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Stretched space far from our own

  1. Jul 27, 2004 #1
    Ok I'm sorry if this is a stupid question I read so many books about this stuff but not all sinks in I try but ok here's the question in Martin Ree's book, Just six numbers he talks about how when the universe was made it starts off at a certain speed and the further you go out like on the boundary of space and time it is going so fast it stretches space like bends it in essence can anyone explain that and another thing in the book faster then the speed out light by Joao Maguiejo he explains how speed of light was always a constant by in the beginning it was not 3 E to the 8 m/s but much faster can someone explain this and if it is even a leading idea he said it is but all my teachers frown upon it but im sure most profound ideas even SR or GR by einstein were frowned upon in the beginning.
    Sorry but i have one more, ok someone please paint a beautiful picture for me for i am truly lost with this. Ok singularity with ifinite mass density blah blah some reason boom and we're off the universe begins heres the things i cannot understand or maybe just picture ok a star that is on the boundary of the universe 10 or 15 billion light years use to in the beginning be right beside us?? true or not and i think thats true so what made it out there and us not like why was it chosen to get out of the gates first i understand once its off and runnin the farthest things runs the fasted i think but if someone can explain this it will help also lets say:
    right when big bang goes off you have a light in your hand and i have a light in my hand. you get off first and i a lil after you now 15 billion years later you are way way out there and i am where we are on earth, can i see your light and can you see my light? like when galaxies are red shifted away from us just because they are moving away that doesnt mean that there light is moving away does it cause it travels constant every which way right??
    just if anyone can answer a few of these i would be happy and sorry for my ignorance i try but maybe not hard enough.
  2. jcsd
  3. Jul 28, 2004 #2
    any idea

    sorry to bother everyone but anyone have a clue
  4. Jul 28, 2004 #3
    Please, try to use periods and commas in your writings, you remember me a member called chosenone
    VSL cosmology is actually out of the mainstream investigation. It is a theory that eliminates inflation, and had in the past problems to create the observed fluctuations in the CMB, but these problems were overcame, and actually the theory can predict these fluctuations
  5. Jul 29, 2004 #4
    sorry bout the periods

    sorry about the periods and commas I'll watch that. Ok VSL is out and now what is in? by the way what does VSL stand for? Also what was the stretched space stuff?
  6. Jul 29, 2004 #5
    VSL stands for Variable Speed of Ligth. The idea that the velocity of light was faster in the early universe was first formulated by Moffat in 1991, though it was generally ignored by the scientific community. In 1998, Albrecht and the portuguese Magueijo formulated their VSL cosmology, in this paper
  7. Jul 29, 2004 #6

    so now VSL is gone and what is the stance on how the inflation took place how do you explain the horizion problem.
  8. Jul 30, 2004 #7
    The idea that the speed of light was faster in the early universe makes a lot of sense to me. By faster, I mean greater motion through space, not through space-time, because the speed of light is constant in space-time.

    Because the speed of light is constant in space-time, as the universe ages, as it passes through greater time, the rate of motion through space correspondingly lessens.

    I think that theories about a slowing through space of light over time might have a rough sell now because we can only see light from such a small part of the universe that our context is not large enough to recognize this phenomenon well.
  9. Jul 30, 2004 #8


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    yes VSL is gone---it was always fringe, not mainstream.
    Another thing: the so-called "horizon problem" has been addressed in various ways
    (back in the 1980s it was addressed by Inflation Stories) and most recently it has been resolved by replacing the classical bigbang singularity by a changeover from contraction to expansion

    the "horizon problem" consisted of people asking why the CMB Microwave Background is very nearly the same temperature or intensity in all directions. How do the Microwaves from over there KNOW to be the same intensity as these other Microwaves coming from the other side?

    that has been answered pretty well by now. I would advise you to worry instead about some more basic things first and afterwards ask again about the "horizon problem" (like, why is it called that---in science almost everything is called by an accidentally chosen possibly misleading name so there is a long story of why it is called "horizon" and not something more reasonable like the "microwave uniform temperature problem"---but naming problems is a technical issue)

