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Edge of universe?

  1. Oct 14, 2012 #1
    I'm not a physicist!
    Just wondering what it is like on the edge of the universe? how many dimensions will be there, what force will be acted upon a close object, and what relativity will become?
    I'm assuming the universe is euclidian (eucklidean? euclidean? my English sucks.) not hyperbolic or whatever geometry so there would be an reachable 'edge'. And under the assumpsion that the universe is constantly expanding.
    Thank You
    From a high school student
    Victor Lu
     
  2. jcsd
  3. Oct 14, 2012 #2

    Simon Bridge

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    What do you mean by "the edge of the Universe".
    That would be a bad assumption.

    Lets say for the sake of an example we were to postulate a Universe with a "reachable edge" - then that edge would have whatever properties we wanted it to have. It could be a brick wall.

    What I am saying is that the question is too wide open.
    Of more interest is the properties of the existing Universe that we live in.
    This one is not Euclidean and has no reachable edge.
     
  4. Oct 14, 2012 #3
    there is no universe such as you imagine...if you make an assumption that isn't accurate, you'll not get much in the way of insightful answers....why do you want to assume Eucledian geometry...a practical issue is that in our real universe you are at the 'center' of it, and so is every other observer!! [That is a very cryptic comment!]

    try starting here:

    http://en.wikipedia.org/wiki/Edge_of_the_Universe


    insofar as is known, 'edges' are probably not what you envision.

    You can read about an actual 'edge of universe' of sorts by checking Wikipedia subjects like
    multiverse or eternal inflation....those posit multiple universes....

    You might also read about black holes as they are causally disconnected from our
    universe in some senses.....and horizons and cosmological horizons also have a sort of 'edge' if you want to call it that...

    When you accelerate [change velocity] you create one type of causal horizon....that is a form of an 'edge'....

    None of these is likely what you have imagined so far.
     
    Last edited: Oct 14, 2012
  5. Oct 14, 2012 #4

    Drakkith

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    We can see back in time about 13.7 billion years and out to about 90 billion light years in diameter and we cannot see an edge to the universe. This doesn't mean that there isn't one, but we simply have no reason to believe that there is an edge.
     
  6. Oct 14, 2012 #5

    Chronos

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    We already reside at the temporal edge of the observable universe. No matter where you look, the universe is younger in every direction. Do you notice anything peculiar? Any other observer in the universe would experience this same illusion, so, the concept of an edge is meaningless. We perceive a temporal edge that ends in the past [at the big bang], but, we cannot observe our future.
     
  7. Oct 23, 2012 #6
    We only "see" the present. We use artifacts, photons, from a past event to form an image within our eyes but we do not see back in time nor do we see out in space. The edge of our visible universe that we do see is the outside edge of matter where photons interact, the inside edge I would think of the oldest artifacts, cosmic background radiation.

    You are a part of the edge of the universe, we think in terms of four dimensions, Gravity is the force acting upon close objects and relativity is how we describe time.
     
  8. Oct 23, 2012 #7

    Drakkith

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    The term "see" can be a little ambiguous. I would take it to mean the comprehension of what the image formed on your retina represents and all the rules involved in how that image was formed. After all, I could claim you only ever see the past because by the time you are aware of it, the event has already passed. Also, your use of "edge" is odd, as the universe is not known to have an "edge" at all, only a horizon beyond which we cannot see thanks to the finite speed of light. This has nothing to do with where matter and light interact and is purely the result of the time of emission of the light.


    I don't know what you are getting at here, as it doesn't seem to make much sense. I recommend not trying to take an unusual stance on what the "edge of the universe" means, otherwise we are likely to get bogged down into a pointless discussion on terminology.
     
  9. Oct 25, 2012 #8

    Simon Bridge

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    Sounds like reading too much Soren Kierkegaard to me :)
    Note: n_kelthuzad (OP: Victor Lu) has yet to chip in to clarify the question - the answer very much depends on what is meant by "edge".
     
  10. Oct 25, 2012 #9

    Garth

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    Hi Victor,

    On the other hand it could explain:
    hubble.jpg
    where all my odd socks have gone!

    As a High School student keep asking questions and learn, soon you will be a physicist!

