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Reasons for expansion

  1. Sep 14, 2014 #1
    Can someone please explain to me why the universe must be expanding and not contracting? Here is my take on this.

    The Doppler Effect tells us that we are moving faster than objects. "Behind" us, and objects "ahead" of us are moving faster still. Hence the inference of expansion. But , if objects were in a period of contraction toward a central point of origin, and curved space (I.e. Gravity) is more severe the closer you get to that central point, then the closer you got to it the faster you would recede from the objects farther away from that point. If the universe was contracting we would expect to see the same Doppler shift that we see. The space between objects would be expanding, but not necessarily the universe as a whole. Objects closer to the central point would accelerate with the curvature of space . In fact, it better explains the observation that the distance between objects is increasing. Main stream notes the increase , but infers that means there is no cycle, and that the universe will expand indefinitely, with no contraction. But they can't explain why the "expansion" would be accelerating. My hypothesis would explain that. In this hypothesis, the universe is contracting toward a central point. The distance between objects in that model would also increase. It's a period of contraction, not expansion.

    Edited. I know that dark energy is used to explain this acceleration of the universe's "expansion" but why is it that it has to be dark energy and expanding and not contracting as I hypothesized.
     
    Last edited: Sep 14, 2014
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  3. Sep 14, 2014 #2

    PeterDonis

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    Not in all directions. If the universe is contracting toward a central point, then that point is in some specific direction from us. (We ourselves can't be at the central point, because if we were, everything would be moving towards us, not away.) An object closer to the central point than us, in the direction of the central point, would appear to be moving away from us, yes (because it would be falling faster than us). And an object further from the central point than us, along the same direction, would appear to be moving away from us (because we would be falling faster than it). But an object in a direction perpendicular to the central point would appear to be moving towards us, not away (because it would be falling in a different direction from us--the same way as two objects both falling towards Earth, from the same height but different directions, will move towards each other).

    So we would not see objects appear to be moving away from us in all directions in your model; but we do actually see that, so your model does not match reality. The reason we adopt the universal expansion model is that it does match our observations, and we don't know of any other model that does. (Btw, in this model, the universe is not expanding away from a "central point"; it's more subtle than that.)
     
    Last edited: Sep 14, 2014
  4. Sep 14, 2014 #3
    How could an object be perpendicular to a central point? Do you mean objects that are perpendicular to the direction we are from that central point? Isn't the andromeda galaxy on a collision course with the milky way galaxy? Wouldn't that be explained by this?
    I just don't understand why their is such resistance to the idea of a contracting universe.

    I don't understand why scientists are so quick to create theoretical dark forces to explain these anomalies but are so unwilling to entertain the idea of contracting.
     
    Last edited: Sep 14, 2014
  5. Sep 14, 2014 #4

    Bandersnatch

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    Draw a circle around the hypothesised central point. All objects on the circumference have the same radial acceleration.
    Now connect two points on the circumference. Those nearby will have minimal acceleration towards each other. The more spaced the points, the higher their relative acceleration. This is contrary to observations, where only the closest neighbourhood shows blueshift.
    Additionally, velocity spread for objects in the radial direction does not follow Hubble law, again contrary to observations.
     
  6. Sep 14, 2014 #5
    I'll think on this some more, Ive only ever taken physics in high school. Its just been a interest of mine so I'd like to do some more research. One question before I do though: It seems there are a lot of theoretical forces being suggested are being used to account for anomalies in an expansion model, why couldn't a theoretical force account for the anomalies in a contraction model?
     
  7. Sep 14, 2014 #6

    PeterDonis

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    The *direction* to the object is perpendicular to the *direction* to the central point. Again, consider the simpler example of two objects falling towards the Earth, from the same height (or approximately the same) but different directions. The direction from either object to the other will be perpendicular (or nearly so) to the direction from either object to the center of the Earth. And the two objects will move towards each other as they fall, not away.

    No. The motion of the Andromeda galaxy towards the Milky Way is explained by their mutual gravitational attraction. There is no need to hypothesize a universal contraction towards any other central point.

    Besides, whatever model you want to use has to account for *all* observations, not just a few chosen ones that happen to fit.

    Because it doesn't explain observations; models in which the universe is contracting make predictions that don't match what we actually observe.

    Dark matter and dark energy are *not* needed to explain why the galaxies, on average, are moving away from each other. They are proposed in order to explain other observations, but not that one.
     
  8. Sep 14, 2014 #7

    Bandersnatch

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    It may seem at first like all that expansion and the dark stuff and what not is just a hodgepodge amalgam of ad hoc ideas, but it all actually fits nicely into one coherent whole.
    A lot of it is a prediction of general relativity, which is as good a foundation as you can get.
    All we can do is advise you to read more about current cosmology, and physics in general to see the big picture.
    If only to be aware of what ideas have been tested and discarded, and why.
    A good rule of thumb is that all the low hanging fruit have been tried, so it's unlikely to come up with a revolutionary idea on one's own.
     
  9. Sep 15, 2014 #8

    Chronos

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    A contracting universe would have difficulty obeying the cosmological principle, as already noted. It would be even weirder than the already weird universe we appear to reside in.
     
  10. Sep 15, 2014 #9

    Chalnoth

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    No, this is wrong. In a contracting universe, everything is getting closer together, so things are blueshfited. It's really that simple. This is derived from General Relativity, so all of the relativistic effects of gravity are taken into account. Adding extra effects will just get things wrong.
     
