« first day (4305 days earlier)      last day (50 days later) » 

3:15 AM
is the only support for the postulate that c (speed of light) is relativistically invariant experimental?
err... well I guess I mean is the reason that the invariance of c is postulated because of experimental evidence? I remember reading that Einstein thought it was true without knowing the results of that one experiment, though
@SillyGoose No.
3:28 AM
what is the non-experimental support? @NikeDattani
@SillyGoose You've caught me at 11:29pm in my time zone. I'm going to sleep soon. Sorry.
no worries!
1 hour later…
4:37 AM
@SillyGoose SR is a metric theory. This means it is based upon the principle that the quantity dτ defined by c²dτ² = c²dt² - dx² - dy² - dz² is the same for all observers. In this equation the quantity 𝑐 is a constant that turns out to be the speed of light.
This means SR requires that the speed of light be a constant otherwise the whole theory falls apart. This is the non-experimental evidence i.e. the consistency of the theory depends on it.
This means that any experimental test of SR is also a test that 𝑐 is constant, and experimental tests of SR are ten a penny.
5:10 AM
@user250478 It's possible for massless particles to form a massive bound state. For example gluons are massless but they can form a massive bound states called a glueball.
Likewise it is in principle possible for massless gravitational waves to form a massive bound state that we call a geon. But no-one has been able to work out an equation to describe a stable geon so we don't know whether they can actually form.
As for what they would look like, a geon would lens light passing through it but not absorb or reflect light. Exactly what the end result would be we don't know since we don't have an equation to describe a geon.
6:06 AM
Okay now Im stuck on equation 2.8. Can someone tell me where it is coming from?

2 hours later…
8:03 AM
@JohnRennie many thanks for such reply, you're incredible (=yours knowledges are very good).
Many thanks @Jim , as said the moderator it is sad because he can't talk about geons.
Two gravitons (assuming gravitons exist) could not form a bound state with each other because they interact too weakly. So there cannot be a gravitational equivalent of a glueball formed from two gluons.
Two gravitational waves could interact to form a bound state, but they equations involved are too hard to solve analytically so coming up with the equations for a geon is formidably difficult.
8:31 AM
I actually don't feel a great loss in my life from not knowing about geons :P
9:07 AM
@SillyGoose Right, Einstein didn't know about the Michelson-Morley experiment when he published SR. But he knew about stellar aberration & Fizeau's measurement of the speed of light in water. See
A: Who discovered the speed of light is constant?

Andrew SteaneNote, the question asked is about history, and historically the definitive statement that the speed of light is independent of other things comes from Einstein's 1905 paper. In developing his thinking Einstein was unaware of the Michelson Morley experiment. To quote from https://arxiv.org/ftp/arx...

9:46 AM
Question about edit summary: why do people write "added insert number characters in the body"? Should I do that too?
@Feynman_00 That is added automatically if you don't enter anything in the edit summary box.
I feel so stupid right now :P
I thought you guys were counting each deleted and added character
I usually try to enter something sensible in the edit box so future editors will have some clue what I did. But whether it's actually that useful is debatable.
9:50 AM
it's like commit messages in software control systems - often it doesn't matter all that much what's written there, but sometimes it's really useful if someone actually described properly what they were doing
10:00 AM
@DIRAC1930 I'm not going to read the paper but it seems that they don't claim that $n$ evolves in the Schrödinger picture, they define an (explicitly time-dep.) operator as a projector on states occupied at time $t$
2 hours later…
11:56 AM
@ACuriousMind Alas that I know so little about geons! My life is over! I shall diminish and go into the West and remain GaJimdriel
@Jim yes, bear news to the lords of Valinor that all their works are futile unless they unearth the mysteries of geons
I guess geons created a new meme
2 hours later…
2:16 PM
I don't know anything about physics but I once heard that the universe is smooth Lorentzian 4-manifold. Is this a consequence of something or just a hypothesis?
@onepotatotwopotato Well, it is the way that the universe is modeled in the theory of relativity. That theory has been accepted - due to a lot of empirical evidence for its predictions - for around 100 years now. Within the modern mathematical formulation of that theory, it is (usually) an axiom (i.e a foundational assumption, not something derived).
