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From: Rowland McDonnell on 5 Mar 2010 15:24 Chris Ridd <chrisridd(a)mac.com> wrote: > Richard Tobin said: > > > chris <ithinkiam(a)gmail.com> wrote: > > > >> I was wondering why they used a signed int. An unsigned int would have > >> been more sensible, but the error checking makes sense. > > > > Why wouldn't you want to represent dates in the past? > > You're never going to be able to represent arbitrary dates using a > built-in integer type. I don't see why not. 64 bit unsigned integers go up to: 18446744073709551616-1 http://en.wikipedia.org/wiki/Age_of_the_universe entertainingly states that the age of the universe is: 13.75+/-0.17 billion years old. So call it 15 x 10^9 years. Or 15 x 10^9 x 365.25 x 24 x 60 x 60 = 473040000000000000 seconds. Which is more than 64 bits. So why not try 128 bit unsigned int: 340282366920938463463374607431768211456-1 So you can fit 38 universe-lifetimes in, using a 1 second resolution clock and a 128 bit unsigned int. Isn't that good enough for arbitrary dates? If you want more resolution, use a 256 bit unsigned int. btw, I've no idea how commonly available big ints like that are - but the fact that a mere 128 bits is enough for 1 s ticks and 38 universe-lifetimes-so-far-by-latest-big-bang-theory-models convinces me that you're not right on that one. > Use struct tm instead. For all I know, that makes more practical sense - but at bottom, even that uses integer data. It's all binary integers at bottom. 1 or 0. Hi or lo state. Tick or tock. It's all these computers have when you get down to it. Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking
From: J. J. Lodder on 5 Mar 2010 17:46 Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > J. J. Lodder <nospam(a)de-ster.demon.nl> wrote: > > > whisky-dave <whisky-dave(a)final.front.ear> wrote: > > > > > "J. J. Lodder" <nospam(a)de-ster.demon.nl> wrote: > > > > Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > [snip] > > > > >> No-one understands time, not yet. > > > > > > > > Because there is nothing to understand. > > > > > > yes there is, the idea that time only travels in one direction. > > > > Irreversibility is well understood. > > <howls of laughter as Rowland rolls around on the floor> > > Crazy Dutchman. > > Have another Grolsch. It's not my fault that you don't know what you are talking about. > Engineers worked out entropy maths in the 19th century. They /thought/ > they had it understood. That's thermodynamics. And they -did- understand that. > Then the 20th century came along and taught > them differently - but the steam engines still work so the engineers can > still pretend that `Irreversibility is well understood'. Engineers had nothing to do with it. Boltzmann and Ehrenfest cleared up the statistical mechanics of irreversibility, around 1900. Jan
From: J. J. Lodder on 5 Mar 2010 17:46 Peter Ceresole <peter(a)cara.demon.co.uk> wrote: > J. J. Lodder <nospam(a)de-ster.demon.nl> wrote: > > > > Not at all. Entaglement is *not* standard quantum mechanics. That's the > > > whole problem. > > > > But it is. > > Only in a very limited way; the greatest problem with it is the > simultaneity of the effect- the breaking of the lightspeed limit. Entanglement is a consequence of standard quantum mechanics. And no, it doesn't violate causality, Jan
From: J. J. Lodder on 7 Mar 2010 04:37 Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > J. J. Lodder <nospam(a)de-ster.demon.nl> wrote: > > > wRowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > > > > > Peter Ceresole <peter(a)cara.demon.co.uk> wrote: > > > > > > > R <me32(a)privacy.net> wrote: > > > > > > > > > > Well, checking Palm desktop running (very nicely) under > > > > > > OS10.4.11, in mid-Feb 2040 it wraps round to 1904. > > > > > > > > > > That's true of real time, too. Physicists haven't noticed. > > > > > > > > They probably have- or they've seen it but not understood the > > > > significance... > > > > > > No-one understands time, not yet. > > > > Because there is nothing to understand. > > You know so much, you are god, perhaps? Because only a god could know > that. > > > > Hell, no-one understand gravity and > > > it's a damned sight easier to investigate than time. > > > > That's the hard one. > > > > > > I absolutely love entanglement, for instance, which proves that we > > > > really haven't got a handle on what our universe is like. > > > > > > I think you'll find that a lot of modern quantum mechanics are getting > > > there these days, or at least, getting a handle on the next stage - none > > > of them