A chat app, which gives you X amount of characters to send. The length of the message is deducted from X when you send a message and you need to move around in the real world at walking/running speeds to replenish the characters.
I think this would actually be better as a forum. Flame wars would get you fit!
Citation needed? Symmetric encryption algorithms like AES (with at least 256 bit key) are considered safe even against quantum computers, based on some reasonable math/qm assumptions.
Yeah, so far as I know the only algorithm that provides an asymptomatic speedup (for AES or similar symmetric key crypto) over a classical computer is Grover's algorithm. That would reduce a 256 bit key to 128, which is hardly disastrous.
Not only that, there are asymmetric encryption algorithms not vulnerable to Shor's algorithm, we're just not using them yet (because they're slower and haven't been as well-studied as RSA or ECC).
The community will just do a blockchain snapshot of balances at an agreed upon block and start a new distributed ledger with quantum resistant encryption
What do you do with old coins? Satoshi's one for example? Or lost coins that nobody has the key for?
Do you set a threshold day, after which all unclaimed coins are just marked destroyed forever? If not, how do you know someone claiming some coins didn't use a quantum computer to get the key?
>What do you do with old coins? Satoshi's one for example? Or lost coins that nobody has the key for?
If those coins hasn't been touched for decades, despite widespread announcements of pre-quantum cryptography (presumably it wouldn't happen overnight), it's safe to say that nobody is going to claim them.
It's easy to add a quantum resistant algorithm, but as it's much more expensive to verify and takes more block space, the transaction fees will be much higher. Transitioning is a huge political problem as well.
People just add flags in their mining protocol that only trigger when a threshold is reached. The last Segwit changes needed a percent change of closer to 90% just to trigger the next change.
We are only assuming that consensus would be reached quickly given the scenario presented. It would be irresponsible to design it to need simultaneous action. People would have to considering to stop using the bitcoin network for X,000 blocks while consensus is being reached, and only until it is reached.
It will. But due to the way things work (and here I'm mostly ignorant of the actual physics) the likelihood of this happening (or really for it to scatter against anything else in the plasma) for a high energy lepton is much lower than for a photon of the same energy. So where the old, cooler photons were hitting things locally and providing pressure that was keeping the core from collapsing, the positrons are escaping farther out and allowing the core to collapse.
The range given by Plait in the article at the top for SN 2016 iet is 120-260 M_{sun}, and towards the lower end would be a pulsational pair instability supernova (PPISN) (the "pulsational", the first P of PPISN, part starts to fall off above 130 M_{sun} and vanishes around 150 M_{sun}).
If you're feeling ambitious you can digest Woolsey 2017 https://arxiv.org/abs/1608.08939v2 which is about pulsational pair instability supernovae (PPISNs) and which by coincidence I had on hand because I was reading about LIGO's 50-135 M_{sun} remnant mass gap[1].
The first couple paragraphs of Woolsey 2017 are a good basis for an answer to the question, "what happens to the positrons?", and the answer is that they and the electrons contribute to complicated nuclear fusion chains more centrally within the star.
The central regions in which these gammas are being produced are extremely dense, and maybe it is helpful to think of a piece of some oxygen or silicon nucleus being squeezed in between the e+e- pair such that electron capture "steals" the electron and its part of the gamma's momentum, and the daughter products include neutrinos (which tend to carry momentum right out of the star system, since practically everything in the area is transparent to neutrinos).
In effect, the momentum of a centrally-produced gamma ray radiation kicks inner parts of the star outwards, but when the gamma ray's momentum "condenses" into e+e- pairs, a good fraction of the momentum ends up trapped within denser nuclei, or converted into neutrinos.
The electric charge is very strong so any "excess" positrons will quickly find another electron to annihilate with -- and there are plenty in the star (say, in less-central regions) to meet. The positron will be "pulled" part way up, and prospective partners with the opposite charge will be "pulled" part way down. They're likely to meet somewhere away from the central region, especially if there is a significant positron excess centrally. An annihilation gamma produced much closer to the surface can only lift the surface matter with the gamma's momentum, doing nothing to lift much more next-to-central regions away from the most central regions. Moreover, since the e+e- annihilation gamma can go in any direction, it has a greater chance of pushing less-central regions towards the centre than a nuclear fusion gamma produced very centrally.
