# So why don’t we know what is beyond our observable universe?... **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2017, 2:43am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739 "2017-11-16T02:43:35Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [November 17, 2017, 7:36pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/21 "2017-11-17T19:36:06Z")
> [@Leo\_Bloom](#): > > Sucks to be space. > > Why does time get a pass in your definition? I have no idea what you’re trying to ask here, or why you say ‘sucks to be space’. ---
**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:** [November 17, 2017, 8:42pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/22 "2017-11-17T20:42:45Z")
I _think_ that what **Leo Bloom** is asking is, why is it possible to have a privileged point in time, when it’s not possible to have a privileged point in space? And the best answer we have to that is just that that’s the way we observe the Universe to be. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [November 18, 2017, 12:12am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/23 "2017-11-18T00:12:24Z")
> [@Exapno\_Mapcase](#): > > If something happens right… NOW a million light years away, it can’t affect us for a million years. Is there a meaningful “right NOW” a dozen Zm away? The shape of spacetime over there is different enough from the shape of spacetime right here. Even on a Gm scale, “now” starts to become a bit hazy. I mean, what were you doing at the precise moment that I was writing/editing this sentence? I do not believe that this very instant can be adequately resolved anywhere but in this exact spot, because neither space nor time are flat enough to allow for that. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 18, 2017, 12:25am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/24 "2017-11-18T00:25:26Z")
> [@Chronos](#): > > I _think_ that what **Leo Bloom** is asking is, why is it possible to have a privileged point in time, when it’s not possible to have a privileged point in space? … Yup. As usual, **Chronos** nails it. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [November 18, 2017, 1:57am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/25 "2017-11-18T01:57:48Z")
> [@eschereal](#): > > Is there a meaningful “right NOW” a dozen Zm away? The shape of spacetime over there is different enough from the shape of spacetime right here. Even on a Gm scale, “now” starts to become a bit hazy. I mean, what were you doing at the precise moment that I was writing/editing this sentence? I do not believe that this very instant can be adequately resolved anywhere but in this exact spot, because neither space nor time are flat enough to allow for that. From a theoretical point of view what constitutes “now” in the Universe can be defined by using a certain set of symmetries of cosmological spacetime. Of course unless there is a clear physical manifestation of this we could still see the idea of a Universal concept of “now” as physically dubious, but there is in that the Universe “now” and “here” looks similar to the Universe “now” and “elsewhere”, for example the temperature of the CMBR would be the same. I still think though you make a good point as “now” is only defined by the gross properties of the Universe, so a giving the Universe a fine scale of time over cosmological distances probably doesn’t have a sound theoretical or physical basis. Or in other words talking about the "matter-dominated era"over a spatial scale that covers cosmological distance makes sense, but talking about the day “5th January 1990” over the same distance probably doesn’t make much sense. ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [November 18, 2017, 11:50am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/26 "2017-11-18T11:50:54Z")
> [@sbunny8](#): > > It’s not clear what’s meant by saying that A is “three times colder” than B. It would be much more clear to say B has three times as much heat as A. This could be measured on any scale where zero is absolute zero, the point at which there is no heat at all. The coldest recorded place on Earth (natural weather only) is −89.2 °C , or −128.6 °F, or 184.0 Kelvin. One third of 184.0 K would be about 61.3 K, which is -349.3 degrees F. It is fair to say that 184 K is three times as hot as 61.3 K, hence 61.3 K could be said to be three times as cold as 184 K. That makes perfect sense. So was that quote referring to -300 Celsius or Fahrenheit? He should have just used Kelvin. ---
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [November 18, 2017, 2:47pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/27 "2017-11-18T14:47:40Z")
> [@Leo\_Bloom](#): > > Yup. As usual, **Chronos** nails it. Your question still doesn’t make sense; I still have no idea what “time gets a pass” is supposed to mean. If I talk about “Christmas”, and say that it’s a time but not a place, does that mean time gets a pass in that definition too? And does that also suck for space? If you’re asking what Chronos nailed then yes the Big Bang describes a point in time but not a point in space because that’s what it’s defined as; it’s a name for a phenomenon that took place at a particular time across all of space (or at least all observable space). But I don’t see how that sucks for space, especially since if you want to be pedantic it actually massively explosively explodes on an almost incomprehensible scale for space 🙂 ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [November 18, 2017, 3:30pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/28 "2017-11-18T15:30:31Z")
