Acceleration and Velocity are vectors. Changes in a velocity vector are an acceleration. Therefore when photons change direction technically it’s a form of acceleration.
I thought photons are always moving in straight lines from their perspective, and it’s space that’s bent. Unless it’s through a medium, then they just get absorbed and re-emitted, sort of.
Space bending is a general relativity thing, which isn’t really related much to how mirrors work.
Regarding the medium bit, photons being absorbed and remitted can’t explain how light moves slower in glass. This is just an extremely popular myth. Photons are only absorbed by atoms at very specific frequencies. Also, the entire reason glass is transparent to begin with is that it’s not absorbing the photons (requires too much energy to bump the electron’s energy level so the photon isn’t absorbed and it keeps on trucking). Also photon absorption and remission is stochastic so there’s no way to control the direction it happens in or how quickly it happens. Random directions of remitted light would make glass translucent, not transparent. So for a few reasons, that’s not how it works.
Ok but photons don’t change direction either. Treating photon scattering as an individual particle accelerating due to an applied force, well that’s just not a correct description of how perturbative QED models photon interactions.
Since photons are indistinguishable, it’s hard to say too much concretely, but it some sense a diffracted photon is different photon. In order for a photon to interact with say, a diffraction grating, the interaction is done with “virtual photons”.
So for a photon to change course, aka accelerate, it does it by absorbing a virtual photon and emitting another. Whether that is the “same photon” after the interaction is kinda more philosophy than physics, at least to me.
Feynman diagrams are surprisingly accessible for how much information they contain. It’s one way to think about photon (and other particle) reactions.
Are you claiming this is done without a force carrier? If you are working outside the standard model, I guess that’s fine, but I don’t want to spend time arguing with you.
Ah, I see. Sorry for the snark. I was thinking more in line with the Compton effect, and thought you were talking about something like that too. (Even though it’s clear that you were explicitly not. I thought you were denying photon-virtual photon interaction because I was talking about it in a funny way.)
I would still say it’s still philosophical whether photons experience acceleration, but I concede that photon-photon interaction is not done by virtual photon exchange.
I am indeed denying the existence of photons interacting with virtual photons. I am also saying there is no tree level photon-photon interaction of on shell photons. Neither Compton scattering nor Bhabha nor pair production nor pair annihilation involves a photon-photon interaction. There is no photon-photon vertex in QED. There is no tree level Feynman diagram that you can look at and say “this is, at least philosophically, a photon changing its momentum”.
There is a 1 loop diagram that represents photon-photon scattering. But even that doesn’t have any photon-photon vertices, instead it is mediated by electron-positron pair.
Non-abelian gauge bosons (gluons) couple to themselves. So does gravity (gravitons). Abelian ones (photons) do not.
Photons don’t accelerate. They are emitted or absorbed. That’s their only interaction.
Look bro. Your top level comment that I replied to was generally correct, and also very helpful. I liked it. I liked the suggestion for people to look at the Feynman diagrams. I agreed with it. I upvoted it.
I hope I’m not giving you the impression that I’m taking a personal issue with you. I’m not. I like you and I hope we’ll still be friends when this is all over. I promise to read Discworld soon.
The only quibble I had with what you wrote was this one sentence:
So for a photon to change course, aka accelerate, it does it by absorbing a virtual photon and emitting another.
Photons do not absorb virtual photons. And real on-shell photons do not interact. In Compton scattering and 1 loop photon-photon scattering, you can think of photons emitting e+e- pairs. But never do they emit or absorb other photons.
Maybe that’s not what you meant with that sentence, and I misunderstood. If that’s the case, my bad. Maybe you didn’t need the explanation. If someone else made the same misunderstanding reading your comment that I did, then maybe my comments will help them even if you don’t need them. Or if not, if it’s just me being dumb, well c’est la vie.
You’re right. And I’m the one being less than friendly. It’s nothing personal. It’s just something I’ve noticed about myself. It’s that I hate talking about physics on the internet.
