You are missing the point. They can't see the black holes directly. that is true. They CAN see all the stellar objects that are interacting gravitationally with the apparent black hole and can clearly see that a simple solution to the field equations that explains the motion of those other objects exists. And that solution indicates an object with a mass density high enough that the escape velocity from its surface exceeds the speed of light.
Your notion that there is something exotic about the existence of such an object doesn't follow from your reasoning. For any object that has a mass, one can define an escape velocity as a function of the radius for that mass based on the density of the object. It would be exotic to propose that it is impossible for the mass density to reach a point that the escape velocity at no point can ever exceed the speed of light. You would have to invent new theories (which have no basis in experimental observations) in order to explain why that cannot happen. The simpler theory of gravitation is the one that doesn't make up artificial constraints.
You are also wrong when you say a black hole is an infinitely dense point mass. You have the definition backwards. A black hole is simply an object from which light can not escape because there is a particular radius below which the escape velocity is greater than the speed of light. You are correct that general relativity predicts that such an object would have an infinitely dense point mass at its center, but that prediction is not the definition of a black hole, it is a consequence predicted by current theory. That prediction though occurs at infinitely small distances where we know that quantum mechanics becomes relevant. We expect general relativity to break down at that point (note: at the point where the mass density becomes infinite and NOT at the point where the escape velocity exceeds c), and since we have no complete unifying theory that merges relativity and quantum mechanics the correct thing to say is we don't know what physical laws dominate at that point.
You also forget that black holes were first postulated in the 18th century by Laplace relying only on Newton's laws long before general relativity was even conceived. The notion that this would mean a singularity only came after general relativity was introduced. But the realization that we would have black holes in a universe that had mass and gravity, and in which light was subject to the force of gravity, is much older than relativity and the notion of singularities. They are independent.
Claiming that its impossible for any object to become dense enough to have an escape velocity that exceeds c simply because doing so would mean the mathematical equations for general relativity predict a singularity is not a good scientific claim... especially once you realize the the basic properties of a black hole (that light cannot escape from it) are still predicted even in the absence of relativity. In other words, an object out of which light cannot escape does not require a singularity to exist. Current relativity theory simply predicts that such a singularity would exist at the infinitely small distances where we already know relativity is an incomplete theory.
I'd also like to point out that you are the one relying on the mathematics to support a postulate for which there is no experimental motivation. Not I. I am simply assuming that there is no arbitrary constraint on the potential mass density and am content knowing that the theory is incomplete once that mass density is exceeded. You are assuming that because the incomplete theory predicts something unintuitive once you exceed that density that exceeding that density isn't possible. But your postulate is the one that requires new theories that have no basis in experiment, not mine. You are the one who will need to invent new theories to explain what force prevents masses from exceeding the densities that could trap light.
You also keep inferring that all cases where the solutions to the gravitational field equations imply a mass density with the properties of a black hole can better be explained with the theory of electromagnetism. Do you have links explaining what this theory is?
Certainly there is always a possibility of other explanations to any observed phenomenon. But the simplest explanation is the one to use unless there is evidence to the contrary. We can clearly see that in the cases where black holes have been inferred that the motions observed for the stellar objects that appear to be subject to the forces exerted by the black hole just happen to be precise solutions to equations of general relativity. If you've an alternative explanation that uses electromagnetism which exactly produces the behavior predicted by the laws of gravitation let's see a link to it. I'm not dismissing the notion that there may be cases where electromagnetism is more relevant than astronomers tend to assume, but it's pretty outrageous to dismiss gravitation and the predicted black hole as the source in cases where general relativity is able to so precisely explain the observed behavior.
In any case, my comments about how everything we know is based on inference are philosophical in nature. You are correct about that. But they are NOT isolated or separate from objective science. My point is that all of objective science is grounded in inference. You cannot dismiss inference as a valid means of making an observation unless you also dismiss all of objective science. For example, you seem to be postulating that electromagnetism could provide a better explanation for some of the stellar motions that are currently explained by black holes... but seriously... are you proposing to prove that without inference? Have you ever actually seen an electromagnetic field? We both know you have not. You've only seen the way the electromagnetic fields impact objects that can be influenced by these fields and have infered that the fields exist because the relevant equations correctly predict observations.
