Not much. Yes, e.g. the phase of a photon from beam 1 may be highly correlated with the phase of the second (or, e.g. the polarisations may be highly correlated), but they will still behave as two particle beams. (Yes, I am a physicist, at least I was 30 years ago;-0).

May I ask why „30 years ago“?

No OP, but another former physicist. There's not much career opportunity in that field, but physicists are eminently hireable in software engineering or investment banking.

Current Physics PhD student here.

Pretty much this is the case. Trying to not get spun out of academia is hard work, due to the limited opportunities. Especially is you're unable to move beyond your own country.

Then the temptation of other jobs that easily pay three, four, fives times the salary creep in.

And FAANG or investment banking pays even higher than then that.

Potentially, there's a lower glass ceiling in the UK

In engineering, probably not so much in banking. Unless you mean class barriers.

I mean SE salaries aren't what you'd get in the US for FAANG.

Banking in the city is probably the higher paid job in the UK

Did my PhD, when I started my studies there were 90 new students each year. Upon my promotion there were 30, and the faculty had merged(!). One of the groups (experimental, not my cup of tea) had been cancelled/stopped. I went into IT. A standard joke I used to say is that everyone who knows something about garden gnomes could go into IT. I knew nothing about garden gnomes (but learned myself C++ to [numerically] solve some nasty path integrals using object orientation) and easily adopted to the IT industry. (Started as a programmer, through DBA work (datawarehouse!), different software/data/business architecture, now a ‘portfolio manager’). I stopped being a physicist in 1997, so perhaps 30 year is overdoing it (26th year now, I guess).

Apparently there can be interference effects between two beams (4th order interference) so maybe such an effect could show up in this case. See Ghosh/Mandel 1987 "Observation of Nonclassical Effects in the Interference of Two Photons"

How does one go about not being a physicist anymore?

Username almost checks out

Yes, my name is another anekdote. (I had a summer school in Krete, Greece; there were people from the Max Planck institute. And yes, I probably made an impression as the organisers used the spelling of my last name to write down the emailadresses of those from the PlanCk institute;-0. But no, no known relation with Dr. Planck, would have been honored (did do my PhD in quantum optics, so in a related field I guess).

Was hoping it was something close to that. DAMN quantum optics. That dissertation must have been a pile of work.

Kudos to you for accepting that it might be stupid. A lot of people say things with complete certainty these days when what they're talking about isn't in their area of expertise.

> "A lot of people say things with complete certainty these days when what they're talking about isn't in their area of expertise."

Far more frustrating and annoying is when people like that say things that are blatantly and provably wrong with complete certainty to an expert in the field and then actively refuse to hear any explanation or proof of the reality of the situation.

Far more annoying, is when an expert is so mired in their professions dogma they lead those trusting them astray. The label "expert" is itself a counter to the skepticism and humility required to reliably maintain a grasp on reality.

Unless that's being assessed by a "skeptic" who literally can't do the math required to fully understand the topic they're being skeptical about.

Tautologies are correct by definition, experts are not.

Based on my observations they seem to be usually perceived as correct by definition, but that [culturally trained and regularly reinforced] perception, and the methodology that produces it, is technically incorrect.

Not sure what tautology you're referring to, but nobody is claiming experts are infallible - that's silly.

I made my comment based on having seen lots of HN commenters confidently dismissing various widely accepted (read: current best) physical theories based on appeals to intuition and specious or incomplete reasoning.

> Not sure what tautology you're referring to

This:

"Unless that's being assessed by a "skeptic" who literally can't do the math required to fully understand the topic they're being skeptical about."

The subset of skeptics who "literally can't do the math required to fully understand the topic they're being skeptical about" (or in other words: aren't smart enough to form a non-incorrect opinion) are necessarily ("by definition") going to be incorrect.

While this sort of rhetorical, heuristic-exploiting language can be persuasive (because it exploits heuristics), it is often misinformative.

This can be easy to notice by replacing "skeptic" with various other categorizations (such as based on race, gender, religion (but often only certain ones)) - if one is to do that, the accompanying logic typically changes, &/or the person will take object level offence at the content of the analogy, causing them to be unable to appreciate that the modification to the topic has caused the logic to change.

> but nobody is claiming experts are infallible - that's silly.

I agree, hence I made no such accusation.

I'm curious why you brought this up - were you under the impression that I had done that, or were you maybe framing the conversation to make it appear that I had done that (which could cause 3rd party readers to have a negative opinion on my other words)?

> I made my comment based on having seen lots of HN commenters confidently dismissing various widely accepted (read: current best) physical theories based on appeals to intuition and specious or incomplete reasoning.

