Do photons have colours?

  • 43 Replies
  • 8645 Views

0 Members and 1 Guest are viewing this topic.

*

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • 513
    • View Profile
Do photons have colours?
« on: 07/07/2015 10:50:01 »
A Boothroyd asked the Naked Scientists:
   
 I have been thinking about it......  And i reckon the "back" of a photon "looks like" is color.  Was wondering if?  That could be the answer because it explains much.

What do you think?
« Last Edit: 07/07/2015 10:50:01 by _system »

*

Offline David Cooper

  • Neilep Level Member
  • ******
  • 1505
    • View Profile
Re: Do photons have colours?
« Reply #1 on: 07/07/2015 18:29:42 »
That's a fantastic new way of explaining things, so it's a powerful idea which might revolutionise the way we see the universe. The back of a horse looks like is hair too! I don't know what it means, given the grammar failure, but what a great explanation!

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2804
    • View Profile
Re: Do photons have colours?
« Reply #2 on: 08/07/2015 02:04:59 »
Quote from: thedoc
A Boothroyd asked the Naked Scientists:
   
 I have been thinking about it......  And i reckon the "back" of a photon "looks like" is color.  Was wondering if?  That could be the answer because it explains much.

What do you think?
No realistic meaning can be assigned to the "back" of a photon. First of all a photon is a point particle and as such the back is the same place as the front. And then there's the fact that one can only view a photon when it impinges on something like a cone (special cells in our eye which detect color) in our eye. When a photon strikes it it does so as it is traveling in the direction from where the photon was to where the eye cell is, i.e. the "front" of the photon if you wish to think of it that way.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #3 on: 08/07/2015 03:08:36 »
why is photon beam able to knock out electrons but not able to bend a flame? even the most powerful laser beam?

if photon has no color, why is my green laser has a green beam and makes a green spot on target?

*

Offline evan_au

  • Neilep Level Member
  • ******
  • 4310
    • View Profile
Re: Do photons have colours?
« Reply #4 on: 08/07/2015 11:28:29 »
Paraphrased Question: "Could a photon have a colour?".
Paraphrased Answer: Yes.

Each photon striking a prism or a diffraction grating will be deflected by an angle which depends on its wavelength*. If a light detector (like a camera's light-sensitive chip) is placed in the right area, you can tell which colour the photon had by which cell of the light sensor has been struck by the photon, liberating an electron.
 
Since the wavelength is directly related to colour, the photon has a colour.

* In the case of a glass prism, the angle of deflection for infra-red, visible light and ultraviolet photons follows a steady progression.
However, for a diffraction grating, a photon will take one of several possible angles on exiting the grating, so the signal from the light sensor does not absolutely uniquely identify the colour.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #5 on: 08/07/2015 18:44:06 »
why is photon beam able to knock out electrons but not able to bend a flame? even the most powerful laser beam?
You could have asked a more intelligent question: "can a photon beam bend a flame?" Yes. When a light beam strikes an air (or flame) molecule it does displace it, but I suspect your laser is not powerful enough to see the effect...

--
lightarrow
« Last Edit: 08/07/2015 18:46:23 by lightarrow »

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #6 on: 08/07/2015 18:55:59 »
if you mix red, blue and green photons, what color photons you get?

if you mix white and black photons, what color photons you get?

why?

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #7 on: 09/07/2015 00:42:53 »
If you mix red, blue and green photons, you get a mixture of red, blue and green photons (in vacuum). It is possible to mix (add) photons together where matter is involved (https://en.wikipedia.org/wiki/Sum_frequency_generation_spectroscopy), but that is quite beyond most of the members of this forum (I suspect)

There are no black or white photons.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #8 on: 09/07/2015 00:55:03 »
most photons are color less, like radio wave photons, x-rays.

strange thing is photons have no mass, no charge, but they carry em fields.

how does an electron knows what color of photons should emit? what direction? how many? what speed?

