Driving Through a Rainbow: The Truth Behind This Phenomenon

[DrZoidberg]

What determines the apparent distance of the rainbow?

 

[Martha]

SophieCentaur said:

"Is there a magenta ring in a rainbow? Perhaps in your world but not in mine."

Yes, apparently we are from different worlds.

Because in my world magenta (and purple) are very important and they ARE present in a rainbow.

"A warm magenta is barely visible on top of the red on a strong rainbow, it's stronger at the cool bottom of the rainbow. Also, yellow will appear again under the magenta on a strong rainbow."

http://realcolorwheel.com/rainbow.htm

If you need "visual" proof:

From “The mathematical colors of the rainbow using HSL” (Hue-Saturation-Luminosity)

Under these words, “A slice was taken through the original image and rotated. The slice at 400%”

See an actual picture of a rainbow in the link that follows

and note the explanation beneath which says: “Of interest in the image is the clear existence of colors noted above, including the equiangular colors such as cyan.

Leaving out "blends" such as red-orange and yellow-orange,

one can identify the presence of red, orange, yellow, green, cyan, blue,

purple, and magenta tones”


http://www.comfsm.fm/~dleeling/cis/hsl_rainbow.html

BTW...Pohnpei is an island. It is one of FOUR of the states of the Federated States of Micronesia. The picture of the rainbow was taken there.

Note the above link indicates a mathematically proposed eight color rainbow. ROYGCB

plus purple and magenta.

Given there are 8 particles in gluons that transmit the strong nuclear force from quark to quark containing 2 color charges, this number of "colors"/ "color particles" maybe indeed accurate.

"There are eight remaining *independent color states*, which correspond to the "eight types" or "eight colors" of gluons." Wikipedia

“Gluons differ from each other only in color, usually expressed as R, G, B, anti-R, anti-G, and anti-B. One would think that three by three possibilities would create nine gluons, but the math of the theory rules on combination out.”

http://washparkprophet.blogspot.com/2010/06/gluon-mass-qcd-developments-and-more.html

Yes, the author is not a scientist; he is a lawyer. Like me, he apparently has a tremendous interest in physics too.

"Color-octet scalars naturally appear in grand unified theories."

"The role of the ***color-octet mechanism*** in hadronic production of quarkonium (a flavorless meson whose constituents are a quark and its own antiquark)."

Leaving 2 "colors" out (magenta and purple) when discussing the math/geometry of a rainbow (which is actually circular when viewed from above) is a mistake, IMO.

Especially magenta which functions as a primary subtractive "color" and secondary additive color. It is very unique.

But I do "get it" i.e.,

"...digital imaging electronics vary greatly from that of the human eye."


Just because you can't see it, doesn't mean it isn't there and should thus not be factored in.

I am going to take this discussion to a different level for those who are interested/curious about a much a "bigger picture".

For those only interested in physics i.e., a "micro" view, and not the part it plays in the UNIVERSE, a "macro" view, you might want to stop reading now.

Just as a rainbow is "visual proof" of an endless existence (the rain WILL stop and sunlight will reappear), there is also "visual proof" in black holes which appear to look like laminin i.e., the "glue" that holds our cells together (a protein with alpha, beta and gamma chains).

This is an actual PHOTO from NASA:

An image of the core of the Whirlpool galaxy M51 (NGC 5149) taken by the Hubble Space Telescope. It shows an immense ring of dust and gas that is thought to surround and

hide a giant black hole in the center of the galaxy.

http://www.scienceclarified.com/Bi-Ca/Black-Hole.html

And yes, I am aware that black holes feed off of nearby stars and that black holes themselves create new stars...some of which ultimately form their own black holes.

And I am aware of the balance of clockwise and counter clockwise galaxies in our "observed universe". It is quite beautiful.

While you may chose to look this way (> (and that's okay and needed!)...

I'm trying to see this: (><) i.e. the micro and the macro view. How did we get from ONE "particle" to an entire never-ending universe?

