# Expanding, and Colliding.

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#### mindmute

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The Universe is expanding in all directions.<br />The farther something is, the faster it appears to be<br />moving away from us.<br />Someone please give me some stats on how many galaxies may actually be moving toward us, and each other. what's the ratio?<br />And I would like to hear postulations on why galaxies rush away from each other, yet still sometimes collide.<br />Is something out there re-shaping space so that objects moving away from each other, have no where to go but smack into another object that should also be rushing away?<br />I can see how this happens with stars all churning about within a galaxy, and how asteroids/comets can be influence in the same, however, I can't seem to wrap my mind around why galaxies should behave this way.<br /><br />anyone?<br /><img src="/images/icons/smile.gif" />

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#### SpeedFreek

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The metric expansion of space only causes an increase in distance outside of gravity-bound systems.<br /><br />Wherever gravity holds an attraction between objects, that gravity overcomes the expansion and binds those objects into a gravity-bound system. Galaxies cluster together because of this and within those clusters, a galaxy can be gravitationally attracted towards another galaxy or they can "swirl" around each other, but outside the clusters, expansion causes the distance to the next cluster to increase.<br /><br />Only outside of the galactic cluster is gravity weak enough for the expansion to overcome it.<br /><br />So it is more accurate to say that the expansion of space causes the distance to increase between the galactic clusters, rather than between each galaxy.<br /><br />Galaxies within our own cluster are moving around or towards us (like Andromeda). But the redshifts caused by those galaxies inertial movement relative to ours is very small (a redshift factor of z=0.1 or less). Any redshift over that is assumed to be caused by the expansion of space.<br /><br />When we look at more distant galaxies the part of their redshift caused by their inertial motion within their local group is so small in comparison to the part of their redshift caused by the expansion of space that we cannot separate it.<br /><br />Redshifts of up to z=0.1 represent objects close to us, in our local group of galaxies, moving around and towards each other. Redshifts over around z=1.5 represent objects receding from us at the speed of light. We have seen objects with a confirmed redshift of z=7 and some as of yet unconfirmed redshifts of up to z=15. The CMBR, emitted at least 100 million years before any objects formed, when the rate of expansion was much faster, has a redshift of around z=1090.<br /><br />The redshift factor represents the amount by which the universe has increased in size since the radiation we are detecting was emitted. So the universe is now 1090 times larger than it w <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

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#### mindmute

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...Thats a hell of a drop off in only 100 million years.<br />the CMBR seems to be quite a few billion light years away.<br />If any quantity of mass existed then, would it not have been so far from any other matter to attract anything?<br />-or- did matter form so quickly, (while the radius of the universe was still only 100 mil.ly.) that there was sufficient gravity to considerably slow the expansion rate? None of what we see from that many billions of years ago can possibly still exist in it's same form today. What will the CMBR look like in 15 billion years?<br /><br />[ speedfreek, your post is very informative, and eloquently expressed. thank you. ]

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#### SpeedFreek

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The CMBR, with a redshift of z=1090 or thereabouts, is around 46.5 billion light years away, and defines the edge of our observable universe. The universe was opaque for around 380,000 years until a phase transition known as "recombination" occurred, atoms formed and photons became independent. At the end of that transition the CMBR was emitted and the universe became transparent. That is as far back in time and space as we can look.<br /><br />During the first 380,000 years the observable universe had expanded to 40 million light years in radius, due to the incredibly fast but swiftly decelerating expansion early on. After that, the atoms in the universe were pretty much evenly spread, with slight differences in density (which were introduced initially by quantum fluctuations during the "inflation" phase when the observable universe inflated from being point-like to the size of a grapefruit during a fraction of the first second!)<br /><br />If the mass was pretty evenly spread throughout the early universe, with slight differences in density, then gravity would cause the slightly denser areas to attract mass from the slightly less dense areas, a process that continued until masses were concentrated enough for the first stars to form.<br /><br />When the earliest objects formed between 100 and 500 million years after the beginning, the observable universe is theorised to have been something around 2 or 3 <b>billion</b> light years in radius!<br /><br />When considering the metric expansion of space, where the <i>metric that defines distance changes over time,</i> it is important to understand the underlying principle.<br /><br />With a constant rate of expansion, all distances change at the same rate. What this means that in the time it takes for 1 meter to double in size, all meters double in size! So if 1 meter becomes 2, 1 light year becomes 2 and the universe doubles in size at the same time.<br /><br />So, if (as a random example to simplify the maths!) it takes 10 billion <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

