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Offline lightarrow

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Photons and why they're so hard to explain
« Reply #50 on: 10/12/2007 20:30:56 »
Electromagnetic radiation without exception, and this includes x-rays, gamma rays as well as visible light and radio waves, follows the inverse square law, that means that it is impossible for an individual photon from a distant star to arrive at the rate of one photon per year. If light from a distant star was detected on earth it would be detected simultaneously at every point on the earth and probably in the entire solar system also, there is no question of an individual photon making it on its own. If one photon is detected then photons of the same intensity would be detected everywhere else on earth at exactly the same time.
Wrong. The computation of the intensity can tell you how is the *probability* of detecting a photon, not where it will be detected; you will have the same intensity and so the same probability on a huge spherical surface centered in the star, but this DON'T mean that you will detect light in every point of that suface.
Welcome in the modern physics world!
 

Offline lightarrow

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« Reply #51 on: 10/12/2007 20:35:30 »
Theoretically if the distance between the source and the detection area were small and it was possible to time the emission of a photon according to its frequency so that only one was released it might be possible to detect a single photon. But in other circumstances, if for instance you have a very dim light source on for several minutes or hours there would be absolutely no truth in it whatsoever. Any source of electromagnetic radiation follows the inverse square law. How do you think we are able to receive radio transmission from Voyager 1, about six billion miles distant from the earth ?
It's only a matter of probability. The low intensity doesn't tell you that you will have a little part of a photon, but only that you will have to wait longer to detect one. Have you ever heard of "Taylor's experiment"? (1909!)

http://www.seas.harvard.edu/brenner/taylor/physic_today/taylor.htm
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Interference fringes by feeble light
We began our tour of Taylor’s research by discussing his first scientific paper, which was published in 1909. This was his only paper that was not classical physics, but it nonetheless bore the experimental characteristics that were to appear throughout his later work. At the request of J. J. Thomson, Taylor performed an experiment (in the children’s room of his parent’s house!) to determine whether there was a qualitative change in a diffraction pattern when the intensity of the light is reduced greatly.3 Taylor indicates that Thomson believed that there would be a change in the pattern. Taylor took photographs of the shadow of a needle, varying the intensity of light by shielding the light source with smoked glass screens. When decreasing the intensity he increased the exposure time to keep the total amount of light on the photograph constant. The longest experiment took three months, corresponding to the intensity of a candle more than a mile away; some of the experiments even took place while Taylor was on a yachting trip. Taylor observed no change in the diffraction pattern, wrote a two-page paper describing this result, and then dropped this line of research.

http://spiff.rit.edu/classes/phys314/lectures/dual3/dual3.html

http://en.wikipedia.org/wiki/Geoffrey_Ingram_Taylor
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His first paper was on quanta showing that Young's slit diffraction experiment produced fringes even with feeble light sources such that less than one photon was present at a time.
« Last Edit: 10/12/2007 21:15:48 by lightarrow »
 

Offline lightarrow

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Photons and why they're so hard to explain
« Reply #52 on: 10/12/2007 21:21:28 »
In explanation of the above two posts see this site on the Hubble law and red shifts. I entered in a value of 500nM and got 550 nm as infinity? Can you explain?
P.S. See table at bottom of page where you can enter values!
If I enter 500 nm as first value and 550 nm as second (red-shifted) value, I get 0.095022624434c as recessional speed of the galaxy.
 

lyner

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Photons and why they're so hard to explain
« Reply #53 on: 10/12/2007 22:50:11 »
RED SHIFT: HOW WE KNOW IT'S HAPPENED

You know that each element has its characteristic spectrum of emission lines; their frequencies are related to each other by characteristic ratios- predicted by QM and confirmed in many experiments. The Cosmological Principle says that Physics is the same everywhere (if not, then what hope is there?) so we assume that a Hydrogen atom does the same thing, even in a distant galaxy.
Light from distant sources contains these patterns of lines, corresponding to the elements on Earth BUT their frequencies are not those of atoms here. Their frequency is nearly always lower. The amount by which their frequency differs from what we would expect is their red shift. A few exhibit blue shift - they must be moving towards us.
It still amazes me that anyone can have opinions about deep matters to do with Physics and Cosmology if they don't know something a basic as this.
 

Offline McQueen

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Photons and why they're so hard to explain
« Reply #54 on: 10/12/2007 23:01:20 »
Reply with quote
RED SHIFT: HOW WE KNOW IT'S HAPPENED
Thank you ! I was wrong !
 