I’m high on lemmy, not in my office. I read a terrible meme. So I open the comments, and see your comment. It was exactly what I was thinking. “Photons don’t accelerate.” Which I took to mean “your meme is bad and you should feel bad”. And again, I agree, it is horrible, this meme.
I like to shoot the shit about, say, quantum loop gravity (i’m honestly clueless about it) with people at the office, but on lemmy, academics piss me off. I don’t know why.
So from your reply, natural question arises: What about diffraction?
You went academic. I’m high. So I just steer them to a right answer while bringing up less academic (but valid (maybe)) ideas about philosophy. I did that because I hate when academics try to seriously discuss that “there is only one electron idea” and similarly unfalsifiable crap. That shit belongs on dumb internet forums with bad memes. And man did I find a bad meme. So was angling for a stupid debate about whether any particle can ever accelerate. You can’t trace them from idenitical copies. Are they the same particle after an interaction knowing that force carriers exist in the standard model? Not an actual quantum field theory debate.
But to give you some closure. I do see that I clearly did imply a tree-level interaction in my initial reply. It is wrong to say a photon emits anything. You were also very direct in your correction. I read it along with other comments and must have confused myself. So in all the back-peddling I was doing, I was avoiding defining “an interaction”. I was just trying to say any influence is an interaction. Not two photons touching on a diagram.
Also, I have a vague memory in grad school. Two people smarter than me were debating whether in a universe consisting only of 3 photons, would they be able to interact? I couldn’t focus on what was said. I was having an existantial crisis. So I had that clacking around in the back of my head. So I’m just going to stop writing now, because as I mentioned, I’m high. So I should just stop.
I’ll level with you. I know how to use QED to compute the cross section of a scattering reaction. But I do not remember, or perhaps never knew, what the QED theoretic description of classical wave mechanical phenomena like diffraction, reflection, refraction, and dispersion look like.
Well… actually of those phenomena, I think diffraction is fine. A single waveform will exhibit diffraction. It doesn’t entail any interactions. A single photon can still exhibit a diffraction pattern. It doesn’t mean that the photon has changed directions or circled around or in any way accelerated. The only reason you might think so is that you’re thinking of photons as billiard ball type classical particles, but of course they are not, they are quantum particles with spread out wavefunctions.
Dispersion I guess is just scattering combined with absorption re-emission (and as we discussed, even scattering is itself a form of absorption & re-emission). But as for reflection and refraction? Those are the phenomena that Entropius was pointing to elsewhere in this thread. I remember how those look in terms of solutions to Maxwell’s equations and boundary conditions, but that’s classical wave mechanics. I do not remember how to translate that into the language of QED.
QED is a fundamental theory, so I assume that a description exists, and of course because I know what QED looks like, so I am certain that it will still be true that in this description, photons will be absorbed & emitted by charged particles, but photons will not interact with photons. However beyond that I cannot say much. How do we describe reflection of light in a mirror as photons scattering off electrons? I don’t know exactly.
One thing I can say is that generally classical states are modeled in quantum mechanics as coherent states, which are eigenstates of the annihilation operator. They look something like exp(N)|0> where N is the number operator, which means that they are states with a superposition of 0 photons, 1 photons, 2 photons, etc. They don’t have a well defined number of particles. So maybe if you want a QED theoretic description of reflection, you can have it, but you won’t be able to talk about specific numbers of photons. But again, I don’t know the details of this.
I wonder whether this concept of classical waveforms as coherent states with a superposition of all numbers of particles will help at all with this philosophical debate about whether two photons are the same particle or not, or about whether you can have a universe with only 3 photons
I’ll level with you. I only called it philosophical so I could hide behind that as a shield against an actual physics debate. But then I so showed my ass and mentioned the standard model. Thus leaving philosophy. I can’t hide behind unfalsifiable bullshit.
So I hope someone read this and went down some wikipedia rabbit holes. I’ll happily be “Cunningham’s fool”. I’ll give you, weird reader, some more wiki nuggets below.
I don’t think you should let some rando make you doubt anything. I don’t have a Ph.D. in physics. I only have a mild intro this stuff. I was on my way to getting a phd in physics (nuclear at that, not particle) and got distracted by math.
