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The speed of our sun

  1. Feb 4, 2008 #1
    Hi,

    Is it posible for us to determine the velocity of our sun?

    The Hubble constant gives a referent for the exspansion of the universe but do we have any way of knowing if the point at the centre of the big bang was, (or is), stationary?

    Do we know in which direction the centre of our universe was, (or is)?

    I understand that we go through a very complex series of motions here on Earth, orbits round our sun, sun orbits galaxy, galaxy orbits other galaxies and on. So I appreciate that putting this in anything other than purely circumstantial language might be a bridge too far. but what is know of this?

    In an expanding universe, I can understand the doppler shift of light in one direction due to the overlay of motion causing an increase in frequency, (please correct me if I am wrong), but a reduction in frequency would suggest motion opposing expansion.

    Is this considdered to be a result of relative motion due to celestial dynamics?

    Any help is greatly appreciated.

    John
     
  2. jcsd
  3. Feb 4, 2008 #2

    chroot

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    The universe has no center. The big bang happened "everywhere at once," and not at all like the explosion of a bomb in space already-extant space. A two-dimensional analogy is the expansion of the surface of a balloon while it is being inflated. The surface of a balloon also does not have a center.

    The universe has no concept of absolute motion, so it's meaningless to ask what the absolute motion of the Sun is. If you provide some other reference point, a reasonable estimate of velocity with respect to it can be worked out, but it will not be of much use to you, or anyone else.

    The fact that (essentially) every galaxy in the universe appears to be receding away from our own is an indication that the universe is expanding. Any observer in any other galaxy would observe the same thing: all other galaxies moving away.

    - Warren
     
  4. Feb 4, 2008 #3
    Thank you for the reply.

    I find it staggering that such missconceptions are allowed to propagate. Every single public reference to the big bang makes it seem that it started as a tiny micro-dot in one place. That it was all compressed together into one single point "in" time and space and then boom.

    What it seems like you are trying to suggest is that there was no extention at all, prior to the big bang! That there was no precursor of anything at all!

    No dimensions, even if void of any content, (I don't care about time). Is that what you are saying?
     
  5. Feb 4, 2008 #4

    chroot

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    The popular press is responsible for literally hundreds of staggering misconceptions in science. I'm not going to write a list, but several dozen pop into my head after only a moment of thought.

    That's correct. We currently have no idea what existed before the big bang, or what exists outside the universe. According to current understanding, these aren't even reasonable questions to ask. The answers may be physically unknowable, and may not be of any consequence for our own universe anyway.

    Space itself (at least, the space that comprises our universe) began with the big bang. There was no space before the big bang, nor did the big bang expand into some existing, enclosing space. At least, that's the current model.

    - Warren
     
  6. Feb 4, 2008 #5
    Thanks Warren

    Gob smacked

    John
     
  7. Feb 4, 2008 #6

    russ_watters

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    So much of that is easy to misconstrue. Ie, if "it [the universe] was all compressed together into one single point" is generally correct. It's just that that point wasn't a point at the center of some void.
     
  8. Feb 4, 2008 #7

    EL

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    Well, at least if we're talking about the observable universe.
     
  9. Feb 4, 2008 #8

    tony873004

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    I believe that the cosmic microwave background radiation is redshifted in one direction and blueshifted in another by an amount that reveals that we are moving about 600 km/s relative to something that would observe no red and blue shifts.
     
  10. Feb 4, 2008 #9

    chroot

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    You are correct, Tony, but there's no reason to believe that reference frame, the comoving reference frame, is any more important than any other.

    - Warren
     
  11. Feb 4, 2008 #10

    marcus

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    Yes, our sun has an absolute velocity with respect to what is called the "Hubble flow" and this has been determined fairly accurately by the COBE microwave background mapping satellite in the mid 1990s.

    This is not what you were asking about, I suspect.

    You were asking about expansionary motion. However there is no centerpoint of expansion.
    We have no absolute recession velocity as part of universal expansion. Distant objects appear to recede from us as if we were the center. And from the standpoint of a distant object we would be receding. Everybody sees himself as the center, and there is no center.

    this expansion is often called the "Hubble flow" and it gives a criterion for when something is STATIONARY with respect to it. If you are stationary then the recession of distant objects is symmetric, the same in all directions.

    If you are moving with respect to the universal expansion, then objects ahead of you will not be receding so fast----they will seem to have a few km/second deducted from the speed they should have according to Hubble law. And objects astern of you will have a few km/second added to the recession speed that the law says they should have.

    Hubble was aware of this in the 1930s, but it is a very slight thing to measure. Actually our sun is moving at about 370 km/second with respect to the universal expansion, in the direction marked in the sky by the constellation Leo.

    Redshifted galaxies in that direction do not look quite as redshifted as they should, given their distance. Galaxies behind us (opposite Leo position in the sky) are slightly more redshifted. In other directions there is little or no effect.

    Our sun has several velocities depending on what you take as standing still. It is circling the center of the Milkyway galaxy at a couple of hundred km/second. The galaxy is moving, our local group of galaxies is moving. But what I have told you is, in some sense, more absolute because it is 370 km/second with respect to the universe as a whole.

