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Author Topic: What radius to a human observer does light fail to give an observation?  (Read 6641 times)

Offline Colin2B

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A vanishing point has no meaning in physics?  I find that very strange when it is a fundamental aspect of relativity.
As Orphiolite pointed out relativity has a very specific meaning in physics, misuse it and you will be misunderstood.


You always elude the actually question and reply with seemingly irrelevant  answers to the actual question.
Alan is not eluding anything, his reply is very relevant to the question.
 

Offline Thebox

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A vanishing point has no meaning in physics?  I find that very strange when it is a fundamental aspect of relativity.
As Orphiolite pointed out relativity has a very specific meaning in physics, misuse it and you will be misunderstood.


You always elude the actually question and reply with seemingly irrelevant  answers to the actual question.
Alan is not eluding anything, his reply is very relevant to the question.

Then I do not understand Alan's post or answers relevance.

Can you please answer the fishing question Colin?
 

Offline Arnie O'Dell

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humans see by the light reflected from the objects around them. The fishing light casts a light and objects close by reflect light back and they can be seen. Objects further away are dimmer as the reflected light spreads and so fades until the far away objects are not discernable. the radius of the "light sphere would depend on the circumstance.
 

Offline evan_au

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Quote from: TheBox
I can not see my friend who is on the next fishing spot along the bank side, he assures  me though he can see me and my head lamp
This is because the light from your headlamp obeys the "inverse square law". The light is dimmer by the time it reaches your friend on the other side of the lake, but it is still bright enough for him to perceive it.

However, for you to see your friend by the light of your headlamp, the light undergoes an inverse square law to reach your friend. Then any light reflected from your friend undergoes another inverse square law before it reaches you. This is an "inverse fourth law", and it means that you can't see your friend by the light of your headlamp, even though he can see your headlamp.
- It is not helped by the fact that you are partly dazzled by the bright light reflecting off nearby objects, so your eyes can't see dim things (like your friend)

This applies in a number of areas:
- Weather radar, Police radar or laser speed checks follow this inverse fourth law
- This problem is overcome for commercial aircraft by having an electronic transponder on the aircraft. When it is interrogated by a radar pulse (inverse square law), the transponder responds with a message describing its location and heading (subject to an inverse square law). This gives the radar much greater range than a radar with the same transmit power, relying on passive reflection (inverse fourth law).
 

Offline Thebox

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Quote from: TheBox
I can not see my friend who is on the next fishing spot along the bank side, he assures  me though he can see me and my head lamp
This is because the light from your headlamp obeys the "inverse square law". The light is dimmer by the time it reaches your friend on the other side of the lake, but it is still bright enough for him to perceive it.

However, for you to see your friend by the light of your headlamp, the light undergoes an inverse square law to reach your friend. Then any light reflected from your friend undergoes another inverse square law before it reaches you. This is an "inverse fourth law", and it means that you can't see your friend by the light of your headlamp, even though he can see your headlamp.
- It is not helped by the fact that you are partly dazzled by the bright light reflecting off nearby objects, so your eyes can't see dim things (like your friend)

This applies in a number of areas:
- Weather radar, Police radar or laser speed checks follow this inverse fourth law
- This problem is overcome for commercial aircraft by having an electronic transponder on the aircraft. When it is interrogated by a radar pulse (inverse square law), the transponder responds with a message describing its location and heading (subject to an inverse square law). This gives the radar much greater range than a radar with the same transmit power, relying on passive reflection (inverse fourth law).


Thank you Evan for confirming my understanding, Do we know  a radius limit of observation compared to the wattage of the light?
 

Offline Thebox

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humans see by the light reflected from the objects around them. The fishing light casts a light and objects close by reflect light back and they can be seen. Objects further away are dimmer as the reflected light spreads and so fades until the far away objects are not discernable. the radius of the "light sphere would depend on the circumstance.

Thank  you Arnie, so are you saying that any objects beyond a certain distance, could be there but not observed dependent to the light?
 

Offline alancalverd

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No, he is just restating reply #3.
 

Offline Thebox

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No, he is just restating reply #3.

Alan please think about what I am asking with some genuine interest and thought and not just reply based on your knowledge. I know you are not stupid and have a good mind, I would really appreciate your own input without the knowledge you recall.

