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Expanding Universe Question

  1. Mar 24, 2005 #1
    First let me thank you for allowing me to attend your forum.

    Two queries actually, but I'll begin with this one. Once again I saw a graphic
    depiction of the expanding universe in a news article. The usual one of course, the expanding balloon with the galaxies tattooed upon it's surface. One that for the most part works very well conceptually for me. I wouldn't have given it a second glance except for the odd comment attached from the scientist being interviewed for the article. I paraphrase here:

    "you can see that as the balloon expands the galaxies move farther apart and yet the galaxies do not grow in size."

    Umm, no, I can't quite see that. In fact this is the first time I've encountered this question. What I see is that as the rubber surface expands, everything moves further apart. From the distance between galaxies to the distance between neighboring stars. The balloon model would suggest that the very substance of space is expanding and carrying evrything with it.

    But if the distances between the stars in our galaxy, indeed between the atoms of our own body, is not expanding in like then I must assume there is a threshold at which expansion loses it's grip. Can this be correct? Has there been any efforts to see if stars in a galaxy are fleeing each other as their parent galaxy is fleeing all others?

    Again, thanks for the invitation
  2. jcsd
  3. Mar 24, 2005 #2


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    The reason Galaxies (and even local galaxy groups) do not expand is that they are bound together by gravity, and gravity at that scale has a greater effect than the expansion of space.
  4. Mar 24, 2005 #3


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    Edwin Hubble noticed that fainter (further) objects seemed to be redshifted in a fairly linear fashion. Cosmologists seized upon this relationship, and using the analogy of the Doppler redshift, proposed that the universe is expanding, and then extrapolated back to a proposed "beginning of the universe". Hubble was not comfortable with this extrapolation even up to his death, although it was a "whiz bang" idea that captured public sentiment.

    It is entirely possible (likely in my view, but who cares?) that the universe is not expanding. It is possible that the universe is relatively static and infinite in extent, and that the Big Bang concepts are incorrect. Unfortunately, there are MANY physicists who will claim that the BB theory is proven to be confirmed to within xxx orders of magnitude, and invoke an era of "precision cosmology". Claims like this are common, and they are worse than silly, since we have exactly one universe to examine (a tiny data set!), and the assumptions that we use to measure the behavior of our universe can yield a WHOLE lot of different results if we change them even slightly.
  5. Mar 24, 2005 #4
    Thanx for your reply. I hope you'll be somewhat tolerant of my hypothetical
    meanderings. I enjoy thinking as some do a good book or movie.

    Accepting the expanding universe for a moment, I would be left to assume
    that in time (a long time to be sure) as the galaxies faded from view we would be quite safe and secure within our own little gravitationally bound bubbles. And, too, the nearest red shifted galaxy would seem to be a very accurate indicator of the distance threshold beyond which gravity yields to expansion. Any galaxy not red shifted of course would indicate that we are moving in unison with each other. Have we discovered any galaxies that do not display a red shift?
  6. Mar 24, 2005 #5
    Could it be that as galaxies disappear behind the cosmological event horizon that the rest of the universe no longer feels their gravitational pull. And so the universe become less and less bound and galaxied start to fly apart? Thanks.
  7. Mar 24, 2005 #6
    Mike2; no.

    oakstick; yes, there are blue shifted galaxies. Andromeda (the closest galaxy to us) has a radial velocity that is blue shifted. I am sure there are more in the local group, but that was the first that came to mind.

    turbo-1; there are more 'bricks to the building' for BB theory than just Hubble flow.

    You may also note that clusters of galaxies do not expand with the hubble flow either, due to the fact they are held together by gravity.