    You already asked a good basic question which would be good to start with.
    You asked how it can be that we two start out close together and then after 13.7 billion years (estimated age of U) we are so far apart.

    there is no fixed reference point, no "zero on the x-axis", in Nature. So it is not like you stayed put and I am the one who is far away. Only the distance between has meaning. We were close then. Now we are far apart.

    that happens even if neither one of us is aware of moving in our local neighborhood of space. We can both think we are standing still in the space around us. But after 13 billion years we find we are far apart! Distances between stationary points increase. AFAIK there is no way to make that easy to grasp.

    If the two points are fairly far apart already then the distance between them can be increasing faster than c. Got that? :smile:
    this is just commonplace mainstream cosmology----not "VSL"
    it is a consequence of Hubble's law and goes back to the 1930s.

    the distances to lots of the galaxies we can see today are at this moment increasing faster than c------this is a consequence of General Relativity (Einsteins 1915 theory) and does not contradict his 1905 Special Relativity.
    the speed limit of Special Rel does not apply to widely separated points where there is curvature. (the never told you the speed limit has limited applicability?:smile: it was a surprise to me too)

    You are asking a good initial question and the answer is already hard to comprehend. distances in nature actually increase, and they even increase faster than the speed of light. things near each other can be wide apart a few billion years later.

    IIRC it is estimated that stuff close to us with the expansion began can now be as far away from us as 46 billion light years. that really takes a stretch to understand. how can it have happened that in only 13.7 billion years some stuff could have gotten from being near us to being 46 billion LY away? It happens because for at least part of the time the expansion of the distance between us was faster than c. I doubt that anybody here finds this easy to understand so if you find it hard dont worry.
  10. Jul 30, 2004 #9
    wow that was very well put

    thanx so much marcus. I didn't know traveling faster than C was possible at any point no matter what the particle was. Can you explain how this is possible, because these galaxies moving away are constituents of matter itself, and if matter travels faster then c i would think all the time backward issues would start popping up, but i am assuming everything is just fine and there is a good explanation, you say it has something to do with curvature of spacetime and GR, kind of like it was traveling close to c already then it hits the curve and boom massive acceleration above c???

    Cheers Woody
  11. Jul 30, 2004 #10
    Great description Marcus!

    Hi Marcus;

    On your reference to expansion/contraction, I must have missed that along the way. But, I am very pleased to learn this from someone in the know. It fits my model to a tee. (sorry for reference to theory) Selfadjoint fussed at me about that. Could you please make reference to where I might find more on this subject. Thanks in advanced for any help.
  12. Aug 1, 2004 #11

    ? any idea ?
  13. Aug 1, 2004 #12


    It can also be explained by a slowing of the speed of light over time since the Big Bang. You are very quick to dismiss this idea as completely implausible. I think that it deserves more consideration. The idea that you contend, that space can somehow move faster than the speed of light, is hardly more appealing.
  14. Aug 1, 2004 #13


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    Marcus is quick to dismiss that idea because it has been exhaustively examined and found inconsistent with observation and prediction many times.
    Last edited: Aug 1, 2004
  15. Aug 1, 2004 #14
    so which one of you is right, not to start anything please but this kind of stuff confuses me, it happens in every thread i post, two super intelligent people argue or something near that i am i like hmmm no clue.

    thanx for anyones help
  16. Aug 1, 2004 #15
    Thanks for claiming to be able to respond for Marcus, but you seem not to have read his post.

    What do you mean by eshaustively. You surely cannot mean that there is no possibility of futher examination.

    Marcus says that VSL is not mainstream. This is hardly a way to phrase a complete rejection. Are you seriously contending that the concept of space expanding faster than the speed of light is a reasonable one, or that it has been so exhaustively demonstrated that other ideas should no longer be considered?

