# The Naked Scientists Forum

### Author Topic: How long would a piece of string have to be before it ''vanished''?  (Read 1370 times)

#### Thebox

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##### How long would a piece of string have to be before it ''vanished''?
« on: 04/06/2016 08:38:40 »
Observer A is ''stationary'' and observe B is in motion travelling directly away from observer A.  Observe B has one end of a huge ball of string, observer A is ''holding'' the ball, at what distance away from A does A no longer observe the piece of string?

I also drew a diagram for understanding of the question relationship.

« Last Edit: 04/06/2016 08:43:00 by Thebox »

#### Bored chemist

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #1 on: 04/06/2016 12:39:25 »
If the string were sufficiently well lit, it would be visible at any distance (assuming nothing was in the way).
Why do you think A would be unable to observe a string that he is holding on to one end of?

The question makes no sense.

#### Thebox

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #2 on: 05/06/2016 08:04:58 »
If the string were sufficiently well lit, it would be visible at any distance (assuming nothing was in the way).

That is not true Mr Chemist, the visual angle of the dimensions of the string will visually contract to 0 dimension whether it is well lit or not .

https://en.wikipedia.org/wiki/Visual_angle

#### Bored chemist

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #3 on: 05/06/2016 11:56:26 »
However, perspective means that you see more of the string in a given angle, so it remains visible.

Part of the reason for that is that you forgot to answer my questions.

If I have one end of a piece of string in my hand, I can see it, no matter what the other end is doing.

#### Thebox

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #4 on: 05/06/2016 12:38:53 »
However, perspective means that you see more of the string in a given angle, so it remains visible.

Part of the reason for that is that you forgot to answer my questions.

If I have one end of a piece of string in my hand, I can see it, no matter what the other end is doing.

''Why do you think A would be unable to observe a string that he is holding on to one end of?''

They would observe the end they were observing  but would observe the string that extending away from them ''vanish'' into the distance.   I think you have read the question wrongly after the above post.

Look out of your window and observe the horizon, ''things'' on the horizon are visually ''smaller'' than they really are in size. The area of the ''things'' visually contracted by the ''length'' away from the observer. The visual angle of light of these ''things'' is relatively ''smaller'', if these ''things'' were to continue in a straight line away from us the visual area of the ''thing'' will contract to visually 0 dimension. This is a fact of observation.
The visual angle of light will also visually collapse to 0 dimension, again a fact of observation.

So at what length extending away from (A) does the string visually contract to visually 0 dimensions?

#### Bored chemist

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #5 on: 05/06/2016 17:47:08 »
The human eye is within an order of magnitude or so of being diffraction limited.
https://en.wikipedia.org/wiki/Diffraction-limited_system

However, at night, just about all the stars we see are "too small" to be seen by that criterion.
If the string was brightly lit you would be able to see it, no matter how far away it was (and even if you don't believe me).

#### Thebox

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #6 on: 06/06/2016 06:50:44 »
The human eye is within an order of magnitude or so of being diffraction limited.
https://en.wikipedia.org/wiki/Diffraction-limited_system

However, at night, just about all the stars we see are "too small" to be seen by that criterion.
If the string was brightly lit you would be able to see it, no matter how far away it was (and even if you don't believe me).

Well I don't believe you because evidence suggests otherwise, you are trying to say that there is no such thing as a vanishing point of an object, this is untrue and provable by using a flash light or any other object. Thank you for confirming what science really is, I wish you all good day and will leave you all to your fairy tales.

#### evan_au

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #7 on: 06/06/2016 11:16:24 »
Quote from: TheBox
there is no such thing as a vanishing point of an object
The "Vanishing Point" is a concept in art that allows architectural drawings with perspective.

The Vanishing Point is not necessarily a physical point that can be reached, but more an asymptote that can be approached by a very long object (such as the hypothetical string in the OP).

I guess when the object subtends an angle of less than 1 arcminute (the resolution of the human eye), the object will be indistinguishably different from the Vanishing Point.

