superposeur

Interesting, thanks for the links. Looking at them, though, it would appear that the two "paths" being interfered differ in length on the order of the separation between the two telescopes -- i.e. meters or kilometers -- rather than astronomical distances. Using the speed of light, this corresponds to a difference in flight time of the light on the order of nanoseconds or seconds. I can imagine how the light traversing the two paths could remain unmolested by stray random, environmental phase shifts during such short times (necessary if you want them to interfere). On the other hand, the double images in the photo would have a difference in flight times of years? But, again, I don't really understand precisely what the astronomer was referring to, or have proper intuition for the conditions of space through which astronomical photons travel...

I seem to remember an astronomer mentioning that it is possible to interfere the light from gravitationally lensed double images. Lacking appropriate intuition, this would be amazing for me as I’d think the photons would lose coherence over the course of their multi billion light year journeys (but maybe not?). Does anyone know about this?

I have the same impulse and also wish to keep a grip on it. Partly, this is from watching the bad example of my boss, who is always making slightly inappropriate jokes in meetings. His behavior communicates insecurity, immaturity, and poor boundaries. To this end, I’ve found that if I can manage to maintain a feeling of being solidly “in my own skin”, then I’m less compelled to joke sarcastically on the proceedings.

It’s worth remembering that Shakespeare puts the most unambiguously wise words of the play into the mouth of this “old fool”:

> ‘This above all: to thine own self be true, And it must follow, as the night the day, Thou canst not then be false to any man.’

Indeed, 1. is a mystery. But, 2. is a consequence of 2nd law of thermo. Specifically, the lighter the mass of a decay product, the larger the number of possible final states in the kinematical phase space (in general). For instance, if there is just enough energy to make a pair of particles, then only one final state is possible: particles sitting at rest. On the other hand if energy is “left over” in addition to rest energy, then there are many possible final states corresponding to the pair flying outward in different directions. Hence, the decay to the lighter products are entropically preferred. This is mathematically encapsulated in Fermi’s Golden Rule.

As an instructor, agree about everything but will add that I try to keep a positive framing.

That people procrastinate and need incentives is human nature — no more use bemoaning this than bemoaning politics. The job of instructor is precisely to enforce a system of rules and incentives while not being too dogmatic about them that the class turns into a grind while promoting enthusiasm for learning while creating inspired course content, while balancing all this with the instructor’s own scholarship priorities. It’s a tall order and very few people do it well.

That mastery is difficult and subtle does not distinguish pedagogy from other professions, but what is different is that every shmo off the street remembers being a student, so thinks they know the secret formula for pedagogy.

Agreed — when I’m on the receiving end of advice, I try to suss out the distinction you describe. Is the advice-giver just lazily ruminating (usually the case) or are they actually thinking through my particular circumstances and reflecting on the optimal path given these constraints and/or plugging a particular blind spot holding me back? You can often feel, viscerally, the difference between the two types of advice-giving.

Yes like listening to a radio talk show or a scene in a play — the participants are sometimes real people I know or imagined people. They seem autonomous but when I think about the context of the whole scene, it’s often transparently and cringeworthily based on whatever concern I have —- “this week on the radio hour! A dialogue demonstrating that none of the participants appreciate Luke. Next week: everyone coming to the realization, in their own way, that this thing Luke came up with is the most brilliant thing ever! Stay tuned”

Interesting - I experience the opposite in that I can only hear imagined “dialogues” involving other people, but have no inner voice of my own. My emotional priorities dictate what the imagined drama is about and, to be sure, this is a whole lot of self-pity … but the voices have distinct identities and sounds, and none of them are “me”.

I seem to have a variant of aphantasia where I can conjure images through dint of will, but they immediately begin wildly revolving in space / mutating as if lacking any stable “camera angle”, then vanish entirely. No matter how hard I try, the images refuse to stay put or to persist in memory. Does any one else have this? / does _everyone_ else have this?

Yes that’s a good point, clear communication is hard in any field. I want to say to everyone, at least make an effort, though, please?

Ok then! Truly impressive that chemists carry around such a store of jargon.