In theoretical parlance cosmological spacetime has the maximal set of spacelike symmetries of spatial translational and spatial rotational symmetry, however cosmological spacetime lacks timelike symmetry and it is clear that no cosmology could have the maximal set of spacetime symmetries as such spacetimes lack any matter (the only form of energy they can have is a cosmological constant). It is an interesting question as to why we should have spatial, but not temporal symmetry, but no-one really knows the answer (though plenty has been written about it). ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [November 18, 2017, 6:25pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/29 "2017-11-18T18:25:11Z")
I am not so sure that time is in fact different from space. Right now, you are moving through space. Rather quickly. Can you find a vector of zero motion? Everything is relative. If you go out to the emptiest region of space that you can find, you will observe distant galaxies that are in constant motion, and their gravity will minutely affect you, changing the literal shape of spacetime, ever so slightly, where you are, so, even if you could “stop dead”, spacetime itself would be moving around you. Zero velocity has zero meaning. ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [November 18, 2017, 8:49pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/30 "2017-11-18T20:49:04Z")
> [@eschereal](#): > > I am not so sure that time is in fact different from space. That’s what puzzles me in some of the replies above which differentiate time and space. I thought that the consensus since Einstein was that there was only spacetime which makes it hard to understand how we can talk of a point in time and a point in space, the one being privileged the other not. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [November 19, 2017, 12:36am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/31 "2017-11-19T00:36:48Z")
Time is weird… Some of the Einsteinian equations are of the form x^2 + y^2 + z^2 - t^2. Time gets a negative coefficient, while the spatial dimensions get a positive one. But, then, heck, everyday experience shows us that time feels a lot different than space. By the “cosmological principle,” every place in the universe is pretty much like every other place. No privilege. But the universe’s past looked very different from now, and the future will look very different yet. Very privileged. Since I’m sitting perfectly still right now…I’m moving at the speed of light…through time! See yer later! ---
**Author:** ![PlaceboTarget](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/placebotarget/32/1073_2.png) [@PlaceboTarget](https://boards.straightdope.com/u/PlaceboTarget)\ **Post date:** [November 19, 2017, 2:23pm UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/32 "2017-11-19T14:23:19Z")
> [@Asympotically\_fat](#): > > It is an interesting question as to why we should have spatial, but not temporal symmetry, but no-one really knows the answer (though plenty has been written about it). With the risk of annoying my detractors, I will defy danger and hypothesize that the nature of time causes symmetry to be quite problematic when discussing time. It may be that in nature symmetry manifests in objects (while they’re in a state where they preserve their shape and size) rather than in phenomena. Phenomena stem from the universe being a constant process. The existence of this gargantuan system can be defined as the constant transformation of energy from one form into another. In this context, time should be considered the pace at which this change takes place. While time is essential in the description of the universe, it is a parameter of a different nature from spatial extent. If the universe can be treated as an isolated system and the second law of thermodynamics can be applied to its entirety then the universe’s entropy will always increase, which leads to the conclusion that time is asymmetrical by definition. This is the perspective of a layman, It should be simplistic but not erroneous. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [November 20, 2017, 2:03am UTC](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739/33 "2017-11-20T02:03:13Z")
> [@Wesley\_Clark](#): > > As far as seeing beyond our universe, you’d have to conduct experiments that proved the existence of something beyond our universe. To my knowledge this hasn’t been done yet. In part because most everything in our universe is confined to our universe. Some things like gravity can supposedly escape our universe, which could be used to experimentally verify them. I have no idea what studies have been done on it though. Anything beyond our universe is unknowable (as far as I have ever read but I am not a scientist). But the question is about the _observable_ universe, and there is more of our universe outside the observable threshold that we can probably speculate reasonably about. [Previous page](https://boards.straightdope.com/t/so-why-don-t-we-know-what-is-beyond-our-observable-universe/801739.md?page=1)