5 ms·

Newbie question: if there are no particles, then why are there quantized packets of energy such as photons?

slacka 10y ago
I'm am not a physicist, but interested in QM. Photons behavior cannot be completely explained by treating them solely as particles. The simples counter example (one you can perform yourself with a laser pointer), is the double-slit experiment. If photons behaved classically (like billiard balls) they'd never interfere with themselves. If you'd like a good intro to QM, youtube is full of great material. Here are some of my favorites: NOVA - The Fabric of the Cosmos: https://www.youtube.com/watch?v=NbIcg0XsbFQ https://www.youtube.com/watch?v=NbIcg0XsbFQ The Secrets of Quantum Physics: https://www.youtube.com/watch?v=VgDlzGZAPcY https://www.youtube.com/watch?v=VgDlzGZAPcY Particle Fever: https://vimeo.com/125987472 https://vimeo.com/125987472
- tachyonbeam 10y ago
  Yes, I'm aware of that, but how are fields quantized (divided into fixed-size packets of energy)?
- jostylr 10y ago
  Particles can interfere with themselves in the double-slit experiment if they are being guided by a wave. This explains wave behavior and particulate events as in Bohm's theory. Sadly, there are issues with photons as particles as their wave equations do not seem to allow for an easy particle interpretation unlike, say, electrons. Of course, the flexibility of QM allows for electrons to have a particle existence and photons to not: http://arxiv.org/abs/quant-ph/0404134 http://arxiv.org/abs/quant-ph/0404134 (I am a coauthor of that paper) And some videos to answer questions about BM: http://www.bohmian-mechanics.net/videos_faq.html http://www.bohmian-mechanics.net/videos_faq.html
empath75 10y ago
A photon is a wave packet.
adrianratnapala 10y ago
Light-particles seem like they exist for two reasons: (1) when you detect things at high sensitivity, you get discrete events. (2) Quantum fields have a thing called a number operator. When you "measure" it (whatever that means) you get an integer. Now your language of "quantized packets of energy" comes from Einstein, who got his Nobel prize for noticing (1) in the form of the photoelectric effect. But that paper, though brilliant, was wrong. Classical fields (with quantum electrons) are enough to derive the photoelectric effect. At first sight (2) seems to back Einstein up, since the number of photons seen on an (ideal) detector is pretty much the measured value of the number operator for the light beam. But while that works in practice, it doesn't work in theory. The number operator is only really defined for monochromatic fields. It seems like you should be able to Fourier transform things until you had one for time-limited or space-limited situations. But I could never make that work.
- lisper 10y ago
  > (whatever that means) That (implied) question has an answer: measurement is the mutual entanglement of a number of degrees of freedom. See: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf Or the movie version: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc

I'm am not a physicist, but interested in QM. Photons behavior cannot be completely explained by treating them solely as particles. The simples counter example (one you can perform yourself with a laser pointer), is the double-slit experiment. If photons behaved classically (like billiard balls) they'd never interfere with themselves. If you'd like a good intro to QM, youtube is full of great material. Here are some of my favorites: NOVA - The Fabric of the Cosmos: https://www.youtube.com/watch?v=NbIcg0XsbFQ https://www.youtube.com/watch?v=NbIcg0XsbFQ The Secrets of Quantum Physics: https://www.youtube.com/watch?v=VgDlzGZAPcY https://www.youtube.com/watch?v=VgDlzGZAPcY Particle Fever: https://vimeo.com/125987472 https://vimeo.com/125987472

tachyonbeam 10y ago
Yes, I'm aware of that, but how are fields quantized (divided into fixed-size packets of energy)?
jostylr 10y ago
Particles can interfere with themselves in the double-slit experiment if they are being guided by a wave. This explains wave behavior and particulate events as in Bohm's theory. Sadly, there are issues with photons as particles as their wave equations do not seem to allow for an easy particle interpretation unlike, say, electrons. Of course, the flexibility of QM allows for electrons to have a particle existence and photons to not: http://arxiv.org/abs/quant-ph/0404134 http://arxiv.org/abs/quant-ph/0404134 (I am a coauthor of that paper) And some videos to answer questions about BM: http://www.bohmian-mechanics.net/videos_faq.html http://www.bohmian-mechanics.net/videos_faq.html

empath75 10y ago

A photon is a wave packet.

adrianratnapala 10y ago

Light-particles seem like they exist for two reasons: (1) when you detect things at high sensitivity, you get discrete events. (2) Quantum fields have a thing called a number operator. When you "measure" it (whatever that means) you get an integer. Now your language of "quantized packets of energy" comes from Einstein, who got his Nobel prize for noticing (1) in the form of the photoelectric effect. But that paper, though brilliant, was wrong. Classical fields (with quantum electrons) are enough to derive the photoelectric effect. At first sight (2) seems to back Einstein up, since the number of photons seen on an (ideal) detector is pretty much the measured value of the number operator for the light beam. But while that works in practice, it doesn't work in theory. The number operator is only really defined for monochromatic fields. It seems like you should be able to Fourier transform things until you had one for time-limited or space-limited situations. But I could never make that work.

lisper 10y ago
> (whatever that means) That (implied) question has an answer: measurement is the mutual entanglement of a number of degrees of freedom. See: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf Or the movie version: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc