Warp schrieb:

>   There seems to be some confusion about what exact does it mean that the
> universe is expanding. I have read two different explanations:
> 
> 1) New space is appearing *everywhere*, making *all* distances larger over
> time, including eg. distances between subatomic particles.
> 
> 2) New space is appearing between galaxies, making only the distance between
> galaxies grow larger over time. (The reason for this is that when you are
> close enough to a galaxy, its gravitational pull is stronger than the
> "outwards" movement caused by the expansion of the universe, which means
> that gravity stops you from getting farther away from the galaxy due to
> this expansion. In a way, you are "tied" to the galaxy and don't get farther
> away from it (from the expansion phenomenon alone).)

I think #2 is just #1 taking into account the attractive forces working 
simultaneously, so I see no difference there; so I'd say space is 
appearing everywhere, but it's not noticeable at subatomic levels 
because the attractive forces compensate for it.

In case the rate of "space growth" should be indeed increasing (as some 
scientists claim it is), then it might be possible that (a) this 
/acceleration of growth/ will cause the distance between subatomic 
particles to increase (as there will be a new distance of equilibrium 
between "space growth" and all the other forces), and (b) the rate of 
"space growth" might some time in the future exceed the attractive 
forces' ability to compensate, so that "space growth" itself (and not 
just the acceleration thereof) might drive even subatomic structures apart.

>   It also seems to be some kind of common misconception that the expansion
> of the Universe would somehow change units of measurements accordingly.

Well, obviously it cannot change units of measurements: Those are 
/defined/. What it /can/ change is (a) practical realizations of 
measurements, and (b) possibly the value of natural "constants" as 
expressed in these units of measurement.

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clipka wrote:
> I was indeed slightly mistaken: The original definition was for water at 
> the /melting point/, which is a bit above 0 degrees C (something like 
> 0.01 degrees C, IIRC).

I think the 4C was because that's the temperature at which liquid water is 
most dense.


-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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Warp schrieb:
> 
>   Think about two small spheres connected by a wire on the surface of a
> balloon: Even if you inflate the balloon, the wire will keep the spheres
> at the same distance from each other, against the separating force caused
> by the inflation of the balloon.

Two spheres connected with a rubber band would be a better analogy: 
While you inflate the balloon, the rubber band would keep the spheres at 
a /constant/ distance, but it would be a different one than if the 
balloon wasn't being inflated.

And the rubber band would be stretched even further if you'd increase 
the rate of inflation.

>>>   The same is true at macroscopic levels: The Earth is not expanding because
>>> atomic bonds and gravity are strong enough to stop any expansive drift from
>>> happening. 
> 
>> It doesn't stop the drift. It compensates for the drift.
> 
>   Terminology.

Not if you think of /changing/ parameters. In that case it starts 
becoming a fundamental difference.

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Darren New schrieb:
> clipka wrote:
>> I was indeed slightly mistaken: The original definition was for water 
>> at the /melting point/, which is a bit above 0 degrees C (something 
>> like 0.01 degrees C, IIRC).
> 
> I think the 4C was because that's the temperature at which liquid water 
> is most dense.

Not exactly: They moved to 4 degrees C because it is the temperature at 
which the density is /most stable/, so the influence of getting the 
temperature wrong is minimized.

(Though of course this is closely related to the fact that at 4 degrees 
C water is most dense, too.)

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clipka wrote:
> which the density is /most stable/,
> 
> C water is most dense, too.)

Um, yes. We call that calculus. :-) But point taken.

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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Darren New schrieb:
> clipka wrote:
>> which the density is /most stable/,
>>
>> C water is most dense, too.)
> 
> Um, yes. We call that calculus. :-) But point taken.

Yes, given the simplicity of the density-vs-temperature function, 
calculus indeed correctly postulates that these temperatures must happen 
to coincide :-)

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clipka <ano### [at] anonymousorg> wrote:
> Well, obviously it cannot change units of measurements: Those are 
> /defined/. What it /can/ change is (a) practical realizations of 
> measurements, and (b) possibly the value of natural "constants" as 
> expressed in these units of measurement.

  I don't think that's the case, given that units of measurements (at least
in the SI system) are defined by natural constants, not the other way around.

-- 
                                                          - Warp

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Mike Raiford wrote:
> http://blogs.ngm.com/blog_central/2009/10/a-grander-k.html

They've been talking about this since at least the mid 90s (when I first 
heard about it), but this is the first time I've actually seen a picture 
of the weight they use.  Nice and shiny :)

...Chambers

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On 10/13/2009 12:59 PM, Warp wrote:
>    As far as I have understood, explanation #1 is a misconception. Distances
> between subatomic particles is not growing because the forces keeping atoms
> and molecules together is way stronger than any minuscule drift that the
> expansion of the universe might cause.

The gravitational force of the sun is also "way stronger" than the 
gravitational force of the Hubble telescope. That doesn't mean it has 
zero effect on us sitting here in front of our computers. :)

-Mike

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Warp schrieb:
> clipka <ano### [at] anonymousorg> wrote:
>> Well, obviously it cannot change units of measurements: Those are 
>> /defined/. What it /can/ change is (a) practical realizations of 
>> measurements, and (b) possibly the value of natural "constants" as 
>> expressed in these units of measurement.
> 
>   I don't think that's the case, given that units of measurements (at least
> in the SI system) are defined by natural constants, not the other way around.

Well, that's actually far from the truth. For instance, the 
gravitational constant is nowhere to be found in the SI system, nor is 
the planck mass, electron charge etc.

As a matter of fact, the only /fundamental/ natural constant presently 
used in the SI system is the speed of light; all other SI units are 
based on physical properties that are only indirectly affected by 
natural constants.

And no, units of measurement cannot change /by definition/, because it's 
by them that we measure the properties of the world, including natural 
constants.

This is counter-intuitive to what any sane person would think (which is 
why you're disputing it I guess) - but who said that scientists are sane 
in the first place?

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