# The Naked Scientists Forum

### Author Topic: How can photons be localised if the universe is expanding?  (Read 46850 times)

#### lightarrow

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##### How can photons be localised if the universe is expanding?
« Reply #100 on: 16/02/2009 19:44:13 »
Yes Lightarrow, I agree to what you write. 'Language' can be hell to interpret at times.
When I was 'discussing' wavelength contra frequency, I meant that my conclusion was, that even though you can say that one wavelength have different frequencys, the 'proportionality' between the wavelength and the frequency remains the same.

Is that wrong?
Yes and no. If you want to consider the case of a single wavelenght having different frequencies, you are necessarily talking about different media in which the wave travels; then the proportionality is valid only in every medium but not both at the same time; nevertheless how can wavelenght be (inversely) proportional to frequency if one wavelenght correspond to 2 different frequencies? Inversal proportionality between frequency f and wavelenght λ means: f = k/λ, where k is a constant, so, if f1 = k/λ1 then you must have f2 = k/λ2 so if f1 ≠ f2 then λ1 must necessarily be ≠ λ2.

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You just 'stretched' that original frequency by putting it through the prisms 'density' and so making the wave crests become wider apart in that wave, if i understood it right.
Wait a moment! Don't know which is the example I made that you are referring to, but when a light wave goes from the void to glass, then the waves are not stretched, they are compressed, infact the wavelenght decreases.
The frequency instead stays the same.

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And in a way that's unintuitive, as one might expect the opposite:)

For example, if I exchange that 'wave' and the prism, and instead try to describe it by a spring and some thick mud. Now I'll try to press that spring through that mud.
What would happen is that the spring would 'compact' by being pressed through that mud, not 'expand', right:)
Yes, it's so.

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So trying to see light as some sort of 'spring' meeting a higher density (mud) doesn't work very well.
But seeing it in terms of density and time does, to me that is:)

If one accept that light will be slowed down by a higher density then it will need more time traversing that density. And those waves will then, in that medium, be observed as changing to a 'greater' frequency as it moves through.
No, the frequency stays the same, but wavelenght decreases, as I said.

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And with 'greater' I mean that the crests and troughs between the waves will have a greater distance between them (red shift) when seen passing a static point of observation inside that medium.

Am I seeing this correct Lightarrow?
No, when light enters glass, the distance between the crests decreases (the "spring" is more compacted). Ok, let's see if I can make a more simple example. Think about soldiers who run, one after the other, at a precise time delay: let's say that when a soldier passes by a point in space, the next one will always pass after exactly 1 second, wherever they are; now you observe them running on a road; you measure the distance between two soldiers and you find exactly 8 metres; now you are able to compute the speed of this soldier's "wave": you know that the next soldier will arrive after 1 second, so he has covered 8 metres in 1 second --> speed = 8m/s.

Now you observe them running in the sand; theyr distance is 5 metres --> speed (= phase speed, as you now have understood) = 5m/s

The frequency of the wave didn't change because there is still 1 second delay between a soldier and the next one, but the wavelenght decreased, they have been "compacted". Incidentally you can observe the same in a F1 race: if the time delay between two cars is the same, they are "compacted" where they go slower (in the bends, for example) and "stretched" where they go faster. It could be strange, but with light it's exactly the same (think: not even need of relativity  )

An interesting thing: Let's have a road and, parallel and next to it, a strip of sand (like a road immediately next to a beach); if you want that your soldiers will go, in the least time possible, from a point A in the middle of the road to another point B, in the middle of the beach and not under (or up) the point A, the the soldiers have to make a path which is exactly the one you can compute with optical geometry and Snell's law of refraction!

http://en.wikipedia.org/wiki/File:Snells_law_wavefronts.gif

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Ahh, but here we have Swedish/English/Italian and then Italian/English/Swedish.
Can you see the possibilities inherent here:)

It's a bleeding miracle that we agree on anything:::)))
I love it :)

Especially when you share your mathematics, then the mix gets explosive...
(Yes, I'm joking Lightarrow:). You are one of the few taking the time to explain your mathematical concepts)

Ah, yes, I totally agree here  .
« Last Edit: 16/02/2009 20:03:03 by lightarrow »

#### yor_on

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##### How can photons be localised if the universe is expanding?
« Reply #101 on: 18/02/2009 01:00:31 »
Awh, there goes my whole plan down the drain, so you say that the light when coming into the glass actually will get a more compressed frequency.

