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> PS: Compare this to biologists, chemists, or engineers. They all 100% agree on all core concepts. Biologists certainly don't. What is a species? Is Linnean t

> PS: Compare this to biologists, chemists, or engineers. They all 100% agree on all core concepts. Biologists certainly don't. What is a species? Is Linnean taxonomy useful or merely confusing and obsolete? What is a gene? > I've never heard a good explanation for what a photon "is", or any particle for that matter. What would such an explanation look like, and why do you think that there is such an explanation? In many cases when people ask what something "is", they want a category defined in terms of categories they are already familiar with. We can build up a set of observations and build a formal model to summarize them whose terms we can map to the results of various observations. We name the various parts of our formal model for convenience. But there is no requirement that the model be able to satisfy queries that depend on things that don't exist in the domain of the model. > 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. Sure, because you're not asking a question about anything observable, so it's a question of how people put names on the various internal parts of their model. It doesn't matter if people agree on that, because when anyone sits down to actually use the formal model to model something, vague naming of internal parts of it is irrelevant. So I think the right answer is: stop looking at the photon! There's a charged thing wiggling somewhere, and the interaction between two charged things that wiggle is quantized. If I have an electron at one point making small oscillations and another electron at another point, I can calculate the transition probability of the first electron oscillating with one less quantum and the second one oscaillating with one more, or vice versa.

jiggawatts 6y ago
> Biologists certainly don't. What is a species? Is Linnean taxonomy useful or merely confusing and obsolete? What is a gene? These are human definitions for classifications, and biologists agree on that. However, if you make a statement that "two groups of animals that can never reproduce successfully with each other are separate species" then nobody will argue that. Similarly, nobody argues about what the mechanism is for species reproduction success or failure. Everyone knows how chromosomes and DNA works. There's no debate. Every chemist uses the same periodic table with the same elements. Etc... > What would such an explanation look like Equations that can be evaluated numerically that shows the behaviour of the EM field, in 4D spacetime, capable of demonstrating interactions with charged particles. That's all. That's not asking much. > why do you think that there is such an explanation? Because it's a thing that happens. There are atoms that have electrons that electromagnetically interact with light and change orbits. Quantum Mechanics provides a highly simplified model of this in a very narrow use-case. That's not wrong, or mathematically invalid. But it's not the whole picture, and isn't a valid source from which to answer questions like "what is a photon". That's not describing the nature of light in the real physical world, it describes the nature of an abstraction in a simplified model. The photon exists in the equations. That's why it's so hard to visualise and "pin down" with a simple description. It's a property of the model, not the world. > We can build up a set of observations and build a formal model to summarize them whose terms we can map to the results of various observations. The models in this case are tiny subsets of all physical behaviour and generally only cover certain categories of scalar observables. E.g.: "The detector went off or not". Hence the cartoon diagrams and focus on the observables covered by the model. > But there is no requirement that the model be able to satisfy queries that depend on things that don't exist in the domain of the model. I agree. But photons are a thing that exist in the model. What I'm saying is that the photons exist only in the model. > Sure, because you're not asking a question about anything observable See, you made the same mistake as everyone else! Atoms aren't the only things that exist! There are free particles in vacuum chambers, particle accelerators, outer space, etc... that aren't atoms. There's a device called a "free electron laser" that has a continuously adjustable output frequency! > There's a charged thing wiggling somewhere, and the interaction between two charged things that wiggle is quantized. Only if they're in potential wells. Even then it's not entirely clear if all interactions are quantised. > I can calculate the transition probability That output is a scalar. The electron is in an orbital though, right? With a defined angular momentum, position in space, and everything. Even if you abandon the concept of point particles, it has a bunch of properties. Now show me all of those properties changing as it absorbs the photon. Classic QM can't, because it doesn't even try. It focuses on the narrow case of "near resonance" light and then handwaves over how the photons actually change their orbitals. Cartoon diagrams and statistics. That's fine if you're designing a laser or something, but that's not what is physically happening with a single electron around a single atom.
