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00:00
ACuriousMin Im not saying this particle exists, Im saying what if
and that is why I said kind of like
not exactly the same
I don't think a theory would be taken seriously if there wasn't any possible way to experimentally verify/disprove it
Not to mention that if you had a completely non-interacting particle, the theory would do just as well without it
"The lazy roommate particle"
well its kind of like complex numbers
Distinguishable from the God particle in that prayers have no effect on it.
00:03
complex number comes from fundamental theory of algebra
in this specific case of discovery the fundamental theory of algebra algebra states that tehre should be 3 solutions
people could only find 1 solution
so this guy just creates complex number to provide 3 solutions people call it imaginary because people just thought it doesn't exist
there could be a scenario where we just bring an unobservant thing into existence to make sense of the other already existing laws
and really what Im trying to say is that physics wouldn't really be able to prove or disprove something that doesn't interact with physical universe
@WantingtobeanAndroidDevelor Once again, you're misrepresenting history. The fundamental theorem of algebra in its modern form already relies on some notion of complex numbers, you can neither state nor prove it without it. Historically, people much rather noted that e.g. for certain values ofthe coefficients, things like Cardano's formula for the roots of a polynomial lead to the idea of taking roots of negative numbers.
The closest thing I can think of would be the interiors of black holes... events inside black holes can't affect the exterior... but the black hole itself has an effect...
yea something like that or anything like that that you can't observe
Well you have gauge invariances where the math is redundant. Or at least that's my level of understanding of them
but computer science kind of could give an explanation, these wouldn't be a physical proof but its better than nothing if you could show that a defined physical universe is turing complete
00:10
@danielunderwood Instead of ranting, I will just link some things I wrote on that: physics.stackexchange.com/a/257100/50583, physics.stackexchange.com/a/127036/50583, physics.stackexchange.com/a/335428/50583
Oh boy. Sounds like I'll either improve my understanding or become more clueless
I see a lot of similarities between computer science. Computer science study general properties of computational machines and physics study properties of a specific computational machine called universe. I don't think its that stupid to try and interpret these properties in terms of hypothetical computational machines in general
E.g. Quantum mechanics require energy to be in quantifiable units rather than a discrete value right? but I think you could say for an e.g. if energy were discrete then it would require infinite information (entropy) to define it any program that require this definition would never halt and so the "universe" program would never run
you know that is e.g. of where things could be interesting if you could bring computer science into physics
That's a gross oversimplication of how QM works, cf. e.g. physics.stackexchange.com/a/226272/50583
QM is so much weirder than simple discreteness it's not even close.
I mean Im not trying to explain how it works
but physicist used to think energy could be represented as a discrete number line
from computer science point of view I could have just said nop this is not possible
come up with new idea no need for physical experiment to show that this is not possible
@WantingtobeanAndroidDevelor What physicist ever thought that? Another historical claim that is not accurate.
Learn physics in depth. Learn computer science in depth. Then see if you still see all these parallels. But at this point it seems you're just extrapolating from a lot of vague and inaccurate claims.
00:22
I still believe they did and history is not really my #1 priority when I learn a physical concept
and i don't understand why you want things to be so historically correct
@ACuriousMind is it supposed to be $\frac{d q^i}{dt}$ in the first equation instead of $\frac{q^i}{dt}$?
4
Q: Example where Hamiltonian $H \neq T+V=E$, but $E=T+V$ is conserved

Nick PI'm looking for an example of a Hamiltonian $H$, where $H\neq T+V$, but the total energy in the system, $E=T+V$, is still conserved. While I'm at it, I might as well add that I'd be most interested in an example from a classical field theory. Furthermore, I am looking for a nontrivial example, ...

