# The Naked Scientists Forum

### Author Topic: How far apart must two bulbs be so as to be invisible to one another?  (Read 2997 times)

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### How far apart must two bulbs be so as to be invisible to one another?
« on: 11/04/2016 07:47:18 »
If we have 2 light  bulbs that are identical and both 100w, both light bulbs , A and B start off next to each other.

AB

We then expand the length between the light bulbs

A→B

A→→B

A→→→B

At what radius does A not observe B and B not observe A any more?

« Last Edit: 11/04/2016 09:01:27 by chris »

#### chris

• Neilep Level Member
• Posts: 5295
• Thanked: 61 times
• The Naked Scientist
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #1 on: 11/04/2016 09:02:42 »
What do you mean by being invisible to one another? Are you referring to the density of photons in any given patch of space?

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #2 on: 11/04/2016 09:51:23 »
What do you mean by being invisible to one another?

Invisible is not really the word, they relatively can not ''see'' each other because as the distance increases apart , relatively they visually contract .

Quote
Are you referring to the density of photons in any given patch of space?

I am referring to light intensity diminishing over a radius.

#### Colin2B

• Global Moderator
• Neilep Level Member
• Posts: 1785
• Thanked: 116 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #3 on: 11/04/2016 10:14:31 »
At what radius does A not observe B and B not observe A any more?
You also have to define what you mean by observe, as you don't use the word in the same way as physicists.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #4 on: 11/04/2016 10:46:32 »
At what radius does A not observe B and B not observe A any more?
You also have to define what you mean by observe, as you don't use the word in the same way as physicists.

Too see...(I know the light bulb has no eyes),

#### evan_au

• Neilep Level Member
• Posts: 3956
• Thanked: 228 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #5 on: 11/04/2016 11:03:27 »
Setting up the Problem...
If A and B are "point sources", then they will "never" intercept any photons from another source, and so the maximum distance is almost zero. So let's assume that both A and B have a finite area in which they intercept photons.

If A and B are both light sources, then A & B don't have to be very far apart before the glow and reflection of their own light source overpowers the low levels of light received from their distant counterpart. So let's assume that they are in a perfect vacuum (no reflection or scattering of light), and they are both emitting light of a different frequency (so they can separate their own light from light emitted by their counterpart).

If A and B have other light sources around them, then A & B don't have to be very far apart before the glow and reflection of these other light sources overpowers the low levels of light received from their distant counterpart. So let's assume that any other light sources are much fainter and farther away than the counterpart they are trying to detect, and don't emit significant light at the frequencies emitted by A and B.

Let's say that A has to detect at least 10 photons from the direction of B before A can declare that it has detected B.

A Solution?
Let's say that A and B are far enough apart that it takes 1 second to collect 10 photons.

Then, if you double the distance between A and B, then it will take 4 times as long to detect 10 photons (by the inverse square law).

There is no limit to how far away A and B can be apart, and still "see" each other, provided both A and B are very patient, and their light doesn't fail.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #6 on: 11/04/2016 15:10:43 »

There is no limit to how far away A and B can be apart, and still "see" each other, provided both A and B are very patient, and their light doesn't fail.

And in a visual sense of the human eye an observer with a 100w flash light  walks backwards along a very long railway track shining the light at the observer, at what distance does the observer not observe the walker any more?

« Last Edit: 11/04/2016 15:14:18 by Thebox »

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1839
• Thanked: 138 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #7 on: 11/04/2016 20:11:21 »

And in a visual sense of the human eye an observer with a 100w flash light  walks backwards along a very long railway track shining the light at the observer, at what distance does the observer not observe the walker any more?

As evan laid out in his post, there are many factors that can interfere with the observation.
There is the issue of clarity of the medium between the source and observer (visibility/foggy/there is a forest in the way...)
There is the issue of competing light sources. Our eyes automatically adjust the brightness of our whole surrounding, so something that would be blindingly bright in the middle of the night might barely be noticeable in the mid afternoon at the beach in the middle of the summer. I can see a single 100 W bulb >10 km away on a clear night out in the countryside, but there is no way I could notice the same bulb during the day at that distance.

There is also the issue of the curvature of the Earth. A very bright lightbulb might in principle be visible from 200 km away, but if both the light and the observer are only 2m above the ground, the ground will be in the way.

#### Bored chemist

• Neilep Level Member
• Posts: 8596
• Thanked: 41 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #8 on: 11/04/2016 20:16:49 »
If you use a big enough telescope you can, in principle, see a lamp  from as far as you like.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #9 on: 11/04/2016 22:24:20 »

And in a visual sense of the human eye an observer with a 100w flash light  walks backwards along a very long railway track shining the light at the observer, at what distance does the observer not observe the walker any more?

As evan laid out in his post, there are many factors that can interfere with the observation.
There is the issue of clarity of the medium between the source and observer (visibility/foggy/there is a forest in the way...)
There is the issue of competing light sources. Our eyes automatically adjust the brightness of our whole surrounding, so something that would be blindingly bright in the middle of the night might barely be noticeable in the mid afternoon at the beach in the middle of the summer. I can see a single 100 W bulb >10 km away on a clear night out in the countryside, but there is no way I could notice the same bulb during the day at that distance.

