Kenneth wrote:
> In other words, does the *relatively*
> vast space inside an atom itself--between the nucleus and its electrons--also
> expand? 

Sure. But then the electrons move closer to the nucleus again.

The math of quantum mechanics all works only if you assume quarks and 
electrons and photons are all mathematical points. So the electrons 
themselves don't expand.

> I find that every time I read about this particular subject, the explanation
> seems to be different than the *previous* explanation I've read. :-/ One
> particularly vexing explanation is this one (which seems kind of dubious): That
> the space between galaxy *clusters* expands, but the space between the galaxies
> *in* the cluster doesn't--"because local gravity effects overwhelm the greater
> cosmic expansion." That may well be true--from a simple observational
> standpoint--but it's no real answer to the more basic question, IMHO.

Because space expands slowly enough that the stars will fall back together 
again faster than the space is expanding, is what I think they're saying.

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

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Darren New <dne### [at] sanrrcom> wrote:

>
> I'm wondering if the fact that baryogenesis happened well after inflation
> had anything to do with it. Basically, there wasn't any mass until after the
> universe was big enough?
>

But energy and mass are equivalent--E=MC^2 and all that--so even before baryonic
matter 'arrived', wouldn't the raw energy content of the universe have exerted
gravity as well? Assuming the laws of nature were the same then (which, upon
further thought, might be a rather large assumption IMO.)

Ken

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Darren New <dne### [at] sanrrcom> wrote:
> Kenneth wrote:
> > In other words, does the *relatively*
> > vast space inside an atom itself--between the nucleus and its electrons--also
> > expand?
>
> Sure. But then the electrons move closer to the nucleus again.

Hmm, don't understand that. You mean, because of the 'set' attractive/repulsive
forces between electrons and nucleus? If so, very interesting--I hadn't thought
of that before. It *would* seem to keep the atom at the same size, regardless of
space expansion. And all of the atom's internal workings the same as well, since
the relative charges and distances haven't changed.
>
> The math of quantum mechanics all works only if you assume quarks and
> electrons and photons are all mathematical points. So the electrons
> themselves don't expand.

Agreed. (The idea of 'point-like' masses--with no spatial extension--is itself a
strange one!)

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Kenneth wrote:
> further thought, might be a rather large assumption IMO.)

I think that's the whole point of the quest for the Higgs, which is the 
particle that imparts mass to matter and energy.  That's why you need 
something awesomely powerful to create it.  Or something like that.

So, yeah, I think it's unclear (certainly to me) at what point general 
relativity kicked in. :-)

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

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Kenneth wrote:
> Hmm, don't understand that. You mean, because of the 'set' attractive/repulsive
> forces between electrons and nucleus?

I think you're going way beyond what I know. But I'm happy to BS for a 
while. ;-)

Electrons like to be a certain size, as provided for in their wavelength. 
(and by "size" I refer to the amplitude (i.e., probability) cloud.)  So you 
can add a tiny bit of space, and the electron will "shrink" in return, just 
like if you had two balls with a spring between them and you slowly slid the 
two halves of the floor apart, the spring would pull the balls back together.

OK, I'm officially not knowing what I'm talking about. But that's what I 
understood - the mutual attractions between things close enough that the 
expansion of space in the middle (gravity or QED) is what holds smaller 
things together even as the bigger things spread apart.

> Agreed. (The idea of 'point-like' masses--with no spatial extension--is itself a
> strange one!)

Well, that's why I clarified that's what the *math* says. Who knows the 
"reality" of it?

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

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Darren New <dne### [at] sanrrcom> wrote:
> Kenneth wrote:
> > Hmm, don't understand that. You mean, because of the 'set'
> > attractive/repulsive forces between electrons and nucleus?
>
> I think you're going way beyond what I know. But I'm happy to BS for a
> while. ;-)

Yes, cosmological B.S'ing is FUN!! (Much of what passes for current cosmological
theorizing by 'the experts' seems to me to be so much arcane B.S.--but that's
just me...)

The idea I had (which you kindled) was rather basic: If atomic forces remain
unchanging as intra-atom space expands, and if neutrons/protons/electrons remain
their same sizes too (points!), then it seems logical that the
attraction/repulsion forces at play would keep the atom the 'same size',
regardless of any expansion of space. (Assuming that the forces themselves don't
diminish as space expands.) Or something like that ;-)
>

> OK, I'm officially not knowing what I'm talking about. But that's what I
> understood - the mutual attractions between things close enough that the
> expansion of space in the middle (gravity or QED) is what holds smaller
> things together even as the bigger things spread apart.

I need to read more about that--sounds suitably cool and interesting, and new to
me. I think you had mentioned something similar in a previous post, which piqued
my interest at the time.

One of my own 'heroes of science' is Michael Faraday. Here was a rather typical
guy, no 'scientist' in any academic sense, with no advanced math training (or
any at all??), who nevertheless, by virtue of sheer *curiosity* and a good
experimental bent, came up with fundamental thoughts on electromagnetism--that
no one else before him had even imagined. There are probably thousands like him
in the world today--most of whom, with no scientific 'credentials,' will
probably never be heard from. But it certainly makes me wonder if seemingly
crackpot ideas by non-experts may, in fact, hold the key to the true
understanding of nature. Alas, it was probably easier (and more fruitful) being
a scientist in Faraday's time; practically *any* learned person could be a
natural philosopher, as there was no specialization then--and there were so
*many* things yet undiscovered.