    This speed was measured in the 1990s by the COBE team, when they found that the microwave background sky was just slightly warmer in the Leo direction (and colder in the reverse direction). they were able to pinpoint it, and to say rather precisely the solar system would have to be moving in order to cause that slight milliKelvin temperture difference.

    If you want a link to the paper that they published about this in the mid 1990s let me know. I or someone will get it. If I remember the lead author was Charles Bennett.


    the expansion has no center. It is a largescale average increase distances between stationary objects---objects which are essentially not moving with respect to the Hubble flow or equivalently the CMB. Ignoring small random motions, basically stationary objects. The current rate of expansion of distance is about one percent every 140 million years.
     
  12. Feb 4, 2008 #11

    marcus

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    that is right, but it is not 600 km/second

    If you are talking about the sun's motion relative to CMB, the speed is about 370 km/second.

    If you are talking about the Milkyway galaxy, it's speed is higher. I recall something like 500-600 km/second.

    the two vectors are in different directions because the sun also has orbital motion around the center of the galaxy. there is some cancelation too.

    =======================

    I see Chroot has already taken care of almost all the questions. I had to do something else halfway thru and didn't get my reply posted. So now I just basically agree with Warren, except possibly on some minor details (maybe he doesnt like the 370 figure or something.)
     
  13. Feb 4, 2008 #12
    Thank you Marcus.

    I will search out Charles Bennett on the web but if you do come across the link that would be great!

    Am I right then, in saying that the expansion is isotropic.

    Can I consider the expansion as a scalar deflection of distance. (Expansion in proportion to the distances between the celestial bodies)?

    John
     
  14. Feb 4, 2008 #13

    chroot

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    Space expands everywhere at the same rate, as far as we know. The further two objects are from each other, the faster they will measure their speed of mutual recession. This is Hubble's law:

    [itex]v = H_0 d[/itex]

    http://en.wikipedia.org/wiki/Hubble's_law

    - Warren
     
  15. Feb 4, 2008 #14
    Thank you Warren

    Marcus, I have found the following pdf:

    First Year Wilkinson Microwave Anisotropy Probe (WMAP1) Observations:
    Preliminary Maps and Basic Results

    Big file with sky maps the lot, thank you

    John
     
  16. Feb 4, 2008 #15
    I see from the WMAP data that CBM are isotropic and I can see how that points to a voidless origin. If the big bang had been in the manner of an explosion in space then CBM would point to that explosion.

    What I am struggling to understand is why CBM don't interact with themselves.

    Do we know anything of the evolution of CBM. Are there any conjectures or theories that look at changes in CBM over the life of the universe.

    I think what I'm asking is, as the universe expands, is the wavelength of the CBM increasing?

    I appreciate that this might be a little ambitious since I am guessing we have only really been studying it for the past 8 years. (It may also be implicit in the WMAP data in some way that I am over looking)

    Any thoughts

    Thank you.
     
  17. Feb 4, 2008 #16

    DaveC426913

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    I think the popular press is only partly to blame. The public take some responsibility for only caring to know as much as fits into a 20 second news clip. Things like the Big Bang and SR and GR simply can not be described in 20 seonds using every day concepts - especially without any foundation of knowledge to build on.

    Too many people are too comfortable thinking about little electron moons orbiting proton planets...
     
  18. Feb 4, 2008 #17

    russ_watters

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    Most of the rest didn't make much sense to me, but yes!, the CMB's wavelength increases as the universe expands. The wavelength of the CMB was predicted by a team of scientists while another team was discovering it.
     
  19. Feb 5, 2008 #18
    Thanks Russ,

    The problem I'm having is with understanding how an isotropic wave system manages not to interfere with itself. I think it is a question about wave dynamics that I perhaps should ask over on the physics section.

    Sorry, it was a bit wishy washy.

    John
     
  20. Feb 5, 2008 #19
    I was just writing out a question about wave dynamics over on the general physics section when something occured to me.

    Is the entire universe beating as one, so to speak. Its pulse being the frequency of the CBM's? Is the entire background of the universe in harmony so that when the upper crest of a wave is detected in orbit around Earth, we can assume the upper crest will also be detectable over at Alpha Centauri?

    As well as being isotropic, do the CBM's also posses spatial symmetry?

    Thanks for your help

    John
     
  21. Feb 5, 2008 #20

    russ_watters

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    The CMB isn't a single uniform, phase-synchronized wave, it is random noise centered around a particular frequency. It works pretty much like the light we see from the sun (the universe was at one time an opaque clump of hot matter). It's a hot object with a bell-curve shaped spectrum of light, centered around a particular frequency.
     
  22. Feb 5, 2008 #21
    Thank you Russ

    Back to studying wave dynamics I think!
     
  23. Feb 11, 2008 #22
    I may be wrong, but as it seams to me that the nature of cosmology itself may be to blame for the many misconceptions. The biggest misconception of all is the idea that the current model is accurate. It seams that the big bang is a semi far fetched impossible to prove model which has been deemed the mainstream guess.