- madhadron 6y ago
  > These are human definitions for classifications, and biologists agree on that. I'm a biologist, and I don't agree. > However, if you make a statement that "two groups of animals that can never reproduce successfully with each other are separate species" then nobody will argue that. You're assuming animals with two sexes, and even there things like ring species throw a wrench into that. > What I'm saying is that the photons exist only in the model. and > See, you made the same mistake as everyone else! Atoms aren't the only things that exist! There are free particles in vacuum chambers, particle accelerators, outer space, etc... that aren't atoms. There's a device called a "free electron laser" that has a continuously adjustable output frequency! But those particles exist to us only as the results of measurements. We cannot impute a category to them that is definable in terms of familiar categories. They are no more or less real than the photon. I don't personally dislike the term "particle" for them, but "vacuum excitation" or similar just doesn't have the same cachet as "particle," and usually carry other undesirable baggage. Even "vacuum" carries problematic classical baggage. > The electron is in an orbital though, right? With a defined angular momentum, position in space, and everything. Even if you abandon the concept of point particles, it has a bunch of properties. Now show me all of those properties changing as it absorbs the photon. No, you can't impute properties like angular momentum to a state outside of measurement. We're used to thinking that we can because of classical systems where we take our sequence of measurements of a phenomenon over time and interpolate them infinitely finely and assume that as we do so the measurements converge to a continuous function. But since that limit doesn't exist for quantum mechanical phenomena, you can only speak in terms of measurement outcomes. Plus, even if you could impute a property before measurement, you could only impute them to pure states. Almost all quantum states are not pure states. So we can't show you those properties changing. All we can speak of is the probable outcomes of sets of measurements. > That's fine if you're designing a laser or something, but that's not what is physically happening with a single electron around a single atom. Is what you consider "what is physically happening" something theoretically observable? > Even then it's not entirely clear if all interactions are quantised. Of course. That's why continuous spectra are a thing.
  - jiggawatts 6y ago
    > I'm a biologist, and I don't agree. I picked a bad example. Well, no, actually, a good one, but an example that does not lend well to online debate. And then I failed to make myself clear. I already know about all of the corner cases, such as ring species, the fuzziness you get during speciation, sub-species, the constant reclassification of taxa, etc.. What I was trying to get at is that "species", like "photon" is a human word. A label for an abstraction that's useful. No working biologist (sans a few creationist crazies) would disagree about that vast, vast majority of what makes a species a species. The chromosomes, the interbreeding capability, the genetics, DNA, etc... Where they disagree is on the finer points of classifications, such as whether two very similar specimens are a species, sub-species, or just a "trait" within a species. Those are just human labels, like the dewy decimal code. They're not the thing. They don't disagree that the specimens exist, that their DNA is different, etc... Quantum theorists disagree with each other on things comparable to the existence of species. As in, some will say that there is such a thing as wave function collapse, others will say that this is nonsense and there's no such thing. They're not disagreeing on exactly when wave function occurs in some obscure corner case. No, they disagree on the existence of the concept itself. This is a crucial distinction. No two chemists will ever disagree that H2O is water or not. Ever. There's just no such argument, and hasn't been for well over a century. In theoretical physics, specifically quantum mechanics and its cousins, there still is debate at this level, and shows no signs of resolution. > But those particles exist to us only as the results of measurements...<snip>... you can only speak in terms of measurement outcomes. That is a complex debate that's been had in the past: is it meaningful to speak of something existing if it cannot be measured, even in principle? The issue with that is that sometimes people just state that certain categories of experiments are impossible, and then it turns out that oops.. no, it was possible, just really hard to do. This is my favourite example: https://tf.boulder.nist.gov/general/pdf/2723.pdf https://tf.boulder.nist.gov/general/pdf/2723.pdf Note the quote at the end: "Some observations can be made on the existence of ‘blinders,’both in theory and in experiment. Some theorists were accustomed to seeing problems in terms of the tools which had previously proven useful for describing experiments with large numbers of atoms, such as the optical Bloch equations. Their intuition seemed to fail for the case of single atoms, and they were unprepared to accept the phenomenon of macroscopic quantum jumps." This is particularly common in the QM field, especially in relation to single particles or atoms. The tools are optimised for ensembles, so... people seem to forget that single particles exist. The experiments involving single interactions are crazy difficult, so some people will simply state that they're impossible, and it's difficult to argue with that when there are so few experimental results available to counter that. Note that GR had some similarly "hard" experiments, such as the detection of gravitational waves. That doesn't mean that people seriously said that talking about gravitational waves was meaningless. > Of course. That's why continuous spectra are a thing. Okay, so you're on the photons-are-not-always-quantised side. I agree with you, but other people don't. This is a fundamental disagreement much like Hinduism and Islam, to pick two random religions. Sure, there are silly people saying things like "all religions are equally valid", but.. no, no they are not. Some of them are just local church traditions, some are full on sects, and others aren't even vaguely compatible.

