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What happens beyond 13,7 billion light-years?

  1. Aug 20, 2014 #1
    Imagine that I draw a sightline from Earth (E) to the most distant observable cosmic structure, called for simplicity X and presumed 13,7 billion light-years away. Imagine that by magic I can instantaneously transport myself on to that structure. If sitting there and keeping looking further along the E→X→ direction, will I then see the rest, the hidden part of the universe for again 13,7 billion light-years ahead?
    The question might seem stupid but is inspired by the consensus in cosmology that every observer, wherever in the cosmos, feels himself as the center of the Big Bang.
    Is it also reasonable to assume that an observer on structure X and looking in the opposite direction ( X → E→) will observe our Earth as the horizon of his observable universe? Many thanks, Jozsef
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  3. Aug 20, 2014 #2
    With "the rest, the hidden part" I guess you mean "another part", right? If so, since we are talking science, I really can not say a definite yes or no (because there are no known way of finding out at the moment). But if you would ask me, I'd say I think it is likely that the answer is "yes, we would see another part".

    I don't think it is a stupid question at all :smile:.

    I suppose you mean "observe our Earth on the horizon of his observable universe?", right? If so, I'd say yes, that's reasonable.
  4. Aug 20, 2014 #3
    [QUPossibly something important escapes to me when I write : 'the rest' of the universe. Intuitively I mean with "the rest": the part of the universe which, for the moment, is not yet accessible for observation due to limitations in our actual technology. Your suggested correction : "an other part" of the universe will surely be of importance. Must I read : " another Universe"?OTE=DennisN;4827687]With "the rest, the hidden part" I guess you mean "another part", right? If so, since we are talking science, I really can not say a definite yes or no (because there are no known way of finding out at the moment). But if you would ask me, I'd say I think it is likely that the answer is "yes, we would see another part".

    I don't think it is a stupid question at all :smile:.

    I suppose you mean "observe our Earth on the horizon of his observable universe?", right? If so, I'd say yes, that's reasonable.[/QUOTE]
  5. Aug 20, 2014 #4


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    Just to point out that the observable universe is bigger than what you think. You can see further than 13.8 light years.
  6. Aug 20, 2014 #5

    Sorry, but can you speciffy?
  7. Aug 20, 2014 #6
    Hmm, we may mean the same thing, but I will be more specific what I mean: It is reasonable that if you are at a position X somewhere on the [STRIKE](area)[/STRIKE] surface of the sphere that represents our observable universe (with Earth at the center), you would see another part which we can not see from Earth. There will also be a part which both you at X and observers on Earth can see, of course. EDIT: a clarification: the observable universe is the part of the universe which can be seen from Earth. The size of the observable universe is known. The size of the entire universe is unknown.

    Good point, I missed that completely, haha :redface:. Jozsef, regarding this you can have a look at Observable universe and Observable_universe#Size.
    Last edited: Aug 20, 2014
  8. Aug 20, 2014 #7


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    The observable universe has a radius of 46 billion lightyears (greater than 13.7 billion lightyears) because of the expansion of space.
  9. Aug 20, 2014 #8


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  10. Aug 20, 2014 #9
    Dear Dennis and Martin, I 'am paralyzed ! Never thought this way. Please allow me to sit down for a while for proper digestion. I 'am really astonished, especially since recent popular TV series alike National Geographic and the Discovery Channels - frequently diffusing cosmological series - never quote about this new insight. I also swallow books on cosmology for breakfast and never read something alike. This recent understanding must probably be very up to date. I realize that I have a serious mental reorganization to perform before Alzheimer strikes. I' am honored and grateful to both of you for sharing this approach and also for the reference to Wikipedia. Respectfully, Jozsef
  11. Aug 20, 2014 #10
    No problem :smile:. Since you seem to be interested in these kind of things, I came to think of this clip:

    The Known Universe by AMNH:
  12. Aug 20, 2014 #11


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    All directions in the universe lead to the past. The most distant point in the observable universe is the CMB at just under 13.8 billion years ago [presently at a distance of 46.6 billion light years]. If you could time travel back to when the CMB photons we now observe were emitted, the universe would be about 400,000 years old, unpleasantly warm, and a bit claustrophobic. If you traveled 'conventionally' at light speed, you would reach the 'current' location of the CMB in 46.6 billion years. Of course the universe would be about 60 billion years old by then and unimaginably enormous.
  13. Aug 21, 2014 #12
  14. Aug 21, 2014 #13


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    Click on the "Quote" button: this will include the message as a quote in a blue box in your reply. If you'd like to break up the quote, or only include part of it, add appropriate QUOTE and /QUOTE tags.
  15. Aug 21, 2014 #14


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    Similar to html, forum markup code works by having text enclosed between two tags like so:
    The first one indicates the start, the second one(with a "/") indicates the end of markup sequence.
    The most common tags are
    "b" for bolding
    "i" for italics
    "quote" for putting text in the quote box
    "url=example.domain" for linking to other webpages (close the tag simply by typing [/url]; no need to retype the address)
    (all in square brackets and without the inverted commas)

    As you can see by looking at your posts, you're breaking either of the tags, so that they're not recognised by the forum software as viable commands. Make sure to click on "preview post" button (not visible when using "post quick reply" box) to see if your post is formatted directly. If not, look for missing or misspelled tags.

    The forum, like most others, streamlines the process of adding tags by having a toolbar over the area where you type(clicking on most icons automatically wraps relevant tags around highlighted text), using hotkeys(ctrl+b nets bolding tags, ctrl+i nets italics and so on), and having the quote and multiquite buttons in the lower-right corner of each post.
    Clicking on "quote" copies the whole post(but without any quotes in it) already wrapped in quote tags. You can split the quote into multiple quotes by manually adding the end quote and start quote tags wherever you want, and typing your response in-between those.

    Clicking on the multiquote button(the "M" button next to the quote button) does nothing by itself, but when you click on a quote button after highlighting some other posts with multiquote, those posts will be quoted(i.e., wrapped in tags) alongside the post that you click the quote button by.

    More commonly used tags can be found by exploring the toolbar, playing with ctrl+(random letter), by the power of google, or by using the quote button on the post that has the tags that you'd like to see - you'll see them displayed together with the quoted text.
  16. Sep 24, 2014 #15

    I think it depends: would you transport yourself "there" is not really a clear definition of "there". Would you transport yourself to see exactly what you're seeing right now, or would you transport yourself in that place in "this right now" moment?

    I first thought it was a silly question, but yeah, it's not that stupid at all.
    If you would transport yourself to that place at the "local time", you would see the earth as the horizon of the events, and nothing would be really that interesting... well, you could see another place of the universe we can't look at because it's outside our observable universe, and that is pretty intriguing by itself yeah, but you would just see the earth and (well, with a right instrument of course!) your family on earth.

    What is intead more interesting, i think is that thinking of transport yourself at the past time, the time we see looking at it. By that time, the earth wasn't here, the solar system wasn't formed yet, and i'm not even sure if the milky way was already there. Anyway, looking where the milky way should be, you would see something... something more dense than it is today, with the clouds of gas still expanding, and probably with nothing there yet (without stars, galaxies...).

    Am i correct?
  17. Sep 24, 2014 #16


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    Instantaneous travel to remote points in the universe will not yield the naively expected result. Say you could instantaneously travel to where the star Betelgeuse now appears to be. Would you be shocked to find Betelgeuse is no longer there? The light you presently observe from earth left Betelgeuse about 640 years ago. Like everything else in the universe, Betelgeuse moves, and continued moving during the 640 years since that light was emitted.
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