are daft enough to think that the next stage is the last one. > > > > > > Once upon a time, Richard Feynmann's point that anyone who thinks they > > > understand quantum mechanics, doesn't - that was true. > > > > A much abuse quote. > > Feynman's idea was not to provide an excuse > > for all kids of obscurantism. > > <puzzled> What, and you're a necromancer and/or mind-reader now? Just reading Feyman. > Or did you write that just to provide a wee bit of a put-down for > Rowland so you could annoy him? > > I really don't see that you're getting at anything here, except > attacking the messenger. > > But: Feynmann's idea was that the Copenhagen interpretation (approx: > shut up and calculate) was the best available. All the words didn't > work. Only the maths worked. The Copenhagen interpretation is not 'shut up and calculate'. > The idea is to blow away all the obscurities of human language when > applied to QM, because the only language that worked was maths. And, of > course, the Feynamnn diagrams for which Dickie boy got himself a gong. That's quantum electro dynamics, not quantum mechanics. > > > But since I left > > > university in 1990, an awful lot of new thinking has turned up and I > > > have an idea that the old cop-out Copenhagen interpretation (grossly > > > simplified: `Stop talking and do the maths') isn't going to last much > > > longer. > > > > That's not Bohr, it's also Feynman. > > What? What Bohr said was rather long-winded and frankly a bit hard to > understand. Feynmann and others tried to precise it and came up with > things such as the quote above. > > - Bohr wasn't a great communicator as was Feynmann. They adressed a different audience. > > He jokingly paraphrased Mussolini as; > > 'BELIEVE! OBEY!! COMPUTE!!!' > > > > > The thing is, anyone who's thinks they're barking up the right tree in > > > interpreting "what `reality' `really' `is'" sounds like a lunatic who's > > > been at the LSD - when heard by normal people. Certainly, the ideas > > > expressed by modern physicists does result in them meeting most of the > > > tick-boxes for a diagnosis of psychotic. > > > > You are projecting? > > You are a clinical psychologist, perhaps? Or is it that you're just > making a baseless pejorative remark to undermine the perfectly sensible > points I'm making by attacking me personally? YOU were attacking (almost) all modern physicists, putting them away as psychotics. So don't complain about replies. > Oh yes, that'd be it. > > > > I can't follow the detail, but I do find the battles fascinating to read > > > about. Einsteinian relativity is due to be shot down in flames any day > > > now - but I'd not bet on what'll replace it. There's the string > > > theorists and the Modified Newtonian Dynamics crowd both with a case > > > that's looking more and more testable every day. > > > > That's what they have been saying for 50 years now. > > No, that's just the false claim made by those who wish to attack the > people doing the work. It's the sort of thing that gets said about > those who like to knock all new efforts, and do down anyone trying > anything a bit out of the ordinary. Then let them show a physical result. > Actually, the truth is that both groups have been saying that they've > got nothing testable until very recently - I've no idea why you claim > otherwise. I agree. Hence my comment that string theory has been a failure so far. > And from what I recall, MOND hasn't been in existence for 50 years. > Didn't it come from Hoyle's starting point? Turned up quite recently, > IIRC. > > > In fact the opposite is true: > > string theory has been a miserable failure. > > That's an absurd idea that could only have come from a person who > doesn't understand either string theory or how physics and maths make > progress. There is no progress, and no result. > String theory is *still* intellectual masturbation because it's not yet > produced testable anything that I've heard of. I've even heard a notable physics nobelist call it a pseudo-science. > But the last thing I heard, the state of play was now `Not produced any > /practically/ testable results yet' - they've got the point where there > are tests that could in principle be done, if only it weren't so bloody > difficult. They are not even capable of retrodicting what we know already. > They've got there, very nearly. It can take a very long time before the > start of this sort of process and something useful. The fact that it's > taken decades already doesn't mean a thing. In their misery they are falling back on anthropic principles. > Even if no