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

[NnnTech]

Homework Statement

The nature of light!

Relevant Equations

Xn

Hello , I have to do some ''homework'' on the nature of light ! I have to write everything I can think of !

When I look in the night sky , between the distant stars it looks observably dark when there is electromagnetic radiation filling that space .

Why does it look dark ?

 

[PeroK]

Homework Statement:: The nature of light!
Relevant Equations:: Xn

Hello , I have to do some ''homework'' on the nature of light ! I have to write everything I can think of !

When I look in the night sky , between the distant stars it looks observably dark when there is electromagnetic radiation filling that space .

Why does it look dark ?

What does it take for something not to "look" dark?

 

[phinds]

Google Olber's Paradox

​

 

[NnnTech]

Google Olber's Paradox

Thank you , I don't see any paradox though but don't want to speculative in fear of warnings . I thought , my opinion , is that it is because there is nothing to see within visual range between these body . I thought the space was transparent . I think it is an optical illusion and not actually dark at all . Additionally in vector terms I thought it was Xn , an unspecified distance ? Have I solved Olber's paradox ?

 

[jbriggs444]

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

This is definitely putting your toes over the line entitled "speculation starts here".

The baseline illumination you get from the gaps between the stars is pretty much the same as what you get emitted from a lump of black soot at about 2.725 degrees kelvin. It's called the Cosmic Microwave Background Radiation.

In a [rather strained] sense, it is an "optical illusion" and is "not actually dark at all". The Cosmic Microwave Background Radiation was emitted by an incandescent plasma and was very bright. We see it as dark because the expansion of the universe has reduced both its intensity and its frequency. The measured effect is real, not an illusion.

 

[NnnTech]

What does it take for something not to "look" dark?

Eye sight ?

 

[phinds]

I thought , my opinion , is that it is because there is nothing to see within visual range between these body

Yes, that is the short answer to @PeroK 's question but the issue is WHY is there nothing in the visual range? In other words, your answer is "it's dark because it's dark".

 

[NnnTech]

This is definitely putting your toes over the line entitled "speculation starts here".

The baseline illumination you get from the gaps between the stars is pretty much the same as what you get emitted from a lump of black soot at about 2.725 degrees kelvin. It's called the Cosmic Microwave Background Radiation.

How are you suppose to answer replies if you can't add opinion based on facts ? Between the distant stars there is electromagnetic radiation ? For something to look in ''darkness' when there is lots of light must be an optical illusion unless you know a better answer ?

 

[PeroK]

Eye sight ?

Okay. What does it take for your eyes to see something?

 

[NnnTech]

Okay. What does it take for your eyes to see something?

Arr yes , that's an easy one , the information has to enter your eyes via light wave function ?

 

[NnnTech]

Yes, that is the short answer to @PeroK 's question but the issue is WHY is there nothing in the visual range? In other words, your answer is "it's dark because it's dark".

It isn't dark though because that would sort of mean opaque from eye to the ''edge of the visual universe'' wouldn't it ?

There is nothing to see in these spaces because our telescopes can only see so far ?

 

[jbriggs444]

How are you suppose to answer replies if you can't add opinion based on facts ? Between the distant stars there is electromagnetic radiation ? For something to look in ''darkness' when there is lots of light must be an optical illusion unless you know a better answer ?

The light was denser and higher frequency when the universe was young. It is sparser and lower frequency now. Google CMBR.

It is not an optical illusion. It is real. Space-time curvature messes with intuitions about how things must remain the same. Keep your eyes out for Noether's theorem.

 

[PeroK]

Arr yes , that's an easy one , the information has to enter your eyes via light wave function ?

So it's not a question of whether space contains EM radiation, it's a question of whether any of it is coming in your direction.

PS Olbers paradox is something else.

 

[NnnTech]

The light was denser and higher frequency when the universe was young. It is sparser and lower frequency now. Google CMBR.

It is not an optical illusion. It is real. Space-time curvature messes with intuitions about how things must remain the same.

Cosmic microwave background radiation , yes that is detectable light from the early universe . So you are saying that between the distant bodies it is really dark ? The space itself is dark ?

 

[NnnTech]

So it's not a question of whether space contains EM radiation, it's a question of whether any of it is coming in your direction.

