The Naked Scientists

The Naked Scientists Forum

Author Topic: How small can a photon get ?  (Read 5295 times)

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
How small can a photon get ?
« on: 26/09/2015 12:37:30 »
I read that at the planck length photons become spheres , in effect being a wave of energy around a core of no energy , is this right ?


 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4123
  • Thanked: 245 times
    • View Profile
Re: How small can a photon get ?
« Reply #1 on: 27/09/2015 00:03:54 »
The Planck length is so small (10-35m) that nobody can take measurements at this scale.

A wavelength of this size would represent a fantastically powerful photon - I would not want to be anywhere near it! Gamma rays are dangerous, and they have wavelengths of only 10-12 m.

Quantum effects mean that it is practically impossible to determine a "shape" for a photon, even at the familiar and safe visible wavelengths.

I think it is best to view the Planck length as theoretical; an attempt to create units which were in some sense "fundamental", rather than arbitrary anthropocentric/geocentric values like the size of the Earth and the density of water.
« Last Edit: 27/09/2015 18:45:46 by evan_au »
 

Offline mathew_orman

  • Sr. Member
  • ****
  • Posts: 132
    • View Profile
Re: How small can a photon get ?
« Reply #2 on: 27/09/2015 09:25:11 »
No smaller than electron...
 

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Re: How small can a photon get ?
« Reply #3 on: 27/09/2015 11:27:05 »
Thanks for your response I guess my question  was a a little  vague so I'll try again , what happens when you reduce the size of the wavelength and amplitude of a photon to the planck scale ? I understand that the planck length is in effect the limit of practical physics so any smaller than that is in effect nothing , so I guess my question is about how close does something that could work in the real world get to that limit ?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How small can a photon get ?
« Reply #4 on: 27/09/2015 13:15:47 »
Thanks for your response I guess my question  was a a little  vague so I'll try again , what happens when you reduce the size of the wavelength and amplitude of a photon to the planck scale ? I understand that the planck length is in effect the limit of practical physics so any smaller than that is in effect nothing , so I guess my question is about how close does something that could work in the real world get to that limit ?
A photon doesn't have an "amplitude", because it's not a wave packet. It has a wavelength because it's the wavelength of its electromagnetic field.
About what happens reducing the wavelength, you already had an answer: the photon's energy increases because it's inversely proportional to wavelength.

--
lightarrow
« Last Edit: 27/09/2015 19:50:13 by lightarrow »
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 144 times
    • View Profile
Re: How small can a photon get ?
« Reply #5 on: 27/09/2015 14:14:43 »
As lightarrow pointed out: photons have no "amplitude," the amplitude of a light wave has to do with the flux of photons and their coherence.

So you are only left with decreasing wavelength, which, many have pointed out: energy is inversely proportional to wavelength (E = hc/λ), where E is energy, h is planck's constant, c is the speed of light and λ is wavelength. Using this equation and evan_au's approximation of the Planck length as 10–35 m, I calculate that a single photon with a wavelength of 10–35 m would have about 20 GJ of energy—that's more energy than gets released by detonating 4 tons of TNT! That's about 100 times the total kinetic energy of the particle beams at the LHC.

What I don't know is how dangerous that would be. It doesn't matter how much energy the photon has, if it cannot interact with any matter. From my understanding, it is possible that this could have so much energy that it couldn't interact with matter very easily. It is also possible that it would.

There has to be a quantum transition in the state of something. For instance:

nuclei in strong magnetic fields absorb or release radio waves as they transition between spin states
polyatomic molecules absorb or release microwaves as they transition between rotational states
polyatomic molecules also absorb or release infrared as they transition between vibrational states
atoms and molecules absorb or release in the visible and near ultraviolet as outer shell electrons transition between orbitals.
atoms and molecules absorb or release in the far ultraviolet as electrons transition between free and outer shell
atoms and molecules absorb or release in x-rays as electrons transition between free and inner shell
nuclei absorb or release gamma rays as they transition between nuclear states

Measuring how compounds interact with EM radiation (spectroscopy)  is (partially) dependent on the fact that whether the photon is absorbed depends on how well the energies match. Photons with the wrong frequency will pass right by with little interaction. I have no idea what sort of transition could absorb a 20 GJ photon (but just cause we haven't had the opportunity to observe how matter behaves at those energies, doesn't mean it won't. it just might not...)
 

