Why does it look dark between the distance stars at night?

[NnnTech]

There are no objects emitting or reflecting visible light along that line of sight, yes.

We have a model of the universe. That model fits what we can see, fits with the behavior of stuff that we can experiment on in a lab and fits with the general theory of relativity.

Of course it is electromagnetic radiation. And of course, it is white noise. Both are other names for black body radiation.

There are some embedding theorems for curved multi-dimensional spaces. However, I do not believe that it is possible to embed a pseudo-Riemannian space into a Euclidean space.

Also, the number of dimensions required can get rather absurd.

I do not know what you mean by this. The universe is what it is. We try to deduce what it is based on what we can see.

Now you are firmly into the grounds of unfounded speculation.

Thank you for some more great information .

How is asking a question speculating ? Isn't any question to be founded in discussion if there is an uncertainty of the answer ?

How can we be certain of d/t (distance over time) if we were traveling into distant intergalactic space ?

A vector needs at least two points of reference doesn't it A and B ?

My understanding from my education is that something that can be any dimension is represented with n for n-dimensional ?

Please correct me if I am incorrect on that !

 

[jbriggs444]

How is asking a question speculating ?

"Could it be <insert random thing here>" is practically the definition of speculation.

How can we be certain of d/t (distance over time) if we were traveling into distant intergalactic space ?

I do not know what you mean by distance over time here. Or why you think that it is relevant.

A vector needs at least two points of reference doesn't it A and B ?

Not really. A vector is simply an element in a vector space. One can have an element of a vector space without needing to have two points in some other space.

If you were talking about a metric space then it would be helpful to have two points to measure the interval between, yes. But a metric space and a vector space are two different things.

My understanding from my education is that something that can be any dimension is represented with n for n-dimensional ?

You should probably take a course in linear algebra before speculating about some sort of vector space which is both n-dimensional and m-dimensional for n different from m.

But honestly, I do not even know what you are trying to say.

 

[NnnTech]

"Could it be <insert random thing here>" is practically the definition of speculation.

I do not know what you mean by distance over time here. Or why you think that it is relevant.

Not really. A vector is simply an element in a vector space. One can have an element of a vector space without needing to have two points in some other space.

If you were talking about a metric space then it would be helpful to have two points to measure the interval between, yes. But a metric space and a vector space are two different things.

You should probably take a course in linear algebra before speculating about some sort of vector space which is both n-dimensional and m-dimensional for n different from m.

But honestly, I do not even know what you are trying to say.

I'm not allowed to say any personal opinion or I could tell you what my opinion is . I did , was going to write a paper on this forum but let's just say it wasn't published and I got points for speculation in a new theory , new being the word there .

 

[NnnTech]

You should probably take a course in linear algebra before speculating about some sort of vector space which is both n-dimensional and m-dimensional for n different from m.

But honestly, I do not even know what you are trying to say.

OK , I have just quickly looked up some linear algebra and returned with my measurement (x1,x2,...xn) for all var (x) ?

(x1,x2,...xn)=(y1,y2,...yn) ?

Scalar ?

I believe this is applicable to distance , intergalactic space and moving bodies ?

I also believe from Einsteins simultaneity , this is relative to the observer ?

Any plotted x-axis to a moving body having relative affect on distance and angles ?

''Scalars as vector components[edit]​

According to a fundamental theorem of linear algebra, every vector space has a basis. It follows that every vector space over a field K is isomorphic to the corresponding coordinate vector space where each coordinates consists of elements of K (E.g., coordinates (a1, a2, ..., an) where ai ∈ K and n is the dimension of the vector space in consideration.). For example, every real vector space of dimension n is isomorphic to the n-dimensional real space
''

Would reversed mapping be : (x1,x2,...xn,...x2,x1) ?

 

[jbriggs444]

OK , I have just quickly looked up some linear algebra and returned with my measurement (x1,x2,...xn) for all var (x) ?

(x1,x2,...xn)=(y1,y2,...yn) ?

What? I have no idea what you are trying to say here.

I believe this is applicable to distance , intergalactic space and moving bodies ?

I have no idea why you think this is applicable.