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Kenneth wrote:
> a scientist in Faraday's time; practically *any* learned person could be a
> natural philosopher, as there was no specialization then--

I have read that Leonardo da Vinci was the last human to know essentially 
everything of importance. :-)

 > and there were so *many* things yet undiscovered.

I'm starting to feel the same way about computers. There's very few fields 
where an individual can really invent something useful without knowing how 
to scale it to run on hundreds of computers.

Smart phone apps and games seem the last bastion of where you can invent 
something by yourself and be a success.

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

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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   1) Spacetime inside an event horizon is pretty weird, and the spacetime
> > we currently reside in isn't (relatively speaking, at least).

> It's only weird if the event horizon is small. A galaxy-sized black hole, 
> you could fall into and not notice.

  I have hard time believing that. Space is extremely warped close to the
event horizon of a black hole. For example, at an altitude (from the central
singularity) of 3/2 of the Schwarzschild radius there exists the so-called
photon sphere: This is an area around the black hole where a photon could
orbit the black hole if it was traversing perfectly parallel to the "surface"
of the event horizon. If you were at that distance from the black hole,
it would look like the event horizon is a plane that occupies half of the
Universe. That's how warped the space is close to the event horizon.

  If you get closer to the event horizon than that, the event horizon will
look like it's curling up, engulfing you, and the rest of the Universe
would look like it would get compressed into an ever-shrinking circle
directly above. (When the circle shrinks to zero size, it means you have
touched the event horizon and are forever doomed. From this point forward
every direction points to the singularity. It's like the singularity would
surround you from all sides.)

  And this is completely independently of how big the black hole is.

  If the black hole is rotating (as most/all of them are assume to be),
it gets even weirder. There are now (AFAIR) two photons spheres of
different shapes, and additionally there's a space outside the event
horizon called an ergosphere which has weird physical properties. If
you get inside this ergosphere you will be dragged at a velocity larger
than c (relative to the rest of the Universe) around the black hole, so
I'm assuming it would look really, really weird.

  So I really don't buy the whole "you wouldn't even notice crossing the
event horizon". Maybe if you are completely blinded, you wouldn't (I really
don't know if there are any physical consequences of being close to the
event horizon of a very large black hole).

>  And it's not like you can get outside 
> the event horizon of the universe.

  Since the Universe is expanding faster than c, there's a so-called
cosmological horizon which limits the size of the observable Universe
(observable to us, of course; the observable Universe would naturally
be different in an alien planet on the other side of the Universe).

  However, this horizon is caused by the expansion of the Universe, not
by gravity, and it's always relative to where the observer is to begin
with.

> >   2) All spacetime geodesics inside an even horizon point towards the
> > singularity. (Ok, in a rotating black hole it's more complicated than
> > that, but in principle I suppose it's the same.) We are not moving towards
> > a singularity; we are expanding, hence moving *away* from any possible
> > "central point" of the Universe. That kind of contradicts the idea.

> Unless there'a big crunch? :-)

  Current observations seem to indicate that there won't be.

> >   Of course I am no physicist, and I have zero knowledge of the GR
> > equations, so I could be completely off track with this. My point is,
> > however, that I just don't understand how that hypothesis could be even
> > worthy of consideration.

> I think it was more popular before people found dark energy and thought we 
> were heading for a "big crunch" or something?

  I think the word "found" is wrong here. It hasn't been measured; it's a
hypothesis. (It could perfectly well be the *correct* hypothesis, but until
it's measured it's just that.)

-- 
                                                          - Warp

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Kenneth <kdw### [at] earthlinknet> wrote:
> Something I've always wondered about (and which I've never been able to find an
> answer to, in any layman's science book) is this: If space expands (not just the
> space *between* objects, but space itself), then at what scale, what microscopic
> level, does this process cease? If at all?

  IIRC the Universe only expands (ie. new space is formed) at intergalactic
space, not inside galaxies. The gravity of galaxies is high enough to stop
(or at least greatly diminish) expansion from happening inside them.

> If it does, then, since essentially *everything* expands equally

  Everything does *not* expand equally. Gravity works against the expansion,
slowing it down (if not even stopping it completely), AFAIK.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:

>   IIRC the Universe only expands (ie. new space is formed) at intergalactic
> space, not inside galaxies. The gravity of galaxies is high enough to stop
> (or at least greatly diminish) expansion from happening inside them.
> [clip]
> Everything does *not* expand equally. Gravity works against the expansion,
> slowing it down (if not even stopping it completely), AFAIK.
>

So in other words, local gravity effects actually keep local *space* from
expanding? If so, that's a new concept for me; I thought space itself--whatever
it actually *is* ;-) --was sort of 'independent' of gravity, expanding at its
own independent pace, as its own 'entity.' Although, now that I think of it,
"gravity warps space," so what you say isn't so weird after all. Geez, that's
always been a difficult concept to grasp. But is 'new space' actually formed? Or
is it just 'stretched' (whatever *that* concept means)?

Ken

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