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Shing
Shing
12:41 AM
Hey, guys. What section of QM should I look up for why we can use a simple oscillator's eigenvector for $N$ photons? (I was reading QFT. and get confused somewhere, and tried to read QM for a solution, but in vain)
 
Secret
Secret
1:03 AM
Last night dream seemed to took inspiration from Egan's infinite assassin, but it is not as crazy as his
 
 
2 hours later…
Secret
Secret
3:07 AM
Basically, my team has 4 people including myself. We then got scattered due to some time anormally. Meanwhile, there's a time portal that stretched from t=0 to t=3, and jumping into it will always return one to t=0. I then used that to buy me a lot of time to regather my team, and then the 4 of us then retrieve data scattered in a couple of computers in the world by repeatedly jumping into the time portal until all paths are explored
And the Egan The Infinity Assassin twist here is that: While the time portal will always send you back to t=0 regardless on which $t \in [0,3]$ you hopped into, it sends you randomly into another timeline. The probability on which timeline you end up is also uneven in that you end up in the middle timeline more often than the other ones, thus multiple jumps are needed to reach the timelines outside the centre one
What's more is that despite to our view we visited each timeline in sequence to obtain the data from each computer and stored in the USB, there is no changing of the past involved since in each timeline, the data transfer (with the USB having the correct ordering of data included) is predetermined, thus the time portal behaves like some form of a CTC
Everyone else can also look very different except for the USB, the data inside and members of my team, which the subjective causality is preserved despite being in different timelines, similar to how the assassin and his counterparts are mostly preserved until he got torn apart near the centre of the whirlpool
The dream however cuts off in this scene when I just regather all my teammates and have done some jumping, thus whether we are successful in the mission is left hanging
 
obliv
obliv
3:35 AM
Hey some random dude started talking about the aether model and I'm pretty sure it's an outdated thing So I was just wondering if anyone here could tell me what mainstream physics regards something like this as naturalphilosophy.org/site/jamesmarsen/2016/12/22/…
 
Secret
Secret
One might be able to do an experiment like this if they use distant starlight and do interferometry on them
similar to how the freewill loophole of the bell experiment is closed by picking distant starlight photons thus the chance for them to be correlated is close to zero
If the aether drag only applies for distances near earth or near the solar system, then there should be some kind of time delay observable in the interferometer due to the light passing through two different aether regions
 
obliv
obliv
yeah that makes sense. I'll let him know.
thanks
 
Secret
Secret
One problem with his proposal is that given our current technology level, it will take way too long to get the result (just notice how long it takes for Voyager 1 to enter interstellar space). and it still take months to reach mars orbit. Not to mention having an interferometer that large you need to start worrying about gravitational waves from mergers can influence the interference pattern and also the logistics required to ensure the 3 ? parts of the infereometer
to maintain alignment at all times to do the measurement
-2
Q: Why hasn't the Michelson Morley experiment ever been conducted on another body of mass in space?

Tyler Einstein stated that if the Michelson-Morley experiment was wrong then relativity is wrong, and isn't this what mainstream physics originates from? It seems pretty counter-productive, and if we receive a null answer then cool; however, if we receive a definitive number larger than zero, how do yo...

general-relativity visible-light speed-of-light relativity
Yeah, up to date, there are no known space based Michelson-Morley probably because it is so resource intensive
But I am surprised there are also no Michelson-Morley based on distant starlight either
 
Bernardo Meurer
Bernardo Meurer
4:36 AM
@JohnRennie I need Windows support :P
Ping me when you're up
pls
 
John Rennie
John Rennie
@BernardoMeurer hi
 
Bernardo Meurer
Bernardo Meurer
@JohnRennie Hi!!
How have you been?
 
John Rennie
John Rennie
Using Windows!!!???
I thought you had a MacBook for the few occasions when you actually wanted to do something productive :-)
 
Bernardo Meurer
Bernardo Meurer
@JohnRennie TL;DR: My laptop has a Validity Fingerprint reader. Reader has no Linux support. I am working on a fork of the library to add rudimentary support. I don't want to worry about reverse-engineering the registration. I need Windows on this machine to register the fingerprint, then nuke it
Ha ha ha very funny you
 
John Rennie
John Rennie
:-)
 
Bernardo Meurer
Bernardo Meurer
4:45 AM
I do have a macbook, but I use my Thinkpad with NixOS for almost everything
Apart from digitally signing documents
 
John Rennie
John Rennie
(John Googles NixOS)
 
Bernardo Meurer
Bernardo Meurer
Anyways, here's the problem: This machine has two, identical, drives. One has Linux, one has nothing
I need to install windows on the drive with nothing
How the heck to I pick the right drive on the windows installer
 
John Rennie
John Rennie
Let me boot up my test machine off an installer USB so I can give you the exact details ...
 
Bernardo Meurer
Bernardo Meurer
Past times I always had drives with different sizes, so it was easy to pick the right one
 
John Rennie
John Rennie
Can't you tell from what partitions are on the disks?
When you get to the What type of installation do you want? dialog choose Custom.
 
Bernardo Meurer
Bernardo Meurer
4:50 AM
Maybe, I guess
@JohnRennie Alright, I'm going in
 
John Rennie
John Rennie
That'll get you to the disk management dialog.
You realise Windows will trample all over Grub?
 
