Bitcoin trader floods market with $300 orders, causing price to flatline - <AUTHOR> https://bitcoinwisdom.com/markets/bitstamp/btcusd?flatine

<comment><USER2> If anyone feels like watching the wall slowly drop in real time, I made a website that uses Bitstamp's websockets API.

[https://alloscomp.com/bitcoin/wall.html](https://alloscomp.com/bitcoin/wall.html)

</comment><comment><USER3> I feel like I must be missing something. Listing such a massive block of bitcoin for sale ($9 million!) shouldn't cause the price to flatline, it should be dropping as more and more sellers realize the price is effectively capped at 300 for the time being.

I can't figure out why more people aren't rushing in to sell in front of the 30k shares. Conversely, why are people buying now when their would seem to be availability at 300 later if the price doesn't actually drop?

This sort of behavior makes it seem like the market isn't nearly as liquid as conventional exchanges.

<comment><USER4> Apparently, a lot of people are happy to buy at $300, and think the price will go up or have some other use for that many BTC.

It'll be neat to see if another whale comes along and cleans it out at the fixed price.

</comment></comment><comment><USER5> Is it possible to see which wallet have recently make a 30k+ BTC transfer to Bitstamp? May help guess how many BTC this trader actually have in stock to sell.

<comment><USER6> [https://blockchain.info/address/1JX5hS3HyVT3VwnEgvoPLVu6ujPF...](https://blockchain.info/address/1JX5hS3HyVT3VwnEgvoPLVu6ujPFH7BvrY) (via [http://www.reddit.com/r/BitcoinMarkets/comments/2icv68/daily...](http://www.reddit.com/r/BitcoinMarkets/comments/2icv68/daily_discussion_sunday_october_05_2014_part_2/cl10h00))

</comment></comment><comment><USER7> Is this a stop-loss thing or am I missing some other motive to sell this cheap? I feel like the price would be rebounding if this wasn't happening.

<comment><AUTHOR> Yes, this trader is single-handedly keeping the price from going above $300.

</comment></comment><comment><USER8> I hope this is still around Monday. I would like to buy a small piece of the lot for sale via my local ATM. As of Sunday evening Austin time, there is still 19878 BTC for sale at $300.00 on Bitstamp.

<comment><AUTHOR> It won't last much longer. The trader started by putting 30k Bitcoin in orders and it's now down to 19k. You can follow along by watching the red line in this chart:

[https://bitcoinity.org/markets/bitstamp/USD](https://bitcoinity.org/markets/bitstamp/USD)

<comment><USER9> Ugg, mBTC quoting, took me a sec to realize

</comment></comment></comment><comment><USER10> Karpeles is liquidating.</comment>


Ask HN: Google's Project Fi? - <AUTHOR>

Anyone tried this? https://fi.google.com/about/<p>My invite came through.  Curious if people have tried it, and what they think. <comment><USER2> From last week: [http://www.paulkuehnel.com/full-google-project-fi-review- a-m...](http://www.paulkuehnel.com/full-google-project-fi-review-a-multiple- cell-phone-network/)

</comment><comment><USER3> I don't like the requirement of using nexus 6 only. I don't mind switching to android from iphone, but nexus 6 is almost 1 year old. and it is huge...</comment>


Amazon Startup Challenge Videos (including Justin.tv) - <AUTHOR> http://developer.amazonwebservices.com/connect/amazon_startupchallenge.jsp

<comment><USER2> I love the Justin.tv guys, but they have some stiff competition. ooyala.com is without a doubt a groundbreaking, utterly game-changing idea. If they can actually do what they say they can in the video, this could change online video and TV forever. perhaps even justin.tv!

<comment><USER3> I don't see what's game-changing about Ooyala. Can you please elaborate?

<comment><USER2> The bit about making elements in video clickable. I don't know if this is automatic detection or a manual process, but either way, ad targeting within video would be pretty phenomenal.

<comment><USER4> Would people use it though? Surely it's a...

"I want to watch the rest of this video" vs "I'm going to click on this toaster and see special offers for toasters"

Seems like either the video will be so boring people will want to escape via adverts, or the video will be interesting and no one will click on 'ads'.

Perhaps I'm missing something.

<comment><USER3> I have the same impression. Plus, I think poor usability will kill it. I can't imagine my mom (the mom test is always important) clicking on objects in a video to see "relevant" offers. And the frustration level will be very high once a user clicks a few times and doesn't get what she wants or expects. Some people would click on an actor to see his bio and others would be interested in his shirt. Others will click on the wrong thing because the scene will have changed at that instant.

It seems like cool technology, but a bad product. I wouldn't invest. Go Justin.tv :)

Aside: the other startups in the challenge -- the ones the didn't get a lot of votes (apparently the voting has turned into a popularity contest) look both interesting and promising. Their founders may not be in their 20's, but I would invest in them over Ooyala and Justin.tv -- especially Commerce360.</comment></comment></comment></comment></comment>


What do you call this in Ruby? - <AUTHOR> https://github.com/JuanitoFatas/what-do-you-call-this-in-ruby <comment><USER2> Such little imagination... You should learn from your forefathers. Quantity is no substitute for quality. ;)

[http://search.cpan.org/dist/perlsecret/lib/perlsecret.pod#SY...](http://search.cpan.org/dist/perlsecret/lib/perlsecret.pod#SYNOPSIS)

<comment><USER3> It would seem like the forefathers won this round. You've got to love the inchworm on a stick.

</comment></comment><comment><USER4> Meanwhile:

        Mathematica 10.0 for Mac OS X x86 (64-bit)
        Copyright 1988-2014 Wolfram Research, Inc.

        In[1]:= FullForm[x->y*z^w]

        Out[1]//FullForm= Rule[x, Times[y, Power[z, w]]]

        In[2]:= x\[UnionPlus]y\[RightTee]z

        Out[2]= x ⊎ y ⊢ z

There's no reason your programming language shouldn't be able to tell you what these things are called in English without an external reference.

<comment><USER5> Some operators are so abstract that they don't really have a good name.

Eg if you are talking about groups in general, how do you pronounce the group operation ∘? At uni, we usually just called it Kringel.

<comment><USER4> The name can be arbitrary, as long as it's unambiguous. By the way, here's what mathematica says when I copy paste that and enter x∘y: SmallCircle[x,y]

Also fun:

        In[3]:= SpokenString[x\[SmallCircle]y]
        Out[3]= "SmallCircle of x and y"

Which can be turned in to sound:

        Speak[x\[SmallCircle]y]

<comment><USER5> Actually, it's not even unambiguous. In some sense, it's like an unbounded variable.

</comment></comment></comment></comment><comment><USER6> Say what you will about us, but Ruby people get to have the most fun.

 _hops on hipster hashrocket and tribbles off into the sunset_

<comment><USER7> > Pythonists are all "explicit is better than implicit" and Rubists are all > like "LOOK AT ME I MADE A BONG OUT OF THIS HAIR DRYER"

[https://twitter.com/geeksam/status/618828713308753921](https://twitter.com/geeksam/status/618828713308753921)

<comment><USER8> "AND CHECK OUT THIS COOL WAY TO TEST IT"

</comment></comment></comment><comment><USER9> I had a Microsoft support technician ask us to press the "flower button" in a powershell script. It took a while to work out he meant { and }.

</comment><comment><USER10> This sums up what I dislike most about Scala (which is an even worse offender in this regard). A rule of thumb: if a 10-year-old wouldn't be able to intuitively read the operator, use words.

<comment><USER11> Written words are symbols as well. What should we do when we don't understand words?

<comment><USER12> We Google them, which is an impossible task for non-alphabetic symbols. :P

<comment><USER11> I wonder at what point people started to expect that search engines can instantly provide all the answers to everything worth knowing. The correct place to find a word you don't know is a dictionary. The correct place to find a symbol in code that you don't know is the definition in the source code (or language reference if it's baked in), or simply ask someone who knows.

<comment><USER12> Asking someone you know is not an approach that scales in the large, and suggesting that all answers can be divined from source both assumes a level of mastery that cannot be expected (e.g. the difficulty of reading the source of C++'s Boost library vs. reaching for the extensive documentation) and denies the existence of questions such as "when is it appropriate to use this operator?" or "what is the worst-case runtime complexity of this operation?"

</comment></comment></comment></comment></comment><comment><USER13> This seems like it could have been prime territory for a bit of surrealist/meta fiction, with gradually stranger descriptions of operators turning into a short story of some kind.

</comment><comment><USER14> I will be using bacon cannon from here on out

</comment><comment><USER15> Normal single-character operators also have names:

[http://www.catb.org/jargon/html/A/ASCII.html](http://www.catb.org/jargon/html/A/ASCII.html)

</comment><comment><USER16> How did hashrocket get named? I would think instead of => a hashrocket would look like: #>

edit: Makes total sense. Thanks for the replies.

<comment><USER17> Ruby's associative arrays are called hashes. That operator is how you assign a value to a key.

</comment></comment><comment><USER18> Wish I worked with a language with a === operator so I could say "threequals". Very clever and fitting.

<comment><USER19> I've worked with Javascript for years and never thought of this. Such wasted opportunity...

</comment></comment><comment><USER5> A select few operators (out of hundreds) for a single Haskell library: [https://github.com/ekmett/lens/wiki/Operators](https://github.com/ekmett/lens/wiki/Operators)

(For full disclosure, the lens library is infamous for this.)

<comment><USER20> You are perfectly fine importing the module Control.Lens.Combinators[0], which has the full functionality of lens except the operators. There's nothing you can do with operators but can't do with normal functions named with words.

[0]: [http://ekmett.github.io/lens/src/Control-Lens- Combinators.ht...](http://ekmett.github.io/lens/src/Control-Lens- Combinators.html)

<comment><USER5> Oh, definitely. Haskell approach to operators and overloading is exactly the Right Way: operators are weirdly syntaxed function, and you can add your own. No need to make bit-shifting do IO.

</comment></comment></comment><comment><USER21> ... is an ellipsis.

! is enunciated as "bang" from BASH parlance, iirc.

<comment><AUTHOR> thank you, added.

</comment></comment><comment><USER22> Looks like quite a few of these were cribbed from the intercal character set[0]. Nice to see that living on.