Offline Soul Surfer

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« Reply #55 on: 11/12/2007 09:13:16 »
The red shift is understandable because we are looking at the spectrum of the object and not one single colour of light.  The spectra of stars and galaxies are highly structured and contain a great deal of information about the composition of the stars and galaxies together with the conditions (pressure and temperature) when they were emitted they are almost as individual as fingerprints.  When red shift occurs one sees all the wavelengths of all the frequencies in the spectrum changed according to exactly the same rule and so it is easy to identify by how much the spectrum has been red shifted.
« Last Edit: 11/12/2007 09:15:53 by Soul Surfer »
 

Offline lightarrow

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« Reply #56 on: 11/12/2007 12:20:04 »
People interested in Doppler effect of light could also watch lesson 23 of these movies:
http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm
 

lyner

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Photons and why they're so hard to explain
« Reply #57 on: 11/12/2007 17:39:38 »
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Reply with quote
RED SHIFT: HOW WE KNOW IT'S HAPPENED
Thank you ! I was wrong !
Spoken like a true gent.
 

Offline that mad man

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Photons and why they're so hard to explain
« Reply #58 on: 11/12/2007 19:23:46 »
Not been around for a while so hi to all!  ;D

Regarding the red shift.

Has anyone read the lectures by Alexander Franklin Mayer?

GTR intro: A New Gravitational Effect. L1: A Correction to the Gravitational Model. L2: The Many Directions of Time.

Fairly large pdf files though and sorry I don't have the link  [:I], you should find him in a search though.

He has some interesting ideas about the red shift, gravity, black holes, dark matter etc.
A long read and much too difficult (math) for me to explain.

Not sure how he is regarded in the physics world.

Hope this post was appropriate given the context.  :)

Bee

 

Offline McQueen

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Photons and why they're so hard to explain
« Reply #59 on: 12/12/2007 15:33:05 »
If I enter 500 nm as first value and 550 nm as second (red-shifted) value, I get 0.095022624434c as recessional speed of the galaxy.

I entered 12000 Mly and got a wavelength of  656 nm red shifted to 2377.11 nm.

I have been thinking about the Doppler red-shift. All waves exhibit, including the electromagnetic,  the Doppler effect. It is really quite a weird phenomenon. If you are on a train approaching a station on which two men are standing, one on the near end of the platform and the other on the further end, and the train driver blows the whistle, something extraordinary happens. You, on the train hear the original frequency of the whistle as it is ‘supposed’ to sound, the man on the nearer side of the platform hears the whistle at a slightly higher frequency as the train approaches the platform and the man on the further side of the platform hears a lower frequency as the train recedes into the distance. Which of these frequencies is the ‘real’ one. The answer of course is that all three people hear a ‘real’ sound and all three frequencies exist according to where the person happens to be located.

What is amazing about this, is that the speed at which these various frequencies are being heard remains constant! Only the frequency of the sound (or light) is varied.


 

Offline lightarrow

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« Reply #60 on: 12/12/2007 17:59:19 »
If I enter 500 nm as first value and 550 nm as second (red-shifted) value, I get 0.095022624434c as recessional speed of the galaxy.

I entered 12000 Mly and got a wavelength of  656 nm red shifted to 2377.11 nm.

I have been thinking about the Doppler red-shift. All waves exhibit, including the electromagnetic,  the Doppler effect. It is really quite a weird phenomenon. If you are on a train approaching a station on which two men are standing, one on the near end of the platform and the other on the further end, and the train driver blows the whistle, something extraordinary happens. You, on the train hear the original frequency of the whistle as it is ‘supposed’ to sound, the man on the nearer side of the platform hears the whistle at a slightly higher frequency as the train approaches the platform and the man on the further side of the platform hears a lower frequency as the train recedes into the distance. Which of these frequencies is the ‘real’ one. The answer of course is that all three people hear a ‘real’ sound and all three frequencies exist according to where the person happens to be located.

What is amazing about this, is that the speed at which these various frequencies are being heard remains constant! Only the frequency of the sound (or light) is varied.

McQueen, you really amaze me. You propose a new theory of photons and you discover NOW sound Doppler effect! Do you want to pull ours leg?
 