So when we have two frames. Frame_A and frame_B moving apart from each other.
And we on frame_A is observing a light beam coming at us from frame_B.
The we will notice a red shift, right.

And that red shift, if visualized, will then as observed have a greater :) distance between its crests and troughs?
But that shouldn't then be seen as a 'weaker energy' per time unit when the light finally is 'hitting' our frame?

If I look at it as I'm used to (particles) i think of them as getting 'spread out' in time as I'm moving from them and therefore 'weaker' per time unit.

And if we were moving those frames towards each other, and observe the light as being blue shifted.
Then that doesn't mean that our frame will receive a larger amount of 'energy' per time unit?

As that then, to me, would mean that those photons (particles) will get compressed as observed per time unit.

As that is why I want those phreaking waves to become of greater (is it 'magnitude' I should use here?) distance between their crests and troughs:) when moving through that prism?

When I think of them (waves) meeting any density (the prism) I see them as becoming 'depleted' of energy in their interactions with the electron clouds and therefore, as I thought, also 'red shifted' (stretched out in time so to speak:).

To me it seems strange to say that they become compressed as I associate that with blue shift.
Do you see how I think here?

Awhhh...

I think I will call on Manuel now:)

----

If one look at waves as getting compressed in that prism, how do one explain the 'photon wikis' statement that the 'energy' of a wave is directly correlated to its frequency?

"The Maxwell wave theory, however, does not account for all properties of light. The Maxwell theory predicts that the energy of a light wave depends only on its intensity, not on its frequency; nevertheless, several independent types of experiments show that the energy imparted by light to atoms depends only on the light's frequency, not on its intensity.

For example, some chemical reactions are provoked only by light of frequency higher than a certain threshold; light of frequency lower than the threshold, no matter how intense, does not initiate the reaction. Similarly, electrons can be ejected from a metal plate by shining light of sufficiently high frequency on it (the photoelectric effect);
the energy of the ejected electron is related only to the light's frequency, not to its intensity.[26]"
http://en.wikipedia.org/wiki/Photon#Historical_development

Waves drive me wild...

Anybody wanna sponsor a ticket to Hawaii?
I heard they have great waves there:)

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If I think of it as photons hitting electron clouds inside that prism I can see how they will interact and energize those clouds, some of the energy of those photons will 'dissapear' as heat etc, but I'm not sure how they will get compressed in time. It seems like if we have a specific amount of 'balls' rolling through :) they all will be 'braked' the same amount inside that prism and became fewer or/and of lesser energy when coming out on the other side.
So yes, you are right, but it still wrecks havoc with my former ideas of their 'expression' as waves.

Am I wrong in how I see them as red and blue shifted relative those two frames then, when they meet my frame_A?
As blueshift to me is a higher frequency and more energy per time unit, and redshift the opposite?
And of course :) that wiki?

-------

Ah, here he are:)
- I know nothing.
- - Noothing I say::))

(So now we are two... Manuel, and me:)
« Last Edit: 18/02/2009 02:06:06 by yor_on »

#### lightarrow

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##### How can photons be localised if the universe is expanding?
« Reply #102 on: 18/02/2009 13:37:49 »
Awh, there goes my whole plan down the drain, so you say that the light when coming into the glass actually will get a more compressed frequency.
NOT FREQUENCY! IT'S WAVELENGHT WHICH IS REDUCED! THE FREQUENCY STAYS THE SAME! How many times have I to write it?  [xx(]

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So when we have two frames. Frame_A and frame_B moving apart from each other.
And we on frame_A is observing a light beam coming at us from frame_B.
The we will notice a red shift, right.
Ok.

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And that red shift, if visualized, will then as observed have a greater :) distance between its crests and troughs?
Yes.

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But that shouldn't then be seen as a 'weaker energy' per time unit when the light finally is 'hitting' our frame?
Yes, but not only because of this! The amplitude is lower, too. Quantistically (without considering the amplitude) you also have *less photons* passing per unit time, in addition to have a reduced energy of every single photon.