One important case in point that is directly relevant to the question of black holes: nobody has seen that any of the planets in the solar system, for example, really move in ellipses around our sun. That has been inferred (by Kepler, using data provided by Tycho Brahe) from careful measurements of the motion of individual planets. The calculations and types of measurements that led to those conclusions are effectively identical to the calculations by which the existence of black holes have been "observed". The equations are somewhat different but the fundamental technique is identical: very careful measurements of velocity and position are made, and then the curves defined by those observations are compared to the curves predicted by the relevant equations to see if a match can be found. Kepler found a match when he postulated his laws. Astronomers that claim to have observed black holes have also found a match. In my mind, neither is any more or less convincing than the other.
You say their existence has only been inferred. That is true. But seeing something with visible light or other electromagnetic radiation and measuring its spectra is no less of an inference then seeing something by making detailed measurements of the impacts of its gravitational field.
In the end, everything we think we perceive in the world is nothing more than inference. I infer the existence of the keyboard under my hands because I can feel tactile input on my finger tips that reminds me of my keyboard (I'm a tough typist...I'm not looking at it:p). I infer the fact that it is currently morning in my time zone by the signals my brain is sending me that tell me the shade of the light coming through the windows. I infer that you exist, because I'm not aware of any other probable mechanism by which a coherent sequence of words could have been placed on slashdot as a response to my earlier post.
So everything you and I think we know is all based on inference.
In conclusion, your definition of "observable" appears to be limited to inferences based on direct observation of the photons radiated or reflected by an object. I think observability includes quite a bit more than that. My confidence that we understand the gravitational interactions between objects well enough to make conclusions about existence based on gravitational effects is just as strong as my confidence that we can do so through observations of an object's electromagnetic effects.
You are mistaken about the evidence for black holes. Black holes have definitely been observed and measured in nature. There is no doubt at this point that they actually do exist.
Of course, I do otherwise agree that the concerns about an earth destroying blackhole being generated by the LHC are silly.
I wouldn't be surprised to find out that the cat enjoys sitting on top of the bird's cage so much that its one of the few orders he's willing to pay attention to. As thought he cat is thinking something like "you know, that's a pretty good idea", rather then "yes master".
i know mine will sit and stare at our hermit crab for hours, without anyone ever ordering him to do so. If I had a bird, I'm sure the cats would hand around the cage even longer.
Bugs aren't even required to explain the non-determinism. Even if their were no bugs, systems as complex as a modern computer (even for a single core computer) would be non-deterministic. The only way you could have complete determinism on the timings is to have precise control of exactly which cycle count every operation occurred on. That would include precise control over the precise cycle count at which the BIOS began and then completed the bring up of each component in the system. And precise control over exactly how many cycles it took to boot the OS once the post was complete, etc. Unfortunately though, the components in the system are running at different frequencies and even the components running at the same frequency in the same package will not precisely agree on "when" each clock cycle begins and ends. One of them may have the rising edge of it's clock occurring at +/-a few pico-seconds relative to the other (assuming GHz frequencies...) and you'll never be able to control which is which unless you had precise control of the electron flow to each from the wall socket through the power supply across the board, and to the component. There's no way to control that skew between components unless all components are in the same die and on the same power plane. And even that might not be enough. Systems have to be designed to handle the skew and deal with it when data crosses clock boundaries.
That is one place at the most basic level where non-determinism begins even before the BIOS has posted. Its not a bug though. It's just the part of the nature of any multiple component digital system.
It isn't surprising at all that increasingly more non-deterministic performance drift can occur once you add on top of that the fact that you have dozens of IO components in the system which all have to be coordinated and managed by the OS. Not to mention that the OS has to boot off of one of those components as well (the hard drive).