Bernardo Meurer
Bernardo Meurer
@JohnRennie I'm using EFI
Shouldn't be an issue, Windows will just add another EFI entry
And if it doesn't I will boot into a liveCD and manually edit the efivars
 
John Rennie
John Rennie
@BernardoMeurer I hope that works out :-)
 
Bernardo Meurer
Bernardo Meurer
Me too :P
Alright, I'll give it a shot
See you on the other side! Thanks!!
Well
That failed quickly :P
 
Sir Cumference
Sir Cumference
@BernardoMeurer YOU'VE RETURNED
 
Bernardo Meurer
Bernardo Meurer
4:58 AM
Can't boot off of an SD card it seems
I'll do this tomorrow when amazon delivers my new usb drive, I guess
@SirCumference Hai
@JohnRennie Gentoo is pretty nice
 
Sir Cumference
Sir Cumference
@BernardoMeurer lol a bunch of people left these past few months
Balarka, Eulb, heather, etc.
 
Bernardo Meurer
Bernardo Meurer
@SirCumference after they banned @0celo7 the soul of this chat was gone
2
 
Sir Cumference
Sir Cumference
@BernardoMeurer Well said. Tho he'll be back in a month
 
John Rennie
John Rennie
@BernardoMeurer I'm generally not that fussed with the stuff you wrap round the core OS, so the differences between the distros largely pass me by.
 
Bernardo Meurer
Bernardo Meurer
He'll be unbanned in a month, back we don't know
I should call him this week, it's been a while
@JohnRennie I compile everything from source with LTO
That's the gist of it
Huuuuuge waste of time
But boy do I have fun debugging GCC's segfaults
 
John Rennie
John Rennie
5:02 AM
It would be interesting to see how much faster the results are.
I get the impression the kernel is now about as optimised as it can be and there isn't a lot more to get from building your own kernel.
 
Bernardo Meurer
Bernardo Meurer
@JohnRennie I agree, I have a very aggressive compiler setting (-O3, IPO, LTO, Graphite (Polyhedral vectorization))
 
DanielSank
DanielSank
5:16 AM
Hi @BernardoMeurer.
 
Bernardo Meurer
Bernardo Meurer
@DanielSank Hi babe
 
DanielSank
DanielSank
<3
I made the greatest Python lib of all time.
 
Bernardo Meurer
Bernardo Meurer
@DanielSank On your readme you should use the output of a REPL session, so the immediate evaluation results show
In particular the last one
 
DanielSank
DanielSank
Yeah good point.
y u no submit patch?
:-D
 
Bernardo Meurer
Bernardo Meurer
I don't even know how to import a package into a python REPL that isn't packaged system-wide
 
DanielSank
DanielSank
5:22 AM
The first place import looks is the cwd.
 
Bernardo Meurer
Bernardo Meurer
Oh, neat
Working on patch
 
DanielSank
DanielSank
Thanks!
zomg
The famous Bernardo Meurer (of Rust fame) is working on my lib!
 
Bernardo Meurer
Bernardo Meurer
:P
If I manage to compile sympy
 
DanielSank
DanielSank
compile?!
Just install it.
pip install sympy
 
Bernardo Meurer
Bernardo Meurer
I run Gentoo
I will die before I defile my machine by using pip
Compiled sympy
 
DanielSank
DanielSank
5:27 AM
dafuq is wrong with pip?
Use virtualenvs and then it's fine.
 
Bernardo Meurer
Bernardo Meurer
There you go
My system has a package manager, portage, I don't need additional ones :P
venvs are fine
But when I need a venv I use NixOS/Nix Shell
 
DanielSank
DanielSank
venvs are excellent, and pip is just fine
Well that works too I guess.
 
Bernardo Meurer
Bernardo Meurer
@DanielSank WTF is YAPF?

https://github.com/DanielSank/constraintula/commit/459fa03172420f5edb70acdd0738a1d57179d92a
 
DanielSank
DanielSank
Yet Another Python Formatter
 
Bernardo Meurer
Bernardo Meurer
Ah
lol
 
PM 2Ring
PM 2Ring
5:36 AM
@bolbteppa Take note of the name of the 14 year old kid.
 
Bernardo Meurer
Bernardo Meurer
@PM2Ring What about it?
 
PM 2Ring
PM 2Ring
@BernardoMeurer It's a joke name: it's April the first in French.
 
Bernardo Meurer
Bernardo Meurer
Oh, lol
Oh my
I did not pay attention :O
 
PM 2Ring
PM 2Ring
I must admit it passed me by on my first reading. But it's a few decades since I did French in school.
 
Secret
Secret
hmm...
I think 3 more Egan style dreams should provide me enough data on whether Egan is more wild than I am in terms of thinking
My current hypothesis is that my subconscious don't like Egan's craziness, because last night dream's adaptation of the ideas in The Infinite Assassin is so tame
But then this is not very surprising as this is not the first time my conscious mind disagree with my subconscious
 
PM 2Ring
PM 2Ring
6:00 AM
@Secret Egan has even wilder ideas than the stuff in The Infinite Assassin. Eg, Dust Theory from Permutation City. You may be able to find a free version of that novel online...
 