tests of string theory ever get made, it's not been a > `failure' because in the last N decades, they've developed a huge range > of new mathematical tools and new ways of addressing mathematical > problems. Mathematics /= physcs. > So string theory can be both a complete wash-out in terms of describing > the world while /also/ being damned interesting to mathematicians. Who > will probably eventually come up with a way of applying it to the real > world - and then totally lose interest in what will have become mere > applied mathemtics... Zero results so far. > > > ... which means it'll be something else that turns up and takes over, > > > I'll bet. > > > > One may hope so, and enough OT for now, > > Jan, you really should learn how to stick to the topic rather than > getting personal. Huh? > There was almost nothing in your reply that wasn't a groundless abusive > remark in some fashion - either directed at me, or nameless researchers. I do have some string theorists in mind, but naming would be even more off-topic. > One might even suggest that you were just trolling. Me? Never, Jan
From: J. J. Lodder on 7 Mar 2010 04:37
Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > J. J. Lodder <nospam(a)de-ster.demon.nl> wrote: > > > Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > > > > > J. J. Lodder <nospam(a)de-ster.demon.nl> wrote: > > > > > > > D.M. Procida <real-not-anti-spam-address(a)apple-juice.co.uk> wrote: > > > > > > > > > Peter Ceresole <peter(a)cara.demon.co.uk> wrote: > > > > > > > > > > > Anybody generating files *now* that need to function operationally > > > > > > then will become aware of the problem quite soon- if they aren't > > > > > > already- and will set about copying and updating their important > > > > > > files to a 64-bit (or more) system. If they don't, they deserve to > > > > > > fail. > > > > > > > > > > This is the kind of thing that makes me doubt that digital archives of > > > > > photographs will last longer than physical ones. > > > > > > > > Why? A .jpeg will sill be a .jpeg hundred years hence, > > > > and there is no reason at all > > > > why it wouldn't be possible to display it, > > > > using a suitable app, if the medium is still readable, > > > > > > Assuming such an application is indeed available, and assuming that the > > > medium is still readable, yes. > > > > > > But you can't rely on either being the case. > > > > Why not? There is so much of it already > > that anything new must be backwards compatible. > > This is why: > > What is new generally fails to be backwards compatible. Nonsense. The data on punched tape for example can be interpreted without any problem, just plain ASCII then, plain ASCII now, and plain ASCII a hundred years hence. And executed, if it is for example PASCAL. > Most cases of new software reading old formats produces errors. Nonsense. It's hardware errors that are the problem. > All the old formats become unreadble by current software at some point > in the future. Also nonsense. Reading isn't the problem. Interpretation may be. The problem isn't data, it's obscure file formats. > That is why - because reality proves you're wrong in your mindless > optimism. > > > And failing that, they could do it your way, > > recompute with pencil and paper. > > That's just you insulting me again, Jan. Why do it? It's a quote from a previous thread. > They could recompute - I'd use a computer, actually - if they had the > algorithms and the programmers and the drives to read the data carrying > medium and if the data carrying medium were still okay and if they had > appropriate interfaces to get the data out. The specs of the jpeg format are -very- unlikely to get lost. Given the specs, images coded as jpeg can be reconstructed. (even from scratch) > A lot of `if's - which experience to date has already demonstrated > cannot be relied upon. > > > > > PS If long term survival bothers you it might be a good idea > > > > to include 10% par2 with your images. > > > > > > That type of thing will eventually be standard for long-term archiving, > > > I suspect. > > > > Should have been standard long ago. > > It doesn't protect against unreadable file systems though, > > without further adaptations. > > Do please engage brain: `that type of thing' is what I wrote. That's so vague it says nothing. > I did not write `This single thing is the one thing that needs to be > done to make all future computer storage systems fully 100% protected > against absolutely all conceivable failure modes'. You rude person, > you. Sure, and I didn't reply to anything you didn't say, Jan |