Where are we

[36grit]

Where are we in the universe? Are we in the middle of the cosmic microwave background?

[AbstractDreamer]

From what I've learnt so far.

 

Since the period of inflation about 13 billion years ago, location is not absolute, as the cosmos is assumed to be homogeneous. Instead position is relative.

 

So to ask "Where are we?" is an incomplete question. More meaningful would be to ask where are we in relation to something else. Then someone can give you spatial coordinates in reference to that something else.

 

But without any frame of reference, the best answer I guess would be "Anywhere" or "Nowhere in particular"

[StringJunky]

You are the at the centre of the observable unverse.

[36grit]

From what I've learnt so far.

 

Since the period of inflation about 13 billion years ago, location is not absolute, as the cosmos is assumed to be homogeneous. Instead position is relative.

 

So to ask "Where are we?" is an incomplete question. More meaningful would be to ask where are we in relation to something else. Then someone can give you spatial coordinates in reference to that something else.

 

But without any frame of reference, the best answer I guess would be "Anywhere" or "Nowhere in particular"

The question was relative to the cosmic radiation background. I am assuming that we are at the center of it.

You are the at the centre of the observable unverse.

And the alien 4 billion light years away is also at the center of the cosmic radiation background? along with everything ever created?

[Klaynos]

I don't think that centre of the CMB is meaningful.

[Strange]

The question was relative to the cosmic radiation background. I am assuming that we are at the center of it.

And the alien 4 billion light years away is also at the center of the cosmic radiation background? along with everything ever created?

 

 

The CMB radiation is homogeneous and isotropic (apart from minute variations). So everyone, everywhere will see it the same in all directions (if that is what being "at the centre of it" means).

 

A really good analogy to understand why is the "surface of last screaming": https://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_2.html

[geordief]

You are the at the centre of the observable unverse.

A bit cheeky?

 

Or are we all at the end points of a network centred on a server(s) running the OSF?

 

..unless we are offline.

Edited December 3, 2016 by geordief

[StringJunky]

A bit cheeky?

 

Or are we all at the end points of a network centred on a server(s) running the OSF?

 

..unless we are offline.

No, because its true; the observable universe is observer-dependent. It is a sphere around the observer. For someone standing on a planet in Andromeda galaxy, his centre will be 2.5m LYRS from yours and will extend that distance from you and vice versa.

[geordief]

No, because its true; the observable universe is observer-dependent. It is a sphere around the observer. For someone standing on a planet in Andromeda galaxy, his centre will be 2.5m LYRS from yours and will extend that distance from you and vice versa.

If the (observable?) universe as a whole has positive curvature would your sphere also exhibit curvature features? Would its radius (admittedly unmeasurably?) fail to fulfill the Euclidean ratio between its radius and its surface area?

Edited December 3, 2016 by geordief

[36grit]

So, the Leo constellation probably looks a little different to an alien four billion light years away, if I am understanding this correctly.

[Mordred]

yes very different

[imatfaal]

!

Moderator Note

 

Purely speculative post by 36grit hidden

 

Do not post this sort of guesswork in the main fora. Open a thread in Speculations if you must - but be prepared to abide by the rules of that subforum.

 

Do not respond to this moderation within the thread

 

[36grit]

Where are we? What determines position? Could one say, that every movement is a repositioning of the center of the universe? Can we predict what the universe would look like a couple billion light years away?

[swansont]

Where are we? What determines position? Could one say, that every movement is a repositioning of the center of the universe? Can we predict what the universe would look like a couple billion light years away?

 

 

There is no center. It's nonsensical to talk of a repositioning of it.

[Phi for All]

Could one say, that every movement is a repositioning of the center of the universe? Can we predict what the universe would look like a couple billion light years away?

 

Since there is no center, since we can't show that with any conviction, why do you insist on there being one?

 

Since we can't observe anything beyond the observable, we have no firm ground on which to speculate. We can only say it's most likely about the same as we observe, but that's probably not good enough for whatever it is you want to predict.

[StringJunky]

Since there is no center, since we can't show that with any conviction, why do you insist on there being one?