Offline McQueen

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Photons and why they're so hard to explain
« Reply #61 on: 13/12/2007 10:50:52 »
McQueen, you really amaze me. You propose a new theory of photons and you discover NOW sound Doppler effect! Do you want to pull ours leg?
No, I think it is quite fascinating that whether you are talking about sound doppler effect or electromagnetic doppler effect, it is possible to have so many views of the same thing.
 

lyner

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Photons and why they're so hard to explain
« Reply #62 on: 14/12/2007 17:02:16 »
Before you hold forth on a particular view, it might be a good idea to get a bit more knowledge, perhaps?
 

Offline McQueen

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« Reply #63 on: 06/02/2008 23:37:12 »
One of the strengths of the Naked Scientist Forum is  it’s excellence in the field of astrophysics, and rightly so given the number of members who have either qualified in this subject or are otherwise interested. What surprises me is that not a single forum member has come forward to elucidate the slightly erroneous impression that members have been left with on this thread with regard to the red shift. The impression that lingers with regard to the red shift is that light as it travels over enormous distances, gradually loses energy resulting in longer and longer wave lengths, so that eventually, one presumes, that there will be nothing left. The Hubble theory of the red shift is in fact exactly the opposite. Hubble theorists, which includes the majority of astrophysicists, believe, that light or electromagnetic radiation, retains its energy (identity) almost indefinitely, and the red shift only occurs if the source is moving away from  a given location. (f it is moving towards the location a blue shift occurs.)  This seems to make sense since then the Doppler effect becomes a part of Einstein’s space time continuum. Therefore to sum up, the Doppler effect only occurs if the source happens to be moving relative to a given location. Any comments ?
« Last Edit: 06/02/2008 23:39:31 by McQueen »
 

Offline DoctorBeaver

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Photons and why they're so hard to explain
« Reply #64 on: 07/02/2008 09:07:54 »
When supernatural phenomena clearly do not exist in the world we live in.

Can you provide definitive proof of that statement? Or is it just a statement of your theory of how things are?

I have personally experienced supernatural phenomena on more than 1 occasion so, as far as I am concerned, your statement is false.

The vast majority of scientists will stick to their guns (or, as you phrased it, be conservative) until something better comes along. If that were not the case then there would be no development. Everyone would be out looking for new things before existing ideas were taken further. There have been a few "quantum leaps" in understanding (such as provided by Newton, Galileo, Einstein, Planck, Dirac, Feynman, etc), but most progress comes from working within an existing framework to gain a better understanding of it and progressing along lines that seem to provide the right answers.

Take Quantum Electro-Dynamics (QED). It is the most tested, consistent and predictively accurate field of physics ever developed (some experiments give an accuracy of 1 part in a trillion). Yet the workings of it are so counter-intuitive as to be almost supernatural in themselves. Borrowing energy from nothing? Borrowing it from the future? That doesn't sound very scientific, does it. But the point is that IT WORKS!

You will not find a scientist anywhere who would say without a caveat that "This is how things are". They all accept that our knowledge is incomplete but that currently-accepted theories accurately predict events in the real world.

Yes, there are holes in existing theories. That is why scientists are looking at Quantum Loop Gravity, extra dimensions, and many other theories. Until a complete TOE is developed, we'll just have to accept that things are as they are because they are as they are.
« Last Edit: 07/02/2008 09:18:47 by DoctorBeaver »
 

lyner

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Photons and why they're so hard to explain
« Reply #65 on: 07/02/2008 10:55:48 »
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I have personally experienced supernatural phenomena on more than 1 occasion so,
Are you referring to 'ectoplasmic phenomena' or to results of scientific experiments which weren't what you expected? There is a big difference between the two.
 

Offline DoctorBeaver

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« Reply #66 on: 07/02/2008 16:04:33 »
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I have personally experienced supernatural phenomena on more than 1 occasion so,
Are you referring to 'ectoplasmic phenomena' or to results of scientific experiments which weren't what you expected? There is a big difference between the two.

Neither.

I was talking to a South African friend of mine who mentioned her friend in Durban. I proceeded to describe the friend's apartment, what could be seen out of the window and even what car she had (I was wrong on the car. I said it was a silver BMW when it was, in fact, a silver Audi). I even had an argument with my friend about the colour of the 3-piece suite. I insisted it was a maroon colour, but my friend said I was wrong and that her friend's suite was, in fact, grey. A couple of days later my friend phoned her friend and - guess what - she'd bought a new 3-piece suite; a maroon coloured 1.

I've done similar things, but that example is the most striking.