  8. Mar 24, 2005 #7


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    There are abotu 30 total galaxies in the local group.
  9. Mar 24, 2005 #8
    i meant more blue shifted galaxies. i am aware there are 30 odd galaxies in our group, thanks anyhow!
  10. Mar 24, 2005 #9


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    This is similar to what we are doing when we plot a Hubble diagram (distance vs. velocity). The distance at which this occurs is determined by Hubble's constant, which is determined by the slope of that graph. The difficulty, it turns out, is in determining the distances to the galaxies independent of their redshift.
  11. Mar 25, 2005 #10


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    And one that appears more likely than most.
    Given that you tossed the gauntlet, and called conventional claims 'silly', offer some evidence that distinguishes your air of authority from a whiff of authenticity.
  12. Mar 25, 2005 #11


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    Claims of certainty of the correctness of the Big Bang to any particular OOM are silly. Go to Google Scholar:


    and type in "tired light" "variable mass" "variable gravity" etc, etc, and you will find more papers than you can read in a lifetime. Not everybody believes that redshift is due to cosmological expansion. Edwin Hubble certainly didn't.
  13. Mar 25, 2005 #12


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    Edwin Hubble died in 1953. :rolleyes:
  14. Mar 25, 2005 #13


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    Yes, he died a while back, but there are still physicists around today who are researching and writing about possible mechanisms to produce non-cosmological redshifts.

    While the majority today hold the view that redshift is indicative of Cosmological Expansion and thus of the distance to the object, we have some observations now that put that blanket assertion to a tough test. For instance, we have observations of z~6.5 quasars powered by multi-billion solar mass black holes residing in ultra-massive trillion solar mass galaxies with super-solar metallicities. Just how these behemoths could accrete in only a few hundred million years with metallicity equal to or higher than our own stellar neighborhood is puzzling. It is at odds with what the standard model has to say about heirarchical galaxy formation and it is very difficult to reconcile with what we think we know about stellar evolution and metal production. If you want links to the papers, I can find them in my bookmarks when I get home.

    These problems go away if the redshift of the quasars is intrinsic, at least in part. Arp, the Burbidges, and quite a few others have been working on this concept for years, but are dismissed by the mainstream as cranks. That's too bad, because we know that gravity can cause redshift. We measured the gravitational redshift of Sirius B decades ago. What if quasars are accreting black holes, and the highest-redshift quasars are those with the smallest accretion disks (closer to the event horizon)? That is a simplistic suggestion, perhaps, but we should admit that not all redshift is cosmological, and that perhaps special classes of objects need to be approached in a special way, lest we overstate their distances, masses, luminosities, etc. I don't think we've got all the answers, yet, and cosmology isn't as nailed-down and precise as some think.
  15. Mar 25, 2005 #14


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    First welcome to these Forums oakstick!

    This is not a trivial question, although it is often given a trivial answer.

    It is normally thought that local objects, galaxies, solar systems, planets and atoms do not expand with the universe because the local gravitational forces, and especially the electromagnetic and nuclear forces that hold an atom together, create much stronger accelerations than the cosmological expansion. However, if we take a local gravitational field as an example, it is normally described by the Schwarzschild solution, and that is embedded in flat Minkowski space-time. It should be embedded in an expanding cosmological space-time when indeed it might expand with the universe.

    Einstein considered this case and resolved it by embedding the Schwarzschild solution in an empty volume which itself was cut out of a cosmological background of constant density.
  16. Mar 25, 2005 #15
    Intriguing question Oakstick. :rolleyes: I remember back a few days ago in my physics class, we were discussing something very similar to your query. Galaxies are flying apart at appalling velocities. When this was first recognized it shocked many physicists and astronomers and cosmologists.

    My class is only a high school physics course, so we did not go into intense detail in the topic. However, one moment...*consulting notes*...we discovered (my class and I) that the universe has been separtating since the big bang happened. Scientists have come with in 10^ -43 seconds of the big bang. They found that before this, one can not define matter, space or energy. They also found the equations they were using did not work and all physics pretty much 'fell apart'. Klein found equations based on an 11 dimensional universe worked. So scientists used these equations, based off Klein's hypothesis, could be used to help them figure out why the universe was flying apart. They suspect the universe was something dropped into nothingness. Which broke the perfect symmetry that exsisted; thus everything expanding and flying apart.

