The size of this universe

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Saint, Jan 14, 2014.

  1. Saint Valued Senior Member

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    If I measure with Cartesian coordinate, in X-Y-Z directions from the earth.
    How far can I go in these 3 directions until the edge of the universe (assume it has a limited size and edge) ?
     
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  3. Grumpy Curmudgeon of Lucidity Valued Senior Member

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    Somewhere between 20 billion lys and 100 billion lys, but recent evidence suggests it is possible it is bigger...

    http://phys.org/news/2014-01-baryon-oscillation-spectroscopic-survey-universe.html

    One of the scientists used the "I" word(infinite), I think he's wrong, no infinities exist in nature. The Universe is extremely "flat", therefore it is right on the line between eventual collapse and continued expansion. A better way of saying that is that the Universe is not closed, we do not live in a Black Hole, nor will the Universe collapse in the future. This finding means that Dark Energy is a constant, a quality of spacetime, it's force is the same for every equal portion of spacetime(more{expanding}spacetime means more total energy). But gravity is proportional to mass and distance, early in the Universe gravity was stronger than Dark Energy and expansion slowed, later they were more or less balanced and the expansion coasted, in the present the Dark Energy is stronger than the gravity between large clumps of matter, but gravity is dominant WITHIN clumps of matter, thus we have strands of galaxy clusters like spider web with growing voids between strands, voids that are already becoming the largest structures in the Universe.

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    Grumpy

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  5. Saint Valued Senior Member

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    Where is our position in the universe? How can we possible see the whole picture of the universe ?
     
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  7. Fraggle Rocker Staff Member

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    We don't know. The universe is so large that the light from its farthest regions has not reached Earth yet. We can only see a sphere roughly 90 billion light-years in diameter, with us at the center, because the light from within that range has reached us.

    There's every reason to assume that there are more galaxies farther out whose light has not yet reached us. After all it would be an incredible coincidence if we actually were at the very center of the universe!

    We can't. It's very likely that more than half of it is beyond our range of vision. If it is actually 200 light-years in diameter, then we're only seeing approximately one percent of it!

    We actually know quite a lot about the universe, although what we don't know is considerably more than what we know.
    • It is approximately 14 billion years old.
    • It is still expanding.
    • As it expands, space itself expands with it. This explains why we can see light from galaxies 40 billion light-years away, even though that light has only been traveling for 14 billion years: the space through which the photons travel has been stretched.
    • Only about 5% of the contents of the universe are matter, as we understand the concept. Most of the universe consists of dark matter and dark energy, things that we only understand superficially.
    • The natural laws (gravity, electromagnetism, force=mass x acceleration, voltage=current x resistance, etc.) appear to be the same everywhere.
    • And others...
     
  8. paddoboy Valued Senior Member

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    We have no preferred position in the Universe.....Our picture of the Universe is governed by the expansion rate attaining the speed of light, thus inhibiting the light from very distant objects ever reaching us. This is our observable Universe and is the same distance in all directions...a spherical bubble if you will surrounding us.
    The whole Universe therefor is Impossible to observe from our position.
     
  9. paddoboy Valued Senior Member

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    Our Observable Universe bubble is around 92 billion L/years in diameter constrained by the expansion rate and the speed of light.
    I would think that the whole Universe as a whole is much much larger and near Infinite in extent, if not Infinite.
     
  10. paddoboy Valued Senior Member

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    Permission has been previously given to post full articles from "Universe Today":

    Universe Could be 250 Times Bigger Than What is Observable
    by VANESSA D'AMICO on FEBRUARY 8, 2011


    Our Universe is an enormous place; that’s no secret. What is up for discussion, however, is just how enormous it is. And new research suggests it’s a whopper – over 250 times the size of our observable universe.
    Currently, cosmologists believe the Universe takes one of three possible shapes:
    1) It is flat, like a Euclidean plane, and spatially infinite.
    2) It is open, or curved like a saddle, and spatially infinite.
    3) It is closed, or curved like a sphere, and spatially finite.
    While most current data favors a flat universe, cosmologists have yet to come to a consensus. In a paper recently submitted to Arxiv, UK scientists Mihran Vardanyan, Roberto Trotta and Joseph Silk present their fix: a mathematical version of Occam’s Razor called Bayesian model averaging. The principle of Occam’s Razor states that the simplest explanation is usually the correct one. In this case, a flat universe represents a simpler geometry than a curved universe. Bayesian averaging takes this consideration into account and averages the data accordingly. Unsurprisingly, the team’s results show that the data best fits a flat, infinite universe.