@ACuriousMind I see. Thank you
(There are certainly debates about whether "smooth" is necessary or $C^p$ for some $p$ isn't enough, but I feel that's not the point of your question)
@ACuriousMind Sup, I agree with you that there is value created to people that is not measured by an exchange of money, I just remembered that point you made. I'm not sure how we can go about measuring what part of all value created that "unrecorded" value is. But whenever there is a voluntary exchange of money, there is value created, you agree with that?
I mean why would anyone give their money to someone if they're not getting any value from that transaction?
@ACuriousMind $C^p$ manifolds are tremendous
I hope GR deals with $C^\infty$ only
Do we mean that by smooth?
2:25 PM
yes, smooth usually means $C^\infty$
Because some books mean $C^p$ for some given $p$
Oh, ok
but sometimes it also just means $C^p$ for large enough $p$ so that everything you just did works
For example, you couldn't define the tangent space as the space of derivations in a point
There is another construction that uses commutative algebra instead and yields the cotagent space but to be honest I found that unintelligible
@JingleBells No. I disagree that transactions, in and of themselves, generate something of value, I disagree with the entire idea of viewing society through a transactional lens, and I would caution that "voluntary" is a dangerous judgement to make about exchanges of money - nothing about my exchange of money for e.g. food or shelter is truly voluntary, because the world we exist in is structured in such a way as to make that an effectively obligatory part of existence.
@Feynman_00 yes, that is a large part of why you want to stick to $C^\infty$
hi everyone
actually why earth crust does not melt? and what make it temp so high?
2:32 PM
I'm genuinely terrified by non-$C^\infty$ functions. Studying real analysis I could never remember what had to be $C^2$ or just twofold differentiable
is it due to radioactive
elements in the earth
why curst is in spherical or HCP shape
these are the some question which puzzling me
@JackRod do you really mean the crust?
because the crust is the outermost layer - at the surface, it's certainly not very hot, we can walk on it every day!
@JackRod as for why things under the influence of gravity tend to become round-ish, see e.g astronomy.stackexchange.com/q/24698/23535
@ACuriousMind If I give you something you want and you give me something I want, hasn't that ability to exchange been valuable to both of us? (only if the transaction has been mutually beneficial). That's what I mean by a transaction. For your second point, I'm not sure what you mean by viewing society through a transactional lens. By voluntary choices, I mean choices made under certain constraints, I don't see how it can be otherwise.
@JingleBells If I'm starving and I give you all my money for an apple, is that "mutually beneficial"?
did both of us "get what we want"?
I pay ACM to beat up someone I don't like, did that create value?
2:42 PM
@fqq depends on the someone ;P
also, in that scenario it's much more likely I end up getting hurt than the target
@ACuriousMind Yes, it is mutually beneficial, regardless of the fact that you're starving. You get something that benefits you and I get something that benefits me. (which is supposedly some pieces of paper in my case)
@JingleBells No, what has happened is that you have exploited my situation for your own personal gain. This is my fundamental disagreement with the idea that all transactions that weren't overtly forced are "voluntary": Transactions can only be truly voluntary - in the sense that they will only happen when both sides think the exchange is fair - when no side has implicit or explicit power over the other. A starving person has no power - they have to take the deal or they die.
"you have exploited my situation for your own personal gain" - I have no idea what you mean by this, we both benefited from the transaction and if it hadn't occurred we both would have been worse off, that is the fact. There is no requirement for mutual agreement on fairness for mutual benefiting to occur. About the voluntary part of the argument, to be honest I don't know what voluntary means, I don't believe in free will so depending on how you define it, we can discuss it.
@JingleBells "we both benefited from the transaction and if it hadn't occurred we both would have been worse off, that is the fact." The latter part is not true. There is another possible world in which this transaction would not have been possible at all: A world in which we consider it our moral duty to not let people starve instead of extracting money from the hungry.
This world is better than the world in which I starve because I didn't buy your food and better than the world in which I had to buy it.
It is a world in which not all transfers of "value" must be transactional. Where it is possible to give without taking in return, simply because it is the right thing to do.
3:00 PM
@ACuriousMind Sure, I could have given you the apple (i.e. create value for you) without you giving me the pieces of paper (i.e. create value for me) but in this way, the total value created overall is less.
why does it matter whether or not we created "value"?
it doesn't matter unless your goal is to maximize the value created
Then that is not my goal.