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #9 on: 09/07/2015 11:28:43 »
if you mix red, blue and green photons, what color photons you get?
if you mix white and black photons, what color photons you get?
why?
Explain the exact meaning of "mix photons", or your question is meaningless.

--
BlueRay

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #10 on: 09/07/2015 14:27:00 »
if you mix red, blue and green photons, what color photons you get?
if you mix white and black photons, what color photons you get?
why?
Explain the exact meaning of "mix photons", or your question is meaningless.

--
BlueRay

shine different color laser beams on the same spot.

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #11 on: 09/07/2015 15:33:41 »
if you mix red, blue and green photons, what color photons you get?
if you mix white and black photons, what color photons you get?
why?
Explain the exact meaning of "mix photons", or your question is meaningless.

--
BlueRay

shine different color laser beams on the same spot.

Unless there is something very special about that spot, this method will only result in a spot that is irradiated with photons of the same colors coming from the lasers (ie nothing interesting)

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #12 on: 09/07/2015 18:14:35 »
photon, a pocket of energy, a mass less particle travels at c speed, is impossible to exist according to energy conservation law.

photons spread into dark space simply vanished and never return. energy is lost.

logically sounding?

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #13 on: 09/07/2015 19:06:28 »
But the energy is not lost. The photon still exists. If it were ever to run into anything else, it could transfer that energy, but that isn't a requirement. The photon could go forever, never interact with anything, and still have exactly the same amount of energy it started with.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #14 on: 09/07/2015 19:41:53 »
so you are suggesting all matters are within a bigger space that has no boundary?

all matters end up gravitation into a hot ball and radiate out photons into space till 0 K and the universe becomes a cold matter ball in infinite space, all energy is missing forever?

or it bounces back bang the matter ball?

is it possible when things go infinity big, they become infinity small?

we had to stand on solid ground, are we sure the size and age of the space yet?

much to think, a small head. help me!


*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #15 on: 09/07/2015 21:02:21 »
i still cannot figure out how photon is emitted.

even if electron really has orbitals and able to move between orbitals, how is the electron's changing momentum transfer into a particle and travel at c?

is photon a pocket of energy condensed into a particle? what kind of energy? momentum? em force? vibration force?

how photon is absorbed? reflected?

use sun light to heat up water, how water atoms eat photons and heat up? electrons eat photons and move to higher orbitals?

or sun light is vibration force that makes water atoms vibrating faster?

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #16 on: 09/07/2015 23:37:54 »
Quote from: jccc link=topic=58323.msg462609#msg462609
shine different color laser beams on the same spot.
If this is what you had in mind, why talking about photons at all?
And however "mixing photons" cannot be what you wrote.

--
lightarrow
« Last Edit: 09/07/2015 23:47:17 by lightarrow »

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #17 on: 09/07/2015 23:41:55 »
photon, a pocket of energy, a mass less particle travels at c speed, is impossible to exist according to energy conservation law.
It's the festival of stupid things? At least ask a question, instead of making bull..... statements.
Photon exists (almost) because energy conservation law is true...

--
lightarrow
« Last Edit: 09/07/2015 23:50:08 by lightarrow »

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4175
  • The graviton sucks
    • View Profile
Re: Do photons have colours?
« Reply #18 on: 09/07/2015 23:52:10 »
i still cannot figure out how photon is emitted.

even if electron really has orbitals and able to move between orbitals, how is the electron's changing momentum transfer into a particle and travel at c?

is photon a pocket of energy condensed into a particle? what kind of energy? momentum? em force? vibration force?

how photon is absorbed? reflected?

use sun light to heat up water, how water atoms eat photons and heat up? electrons eat photons and move to higher orbitals?

or sun light is vibration force that makes water atoms vibrating faster?

If particle physics were easy then everyone would know the answers. You are starting from a position of ignorance and hoping to be spoon fed the answers. Even when you get the answers this doesn't satisfy you. Go and read a particle physics text. It'll stop you right in your tracks.