Finally, Plait's Bad Astronomy article at the top also links to Plait's earlier https://www.syfy.com/syfywire/the-star-that-blew-up-a-little... which tries to describe PISNs for the readers following the sentence, "What follows is still somewhat hypothetical, but astronomers are working on this problem, and many think this can explain this very odd class of exploding star …"
- --
[1] There's a lack of observational evidence for black holes in that mass range, and if PPISNs are commonplace that might be why they don't exist, as opposed to other possibilities such as massgap BHs exist but their near-regions don't radiate much compared to the background). In essence PPISNs and PISNs reliably throw away enough mass that ~ 55-133 M_{sun} SN remnants are prohibited, and we can only get compact objects in that massgap through mergers or the like. More here https://arxiv.org/abs/1709.08584 if you're very interested, and the two authors are worth an author-search as they are prolific in this area.
The electron half of a pair produced very centrally within a star is very likely to be captured very quickly into a nuclear reaction.
This can produce central regions of pair-producing-but-election-capturing fusion, and a substantial excess of positrons. There are plenty of electrons away from these central regions for these positrons to meet by mutual attraction (and positron-positron repulsion). When they meet they annihilate, producing a gamma which can go in any direction, and which most likely will quickly deposit its momentum mostly-elastically into a nearby nucleus.
Very centrally produced gammas push nuclei outwards from the centre of the star; and the less centrally the gammas are produced, the greater the chance that the nuclei are pushed in some other direction (including inwards).
The chances of collision are low enough that there are few enough of them to fail to offset the now-missing original radiation pressure, which then allows a gravitational collapse to begin and progress.
What do you mean? Taking a guess at answering that, electrons and positrons aren't electrically neutral: they are very very strongly attracted to one another, especially compared to
> gravitational collapse
so the probability of electron-positron annihilation immediately after pair production is in general extremely high! (In lab settings you need strong magnetic traps to avoid that.)
The "trick" in the star's core is to remove the electrons locally, or alternatively to convert the mostly-elastic photon-nucleus scattering with a much more inelastic photon-nucleus scattering.
I've described the former in sibling comments -- oxygen and silicon are present in these stellar cores and aggressively capture electrons. The positrons then are pulled outwards by electrons outside the core, and annihilate there. I omitted that an electron-positron annihilation produces two (or more) gammas rather than one, and that the photons can go in (different) arbitrary directions.
The latter is also an important contributor. The gammas in question are not even close to being in free space. They're in a region densely populated by high-atomic-number nuclei, and the Z^2 contribution in https://en.wikipedia.org/wiki/Quantum_mechanical_scattering_... dominates. If the region were all lighter nuclei (hydrogen, helium) the probability of pair production would be much lower.
Roughly speaking, in the absence of immediate electron capture by the nucleus the pair-producing gamma "hits", the momentum of the gamma is split three ways: into each of the electron and positron, and into the nucleus. Electron capture is in effect just an extreme inelastic collision.
In the no-electron-capture case, the heavy nucleus, having absorbed the "recoil" proportion of the gamma into its internal degrees of freedom, has several ways to get rid of that momentum, re-emission of one or more photons with lower energy than the gamma, or transmutation (which might produce neutrinos).
If the electron and positron pair immediately annihilate, they do so minus the "recoil" energy to start with; additionally they produce more than one gamma, and in arbitrary directions. Consequently, there is less momentum available for subsequent elastic collisions.
If the Japanese, with their image of professionalism, smartness, ultra advanced technology, and total dedication to their job failed so spectacularly to manage a plant, nobody will believe any safety promise anymore, at least in places where people are asked about it (ie: not China)
Now add the Chernobyl TV series on top, it will be replayed and memefied everywhere a plant is proposed.
Of course, this being HN, I welcome the incomming ban.
> "If the Japanese, with their image of professionalism, smartness, ultra advanced technology, and total dedication to their job"
You're just cherrypicking positive stereotypes while ignoring negative stereotypes relevant to the matter, such as the trait of not making waves with your superiors and papering over problems to avoid embarrassment. These themes are explored in Shin Godzilla, which was a huge commercial success in Japan, undoubtedly because the Japanese public recognized some truth in how the movie depicted government incompetence in Japan.
I see your point, but I think the original point still stands - even if we take into account the shortcomings of Japanese business culture, what developed country is without its fatal flaws? In other countries, especially less developed ones, they might lack the negative stereotypes of not questioning superiority because they're too busy fighting worse stereotypes like greed, incompetence, or ignorance. What threshold of perfection does a country have to attain before it can be trusted to utilize nuclear power? And I would say Japan does set a pretty high bar when compared with most of the rest of the world.