[0] [http://www.muppetlabs.com/~breadbox/intercal- man/tonsila.htm...](http://www.muppetlabs.com/~breadbox/intercal- man/tonsila.html)

</comment><comment><USER23> Just added a PR for the spermy operator (~>).

<comment><USER24> For those wondering, here's the request: [https://github.com/JuanitoFatas/what-do-you-call-this-in- rub...](https://github.com/JuanitoFatas/what-do-you-call-this-in-ruby/pull/4)

Here's the response: _Hi Christian, thanks for the Pull Request! But I think this is not appropriate rubygems /rubygems#124. :bow:_

<comment><USER23> Can someone explain to me, why this is not appropriate?

<comment><USER24> Sperm comes from ejaculate. Ejaculation is a bodily function. Bodily function is likely not going to be proper in a professional environment.

<comment><USER25> Really? What about sleep/wake?

<comment><USER24> Specifically, sex makes many people uncomfortable. Sure, it's natural function but it's not a topic many people are comfortable talking about openly. Not me but you can understand how this would be a sensitive enough topic for enough people that they'd leave it out, no?

</comment></comment></comment></comment></comment></comment><comment><USER26> my favorite is the "Elvis operator" in kotlin ?:

Took me a while to figure out why it was called that way.

</comment><comment><USER27> > =~

Cigarette operator! This list is on fire.

</comment><comment><USER28> I like to call crab clows 'insert.'

<comment><AUTHOR> I added, thank you.

</comment></comment><comment><USER29> '!!' -> "truthy?"

<comment><USER24> ! -> "not truthy". So !! means "not 'not truthy'" which is truthy.

Truthy is something that isn't exactly a true boolean but will equate to true(thy) when evaluated with this type of comparison. Things like undefined, null, and empty string will not be truthy.

More info on what's truthy (for JavaScript at least) is here [http://james.padolsey.com/javascript/truthy- falsey/](http://james.padolsey.com/javascript/truthy-falsey/)

edit: typically, if you want to test for truthy, you'll just evaluate it like so

if (my_object) { //truthy }else{ //not truthy }

Does anyone know a time when you'd use !! instead of just the object in the evaluation? I'm not a Ruby dev, so I don't know specific cases for needing !!

<comment><USER30> One typical use for !! in JavaScript or Ruby is where a function/method returns a boolean value that indicates the presence or absence of an object.

You could just use:

      return myObject;

Since that value will be truthy or falsy, any code that tests it will generally work, as your if statement example demonstrates.

But there are two advantages to doing this instead:

      return !! myObject;

1) Now you are returning an actual boolean value, not just a truthy/falsy value.

2) Sometimes more importantly, you are now _releasing_ this function's reference to the object, instead of possibly keeping that reference around much longer than needed and preventing it from being garbage collected.

</comment></comment></comment><comment><USER31> i like the yoda operator: !!!

i've never used it... what's a good use case?

</comment><comment><USER32> stabby lambda is my favorite.

<comment><USER33> I like the name "stabby lambda", but I dislike its use. It seems less readable to me. The again I also think ruby 1.9 Hash syntax is less readable, so maybe my judgement is suspect.

</comment></comment><comment><USER34> dat bacon cannon</comment>


Mixtape of the Lost Decade (2011) - <AUTHOR> http://boingboing.net/2011/10/11/mixtape-of-the-lost-decade.html

<comment><USER2> A boingboing content piece _without_ an absolutely shameless amazon affiliate link ?

That's incredible. Truly amazing.

</comment><comment><USER3> Oh, the 19A0s. I'm surprised jwz doesn't have a tag for them; he's definitely labelled bands befitting that era. Here are some relevant computer GUIs:

[http://visualpunker.tumblr.com/post/49438567333/retro- user-i...](http://visualpunker.tumblr.com/post/49438567333/retro-user- interface-06-primitive-computer)

</comment><comment><USER4> Cool, reminds me of a R. A. Lafferty short story with a similar premise, titled "And Read the Flesh Between the Lines".

</comment><comment><USER5> fnord. Hmm, this seems very well thought out and interesting; I wonder what the rest of HN thinks.

<comment><USER6> To me it appears to be completely incoherent conspiracy theory babble mixed in with a pretty random looking selection of music. Must be some kind of a joke that I'm missing.

<comment><USER7> It's not meant to be _funny_ , it's meant to be artsy and surreal.

<comment><USER8> Consider the past as a continuum of psychological accessories.

And drum loops.</comment></comment></comment></comment>


Ask HN: Where to run a large data project - <AUTHOR> I've been asked to do a data processing job by a friend. As part of the job, I'm supposed to download and process roughly 1.5tb of data. That's a problem because my local ISP data cap is 300gb a month.
So I'd like to ask: what recommendations does hn have for me? I was thinking of getting a private server and trying to get some cheap storage, but I'm not sure where to go for that.
Side note: not only do I have to download a huge data set, but I have to make a bunch of whois calls based on some IPs in the data set. <comment><USER2> The usual cloud offerings, e.g. Amazon AWS, Azure, Digital Ocean, are relative expensive when you need large harddrives. At least when you rent for several weeks. My typical projects need 1TB fast SSD.

If drive speed is not an issue, it sounds like download speed is, have a look at a server auction [https://www.hetzner.com/sb](https://www.hetzner.com/sb) Those are servers other companies custom-ordered and no longer use. "2x 3TB" give you about 2.8TB usable space (drives are mirrored for redundancy by default, but you can change that and combine them).

<comment><AUTHOR> Wow! That's a great site. Thanks for the tip.</comment></comment>


Jison - <AUTHOR> http://zaach.github.com/jison/docs/ <comment><USER2> Here's a link to CoffeeScript's Jison grammar. It's written in a small inline DSL (the "o" business at the top of the file) that makes it a little bit cleaner to add rules.

[http://jashkenas.github.com/coffee- script/documentation/docs...](http://jashkenas.github.com/coffee- script/documentation/docs/grammar.html)

</comment><comment><USER3> A friend and I have a WIP lisp compiler targeting JS that uses this <http://github.com/alandipert/pantless>

</comment><comment><USER4> I may want to write a more BASIC scripting language that falls back into Javascript APIs so that IT professionals can write plugins without having to know Javascript to do it. This looks like it was the key I was looking for.

How similar is this to ANTLR - which is my only implementation experience with context-free grammars (although I've studied formal languages in uni)?

</comment><comment><USER5> FYI: This is what CoffeeScript uses.

</comment><comment><AUTHOR> And Orderly[1] too...

[1]<http://github.com/zaach/orderly.js></comment>


Top 10 Parse Migration Guides Comparison - <AUTHOR> http://parse-hosting.oursky.com/blog/2016-04-06-top-10-parse-migration-guides <comment><USER2> Cool :) and the Parse Open Source Community is there too :)</comment>


How to Square numbers made up of repeating '3' mentally in 2 seconds - <AUTHOR> http://mathema-tricks.blogspot.com/2012/02/squaring-numbers-made-up-of-repeating_22.html http://mathema-tricks.blogspot.com/ <comment><USER3> This is cool and all, but I don't see how it's useful. It's a very narrow algorithm that you might use once and a while.

On the other hand, this is a perfect example of mathematical beauty.

</comment><comment><USER4> square(333) is the addition of 999 + 9990 + 99900 = (1000 - 1) + (10000 - 10) + (100000 - 100) = 111000 - <USER2>

The more '3' you add, the more '1' and '0' you get. square(333) = 11110000 - 1111

It is actually a very binary computing.

</comment><comment><AUTHOR> <http://mathema-tricks.blogspot.com/>

</comment><comment><USER5> title should read:

 _How to Square numbers made up of repeating '3' mentally in 3 seconds_

just so much catchier. OTOH, link-bait title would read "How three Indian university students came up with..."</comment>


Samsung DeX Now Runs as a Windows and macOS App - <AUTHOR> https://www.androidpolice.com/2019/08/11/samsung-dex-now-runs-as-window-in-windows-and-macos/ <comment><USER2> I'm still waiting for the dockable phone that doubles as a PC to be viable. Motorola tried it with the Atrix but it was too ahead of it's time.

I feel that we are close though. With the iPhone Ax chip being comparable to low end laptops, this is going to be a game changer.

</comment><comment><USER3> Years ago, I proposed using our research on Zap ([https://systems.cs.columbia.edu/projects/zap/](https://systems.cs.columbia.edu/projects/zap/) \- arguably the spiritual ancestor to CRIU) to create simple mobile devices (say a tablet that provided a consistent storage environment) and enable the "desktop environment" to migrate from the tablet to a more powerful PC when docked with it (and migrate back to the tablet when one wants to undock).

We demonstrated it using a portable hard drive migrating desktop environments between PCs ([https://systems.cs.columbia.edu/archive/pub/2006/09/highly-r...](https://systems.cs.columbia.edu/archive/pub/2006/09/highly- reliable-mobile-desktop-computing-in-your-pocket/) \- with the portable hard drive providing the consistent storage environment).

We demonstrated being able to checkpoint a desktop (in this case with the fs as well) very quickly ([http://systems.cs.columbia.edu/archive/pub/2007/10/dejaview-...](http://systems.cs.columbia.edu/archive/pub/2007/10/dejaview- a-personal-virtual-computer-recorder/))

I argued that Microsoft's work on their Metro interface (i.e. UI elements introduced with win8 - the touch friendly stuff) could actually enable this model with tablet. If developers were able to write UIs for their apps that were able to switch between touch optimized modes and WIMP optimized modes (as lets be honest, they aren't the same and we haven't found anything better for desktop use as of yet than WIMP to the point that Samsung tries to make android play well in a WIMP environmnt with DeX).

</comment><comment><USER4> I've tried Dex and I really like the ability to run the apps on my phone on a PC (your data and credentials stay on your phone). This article is about not requiring a screen switch to your phone but using your phone apps within a window on your mac or windows session.