If you sit down and think about all the things that have to happen correctly, of how many disparate components are involved, and how many clock boundaries are crossed back and forth hundreds of times....all just to get the BIOS to post...it's pretty amazing that the PC under your desk (or in your lap) turns on at all.
But I am digressing. My point is, that even if every component was bug free, the initial state of the system at the moment the BIOS completes the post would never be completely deterministic even for two consecutive boots of the same physical system.
You'd probably have to literally be maxwell's demon to have that kind of control over the system.;)
While I do agree that the American education system is a bit of a mess at the moment, and that feel good programs like "no child left behind" are doing a poor job of making the situation any better, I do feel a need to make one point about a lot of misconceptions I am seeing about "no child left behind".
Do you guys realize that No Child Left Behind doesn't really "leave no child behind" and isn't really designed to do so? I'm pretty sure it just has that title because it makes the initiative sound good.
Let me explain what I mean. No child left behind mandates that all schools that receive federal funding be tested every year to evaluate their performance. Schools that fail to meet the performance metrics (which are rather convoluted) become a "needs improvement" school. They are then given some window of time to "improve" and if they don't....they lose their federal funding.
The program does not mandate that the govenment spend tons of mony to make sure every student does well. It mandates that the government penalize poorly performing schools by taking away their funding.
Do you have any data to back up this claim that all the countries that America is behind in science have a standardized curriculum?
While standards are important, I find the notion that a standardized curriculum is the solution to the problem to be rather simplistic.
Afterall, the American education system used to produce students that were stronger in science and math then they are now, and America has never had a standardized curriculum.
I'm also very worried about the notion of a standardized curriculum here in the US for a different reason: I don't trust that the bureaucrats who would make the decision about which curriculum to use are particularly competent.
I'm fairly certain that they will not re-enter if they can't patch the heat shield. If all attempts at fixing it fail they'll likely find another way down.
I hadn't thought of that before (the fact that the shuttle is on the side of the rocket during take off probably does increase the odds of structural damage to the underside considerably). But now that you mention it, that is a good point.
I would like to add one counterpoint though: the 1986 accident was caused by a faulty O-ring (on the oxygen fuel tanks I believe) that shifted in shape beyond the design specs because of the extreme cold the night before that launch, and led to leakage of fuel and an eventual explosion of the tank. That one wasn't caused by falling debris of any sort.
I don't think he was trolling either. Sun's CPU design division is in decline in my opinion. I fully expect that at some point in the next 5 to 10 years Sun will be selling off its CPU design resources to either Intel or AMD. I expect they will eventually pull out of the design side of the market just like Compaq and HP did. Just my prediction.
I've seen no indication that this newest chip from Sun is technically the best chip out there either. I expect it to be fairly good at the types of workloads that Sun's current T1 customers run most frequently. But expect it will probably be rather mediocre at other tasks.
I've no data to back that up, but there's no data being offered by Sun or anyone else to prove otherwise either. So who knows for sure?
Your are right on most points, but you have point 1 backwards. The fact that the processors are not bandwidth limited means it actually makes sense to put 4 cores in the same die. The common complaint about Intel's current Quad-Core designs is that there isn't enough FSB bandwidth to feed 4 cores. Anandtech's data actually disproves that claim.
That said, it is still true that there is not much performance benefit to having 4 cores over 2, but the reason for that is very few users are doing the sort of work on their machines that would would benefit from having 4 cores.
I have no particular opinion for or against software patents, but have to point out that your reasoning has a hole in it.
consider this scenario: big powerful software company X has a new competitor that has a software patent on some new idea they have developed. big company X considers this software a threat... so they duplicate the patented algorithm in a piece of software they write and provide it for free to their customer's in an effort to stiffle this new competitors primary revenue stream.
If it's okay to violate a patent so long as you do so at no profit to yourself, then the scenario I just described would be perfectly legal.