I was studying light and sound (to heal) when I read in Discover magazine that Kent State math students (via massive computer help) had found "God's algorthim" to be 20. In other words, in 20 "moves" He created order out of chaos. This "number" is NOT God, it was His solution. That is astounding given the number of possibilities.

Using a "clock" drawing (time), I began to correlate numbers with their corresponding colors and charges and even to their corresponding elements. What I ended up with is a pattern that even surprised me. It directly matches an ancient Chinese drawing to explain "evolution".

Do you know 432Hz = the "frequency of light"? Square it. It correlates to "perfect A" (musically).

Do you know that SSS is the signal for a "Proton Flare"? Do you know what it represents translated to Morse Code? ... ... ...

Do you know that a tiny pulse of blue mimicks a computer's logic when it *carries* digital "ONE"?

Do you know in the Phoenician alphabet #1 = aleph which represents an "ox" and the last letter (#23) is Tau/tav and it represents a Tree? In olden times we used an ox to plow the earth. In doing so, we kept our eye on a distant Tree in order to plow a straight line.

There is so much significance/meaning to symbols that ancient civilization have left for us!

Another example:

^ = alpha/heaven/man
v = omega/earth/woman (think virgin)

When you use Greek symbols, think about their significance and be aware of the various forms they take.

Have you seen Carl Sagan explain the FOURth dimension (on YouTube)? It is FASCINATING. I wonder if his choice to use an apple was intentional? ;-)

There are two quotes that have driven my research and my attempt to understand how this all could be possible.

1. Gaudi (architect whose designs mimicked nature and are incredibly strong) said: "The straight line belongs to man. The curved line belongs to God."

2. "For behold, My imaged universe is ***mirrored*** to infinity;
it is repeated to the endless end;
yet there are but multiples of three in all My universe.
And again I say to thee,
***two of those very three are naught ***but My imaginings,

for My Trinity is but One.

(TSOL p. 138)

(TSOL refers to the “Secret of Light” by Walter Russell)

I DO believe in God and I DO believe in an Endless Universe. I DO believe that evolution/we DID have an "origin" and that He was/is the origin.

However, I also believe that evolution -> steady state universe.

It is very possible that our "Endless Universe" is that suggested by Paul Steinhardt i.e., two interconnected Klein bottle (shapes). Paul Steinhardt is a professor of physics at Princeton. I have his book on order.

It is my hope that someday science will prove religion is truth, not fiction. I hope that someday everyone will know that indeed God does exist and not just take His existence on "faith" alone.

Find the "God particle". It IS there and it IS within us.

Years ago, I was a maternity nurse in labor and delivery. Birth, life, is awesome.

Okay...I've probably overstayed my welcome in your world SophieCentaur. Bye.

 

[sophiecentaur]

A long and colourful reply! I LURVE Gaudi. I could end my days in Barcelona with pleasure.
Yes, the electronic analysis of light is a poor substitute for the real thing but, still, colour TV does a pretty damned good job,considering.

The "Magenta" issue.
This is a language problem. I thought that you were referring to the 'accepted' term Magenta. Magenta is not a spectral colour. The 'purple-ish" colours which you can see in a rainbow are spectral Indigo and Violet. Magenta is a specific, saturated, colour that is a mixture of Red and `blue primaries. In RGB terms, it is R=1,G=0,B=1. In colour-subtractive systems, magenta is 'Minus Green' There is a lot of confusion about 'formal' colourimetry terms and this particular region of colour is particularly confusing because it involves mainly the short wavelength receptors of the eye and is, subjectively, a bit uncertain. (When did anyone actually see indigo on TV?)

 

[sophiecentaur]

I meant: Move at 42° to the sun rays, which are almost horizontal. I see nothing that would stop me from doing so.

You can move to the left or to the right. BUT, the line from the Sun, through your eye, will also shift. That moves the whole cone at the same time. You will still see the rainbow at the same angle to that new line. i.e the cone moves to the left or right by just the same amount as you moved.

