# The Naked Scientists Forum

### Author Topic: What radius to a human observer does light fail to give an observation?  (Read 5893 times)

#### evan_au

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #50 on: 16/02/2016 11:09:11 »
Quote from: TheBox
You say he will always appear as a point source of photons, what do you mean by will always and point source ?
Like your headlamp on a dark night, your fishing friend can still see the light source (perhaps 2-20mm across) even though he cannot see you.
1. This assumes that the light source is bright enough to be above the random nerve activity in your eyeballs. I have heard that this requires at least 2 photons to strike the same rod cell in your retina within a fairly short time interval.
2. It also requires that the light source be much brighter than the surroundings (ie very dark night, and a very bright light).

But given these conditions, your dim friend can still see your lamp, even though its apparent size might be far less than the resolving power of the human eye. It has become a "point source".

Stars are also "point sources", but we can still see them; the reason they appear to twinkle is that specks of dust in the upper atmosphere get between the star and your eyeball (plus heat haze in the atmosphere diffracts it a bit).

#### Thebox

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #51 on: 16/02/2016 11:10:11 »

Let me explain this diagram

Observer A and Observer B are at a central point together, Observer B travels away from observer A who is relatively stationary.  Both observers can tell neither who is moving while at a constant speed , both observers always remain a linearity no matter what the velocity. Both observers equally contract following the lorentz  transformations and relative to each observation to a length of relative a zero point.

Showing that not only does light fail to give an observation at distance, but also Lorentz contraction causes the object to fail to give an observation at distance.

#### Thebox

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #52 on: 16/02/2016 11:11:46 »
Quote from: TheBox
You say he will always appear as a point source of photons, what do you mean by will always and point source ?
Like your headlamp on a dark night, your fishing friend can still see the light source (perhaps 2-20mm across) even though he cannot see you.
1. This assumes that the light source is bright enough to be above the random nerve activity in your eyeballs. I have heard that this requires at least 2 photons to strike the same rod cell in your retina within a fairly short time interval.
2. It also requires that the light source be much brighter than the surroundings (ie very dark night, and a very bright light).

But given these conditions, your dim friend can still see your lamp, even though its apparent size might be far less than the resolving power of the human eye. It has become a "point source".

Stars are also "point sources", but we can still see them; the reason they appear to twinkle is that specks of dust in the upper atmosphere get between the star and your eyeball (plus heat haze in the atmosphere diffracts it a bit).

Yes stars are point sources, what happens to the star point source when they continue down the railway track?  0 diameter I believe?

Which brings me to light limit and red shift, how do we know redshift is not the light limit and stretching of the limit, i.e the furthest away thing we can observe is at a position of its maximum stretch, so hence the light is weaker so we observe redshift, a bit like observing a rainbow effect in space?

For all those who may not understand what we are discussing is this -

feature=youtu.be

We are considering either objects perceived observation of each other and the perceived contraction of each other as in Lorentz transformations relative to the inverse square law of light  and spherical radius of the affect on observation.

« Last Edit: 16/02/2016 13:45:42 by Thebox »

#### alancalverd

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #53 on: 16/02/2016 13:19:08 »

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

Quote
Point source means bugger all.
or, more politely, of negligible or infinitesimal dimension - again, correct.

You see, we do speak the same language, but you just refuse to admit it!

#### Thebox

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #54 on: 16/02/2016 13:41:22 »

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

Quote
Point source means bugger all.
or, more politely, of negligible or infinitesimal dimension - again, correct.

You see, we do speak the same language, but you just refuse to admit it!

Well sometimes my thoughts are before I know anything about the knowledge or what the knowledge is called, I have only just discovered Lorentz contraction and a full read me of relativity and special relativity, I had not read it before.   My ideas are from my own thinking and thinking about things but yes I agree we are starting to speak the same language the more I learn from discussion.

I think we should define it for discussion purpose,   as a ''zero point source'' to represent that not even a point of visual existence, exists, identifying relative ''empty''distance, then define point sources as objects to define spacial lengths between point sources.  Also I feel to express that all objects are in motion relative to each other but are also moving relative to the stationary observed space?

Also to consider in the discussion the ''expansion'', is it the length between point sources that is changing rather than the distance of zero point sources?

It is a part of the question, discussing radius and the affect observed .

« Last Edit: 16/02/2016 14:00:27 by Thebox »

#### evan_au

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #55 on: 16/02/2016 16:33:04 »
Quote from: TheBox
how do we know redshift is not the light limit and stretching of the limit, i.e the furthest away thing we can observe is at a position of its maximum stretch?
I think that you might be describing the concept of the observable universe?

There is a certain distance where, even if there is matter beyond it, we would not be able to observe it, due to the expansion of the
universe. Any light would have been red-shifted away to oblivion.

Quote from: Wikipedia
It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×1026 metres or 5.5×1023 miles)

#### Thebox

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##### Re: What radius to a human observer does light fail to give an observation?
« Reply #56 on: 16/02/2016 16:40:22 »
Quote from: TheBox
how do we know redshift is not the light limit and stretching of the limit, i.e the furthest away thing we can observe is at a position of its maximum stretch?
I think that you might be describing the concept of the observable universe?

There is a certain distance where, even if there is matter beyond it, we would not be able to observe it, due to the expansion of the
universe. Any light would have been red-shifted away to oblivion.

Quote from: Wikipedia
It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×1026 metres or 5.5×1023 miles)

Thank you, yes I refer to the  observable Universe , the observable Universe not being the size of space itself, but ''93 billion light-years'' being a length of space between two observers that takes ''time'' to travel at c.

If you travelled 93 billion ly, you can be assured there after is another 93 bly

« Last Edit: 16/02/2016 16:47:26 by Thebox »

#### The Naked Scientists Forum

##### Re: What radius to a human observer does light fail to give an observation?
« Reply #56 on: 16/02/2016 16:40:22 »