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#### SpeedFreek

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I said 46.5 billion <i>light</i> years. The universe is theorised to be 13.7 billion years old, but the observable universe is theorised to be 46.5 billion <i>light</i> years in radius, due to the metric expansion of space, as explained above in my earlier post.<br /><br />But yes, perhaps it was a little misleading as I was simplifying the explanation.<br /><br />I explained in my post how the metric expansion of space caused the distance between the edges of our observable universe to move apart faster than the speed of light. The edge of our observable universe is defined by the oldest thing we can observe, which is the CMBR. We cannot see all the way back to the big-bang, as the universe was opaque and photons did not exist independently until the CMBR was emitted.<br /><br />The observable bubble of space which we are at the centre of was only 40 million light years in radius when the CMBR was emitted and the CMBR filled the universe. The edge of that observable bubble is now 46.5 billion light years away, so that is now the radius of our observable universe. I said that is the distance to the CMBR, when I perhaps should have said that is the distance to the point back in time (in all directions) where the CMBR was emitted.<br /><br />The distance scale I am using is the "comoving" distance, which is the distance that cosmologists estimate that an object is <b>now</b>, when we are receiving the light or radiation that was originally emitted. Check out that link I provided in my previous post for a more thorough explanation, with diagrams.<br /><br />Getting your head around the concept of an observable universe that has been expanding is not easy. I try to post explanations that can help with understanding, using the currently most accepted model in cosmology, the Lambda-CDM concordance model.<br /><br /> Timeline of the big-bang<br /><br />After less than a second from the beginning, the edge <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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<font color="yellow">Someone please give me some stats on how many galaxies may actually be moving toward us, and each other. what's the ratio?</font><br /><br />Check out the Local Group<br /><br />By far, the number of the estimated 125 BILLION galaxies in the Universe are moving away from us. We're in a group of 30 that are gravitationally attracted to one another.<br /><br /><font color="yellow">And I would like to hear postulations on why galaxies rush away from each other, yet still sometimes collide. </font><br /><br />That all depends on whether their relative velocities overcome the gravitational influences that galaxies exert on one another.<br /><br /><font color="yellow">Is something out there re-shaping space so that objects moving away from each other, have no where to go but smack into another object that should also be rushing away?</font><br /><br />From all the detectable evidence we have, space itself is still expanding, and doing so at an accelerating rate. Even given that galaxies are moving in an infinite number of directions at different relative velocities, some are and will always be close enough to one another for gravity to pull them together as opposed to expansion pulling them apart.<br /><br />It all boils down to how crowded the "neighborhood" is where your galaxy lives.<br /><br /><font color="yellow">I can see how this happens with stars all churning about within a galaxy, and how asteroids/comets can be influence in the same, however, I can't seem to wrap my mind around why galaxies should behave this way. </font><br /><br />Let's use our Solar System as an example. Over time, every planet, asteroid and comet that is affected by our Sun's gravity likes to find a "balance". They all want to have an orbit that allows them to have a happy little, stable orbit so that they can go about their business.<br /><br />Now and then, something big enoug <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

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#### mindmute

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Awesome, speedfreek.<br />Thanks!<br />My "inter-dimensional relation theory" predicted an FTL component to all this. I was not aware that this concept had already been accepted. <br />(my theory, IDRT, is probably the same thing everyone else is seeing, just expressed a different way).<br />Before I elaborate on how this fits into my theory, let me first test how my predictions have been going in my absence; (I put my chalk down 10 years ago).<br />Has anyone to date, if you know, calculated how much of an effect this unseen universe will have on the observable universe gravitationally?<br />The model you've outlined implies that we will never see, or feel the light/gravity from the unseen universe.<br />(am i wrong?)<br />If space is expanding faster, could the gravitation of the unseen universe be causing it?<br />Could our "part" of the universe be less massive? could it be younger?<br />My predictions indicate that there should be a way to observe how light from the unseen universe interacts with the light we see from the most distant part of our observable universe. <br />Is the CMBR totally uniform in all directions?<br /><br />Thanks for the time you take on your very informative posts. <img src="/images/icons/smile.gif" /><br /><br />

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#### SpeedFreek

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i'm not sure I am qualified to answer these questions, but I will have a go at what I can.<br /><br /><font color="yellow">Has anyone to date, if you know, calculated how much of an effect this unseen universe will have on the observable universe gravitationally?</font><br /><br />If we assume the universe is homogeneous and isotropic as the cosmological principle would have it, then the net effect would be zero, as the whole universe would be very similar to our observable portion of it. I am unsure if the expansion could be explained by gravity as the theory proposes it only happens where there is almost no gravity.<br /><br /><br /><font color="yellow">The model you've outlined implies that we will never see, or feel the light/gravity from the unseen universe.<br />(am i wrong?)</font><br /><br />Well, that depends on the rate of expansion. If the rate accelerates we will see less and less of our own observable universe as time goes on. If the rate decelerates we see more of the previously unobservable universe. If the expansion stops completely, we might eventually be able to see the whole thing after a very long time (dependent on its overall size).<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

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