It is possible to have a vanishing point which is not reached. Have a look at the example on the right of this link, showing an example of a building with two vanishing points. The vanishing points are purely conceptual, but the finite size of the building does not let the drawing approach anywhere near the vanishing point.

See: https://en.wikipedia.org/wiki/Vanishing_point#Curvilinear_and_reverse_perspective

#### Thebox

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #8 on: 06/06/2016 16:51:10 »
Quote from: TheBox
there is no such thing as a vanishing point of an object
Quote from: Evan
The "Vanishing Point" is a concept in art that allows architectural drawings with perspective.

I can't seem to find where you have quoted me from saying ''there is no such thing as a vanishing point''?

I understand the concept of a vanishing point is related to art and technical drawings, however a ''vanishing point'' is quite clearly also a physical process involving sight and the visual area of an object. When an object is viewed in the distance , the object is visually down scaled from its real size, this being relative to the visual area of ''light'' being observed  of the object.

Quote from: Evan
The Vanishing Point is not necessarily a physical point that can be reached, but more an asymptote that can be approached by a very long object (such as the hypothetical string in the OP).

The ''vanishing point'' is a geometric point that can be reached by any observer relative to another observer.
Einstein's ''thing'' where neither observer knows who is moving, if you travelled a vector away from me, both I and you will visually contract in the area of ''light'' observed by each other to a ''vanishing point'' where neither I see you or you see me and our relative visual dimensions becomes 0 or in your terms less than 1 arcminute.

Quote from: Evan
I guess when the object subtends an angle of less than 1 arcminute (the resolution of the human eye), the object will be indistinguishably different from the Vanishing Point.

Thank you for that one sentence , I could probably write this up proper now.

Quote from: Evan
It is possible to have a vanishing point which is not reached. Have a look at the example on the right of this link, showing an example of a building with two vanishing points. The vanishing points are purely conceptual, but the finite size of the building does not let the drawing approach anywhere near the vanishing point.

See: https://en.wikipedia.org/wiki/Vanishing_point#Curvilinear_and_reverse_perspective

added- we can clearly see in this footage from youtube, that the 3 dimensional vehicles at the ''bottom'' of the screen, turn into visual 2d before the area contracts further up the screen.

« Last Edit: 06/06/2016 17:28:16 by Thebox »

#### Bored chemist

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #9 on: 06/06/2016 22:00:01 »
The human eye is within an order of magnitude or so of being diffraction limited.
https://en.wikipedia.org/wiki/Diffraction-limited_system

However, at night, just about all the stars we see are "too small" to be seen by that criterion.
If the string was brightly lit you would be able to see it, no matter how far away it was (and even if you don't believe me).

Well I don't believe you because evidence suggests otherwise, you are trying to say that there is no such thing as a vanishing point of an object, this is untrue and provable by using a flash light or any other object. Thank you for confirming what science really is, I wish you all good day and will leave you all to your fairy tales.
No, the fairy tale is that idea that there is "a vanishing point".
Use a brighter flash light and you can see it from further away.
So there's nothing special about the distance- it just depends on how bright the illumination is.
And that's what I have said all along.

On a related note, the image on the screen is always "flat" the vehicles are never 3D so it's clearly impossible for them to change into 2D.
And this
"
I understand the concept of a vanishing point is related to art and technical drawings, however a ''vanishing point'' is quite clearly also a physical process involving sight and the visual area of an object. "
Is just plain wrong.

You might want to learn some science before making insulting remarks like that- at best you are going to look silly.
« Last Edit: 06/06/2016 22:06:08 by Bored chemist »

#### Thebox

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #10 on: 08/06/2016 07:00:07 »
Hmm, a vanishing post never mind a vanishing point.   You know you have lost the discussion so again move the post and ignore, how ignorant of science.

#### Colin2B

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##### Re: How long would a piece of string have to be before it ''vanished''?
« Reply #11 on: 08/06/2016 10:45:08 »