PM 2Ring
PM 2Ring
6:10 AM
For those interested in the XKCD emoji battle, there are several results viewers linked in the comic forum thread
 
Secret
Secret
@PM2Ring Kinda reminds me of those discussions where Sagan, Susskind and co. said quantum entanglement is all that is needed for spacetime to emerge
If you think about it, the perception of time comes because events are arranged in a linear order. In theory, say the event goes 1,2,3,4,5,6, then no matter how it is permuted, there is still a linear order. It might look strange to us humans because we are used to see progression in the form 1,2,3,4,5,6 (this has to do with objects are never known to suddenly teleport large distance in their motion), but it is still motion nevertheless
thus only when the events are arranged as 1,2,3,4,5,6 (e.g. 6 frames of a ball rolling off the table) do we get a sense of progression
 
PM 2Ring
PM 2Ring
6:37 AM
@Secret Yes. In a (non-relativistic) simulated world, the events could be generated in any order, as long as each event has the an appropriate timestamp. The inhabitants of the world will experience the events in proper timestamp order. Of course, that doesn't work in relativity, since simultaneity is local, and events with spacelike separation have no absolute ordering.
 
Secret
Secret
ah right, I forgot relativity
 
PM 2Ring
PM 2Ring
But I guess a scheme that is compatible with relativity could be cooked up, that uses Lorentz transformation to generate proper time stamps from spacetime coordinates.
 
Secret
Secret
I think something in the Dichronaut universe has something similar as how the 2nd time axis basically lead to orientations being restricted by the geography of the land or something
so everything has to point in a fixed direction more or less
 
PM 2Ring
PM 2Ring
That sounds right, but I haven't read Dichronauts, just the excerpt on Greg's site. And played with the app.
 
Secret
Secret
same, I only have read the description of the space itself, not the novels yet
Also you might be interested in this rambling I had in my room here, where I tried to figure out what is motion:
in SecretLabs (SE Branch), Jan 22 at 23:05, by Secret
Motion in a timeless world
I have not figure out how to adapt that to a relativistic scenario though
(ignore that next box that follows where you see Einstein and stuff, that is a totally unrelated post)
To clarify (because the sentence there is not clear):
in SecretLabs (SE Branch), Jan 22 at 23:08, by Secret
> Postulate: Motion of an object is defined to a directed rule that governs how the position of identical copies of said object are related in a sequence
It should read:
Postulate: Let $X$ be an object, and let $X'$ be its copies distributed in space. Then the motion of $X$ is defined to be some relation $R$ that induces a preorder to $X$ and the $X'$s
thus in the ordinary case, $R$ tell us that given a pair of $X$ and $X'$, which one is later in time
 
PM 2Ring
PM 2Ring
6:54 AM
It's an interesting exercise to contemplate "funny" time ordering. OTOH, models where the state of the world evolves as a function of the current state have mostly been very successful. ;)
 
Secret
Secret
(cont.) Now if you index each $X,X'$ by its time $t$, and for each $t$, you only see a unique $X,X'$, then by increasing $t$, you get the illusion that $X$ is moving
 
PM 2Ring
PM 2Ring
But of course, we shouldn't rule out other models merely because they're counter-intuitive. However, we shouldn't waste time & energy on models that don't actually give us anything useful.
@Secret Sure. Like in Conway's Game of Life, a glider doesn't really glide, it just looks like it does.
 
Secret
Secret
@PM2Ring Regarding that, I recalled a paper by Vaccaro explored this, it basically has something to do with how objects are completely delocalised in time (i.e. no sudden teleporting motions), but localised in space (you can confidently say in what region you can find the object)
The experiment to test her theory on why time only flows forward has not been done yet however
I might study all of these later after dealing with some PhD stuff
As for "shouldn't waste time & energy on models", I think if there is a mathematical framework to generate all possible time orderings, and hence all possible types of motions and dynamics, it could be useful to filter those that does not work easily, and then focus on those which work
Though the main reason why I do that exercise is I am trying to understand what really is motion and whether time is necessary for motions to exist (thus a philosophical question)
 
PM 2Ring
PM 2Ring
7:13 AM
In the Life universe, there's an arrow of time because forward evolution is deterministic, but reverse evolution is ambiguous. OTOH, the fastest Life algorithms don't just use simple forward evolution. They cache results of periodic sub-patterns so they don't need to be recalculated, and so you can evolve the state in large timesteps.
 
Secret
Secret
What do you mean by ambiguous, is it like the outcome is statistical, has multiple past states or something more unpredictable than that?
 
PM 2Ring
PM 2Ring
@Secret I could accept a model where time isn't fundamental, but is instead some kind of emergent property, so that the arrow of time arises as the only consistent ordering of events for each observer.
@Secret There's no randomness, but there's ambiguity because the current state could arise from multiple previous states.
 
Secret
Secret
right
like the same oscillator can arise from a mob of chaotic cells that eventually settled there
 
PM 2Ring
PM 2Ring
Eg, any state consisting of isolated live cells will totally die on the next timestep. So an empty universe has (at least) all of those possible arrangements as its possible predecessor states.
@Secret Indeed.
 