In Japan they shut down each plant yearly for inspection. Everywhere else it's done on the refueling cycle. The plant I worked at was on a two year cycle so each year one of the two plants shut down for about an 8 week refuel/overhaul outage.
2 Japanese business culture is very deferential and top down. The amount of lying and covers ups around the Fukushima disaster was and is horrifying. Having worked for Sony I can say that there is an awful lot of dead wood in Japanese class system culture just as there is in the English class system, and that is not a healthy way to run something potential deadly on a global scale.
I'm on the fence about nuclear power largely because of the above. It's not the technology, it's human and bureaucratic fallibility and greed that is the weak link
That's fair enough but shouldn't you have the same hesitancy about say, solar panel production or coal mining or oil production or wind farm installation and maintenance? All of these can be just as deadly and potentially more polluting.
True, no one died, but it was immensely expensive. And that is important because one of the main selling points for nuclear is that it is supposed to produce electricity cheaper than any other source.
Total nonsense, Fukushima was designed in the 50s only around 15 years after we first invented nuclear power and then started construction around a decade after that using that old technology. It is like using a Model-T as an example of why cars are too dangerous to use. Or judging flight safety based on wood and canvas planes.
> Computed risks for new reactors are lower than for current designs "when only internal events are considered," according to a 2009 report that the Nuclear Energy Institute wrote for the NRC. (That includes fires or pipe breaks, for example.) But when risks of damage caused by external events — earthquakes, for example — are factored in, the new reactors are no safer than older reactors. In addition, because utilities have no operating experience with the new reactors, the probable risk assessments are purely theoretical and not as reliable as years of actual operating data from existing plants.
> The new designs are engineered only to withstand a predictable sequence of events, something engineers theorize may happen. In nuclear parlance that is called a "design basis accident." The new reactors, like their older counterparts, are not designed to survive an unexpected sequence of events. That is the critical flaw, says Lyman: "Three Mile Island was a beyond-design-basis accident."
>Now add the Chernobyl TV series on top, it will be replayed and memefied everywhere a plant is proposed.
btw are there other people who thought the show was really awful? I know this is a contrarian take but the constant <dialog about soviet doublethink> every three minutes was about as subtle as a sledgehammer.
About half an hour into the first episodes I was like, yeah I get it these people lie a lot to save their own skin. And while I'm not exactly crazy about physics correctness, the way it radiation was dramatized was just unnecessary, a pregnant woman isn't suddenly going to die or get birth defects from standing next to someone was exposed to radiation. The show gave the whole incident the flair of a zombie apocalypse.
the wikipedia article claims that the child's illness was radiation induced but the provided source does not.
Just to give you an actual statistic rather than anecdote, among Hiroshima bomb survivors the incidence of birth defects was about 0.9%, or about 500 children in total. I'm not entirely sure how trustworthy this story is.
I didn't downvote you, but I'm quite surprised by that remark. Say what you will about HN, but it seems to me it's damn near the only medium in the world that mostly doesn't use censorship to control the Overton window, that is genuinely quite open to contrarian views. (As seen in this discussion, where there is vigorous debate going on.)
If there's one thing you probably shouldn't lecture France about, it's nuclear electricity production and its environmental impact : https://www.electricitymap.org
Those definitely didn't help, but the Chernobyl disaster and fear have been handicapping nuclear energy for decades. It was a big mistake (wrt climate change) that we didn't invest a lot more in nuclear technology.
Not really, parsing JSON is probably a recursive algorithm and Windows gives processes way less stack space than Linux (generally 1MB vs 8MB). It could totally be that the code is the same, but the particular JSON string blows up the stack in Windows but not Linux.
Eh... not really if you're referring to call stacks. Rust at one point had growable stacks. That was removed for performance reasons. Haskell with GHC kind of has growable stacks (basically IIRC most function calls occur on the heap) and its stack overflows take a different form. SML I think at one point also had an implementation with a growable call stack.
If by limited you mean limited by the amount of memory your machine has then yes it's limited, but I don't think that's what parent was getting at, since in that sense everything about a computer is limited.
Mainframes used to explore this long ago, leveraging different microcode for different workloads keeping the hardware of processing unit the same, https://en.wikipedia.org/wiki/ZIIP
On the other side of the computing spectrum, there were a couple of papers in 2010s about offloading most common mobile tasks (like CSS layouting) to the specialized mobile CPU subsystems. Maybe this should have been implemented if Google made their own mobile CPU.
