One of the other things about Singapore is that they will bring the hammer down on you for abusing the public housing. If you pee in an elevator, the doors will shut and the police will come. Compare that to public housing in America...
Monopoles are already accounted for though, because they’re explicitly ruled out by the character and form of the laws of electromagnetism. ∇⋅B = 0, or “the divergence of the magnetic field is zero”.
When Maxwell first published his work with the equations, it contained non-zero B divergence. We say that density of magnetic monopole (which should be there instead of zero) is zero because we did not find any monopoles yet (maybe ever!). If we discover a monopole, and we remove this zero, there will no problems with EM theory, and actually we can explain some other things like quantization of electric charge (why all charge are integer multiple of electron charge).
So no, it was not explicitly ruled out by Maxwell's equations. It is not even ruled out because we did not explore the full phase space. And it depends on which monopole you are talking about (Dirac monopole, GUT monopole or EW monopole).
I mean I we found a magnetic monopole then we'd just change that one of Maxwell's equations so it looks like the corresponding electrical equation Div(E) = ρ/ε. It essentially just happens that the thing which correspond to ρ for the B field is 0.
Except that if the divergence of the magnetic field were anything other than zero, the laws as presently written wouldn’t successfully predict electromagnetic effects. Because the laws as currently written _do_ make predictions, and exquisitely precise predictions at that, the divergence must be zero with no monopoles at all or so close to zero that monopoles would be extraordinarily weak if they did exist. Their effects would be so slight that they would be useless for any practical purpose except possibly impressing the Nobel committee.
The fact that standard EM theory with zero magnetic charge works well only proves that normally there aren't lots of magnetic monopoles floating around: they could be very short-lived particles or strange phase of the matter, but still real and Maxwell's equations don't say anything about this.
As far as I know there's no mathematical or physical reason to outright forbid magnetic monopoles. On the contrary, there is a well-known argument by Dirac that says that if they would exist then charge is quantised, which we know it is. This is one of the reasons people are still looking for magnetic monopoles.
I don't really understand your point here. If we do discover magnetic monopoles (which would not necessarily be very weak but instead very rare) then we would take the equation
Div(B) = 0
And update it to say
Div(B) = sigma
Where sigma is a field describing the monopole density. Theres a ready "gap" in Gauss' law for magnetism where you can easily stick monopoles. Of course the divergence would be zero in the absence of monopoles, just as the divergence of the electric field is zero in the absence of electric monopoles, but decidedly non-zero when there's an electron around.
I think your point is the current Maxwell equations explain physics so well that if we change them to accommodate magnetic monopoles they would have to be worse. If I understand you right, it overlooks that we can add terms[0] to Maxwell's equations that don't affect predictions in a world free of magnetic monopoles:
∇⋅E = ρ(electric) / ϵ0
∇⋅B = μ0 * ρ(magnetic)
∇⨯E = -μ0 * J(magnetic) - ∂B/∂t
∇⨯B = μ0 * J(electric) + (μ0)(ϵ0)(∂E/∂t)
We could switch every physics textbook to using the above today, and the only difference would be setting ρ(magnetic) and J(magnetic) to zero when there are no monopoles in the problem.
[0] Griffiths Introduction to Electrodynamics 3E, Section 7.3.4
If anything it's frustrating that there aren't monopoles, because if there were, we could make the E and B equations symmetrical under interchange of the fields. It would be a lot prettier, and I think it would be easier to teach to undergrads.
I mean you could just do that and tell the students that the magnetic charge and current densities are always zero unless we eventually discover monopoles.
This is incorrect, you can put non-zero divergence of magnetic field and all the equations and predictions stays the same. Better it would make Maxwell's equations symmetric under exchange of fields and sources. \
> so close to zero that monopoles would be extraordinarily weak if they did exist
Why? I can't think of a reason why would this be the case? You are not solving Maxwell's equation for the universe. You can have divergence of electric field closed to zero because you have very low density (the field source) in the region you are studying.
> Wait, how can algebra not depend on arithmetic? Something simple like x+20=3x+8.
If your Q could be restated as: How can a student struggle with one while excelling at the other?
The answer is: When we learn the answer we'll be able to help more dyslexic kids than we are now.
I failed basic 3rd grade math tests for so long they finally quit testing me. Eventually, I was the only one of those kids doing algebra in the 6th grade.
My longish life is loaded with similar discontinuity-of-ability. Adult me obfuscates it so well I rarely experience other people's incredulity. Grade school me could have put that to good use.
Frustrating that op doesn't straight answer the question. I think what he's getting at is that you can do the usual steps without having to interpret what the mean. For example, you don't have to say that you're subtracting 8 from 20. Instead you say that all things without x must be on the same side, and signs change when you move across. So one step is x+20-8=3x. Nevermind what those symbols mean, you just memorize the rules. At the end you have x=(20-8)/(3-1) and you put that into the calculator.
To me this seems that you're hacking the system. You're avoiding learning how to think and understand, you're just learning how to pass the class.