Let us discuss an analogy,

Let us take A and B divided by a length of space.

We can imagine a train track and both observers are standing on the same track a length apart.


r=X

A...................................................................B


It is daylight ,  (A) can see (B) and (B) can see (A)   


(B) moves away from (A) while (A) remains in a fixed position,


A..................................................................→→→→→→→→→→→→→→→→→→→→→→→→→→→→→B



Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way? 



This is NOT a new theory , it is a discussion between us, if we make a new theory by the end between us, that is another story.











« Last Edit: 15/02/2016 10:51:45 by Thebox »
 

Offline evan_au

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Quote from: TheBox
Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way?
In daylight:
- Let us say that the distance to B has doubled.
- That means that the apparent "area" of B (as seen by A) has dropped by a factor of 4.
- The angular resolution of the human eye is about 1 arcminute, ie it is impossible to recognize B as human beyond about 1 km (although you might be able to recognize him by the way he walks).

If the only illumination is at A, then the illumination of B will drop by a factor of 4 (as seen by B).
- If A is trying to see B, he will see the brightness of B will drop by a factor of 16.
 

Offline Thebox

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Quote from: TheBox
Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way?
In daylight:
- Let us say that the distance to B has doubled.
- That means that the apparent "area" of B (as seen by A) has dropped by a factor of 4.
- The angular resolution of the human eye is about 1 arcminute, ie it is impossible to recognize B as human beyond about 1 km (although you might be able to recognize him by the way he walks).

If the only illumination is at A, then the illumination of B will drop by a factor of 4 (as seen by B).
- If A is trying to see B, he will see the brightness of B will drop by a factor of 16.

Thank you Evan I would shake your hand if I was there your brilliant.

Yes indeed the area of (B) contacts relative to (A)'s perspective but also the area of (A) contracts relative to (B)'s perspective.  Relatively both (A) and (B) contract to the factor of 4.


So at what radius apart would the factor decrease cause  more than  it is impossible to recognize B as human, it would be impossible to even see  (B) was even there?














« Last Edit: 15/02/2016 11:50:15 by Thebox »
 

Offline Colin2B

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So at what radius apart would the factor decrease cause  more than  it is impossible to recognize B as human, it would be impossible to even see  (B) was even there?
You can work it out from info Evan gave "The angular resolution of the human eye is about 1 arcminute". Make it easy by assuming the human is 2m tall - not quite accurate because the theory assumes a disc/point source. Remember resolution assumes adequate contrast and illumination eg human dressed in white against a black background or black against white, reduced contract will reduce the resolving power.
As you can see from all of this, there is no set sphere or radius of observation, it depends on size, reflection (albedo) and illumination of the objects you are viewing and as Alan has pointed out it is different for a light source.
 
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Offline puppypower

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The relationship between distance and apparent height of objects is an inverse-linear function:
h=a\d   where h is the apparent height, d is the distance of the object, and a is the actual size of the object. if we solve this for d we get d=a/h

Say we can detect one photon per cm of height (or width). The source light emits X photons/cm of height (or width). As the light moves away the brightness gets less and less; d=X.

A one light year distance, is 9.461 x10 17  cm.

The source will need this same light density of photons/cm height to be seen from earth.
 
 
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Offline Arnie O'Dell

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I think the limiting factor would be the speed of light. I can see the light from the stars that outline the big dipper and they are many light years away. They are within the light cone from my vantage point. Any light signals outside my light cone would appear dark. The farther away the light source the wider the field of vision.
 

Offline Thebox

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The relationship between distance and apparent height of objects is an inverse-linear function:
h=a\d   where h is the apparent height, d is the distance of the object, and a is the actual size of the object. if we solve this for d we get d=a/h

Say we can detect one photon per cm of height (or width). The source light emits X photons/cm of height (or width). As the light moves away the brightness gets less and less; d=X.

A one light year distance, is 9.461 x10 17  cm.

The source will need this same light density of photons/cm height to be seen from earth.
 

Thank you Puppy, I think sometimes when we get to discussing the technical aspect and fine details I get lost as the knowledge I don't always know.