you can still make a constructive argument even if it is hypothetical
@WantingtobeanAndroidDevelor Then don't make claim about history like what physicists "used to think"
you could just note it as side note and move onto what I am actually asking
rather than stopping the conversation there
@danielunderwood Yup, fixed
00:26
I mean look at these guys they seems to be absolutely fine with idea that classical physics thought energy was continuous
I mean look at these guys they seems to be absolutely fine with idea that classical physics thought energy was continuous
socratic.org/questions/…
What does it mean for energy to be 'continuous'?
I mean its explained in the link right?
I think I could just say you could have energy with near infinite decimal places
Energy doesn't have a universal character of being discrete or continuous. It depends on the problem at hand.
so may I ask what problem give energy characteristic of being continuous?
And also on the theory you use to extract the possible values of energy.
00:39
theory?
what theory?
@WantingtobeanAndroidDevelor Classical mechanics has a continuous energy spectrum, typically.
it isn't really though, in classical mechanics, it generally allows us to assume that its continuous because energy we are dealing with is so large right?
@WantingtobeanAndroidDevelor Whichever one you use to solve the problem. Classical mechanics, quantum mechanics or anything else.
?
for e.g.?
its like saying Galilean relativity is correct
its not really correct it just gives us good enough assumptions in real life scenarial
Yes. Every theory in that sense is effective. They describe physics within their regime of validity.
No one knows what the final exact theory is.
00:45
so really its not valid to think energy is continuous its just negligible
so
I could argue no energy is not continuous
Like I said, what you're asking depends highly on the problem at hand. Energy can take different meanings in different theories.
What is the premise of your question, though? Why does it matter whether energy is continuous or not?
well you need to define energy to use the concept
and this definition ideally should be a general definition that works with all physical theory that use the concept of energy
and this definition matters to me because if it is continuous it does not make sense from computer science prospective of view
@WantingtobeanAndroidDevelor Yes. And the definition depends on the theory you're looking at.
In other words, there is no universal concept of energy that you can apply to all theories.
no I could just define it once and use the universal definition of energy I do not need to keep on changing the definition for different theory
I could just say energy is discrete and it can be applied to all theory that we know
The moment you say 'energy is discrete', you restrict yourself to a class of theories.
Instead of all theories.
There is no reason, a priori, to believe that energy is discrete. Universally.
00:54
but my point is saying that it is discrete does not restrict my self from any class of theory but saying that it is continuous does
like
I don't understand why you are so upset about this
I'm not upset haha.
Even saying that energy is continuous restricts you to a class of theories.
yes saying energy is continuous restricts it but saying that it is not continuous doesn't
Why not?
because its not and if you want e.g.
you just have de that is very small so it just looks like it is continuous but it isn't the theory in macroscopic world doesn't care if it is continuous or not
but in a macroscopic world they only accept non continuous concept of energy
so non continuous idea works in both world but continuous idea doesn't hold in both
so I just say it is not continuous to make it work in both world
What is your definition of a macroscopic world?
01:01
atomic level I guess
So again, you chose a length scale for your theory. It's not universal.
I'm just saying. You know what I mean.
I hope.
and yes you could argue that quantum mechanics is not a universal theory even though it kind of is but in something like condensed matter theory the definition of energy still holds
 
3 hours later…
03:51
Is there a standard reference for something that handles Lie algebras in the context of classical mechanics? Arnold?
04:12
@danielunderwood Schwarzenegger?
He's a man with many hats
Imagine if there's a new book on Lie Algebras by Arnold Schwarzenegger
Terminating lie algebras with Arnold
I'd pre-order that
QFT for the gifted amateur
QFT for dummies
QFT without math
QFT for middle school dropouts
04:28
Ahhh I keep clicking on related questions that people mention in comments/answers. I don't think I've read the actual answers I started reading hours ago. It's a never-ending cycle
Welcome to PSE
I had so many tabs in one window for papers, webpages, etc. that it got impossible to navigate them. Opened a new window and moved half of the tabs there.
That's the standard situation when solving a programming problem for me...or when reading stuff on here
I'd like to see a map of all the links Qmechanic has made
@ACuriousMind I don't really know anything about Legendre transforms, but should one of the derivatives be with respect to position instead of velocity in the determinant expression? physics.stackexchange.com/a/335428/24839
Also that answer had 4 "this answer of mine"s...I'm in for a long journey if I have $4^n$ answers to read
 
6 hours later…
10:22
@danielunderwood No. What needs to be invertible is the map from generalized velocities to momenta, i.e. $\dot{q}\mapsto p(\dot{q}) = \partial L/\partial\dot{q}$. By the inverse function theorem, that map is locally invertible as a function of $\dot{q}$ if its Jacobian $\partial p/\partial\dot{q}$ is invertible.
 
