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Degenrate answers

  1. Apr 14, 2005 #1
    There are many qusetions in science & cosmology which
    have degerate answers some of them are as follows:

    1. In the presence of matter space get curved so
    massive particles as well as light photons do not move
    along stright line. Now one could always assume that
    photons also carry gravitational mass so they also get
    attracted in gravity in place of assuming that space
    get curved. Note that assuming that photons carry gravitational mass we are just postulating about photons but assuming that space get curved we are postulating about the behaviour of many unknown forms of matter.

    2. Postulating that the space is expanding leads to the conclusion that remote galaxies are moving away from us.
    But assuming that these are actually galaxies which are moving away from us in a non-expanding universe also leads same conclusion as well as observation. I know, that assuming that galaxis are moving in a fixed background leads to many difficult questions but does the
    first option not ? i.e., what the space expanding into ?
    (nobody like to talk about this issue and says that this is not expanding into anything, my objection is that if this is not expanding into anything then this is not the type of
    expansion that we encounter in the daily life i.e., which
    always expands into something. If the expansion of the universe is not the type of expansion which we face in daily life then why we call it expansion at all).

    3. In special theory of relativity postulating that nothing can travel faster than the speed of light we
    restrict the behaviour of that which have not been
    yet discovered (fastets than light signal). Note that in
    place of assuming that time interval get changed in moving frame we can always say there is a minium limit on the time interval which we need for communication.
  2. jcsd
  3. Apr 14, 2005 #2
    I Agree with everything you say. Physics has many flaws with these areas and unifying the different branches of physics as well. To say spacetime expands using the definition that space is the absense of matter and energy automatically leads to a contradication. How can "nothing" bend or curve. It doesn't make sense. Einstein was obviously wrong on this matter unless he did define space as matter which in that case space would bend or curve.

    And the whole thing about nothing going faster than light is bull. Gravitons go faster than light. if they didn't then we wouldn't be able to feel the force of gravitation by black holes but according to current science we can. Contradiction again.

    Also like you say to assume that the "universe" is expanding is to be in agreement with the Big Bang theory which has way to many flaws to list.
  4. Apr 15, 2005 #3
    If people would just accept my theory about "how it all happened" no one would have anymore questions. My theory is: if "nothing" can't exist than "something" always has to. That "something" would have to be matter and energy. That eliminates the possibility of people asking "well, where did that matter come from." You just respond it's not possible for something to come from nothing and therefore something(matter, energy) always had to be there. The problem is people keep thinking there was a begininng. It was always there, therefore its infinite. Then one day, due to the laws of attraction, particles came together and created an explosion. this fills in the gaps of the Big Bang theory. This theory explains the reasons for why matter is still expanding in the Universe and the problem with assuming that there was a begining. I can't find any flaws with it.
  5. Apr 15, 2005 #4
    These problems always come when we make a sentence without understanding it completely.

    This is interesting that gravity travels faster than the
    speed of light. Because we see that there sits a supermassive black holes that affect the surrounding material by gravity and this is possible if gravity tarvels faster than the speed of light. Since I have not
    reach about this issue so I cannot say anything.
    Let me put one more qusetion that has degerate answers.

    4. Dark matter was mainly invoked for explaing the circular speeds of objects in outer parts of galaxies but
    one can expalin it by using MOND also. There is nothing holy about the Newtonian mechanics. Even this is true for
    GTR also one can always assume that gravity becomes repulsive at large distances in place of invoking the concept of dark energy about which we do not know anything.
  6. Apr 15, 2005 #5
    very true. This too: Also its nearly accepted that gravity exist and gravity is defined as the force of attraction between everthing. Electrons and protons attract each other because of their opposing signs but according to current science gravity can attract eveything. If this is true, then WTF sign does gravity have¿¿¿ its not so much a contradiction as much as it is just unknown
  7. Apr 15, 2005 #6


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    No, it contains significantly less problems.
    Ironically, you hit the nail on the head: no, it is not quite the same as the expansion we see in every day life. But why should it be? We can use examples in every day life but you need to avoid getting too attached to such analogies. They are imperfect.

    One analogy that works reasonably well is the surface of a balloon: When you blow up a balloon, the 2d surface is expanding. What is the surface expanding into?
    That is not correct. The postulate exists because it must exist as a postulate for the sake of building a theory around it. Do not confuse that with meaning that the assumption has no experimental basis. It does have experimental basis and make no mistake: the fact that it is assumed doesn't preclude finding that the assumption is wrong.
  8. Apr 15, 2005 #7
    If it is not like the expansion we are familer with then
    why we should call it expansion at all ? since it create unnecesary confusions.

    It expands into a 3-dimensional space.I know it is not
    always that a 'n' dimensional space requires 'n+1' dimensional space, sometime an 'n' dimensional space can expands in a 'n' dimensional space also, e.g., a flat sheet can expand in a '2' dimensional space. Actually problem of the expansion of the universe is as follows.