Is this not the most elementary bit of geometry you could ever think of?

 

[Integral]

What determines the apparent distance of the rainbow?

A combination of the number of raindrops and the intensity of the sun. Once while trying to drive in a very intense thundershower I observed the end of the rainbow to be on my hood.

The amount of light from each raindrop should be pretty constant, so the more raindrops in the cone, the more light returned. Where the rainbow appears along the cone will be determined by the amount of light needed by the eye to resolve the colors. Anytime light changes direction your brain assumes that the source of the light lies somewhere along the projection of a line from your eye to the bend (read raindrop).

 

[sophiecentaur]

It's interesting (but not surprising, I suppose, because it correlates with the weather) that 'strange' experiences with rainbows seem always to be associated with driving. If the observer is actually driving at the time then the rainbow is (hopefully) not getting the full attention of that driver. This may add to the confusion as to what is actually being seen. Also, the drops / smears on the windscreen can affect what is obesrved.

The straightforward model of a rainbow is that light of one colour that is seen by the observer is produced at the same angle from all drops (near or distant). If the observer moves from side to side (or used binocular vision) this must be interpreted as if the image is at infinity. On the face of it, there is no way of locating a 'position' for the bow as being other than at infinity, if that's the only evidence available to the observer. This is not a very satisfactory conclusion for the brain to come to; we want things to be in a more definite position so our brains look for an improved location to place it in our perception space.
A rainbow is a very fuzzy object, for a start, so other clues are grabbed at. We are not disturbed by the minuscule de-focussing effect because we are focussed at nearer objects and so we 'place it' near us. We are not used to transparent objects (during our evolution, particularly) so, whenever we see a solid object in line with part of the rainbow (hill / wall / road / car bonnet) we 'reason' that the rainbow image must be in front of that object - even though there is strong parallax information which tells us otherwise. We just say that the rainbow moves. Contrast this with our assessment of what we see when observing distant mountains. We see exactly the same apparent movement but we don't believe they actually move as we drive through the countryside.

In the case of a garden spray, the spray itself is very visible and so we, again, are likely to 'see' the bow as being right next to us.

One thing that is pretty unarguable, however, is the direction that the bow appears with respect to the line of the Sun through our eye. Whatever else people may imagine they have seen, they cannot have moved to one side or the other of the rainbow, because that 'cone' we talk of, moves to prevent it. It always stays symmetrical, whether or not there is full or partial cover of the visual field by suitable rain drops and is locked to that axial line.

@A.T.
I think the following definition of an Image, one of several, taken from Websters, is reasonable:
"the optical counterpart of an object produced by an optical device (as a lens or mirror) or an electronic device."
(Nothing is implied here about quality or position.)

 

[A.T.]

You can move to the left or to the right. BUT, the line from the Sun, through your eye, will also shift. That moves the whole cone at the same time. You will still see the rainbow at the same angle to that new line. i.e the cone moves to the left or right by just the same amount as you moved.

Is this not the most elementary bit of geometry you could ever think of?

Sure, and what is your point here again?

 

[sophiecentaur]

My point is that, contrary to what you have written, you can't drive to the base of a rainbow. It isn't there.

 

[A.T.]

My point is that, contrary to what you have written, you can't drive to the base of a rainbow. It isn't there.

By "driving trough it" I meant driving into the rain, so you don't see the near boundary of the arc on the ground coming towards you anymore. This will create an effect close to what Neveos described.

But I thought you were trying to explain this here:

You drive at the base and it just moves to one side to avoid you.

I still don't know why this would happen, if the sun is quite low over the horizon, and you drive directly towards the arcs base (holding 42° to the anti-solar point).

 

[sophiecentaur]

So, when you steer (left, say) towards the 'base' (that's where the arc ends at the ground?), do you not realize that the 'base' just moves over to the left so that it remains at the same angle to the axis of the cone because the axis is still a line from the Sun through your head. You don't just leave the original axis behind. It's bolted to you.

