# cosmologists, come on in! - universe size question **URL:** \ **Category:** Factual Questions\ **Created:** [January 22, 2012, 7:40pm UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324 "2012-01-22T19:40:44Z")\ **Posts on this page:** 10\ **Page:** 3
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [January 25, 2012, 11:40pm UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/41 "2012-01-25T23:40:47Z")
> [@Terr](#): > > No, they aren’t. They specifically are talking about expansion that proceeds faster than the speed of light - thus creating regions in the universe that are far far away from the “visible universe”. > > Here’s another one: [Big Bang models back to Planck time](http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html) > > Then the universe was less than a billionth of a billionth of a billionth of a second old, it briefly went through a period of superchanged expansion, ballooning from the size of a proton to the size of a grapefruit (and thus expanding at many, many times the speed of light). No. If you read that link closely you’ll note that they use the phrase “universe” and “observable universe” loosely and interchangeably. For example, in the section on the Inflationary Period the graph is labelled “Radius of the Observed Universe” while the text just says “universe”. In an expanding universe the farther apart two points are in space, the more rapidly they move apart. If you pick a point far enough away from Earth, it’s receding from us at faster than the speed of light RIGHT NOW. During the inflationary period, the rate of expansion was much faster, so points that were much closer together receded at greater than the speed of light. This fact has nothing to do with creating “regions of the universe that are far far away from the ‘visible universe’.” The observable universe has diameter of about 93 billion light years. Everything within it was indeed packed into space smaller than an atom prior to inflation. However, there’s much more to the universe than the part we can observe. As far as we can tell the universe is infinite in extent and has always been so. ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [January 25, 2012, 11:47pm UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/42 "2012-01-25T23:47:22Z")
> [@The\_Hamster\_King](#): > > No. Ok, here is one more (see the illustration that goes with the text below): [http://abyss.uoregon.edu/~js/cosmo/lectures/lec20.html](http://abyss.uoregon.edu/~js/cosmo/lectures/lec20.html) Although we have little knowledge of the Universe before the Planck time, only speculation, we can calculate when this era ends and when our physics begins. The hot Big Bang model, together with the ideas of modern particle physics, provides a sound framework for sensible speculation back to the Planck era. This occurs when the Universe is at the Planck scale in its expansion. **Remember, there is no `outside’ to the Universe.** [which means they are not talking about “observable universe” only - Terr] ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 25, 2012, 11:58pm UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/43 "2012-01-25T23:58:44Z")
**Terr** , you’re wrong on this point. Any source that gives specific values for the size of the Universe before or after inflation, or at any other point, is either referring to the observable Universe and being sloppy in their terminology, or is deeply confused in some way. > [@](#): > > Quoth **erislover** : > I had read that someone tried to calculate the size of the universe, and showed it was possible that the size of the universe is actually smaller (slightly) than the size of the visible universe—we just don’t recognize we’re looking at the backs of our heads, so to speak. Still plausible, or has new data come in to refine this calculation away from such a weird but neat conclusion? Depends on what you mean by “observable”. The true size of the Universe is larger than the distance to the source of the microwave background radiation, or we would have seen evidence of it in the patterns of that background (there are some groups who do claim to see such patterns, but their statistics are extremely shaky, and it’s almost certainly just a coincidence). The source of the microwave background radiation is as far back as we can, in practice, see using electromagnetic radiation, but one could in principle “look” deeper using some other means such as neutrinos or gravitational waves. One might then define the observable Universe to mean the ultimate limit of what we could even theoretically detect with any kind of radiation. By that definition, it still can’t be ruled out that the size of the entire Universe might be smaller than the observable Universe, but larger than the scale of the microwave background radiation. We could in principle test this, but we haven’t yet managed to successfully detect _any_ gravitational waves, and the sort of gravitational wave detector we would need for this task would be at least two generations beyond the ones that we don’t even have yet. ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [January 26, 2012, 12:36am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/44 "2012-01-26T00:36:22Z")
> [@Chronos](#): > > **Terr** , you’re wrong on this point. Any source that gives specific values for the size of the Universe before or after inflation, or at any other point, is either referring to the observable Universe and being sloppy in their terminology, or is deeply confused in some way. Give me a link that says otherwise. Is it your contention that at Planck era the universe was infinitely large and infinitely dense? ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 26, 2012, 12:53am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/45 "2012-01-26T00:53:46Z")
> [@Terr](#): > > Give me a link that says otherwise. Is it your contention that at Planck era the universe was infinitely large and infinitely dense? [Here’s one](http://www.astro.ucla.edu/~wright/infpoint.html) from an astronomer at UCLA. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 26, 2012, 1:01am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/46 "2012-01-26T01:01:12Z")
Do a ctrl-f on “did the universe expand from a point” on [this page](http://www.cfa.harvard.edu/seuforum/faq.htm) and you’ll see another relevant text. ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [January 26, 2012, 1:25am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/47 "2012-01-26T01:25:18Z")
> [@Frylock](#): > > Do a ctrl-f on “did the universe expand from a point” on [this page](http://www.cfa.harvard.edu/seuforum/faq.htm) and you’ll see another relevant text. Ok, I see. So - let’s try the assumption that the universe is bounded, but the curvature is so small that it cannot (yet?) be detected. If so, the universe (non-observable plus observable) is not infinite - did it then “expand from a point”? ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [January 26, 2012, 1:31am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/48 "2012-01-26T01:31:50Z")
> [@Frylock](#): > > [Here’s one](http://www.astro.ucla.edu/~wright/infpoint.html) from an astronomer at UCLA. I guess there is a reason why I prefer the ekpyrotic universe theory. Makes more sense. ---
**Author:** ![erislover](https://avatars.discourse-cdn.com/v4/letter/e/71e660/32.png) [@erislover](https://boards.straightdope.com/u/erislover)\ **Post date:** [January 26, 2012, 1:35am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/49 "2012-01-26T01:35:24Z")
Thanks, **Chronos**. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 26, 2012, 2:15am UTC](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324/50 "2012-01-26T02:15:50Z")
> [@](#): > > Give me a link that says otherwise. Is it your contention that at Planck era the universe was infinitely large and infinitely dense? Neither I nor any other reputable cosmologist makes any contention whatsoever about the Planck era. At best, all anyone has for that is guesses. [Previous page](https://boards.straightdope.com/t/cosmologists-come-on-in-universe-size-question/610324.md?page=2)