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Thread: expansion of space quick question

  1. #1 expansion of space quick question 
    Forum Sophomore somfooleishfool's Avatar
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    expansion of space is said to not be limited by c, but does it have a speed limit? is there a "fastest" expansion of space?


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    Nope. However, there is a limit on how fast we can see something recede. If it recedes fast enough, we will never get information about it.


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  4. #3  
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    Quote Originally Posted by PhysBang
    Nope. However, there is a limit on how fast we can see something recede. If it recedes fast enough, we will never get information about it.

    And if the accelerated expansion of space continues eventually a lot of things that are observable today will disappear forever.

    http://en.wikipedia.org/wiki/Hubble_volume
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by PhysBang
    Nope. However, there is a limit on how fast we can see something recede. If it recedes fast enough, we will never get information about it.

    And if the accelerated expansion of space continues eventually a lot of things that are observable today will disappear forever.

    http://en.wikipedia.org/wiki/Hubble_volume
    What is the difference between the Hubble Volume, Visible Universe and Observable Universe? I know they're not the same but I just don't know the difference.

    P/S DR Rocket, you seem to be very knowledgeable, I've noticed in depth answers on many posts. If its not too much of a personal question, what education have you done and perhaps what is some of your experience in the field?
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  6. #5  
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    Quote Originally Posted by somfooleishfool
    Quote Originally Posted by DrRocket
    Quote Originally Posted by PhysBang
    Nope. However, there is a limit on how fast we can see something recede. If it recedes fast enough, we will never get information about it.

    And if the accelerated expansion of space continues eventually a lot of things that are observable today will disappear forever.

    http://en.wikipedia.org/wiki/Hubble_volume
    What is the difference between the Hubble Volume, Visible Universe and Observable Universe? I know they're not the same but I just don't know the difference.

    P/S DR Rocket, you seem to be very knowledgeable, I've noticed in depth answers on many posts. If its not too much of a personal question, what education have you done and perhaps what is some of your experience in the field?

    Hubble volume -- everything receding from us now at less than c

    Visible universe -- most often synonymous with observable universe. May also mean everything that is bright enough to actually see now with available instruments. Not the usual terminology.

    Observable universe -- everything that is close enough for photons emitted to have reached us, despite the fact that it may be too dim to actually be seen or that photons emitted prior to the recombination epoch (i.e. prior to the "surface of last scattering") would have been absorbed. It would include everything that we can see with gravity waves if they exist and if we evre figure out how to detect them.

    Universe -- the whole enchilada, everything that came from the big bang. Nobody really knows how big it is, but it is humongous.

    Check your PM box.
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    Quote Originally Posted by DrRocket
    Observable universe -- everything that is close enough for photons emitted to have reached us, despite the fact that it may be too dim to actually be seen or that photons emitted prior to the recombination epoch (i.e. prior to the "surface of last scattering") would have been absorbed. It would include everything that we can see with gravity waves if they exist and if we ever figure out how to detect them.
    That's a very complete description and represents our observable universe, given our current understanding, if we could detect events prior to recombination.

    To (hopefully) avoid any confusion, when the OP sees references to things like the size of the observable universe, cosmologists currently use a definition based on the surface of last scattering, as it currently represents our particle horizon - the limit of what is observable.
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    So, is the "size" of the observable universe (from our viewpoint) increasing by every second? In other words, are we able to see another ~300 million metres of the universe every second from where we "sit" in space (as the photons from these distant objects only just begin to reach us)? That's what would seem obvious to me, but I just want to see if that's a correct assumption.
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    No. If it was like that, the observable universe would have a radius of 13.7 billion light years. Instead what's called the "particle horizon" has a radius of circa 46 billion light years.

    Imagine the universe is a sphere, and you're in the middle of it. If the universe wasn't expanding at all, what you could see of it would be expanding at the rate you said, like a sphere expanding within the sphere. But then on top of that, you've got to add in the fact that the whole universe-sphere is expanding.