    Our three dimensional space could be embedded into a
    four dimensional space. For example, in FRW cosmology if we take 'k=+1' then this means that our universe is a
    postively curved three surface like 'S3' which is embedded in a four dimensional 'R4' space. For 'k=-1' and
    'k=0', we have three dimensional 'H3' and 'R3' surfaces
    embedded in 'R4' space. This all looks easy mathematically, however, it is very very difficult to assume that how a 'R4' world will physically look like and why only 'R4', our three dimensional space which could be 'R3', 'S3', 'H3', 'T3' or whatever can always be embedded in a space of '3+n', dimensions where 'n' could vary from 0 to infinity. Nevethless, I still found it difficult to assume that an empty space can expand.
    Last edited: Apr 15, 2005
  9. Apr 15, 2005 #8


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    "Expansion" is accurate, its just not the same as the expansion we are used to seeing. A circle on a piece of paper can be animated to expand in 2d, while the circumference is expanding in 1d. A sphere (my balloon analogy) can be made to expand in 3d while the surface expands in 2d. We live in a 3d space that is expanding in 4d. Its still expansion, its just not something easy (possible) to visualize. But it does seem you basically understand it...
    And that's the rub - our preconceptions make it difficult to visualize, but why should that limit our understanding? To learn, you often have to let go of preconceptions.
    Its not an assumption, its an observation. There is an enormous amount of observational evidence of this expansion.
  10. Apr 15, 2005 #9
    i don't understand how a circle can be animated expand in 2d but its circumference can only expand in 1d. I always thought that anything that is on paper (2d) can only be 2d. how is it possible for something (the circle) in a purely 2d realm to exist in a 1d realm (the circumference).
  11. Apr 15, 2005 #10


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    When you write it out in English, it gives me a headache :cry:

    How about approaching it somewhat differently ... there are a bunch of good observational and experimental results, and there is a theory (General Relativity) which can 'account for' all those results, even to 4 (now 5?) decimal places. Further, you can 'do stuff' with GR, such as build a GPS system. Better yet, you can make predictions about what you will find (or see) if only you {did this experiment} or {observed these things in the universe}. In this sense, GR is a pretty good theory, and all ( :surprised ) you need to do is become 'fluent' in the relevant math ... the extent to which you tell yourself a satisfying story about the concepts is your privilege.

    (You may consider this discomforting ... why can't astrophysicists write GR out in an intuitive, 'non-degenerate' fashion? Well, GR is a piece of cake compared with QM!)
    Russ has already addressed this well; just to add a few words on perspective/approach ... in one sense, science resembles nature - it abhors a vaccuum! :wink: Generally speaking, you need something to do your research on, and 'theory-free' research is a myth, so we always have some view (idea, hypothesis, theory, ...) that we're working within. You're free to postulate a 'fixed' universe in which galaxies 'expand away' from each other; your challenge is to build a model with your ideas such that it isn't strongly inconsistent with good observational and experimental results (and good theories, where the domains of applicability overlap, and ...). Indeed, if you do build a new theory that's 'better' in the sense that GR is 'better' than Newtonian physics, you will likely become famous, and have hundreds of books written about you! :cool:
    Indeed. So if (when?) we discover an FTL signal, SR will be given the heave-ho! :approve:
    This one is quite different from your other 3 ... most of the DM in the universe is in rich clusters of galaxies, not the halos of galaxies, and several independent lines of work give comparable values for the amount, distribution, non-collisional character, 'temperature', etc of DM. Of course, if MOND (or super-MOND) can get rid of the need for DM (i.e. 'account for' all the relevant good observational results), then Milgrom will become a hero. :smile:

    In fact, there are some 'super-MOND' theories being published - check out the relevant threads here in PF's GA&C!
  12. Apr 15, 2005 #11


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    IIRC, you posted something similar elsewhere in PF ... have you written a paper on 'your theory' and submitted it to a peer-reviewed astrophysics/physics journal? If not, why not?
  13. Apr 15, 2005 #12


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    Everything you write Dragongod may be good and true ... or it may be 'mental vomit' (or worse). Your challenge, if you choose to accept it, is to stop handwaving and pretend we're all from Missouri - show us that your ideas are consistent with all good experimental and observational results.
    1) 'gravitons' don't exist, except in a consistent theory of quantum gravity (which itself doesn't exist).
    2) GR gives a perfectly consistent description of how 'you' are 'able to feel the force of gravitation by black holes' - may I suggest you post a question* in the SR&GR section of PF? I'm confident you will get a well-constructed, patient reply.
    Humour me please, list the three most egregious flaws (from your POV).

    *e.g. "Within GR, how is it possible that we can feel the force of gravitation by black holes?"
  14. Apr 16, 2005 #13


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    The edge of a circle is a line. A line is 1d: it has length but no width. Similarly, the surface of a balloon is a surface: it has length and width, but no height.
  15. Apr 16, 2005 #14
    I will argree this part of your statement is very true. There are many questions everywhere in every scientific field which people are striving to answer.