</comment><comment><USER5> anyone know where you can get a copy of this app?</comment>


Two Weeks Vacation is only a Recommendation, not a Rule - <AUTHOR> http://www.expatsoftware.com/articles/2007/02/two-weeks-vacation-is-only.html <comment><USER2> I've implemented a "get it done" based vacation policy at my company. I.e., as long as my devs are getting the work done, I couldn't care less about their seat time, physical location, state of dress, etc. Hell, if you're on a beach in Cancun and only working a couple hours a day, that's cool, just make sure you get your code checked in and answer emails within a reasonable timeframe so we don't miss a deadline. And wear sunscreen. Developers and sunlight don't usually mix well.

With that said, if one of my guys did what this guy is advocating, I'd have little choice but to replace them. I have to be able to rely on my guys; I trust the hell out of them. Bailing for a month plus with little to no warning...that fractures our relationship of trust, and no relationship can succeed in that condition.

<comment><USER3> Good points, and wow, I didn't expect to find myself defending a four year old blog post today.

I'm not sure where you get the "little to no warning" bit from what I wrote. In the examples I cited, I gave about 2 months notice in both cases. The idea is certainly not to burn bridges or blackmail your employer. Just that it's OK to take the odd sabbatical.

I eventually migrated to consulting, where I could simply end a contract then disappear for the rest of the year. And from there, I migrated further to running my own product company, where you can disappear for 4 years straight as long as you have a laptop along.

Still, if I had a job today I wouldn't limit myself to 2 weeks vacation.

<comment><USER4> I think the no warming comes from this

"Two days later, ticket in hand, I strolled into the office of my department head."

Got a ticket and then sounds like you leave on Friday for three months.

<comment><USER3> I'm with you. I should have added "... but not actually wheeling a little suitcase behind me..." to that sentence.

The next sentence is also ambiguous. It should mentally read "...before heading out 2 months later...".

The funny thing is, this went to page one on Reddit back when it came out and nobody there misredd it.

</comment></comment></comment></comment><comment><USER5> I _wish_ I could take a month off! My manager won't let me, unfortunately: he gets all anxious and irritable after a few days whenever I don't show up at work.

(I'm self-employed.)

<comment><USER6> I never considered that before - how DO entrepreneurs take time off? Is this done post-post-/Ramen profitability? Never? Just for a day at a time? Or does the flexible schedule prolong burnout?

<comment><USER7> You don't.

This is one of the first things you'll notice being in business for yourself. It's hard to arrange time off. One of the benefits of working for a company is that there's a team in place to make sure the train stays on the rails while you're gone.

You also don't get sick days.

<comment><USER8> This may be the median startup behavior, but I've seen plenty of counterexamples, at some quite successful startups.

</comment></comment></comment></comment><comment><USER9> About three weeks ago, I went to my employer to negotiate part-time employment. I am now working 3 days a week at 2/3 pay, full benefits, and prorated vacation.

The caveats are that I was prepared to resign, the agreement includes a stipulation that either side can rescind the arrangement with 30 days notice, and our HR department was already set up to handle such arrangements.

I wanted to do something like this for a long time, but I was too afraid to ask.

<comment><USER10> I've been considering negotiating part-time with my employer for awhile as a prudent middle ground between recklessly jumping ship (a la <http://news.ycombinator.com/item?id=1451175>) and continuing to let my UI project crawl along at a near-standstill.

Your listed caveats help me form a good picture of what I should be ready to concede. Any more tips on negotiating? I know there are always a lot of variables from company to company, but was it hard to keep full benefits?

<comment><USER9> I wish I could say that I drove a hard bargain to get full benefits, but it happens to be company policy. I went in to the meeting prepared to increase my portion of the cost of my healthcare if necessary.

My biggest concerns prior to initiating the negotiations were 1) affecting morale if someone else is forced to compensate for my reduced hours, 2) the fact that I occasionally do freelance mobile development on the side, and 3) possibly being let go as my company is going through a downsizing. So far, it hasn't been an issue, but it's early.

It turns out that my freelance work is a non-issue according to my employment contract and IP agreement. I didn't really reduce my hours to do freelance work. Instead, I was doing freelance work to insure some modest income should I be forced to resign, and I may reduce my efforts there since I can easily live just on the income from my part-time work. My boss and his boss were cool about the freelancing, but they told me to keep it to myself, and I wish that I had been more private about my side interests prior to asking to go part time.

In your case, I would check up on the IP situation. You don't really want to be in a position where there are questions about who owns your side project.

As far as negotiating tips, what worked for me - I don't know that this is great advice necessarily but I had to do it this way because it addressed the worst case scenario in terms of short-term income - was that I was resolved to resign, even though it wasn't really my first choice in improving my situation. However, I have about 1 year's living expenses saved up and I'm making close to $1K a week doing 20 hours of freelance mobile development and turning down projects just about every day. That gave me the confidence to start the conversation by saying, "I am considering resigning." Eventually, I suggested the work schedule that I was willing to consider. I had researched the company HR site to know what options were available to me. I also felt reasonably confident that they want me to stay and that it would be hard to replace me, at least in the short term.

One thing that is bad about bringing up resignation is that it will likely keep you from collecting unemployment if your employer plays hard ball. I never said "I resign," just that I was considering it, but I have been advised since then that it was probably a bad idea from that standpoint. It probably didn't matter in my case because I wouldn't be eligible anyway due to my freelance income.

Also, I have a very friendly relationship with my boss, so that helps a lot. It seemed that he really wanted to help me, and he played up the cost savings angle up the management ladder to help me get what I wanted.

<comment><USER11> Having been in a similar situation ("I need to resign or work part time"), I think the best thing you can do is show awareness of the effect it will have on your coworkers and suggest ways in which this will work out.

For example: "I suggest I keep the 60% of my job that is the most onerous for someone else to take and/or requires the most prior experience and/or is best matched to my skills. As for the other 40%, I suggest task A should go to Fred - he is ready for more experience, it will be good for him. Task B can be phased out when the new project is completed anyway. Jane has agreed to roll in Task C with the similar Task D that she already performs".

I have been doing this for several years, and it has worked out great for everybody. The only issue is whether the tasks you give up are important for your career development - sometimes they are, so you will have to make some serious choices.

</comment></comment></comment></comment><comment><USER12> _It is nearly impossible to hire a good developer_

[Sigh]

He's right. And it's getting worse. We have a bunch of open req's right now as we're staffing up a new project and you'd think with all the handwringing about the economy and how many great engineers are being laid off it would be easy, right? Nope. It actually seems like the quality of applicants has gone _down_ since the last time I was interviewing people.

Out of all the people we've interviewed, there's ONE that I would say is a good hire (as opposed to just "can probably do the job with some hand- holding"), and the rest of the interview team is lukewarm on him. And this is after HR has screened out the bottom of the barrel and our technical phone screens have filtered out a few more. ONE person who's just a "nice to have" and there's a good chance we're going to pass on him.

If anyone here threatened to quit, at this point we'd probably chain him to his desk :-)

<comment><USER13> You are in Minnesota. I know loads of great developers who left Minnesota because interesting and well-paid programming jobs were nonexistent.

<comment><USER14> Minnesota is polarized - there are a lot of independent developers and a lot of Fortune 500 programming jobs. Not a lot in between.

I've hired a dozen programmers here in my day, and so it is definitely possible to find good developers. But you really have to know the right communities, user groups, etc. to find them. Of course, I expect that isn't MN-specific.

</comment></comment></comment><comment><USER15> He's right about two weeks not being the rule; in most western countries four or five weeks is the rule.

To me the amount of holiday/vacation is a Big Deal. I was lucky when I lived in the US that my company offered four weeks (and I could earn extra comp days doing weekend tech support). Although I once had the general manager ask me point blank how I was taking more time off for a trip to Peru, so I went through and proved I had enough vacation days left. He still didn't seem too happy about it though. Perhaps most people didn't use all their vacation days?

Lack of vacation days is one of the reasons I'd be uncomfortable about living in the US again, so I could definitely see myself taking unpaid leave every few years like TFA suggests or just quitting my job. Then I could do important things like visiting family in NZ or getting in some serious skiing.

<comment><USER16> Meanwhile, in Sweden, 5 weeks paid vacation per year is the legal minimum, and everyone has the legal right to get 4 weeks continuous vacation in the period between June-August if they want it.

(I think you have to spend a few winters up here to understand why we appreciate summer vacations so much. :-) )

<comment><USER17> Shouldn't you be enjoying the summer in Sweden, then, and taking vacation in the winter?

<comment><USER18> Here in Europe vacation does not necessarily imply that you're flying somewhere else. For example, I currently have 3 weeks of, but I'm only spending one of these weeks hiking. During the other weeks I'll do just whatever makes fun (maybe going on a multi-day bike ride).

Of course, you can also take less vacation in one year, and therefore take more in the next year. For example, I only took 3 weeks of vacation last year, and I've planned 7 weeks of vacation this year. All of them paid. :)

</comment></comment></comment></comment><comment><USER19> You'd want to be pretty sure of your value to your employer before trying this stunt. Here's a counter-example: a young guy that reports directly to me tried to reduce the number of hours he has to work, by threatening to leave if we didn't reduce his hours (whilst keeping pay at the same level). This conversation was with my boss, I only gave him work to do, HR stuff was always handled by my boss. He was out the door of the company 24 hours later.

<comment><USER20> I wouldn't really consider it a counter-example since in your case the guy was essentially demanding a raise. It's all about how you ask and being reasonable. Less hours for the same pay is not reasonable. Less hours for less pay would be far more reasonable, and might even have been accepted.

<comment><USER21> Less hours for same pay is an extremely reasonable compromise, in these times when many companies can't/won't pass out much in the form of direct raises.

 _Explicitly threatening to quit_ during any negotiation is the unreasonable part. Frankly, it's an implied threat in any conversation about compensation, just as being fired is an implied threat in any conversation about performance.

But coming out and _saying it_ , is wildly unprofessional and immature; there's just no up-side.

<comment><USER22> >Explicitly threatening to quit during any negotiation is the unreasonable part. Frankly, it's an implied threat in any conversation about compensation, [...] coming out and saying it, is wildly unprofessional and immature; there's just no up-side.

If it's implied then making it explicit is simply clarifying one-anothers position. I can't see how that's unprofessional: Being honest, open and explicit about your intentions.

