Thread: Photons (again)

First Question: What process happens when things absorb light ? Like something that is black for instance, or something that is red or green, (abosorbing all of the different wavelengths of light except the red or green ones) - What does it mean to absorb the light / photons ? Where do they go ?

Second Question: White light, is it single photons of white light containing the whole of the visible spectrum of wavelengths in a single quanta. OR is it that the photons are of ALL different wavelengths are bombarding your eyes; and you percieve them to be white as they would be travelling too quickly and in such numbers that your brain is not quick enough to differentiate between each one ?

Third Question: Can photon's bump into each other ? What happens when they do ?

Fourth Question: Standing anywhere in what appears to be an "empty space" somewhere in the cosmos (pick any or loads of random spots to stand) and you will see stars; you will see the light of stars; does this mean that in effect; doesnt matter where you are, there will ALWAYS be a photon there ?

Originally Posted by leohopkins

First Question: What process happens when things absorb light ? Like something that is black for instance, or something that is red or green, (absorbing all of the different wavelengths of light except the red or green ones) - What does it mean to absorb the light / photons ? Where do they go ?

I've got a model in my head that says a photon is a travelling stress and an electron is a moebuis rotating stress usually bound via another stress into an atom. A free electron can't absorb or emit an electron, but a bound electron can because the photon stress is either added to or subtracted from the binding stress. I'd maybe need to write a whole essay to explain this properly.

Second Question: White light, is it single photons of white light containing the whole of the visible spectrum of wavelengths in a single quanta. OR is it that the photons are of ALL different wavelengths are bombarding your eyes; and you percieve them to be white as they would be travelling too quickly and in such numbers that your brain is not quick enough to differentiate between each one?

The latter. There's no white in a rainbow.

Third Question: Can photons bump into each other ? What happens when they do?

No. They are stresses with no tangible surfaces. If you shine a beam of light at right angles across another beam of light, the beams don't merge or stop.

Fourth Question: Standing anywhere in what appears to be an "empty space" somewhere in the cosmos (pick any or loads of random spots to stand) and you will see stars; you will see the light of stars; does this mean that in effect; doesnt matter where you are, there will ALWAYS be a photon there ?

Pretty much I guess. I've heard say that space doesn't exist unless a photon or something else is there to give it some existence, but I can't justify this.

Okay so if at every point in the universe there is a photon or something else then that means that everything is connected to everything else within the universe, still. What affects one thing will always effect another thing, even if it is light years away, eventually it will be affected.

I am trying my best to think also on what you mean by "stresses"
To me, a "stress" has always been a force which acts on something else to change something about it, or its something given to me by my wife.

Can you explain to me what you mean by stresses please ?

With regards to the answer to the third question. I can remember that I once pointed one of those laser pens at a fire once, and it seemed to stop...it didnt penetrate the flame and appear the other side. ?

Get hold of a rubber across the middle. Sorry, I'm English, translate "rubber" into "eraser". OK, now squeeze it. You are stressing the eraser. Stress is force per unit area, and energy is stress multiplied by volume, so you are putting energy into the eraser. Note that the long ends extend outwards a little, because there's always an orthogonal tension. Now imagine that our whole universe is a solid block of rubber, and you somehow hit an internal portion of it with a hammer: wibble wobble, the stress and tension will travel. Now replace the rubber with something less substantial, called space. Farsight sucks teeth: that's kind of how it works.

Okay.........a rubber is tangible but space ISNT. So whilst I can understand what you are saying, I cannot fathom how something such as space can be stressed. In order for space to be stressed, logic and common sense tells me that in that case space MUST be made of SOMETHING.

I also feel that my head is about to explode becasue im thinking about this problem....a star is a sphere in 3d space which would be the 3d equivalent of a circle in 2d, right ?

So ill explain it in terms of 2d to simplify it and to stop myself from going mad -- oops too late ! lol

Anyway.....so you have a circle, now draw lines from the edge of the circle radiating outwards, okay ? (this is the light radiating outwards)

Now, no matter how many lines you have drawn radiating outwards; the father you draw away from the circle (presuming you can draw straight lines, as this is the path which light follows) the more of a gap appears between the lines. I shall go no further with this comment, but can you see what im getting at ?