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If I look at it as I'm used to (particles) i think of them as getting 'spread out' in time as I'm moving from them and therefore 'weaker' per time unit.
Yes, see up.

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And if we were moving those frames towards each other, and observe the light as being blue shifted.
Then that doesn't mean that our frame will receive a larger amount of 'energy' per time unit?
Yes.

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As that then, to me, would mean that those photons (particles) will get compressed as observed per time unit.
Yes, in the sense I wrote up.

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As that is why I want those phreaking waves to become of greater (is it 'magnitude' I should use here?) distance between their crests and troughs:) when moving through that prism?
1. What happens to waves when they enter through a prism has *nothing to do* with changing frame of reference! The energy of the wave *doesn't vary at all* inside the prism. The fact it has a smaller wavelenght has nothing to do with the energy, but only with the fact that phase velocity is smaller. Have I clarified it now? (Please, tell me yes   )
2. You MUST use the proper terms: the distance between two next crests is *wavelenght*.

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When I think of them (waves) meeting any density (the prism) I see them as becoming 'depleted' of energy in their interactions with the electron clouds and therefore, as I thought, also 'red shifted' (stretched out in time so to speak:).

To me it seems strange to say that they become compressed as I associate that with blue shift.
Do you see how I think here?

Awhhh...

I think I will call on Manuel now:)

----

If one look at waves as getting compressed in that prism, how do one explain the 'photon wikis' statement that the 'energy' of a wave is directly correlated to its frequency?
THE FREQUENCY STAYS THE SAME! IT'S WAVELENGHT WHICH IS REDUCED!

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"The Maxwell wave theory, however, does not account for all properties of light. The Maxwell theory predicts that the energy of a light wave depends only on its intensity, not on its frequency; nevertheless, several independent types of experiments show that the energy imparted by light to atoms depends only on the light's frequency, not on its intensity.
This phrase is wrong, if you don't interpret it in the correct way; you have to specify what does it mean and in which conditions. It refers to photoelectric effect, not to an EM wave in general. It also explain it, it says: "the energy imparted by light to atoms", it doesn't say: "the energy of the EM wave".
« Last Edit: 18/02/2009 13:40:40 by lightarrow »

#### yor_on

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##### How can photons be localised if the universe is expanding?
« Reply #103 on: 18/02/2009 13:49:20 »
Awh:)

Don't kill me now::))
I told you I was sloow.

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The wavelength becomes smaller between crests, ok.
My thick head sees those 'wavelengths' as the 'parts' making up a 'frequency' when put together Sir.
*Hiding under a table*

Ah, when you put it like that... [B)] [B)]
(yep, browbeaten to a pulp, that's me:)

Who can refuse such an earnest request.
So... Maybe:)

-----
I need to make a picture of it in my head sort of Lightarrow.
Don't give up on me now, we are closing in on the culprit I think (I think?)

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Those dastardly waves.
""They seek him here, they seek him there, they seek that, ah, wave everywhere."
As a obnoxious friend of mine once wrote:)

--------

'But that shouldn't then be seen as a 'weaker energy' per time unit when the light finally is 'hitting' our frame?'

" Yes, but not only because of this! The amplitude is lower, too. Quantistically (without considering the amplitude) you also have *less photons* passing per unit time, in addition to have a reduced energy of every single photon."

So the frames (_A and _B) moving away from each other in this scenario also, somehow, reduces the 'energy' inherent (if I may use that expression) in those 'single' photons. That you will need to explain to me.
« Last Edit: 18/02/2009 14:29:29 by yor_on »

#### Vern

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##### How can photons be localised if the universe is expanding?
« Reply #104 on: 18/02/2009 14:09:05 »
Quote from: yor_on
The wavelength becomes smaller between crests ok.
My thick head sees those 'wavelengths' as the 'parts' making up a 'frequency' when put together Sir.
*Hiding under a table*
The wavelength can have closer crests and the time spent traversing the media can be greater. It requires wavelength plus time to produce frequency.