Leaving because negotiation didn't work for you when you made no explicit indication that your staying was part of the negotiation, that seems wrong to me.

<comment><USER21> > _"If it's implied then making it explicit is simply clarifying one-anothers > position"_

The only reason to state it is to add emotion to the argument: to _dramatically_ emphasize your resolve. And the problem with that, is the _next_ negotiation has to go to _at least_ that point again to convince the other party you really do mean it.

So if you were earnest about having been at the end of your rope in the first negotiation, you earn only the certainty of being pushed back to the end of your rope in every subsequent negotiation. It's self-defeating and adds wholly unnecessary stress to the workplace.

And if you're advocating emotional argument in every negotiation... well, good luck with that. It adds a tangible degree of stress to everyone around you and they won't appreciate it.

<comment><USER22> >he problem with that, is the next negotiation has to go to at least that point again to convince the other party you really do mean it.

But you were saying that the argument is already at that point but that card is just being held below the table despite everyone being aware that it is there.

It's not necessarily emotional - I can say "I'll leave if I don't get these terms", that's not inherently an emotional demand, nor is it overly dramatic if that's your intention.

It's pretty much all-in wrt the negotiation so yes I can see that it increases the stress until terms are agreed. But then the terms from the other side would have to include something to avoid such negotiations if they found it too stressful and/or emotional.

Nor does this necessarily lead to future difficulties in negotiation.

For sure someone could attempt to use this sort of situation for emotional leverage - I guess it depends whether you're talking about negotiation pay+conditions for a job or negotiating terms of a personal relationship.

</comment></comment></comment></comment></comment></comment><comment><USER23> At my last "real" full-time job, developers could accumulate vacation time that was not used in a given year. Sometimes it was on purpose, so as to take longer vacations later on, often it was required because of deadlines, staffing shortages, whatever.

Then one day the new company owner declares that vacation time could no longer be accrued. Use it or lose it. Some folks had many weeks of time saved up.

The owner said that people can use up what they've already saved, but added, Keep in mind that if your department can afford to do without you for several weeks then perhaps you're not so essential. He all but winked when he said it.

This was just one of the things that convinced me to just leave and work for myself.

<comment><USER24> I have a somewhat-related story about the last place I worked. During my first year there the company was in the process of replacing half a dozen consultants with a handful of full-time employees. We worked very hard with limited resources and weren't allowed to take a vacation. Even working on the end-of-year holidays to complete deadlines before the end of the calendar year. Our manager kept telling us that we could carry over our accrued vacation time and be "taken care of" next year. And there was a policy of carrying over vacation days to the next calendar year.

So the start of the next year comes and my team gets our first paycheck and for some reason we all have zero vacation time. We are all stunned and quickly talk to HR. It turns out that employees can carry over vacation days, but _NOT_ in your first year of tenure. So the team lost all of our vacation days and restarted at zero. Our manager looked into it and discovered that those were the rules. He went to his manager to see if we could get our vacations back but he couldn't get anyone from HR to change their mind as "that was the policy". Needless to say, we were pretty pissed off.

<comment><USER25> If all you were is pissed off then he has good reason to exploit you like this over and over.

</comment></comment></comment><comment><USER26> I like the message given about taking time for yourself - relaxing, etc. I do it far too infrequently and every time I do take a real vacation I realize how badly I need to.

But to walk in with no notice and tell your employer that you're disappearing for 3 months is unprofessional and unreasonable. You work for a company which has schedules and deadlines; just as you expect them to pay you on time, they expect to have at least a little bit of warning before you up and disappear on them.

3 Months vacation - great. Presumably you expect to get it unpaid (Your employer probably gives you 2 weeks PAID vacation) and many employers with a few weeks warning would be happy to accomodate you. But to tell them "I'm leaving - see ya!" and expect to have a job waiting for you? Come on.

<comment><USER27> I think he said he had a ticket, which is best bought months in advance.

<comment><USER28> And if you don't bother telling your manager ahead of time - you run the very real risk of his ire and wrath...

As the trunk poster said - you can only pull this off if you are really good at what you do, and prepared for the negative consequences if they happen.

</comment></comment></comment><comment><USER29> That's one of the few things I like about our dirty socialist system over here in Europe: it recognizes that 2 weeks of holidays / year simply is not enough.

</comment><comment><USER30> I don't live in the U.S. and I have five weeks of paid vacation in a year, but I usually take several weeks of unpaid vacation as well to go with it. My employer doesn't really care which type it will be, they're more concerned about schedules etc. In fact, after I've got the time of my vacation approved, I'll just mark some days as paid and some days as unpaid and they don't mind.

With regard to vacation allocations, I play it safe: if I need anything longer than a week off, I'll request the absence in good time. This works well because a) they can project it into the project schedules and b) if I want six weeks off next fall, they really don't have a practical schedule for next fall yet, so I get implied priority.

Oh, and I work part time as well. There was more to that when I started it but basically it boiled down to them saying "we'll rather keep a good guy working less for us than not at all". I get roughly the same amount of work done as before, the shorter days just mean that if I want to take a half a day off and go cycling, that's actually the default mode of operation as nobody expects me to work till 5 or 6pm.

</comment><comment><USER31> I work for Microsoft in Ireland. We get 25 vacation days (5 weeks) as soon as we are hired! Getting an extra week of unpaid leave is common enough with very little hassle.

Instead of gambling your job, move to Europe.

</comment><comment><USER32> Fortunately, I work at a shop where I don't need to force this issue. I took four weeks off this spring to road trip and climb with my family. I had three weeks of PTO in hand, and my manager, and his manager said go for it, under the condition that I wouldn't go dark for more than a few days at a time. So, I checked my email every few days, and I think twice over the course of that month I actually had to fire up my laptop and spend 30-60 minutes to troubleshoot an issue. That's a compromise I can live with.

</comment><comment><USER33> Vacation time is a brutal inhumane joke in America, IMHO. There's no minimum, and a number of companies provide no vacation time for employees in their first year. Even when vacation time is provided, sometimes its pretty limited or the company culture makes it hard to take all the time allowed.

Other countries, particularly in Europe, get it, but we don't. I recommend reading "Work to Live" (as opposed to 'live to work') by Joe Robinson <http://www.amazon.com/Work-Live-Joe-Robinson/dp/0399528504> for an overview of the US vs. European nations.

I'm all for having a killer work ethic, but I believe you're more efficient when you're refreshed and not burned out. And sometimes your subconscious mind works well on solving problems that you wouldn't be able to tackle if you keep down in the trenches without a break.

</comment><comment><USER34> I've found that frequent, little getaways (3-day weekend, for example) are more refreshing and improve my quality of life more than one rare, large vacation. YMMV.

<comment><USER35> I need at least 3 days to START feeling like I'm on vacation. 10 days and I start to forget where I used to work. Something in between is good.

<comment><USER34> That might be a sign that your typical workweek is too stressful. For most jobs I've had, it took zero or one day to wind me down. My most stressful job (as a middle school teacher) took me two days to wind down.

</comment></comment></comment><comment><USER36> It all depends on where you are. One guy tried to get 4 weeks off at a place I used to work. He needed sign off from a high up manager to do this. The manager retorted if we can get by without this guy for 4 weeks, why do we really need him at all? Suffice to say, he didn't take his 4 weeks holiday.

<comment><USER18> Honesty, I wouldn't want to work at such a place but rather quit.

</comment></comment><comment><USER37> What typically happens to your benefits (Health insurance?) while taking a leave of absence? Is it reasonable to expect my employer to maintain them?

<comment><USER38> yeah, this sounds fine for the bachelor developer with no one dependent upon them. When you have a family things change. I am good at what I do and I have plenty saved up in an emergency fund, but the risk of potentially losing my job, benefits, etc. just to take a month off isn't worth it. That being said, I do get 4 weeks PTO (no sick/vac all is PTO), so I suppose I could take a month off if I wanted to. But I'd rather split it up during the year.

</comment></comment><comment><USER39> Aah Sweden is good sometimes, 5 weeks paid vacation every year, and you have to take out a minimum of 3 consecutive weeks. It's the law... :)

<comment><USER40> Idea for my fellow Americans: we need to ask our bosses here for a 5-week leave of absence so we can vacation in Sweden. Once in Sweden start looking for a job and then citizenship. :)

</comment></comment><comment><USER41> "Cut to 3 years later, and I'm on a small, tight programming team for a little dot-com startup. I've been there for almost a year, and it's time for a bit of R&R in Central America. 6 weeks off should just about do it"

Does this remind anyone of yesterdays article about the guy who took a month off for a honeymoon? It's one thing to take advantage of a large corporation but if you are screwing your startup for your own vacation, you are being extremely selfish and possibly detrimental to the company. It's fine if you need to recharge your batteries, but its another thing entirely to leave your startup, and your friends, to get more vacation time. If the startup failed, you lost much, much more than you gained by going to Costa Rica.

<comment><USER42> Slavery (in America) died in the 1800s. Your job doesn't own you.

<comment><USER41> I'm not talking about working at a normal job, I'm talking about working at a startup. At a startup you have a tremendous amount of responsibility because a large portion of the companies success/failure rests on your shoulders. You also have other people who have put a tremendous amount of faith in you and rely heavily on you.

If you would rather take month long vacations to go backpack around exotic locations, go work for a big company. If you do this at a startup, chances are you are putting your company, and your co-workers, future at risk.

If you want to work at a startup, especially as an early employee, there are certain responsibilities that you must live up to. This author, like the founder of the failed YC company, is selfish. Either life gets in the way of a startup or a startup gets in the way of life, but its not often you get both.

<comment><USER43> > This author, like the founder of the failed YC company, is selfish

Everyone is selfish.

</comment></comment></comment></comment><comment><USER44> Just make sure it would take longer to hire and train someone for your job than your vacation is.

</comment><comment><USER45> I completely agree. Many Indians here often travel to India for a month or two and even save up vacation time over a couple years and use it all at once.

</comment><comment><USER46> You have to take this advice on a case by case basis. At my last job they offered me a 10k raise as I was walking out the door, but also got upset when anyone used more than 3 sick days a year. At my current job I take 4-8 weeks of paid vacation a year and probably could take more, but if I asked for a 10k raise they would tell me to move into sales.

