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Understanding the big bad

  1. Nov 22, 2004 #1
    understanding the big bang

    The universe is expanding and I read that at the border of the expansion, there are new galaxies being created. How is that possible when the mass is already distrubuted during the big bang? Shouldn't there be just a certain amount of mass in the universe and then just expanding space? How is there still creation of more galaxies?
    Last edited: Nov 23, 2004
  2. jcsd
  3. Nov 22, 2004 #2


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    Light does not travel instantaneously. We see very distant galaxies as they were a very long time ago -- hence, as they are being formed.

    - Warren
  4. Nov 23, 2004 #3


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    The border of the universe is time itself. A few references
    From z>6 to z~2: Unearthing Galaxies at the Edge of the Dark Ages
    A clear trend of size with redshift has been identified

    Lyman alpha forest
    There is strong evolution with redshift!

    Hubble Ultra Deep Field
    there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge.
  5. Nov 23, 2004 #4
    Does this mean that the big bang dispersed matter with different inital velocities? Since some galaxies' light are only reaching us now that means they were thrown father in the inital explosion?
  6. Nov 23, 2004 #5
    This is quite right.
  7. Nov 23, 2004 #6


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    but not many people would agree with you!

    The normal interpretation of cosmological observations according to GR is that it is the fabric of space-time that is spatially expanding and the galaxies are being carried along with it.

    There is no one position where the Big Bang happened, and from which galaxies are receeding; it happened everywhere and each point in our epoch of the cosmos is receeding away from every other point, just like dots on a balloon that is being blown up.

    Consider an inflating balloon, mark one point X and then two other points Y (at y cms. from X) & Z (at z cms. from X).

    Watch what happens if the balloon doubles in size in one second, each distance along the surface of the balloon doubles, so Y receeds to 2y cms. from X and Z receeds to 2z cms.

    In other words Y moves away from X at y cms/sec and Z at z cms/sec.

    Their velocities of recession are proportional to their distance away from X. And this would be true if we took any point on the balloon as X. Just as we find with the Hubble flow.

  8. Nov 23, 2004 #7
    You need to be careful here. It is not the case that a fully formed galaxy suddenly comes into our past light cone. If you can see it today then the whole of its past will be in our past light cone (unless you have some funny model when the expansion of the universe alternately slows down and speeds up).

    There is something known as a particle horizon, meaning that the whole of the universe isn't in our past light cone, but when a part of the universe enters our past light cone, it will be as it was immediately after the big bang, rather than as a fully formed galaxy.
  9. Nov 23, 2004 #8


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    No, no, no.

    This is a common misconception. The Big Bang was not an explosion of stuff into space. It was the rapid expansion of "all-space" (as well as marking the beginning of all time, space, & energy in the universe).

    During the early universe, all of space was filled with a type of energy that cooled as space expanded (cooled because it was spread out). At first, there was a hot plasma of fundamental particles throughout the universe. Eventually, that cooled enough for the particles to join together and form atoms. Gravity pulled the atoms into stars and galaxies….throughout the universe, because that energy/particle soup was already throughout the universe.

    Now, as chroot said, it takes time for light to travel across space. So, the farther away we look, the older the image we see (kind of like looking back in time). Right "now", distant galaxies are mature just like our own Milky Way galaxy. But because they're so far away, only the light from their earlier times is reaching us. So, we see other galaxies in a younger state than they are "now". The farther away we look, the younger stages we see. The most distant images are of the youngest stages (when galaxies were first forming).
  10. Nov 23, 2004 #9
    It's an expansion of all space, and you said no to "different inital velocities." Then why are we not at the same place as all the galaxies? Why are we farther away?

    And how is it possible that the galaxies are moving away from the earth when you say that they all have the same inital velocities?
    Last edited: Nov 23, 2004
  11. Nov 23, 2004 #10


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    In observational astronomy, we have to take into account the proper motion of galaxies as we look at their redshifts and relationships. In the Big Bang model (with a constant speed of light) we have to ascribe the redshift of distant galaxies to cosmological expansion, because to assume otherwise would imply a variable speed of light OR that every distant galaxy is fleeing from us, which is logically untenable. In other words, the BB view is that the distant galaxies are not moving away from us, but the space in which our galaxies are embedded is expanding, giving us the impression that they are all moving away from us. This may seem like a subtle distinction, but it is key to the BB view.
  12. Nov 23, 2004 #11
    ahhh, I understand what you mean.

    Is the space being "stretched" or "created"?

    If it was being created, then I dont see how that would expand the space between this galaxy and another. If space was expanding, then it would only create more space. Unless it was actually stretching it. Which then brings to the point of the big bang and how there has to be space already there for it to be stretched.
  13. Nov 23, 2004 #12


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    Now THAT is a very astute question, and it leads logically to a couple of concepts:

    1) If the space between our galaxy and another distant galaxy is expanding, do the units of space-time between us expand to suit the expansion? If not:

    2) Is the fine texture of space-time set in fixed units, so that space-time has to constantly be created to fill the gaps?

    The viability of these concepts have some very real consequences for the life of the standard cosmological model, especially in its treatment of redshift, constancy of speed of light, and a lot of other fundamental things.