Maybe we should have started from that XD
So this should be our fundamental disagreement?
@JingleBells Did you already forget our last discussion? The problem is not that you want to maximize "value" and I don't, the problem is that we disagree about what value is - you think it's reflected in money because to you money is a reification of personal preferences; I don't.
3:10 PM
@ACuriousMind I don't think money has to be involved for value to be created - if I give an apple and you give me a banana that means that I value the banana more than the apple and you vice versa, so in that transaction value is created for both of us. I wouldn't want to tell anyone what is valuable to them and I hope you don't too.
@JingleBells note how you altered the example - if we both have food and just exchange it so we both get the food we like more, that's a truly voluntary transaction because none of us holds power over the other
@ACuriousMind I can understand what you mean, my point though is that in both versions value is created for both of us, it's just that in the previous version I wanted pieces of paper for some reason instead of a nice juicy banana. What difference does it make if you (the starving person) have pieces of paper instead of a banana when in both cases you can exchange your thing for something you want more?
Where is all of this going?
3:28 PM
@JingleBells Humans generally can't eat paper.
@ACuriousMind I agree :D
If I have no food, I have no choice but to accept pretty much any way of getting it
I agree
well you have the choice to die :P
and that means that I will have to accept whatever the people who have it demand of me
I agree
unless you prefer to die
3:31 PM
so that I enter into the transaction doesn't mean anything - the price I pay doesn't represent how highly I "value" the food, it just represents how much the people with the food were willing to demand.
@ACuriousMind Entering into the transaction means that you're going to get the apple and not die. I agree that the price you pay doesn't represent anything about how much you value the food in the scenario that we're talking about.
So where is this going?
@JingleBells This is the core of my objection to the idea that the amount of money that changes hands in a transaction represents how much the people involved value the goods exchanged.
@ACuriousMind Yeah but most people in developed countries are not starving and there are plenty of people demanding and supplying apples. The example that supports your core objection doesn't reflect the real world.
3:49 PM
@JingleBells and that's where we disagree - most people in developed countries are not actively starving or homeless, but still they have to pay for food and shelter and other things that are essentially necessary for participation in society. They're still subject to this same kind of exploitation - or, conversely, power is wielded over them with the threat of such exploitation (e.g. "Don't be against factory farming or destructive agriculture because then your food will get more expensive").
or the size of rent, for instance, as a proportion of low incomes is an essential factor in preventing accumulation of wealth/causing debt by low incomes
Implicitly, this is also part of the reason many low-qualified jobs can pay low wages - since workers have no choice but to work to subsist, the same argument applies again to show their wages don't represent the "value" of their work
Alrighty let's take it step by step
@ACuriousMind "Most people in developed countries are not actively starving or homeless, but still they have to pay for food and shelter and other things that are essentially necessary for participation in society" - I agree with that, it's a fact. "They're still subject to this same kind of exploitation" - I still don't understand what you mean by exploitation and how it is bad. Remember this time we're talking about the majority of the people in developed countries with a lot of supply and demand.
Helu? :3
@ACuriousMind Btw I hope there are no hard feelings between us about these discussions, I'm genuinely here just to learn some new stuff and challenge my views, I have nothing against you just because we differ in some opinions :3
I'mma go eat dinner and I hope we can continue this because it's super interesting, hope you feel the same at least to a degree.
4:12 PM
Is this how one uses latex in physics forums?
[ tex ] \nu (U,u) [ \tex ]
@JingleBells The exploitation is in that there is a class of people who controls the means by which these necessities are produced and another class of people who has to work to pay them for these products
First time over there
I've never used physics forums :P
@ACuriousMind Hmm ... didnt physics forums come before PSE?
Jun 24, 2020 at 17:47, by user434058
23 hours ago, by ACuriousMind
May 3 at 9:46, by Loong
Jan 5 '16 at 22:43, by ACuriousMind
Jun 17 '15 at 6:43, by DanielSank
I regard online chat as an asynchronous communication protocol :-)
If I don't answer immediately that is usually just a sign my attention is focused elsewhere :P
@MoreAnonymous ...so?
