A space expansion question

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origin

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<p>The evidence indicates that space is expanding.</p><p>On the local level we do not see that expansion due to gravity.</p><p>My question:</p><p>Is space expanding locally and gravity is holding the local group of galaxies together so that space is sort of sliding under our feet so to speak or is gravity not allowing space to expand in this local area?</p><p>Another way to phrase it is to say&nbsp;if space is like a stretching&nbsp;rubber sheet&nbsp;and our galaxy is like a&nbsp;dinner&nbsp;plate - is the sheet stretching underneath the plate or is the plate glued to the sheet not allowing the sheet to expand under the plate?</p><p>I have not been able to get a clear explanation of this.&nbsp; I hope what&nbsp;I wrote makes some sense.&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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Saiph

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<p>I understand exactly what you're saying...and my answer is:&nbsp; I don't know actually.&nbsp; In all honesty I don't know.&nbsp; Personally I tend to visualize and explain it as gravity holding the galaxies in place agianst the "current" that is expansion.</p><p>&nbsp;But...I can see where a case can be made that gravity halts local expansion entirely.&nbsp; I'll see what I can dig up.&nbsp; Anybody else have a clue? </p> <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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centsworth_II

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'><font color="#666699">...Is space expanding locally and gravity is holding the local group of galaxies together so that space is sort of sliding under our feet so to speak or is gravity not allowing space to expand in this local area?<br /> Posted by origin</font></DIV><br />Great question!&nbsp; And, no, I don't have a clue.&nbsp; I'm not sure anyone has. No one knows <strong>what </strong>the "dark energy" is that is forcing the expansion.&nbsp; No one knows the real nature of space -- is it quantized? Some even think there is no "dark energy" and that the expansion of space, as calculated from astronomical observations, is essentially an optical illusion. </p><p>If there is a dark energy expanding space, and if it is present throughout&nbsp; all space, even that in out own local group, I imagine the space in which our local group is located <span style="font-weight:bold">is</span> expanding, but slipping past the "ordinary matter" being held together by gravity.&nbsp; I can even see this as&nbsp; taking place in our own bodies:&nbsp; The quarks and electrons forming the matter of our bodies are surrounded by a sea of "space" that is expanding and flowing around the matter particles which are held together by the electro-weak force.</p><p>So maybe space <span style="font-weight:bold">everywhere</span> -- even inside atoms -- is expanding but does not carry matter that is held together by the electro-weak or gravity forces with it. </p> <div class="Discussion_UserSignature"> </div>
 
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origin

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Some even think there is no "dark energy" and that the expansion of space, as calculated from astronomical observations, is essentially an optical illusion. If there is a dark energy expanding space<br />Posted by centsworth_II</DIV></p><p>Just a quick&nbsp;clarification, dark energy is not necessary for the expansion of space.&nbsp; It is hypothesised to explain the <em>acceleration</em> of the expansion.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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SpeedFreek

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<p>Ahh, one of my favorite topics! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p><p>There is no actual concensus yet as to the answer to your question and you have described both views pretty well.</p><p>Some astrophysicists don't like to use the term "the expansion of space" as it implies an intrinsic quality that might have nothing to do with "space" itself. How can empty space expand? If you take a sealed vessel (say, a balloon) and somehow enlarge it (say by decreasing the pressure <em>outside</em> the balloon), did the space inside it expand and if so was it the space itself that caused that expansion? To me, the space only expanded <em>conceptually.</em> Then again, whatever <em>filled</em> that space and thus caused the internal pressure might be thought to have caused the expansion... but it wouldn't have happened without the reduction of pressure outside. </p><p>This is the nature of the problem. We can say that space expands as long as we don't simply assume that it is the empty space that is causing that expansion. All we think we know is that distances between coordinates that arent within a gravity-bound system seem to increase over time.</p><p>If you want to think of gravity holding objects in place against a "current" or "flow" of expansion, consider that the current must emanate in all directions from every gravity-bound system... perhaps it is a function of the <em>Higgs Ocean</em>. Then again, perhaps it is something to do with the shape of the universe - is it being pushed or pulled apart? </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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dragon04