Secret
Secret
Regarding the time is emergent, I think most physicists who are researching the nature of time are heading towards that direction of thinking, unless I am missing some recent changes in the trend
In fact, most who do quantum gravity believed spacetime itself is emergent from some background whose properties we don't quite understood
and there are also many researchers thinking about that background may be largely information
 
PM 2Ring
PM 2Ring
7:26 AM
There have been some attempts to create cellular automata that don't have a universal absolute timestep, in order to model relativity, but AFAIK nothing satisfactory has yet emerged.
 
Secret
Secret
20
Q: Relativistic Cellular Automata

Hans-Peter StrickerCellular automata provide interesting models of physics: Google Scholar gives more than 25,000 results when searching for "cellular automata" physics. Google Scholar still gives more than 2.000 results when searching for "quantum cellular automata". But it gives only 1 (one!) result when search...

special-relativity models cellular-automaton
seems the main challenge is to scale it up to 3D
 
PM 2Ring
PM 2Ring
@Secret One concept that I find appealing is that in the very early universe, on the scale around the Planck time, the arrow of time hasn't yet been established, and it's not possible to assign an ordering to those early events.
@Secret Thanks!
 
Secret
Secret
That concept might be related to Rovelli's thermal time hypothesis, where there could be multiple universes with different arrows of time spawned from a directionless time one
If time is emergent, then it is likely the arrow of time itself has to be, and thus it should be possible to talk about how it "takes time" to emerge from the dynamics (for a lack of better terminology to talk about evolution in a timeless world)
 
PM 2Ring
PM 2Ring
This answer makes a good point. A Turing-complete CA can compute anything that's computable. So if all the laws of physics are, in fact, computable, then the universe can be simulated perfectly in a CA.
 
Secret
Secret
7:43 AM
I think it will be more exciting for me if the universe cannot be fully computable, because it will mean we are not living in a simulation
also, any phenomenon that cannot be computed may contain a candidate of physical infinity
 
Slereah
Slereah
@PM2Ring It can also be simulated by the wikipedia scripting language
Also it's very dumb to assume that because something is computable it is not a simulation
That's assuming that the above universe has to have physical laws allowing the same computing power
 
PM 2Ring
PM 2Ring
But don't expect it to be fast. ;) A decade or so ago, I created a Life pattern that calculates Fibonacci numbers as a bit string composed of gliders. I use a fixed maximum string size of 70 bits, IIRC, (although it's very easy to modify the pattern to use a larger size). Each cycle is 2100 steps (IIRC).
Adam Gouger then built a Life pattern based on a universal constructor that produces Fibonacci numbers with no size limit. But his pattern is much larger than mine, and has a cycle time of over a million.
 
Slereah
Slereah
Turing wrote a whole paper about the hierarchy of machines more powerful than Turing machines
 
Secret
Secret
yeah, you have oracles, hyper computations and so on
@PM2Ring Sometimes I do wonder, how do we prove something is uncomputable, because by definition, uncomputability means the process goes forever and does not stop, so we cannot tell whether something is uncomputable or has not finished yet (cf halting problem)
the only other candidate is to make all conceivable algorithms and showed that target phenomenon cannot be simulated by any of them, hence ruling out all computable models of it, but again we have no way to tell whether we have tested all of them
 
Slereah
Slereah
You can't actually show if the universe is computable or not.
Not by experiment anyway
There's always a computable model to account for any countable number of observations
 
PM 2Ring
PM 2Ring
7:52 AM
@Secret Yes, it's closely related to the halting problem. You can't just test stuff & see what happens. You have to use a clever logical proof, like how we prove that a plain Turing machine cannot be a halting oracle for plain Turing machines.
 
Slereah
Slereah
Also whether our universe is computable or not
is complicated
Depends on initial conditions and such
which are like 100% impossible to actually know properly
Classical mechanics isn't computable given particular initial conditions
Also something being uncomputable in theory doesn't translate as uncomputable in practice
it's the whole deterministic/predictable/computable thing
 
PM 2Ring
PM 2Ring
And even if a system is computable in theory, that doesn't make it computable in practice. Even in a simple universe like Life, it takes a lot of processing power to fully investigate anything but the simplest systems. We still haven't enumerated all 3 glider collisions yet, and a new interesting one that leads to a pattern with infinite growth was only discovered a few years ago.
 
Slereah
Slereah
yeah basically none of the trifecta of deterministic/predictable/computable imply each other
You can have a deterministic universe that isn't predictable or a predictable system that isn't deterministic
and so forth
 
Secret
Secret
hmm, "predictability" is a new concept to me, I have heard about deterministic a lot before. Let me look that up...
 
Slereah
Slereah
Deterministic means that it relies on laws where you can find out future configurations from initial conditions, in theory
Predictable means that given past measurements, you can predict future measurements
they are not the same due to the quality of measurements you can get
bad measurements can "smooth out" non-deterministic behaviours
as they usually do with quantum business for instance
Classical mechanics (given non-stupid initial conditions) is deterministic, but it may not be predictable if you have imperfect measurements
especially in chaotic systems
 
Secret
Secret
8:06 AM
I see
@PM2Ring Sometimes these proofs always amazes me on how they can bypass the explicit need to compute infinite steps to get the answer. Like the proof of the halting problem relies on the halting program to produce a logical contradiction very similar to the way the liar sentence work. It's as if despite these objects are infinite in practice, they have properties that can be handled in a finite number of steps, hence bypassing the computation
I am sometimes wondering that the reason these proofs works is because there are logical truths that follows a well defined pattern that is independent on which step of the computation it is in. For example if the halting program halts, then you can deduce it does not halt, and vice versa, that's a well defined pattern of sorts
It is the steadiness of these patterns in the proof that allows the need to compute infinite steps to be bypassed, I think
 
PM 2Ring
PM 2Ring
In Life there's a fairly small pattern that calculates prime numbers. Let the cycle period = T. Then on generation nT it emits a glider iff n is prime. The pattern is essentially a prime sieve that grows over time. A modified version of this pattern emits a glider iff n-2 & n are twin primes. So a proof that this pattern never stops emitting gliders is a proof of the twin primes conjecture.
 