2 hours later…
Anonymous
12:41
@Avantgarde You missed QFT for babies.
13:09
Is eddy current only on the inside of the conductor being induced
vzn
vzn
13:49
> Professor Ryan Nichol said, “This is the first step on the road to having the gigantic DUNE detectors. They will let us test how the universe works with unprecedented precision using a beam of particles that pass through over 1000km of the earth.”
Anonymous
@JacobP.J Yes
vzn
vzn
wait, what? its not a human generated beam is it?
@Blue why not on the outside?
Anonymous
@JacobP.J I don't quite understand your question. Eddy currents by definition are the loops of current induced inside/within a conductor due to a time-varying magnetic field. Outside a conductor, there is usually air or some other insulating material. It doesn't make sense to talk about eddy currents outside a conductor.
@Blue In the event of the outside being vaccum and there is no lamination
would there be eddy currents on the outside
Anonymous
13:54
@JacobP.J 1. What is the definition of current? 2. What is the definition of vacuum?
Isn't there current on the surface of a conductor
Anonymous
@JacobP.J Firstly, "outside a conductor" $\neq$ "on the surface of a conductor". Secondly, yes there could be eddy currents circulating on/near the surface. The circulation of eddy current almost completely depends on the direction of the time-varying magnetic field.
I meant to say On the surface of a conductor
Anonymous
Okay. Anyhow, this is something related which you might find interesting:
Anonymous
Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents...
Anonymous
14:04
1
A: Cause of skin effect: eddy current inside conductor

MBerkaYes, the magnetic field is densest at the surface, but the eddy currents are not. The main current induces the magnetic field, H. The H field forms rings with the greatest intensity near the surface, and induces eddy currents. The eddy currents flow in rings around the magnetic field lines. It i...

vzn
vzn
14:44
TIL on reddit that most neutrino detectors going back decades have been working with generated beams run thru earth sections from earth-based collider sources! a bit )( gobsmacked! thought they were all oriented around nonartificial/ stellar sources...
 
2 hours later…
user351417
16:58
math.ucr.edu/home/baez/crackpot.html I just realized that the Evans Field thing is real.
> See also:
List of topics characterized as pseudoscience
oof
Anonymous
@Chair That reminds me: I came across this page a few months ago primes.utm.edu/notes/crackpot.html
Anonymous
It's inspired from Baez's page :P
Anonymous
But yeah, Baez's is classic
I kind of just want to send an email that hits every one of the items
Evidently comparing themselves to Einstein is a characteristic of math crackpots too? lol
Anonymous
17:08
@danielunderwood I'd be happy to give a helping hand, lol
Anonymous
I find points 11 and 12 to be the most annoying of all btw (in the primes page)
Anonymous
Others are just....funny
> 20 points for each of the following conjectures that you purport to have solved: Goldbach's conjecture; twin prime conjecture; Riemann Hypothesis, GRH; Fermat's Last Theorem (*); infinitely many Mersennes, Fermats, primes of the form n2+1...; or finding new patterns in the primes.
Anonymous
> 30 points for eliciting support from, or expressing support for, well-established crackpots.
Anonymous
Gosh, that so reminds me of two people in particular XD
17:13
JD and forgot
that will only work if superfluid vacuum theory is true
A quantum vacuum thruster (QVT or Q-thruster) is a theoretical system that uses the same principles and equations of motion that a conventional plasma thruster would use, namely magnetohydrodynamics (MHD), to make predictions about the behavior of the propellant. However, rather than using a conventional plasma as a propellant, a QVT uses the quantum vacuum fluctuations of the zero-point field. If QVT systems were to truly work they would eliminate the need to carry any propellant, as the system uses the quantum vacuum to assist with thrust. It would also allow for much higher specific impulses...
and more weirdness
@vzn Now come on. Even if you don't know anything about neutrino physics you at least knew about OPERA, fercristsssake.
But there are basically only three classes of "natural" neutrinos that we can study: the sun, cosmic rays, and a geological decays. Musing on it I think I can either name or describe about a dozen experiments that focused on those (plus maybe a handful of proton decay instruments that did neutrino physics while they waited).
But neutrino beams have been an industry for about three decades now.
17:34
@Blue QFT for your dog
0
Q: Unvote to open my question

Sachin Kumar I have a question about my Physics Stack Exchange post: Physical transformation associated with a Pseudo-Orthogonal matrix I was closed because of a unclear ques. Now I have reworded it, it is more clear, still, No one opened it again?

