9 ms·

What is a photon? (2017)

92 points by memexy 6y ago

GolDDranks 6y ago
This is a nice article, but it feels like it leaves a half of the puzzle to the table. We know by everyday experience that photons _do_ have some time- and place-varying properties: my WiFi has a perfect strength here, but absolutely zero at my friend's house 5 kms away. The photons emitted by my LED lamp are not a static field: I can switch it off by pressing a button so it's time-varying. The article acknowledges place only in this short sentence in the end: > This means that adding a quantum to a system has an effect that extends across the entire system. That makes it problematic to talk about the location of a photon. But then leaves the experience gap between the model and our everyday experience totally without discussion.
- GolDDranks 6y ago
  Btw. I have an impression that time- and place-local behaviour can be modelled as a collection of photons that destructively interfere "elsewhere" than where we tend to actually see light. Fourier transform seems to play a big role here.
  - krastanov 6y ago
    Your statement is not very rigorous, but the intuition it provides is spot on. It is pretty much exactly this intuition I convey the first time I teach such topics.
- noobermin 6y ago
  This is written by a theorist so they do leave the important bit out. Of course, you know just from fourier analysis the uncertainty principle. The thing is treating photons as plane waves is an approximation (a fine one for most things, particularly theoretical calculations). A better approximation is thinking of photons as wave packets that thus have some localization but not so defined as to make their bandwidth too wide (so they can be considered monochromatic). The important thing to remember is that photons, like the very idea of a planewave is always an idealized approximation.
jiggawatts 6y ago
Unfortunately, like all such descriptions, this one misses the mark also. I've never heard a good explanation for what a photon "is", or any particle for that matter. That's because physicists don't know either. No, seriously. Ask a randomly selected set of physicists about any core concept in Quantum Mechanics and you'll discover that their answers diverge wildly. Ref: https://arxiv.org/abs/1301.1069 https://arxiv.org/abs/1301.1069 Basic things like: "Are the photons quantised or is it just the photon interaction with atomic orbitals that's quantised?" I've personally asked this question and had working physicists confidently state that either the former or latter is true, and the other is false. (PS: Compare this to biologists, chemists, or engineers. They all 100% agree on all core concepts. So do astronomers, and physicists studying classical mechanics and relativity. It's only quantum mechanics that's so fragmented.) Ask any working QM researcher to clearly show how "a single photon" interacts with an electron in an orbital and they will without a doubt draw you a cartoon diagram. Never in the history of theoretical physics has anyone, ever, anywhere made a numerical visualisation of this. This is because both the QM mental model and the mathematical theory applies only to ensembles in potential wells. This is a very narrow scope of applicability that was explicitly called out in the QM papers back in the early 1900s, but is now glossed over. People assume that what applies to a special case is the hard rule that applies to all things. It doesn't. There are no photons in free space. There are no little hard particles of light. You can't have a point with a wavelength. You can't have a single pure frequency with a finite duration. This is all gibberish, it's just a simplification to make the maths tractable when done with pencil and paper for special cases! The output of this simplified model is a 0-dimensional scalar. It can't do output much else, such a simulation of a full 3D interaction of any type. Trying to work backwards from such an oversimplified model in order to explain the deep nature of reality is futile. This is like pointing at the bandwidth measurement in Windows Task Manager and saying "we can understand how the Internet works by watching this number go up and down".
- mhh__ 6y ago
  > I've never heard a good explanation for what a photon "is", or any particle for that matter. That's because physicists don't know either. The aim of many/most physicists is to predict rather than to know. Biologists, Chemists, Engineers can agree all they want but their theories aren't tested to 5-sigma (I'm sure some are but that's not as good of a metaphor). We have extremely accurate and predictive models of how photons behave (Quantum Field Theory not solely Quantum Mechanics). You're arguably right, we don't really know - however, we can only know what we can see with our eyes. There may be some all-encompassing structure hiding at any energy level we haven't yet reached but the explanation given is as good as it gets in terms of explainable what we have observed in nature. As to Quantum Mechanics, the only place you'll find Physicists disagreeing about the "core concepts" is on the absolute fringes of what can be considered science. You will find Physicists arguing about the interpretation of those concepts but it's not like they don't work. As to that interpretation, there is disagreement but I think it is fair to say that very few physicists actually think about it - i.e. "Shut up and calculate" is a common outlook.
supernova87a 6y ago
