Expanding space ?

[Dart15]

Hi All,

 

I am new to this forum.

 

I have a question that may well have been explored before :

 

"If space is expanding and it is expanding everywhere, does that mean that the space within an atom is expanding also. If so, has anyone ever calculated how long it will be before the forces holding the various parts of an atom together no longer work"

 

Stupid question ?

 

Dart15

[Airbrush]

Space is expanding, but only between superclusters of galaxies. Space is not expanding within galaxies, nor within solar system, and certainly not within atoms. Gravity overcomes the expansion of space, and certainly the atomic forces prevent atoms from expanding.

[sananda]

interesting question though... if everything was expanding in unison, then how would we ever know...

[Spyman]

If so, has anyone ever calculated how long it will be before the forces holding the various parts of an atom together no longer work

 

Like Airbrush says, gravity and atomic forces overcomes the expansion and keeps stuff in place, but it has been calculated:

 

In their paper they consider an example with ω = -1.5, H0 = 70 km/s/MPsec and Ωm = 0.3, in which case the end of the universe is approximately 22 billion years from now. This is not considered as a prediction, but as a hypothetical example. The authors note that evidence indicates ω is very close to -1 in our universe.

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

 

If ω is precisely -1 the Universe will continue to expand forever but not get ripped apart and with ω smaller than -1 the Universe will eventually start to collapse.

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

[Martin]

...

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

...

 

Often it's really helpful to quote Wikipedia---they have some excellent articles. But every now and then they have a bad one. Here they mix up w and omega. The italic w does look like the lowercase Greek letter. And they cite a single peer-reviewed source article and copy just one equation from it----and screw up. They don't copy it right, so they would get a negative time between now and big rip.

 

You might want to check the source they cite. It is from 2003 and one of the authors is Marc Kamionkowski. They give a link.

Edited September 2, 2009 by Martin

[Spyman]

Here they mix up w and omega.

Thanks for the correction Martin, actually I think I caused the mixup myself and not Wikipedia.

 

They increased Dark Energy and not Omega to simulate the Big Rip in their paper.

 

 

Here is the correct quote from Wikipedia:

 

Closed universe

If Ω > 1, then the geometry of space is closed like the surface of a sphere. The sum of the angles of a triangle exceeds 180 degrees and there are no parallel lines; all lines eventually meet. The geometry of the universe is, at least on a very large scale, elliptic.

 

In a closed universe lacking the repulsive effect of dark energy, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch," by analogy with Big Bang. However, if the universe has a large amount of dark energy (as suggested by recent findings), then the expansion of the universe can continue forever – even if Ω > 1.

 

Open universe

If Ω < 1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of such a universe is hyperbolic.

 

Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip," where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak binding forces.

 

Conversely, a negative cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a big crunch. This option has been ruled out by observations.

 

Flat universe

If the average density of the universe exactly equals the critical density so that Ω=1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance.

 

Absent of dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching a fixed rate. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe.

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

 

 

And here is a quote from the "Phantom Energy and Cosmic Doomsday" paper:

(by Robert R. Caldwell, Marc Kamionkowski and Nevin N. Weinberg)

 

As we now show, if w < −1 persists, then the fate of the Universe is quite fantastic and completely different than the possibilities previously discussed. To begin, let us review these other fates. In a flat or open Universe without dark energy, the expansion continues forever, and the horizon grows more rapidly than the scale factor; the Universe becomes colder and darker, but with time the co-moving volume of the observable Universe evolves so that the number of visible galaxies grows. If the expansion is accelerating, as a consequence of dark energy with −1 ≤ w < −1/3, then the expansion again continues forever. However, in this case, the scale factor grows more rapidly than the horizon. As time progresses, galaxies disappear beyond the horizon, and the Universe becomes increasingly dark. Still, structures that are currently gravitationally bound, such as the Milky Way and perhaps the Local Group, remain unaffected. Thus, although extragalactic astronomy becomes less interesting, Galactic astronomy can continue to thrive. ... If Ω ~ 0.3, then the Universe is already dark-energy–dominated, and for w < -1 it will become increasingly dark-energy–dominated in the future.

http://arxiv.org/PS_cache/astro-ph/pdf/0302/0302506v1.pdf

[TheStones]

think of it as a city..... it will continue to expand to the outer regions of the city.... but the inner city, say the streets, or the buildings... they do not expand... they stay the same size... just like the atoms in the Universe... they stay the same size while our Universe expands into a "void" if i may call it that, that we didn't yet call it our Universe that it expands into. i hope i made the comprehendible to something you can relate too!!!!