PS Then try group theory.
« Last Edit: 09/07/2015 23:54:07 by jeffreyH »
Fixation on the Einstein papers is a good definition of OCD.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #19 on: 10/07/2015 00:26:57 »
nature is simple, straight forward. follow physics laws, all things work well.

men invented science, science is always correcting, particle physics have many holes.

no 1 can explain how 1 electron and 1 proton make up an atom yet.

can you answer how electron emit photon? in detail and laws?

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #20 on: 10/07/2015 00:39:51 »
Nature is not simple. If it were we wouldn't exist, because we are not simple.

Science is much simpler than nature is. That's what science is about, simplification (approximation) of the extremely complex to the point that it can be understood by mere humans.

Just because YOU don't understand the explanation of a hydrogen atom, doesn't mean WE can't explain it. Can an orangutan claim that evolution is wrong because it doesn't understand?

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4175
  • The graviton sucks
    • View Profile
Re: Do photons have colours?
« Reply #21 on: 10/07/2015 00:58:00 »
nature is simple, straight forward. follow physics laws, all things work well.

men invented science, science is always correcting, particle physics have many holes.

no 1 can explain how 1 electron and 1 proton make up an atom yet.

can you answer how electron emit photon? in detail and laws?

Until you can understand the tools that science uses you will be repeating yourself endlessly. You also need to understand that these tools model the processes. A model is ultimately an approximation. If you don't understand the models and what they represent you will never make progress. No one knows WHY an electron and proton make up an atom. Just as no one knows why the electron emits a photon. They just do. You are really asking the wrong questions.
Fixation on the Einstein papers is a good definition of OCD.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #22 on: 10/07/2015 01:30:06 »
i know what's going on. i explained in my theories. you just don't understand/accept.

rather say they just do.

any of my ideas has any logic problem? be appreciate you point it put, so we all can learn from you.


*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #23 on: 10/07/2015 02:29:43 »
Quote from: jccc link=topic=58323.msg462702#msg462702 date=1436488206

any of my ideas has any logic problem? be appreciate you point it put, so we all can learn from you.
[/quote

Yes your theories have three major flaws that come to mind: One, you assume that very small things (like electrons) act in a manner similar to things that are big (this is not observed to be true, in fact very small things act very different). Two, you assume there is a simple explanation for everything, when many things are in fact extremely complicated. Three, you ignore reams of evidence that have been gathered and verified by thousands of scientists for centuries(for instance, all of the evidence that light is electromagnetic).

Address these flaws in your logic, and you may have more luck with your theories.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #24 on: 10/07/2015 02:55:34 »
light is em wave? or photon particle? or both?

why is powerful laser particle beams able to cut metal but not bend flame?

how sunlight heats up water? photons hit water atoms so electrons in water jump to higher orbitals?

if you answer those questions to understandable logic, i'll accept your theory of light.

all scientist can be wrong,  before science able to explain everything in detail perfectly. like how electrons emit photons.

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #25 on: 10/07/2015 03:31:56 »
light is em wave? or photon particle? or both?

both, just like electrons are particles and waves.

why is powerful laser particle beams able to cut metal but not bend flame?

I don't understand why you think being able to bend a flame is important or relevant. Of course a laser isn't going to move a flame, just like shooting the ocean with a machine gun doesn't move the ocean. There are still interactions between the flame and the photons, if you just look for it (for instance, a candle flame casts a shadow if you shine a bright light on it. (https://www.youtube.com/watch?v=dl3v0Y0adLY)

Light does have momentum, and it has been harnessed by a light sail:
https://www.youtube.com/watch?v=kDBzRa9RzfM
https://www.youtube.com/watch?v=d8NUCOMmCpY

how sunlight heats up water? photons hit water atoms so electrons in water jump to higher orbitals?