That said, I cannot concieve that some kids don't understand 20-8. I wish I could chat to some of them to see what's going on.
> To me this seems that you're hacking the system. You're avoiding learning how to think and understand, you're just learning how to pass the class.
I can certainly grasp that these are literally different, but are they practically different for most people?
Eg I know that some of my clothes need to be washed with cold water. I don't know why, but it's never made a difference in my life.
I know my car needs oil changes, but I don't specifically know why. Some kind of lubrication, but for what and why it goes bad I have no idea.
We all do hundreds of things algorithmically without really understanding what we're doing or why. We know enough to get the answer we want and that's good enough.
The kids that do algebra algorithmically probably aren't going to be math professors, but neither am I, and there are plenty of lucrative and productive professions that are fine with getting the right answer without knowing why.
On some level, most people are doing arithmetic algorithmically anyways, based on rules structured around base 10. Ask some people you think have passable arithmetic skills to do addition and subtraction in like base 5 and watch the smoke come out of their ears. I'm not casting aspersions, I'd have a hard time too past a couple digits.
I would wager most of them can't explain why we carry numbers over, they just know it needs to happen to get the right answer. I don't think I'm much better; I'm sure there are dozens of things in basic math that I just do without really understanding why.
> That said, I cannot concieve that some kids don't understand 20-8.
I would almost put money down that it's around carrying the 1's. I've met a few people that struggled with arithmetic, and they almost always get lost around carrying over numbers.
Regarding doing things algorithmically without understanding what's going on: sure, you have a point no doubt. But here's my counterpoint. What is the point of school? If you're teaching kids because you want them to be able to solve problems, why teach them algebra? How many times in their life does an average person have to find the solution to x+20=3x+8 to solve a real life problem? If you want to teach useful algorithms you should get rid of algebra and have schools teach taxes, personal hygiene, physical exercise, maintenance of house, car, etc and stuff like that.
But if the point of school isn't "teach them practical algorithms", but instead learning how to think, then it makes perfect sense to teach them equations, and have them actual understand.
I'm short, if the point of school is to learn how to think, teaching them some mysterious algorithms isn't going to achieve that. If the point is to learn useful algorithms, I can think of 100 better things than algebra.
With this explanation, you've inadvertently convinced me of the op. Being able to get to the "x = number" is the whole point of algebra. More often, students find the difficulty in trying to do arithmetic on things that can't be(what's x +y? it isn't xy and it isn't some new letter).
Doing this way means that you've actually understood algebra, and honestly, the only step of memorization is the substraction itself.
Whether you pull out the calculator at 2 +3, or (23449)/(!6 + root(34/5) ) is sorta irrelevant.
The way I taught was to delay the arithmetic to the end, then use a calculator (if necessary).
Moreover -- the concepts taught in algebra are only loosely related to arithmetic. The important concept being taught is that of principled symbolic manipulation; the domain just happens to be over real numbers.
Essentially that's what I did -- the way I taught this was:
1. All operators are written explicitly, and parentheses are used around every operation. (Order of operations is a huge tripping stone.)
2. All allowed algebraic manipulations were clearly named and diagrammed, and we applied them step by step (no leaps of intuition allowed -- another tripping stone).
3. Save all arithmetic to the end. I.e. numbers and variables function identically. But -- try to move numbers around so they're in operators together.
4. Once the equation is solved (or whatever task is required), now take out the calculator and do the arithmetic required.
I completely agree subtraction is a more useful real world skill. But like you said -- calculators exist. So no reason to let that be the reason to hold kids back from learning algebra.
2GB is really low. I've been able to use A111 stable diffusion on my old gaming laptop's 1060 (6GB VRAM) and it takes a little bit less than a minute to generate an image. You would probably need to try the --lowvram flag on startup.
That isn't carjacking. That's auto theft. Carjacking is when a criminal takes over a running car, oftentimes via threat of violence. No interlock is stopping that.
Same. Only time I ever dealt with shipping on FB marketplace was the time I was selling my Steam Deck and some guy didn’t want to drive. So I said “How about I list it on eBay so we’re both protected, send you the link, and you buy it there”. He was on board and it worked well. Of course I had to eat eBay’s fee but better than getting scammed.
I've had good success with a couple buyers who mail stuff over marketplace.
I used the same criteria: Number of items listed, number of items sold, how long they have been on the platform. For good measure, I cyber stalk them a little bit to make sure they exist.
Even with an Ebay-like ratings system, one of the thing which happens is legit accounts get hacked and go rogue. (I am guessing they got hacked; someone who was legit could also just randomly decide to go rogue) You're always going to be at risk of that.
>I avoid FB Marketplace like the plague. Just seems like a great place to get scammed
There are scams but I think they are avoidable.
My next door neighbor has spent many thousands of dollars on FB Marketplace and has never been scammed. He buys tools and construction supplies and equipment. Usually gets the stuff 90%+ off retail price and sometimes free.