The blog post was interesting, but I wouldn't say it explained "what is a photon", it explained more, why do photons have energies and propagation properties that they do. The first 2/3 of it I was wondering, why go through all this intro about springs... Although, there is one thing that I have always searched for an explanation of -- why the speed of light is invariant with reference frame. The idea that space is filled with springs might help me with that. If light/photons are the passage of a wave from spring to spring, then the speed of that propagation is always at the "spring speed" however you measure it, or however fast you are going. You can only ever receive the microscopic spring transmission speed of the photon at the place you receive it. (Although it brings up the complicated followup of, how are you traveling through the "springs", etc, I guess). But I'm sure I'm wrong about that too -- if anything QM has taught me is that my attempts at physical intuitions are usually wrong about QM.
Zamicol 6y ago
What is the amplitude of a single photon's wave? Yes, it's well taught that wavelength is related to frequency. Higher frequency is higher energy energy and lower frequency is lower energy, but it's the frequency of what? Unlike ocean waves, photons do not have a spacial amplitude. A photon does however have a spacial wavelength. This distinction between photonic wavelength and amplitude I've never heard explicitly addressed. My understanding is that a photon's amplitude is the likelihood of interaction at a specific point in space. High amplitude is likely interaction, low amplitude is low likelihood of interaction. This means at a photon's peaks/crests it has high interaction and at its troughs the photon has low interaction likelihood. These likelihoods are repeated every wavelength, a length measurable in physical space. This is some of the reason why an antenna for a given frequency range needs to be a specific size. Too small and there's a good chance of missing a signal. A proper sized antenna, related to wavelength, guarantees high interaction somewhere along the length of the antenna. When speaking of many photons, amplitude (like AM radio) is simply flux, how many photons at a particular frequency exist during a given unit of time. That's not related to the amplitude of a single photon and not what I'm talking about here.
- noobermin 6y ago
  Quanta are specifically the quantization of the EM field, so if you will, a single photon at least theoretically is the smallest amplitude of an EM wave you can have. You can see this mostly by noting the expectation of the number operator gives essentially the radiant intensity.
- pdonis 6y ago
  > My understanding is that a photon's amplitude is the likelihood of interaction at a specific point in space. Not really, because there isn't really a well-defined wave function for a photon in the position representation (which is the one that has the interpretation "the likelihood of detection at a specific point in space"). > When speaking of many photons, amplitude (like AM radio) is simply flux, how many photons at a particular frequency exist during a given unit of time. There isn't a well-defined answer to this question, because a state like this (which is a coherent state) is not an eigenstate of the photon number operator. (Also, energy flux is really amplitude squared.) A good, if somewhat lengthy, discussion of the "photon" concept can be found here: http://math.ucr.edu/home/baez/photon/schmoton.htm http://math.ucr.edu/home/baez/photon/schmoton.htm
gfody 6y ago
another great explanation here https://www.youtube.com/watch?v=MzRCDLre1b4 https://www.youtube.com/watch?v=MzRCDLre1b4 also from 2017
pdonis 6y ago
The article leaves out a crucial item. When it says: "The normal modes are plane waves traveling at the speed of light in a particular directions with a given frequency." This is not quite correct. A correct statement would be that plane waves are one possible choice of "normal modes" for the quantum electromagnetic field. But not the only possible choice. (In more technical language, they are one possible choice of basis for the Hilbert space of states of the quantum electromagnetic field, but not the only possible choice.) In fact, the plane wave states (whose technical name is "Fock states") are often not very useful, because they are very hard to produce experimentally and pretty much never occur naturally. The states that are closest to naturally occurring states and which are easy to produce experimentally (for example in a laser) are coherent states. But coherent states are nothing like plane waves.
- krastanov 6y ago
  I am pretty sure you are confounding the basis of functions (harmonics) that one can use to describe an EM field, with the basis of a Hilbert space used to quantize them. You can have a mode (e.g. a plane wave) and the field of that particular mode can be quantized and you get to pick whether to use Fock states or coherent states or any other basis. In other words, "plane wave" refers to a particular mode of the field and Fock/coherent states refer to the quantum state of that particular mode. Two different plane waves are two completely different modes, e.g. two completely different Hilbert spaces, not basis vectors of a given Hilbert space.
  - pdonis 6y ago
    > I am pretty sure you are confounding the basis of functions (harmonics) that one can use to describe an EM field, with the basis of a Hilbert space used to quantize them. No, I'm not. The same mathematical functions can appear in both classical and quantum treatments, but I'm talking about the basis of the quantum Hilbert space. > Two different plane waves are two completely different modes, e.g. two completely different Hilbert spaces No. They are different Fock states in the same Hilbert space; in the Fock state basis for that Hilbert space, they are two different, orthogonal basis vectors. And that same Hilbert space can also have other choices of basis besides the Fock state basis.
carrolldunham 6y ago