    But what if the Universe turns out to be closed, and thus has a finite size after all? Cosmologists often refer to the Hubble volume – a volume of space that is similar to our visible Universe. Light from any object outside of the Hubble volume will never reach us because the space between us and it is expanding too quickly. According to the team’s analysis, a closed universe would encompass at least 251 Hubble volumes.
    That’s quite a bit larger than you might think. Primordial light from just after the birth of the Universe started traveling across the cosmos about 13.75 billion years ago. Since special relativity states that nothing can move faster than a photon, many people misinterpret this to mean that the observable Universe must be 13.75 billion light years across. In fact, it is much larger. Not only has space been expanding since the big bang, but the rate of expansion has been steadily increasing due to the influence of dark energy. Since special relativity doesn’t factor in the expansion of space itself, cosmologists estimate that the oldest photons have travelled a distance of 45 billion light years since the big bang. That means that our observable Universe is on the order of 90 billion light years wide.


    To top it all off, it turns out that the team’s size limit of 251 Hubble volumes is a conservative estimate, based on a geometric model that includes inflation. If astronomers were to instead base the size of the Universe solely on the age and distribution of the objects they observe today, they would find that a closed universe encompasses at least 398 Hubble volumes. That’s nearly 400 times the size of everything we can ever hope to see in the Universe!
    Given the reality of our current capabilities for observation, to us even a finite universe appears to go on forever.


    Read more: http://www.universetoday.com/83167/...bigger-than-what-is-observable/#ixzz2qPAlMF42
     
  11. Fraggle Rocker Staff Member

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    The Big Bang model--the only one we've got that doesn't rely on religious woo-woo--insists that the universe began as a point and began expanding. Even with the stretching of empty space, the stretching speed is finite, as is the expansion speed.

    Therefore the universe cannot have stretched and expanded to an infinite diameter in a finite time.
     
  12. paddoboy Valued Senior Member

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    Hmmmmm, Firstly Infinity really boggles my brain, and I did also use the metaphor "near infinite".....But the Universe being topologically flat, does infer this...Secondly [and I'm willing to be corrected on this] the BB model I think only applies to the Observable universe.
    Something along these lines was explained to me once before, but I'm not sure I understood it properly.
     
  13. paddoboy Valued Senior Member

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    Just to elaborate slightly, when we say the Universe was once compacted to within the volume of an atomic nucleus, we mean the Observable Universe was compacted to within the volume of an atomic nucleus.

    That doesn't mean that I can then explain the whole Universe! Because at this stage I really cannot.... HELP!!!!!

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  14. Boris2 Valued Senior Member

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    if it is infinite now then it has always been infinite. infinite doesn't mean it was really big. remember all of spacetime was contained in the early universe just as it is now.
     
  15. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Yes, every astrophysicist's dilemma.

    Here's how I visualize it. When you look in a single direction, at about 12.7 billion light-years, we see a hot plasma receding from us at a temperature of about 2,700 degrees K; but because of relativity, and its high recessional velocity of about .999999c (z = 1071?), the photons are red-shifted to the microwave region, which is physically equivalent to a stationary blackbody (relative to us) of 2.7 degrees K.

    Now, if we turn around, and look in the opposite direction; we see something similar (not the same, because it is a different part of the universe). That is, a hot plasma receding at close to c. Those two regions of the universe that we 'see' via their microwave radiation are going in opposite directions (relative to us), and are exceptionally far apart.

    If you were at one of those two regions of the universe, looking back at the Milky Way, the Milky Way would not appear as it now is, but rather it would appear as a hot expanding plasma (as our region once was), and we would see it via the microwave radiation at 2.7 K; Now, if we were to try to look beyond the Milky Way to that region that from Earth is in the opposite direction, we could not see that other region of the universe that we can see from Earth, as it would be beyond the 'opacity wall', and not become visible for billions of years thereafter.

