# Does Quantum Theory assumes the wave nature of light?

If not then whose frequency does 'v'(new) denotes in the expression E = hv

### 6 Answers

- pzifissshLv 71 decade agoFavorite Answer
Yes, quantum theory is a theory of waves.

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OldPilot said, "QM uses the concept of a 'de Broglie' wave for a particle."

That's a name that probably has not been heard outside of high-school physics books for something close to a century. It's true that Louis DeBroglie's theory was the first in a string of ideas that eventually led to the formulation of modern quantum field theory, but the fact that you say, "de Broglie wave" is telling.

"...the 'Dirty Little Secret' of Theoretical Physics: We have NOT yet figured everything out."

Well Yeah! What do scientists do for a living? They try to figure stuff out. The day when everything has been figured out is the day when the last scientist cleans out his desk and goes home.

"The universe is governed by whole sets of 'Laws'..."

No. The universe is not governed by our laws. A scientific law is a formal (mathematical) description of some pattern or phenomenon or behavior that, as far as we know or as far as we have observed, is always the same. We make the laws to fit what we see. It doesn't work the other way 'round.

"...that do NOT agree and are mutually exclusive..."

In order for something to be called a 'Law' it *MUST* agree with nature. It is simply not possible for two scientific laws to disagree with one another, because they both must agree with reality. I think that you are confusing 'Law' (see above) with 'Theory.'

Scientific theories can be, and often are, incompatible with one another. The best example probably is the clash between general relativity and quantum field theory. The laws of gravity (as predicted by general relativity) agree with everything we have observed about gravity. The laws of particle physics (as predicted by quantum field theory) agree with everything we have observed about certain other forces (e.g., electromagnetism). Physicists would like to believe that some common structure underlies both gravity and electromagnetism. Unfortunately, the mathematical structure of QFT is deeply incompatible with the structure of GR.

If a common theory ever is found, then it will invalidate either QFT, or GR, or both, but it will not invalidate the laws (i.e., the patterns and behaviors and phenomena that we have actually observed in nature.)

"...2 slit experiment...explain how a particle orders of magnitude smaller than the distance between the slits somehow...interferes with itself. Problem, we cannot explain this well using 'quanta' (Particles, photons). Wave mechanics gives a simple easy to understand explanation."

You misunderstand the meaning of the word "Quantum." Quantum theories are WAVE theories. Things are quantized because of the fundamental, inevitable ways in which standing waves behave. That's what set de Broglie off in the first place. His peers were observing energy levels that were quantized, and everyone was trying to figure out how could that be? De Broglie's insight was that the energy levels of a standing wave were quantized, and so he proposed that maybe the energies were quantized because the so-called "particles" were, in actuality, standing waves.

"What to do? We cheat! We say that electromagnetic radiation has a dual nature..."

The authors who write pop-science books still say that. Physicists don't---not anymore. (see below)

"Quantum Mechanics gets out of this mess by introducing the Uncertainty Principle, Indeterminacy, and the Copenhagen Interpretation of QM."

The so-called copenhagen interpretation is one of about six different approaches to what is known as the "measurement problem." It is still considered to be main-stream, but the number of adherents is dwindling. Copenhagen believers say that the waves in quantum theory are not the reality, but rather, that they merely represent what the experimenter KNOWS about the reality. The problem with this viewpoint is that it fails to explain how it is that our knowledge can be so precisely constrained by wave mechanics if the waves are not somehow 'real.'

In all of the other main interpretations, the waves are indeed considered to be part or all of the reality. A growing number of physicists however are beginning to back off from trying to understand what QFT actually MEANS, and they just say, "It works as far as it goes, but we've still got a lot to learn."

That 'dirty little secret' is not as secret as you think.

Source(s): http://en.wikipedia.org/wiki/De_broglie http://en.wikipedia.org/wiki/Measurement_problem http://en.wikipedia.org/wiki/Interpretations_of_qu...- Login to reply the answers

- 1 decade ago
No. Quantum theory simply observes that particles have a wave-like behavior. This particle/wave is a wave spread over the entire universe and represents the probability that a particle exists at any given location. Particle/waves behave much like a water waves, but they represent probability rather than a physically tangible thing such as water molecules. The v in E=hv refers to the frequency of this probability wave. This is why quantum physics is so baffling. It is as if probability itself becomes a physical thing at the quantum level.

One resolution to this seeming paradox is the Many-World Interpretation (MWI) of quantum mechanics. Basically, it theorizes that everything is made of particles, but time is actually branching, rather than linear, and the effects of this become very apparent at the quantum level. MWI is the currently held scientific consensus for the strange behavior of quantum particles.

If you want to really understand this I would highly recommend the book "QED: The Strange Theory of Light and Matter". This book is a very short summary of Quantum Electrodynamics (the core theory of quantum physics) for the layman. It is, by far, the best book out there for the layman and, as a bonus, it was written by Feynman himself (a giant in physics, second only to Einstein in my opinion). Feynman has a knack for making the quantum world fun and explaining it in simple terms. It's a fun read and you'll come away with a much deeper understanding of quantum physics.

p.s. Please choose my answer, I really need the points and none of the other answers are correct. All of the ones that answered "yes" or "yes and no" are incorrect, and the ones that answered "no" were correct, but for the wrong reasons. Quantum physics is a difficult field and the other incorrect answers to this question reflect this fact.