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Re: How small can a photon get ?
« Reply #6 on: 27/09/2015 15:42:41 »
Ok I think I can wrap my head round your answer so at what scale does an EM wave which does have wavelength and amplitude become a photon that doesn't have amplitude while retaining wavelength ? Or is that a question that makes no sense ?
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 144 times
    • View Profile
Re: How small can a photon get ?
« Reply #7 on: 27/09/2015 15:57:10 »
The photon is the smallest possible part of a ray of light. It is the quantum of amplitude.
 

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Re: How small can a photon get ?
« Reply #8 on: 27/09/2015 18:35:43 »
Sorry I guess my earlier remark about wrapping my head round this was way off the mark :) So at what scale do the amplitude of electric field and the amplitude of magnetic field in an an EM wave stop having a size that has a physical measurement ? If the wavelength can be defined in those terms ie it has a wavelength of 1 m or 10 planck lengths , at what scale does amplitude stop having those qualities ?
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4123
  • Thanked: 245 times
    • View Profile
Re: How small can a photon get ?
« Reply #9 on: 27/09/2015 19:05:38 »
Quote from: Lightarrow
A photon doesn't have an "amplitude", because it's not a wave packet.
I suggest that a propagating photon has a maximum E & B field intensity, which could be considered the amplitude of a wave packet.

Quote from: ChiralSPO
I have no idea what sort of transition could absorb a 20 GJ photon
The energies don't have to match exactly - in Compton Scattering, electrons gain energy when struck by gamma rays (the energy coming from a reduction in the frequency of the gamma ray photon). A single gamma ray photon will bounce off many electrons before finally being absorbed.

If the energy of a gamma ray is high enough, it will interact with matter to produce electron/positron pairs. I imagine a 20GJ photon would produce a host of more massive particles, like protons & anti-protons (and even more exotic, short-lived particles, too).

I imagine that with a 20GJ photon, not just electrons, but also protons, quarks and "empty space" would be given an intense kick, much greater than the LHC physicists could even dream of building after the LHC!

The LHC tunnel is not the place to be when the LHC is operating!

Of course, this much energy in a small space may produce a pico black hole, which (according to Hawking) would instantly evaporate explosively...
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How small can a photon get ?
« Reply #10 on: 27/09/2015 20:01:09 »
Quote from: Lightarrow
A photon doesn't have an "amplitude", because it's not a wave packet.
I suggest that a propagating photon has a maximum E & B field intensity, which could be considered the amplitude of a wave packet.
Maximum intensity? What do you mean? I would say it's a minimum, fixed the frequency: if frequency doesn't change, the em wave intensity is proportional to the number of photons.
 

Offline mathew_orman

  • Sr. Member
  • ****
  • Posts: 132
    • View Profile
Re: How small can a photon get ?
« Reply #11 on: 28/09/2015 08:07:42 »
Thanks for your response I guess my question  was a a little  vague so I'll try again , what happens when you reduce the size of the wavelength and amplitude of a photon to the planck scale ? I understand that the planck length is in effect the limit of practical physics so any smaller than that is in effect nothing , so I guess my question is about how close does something that could work in the real world get to that limit ?
Again the answer is an electron... Or the size of an electron...
Plank numbers are to satisfy mathematical rules and laws...
Forces of reality do not obey orders of mathematicians...
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How small can a photon get ?
« Reply #12 on: 28/09/2015 11:51:13 »
I know im none conventional, but I cant help it, its not my fault.
space is made up of little magnetic dipoles. A photon is a dipole spinning end over end, the frequency of the photon is given by the rate at which it turns, you can effectively have a photon that isnt spinnning at zero hertz, still travelling at light speed. The minimum size a photon can have is the plank limit, space behaves like a perpetual spring driving photons at light speed once they get moving in any particular direction.
Radio waves are made up of photons, arranged like a sine wave as they travel, sorry I dont have  a better analogy.