As I have frequently written. You need to draw this out if you want to understand it. Your mental picture is just flawed.

 

[Martha]

Touching rainbows...the why not:

http://www.wonderquest.com/touching-rainbows.htm

It is not a good idea to look into the sun directly (= eye damage), but we CAN enjoy the "distorted" image of the sun. *Order* is a nice thing to observe!

I wish my closet looked like this (it doesn't!):

http://www.apartmenttherapy.com/la/inspiration/the-color-coded-closet-041848

Organizing by colors brings excitement and *meaning*...

 

[sophiecentaur]

Touching rainbows...the why not:

Long arms? haha

 

[daveyjones97]

i didnt have time to read every post in this thread but wanted to share my experience. several years ago i was on the m25 (large very busy freeway in england) in light rain with the sun to my right when the traffic slowed, then the light seemed to take on a red,orange, yellow etc tinge about as quick as you could say it. (50ish mph) stopping in the right spot was totally out of the question even though i badly wanted to. the tint in light was about the difference between low sun on a fine autumn day and blueish light on a bright overcast day. i don't think I am nuts and if i hadnt experienced this i wouldn't believe it either but its the truth, no exagerations.

 

[sophiecentaur]

That shows the difference between a subjective experience and an objective measurement.
A great and enjoyable thing to see, in the same way that a movie on a cinema screen or a TV display can give you an impression of something happening. Bambi's mother doesn't really die but you see it happen on the film, drawn frame-by-drawn frame. Light behaves consistently in all everyday circumstances. The Physics can't be wrong.

 

[lookbehindu]

I could even give an explanation of how a hologram works, with diagrams and how an image can be seen.

Sorry to bring this thread back from the dead but could you?

I tried PM'ing you but it says you don't accept 'em.

Do you have any helpful links (excluding wikipedia and the obvious other generic informational links) to help me understand the topic better. Also if you know of any video showing someone creating or viewing a hologram or a video explanation of how they work/ how they are made.

Thus far this video has been the best video of a hologram I've found and it's truly amazing. http://vimeo.com/8078523.

Thanks

 

[sophiecentaur]

Hi - you have put me on the spot!

Remember that a hologram is just a diffraction pattern, made by combining the light reflected from an object with a reference beam. It is easiest to describe the early types of hologram which are 'transmission holograms'. This is arranged using half silvered mirrors which split laser light so that one part illuminates the object and the other acts as reference beam (there are loads of diagrams around which show this basic setup). This will produce a very complicated diffraction (interference) pattern between the two components of the laser light but any area of the pattern can be recorded on a piece of film placed there. In practice, of course, you use clever optics to get a bright enough image where you want to put the film so that you get adequate exposure. The interference pattern is very fine and you need a long exposure [Edit:and] to avoid getting a blurred image on your film (the hologram). When you shine light on the developed piece of film, you will see a diffraction pattern, caused by the hologram, which will be the same as the original object, as viewed from that direction. Different areas of the hologram contain information about the view from different directions - hence the 3D appearance. But you don't get something for nothing. The resolution of the hologram is limited so that limits the actual quantity of information that can be stored. It is totally magic, though.

The basic principle is much the same as the two slits experiment - one slit can be looked upon as the object and the other as the reference. The interference pattern can be recorded on film and, if you illuminate the film from behind and look through this pattern, you will actually see two slits. The simplest hologram you could imagine. Another simple precursor of the hologram is the zone plate, which is like a photograph of the Newton's rings you get with a convex surface resting against a plane surface. That zone plate will produce a 'focussed' point image when a wide beam of light falls on it - just like a convex lens will do.

The reason that holograms work is that the diffraction pattern is a Fourier transform of the object and the Fourier transform of the hologram looks like the original object. This wiki link discusses how holograms can be constructed without using light beams and it may help you.

 

[Darwin123]

Is it physically possible to drive through a rainbow? Why or why not?

I agree with most of the replies. You can't drive through a rainbow because the rainbow is not an image. The light rays of a rainbow at anyone wavelength are parallel. They don't meet anywhere. So the rainbow will always be far away.