I don’t want to be super specific so as to not dox myself with a research fingerprint, but my research has crossed paths with things like Agmon metrics. Which although feels like I’m doing physics, it doesn’t change the fact that physicists don’t read my papers.
So I do find myself saying “apparently these graded algebras show up in quantum mechanics” and stuff like that. Maybe some day I’ll go back and learn it deeper, but I doubt it.
So online, I’d rather play the role of a street preacher spouting things like “nature can’t take a derivative. there is no continuum.” and hoping people read the links when I claim nature solves differential equations by means of weak solutions thereby only integrates. Integration is what nature does. I know that the phrase “nature solves differential equations” is nonsense. But it’s fun. So going deeper, nature can’t take a derivative because the idea of point particles destroys continuity. This is what saves the natural world from pathologies like the Banach–Tarski paradox. Those ideas are kinda basic, but I’m shooting for 1 in 10,000 read to whom the topic is both new and interesting for.
Sorry that you engaged with an internet crazy person. I hope it wasn’t too infuriating.
Lie groups are my favorite thing in all of mathematics, and gauge theory is my favorite thing in physics. E8 and all its connections to other subjects is one example of how amazing this subject can be.
It would be a coup de grace of the highest order, just the crowning intellectual achievement of mankind, if we could stumble upon a theory of everything explaining the entire Standard Model, just by fiddling around with how to fit SU(3)xSU(2)xU(1) fits inside E8 or whatever.
I have a friend who’s an artist and has sometimes taken a view which I don’t agree with very well. He’ll hold up a flower and say “look how beautiful it is,” and I’ll agree.
Then he says “I as an artist can see how beautiful this is but you as a scientist take this all apart and it becomes a dull thing,” and I think that he’s kind of nutty. First of all, the beauty that he sees is available to other people and to me too, I believe. Although I may not be quite as refined aesthetically as he is … I can appreciate the beauty of a flower.
At the same time, I see much more about the flower than he sees. I could imagine the cells in there, the complicated actions inside, which also have a beauty. I mean it’s not just beauty at this dimension, at one centimeter; there’s also beauty at smaller dimensions, the inner structure, also the processes.
The fact that the colors in the flower evolved in order to attract insects to pollinate it is interesting; it means that insects can see the color. It adds a question: does this aesthetic sense also exist in the lower forms? Why is it aesthetic? All kinds of interesting questions which the science knowledge only adds to the excitement, the mystery and the awe of a flower. It only adds. I don’t understand how it subtracts.
Kinda related, in the company I used to work everything was done in SAS, an statistical analysis software (SAS duh) that fucking sucks. It’s used to be great, but once your on their environment you are trapped for fucking forever. I hated it and refuse to learned it over what was basic for my daily tasks. A couple of months I moved to another company that used to pay a consulting firm for my job, so my boss and me had to start everything fresh and the first thing we did was to study what are going to use as statistics software and I fight tooth and nails for Python and one of the points I pushed was that if in the future we decide to move out of Python we could easily can do it, while other solutions could locked up us with them.
If you rely on free packages in Python for processing, those are as likely to become obsolete as anything else (if not more likely). I also really dislike the compatibility issues with different versions of different packages, the whole environment aspect. Buying new computer with different version of windows? Who knows what will work there.
In this sense for scientific computation I prefer something like MATLAB. Code written 40 years ago, most likely would still work. New computer? No problem, no configuration, just install Matlab, and it runs! Yes, it costs money, but you get what you paid for. Mathematica is another option, but I mean ugh!
I mostly use pandas that I don’t think is going anywhere, we’re also going to start tests with a library called ‘chainladder’ that is used for some actuarial reserves calculations, from everything else I’m programming custom functions because as far as I know, there’s not a lot of actuarial mathematics libraries on Python (R have much more support for that, but I prefer the flexibility of Python, like a good portion of my job is scrapping our regulatory body website for information and not sure how good R work on that).
Matlab is ugly because it’s so backwards compatible. And it only is backwards compatible until someone decides to use it to interface with external hardware that you need a specific version of some library for.