Kind Regards

You must have smoked strong stuff recently  :)

--
lightarrow
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How small can a photon get ?
« Reply #13 on: 28/09/2015 11:52:52 »
Thanks for your response I guess my question  was a a little  vague so I'll try again , what happens when you reduce the size of the wavelength and amplitude of a photon to the planck scale ? I understand that the planck length is in effect the limit of practical physics so any smaller than that is in effect nothing , so I guess my question is about how close does something that could work in the real world get to that limit ?
Again the answer is an electron... Or the size of an electron...
Plank numbers are to satisfy mathematical rules and laws...
Forces of reality do not obey orders of mathematicians...
As meaningles as the color of the number "2".

--
lightarrow
 

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Re: How small can a photon get ?
« Reply #14 on: 28/09/2015 19:13:11 »
Ok I realize that some ideas that come up may be rather unconventional , even complete nonsense .  As conventional  science doesn't know what makes up over 80 percent of the mass of the observable universe or what force is causing the universe to expand at its current rate you could say the standard model is a little off  the mark :) Which means new ideas have to be given a fair hearing , after all you can't prove there are other dimensions but plenty of people still do the math with them . I suspect scientist are a little sick of hear this :)
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4123
  • Thanked: 245 times
    • View Profile
Re: How small can a photon get ?
« Reply #15 on: 28/09/2015 22:21:56 »
Quote from: CorneliusDalvert
As conventional  science doesn't know what makes up over 80 percent of the mass of the observable universe ... Which means new ideas have to be given a fair hearing
We do try to give all ideas a fair hearing - and point out any flaws we can see.

However, you can't deduce that just because Dark Matter is a mystery, therefore electromagnetic radiation must also be a mystery.

We now have a good theoretical and practical understanding of electromagnetic radiation - the phone in your pocket can generate and detect it with great precision, based on theories from Maxwell, Einstein and others.

So, if you have theories about Dark Matter, by all means throw them into the ring with all the other theories. Even better, if you have some experimental evidence for this theory, you will be in the running for a Nobel Prize!

However, alternative theories about electromagnetic radiation should go into the "New Theories" section of the website (unless you have some experimental evidence that it is better than the old theory, in which case the Nobel committee will still be interested).
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: How small can a photon get ?
« Reply #16 on: 29/09/2015 04:40:54 »
Quote from: CorneliusDalvert
As conventional  science doesn't know what makes up over 80 percent of the mass of the observable universe or what force is causing the universe to expand at its current rate you could say the standard model is a little off  the mark :) Which means new ideas have to be given a fair hearing , after all you can't prove there are other dimensions but plenty of people still do the math with them . I suspect scientist are a little sick of hear this :)
Ideas rarely get into journals unless the idea can be formulated as a theorem or a postulate. In the later case the postulate must be very obvious and well tested. Otherwise the article won't get through the peer review process.
 

Offline mathew_orman

  • Sr. Member
  • ****
  • Posts: 132
    • View Profile
Re: How small can a photon get ?
« Reply #17 on: 29/09/2015 08:18:56 »
It is a very relevant question and my answer stands: It cannot be smaller than electron...
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4123
  • Thanked: 245 times
    • View Profile
Re: How small can a photon get ?
« Reply #18 on: 29/09/2015 11:52:18 »
Quote from: mathew_orman
(a photon) cannot be smaller than electron...
Gamma Rays have wavelengths around a picometer (shorter at higher energies). You could loosely say that a gamma ray photon is about a picometer across (even though PmbPhy points out that a photon is a point particle).

An electron in a hydrogen atom is contained within the covalent radius of a hydrogen atom, about 60 picometers across.

