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Age of the universe

  1. May 8, 2007 #1
    I've heard stated by experts that the approximate age of our universe is about 13.5 billion years of so. The thing that doesn't make sense to me about this is that we can see more time than this. The famous Hubble deep field shot taken in the northern hemisphere shows about 13 billion years or so into the past and the other deep field Hubble shot to the south is about 12 billion years. Add them together and we can see more than 25 billion years of our universe's history and it seems to have looked quite similar to what we see in the more recent universe.

    Am I missing some fundemental fact here?
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  3. May 8, 2007 #2


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    Yes. The fact that light itself is carried along with the expansion of space.

    Therefore we can see objects that are moving away from us at speeds greater than c and as a consequence we can see objects further away in light years than the age of the universe is in years.

    Also, the fact that we can look in two opposite directions and yet see these ancient objects in both directions is irrelevant.

    The ancient high z universe is different from the recent low z one.

    However, there are interesting high iron abundance objects that appear to be too old for the young universe they inhabit, this leads to the question Is there an Age Problem in the Mainstream Model?.

    Last edited: May 9, 2007
  4. May 8, 2007 #3


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    If two people walk away from you for 5 minutes apiece in opposite directions, does that make them 10 minutes apart...?
  5. May 8, 2007 #4


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    the stuff that made the CMB, cosmic microwave background radiation, is currently at an estimated distance of 45 billion LY.

    the farthest we can theoretically "see" at the present moment is about 46.5 billion LY. that is how far stuff could be from us and we would be getting radiation emitted from it today.

    the farthest back in time we can see is 13-14 billion years.
    that is, the oldest light we can see is about 13 billion years old, it was emitted by stuff 13 billion years ago.

    when we get instruments that can detect bigbounce neutrinos (or "bigbang" neutrinos if you like bang better than bounce:smile: ) then we will still be only looking back 13-some billion years.

    the neutrinos will be, say, 13.6 billion years old, and the crud that emitted them will be about 46.5 billion lightyears away at present, and they will have been traveling towards us for 13.6 billion years.

    Garth's post explained away the apparent paradox. Look back at what he said.

    The expansion of space is different from a rocket ship. Recession speeds are not limited by the speed of light.
  6. May 8, 2007 #5


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    This is why astronomers, contrary to popular belief, do not actually use 'light year' as a measure of distance. In fact distance is a surprisingly slippery concept in general relativity and cosmology, there are several active threads around the place here discussing some of the issues with defining distance that you may want to look at (I'm talking to the OP here, I think the rest of the posters are the ones doing the discussion in the other threads I'm referring to!).
  7. May 8, 2007 #6
    If what we see at 45 billion LYs away was emitted 13 billion years ago, then the actual object is much further away today, if it still exists. This would make the universe much larger than 90 billion LYs accross. If the universe expansion rate is the same as it has averaged over the past 13 billion years the universe would have a diameter of roughly (45/13)*90 billion LYs or 300 billion LYs. I understand that the expansion rate is increasing making the size even larger. Is this logic correct?
  8. May 9, 2007 #7
    The whole concept of expansion of space seems confusing. Space by definition is nothing is it not? How does "nothing" expand and what would be beyond this definable "nothingness"?

    Are there any models out there that suggest a more infinite universe as applied to it's age and perhaps even size?
  9. May 9, 2007 #8
    In reference to the speed of walking, yes they are.
  10. May 9, 2007 #9


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    you havent got the concept. You just have some words. the words ARE confusing.

    the concept, when properly defined using geometry, is NOT confusing.

    the basic element you are missing is the METRIC
    just a technical name for the DISTANCE FUNCTION that keeps track of all the distances between events.