The author left off at precisely the point I was hoping they would get across: How the wave that extends everywhere in space, obviously doesn't. I mean, I know you can make a localised 'packet' or whatever with an infinite sum of sine waves, but then wouldn't you have to talk about infinite photons moving every time 'one photon' hits a detector?
- krastanov 6y ago
  It is a neat trick actually. If you superimpose a few of these waves with frequencies that are fairly close, then you will see how they cancel out in the distance, while they reinforce each other in the center. This is called a "wave packet". 3blue1brown was somewhat useful, somewhat tangential video on the topic https://www.youtube.com/watch?v=MBnnXbOM5S4 https://www.youtube.com/watch?v=MBnnXbOM5S4 The more rigorous way to say "superimpose a few of these waves", is to say that there is some uncertainty in the frequency. This uncertainty in the frequency lets you have more certainty about the position (the wave packet is centered somewhere, instead of being completely distributed the way an infinite plane wave is)
- l33tman 6y ago
  It's an infinite sum of variations of the same photon, not an infinite amount of photons. When it hits the detector (or, really, when the researcher eventually gets entangled with the experiment) it is detected as a single interaction. This is why the terminology is confusing. A "classical" photon just doesn't exist in the modern treatment but we still need it to talk about what we do.
remote_phone 6y ago
One question I have: One thing I remember is that as something approaches the speed of light, its mass increases. This is why we can never achieve the speed of light because as we approach the speed of light, our mass increases which requires more energy to accelerate. If that’s the case, the how can photons have a mass? Wouldn’t something traveling at the speed of light need to have infinite mass, regardless of how light it started off with?
- krastanov 6y ago
  There is rest mass, which is the mass of an entity when it does not move. And there is relativistic mass, which is the rest mass plus the mass due to all of the kinetic energy of the entity. Photons have zero rest mass, but depending on the energy they carry, they have different relativistic masses. By the way, only entities with zero rest mass can move at the speed of light. Actually, in relativity it is mathematically inconsistent for something with zero rest mass to exist unless it is moving at the speed of light.
  - remote_phone 6y ago
    Very excellent answer, thank you for this! I will do more reading in this direction!
- brutt 6y ago
  It's "fake" mass. Regular waves have "mass" too, due to contraction (for 3D) or raising (for 2D) of conducting matter, so it's mass of contracted air/water/etc.
maxk42 6y ago
What I really want to know is: Can someone describe what "heat" is to me?
gigama 6y ago
"I'd like to have an argument please." [1] https://genius.com/Monty-python-argument-lyrics https://genius.com/Monty-python-argument-lyrics
mike1101 6y ago
How does this explain the duel split experiment?
- jabl 6y ago
  It doesn't directly address it. But they key is right there in the beginning; photons are NOT small billiard balls moving along ballistic trajectories. "Wave-particle duality" doesn't mean that you can think of flicking a light switch as alternatively an electromagnetic field propagating from the light bulb, or that the light bulb shoots out a stream of tiny billiard balls. No, there's only the electromagnetic field. However, if you squint closely enough you see that the energy levels of the field are quantized (aka photons). Now, back to the double slit experiment. So a wave propagates from the source, through the slits, interferes constructively or destructively, and then hits the detector screen. However, due to the quantum nature of, well, everything, the "hits the detector" interaction is quantized. The field "deposits" quantas of energy (photons) to the screen in a localized interaction (say, a photon causes an electron in the screen to jump to a higher energy level). If the detection apparatus is sensitive enough you'll see that single interaction as a dot on the screen, rather than a faint interference pattern (which you'll eventually start to see if you repeat the experiment long enough). So: Lets forget about the "wave-particle duality" already. There's only fields. Fields which interact in a quantized fashion.
cycomanic 6y ago
I'm surprised that nobody pointed out yet, that harmonic oscillators have discrete energy states as well. I think that's why the explanation is somewhat makes things more confusing. The fundamentally different thing about quantum mechanics is that even waves in free-space have discrete energy states. I think the video by 3blue1brown posted by someone else is a much better explanation.
MaXtreeM 6y ago
For others who like to learn from video, here is lenghtier explanation of quantum fields, discrete energies, plane waves, etc. from Sean Carroll: https://www.youtube.com/watch?v=Dy1LNk_B6IE https://www.youtube.com/watch?v=Dy1LNk_B6IE
anonymousiam 6y ago
WiFi could also interfere with other frequencies if a non-linear device is nearby. See: https://en.wikipedia.org/wiki/Intermodulation#Passive_intermodulation_(PIM) https://en.wikipedia.org/wiki/Intermodulation#Passive_interm... The article does not consider this, but it works with light as well as RF.
mikhailfranco 6y ago
sigfpe is too simplistic and conflates a few different aspects of atomic spectra, photons and EM fields. The sci.physics reference for this is Baez & Weiss: http://math.ucr.edu/home/baez/photon/schmoton.htm http://math.ucr.edu/home/baez/photon/schmoton.htm If you have read that, you know the number of photons is just another quantum number, with aspects of uncertainty, superposition and entanglement, so this will not be a surprise: https://phys.org/news/2019-08-photon-number-quantum-superposition.html https://phys.org/news/2019-08-photon-number-quantum-superpos...