Which isn't to say that I think software patents should be upheld, but only to say that the line you are trying to draw between when a software patent should and should not apply doesn't seem to make much sense.
But that is how current CISC/RISC processors function in practice. They all contain large bypass networks that feed data directly from the output of one instruction to the input of the next whenever they can. The register file is there, but for instructions on the critical execution path it is largely an abstraction and those critical instructions rarely ever directly read from the register file anyway.
I understand that this new EDGE ISA is apparently aiming to formalize that and abstract the register file away completely. But whether there is really any benefit to doing that formally or whether most of the benefit is already available in how current processor's handle the register bypass network is an open question.
I wish the article linked to at the top of this discussion contained a discussion in those terms rather than what it said, but that's an aside.;-)
Much of what you list is already in current processors (aggressive branch prediction, memory dependence predictors, direct ALU-ALU bypasses). What current processors do lack is the deep 1024 out-of-order buffer and the large 64 entry cache miss buffers. But current applications don't really benefit much from going that deep and on the few workloads that theoretically could, a compiler that is very aware of the cache sizes and latencies could probably schedule carefully enough to avoid the need for such a deep OOO buffer.
I do understand though that you are saying that your ISA is designed to work around that. I'm dubious that an ISA can make that kind of difference, but maybe it could.
I am wary of an approach that depends so much on the compiler. This can lead to backward compatibility issues. Users expect programs that ran well on revision X of the processor to run better on revision X+1 of the processer and will be annoyed if they have to rebuy their software because they have upgraded their processor. That doesn't have to be an issue. It would depend upon which market these processors are being sold into (assuming something like them is ever sold). It would probably also depend upon the degree to which the information the compiler is communicating through the ISA (with which I am totally unfamiliar) depends upon the compiler's knowledge of the low level details of the internal hardware and whether it needs to be reconstructed (in your case: recompiled) when the hardware changes, in order to perform well.
That particular point is something that on-the-fly construction of the dependency graph in-hardware deals with very well. It gives you a buffer against poorly written or poorly compiled code (which some users are going to run no matter what you may intend) and lets you deal fairly well performance-wise with legacy code that may be decently written but poorly optimized for new hardware. That is something that future ISA's will have to deal with if they ever intend to replace the ISA's that are currently in widespread use (in my only partially educated opinion).
Don't know if yours does though. Just my thoughts.
yes. but that isn't usually why the resources go unused. The more common problem is data dependencies. No amount of widening the core is going to resolve those. What frequently happens on current applications is that there is an instruction in the scope of the OOO buffer that could use the unused resources but there is a data dependency between it and some other un-issued or unfinished instruction in the pipeline that prevents the dependent instruction from issueing. Deepening the OOO buffer can help with that, but that technique hits diminishing returns very fast (though I'll acknowledge that there are some academics who have published papers claiming otherwise [I don't agree with them]).
More generally, the current ratios of integer to fp to branch to load/store units in most modern cores tends to reflect the typical number that most applications currently in use will need. Those ratios are not picked at random. Architects analyis typical usage models when deciding how many of each type of pipeline to put in there. FP pipelines are one exception. FP pipelines draw too much power and that tends to be a limiting factor. But only a heavy floating point application would benefit from that and there aren't really that many users running those regularly.
That is exactly what Itanium's ISA does... Itanium is designed around the idea that the compiler knows best and provides a lot of tools to the compilers to enable the types of things you are talking about. But compilers either are not making use of it (or are unable to). It's not clear which.
of course loop unwinding works fine... when you have a long loop. it does though have two problems. 1) it only works when you have very long loops where there are very little dependencies between the consecutive iterations of the loop 2) even when it does work, it causes the code footprint of the application to be much bigger which means you end up putting a lot more stress on your cache pipeline, requiring bigger caches and a wider fetch engine.
And that all aside, what about the vast majority of code segments where massive parrallelizable loops are not being executed? Loop unwinding isn't going to help at all for those.