#### yor_on

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##### How can photons be localised if the universe is expanding?
« Reply #105 on: 18/02/2009 14:16:12 »
So is this a description without a time variable?
It's me not getting the concept here, I know [:I]

#### yor_on

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##### How can photons be localised if the universe is expanding?
« Reply #106 on: 18/02/2009 14:26:09 »
--
It's like there is two simultaneous descriptions.
One treating the idea of a wavelength, not considering it/them 'building up' to a frequency.
Another treating just a frequency.

What exactly is seen as a energy in a compressed wave.
I think I might get it?
What we are discussing here is not so much the waves 'compression' as the relation between a wave and the medium through which it traverse, am I right?

#### lightarrow

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##### How can photons be localised if the universe is expanding?
« Reply #107 on: 18/02/2009 15:07:59 »
The wavelength becomes smaller between crests, ok.
My thick head sees those 'wavelengths' as the 'parts' making up a 'frequency' when put together Sir.
As Vern have already said (don't want to say that I already said this too, because it would be the second or third time I say that "I've already said it"  ) wavelength is not enough to "make up" frequency, you *also* need the speed of propagation of waves, that is phase speed. I also made the example of the soldiers, which are evenly delayed in time and that this time delay *doesn't vary* and so *the frequency doesn't vary* while their spacing, and so the wavelenght *does* vary, when they move from a medium to another and so when their (phase) velocity varies. What's wrong with that example?

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Ah, when you put it like that... [B)] [B)]
(yep, browbeaten to a pulp, that's me:)

Who can refuse such an earnest request.
So... Maybe:)

-----
I need to make a picture of it in my head sort of Lightarrow.
Don't give up on me now, we are closing in on the culprit I think (I think?)

----------
Those dastardly waves.
""They seek him here, they seek him there, they seek that, ah, wave everywhere."
As a obnoxious friend of mine once wrote:)

--------

'But that shouldn't then be seen as a 'weaker energy' per time unit when the light finally is 'hitting' our frame?'
Here, again, you are talking of different frames of reference, not about light going through a glass, are you aware of this?

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" Yes, but not only because of this! The amplitude is lower, too. Quantistically (without considering the amplitude) you also have *less photons* passing per unit time, in addition to have a reduced energy of every single photon."

So the frames (_A and _B) moving away from each other in this scenario also, somehow, reduces the 'energy' inherent (if I may use that expression) in those 'single' photons. That you will need to explain to me.

Ok. The fact that a single's photon's energy (what you say 'energy' inherent, which is not correct, because it reminds "intrinsic" which is wrong, because a photon has zero intrinsic energy because intrinsic means without considering kinetic energy) varies from a ref. frame to another is because the wavelenght, and so the frequency of the EM wave varies (be careful here! Now, I *can* say: "the wavelenght, and so the frequency", because we are considering *one only* medium, so phase velocity is constant, so frequency here *is* inversely proportional to wavelenght and so, one frequency ↔ one wavelenght); furthermore (but you can't understand this without knowing Maxwell's equations AND relativity) the electric and the magnetic field amplitudes (= "strenght" of the fields, to say it in a more simpistic way) varies: for a light source which is approaching, the fields increases, if it recedes, the field decreases.

Quantistically: we have said that a single photon's energy is reduced (a source which is receding); why also, the number of photons passing (or emitted, or absorbed, or detected) in the unit time is reduced too? That's very simple: exactly in the same way as if you shooted away balls (or anything else) at a constant rate (in your frame of ref.) and with constant speed to a friend still on Earth while receding from him: he will receive less balls per unit time, with respect to the case in which you don't move at all.
« Last Edit: 18/02/2009 15:14:09 by lightarrow »

#### yor_on

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##### How can photons be localised if the universe is expanding?
« Reply #108 on: 18/02/2009 19:29:09 »
You say "Here, again, you are talking of different frames of reference, not about light going through a glass, are you aware of this?"
Yes, but I see our observation of that light inside that prism as two frames too, one is what happens inside that prism, the other frame is us outside, observing it.
As I said before, I'm not really sure on where the the definition of frames are valid in physics:)

But ok, we have the velocity, which is a measure of distance in time units, right?
And if we are talking about a massless photon that should be momentum?

Then we have the wavelength, which is a measure of distance between crests in time.

