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Offline Nieuwenhove

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expansion of space
« on: 17/08/2006 17:50:11 »
The expansion of space (Big Bang scenario) is generally thought of as occuring everywhere. On the other hand, atoms keep their same size, the distance between the earth and the moon seems to be constant, the distance between the planets and the sun is constant, the size of our galaxy seems to be constant, and so on. So, there seems to be large pathches of space which seem to be immune to expansion. Maybe one could argue that "bound systems" do not expand, but why should this be so ? Also galaxies can form clusters and even superclusters which do not follow the expansion of space. So, in the end, our universe is only allowed to expand in some "limited regions" in between all these bound systems. What kind of magic prevents such large regions of space to expand ?


 

Offline Mad Mark

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Re: expansion of space
« Reply #1 on: 17/08/2006 18:22:45 »
As far as I know which is not a lot!The only thing in your post that is constant is the size of the atom.
That is governed by zero point energy that holds the orbits of electrons around the nucleous .It is a highly tuned form of control,so high in fact that it gives rise to probably only 2 posibilities,either our Universe was god created or we are just one of a infinet multiverse.

Tomorrow lies outside our universe without it there would be no tomorrow.
 

Offline Nieuwenhove

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Re: expansion of space
« Reply #2 on: 17/08/2006 19:29:29 »
quote:
Originally posted by Mad Mark

As far as I know which is not a lot!The only thing in your post that is constant is the size of the atom.
That is governed by zero point energy that holds the orbits of electrons around the nucleous .It is a highly tuned form of control,so high in fact that it gives rise to probably only 2 posibilities,either our Universe was god created or we are just one of a infinet multiverse.


I should clarify my initial comment: With constant (size or separation) I mean not affected by the expansion of the universe. It is clear that the distance between earth and moon is not really constant, but this is due to other factors.
 

Offline Mad Mark

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Re: expansion of space
« Reply #3 on: 17/08/2006 20:41:05 »
I once posted a topic about everything expanding in scale including us, but because are measuring stick expanded aswell there would be no reference point to say if this is happening.

Tomorrow lies outside our universe without it there would be no tomorrow.
 

Offline lightarrow

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Re: expansion of space
« Reply #4 on: 19/08/2006 01:56:38 »
quote:
Originally posted by Nieuwenhove

 Also galaxies can form clusters and even superclusters which do not follow the expansion of space. So, in the end, our universe is only allowed to expand in some "limited regions" in between all these bound systems. What kind of magic prevents such large regions of space to expand ?

If I remember correctly, in a theory, it was proposed that quantum energy fluctuations in the primordial universe created a disomogeneity in the energy density, that couldn't later dissolve because it didn't have time, since (hypotesys ad hoc) there would have been a period of sudden great expansion (the "inflaction") which cooled down the universe "freezing" those disomogeneities, which then became galaxies, galactic clusters ecc.

As you say, these big structures are, however, a sort of bound systems, in which gravity attraction is (more?) important than the overall expansion.
« Last Edit: 19/08/2006 02:01:00 by lightarrow »
 

Offline Radrook

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Re: expansion of space
« Reply #5 on: 04/09/2006 00:31:36 »
The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion. These areas where gravity predominates over expansion are galactic clusters superclusters. So we have the spectacles of a universe in which distances between superclusters increases due to universal expansion and areas where matter cancels it out LOCALLY and prevents it from causing everything everywhere to fly apart. That's why scientists predict that in the far future we will be only able to see our local galaxies and nothing beyond because everything beyond will have faded into the distance and since the distance will be increasing faster than light the light from those now visible sources will not be able to reach us.

BTW
The expansion of space itself is not limited to light speed. The matter within the expansion is.
« Last Edit: 04/09/2006 00:34:13 by Radrook »
 

Offline Nieuwenhove

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Re: expansion of space
« Reply #6 on: 04/09/2006 06:26:18 »
quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?
 

Offline Radrook

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Re: expansion of space
« Reply #7 on: 04/09/2006 07:32:18 »
quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?




Scientists say that the expansion merely reacts to the density of matter in those regions by being unable to create distance between objects in those regions. How would that reaction be any different from the reaction of everything else to the force of gravity?