 

Since we can't observe anything beyond the observable, we have no firm ground on which to speculate. We can only say it's most likely about the same as we observe, but that's probably not good enough for whatever it is you want to predict.

Strictly speaking, you can't get beyond the OU, no matter how far you travel; it's a carrot-and-stick job.

[geordief]

Strictly speaking, you can't get beyond the OU, no matter how far you travel; it's a carrot-and-stick job.

Can we infer (not just guess or extrapolate) what conditions are like beyond what we can directly observe?

 

Are there observations we can make that lead us to make assessments about that which we cannot observe?

 

Can this be made circular so that we could make predictions about what we can observe based on those inferences?

 

EDIT: "carrot and stick" ? You don't mean "catch 22" ,do you?

Edited December 5, 2016 by geordief

[Mordred]

Can we infer (not just guess or extrapolate) what conditions are like beyond what we can directly observe?

Good question. The answer surprisingly is yes to a certain extent. To understand that you can examine expansion itself. If the region immediately outside or observable portion had a different mass distribution. Ie one greater or less mass average per volume. This would influence our observable portion by causing a preferred direction to expansion.

 

Ie you would have an effective pressure gradient. So if the pressure outside our OU. Is less than our OU expansion will be anistropic. Same if the pressure is greater it would essentially compress our OU.

 

As we do not see any anistropy in expansion we can safely assume it has the same mass distribution as our observable portion.

 

Lol you have no idea just how many altetnative models get overthrown by not being able to maintain the cosmological principle.

 

However there is a limit to how far we can apply this. For example if your far enough away from our OU that there can never be any possible causal connection. You can have a completely different dynamic that will never influence our OU.

Edited December 5, 2016 by Mordred

[Airbrush]

IF the universe is finite in size, then (1) we have an exact location, and (2) there is an exact center of gravity, (or center of the universe) within that finite volume, defined by x,y,z coordinates. The center of the universe would have coordinates (0,0,0).

Edited December 5, 2016 by Airbrush

[StringJunky]

EDIT: "carrot and stick" ? You don't mean "catch 22" ,do you?

No. The carrot on the end of the stick will always be the same distance from you.

[geordief]

No. The carrot on the end of the stick will always be the same distance from you.

That is new to me. You do know that is not how the expression is normally used over this side of the water?

IF the universe is finite in size, then (1) we have an exact location, and (2) there is an exact center of gravity, (or center of the universe) within that finite volume, defined by x,y,z coordinates. The center of the universe would have coordinates (0,0,0).

That also occurred to me. Is this "centre of the universe is everywhere" idea predicated on the universe being infinite?

Edited December 5, 2016 by geordief

[Delta1212]

That is new to me. You do know that is not how the expression is normally used over this side of the water?

 

That also occurred to me. Is this "centre of the universe is everywhere" is idea predicated on the universe being infinite?

Either infinite or finite but unbounded.

 

A finite and bounded universe would have a definite center.

[Phi for All]

That is new to me. You do know that is not how the expression is normally used over this side of the water?

 

Two different carrots and two different sticks. You're thinking of the set that involves either beating the donkey to get him to move, or enticing him with a carrot. Carrot OR the stick.

 

The other set involves tying the carrot to the end of the stick, and holding it in front of the donkey, so he moves forward to get the carrot, but it always stays the same distance away from him. Carrot AND the stick.

[StringJunky]

That is new to me. You do know that is not how the expression is normally used over this side of the water?

I should have said: dangling a carrot on a stick.

 

 

Edit: Phi knows what I meant. This one's without the donkey.

 

 

That also occurred to me. Is this "centre of the universe is everywhere" is idea predicated on the universe being infinite?

Wherever you are, the universe looks the same all around you at a big enough scale.

Edited December 5, 2016 by StringJunky

[Phi for All]

No. The carrot on the end of the stick will always be the same distance from you.

 

So our ability to see that far isn't bounded by our technology; it's bounded by the light's ability to reach us from that far away, correct? New technology isn't going to make the pole longer.