The motivations for this technology provided in the article ignore some rather basic facts.
They point out that current multi-core architectures put a huge burden on the software developer. This is true, but their claim that this technology will relieve that burden is dubious. They mention, for example, that current processing cores can typically only perform 4 simultaneous operations per-core, and imply that this is some kind of weakness. They completely fail to mention that the vast majority of applications running on those processors don't even use the 4 available scheduling resources in each core. In other words, the number of applications that would benefit from being able to execute more than 4 simultaneous instructions in the same core is vanishingly small. This is why most current processors have stopped at 3 or 4. Not because they haven't thought of pushing it beyond that, but because it is expensive, and because it yields very little return on the investment. Very few real-world users would see any performance benefit if the current cores on the market were any wider than 3 or 4. Most of those users aren't even using the 4 that are currently available.
Certainly the ability to do 1024 operations simulatenously in a single core is impressive. But it is not an ability that magically solves any of the current bottlenecks in multi-threaded software design. Most software application developers have difficulty figuring out what to do with multiple-cores. Those same developers would have just as much (if not more) difficult figuring out what to do with a the extra resources in a core that can execute 1024 simultaneous operations.
Gore's movie = the change in public perception ?
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An Inconvenient Truth
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The review above states that Gore's movie is the thing that has changed public perception regarding Global warming issues. I see no evidence of this. In fact, it seemed to me fairly clear that perception was shifting before the movie was even released. I'm not sure what led to the shift. Probably not any one thing. But I'm hoping the shift sticks. True or not. Overstated or not. Global warming is an issue that has to be taken seriously.
That said, I do have an alternative opinion on that question. I personally think that a major impetus in the shift of recent perceptions on this issue was the recent hurricane that hit New Orleans, and the realization at about that time that the hurricane season in and around the gulf of mexico really have been getting more intense the past few years. that may not even be caused by global warming. It could be an unrelated fluctuation in nominal weather patterns. But that doesn't matter. It's the perception that matters.
And in my opinion, the hurricanes that season struck a nerve with a lot of people. People realized that weather can be serious business and shouldn't be taken lightly. I think those events spooked the nay sayers, and gave the advocates for global warming awareness some needed leverage with the media and, indirectly, the public. I think the timing and reach of Gore's movie is building on that, but not driving it.
>>How often do you see kids playing in your neighborhood on a summer's day? I was visiting my folks this summer and I know for a fact the neighborhood they live in is filled with little kids. Not a single one went outside to play the several days I was there. This is pretty much the norm.
It pretty much is not the norm. Maybe where you live but not here in my corner of California. I can confirm that my neigbors' children are out playing in their yards and in the street every day. Not just some of my neighbors. All of them (it's a young neighborhood). The annoying little pests are everywhere. They seem to like me and my dog well enough. Maybe tomorrow morning while the dog and I are on our morning walk I can corrupt some of them into spending more time inside by introducing them to the video games that have cursed my life. That way I wouldn't have to worry about running them over while driving home from work in the evening.:-b I already ran over one of their bicycles after all (they left it in my driveway right underneath the back tire of my car...). I figure that accidentally running over one of the children is just a matter of time.... They'd best stay inside.
Asheron's Call never was as popular as WoW is. Who cares if AC did it. Why would the people who run WoW look to an MMO that is vastly less successful than they are for examples of how to improve??
As for me: i was WoW player. loved it for a long while. not long after I hit level 60 though, I lost interest and closed my account. I'm glad for the people who are enjoying the game beyond that. The appeal of the grind for more stuff isn't enough to keep me playing. WoW has made the perfect game I think for the people who like that sort of thing above all else....
you are mostly correct about how grinds evolve. one exception to that is probably the first iteration of SWG. There was such a decided lack of quest content in that game that the developer's seemed to intentionally place tedious roadblocks in the path toward finishing them. tedious roadblocks that I would classify as a grind.
as for second life: i can think of one reason why the MMORPG crowd wouldn't flock to second life: the graphics are horrid. worse than EQ1. the fast majority of what you encounter if you can stomach walking around in that gameworld for any significant period of time is utter drivel, more akin to the graphiti on the interior wall of a bathroom stall than it is to anything in one of the more conventional MMOs. the gameplay is also so amorphous that there is no real gameplay at all. second life is to conventional MMORPG's what a blank piece of paper is to pen-and-paper RPG's.