Slereah
Slereah
8:22 AM
Game of life is kind of overrated
There's plenty of other fun cellular automata
such as Wireworld~
or that weird von Neumann one
the von Neumann one is neat because it has a known self-duplicating pattern
 
PM 2Ring
PM 2Ring
I've played with a few other CAs, but I'm emotionally attached to Life. :)
 
Slereah
Slereah
aren't we all
 
PM 2Ring
PM 2Ring
:D
 
Slereah
Slereah
8:39 AM
I used to really be into computability stuff
it's a weird sort of field
there's plenty of strange models
you can throw together two tincans and you'll get a Turing complete system
 
Novalium Company
Novalium Company
9:15 AM
Is it possible the first cell emerged from randomly scattered atoms? I mean, the atoms just randomly aligned themselves to form a functioning cell, just out of pure luck?
 
PM 2Ring
PM 2Ring
@NovaliumCompany I highly doubt it, the probability is tiny. A modern cell is a pretty complex thing, and even the most ancient cells would have been fairly complex. So the earliest biochemistry must have occurred without a protective cell environment.
From en.wikipedia.org/wiki/Abiogenesis#Clay_hypothesis "Montmorillonite, an abundant clay, is a catalyst for the polymerization of RNA and for the formation of membranes from lipids. [...] The clay hypothesis postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in solution".
 
knzhou
knzhou
10:02 AM
@obliv The guy's right that the Michelson-Morley experiment alone doesn't disprove ether.
If it was just that, ether and SR wouldn't be too far apart.
He's forgotten that over the 35 years after the Michelson-Morley experiment, there were over 10 more experiments which tested different aspects of the ether drag hypothesis.
The textbooks skip this to save space, but basically we have already done the thorough investigation he's proposing.
We checked if stars drag ether, if the Sun drags ether, if the Earth drags ether, if moving air and water drag ether, and so on, in a lot of different combinations, and there was no reasonable way to account for all the results at once.
 
Shing
Shing
10:24 AM
I tried to look up on my QM book by Townsend. But nowhere of it mentions any second quantization. However, I think I figure out why we can use the harmonic oscillator's eigenvector for $N$ photons... because the total energy of a given frequency always come as $1E, 2E,3E...$etc. which is exactly the point of $[a,a^\dagger]=1$
Am I correct?
 
Emilio Pisanty
Emilio Pisanty
10:39 AM
 
Shing
Shing
10:57 AM
@EmilioPisanty glad to hear that!
 
Secret
Secret
> “Even with the core idea in hand, it isn’t at all obvious that the experiment is actually feasible,” says Emilio Pisanty of the Institute of Photonic Sciences in Barcelona, Spain. “If anyone had suggested this idea 10 years ago, they would have been laughed out of court for suggesting the impossible.”
impossibility is not a rare breed
In fact, it is getting more and more common now as information on how to do things continue to explode
On the dark side, it can even be argued that the current highly turbulent political and social climate also facilitate this, as lacking a dominant idea that give stability, many ideologies and movements compete and as a result a lot more cross pollination of ideas occured
As for the research highlighted in that article, it is actually useful since measurement techniques that encodes phase information is still not as common as amplitude based ones, and this experiment basically take phase based measurements to the XUV domain, which is a hotbed of attosecond experiments such as very fast chemical reactions in the atmosphere
 
Emilio Pisanty
Emilio Pisanty
11:13 AM
@Secret I just really appreciate the guts it took to take the idea and run with it.
 
Secret
Secret
11:34 AM
no problem with that. I like when people make impossibles into possible. After all, this is what we scientists all do on a daily basis
some of the finest analytical machinery are not assembled by companies, but home built in the labs where researchers double as engineers
Voicing out what is likely impossible is important, because it helps the community to better allocate resources. I always enjoy reading many things when people said X is impossible, and also when people make some previously impossible things possible. Be saying these out aloud, it is enough to stir imagination
and yes, it takes a lot of courage. Had Einstein, Maxwell etc. don't took their ideas, believed to be quite outlandish at the time, and push through it, we might not have the medium to even chat at long distance
Having said that, I do hope someone actually do some curation on the impossibilities, something like a Journal of Claimed Impossiblities, I felt the next major breakthrough in science may have a lot to do with better understanding just what underlying rule governs dead ends and surprise breakthroughs
--Sorry if this looks too verbose, it's just as I type this out, the number of things I want to say just explode as ideas inspires ideas
 
Danu
Danu
12:34 PM
o/
I realized we have a mutual acquaintance @EmilioPisanty
 
Shing
Shing
we know that in QM, if we repeatedly (fast enough) measure a state, it will generate same outcome, but I am concerned how practically we are able to do this?
(experimentally)
btw, is my question about why we can use harmonic oscillator's $\left| N \right>$ for $N$ photons too dumb? I am doing a "free sole" on QFT (I left school a few years ago), so it is easy for me to get a bit nervous on some seemingly trivial question.
 