For once, it needs to be an attractive number for Denmark, more attractive than the unknown, but probably huge future value of such a big uninhabited place. $5T is about 12 years of Denmark GDP, and 10-20 times earnings is a good company acquisition price metric.
We are talking selling it forever. Just think how ridiculously cheap previous land purchases (Alaska, ...) now seem in hindsight.
Denmark is not really in the position to really use that place, even in the future. The only thing they can do with it is sell it, so the question becomes when and for how much.
Timing is also important. Apparently Greenlanders don't feel very Danish. At what point in a rise to prosperity would they simply demand independence? Not even a sale, just Greenland being its own independent nation. It'd be unseemly for a modern progressive state like Denmark to demand tribute in exchange for freedom.
If I'm a superpower with plans for Greenland, using the usual tricks to create unrest that leads to calls for independence would be a likely first step.
> "Denmark is not really in the position to really use that place, even in the future. The only thing they can do with it is sell it, so the question becomes when and for how much."
Greenland is a dependent territory, but it is not part of Denmark. I invite you to review the right to self-determination as enshrined in the charter of the United Nations.
It would ultimately be up to the people of Greenland whether they want to "sell" their country. Not, according to the principles of the UN, something that Denmark could do unilaterally.
Well here's the premise that nobody is talking about -
If China continues to ascend toward military superpower status and they aggressively press on a position regarding Greenland, the US will invade Greenland to secure the territory.
The US has been willing to invade all manner of foreign nations over the past ~75 years for varying reasons. The idea of China occupying Greenland militarily in any manner will never - not under any circumstances - be tolerated by the Pentagon and politicians in DC. Greenland is a militarily critical territory for the US superpower. The US military will invade and occupy Greenland, against the protest of the EU, Denmark, Russia and everybody else. It'll be argued as a national security matter of utmost importance and that will be the justification. They'd also say it's temporary (it wouldn't be). It'd be an annexation in everything except for name.
The US will take Greenland for $0, outside of the cost of occupation.
edit: people will downvote this because it's so upsetting. I understand. Back in reality, it's by far the most likely scenario in the next 30 years. The US paying $5t or $10t? It would never happen. Why would you do that if you're a military superpower, when you can trivially invade any time you want to, under any pretense. The US went into Vietnam and fought in a civil war that wasn't its own, a war that killed millions. But the US won't invade Greenland (a whopping 56k people) and occupy it, to keep it from China (a new military superpower setting up shop right up the street from the US)? Yeah right. An interesting part of this, is that the same people that think the US is an evil superpower, will pretend this isn't the obvious scenario that is going to happen (we'll go into Iraq, but not Greenland, etc). The US will declare that it's necessary to keep Greenland and its people safe.
Here's the propaganda bumper sticker for when it happens: Keep Greenland Safe! Short & easy to sell to the American people, it'll be on every truck.
Greenland is a NATO member and, via Denmark, represented in the European Union. Greenland ain't worth picking that fight over. China won't invade it for much the same reason.
There would be no fight over it. It's a territorial protection maneuver to protect Greenland, led by the US.
US media combo military industrial complex headline: US does the security job that some NATO members refuse to do.
The PR push would be that it's not an annexation. It's not an occupation. It is temporary. It's about keeping Greenland safe, defending Greenland.
The representation at the EU via Denmark is meaningless. Neither Denmark nor the EU have any military power to stop the US from doing this. The US will easily be able to muddy the water enough politically by leaning on allies in Europe like Poland and Britain, to argue that it is in fact important to keep Greenland safe. In the end nobody will really do anything to stop it.
Which part of NATO is going to fight the US to stop this exactly? Right, none of it.
You know how batshit crazy Iraq was? 10x more so than what going into Greenland would be by comparison. And yet the US won't do it? Of course it will, if it thinks it needs to in order to prevent China from setting up there militarily. There are countless ways to spin it, to play it, in order to get from point A to point occupation re NATO.
Why invade? The Navy would just form a blockade to prevent Chinese ships from approaching if it ever came to that.
China has zero force projection capability outside of Asia. Their is no chance they are pulling off an invasion of Greenland anytime in the foreseeable future.
Also we already have an Air Force base in Greenland--there is no realastic scenario where a US invasion is necessary or even useful.
"Nope we aren't leaving. Any attempt to force us to leave will be seen as a hostile action, as will any attempt to establish a Chinese military presence."
