What is energy, exactly?

[elemental]

Isn't the quantum a smaller measure of energy than a photon?

 

Can't photons be different multiples of quanta?

[Aethelwulf]

Quantum tends to be as ''elementary'' as you can get for any particle. There is such a thing as a quantum number for photons, called their spin states.

[pantheory]

Isn't the quantum a smaller measure of energy than a photon?

 

Can't photons be different multiples of quanta?

elemental,

 

Quanta is singular in Latin, and quantum is plural.

 

According to Plank quantum (plural) were a packet of particles composed of individual quanta. But this has not been considered theoretically by any other mainstream model since because the existence of individual quanta seems to be unprovable.

 

Photons, according to theory, are exactly the same thing as quantum. Newton named his theoretic particles of light corpuscles. Max Planck conceived a similar entity which he conceived as a bundle of particles which he called quantum. Einstein also theorized a light particulate which he called a photons.

 

"In 1926 the chemist Gilbert N. Lewis (first) coined the name photon for these particles, and after 1927, when Arthur H. Compton won the Nobel Prize for his scattering studies, most scientists accepted the validity that quanta (quantum) of light have an independent existence, and Lewis' term photon for light quanta was accepted." (parenthesis added)

 

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

 

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Edited June 24, 2012 by pantheory

[imatfaal]

elemental,

 

Quanta is singular in Latin, and quantum is plural.

 

//

 

http://en.wiktionary.org/wiki/quantum

http://www.thefreedictionary.com/quantum

 

Quanta is plural and quantum is singular. The Latin is difficult to be sure of as quantum does not seem to be a noun in Latin; quantum in Latin is an adjective, meaning "how much'. Modern European languages took this word and used it as a noun to express the quantity of a substance or amount of money; for instance, many years before Max Planck, English courts would ask "What's the quantum?" meaning "How much money are we arguing about?"

 

Skitt's law is unavoidable; probably even in this post.

[pmb]

"In 1926 the chemist Gilbert N. Lewis (first) coined the name photon for these particles, and after 1927, when Arthur H. Compton won the Nobel Prize for his scattering studies, most scientists accepted the validity that quanta (quantum) of light have an independent existence, and Lewis' term photon for light quanta was accepted." (parenthesis added)

Yes. The term was what was accepted. However the concept as he defined it was rejected. Gilbert thought of his photons as existing inside atoms and moved from atom to atom as a conserved quantity. The photon we know today is not a conserved quantity. They can be created and destroyed.

 

As that wiki article explains

Gilbert Lewis, who published a speculative theory in which photons were "uncreatable and indestructible".[6] Although Lewis' theory was never accepted as it was contradicted by many experiments, his new name, photon, was adopted immediately by most physicists

Edited June 25, 2012 by pmb

[pantheory]

http://en.wiktionary.org/wiki/quantum

http://www.thefreedi...ary.com/quantum

 

Quanta is plural and quantum is singular. The Latin is difficult to be sure of as quantum does not seem to be a noun in Latin; quantum in Latin is an adjective, meaning "how much'. Modern European languages took this word and used it as a noun to express the quantity of a substance or amount of money; for instance, many years before Max Planck, English courts would ask "What's the quantum?" meaning "How much money are we arguing about?"

 

Skitt's law is unavoidable; probably even in this post.

 

Thanks for the correction imatfaal. I even "double-checked" it wrongly maybe a kind of dyslexia

 

Cool linguistic info also

Edited June 25, 2012 by pantheory

[elemental]

I must have misread something along the way and took Max Planck's h ( a quantum of action ) to be more fundamental, more general, than the photon as a quantum of action.

 

Planck's constant is a proportionality constant and as pantheory pointed out, the h is theoretical. It must be impossible to detect, or even emit one h, so it can't be verified as an entity.

 

So, what is the lowest energy single photon that can be detected?

[swansont]

I must have misread something along the way and took Max Planck's h ( a quantum of action ) to be more fundamental, more general, than the photon as a quantum of action.

 

Planck's constant is a proportionality constant and as pantheory pointed out, the h is theoretical. It must be impossible to detect, or even emit one h, so it can't be verified as an entity.

 

So, what is the lowest energy single photon that can be detected?

 

There is no lowest energy. Photon energies are quantized in bound system transitions, but not all photons come from them. h is the quantum of angular momentum; all changes in angular momentum are in increments of h (or hbar, depending on where you account for the 2*pi).

[pmb]

Isn't the quantum a smaller measure of energy than a photon?

 

Can't photons be different multiples of quanta?

Photons are quanta of light. As such there is nothing which restricts either the energy or momentum of a photon to a multiple of a fundamental quantity. You can always find a photon at any energy that you desire. A simple way is through the Dopler Efect, i.e. by merely changig your frame of refrence to a new one moving relative to your initial frame. In general the photons energy will be anything you desire merely by carefull selection of the new frame of refernce.

