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

[NnnTech]

You appeared to be trying to expound on the Special Theory of Relativity, relating it to some diagram with circled x's. Einstein's 1905 paper does a much better job. Modern textbooks do better still.

However, we need the General Theory of Relativity from Einstein's 1915 paper to create a model compatible with modern cosmology. An expanding universe. The Big Bang.

This is well accepted textbook science.

Sorry I assumed you'd understand that the circles represented bodies that reflect of emit light , our visual reference frame that we require to work out any distances . The Xn being a defined vector into ''outer space'' , space that is beyond the furthest bodies we can presently observe . Isn't Xn correct then ? An unspecified length ?

 

[NnnTech]

I have doodled a better picture that you'll probably relate more too that is asking a question ?

 

[jbriggs444]

Sorry I assumed you'd understand that the circles represented bodies that reflect of emit light , our visual reference frame that we require to work out any distances . The Xn being a defined vector into ''outer space'' , space that is beyond the furthest bodies we can presently observe . Isn't Xn correct then ? A unspecified length ?

I struggle to understand what you are thinking.

So your two-dimensional drawing is for a section of sky that we are looking at. The X's are stars that we can see. The Xn is a direction where no stars are visible.

So this "Xn" is a direction from which no visible light is received. It is not a distance. It is an angle.

Yet if we point radio-telescopes in that direction, microwave radiation is received. Remarkably uniform microwave radiation from all directions. At a wavelength corresponding to a black body temperature of some 2.7 degrees Kelvin.

So we surmise that we are looking through space at something -- a surface of last scattering. We know how far away from us it is. Light from the surface of last scattering is about 13.8 billion years old. Converting that to a distance can be done in a number of ways (distance is not a simple concept in an expanding universe). It is just as well for us to leave it as an age rather than a distance.

 

[phinds]

I struggle to understand what you are thinking.

+1 on that

 

[NnnTech]

I struggle to understand what you are thinking.

So your two-dimensional drawing is for a section of sky that we are looking at. The X's are stars that we can see the the Xn is a direction where no stars are visible.

So this "Xn" is a direction from which no visible light is received. It is not a distance. It is an angle.

Yet if we point radio-telescopes in that direction, microwave radiation is received. Remarkably uniform microwave radiation from all directions. At a wavelength corresponding to a black body temperature of some 2.7 degrees Kelvin.

So we surmise that we are looking through space at something -- a surface of last scattering. We know how far away from us it is. Light from the surface of last scattering is about 13.8 billion years old. Converting that to a distance can be done in a number of ways (distance is not a simple concept in an expanding universe). It is just as well for us to leave it as an age rather than a distance.

Thank you for that very useful information ! Aren't angles relative to the observer ?

You now understand my question perfectly with the explanation you replied back .

There is nothing to visually observe by the human eye in this region of space because there is no spatial bodies emitting or reflecting light between 450nm-750nm , the visible spectrum ! Is that a correct statement ?

We can detect from these ''dark'' regions of space a microwave radiation that has a specific uniform wavelength that is relative too a black body temperature . I am not sure how distance can apply to such a detection to be honest , that seems a nonsense way and rather vivid imagination . If it is a constant or uniform as you say , how do you know it isn't just electromagnetic radiation we are detecting or a ''white noise'' ?

In my last doodle I supplied the reference , R^n which represents real coordinate space and is n-dimensional . Isn't it true that xyzt can always ''fit'' within a R^n reference frame ?

Isn't our visual universe based on visual matter rather than ''dark'' regions of space ?

Could it be possible these ''dark'' regions of space using vectors can be (X^n,Y^n,Z^n) ?

Does our visual universe exist within a R^n universe ?

 

[NnnTech]

+1 on that

I am thinking that the ''dark'' regions of space could be any distance and we don;t have real proof to think otherwise . I am also thinking about whether these ''dark'' regions are actually dark or not . Darkness is the absence of light so how can these ''dark'' regions be in darkness?

 

[PeroK]

I am thinking that the ''dark'' regions of space could be any distance and we don;t have real proof to think otherwise . I am also thinking about whether these ''dark'' regions are actually dark or not . Darkness is the absence of light so how can these ''dark'' regions be in darkness?

If you have your own personal definitions for things, then you will quite quickly lose touch with mainstream scientific ideas. This is the case here. You are not learning anything about modern cosmology now. Instead, you are simply playing about with words.

 

[NnnTech]

If you have your own personal definitions for things, then you will quite quickly lose touch with mainstream scientific ideas. This is the case here. You are not learning anything about modern cosmology now. Instead, you are simply playing about with words.

In leaning online it is important to be sure that you understand things correctly and ask questions of uncertainty . I am not making up my own definitions , where did you get such an idea ?

Most of my posts have been questions about light or related to light .

These ''dark'' regions of space between distant visual bodies are fascinating . I am assuming any bodies that may not be visible in these regions are too far away for us to observe , any light so red-shifted by the time it gets to us that we can't see them ?

 

[PeroK]

These ''dark'' regions of space between distant visual bodies are fascinating . I am assuming any bodies that may not be visible in these regions are too far away for us to observe , any light so red-shifted by the time it gets to us that we can't see them ?

It's more a question of time than distance. There are no dark regions, only regions without visible light. The CMB radiation is detected in all directions. Note that scientifically all EM radiation is light, not just radiation from the visible spectrum.