    By that analysis, the Universe is actually infinite in extent, when one includes the parts we can't yet see, which is mind-boggling for most astrophysicists (or, at least, most of the others I've met).
     
  16. Saint Valued Senior Member

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    The universe was about 14B years old since Big Bang, but we can see things 40 B light-year away?
    Is that the Exact distance at the moment we observe it?
    When we calculate this distance, do we take into account of the space expansion speed?

    Let's say there is a distant star observable from here by telescope,
    how do we measure its "current distance" from here? What mathematics do we use? What assumption do we make?
     
  17. paddoboy Valued Senior Member

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    There is no Universal now in the Universe...so I would say no to that question.
    The distance we do measure though includes the amount space/time has expanded from the time light left the star until we take the reading.

    Relatively close stars are measured by simple parallex error....further ones are measured by what are called "standard candles" which are type 1a Supernova and Ceipheid Variables.
     
  18. Grumpy Curmudgeon of Lucidity Valued Senior Member

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    Saint

    We see things at 13.7 billion lys away, they are currently 40 billion lys away(yes, by calculating the effects of measured expansion)but the light that is currently coming from them will never reach us. What we see 13.7 billion lys away was light those things released 13.7 billion years ago, they no longer exist in that form, but have evolved like our own galaxy did. But in a real sense, distance in time is what we are seeing, and as to our position, it is right in the "center", just like every other particle or lifeform would see itself, 13.7 billion years ago every atom in your body was in the Singularity, everything else was too. And, if you had been there you would have seen spacetime expand away from yourself in the middle, it still looks that way today. But that is true for every point in the Universe, there are no edges unless you count the Event Horizons of Black Holes. And since the whole thing had a beginning there will always be a finite time until the present(IE currently only 13.7 billion years have passed since the beginning)and since it once occupied zero volume, it has a finite size at the present time(and always will), it is not infinite in size. And to all appearances, we are smack dab in the center of it all. But so is everything else.

    Grumpy

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  19. paddoboy Valued Senior Member

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    Hiya Grumpy......
    There still seems to be differences of opinion out there about whether the Universe is finite or infinite.
    Getting into the depths of either certainly sets my mind boggling.
    Infinity, well does anyone really comprehend it?
    Finite, although seemingly acceptable on face value, also raises a myriad of questions.
    Your take on a finite Universe I cannot argue against really, but I have also seen/heard reputable scientists saying it is Infinite with equally convinceable arguments.
     
  20. Saint Valued Senior Member

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    We can estimate distance, how about volume?
    Because it is Space, it is 3D, it has volume.
    what is the estimated volume of the observable universe?
     
  21. Saint Valued Senior Member

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    Let us take an example,
    assume at this moment, there is a new-born star which is exactly 100 light-year from the Earth,
    at this moment we can't see it, because the light hasn't reached us yet.
    while the light is travelling towards us, the space between us and the star is also expanding,
    So, are we sure 100 years later we can see the star?
    If yes, after 100 years, what is the exact distance of this star from us?
    It should be >100 light-year because the space is stretching to a larger distance.

    Can you answer this question?
     
  22. paddoboy Valued Senior Member

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    100 L/years is a piss in a bucket distance when talking of the Cosmos.
    I hope I don't confuse things here, but when we say the Universe is expanding, we mean expanding over the larger scales. But when we have conglomerations of galaxies/walls of galaxies relatively close together [eg: Our local group of galaxies, Milky Way, M31, M33 etc] they are gravitationally bound...or to put that another way, the mass/energy density of regions like our local group and even further afield, are "decoupled"from the overall expansion rate.
    So a star measured at 100 L/years would only be undergoing local proper motion.
    But [if this is what you were asking] if we look at the Alpha Centauri tonight, we know it is 4.3 L/years distance, we are looking at that 4.3 years ago, and theoretically speaking, if it disappears tonight, [ in its own FoR] we will not see it extinguished for 4.3 years.
     
  23. paddoboy Valued Senior Member

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    If we assume you mean a billion L/years away, the star's distance would have changed by the amount that space/time has expanded obviously.
    This I think, not sure, would be calculated by the amount of redshift observed.
    Someone more attuned to the mathematical side of things, may like to do some calculations for you.

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