An electron in a high energy electron microscope can resolve features as small as 50 picometers.

So I would conclude that a gamma ray photon can be smaller than an electron.

Of course, gamma rays tend to be generated by nuclear processes, and protons are a lot smaller than an electron.
« Last Edit: 29/09/2015 22:24:16 by evan_au »
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How small can a photon get ?
« Reply #19 on: 29/09/2015 12:05:56 »
It is a very relevant question and my answer stands: It cannot be smaller than electron...
Prove it.

--
lightarrow
 

Offline mathew_orman

  • Sr. Member
  • ****
  • Posts: 132
    • View Profile
Re: How small can a photon get ?
« Reply #20 on: 29/09/2015 12:14:24 »
It is a very relevant question and my answer stands: It cannot be smaller than electron...
Prove it.

--
lightarrow
Sorry, this would require giving away proprietary info...
Again, it is not an argument, it is a tip or a hint....
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: How small can a photon get ?
« Reply #21 on: 29/09/2015 13:01:17 »
Quote from: Aquarius
People claim here that you have a good understanding of electromagnetic radiation, you completely miss how it is transmitted.
When you make comments like this directed to a person, i.e. the "you", that you mentioned, you need to tell us who it is that you're talking to. Otherwise nobody will know who it is that you're talking to and won't necessarily respond.

Quote from: Aquarius
A photon is one of these spinning pole over pole.
Photons don't have poles and the spin is not like spin in classical mechanics. In this case that means that photons don't behave as "spinning pole over pole."

Quote from: Aquarius
An electron is made up of quarks, which are force carriers spinning radially.
You're very wrong here. Electrons are not made of quarks. Only hadrons are made of quarks and an electron is a lepton, not a hadron.

See the following entries at Wikipedia:

https://en.wikipedia.org/wiki/Electron
https://en.wikipedia.org/wiki/Lepton
https://en.wikipedia.org/wiki/Hadron
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: How small can a photon get ?
« Reply #22 on: 29/09/2015 16:48:37 »
I guess that shows how long since I was in school, and how outdated the few books I have are.

I will go and find an internet café with a fast connection and have a look at all your links, you putting out. The last bit of advice you gave me turned up gravity fro me.

Kind regards ::)
Aquarius - I'm quite please at your response and the way you accept correction. This is exactly the kind of people we like to get on my forum. Membership is invitation only. I'm offering you membership if you'd like to join. Just read the following rules and know that they are rigidly enforced - http://www.newenglandphysics.org/amateur_forum/forum_rules.htm

We won't allow anybody to give you a hard time or be impolite to you in any way. You just have to do the same to others. After you've read the forum rules then go to:
http://www.newenglandphysics.org/amateur_forum/index.php

And register. Make sure you send me an e-mail as soon as you can so I know which of the many e-mails I get is yours. That e-mail account is full of spam by people who are trying to join to post advertisements. When I see your e-mail I'll accept your registration and you'll be a member. I sent you a PM with my e-mail address in it.
 

Offline CorneliusDalvert

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Re: How small can a photon get ?
« Reply #23 on: 29/09/2015 18:18:20 »
I just read PmbPhy's post on the shape of light , so if the oscillating E and B  fields could act as an amplitude ( using their maximum range within their fields as a point of measurement ). What would be the effect of reducing this and the wavelength to the planck length scale , let's say between 5 and 10  planck lengths ,would the photon become a sphere ? Also if I didn't have some faith in the standard model I'd ask pixies for answers not scientists . PS lightarrow the colour of the number 2 is usually brown  :)
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: How small can a photon get ?
« Reply #24 on: 30/09/2015 15:40:43 »
Quote from: Aquarius
Where is this information located.  :)
Start here: https://en.wikipedia.org/wiki/Photon

In the future you can't expect that you can learn everything about something from, one source. We physicists spend a great deal of time learning from a string of sources.
 

The Naked Scientists Forum

Re: How small can a photon get ?
« Reply #24 on: 30/09/2015 15:40:43 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums