From the abstract of the paper, energy equivalent to three solar masses were radiated away in gravitational waves. That's a simply incredible amount!
Possibly stupid question: Given how far away it was, and that the inverse square law applies, would the effect of these waves be visible on the human scale if we were closer? We can see the effects of the compression of spacetime with LIGO after all, so presumably we could?
This thing was a billion light years away. Say it were closer; let's put it at a single light year away.
LIGO measures wave amplitude, as far as I can tell, which goes down linearly with distance (unlike wave energy, which goes down quadratically, since it's proportional to square of the amplitude). So we could expect to see an effect about a billion times bigger.
The detected effect was a change in metric of one part in 6e20 if I'm not mistaken: (4e-3 * (diameter of proton))/4km based on the article's claim of "four one-thousandths of the diameter of a proton". So at one light year distance we could expect an effect of one part in 6e11.
Not really visible on the human scale, seems to me. You could detect it easily with something like the Mössbauer effect, I expect. Your typical lab bench laser interferometer has errors on the order of 1 in 1e6 as far as I can tell, so probably wouldn't be able to pick this up.
Disclaimer: I could be totally off on what a lab bench laser interferometer can do. I'm pretty confident in the rest of the numbers above.
On the other hand, we may well detect the 3 solar masses radiated away as energy. That decreases as an inverse square law, so as one solar mass is about 10^30kg, and 1kg gives off about 10^17 J, we're talking about an explosion releasing something around 10^47 J. For comparison, a 1 kiloton nuclear bomb gives off about 10^15 J.
So, inverse square that explosion... 1 light year is about 10^16m, so we square that and get 10^32m, so we're now talking about ... 10^15 J.
So, unless my maths is all off (which is possible), if this happened about a light year away, whoever's on the side facing towards the blast wouldn't get to observe very much because they'd feel as if a 1kt nuke just went off above their head. Not a great way to start the day.
Chances are it would wipe out life on Earth too, through the ensuing side-effects like lighting the atmosphere on fire, sterilising half the planet, significantly heating up the oceans, possibly even stripping part of the atmosphere away, etc.
For a great novel based around a strikingly similar premise to what was just observed (and the main reason I even bothered to calculate this), Diaspora by Greg Egan is a fantastic book.
The big question is how much of the energy would get transferred in practice.
I agree that 3 solar masses worth of electromagnetic radiation at 1 light year distance would feel like a nuke going off. What I don't know is to what extent the energy of the equivalent gravitational waves (which _would_ have a lot of energy I agree) would actually get transferred to things we care about, like the atmosphere and us. If it's a few percent, say, we'd clearly be in trouble. If it's more like what neutrinos do, it would probably be detectable but probably not by unaided human senses.
I tried doing some quick looking around for estimates of gravitational wave coupling and energy transfer and didn't find anything so far...
I would like to understand why a gravitational wave distorts length in relation to normal gravity wells; specifically is this particular to waves? Why don't lengths get distorted in a normal gravity well, or do they? In essence, what is different between a gravity wave and a gravity well, which i understand both distort space, but only the wave distorts it in a way we can measure? Does the gravity well change lengths proportionally in all directions and thus isnt measurable?
A gravity well also distorts lengths, as best I understand (which is not very well, to be honest; take everything I'm saying here with a big grain of salt).
The difference in terms of detection is that the wave does this in a time-varying, periodic fashion.
For something like LIGO, we're trying to measure length changes on the order of 1e-18 meters. We're not actually measuring the lengths of LIGO's arms to that accuracy, though. What we're measuring is the difference between the times light takes to travel down those arms. And even that's hard to measure on an absolute scale, so what we really measure is how that difference changes in time.
Or put another way, the effect of Earth's gravitational well is not really distinguishable from inaccuracies in making the two legs of the interferometer equal length to start with, and is a much smaller effect than those inaccuracies. Again, if I understand this right...
Actually, we have ample proof of the distortion of spacetime in a gravity well - gravitational lensing. It's an observed effect around very massive objects and we have been able to see it at work very well. Also, arguably, the fact that we're not falling towards the sky is itself evidence of a spacetime gradient near the Earth, but that was also explained by Newton's Law of Gravitation.
But back in 1916, Einstein also theorised, as part of his general theory of gravitation, that there would be such things as gravity waves, caused by very massive objects moving through spacetime making 4-dimensional ripples appear in spacetime. Until today, that was just an unproven theory, though everyone believed it was likely to be true. There is now solid evidence to back it.
Agree... my question, though poorly worded, is less about proof of spacetime gradients (they do in the ways you describe).
It's more about understanding what the measurable effects of a gravitational well on earth has on the LIGO experimental setup (or a similar one with infinite precision), in the absence of gravitational waves.
Well, something like LIGO can only measure gravitational waves, because it looks for changes in the geometry of spacetime. If you were to move the LIGO in and out of Earth's gravitational well, I guess then it would record a shift.
That is a good point - perhaps it would all come out as neutrinos or gravitons... then we'd be fine. I doubt such an event would result in no electromagnetic radiation at all however... Why would it? The creation of a new black hole typically releases enormous amounts of all kinds of energy, electromagnetic as well as in the form of neutrinos.
The energy was all dumped into the gravitational waves we detected, not into electromagnetic radiation: Gravity waves don’t interact with matter very much (the cross section of the graviton is believed to be extremely small) so the quantity of energy transferred to matter as the wave passes through is likewise extremely small. I haven’t run the numbers, but I’m not sure you’d notice this even from a light year away without fairly sensitive detectors.
What I didn't understand after reading the article is how do they separate out a set of waves for one specific thing vs. the many other objects sending out waves. Is it just that the set of blackholes are the strongest set of waves and thus the ones we can detect?
That, and the high frequency. For example, the Earth orbiting the Sun produces gravitational waves at a frequency that's about (factors of 2 and pi here and there) the orbital frequency; order of 1e-8 Hz. The black holes were producing 250Hz waves if I read the article right.
The longer the interferometer arms, the better you can do in sensitivity. The reason LIGO has 4000 m long arms is that it makes the experiment 4000x more sensitive than something you can do on a bench. (and their laser stabilization is excellent, improving things further)
Sure, but LIGO is sensitive at something like 1 part in 1e20, which is a lot more than 4000x better than 1 part in 1e6. I agree that their laser stabilization is likely much better, their vacuum is likely a lot better, etc. I was just surprised by how much better, I guess; 10 orders of magnitude is a lot.
Part of the reason for that is that LIGO isn't exactly a Michaelson interferometer in that it has an extra pair of mirrors in each arm. If you look at this schematic  then in a traditional Michaelson interferometer you would only have the mirrors that are at the end of both arms.
With LIGO there is an extra set of mirrors within the arms this allows the light from the laser to bounce between them ~100 times or so increasing the effective path length greatly.
The energy is dumped into gravitational waves rather than electromagnetic radiation & they don’t interact with matter much. I’m not sure you’d notice it happening in the same galaxy unless you were looking for it.
I agree, I'm also not at all a fan of in-browser apps. The benefits all seem to accrue on the maker's side: faster deployment & distribution, single codebase for multiple platforms, assurance of common versions across the user base, and not least easier and more complete monetization. The drawbacks are all for us users to suffer: idiosyncratic UX, unpredictable performance, poor interoperability with other apps, limited offline use, everything's gone if the company fails.
That was interesting, and a surprising result. Thanks for sharing.
There is a bit of magic: the Epstein Drive, allowing for 1G continuous acceleration 'torch ships'. IIRC if they're gone I don't think it breaks the plot much, but without them it's hard to imagine that there'd be quite such a thriving solar system society; it'd be much less interconnected and a much smaller economy without the ability to support large-scale stations by shipping large volumes of necessary supplies (e.g. ice) around easily.
The texturing just helps your eye "fill in the gaps." As far as difficulty, I just don't know of a general way to do it. The only thing that comes to mind is some sort of iterative approximation or something.
If I understand correctly, we want to compute co-edges here. I believe there are algorithms to do this, I know SketchUp has this feature ; also Gmsh ; and I remember seeing Blender plugins that do the same thing (can't seem to find them now...) (edit: Actually Blender does this without plugins: "Join" 2 intersecting objects, use the "Intersect" feature, and it will generate and select the exact co-edges.)
unless you're dealing with sufficiently large integers computing the intersect between a line and a plane with any robustness is impossible on modern computers with float or double. sometimes when you intersect meshes that have nearly coplanar faces, the intersection might shoot vertices near some infinity because of division inaccuracy.
I actually think that's rather magnificent. Mr Whiny can't have his toy anymore. Yeah it's bad PR, probably, but I can't be the only one who thinks these rude blog posts directed at well-known strangers saying variations of 'dear so-and-so you should be ashamed of yourself' are a bit tasteless, crass, and low class.
I mean, the VC wrote his original post as a direct personal attack and then distributed it in public on a widely-read platform. That's pretty nuclear. In ascending order of severity he could have:
- Contacted Tesla directly
- Written to Elon Musk directly, privately
- Written a blog post about his crappy experience at the event
- Tweeted Elon with a link to his blog post
All of which might have made him feel better about wasting his evening and maybe got him some compensation (jumping a few places in the waitlist, or something) while not being actually offensive.
The best part is that he wasn't even "banned by Tesla," he cancelled his order out of spite and so he could thrust himself into the spotlight again.
Honest to god, some people are insufferable blowhards. Sure, the event started late, sure Elon might have acknowledged that, but if he thinks that (a) any of this matters enough to write TWO articles about and (b) that anyone really cares what he thinks, he's deluding himself. Moreover, he just looks like a complete fool for posting this kind of garbage and expecting a positive response.
Wait, what? He as in the VC author cancelled his own order? Oh man. I read it as Elon instructed Tesla to cancel his order.
Edit: I think I was right. Here's the direct quote from first paragraph: I also hear that you are not comfortable having me own a Tesla car and have cancelled my order for a Tesla Model X. Maybe you read a phantom "I" between 'and' and 'have'?
Well this is prima facie bad, but actually we're not in such a terrible spot as a society: the bulk of supermarket chicken and beef might be corn-fed, bland, watery mush these days, but it's a hell of a lot cheaper than it ever used to be, and that means that a wider segment of the population can afford reasonably good meat on a regular basis. Better nutrition means healthier kids who can do better in school, and you know the rest. The stuff isn't bad, it's just not as good as it used to be. But neither is it as exclusive as it used to be either.
Those of us with more money still have the option to buy tasty, grass-fed beef steaks from niche producers. It takes more effort of course. Quite often I find that arguments against bland, cheap, tasteless food are really about unrealistic people expecting cheapness, high quality, and great convenience. You can't have all three!
Of course, it is good to have realistic expectation and not bite the hand that literally feed you. But were comes this above reproach that the food industry enjoy ?
> Convenience, High Quality, Cheapness you can't have all three.
What about ... everything else that is usually discussed here on HN.
The food industry is as bad as the oil, banking, car, movie and music. It is generating a enormous amount of money, concentrated in few hands, is repeatedly involved in scandal, benefit from opaque government protections and regulations. There is 0 reason to think that the food that reach our table, is anything close to an optimum.
It's true but it still means we could do better by trying to optimise for nutrition value as well - which seems to somehow hidden from us. You often don't taste or see nutrition value.
Also what does it mean for food recommendation if one strawberry has completely different vitamins/minerals/etc than the other one? Eating strawberry A and B means completely different things now. "One fruit a day" or "One cheap fruit a day + supplement pill"?
Well, we've optimized for yield (=> cost) exclusively. Taste and nutritional value are other axes. In a way you're saying the same thing as the article - that it's a shame to focus only on yield.
To answer your question, I think its important to first understand whether the nutritional gap between zero strawberries and modern strawberries is much greater than that between modern strawberries and old-fashioned low yield tasty strawberries. My opinion (worth nothing of course) is that it's better to have some fruit than no fruit, and high yield, cheap produce allows that.
I remember when I was a kid (Back in my day :-)) roast chicken was an expensive Sunday treat. Then at some time they become really cheap and you could eat chicken whenever you wanted. Now no one bothers roasting their own chickens, they're all cooked for you.
Funny thing is roasted chickens are a loss leader and often cheaper than the raw ones. If I could get an organic pastured chicken preroasted as a loss leader I would, but usually the $5 bird has broken bones and a weak taste.
Depends where you live I suppose, Have a couple of local chicken shops that make great roast chickens, and of course supermarket ones nearby. I'm in Australia though, and I suspect our experience is different from the US.
The headline is "Toronto family ditches the city for old school fixer-upper in country" (at least in the <title>) and the tagline says "the obstacles they overcame in moving to the country." It seems quite clearly to be talking about a family who moved from Toronto, the city, to the country, not that their endpoint is in the city.
That's a 1.5 hour drive from Toronto, not even considered the Greater Toronto Area. I am sure the Globe is putting them under the Toronto umbrella to get views; who the hell could afford to do this in Toronto... oh wait it's not Toronto, but you already gave them your traffic.
See my comment to your parent. I don't think it's about getting more views, when talking about a transition from city to country. In the second paragraph: "They had been ruminating for years, however, about leaving Toronto for a more free-spirited life in the country with their three young daughters."
Americans just assume that in Canada, taxes are slightly higher, corruption in local government less prevalent, and land use restrictions less severe.
Of course, some of us may also believe that Canadian taxes may be paid in maple syrup, Molson lager, or ketchup chips, and that the revenue agency is required to sincerely apologize for every remittance accepted.
As a national aggregate, we don't get out much, even to visit the neighbors.
My question was based on the opposite actually: I had an assumption that US property tax would be higher, building code more strict, and zoning laws less permissive. I just felt like buying a gigantic old school and living in it would be a massive administrative pain in the backside in the US, but sort of a nicely achievable bit of whimsy in Canada.
(I'm British, but own property in the US, and I'm staggered by the size of my property tax bills here vs. the UK, and more so by the sheer number of permits I have to get for doing trivial work I'd tackle myself in the UK).
Americans love burdensome zoning laws. They appeal to our inner racist. Unfortunately for them, buildings like schools, fire stations, and police stations are usually in residential zones anyway. The major problem in the US is that there's just no way you would be able to set up a bed and breakfast as easily as the article implied.
Our property taxes vary wildly in the US. One place, you might pay 3% of the fair market value, and in another, only 0.25%. Or maybe the assessment value is restricted by some formula. Maybe it's reassessed annually, or maybe every 3 years. There's really very little consistency, because property taxes are usually assessed locally and the major service provided from them is the local public schools.
Building codes between Canada and the US are pretty much the same. In either place, there's a "model code", but each locality has to adopt it explicitly for it to be in effect. Some places adopt it without modification, and others amend it heavily. A Canadian town could adopt the American model code (called the international building code, of course) if it wanted to, or vice versa.
But for the most part, they have nearly identical intent, even if the implementations are far apart. As long as you hire local contractors for the work, you shouldn't need to know the particular variances in the building codes. Either way, you won't be allowed to do anything serious without a work permit, and someone will inspect the heck out of it.
(Of course, the permits and inspections are often ignored for DIY work.)
I doubt you would even be able to buy an old public school building in many places in the US. Perhaps in Detroit. Most local governments would rather board it up or use it for administrative offices than sell. You would have better luck finding an old church.
In the firm I work for, we deal with much secret information and many paranoid clients. Generally when someone is terminated we give them a severance contingent on signature of a pretty ironclad non-disparagement letter and a further reinforcement of existing NDA. You could extend this concept to this situation, crafting a letter such that if he does ever leak that data, his liability is assured and his incentives are aligned with yours.
This is a time to spend a bit of money and speak to your external counsel. They will have a good solution for you.
To me, non-disparagement agreements are an instant red flag that a company is doing something heinous. I don't think anyone has problems with NDAs, but when I see non-disparagement, that instantly translates to "We know we're doing something really shitty, and you'd be right to warn others about us, so we're going to threaten you with our lawyers to keep you from talking about it."
Eh, when they're dangling several months salary in front of you, signing a non-disparagement is a pretty hard thing to pass up.
Regardless it's pretty juvenile and self-destructive behavior to go around disparaging an employer for firing you to begin with. Getting a cash bonus for the self-censorship a rational adult should be exhibiting anyhow, is not such a bad thing
I want to make sure it's understood that I was recommending OP use the concept of tying a severance payment to signature of a legally binding document that serves the company's interest, not that non-disparagement or NDA were the right tools to use in this instance.
Onto your specific point, N-D is not unusual for senior employees with strong contacts in the company's target market (like e.g. sales & project management). They're not necessarily a sign that the company is doing anything shady, but they are a strong tool for preventing disgruntled former employees from saying bad things which might hurt a business. They're pretty aggressive, granted, but they serve a purpose. Most people's umbrage can be satisfied for a price.
A N-D keeps you from saying anything that a court might rule is negative regardless of truth.
For instance if I say, "I liked working at Company X but I think the CTO lacked leadership skills/vision" that's disparagement. It subjective/opinion, but assume you have factual reasons you could use to back-up how you formed that opinion.
Retaining him - rewarding him, even - in contravention of company policy seems to create a great deal of liability for the firm if there is any PII leakage. "My client's personal data was stolen from your firm, and we found that you have this employee, who had the client database on his home laptop, but you didn't fire him? Here's a lawsuit."
hey, id like to fire you, but you have sensitive information on your laptop, so instead im promoting you to the position of data security, and your job is to create and enforce policies so i never get in this situation again. consider yourself lucky.