Well sure: skeptics, being humans, are often incorrect. But similarly, I've also seen lots of HN commenters who identify as ~"scientific thinkers" confidently dismissing various widely accepted theories (and various other cognitive errors) based on appeals to intuition and specious or incomplete reasoning. Consequently, I am "not a fan" of these sorts of people - however, the degree to which* various subgroups of people are guilty of various crimes is a very easy thing to get an inaccurate read on, since perceptions seem to necessarily rely upon substantial heuristic thinking (which makes sense if you think about it).

This is getting a bit hair-splitty for me, but in case it helps, I think you're misunderstanding the thread, or at least interpreting it entirely differently than I am. Here's my take on where we are in case you find it helpful or interesting.

> The subset of skeptics who "literally can't do the math required to fully understand the topic they're being skeptical about" (or in other words: aren't smart enough to form a non-incorrect opinion) are necessarily ("by definition") going to be incorrect.

My post was intended to highlight my perception of the prevalence of a certain type of argument made in this context, and you're objecting to my description as if it was a logical argument. You are responding as if I am somehow logically comparing "experts" and "skeptics", as if one or the other category implies correctness. I didn't intend to make any such comparison, so I am left struggling a bit as to how to respond.

I intended to say, essentially: "In this context there are people working from incorrect assumptions and with insufficient knowledge, and it annoys me." You responded, essentially: "If people work from incorrect assumptions they are necessarily wrong, so that's a tautology." I don't believe that reasoning is either correct or helpful.

You are correct that I am using a number of heuristics, because that's how people generally communicate. In this case, I've seen a large number of discussions adjacent to the parent thread, and so I necessarily posses a heuristic to identify commonalities. The comment I replied to is not incorrect:

"Far more annoying, is when an expert is so mired in their professions dogma they lead those trusting them astray. The label "expert" is itself a counter to the skepticism and humility required to reliably maintain a grasp on reality."

That describes a real phenomenon, and I agree with the poster that it is annoying. I also see this sentiment overused and applied by people matching the heuristic I described, thus the comment. Ultimately, the discussion was a subjective comparison of the perceived relative prevalence of certain types of claims in online forums like this, and the attitudes of the posters about them.

To continue, you said:

> I agree, hence I made no such accusation. I'm curious why you brought this up - were you under the impression that I had done that, or were you maybe framing the conversation to make it appear that I had done that (which could cause 3rd party readers to have a negative opinion on my other words)

I'm certainly not trying to put words in your mouth, but I felt that you were trying to force me into a comparison I was not intending to make. The perception of experts as "correct by definition", to me, is orthogonal to the discussion which was going on. Sure, that happens and it's not correct. Nevertheless, working to develop reasonable heuristics about when to trust expertise is a rational thing to do.

> the degree to which* various subgroups of people are guilty of various crimes is a very easy thing to get an inaccurate read on, since perceptions seem to necessarily rely upon substantial heuristic thinking (which makes sense if you think about it).

I agree with that, and perhaps my attitude has also been unhelpful. To be clear, I don't have any sort of general opinion about how often "experts" and "skeptics" are correct, because those terms are vague and get used differently in different contexts, and because "being correct" is also pretty squishy if you drill down to any particular area. To make matters more confusing, I find that the most vocal anti-expertise skeptics are usually experts in something other than what they're skeptical about.

I'm not sure where that leaves this conversation, except that I think we differ somewhat in how useful we think heuristics are when reasoning under uncertainty and imperfect knowledge. This is also more abstract than I think is probably useful.

I agree there's been a misunderstanding. Also, it's probably worth noting that you seem like a very nice person, whereas "nice" is not a word that many people would assign to me, including myself.

I'll try to explain inline...

> My post was intended to highlight my perception of the prevalence of a certain type of argument made in this context, and you're objecting to my description as if it was a logical argument. You are responding as if I am somehow logically comparing "experts" and "skeptics", as if one or the other category implies correctness. I didn't intend to make any such comparison, so I am left struggling a bit as to how to respond.

You were speaking colloquially (where inaccuracy is not just common, but culturally enforced).

Colloquial (inaccurate) speech is typically not realized as such, and thus spreads into other minds and is stored as facts.

Repeat for several zillions iterations, all the nodes in your network have a false representation and do not realize it.

This phenomenon is very harmful, thus I oppose it in principle and action. I would say: my normal actions are consistent with people's theoretical/intentional behavior. Of course, saying such things tends to invoke a negative reaction on the other end of the wire (/r/iamverysmart, etc), so I am attaching this additional idea to the ~offensive message (and as a computer guy, you likely are smart enough to understand what I'm talking about....except you and I are in an internet ~argument, which interferes with cognition....so hard to say what will happen - let's find out!).