The CMB radiation was emitted about 13.8 billion years ago. That light is only reaching us now. Stars and galaxies have formed in those directions but the light has not had time to reach us yet.

 

[phinds]

I am not making up my own definitions , where did you get such an idea ?

Probably from most everything you have said but particuarly your most recent personal definition of "dark regions". I think to some extent the issue here might be that you are not as confused as you sound but you are expressing yourself poorly due to a lack of understanding of the fundamentals of cosmology.

 

[NnnTech]

Probably from most everything you have said but particuarly your most recent personal definition of "dark regions". I think to some extent the issue here might be that you are not as confused as you sound but you are expressing yourself poorly due to a lack of understanding of the fundamentals of cosmology.

Well I assumed seems as I have presented diagrams to my question and another poster explained back precisely what my reference was too, ''dark'' regions would be easy to understand . What do you call these ''dark'' regions of space between the distant stars ?

 

[PeroK]

Well I assumed seems as I have presented diagrams to my question and another poster explained back precisely what my reference was too, ''dark'' regions would be easy to understand . What do you call these ''dark'' regions of space between the distant stars ?

Intergalactic space. Or, nearer to home interstellar space.

But then, of course, the only way that distant light can reach us is by traveling through intergalactic and interstellar space. If there is another star or galaxy in the way then we see that instead.

That's why we have a 3D spatial model of the universe, not only a 2D model of what we observe from Earth.

 

[NnnTech]

Intergalactic space. Or, nearer to home interstellar space.

According to google that is the spaces between Galaxies which I did not know . Thanks for the information but does that also apply to the space between distant Galaxies ? I assume so !

My question , thread title , should of asked : Why does distant intergalactic space look ''dark'' to the observer while near by interstellar space looks ''transparent'' to the observer ?

Is that worded better ?

 

[PeroK]

Why does distant intergalactic space look ''dark'' to the observer while near by interstellar space looks ''transparent'' to the observer ?

There's no distinction. Light travels across space in all directions equally.

 

[NnnTech]

There's no distinction. Light travels across space in all directions equally.

Is there math for this travel and proportional divide ?

I know we have the speed of light c and I know we also use hf to represent photon energy .

 

[PeroK]

Is there math for this travel and proportional divide ?

At a basic level, space is assumed to be the same everywhere. This is called the cosmological principle. There is no evidence to the contrary. The laws of physics appear to be the same everywhere. Again, we have no good evidence of them changing from place to place.

 

[NnnTech]

At a basic level, space is assumed to be the same everywhere. This is called the cosmological principle. There is no evidence to the contrary. The laws of physics appear to be the same everywhere. Again, we have no good evidence of them changing from place to place.

What is space according to you ?

I find when speaking of space , that people consider space in a generalized manner rather than an independent vast expanse with unspecified dimensions . I have even heard space can curve although an independent space has no physical properties to curve .
Doesn't Einsteins space-time curvature actually relate to field curvature rather than an independent space ?

 

[PeroK]

What is space according to you ?

The universe has four dimensions of spacetime. If we use time as measured on Earth, then in simple terms the universe has three spatial dimensions. Technically, this spacetime is curved but that's another story.

Spacetime is the background on which physics takes place. It's such a fundamental notion that it may be hard to define.

You should be familiar with the concept of motion through space?

 

[NnnTech]

The universe has four dimensions of spacetime. If we use time as measured on Earth, then in simple terms the universe has three spatial dimensions. Technically, this spacetime is curved but that's another story.

Spacetime is the background on which physics takes place. It's such a fundamental notion that it may be hard to define.

You should be familiar with the concept of motion through space?

I am aware of space-time and Newtons laws of motion , I am also aware of the electrodynamics of moving bodies . I am also aware the Big Bang theory has no prequel information and is a shortfall in information .
It bewilders me when people say no space existed before the Big Bang , I don't even think the theory suggests that . The Big bang theory starts with the suggestion that the Universe started from a ''hot dense state'' , the Big Bang theory neither suggests that the expansion is not into more space . I feel that is meant to be assumed by the reader , knowing expansion , requires expansion space .
The expansion of the visual universe we observe is based on red-shift and visual bodies ? Not the Intergalactic space ?

 

[jbriggs444]

There is nothing to visually observe by the human eye in this region of space because there is no spatial bodies emitting or reflecting light between 450nm-750nm , the visible spectrum ! Is that a correct statement ?

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

Edit: I should correct myself here. The CMB is generated as visible light, but is red-shifted into microwave radiation.

We can detect from these ''dark'' regions of space a microwave radiation that has a specific uniform wavelength that is relative too a black body temperature . I am not sure how distance can apply to such a detection to be honest , that seems a nonsense way and rather vivid imagination . If it is a constant or uniform as you say , how do you know it isn't just electromagnetic radiation we are detecting or a ''white noise'' ?

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.

In my last doodle I supplied the reference , R^n which represents real coordinate space and is n-dimensional . Isn't it true that xyzt can always ''fit'' within a R^n reference frame ?

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.

Isn't our visual universe based on visual matter rather than ''dark'' regions of space ?

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.

Could it be possible these ''dark'' regions of space using vectors can be (X^n,Y^n,Z^n) ?

Does our visual universe exist within a R^n universe ?

Now you are firmly into the grounds of unfounded speculation.

 

[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.