On 30-3-2010 20:15, Darren New wrote:
> andrel wrote:
>> On 30-3-2010 18:11, Darren New wrote:
>>> andrel wrote:
>>>>> How about the fact that the stars of the universe are all 
>>>>> red-shifted the farther they get from *us*?  Or the fact that we 
>>>>> seem to be the only creatures in the entire *universe* that 
>>>>> broadcast radio signals?
>>>>
>>>> For the latter see the Drake equation.
>>>
>>> I'm familiar with it. What about it?
>>
>> All we know that there are no radio signals broadcasted from a place 
>> exactly the right time ago to be just reaching us now, send towards 
>> us, and in a format that we recognize. Which is quite a long way away 
>> from a conclusion that no signals are send at all.
> 
> Yes. Hence the "seems to". Anyway, you understand my point even if you 
> disagree. :-)

yes

>>> Yep. That doesn't mean things are moving away from us. We can't 
>>> measure whether they're moving away from us. All we can measure is 
>>> the red shift. The assumption is that the red shift is caused by 
>>> relative motion, and not the geometry of the universe.
>>
>> I don't understand that last sentence, but that may be my physics 
>> background.
> 
> 
> We assume that the distant galaxies are red-shifted *because* they are 
> moving away from us. We don't assume that the Milky Way has the lowest 
> speed of light in the universe, or that time runs slower the farther you 
> get from humanity, or that the gravitational constant is slowly 
> increasing the farther you get from humanity.  *If* you assume that all 
> other places in the universe will see the same thing when they look 
> around, *then* all the galaxies must be moving away from each other.  
> *If* you assume we're in a unique and privileged place in the universe, 
> there are all kinds of things that could be causing it.

hence my "We say that because we believe in Lorentz invariance" as a 
abbreviation of a couple of paragraphs like the one above ;)

Post a reply to this message