> I intended to say, essentially: "In this context there are people working from incorrect assumptions and with insufficient knowledge, and it annoys me." You responded, essentially: "If people work from incorrect assumptions they are necessarily wrong, so that's a tautology." I don't believe that reasoning is either correct or helpful.

I don't disagree so much, but then "I made my comment based on having seen lots of HN commenters confidently dismissing various widely accepted (read: current best) physical theories based on appeals to intuition and specious or incomplete reasoning" has the appearance of being not correct/helpful to me (as someone who regularly disagrees with mainstream narratives, and has higher than average concern about the state of affairs on this planet).

>> "Far more annoying, is when an expert is so mired in their professions dogma they lead those trusting them astray. The label "expert" is itself a counter to the skepticism and humility required to reliably maintain a grasp on reality."

> That describes a real phenomenon, and I agree with the poster that it is annoying. I also see this sentiment overused and applied by people matching the heuristic I described, thus the comment.

The optimal level of deployment/distribution of this idea is not known though - it very well may be that it would be optimal to discuss this 10 times more often than we currently do. And while this "is" "pedantic", perhaps, it can also be very important simultaneously.

> I'm certainly not trying to put words in your mouth, but I felt that you were trying to force me into a comparison I was not intending to make. The perception of experts as "correct by definition", to me, is orthogonal to the discussion which was going on.

Where you consider it to be orthogonal, I consider it to be fundamental. It is the "water" in:

There are these two young fish swimming along and they happen to meet an older fish swimming the other way, who nods at them and says “Morning, boys. How’s the water?” And the two young fish swim on for a bit, and then eventually one of them looks over at the other and goes “What the hell is water?”

Or more technically/academically: https://en.wikipedia.org/wiki/Semiotics

> I agree with that, and perhaps my attitude has also been unhelpful.

Nor is mine! It's pretty rare to encounter someone who's interested in a serious conversation on such matters, so I mostly just "spread the good word" in a semi-serious and not very polite way....for me it accentuates the absurdity of the situation, and thus the enjoyment.

> To be clear, I don't have any sort of general opinion about how often "experts" and "skeptics" are correct....

I'd say: I bet if you could peel back your skull and see what's going on inside, it would be a LOT more complicated than this!

>...because those terms are vague and get used differently in different contexts, and because "being correct" is also pretty squishy if you drill down to any particular area.

Pretty squishy as it is. A not great analogy would be how it took a really long time to get from London to New York, prior to airplanes being invented.....the point being: humans can improve over time (though, they do not necessarily).

> To make matters more confusing, I find that the most vocal anti-expertise skeptics are usually experts in something other than what they're skeptical about.

If that! I'm a conspiracy theorist, so I'm fairly well versed in the substantial shortcomings of my brethren. "There but for the grace of God go all of us"....or so we like to think (that it has not already happened)!

> I'm not sure where that leaves this conversation, except that I think we differ somewhat in how useful we think heuristics are when reasoning under uncertainty and imperfect knowledge.

Well I think it is a lovely conversation!

> This is also more abstract than I think is probably useful.

Right, but how would one even go about accurately estimating utility for this sort of thing? Like: useful with respect to what? "Enjoyment"? According to mods, that's what HN is about, and going beyond that is "generally not advisable", for reasons that seem to be available only on a "need to know" basis (if you don't mind a little bitterness/cynicism).

Not a physicist, but if you put one beam through each slit, it's no longer the double slit experiment. Instead it's just two single slits. So no interference pattern, just two spots of light.

Not exactly what you asked, but you might find this interesting nonetheless:

https://www.youtube.com/watch?v=dEaecUuEqfc

(Or https://flownet.com/ron/QM.pdf if you don't want to sit through a video.)

As others have mentioned, the double-split experiment is interesting in that when you leave a quantum system alone and let it travel through the double slit experiment, the interference pattern occurs. If you "force" an entangled system into a particular slit, then you don't have a quantum entangled system by definition; the entanglement comes from the quantum interaction of the system and how we can only describe it via an entangled wave function.

I think in terms of practical use cases, generally for entanglement, it allows for high amounts of encoding since the particular basis used to describe each individual constituent becomes coupled with one another e.g. (|PsiA, PsiB> = (|A1> + |A2> + ... + |An>) * (|B1> + B2> + ... + |Bn>)) allow for a high number of configurations of a problem space to be encoded. I suppose there could be some interesting optical phenomena used for optical experiments/pulsed lasers but you'd probably need to discuss this with an optics expert :-)

What would happen if you send one beam through double-slit and see how the other beam projects.

Would it also form a pattern as the first one?