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Is Universe really expanding

  1. Mar 4, 2006 #1
    I want to start with a question that is universe is really expanding? According to my view it is to be like this: (To get this one should be well versed in Doppler’s effect)

    Suppose we had gone to mars & placed a light source there & came back. Now we know orbital velocity of earth is more than that of mars, so as a result earth moves away from it. Now observe the spectrum of the light of mars we will defiantly got red shift. Now suppose we do similar experiment with Venus we will get blue shift as earth is approaching toward it.

    Now similarly it can be assumed that galaxies in stead of getting away as we are assuming at present are also revolving around a centeral body of gravitational force which tends to infinity. So we are getting red shift as we are getting away from it (in our frame), also there will be a galaxy from which we are getting blue shift(just as in case of Venus).
    So we can assume that, universe is not expanding but galaxies are revolving around a body of high gravity.

    If, that was the practical which showed that Universe is epanding, so it may be wrong; or the method was different.
     
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  3. Mar 4, 2006 #2

    Chronos

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    Hi shanu! Assumptions will trip you up. There is no center of gravity in this universe. Countless studies have ruled out that possibility.
     
  4. Mar 4, 2006 #3

    Janus

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    The problem is that the Earth is not always moving away from Mars or towards Venus. Sometimes the Earth is catching up to Mars in its orbit and we would see a blue shift, and there are times after Venus has passed us in its orbit and we will get a red shift from it.
    But then there would be a distinct pattern to the shifts. Galaxies "inward" and "behind" us, and galaxies "outward" and "ahead" of us would show a blue shift, while qalaxies in the opposite quadrants would show a red shift.
    Instead, we see galaxies with increasing red shifts with distance in all directions, with no such pattern.
    Since the distribution of red shifted galaxies doesn't match that which would be required by your suggestion, we can conclude that it has no validity.
     
  5. Mar 5, 2006 #4

    Chronos

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    Affirming what Janus said. There is absolutely no evidence of bias in the redshift of galaxies with respect to our galaxy.
     
  6. Mar 5, 2006 #5

    DM

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    A vast number of people get easily carried away by Hubble's expanding law theory. Could I just point out that red and blue shifts do not necessarily mean 'expanding'. Galaxies could be simply moving away or towards us without relying on the possibility of a universe expansion.

    We're invariably assuming to know a great deal about a 'center of gravity', even when this is corroborated by scientists' claims to test the untestable. If Astrophysics has taught us one thing about the universe is that we can never state with absolute confidence that we know things for a fact. This applies for or against theories.

    How would we know for instance, that red and blue shifts are not caused by quasars present at the center of galaxies? We don't even know for sure what these objects are, why should we formulate things for or against it?
     
    Last edited: Mar 5, 2006
  7. Mar 5, 2006 #6

    hellfire

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    Gravitational redshift in quasars cannot account for high redshifts (higher than ~ 3) if the objects we are observing are gravitationally stable. On the other hand, you should note that redshift is not the only proof for expansion of space; alternative models must explain also things like the variation of the surface brightness, the variation of the angular diameter, the cosmological time dilation, etc.
     
  8. Mar 5, 2006 #7

    SpaceTiger

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    Are you referring to the Milne Universe -- that is, a universe in which a spacetime itself isn't expanding, but the objects within it are? If so, this has been ruled out by observational data. Specifically, it mispredicts the current expansion rate.


    What do you mean? The gravitational field of a quasar is not strong enough to redshift an entire galaxy's light.


    We're pretty confident that quasars are accreting black holes. I've not met any mainstream astrophysicists who think otherwise.
     
    Last edited: Mar 5, 2006
  9. Mar 5, 2006 #8

    DM

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    Yes, indeed they are accreting discs but can you honestly tell me that all astrophysicists strongly believe in this giant black hole? There is plenty of controversy revolving around this particular problem. You say you have not met any mainstream astrophysicist attempting to disprove it. I'm quite surprised as all I have to do is open up acclaimed Astrophysics books - mainly university textbooks - and find information addressing the validity of these theories. Finally allow me to point out that the reason it leads most astrophysicists to believe it's a black hole, is purely down to the similar theory applied to independent black holes. And indeed it does seem the objects present at the center of galaxies exhibit alike behaviours to black holes BUT can you prove it? Can anyone prove it?
    Show me hard evidence, not theories.