    Furthermore, what is this it that you refer to as having been exhaustively examined? Surely, you cannot be claiming that there is no purpose at all in considering the possibility that the speed of light, although constant in space-time, might not be constant throughout time. How could it? This violates the notion that the speed of light is constant in space-time.
    Last edited: Aug 1, 2004
  17. Aug 1, 2004 #16


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    :rofl: this had me laughing out loud----I guess there are superintelligent people in the world but at PF we are all pretty much equally like hmmm no clue (at least I may speak for myself in that regard!)

    chronos thanks for the moral support.

    the simplest is for me to withdraw what offends Prometheus and to assure him that I do not peremptorily dismiss "VSL"
    I just want to make very forcefully the point that faster-than-light recession speed has been a standard premise of mainstream cosmology for 70 years. It is not my idea and it is not controversial

    (this is what prometheus apparently has not realized yet)

    so it is not a novel scenario like "VSL" . it is not to be compared with somebody's new idea----it is just an everyday feature of mainstream cosmology.

    Of course Einstein could be wrong and the basic Einstein-Friedmann equation of standard cosmology could be wrong and the universe could be in some clever way NOT be expanding in the linear hubble-law way that cosmologists grow up assuming. Maybe it isnt expanding at all!!! :smile:

    But if you want to talk with people you have to understand the basic mainstream model. And it is an essential part of that model that you have FTL recession speeds beyond the Hubble distance. The model WILL NOT WORK WITHOUT THIS. And you have to understand that many of the galaxies we observe today were receding from us faster than c at the moment when they emitted the light that is now reaching us.

    If you dont understand this, you remain confused about the standard model.
    the standard model is the usual point of departure for discussion so its really hard to have a cogent discussion if you ignore it.
  18. Aug 1, 2004 #17


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    What exactly is the problem with recession velocities greater than c?
    Expansion is just a result of general relativity and you get recession velocities greater than c in any universe described by general relatvity that is large enough/ has a large enough scale factor. Do you disagree with general relativity?

    Clearly a non-varying lightspeed as well as fitting in with observation DOES NOT violate anything in relativty as it axiomatic in relativity.
  19. Aug 1, 2004 #18


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    there is a good source for mainstream cosmology on the web
    which is ned wright site

    he teaches cosmology (grad and undergrad courses) at UCLA and is one of the co-leaders of WMAP (satellite microwave observ.----the world's premier source of cosmology data)
    he's an easygoing california dude with a beard who happens to be one of the worlds top cosmologists, check out the site
    check out the cosmology FAQ
    and the tutorial (introductory cosmology)
    and check out the calculator

    just say Ned Wright to google
    and if you cant find any of that stuff, post back to this thread and
    I or someone will give links.
    the cosmology calculator is an essential part of the package
    because it embodies in a concrete form as nothing else on the web does
    the nuts and bolts standard cosmology model
    with the standard parameters

    H is 71
    Lambda is 0.73
    Omega-sub-matter is 0.27

    you take anybody's cosmology calculator and put those parameters in
    and you have the universe in your hand.
    If you hear that somebody observed a galaxy with redshift z = 6

    which means the wavelengths are stretched out by a factor of 7

    then you put z = 6 into that calculator and it tells you how far away the thing is. Anyone interested at all in cosmology shd really try this.

    It doesnt just tell you how far away the thing is now. It tells you how long ago it emitted the light and how far away it was when it emitted the light.

    I've spent a while trying different z, and trying to picture our U with those galaxies and the overall shape of the expansion. the calculator is a good tool. or I find it so anyway.