I got scammed from a FB advert selling clothing, turned out the company is a scam and sends nothing, FB have allowed them to still advertise for months still.
I get downvoted for saying this every time I post it here, but a huge number of facebook adverts are scams of various sorts.
Some are as you say - you order something and never receive it. Straight up
Some are fast fashion companies which get spun up quickly with slick ads and websites, which are somehow "going out of business" even though they were registered less than 2 months ago.
Some are kickstarters for products which obviously are just clones of other products which already are ubiquitous.
A lot are drop shippers who use slick ads to sell you something they aren't even in possession of, at 2-3x the price which you could get it for if you just took the time to look elsewhere.
Back in the day, you'd see some semi-truck park in a lot and then two dudes with thick AF Southern accents would get out and tell people they tried to deliver all these items to the warehouse, but the warehouse refused the shipment (insert various reasons why) and they can't go back to Ken-tuck-yee without getting rid of it all.
They said they're selling (furniture, electronics, clothing, art) it all for 80-90% off retail. You know, just so they get it off the truck and get back home. I remember working in a commercial area and the owner of the business would come and tell the guys to GTFO their property so they'd pull out and then pull into the next driveway over and rinse and repeat until they were out of the area.
It was a total scam though. My boss bought some couch and said it started falling apart after a few months. I'm not sure these guys had stolen all the stuff, or if the truck got hijacked our what, but during the Summer it was a regular thing that happened a few times every month.
I'd be interested to find out if anybody else remembers these "truck load" scams in the late 90's early aughts.
There's a truck I've seen that sells meat at stupidly low prices, but they're sold in boxes so you don't really know what you're getting.
They'll sell you a box of 20 ribeye steaks for only $40, but you open the box and realize that each "steak" is only about 1/4 inch thick and is absolute dog-food level marbling, completely zero intra-muscular fat.
I bought two of the “white van speakers” in the late 80s. They were unexceptional but okay and lasted 5+ years of heavy college and immediately post-college usage.
* I see an ad that says "do you want to buy this item for this price?"
* If I like the price, I can buy the item. I got what was promised.
The fact that maybe I could have bought the same item elsewhere for less doesn't make it a scam. Lots of things are offered at different prices in different places at the same time. That's not a scam.
It's not a capital 'S' scam in a legal sense, but it's a scam in that they are playing a trick on you by jacking the price way up and relying on your ignorance to make the sale at an inflated price.
If we consider a door-to-door salesman who is selling (say) basic Android phones in retirement communities where hypothetically some folks have never used a smartphone, they might get away with selling a $100 basic phone for $1000. That's not illegal, but it surely is a scam in the ethical sense.
yes, they fit this pattern exactly. I only discovered this issue after being scammed. There are hundreds of people for example who got scammed by a company advertising dolphin blankets, as described by reddit users who where victims of it, and the adverts and company have still not been taken down by FB.
Since I only deal with "in person" sales, to me it's less sketchy than most eBay purchases. I had a similar happening to this story, but with eBay. I don't know why they bothered trying the scam, I got my money back relatively easy, just had to be patient.
That limits you to buying stuff locally, its a good precaution but means you can't buy anything that is only available further away. I've had good luck buying stuff so far and saved money, I certainly could have got scammed and that would suck.
>That limits you to buying stuff locally, its a good precaution but means you can't buy anything that is only available further away.
To me, that's an entirely reasonable trade-off. You sacrifice the breadth of the market available to you in exchange for greatly reducing your attack surface. You'll easily filter out the legions of machine-assisted international scammers if you require transactions to be in-person with cash.
Like most people - I have a niche interest that doesn't have a large market locally. When I want something that everyone in the country has there is no problem. When I want something unusual though I need to expand to a larger market than local to have a chance of finding it.
I know others have had good success with FB Marketplace, but man I only see scams. I've posted stuff there and on Nextdoor and CL, and I get 10x the number of scam buyers on FB. I stopped even trying to post stuff there, since it was all chaff and no wheat. Kind of surprising, considering I live in SV, just a few miles from FB HQ. I'd think there would be plenty of legit users here!
I've bought and sold so much stuff on Facebook marketplace. Almost always in person and in cash and always a good experience.
At least one time I broke the rule and actually sent money up front for an item but the seller packaged up and sent it right away. The amount was low enough that I wasn't worried about losing it, the item was pretty unique, and I spent a bunch of time checking on things before I decided to trust.
I sold a handful of items on FB Marketplace. Sold in-person for cash. No problems, except for one attempted fraudster who was very obvious. People show up in person, hand over cash, take away items to declutter my garage.
I even managed to sell a nearly-new MacBook Pro for $1900 on FB Marketplace (employer let me keep it after layoff). Local buyer for cash. The buyer was super careful and had the Apple store verify everything about the MacBook.
I've bought/sold hundreds of items on FB Marketplace and never had a problem. The quality and response rate is significantly better than Craigslist, Nextdoor and others. The simple rule is – local, in-person meetup and cash only. If someone insists on anything else then just block and report them.