4:14 PM
@ACuriousMind Oh just imagined you would have been active then as well in the physics online community
how old do you think I am :D
@ACuriousMind 35?
eh, close, but still 6 years too old
You can still do a Phd @ACuriousMind
join the dark side :P
I know, but I don't want to
4:16 PM
@ACuriousMind I want to but I don't think i'll have a shot unless I have a paper out ...
(which is something Im working on)
I mean I've seen the difference in training from the elite institutions and rank 4 ...
which is why i wanna go to some of the best for training
@Feynman_00 have you used physics forums?
Sometimes I read something but I trust SE way more
I need to figure out how to use latex there
@Feynman_00 Me too
Latex is diffeomorphism invariant
@MoreAnonymous My guess was far better :P
@ACuriousMind That's news to me. I thought string theory was PhD material
@Feynman_00 It is ... But our hero has chosen the dark side!
@Feynman_00 there was a regular course where I studied that was usually a mix of master students and aspiring PhDs
it's pretty pointless to think something is "PhD material" - if you know the prerequisites, you can study something, and at which stage in your formal career you have which prerequisites is extremely varied
4:24 PM
@MoreAnonymous try ##LateX##
@ACuriousMind Yeah of course, people can study anything on their own. That was an innocent hypothesis
And I also assumed that because you seem way above the level I think I'll reach after my master's
@ACuriousMind Gotchya
@ACuriousMind "There is a class of people who controls the means by which these necessities are produced" - I agree. "and another class of people who has to work to pay them for these products" - I agree but the working people get paid to pay for the products they or other workers produce. I don't see how that's bad.
@Feynman_00 don't worry too much about it - remember that you mostly observe me talking about stuff (I think) I know here, not the stuff I've never heard of ;)
4:49 PM
EDIT: =) looks better
@JingleBells there are many problems with that, e.g.: 1. This structure is resistant to true upwards mobility because wealth/lack of wealth is inherited. 2. The amount people are paid for their work is decoupled from the actual "value" their work creates - as long as a job allows for minimal subsistence and there's a lot of people who can potentially do it, there will be someone who takes it; there is no mechanism here that limits the profits the owning class can extract
(even while merely owning and not working, mind you!). 3. It disregards completely people who, for some reason or another, cannot do enough work to subsist.
4. A point fqq implied earlier: What about jobs that are actually destructive in nature (in the extreme hypothetical killing people, but in more realistic scenarios destroying natural habitats, etc.) that either harm many people indirectly or the worker directly (e.g. mining work in many countries) but which the workers will effectively be forced to perform because they get paid for them and so can continue to subsist?
5:12 PM
@ACuriousMind No I meant core
one which is as deep as 2,300 km
@JohnRennie hi sir
@ACuriousMind 1. What does "true upwards mobility" mean? And btw most of the wealth is not inherited. 2. What does "actual value" mean? Wages are determined mainly by supply and demand and it's true that if there are a lot of people who can do what you do then your pay goes down and the opposite is true as well. The controlling class does indeed get money for the value that they create
3. If you don't create value to society then you shouldn't expect society to create value to you. Of course people should be free to help out people that don't create enough value but not forced. 4. In these cases I think government intervention might be a good idea but it really depends. What if people value more the building than the natural habitat it's destroying?
No worker is forced to do a dangerous job, in most cases such jobs are paid pretty well precisely because workers don't want to do them (less supply). If you can get a mining job you can surely get something more safe as well, like a cleaner or whatever. Someone has to get the mining job done anyways though, what solution do you offer to that if not sending humans?
5:29 PM
@JingleBells "If you don't create value to society then you shouldn't expect society to create value to you." Ah, now you've said what I was waiting for: This is decidedly different from the purpose of "we want to satisfy the most needs of most people" you started out trying to convince me markets were good at. This is the attitude I really find distasteful, and this is exactly what I meant by the "transactional view of society" earlier.
@ACuriousMind We can get into that definitely, what about my other points? (I'm really just trying to see if there's anything wrong with them and learn something new :P)
Every human has immeasurable value, to me, and I reject ideologies that discount those that do not create whatever it has decided "value" is. I believe in a universal moral duty to help our fellow creatures - in solidarity that is not bought but freely given - and if your model of society doesn't contain that then I'm not interested in it.
@ACuriousMind Are we gonna discuss the other points first or should I just jump into what you're currently talking about?