If you really don’t want to spend money, there’s always GNU Octave. Sure, it doesn’t have the thousands of matlab toolboxes, but if you’re running code from 40 years ago it shouldn’t need those anyway. I wrote a couple of scripts recently and then rewrote them slightly so that they would be compatible with octave.
Melt is crazy good. Half sandwiches, vegan, gluten free, or full on grease and meat and dairy. I go once every time I visit Ohio. I’d go twice if I hated my body.
I think the word you’re looking for is physicist. A physician is a medical doctor (as in a person that treats sick people). A physicist is a person that studies physics (as in a person that knows how to solve word problems involving pool tables).
The entire post-PhD phase put me off getting a PhD. I’d rather work an office job than trying to constantly scramble for Grant funding literally all the time on top of the demands of teaching, research, and the constant pressure to write papers.
I did one year of a postdoc in the neuroscience/endocrinology of stress and trauma. I dragged my wife and daughter from Ohio to NY, not quite NYC but close enough to feel the pain of its cost of living, and nearly ruined my marriage trying to support the three of us on the stipend. I wrote a grant proposal about nine months in, but I was so stressed out over everything (fitting for the research, no?) that I already decided I was done with the whole thing before I even submitted it. We moved back to Ohio, and I did a couple of semesters as an adjunct prof, after which I swore never to do it again.
I interviewed for other fellowships prior to that one; one lab, a very well-regarded lab at Michigan focusing on functional MRI and affective neurophysiology, stood out to me because none of the seven postdocs the lab already had had authored a single paper even after having been there for years. The two PIs running the lab, a husband and wife team, collaborated so much with other labs that they never gave their postdocs any opportunities to work on their most pivotal, high-profile projects. After I interviewed, one of them took me aside and said that it would not be a good opportunity for that reason, and that his experience in academia was not an isolated one. The others ranged from being similarly jaded to… idk, having some kind of Stockholm syndrome.
Between these experiences and the long chats I’d have with my similarly disenchanted labmate from grad school, I gave up on all of it and looked for alternatives. I’ve been working as a sci-comms writer in the pharma industry, in the agency setting, for almost five years now and I’m way better off. Being in academia for a year after defending just straight-up murdered my idealistic outlook on research. I’m not in love with the job I have now, but I’m in a mindset anyway where I don’t want to be defined by my career, it’s just something that pays the bills, but it does it very well.
I hear ya. Grad school did a number on my mental health. The fear of failure is embedded in just about everything, from the high GPA expectations (even from your first semester), to the quals, to the thesis. The pressure on yourself can be too much to bear.
I find myself less stressed in industry having worked in various positions over the years, and despite all the college I have yet to use calculus at all (it’s spreadsheets as far as the eye can see) and rarely have to use any of the other number of subjects I took in college. The one school course that had helped me the most in my actual work career has been my middle school typing course, I can type super fast as a result lol. Maximum productivity with my mechanical keyboard at work, keycaps go brrrrrrr.
I used to feel ashamed at myself for not going all the way, for withdrawing soon after I got my masters. I felt like a complete failure. This has lessened over time as I realize that the entire rest of everyone’s working life is a grind regardless of how far up in academia you go, and that I would be in a very similar position otherwise.
What if so? Well, then that’s not the whole of academia that they dislike, only maybe those parts being mixed with the others, and as you note, there are apparently jobs in the field/industry that do allow one to avoid some of those parts they dislike.
This is fake news. It’s not gassing, it’s stoning. Smoke is weed for bees. We trading drugs for honey. They can leave if they want, cause they can fly.
I found a bee near death outside once, and I picked him up with an envelope then dropped him in some manuka honey. He landed upside down, but I flipped him over, then he started drinking the honey. The next morning I saw a smudge on the floor and thought a housemate had squished him, but then I opened the door to the front room and he did a little dance in front of my face before I let him outside.
Suffice it to say, bees love honey just as much as we do.
BTW that bee you saved was probably a female. Women do all the outdoor work in bee society, the males’ primary job is to fuck the queen. They’re little stay at home sluts.
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