    Did you know there are astrophysicists who do not believe in black holes? That they believe in something else?

    Am I one of them? No, I'm certainly not but all I'm saying is that one needs to be awfully careful when claiming up things. Theories are proven to be right in certain situations/cases but again, our knoweldge about the universe is 90% - if not more - dependent on theories.

    I'm not trying to wage a war here, not my character at all, in fact I would never compare myself to you guys - extremely qualified etc - but it does disappoint me somehow when scientists don't reflect upon these little things. Little things that I would regard awfully big.
     
    Last edited: Mar 5, 2006
  10. Mar 5, 2006 #9

    DM

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    Could I just clarify that those text books do not disprove nor approve the theory of black holes at the center of galixies. They do mention of such theories but do emphasize the absence of hard material, hence why almost all of them advice readers not to strongly believe in them.
     
    Last edited: Mar 5, 2006
  11. Mar 5, 2006 #10

    SpaceTiger

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    There are usually a few naysayers, but the vast majority (and all that I've met) do believe they're black holes. The event horizon of a black hole has not been directly observed (it's an extremely difficult observation to make), but we have observed objects that behave very much like black holes in every other way. Also, we've ruled out all other objects expected from mainstream theory, so if it's not a black hole, one will need a new theory to describe it.


    Scientists do not usually (and are not supposed to) approach problems with the intention of proving or disproving a particular theory. There are scientists who are trying to observe near the event horizon of black holes, but not with the specific intention of disproving any theory. There are also physicists who are working on alternatives to black holes, but to my knowledge, they're not taken very seriously in the physics community.


    Could you be a bit more specific? Which theories? How old are the books?

    The evidence for black holes has increased quite a lot in the last decade because of the observations of supermassive objects at the centers of galaxies. As I said before, we haven't proven that black holes exactly like those in GR exist in the universe (we'd have to observe near the event horizon), so it would be irresponsible for the textbook authors to say that we have. That doesn't mean, however, that the astrophysics community isn't sold on the idea. Every recent theoretical paper about quasars that I can think of works under the assumption that they're accreting black holes.



    We can never prove a theory 100% -- we can always measure to higher precision or in more repetitions. In the mind of an astrophysicist, the real question is, do these objects behave like black holes in the regimes we can test? This question is particularly relevant to the issue you brought up, as you suggested that black holes at the centers of galaxies could cause light from the entire galaxy to redshift. This is absurd and certainly ruled out by observations.

    As time goes on, we'll be able to test the black hole theory to higher precision and perhaps (in fact, I hope) there will be some surprises. Any discrepancies, however, should only be observable near the black hole.


    I don't doubt it, I just said I'd never met one. If I do, I'll be curious to hear what they have to say.


    For someone who's not trying to wage a war, I find your statements puzzling. You said,

    ...suggesting that until we were 100% sure about a theory, it wasn't worth exploring. That's really reaching, don't you think? In fact, the original topic of discussion was the expanding universe paradigm, for which there is much, much more evidence than the existence of black holes. The whole point that I was trying to make in my original response to you was that there are currently no other explanations for cosmological redshift that are being explored in the mainstream and that you were making it seem deceptively simple to concoct a viable alternative.

    The idea here is similar to the one ZZ was making in this thread:

    dark matter, dark energy & gravity

    Science is not about belief in the usual religious or casual sense. Scientists form their "opinions" through consideration of the experimental/observational evidence that's available, not by a flight of fancy. The standard model of cosmology is no exception. If it were a simple matter to explain cosmological observations in some other way, then we would be actively trying to distinguish between those models. As it stands right now, we're trying to make high-precision measurements of the parameters of the standard model -- many steps beyond proving expansion.

    Just because you're only familiar with a particular part of the picture (say, the redshifting of light) doesn't mean that there isn't more to the story. In short, give us a little credit.
     