    Because the universe looks 'isotropic', that is on the largest scales it looks the same in all directions right back to the Cosmic Microwave Background it is usual to assume that on the largest scales the universe is isotropic, and because we cannot claim to be at any special place in the universe (the 'Copernican Principle) it is therefore also logical to assume that the universe is 'homogeneous', that is on the largest scales it is the same everywhere. So the galaxies and clusters of galaxies on these scales can be treated like the molecules in an ocean. The ocean being the universe itself in this analogy.

    With these assumptions there is no edge, as the medieval woodcut above imagined, the 3D space around us could be spherical (closed) like the surface of the Earth, so if you went off in a straight line you would end up coming back to your starting place, (though the expansion of the universe renders this trip impossible), it could be flat (Euclidean) or it could be hyperbolic (saddle shaped).

    We don't know which it is; it is too close to call, although the weight of observations leans slightly to the closed, spherical case.

    I hope this helps,
    Garth
     
    Last edited by a moderator: May 3, 2017
  11. Oct 25, 2012 #10

    Chronos

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    Because we are observationally limited by the hubble parameter, I doubt we will ever know with any certainty if the universe is closed or open.
     
  12. Oct 26, 2012 #11
    I would think that the point where matter and light interact would always be an edge. A temporal edge to our universe using a photon as a ruler would be the difference between the durations of photons, oldest and youngest. The oldest from CMB and the youngest from matter, emission til reception or the travel time between the edges of our visible universe. The question was what is would be like at the edge of our universe, I did not think talking about something we can not see was needed to answer the question, shape of universe.
     
  13. Oct 26, 2012 #12

    Drakkith

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    I don't understand this statement. What do you mean by "point" and "edge"? Are we talking about a horizon somewhere, or something else? Where is this matter and light interacting at?

    The CMB was emitted by matter, so your distinction between the CMB and other light is confusing. In any case the "age" of the photons, or the flight time, is what you could use for a ruler if you had a way of measuring how long that photon has existed. The CMB is indeed the "oldest" light there is.
     
  14. Oct 26, 2012 #13

    Chronos

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    The temporal edge of the universe is a very 'real' effect experienced by any and all potential observers in the universe. It is a direct consequence of the finite speed of light and only confusing when you try to apply the concept of simultaneity. We humans have a logical weakness for that trap. One of the most important concepts of GR is the notion of 'simultaneity' is an illusion.
     
  15. Oct 28, 2012 #14
    Edge as in a line where an object begins or ends or a point near the beginning or the end, both would describe a photon with a emission/reception point. The youngest photons that I share the present moment with looks to be the outer edge of the universe I see. The other edge between the stars is the CMB or the oldest photons I see as the inner edge of my visible universe. The edge where matter ends and a photon begins or the edge where photon ends and matter begins both interactions make up the universe I see.
     
  16. Oct 28, 2012 #15

    Simon Bridge

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    Yes we know we can think of "edge" etc to be anything we like - surely what is important is how OP (n_kelthuzad) is thinking of it. OP has yet to return to clarify this issue. Until then we are all just relieving our bladders against the airflow.
     
  17. Oct 28, 2012 #16

    Drakkith

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    The youngest are the outer edge, the oldest are the inner edge, matter beginning and ending? Do you realize how confusing you are making this? I think the other explanations are more than enough to satisfy the OP for now.
     
  18. Oct 29, 2012 #17

    Chronos

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    None of this makes sense, so I am bailing from this thread.
     
  19. Oct 29, 2012 #18

    Simon Bridge

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    Well ... people have started "playing around" and OP does not seem to be interested in the replies so...
     
  20. Oct 30, 2012 #19
    I don't think anybody mentioned this, but Euclidian geometry does not imply edge and I don't get why you'd think it does.
     
  21. Oct 30, 2012 #20
    Looking out into space is the same as looking back in time. Looking out and seeing signals from one event in every direction such as the surface of last scattering appears to be seeing from the inside of the event sort of like seeing the inside walls of my den. Looking at the keyboard in front of my face I see the outside of the keyboard. The only edge I can see of the universe is the edge formed by matter I see these edges via photons which thanks to their spectral lines we can even think of them as having an edge.

    I would think the GPS clocks prove that simultaneity of matter is real, it is the view we observers have of the present via photons that is the illusion.

    Sorry I am so confusing.
     
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