I just reread your question and I am begining to see what you mean.
Why should there be regions of space where matter overcame the expansion in the first place? One thing to keep in mind is that the universe wasn't as large as it was now and things were much closer together so that they could interact with each other.

In any case,the following article providesmuch info.
http://en.wikipedia.org/wiki/Big_Bang [nofollow]

« Last Edit: 04/09/2006 07:57:24 by Radrook »
 

Offline Nieuwenhove

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Re: expansion of space
« Reply #8 on: 04/09/2006 07:56:59 »
quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?




Scientists say that the expansion merely reacts to the density of matter in those regions by being unable to create distance between objects in those regions. How would that reaction be any different from the reaction of everything else to the force of gravity?



Suppose the expansion of space is occurring intrinsically everywhere including within our solar system. For the local gravity between say earth and sun to suppress this expansion, the effect of gravity would be to contract the space between earth and sun at exactly the right rate such that the net expansion would be zero. However, I do not know that a "space contraction effect by gravity" is predicted or included by general relativity. And if this is not the case, we are back at the original question ; what prevents the expansion of space within our solar system ?
 

Offline Soul Surfer

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Re: expansion of space
« Reply #9 on: 04/09/2006 09:19:15 »
The problem is one of measurement.  All space is probably expanding but you neeed one hell of a lot of space before you can measure it  by the time you have taken the Hubble constant which is about 70km/sec per Megaparsec down to human scale measurements.  It is totally unmeasurable.

To illustrate this the nearest stars are about 1 parsec away so the expansion on this scale is    70,000/1,000,000  meteres per second  ie a bit less than 1 cm/second  by the time you get down to earth sized distance it is way less than the seperation between one atom and the next and completely undetectable.

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Offline Nieuwenhove

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Re: expansion of space
« Reply #10 on: 04/09/2006 10:38:04 »
quote:
Originally posted by Soul Surfer

The problem is one of measurement.  All space is probably expanding but you neeed one hell of a lot of space before you can measure it  by the time you have taken the Hubble constant which is about 70km/sec per Megaparsec down to human scale measurements.  It is totally unmeasurable.

To illustrate this the nearest stars are about 1 parsec away so the expansion on this scale is    70,000/1,000,000  meteres per second  ie a bit less than 1 cm/second  by the time you get down to earth sized distance it is way less than the seperation between one atom and the next and completely undetectable.

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Offline Nieuwenhove

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Re: expansion of space
« Reply #11 on: 04/09/2006 10:49:06 »
quote:
Originally posted by Soul Surfer

The problem is one of measurement.  All space is probably expanding but you neeed one hell of a lot of space before you can measure it  by the time you have taken the Hubble constant which is about 70km/sec per Megaparsec down to human scale measurements.  It is totally unmeasurable.

To illustrate this the nearest stars are about 1 parsec away so the expansion on this scale is    70,000/1,000,000  meteres per second  ie a bit less than 1 cm/second  by the time you get down to earth sized distance it is way less than the seperation between one atom and the next and completely undetectable.

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Something went wrong with my last reply, so I'll try again ..

Thanks for your comment. I appreciate your statement that expansion of space is indeed occuring everywhere. And indeed, on the scale of the earth the effect would be unmeasurable. But what about expansion on the scale of a galaxy or even a cluster of galaxies ? I read that also these are not subject to the expansion of space.
 

Offline syhprum

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Re: expansion of space
« Reply #12 on: 04/09/2006 11:43:09 »
I agree with 'Soul Surfer' that on a local scale the Hubble expansion of space would be immeasurably small, as for the effect on local galaxies it is swamped by movements caused by gravity

syhprum
 

Offline Radrook

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Re: expansion of space
« Reply #13 on: 04/09/2006 18:17:10 »
quote:
Originally posted by syhprum

I agree with 'Soul Surfer' that on a local scale the Hubble expansion of space would be immeasurably small, as for the effect on local galaxies it is swamped by movements caused by gravity

syhprum



But since that too is not scientifically verifiable, as you yourself pointed out,then it is an assumption. Why should gravity be assumed incapable of halting the expansion completely in some areas? What is it that we are assuming about the nature of the expansion that prevents gravity from completely halting it in local areas?
« Last Edit: 04/09/2006 18:19:21 by Radrook »
 

Offline Radrook

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Re: expansion of space
« Reply #14 on: 04/09/2006 18:29:41 »
quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?






