The wave and particle theory of light

[exchemist]

I'm not sure what your educational background is? Try this as a starter
Mass–energy equivalence - Wikipedia

I have an MA degree in chemistry.

How about answering the questions I posed. Can you do that?

 

[Subduction Zone]

I have an MA degree in chemistry.

How about answering the questions I posed. Can you do that?

Sadly it looks as if the "Optimistic" frubal that I gave you earlier was merited. I have a feeling that he won't answer.

 

[exchemist]

Sadly it looks as if the "Optimistic" frubal that I gave you earlier was merited. I have a feeling that he won't answer.

It looks that way, certainly.

I wonder if @idea has ever come across E² = (mc²)² + p²c². Perhaps not.

 

[idea]

E = mc² does not work for light.

Consider these two questions:

1) Does a photon have energy?

2) What is the rest mass of a photon?

And then look again at that formula.

Mass and energy are equivalent. It is impossible to measure the rest mass of a photon as they can never be measured in a frame where they are at rest. The mass of a system emitting a photon does decrease by its relativistic mass.

Lol, semantics, call it relativistic mass, a rose by any other name.

MA in Chem, not physics but nice .

 

[Subduction Zone]

Mass and energy are equivalent. It is impossible to measure the rest mass of a photon as they can never be measured in a frame where they are at rest. The mass of a system emitting a photon does decrease by its relativistic mass.

Lol, semantics, call it relativistic mass, a rose by any other name.

MA in Chem, not physics but nice .

No, relativistic mass is a very important concept. The mass of a system does go down when a photon is emitted. The question is "how much"? If you observed a photon and were able to determine its energy then you could you use E = mc^2 to determine how much rest mass the other system lost?

 

[exchemist]

Mass and energy are equivalent. It is impossible to measure the rest mass of a photon as they can never be measured in a frame where they are at rest. The mass of a system emitting a photon does decrease by its relativistic mass.

Lol, semantics, call it relativistic mass, a rose by any other name.

MA in Chem, not physics but nice .

Yes, I'm afraid I'm not a real physicist, I just know the physics needed for chemistry: quantum theory, statistical thermodynamics, that sort of thing. But I get by: at least I'm numerate and have some grasp of physical science.

And you? Some sort of engineer, perhaps?

But back to the topic, I notice you seem to claim my question about the rest mass of a photon can't be answered - or at least you can't seem to answer it. You are right that you can't stop a photon to measure its rest mass, but you can define its invariant mass, which is a more correct way of saying the same thing. And it is a well known fact of physics that a photon has zero invariant mass.

What you do not mention, rather curiously, is that E=mc² is a reduced, special case of Einstein's full expression for energy, which includes another term. It is that second term that accounts for the energy of photons.

The correct, full expression to use is: E² = (mc²)² + (pc)² (m here being the rest or invariant mass, and p the momentum). For a photon, the invariant mass is zero, but the momentum is not, so we are left with E=pc.

As a chemist, I'm familiar with this, as by de Broglie's relation, p =h/λ , where h is Planck's constant and λ is the wavelength of the QM entity due to its momentum. Knowing the standard relation between wavelength and frequency,ν, (c = νλ), we can re-express the energy in terms of frequency and we get E = pc = c(h/λ) = ch/(c/ν) or ch(v/c) = hν. Et voila, we have Planck's famous relation between the energy of a photon and its frequency: E=hν. This is something we chemists use all the time, in everything from spectroscopy to photochemistry.

 

[shunyadragon]

Will he get it? Photons are weird. Their "frequency" (that raises another question, how does a single photon have a frequency?) depends on the relative motion between source and receiver. That just shows that classical physics has limits in its ability to explain.

Careful about describing or not describing light and Einstein''s equation in terms of the contemporary 'classical physics.'

Photons are photons and not weird. The nature of photons are described more accurately in terms of Quantum Mechanics, and do not violate necessarily Einstein's equation.

 

[Subduction Zone]

Careful about describing or not describing light and Einstein''s equation in terms of the contemporary 'classical physics.'

Photons are photons and not weird. The nature of photons are described more accurately in terms of Quantum Mechanics, and do not violate necessarily Einstein's equation.

When one only thinks classically they seem quite weird. On a moderate scale the universe appears to be classical. But when one deals with the vey small or the very large one realizes that that is not the case. The universe still follows clear cut laws, they are just not the laws of our not too small not too large world.

Just as if one limits the world a bit more it can appear to be flat. Though it does not take too much in the way of observations and logic to show that is wrong. But at least the physics is much easier and geometry? Why even bother with it? (especially if understanding of it almost instantly refutes the Flat Earth).