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Comment by consilient | Hacker News Reader

> So from a classical point of view light travels as a wave but interact as a particle.

And the classical point of view is wrong. Photons resemble classical particles in a few respects, and classical waves in a few others, but at the end of the day they're neither.

> Still the point stands that we never observe light directly but only through its effects on electrons and other charged particles.

This is true of literally everything. "Direct" observation does not exist. Every atom, every cell, every person, every planet, every star - you know them by their effect on your sense-data, or else not at all.

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photons dont exist, dude, except in connection with and at the site of the detector. study some qft and then you can go talk about it on the internet with authority.

and yes direct observation exists. that's what measurement is. and that's all you can ever "observe" unless you incorporate the wavefunction, which also doesn't "exist".

This comment is needlessly hostile. It's ok to correct someone if you think they're wrong, but this tone isn't conducive to curious conversation.

so it's the tone of my textual words? i think you're mistaking my laughter at their blatant and willful ignorance for hostility, and quite honestly it sounds like you're projecting that hostility. from the start I've been incorrectly downvoted and critiqued while being the primary commenter in this child thread providing a semblance of correct view. to be quite frank i deserve an apology, not some nitpick that comes from your personal assumption about my tone. but i know i won't get one because it's not hostility you care about at all. a lot of you commenters here are pretty hilarious. but not in a good way.

At this point anyone who is as certain about the nature of light as you seem to be may well be right, but is demonstrating a level of confidence the literature does not yet seem to support.

Although there are those who believe that photons only exist at source and at the detector, there is some experimental evidence which contradicts that (for example, this 2013 paper in which researchers 'read' information from a photon without destroying it, which implies its continued existence between creation and observation: https://doi.org/10.1126/science.1246164).

For what it's worth, I am also of the opinion that your tone was hostile, and yes, 'textual words' can and do have a (metaphorical) tone. Regarding downvoting and critiquing, there's an old adage about if you walk into a room and it smells of dog shit, maybe someone in the room stepped in something on the way in, but if every room you walk into all day stinks, well maybe you should check your own shoes.

so, you're trying to tell me that such reasoning about "dog shit" applies to the ignorance of humanity in general? The reality is the very few people actually understood what they were talking about and a lot of people went around operating on what they didn't really know. So while you call me an asshole for correcting a number of incorrect people in this thread who are themselves rather overconfident, I have to again insist that because I am correcting them or destroying their delusions does not make me hostile and there's a very good chance that you're projecting that impression. The definition of hostility includes the intent to do harm or to be unfriendly, which is in fact what the people I am replying to are doing by spreading misinformation, as if they know. If that's too difficult for you to accept, then best that you do not reply to me, because it would be a waste in both of our time. "falsehood travels a great distance in one night before the truth even crosses the threshold of the door". And the masses sentences Socrates to death just because he called them hypocrites. It's a good thing I know these truths or I would have been damaged by you. It still makes me sad though.

and for what it's worth I don't believe the paper you linked says what you think it says.

OK.

> study some qft

I have. Srednicki and Weinberg are sitting on my bookshelf right now.

> photons dont exist, dude, except in connection with and at the site of the detector.

Exactly backwards.

Photons fall out of mode-expanding asymptotic EM field states just like any other particle. It's the interaction picture that can't be rigorously built up out of particle states.

good to know you're informed, but it doesn't mean we're communicating effectively.

what i said is not backwards unless you use the inverse understanding of "exist". and how can photons exist without interaction? they don't. they're localizations by detectors. until then, they only "exist" as the probability wave. that's due to nothing localizing them. that's how i mean "exist". so it's not really meaningful to use that word.

btw "any other particle" doesn't fall out of EM fields.

> btw "any other particle" doesn't fall out of EM fields.

I very obviously meant that XYZ-particle states fall out of mode expansions of the XYZ-field, not that all particles are EM quanta.

> what i said is not backwards unless you use the inverse understanding of "exist". and how can photons exist without interaction?

Exactly the same way any other field configuration can? The state space of the free EM field simply is the photon Fock space.

The state space of an interacting 4D EM field is unknown and may well not exist, hence the need for perturbative approaches and renormalization - in which particle states again emerge as terms in the perturbation series.

I'm pleased to talk with you given that you're familiar with the topic.

> The state space of the free EM field simply is the photon Fock space.

but I'm not sure what your point in mentioning this is. When people hear things like "particles exist between their emission and measurement", they might get the idea that there could be said to be any reality to the existence of particles in transit. They simply aren't particles the way people think of them - they are probability waves. A great example we could discuss is the HBT experiment in which photon bunching was seen. If the bunched photons were really "particles" by any sense of the word, they wouldn't bunch in time of detection merely by the fact they are entangled with each other. That would be like saying entanglement affects the flight of a particle which is simply not able to be said.

> They simply aren't particles the way people think of them

They're not anything the way laymen think of them. They're not classical particles, they're not classical waves, they're not classical anything. They're not really probability waves either, for that matter, or even field configurations - the real object is the algebra of observables. But laymen don't get to dictate the vocabulary of physics, and neither do mathematicians. Fields are the things that would be dual to the observable algebra, were it always equipped with a dual; particles are the things whose creation and annihilation operators would generate it, were there only always such things.

Well, you are still talking about models. The creation and annihilation operators are also mathematical structures. That does not mean, as you seem to imply, that "particle" physics cannot be conceptualized outside of QFT. QFT may be superseded someday and the physical systems we try to describe will still be exactly as they are. I'm not sure if you'll agree with me since I suspect you've got a reason not to.

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