And frequency which is a measure of oscillating ( = vibrating ) 'periodic' waves which seems to mean waves that follow one another in regular succession.

Those periodic waves can be split into transverse and longitudinal waves, and here we come in on Verns favorite electromagnetic description of photons :) i think? And also on Lightarrows, as seen of lately, desperate tries to pommel some sense into my poor head relating to waves universe and all.

'Normal' electromagnetic waves can be seen as propagating (moving:) in a transverse manner.
a regular up-and-down pattern (sinusoidal) in which the 'vibration' or motion is perpendicular to the direction the wave is moving.
'Perpendicular' here means, seen as a straight line at right angles to another line , and the idea is like what you will see when you use a whip or if you look on how a snake travels on the ground.

And a longitudinal wave is a wave just like a sound wave, and that kind of waves spreads out in circles from a center point, like a siren f ex. and the 'vibration' of that motion moves in the same direction as the 'circle' of sound itself (360 degrees).

---

Btw: Siren should be understood as a warning signal that is a loud wailing sound.
And not as a woman who is considered to be dangerously seductive...
(not that I would mind though:)

------

But now the real headache starts:)

For we have been speaking of frequency as having a oscillating (vibrating) property, right?
But there are some property's that aren't related to those oscillating (whips & snakes, if transverse) properties at all, according to Lightarrow (and other Wizards and occult materials I've now consulted in my hunt for the holy grail, yes, the hermetic arts is near:)

So open your eyes now and hearken Romans Swedes and assorted other nationalities...

One of them 'non oscillating' is wavelength, (distance between crests), and yet another is called amplitude.
(height of wave, as seen from a thought 'middle line' splitting horizontally trough from crest).

Although wavelength isn't related to frequency mathematically, it still plays an important role together with amplitude when listening to sound.

And it is here I kind of lose it:) To me wavelengths seems a very simple concept where lots of the same sort of them, following each other in time, definitely  will give a frequency.

But according to this they don't have any oscillating (vibrating) property's, and to give a description of them we need a new arcane concept. Here it comes, period...

Yep, that's it.
'Period' in a transverse wave (think snake:) is the time it will take for one 'cycle' from trough to crest and back to trough.
So with any 'oscillator' frequency will be the amount of time (seconds usually) it took to finish a cycle.

And in a longitude wave it will be the distance (interval) in time between those concentric circles of sound, or that stone you threw into the pond and the distance between those circles that you see expanding in the water.

But here we are discussing transverse waves, and in a 'oscillator' the frequency will be the number of cycles per second, and in wave motion  (snake:) the number of waves that pass a given point per second, expressed in Hertz (Hz) after Heinrich Rudolf Hertz.

And so far so good, but I still haven't found out how wavelength suddenly is exchanged for period?
As wavelength is a description of crest to crest one might say that it is a metaphysical 'band aid' for explaining how waves compresses while periods is more like a 'three dimensional' description of something 'real' just as 'frequency' could be seen as, well, ah, as they have a direct relation.

And now I will hide behind the couch again :)
« Last Edit: 18/02/2009 19:54:13 by yor_on »

#### lightarrow

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##### How can photons be localised if the universe is expanding?
« Reply #109 on: 19/02/2009 09:21:38 »
You say "Here, again, you are talking of different frames of reference, not about light going through a glass, are you aware of this?"
Yes, but I see our observation of that light inside that prism as two frames too, one is what happens inside that prism, the other frame is us outside, observing it.
As I said before, I'm not really sure on where the the definition of frames are valid in physics:)
No, we talk of different frames of reference, in relativity, when we are still or we are moving with respect to the physical system under analysis. When light enter a prism, we are still fixed in our chair in the laboratory, we don't suddenly move ourselves! You would measure a difference in the wave's wavelenght propagating in only one medium, only if you would change your speed with respect to the wave source (it means that you or the wave source (the lamp, the laser, ecc.) at a certain moment start moving). The fact light wave changes wavelenght when entering a prism is *all another physical principle* and for this reason the energy doesn't change, the frequency doesn't change (as, instead, in the previous case of two different frame of reference moving with respect to each other). Can I say that you have "integrated" this fact?
If you still have doubts on this, I go towards suicide!  [:-'(]