PS Olbers paradox is something else.

I see what you are saying but even without us to observe the universe , the sun would still be a bright ball , orange looking in the sky ?

 

[jbriggs444]

Cosmic microwave background radiation , yes that is detectable light from the early universe . So you are saying that between the distant bodies it is really dark ? The space itself is dark ?

Yes. Space is both dark and transparent. You can see through it all the way to the incandescent plasma that is the CMBR. But you see it hideously red-shifted so that it is dark now even though it was bright then.

When I say that "space is dark", I mean that the space around us is not carrying much light. What you see is what is there. It is not brightly illuminated except in the neighborhood of stars.

 

[NnnTech]

Yes. Space is both dark and transparent. You can see through it all the way to the incandescent plasma that is the CMBR. But you see it hideously red-shifted so that it is dark now even though it was bright then.

How can it be red-shifted light when the distant stars are local relatively to that distant ?

Are you saying if an Earth like body was traveling -ve towards the Earth and came within visual range where the distant stars were positioned , we wouldn't see that body ?

 

[PeroK]

I see what you are saying but even without us to observe the universe , the sun would still be a bright ball , orange looking in the sky ?

That's not the point. You can't see light unless it enters your eyes. When you see a searchlight shining up into the sky, what you are seeing is some of the light being scattered off particles in the air. If A searchlight was shining up through a vacuum you would see nothing.

The solar system is permanently flooded with light from the Sun, but we don't see it at night except where it reflects off the moon or the planets.

 

[jbriggs444]

How can it be red-shifted light when the distant stars are local relatively to that distant ?

Are you saying if an Earth like body was traveling -ve towards the Earth and came within visual range where the distant stars were positioned , we wouldn't see that body ?

Cosmological red shift due to the expansion of the universe.

 

[NnnTech]

Cosmological red shift due to the expansion of the universe.

That is +ve not -ve ! My question asked about -ve , which would blueshift wouldn't it ?

 

[jbriggs444]

That is +ve not -ve ! My question asked about -ve , which would blueshift wouldn't it ?

The surface of last scattering is red-shifted. That's a cosmological red shift.

I do not know why you are babbling about an incoming planet with a kinematic blue shift.

 

[NnnTech]

The surface of last scattering is red-shifted.

I do not know why you are babbling about an incoming planet with a kinematic blue shift.

Between the distant stars is Xn ? An unspecified distance ?

 

[jbriggs444]

Between the distant stars is Xn ? An unspecified distance ?

The surface of last scattering is not composed of stars. It is composed of incandescent and, accordingly, opaque plasma. No stars. Galaxy formation had not yet begun. We are talking about a time about 380,000 years after the big bang.

 

[NnnTech]

The surface of last scattering is not composed of stars. It is composed of incandescent and, accordingly, opaque plasma. No stars. Galaxy formation had not yet begun.

Einsteins space-time xyzt is based on visual matter . I have drawn up a quick doodle of my question for clarity .

 

[jbriggs444]

Einsteins space-time xyzt is based on visual matter.

No. It is not.

 

[NnnTech]

No. It is not.

I am impressed if you can measure distance with only one point of reference ! Can you explain how to measure A to ?

 

[NnnTech]

That's not the point. You can't see light unless it enters your eyes. When you see a searchlight shining up into the sky, what you are seeing is some of the light being scattered off particles in the air. If A searchlight was shining up through a vacuum you would see nothing.

The solar system is permanently flooded with light from the Sun, but we don't see it at night except where it reflects off the moon or the planets.

I agree we can't see light unless it enters our eyes because I can't see if I close my eyes or I am in a dark room . However the light still exists without us and has a nature doesn't it ?

 

[PeroK]

I agree we can't see light unless it enters our eyes because I can't see if I close my eyes or I am in a dark room . However the light still exists without us and has a nature doesn't it ?

The radiation is there - in terns of measurable EM fields- but we on Earth can't see it.

 

[jbriggs444]

I am impressed if you can measure distance with only one point of reference ! Can you explain how to measure A to ?

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.

 

[PeroK]

I am impressed if you can measure distance with only one point of reference !

Thanks to type 1a supernovae it is possible!

 

[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.