</comment><comment><USER47> White Oak Technologies in the Washington DC area has more than 2 dozen job openings offers 5 weeks Vacation after one year.

<http://woti.com/benefits.cfm> <http://woti.com/jobs.cfm> ___Must be a US citizen_ __

</comment><comment><USER48> Depends on your current projects, don't think I would be comfortable coming in one day and telling my coworkers that what I was working on is going to stand still for a month or someone else was going to have to pick it all up if a project is at a key point in development.

<comment><USER49> There was a big emphasis in the post about making sure your projects are tied up before you leave. I don't think anybody is advocating leaving your coworkers high and dry by skipping out on your deadlines at the drop of a hat.

</comment></comment><comment><USER50> Yeah, he is right on with respect to "your employer needs you more than you need them". We have been trying to hire someone for months, and it's just insanely difficult. If I left for some reason, I would get an instant raise for going to a competitor, and the department's productivity would be lower until they could find a replacement, which is very difficult and expensive.

Fortunately, I have never even had to hint at this option.

</comment><comment><USER51> I'd wager this gets you fired more often than not. Nobody is so great at what they do that they can contribute while not working.

When I've people try something similar at work, the request is met with "lets have a talk". The guy making the request usually leaves the company a few days/weeks/months later, as it "just wasn't working out".

<comment><USER43> But you're saying the guys are leaving, they're not fired. Maybe after the talk they realise that their life is more important than being loyal to a company that won't let them take a little time off.

<comment><USER51> Absolutely. Most people leave before they get fired in my experience. When something's not working, you tend to leave. Sometimes for good reason.

</comment></comment></comment><comment><USER52> totally true. the most valid point being that you have to be good at what you do. hell, you can do even better if you are really good. I wanted to see what it was like to live in London so I told my boss I'll be working out of there is he's okay with it. If not I'll be taking a leave of absence. He agreed to the work remotely. Tap on 3 weeks on vacation to the end of that and you feel like half the year is done for.

</comment><comment><USER53> Lots of Swedes in this thread huh!

In Austria, 5 weeks is also the legal minimum for paid vacation - not to mention all those holidays…

</comment><comment><USER54> I'm not saying we shouldn't live a relaxed, sustainable work-life, but seriously?

Sounds to me like you abused your leverage. Almost any employee, especially at a small company, is extraordinarily valuable and, sure, can use that to take (see: extort) 6 weeks vacation, but it's disrespectful to the organization. The cost to replace you outweighs the cost of letting you leave for 6 weeks if you are good. You're right economically.

Ethically it's a dick move (even if you do it "once every few years" 6 weeks of unannounced leave is really not cool). And if you don't feel like you have a relationship with your work where you have to respect it you shouldn't come back from that vacation.

<comment><USER55> i strongly endorse employees exploiting their employers as much as employers exploit their employees.

<comment><USER56> The employer-side of that exploitation-maneuver would be your boss telling you: "We do not have anything for you to do the next 6 weeks, starting tomorrow. You will not be paid but if you want, you can come back later."

If that happens at your company, go ahead and take your leave. If it does not happen, you may be overplaying your exploitation a little.

<comment><USER57> This happened to me. I promptly informed them that they hadn't hired me as a contractor, hand't been paying me the rates I demand as a contractor, and bid them farewell.</comment></comment></comment></comment>


Does gravity CAUSE the bending of spacetime, or IS it the bending of spacetime? - <AUTHOR> https://physics.stackexchange.com/questions/413846/does-gravity-cause-the-bending-of-spacetime-or-is-gravity-the-bending-of-spacet <comment><USER2> So correct me if I'm wrong, but if gravity is merely a curvature in space- time, does that mean there's no such thing as a graviton?

<comment><USER3> General Relativity is a classical field theory, so there's no graviton in it.

However, there are various quantum gravity research programmes which have tried to quantize the (classical) tensor fields of General Relativity in one way or another, for instance by turning (classical) gravitational waves or position and momentum variables into quantum particles. In these theories the graviton is a spin-2 gauge boson and induce an attractive force on fermions with like gravitational charge. This compares with the photon, a spin-1 gauge boson that induces a repulsive force on fermions with like electric charge (and an attractive force on fermions with opposite electric charge). The spin also corresponds with the rank of the (classical) fields, where in General Relativity we have rank-2 tensors and in electrodynamics we have vectors (which are rank-1 tensors).

Unfortunately this approach has a problem: particles other than fermions also have a gravitational charge, including gravitons themselves. (Photons do not have an electric charge, but they _do_ have a gravitational charge). Quantum field theories use a variety of tricks to remain linear theories, but General Relativity's Einstein Field Equations are non-linear. That non-linearity manifests in graviton-graviton interactions in this sort of quantized General Relativity, and we do not know how to stabilize the resulting quantum field theories.

In more concrete terms, let's "drop" an electron from higher potential to lower potential. The electron is a fermion with electric and gravitational charge. When we drop it from higher to lower electric potential, out pops a photon. When we drop it from higher to lower gravitational potential, out pops a graviton. But we can't move the photon around the electric field and get it to produce another photon, because the photon is not self-interacting. A graviton, on the other hand, can be dropped down a gravitational potential causing it to emit another graviton. That in turn influences the potential, making it easier for those two gravitons to each emit a further graviton, which influenes the potential, making it easier for those ... and so forth to infinity. Our original electron is in that potential too, so it in turn can emit further gravitons as well. Fortunately this explosion of gravitons only happens in strong gravity, and we only find that deep inside black holes (or in the very early universe), rather than somewhere we can outright observe (assuming the cosmic censorship principle is true), so we can still use this type of theory to describe most of the universe.

Unfortunately, gravitational waves are hard enough to detect; when they are quantized, they turn into lots and lots and lots of gravitons, each of which has a tiny fraction of the detectability of a gravitational wave. Detecting an individual graviton experimentally is beyond the ability of present human technology, or anything reasonably likely to appear in the next few decades. So if we ever figure out how to stabilize this type of approach to quantum gravity, we will only be able to assess it against observations of many- graviton systems, likely at extreme events like black hole/neutron star mergers or asymmetrical hypernovae.

This is just one broad example of quantum gravity; there are several other approaches, some with a "graviton" dynamics (e.g. string theory's gravitons are a string state) and some without.

All these approaches share a common problem: General Relativity describes our universe exceptionally well in practice, and its fundamental components are among the best-tested of any scientific theory to date. Where there is weak gravity, barring significant masses in superpositions of position, any type of quantum gravity has to _exactly_ reproduce the results of General Relativity.

It is likely that we will be able to bring microgram masses into such superpositions in the next few years, and we will be able to directly probe one aspect of quantum field theory on (classical) curved spacetime (aka semiclassical gravity). However, _if_ General Relativity fails in that situation, it would certainly allow some useful comparisons between competing theories (with and without gravitons) hoping to extend General Relativity as it in turn extended Newtonian gravity. If only graviton-containing theories match the experimental results, that would be evidence in favour of the existence of a graviton, even without direct detection; conversely, perhaps only non-graviton theories match, in which case the existence of a graviton would seem pretty dubious.

Right now, though, we just don't know: in the absence of evidence for or against, gravitons are purely theoretical.

<comment><USER4> Is there any implication with the gravity wave detection, that since gravity has been verified to travel the speed of light that it is transmitted via particle?

I would think that as inflation is not limited by the speed of light, gravity as a purely geometric phenomenon, would possibly function at supra-lightspeed.

<comment><USER3> > [does gravitational wave detection imply the waves are particles]

No, not really.

However, if we deliberately quantize the gravitational waves, replacing the classical waves with large numbers of particles, the fact that the classical waves propagate at the speed of light means that the particles must be _massless_ , like photons.

There are a couple of families of alternatives to General Relativity that have "massive gravity", which requires that gravitational waves (or the particles, if we quantize gravitational waves) have a small nonzero mass. This means light will propagate faster than gravitational waves, and with some care, this can solve a couple of the handful of problems about the very early hot dense universe, namely in how it became so thermalized across huge regions of space: any sort of pressure density released lots of photons which carried the local energy away faster than gravitation could "react" and contain the heat locally. Unfortunately for such theories, the mass of gravitational waves has to decay away well before the formation of the cosmic microwave background, since massive gravity would leave unmistakeable markings in it that we do not see.

Verifying that gravitational effects do not outrace optical effects effectively kills off all but the most complicated (early-decaying, thus dynamical) massive gravity theories, and those are rejected on parsimony grounds (the complexity is not needed to describe observations).

You're right that matter embedded in an inflating universe is not limited by the speed of light. As with galaxies now, the matter remains more-or-less at the same comoving coordinates throughout the history of the universe, even during inflation. We don't see shear effects in distant galaxies even given the redshift (if all Doppler/motion related) implies ultrarelativistic recession velocities. The galaxies far away look pretty normal, moving slowly within clusters, with the clusters separating. However, lots of new space is being created between each and every galaxy cluster, but the galaxies do not "feel" acceleration. They continue merrily along their almost exclusively timelike worldlines.

Inflation is essentially an extremization of this: lots of new space gets created in between the hot dense low-entropy matter of the pre-inflationary universe, and more new space gets created in less-dense/higher-entropy spots, which makes them even less dense / higher-entropy, which lets yet more space be created there, and so forth, for many "e-foldings". The pockets of gas do not "feel" like they are moving relative to one another, although if they had radars or the like, they could certianly see that during inflation they get much further away from each other (lots of radar signals will simply never return to the sender, or even be received at the target).

At some point in the inflationary epoch the production of new space "cools off" and inflation ends, after which the accelerating expansion is driven by the residual small positive cosmological constant. Structure formation then collapses the relatively dense relatively low entropy matter into the first stars and galaxies, while the space between these areas gets ever less dense and ever higher entropy. Some time after inflation we switch to the modernized version of the expanding Einstein-de Sitter universe (1932), which in the late 1980s/early 1990s was the starting point for the current standard cosmology (\Lambda-CDM). \Lambda-CDM does a much better job describing observations relating to the early universe (before the first galaxies) and recent-epoch acceleration than the Einstein-de Sitter model.