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But ok, we have the velocity, which is a measure of distance in time units, right?
And if we are talking about a massless photon that should be momentum?
No, momentum is all another thing. If you want to compute a photon's speed making the limit of the speed of a massive particle, when mass m goes to zero, you can do it! :

a massive particle's momentum is

p = m*v/Sqrt[1-(v/c)2]   that is:   p2 = m2v2/[1-(v/c)2]

on the other hand, from the special relativity relation between momentum and energy we have:

p2 = E2/c2 - m2c2

equating the two:

m2v2/[1-(v/c)2] = E2/c2 - m2c2

after various passages, we can extract v2:

v2 = (E2 - m2c4)/[m2c2 + (E2 - m2c4)/c2]

now we make the limit for m who goes to zero:

lim v2 =
m→0

= lim (E2 - m2c4)/[m2c2 + (E2 - m2c4)/c2] =
m→0

= E2/(E2/c2) = c2

So we have proved that any massless particle, with non-zero energy, must move at c.

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Then we have the wavelength, which is a measure of distance between crests in time.

And frequency which is a measure of oscillating ( = vibrating ) 'periodic' waves which seems to mean waves that follow one another in regular succession.
Ok, however remember that, to talk of frequency, these waves *must* move, or you won't measure a periodic effect *in a fixed point of space*; to talk of wavelenght, you don't need to know if they are moving or not, because you don't measure an effect on time, but on space, fixed the time; have you "taken" this?

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Those periodic waves can be split into transverse and longitudinal waves, and here we come in on Verns favorite electromagnetic description of photons :) i think? And also on Lightarrows, as seen of lately, desperate tries to pommel some sense into my poor head relating to waves universe and all.

'Normal' electromagnetic waves can be seen as propagating (moving:) in a transverse manner.
Even "no-normal" ones  .  Light waves cannot have longitudinal components, or they would have a mass (and they don't have...)

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a regular up-and-down pattern (sinusoidal) in which the 'vibration' or motion is perpendicular to the direction the wave is moving.
'Perpendicular' here means, seen as a straight line at right angles to another line , and the idea is like what you will see when you use a whip or if you look on how a snake travels on the ground.

And a longitudinal wave is a wave just like a sound wave
...in air; (in a solid it can have transverse components).

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and that kind of waves spreads out in circles from a center point
why, transverse waves can't spread out in circle? They can too.

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, like a siren f ex. and the 'vibration' of that motion moves in the same direction as the 'circle' of sound itself (360 degrees).

---

Btw: Siren should be understood as a warning signal that is a loud wailing sound.
And not as a woman who is considered to be dangerously seductive...

Quote
(not that I would mind though:)

------

But now the real headache starts:)

For we have been speaking of frequency as having a oscillating (vibrating) property, right?
Again, remember that this oscillation happens *in the time* fixed the space, otherwise you can't talk of frequency.

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But there are some property's that aren't related to those oscillating (whips & snakes, if transverse) properties at all, according to Lightarrow (and other Wizards and occult materials I've now consulted in my hunt for the holy grail, yes, the hermetic arts is near:)

So open your eyes now and hearken Romans Swedes and assorted other nationalities...

One of them 'non oscillating' is wavelength, (distance between crests), and yet another is called amplitude.
(height of wave, as seen from a thought 'middle line' splitting horizontally trough from crest).

Although wavelength isn't related to frequency mathematically,
maybe you intended "physically".

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it still plays an important role together with amplitude when listening to sound.

And it is here I kind of lose it:) To me wavelengths seems a very simple concept where lots of the same sort of them, following each other in time, definitely  will give a frequency.
No; if "the snake" doesn't move, you still have wavelenght (distance between its crests or its "curls"), but you don't have any frequency at all.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11582
• (Ah, yes:) *a table is always good to hide under*
##### How can photons be localised if the universe is expanding?
« Reply #110 on: 20/02/2009 15:38:01 »
Ah, we agree on the Sirens :)
I will reread you, and hopefully come up with something (driving you to new heights of despair:) soon Lightarrow.

#### The Naked Scientists Forum

##### How can photons be localised if the universe is expanding?
« Reply #110 on: 20/02/2009 15:38:01 »