What radius to a human observer does light fail to give an observation?

  • 56 Replies
  • 7162 Views

0 Members and 1 Guest are viewing this topic.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
I think that if a person was at any reference point in the Universe a human would have a spherical view, this sphere of sight has a radius limit, what is the radius of sight ratio to magnitude of light?
« Last Edit: 09/02/2016 09:52:47 by Thebox »

*

Offline Atomic-S

  • Hero Member
  • *****
  • 960
    • View Profile
I don't quite understand your question. Are you asking how far away a star can be and still be visually bright enough to be seen with the naked eye?
 

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
I don't quite understand your question. Are you asking how far away a star can be and still be visually bright enough to be seen with the naked eye?

Yes and no, Imagine you are the star, how far can you see by your own light magnitude?

Then the second part, at what distance does vanishing points play a role?


added - I drew my question for you.

[attachment=20940]


And in quantum weirdness, if you was the sun and there was nothing reflecting light or emitting light, you would observe darkness even though you were emitting light.









« Last Edit: 12/02/2016 10:13:04 by Thebox »

*

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
"Vanishing point" is an invention of artists, architects and cartographers. It is also a classic road trip film - to my mind the best ever. It has no meaning in physics.

The human eye can probably detect a single photon, though in practice we could not distinguish it from the background "noise" in our brains, so in principle there is no limit to the distance at which you could detect a single source in an otherwise empty universe, provided you can wait long enough.

As for your second point, it's nothing to do with quantum weirdness. On a really clear, dry night you can shine a laser into the sky and not see the beam if it's pointing away from you. 
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
"Vanishing point" is an invention of artists, architects and cartographers. It is also a classic road trip film - to my mind the best ever. It has no meaning in physics.



A vanishing point has no meaning in physics?  I find that very strange when it is a fundamental aspect of relativity.

An object moving away from an observer relative decreases in size , does know one think of this?

''As for your second point, it's nothing to do with quantum weirdness. On a really clear, dry night you can shine a laser into the sky and not see the beam if it's pointing away from you. ''

Why are you changing the natural scenario to observer effect and using a laser?

If you was on the Sun looking away from the sun, and there was no other matter or stars, I assure you that you will observe only darkness.  Your Universe would be has high as you could jump.




*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
A vanishing point has no meaning in physics?  I find that very strange when it is a fundamental aspect of relativity.
Vanishing point and perspective have no connection to relativity. Is this a New Theory?
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile

Why are you changing the natural scenario to observer effect and using a laser?


In order to replace your hypothetical absurdity with a practical experiment that is simple enough for a moron to comprehend. I'm sorry you didn't.
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile

Why are you changing the natural scenario to observer effect and using a laser?


In order to replace your hypothetical absurdity with a practical experiment that is simple enough for a moron to comprehend. I'm sorry you didn't.

A practical experiment that only a moron would presume is anything like the nature of light. A laser is a linearity where as light from a body is isotropic. You would not see a laser beam unless there was a dense medium.

« Last Edit: 13/02/2016 08:10:22 by Thebox »

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
A vanishing point has no meaning in physics?  I find that very strange when it is a fundamental aspect of relativity.
Vanishing point and perspective have no connection to relativity. Is this a New Theory?

Is this  a new theory?  No Colin it is discussing a definition apparently not used in science although it is very relative.


*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
..... it is discussing a definition apparently not used in science although it is very relative.
Then it is a new theory, or more likely 'that can't be true', so don't discuss it here
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
..... it is discussing a definition apparently not used in science although it is very relative.
Then it is a new theory, or more likely 'that can't be true', so don't discuss it here

Huh?  how is talking about perspective view, vanishing points, and objects relatively look smaller at a distance a new theory?

You obviously call vanishing points and perspective view something different.



« Last Edit: 13/02/2016 09:16:32 by Thebox »

*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile

Huh?  how is talking about perspective view, vanishing points, and objects relatively look smaller at a distance a new theory?
It is if you try to relate it to relativity, which you were doing.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile

Huh?  how is talking about perspective view, vanishing points, and objects relatively look smaller at a distance a new theory?
It is if you try to relate it to relativity, which you were doing.

I am not trying to relate it to relativity, it is an axiom that it is related to relativity, things at a distance relative to the observer look smaller than they actually are.

Things that move away relatively to the observer decrease in visual size.

I am not relating it, it is already related, I miss your point.


*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
... it is an axiom that it is related to relativity,
It is not an axiom, and yes you miss my point.
This is not the thread to discuss your theory of relativity and vanishing points.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
What radius to a human observer does light fail to give an observation?
What is the point of me asking a question if you are not willing to discuss the question?

What radius to a human observer does light fail to give an observation is the question, now if light has failed to give an observation, the objects has vanished relative to the observation, so at that very point, ''the vanishing point'', is very related to the question and not a theory.

*

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
The question was answered in reply #3. What is the point of asking a question if you intend to disagree with the answer?
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
The question was answered in reply #3. What is the point of asking a question if you intend to disagree with the answer?

The question I asked was not answered, I will rephrase,

What is the radius from a light source where matter fails to reflect enough light to observe the object?