Scientists say that the expansion merely reacts to the density of matter in those regions by being unable to create distance between objects in those regions. How would that reaction be any different from the reaction of everything else to the force of gravity?



Suppose the expansion of space is occurring intrinsically everywhere including within our solar system. For the local gravity between say earth and sun to suppress this expansion, the effect of gravity would be to contract the space between earth and sun at exactly the right rate such that the net expansion would be zero. However, I do not know that a "space contraction effect by gravity" is predicted or included by general relativity. And if this is not the case, we are back at the original question ; what prevents the expansion of space within our solar system ?




That would require us to assume that universal expansion is powerful enough to make local gravitational predominance waver and readjust.
But let us suppose that gravity keeps these areas stable without any need to contract or readjust. Then it would be similar to a brick wall which maintains its position and shape though air expands and contracts around it. Is that an acceptable supposition as well? If not-why not?

 

Offline Nieuwenhove

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Re: expansion of space
« Reply #15 on: 04/09/2006 18:49:00 »
quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?






Scientists say that the expansion merely reacts to the density of matter in those regions by being unable to create distance between objects in those regions. How would that reaction be any different from the reaction of everything else to the force of gravity?



Suppose the expansion of space is occurring intrinsically everywhere including within our solar system. For the local gravity between say earth and sun to suppress this expansion, the effect of gravity would be to contract the space between earth and sun at exactly the right rate such that the net expansion would be zero. However, I do not know that a "space contraction effect by gravity" is predicted or included by general relativity. And if this is not the case, we are back at the original question ; what prevents the expansion of space within our solar system ?




That would require us to assume that universal expansion is powerful enough to make local gravitational predominance waver and readjust.
But let us suppose that gravity keeps these areas stable without any need to contract or readjust. Then it would be similar to a brick wall which maintains its position and shape though air expands and contracts around it. Is that an acceptable supposition as well? If not-why not?





I know what you mean but this is not really satisfying: Suppose indeed that gravity stabilises space, then the question still remains why and how. Is the strength of the field the determining factor ? I would not think so because there are also strong gravitational fields outside a galaxy where space is expanding. So, where should one draw the line ? There seems to be missing a criterium (or unknown property) to tell where space should be stable and where not.
 

Offline Radrook

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Re: expansion of space
« Reply #16 on: 04/09/2006 19:07:35 »
quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Radrook

The expansion is universal but it does not affect all space equally. That's because there are areas where gravity predominates and cancels the otherwise local expansion.

Yes, I know this argument. The fact that gravity predominates does not in itself justify why the expansion of space would STOP COMPLETELY in such a region. How does space "know" in which regions it should expand and in which regions it shouldn't ?






Scientists say that the expansion merely reacts to the density of matter in those regions by being unable to create distance between objects in those regions. How would that reaction be any different from the reaction of everything else to the force of gravity?



Suppose the expansion of space is occurring intrinsically everywhere including within our solar system. For the local gravity between say earth and sun to suppress this expansion, the effect of gravity would be to contract the space between earth and sun at exactly the right rate such that the net expansion would be zero. However, I do not know that a "space contraction effect by gravity" is predicted or included by general relativity. And if this is not the case, we are back at the original question ; what prevents the expansion of space within our solar system ?




That would require us to assume that universal expansion is powerful enough to make local gravitational predominance waver and readjust.
But let us suppose that gravity keeps these areas stable without any need to contract or readjust. Then it would be similar to a brick wall which maintains its position and shape though air expands and contracts around it. Is that an acceptable supposition as well? If not-why not?





I know what you mean but this is not really satisfying: Suppose indeed that gravity stabilises space, then the question still remains why and how. Is the strength of the field the determining factor ? I would not think so because there are also strong gravitational fields outside a galaxy where space is expanding. So, where should one draw the line ? There seems to be missing a criterium (or unknown property) to tell where space should be stable and where not.