92 points by memexy 6y ago

This is a nice article, but it feels like it leaves a half of the puzzle to the table. We know by everyday experience that photons _do_ have some time- and place-varying properties: my WiFi has a perfect strength here, but absolutely zero at my friend's house 5 kms away. The photons emitted by my LED lamp are not a static field: I can switch it off by pressing a button so it's time-varying. The article acknowledges place only in this short sentence in the end: > This means that adding a quantum to a system has an effect that extends across the entire system. That makes it problematic to talk about the location of a photon. But then leaves the experience gap between the model and our everyday experience totally without discussion.

GolDDranks 6y ago
Btw. I have an impression that time- and place-local behaviour can be modelled as a collection of photons that destructively interfere "elsewhere" than where we tend to actually see light. Fourier transform seems to play a big role here.
- krastanov 6y ago
  Your statement is not very rigorous, but the intuition it provides is spot on. It is pretty much exactly this intuition I convey the first time I teach such topics.
noobermin 6y ago
This is written by a theorist so they do leave the important bit out. Of course, you know just from fourier analysis the uncertainty principle. The thing is treating photons as plane waves is an approximation (a fine one for most things, particularly theoretical calculations). A better approximation is thinking of photons as wave packets that thus have some localization but not so defined as to make their bandwidth too wide (so they can be considered monochromatic). The important thing to remember is that photons, like the very idea of a planewave is always an idealized approximation.