Don’t intend to make snap judgment (despite my unfortunate tone) — the question is a genuine one. Does it really have to be so inaccessible from start to finish? Maybe yes is the answer, that’s the nature of the thing. Physics is not like that, for instance.

To be clear, despite the slightly snarky tone, I don’t mean to condescend to chemists! Quite the opposite, this is borne out of disappointment when I listen to a whole chem presentation and fail to grasp even one simple idea. I’m a physicist, btw, and could easily fill a presentation with inscrutable equations but what would be the point of that? Instead I make sure that everyone (even a scientifically literate layperson) can stay on board at least the first third of the presentation.

Thanks for this clear account. This proves that it is possible (at least occasionally) to describe a chemistry project using ordinary language to a non-chemist.

By contrast, every single chemistry poster session or talk seems instead to consist of inscrutable walls of long technical terms and impossibly convoluted flow charts. I’ve often wondered whether this really all makes perfect sense to chemists themselves? Like, if I were to surreptitiously change one syllable out of a 10-syllable word, or reverse a couple of the arrows on a flow chart, would anyone in the audience notice? If not, then why is the information being conveyed in this way, seemingly without any effort at comprehensibility?

Edit: don’t mean to condescend to chemists. The question is a genuine one. Does it really have to be so inaccessible from start to finish? Maybe yes is the answer, that’s the nature of the thing. Physics is not like that, for instance.

Definitely was there (note the lack of “edited” tag) :) no biggie, not trying to pick a fight

Yes, hence my parenthetical phrase:

> … (although it is possible to “teleport” the exact quantum state by transmitting its information, provided one is willing to mess up the original).

More precisely, the “no-cloning theorem” of quantum mechanics implies that one cannot replicate the exact quantum state of a clump of matter in a second clump of matter (although it is possible to “teleport” the exact quantum state by transmitting its information, provided one is willing to mess up the original).

However, although no one knows for sure, it seems likely that the operations of consciousness are purely “classical” in the sense that the exact quantum state is not needed (Roger Penrose’s ideas not withstanding).

Yes, most physicists agree that human observers are not required to collapse a wave function. Even the QBists speak of “agents” that are abstract entities, not necessarily human beings. (An agent is something like a “point of view” or a “reference frame” in that it can be thought to exist independently of a living, breathing human who inhabits it.) However, n.b. that the great Nobelist Eugene Wigner did seriously think it had to be an actual human consciousness. (Or a dog, but not an insect.)

Full disclosure that I’ve never really been able to pin down the QBist notion of an agent myself and do not find QBism (or any such “instrumentalist” interpretations” of QM) appealing.

If you travel through a localized clump of stars then yes, as you describe, the clump would be pancake-shaped. However, the Lorentz transform of an infinite lattice is another infinite lattice, just one in which the spacing between stars in one of the three directions is smaller. So, in particular, the average density everywhere remains uniform (no matter where you are situated within the lattice).

The reason you don’t see an isotropic distribution of light from this uniform density is the distortion due to aberration + the synchrotron effect you mention (which makes the stars in the forward direction brighter).

So, in conclusion no “critical angle” but the dots of light appear more densely concentrated toward front and they are brighter, bluer.

Assuming N<1, you see a scrunched up, blue-shifted version of the night sky in the forward direction and very little in the aft direction... this is a combination of the fact that the stars at the various grid points where the stars are now are truly Lorentz-transformed to be more numerous in the forward direction + the usual "aberration" effect accounting for the fact that you are seeing the stars at the retarded time where they were when their light was emitted, not right now. See: https://math.ucr.edu/home/baez/physics/Relativity/SR/Spacesh...

> how you can be sure about the state of the other particle, what if someone already measured it and then did something to it?

Indeed, you are only sure about the state of the other particle in the instant just after they measured it. Whoever measures first instantly destroys the entanglement link, so if they chose to manipulate the particle after measurement, you will have no knowledge of these manipulations.

More generally, note that in quantum mechanics "reading" the state of a particle (i.e. performing a measurement) is drastically different than "writing" information by manipulating a particle. Most entanglement-related weirdness hinges on this fundamental asymmetry between "read" and "write" operations for quantum information.