[purintjp]

Flat universe

If the average density of the universe exactly equals the critical density so that Ω=1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance.

 

Absent of dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching a fixed rate. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe.

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

 

 

As I understand it, it is believed that the universe is flat as stated above

by current thinking.

 

I was wondering how those lines stay parallel when they get beyond our

local galaxy cluster and are affected by the expansion of space so that

they are no longer parallel; ie., as two laser beams shot parallel into

space. It seems to me that the expansion creates a defacto curved space.

[Airbrush]

The concept that the universe is flat, or so nearly flat that any curvature is not detectable, means that it curves back on itself. Parallel lines may meet. Expansion of space, although may be a kind of curvature of space as you argue, is not the kind of curvature that the closed universe concept implies.

[zombie]

Aren't all galaxies headed into the same direction? a 20 degree area in space relative to our location between the constellations of Centaurus and Vela (Dark Flow)

 

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

[Martin]

It's controversial still, as far as I'm aware.

Ned Wright criticized Kashlinsky et al's paper.

At first I thought the crit would probably stick and Kashlinsky "dark flow" was effectively tossed out.

But then Kashlinsky answered the criticisms and made some corrections and admitted some of Ned Wright's points. But it seems to still stand.

 

They say they tested out to a distance of 1.3 billion or 1.4 billion lightyears.

 

I don't know how solid the statistics are and how much random variation.

 

The average speed of the drift, according to them, was around 600 km per second.

 

Have to keep in mind that it is controversial. Hasn't been confirmed by any other study that went out such a large distance.

 

It has been known for quite a while that there was an average motion in our immediate neighborhood (Virgo Cluster and surrounding smaller stuff) in that Hydra etc direction of about that size like 600 km/'s.

 

What Kashlinsky is saying is that this known motion extends 10 times farther out, includes a much larger flock of galaxies.

 

It is still not ALL galaxies. The catalog they used only goes out to like 1.4 billion LY, present distance. And we actually see galaxies out much farther.

Like redshift z = 7, corresponding to a present distance of about 29 billion LY.

 

I don't know how far out their method of estimating the speed of a galaxy through the CMB would be valid. At this point I'd be cautious about drawing any conclusion.

Maybe someone who has a more recent source will give us an update on this.

 

Here's a Kashlinsky et al source paper:

http://arxiv.org/abs/0809.3734

Published in Astrophysical Letters October 2008.

Edited September 21, 2009 by Martin

[axenome]

I wonder... just how "clean" is the vacuum between galaxy clusters? And how that mean density affects spacetime in relation to curvature? If what we perceive as linear space is itself curved by another force not being countered by the gravitational forces we ourselves experience in more dense regions, could that curvature account for red shift more logically than assuming the rest of the universe is speeding away from us? Especially since our closest cosmic neighbors seem to actually be geting closer?

 

Okay let me elaborate- if you impose a linear sine wave on a euclidean graph paper next to a parabola, then traverse the parabola to experience the crests and troughs of that sine wave from the perceived reality of the hyperbola, then the further away from the closest interval between the parabola and the sine wave corresponds to a larger interval between our perceptions of the crests and troughs, thus immitating a doppler effect although for different reasons than would be logical in linear, transitional space. There would be a perceptual oddity in the trough-to-crest measurement compared to the crest-to-trough measurement, but for a shallow enough parabola it might really be all but indistinguishable for us unless we were to deliberately look for it with instrumentation exacting enough to tell the difference between a skewed sine wave and a pure one. A steady motion away from one another would, through the change of the source of the sine wave, be easily misconstrued as an acceleration in the expansion of the universe.

Edited October 1, 2009 by axenome

[rrw4rusty]

interesting question though... if everything was expanding in unison, then how would we ever know...

 

Time travel! Before I understood that 'everything' was not expanding I had some interesting sci-fi stories planned on time travel!

 

Imagine moving forward in time and suddenly your an inch tall!

 

Or going back in time and having to duck to keep from hitting your head on the moon!

 

From the armchair,

Ron