    I'm not sure if it is possible for something to be so far away that it's gravity no longer has an effect on it's surroundings. :rolleyes: Its an interesting thing to ponder.

    Related question: If it is true the objects in the universe could eventually have distances so great their gravities stop effecting the surroundings, how would this effect the potential heat death theory?

    Turbo, when I was reading one of your posts, you mentioned the universe may not be expanding the way some people think it is. If it's not expanding then is it possible it might be shrinking?

    I hope my asking this doesn't upset anyone. I was reading through everyones' posts. As I was reading I found there were a few terms I didn't understand. So in an attempt to expand my knowledge of the universe, I consulted my physics text book. Come to discover my book doesn't have any of these terms. So if it alright I was hoping someone could define them for me.

    The list:
    Red and Blue galaxies
    Red Shift
    Blue Shift
    Arp? (I have no idea what this is)
  17. Mar 25, 2005 #16
    misskitty, you should try google for these, but i will do my best:

    Quasars: Also known as a "quasi-stellar object". They are galaxies with extremely active nuclei. A central black hole is thought to drive the powerful emission through accretion processes. Extremely high radio powers.

    Red and Blue galaxies: just referring to the colour of the galaxy. Red galaxies have a higher population of older stars (old stars = redder) whilst bluer galaxies have a higher population of young stars (young stars = bluer).

    Red shift: a galaxy receding from us has it's spectrum shifted towards the red end of the spectrum (ie longer wavelengths).

    Blue shift: a galaxy approaching from us has it's spectrum shifted towards the blue end of the spectrum (ie shorter wavelengths).

    Burbidges and Arp: 3 astrophysicists (Harold Arp, Margaret and Geoffrey Burbidge) who consider alternatives to big bang cosmology. Arp is (in my opinion) more famous for his catalogue of irregular galaxies.
  18. Mar 25, 2005 #17


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    Quasars [stands for quasi-stellar objects] are immensely bright objects in the central regions of certain galaxies. Many are so distant the host galaxy cannot be seen, only the quasar. The relatively small objects [~ a light day] can be brighter than hundreds of galaxies. They are believed to be supermassive black holes on a feeding frenzy. The infalling matter is dense enough to emit enormous energy as it spirals in.

    Red and blue galaxies typically refers to their doppler/cosmological shift. Most galaxies are redshifted, meaning they are receding from us. Some nearby galaxies, like Andromeda, are blueshifted, meaning they are moving towards us.

    The Burbridges and Arp are among a small number of scientists who do not believe redshift is strictly due to recession - a perspective normally accompanied by the belief that the Big Bang theory is wrong. Halton Arp is the most famous/notorious figure among the disbelievers. He wrote a book championing the cause not long ago, "Seeing Red".
  19. Mar 25, 2005 #18
    Matt.O, those definitions are perfectly fine. :smile: I can't run an internet search to save my soul. lol

    So a quarsar is another kind of galaxy? And instead of having stars in their centers (like the Earth has the Sun), they have black holes? :bugeye: I thought that black holes had gravitational fields that are so dense and have so much force that they suck everything into them...
  20. Mar 25, 2005 #19
    Whoa... :surprised So it contiunally collapses on itself?

    Is it possible that their galaxy will move so close to ours that they will interact with each other? :bugeye: What would happen if they did come in contact?

    So if they think the big bang theory is wrong, how do they expalin the creation of the universe? Can I find that book on Amazon?
  21. Mar 25, 2005 #20
    This is untrue. Red and Blue galaxies typically refers to the colour of the galaxy due to the different stellar populations residing in them.

    no, it accretes matter from a surrounding accretion disk.

    Yes. Go to http://hubblesite.org and check out some of the interacting galaxies in the gallery.

    You really need to learn to use google, or even better http://scholar.google.com for papers etc.
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