(Note, this is a broad stereotyping of cosmic inflation models; and for completeness, one can still get \Lambda-CDM from the hot dense phase (the "big bang") without inflation. Evidence from e.g. the Planck satellite has killed off some flavours of inflation and non-inflation proposals, and forthcoming evidence from Planck and other platforms will surely kill off many more.)

</comment></comment></comment></comment><comment><USER5> I try to be well read on physics, but a lot is admittedly beyond my grasp at the moment, so forgive me if this is a silly question.

Is this saying that gravity would not be possible without the curvature of space because if space-time paths, then no matter as we know it would be possible because all particles would be on their own timeline orthogonal to all others? And since no collisions could happen if this were the case, no energy in the system would be converted to mass to bend the space-time and create the geodesic curvature gravity emerges from? If I have this right, does this mean all energy in this system would be massless (photons?)

<comment><USER3> I'm not sure what you're asking, exactly. Please ask again, if this doesn't help:

Photons have "gravitational charge", in that they both feel other bodies' gravitational influence, and induce a gravitational influence on other bodies. One sees the "feeling" part in observations of gravitational lensing even around our own sun; the generating part is harder to demonstrate, but consider [https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)](https://en.wikipedia.org/wiki/Kugelblitz_\(astrophysics\))

In General Relativity, we explain the gravitational charge in terms of spacetime curvature; light both generates curvature (because it has momentum) and responds to curvature (because of the universality of free fall).

An isolated photon (or even a non-extreme classical beamlike pulse of light) generates so little curvature that we can safely ignore it in an otherwise Minkowski (flat) spacetime; however, in both cases if it traverses a region of spacetime that is not flat, the isolated photon and classical pulse will respond accordingly.

More technically, light contributes to the matter tensor, whose components encode the flux of momentum from one direction to another. Although light has no rest mass, it does have energy-momentum (in special relativity, E = pc; additionally, the Planck-Einstein relation for photon energy E = h\nu, where h is Planck's constant and \nu is the frequency of the photon). So a higher frequency photon contributes more to the stress-energy tensor than a lower frequency photon, and even the lowest-frequency imaginable contributes more than vacuum. (Aside: General Relativity runs into localization problems with extremely low frequency photons if one piles up a lot of them in a region of space comparable in diameter to their wavelengths; they should mutually gravitate, and possibly collapse, but exactly how is so hard to show that probably nobody's done so successfully. How do gravitational interactions among the photons change their wavelengths? (This is an aspect of quantum gravity; there are related practical problems with Hawking radiation, especially near final evaporation, for instance)).

> particles would be on their own timeline orthogonal to all others

You can contrive a "dimpled" mostly-flat spacetime in which small masses are so widely separated that the curvature they induce is not felt by their neighbours or vice-versa. The contrivance is not especially awful, because we do something similar with "swiss cheese" models of cosmology, where the holes in the cheese are galaxy clusters generating a non-expanding or even collapsing metric (like Schwarzschild or Lemaître-Tolman-Bondi) and the body of the cheese is an expanding Robertson-Walker metric. Already separated holes "float" in the cheese, and the expansion just separates them with ever more cheese, without interfering in the evolution of the galaxies etc. in the holes. Holes which are too close together coalesce into a single larger hole. The spacetime curvature of an expanding "swiss cheese" is extremely strong, but we can turn off the expansion and it is similar to the "dimpled" mostly- flat one; in fact you could model the "dimples" as tiny patches of Schwarzschild space stitched into Minkowski space [1]. The "holes" that are sufficiently separated by the non-growing cheese would stay separated forever. In all these cases, the worldlines of the centres of masses of the holes are essentially entirely timelike.

\- --

[1] This kind of "stitching" using junction conditions is straightforward if extremely complicated and subject to a number of conditions/assumptions. Misner, Thorne & Wheeler's _Gravitation_ has a chapter on Israel junction conditions, and various authors notably Darmois, O'Brien, Synge, Bonnor and Raju have catalogued stitchings of different types of metrics into one another. Most of these would likely require a trip to sci-hub, as they were written largely in the 1970s to 1990s. Unfortunately, wikipedia seems very sparse on this topic (see for example the Inhomogenous cosmology entry, which is desperate for some love [<\- possible note to self]).

</comment></comment><comment><USER6> I think a mass bends/distorts spacetime the effect of this bent/distorted spacetime on other masses is what we describe as gravity.

<comment><USER7> IANAPhysicist.

In other words, most likely the following is totally wrong armchair physicist speculation. :) If there are any experts (=physicists) around, I'd love to know why it's wrong.

What if mass doesn't even distort spacetime, but only "slows" down time locally.

Maybe there's a some sort of "quantum progression" limit per volume of space.

You'd get gravity out of local time slowdown, because of gradient effects. The object under influence of gravity would experience time slightly slower on the side that is closer to a gravity well. This should cause acceleration towards the larger mass.

Gravity's inverse square law could be a result of this local effect depending somehow on wavelength. Longer wavelengths would affect objects further away.

Perhaps you could derive theory of relativity out of a local quantum progression limit.

<comment><USER3> The problem here is that you can't represent tidal deformations purely through time dilation, since they bring (parts of) objects closer together. The tl;dr is: "how does your idea explain that Earth is oblate, with objects at the two poles slightly closer together than objects on the equator but on opposite sides of the planet?" General Relativity explains this as tidal forces acting on the planet, which is in approximate hydrostatic equilibrium, but rotating. The same features explain why a measurement of the local gravity (the field strength "g") at the poles gives a higher number than at the equator. It also explains the shape of the moon in its synchronous orbit.

In General Relativity we can decompose the Riemann curvature tensor into the Weyl tensor, the Ricci tensor, and the metric tensor. The Weyl tensor encodes the squash-stretch deformation of moving objects experiencing shear, for example, a rotating spherical body deforming into an oblate spheroid, or a spherical body moving close to (including synchronously orbiting) a large mass deforming into a scalene ellipsoid. The Ricci tensor encodes the volume deformation of a body experiencing tidal forces; if we drop a ball of dust (think very loosely packed coffee grounds) onto a planet, the Ricci tensor describes the tendency of the individual dust particles to converge into a smaller volume as they each fall "straight down" on individual lines converging at the centre of the planet.

Naively, we could say that there is a clear relationship between the Ricci tensor and gravitational time dilation, since time is running slower in the direction where the individual fall paths ("geodesics") converge. However, we can make the Ricci tensor go to zero by dropping the dustball onto a planet with enormous radius, such that it's effectively flat. Similarly, ultra massive black holes have essentially no Ricci curvature just outside the horizon, while low-mass black holes have significant Ricci curvature. However, gravitational time dilation is still very strong just outside the horizon of such a massive black hole. In this way we can distinguish between spatial curvature (or if you like, length contraction) and curved time (or if you like, time dilation) in the region around massive bodies. Gravitational time dilation is not a tidal effect, but rather depends on the gravitational potential, which in General Relativity is encoded in the metric tensor.

If we orbit our dust ball very rapidly around a heavy planet, it will have substantial Weyl curvature (squashed along its axis of motion, stretched on the other two spatial axes). If the planet has a big enough radius, the Ricci tensor vanishes, leaving us with just the Weyl curvature. In that case, if we measure periodic microscopic processes ("clocks") closest to the planet and furthest from the planet, we will see that the latter are running faster than the former, and the difference is precisely that of gravitational time dilation. Again, this lets us distinguish between changes in length and changes in duration in the region around massive bodies.

Gravitational effects are the result of curved _spacetime_ , although in special circumstances practically all of the curvature can be in the timelike axis, and in other special circumstances practically all of the curvature can be in the three spacelike axes.

I don't understand what you mean by "quantum progression".

<comment><USER7> Thanks for your reply, I'll try to digest all that. :)

I don't yet understand why "local" slowing of time wouldn't generate all of those tensor components.

> I don't understand what you mean by "quantum progression".

Just hypothetical local limitation on quantum state changes (=progression).

<comment><USER8> I think any computer scientist naturally and naively thinks about your 'quantum progression', since it relates to a transactional rate on interactions experienced in the local proper time of a particle, as it interacts with other real/virtual particles/fields.

For example, a particle in deep space experiences faster relative time, compared to one on Earth, because it has 'fewer transactions slowing it down'. The discrete 'tick' of proper time is then one iteration of the spinning polling loop the particle executes while waiting for something to interact with.

So if existence is (or requires) computation, then ....

<comment><USER3> > a particle in deep space experiences faster relative time, compared to one > on Earth, because it has 'fewer transactions slowing it down'.

Transactions with what? Other matter?

A precise weather and waterproof clock on the ground (so in air) on the surface at the north pole will tick more slowly than an identical clock immersed in seawater several metres below the sea level at the equator, thanks to the oblation of the Earth (and the rotation that causes the oblation). The equatorial water is much denser and warmer than the arctic air, so surely there are more interactions between the water and the clock?

See the Early observations subsection of the Gravity measurement section of, starting with 1672 :

[https://en.wikipedia.org/wiki/Pendulum?oldformat=true#Early_...](https://en.wikipedia.org/wiki/Pendulum?oldformat=true#Early_observations)

</comment></comment></comment></comment></comment></comment><comment><USER9> If you reduce all energy exchange to particles in a vacuum, most of the particles transfering energy are photons. Energy transfer, in general is mostly reducible to photons at a fundamental level. In other words, across the vacuum of space, in an idealized model, where there is nothing but void, any exchange or transfer is via particles traversing the emptiness, and most often, those particles are photons.

If two bodies at absolute zero are suspended in a void, and the limits of that void are walls of matter frozen at absolute zero, light years away, and nothing in the scene is emitting photons, what reason would drive the to objects to be attracted toward one another?

This is to say, if the arrow of time is a deterministic effect of entropy, and the irreversible aspect of time is a result of the chaotic interactions of many discrete subatomic entities, why would spacetime still be curved by two dark, massive, cold bodies, such that, even in the absence of photon exchange between the two, there are forces acting upon them at a distance, leading them to cross a void, travel down some unseen curvature or gradient and collide?

If empty space truly is nothingness and void, then entropy, and by corollary, the arrow of time, only exists in the quantum state of each material body.