There is also the issue of the curvature of the Earth. A very bright lightbulb might in principle be visible from 200 km away, but if both the light and the observer are only 2m above the ground, the ground will be in the way.

The answers seem to be avoiding the actual question I have asked and the answers are not factors I asked to take into consideration. My drawing shows a dark clear night and an x-axis with no curvature of the earth, it is a hypothetical question and you are adding content to the question.   Your answers thus far have only  been related to light magnitude and no mention of the relative visual contraction of the bulb, how can you see a bulb over a great distance with the eye if the bulb has relatively visual contracted to a visual 0 point source .

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1839
• Thanked: 138 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #10 on: 11/04/2016 22:27:27 »

And in a visual sense of the human eye an observer with a 100w flash light  walks backwards along a very long railway track shining the light at the observer, at what distance does the observer not observe the walker any more?

As evan laid out in his post, there are many factors that can interfere with the observation.
There is the issue of clarity of the medium between the source and observer (visibility/foggy/there is a forest in the way...)
There is the issue of competing light sources. Our eyes automatically adjust the brightness of our whole surrounding, so something that would be blindingly bright in the middle of the night might barely be noticeable in the mid afternoon at the beach in the middle of the summer. I can see a single 100 W bulb >10 km away on a clear night out in the countryside, but there is no way I could notice the same bulb during the day at that distance.

There is also the issue of the curvature of the Earth. A very bright lightbulb might in principle be visible from 200 km away, but if both the light and the observer are only 2m above the ground, the ground will be in the way.

The answers seem to be avoiding the actual question I have asked and the answers are not factors I asked to take into consideration. My drawing shows a dark clear night and an x-axis with no curvature of the earth, it is a hypothetical question and you are adding content to the question.   Your answers thus far have only  been related to light magnitude and no mention of the relative visual contraction of the bulb, how can you see a bulb over a great distance with the eye if the bulb has relatively visual contracted to a visual 0 point source .

The bulb won't contract to 0 until you're infinitely far away...

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #11 on: 11/04/2016 22:36:59 »

The bulb won't contract to 0 until you're infinitely far away...

That is not true, I go night fishing regular, I have observed you statement is false by evidence of observation.   you are clearly mistaken.

Please feel free to try the experiment using a pen torch and an open field.

« Last Edit: 11/04/2016 22:40:34 by Thebox »

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1839
• Thanked: 138 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #12 on: 11/04/2016 22:45:48 »

The bulb won't contract to 0 until you're infinitely far away...

That is not true, I go night fishing regular, I have observed you statement is false by evidence of observation.   you are clearly mistaken.

Please feel free to try the experiment using a pen torch and an open field.

Your observations while fishing are due to "the added content" we talked about earlier that you then brushed off...

And in a visual sense of the human eye an observer with a 100w flash light  walks backwards along a very long railway track shining the light at the observer, at what distance does the observer not observe the walker any more?

As evan laid out in his post, there are many factors that can interfere with the observation.
There is the issue of clarity of the medium between the source and observer (visibility/foggy/there is a forest in the way...)
There is the issue of competing light sources. Our eyes automatically adjust the brightness of our whole surrounding, so something that would be blindingly bright in the middle of the night might barely be noticeable in the mid afternoon at the beach in the middle of the summer. I can see a single 100 W bulb >10 km away on a clear night out in the countryside, but there is no way I could notice the same bulb during the day at that distance.

There is also the issue of the curvature of the Earth. A very bright lightbulb might in principle be visible from 200 km away, but if both the light and the observer are only 2m above the ground, the ground will be in the way.

The answers seem to be avoiding the actual question I have asked and the answers are not factors I asked to take into consideration. My drawing shows a dark clear night and an x-axis with no curvature of the earth, it is a hypothetical question and you are adding content to the question.   Your answers thus far have only  been related to light magnitude and no mention of the relative visual contraction of the bulb, how can you see a bulb over a great distance with the eye if the bulb has relatively visual contracted to a visual 0 point source .

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #13 on: 11/04/2016 22:49:13 »
]

Your observations while fishing are due to "the added content" we talked about earlier that you then brushed off...

I have not brushed off ambient light etc, the point you are missing is that yes the light extends to infinite but the visual contraction of the source doe's not.  For example you can not see dust particles in the air no more than a few feet away from you.

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1839
• Thanked: 138 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #14 on: 11/04/2016 22:53:15 »
]

Your observations while fishing are due to "the added content" we talked about earlier that you then brushed off...

I have not brushed off ambient light etc, the point you are missing is that yes the light extends to infinite but the visual contraction of the source doe's not.  For example you can not see dust particles in the air no more than a few feet away from you.

You CAN see the dust, you just don't NOTICE it. And you can see specks of dust from across the room with a bright flashlight in a darkened room.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #15 on: 11/04/2016 23:01:32 »

You CAN see the dust, you just don't NOTICE it. And you can see specks of dust from across the room with a bright flashlight in a darkened room.