Slashdot Mirror
You are missing the point. They can't see the black holes directly. that is true. They CAN see all the stellar objects that are interacting gravitationally with the apparent black hole and can clearly see that a simple solution to the field equations that explains the motion of those other objects exists. And that solution indicates an object with a mass density high enough that the escape velocity from its surface exceeds the speed of light.
Your notion that there is something exotic about the existence of such an object doesn't follow from your reasoning. For any object that has a mass, one can define an escape velocity as a function of the radius for that mass based on the density of the object. It would be exotic to propose that it is impossible for the mass density to reach a point that the escape velocity at no point can ever exceed the speed of light. You would have to invent new theories (which have no basis in experimental observations) in order to explain why that cannot happen. The simpler theory of gravitation is the one that doesn't make up artificial constraints.
You are also wrong when you say a black hole is an infinitely dense point mass. You have the definition backwards. A black hole is simply an object from which light can not escape because there is a particular radius below which the escape velocity is greater than the speed of light. You are correct that general relativity predicts that such an object would have an infinitely dense point mass at its center, but that prediction is not the definition of a black hole, it is a consequence predicted by current theory. That prediction though occurs at infinitely small distances where we know that quantum mechanics becomes relevant. We expect general relativity to break down at that point (note: at the point where the mass density becomes infinite and NOT at the point where the escape velocity exceeds c), and since we have no complete unifying theory that merges relativity and quantum mechanics the correct thing to say is we don't know what physical laws dominate at that point.
You also forget that black holes were first postulated in the 18th century by Laplace relying only on Newton's laws long before general relativity was even conceived. The notion that this would mean a singularity only came after general relativity was introduced. But the realization that we would have black holes in a universe that had mass and gravity, and in which light was subject to the force of gravity, is much older than relativity and the notion of singularities. They are independent.
Claiming that its impossible for any object to become dense enough to have an escape velocity that exceeds c simply because doing so would mean the mathematical equations for general relativity predict a singularity is not a good scientific claim... especially once you realize the the basic properties of a black hole (that light cannot escape from it) are still predicted even in the absence of relativity. In other words, an object out of which light cannot escape does not require a singularity to exist. Current relativity theory simply predicts that such a singularity would exist at the infinitely small distances where we already know relativity is an incomplete theory.
I'd also like to point out that you are the one relying on the mathematics to support a postulate for which there is no experimental motivation. Not I. I am simply assuming that there is no arbitrary constraint on the potential mass density and am content knowing that the theory is incomplete once that mass density is exceeded. You are assuming that because the incomplete theory predicts something unintuitive once you exceed that density that exceeding that density isn't possible. But your postulate is the one that requires new theories that have no basis in experiment, not mine. You are the one who will need to invent new theories to explain what force prevents masses from exceeding the densities that could trap light.
You also keep inferring that all cases where the solutions to the gravitational field equations imply a mass density with the properties of a black hole can better be explained with the theory of electromagnetism. Do you have links explaining what this theory is?
Certainly there is always a possibility of other explanations to any observed phenomenon. But the simplest explanation is the one to use unless there is evidence to the contrary. We can clearly see that in the cases where black holes have been inferred that the motions observed for the stellar objects that appear to be subject to the forces exerted by the black hole just happen to be precise solutions to equations of general relativity. If you've an alternative explanation that uses electromagnetism which exactly produces the behavior predicted by the laws of gravitation let's see a link to it. I'm not dismissing the notion that there may be cases where electromagnetism is more relevant than astronomers tend to assume, but it's pretty outrageous to dismiss gravitation and the predicted black hole as the source in cases where general relativity is able to so precisely explain the observed behavior.