Your diagram only looks at one perspective view, the view is mirrored relatively, what I mean by this is that (A) and (B) both experience the contraction perspective of each other to a point where neither exist to each other because the light is ''narrowed'' to a ''vanishing'' point.

Do you account for this?






« Last Edit: 15/02/2016 15:28:04 by Thebox »
 

Offline Thebox

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I think the limiting factor would be the speed of light. I can see the light from the stars that outline the big dipper and they are many light years away. They are within the light cone from my vantage point. Any light signals outside my light cone would appear dark. The farther away the light source the wider the field of vision.

The farther away the source the narrower the field of vision?
 

Offline Arnie O'Dell

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I would if the event was in the past. Now that you mention it the light from stars is often very old and so is in the past so maybe that is the correct view, that the field of vision narrows for light signals received. The fact that we have no access to the past except through records may make that a moot point. The only light signals that can be experienced are in the now. It is possible that each observation needs to be accompanied by a Lorentz frame.
 

Offline Thebox

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I would if the event was in the past. Now that you mention it the light from stars is often very old and so is in the past so maybe that is the correct view, that the field of vision narrows for light signals received. The fact that we have no access to the past except through records may make that a moot point. The only light signals that can be experienced are in the now. It is possible that each observation needs to be accompanied by a Lorentz frame.

Well, I can't go into simultaneity or the thread will be removed to new theories, So I can only really discuss the actual question although simultaneity is relative the question in my opinion.
 

Offline alancalverd

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Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way? 


B subtends a smaller angle at A as he moves away. At some distance the angle will be less than the angular resolution of A's equipment so A will not be able to determine the size or shape of B (by direct observation, but there are indirect methods of estimating the mass of B at any distance)  but if he is emitting or reflecting light he will always appear at least as a point source of photons.
 
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Offline Thebox

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Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way? 


B subtends a smaller angle at A as he moves away. At some distance the angle will be less than the angular resolution of A's equipment so A will not be able to determine the size or shape of B (by direct observation, but there are indirect methods of estimating the mass of B at any distance)  but if he is emitting or reflecting light he will always appear at least as a point source of photons.

You say he will always appear as a point source of photons, what do you mean by will always and point source ? 

 
« Last Edit: 15/02/2016 19:28:36 by Thebox »
 

Offline alancalverd

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My words have their usual meanings to those familiar with English, which has succeeded Latin as the principal means of communication between scientists and businessmen on Earth. What planet are you from? And do the words "at least" not figure in your mathematics?
 

Offline Thebox

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My words have their usual meanings to those familiar with English, which has succeeded Latin as the principal means of communication between scientists and businessmen on Earth. What planet are you from? And do the words "at least" not figure in your mathematics?

Will always means like indefinitely, infinite, forever, several thing.

Point source means bugger all.
 

Offline Colin2B

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Point source means bugger all.
It means precisely what it says.
Imagine you blackout a room by covering the windows with lightproof black paper, now take a pin and make the smallest hole you can in the paper. Point source. You can in theory make it as small as you like eg one atom.
What's so difficult about that.
 

Offline Thebox

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Point source means bugger all.
It means precisely what it says.
Imagine you blackout a room by covering the windows with lightproof black paper, now take a pin and make the smallest hole you can in the paper. Point source. You can in theory make it as small as you like eg one atom.
What's so difficult about that.

It is not difficult now you  have clarified what Alan meant by point source.   It is what I thought he meant, but I wanted to clarify for my understanding we mean the same thing.   What is wrong in wanting to be sure?


Now take your paper and point source and move it away from you, you will observe no pin hole after a short distance, what is hard to understand about that?

Move the paper even further away, and you will observe no paper, what is hard to understand about that?





 

Offline Colin2B

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Not that difficult to understand, but you are still missing Alan's point  ;)
 

Offline Thebox

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Not that difficult to understand, but you are still missing Alan's point  ;)

Alan made the point of always, I miss no points , it is only distance when we miss points. :)

Can I try some maths on you ?




d=0→σ 4/3 pi ∞0


which says distance is equal to,  zero to  a zero infinite sphere

L=r=0→σ0

which says a length or radius is equal to 0 to a variation of 0.



« Last Edit: 16/02/2016 10:56:44 by Thebox »
 

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