    Siobahn Morgan's site has a better laid-out calculator than Ned Wright's
    even tho he is more the prominent cosmologist. they give the same distances and times but hers gives recession speeds too.
    from post 136407 in Astro sticky:

    Ned Wright's

    Siobahn Morgan's
    http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html [Broken]

    homepage for Siobahn in case you want to see who she is
    http://www.earth.uni.edu/smm.html [Broken]
    homepage for Ned in case you want to see who he is

    Last edited by a moderator: May 1, 2017
  20. Aug 1, 2004 #19

    Marcus, can you show me how this is derived, i'm sure it can be if you say so, i dunno enuff about the subject so maybe there is a GR way to show or proof it at least in the model we are speaking about. My prof in phys said that galaxies never move faster than speed of light and he is a GR man through and through so i thought maybe if i had a equation of GR for this model it mighthelp.

  21. Aug 1, 2004 #20


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    for people like your prof there is an article
    called "Expanding Confusion: Common Misconceptions..."
    by Tamara Davis and Charles Lineweaver
    it is a tutorial on popular confusion about recession speed.
    look at it yourself before you give it to him.

    Davis and Lineweaver
    "Expanding Confusion:common misconceptions of cosmological horizons and the superluminal expansion of the Universe"

    Lineweaver and Davis are at the University of New South Wales.
    Lineweaver was a co-leader of the COBE project (satellite
    mapping the cosmic microwave background in the 1990s)

    Lineweaver is one of the world's top cosmologists and Davis is his grad student. She just got her PhD and her thesis is on this very same topic
    http://arxiv.org/astro-ph/0402278 [Broken]

    Tamara Davis thesis (advisor Charles Lineweaver)
    "Fundamental Aspects of the Expansion of the Universe and Cosmic Horizons"

    the main point is there are two kinds of speed-----so different that it is confusing we have the same word in both cases:

    ordinary speed and recession speed

    recession speed is the rate at which the distance to a far-off galaxy is increasing----it can easily be 600,000 kilometers a second or twice c.

    that is not the same as the speed of a bird flying past your house or of a spaceship flying past the earth

    a galaxy can easily be receding at 600,000 kilometers a second but this does not mean that it could ever catch up with and pass a photon of light
    because the space around the galaxy and everything else that far away from us is receding at 600,000 km/s.
    The galaxy thinks it is sitting still (approximately, say with respect to the microwave background) and for all we know it IS sitting still. the curious thing is the distance from us to it is increasing superluminally.

    the mathematical proof is easy if you know Hubbles Law
    which is
    v = Hd
    (Ned Wright explains this and makes the point emphatically that v is the current speed and d is the current distance. Hubble's Law is NOT about "doppler shifts" or redshifts----it is a linear relation of presentday recessionspeed and presentday distance)

    if your prof knows GR then he probably knows the FRW type of metric that cosmologists normally use. this is how the presentday distance is defined. and it has a distinguished time parameter---these are technicalities
    (if he doesnt know the Friedmann-Robertson-Walker metric he may not "get" the idea of the instantaneous presentday distance to a galaxy and he may not understand the v = Hd law.)

    Anyway if he knows the Hubble law then the derivation you asked for is clear:
    H = 71 km/sec per megaparsec
    so just divide 300,000 by 71
    that gives the distance in megaparsecs

    You go that distance out===and the recession speed is c.
    You go twice that distance out====and it's 2c
    You go three times that distance out====and things receed at 3c.

    this magic distance called Hubble distance, gotten by dividing 300,000 by 71, is 4225 Mpc-------4225 megaparsecs.

    a parsec is 3.26 lightyears so a megaparsec is 3.26 million LY.
    so hubble distance is 13.8 or about 14 billion LY.

    Anything that far from us at this moment is at this moment receeding at c.

    there is lots more potential for confusion. Your prof may say something like "but of course we can't see things that are 14 LY away, they are not in our observable universe." Wrong. get to use Ned Wright's calculator, or Siobahn Morgan's. Dont believe that nonsense. We are currently observing galaxies farther away than that. because the expansion of space actually helped (after a photon has covered a certain distance that distance expands) in a certain sense. But that is another discussion.

    of course he many never understand and you risk a bad grade in the course.
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