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Ahh, one of my favorite topics! There is no actual concensus yet as to the answer to your question and you have described both views pretty well.Some astrophysicists don't like to use the term "the expansion of space" as it implies an intrinsic quality that might have nothing to do with "space" itself. How can empty space expand? If you take a sealed vessel (say, a balloon) and somehow enlarge it (say by decreasing the pressure outside the balloon), did the space inside it expand and if so was it the space itself that caused that expansion? To me, the space only expanded conceptually. Then again, whatever filled that space and thus caused the internal pressure might be thought to have caused the expansion... but it wouldn't have happened without the reduction of pressure outside. This is the nature of the problem. We can say that space expands as long as we don't simply assume that it is the empty space that is causing that expansion. All we think we know is that distances between coordinates that arent within a gravity-bound system seem to increase over time.If you want to think of gravity holding objects in place against a "current" or "flow" of expansion, consider that the current must emanate in all directions from every gravity-bound system... perhaps it is a function of the Higgs Ocean. Then again, perhaps it is something to do with the shape of the universe - <strong>is it being pushed or pulled apart?</strong>Posted by SpeedFreek</DIV></p><p>Now you've hit one of <strong>my</strong> favorite topics. I really don't have the maths, but it occurs to me that an explanation including the universe being <strong>pulled</strong> apart from "outside" is less problematic than one getting <strong>pushed</strong> apart by all this exotic "dark energy" and "dark matter".</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>
 
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Saiph

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Of course, you then have to figure out what is "outside"...we are talking about the universe here.&nbsp; Being "outside" the universe always made my head hurt. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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SpeedFreek

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<p>Well, if it's being "pulled apart from outside" then we aren't simply talking about influence from a very long distance away. I would imagine that distances are increasing at the edge of our observable universe <em>now,</em> at a similar rate to how they are increasing over here!&nbsp;</p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The evidence indicates that space is expanding.On the local level we do not see that expansion due to gravity.My question:Is space expanding locally and gravity is holding the local group of galaxies together so that space is sort of sliding under our feet so to speak or is gravity not allowing space to expand in this local area?Another way to phrase it is to say&nbsp;if space is like a stretching&nbsp;rubber sheet&nbsp;and our galaxy is like a&nbsp;dinner&nbsp;plate - is the sheet stretching underneath the plate or is the plate glued to the sheet not allowing the sheet to expand under the plate?I have not been able to get a clear explanation of this.&nbsp; I hope what&nbsp;I wrote makes some sense.&nbsp; <br /> Posted by origin</DIV></p><p>&nbsp;</p><p>Assuming you're referencing the Hubble Constant, it is 'sliding under our feet' as you put it.&nbsp; Sort of like a magnet on your refrigerator.&nbsp; The magnet isn't manipulating gravity, it is simply stronger.&nbsp; The gravity between two systems is strong enough at short enough distances to overcome the expansion.&nbsp; The Hubble constant is just that... constant.&nbsp; At least, that how I see it... i could be wrong.</p><p>Dark energy, on the other hand... i have no clue.&nbsp; What ever dark energy is, needs to be defined first. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>This is the nature of the problem. We can say that space expands as long as we don't simply assume that it is the empty space that is causing that expansion. All we think we know is that distances between coordinates that arent within a gravity-bound system seem to increase over time.<br /> Posted by SpeedFreek</DIV></p><p>&nbsp;</p><p>I like to think of expansion as being a consequence of space being 'empty'.&nbsp; I've often wondered if the filament or web structure of matter in the universe is due expansion pushing them into this form vs. gravitational clumping.&nbsp; Most likely a combination of the two with the expansion being the major factor.&nbsp; These voids would seem to be too large for clusters to have traversed them.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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astralith

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<p>Another space expansion question, if I may...</p><p>Increased red shift says the galaxies are accelerating. Current science says its due to "Dark Energy". Could it be the universe has actually crunching but it only LOOKS like it is expanding due to relativity?</p><p>Analogy: Flies (galaxies) are stuck in a bucket of paint (space). The paint&nbsp;is poured over a glass sphere (time). The last dropletts (containing&nbsp;us,&nbsp;the Milky Way fly)&nbsp;look at the flies about to converge at the bottom and&nbsp;observe that they are moving faster&nbsp;(twice as fast) than the our local group RELATIVELY.</p><p>&nbsp;Can this be?</p>
 