    Russ has provided a very good explanation of your second query. If it's alright, I'd like to add to it. With space expanding, everything in it might be expanding as well. Meaning us too. So we may not even notice that the universe is expanding in our everyday lives; especially if we are expanding proportionally to the rest if the universe. However, I do believe Russ did mention something about evidence supporting the expansion of the universe, so I may be wrong. It is definitely something to think about when looking at the expansion query.
  16. Apr 17, 2005 #15
    Dear Friends,
    As most of you are agreed that there are degenracies in
    scientific explanations. These are mainly due to "observation selection bias". I think most us will agree
    that scientific explanations are not the final truths, they are just models, they give one of the possible explanation for any observational feature in the universe. In this discussion one of the main issue which I raised was: in what the universe is expanding into ? let me put my answer which most of you might be familier with but nobody has posted.

    It is well known that our universe is three dimensional so one can think that it is embedded into a '3+n' (where
    n is an integer between 0 and infinity) dimensional space. In FRW cosmology we assume that it is
    embedded into a 4-dimensional space. Actually a universe with non-zero curvature expands along the fourth dimension just like when we inflate a baloon it expands into a three dimensional space particularely one can think it expands radially. At this point there is no ! difference between the expansion of the universe and that of the baloon. Here main problem is that we can not visulaize the forth dimension (let us call it radial) along which the universe expands. It is like for a two dimensional creature it is difficult to visulaize the third dimensions. I will come back with more explanation.
  17. Apr 18, 2005 #16
    :blushing: Now I feel rather stupid. Your last post made more sense. Now I feel really stupid. :redface:. We don't know what space is expanding into. We may not ever know.
  18. Apr 18, 2005 #17


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    The fourth dimension is time. You visualize it every time you go to the movies.
  19. Apr 18, 2005 #18
    I knew that. It's the same when you watch tv.
  20. Apr 18, 2005 #19
    Excatly ! in order to feel or to understand where our
    three dimensional space in expanding into we have to
    go away from it along the fourth dimension which seems
    to be impossible.
  21. Apr 18, 2005 #20
    This is totally wrong. The fourth dimension which I am talking about is not time. If you do not mind please look
    at the derivation of FRW line element in any text book (Peebles physical cosmology etc). There we start with the
    discussion of embiddeing a three dimensional space in a four dimensional (all are spatial dimenions) flat or Eucledian space.

    Note that time is considered a fourth dimenions only in special theory of relativity.
  22. Apr 19, 2005 #21


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    Agreed, with the caveat it is what follows, not preceeds this assertion that is wrong:
    Where did Peebles assert three dimensional space is embedded in a fourth spatial dimension?

    And general relativity does not?
    Last edited by a moderator: Apr 19, 2005
  23. Apr 19, 2005 #22
    Principle of physical cosmology page 60

    In case fou do not find it look at my notes

    Last edited: Apr 19, 2005
  24. Apr 19, 2005 #23


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    As this thread seems to have become 'about' GR (in the cosmological sense), I'm moving it to a place where it may get more technical expert attention.
  25. Apr 19, 2005 #24


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    I gather this is a "transplanted" thread from somewhere?

    This is actually not an example of "degeneracy", because there are experimental differences between the two theories. GR, with space-time curvature, predicts twice the deviation of a photon than a Newton-like-theory which is couched in terms of forces. The difference is due to the space-space curvature terms in the space-time curvature tensor, i.e. it's due to the effects of pure spatial curvature.

    You are probably visualizing non-euclidean geometry as a curved surface embedded in a higher dimensional geometry. While this is not a bad visual aid, it's not the only way of dealing with non-euclidean geometry. The approach used in GR is to define a metric at every point in space-time, similar to the way that one defines a metric on the curved surface of the Earth. The purpose of the metric is to compute local distances from generalized coordinates. For instance, on the Earth, we can locate any point by two coordinates, such as lattitude and longitude. Ignoring the non-sphericity of the Earth for the time being, it is sufficint to point out that while a minute of lattitude always represents the same distance (one minute = 1 nautical mile), a minute of longintude does not represent the same distance - a degree of longitude is significantly smaller near the poles than it is near the equator. Thus the shape of the Earth can be studied purely in terms of its intrinsic geometry.

    The "embedding" approach does not yield unique answers, there are many ways a specific geometry can be instantiated by different embeddings which all have the same intrinsic properties. Hence the metric approach is preferred, because it models what we can actually measure.

    Your question regarding "what is the universe expanding into" is also a quesiton that does not yield itself to experimental testing - that's why it is a philosophical question, and not a scientific one.

    It sounds like you are complaining about the fact that a theory makes a prediction. That's the job of theories - to make predictions that we can test.

    That's not the only problem with your statements. For instance, tachyons are possible under special relativity, though they have stability problems, and may not yield FTL comm;unication even if they exist. Wormholes are another counter-example. Wormholes may not exist, but the fact that they are being seriously investigated theoretically shows that the topic of FTL and relativity is more complicated than you indicate. Note that it is still true that relativity predicts that one cannot exceed the speed of light by, for example, simply accelerating continuously in one direction.
  26. Apr 19, 2005 #25
    So if the fourth dimension isn't time in this case; what is it? I'm just breaking into GR so I haven't even hit special relativity yet.

    Sidenote: someone please tell me what a tachyon is?
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