jiggawatts 6y ago

> Biologists certainly don't. What is a species? Is Linnean taxonomy useful or merely confusing and obsolete? What is a gene? These are human definitions for classifications, and biologists agree on that. However, if you make a statement that "two groups of animals that can never reproduce successfully with each other are separate species" then nobody will argue that. Similarly, nobody argues about what the mechanism is for species reproduction success or failure. Everyone knows how chromosomes and DNA works. There's no debate. Every chemist uses the same periodic table with the same elements. Etc... > What would such an explanation look like Equations that can be evaluated numerically that shows the behaviour of the EM field, in 4D spacetime, capable of demonstrating interactions with charged particles. That's all. That's not asking much. > why do you think that there is such an explanation? Because it's a thing that happens. There are atoms that have electrons that electromagnetically interact with light and change orbits. Quantum Mechanics provides a highly simplified model of this in a very narrow use-case. That's not wrong, or mathematically invalid. But it's not the whole picture, and isn't a valid source from which to answer questions like "what is a photon". That's not describing the nature of light in the real physical world, it describes the nature of an abstraction in a simplified model. The photon exists in the equations. That's why it's so hard to visualise and "pin down" with a simple description. It's a property of the model, not the world. > We can build up a set of observations and build a formal model to summarize them whose terms we can map to the results of various observations. The models in this case are tiny subsets of all physical behaviour and generally only cover certain categories of scalar observables. E.g.: "The detector went off or not". Hence the cartoon diagrams and focus on the observables covered by the model. > But there is no requirement that the model be able to satisfy queries that depend on things that don't exist in the domain of the model. I agree. But photons are a thing that exist in the model. What I'm saying is that the photons exist only in the model. > Sure, because you're not asking a question about anything observable See, you made the same mistake as everyone else! Atoms aren't the only things that exist! There are free particles in vacuum chambers, particle accelerators, outer space, etc... that aren't atoms. There's a device called a "free electron laser" that has a continuously adjustable output frequency! > There's a charged thing wiggling somewhere, and the interaction between two charged things that wiggle is quantized. Only if they're in potential wells. Even then it's not entirely clear if all interactions are quantised. > I can calculate the transition probability That output is a scalar. The electron is in an orbital though, right? With a defined angular momentum, position in space, and everything. Even if you abandon the concept of point particles, it has a bunch of properties. Now show me all of those properties changing as it absorbs the photon. Classic QM can't, because it doesn't even try. It focuses on the narrow case of "near resonance" light and then handwaves over how the photons actually change their orbitals. Cartoon diagrams and statistics. That's fine if you're designing a laser or something, but that's not what is physically happening with a single electron around a single atom.

