed faster than c with respect to the rest of the universe. Again,
this does not contradict GR. On the contrary, this is a *prediction* of GR.

  Secondly, the expansion of the universe causes for the change in distance
between galaxies to accelerate. The speed at which some galaxy is receding
from us is today higher than it was a billion years ago.

  What we are seeing in the ultra deep field picture is what those galaxies
looked like billions of years ago. At this moment (in other words, billions
of years *after* the galaxies in question sent those photons which were
captured by Hubble) their recession speed has accelerated to the point
that they are receding from us faster than c.

  Again, not against GR, but supported by it.

-- 
                                                          - Warp

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On 01/12/2010 6:10 PM, Warp wrote:
>    And exactly what is wrong about that statement?
 > ...

So you are saying that the universe is expanding at a speed faster than 
the speed of light?

And, if you heard the commentary in Finish you might agree that it is 


-- 
Regards
     Stephen

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Stephen <mcavoys_at@aoldotcom> wrote:
> On 01/12/2010 6:10 PM, Warp wrote:
> >    And exactly what is wrong about that statement?
>  > ...

> So you are saying that the universe is expanding at a speed faster than 
> the speed of light?

  Yes.

http://en.wikipedia.org/wiki/Metric_expansion_of_space

"While special relativity constrains objects in the universe from
moving faster than the speed of light with respect to each other,
there is no such theoretical constraint when space itself is
expanding. It is thus possible for two very distant objects to be
moving away from each other at a speed greater than the speed of light
(meaning that one cannot be observed from the other). The size of the
observable universe could thus be smaller than the entire universe."

> And, if you heard the commentary in Finish you might agree that it is
> "dumbed down".

  I don't understand this comment.

-- 
                                                          - Warp

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On 01/12/2010 7:01 PM, Warp wrote:
> Stephen<mcavoys_at@aoldotcom>  wrote:
>> On 01/12/2010 6:10 PM, Warp wrote:
>>>     And exactly what is wrong about that statement?
>>   >  ...
>
>> So you are saying that the universe is expanding at a speed faster than
>> the speed of light?
>
>    Yes.
>
> http://en.wikipedia.org/wiki/Metric_expansion_of_space
>

OK, thanks. I did not know that.


>> And, if you heard the commentary in Finish you might agree that it is
>> "dumbed down".
>
>    I don't understand this comment.
>


not prepared to do that.  Sorry.

-- 
Regards
     Stephen

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On Wed, 01 Dec 2010 20:37:51 +0200, Stephen <mcavoys_at@aoldotcom> wrote:

> On 01/12/2010 6:10 PM, Warp wrote:
>>    And exactly what is wrong about that statement?
>  > ...
>
> So you are saying that the universe is expanding at a speed faster than  
> the speed of light?
>
This looks like a misunderstanding to me. Isn't that like saying if 2 cars  
are moving away from each other each with a speedo reading of 100kph that  
they are moving at 200kph?

-Nekar Xenos-

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And lo On Thu, 02 Dec 2010 07:45:38 -0000, Nekar Xenos  
<nek### [at] gmailcom> did spake thusly:

> On Wed, 01 Dec 2010 20:37:51 +0200, Stephen <mcavoys_at@aoldotcom> wrote:
>
>> On 01/12/2010 6:10 PM, Warp wrote:
>>>    And exactly what is wrong about that statement?
>>  > ...
>>
>> So you are saying that the universe is expanding at a speed faster than  
>> the speed of light?
>>
> This looks like a misunderstanding to me. Isn't that like saying if 2  
> cars are moving away from each other each with a speedo reading of  
> 100kph that they are moving at 200kph?

But they are from each other's perspective. If you stood there and watched  
them drive away you'd see them both doing 100kph, but why is your  
viewpoint more valid than that of either driver's?

A poor analogy for the galaxy movement is to imagine a flag placed either  
side of a tectonic rift. With either the plates moving apart or together  
can it be really stated that it's the flags that are moving?

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

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Le 02/12/2010 11:25, Phil Cook v2 nous fit lire :
> And lo On Thu, 02 Dec 2010 07:45:38 -0000, Nekar Xenos
> <nek### [at] gmailcom> did spake thusly:
> 
>> On Wed, 01 Dec 2010 20:37:51 +0200, Stephen <mcavoys_at@aoldotcom> wrote:
>>
>>> On 01/12/2010 6:10 PM, Warp wrote:
>>>>    And exactly what is wrong about that statement?
>>>  > ...
>>>
>>> So you are saying that the universe is expanding at a speed faster
>>> than the speed of light?
>>>
>> This looks like a misunderstanding to me. Isn't that like saying if 2
>> cars are moving away from each other each with a speedo reading of
>> 100kph that they are moving at 200kph?
> 
> But they are from each other's perspective. If you stood there and
> watched them drive away you'd see them both doing 100kph, but why is
> your viewpoint more valid than that of either driver's?

Seeing them going away at about 100kph each. In the "about", you must
put the speed of the light... you can neglect it for car, but not galaxy
far far away in the universe. Same goes for a driver, it's also about
200kph, with yet that speed of light to take into account.
(but the red shift for the car is really so small...)

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Nekar Xenos <nek### [at] gmailcom> wrote:
> On Wed, 01 Dec 2010 20:37:51 +0200, Stephen <mcavoys_at@aoldotcom> wrote:

> > On 01/12/2010 6:10 PM, Warp wrote:
> >>    And exactly what is wrong about that statement?
> >  > ...
> >
> > So you are saying that the universe is expanding at a speed faster than  
> > the speed of light?
> >
> This looks like a misunderstanding to me. Isn't that like saying if 2 cars  
> are moving away from each other each with a speedo reading of 100kph that  
> they are moving at 200kph?

  No, it's not like that. The expansion of the universe is not galaxies
moving away from each other because they had an initial velocity towards
some direction. It's about the space itself expanding, its geometry
changing.

-- 
                                                          - Warp

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Warp wrote:
> Nekar Xenos <nek### [at] gmailcom> wrote:
>> On Wed, 01 Dec 2010 20:37:51 +0200, Stephen <mcavoys_at@aoldotcom> wrote:
> 
>>> On 01/12/2010 6:10 PM, Warp wrote:
>>>>    And exactly what is wrong about that statement?
>>>  > ...
>>>
>>> So you are saying that the universe is expanding at a speed faster than  
>>> the speed of light?
>>>
>> This looks like a misunderstanding to me. Isn't that like saying if 2 cars  
>> are moving away from each other each with a speedo reading of 100kph that  
>> they are moving at 200kph?
> 
>   No, it's not like that. The expansion of the universe is not galaxies
> moving away from each other because they had an initial velocity towards
> some direction. It's about the space itself expanding, its geometry
> changing.

It's like two cars on a drawbridge, sitting still while the bridge opens, 
and hence moving away from each other even tho the parking brakes are on. :-)

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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