That's part of it, although, you'll notice that water is essentially colorless, so it's not visible light that's getting absorbed. Some is ultraviolet, but mostly it's infrared light that's getting absorbed by the water. Instead of exciting the electrons, it causes the water molecules to vibrate directly (get warm). https://en.wikipedia.org/wiki/Infrared_spectroscopy
This is also what makes water and carbon dioxide greenhouse gases.

if you answer those questions to understandable logic, i'll accept your theory of light.

Good. I guess my work here is done. Thanks for accepting my theory.

all scientist can be wrong,  before science able to explain everything in detail perfectly. like how electrons emit photons.

It's true, all scientists can be wrong. But it will be another scientist who disproves them.

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #26 on: 10/07/2015 03:46:12 »
why is photon particle beam able to cut metal not move flame? not relevant?

shooting gun able to move water, produce water flow, observable. move a flame is not move ocean. your argument is pretty weak.

agree?

*

Offline jccc

  • Hero Member
  • *****
  • 990
    • View Profile
Re: Do photons have colours?
« Reply #27 on: 10/07/2015 04:17:38 »
is any light sail bigger than earth?

why is sunlight photons momentum not sailing earth? did we changed orbit?

if sunlight has momentum, the space station will be pushing away from the sun, did it happen?


*

Offline evan_au

  • Neilep Level Member
  • ******
  • 4310
    • View Profile
Re: Do photons have colours?
« Reply #28 on: 10/07/2015 11:40:04 »
Quote from: jccc
most photons are color less, like radio wave photons, x-rays.
I think you need to define what you mean by "color-less"; I assume you mean "invisible to humans".
  • Bees can use ultraviolet light to select flowers with nectar, even though it is invisible to humans.
  • Some snakes can use infra-red light to catch mice, even though it is invisible to humans.
  • An AM radio can detect frequencies around 1 MHz, even though it is invisible to humans
  • An X-Ray machine can detect X-Rays to detect broken bones, even though it is invisible to humans.
  • The mantis-shrimp can detect subtle hues that are invisible to humans.
  • But all of these are electromagnetic radiation.
  • So almost any form of electromagnetic radiation can be detected or "seen" if the radiation is powerful enough, and you have the right sort of detector. 
We unify these different electromagnetic phenomena by describing these different parts of the  spectrum by the photon energy, which can also be determined by photon wavelength and frequency. These concepts are a generalisation of the term "color".

Quote
how does an electron knows what color of photons should emit?
When an electron jumps between two orbitals of an atom, the energy difference between the two orbitals determines the color of the photon emitted (or absorbed).

There are also other mechanisms of emitting photons, depending on the frequency. For example, a radio antenna emits photons at a frequency where the electrons in the wire are driven backwards and forwards by the RF amplifier. (And in this case, the RF amplifier often obtains this frequency from the mechanical vibration of a quartz crystal*.)

Quote
what direction?
Apart from lasers, where the stimulated photon has the same direction as the incoming photon, most photon emission mechanisms are fairly random in their direction.

To some extent, you can steer where photons appear by using reflection, refraction and interference, despite the original random direction.

Quote
how many?

One per orbital change. Sometimes a photon can quickly cascade down a number of orbital changes, producing a shower of photons.

Quote
what speed?

c (in a vacuum). It is lower in a non-vacuum.

*Don't get your hopes up that every form of electromagnetic vibration can be produced from a mechanical vibration. By the time you get to visible light and shorter wavelengths, mechanical vibrations of atoms & molecules are too sluggish to make a strong contribution to light output.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #29 on: 10/07/2015 16:59:36 »
I don't understand why you think being able to bend a flame is important or relevant. Of course a laser isn't going to move a flame, just like shooting the ocean with a machine gun doesn't move the ocean.
But of course it depends on the laser power.
Try with a 500TW laser like this one and then tell me:
https://en.wikipedia.org/wiki/National_Ignition_Facility#Impetus

Quote
In total these amplifiers boost the original 6 J provided by the PAMs to a nominal 4 MJ.[10] Given the time scale of a few billionths of a second, the peak UV power delivered to the target is correspondingly very high, 500 TW.