    It's a bit more complicated than that of course. If you're up for it, have a read of Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe.
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    Nice post, Farsight!

    There is also a "layman's" version of that paper, or more accurately a Scientific American article, by the author of that paper:

    http://www.mso.anu.edu.au/~charley/p...DavisSciAm.pdf
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    Ah, yes. I see what you're saying- that makes sense actually, I should've thought about that!
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    New question but fairly related so I figured I'd post here.

    Would it be accurate to say that the volume of a given amount of space is growing when expansion of space occurs?

    The reason I ask this is that I posted a question a wee while ago which never got answered but I decided if the answer to the above question is "no" then my question is answered.

    The question was as follows.
    The expansion of space is said to happen at faster than c, and *the Higgs Boson is said to occupy every bit of space at all times*. but if the expansion of space were to be creating "pockets" of space growing faster than the speed of c, then the Higgs Boson particles would not be fast enough to fill in the gaps created thus making null of statement *

    PS.... just now I got to thinking, and if the answer to the first question were "no" then the universe would only be 13.XX light years big. but ill leave everything I have written incase some new light can be shed on it, but it seems to me a paradox if the answer is "no" and a paradox if the answer is "yes"
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    Your question about the Higgs boson got answered. The answer was that the question doesn't make sense and you'd misunderstood something.

    As for your new question, I'm no expert, but I think you'll have trouble defining "a given amount of space" well enough to get a straight answer to the question. To the best of my understanding, there is no coordinate system you could use to mark off a part of space for measurement. (Actually, it'd probably be best just to let someone who understands this better give a clearer answer.)
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    Quote Originally Posted by somfooleishfool
    The expansion of space is said to happen at faster than c, and *the Higgs Boson is said to occupy every bit of space at all times*. but if the expansion of space were to be creating "pockets" of space growing faster than the speed of c, then the Higgs Boson particles would not be fast enough to fill in the gaps created thus making null of statement *
    The expansion of the universe is only faster than c across a certain distance, currently around 14 billion light-years! Any "pocket" less than 14 billion light-years across would easily get filled.
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    Quote Originally Posted by MagiMaster
    Your question about the Higgs boson got answered. The answer was that the question doesn't make sense and you'd misunderstood something.

    As for your new question, I'm no expert, but I think you'll have trouble defining "a given amount of space" well enough to get a straight answer to the question. To the best of my understanding, there is no coordinate system you could use to mark off a part of space for measurement. (Actually, it'd probably be best just to let someone who understands this better give a clearer answer.)
    the question wasnt answered, it was only stated that i was missinterpretting the higgs boson as a single particle as opposed to several particles. it still stands that higgs boson particles occupy everywhere.

    so what if the "pocket" is 18b light years. and i had suspected the answer might be in defining the "pocket"
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  16. #15  
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    If the expansion of space is only faster than light between distances larger than 14 billion light-years, then any increase in space due to expansion is always less than c, locally to whoever is measuring it. The space near everyone is expanding at less than c, but the cumulative effect of that expansion over great distances leads to apparent recession speeds of c, at great distances.

    So, anywhere in the universe, higgs bosons would have absolutely no problem filling any space created.
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    I don't understand why you speak of the Higg's boson as if it was real and had been observed.

    When the universe reached the weak interaction energy ( about 250 GeV ) the scalar field which permeated the universe spontaneously broke symmetry. This phenomenon is called the Higg's mechanism and it gives rise to the mass of the force carrying bosons ( +/-W and Z ). The scalar Higg's field is a quantum field and QFT predicts the spontaneous creation of particles as 'bumps' in the smooth field. These are conjectured to be the Higg's bosons... but don't break open the champagne yet as none has been found ( yet, I'm hedging my bets ).
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  18. #17  
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    Quote Originally Posted by somfooleishfool
    Quote Originally Posted by MagiMaster
    Your question about the Higgs boson got answered. The answer was that the question doesn't make sense and you'd misunderstood something.