This would seem to herald a fact that the bodies each move themselves toward eachother, as an incidental phenomenon of being condensed from raw unbound energy to systems of materialized standing waves, (subatomic particles trapped in fixed discrete systems of balanced energy, which does not readily decay into other particles without action from external entities).

In total darkness, without the exchange of photons, why would two massive, cold, inert objects move inexorably toward one another?

How would each massive object find the other's location and accelerate toward the other, if there is nothing but empty space between?</comment>


Show HN: Build A Personal Power Plant for $200 - <AUTHOR> http://gridlesskits.com/2017/09/06/burning-man-update.html <comment><USER2> Here is the much more portable and expensive version of this kit.

Anker PowerHouse to store the energy. 400 WH which is about the same capacity as the deep cycle battery listed, but this is lithium based so it's much lighter (9.3 lbs vs about 30 lbs for the deep cycle version). $500 [https://www.amazon.com/Anker-PowerHouse-Generator- Alternativ...](https://www.amazon.com/Anker-PowerHouse-Generator-Alternative- Rechargeable/dp/B0196GQAKM/ref=sr_1_1?ie=UTF8&qid=1505144286&sr=8-1&keywords=anker+powerhouse+120000)

Foldable 80W solar panel. $190 [https://www.amazon.com/ALLPOWERS-Foldable- SunPower-Technolog...](https://www.amazon.com/ALLPOWERS-Foldable-SunPower- Technology- Notebooks/dp/B01M5DCPKD/ref=pd_sbs_107_1?_encoding=UTF8&psc=1&refRID=AAP7K0VNKBN6G93D6MBR)

Extension cord for solar panel to battery. $8 [https://smile.amazon.com/gp/product/B00FTFYH0U/ref=oh_aui_de...](https://smile.amazon.com/gp/product/B00FTFYH0U/ref=oh_aui_detailpage_o06_s01?ie=UTF8&psc=1)

Evaporative Cooler instead of building your own. $112 [https://smile.amazon.com/gp/product/B007SNQ4FM/ref=oh_aui_de...](https://smile.amazon.com/gp/product/B007SNQ4FM/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1)

$810 for the total package. The benefits are that you get to use a lithium- based battery which is 20 lbs lighter, you can use a foldable solar panel which is more portable, and you buy a pre-assembled evaporative cooler which has nice features like swinging. Mainly this is a good solution for those that just want to press buttons and set up their configuration in a few hours otherwise the kit seems like a good option too.

I used this configuration at burning man and the battery was permanently charged even with the cooler on the whole time. I needed another shade structure for the tent to keep it down a couple more degrees but I was able to sleep until noon with this set up and be totally off grid and have enough power left over for lights and music.

<comment><USER3> Is there a major difference between lithium and deep cycle lead acid batteries with respect to battery life versus amount of discharge per usage or is it a wash?

<comment><USER4> There are indeed several major differences. The first one that comes to mind is to get the most cycles out of a lead acid battery, they recommend not discharging it below 50% capacity. Lithium ion batteries are usually good to 85% - 90% discharge.

<comment><USER5> And on the other hand shouldn't be fully charged. Only going to 90% capacity does wonders for their lifetime.

<comment><USER6> Yes, but you're still talking hundreds of charges to 100% for a Li-ion before you lose capacity. A regular charge to 90% and then only charging to 100% on the odd occasion you need the little bit extra gives you the best of both worlds.

Do even a handful of deep discharges on a lead-acid battery and you'll kill it.

</comment></comment></comment></comment></comment><comment><USER7> This got mentioned under another comment but it is worth stating at the top level: always use fuses or breakers in any kind of system, that battery is a fire/bomb waiting to happen if there is a dead short. Charge controllers can do this when they fail (I had a 30A MPPT CC do this, and not a cheap one). I wouldn't sleep next to this thing without it (I didn't look in incredible detail at their site but a cursory search didn't find anything about current protection).

DC systems and AC systems also require differently rated components. You cannot just go buy a 30A 120V AC breaker from home depot for the DC side of your system. It takes a lot more to disconnect DC than it does in AC (because AC cycles to 0V 60x/s it doesn't take much of a gap/insulator to break a connection, DC is not the same. Trying to use a light-switch for a DC light can result in problems [1].

I've had good luck with midnite products (charge controllers and breakers, etc) [2]. Their breakers are 100% rated in that if you expect your max current output to be 30A DC (12v probably), you can use a 30A breaker and not have to oversize it, they are rated to take the guess work out of how to size your breakers which is nice.

Edit: I tried to find some info on the CC they use (in case it had internal protection which I wouldn't trust even if they said it did) and no luck. Given its pedigree and price (most charge controller add on displays cost more than this thing) you definitely don't want to take any chances. Price doesn't always mean quality but there is probably a good reason they are usually more expensive than this.

[1] [http://blog.gogreensolar.com/2015/02/ac-vs-dc- breakers.html](http://blog.gogreensolar.com/2015/02/ac-vs-dc-breakers.html)

[2] [http://www.midnitesolar.com/products.php?menuItem=products&p...](http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=16&productCatName=)

</comment><comment><USER8> I figured this to be some rinky-dink setup with some teensy pocket solar panel. I mean, $200? Hell, a decent 100W panel will cost you that much.

100W panels are $94 now? Holy crap, if we used more power boondocking I'd cover the roof of the camper with them. But we don't use the power we make now, with a propane-powered refrigerator and LED lighting. And that's the problem with solar, it can power the little stuff, like LED lights or a small invertor, and 100W panels are almost overkill. But get to something like a fridge or A/C for even a small camper, and one will need multiple panels and a big set of batteries.

Nice setup, and I wish them well with their turnkey solution.

<comment><USER9> They mention a swamp cooler in the article, which is surprising. I would expect those to have a big power hungry fan motor that's too much for the panel.

They do say it's a DC based swamp cooler. Looks home made though...more detail on it would be interesting.

<comment><USER8> After a relatively blistering summer here in Seattle, here's something I've considered building for when we leave dogs in the camper: [http://www.mdpub.com/swampcooler/index.html](http://www.mdpub.com/swampcooler/index.html). Eight watts for the fans, and the bird bath pump can't be but a couple of watts. Easily done with a 100W panel, should be able to run overnight with a reasonable battery. That's going to cool a room or a camper, though, and not a house.

<comment><USER10> Isn't the humidity in the PNW way too high for swamp coolers to work?

<comment><USER8> High? I keep an accurate and calibrated hygrometer in the musical instrument room, and it's the rare day when it goes over 50% in Redmond. That said, I've never used one in the PNW.

According to the chart at the bottom of this article, it's not optimal, but it'll take the edge off: [https://www.air-n-water.com/common-swamp- mistakes.htm](https://www.air-n-water.com/common-swamp-mistakes.htm). And for most summers, this one being an exception, our problems with heat are in the high desert east of the mountains.

</comment></comment></comment></comment></comment><comment><USER11> This reminds me of a power box I built for Burning Man this year. The I had ~700W of solar panels, and in a box I put an MPPT charge controller, rather than the PWM charge controllers shown here, I had a 1kW inverter rather than 150W one shown here, but also tried to make most people in my camp use DC when possible, offering 2 USB plugs for each person in the camp, radio charging with a DC-to-DC converter, and a fuse box to prevent accidents. It worked out quite well, and we successfully ran a chest freezer and a number of other things off solar in the middle of the desert for a week.

Also, I used 2x100Ah deep cycle marine batteries + 2 additional batteries of unknown capacity, probably between 50 and 100Ah

<comment><USER3> Does battery type matter for the charge controller? Just learning about the differences between deep discharge lead acid versus lithium in another thread - can the charge controller optimize for battery life of either type?

<comment><USER7> In short, yes. In my experience MPPT and PWM generally are used in similar situations, the difference mainly being in how they charge and MPPT "making the most" of the available power (which is why they tend to be more expensive) and charge the same types of batteries.

Both charge batteries using pulses rather than a constant voltage which extends the lifetime of the batteries compared to a cheap automotive charger that would over time reduce the capacity of the battery), all of which is geared towards lead acid.

Most PWM or MPPT charge controllers I've seen only support lead acid (which come in a variety of configurations, some vented some not) and do not do li- ion, at least not out of the box. Theoretically they have the hardware to do it (my CC can do 12v, 24v, and 48v systems) but maybe not the software.

Lead acid batteries have been probably the most commonly used in renewable energy projects for a while due to their cost-density but li-ion seems like a superior choice if you can front the initial cost. I've been looking at them but also feeling like in 5-10 years there might be more alternatives so replacing lead acid batteries every 5-10 years seems better for me at this point.

</comment></comment></comment><comment><USER12> Refreshingly practical site.

This is exactly why I think solar will beat nuclear hands-down. Solar enables gradual adoption, unlike nuclear's power-plant sized step function. Regardless of the actual price in $/kWh, people like doing easy things.

<comment><USER13> If you're going to be grid free you're going to need some kind of power storage.

So unless you can build a flywheel for $100 you're kind of stuck with batteries.

<comment><USER14> What is the problem with batteries?

</comment></comment></comment><comment><USER15> This article and its predecessor made me think about smaller-scale solar, and I actually bought a 100W panel out of the Amazon gold box last week to start playing around myself.

My first plan is to use the panel and battery to run a set of 12V led outdoor lights, but I'm also thinking about trying to tie into the existing 12V system that I never bother turning on.

That's got me thinking about taking it a step further and adding some capacity to power my Christmas lights this year. Now that they're LEDs as well, it seems it should be possible, but probably not cost effective.

I keep thinking there must be a decent market in between tiny panels powering path lights and a full rooftop system. Like a standalone patio cover or pergola that has solar panels for a roof. That should give a decent amount of power, and it could be an easier sell to people instead of permanently attaching something to their roof.

Actually, I was trying to think of a way to run a small air conditioner from solar—like one of those split systems. The AC could run when the sun is out, which is when the upstairs of my house gets hot. It would be a supplement to my central AC, so I wouldn't be worried about it not running at night or cloudy days. So, I don't need a lot of storage or even worry about tying into the grid.

Again, though, it's probably not cost effective piecing it together, but still the solar patio cover seems like something that should available in a big box at Home Depot or Costco these days.