PM 2Ring
PM 2Ring
Weird. The OP of this HNQ accepted my answer, then half a day later they unaccepted it, but didn't accept another answer, and didn't leave a comment. Oh well.
 
JMac
JMac
1:01 PM
@PM2Ring at least you got to reap those sweet virtual points from being the accepted answer while in the HNQ
 
Emilio Pisanty
Emilio Pisanty
@Danu that's... hard for me to evaluate
who?
(contact me out of band if you want to)
 
bolbteppa
bolbteppa
Quantization of the electromagnetic field
The quantization of the electromagnetic field, means that an electromagnetic field consists of discrete energy parcels, photons. Photons are massless particles of definite energy, definite momentum, and definite spin. In order to explain the photoelectric effect, Einstein assumed heuristically in 1905 that an electromagnetic field consists of parcels of energy of amount hν, where h is Planck's constant and ν is the wave frequency. In 1927 Paul A. M. Dirac was able to weave the photon concept into the fabric of the new quantum mechanics and to describe the interaction of photons with matter. He...
@Shing "Since harmonic oscillator energies are equidistant, the n-fold excited state $ {\displaystyle |n\rangle }$; can be looked upon as a single state containing n particles (sometimes called vibrons) all of energy hν. These particles are bosons."
 
Danu
Danu
1:22 PM
@EmilioPisanty It's a PhD student in Barcelona
 
Emilio Pisanty
Emilio Pisanty
@Danu huh
yeah, I know a fair few of those
 
Danu
Danu
In the quantum optics theory group
He did the same master's degree as me (Math. Phys. in Munich)
 
PM 2Ring
PM 2Ring
@JMac Very true. And to have 2 HNQ answers on the same day is rather nice. But the points are secondary, I'm mostly curious why the OP changed their mind. I guess I could ask them, but I don't want to look like I'm begging.
 
Shing
Shing
@bolbteppa thanks! So they just share same mathematical structure, right?
 
bolbteppa
bolbteppa
1:37 PM
@Shing right
 
Shing
Shing
thanks again!
 
Emilio Pisanty
Emilio Pisanty
2:21 PM
@Danu yeah, that does narrow it down
it just so happens that I am in the quantum optics theory group
yeah, I think I know who that is
 
PM 2Ring
PM 2Ring
3:05 PM
I give up. This guy's opinion is impervious to change. physics.stackexchange.com/questions/470049/…
 
rob
rob
3:34 PM
@PM2Ring I realized that only slightly earlier than you did.
 
Emilio Pisanty
Emilio Pisanty
@PM2Ring it's gone
 
PM 2Ring
PM 2Ring
@EmilioPisanty Yay! Truth can triumph over ignorance. ;)
 
Emilio Pisanty
Emilio Pisanty
eh
 
rob
rob
@PM2Ring I don't know if erasing evidence of ignorance counts as a triumph, but sometimes it's the best we can manage.
 
PM 2Ring
PM 2Ring
@rob Fair call. At least it stops the error from spreading.
 
Emilio Pisanty
Emilio Pisanty
3:48 PM
@rob we're not erasing "evidence of ignorance", we're erasing misinformation
there's a difference
 
Sir Cumference
Sir Cumference
Is the set of all cardinal numbers countable?
 
PM 2Ring
PM 2Ring
@SirCumference Depends. Do you want it to be? ;) See en.wikipedia.org/wiki/Large_cardinal
 
Sir Cumference
Sir Cumference
@PM2Ring I mean yeah personally lol
But in seriousness I'm curious
Math room tells me it's not even a set
 
PM 2Ring
PM 2Ring
@SirCumference You run into Russell's paradox about sets containing themself if you make it a set, so it's usually called a class.
 
Sir Cumference
Sir Cumference
4:03 PM
@PM2Ring The set of cardinals wouldn't contain the set of cardinals :P
Assuming such a set existed
 
PM 2Ring
PM 2Ring
You just can't get to the really large cardinals if you restrict yourself to sets, IIRC. But it's 3AM here, and I haven't thought much about transfinite set theory for a few decades. So feel free to ignore me. ;) Rudy Rucker might have some good info on his site. His PhD thesis was on this topic, and he's covered it in a couple of his popular books, and transfinite sets are connected with the plots of a couple of his scifi stories.
Here we go! He's made a free online version of Infinity and the Mind. I have a copy on my bookshelf, but it's rather tattered. I lent it to a friend years ago, and it came back with a section of pages missing. :(
 
Anonymous
4:19 PM
@EmilioPisanty You're getting famous it seems. :P
 
Emilio Pisanty
Emilio Pisanty
@Blue I dunno if 'famous' is the right word, but it does seem like it
I reckon it's more like I've been admitted to the Science Establishment
presumably my ID card is in the mail
 
JMac
JMac
@EmilioPisanty Has NASA sent you a huge check yet for helping fool everyone on the globalist conspiracy? From the research I've done on Youtube, that's a very important step in becoming part of the science cabal.
 