So what you described couldn't be "driving through a rainbow". However, there are other effects in atmospheric optics that could produce colored illumination. Almost all of them would involve parallel light rays, however. So the source of illumination has to appear very far away.

What you described couldn’t be a true rainbow. However, there are many phenomena in atmospheric optics which result in a separation of colors.

I suggest that what you saw may be related to crepuscular rays and anticrepuscular rays. Sometimes, they even appear simultaneously with rainbows!

I could also be sundogs, where the sun was hidden behind a mountain or cloud. Sundogs can be very bright. They are multicolored.

Here are some links, some of which have pictures. Is there anything like this?


http://en.wikipedia.org/wiki/Crepuscular_rays
“Crepuscular rays ( /krɨˈpʌskjələr/) in atmospheric optics, are rays of sunlight that appear to radiate from a single point in the sky, specifically, where the sun is. These rays, which stream through gaps in clouds (particularly stratocumulus) or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. The name comes from their frequent occurrences during crepuscular hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin word "crepusculum", meaning twilight.
…
Crepuscular rays are usually red or yellow in appearance because the path through the atmosphere at sunrise and sunset pass through up to 40 times as much air as rays from a high midday sun. Particles in the air scatter short wavelength light (blue and green) through Rayleigh scattering much more strongly than longer wavelength yellow and red light.”

http://www.atoptics.co.uk/atoptics/antray1d.htm
Sometimes when there is a rainbow, anti-crepuscular rays can look like the spokes of a wheel with the bow as its rim. The rays and rainbow share the same centre - the antisolar point.


http://en.wikipedia.org/wiki/Atmospheric_optics#Fata_Morgana
Atmospheric optics deals with how the unique optical properties of the Earth's atmosphere cause a wide range of spectacular optical phenomena. The blue color of the sky is a direct result of Rayleigh scattering which redirects higher frequency (blue) sunlight back into the field of view of the observer. Because blue light is scattered more easily than red light, the sun takes on a reddish hue when it is observed through a thick atmosphere, as during a sunrise or sunset. Additional particulate matter in the sky can scatter different colors at different angles creating colorful glowing skies at dusk and dawn. Scattering off of ice crystals and other particles in the atmosphere are responsible for halos, afterglows, coronas, rays of sunlight, and sun dogs. The variation in these kinds of phenomena is due to different particle sizes and geometries.

 

[Feodalherren]

SophieCentaur said:

"Is there a magenta ring in a rainbow? Perhaps in your world but not in mine."

Yes, apparently we are from different worlds.

Because in my world magenta (and purple) are very important and they ARE present in a rainbow.

"A warm magenta is barely visible on top of the red on a strong rainbow, it's stronger at the cool bottom of the rainbow. Also, yellow will appear again under the magenta on a strong rainbow."

http://realcolorwheel.com/rainbow.htm

If you need "visual" proof:

From “The mathematical colors of the rainbow using HSL” (Hue-Saturation-Luminosity)

Under these words, “A slice was taken through the original image and rotated. The slice at 400%”

See an actual picture of a rainbow in the link that follows

and note the explanation beneath which says: “Of interest in the image is the clear existence of colors noted above, including the equiangular colors such as cyan.

Leaving out "blends" such as red-orange and yellow-orange,

one can identify the presence of red, orange, yellow, green, cyan, blue,

purple, and magenta tones”


http://www.comfsm.fm/~dleeling/cis/hsl_rainbow.html

BTW...Pohnpei is an island. It is one of FOUR of the states of the Federated States of Micronesia. The picture of the rainbow was taken there.

Note the above link indicates a mathematically proposed eight color rainbow. ROYGCB

plus purple and magenta.

Given there are 8 particles in gluons that transmit the strong nuclear force from quark to quark containing 2 color charges, this number of "colors"/ "color particles" maybe indeed accurate.