madhadron 6y ago
> These are human definitions for classifications, and biologists agree on that. I'm a biologist, and I don't agree. > However, if you make a statement that "two groups of animals that can never reproduce successfully with each other are separate species" then nobody will argue that. You're assuming animals with two sexes, and even there things like ring species throw a wrench into that. > What I'm saying is that the photons exist only in the model. and > See, you made the same mistake as everyone else! Atoms aren't the only things that exist! There are free particles in vacuum chambers, particle accelerators, outer space, etc... that aren't atoms. There's a device called a "free electron laser" that has a continuously adjustable output frequency! But those particles exist to us only as the results of measurements. We cannot impute a category to them that is definable in terms of familiar categories. They are no more or less real than the photon. I don't personally dislike the term "particle" for them, but "vacuum excitation" or similar just doesn't have the same cachet as "particle," and usually carry other undesirable baggage. Even "vacuum" carries problematic classical baggage. > The electron is in an orbital though, right? With a defined angular momentum, position in space, and everything. Even if you abandon the concept of point particles, it has a bunch of properties. Now show me all of those properties changing as it absorbs the photon. No, you can't impute properties like angular momentum to a state outside of measurement. We're used to thinking that we can because of classical systems where we take our sequence of measurements of a phenomenon over time and interpolate them infinitely finely and assume that as we do so the measurements converge to a continuous function. But since that limit doesn't exist for quantum mechanical phenomena, you can only speak in terms of measurement outcomes. Plus, even if you could impute a property before measurement, you could only impute them to pure states. Almost all quantum states are not pure states. So we can't show you those properties changing. All we can speak of is the probable outcomes of sets of measurements. > That's fine if you're designing a laser or something, but that's not what is physically happening with a single electron around a single atom. Is what you consider "what is physically happening" something theoretically observable? > Even then it's not entirely clear if all interactions are quantised. Of course. That's why continuous spectra are a thing.
- jiggawatts 6y ago
  > I'm a biologist, and I don't agree. I picked a bad example. Well, no, actually, a good one, but an example that does not lend well to online debate. And then I failed to make myself clear. I already know about all of the corner cases, such as ring species, the fuzziness you get during speciation, sub-species, the constant reclassification of taxa, etc.. What I was trying to get at is that "species", like "photon" is a human word. A label for an abstraction that's useful. No working biologist (sans a few creationist crazies) would disagree about that vast, vast majority of what makes a species a species. The chromosomes, the interbreeding capability, the genetics, DNA, etc... Where they disagree is on the finer points of classifications, such as whether two very similar specimens are a species, sub-species, or just a "trait" within a species. Those are just human labels, like the dewy decimal code. They're not the thing. They don't disagree that the specimens exist, that their DNA is different, etc... Quantum theorists disagree with each other on things comparable to the existence of species. As in, some will say that there is such a thing as wave function collapse, others will say that this is nonsense and there's no such thing. They're not disagreeing on exactly when wave function occurs in some obscure corner case. No, they disagree on the existence of the concept itself. This is a crucial distinction. No two chemists will ever disagree that H2O is water or not. Ever. There's just no such argument, and hasn't been for well over a century. In theoretical physics, specifically quantum mechanics and its cousins, there still is debate at this level, and shows no signs of resolution. > But those particles exist to us only as the results of measurements...<snip>... you can only speak in terms of measurement outcomes. That is a complex debate that's been had in the past: is it meaningful to speak of something existing if it cannot be measured, even in principle? The issue with that is that sometimes people just state that certain categories of experiments are impossible, and then it turns out that oops.. no, it was possible, just really hard to do. This is my favourite example: https://tf.boulder.nist.gov/general/pdf/2723.pdf https://tf.boulder.nist.gov/general/pdf/2723.pdf Note the quote at the end: "Some observations can be made on the existence of ‘blinders,’both in theory and in experiment. Some theorists were accustomed to seeing problems in terms of the tools which had previously proven useful for describing experiments with large numbers of atoms, such as the optical Bloch equations. Their intuition seemed to fail for the case of single atoms, and they were unprepared to accept the phenomenon of macroscopic quantum jumps." This is particularly common in the QM field, especially in relation to single particles or atoms. The tools are optimised for ensembles, so... people seem to forget that single particles exist. The experiments involving single interactions are crazy difficult, so some people will simply state that they're impossible, and it's difficult to argue with that when there are so few experimental results available to counter that. Note that GR had some similarly "hard" experiments, such as the detection of gravitational waves. That doesn't mean that people seriously said that talking about gravitational waves was meaningless. > Of course. That's why continuous spectra are a thing. Okay, so you're on the photons-are-not-always-quantised side. I agree with you, but other people don't. This is a fundamental disagreement much like Hinduism and Islam, to pick two random religions. Sure, there are silly people saying things like "all religions are equally valid", but.. no, no they are not. Some of them are just local church traditions, some are full on sects, and others aren't even vaguely compatible.