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SpeedFreek

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<p>The way I understand it, we noticed the acceleration of the expansion when we saw that some relatively close supernovae had longer durations and were dimmer than was predicted when using our (then) current model of expansion which was derived from more distant objects redshifts.</p><p>Then we looked at those supernovae over the whole range of distances and "recalibrated" the model using their data and found that the rate of expansion, that we had previously thought to have been slowing down all the way from the beginning to the present, had actually levelled out around 6 billion years ago and had since started to accelerate.</p><p>Those supernovae, known as type 1a, are used as "standard candles" by astronomers as at a given distance they always burn for the same duration and with the same brightness. This allows astronomers to look at these supernovae across a range of distances and work out how much the universe has expanded, by looking at how their durations have been "stretched" by that expansion - this is known as time dilation.</p><p>It is the difference in the observations of the <em>closer</em> supernovae that tells us that the expansion has "recently" started to accelerate, not the most distant ones. </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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baulten

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Another space expansion question, if I may...Increased red shift says the galaxies are accelerating. Current science says its due to "Dark Energy". Could it be the universe has actually crunching but it only LOOKS like it is expanding due to relativity?Analogy: Flies (galaxies) are stuck in a bucket of paint (space). The paint&nbsp;is poured over a glass sphere (time). The last dropletts (containing&nbsp;us,&nbsp;the Milky Way fly)&nbsp;look at the flies about to converge at the bottom and&nbsp;observe that they are moving faster&nbsp;(twice as fast) than the our local group RELATIVELY.&nbsp;Can this be? <br /> Posted by astralith</DIV><br />I once had an idea like this.&nbsp; Since gravity accelerates objects, if everything was collapsing towards a central point, it may seem like the galaxies far away are moving away faster and faster (since we're accelerating toward the source since we are nearer to it) and galaxies near us appear the same because they are experiencing roughly the same acceleration.</p><p>The fact that every distant galaxy in the observable universe is apparently accelerating away from us seems to destroy that idea, though. </p>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I once had an idea like this.&nbsp; Since gravity accelerates objects, if everything was collapsing towards a central point, it may seem like the galaxies far away are moving away faster and faster (since we're accelerating toward the source since we are nearer to it) and galaxies near us appear the same because they are experiencing roughly the same acceleration.The fact that every distant galaxy in the observable universe is apparently accelerating away from us seems to destroy that idea, though. <br /> Posted by baulten</DIV></p><p>&nbsp;</p><p>Not a bad analogy if you consider that central point source is the edge of the dimension that we are in but can never quite reach it as we accelerated towards it.&nbsp; Of course, now you have to accept that this 'source' is everywhere and every observer experiences the same phenomena. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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baulten

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<p>Well, right, it could be something like that.&nbsp; I was talking about collapsing toward a central point, but that's impossible as I said.</p><p>It was just an idea I had a while ago when I knew less about physics and the universe. </p>
 
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astralith

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<p>"...I was talking about collapsing toward a central point, but that's impossible as I said."</p><p>Don't sell your theory short because that's just what I was thinking and I'm not so sure it's impossible. To me, it seems likely even.&nbsp;If we are within a singularity&nbsp;(simply, a place were space/time is wound to tight no light can escape, i.e., our universe)&nbsp;the place to which all the galaxies are headed&nbsp;IS one single spot. Are we holding to such notions that the sun goes around a flat earth because it looks that way? Call me crazy.</p><p>&nbsp;"Not impossible... only impossible in your mind!"</p>
 
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astralith

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<p>This was going to be an addendum but for some reason my work computer wont go to the edit page...</p><p>&nbsp;I also believe deeply that there aren't singularities. There's only one singularity and it may just be the same one that we are in. I feel that all black holes reach back to the birth of the universe and that individual black holes are just seperate openings. The material that falls in recycles into the material that falls in, which recycles into the stuff that falls in...</p><p>Yes, black holes are the great aquarium water filter of the cosmos.</p>
 