@Secret One of the most widespread misconceptions? Really? I have never heard anybody saying that iodine cannot melt.
Well back in my undergrad, our lecture notes and textbook just said iodine subimate
it's only from a passing tutorial that a tutor said iodine can actually melt
Anonymous
I guess that misconception gets cleared for most in the phase diagram lectures
Can most substances exist in any of the 3 phases under some condition?
17:42
Yeah, most say that iodine sublimates, which isn't wrong, maybe just sloppy about the boundary conditions.
Anonymous
@danielunderwood Yes
Reminds me that I should finish a safety report about iodomethane.
So from the phase diagram on wikipedia, it looks like water can settle into multiple crystal structures. I suppose that's a common thing as well?
And sounds like a nice, relaxing weekend activity
It also seems like it would be quite difficult to measure those crystal structures. You'd either have to have equipment that worked in those environments or could work through whatever chamber was containing the substance
 
1 hour later…
18:58
hey @ACuriousMind! long time no chat. would you mind if I ask you a question?
Guys, this may be a bit obvious, but I just want to confirm: I'm wanting to do a Master thesis outside my university (like a company, other university, etc). If I get accepted in more than one, I'll have to decline some... How bad is this for an hypothetical future application (for a job or something), after I finish my thesis
Anonymous
@Kelthar Hi. Not experienced enough to answer, but may I know what the thesis will/may be based on?
@Blue Something related to either AI or quantum computing
Anonymous
@Kelthar I see, cool. I doubt the companies actually keep in mind which candidates earlier rejected their offer. It happens all the time to them. But then, I don't have much idea about the industry. Quantum computing companies are pretty rare btw. Are you in the US?
No, I'm from Portugal. quantum computing wise, I'd apply to something like qutech and such... I'm thinking about doing this in Europe
19:12
@ShaVuklia Hi there! Go ahead
Anonymous
@Kelthar Interesting. For what it's worth, you may check out academia.stackexchange.com and workplace.stackexchange.com. At least one of them accepts questions of this nature. You're more likely to find experienced people there who can reliably answer your questions.
haha, yea I was just typing that I don't think I have a question anymore, because I think I'm sure about it anyways:) @ACuriousMind. It's just that it somehow took me very long to realise this, so I will shortly write it down just to be sure that I'm correct about this once and for all:d
So, in Griffiths, there is this chapter called Formalism. And they say hermitian operators which represent variables are complete, but of course only for the Hilbert space we're working in. I was always kind of confused by the 'independency' between non-isomorphic Hilbert spaces so to say, like the inifnite-dimentional function space and a 2-dimensional vector space, because I guess intuitively I excepted every 'component' of a wave function to be interconnected in one way or the other.
But actually Griffiths doesn't mention any dependency, as we're only concerned with the operators, vectors, and eigenfunctions within a certain Hilbert space. So if we're considering a particle with a wave function that is a tensor product, we can just treat everything separable, I assume? Or am I wrong after all? I hope you understand what I mean.
As an example, when dealing with a (position) wave function $\Psi(x,t)$ and spin, we always seem to work with them independently. But I guess there really is no reasonable way to connect the two right?
I know this might all sound kind of obvious, but I just didn't realise what "completeness of eigenvectors" really meant until now. Somehow I just never realised we still have to take into account the Hilbert space we're working in.
@ShaVuklia Well, you "connect" the two by tensoring them - which in this case would effectively mean thinking about $\Psi(x,t)$ as taking values in the spin space
yes, but tensoring it just sticking two things together, without any dependence between them right
You could say that
19:21
alright cool:)
also, if you don't mind just one more question, which is something I've always wondered
is there some 'illuminating' explanation for the complete state of the electron to be just the position wave function + spinor? I mean, I can see that this way certain things about electron theory are described correctly
or should I wait for QFT to think about such explanations? because from what I've understood, QFT also explains why each elementary particle has a certain fixed spin
Not really. Spin...just is.
What QFT can plausibly speak to is why the options being spin-0,spin-1/2,spin-1, etc make sense
Hm? That spin is a half-integer is already seen in QM, that's just representation theory of SO(3)
true. I have in mind spin statistics stuff
The "mystery", at least to me, is why elementary objects should transform non-trivially under the rotation group at all
19:33
Unfortunately qft basically just assumes spin 0, 1/2, 1 and 2 are the things to use and not higher spins :p
so QFT won't explain why spin states are fixed?
that's just what we assume, since it works?
You don't need qft for spin
@Semiclassical spin-statistics just explains why bosons are integer and fermions half-integer
hmm, fair
@ShaVuklia What do you mean by "fixed"?
19:34
that a certain elementary particle always has one specific spin
