<p>It sounds like your question is about the single most important principle of cosmology, called the cosmological principle.  This asserts that as long as all our observations are consistent with the idea that the universe is the same everywhere at a given age, we will continue to use a model with that attribute.  There are lots of good reasons for adopting that principle, the least of which is not that it allows us to have a model in the first place.  So what this means is, our answer to what is beyond what we can see is that we don't know, but we are going to model it in a way that makes sense to us, so we will use the cosmological principle.   You have to be able to distinguish what we know in the sense of having direct information about, versus what we know about our own best models.</p>

CC BY-SA 3.0
2016-09-24T04:10:31.827Z
I think I understand what you're saying; That since we don't know and can't observe that we would have to base any assumptions we make on what we have observed? Does that sound about right?
CS2016
CC BY-SA 3.0
2016-09-24T04:15:33.930Z
I would say we often extend our models beyond what we can actually observe, but this is because we want to keep our models as simple as possible.  We have to know the difference between what we have tested, and what we haven't, but we can still use the simplest picture that works.  So it is with the cosmological principle.
Ken G
CC BY-SA 3.0
2016-09-23T16:20:19.357Z
2016-09-23T16:20:19.357Z
Ken G
<p>Forgive any kind of "dumb" question I may ask as this is a new interest of mine and I know it's purely hypothetical. </p>

<p>If one were able to surpass light speed and the expansion of space to go beyond the particle horizon, what could be out there? Could it just be an empty void? Could it loop around to the other side of the particle horizon? I'd love to read about any kind of theories or research done on this subject.</p>

CC BY-SA 3.0
2016-09-23T05:06:36.053Z
While there's no way of knowing for 100% sure, what's probably beyond the particle horizon is more of the same stuff, galaxies, dark matter, stars, planets, photons, neutrinos, hydrogen, helium coalescing etc.   Your question is basically about the shape and/or edge of the universe.  Both have been asked before.     http://physics.stackexchange.com/questions/2916/shape-of-the-universe and http://physics.stackexchange.com/questions/51213/how-would-it-be-to-look-at-the-sky-if-the-earth-were-near-the-edge-of-the-univer
userLTK
<astrophysics><big-bang-theory><horizon><particles>
What could be past the particle horizon?
CS2016
# What could be past the particle horizon?

(Asked by: username_0 on 2016-09-23)

Forgive any kind of "dumb" question I may ask as this is a new interest of mine and I know it's purely hypothetical.

If one were able to surpass light speed and the expansion of space to go beyond the particle horizon, what could be out there? Could it just be an empty void? Could it loop around to the other side of the particle horizon? I'd love to read about any kind of theories or research done on this subject.

**Tags:** astrophysics, big-bang-theory, horizon, particles

> **Comments:**
> **username_1**: While there's no way of knowing for 100% sure, what's probably beyond the particle horizon is more of the same stuff, galaxies, dark matter, stars, planets, photons, neutrinos, hydrogen, helium coalescing etc.   Your question is basically about the shape and/or edge of the universe.  Both have been asked before.     http://physics.stackexchange.com/questions/2916/shape-of-the-universe and http://physics.stackexchange.com/questions/51213/how-would-it-be-to-look-at-the-sky-if-the-earth-were-near-the-edge-of-the-univer  

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## 1 answers

### Answer by username_2 on 2016-09-23. Score: 1 | Accepted answer

It sounds like your question is about the single most important principle of cosmology, called the cosmological principle. This asserts that as long as all our observations are consistent with the idea that the universe is the same everywhere at a given age, we will continue to use a model with that attribute. There are lots of good reasons for adopting that principle, the least of which is not that it allows us to have a model in the first place. So what this means is, our answer to what is beyond what we can see is that we don't know, but we are going to model it in a way that makes sense to us, so we will use the cosmological principle. You have to be able to distinguish what we know in the sense of having direct information about, versus what we know about our own best models.

> **Comments:**
> **username_0**: I think I understand what you're saying; That since we don't know and can't observe that we would have to base any assumptions we make on what we have observed? Does that sound about right?  
> **username_2**: I would say we often extend our models beyond what we can actually observe, but this is because we want to keep our models as simple as possible.  We have to know the difference between what we have tested, and what we haven't, but we can still use the simplest picture that works.  So it is with the cosmological principle.  

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