"There are eight remaining *independent color states*, which correspond to the "eight types" or "eight colors" of gluons." Wikipedia

“Gluons differ from each other only in color, usually expressed as R, G, B, anti-R, anti-G, and anti-B. One would think that three by three possibilities would create nine gluons, but the math of the theory rules on combination out.”

http://washparkprophet.blogspot.com/2010/06/gluon-mass-qcd-developments-and-more.html

Yes, the author is not a scientist; he is a lawyer. Like me, he apparently has a tremendous interest in physics too.

"Color-octet scalars naturally appear in grand unified theories."

"The role of the ***color-octet mechanism*** in hadronic production of quarkonium (a flavorless meson whose constituents are a quark and its own antiquark)."

Leaving 2 "colors" out (magenta and purple) when discussing the math/geometry of a rainbow (which is actually circular when viewed from above) is a mistake, IMO.

Especially magenta which functions as a primary subtractive "color" and secondary additive color. It is very unique.

But I do "get it" i.e.,

"...digital imaging electronics vary greatly from that of the human eye."


Just because you can't see it, doesn't mean it isn't there and should thus not be factored in.

I am going to take this discussion to a different level for those who are interested/curious about a much a "bigger picture".

For those only interested in physics i.e., a "micro" view, and not the part it plays in the UNIVERSE, a "macro" view, you might want to stop reading now.

Just as a rainbow is "visual proof" of an endless existence (the rain WILL stop and sunlight will reappear), there is also "visual proof" in black holes which appear to look like laminin i.e., the "glue" that holds our cells together (a protein with alpha, beta and gamma chains).

This is an actual PHOTO from NASA:

An image of the core of the Whirlpool galaxy M51 (NGC 5149) taken by the Hubble Space Telescope. It shows an immense ring of dust and gas that is thought to surround and

hide a giant black hole in the center of the galaxy.

http://www.scienceclarified.com/Bi-Ca/Black-Hole.html

And yes, I am aware that black holes feed off of nearby stars and that black holes themselves create new stars...some of which ultimately form their own black holes.

And I am aware of the balance of clockwise and counter clockwise galaxies in our "observed universe". It is quite beautiful.

While you may chose to look this way (> (and that's okay and needed!)...

I'm trying to see this: (><) i.e. the micro and the macro view. How did we get from ONE "particle" to an entire never-ending universe?

I was studying light and sound (to heal) when I read in Discover magazine that Kent State math students (via massive computer help) had found "God's algorthim" to be 20. In other words, in 20 "moves" He created order out of chaos. This "number" is NOT God, it was His solution. That is astounding given the number of possibilities.

Using a "clock" drawing (time), I began to correlate numbers with their corresponding colors and charges and even to their corresponding elements. What I ended up with is a pattern that even surprised me. It directly matches an ancient Chinese drawing to explain "evolution".

Do you know 432Hz = the "frequency of light"? Square it. It correlates to "perfect A" (musically).

Do you know that SSS is the signal for a "Proton Flare"? Do you know what it represents translated to Morse Code? ... ... ...

Do you know that a tiny pulse of blue mimicks a computer's logic when it *carries* digital "ONE"?

Do you know in the Phoenician alphabet #1 = aleph which represents an "ox" and the last letter (#23) is Tau/tav and it represents a Tree? In olden times we used an ox to plow the earth. In doing so, we kept our eye on a distant Tree in order to plow a straight line.

There is so much significance/meaning to symbols that ancient civilization have left for us!

Another example:

^ = alpha/heaven/man
v = omega/earth/woman (think virgin)

When you use Greek symbols, think about their significance and be aware of the various forms they take.

Have you seen Carl Sagan explain the FOURth dimension (on YouTube)? It is FASCINATING. I wonder if his choice to use an apple was intentional? ;-)

There are two quotes that have driven my research and my attempt to understand how this all could be possible.

1. Gaudi (architect whose designs mimicked nature and are incredibly strong) said: "The straight line belongs to man. The curved line belongs to God."