    If you think about it, you'll see that there has to be a distance function to catalog the distances between things that happen. Its basically simple: there are distances between welldefined events. what they call the metric keeps track of them.

    the metric is what is governed by the 1915 law of gravity called GR, that replaced Newton's 1680 force model.

    the metric is what "expands", in the obvious sense that on average largescale distances in the catalog are forced to get larger by the 1915 law of gravity which governs the metric.

    that is not the only way it could work out but it characterizes a large class of solutions----there are also contracting solutions where largescale distances get smaller by a certain percentage step by step.

    when you say "space is nothing and how can nothing expand, so how can space expand?" you miss the point. I am not talking about "nothing". I am talking about the METRIC----the distance function---that defines our geometry. It is not a material---an expanding material analogy doesnt work. So what should I say?
    "The distance function enlarges itself"
    "the distances in the catalog increase bit by bit percentagewise."
    That's awkward to say. so how about "The metric expands."

    Does that work for you, BoomBoom?
  11. May 9, 2007 #10
    Are these distances from us or from eachother or both? Are things closer together the further back in time we look? Or is the metric calculated based on the prediction of where things should be in the present considering speed and direction of movement of where they were when the light left them?

    Please pardon my ignorance in these matters, I am trying to wrap my mind around the concept of inflation of space-time. It seems as if the universe expansion (space-time if you want to call it that) was supposed to be at a rate not possible to account for the "history" we see today.
  12. May 9, 2007 #11


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    not sure I understand the question. the metric is a SOLUTION of the law of gravity with two or three parameters plugged in. the law of gravity (einstein's GR equation) is a differential equation governing how metrics evolve. you find out the correct values of the parameters by adjusting them so as to get the best fit to the data
    Why does it seem that way? I don't understand.

    Be sure you don't confuse expansion with inflation.
    Routine expansion of the universe is a familiar feature which has been understood since 1930 (or earlier by some) and fits the observations in a beautifully consistent way. Also our law of gravity forces it on us---solutions of the basic gravity equation typically have expanding or contracting distances.

    It is as if the universe is trying to teach us to realize that it is not in the nature of distances between things to remain constant (unless bound together by atomic molecular or some other force)

    But inflation is something else---it refers to a scenario which might have occurred in the first fraction of a second of expansion where there was a different mechanism in control, that goes beyond ordinary matter and the law of gravity we can see working and test experimentally. Inflation could well be fantasy. Although a lot of experts favor the notion. We don't have proof of it, only plausibility.

    Inflation is a conjectured (fantasized) feature of the first fraction of a second.
    Expansion has been a familiar part of our worldview since 1930s and checks nicely with huge numbers observations made over the years.
    Last edited: May 9, 2007
  13. May 9, 2007 #12

    That is precisely what I did. Thanks for catching that one.
    I was actually referring to inflation in which the size of the universe expanded at an "impossible" rate.

    ...and thanks for your answers Marcus, I have a much better idea now of what they are actually measuring.
  14. May 9, 2007 #13


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    You are welcome! I didn't actually see a case where you were confusing ordinary expansion with inflation, BoomBoom. I only meant to warn against getting the two confused. (there was no implied criticism.)
    I still don't fully understand some of what you are saying about "impossible" rates of expansion.

    Ordinary expansion of the sort that has been going on for most of the age of the universe does involve superluminary recession speeds, so it boggles some people and they think of it as impossible.

    but I think you understand how there can be superluminary recession speeds (ask about it if you don't) and you see that aspect of ordinary expansion is not "impossible"

    I wont try to secondguess and speculate as to what you find strains credulity.
  15. May 9, 2007 #14


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    I worded that badly, or perhaps didn't finish the thought: does the fact that they are now 10 "walking-minutes" apart mean that they have been walking for 10 minutes? No - the elapsed time is still only 5 minutes. That's exactly like the HDF and UDF only showing ~14 billion years of age even though the depth of the two images added together would be 14+14=28 billion light years. In both cases, we're in the middle, so the distance traveled is half the total distance between the two.

    I think everyone else added complexities to this about inflation that aren't really necessary for explaining the initial question.
    Last edited: May 9, 2007
  16. May 9, 2007 #15
    Would that not require the assumption that we are sitting on ground zero of the BB?
  17. May 10, 2007 #16


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    There you go again, BoomBoom, with your obsession about ground zero, or the "center point" of expansion.