    As for your new question, I'm no expert, but I think you'll have trouble defining "a given amount of space" well enough to get a straight answer to the question. To the best of my understanding, there is no coordinate system you could use to mark off a part of space for measurement. (Actually, it'd probably be best just to let someone who understands this better give a clearer answer.)
    the question wasnt answered, it was only stated that i was missinterpretting the higgs boson as a single particle as opposed to several particles. it still stands that higgs boson particles occupy everywhere.

    so what if the "pocket" is 18b light years. and i had suspected the answer might be in defining the "pocket"
    The cosmic microwave background (composed of photons) is also everywhere. Also, I don't think the Higgs bosons occupy literally every single point in space, the same way the CMB doesn't. They're just everywhere in the sense that they have a non-zero density (at least statistically) over any given region. (Someone correct me if I've got that wrong.)
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  19. #18  
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    You can describe a particles position, yet not it's momentum. Higg's needs vacuum energy.
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  20. #19  
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    Quote Originally Posted by SpeedFreek
    If the expansion of space is only faster than light between distances larger than 14 billion light-years, then any increase in space due to expansion is always less than c, locally to whoever is measuring it. The space near everyone is expanding at less than c, but the cumulative effect of that expansion over great distances leads to apparent recession speeds of c, at great distances.

    So, anywhere in the universe, higgs bosons would have absolutely no problem filling any space created.
    wow thanks. makes sence.

    I cant decide if im glad to be proven wrong (learning) so often on this forum or if its dissapointing
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  21. #20  
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    Quote Originally Posted by somfooleishfool
    Quote Originally Posted by SpeedFreek
    If the expansion of space is only faster than light between distances larger than 14 billion light-years, then any increase in space due to expansion is always less than c, locally to whoever is measuring it. The space near everyone is expanding at less than c, but the cumulative effect of that expansion over great distances leads to apparent recession speeds of c, at great distances.

    So, anywhere in the universe, higgs bosons would have absolutely no problem filling any space created.
    wow thanks. makes sence.

    I cant decide if im glad to be proven wrong (learning) so often on this forum or if its dissapointing
    Be glad.
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  22. #21  
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    Quote Originally Posted by MagiMaster
    Quote Originally Posted by somfooleishfool
    Quote Originally Posted by SpeedFreek
    If the expansion of space is only faster than light between distances larger than 14 billion light-years, then any increase in space due to expansion is always less than c, locally to whoever is measuring it. The space near everyone is expanding at less than c, but the cumulative effect of that expansion over great distances leads to apparent recession speeds of c, at great distances.

    So, anywhere in the universe, higgs bosons would have absolutely no problem filling any space created.
    wow thanks. makes sence.

    I cant decide if im glad to be proven wrong (learning) so often on this forum or if its dissapointing
    Be glad.
    Haha noted. You made me laugh
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  23. #22  
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    Quote Originally Posted by MigL
    I don't understand why you speak of the Higg's boson as if it was real and had been observed.

    When the universe reached the weak interaction energy ( about 250 GeV ) the scalar field which permeated the universe spontaneously broke symmetry. This phenomenon is called the Higg's mechanism and it gives rise to the mass of the force carrying bosons ( +/-W and Z ). The scalar Higg's field is a quantum field and QFT predicts the spontaneous creation of particles as 'bumps' in the smooth field. These are conjectured to be the Higg's bosons... but don't break open the champagne yet as none has been found ( yet, I'm hedging my bets ).
    I was speaking to a professor who works on the ALICE experiment at the LHC the other day, and apparently particle physicists and theoretical physicist are giving themselves a deadline of December 2012 for discovering (which is defined as a 5-sigma event in particle physics) the Higgs Boson- as they think that if it does exist, it should be found by then.

    It was quite interesting, however, as this professor was saying that he hopes it isn't real and that it's not discovered as it would be much more exciting for particle physics as he claimed that the whole of the standard model would have to be thrown out (not just a little tweak, a complete rewrite) and particle physicists would "start over". Interesting!
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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