*

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
The answer remains the same:

In principle there is no limit to the distance at which you could detect a single source in an otherwise empty universe, provided you can wait long enough.

From the observer's point of view there is no difference between a primary source and a reflector.
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
The answer remains the same:

In principle there is no limit to the distance at which you could detect a single source in an otherwise empty universe, provided you can wait long enough.

From the observer's point of view there is no difference between a primary source and a reflector.

HUh ? I thought light diminishes at a distance in compliance with the inverse square law?

If the light diminishes then surely any  matter receiving the diminished light reflects a lesser magnitude?

If the boundary  is limitless, why do I need a more powerful flash-light to see further?

« Last Edit: 14/02/2016 16:11:52 by Thebox »

*

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
HUh ? I thought light diminishes at a distance in compliance with the inverse square law?


Exactly. And 1/r2 > 0 for all values of r, so there will always be a photon if you wait long enough.

The devil is in that last detail - if you wait long enough. As I pointed out way back in this discussion, yopu won't be able to distinguish a single photon from noise in the real world, so you need a bigger flashlight to see objects further away in the presence of air, dust, starlight, and the thermal noise in your brain, but you could use an integrating image amplifier (your mobile phone camera set to "night" mode) or a photomultiplier attached to a telescope instead.     
« Last Edit: 14/02/2016 17:52:47 by alancalverd »
helping to stem the tide of ignorance

*

Offline Ophiolite

  • Hero Member
  • *****
  • 718
    • View Profile
I am not trying to relate it to relativity, it is an axiom that it is related to relativity, things at a distance relative to the observer look smaller than they actually are.

Things that move away relatively to the observer decrease in visual size.
I am not relating it, it is already related, I miss your point.
The point is that when you say relativity on a science forum it is understood that you are referring to Einstein's theories of Special and General Relativity unless you explicitly state otherwise. Ignoring this basic point is at best foolish and at worst deliberately obtuse, hence rude.
Observe; collate; conjecture; analyse; hypothesise; test; validate; theorise. Repeat until complete.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
I am not trying to relate it to relativity, it is an axiom that it is related to relativity, things at a distance relative to the observer look smaller than they actually are.

Things that move away relatively to the observer decrease in visual size.
I am not relating it, it is already related, I miss your point.
The point is that when you say relativity on a science forum it is understood that you are referring to Einstein's theories of Special and General Relativity unless you explicitly state otherwise. Ignoring this basic point is at best foolish and at worst deliberately obtuse, hence rude.

Did I even say relativity?  I said relatively

''relatively
ˈrɛlətɪvli/Submit
adverb
in relation, comparison, or proportion to something else.
"they were very poor, but, relatively speaking, they had been lucky"
regarded in comparison with something else rather than absolutely; quite.''

added- yes I did say relativity but I mean the relativity of something.
« Last Edit: 14/02/2016 20:44:44 by Thebox »

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
HUh ? I thought light diminishes at a distance in compliance with the inverse square law?


Exactly. And 1/r2 > 0 for all values of r, so there will always be a photon if you wait long enough.

The devil is in that last detail - if you wait long enough. As I pointed out way back in this discussion, yopu won't be able to distinguish a single photon from noise in the real world, so you need a bigger flashlight to see objects further away in the presence of air, dust, starlight, and the thermal noise in your brain, but you could use an integrating image amplifier (your mobile phone camera set to "night" mode) or a photomultiplier attached to a telescope instead.   


You always elude the actually question and reply with seemingly irrelevant  answers to the actual question.
« Last Edit: 14/02/2016 21:36:33 by Thebox »

*

Offline Arnie O'Dell

  • First timers
  • *
  • 9
    • View Profile
Are you talking about light cones?

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
Are you talking about light cones?

I am asking about light ''spheres'' that diminish at a distance from an ''inside'' observers perspective.

Putting the question a different way.

Hello science , I go night fishing, which means I go fishing in the dark, I use a head lamp, however my vision is limited to the wattage of the bulb, I can only observe so far then all things fade out , I can not see  the other side of the lake, 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, I can see my rods reflecting light, why can't I see my friend reflecting light, why does this happen?

« Last Edit: 14/02/2016 23:52:22 by Thebox »

*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
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.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • First timers
  • *
  • 9
    • View Profile
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

  • Neilep Level Member
  • ******
  • 4310
    • View Profile
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

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
No, he is just restating reply #3.
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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? 

[attachment=20947]

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

  • Neilep Level Member
  • ******
  • 4310
    • View Profile
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

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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?

[attachment=20951]

[attachment=20955]

[attachment=20953]


[attachment=20957]





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

*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
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.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline puppypower

  • Hero Member
  • *****
  • 593
    • View Profile

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.
 

*

Offline Arnie O'Dell

  • First timers
  • *
  • 9
    • View Profile
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

  • Neilep Level Member
  • ******
  • 3250
    • View Profile

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?

[attachment=20961]




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

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • First timers
  • *
  • 9
    • View Profile
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

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
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.
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4894
  • life is too short to drink instant coffee
    • View Profile
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?
helping to stem the tide of ignorance

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
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.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
Not that difficult to understand, but you are still missing Alan's point  [;)]
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
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 »