  11. Sep 16, 2014 #10
    A little about myself which might help explain where I am coming from and my underlying question. I just got my finance degree from Lehigh and one of the professors here is a leading theorist on Intelligent Design. Most of the student body finds the theory ridiculous on the grounds of evolution and think its equivalent to creationism. This was my first real experience with how dogmatic science can be. It becomes very apparent with evolution, medicine, physics, biology, climate control, and many other fields in sciences. Its Always Sunny did an excellent analogy of religion vs atheism which was basically showing how both the mainstream religious and atheists blindly follow what was written in a book by people they don't know using evidence they never viewed to support a claim they did not reach themselves. This would be fine but in this day and age controversial conclusions or research aimed at disproving mainstream beliefs will find themselves with significantly less, if any, funding and will be an outcast in the scientific community.


    My thoughts are that an expanding universe is predicated on the hubble's conclusion of an expanding universe. Research was primarily focused on reworking that model and theoretical forces to explain anomalies in the model. A contracting universe was not heavily researched. Why is it that a contracting model cannot work with theoretical forces? Why can the laws of thermodynamics be adjusted to work with black holes? If there has been significant research done in a contracting or spinning universe I would very much like to be pointed in the right direction.
     
  12. Sep 16, 2014 #11

    PeterDonis

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    This is way too broad. If you want to say those particular students are dogmatic, because they are rejecting Intelligent Design without really understanding the arguments against it and for evolution, that's one thing. But if you are saying "science" is dogmatic, you are saying that there aren't any good scientific arguments for evolution (or against Intelligent Design). That's false; there are, even if the students in your particular classes don't know them. That's not really on topic here, but PF does have a Biology forum where those kinds of things are discussed:

    https://www.physicsforums.com/forumdisplay.php?f=82

    This is way too broad as well. In fields where experiments can be done that can disprove the current mainstream beliefs, doing those experiments, and properly documenting the results, works just fine. But you have to actually do it; just saying "I think the current mainstream beliefs are wrong" isn't enough.

    In fields where experiments *can't* be done, or where doing them in a controlled fashion is much more difficult, then yes, it's more difficult to dislodge mainstream beliefs. But General Relativity is not such a field. So, even if you were justified in being skeptical of claims like those of the students in your classes, that would not justify the same kind of skepticism about the topic of this thread. (Evolutionary biology isn't really such a field either; you can do controlled experiments, though I think it's harder than it is in physics. But that's a topic for the Biology forum.)

    That's certainly one piece of data, yes. But it's by no means the only one. Check out Ned Wright's cosmology tutorial:

    http://www.astro.ucla.edu/~wright/cosmolog.htm

    The "Frequently Asked Questions" and "Enter the Tutorial" links are the best ones to start with. Wright goes into some detail about the multiple lines of evidence we have that ground our current cosmological models. It's much more robust than you appear to think it is.

    Because it fails to fit the data at a very basic level. We've been over this; have you not read the responses to you in this thread?

    Again, have you not read the responses to you in this thread? You haven't responded to those criticisms of a contracting model at all.

    What does that have to do with the topic of this thread? Not that it isn't an interesting question, but it seems to me like it should have its own thread if you want to go into it.
     
  13. Sep 16, 2014 #12
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  14. Sep 16, 2014 #13

    PeterDonis

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    This makes it a lot harder to quote your responses, so my quotes will be brief.

    This is much better phrasing than "how dogmatic science can be".

    Dark energy is not an "external force". It's an aspect of gravity--just an aspect that doesn't come into play in our ordinary conception of gravity, which is based on our limited experience of gravity on Earth and in the solar system. Dark energy (i.e., a cosmological constant) appears naturally in GR; from a theoretical perspective, it *should* be there. The same would *not* be true for any "external force" that could modify the motion of objects in a gravity well so that they appeared to be moving away from each other in all directions.

    The laws of thermodynamics were not "adjusted" to account for black holes. They were *applied* to black holes. The alternative was not to just go along without applying thermodynamics to black holes: the alternative would have been to have the laws of thermodynamics *violated* in any system where black holes were present (for example, if black holes did not have the entropy they have according to the laws of black hole thermodynamics, you could violate the second law by dumping entropy down a black hole). In other words, like dark energy above, the laws of black hole thermodynamics *should* be there; that's the simplest alternative given the way those laws apply to everything else.

    In short, you appear to think that our current physical theories include ad hoc additions to account for things like the expansion of the universe accelerating and black hole thermodynamics; but in fact our current theories are just the simplest possible applications of existing theories (general relativity, ordinary thermodynamics) to the domains of cosmology and black holes--what you would get if you just took the entities that already exist in those theories and applied them to the given domains. Any other model, such as those you suggest, would have to be more complicated in order to explain the same data (since you would have to add "external forces" that don't appear in any of our other theories).
     
  15. Sep 16, 2014 #14

    Chalnoth

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    While there are many people that are dogmatic in their opinions regarding various scientific ideas, those people are usually not scientists (sadly, some are....but I guess we're all human).

    Also, it seems that most of the people who complain about others being "dogmatic about science" are really just upset that others don't painstakingly explain the answers to exceedingly basic scientific questions, even though those questions are brought up again and again and again ad nauseum.

    There's a reason why you'll sometimes get a rather curt reply if you ask certain questions, and usually that reason is just that that question has been asked so many times that it has become irritating. If somebody tells you to, "learn some basic science," it's usually (though not always) the case that you've transgressed on a very basic understanding of how the world works, and should take the time educate yourself before continuing. If you really want other people to help you, you'll do better by asking honest questions rather than presenting assumptions.
     
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