    In science, the assumptions that accompany any cosmological model have effects on the way that we interpret observational data. Sometimes interpretation tends to support theory and vise versa, even though the theory can be wrong, and that dynamic can stifle real scientific progress for long periods of time.

    As scientists, we have to understand the principles of epistemology and learn to apply it rigorously. Epistemology requires that we examine how each "rule", "law", etc has come into existence and re-evaluate it as new knowledge becomes available. If we cannot question the validity of the assumptions behind each rule or law, science is dead - it is no better than religion or superstition. I won't bore you with Einstein's quote on the subject, but if you'd like to read it, let me know and I'll zap a copy over.
  14. Nov 23, 2004 #13
    There is a hypothesis that dark energy is what is accelerating the expansion of the universe. Do you think that maybe space isn't being stretched. Space is being created and the reason why we see the galaxies moving at a red-shift is because of the interference with dark enery, pushing the other galaxies.

    This would mean that the dark energy is distributed first. In doing so, the dark energy constantly push the universe further apart but at the same time, push the more distant galaxies, producing a red shift in reference to us.

    So, if we were on the distant galaxy, we would be pushed by dark energy so it would seem like Earth was moving farther from us. Either way, it would produce a red shift.
  15. Nov 24, 2004 #14


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    The most widely held view [concordant cosmology] is based on the preponderance of evidence pointing to a universe both finite in age and expanding. All the talk about dark matter and dark energy is based on missing pieces that need answers to make the concordant model work. The pieces of theory that do not meet observational constraints are routinely discarded. There are, of course, other models that better explain some observations, but, none that do a better job at tying them all together. That is why it is so popular.
  16. Nov 24, 2004 #15
    so do you mean it is unwise to assume that dark energy can effect the distance between us and another galaxy because dark energy is not observed but only based on answering the current expansion model?

    As Warren said:

    then there has to be a force pushing on the distant galaxy, or a force pushing on this galaxy for the light to travel that "very long distance" or something that is "making" space between our galaxy and the distant one.

    Here's another thougt. Could during the big band, matter became scattered uniformly and now matter is dispersing in a ring like pattern. If we think about it, when we observe "distant" galaxies, the galaxy would be moving away from us. That is not beacuse of the streatching of space, but because they are being pushed the other way (other side of the sphere) during the big bang.
  17. Nov 27, 2004 #16


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    Whew! Quite a lot packed into such an innocous sentence!

    First, I think you mean 'affect' (not 'effect').

    Second, 'dark energy' will indeed affect the distance we measure, today here on Earth, to a distant (z~>0.2??) galaxy ... if it didn't, there'd be no need to introduce such a disturbing concept (well, that's not entirely accurate, think of Einstein and the cosmological constant).
    This is not how I understand the nature of 'space-time expansion' ... in GR, there are no static cosmological solutions, so space-time is either expanding or contracting (unless there's something else at play, e.g. dark energy) ... I'm not sure that it's very helpful to understanding to describe this GR stuff as 'a force pushing on the distant galax[ies]'
    Anything with departs from 'in all directions, equally' is 'anisotropic'. IIRC, the unanimous result from all studies to date (e.g. 2dF, SDSS, their predescessors, WMAP, COBE) is that the universe is isotropic, on very large scales (>~500 MPc?). Specifically, there is no observational evidence of any ring like patterns (other than that in the plane of the Milky Way).
  18. Nov 27, 2004 #17
    First, I think you mean 'innocuous' (not 'innocous'). :biggrin:

    basically, you're saying that dark energy elongates the space between us as the distant galaxies? So is dark energy thoughout the universe? I thought that dark energy was the cause of the accelerating expansion of the universe. So that means that dark energy is "pushing" on the borders of the universe, how is it in between two galaxies? Also, for dark energy to be expanding the universe at an accelerated rate, is the dark energy the first energy to be emitted during the big bang? Because that way, it can be at the borders of expansion.

    Is this because of the different concentration of dark energy during the big bang?
  19. Nov 27, 2004 #18


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    Yes, yes, yes.
    The universe does not have a border, it is unbounded. Dark energy permeates the entire universe
    You have pretty much outlined the inflationary scenario. Dark energy gave the early universe a huge jolt, causing superluminal expansion of space [which is not forbidden by relativity]. Much of that energy is thought to have been converted to matter. Several billion years later, the universe apparently got another jolt of dark energy causing expansion to accelerate, as is presently the case. That has not yet been explained. But, we already knew the universe has a wierd sense of humor and likes to play practical jokes on cosmologists.
  20. Nov 28, 2004 #19
    How do we know that the universe is expanding then?

    where, location wise, did this jolt come from? The same place as where the big bang started? Is this "extra" jolt the explanation for the isotropic expansion of the universe?

    Say the universe is expanding anisotropicly, then, the second jolt (not in the origin of the big bang) sparked the isotropic expansion.

    Then Dark energy can dark energy be considered a wave since if we found where the jolts were, it could act like a stone being thrown into a pond. For example, the first stone describes the anisotropic of the big bang. Then another stone is thrown in to make the expansion isotropic. Then more is thrown in. So the question is who is throwing the stones?

    any thoughts?
  21. Nov 28, 2004 #20


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    I think a wave form model with resonance could explain that.
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