jiggawatts 6y ago

Unfortunately, like all such descriptions, this one misses the mark also. I've never heard a good explanation for what a photon "is", or any particle for that matter. That's because physicists don't know either. No, seriously. Ask a randomly selected set of physicists about any core concept in Quantum Mechanics and you'll discover that their answers diverge wildly. Ref: https://arxiv.org/abs/1301.1069 https://arxiv.org/abs/1301.1069 Basic things like: "Are the photons quantised or is it just the photon interaction with atomic orbitals that's quantised?" I've personally asked this question and had working physicists confidently state that either the former or latter is true, and the other is false. (PS: Compare this to biologists, chemists, or engineers. They all 100% agree on all core concepts. So do astronomers, and physicists studying classical mechanics and relativity. It's only quantum mechanics that's so fragmented.) Ask any working QM researcher to clearly show how "a single photon" interacts with an electron in an orbital and they will without a doubt draw you a cartoon diagram. Never in the history of theoretical physics has anyone, ever, anywhere made a numerical visualisation of this. This is because both the QM mental model and the mathematical theory applies only to ensembles in potential wells. This is a very narrow scope of applicability that was explicitly called out in the QM papers back in the early 1900s, but is now glossed over. People assume that what applies to a special case is the hard rule that applies to all things. It doesn't. There are no photons in free space. There are no little hard particles of light. You can't have a point with a wavelength. You can't have a single pure frequency with a finite duration. This is all gibberish, it's just a simplification to make the maths tractable when done with pencil and paper for special cases! The output of this simplified model is a 0-dimensional scalar. It can't do output much else, such a simulation of a full 3D interaction of any type. Trying to work backwards from such an oversimplified model in order to explain the deep nature of reality is futile. This is like pointing at the bandwidth measurement in Windows Task Manager and saying "we can understand how the Internet works by watching this number go up and down".

mhh__ 6y ago
> I've never heard a good explanation for what a photon "is", or any particle for that matter. That's because physicists don't know either. The aim of many/most physicists is to predict rather than to know. Biologists, Chemists, Engineers can agree all they want but their theories aren't tested to 5-sigma (I'm sure some are but that's not as good of a metaphor). We have extremely accurate and predictive models of how photons behave (Quantum Field Theory not solely Quantum Mechanics). You're arguably right, we don't really know - however, we can only know what we can see with our eyes. There may be some all-encompassing structure hiding at any energy level we haven't yet reached but the explanation given is as good as it gets in terms of explainable what we have observed in nature. As to Quantum Mechanics, the only place you'll find Physicists disagreeing about the "core concepts" is on the absolute fringes of what can be considered science. You will find Physicists arguing about the interpretation of those concepts but it's not like they don't work. As to that interpretation, there is disagreement but I think it is fair to say that very few physicists actually think about it - i.e. "Shut up and calculate" is a common outlook.

supernova87a 6y ago

The blog post was interesting, but I wouldn't say it explained "what is a photon", it explained more, why do photons have energies and propagation properties that they do. The first 2/3 of it I was wondering, why go through all this intro about springs... Although, there is one thing that I have always searched for an explanation of -- why the speed of light is invariant with reference frame. The idea that space is filled with springs might help me with that. If light/photons are the passage of a wave from spring to spring, then the speed of that propagation is always at the "spring speed" however you measure it, or however fast you are going. You can only ever receive the microscopic spring transmission speed of the photon at the place you receive it. (Although it brings up the complicated followup of, how are you traveling through the "springs", etc, I guess). But I'm sure I'm wrong about that too -- if anything QM has taught me is that my attempts at physical intuitions are usually wrong about QM.

Zamicol 6y ago

What is the amplitude of a single photon's wave? Yes, it's well taught that wavelength is related to frequency. Higher frequency is higher energy energy and lower frequency is lower energy, but it's the frequency of what? Unlike ocean waves, photons do not have a spacial amplitude. A photon does however have a spacial wavelength. This distinction between photonic wavelength and amplitude I've never heard explicitly addressed. My understanding is that a photon's amplitude is the likelihood of interaction at a specific point in space. High amplitude is likely interaction, low amplitude is low likelihood of interaction. This means at a photon's peaks/crests it has high interaction and at its troughs the photon has low interaction likelihood. These likelihoods are repeated every wavelength, a length measurable in physical space. This is some of the reason why an antenna for a given frequency range needs to be a specific size. Too small and there's a good chance of missing a signal. A proper sized antenna, related to wavelength, guarantees high interaction somewhere along the length of the antenna. When speaking of many photons, amplitude (like AM radio) is simply flux, how many photons at a particular frequency exist during a given unit of time. That's not related to the amplitude of a single photon and not what I'm talking about here.