 

In modern use the term quanta is a small finite unit of something. A quantum of charge is the value of the charge of an electron. In the case of charge, any charge is a multiple of the value f an elctrons harg. A quantum of ligt is a photon, i.e. a quantum of electromagnetic radiation. Therefore in modern lingo photon and qantum are not the same thing.

Edited June 27, 2012 by pmb

[Aethelwulf]

There is no lowest energy. Photon energies are quantized in bound system transitions, but not all photons come from them. h is the quantum of angular momentum; all changes in angular momentum are in increments of h (or hbar, depending on where you account for the 2*pi).

 

Err there is a lowest energy. It is called the Zero Point Energy and always corresponds to

 

[math]\frac{1}{2} \hbar \omega[/math]

 

Of any quantum of energy.

 

This is why we say, ''the lowest energy a photon can have resides at the zero point energy scale''.

[swansont]

Err there is a lowest energy. It is called the Zero Point Energy and always corresponds to

 

[math]\frac{1}{2} \hbar \omega[/math]

 

Of any quantum of energy.

 

This is why we say, ''the lowest energy a photon can have resides at the zero point energy scale''.

 

Zero point is not a photon.

 

[math]\omega[/math] does not have a set value

[Aethelwulf]

Zero point is not a photon.

 

[math]\omega[/math] does not have a set value

 

It's a limit for any energy and may very well apply to a photon - in fact, Einstein's original work on a zero point energy involved quantum oscillators - these include all particles of energy belonging to the electromagnetic field, fermion fields, gauge fields ect

[pmb]

Err there is a lowest energy. It is called the Zero Point Energy and always corresponds to

 

[math]\frac{1}{2} \hbar \omega[/math]

 

Of any quantum of energy.

 

This is why we say, ''the lowest energy a photon can have resides at the zero point energy scale''.

Zero point energy only pertains to bound states.

[Aethelwulf]

I still look at it though as the lowest energy state for any quantum oscillator.

[pmb]

I still look at it though as the lowest energy state for any quantum oscillator.

It is. It just doesn't mean that all photons are the multiple of a photon of minimal energy. Given any photon you wish you can change the inertial coordinate system to a new one in which the photon has the exact frequency that you'd like.

[elemental]

For optical photons E=hv, indicating a fundamental measure of energy.

Edited June 28, 2012 by elemental

[pmb]

For optical photons E=hv, indicating a fundamental multiple.

Hi 'elemental' - Welcome to the forum!

 

E = hv does not indicate a fundamental multiple. I'm at a loss to see how you arrived at that conclusion. Can you explain it for me? Thanks.

 

Note: E = hv holds for all photons, not just optical ones.

Edited June 28, 2012 by pmb

[elemental]

pmb;

 

You should have seen how far off my first try was. I had to edit to make the meaning clearer and still missed the mark.

 

Max Planck's h is a discrete amount of energy, maybe fundamental was the wrong word to use. The v is of course the multipler.

 

The OP asked a question. What is energy? With Max Planck's h we have a very small discrete amount of energy to consider. I read that Planck was disturbed by any physical interpretation of h. If someone can explain what h is instead of just being an amount, it would be an explanation for one manifestation of energy.

Edited June 28, 2012 by elemental

[pmb]

pmb;

 

You should have seen how far off my first try was. I had to edit to make the meaning clearer and still missed the mark.

Yeah. I do that a lot. I often edit my responses several time before I'm satisfied with it.

 

Max Planck's h is a discrete amount of energy, maybe fundamental was the wrong word to use. The v is of course the multipler.

h is the multiplier and v is the frequency variable of the photon whose energy is being determined, i.e. for a photon of frequency v it has an energy E = hv.

 

The OP asked a question. What is energy?

Yep. If you recall, I answered with my web page. This question comes up a lot in physics forums. Instead of writing the same ole thing over and over I took some time to do it right and then post it when the question comes up. The page is at

http://home.comcast.net/~peter.m.brown/mech/what_is_energy.htm

 

With Max Planck's h we have a very small discrete amount of energy to consider. I read that Planck was disturbed by any physical interpretation oh h. If someone can explain what h is instead of just being an amount, it would be an exlpanation for one manisfestation of energy.

I see it as simply a constant of proportionality between an oscialltor of frequency v having energy E = hv.

[swansont]

Max Planck's h is a discrete amount of energy, maybe fundamental was the wrong word to use. The v is of course the multipler.

 

Note that h does not have units of energy, it has units of angular momentum. h is the quantum of angular momentum. It is not the quantum of energy, since the frequency is not necessarily a quantized value, whereas both spin and orbital angular momentum are.

[elemental]

Planck's constant has the dimensions of energy multiplied by time.

 

h=6.62606957x10^-34 erg.s

[elemental]

This is not really my point, but someone might find it interesting:

 

http://motls.blogspot.com/2011/09/why-is-there-energy-and-what-it-isnt.html#more