    Last edited: Mar 5, 2006
  12. Mar 5, 2006 #11

    pervect

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    There is at least one paper which addresses the experimential issue of whether or not the objects we are calling black holes have event horizons. The evidence is not currently strong enough to absolute rule out all other possibilities, but it is consitent with and strongly suggests that black holes do have event horizons. The fundamental idea for the test is very simple - if light cannot escape from the surface of black holes, black holes should be darker than other sorts of objects with strong gravity (i.e neutron stars). Experiment confirms this prediction.

    http://arxiv.org/abs/astro-ph/0107387

     
    Last edited: Mar 5, 2006
  13. Mar 6, 2006 #12

    SpaceTiger

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    Yeah, that certainly qualifies. I must say, though, that astrophysicists have been notoriously bad at modeling accretion systems in the past and advection-dominated accretion flows are a matter of great debate in the community. I'm immediately suspicious of any result that depends on an understanding of accretion physics.

    That said, however, I think it probably indicates that these objects, even if not black holes, are quite different from neutron stars. The evidence will become more convincing and straightforward as we delve closer to the event horizons of the supermassive black holes at the centers of the Milky Way and Andromeda.
     
  14. Mar 6, 2006 #13

    DM

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    Yes, the fear of not being able to authenticate the credibilty of my statement with simple words to you has been proven.

    It's a perfect question with negative conclusions from your behalf.

    I suggest you re-read my posts again, I stressed the importance of not postulating theories with 100% certainty but to entwine some caution with them.

    I believe you've misread it, this is what I proposed:

    How would we know for instance, that red and blue shifts are not caused by quasars present at the center of galaxies? We don't even know for sure what these objects are, why should we formulate things for or against it?

    I am not asserting theories, only asking how an astrophysicist would handle this situation and why should they/you formulate things for or against it. I picked black holes at the center of galaxies because these objects are further away from us; hence much more difficult to make any REAL and FACTUAL inductive conclusions.
     
    Last edited: Mar 6, 2006
  15. Mar 18, 2006 #14
    According to the knowledge of mine and whatever I've read; the universe is expanding ( the galaxies are moving away from each and other & the space is under an enlargement ) Is there any evidence or theory proposing that we are expanding too? I mean that the dark Energy ( or any other force ) causing the quarks to increase in size?????????
     
  16. Mar 19, 2006 #15

    Chronos

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    Physics 101.

    Physics 101.

    Yes you are. You are asserting scientists are intellectual drones.
     
  17. Mar 22, 2006 #16
    First of all there are few things in the world which can't be detected directly like predicted strings so how will we get what is happening really in nature. But, there is one more power having by us i.e. mathematics. If from maths' view we get that there is centre of gravity and if countless practicals and studies prove it so nothing can stop us from accepting it.
     
  18. Mar 22, 2006 #17
    A'ight actually I want to say that suppose you're sitting on hour-hand of the clock where 1 second is equal to 1 crore years and it is time 2:25.

    If you see the minute-hand you will get that it is going a lot far from us and you can say that clock( as universe ) is expanding but actually everything is revolving around one center. Don't you think it was our misconception that we understood that Universe is really expanding.
     
  19. Mar 22, 2006 #18

    ZapperZ

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    You need to give people in this field of study a LOT more respect than this. Don't you think they would KNOW such a thing? Furthermore, this "expansion" that is being talked about isn't just a simple expansion of an object already in an established space. It is quite more complicated than that!

    So maybe it is you who had the misconception of the issues you are trying to discuss here. I will also remind you of the PF Guidelines that you have agreed to regarding speculative posts, especially when your knowledge in this area of study is still in its "learning" stages.

    Zz.
     
    Last edited: Mar 22, 2006
  20. Mar 22, 2006 #19

    russ_watters

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    The math rules it out as well...
     
  21. Mar 22, 2006 #20
    We don't know what it is, but we do know it posses certain qualities. For example we know how massive a quasar is, and from that we can calculate how much redshift it can produce. I'll admit along time ago I thought that the mass of a galaxy might account for the redshift we observe, but after I made the calculation I realized it didn't even come close.
     
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