    You've got to purge your head of that.

    Have you ever thought about the Balloon Analogy?

    You must have encountered it many times in previous discussion boards and elsewhere.

    As a purely geometrical analogy, it is very good. Just don't take the rubber material the balloon is made of as part of the analogy.

    The geometrical analogy is simply that at least IN SPACE WHERE WE ARE there is no center of expansion. Each point on the expanding balloon surface is equally a point from which the others are receding.
    the other points are all getting farther from it.

    to follow the analogy you have to put yourself into the 2D surface of the balloon and look at things as a 2D-critter.
    there is no other space, outside the balloon surface.
    that is how to think of the analogy.

    distances between galaxies increase like the distances between pennies glued to the surface of a gradually expanding balloon.

    everybody gets repeatedly exposed to this analogy. and learn from it that IN THE SPACE WHERE WE ARE there is no one central point to the expansion.

    do you have real trouble grasping that? or are you just kidding (to drive the rest of us nuts) when you keep returning to the "ground zero" idea?
  18. May 10, 2007 #17
    edit due to duplicate post
    Last edited: May 10, 2007
  19. May 10, 2007 #18

    It may help if you consider the raisinbread analogy. Think of a loaf of raisinbread as it cooks. It expands in all directions with the raisins moving away from each other. Think of each raisin as a galaxy. An observer on one raisin sees the others moving away. While an observer on a distant raisin sees the same thing.

    It may also help if you consider that there is more to the universe than we can observe optically. What we can see tends to put us in the center of the observable area of the universe. There is more, and we can't be sure of where we are with respect to the "edge". If there is an "edge".

    We say the universe is expanding due to the redshifts we observe. There is a redshift caused by the velocity of a galaxy, and one caused by the expansion of space. Using these, we can calculate where a galaxy is currently.

    I hope I have helped and not hindered your understanding. As a fellow laymen I thought I would share my understanding of things. There are several discussions on this forum dealing with these questions. Use the search function and search for "universe expansion".

    NASA also has a site that is useful in answering questions about the universe.


    Also check out these sites.


  20. May 10, 2007 #19


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    that is a very useful analogy, thanks for presenting it! and also the excellent links.
    as I picture it, the raisinbread-dough is being allowed to "rise" by yeast action, before baking, and I think of the dough as filling all the space I can imagine, extending indefinitely in all directions (so that it will not have any boundary and will never meet a wall)

    the balloon surface also has this feature of having no boundary---from the 2D-creatures standpoint.

    an important thing to warn about, in either case, is thinking of space as a material (like rubber or dough)
    the analogy is the geometrical relation between the pennies stuck on the balloon surface---the fact that distances between all are increasing---or the geometrical expanding-distance relation between the raisins

    another thing to stress is that GR is a theory of spacetime geometry in which there is no prior space, no rigid framework in which things happen
    and therefore the "bigbang" or expanding-space cosmology is not an explosion of crud outwards into a pre-existing empty space
    it is an expansion which includes space itself, or more precisely it is an expansion of the metric which is the sum of all geometric relationships.

    the material crud is basically just getting a free ride, like the raisins and pennies

    so it is impossible to think meaningfully of some kind of 'center point' of the expansion. what is expanding has no boundary and no center.
    Last edited: May 10, 2007
  21. May 10, 2007 #20
    Yes thanks Wilgory (and Marcus). Great links!

    I still have a hard time understanding how the immense size of the universe could have come about in such a short period of time, it seems as if the age should be much older to account for this. I don't see why it necessarily needs a "birth", but I guess if we can see another few billion LYs and don't see any formed galaxies that would be proof correct? If we do keep seeing further and further and still see formed galaxies, I guess they will need to keep adjusting the age estimation?

    Even a loaf of bread has a center, if the universe is expanding in all directions and it is assumed it had a "birth" from a much more dense and compact state, then there must be a point (or area) of origin.

    I will work on educating myself on these matters. Thanks again for your input.
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