2. "For behold, My imaged universe is ***mirrored*** to infinity;
it is repeated to the endless end;
yet there are but multiples of three in all My universe.
And again I say to thee,
***two of those very three are naught ***but My imaginings,

for My Trinity is but One.

(TSOL p. 138)

(TSOL refers to the “Secret of Light” by Walter Russell)

I DO believe in God and I DO believe in an Endless Universe. I DO believe that evolution/we DID have an "origin" and that He was/is the origin.

However, I also believe that evolution -> steady state universe.

It is very possible that our "Endless Universe" is that suggested by Paul Steinhardt i.e., two interconnected Klein bottle (shapes). Paul Steinhardt is a professor of physics at Princeton. I have his book on order.

It is my hope that someday science will prove religion is truth, not fiction. I hope that someday everyone will know that indeed God does exist and not just take His existence on "faith" alone.

Find the "God particle". It IS there and it IS within us.

Years ago, I was a maternity nurse in labor and delivery. Birth, life, is awesome.

Okay...I've probably overstayed my welcome in your world SophieCentaur. Bye.

What the hell just happened?!

 

[jtbell]

What the hell just happened?!

It actually happened more than a year ago.

 

[sophiecentaur]

What the hell just happened?!

Wow. I didn't read that, first time round. Goes on a bit, doesn't it?
Someone clearly doesn't know the difference between spectral Indigo and Violet (which your display can't show you) and the colour Magenta (as defined in all colour systems - additive and subtractive) - which is either R+B or -Y.

 

[lookbehindu]

Hi - you have put me on the spot!

Remember that a hologram is just a diffraction pattern, made by combining the light reflected from an object with a reference beam. It is easiest to describe the early types of hologram which are 'transmission holograms'. This is arranged using half silvered mirrors which split laser light so that one part illuminates the object and the other acts as reference beam (there are loads of diagrams around which show this basic setup). This will produce a very complicated diffraction (interference) pattern between the two components of the laser light but any area of the pattern can be recorded on a piece of film placed there. In practice, of course, you use clever optics to get a bright enough image where you want to put the film so that you get adequate exposure. The interference pattern is very fine and you need a long exposure [Edit:and] to avoid getting a blurred image on your film (the hologram). When you shine light on the developed piece of film, you will see a diffraction pattern, caused by the hologram, which will be the same as the original object, as viewed from that direction. Different areas of the hologram contain information about the view from different directions - hence the 3D appearance. But you don't get something for nothing. The resolution of the hologram is limited so that limits the actual quantity of information that can be stored. It is totally magic, though.

The basic principle is much the same as the two slits experiment - one slit can be looked upon as the object and the other as the reference. The interference pattern can be recorded on film and, if you illuminate the film from behind and look through this pattern, you will actually see two slits. The simplest hologram you could imagine. Another simple precursor of the hologram is the zone plate, which is like a photograph of the Newton's rings you get with a convex surface resting against a plane surface. That zone plate will produce a 'focussed' point image when a wide beam of light falls on it - just like a convex lens will do.

The reason that holograms work is that the diffraction pattern is a Fourier transform of the object and the Fourier transform of the hologram looks like the original object. This wiki link discusses how holograms can be constructed without using light beams and it may help you.

Once the reference and object beam reach the plate haven't they undergone spreading (similar to incoherent light). Also when both beams reach the plate aren't they not in phase anymore? So what was the point of keeping them in phase until that point? Also I'm having a hard time understanding the divisibility principle (how can a tiny piece contain the entire image minus perspectives).

 

[sophiecentaur]

Once the reference and object beam reach the plate haven't they undergone spreading (similar to incoherent light). Also when both beams reach the plate aren't they not in phase anymore? So what was the point of keeping them in phase until that point? Also I'm having a hard time understanding the divisibility principle (how can a tiny piece contain the entire image minus perspectives).

That is the very same question I asked my lecturer at University in 1966! (Nothing is new under the Sun ) He was actually flummoxed by the question and I only came to terms with the problem years later, when I approached it again.