In any case, my comments about how everything we know is based on inference are philosophical in nature. You are correct about that. But they are NOT isolated or separate from objective science. My point is that all of objective science is grounded in inference. You cannot dismiss inference as a valid means of making an observation unless you also dismiss all of objective science. For example, you seem to be postulating that electromagnetism could provide a better explanation for some of the stellar motions that are currently explained by black holes... but seriously... are you proposing to prove that without inference? Have you ever actually seen an electromagnetic field? We both know you have not. You've only seen the way the electromagnetic fields impact objects that can be influenced by these fields and have infered that the fields exist because the relevant equations correctly predict observations.
One important case in point that is directly relevant to the question of black holes: nobody has seen that any of the planets in the solar system, for example, really move in ellipses around our sun. That has been inferred (by Kepler, using data provided by Tycho Brahe) from careful measurements of the motion of individual planets. The calculations and types of measurements that led to those conclusions are effectively identical to the calculations by which the existence of black holes have been "observed". The equations are somewhat different but the fundamental technique is identical: very careful measurements of velocity and position are made, and then the curves defined by those observations are compared to the curves predicted by the relevant equations to see if a match can be found. Kepler found a match when he postulated his laws. Astronomers that claim to have observed black holes have also found a match. In my mind, neither is any more or less convincing than the other.
You say their existence has only been inferred. That is true. But seeing something with visible light or other electromagnetic radiation and measuring its spectra is no less of an inference then seeing something by making detailed measurements of the impacts of its gravitational field.
In the end, everything we think we perceive in the world is nothing more than inference. I infer the existence of the keyboard under my hands because I can feel tactile input on my finger tips that reminds me of my keyboard (I'm a tough typist...I'm not looking at it :p). I infer the fact that it is currently morning in my time zone by the signals my brain is sending me that tell me the shade of the light coming through the windows. I infer that you exist, because I'm not aware of any other probable mechanism by which a coherent sequence of words could have been placed on slashdot as a response to my earlier post.
So everything you and I think we know is all based on inference.
In conclusion, your definition of "observable" appears to be limited to inferences based on direct observation of the photons radiated or reflected by an object. I think observability includes quite a bit more than that. My confidence that we understand the gravitational interactions between objects well enough to make conclusions about existence based on gravitational effects is just as strong as my confidence that we can do so through observations of an object's electromagnetic effects.
You are mistaken about the evidence for black holes. Black holes have definitely been observed and measured in nature. There is no doubt at this point that they actually do exist.
Of course, I do otherwise agree that the concerns about an earth destroying blackhole being generated by the LHC are silly.
heh. Isn't that true.
I wouldn't be surprised to find out that the cat enjoys sitting on top of the bird's cage so much that its one of the few orders he's willing to pay attention to. As thought he cat is thinking something like "you know, that's a pretty good idea", rather then "yes master".
i know mine will sit and stare at our hermit crab for hours, without anyone ever ordering him to do so. If I had a bird, I'm sure the cats would hand around the cage even longer.
Bugs aren't even required to explain the non-determinism. Even if their were no bugs, systems as complex as a modern computer (even for a single core computer) would be non-deterministic. The only way you could have complete determinism on the timings is to have precise control of exactly which cycle count every operation occurred on. That would include precise control over the precise cycle count at which the BIOS began and then completed the bring up of each component in the system. And precise control over exactly how many cycles it took to boot the OS once the post was complete, etc. Unfortunately though, the components in the system are running at different frequencies and even the components running at the same frequency in the same package will not precisely agree on "when" each clock cycle begins and ends. One of them may have the rising edge of it's clock occurring at +/-a few pico-seconds relative to the other (assuming GHz frequencies...) and you'll never be able to control which is which unless you had precise control of the electron flow to each from the wall socket through the power supply across the board, and to the component. There's no way to control that skew between components unless all components are in the same die and on the same power plane. And even that might not be enough. Systems have to be designed to handle the skew and deal with it when data crosses clock boundaries.
