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From: thejohnlreed on 1 Aug 2010 19:57

I am not picking on you PD but you brought up the subject of "light"
via "photons" in response to my post on mass and gravity. I had
expected you to cite Roemer at some point but no further response from
you occured. So this is where it was left and on the end I have
included Roemer:

PD
> This is wrong. We do not "see" an object directly. We see light
> (electromagnetic radiation) emitted or scattered from the object. Our
> eyes are sensitive to electromagnetic radiation within a certain
> range
> of frequencies.

> jr writes>
> Yes I know. There is the band we call visible light. But our eyes see
> objects illuminated at these frequencies. We do not see the actual
> naked EMR. Look at the night sky. EMR gushing every which a way. We
> only see illuminated objects. Consider the high school physics lab
> demonstration where the beam of light passes through the evacuated
> bell jar and we see the point of entry and exit but the light beam is
> broken to our vision inside the evacuated jar.


This is exactly what I was telling you. It's the reason the sky is
blue, by the way.
The light is passing from left to right, not on a path that would
intercept your pupil or your retina.

jr writes> This appears to be a bit too idealized. Surely some of the
light makes it through straight on, if only as a result of scattering.
The sky looks large and significant from the surface of the earth,
where it is merely a thin and thinning layer of gas when viewed from
space. I think that where we can theorize neutrinos small enough to
pass through the earth without being scattered, certainly a bit of
light can pass through a thin layer of gas.

But the glass *scatters* some of
that light sideways so that some of the light does come toward your
eyes.

jr writes>
Don't we require some objective measure confirming this? That light
has to reach our eyes for us to see what it illuminates. If we are in
a dark cave and round a corner of the cave and see in the distance a
light. Or in a tunnel. Where the light casts precise shadows that are
headed away from the tunnel or cave opening. You say that the function
of our vision depends on the reflection or scattering of light
(Photons) down that tunnel to our eyes even when the shadow of the
tree near the opening is near its maximum projected size in the
opposing direction. So not that unlike Rutherford's amazement, we have
photons traveling straight down the tunnel perfectly avoiding its
sides to arrive at our eyes revealing a perfect shape of the hole the
scattered opposing light enters. Well we can stretch our quantities
as far as required to support our prevailing ignorance. And this is an
area where spandex rules.

The same is true for blowing smoke in the path of a laser. The
smoke particles divert some of the light toward your eyes.
Without the illumination (the incidence of light), you cannot see
objects.

jr writes>
This is good information. Are you confirming here that we also cannot
see the laser light as it passes through the evacuated bell jar?

You see this (no pun here) as invisible little photons carrying
information that passes through our binocular eyes into our brains.
But you see it also as something we see at a distance through
binocular vision. If the eye had to wait on photons containing old
information what is the property of these traveling photons that
conveys depth of vision. If we cannot see through the distance, how is
it the physical photons know that and compensate for that utilizing
our binocular eyes to make it appear so?

The only reason you can see objects is because light incident
on those objects caroms off the object and some of it enters your
eye.

jr writes> I have read just about every publication on science I have
been exposed to. I have learned that when author's say "The only
reason..." or some similar directing phrase they are seldom correct,
if ever. So when I shine a light on someone I must wait for the light
to reflect back to me to see what I have illuminated. Where what I
have illuminated must wait for that light to return to its source to
be seen.

> Our eyes are sensitive
> to illuminated objects at certain frequencies but we require the
> illuminated object. Which is effective in terms of natural selection.
> Now I know that you will protest this because you believe that our
> brains react to naked EMR (somehow) and build old historical images
> from that old arriving EMR.

Yes, indeed. This light propagation time is *measurable*.

jr writes>
I really wanted to do the gravity thing and then the atomic structure
thing and then the light thing, but when they are all entwined and
loosely supporting each other I suppose my path is directed
accordingly.

I have at my side say, an emitter and a receiver of "light". I emit a
signal aimed at a target that reflects that signal back to me where my
receiver detects its return. An interval has passed which I record and
from that I can measure the speed and/or distance etc. I acquire a
speed for "light" and because I believe that my binocular eyes must
wait for photons to arrive I calculate the transmission of information
correctly wrt my mechanical detection and submission aparatus, and
because my eyes depend on the same transmission principle, I see the
universe as a fairy might cast it upon me to see.

> Like a geiger counter or other passive
> receptive device that relies on arriving or reflecting EMR rather than
> a capability to respond directly to a distance object's frequency.
> The Fizeau experiment sets up such a synchronous frequency response.
> But it is a matter of interpretation.
> You know that the eye brain connection is mind boggling in its
> complexity. Our eyes see through space. If our eyes had to wait for
> old photons (Einstein's billiard balls) to deliver a historical image,
> that no longer exists, what is the purpose of the capability to see
> through space?

It doesn't HAVE a purpose to see through space. The purpose is to see
things in the immediate vicinity (for our survival), where the
propagation time is so small it doesn't matter.

> I guess it is on that point we disagree here. You think
> the eye is passive and must receive photons that carry old images in
> some kind of electromagnetic code and I consider that notion quite
> absurd.

But WHY do you think it is absurd? Because it offends you that we
cannot see distant objects as they are right now?

jr writes>
I had the good fortune of spending my 2nd 3rd and 4th grades in
Japan. Japan is one of the places on Earth where the Rubaiyat
delivers a powerful message. The night sky was pristine and awesome to
a 3rd grader. And that 3rd grader had been told that all those stars
up there were just a figment of his imagination. I was like the child
that said: "but Mama the emperor is naked", only I said nothing. I
knew I had a job to do, I just had no clue as to the effort it would
require.
Have a good time PD
jr

jr writes>
I can explain Roemer as follows. When an object is occluded from our
vision by passing behind an object, we will no longer see it
immediately even though its trailing EMR may still be heading our way.
On the other hand, when an object returns to our line of site from
passing behind an object, we will not see that object again until its
EMR has reached our eyes. Once that EMR has arrived we will see the
distant object in realtime because our eyes detect the frequency of
light.

The same principle applies to stars. If a new star is born 1 light
year away it may take a year for its light to reach us but once it has
arrived we will see the star in real time.

So if you are going to discontinue the discussion I at least want to
include the above. I have other lesser arguments for Roemer if this is
proven inadequate.
Have a good time PD
jr
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