I also believe from Einsteins simultaneity , this is relative to the observer ?

Your prior remarks above did not mention a time coordinate or the possibility of multiple frames of reference. So why a concern about simultaneity now?

Any plotted x-axis to a moving body having relative affect on distance and angles ?

You are worrying about abberation?

''Scalars as vector components[edit]​

According to a fundamental theorem of linear algebra, every vector space has a basis. It follows that every vector space over a field K is isomorphic to the corresponding coordinate vector space where each coordinates consists of elements of K (E.g., coordinates (a1, a2, ..., an) where ai ∈ K and n is the dimension of the vector space in consideration.). For example, every real vector space of dimension n is isomorphic to the n-dimensional real space
''

Would reversed mapping be : (x1,x2,...xn,...x2,x1) ?

You can map from a vector to a coordinate tuple. Or from a coordinate tuple to a vector. But so what?

But no, reversing the ordering of the coordinates is not reversing the mapping.

 

[david2]

I read the universe is not filled with light because it had a beginning. Do not understand it so do not ask any further. lol

 

[NnnTech]

What? I have no idea what you are trying to say here.

I have no idea why you think this is applicable.

Your prior remarks above did not mention a time coordinate or the possibility of multiple frames of reference. So why a concern about simultaneity now?

You are worrying about abberation?

You can map from a vector to a coordinate tuple. Or from a coordinate tuple to a vector. But so what?

But no, reversing the ordering of the coordinates is not reversing the mapping.

I guess I do need some serious practice at Algebra , I thought xyz was a coordinate reference ? Beginning with (x0,y0,z0,) ?

 

[jbriggs444]

I guess I do need some serious practice at Algebra , I thought xyz was a coordinate reference ? Beginning with (x0,y0,z0,) ?

Unless you provide details, x, y and z are variables with no assigned meaning.
Just like x0, y0 and z0 are variables with no assigned meaning.

Just writing down (x,y,z) does not mean anything. It is a hint that you are working within a three dimensional vector space, but nothing else. You might also use the same notation to denote a set with three unidentified elements. You really need to put some explanation around your notations.

 

[NnnTech]

Unless you provide details, x, y and z are variables with no assigned meaning.
Just like x0, y0 and z0 are variables with no assigned meaning.

Just writing down (x,y,z) does not mean anything. It is a hint that you are working within a three dimensional vector space, but nothing else. You might also use the same notation to denote a set with three unidentified elements. You really need to put some explanation around your notations.

Sorry ,we are talking about vector spaces and scalar measures so I again made assumptions you'd understand .
From any observers spatial position , relative to them their coordinates are (x0,y0,z0,) . If the observer plotted a vector they were going to travel and ''aimed'' for distant intergalactic space , the distance and path they would travel would be (x1,x2,...,n,) choosing the plotted x linear vector ?

 

[PeterDonis]

I'm not allowed to say any personal opinion or I could tell you what my opinion is . I did , was going to write a paper on this forum but let's just say it wasn't published and I got points for speculation

And it's still speculation, so it's good that you're not stating it here; but evidently it's still there in your thinking, because of this remark of yours way back in post #4 of the thread:

I think it is an optical illusion and not actually dark at all .

The visible darkness in directions other than those in which we see stars is not an optical illusion: it is a simple consequence of the fact that no radiation in the range visible to our eyes is coming from those directions.

However, as @jbriggs444 pointed out way back in post #5 of this thread, there is other radiation besides visible radiation, and there is such radiation coming from every direction (if nothing else, the CMBR comes from every direction--we know because we have detected it). But that radiation, aside from not being in the visible range (which is why we can't see it with our eyes), also has negligible energy density, which means that the sky being "dark" in those directions, in the sense of "cold"--not delivering any significant energy to us--is also not an optical illusion (@jbriggs444 said in post #5 that it could be interpreted as an optical illusion in a "strained sense", but I prefer to just be straightforward and say it isn't; there is a simple explanation for what we see and don't see that doesn't require any optical illusions at all).

So the basically correct answer to your question was given way back in post #5, and since then the thread has gone all over the place without adding anything substantive to that. Enough is enough. Thread closed.