To be honest I'm not really interested in discussing this any further; I've seen this rhetoric before many times, and I've said all I wanted to say.
5:47 PM
@ACuriousMind How can you know what I'm about to say for you to not be interested in it? We're just having a normal discussion, I'm not judging you for anything nor am I screaming at you because we disagree. I'm interested and curious about how you see the world and I want to ask a few questions to learn more. I'll go ahead and ask because I know I shouldn't ask if I can ask XD
So first of all, I see nothing wrong with wanting to create value to people that don't (for whatever reason) create value to society back. I'm not against you going and giving your apple to a homeless person, you have your moral duties and you have the right to act on them. The problem I have is when you force me to give my apple to a homeless person, in other words when you try to impose your moral duties on other people.
@ACuriousMind I would like to add a last comment, with all respect to your person about (I feel it as a friendly reply) your last message
"I actually don't feel a great loss..." I think that it is important to emphasize that there was an age in which physicists doubted the existence of black holes, and you can to ask about the illusion that have many persons about travels exploiting wormholes. It is important also to add that was a great physicis who is the author of the concept (I refer the Wikipedia Geon (physics)).
@ACuriousMind By the way, if giving an apple to a homeless person will get him/her to start creating value to society, then I'll give my apple, but if it has the opposite effect and incentivizes unproductivity then I won't give my apple.
hey can anyone help me in getting undersdand how quantum simulation is better option than
it peer standard simulation
6:05 PM
@user250478 I'm not saying no one should think about geons or anything - but I'm not even a professional physicist, so I don't really have to care about every speculative idea
@JackRod what is "quantum simulation"
Many thanks for your reply again (as I said I felt your last, as a friendly reply). I'm not agree with you: we live only once @ACuriousMind
@JingleBells What do you think the laws protecting your precious free economy are if not the imposition of the moral values of the lawmakers on other people? You don't get to pretend taking the high road here - every society with any form of laws thereby imposes moral values on its constituents.
@ACuriousMind Under my system I get to follow my moral duties and you get to follow yours. Under your system, I'm forced to follow your moral duties. How is my system not taking the "high road" here?
6:21 PM
@JingleBells No, I'm not - I am, for example, not allowed to perform actions that break the laws that protect the accumulation of wealth; The almost unconditional protection of property represents itself a moral position: Property is more important than people. Your rhetoric implicitly reduces morality to "the choice between all actions considered legal in a neoliberal system".
And in case you're wondering: This idea that neoliberalism among all ideologies is uniquely "not an ideology", and it uniquely takes no moral stance, is so common I have of course heard it before; now I am really tired of this discussion.
@ACuriousMind I agree with what you just said that different systems impose different moral values on the citizens, and to say that my system is the "high road" based on a single thing (i.e. the choice to give stuff to homeless people) would be a mistake.
If you're tired of this discussion then we can stop. I have last 2 questions and I'm ready to wrap this up - what would you say our fundamental disagreement is, and second, if you were given the power to change the current system in some way (maybe fundamentally) what would you do?
6:53 PM
When all your friends are in the bar but you seem to be barred :/
@ACuriousMind ^ Even the chat room got tired of our discussion XDD
Btw ACM while we may disagree on quite a few things, I like that you are not opposed to jumping in and discussing/debating with people who disagree with you, this is a very useful and important quality and I respect when people don't run away from information that contradicts their beliefs because that's hard but a necessary step to being more informed and sometimes reaching further to the truth
@JingleBells I doubt you provided any such information honestly :/
Information that contradicts his beliefs?
@JingleBells yup ...
ACM is quite well read. I'm surprised someone who hasn't even joined a university has strong political beliefs of your type.
I'm sure university will be a great experience for you btw :)
Are you saying that my beliefs are wrong because I haven't gone to university?
7:02 PM
@JingleBells No. Of course not
Come on, he's not saying that
Sorry, what do you mean More?
@JingleBells I mean university is a great place to learn. So I'm sure it will inform your beliefs in a good way
Even if you stick to your position
You will argue it more coherently
@MoreAnonymous Btw I was respecting his willingness to discuss with someone who opposes his views and taking a risk (even though a small one) of being presented with opposing information.
@Feynman_00 Thanks ... though I ended up asking the question here on PSE
@JingleBells Fair
@JingleBells can I ask which books have influenced your line of thought? Or is it the youtube algorithm?