Originally Posted by leohopkins

Okay.........a rubber is tangible but space ISNT.

What's a rubber made out of when you get down and dirty, leo? Molecules? Atoms? Electrons? Protons and Neutrons? Quarks? What are these bottom-line things made out of? Stressed space is what.

So whilst I can understand what you are saying, I cannot fathom how something such as space can be stressed. In order for space to be stressed, logic and common sense tells me that in that case space MUST be made of SOMETHING.

It sure gets tricky. The easiest way to think about it is if you're travelling along and you hit a patch of this stressed space you feel a bump. Like you feel an air pocket when you're in a plane. Read the Mass Explained thread.

I also feel that my head is about to explode because I'm thinking about this problem....a star is a sphere in 3d space which would be the 3d equivalent of a circle in 2d, right? So I'll explain it in terms of 2d to simplify it and to stop myself from going mad -- oops too late ! lol. Anyway.....so you have a circle, now draw lines from the edge of the circle radiating outwards, okay ? (this is the light radiating outwards) Now, no matter how many lines you have drawn radiating outwards; the further you draw away from the circle (presuming you can draw straight lines, as this is the path which light follows) the more of a gap appears between the lines. I shall go no further with this comment, but can you see what I'm getting at?

Uh, no. Maybe you need to draw your lines on a rubber sheet. Then you can stress it by giving it a squeeze, or put it under tension (the opposite of stress) by pulling it. Your lines curve. But it's like you're made out of the same old rubber sheet, so you don't see the curves directly. You just feel forces.

Okay. How does one "stress space"

I am presuming that this is done during the initial inflationary stages of the universe ?

I heard one thoery suggesting that if you concentrate two infinately dense photon beams and make them cross, that it will produce matter and anti-matter. Is this true ?

If so, is it photons themselves that stress space ?

Leo, I really think you ought to forget everything you've picked up from non-scientific sources, go to our links section, read the book that's free there, then come back and ask questions, I think it was river rat told you that photon's do not interaract with each other, and here you are asking the same question again after just an hour! they simply [as dar as is known] do not interact, think of a laser the photons neither widen the beam nor 'sharpen it' .

Erm.......

Now I have just realised where I read that "theory". It was in Dan Browns novel of "Angels & Demons " !

I have also read:

A short history of nearly everything
A brief history of time
The universe in a nutshell
Quantum mechanics and classical physics.

So yes, it is okay you saying that they dont interact with each other, but is it not always good to question the "known" ? Afterall if we took everything that we learn from our great teachers as fact then we'd still be thinking that the world was flat.

Originally Posted by leohopkins

Erm.......

Now I have just realised where I read that "theory". It was in Dan Browns novel of "Angels & Demons " !

I have also read:

A short history of nearly everything
A brief history of time
The universe in a nutshell
Quantum mechanics and classical physics.

So yes, it is okay you saying that they dont interact with each other, but is it not always good to question the "known" ? Afterall if we took everything that we learn from our great teachers as fact then we'd still be thinking that the world was flat.

Apart from a Victorian club started by an eccentric twat, can you name me just one group of people in history who thought the world was flat?

Eratosthenes confirmed it was round well before 200BC and got the circumference to within 2%.

Originally Posted by leohopkins

Okay. How does one "stress space"?

Same way you stress anything. You press it. Or kick it. But this is electric stress. You have to have some charge to be able to do it. So it's easier to kick a charged particle.

I am presuming that this is done during the initial inflationary stages of the universe?

Yes and no. One stress causes another. Read Energy Explained.

I heard one theory suggesting that if you concentrate two infinitely dense photon beams and make them cross, that it will produce matter and anti-matter. Is this true?

No. The intensity doesn't cut the mustard. You have to have a high-energy gamma-wave photons. But all you need to do is fire one at an atomic nucleus so it splits into er, two swirling rings. One's an electron, one's a positron.

If so, is it photons themselves that stress space?

No, the photons are stressed space.