--
lightarrow

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2804
    • View Profile
Re: Do photons have colours?
« Reply #30 on: 10/07/2015 21:05:59 »
Quote from: lightarrow
But of course it depends on the laser power.
Try with a 500TW laser like this one and then tell me:
https://en.wikipedia.org/wiki/National_Ignition_Facility#Impetus

Quote
In total these amplifiers boost the original 6 J provided by the PAMs to a nominal 4 MJ.[10] Given the time scale of a few billionths of a second, the peak UV power delivered to the target is correspondingly very high, 500 TW.
That has absolutely nothing to do with bending a flame. Let us not forget that a flame is basically the visible part of a gaseous part of a fire, nothing more and nothing less. Think of it like this. Consider a laser beam passing through a spherical ball of hot gas, so hot as to be visible, i.e. a spherical flame (what happens when you try to light a match in a zero-g environment). The properties of the gas are uniform so if the flame was bent as it went in and was deflected then it would break the symmetry of the setup and there's nothing in the symmetry which would allow for that. That's a layman's description and one that's easy to see for anybody.

*

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • 1932
    • View Profile
Re: Do photons have colours?
« Reply #31 on: 10/07/2015 21:24:16 »
why is photon particle beam able to cut metal not move flame? not relevant?

shooting gun able to move water, produce water flow, observable. move a flame is not move ocean. your argument is pretty weak.

agree?


Imagine you are looking at the ocean from 4 ly away. With a big enough telescope you can see the Earth, and even see that it has oceans, but good luck seeing any effect the bullets have. Same with photons and flame. The photons move some of the gas particles around, but nothing you could see, even with the best microscopes and high-speed cinematography.

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2804
    • View Profile
Re: Do photons have colours?
« Reply #32 on: 10/07/2015 21:57:53 »
Quote from: jccc
shooting gun able to move water, produce water flow, observable. move a flame is not move ocean. your argument is pretty weak.
Oh good Lord. I swore that I'd ignore you forever but when you make such horrible claims I just can't let them pass. You're deduction is totally without any reason whatsoever. His analogy is quite accurate. A photon can interact with the flame by interacting with individual atoms by exciting them to higher energy levels. The amount of momentum transferred to them by the photon is so small that there is virtually no cumulative effect on the flame itself. This is exactly analogous to shooting a wave with a gun. Your deduction skills are still as horrible as they ever were. Is it no wonder to you why I won't converse with you anymore?

*

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • 4175
  • The graviton sucks
    • View Profile
Re: Do photons have colours?
« Reply #33 on: 10/07/2015 22:21:39 »
He doesn't understand that it is elementary physics my dear Watson.
Fixation on the Einstein papers is a good definition of OCD.

*

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • 1093
    • View Profile
Re: Do photons have colours?
« Reply #34 on: 11/07/2015 04:05:23 »
why is sunlight photons momentum not sailing earth?
It essentially does.
Quote
did we changed orbit?
Earths orbit is slightly different than it would have been if the Sun wasn't shining, but it has a similar effect as if the Sun was a bit less massive (sunlight pressure goes inverse square law just like gravity does.)
Quote
if sunlight has momentum, the space station will be pushing away from the sun, did it happen?
Oh yes, certainly. Allowance for light pressure is routinely made with satellites. It definitely changes orbits, albeit only very slightly, and more significantly, causes torques on satellites.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #35 on: 11/07/2015 07:58:36 »
Quote from: lightarrow
But of course it depends on the laser power.
Try with a 500TW laser like this one and then tell me:
https://en.wikipedia.org/wiki/National_Ignition_Facility#Impetus