    I don't think people should believe anything cosmology claims as truth. The farthest that the truth goes in cosmology doesn't take you very far in conclusions. The details, like what was before the big bang, if there there even was a big bang etc are all speculation. What we know is that about 50 or so observed galaxies, out of more than we even know exist, are becoming farther apart. Throw in the cosmic background radiation, and they have made a model trying to explain every detail.

    It is like having 2 blank red pieces of 1000 piece puzzle and claiming to think that the puzzle is of the chinese flag.

    If you notice misconceptions in the media, that is because it is highly likely that the majority of what you here from cosmologists are misconceptions.

    One possible reason is, that the conclusions must be stretched to get public interest. What they should do if they want to be true to the people, is they should show only the facts and evidence and go more in depth with it. I don't see why they give us only the speculation and don't go into detail on what is fact and observable.

    Here is a simple deductive logic example.

    If X is impossible to conceptualize,
    And X is conceptualized,

    The product will me a misconception
     
    Last edited: Feb 11, 2008
  24. Feb 11, 2008 #23

    chroot

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    No scientist would ever suggest that you should accept a model as absolute truth -- it's just a model, nothing more, nothing less. In time, it will be replaced with a different or more complete model that will answer more questions.

    Redshifts have been measured for thouuuuuuuuuusands of galaxies. And you really think that's all the evidence involved? You really underestimate those pesky scientists, don't you?

    http://www.talkorigins.org/faqs/astronomy/bigbang.html

    You do understand that scientists publish evidence, analyses of evidence, expose holes in the arguments of others, and debate about open questions every single day right? What you're looking for is a journal. Perhaps you should try going to your local university library and pulling out a few to see how scientists talk among themselves. Everything you seek and more will be provided therein. You seem to be pretty ignorant of the entire process of science, so I suggest you select and begin regularly reading a few journals before making such statements again in public. They're a little, well, embarrassing.

    - Warren
     
  25. Feb 11, 2008 #24
    I'm sorry, I didn't mean to offend anyone. It isn't the fault of the scientists, it is the fault of the field that I was talking about. I know that the scientists working in the field of cosmology are no doubt very smart people who are doing great work. The problem is that they are in a very hard field which will always be a theoretical field. Everyone loves to think that they have figured out the secret of the universe, but it is ignorant for someone to think they have. On television cosmologists act as if they have and take it way too far. People tend to believe what scientists say, and when you have scientists claiming they know how the universe began, know that there was a beginning to time, that the universe is 13 billion years old, that the universe was once an infinately dense point etc., people tend to think they must be right. The way that cosmology is presented to the public it is almost starting a cult of people who believe in the model with faith. Like I said before, to be true to the people, more of the specs and details should be made public in the media and less of the speculation. I know that scientific journals are made public, and I am sorry if I seamed to include journals. I also think that you guys at physics forums are great and if it wasn't for you, then the misconceptions would run wild. I am very gratefull to be able to ask the scientists on this forum about my misunderstandings. Again it is the media that I have a problem with.
     
    Last edited: Feb 11, 2008
  26. Feb 11, 2008 #25

    chroot

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    Which cosmologists have you seen on TV? I can't even think of a single example of a cosmologist who has made a TV appearance.

    There is a vast preponderance of evidence in favor of the big bang model. Similarly, there is a preponderance of evidence for Newton's law of gravity. Are either of these theories absolutely right, or beyond suspicion? No.

    You're "preaching to the choir," W3pcq -- no scientist worth his salt will tell you that he or she has all the answers, or knows any of our models to be absolutely right.

    The reason I'm being gruff with you is because your argument (scientists think they have all the answers, but they're just pompous because they obviously don't know everything yet) is a recurring strawman argument. The conclusion assumes the premise -- your conclusion only makes sense if scientists really do think they have all the answers, but you'll never meet a single scientist, ever, who will ever say any such thing. Even if TV popularizations and textbooks sound authoritative, no scientists anywhere will claim to have all the answers. Not only would that counter the scientific method and the spirit of scientific endeavor, it's demonstrably false. We know our theories are incomplete.

    Is it? Do you have some evidence to support this claim?

    Journals are public. Any university library will let anyone who desires to walk in and spend as much time as they want reading them. If you're talking about the tripe that's published in USA Today or sound bites on CNN, well, remember that those are not produced by scientists! They're produced by people with degrees in english or communication, and they're trying to water down the topic into a format that's immediately accessible to everyone, including school children. It's almost impossible to imagine a non-scientist trying to explain, say, string theory to a sixth grader in a way that wouldn't make a real string theorist cringe. To be frank, they're also in the business of selling newspapers or recruiting advertising dollars, not the business of properly educating the public. We'd all love it if the news media made the effort to improve the quality of their depictions of science, but it would be far easier to simply direct eager people to better sources of information.

    The popular news media is not the appropriate place to obtain deep scientific knowledge! You simply cannot learn science from human interest pieces in the variety section of the Sunday newspaper. Try to find better sources, and you will no longer be so concerned.

    - Warren
     
    Last edited: Feb 11, 2008
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