7:10 PM
@MoreAnonymous I think I've read a few random economics books and some part the youtube algorithm but it's mainly me sitting and questioning stuff
I think it fundamentally starts with some values you hold and then you research to figure out what suits them best
@JingleBells Hmm ... The youtube algorithm is crap. I'd advise not to use youtube. Since it seems to throw people on a slope heading towards the political left or right
@JingleBells Try reading Chomsky? His take on politics is quite good
@MoreAnonymous I agree, I'm mainly having discussions with ACM to see where I'm wrong :P
He's considered old school left
@MoreAnonymous What is your take on economics and stuff?
@JingleBells I'm honestly not well read enough to say much. But my observations are people seem to want change and there are people who don't like any sort of change. Why? Cause the current system is stable and works for some and they are afraid (or so they articulate) the new changes proposed will lead us all to self annihilation
My personal take is: the social contract is the bare minimum of any democratic state. Beyond that well I dunno
7:19 PM
@MoreAnonymous You might be right, I don't know. Btw you don't need to be 100% in your opinions to share them :-)
As a younger adult you may be excused but if I started saying stuff like this
Aug 15 at 15:14, by JingleBells
@ACuriousMind what is ridiculous about "poor people are poor because they don't make stuff" (again I'm talking about Africa, India, etc.)
Oh boy
your voice has consequences. Inquiry is good. But try to tread carefully.
I still don't understand what's controversial about that. I was not saying that African people are able to make stuff, or that their circumstances are suitable for that. I was just pointing out the fact that if they made stuff and got to consume that stuff, there would be growth and less poverty, am I wrong?
@MoreAnonymous Agreed, it came out sounding as if I think African people are lazy and that's their only problem, which is completely false
Words have power. They reveal to others who we are, and not always in the ways we intended them to.
@JingleBells I'm not going to take ACM's place. I think he's better at handling this.
@ACuriousMind So just because I didn't clarify that I wasn't talking about them being lazy it immediately must mean that secretly I'm despising them? I'm assuming that from what you're saying, I could be wrong, no offense.
Pff I'm tired as well lol
We've been doing this with ACM for hours XDD
@ACuriousMind I actually haven't asked this - why are you having these long discussions with me?
7:34 PM
@JingleBells The places you are talking about have a long history of being brutally exploited, first by colonial powers, now by their descendants. A lot of their production goes directly to the "developed world" (think of e.g. sweatshops in India making textiles for the fashionable clothes of the West) - and the return they receive for that is still disproportionate (because they are poor, the wealthy don't have to pay them as much - there's the exploitation of the need to subsist again!).
Wealth and modern means of production do not appear overnight just by working, they have to be accumulated, and the heirs of colonial power - the West, mostly - have given themselves a cruel headstart. Saying "they're poor because they're not making anything" erases this history - even if you don't mean to imply anything about their current ability or character, you are acting as if the weight of history counts for nothing.
@JingleBells Same reason I've written over 1500 answers on the site - if I can make a difference, I should.
@ACuriousMind I agree about the brutal exploitation by colonial powers and stuff in Africa and that they don't get to consume the stuff they produce. In order to have less poverty you need both production AND consumption by African people, and as you said you need time to develop the technology.
@ACuriousMind Btw, what would giving more money to Indian people change (the so called exploited by the West)? It's just gonna raise their prices but not their underlying productivity?
@ACuriousMind Thanks, just another example that wherever there's value there isn't always money
@ACuriousMind That's commendable. If you asked me why I like to answer questions (in life) I would answer that I like hearing myself improve with my explanation skills :P
@Feynman_00 I won't deny that there is also an element of me just liking hearing myself talk :P
I think that's also what makes physicists
Furthermore, the tendency to explain is in human nature
8:30 PM
@ACuriousMind I feel so bad now :P I've only answered 5 questions :P
2 hours later…
10:05 PM
Q: Why does titanium oxide around Betelgeuse produce this particular sawtooth-shaped absorption spectrum?

uhohBetelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse suggests that the recent dimming might be caused by increased optical absorption by dust around the star, based on a spectral analysis. Question: The images below show absorption feature...

Bountied in Astronomy SE

« first day (4305 days earlier)      last day (50 days later) »