PM 2Ring
PM 2Ring
4:35 PM
@EmilioPisanty Do you have a better answer for this? physics.stackexchange.com/questions/470084/…
 
Shing
Shing
I was doing a dimensional analysis for the relation between speed of light and pressure (in a gas) , and obtained result: $v ~ e^{-dT/P}c$, where d is density, T is temperature. P is pressure. I was trying to check my result, but I could not find any "real hard-core" result!
anyone could give me some direction, please?
damn .... the connection delay.... I mean $v(P,T,d)$ ~ $e^{-dT/P}c$
um... it fails ultracold atomic gas...
if considering ultracold atomic gas, I may need to introduce hbar
 
Akash. B
Akash. B
@JohnRennie
 
John Rennie
John Rennie
@Akash.B hi :-)
 
Akash. B
Akash. B
Hi
I would like to ask you a question
Earth is curved, right?
 
JMac
JMac
so curved that the curve actually connects back onto itself even!
2
 
John Rennie
John Rennie
4:49 PM
@Akash.B the surface of Earth is curved yes, because it's a sphere.
 
Akash. B
Akash. B
Then why don't the ball keep on rolling untill it reaches the poles?
 
JMac
JMac
@Akash.B Why would you expect a ball to roll towards a pole?
 
Akash. B
Akash. B
The ball always remains stationary whenever i keep it on ground
 
John Rennie
John Rennie
@Akash.B actually that's a good question.
 
ACuriousMind
ACuriousMind
@Akash.B Gravity pulls towards the center of the sphere, not towards the poles.
 
John Rennie
John Rennie
4:51 PM
The answer is that on long timescales the rock in the earth behaves like a fluid, so it flows until it is effectively at the same level everywhere on Earth.
 
JMac
JMac
@Akash.B You could also ask, "why doesn't the ball roll towards the equator", no. Is there something special about the poles you're curious about?
 
John Rennie
John Rennie
As a result the earth is fatter at the equator than it is at the poles.
If the Earth was a perfect sphere then a ball placed at the pole would roll towards the equator.
 
ACuriousMind
ACuriousMind
@JohnRennie ???
 
Akash. B
Akash. B
Hmm
 
ACuriousMind
ACuriousMind
I'm either not understanding what you're saying, or you're wrong :P
 
JMac
JMac
4:53 PM
@JohnRennie Do you mean like if the ball also had no friction acting on it but this sphere earth was still spinning?
 
John Rennie
John Rennie
@ACuriousMind it's true!
@JMac yes
 
Akash. B
Akash. B
How does it prevent ball from rolling?
 
ACuriousMind
ACuriousMind
@JohnRennie What force would act on the ball placed at the pole to pull it towards the equator?
 
JMac
JMac
@Akash.B Same way to stops you from sliding away basically
 
Akash. B
Akash. B
I don't understand
 
John Rennie
John Rennie
4:55 PM
@ACuriousMind if the Earth were a perfect sphere the gravitational force would be identical everywhere on its surface, but the the centrifugal (pseudo) force would be greater at the equator than at the pole.
The ball would lower its potential energy by rolling from the pole to the equator.
The Earth is an oblate spheroid precisely because the mantle flowed from the poles to the equator.
2
 
ACuriousMind
ACuriousMind
@JohnRennie The centrifugal force from the earth's rotation around its own axis? Wouldn't it be zero at the pole?
 
JMac
JMac
@Akash.B Friction. It helps keep the ball in place, the same way that you don't slide towards the poles due to the bulge. There are plenty of forces resisting the motion
 
ACuriousMind
ACuriousMind
@JohnRennie I'm aware of why the earth is fatter at the equator, I'm just questioning that a ball at a pole would move at all
 
Akash. B
Akash. B
But what about ocean?
 
John Rennie
John Rennie
@ACuriousMind ah, OK, yes if you mean the net force precisely at the pole is zero then I agree.
 
PM 2Ring
PM 2Ring
4:57 PM
Surely, if the ball were exactly at a pole it'd stay there?
 
Semiclassical
Semiclassical
is it a stable or unstable equillibrium tho
 
ACuriousMind
ACuriousMind
@Semiclassical stably unstable :P
 
dmckee
dmckee
But the equilibrium would be unstable.
 
John Rennie
John Rennie
But given it's impossible to place the ball precisely at the pole there would always be a non-zero force towards the equator.
 
JMac
JMac
@Akash.B What about an ocean? Oceans have resistance too
 
Shing
Shing
4:58 PM
If the shape at the pole were just like Norton's dome....
 
Akash. B
Akash. B
Resistance?
 
PM 2Ring
PM 2Ring
At the pole, it would be an unstable equilibrium.
 
John Rennie
John Rennie
Perhaps to keep those of a theoretical bent happy I should clarify my statement to if you place a ball near the pole it would roll towards the equator.
 
dmckee
dmckee
We have a nice question on the site about the nature of the oblateness. It's fatter than the naive effects of centifrugal pseudo-force would imply. And the reason is an introduction to classical perturbation theory.
 
JMac
JMac
@Akash.B Resistance to relative motion. It's how a lot of things on Earth's surface stay stationary relative to the surface of the earth. There are forces pulling us a lot of ways, but generally the force of friction is enough to keep them from moving us
 
dmckee
dmckee
4:59 PM
61
Q: Why is the Earth so fat?