Quote
In total these amplifiers boost the original 6 J provided by the PAMs to a nominal 4 MJ.[10] Given the time scale of a few billionths of a second, the peak UV power delivered to the target is correspondingly very high, 500 TW.
That has absolutely nothing to do with bending a flame. Let us not forget that a flame is basically the visible part of a gaseous part of a fire, nothing more and nothing less. Think of it like this. Consider a laser beam passing through a spherical ball of hot gas, so hot as to be visible, i.e. a spherical flame (what happens when you try to light a match in a zero-g environment). The properties of the gas are uniform so if the flame was bent as it went in and was deflected then it would break the symmetry of the setup and there's nothing in the symmetry which would allow for that. That's a layman's description and one that's easy to see for anybody.
?
I had understood nothing of what you have written.
Anyway if you don't know what is "bending a flame" take a look at this:
https://www.youtube.com/watch?v=a7_8Gc_Llr8

Question: can you do the same with a 500TW laser?

--
lightarrow

*

Offline PmbPhy

  • Neilep Level Member
  • ******
  • 2804
    • View Profile
Re: Do photons have colours?
« Reply #36 on: 11/07/2015 15:02:35 »
Quote from: lightarrow
I had understood nothing of what you have written.
Why? It was so clearly written to. What I said was basically this; You asked why if a laser is able to cut metal but not bend flame? Suppose it did bend the flame. In what direction would the flame be bent? Let's use a spherical flame like that which is created when you first strike a match in a zero-g environment like they did aboard a shuttle flight at one time. It doesn't burn long because oxygen can't get to the match head where the fuel is. However it can be done if done properly. So if they have a spherical flame and they pass a laser beam through the center of the flame then in what direction is the flame bent and why?

Quote from: lightarrow
Anyway if you don't know what is "bending a flame" ..
Who said that I didn't know what a bent flame is? I was asking what you had in mind as far as a bent flame.
There's a big difference there.

Quote from: lightarrow
...take a look at this: https://www.youtube.com/watch?v=a7_8Gc_Llr8
Unrelated since the flame isn't bending but is being spread apart. The part of the gas with positive ions are pulled in one direction while the negative ions are pulled in the opposite direction. Hence the flame is parted, not bent.

Quote from: lightarrow
Question: can you do the same with a 500TW laser?
No. Absolutely not. There is nothing to cause the flame to bend and if there's no cause for it then it doesn't happen. Understand now?

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Re: Do photons have colours?
« Reply #37 on: 11/07/2015 19:38:51 »
Quote from: lightarrow
I had understood nothing of what you have written.
Why? It was so clearly written to. What I said was basically this; You asked why if a laser is able to cut metal but not bend flame?
Not at all, it was jccc to ask this, I replied to him.
Quote
. Suppose it did bend the flame. In what direction would the flame be bent?
Obviously in the direction of k, that is of the beam propagation: photons have momentum and a part of this is transferred to the air/flame molecules after scattering.
Quote
Unrelated since the flame isn't bending but is being spread apart. The part of the gas with positive ions are pulled in one direction while the negative ions are pulled in the opposite direction. Hence the flame is parted, not bent.
You mean it's a linguistic problem?
I don't know if it moves in the same direction of the positive or the negative ions, but it moves. I see a bent flame and this is enough for me.

--
lightarrow

*

Offline evan_au

  • Neilep Level Member
  • ******
  • 4310
    • View Profile
Re: Do photons have colours?
« Reply #38 on: 12/07/2015 06:56:37 »
Quote from: jccc
if you mix red, blue and green photons, what color photons you get?
if you mix white and black photons, what color photons you get?

I think there is a confusion here between the color that can be expressed by a single photon, and the colors that can be perceived by a human when viewing a light beam containing many photons, usually of different colors/frequencies/wavelengths.

The human visual system has three color receptors producing conscious images, which are most sensitive to photons of red, green and blue*. However, each receptor is also partially sensitive to other colors.

In principle, a single photon could excite only a single cone cell, and produce only the sensation of red, green or blue.

However, light intense enough for humans to perceive color contains many photons. If these photons have the same color (ie same frequency and wavelength, such as from a laser), the many photons can excite many cone cells at once. Depending on the relative strength of excitation, additional colors may be perceived which includes all the colors of the rainbow, including orange & yellow (for partial excitation of both red and green receptors) or violet (which excites the blue receptor, but has almost no response from the red & green receptors). 