noobermin 6y ago
Quanta are specifically the quantization of the EM field, so if you will, a single photon at least theoretically is the smallest amplitude of an EM wave you can have. You can see this mostly by noting the expectation of the number operator gives essentially the radiant intensity.
pdonis 6y ago
> My understanding is that a photon's amplitude is the likelihood of interaction at a specific point in space. Not really, because there isn't really a well-defined wave function for a photon in the position representation (which is the one that has the interpretation "the likelihood of detection at a specific point in space"). > When speaking of many photons, amplitude (like AM radio) is simply flux, how many photons at a particular frequency exist during a given unit of time. There isn't a well-defined answer to this question, because a state like this (which is a coherent state) is not an eigenstate of the photon number operator. (Also, energy flux is really amplitude squared.) A good, if somewhat lengthy, discussion of the "photon" concept can be found here: http://math.ucr.edu/home/baez/photon/schmoton.htm http://math.ucr.edu/home/baez/photon/schmoton.htm

gfody 6y ago

another great explanation here https://www.youtube.com/watch?v=MzRCDLre1b4 https://www.youtube.com/watch?v=MzRCDLre1b4 also from 2017

pdonis 6y ago

The article leaves out a crucial item. When it says: "The normal modes are plane waves traveling at the speed of light in a particular directions with a given frequency." This is not quite correct. A correct statement would be that plane waves are one possible choice of "normal modes" for the quantum electromagnetic field. But not the only possible choice. (In more technical language, they are one possible choice of basis for the Hilbert space of states of the quantum electromagnetic field, but not the only possible choice.) In fact, the plane wave states (whose technical name is "Fock states") are often not very useful, because they are very hard to produce experimentally and pretty much never occur naturally. The states that are closest to naturally occurring states and which are easy to produce experimentally (for example in a laser) are coherent states. But coherent states are nothing like plane waves.

krastanov 6y ago
I am pretty sure you are confounding the basis of functions (harmonics) that one can use to describe an EM field, with the basis of a Hilbert space used to quantize them. You can have a mode (e.g. a plane wave) and the field of that particular mode can be quantized and you get to pick whether to use Fock states or coherent states or any other basis. In other words, "plane wave" refers to a particular mode of the field and Fock/coherent states refer to the quantum state of that particular mode. Two different plane waves are two completely different modes, e.g. two completely different Hilbert spaces, not basis vectors of a given Hilbert space.
- pdonis 6y ago
  > I am pretty sure you are confounding the basis of functions (harmonics) that one can use to describe an EM field, with the basis of a Hilbert space used to quantize them. No, I'm not. The same mathematical functions can appear in both classical and quantum treatments, but I'm talking about the basis of the quantum Hilbert space. > Two different plane waves are two completely different modes, e.g. two completely different Hilbert spaces No. They are different Fock states in the same Hilbert space; in the Fock state basis for that Hilbert space, they are two different, orthogonal basis vectors. And that same Hilbert space can also have other choices of basis besides the Fock state basis.

carrolldunham 6y ago

The author left off at precisely the point I was hoping they would get across: How the wave that extends everywhere in space, obviously doesn't. I mean, I know you can make a localised 'packet' or whatever with an infinite sum of sine waves, but then wouldn't you have to talk about infinite photons moving every time 'one photon' hits a detector?

krastanov 6y ago
It is a neat trick actually. If you superimpose a few of these waves with frequencies that are fairly close, then you will see how they cancel out in the distance, while they reinforce each other in the center. This is called a "wave packet". 3blue1brown was somewhat useful, somewhat tangential video on the topic https://www.youtube.com/watch?v=MBnnXbOM5S4 https://www.youtube.com/watch?v=MBnnXbOM5S4 The more rigorous way to say "superimpose a few of these waves", is to say that there is some uncertainty in the frequency. This uncertainty in the frequency lets you have more certainty about the position (the wave packet is centered somewhere, instead of being completely distributed the way an infinite plane wave is)
l33tman 6y ago
It's an infinite sum of variations of the same photon, not an infinite amount of photons. When it hits the detector (or, really, when the researcher eventually gets entangled with the experiment) it is detected as a single interaction. This is why the terminology is confusing. A "classical" photon just doesn't exist in the modern treatment but we still need it to talk about what we do.