That's very interesting.
Can you please provide an example of an area where gravitational influence is supposed to predominate over expansion but doesn't?


As you know, the universal expansion is said to occur the spaces or voids between galactic superclusters where distances make gravity too weak to interfere giving the universe a bubble-bath-like aspect. So I assume that the example you  will not be in that region?

http://supernova.lbl.gov/~evlinder/umass/faq.html [nofollow]


« Last Edit: 04/09/2006 19:17:03 by Radrook »
 

Offline Radrook

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Re: expansion of space
« Reply #17 on: 04/09/2006 19:14:44 »
quote:
Originally posted by Mad Mark

I once posted a topic about everything expanding in scale including us, but because are measuring stick expanded aswell there would be no reference point to say if this is happening.

Tomorrow lies outside our universe without it there would be no tomorrow.



Here is one explanation I thought you might be interested in:

Excerpt

By

Eric V. Linder

If everything in the universe is expanding, how could we detect it since our measuring rods would also be expanding?

You can measure by other means than rulers, for example the force of gravity between two objects would be different, as would their densities. But only the very largest scale objects are expanding, on sizes beyond those of clusters of galaxies; things in our laboratories, our solar system, our galaxy do not partake of the ``universal'' expansion.

http://supernova.lbl.gov/~evlinder/umass/faq.html [nofollow]
« Last Edit: 04/09/2006 19:15:38 by Radrook »
 

Offline Soul Surfer

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Re: expansion of space
« Reply #18 on: 05/09/2006 09:10:28 »
You don't need to rabbit on about it in ever increasing depths of quotes. You need to get down and think about it properly and put some numbers to your thoughts.

I mentioned above that on a stellar scale the Hubble constant is a bit less than 1cm/sec per parsec.  Galaxies are of the order of 10,000 - 100,000 parsecs or so so the expansion across a galaxy sounds to be quite a bit at .7 - 7 km/sec but the orbital velocity of stars in a galaxy are around 200Km/sec so the expansion effect is still pretty small.  Dark matter clearly helps this a bit.  Note the expansion appears to weaken gravity not strengthen it as observed dark matter effects show.

It doesn't even have much effect at the level of clusters of galaxies where distances are around 1 mega parsec and the expansion is around 70km/sec  typical velocities in galaxy clusters are in the high hunderds of km.sec  (our galaxy has a velocity of about  600km/sec with respect to the cosmic microwave background so it's still less than 10% of the typical speed of things at that scale.

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« Last Edit: 05/09/2006 09:17:43 by Soul Surfer »
 

Offline Radrook

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Re: expansion of space
« Reply #19 on: 06/09/2006 11:00:03 »

I'm familiar with the concepts you post such as the Hubble constant, the dark matter which supposedly accelerates the expansion and which has as yet to be identified, the initial exponential nature of the expansion and subsequent temporary slowdown, its plasma and particle stages prior to star formation, its matter anti matter proportional discrepancy, the cosmic background radiation which caused by the Big Bang.

BTW

Can you please provide a reliable source from whence you derived the idea that the galaxies themselves are expanding due to universal expansion?

Also, you seem to ignore differential rotation by claiming that 200 km/sec orbital speeds are common to all stars within galaxies.

This is impossible since those nearest the hub are forced to orbit more rapidly in order to avoid being swallowed by the 2.6 0.2 million solar mass black hole which is suspected of lurking there. The Sun which is located at 8500 parsecs (25000 light years) from the galactic center is one of the stars which moves at the 220 km/sec you mentioned and takes an estimated 240 million years for one orbit. But  stars nearer to the hub complete the orbit in 15 years. Quite a difference.
« Last Edit: 06/09/2006 12:56:39 by Radrook »
 

Offline Soul Surfer

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Re: expansion of space
« Reply #20 on: 06/09/2006 12:47:46 »
The dark matter in the galaxies causes the rotational velocity to be remarkably constant in the outer regions of a galaxy (note this is not he orbit time)  this was the first clue that lead us to the theory of dark matter.

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Re: expansion of space
« Reply #20 on: 06/09/2006 12:47:46 »

 

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