Source(s): QED: The Strange Theory of Light and Matter; Wikipedia; Undergraduate quantum physics courses- Login to reply the answers

- flutzpahLv 51 decade ago
Yes and no :)

Quantum theory says that light can be considered a wave. When you do experiments (two-slit experiments, etc.) to look at the wave nature of light, then you see interferences, and so on. On the other hand, when you do experiments to probe the particle nature of light, then you see discrete events (as from particles).

When one says "assumes" in science (especially in mathematics), that usually means that other, mutually-contradictory things can't be assumed within the same framework. In that sense, quantum theory does NOT assume the wave nature of light, since other results (wave-particle duality) can be incorporated.

Richard Feynman, in a question-and-answer session about "QED", said that he *always* thinks of photons as particles. The wavelike nature comes from the rules used to calculate the probabilities involved when photons go from here to there.

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- mangelsLv 44 years ago
Gravitons are the theoretical and as yet undetected stress donning debris of the gravitational stress. In relativity, gravity is defined because of the fact the warping of area/time. Quantum mechanics describes the reason on the subatomic point, relativity describes the effect interior the macro sized universe.

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- OldPilotLv 71 decade ago
No!!!

QM uses the concept of a "de Broglie " wave for a particle

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

WARNING! I am a heretic. According to the Physics Majors, the following is “misleading” or “nonsense.”

Yours is a very profound question. I can tell from your question that you are ready to be let in on the "Dirty Little Secret" of Theoretical Physics: We have NOT yet figured everything out. The universe is governed by whole sets of "Laws" that do NOT agree and are mutually exclusive (http://en.wikipedia.org/wiki/Wave-particle_duality - .... all particles behave as waves according to the de Broglie wavelength, these "wavicles" exhibit a freedom to behave in more "wave-like" or more "particle-like" manners (these behaviors being mutually exclusive) or illogical ( Google Schrodinger's Cat, if you are interested in the illogic). This is a great embarrassment. We assume we live in an orderly, rational universe that makes sense. Perhaps when Quantum Mechanics and General Relativity are unified we will have a better answer to your question.

For now:

We need the concept of alternating electromagnetic fields (waves) to explain certain physical phenomena, like the interference pattern in the 2 slit experiment. So we keep that. We must somehow explain how a particle orders of magnitude smaller than the distance between the slits somehow passes through both slits and interferes with itself. Problem, we cannot explain this well using "quanta" (Particles, photons). Wave mechanics gives a simple easy to understand explanation.

We need the concept of quanta (particles, photons) to explain other phenomena, like the Photoelectric Effect. So we keep that too. But, this means we use 2 different, mutually exclusive systems of mechanics to explain electromagnetic radiation.

What to do? We cheat! We say that electromagnetic radiation has a dual nature and choose the system of mechanics that works best for the problem at hand.

Quantum Mechanics gets out of this mess by introducing the Uncertainty Principle, Indeterminacy, and the Copenhagen Interpretation of QM. If we do NOT know which slit the particle went through, then the particle is "smeared out in equal parts" and goes through both slits. It turns into a fog. As long as it is a fog, it can pass through both slits. That is: The particle occupies a volume of space with some probability. QM says that so long as the position is not known, the particle occupies the entire volume. If we learn its position, the fog condenses into that location and the particle goes through one slit. (The problem with this is: Fog does not form interference, waves do. Sooner or later, in those problems where appropriate, you must give up particles and fogs and start cranking through the equations of Wave Mechanics) But, Quantum Mechanists prefer “fog” to, "The particle turns into a wave and goes through which ever slits are open. One slit, no pattern. Two slits, pattern. “ Take your choice of which mental picture you form.

Rule of Thumb that got me through QM: If its’ position is known, it is a particle. If its’ position is unknown, it is a wave. Here is where you plug in http://en.wikipedia.org/wiki/Matter_wave This works because the equations of Wave Mechanics work, if the position is unknown. If you don’t tell anybody, no one will know the mental picture you formed to solve the problem. (This may not always work, but I do not remember a case where it failed.)

It is not uncommon for engineers to accept the reality of phenomena that

are not yet understood, as it is very common for physicists to disbelieve

the reality of phenomena that seem to contradict contemporary beliefs of

physics - H. Bauer

EDIT: I admit to being a Heretic

“The universe is governed by 2 sets of laws that do not agree.” – Brian Greene, The Elegant Universe.

http://www.pbs.org/wgbh/nova/elegant/program.html

See hour 2 for the conflicting laws discussion

General Relativity, The Macro Universe (Things larger than an atom) that are high energy/mass

Quantum Mechanics, The Micro Universe (Things smaller than an atom) that are low energy/mass

We have no working theory for things that are small and high mass/energy. Inside the Event Horizon of Black Holes, the Big Bang, etc The math and theory of both GR and QM break down and give nonsense answers..

OK, I give up. How do you calculate the interference fringe spacing for electrons in the 2-slit experiment given electron energy, momentum, slit spacing, and distance to screen. If this calculation involves a "wave length." How is that value arrived at?

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- 1 decade ago
Quantum theory does not consider light as a wave.

And the "new" is for frequency of light.

Source(s): REad somewhere.....- Login to reply the answers