remote_phone 6y ago

One question I have: One thing I remember is that as something approaches the speed of light, its mass increases. This is why we can never achieve the speed of light because as we approach the speed of light, our mass increases which requires more energy to accelerate. If that’s the case, the how can photons have a mass? Wouldn’t something traveling at the speed of light need to have infinite mass, regardless of how light it started off with?

krastanov 6y ago
There is rest mass, which is the mass of an entity when it does not move. And there is relativistic mass, which is the rest mass plus the mass due to all of the kinetic energy of the entity. Photons have zero rest mass, but depending on the energy they carry, they have different relativistic masses. By the way, only entities with zero rest mass can move at the speed of light. Actually, in relativity it is mathematically inconsistent for something with zero rest mass to exist unless it is moving at the speed of light.
- remote_phone 6y ago
  Very excellent answer, thank you for this! I will do more reading in this direction!
brutt 6y ago
It's "fake" mass. Regular waves have "mass" too, due to contraction (for 3D) or raising (for 2D) of conducting matter, so it's mass of contracted air/water/etc.

maxk42 6y ago

What I really want to know is: Can someone describe what "heat" is to me?

gigama 6y ago

"I'd like to have an argument please." [1] https://genius.com/Monty-python-argument-lyrics https://genius.com/Monty-python-argument-lyrics

mike1101 6y ago

How does this explain the duel split experiment?

jabl 6y ago
It doesn't directly address it. But they key is right there in the beginning; photons are NOT small billiard balls moving along ballistic trajectories. "Wave-particle duality" doesn't mean that you can think of flicking a light switch as alternatively an electromagnetic field propagating from the light bulb, or that the light bulb shoots out a stream of tiny billiard balls. No, there's only the electromagnetic field. However, if you squint closely enough you see that the energy levels of the field are quantized (aka photons). Now, back to the double slit experiment. So a wave propagates from the source, through the slits, interferes constructively or destructively, and then hits the detector screen. However, due to the quantum nature of, well, everything, the "hits the detector" interaction is quantized. The field "deposits" quantas of energy (photons) to the screen in a localized interaction (say, a photon causes an electron in the screen to jump to a higher energy level). If the detection apparatus is sensitive enough you'll see that single interaction as a dot on the screen, rather than a faint interference pattern (which you'll eventually start to see if you repeat the experiment long enough). So: Lets forget about the "wave-particle duality" already. There's only fields. Fields which interact in a quantized fashion.

cycomanic 6y ago

I'm surprised that nobody pointed out yet, that harmonic oscillators have discrete energy states as well. I think that's why the explanation is somewhat makes things more confusing. The fundamentally different thing about quantum mechanics is that even waves in free-space have discrete energy states. I think the video by 3blue1brown posted by someone else is a much better explanation.

MaXtreeM 6y ago

For others who like to learn from video, here is lenghtier explanation of quantum fields, discrete energies, plane waves, etc. from Sean Carroll: https://www.youtube.com/watch?v=Dy1LNk_B6IE https://www.youtube.com/watch?v=Dy1LNk_B6IE

anonymousiam 6y ago

WiFi could also interfere with other frequencies if a non-linear device is nearby. See: https://en.wikipedia.org/wiki/Intermodulation#Passive_intermodulation_(PIM) https://en.wikipedia.org/wiki/Intermodulation#Passive_interm... The article does not consider this, but it works with light as well as RF.

mikhailfranco 6y ago

sigfpe is too simplistic and conflates a few different aspects of atomic spectra, photons and EM fields. The sci.physics reference for this is Baez & Weiss: http://math.ucr.edu/home/baez/photon/schmoton.htm http://math.ucr.edu/home/baez/photon/schmoton.htm If you have read that, you know the number of photons is just another quantum number, with aspects of uncertainty, superposition and entanglement, so this will not be a surprise: https://phys.org/news/2019-08-photon-number-quantum-superposition.html https://phys.org/news/2019-08-photon-number-quantum-superpos...