Mark EichenlaubI made a naive calculation of the height of Earth's equatorial bulge and found that it should be about 10km. The true height is about 20km. My question is: why is there this discrepancy? The calculation I did was to imagine placing a ball down on the spinning Earth. Wherever I place it, it sh...

rotational-dynamics geophysics newtonian-gravity centrifugal-force equilibrium
 
Akash. B
Akash. B
Oh i have to go now😭😭😭😭
 
John Rennie
John Rennie
I wonder if the Norton's dome argument would apply i.e. if you roll a ball towards the pole on a rotating sphere would it reach the pole and stop in a finite time?
 
Semiclassical
Semiclassical
@JohnRennie when you say "potential energy" here, are you intending in the sense of the effective potential?
 
John Rennie
John Rennie
@Semiclassical yes
 
Semiclassical
Semiclassical
thought so, just wanted to confirm
 
Shing
Shing
5:07 PM
I was just trying to make a terrible joke
 
John Rennie
John Rennie
5:19 PM
There are lots of rumours that the Event Horizon telescope is about to announce observations of the black hole at the centre of the Milky Way.
 
ACuriousMind
ACuriousMind
@JohnRennie No. The force on the ball is a polynomial in the radius from the axis (as I just checked), so no Nortonian solutions are admitted since Picard-Lindelöf holds.
 
John Rennie
John Rennie
@ACuriousMind oh well ...
Given that all I wanted to do was entertain Akash with some cool physics the conversation got away from me somewhat.
 
PM 2Ring
PM 2Ring
5:40 PM
On a related note, if you could spin the Earth up so that a day were 1h24m24s, you'd be weightless at the equator. Of course, the Earth wouldn't cope too well with all that angular momentum. ;)
 
JMac
JMac
@PM2Ring Weightless at the equator while being mangled from flying Earth debris? Fair tradeoff.
 
PM 2Ring
PM 2Ring
Even if the crust coped with the strain, the loss of atmosphere, and the oceans flying away, would cause a few problems.
 
thermomagnetic condensed boson
thermomagnetic condensed boson
5:56 PM
@knzhou hello, I have read on Motl's blog and here on PSE that the wavefunction is subjective. so psi can be different, according to which observer we ask. do you agree with that?
it could be collapsed into an eigenstate for an observer, but still in superposition for another observer(s)
the collapse is apparently not "an event"
 
ACuriousMind
ACuriousMind
@thermomagneticcondensedboson Quantum interpretations can be partitioned into two rough sets according to whether or not they believe that "collapse is real"
 
thermomagnetic condensed boson
thermomagnetic condensed boson
im trying to convince myself of that but I have a hard time someone help
 
ACuriousMind
ACuriousMind
No one can tell you whether it is or not because it makes no observable difference.
 
thermomagnetic condensed boson
thermomagnetic condensed boson
damn I tried to stay away from any interpretation
@ACuriousMind I dont quite understand that Acuriousmind
if 2 psi differ, the coefficients (probabilities to fall into a particular eigenstate) are dofferemt. or not?
i might confused the expansion of psi with the eigenvalues of the operator
 
ACuriousMind
ACuriousMind
@thermomagneticcondensedboson But we can't measure "psi"
 
thermomagnetic condensed boson
thermomagnetic condensed boson
6:04 PM
@ACuriousMind you can basically determine it by replicating the system infinitely many times and perform the measurement once per system, or not?
 
ACuriousMind
ACuriousMind
@thermomagneticcondensedboson Yes, but you'll note that we neither have a procedure to clone arbitrary quantum states nor to perform infinitely many measurements on them
 
thermomagnetic condensed boson
thermomagnetic condensed boson
@ACuriousMind I agree, but if we could, then it would be possible to obtain "psi". i.e. "psi" seems well defined
that's something all observers should agree on, I suppose
oh damn it I think I start to understand stuff
there is no such universal psi
it's perfectly fine if 2 dudes have 2 different psi's to describe the same system. once a measurement is made and the two observers can see the result, they will "update" their psi into the same eigenstate, I suppose
in that sense psi is subjective
 
ACuriousMind
ACuriousMind
Whoa, slow down there.
1. Pedantically, what we're measuring is still just the squared coefficients for the eigenstates. "psi", or more abstractly a vector in Hilbert space is not a unique quantum state
Quantum states are equivalence classes of wavefunctions with the same psi-squared up-to a zero measure set, or more abstractly rays in Hilbert space. Using "psi" as a shorthand for state is common, but this is a distinction that is sometimes important. It's not really relevant to this discussion, however...
2. it is not evident that all observers must "agree" on what state something is in, in particular since there is no measurement you can perform on a single state to tell what state it is in. The only consistency requirement is that the observations of the results of measurements of one observer should not contradict the observations of another
 
bolbteppa
bolbteppa
What does the wave function being 'subjective' mean
 
Semiclassical
Semiclassical
something something wigner's friend
 
thermomagnetic condensed boson
thermomagnetic condensed boson
6:16 PM
@ACuriousMind thank you I am going to save your text/words for future reference
 
bolbteppa
bolbteppa
6:26 PM
He doesn't say the wave function is subjective in his recent post on it
 
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