To answer your main question, the reason that you get a diffraction pattern is that the various light paths through the system are all different - their relative phases, where they are detected (the film) are different from place to place on the film. That's why you get the light / dark fringes of the hologram. For a simple two slits, the effect is easily explained (in wiki and all over) - at different angles, the phase relation between light from the two slits is different, which gives you the fringes. You can do the two slits with almost any old light source and get fringes over a limited range of angles. To work well, you need good coherence so that, even at large angles, the different wave trains that make up the light source are still long enough for self interference to occur. (For a pair of radio signals, for instance, the coherence is almost perfect and the interference is more or less textbook and a laser is about as good)

For a hologram to work, the requirement is even more strict because you need a broad, coherent wavefront for your reference and a broad, coherent wavefront hitting the object. The resultant (max / min / intermediate value) at any single point on the film is due to light reflected from every point on that side of the object, interfering with the reference beam and with itself (of course). To one side of that point, you will get the interference result from a slightly different direction from the scene. When the hologram is reconstructed, you are looking through the film, from one point of view, at light coming through the hologram through a small cone (iris width). That cone of light will have passed through a small disc (part of the whole hologram) and what gets into your eye will be another interference pattern (i.e. viewing light through the fine, complicated hologram pattern). This interference pattern is an approximate version of a picture of the whole original scene from that point of view. The resolution is limited (I think) by the aperture of your eye as well as the quality of the equipment.
Did you look at that wiki article on computer generated holograms? If you can understand the bit involving the Fourier transform it becomes clearer. If you aren't familiar with that then you may just have to accept the fact that 'it works'. (Btw, Fourier transforms work on spatial frequencies and variations in the same way that they work on sound frequency spectra and waveforms - same Maths involved with each)

 

[lookbehindu]

That is the very same question I asked my lecturer at University in 1966! (Nothing is new under the Sun ) He was actually flummoxed by the question and I only came to terms with the problem years later, when I approached it again.

To answer your main question, the reason that you get a diffraction pattern is that the various light paths through the system are all different - their relative phases, where they are detected (the film) are different from place to place on the film. That's why you get the light / dark fringes of the hologram. For a simple two slits, the effect is easily explained (in wiki and all over) - at different angles, the phase relation between light from the two slits is different, which gives you the fringes. You can do the two slits with almost any old light source and get fringes over a limited range of angles. To work well, you need good coherence so that, even at large angles, the different wave trains that make up the light source are still long enough for self interference to occur. (For a pair of radio signals, for instance, the coherence is almost perfect and the interference is more or less textbook and a laser is about as good)

For a hologram to work, the requirement is even more strict because you need a broad, coherent wavefront for your reference and a broad, coherent wavefront hitting the object. The resultant (max / min / intermediate value) at any single point on the film is due to light reflected from every point on that side of the object, interfering with the reference beam and with itself (of course). To one side of that point, you will get the interference result from a slightly different direction from the scene. When the hologram is reconstructed, you are looking through the film, from one point of view, at light coming through the hologram through a small cone (iris width). That cone of light will have passed through a small disc (part of the whole hologram) and what gets into your eye will be another interference pattern (i.e. viewing light through the fine, complicated hologram pattern). This interference pattern is an approximate version of a picture of the whole original scene from that point of view. The resolution is limited (I think) by the aperture of your eye as well as the quality of the equipment.
Did you look at that wiki article on computer generated holograms? If you can understand the bit involving the Fourier transform it becomes clearer. If you aren't familiar with that then you may just have to accept the fact that 'it works'. (Btw, Fourier transforms work on spatial frequencies and variations in the same way that they work on sound frequency spectra and waveforms - same Maths involved with each)

Thanks. I think I understand it a bit better. One more question...how does the hologram divisibility principle work. Is it a trick of the eye? If instead of cutting a piece off you placed a sheet over and cut a hole in the center of the sheet would the effect still occur and would you be able to see the entire image through that "peephole"?