You are twisting the question.

Sam observes the sky, he notices nothing for a while then notices a tiny speck in the sky getting nearer to him, as the speck gets nearer the speck relatively expands , when it gets close to identify the dimensions Sam notices its an aeroplane, as the aeroplane passes above Sam he can observe the aeroplanes rest length, as the aeroplane passes him , he notices the aeroplane starts to relatively contract and shrink back down to a speck before eventually becoming dimensionless.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #16 on: 11/04/2016 23:05:36 »
O dimension of light

n=0xyz

« Last Edit: 11/04/2016 23:26:03 by Thebox »

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #17 on: 11/04/2016 23:31:11 »
All pics courtesy of google and edited.

Relativity and visual  length contraction .

« Last Edit: 11/04/2016 23:38:39 by Thebox »

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #18 on: 11/04/2016 23:49:41 »
Sorry for going slightly off key, notice in this video at 4.19 the near side trains length expands.  It looks like it stretches it is quite cool.

#### chiralSPO

• Global Moderator
• Neilep Level Member
• Posts: 1839
• Thanked: 138 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #19 on: 12/04/2016 00:35:05 »
This becomes a question about the resolution of the human eye, not one of general physical principles. If you cared about how close something has to be for our eye to make out its dimensions accurately, you should have asked a question about peoples eyes from the very start. Posing the question as two light-emitting objects without eyes in makes it sound like a question of the fundamental properties of light. Which is it?

#### agyejy

• Sr. Member
• Posts: 208
• Thanked: 21 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #20 on: 12/04/2016 02:06:44 »
This becomes a question about the resolution of the human eye, not one of general physical principles. If you cared about how close something has to be for our eye to make out its dimensions accurately, you should have asked a question about peoples eyes from the very start. Posing the question as two light-emitting objects without eyes in makes it sound like a question of the fundamental properties of light. Which is it?

As far as I can tell this is fundamental problem with all of the "questions" TheBox asks. There seems to be a complete inability to comprehend the difference between the fundamental properties of something and observation dependent issues that can be traced back to the equipment being used to measure a thing.

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #21 on: 12/04/2016 09:17:24 »
This becomes a question about the resolution of the human eye, not one of general physical principles. If you cared about how close something has to be for our eye to make out its dimensions accurately, you should have asked a question about peoples eyes from the very start. Posing the question as two light-emitting objects without eyes in makes it sound like a question of the fundamental properties of light. Which is it?

It's both, it's observation and relativity.

When an object moves away from us it relatively visual contracts to the eye, the light that we did see in 3 dimensional form of the object becomes 0 dimensional over a distance away ,   relative to the observation and the object the light between eye and object collapses from 3d into a 1d singularity whole, a thread with zero diameter.
This is true no matter which direction you look into space.
When you look at the black background of space, it is not an edge or an expanding space, it is simply there is nothing in range to see, the two reasons are the inverse square law and the relative observation contraction of objects., showing space to be n-dimensional.

n to n is a singularity of zero, 1 to 1 is a length and relative visual dimension of light.

« Last Edit: 12/04/2016 09:26:51 by Thebox »

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #22 on: 12/04/2016 09:31:42 »
The quanta visual tunnel collapses to n.

« Last Edit: 12/04/2016 09:37:28 by Thebox »

#### Thebox

• Neilep Level Member
• Posts: 3139
• Thanked: 42 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #23 on: 12/04/2016 10:05:17 »

Each individual Galaxy must be an individual singularity , (singularity your definition).?

Maybe even every single particle?

Could there be a singularity single particle(s)?

« Last Edit: 12/04/2016 10:07:19 by Thebox »

#### evan_au

• Neilep Level Member
• Posts: 3956
• Thanked: 228 times
##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #24 on: 12/04/2016 11:40:18 »
Quote from: TheBox
When an object moves away from us it relatively visual contracts to the eye, the light that we did see in 3 dimensional form of the object becomes 0 dimensional over a distance away..., a thread with zero diameter. ... there is nothing in range to see

When an object is close, you can perceive it as a 3-dimensional object because of binocular vision. But this only works out to about 5m, after which it is effectively 2-dimensional (although, if it is a familiar object, your brain can fill in the third dimension).
See: https://en.wikipedia.org/wiki/Stereopsis

The angular resolution of the human eye is about 0.02 degrees. When an object subtends less than this angle, it effectively decreases to a point. It appears zero-dimensional.
See: https://en.wikipedia.org/wiki/Naked_eye#Basic_accuracies

But humans can see things that are farther than this. The star Sirius subtends an angle of 0.006 seconds = 0.0001 minutes = 0.000002 degrees. According to this theory, it should be zero-dimensional and invisible; and yet it is easily visible as one of the brightest stars in the night sky.
See: https://en.wikipedia.org/wiki/Angular_diameter#Use_in_astronomy

The following users thanked this post: jeffreyH, Thebox

#### The Naked Scientists Forum

##### Re: How far apart must two bulbs be so as to be invisible to one another?
« Reply #24 on: 12/04/2016 11:40:18 »