I promise you this is all true. Believe it or not, as you please.
 

lyner

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Photons and why they're so hard to explain
« Reply #67 on: 07/02/2008 19:01:59 »
The experiences which you describe as supernatural are very much 'personal' and open to different interpretations. I am a great believer in statistical significance tests with measurements before I can bring myself to believe that an event is anything but random.
The oddities associated with quantum physics are a lot more 'concrete' in as far as they can be repeated in many different experiments and the resulting probability distributions, for example, fit the pattern.
Duality doesn't have to be a problem as long as we don't insist on bringing too much classical baggage with us into the subject.
 

Offline DoctorBeaver

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Photons and why they're so hard to explain
« Reply #68 on: 07/02/2008 19:06:31 »
I wasn't saying that we need to look to the supernatural for explanations. I don't think we should. I think there's probably a rational explanation for the sort of things I've experienced but we just don't know what those explanations are yet.
 

Offline lightarrow

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« Reply #69 on: 07/02/2008 20:20:02 »

I was talking to a South African friend of mine who mentioned her friend in Durban. I proceeded to describe the friend's apartment, what could be seen out of the window and even what car she had (I was wrong on the car. I said it was a silver BMW when it was, in fact, a silver Audi). I even had an argument with my friend about the colour of the 3-piece suite. I insisted it was a maroon colour, but my friend said I was wrong and that her friend's suite was, in fact, grey. A couple of days later my friend phoned her friend and - guess what - she'd bought a new 3-piece suite; a maroon coloured 1.

I've done similar things, but that example is the most striking.

I promise you this is all true. Believe it or not, as you please.

You don't know how much I would like to meet you... :)
 

Offline DoctorBeaver

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« Reply #70 on: 07/02/2008 20:27:53 »

I was talking to a South African friend of mine who mentioned her friend in Durban. I proceeded to describe the friend's apartment, what could be seen out of the window and even what car she had (I was wrong on the car. I said it was a silver BMW when it was, in fact, a silver Audi). I even had an argument with my friend about the colour of the 3-piece suite. I insisted it was a maroon colour, but my friend said I was wrong and that her friend's suite was, in fact, grey. A couple of days later my friend phoned her friend and - guess what - she'd bought a new 3-piece suite; a maroon coloured 1.

I've done similar things, but that example is the most striking.

I promise you this is all true. Believe it or not, as you please.

You don't know how much I would like to meet you... :)

I knew you were going to say that  :D
 

Offline McQueen

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Photons and why they're so hard to explain
« Reply #71 on: 09/02/2008 09:55:58 »
Wot about my question Luv?????? Does light fade with distance or only with the doppler effect??????
 

Offline McQueen

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Photons and why they're so hard to explain
« Reply #72 on: 09/02/2008 10:13:17 »
Quote
Wrong. The computation of the intensity can tell you how is the *probability* of detecting a photon, not where it will be detected; you will have the same intensity and so the same probability on a huge spherical surface centered in the star, but this DON'T mean that you will detect light in every point of that suface.
Welcome in the modern physics world!
You are way wrong man. Space exploration, especially the Voyagers would not have been possible with your crummy theory. If you want to argue get out your pen and pencil!!!
 

Offline DoctorBeaver

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« Reply #73 on: 09/02/2008 12:01:11 »
Quote
Wrong. The computation of the intensity can tell you how is the *probability* of detecting a photon, not where it will be detected; you will have the same intensity and so the same probability on a huge spherical surface centered in the star, but this DON'T mean that you will detect light in every point of that suface.
Welcome in the modern physics world!
You are way wrong man. Space exploration, especially the Voyagers would not have been possible with your crummy theory. If you want to argue get out your pen and pencil!!!

I think you'll find that lightarrow knows a bit more about this than you do.
 

Offline lightarrow

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« Reply #74 on: 09/02/2008 16:12:37 »
Quote
Wrong. The computation of the intensity can tell you how is the *probability* of detecting a photon, not where it will be detected; you will have the same intensity and so the same probability on a huge spherical surface centered in the star, but this DON'T mean that you will detect light in every point of that suface.
Welcome in the modern physics world!
You are way wrong man. Space exploration, especially the Voyagers would not have been possible with your crummy theory. If you want to argue get out your pen and pencil!!!
What does space exploration have to do with it?
The fact is that no-one can tell you where the photon will be detected.
P.S.
It's not my theory, it's called "Quantum Mechanics". (I wish it was, my theory!  :))
 

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Photons and why they're so hard to explain
« Reply #74 on: 09/02/2008 16:12:37 »

 

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