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SpeedFreek

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If we are within a singularity&nbsp;(simply, a place were space/time is wound to tight no light can escape, i.e., our universe)&nbsp;the place to which all the galaxies are headed&nbsp;IS one single spot. Are we holding to such notions that the sun goes around a flat earth because it looks that way? Call me crazy.&nbsp;"Not impossible... only impossible in your mind!" <br /> Posted by astralith</DIV></p><p>Are all the galaxies heading towards <strong>US?!</strong> <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-surprised.gif" border="0" alt="Surprised" title="Surprised" /> </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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dragon04

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Of course, you then have to figure out what is "outside"...we are talking about the universe here.&nbsp; Being "outside" the universe always made my head hurt. <br /> Posted by Saiph</DIV></p><p>It makes my head hurt too, but it <em>has</em> to be there. I'm using Occam's Razor. If there's nothing readily available "within" the 4 dimensional space-time of our Universe to explain accelerating expansion, then there must be something acting from either "inside" or "outside".</p><p>Do me a favor. You know those beige colored rubber bands? The fat ones you use in the office?</p><p>Take one, lay it flat, and with an ink pen, draw vertical lines across it from end to end. Now, stretch it with your finger or a pencil tip holding it down in the very middle, and observe the lines.</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>
 
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derekmcd

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Asking what is outside the universe is like asking what is north of the north pole. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Asking what is outside the universe is like asking what is north of the north pole. <br />Posted by derekmcd</DIV></p><p>That is actually a pretty good analogy.&nbsp; The surface of the earth is a 2-manifold.&nbsp; That is it is a surface that locally looks like a piece of the plane.&nbsp; It is in fact compact (what physicists call "closed") and without boundary (it has no edge).&nbsp; There is indeed then nothing north of the north pole and there is only a notion of inside and outside of the sphere because we view it as imbedded in a larger 3-dimensional Euclidean space.&nbsp; Manifolds with boundary are not really manifolds and are a somewhat specialized mathematical topic.&nbsp; The universe is also thought to be a manifold, in this case a 4-manifold known as space-time.&nbsp; It is not known if that manifold is compact or not (what physicists call open or closed).&nbsp; However, there is no thought that it is anything other than a true 4-manifold and in particular there&nbsp;is no edge.&nbsp; There are possibly singular points (like cusps) at the heart of black holes, but again that is an area where the theory is not complete.&nbsp; There is, however, no outside or inside.&nbsp; The notions of outside and inside are only germaine to the notion of an imbedded manifold, that is a manifold that is realized as some subset of a larger dimensional Euclidean space, and that is not the case with the formulation of general relativity as it stands.&nbsp; Rather general relativity formulates the notion of the universe as an&nbsp;intrinsic 4-manifold and then describes the curvature tensor for that manifold in terms of the distribution of mass (mass tells space how to curve).</p><p>In fact were there a notion of an inside or outside you would immediately have redefined the notion of the universe and then the problem starts all over again.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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derekmcd

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<p>&nbsp;Thank you for that excellent explanation, you put it into far better terms than could I. </p><p>&nbsp;</p><p><strong><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In fact were there a notion of an inside or outside you would immediately have redefined the notion of the universe and then the problem starts all over again. <br /> Posted by DrRocket</DIV></strong></p><p>&nbsp;</p><p>This is why the balloon analogy, though useful, can be very misleading as it leads to questions about the inside and outside of the ballon.&nbsp; I try to get around this by describing it as time.&nbsp; The center of the balloon is T=0.&nbsp; Anything below the 2 dimensional space is the past and anything above is the future.&nbsp; I think the same can be related to our 3d existence in that there is no inside or outside the universe. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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anOPINIONATEDsob

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In order to understand the answer to the original threads question&nbsp;you must factor in the scale of the effect locally as a factor of the scale of the expansion of the total universe. Also you must factor in the question of time as it affects the local motion vs. the grand expansion of the universe. In English, the universe is expanding at a speed and distance scale that the local effect is so infantesimal as to be immeasureable by human standards of either time or distance. In the grand scheme of things, we just don't amount to nearly as much as we think we do.
 
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i_think

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<font size="2">Is it possible that space is quantifiable and is subdividing rather than expanding?&nbsp; Sort of like&nbsp;a&nbsp;commute from the&nbsp;country&nbsp;to the city taking longer&nbsp;than it used to, but&nbsp;not because the distance changed, rather because there are now twice as many roads, intersections,&nbsp;and traffic lights that you must pass on the way.</font>
 
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