You have to do some reading, like Megabrain said.

Okay thanks, i think i get the general gist of it, I will do some more reading as suggested and no diubt come back with some more elaborate ideas and arguments.

One of the most amazing things that I have always thought was that 99.9% of my total body size is composed of absolutely nothing.

Originally Posted by Megabrain

Leo, I really think you ought to forget everything you've picked up from non-scientific sources, go to our links section, read the book that's free there, then come back and ask questions, I think it was river rat told you that photon's do not interaract with each other, and here you are asking the same question again after just an hour! they simply [as dar as is known] do not interact, think of a laser the photons neither widen the beam nor 'sharpen it' .

Hi megabrain - just to clear up two points, i was talking about photons interacting with dark matter. I cant remember ever talking about photons interacting, simply because up to now i have never thought about it! Doing some quick research i came up with this http://en.wikipedia.org/wiki/Two-photon_physics which seems to suggest that two photons can "collide", but in the loosest sense of the word!

Originally Posted by leohopkins

I heard one thoery suggesting that if you concentrate two infinately dense photon beams and make them cross, that it will produce matter and anti-matter. Is this true ?

If you can (but I think it'll be hard to find...) try to read about Delbruck scattering.

Cheers,
william

Also read about the Kapitza-Dirac effect. This is where matter is in essence refracted using a lens made out of light. Search on Freimund, whose dissertation describes the construction of the apparatus.

http://www.nature.com/nature/journal.../413142a0.html

Quote:
White light, is it single photons of white light containing the whole of the visible spectrum of wavelengths in a single quanta. OR is it that the photons are of ALL different wavelengths are bombarding your eyes; and you percieve them to be white as they would be travelling too quickly and in such numbers that your brain is not quick enough to differentiate between each one?

The latter. There's no white in a rainbow.

I never reacted on this forum but I wonder: with this theory why do we see something white completely different compared with when we look at the sun or a lightbulb?

Okay........I am going to have a go at answering your question if I Can.......

....I think it would have something to do with the fact that a white object; whilst reflecting back light looses information. (Possibly due to some (but not all) photons being absorbed ?

It may also have to do with the fact that a light bulb or the sun produces a great intensity of photons. A white sheep for instance, doesn't it merely reflects them.

I would say that if you put a light bulb really close to something white and looked at the direct contacy patch, you will see a glow, rather like that of the lightbulb; as the white thing reflects a greater insity of light within that local region.

Here's a fun question for you to try and answer:

What colour is a mirror ?

No leo, You need to look at the spectral distribution of energy for the device providing the light, THe sun has a huge range whereas a lightbulb tails off before it get's to the blue end. Spectral emission from lightbulbs is tied to 'blackbody temperature'. In essence blue light is needed to make things look 'white' Bulbs emit little blue light but lots of green and read hence everything looks yellow. It's a complex subject and you do not always see the colour you are looking at, it depends upon the surrounding color. Flourescent lights create ultraviolet photons which then strike the white coating on the inside of the glass, the electrons re-emit photons at a lower wavelength, [in fact at many different narrow band wavelengths].

Incidentally with a narrow slit and a CD you can make a very simple photo-spectrometer and prove it for yourself - I'll look for a link and add it.

http://www.cs.cmu.edu/~zhuxj/astro/h...ctrometer.html

Try this I made one for the lad next door and they do work !!

Thanks, will give it a go.

So UV lighting then is just flourescent tubes without the white stuff inside ?

http://en.wikipedia.org/wiki/Fluorescent_lamp

Read the Para called "Principles of operation" to save me spurting it all out again.

Both the UV tubes I have are essentially Flourescent without the phosphor coating. I use them for erasing the contents of Eproms (computer memory chips) rior to re-programming.

i know eproms.

my first ever computer was the sinclair zx spectrum 128k. it had a reset button on the side, but i noticed a neat trick..........if i put a magnet near the back of it it would reset automatically.

A real neat trick i thought..until one day the computer stopped working completely :?

Just been reading up about AC & DC currents, apparently you cannot step-up or down the voltage using a transformer on a DC current. (I didnt know that)