In the PCT book they link spin-statistics to connectivity of the Lorentz group as part of the proof
you could plausibly say that "an electron is a fermion because it's spin-1/2"
@ShaVuklia ah. Well, that particles don't vary in spin is part of the definition of what a particle is.
The same issue arises for connectivity of the rotation group in non-rel QM
but why it's spin-1/2 in the first place is something QFT doesn't answer, no
19:35
alright
and then one laaassst question; in any system, can we always assume that in theory we should be able to find the hamiltonian? because for any system, we should be able to measure energy?
It's confusing as heck that spin is linked to the topology of groups
I think you can take the tactic of: "We know electrons behave in a certain way, and therefore spin-1/2 is apparently the correct description of them."
But there's no derivation of the electron from pure thought alone
@ShaVuklia Um, well...we don't "find" the Hamiltonian. In Hamiltonian mechanics, a physical system is defined by its Hamiltonian, and it is not always the energy.
If you want to talk about finding/deriving the Hamiltonian, then you must specify how else you are defining your system.
For a Lagrangian system, you can always find a Hamiltonian. But then the question just becomes how you got the Lagrangian.
Stuff like dissipation is problematic in that regard
hm, I was asking because of this part in Griffiths
because at first I was surprised why we knew there would be a Hamiltonian in the first place, but I guess that's how physical systems are defined then? as you said, @ACuriousMind
19:42
@ShaVuklia Yes. In Hamiltonian mechanics and therefore also in a large part of quantum mechanics, the existence of the Hamiltonian is an axiom - it is part of the data that defines the physical system under consideration
gotta have some way to tell the wavefunction how to evolve in time
right, I guess that makes sense, as I'm thinking of V en K in classical mechanics, which also defines the physical system as far as I know
It defines the Lagrangian and therefore the Hamiltonian, sure.
right, I somehow never connected all these things, but I do now, so I'm happy about that
vzn
vzn
20:18
@dmckee :( not a very friendly response, afraid to respond myself... but how many of them run the neutrinos thru large barriers before detection? eg earth separation? etc
Wow the right-hand side knowledge panel shown when Googling something (usually taken from the corresponding Wikipedia article) is updated within 1-2 minutes after editing the article!
@lılostafa it wouldn't surprise me if they fetch it at the time you do the search, unless it's a particularly frequent search term
@DavidZ I don't think so...I googled Brett Kavanaugh and the knowledge panel contained text from its few-minutes-old WP article
I opened the wikipedia article, and after reading the first paragraph Googled the term again, and it was updated
Anonymous
20:36
@lılostafa For knowledge panels linked to Wikipedia articles, the update frequency is higher. It's lower for the panels based on Maps, My Business and others.
Anonymous
It makes sense because the popular Wikipedia articles get updated almost every day. And the most popular ones get updated every hour or so.
Anonymous
I suppose that they also use some algorithms to update the popular topics at a higher frequency.
@vzn Mmmm. Please accept my apologies for the short tone.
After the early generations machines most of the had at least a few hundred meters of "through the dirt" for the simple practical reason that something has to stop the remaining muons from the progenitor beam. If you don't use the planet you have to build an absorber which is a waste of perfectly good money.
@lılostafa I figure google probably has some pretty crazy caching going on that may involve detecting trending topics
vzn
vzn
20:55
@dmckee so neutrinos have been detected (not merely stopped) after being generated/ passing thru hundreds of meters of dirt for decades? thought the whole idea of most detectors was to maximize detector efficiency ie remove any obstacles but maybe this is something like the opposite idea...
May be of interest to folks here: particlesforjustice.org (apologies if I'm repeating something someone else already mentioned).
2
hat-tip to HDE<number>
 
1 hour later…
22:20
@Mithrandir I have not seen his full presentation, but a lot of institutions do favor minorities (one of them are women) when considering applications and clearly state this on their websites.
"Inclusive" shouldn't mean 50% men and 50% women
22:49
What an insane presentation
The determinant on slide 8 is a real red flag on the mentality here
23:07
@bolbteppa slide 15 is the one that caught my eye
"I'm a man with a lot of citations and I didn't get hired, so obviously gender bias against woman can't exist"
That, 20, 24 and 25
Unreal :p
on another note, i always find it weird when I'm watching something on youtube and suddenly the phrase sjw pops out of nowhere
"oh hey culture war, I didn't expect to see you here"
The irony to me is that people argue against sjw's for being authoritarian and end up siding with the authoritarians
yeah, isn't that fun
i tend to follow video game news stuff
Ahah, gamergate
23:11
yup
i sorta missed at that at the time
i wasn't following it at that point
I just watch a few videos to laugh at the insanity
Pure gold
if they use sjw unironically, that's a pretty solid tip off
Ahah
You learn a new word (bottomfrag) everyday
23:28
yup
that and portsgnidts
23:39
haha
Indeed

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