There are many additional colors which do not appear in the rainbow, such as white and magenta. These can only be generated by a mix of photons of different frequency; for example the sensation of white requires a mix of photons which excite the R, G & B receptors roughly equally.

The sensation of white can also occur when the intensity of light falls below the sensitivity of the cone cells, leaving the rod cells to detect light; the rod cells are only "black and white". The sensation of Black occurs when the intensity of light is below the sensitivity of the human rod cells.

So a "Starry, Starry Night" appears predominantly as white stars on a black background, even though the different stars have quite different colors which can be seen in a long exposure photograph of the night sky.

* The cone cells are not very sensitive to light, so it takes many photons to evoke a sensation of color. But I'll ignore that here.

*

Offline Thebox

  • Neilep Level Member
  • ******
  • 3250
    • View Profile
Re: Do photons have colours?
« Reply #39 on: 12/07/2015 11:00:01 »
A Boothroyd asked the Naked Scientists:
   
 I have been thinking about it......  And i reckon the "back" of a photon "looks like" is color.  Was wondering if?  That could be the answer because it explains much.

What do you think?

There is no ''colour'' in or of a photon, ''colour'' is a process of interpretation by the brain or use of device. ''Colour'' is frequency difference, an energy difference detected by us and device. No more than a sound is not a sound until it is heard.
The constant of light in space is colourless, only by interaction of Em radiation with matter is ''colour'' detected by us.
''Colour'' is a wave breaking on a surface, a spectral diffusion of thermal differences. Signatures we detect by sight through the otherwise colourless constant of Em radiation. A radiation we evolved to see through, making a clarity of space, crystal clear to the eye.
« Last Edit: 12/07/2015 11:19:21 by Thebox »

*

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • 2079
    • View Profile
Re: Do photons have colours?
« Reply #40 on: 12/07/2015 17:47:08 »
''Colour'' is frequency difference
not quite. The colour of the light is determined ny it's frequency, not the difference between that and any other frequency.
This is the same with sound where frequency = pitch
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

*

Offline David Cooper

  • Neilep Level Member
  • ******
  • 1505
    • View Profile
Re: Do photons have colours?
« Reply #41 on: 12/07/2015 18:08:49 »
In Einstein's model of reality, a photon should not have a specific colour because it has no specific frequency - its frequency varies infinitely as you test it from different frames of reference. Colour can only come into being when the photon interacts with something else (which happens at either end of its journey, and the two colours it has may be very different).

*

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • 1093
    • View Profile
Re: Do photons have colours?
« Reply #42 on: 12/07/2015 19:41:32 »
No, theBox is precisely correct, colour is a perceptual thing, and it is mostly differences between colours that is perceived; that's because lighting varies enormously, but our perception interpolates around that and gives things a (mostly) stable colour for us.

The wavelength or frequency of a photon are related by Einstein's equations.

*

Offline David Cooper

  • Neilep Level Member
  • ******
  • 1505
    • View Profile
Re: Do photons have colours?
« Reply #43 on: 12/07/2015 20:56:09 »
No, theBox is precisely correct, colour is a perceptual thing, and it is mostly differences between colours that is perceived; that's because lighting varies enormously, but our perception interpolates around that and gives things a (mostly) stable colour for us.

If you're talking about the colour qualia in our heads, that's fine, but it doesn't apply to photons and their frequencies which have measurable values - the only way for these to vary is by varing the speed of collision of the detector with them.

Quote
The wavelength or frequency of a photon are related by Einstein's equations.

Lovely, but if you accelerate towards a laser which is sending a beam of light towards you, the colour you detect will change, and if you stop accelerating at various times and declare yourself to be stationary while you determine what colour the light is, you will produce a variety of different answers which demonstrate that the light is not tied to any specific colour (unless you're working under a different theory like LET where the colour of a photon has an absolute frequency.)