<comment><AUTHOR> Wow, this is a great point – put a lot into perspective for me. This is exactly where I think there may be a gap in the market too – between path lights and rooftop solar. How to make a business around it without it being straight commoditized to Costco or Home Depot, though? Not that ending there would be a bad thing, but it makes it less of a viable business to build in the US...

</comment></comment><comment><USER16> Some additional data (and comments) From the previous post about the system: [https://news.ycombinator.com/item?id=14821478](https://news.ycombinator.com/item?id=14821478) here.

</comment><comment><USER17> The kit consists of a 100W Pmax solar panel and a 420Wh [edited: this falsley said 420Ah before] deep cycle lead acid battery. The battery is pretty heavy and in the picture the setup is mounted on a car.

Let's keep in mind that a car alternator has 0.5-2kW and you need to burn <0.1l of gas to charge that battery once with the alternator. I'm not sure its worth all the extra equipment and cost to go full solar.

Edit: The solar panel probably gets you 360Wh to 900Wh per day, depending on how sunny the region you live in is. This is not enough to run a household refrigerator, but enough to charge your phones or laptops and some lights.

<comment><USER18> Optimizing for cost is not always the top priority.

For example, when you're camping or at another event with lots of people around. There's nothing quite as abominable as a fleet of autos chugging along in a loud cacophony.

<comment><USER19> > There's nothing quite as abominable as a fleet of autos chugging along in a > loud cacophony.

If you have been to burning man you know there are things way more abominable.

That said, I agree cost is not the priority. Convenience is.

</comment></comment></comment><comment><USER20> Looks like this is a new site.

The previous 'post' focused on apartments was discussed [https://news.ycombinator.com/item?id=14821478](https://news.ycombinator.com/item?id=14821478)

</comment><comment><USER21> I have a desire to use something like this for a mining rig with 4 nvidia 1070 cards, but have conflicted info in what need.

According to [https://www.nvidia.com/en- us/geforce/products/10series/gefor...](https://www.nvidia.com/en- us/geforce/products/10series/geforce-gtx-1070/), the cards pull 150w. But how to know what setup work?

BTW: I live in Medellin, Colombia and have sun like half-day for sure.

<comment><USER22> Energy is interchangeable. You don't need to attach the solar power to the mining rig.

Just use solar power for whatever, and grid power for the mining rid and it works out the same.

<comment><USER21> Ok, but how calculate what I need (ie: How many solar panels, battery, etc)?

</comment></comment></comment><comment><USER23> This is described as "green" but as a portable the panel will never produce as much energy as it took to manufacture it. Taking this deficit into account plus the energy and other environmental harm embodied in the battery, which will also likely be sparsely used, and its doubtful you beat diesel by much.

To truly be green you would either do without or not go.

<comment><USER24> I've always wondered about this logic... Seems like the greenest thing a human could do would be to decompose underground.

<comment><USER25> That's probably true, if you don't want to count your influence on the carbon footprints of other people when calculating your "greenness". You should probably count it though.

So then, the very greenest things you can do probably involve mass murder and industrial sabotage.

Further down the list, after those, you have leading an ascetic life of minimal consumption and minimal travel while devoting yourself to the right sort of political advocacy.

A bit further down is dying underground as soon as possible. But it's important to note that a small amount of advocacy, sabotage, or murder per year can make it a net positive for you to continue living.

Way below all that stuff that nobody wants to do (and who can blame them) are (a) living as a hermit in the woods eating only berries and mushrooms or (b) living a normal life with a normal career and making consumer choices like buying solar panels and electric cars when other people might buy various combustion machines.

If you're not counting your effect on other people, (a) is a clear winner. However, people's consumer choices do have an effect on the direction of the economy. And, if you take those effects into account, I honestly don't know how to decide whether (a) or (b) appears higher in the greenness ranking.

</comment></comment></comment><comment><USER26> Is it safe? Is the battery protected against going under or over capacity?

<comment><USER27> They include a solar controller + battery regulator in the parts list.

<comment><USER13> I don't think the solar controller or the inverter has undervoltage protection.

</comment></comment></comment><comment><USER28> Not nearly as turnkey, but for a little extra fun you can also build your own battery bank from reclaimed laptop batteries. Search youtube for 18650 battery bank.

<comment><USER29> Actually, if you want a (relatively) cheap battery bank for solar, find a place to sell you used golf cart batteries. They are typically 6 volt, but are deep cycle (big and heavy). Wired up properly, they can work really well, and cost a fraction of what new batteries would.

</comment></comment><comment><USER30> How many months / years would it take for this to generate $200 worth of electricity at some normal price for electricity in the US?

<comment><USER22> It generates about 1kw per day. Worth say $0.15. So about 4 years, if you never have clouds.

In the real world I'd probably double that to 8 years.

<comment><USER30> Oh.. so I guess it wouldn't be worth it unless you are away from the grid.

<comment><USER22> Keep in mind part of the cost is the battery, and you would not need that if you are grid connected.

On the other hand the inverter would be more expensive, since you can't just use any old cheap inverter, but you need one that is true sine wave (cheap ones are filtered square wave), and able to phase and voltage match to the grid.

<comment><USER31> People said this on the previous DIY solar thread, but I wasn't sure where to exactly look for one. Could you link me to one that is a true sine wave?

And how would I verify that this works for my electricity provider (PG&E in San Francisco)?

<comment><USER22> Sorry, I don't have any product suggestions. Google for "Grid-tie inverter".

And don't forget true sine wave is not enough, it must also voltage, and even more important, phase, match.

You don't need anything specific to any particular electricity provider.

</comment></comment></comment></comment></comment></comment><comment><USER32> As soon as you get into batteries, aren't you still treading into non-eco friendly waters? I suppose this is more about self-sufficiency, but you're still relying on rare metals that come from questionable sources and are excavated by the same old diesel power.

<comment><USER3> Is the alternative no batteries at all for no power at night/overcast days or is lead-acid OK over lithium or not?

<comment><USER29> Most batteries are made to be recycled. Only a fool throws rechargeable batteries in the trash (not to mention such batteries being bad for the environment disposed of in such a manner).

There are plenty of places to recycle both lithium-chemistry and lead-acid batteries (plus any mercury containing hearing-aid and similar cells). For car batteries, you can usually trade in the old battery for the "core charge", otherwise there are places that purchase old lead acid car batteries and similar.

Virtually everything in those batteries is recycled, and usually turned into new batteries again (heck, I think they ever recycle the sulphuric acid, too).

</comment></comment></comment><comment><USER33> .. I'm guessing I'm not the only one who would be quite happy if someone would do a smaller, lighter, cheaper version of this:

[http://smartflowersolar.com](http://smartflowersolar.com)

Perhaps DIY is the way to go.

</comment><comment><USER34> This would be a really great small-generator alternative for hurricane zones

<comment><USER35> Not much sun in the middle of a hurricane.

<comment><USER36> There is afterwards when you don't have power for two weeks. I sure could have used _anything_ after Wilma in 2005 to beat the heat.

</comment></comment></comment><comment><USER37> To save people some time:

Solar panel can push 100W in. Invertor can pull 150W out.

<comment><USER38> Can you elaborate? I'd love to get 150 joules out of a system I only put 100 joules in to...

<comment><USER37> Time is a factor. You have to charge for 1.5 hours to be able to pull in 1 hour (minus system losses)

</comment></comment></comment><comment><USER39> Why do the green straps appear to be going directly over the panel? Surely that is not the final mount position?

<comment><AUTHOR> The winds in the dust storms were mad strong – I think Sean battened it down with the straps for safety. I still regret not getting a photo when he initially had the panel tipped forwards towards the camera (worse for generation, better for photos...).

</comment></comment><comment><USER40> What if I source the parts from AliExpress instead of Amazon? Should be quite a bit cheaper, right?

<comment><USER41> Possibly not UL approved though.

<comment><USER42> I'd recommend adding fuses. One between the panel and charge controller, and one on V+ to the battery.

<comment><USER7> I would say it is an absolute necessity. Charge controllers have a tendency to fail resulting in a dead short (connecting + to - on the battery, resulting in a fire, explosion or something in between).

I had this happen on a properly wired off-grid system (bad diode) and it would have been quite bad had it not had a breaker of the appropriate size. I would not sleep next to a battery that wasn't fused or breakered.

Reminder: DC systems and AC systems require differently rated components. You cannot just go buy a 30A breaker from home depot for the DC side of your system. It takes a lot more to disconnect DC than it does in AC (because AC cycles to 0V 60x/s it doesn't take much of a gap/insulator to break a connection, DC is not the same. Trying to use a light-switch for a DC light can result in problems [1].

I've had good luck with midnite products (charge controllers and breakers, etc) [2]

[1] [http://blog.gogreensolar.com/2015/02/ac-vs-dc- breakers.html](http://blog.gogreensolar.com/2015/02/ac-vs-dc-breakers.html)

[2] [http://www.midnitesolar.com/products.php?menuItem=products&p...](http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=16&productCatName=)

</comment></comment></comment></comment><comment><USER43> Pretty neat, but how do you get ice to burning man for the swamp cooler?

<comment><USER44> Ice is one of the two things they sell at Burning Man.

(Officially. In reality there are a few more things that they sell, but the 'only two things' label has stuck).

Edit: Also, you don't need Ice for a swamp cooler. You don't even need cold water. The water temperature doesn't really matter, as the temperature drop comes from the evaporation, not the water temperature.

</comment></comment><comment><USER45> Why not use a ups for the battery?

<comment><USER5> Can't efficiently charge from solar, so you need an external charger anyways. Not really cheaper than an inverter. Cheaper ones are not intended to run continuously and may overheat.

<comment><USER46> Also, most will beep annoyingly once the sun goes down.</comment></comment></comment>


What to do when someone copies your startup - <AUTHOR> http://pandodaily.com/2012/07/05/what-to-do-when-someone-copies-your-startup/

<comment><USER2> <http://news.ycombinator.com/item?id=4204911>

<comment><AUTHOR> Good catch. I figured HN would reject it if it had already been posted. Was surprised when it went through, actually.</comment></comment>