That is one place at the most basic level where non-determinism begins even before the BIOS has posted. Its not a bug though. It's just the part of the nature of any multiple component digital system.
It isn't surprising at all that increasingly more non-deterministic performance drift can occur once you add on top of that the fact that you have dozens of IO components in the system which all have to be coordinated and managed by the OS. Not to mention that the OS has to boot off of one of those components as well (the hard drive).
If you sit down and think about all the things that have to happen correctly, of how many disparate components are involved, and how many clock boundaries are crossed back and forth hundreds of times....all just to get the BIOS to post...it's pretty amazing that the PC under your desk (or in your lap) turns on at all.
But I am digressing. My point is, that even if every component was bug free, the initial state of the system at the moment the BIOS completes the post would never be completely deterministic even for two consecutive boots of the same physical system.
You'd probably have to literally be maxwell's demon to have that kind of control over the system. ;)
While I do agree that the American education system is a bit of a mess at the moment, and that feel good programs like "no child left behind" are doing a poor job of making the situation any better, I do feel a need to make one point about a lot of misconceptions I am seeing about "no child left behind".
Do you guys realize that No Child Left Behind doesn't really "leave no child behind" and isn't really designed to do so? I'm pretty sure it just has that title because it makes the initiative sound good.
Let me explain what I mean. No child left behind mandates that all schools that receive federal funding be tested every year to evaluate their performance. Schools that fail to meet the performance metrics (which are rather convoluted) become a "needs improvement" school. They are then given some window of time to "improve" and if they don't....they lose their federal funding.
The program does not mandate that the govenment spend tons of mony to make sure every student does well. It mandates that the government penalize poorly performing schools by taking away their funding.
Do you have any data to back up this claim that all the countries that America is behind in science have a standardized curriculum?
While standards are important, I find the notion that a standardized curriculum is the solution to the problem to be rather simplistic.
Afterall, the American education system used to produce students that were stronger in science and math then they are now, and America has never had a standardized curriculum.
I'm also very worried about the notion of a standardized curriculum here in the US for a different reason: I don't trust that the bureaucrats who would make the decision about which curriculum to use are particularly competent.
I'm fairly certain that they will not re-enter if they can't patch the heat shield. If all attempts at fixing it fail they'll likely find another way down.
I hadn't thought of that before (the fact that the shuttle is on the side of the rocket during take off probably does increase the odds of structural damage to the underside considerably). But now that you mention it, that is a good point. I would like to add one counterpoint though: the 1986 accident was caused by a faulty O-ring (on the oxygen fuel tanks I believe) that shifted in shape beyond the design specs because of the extreme cold the night before that launch, and led to leakage of fuel and an eventual explosion of the tank. That one wasn't caused by falling debris of any sort.
I don't think he was trolling either. Sun's CPU design division is in decline in my opinion. I fully expect that at some point in the next 5 to 10 years Sun will be selling off its CPU design resources to either Intel or AMD. I expect they will eventually pull out of the design side of the market just like Compaq and HP did. Just my prediction. I've seen no indication that this newest chip from Sun is technically the best chip out there either. I expect it to be fairly good at the types of workloads that Sun's current T1 customers run most frequently. But expect it will probably be rather mediocre at other tasks. I've no data to back that up, but there's no data being offered by Sun or anyone else to prove otherwise either. So who knows for sure?
Your are right on most points, but you have point 1 backwards. The fact that the processors are not bandwidth limited means it actually makes sense to put 4 cores in the same die. The common complaint about Intel's current Quad-Core designs is that there isn't enough FSB bandwidth to feed 4 cores. Anandtech's data actually disproves that claim.
That said, it is still true that there is not much performance benefit to having 4 cores over 2, but the reason for that is very few users are doing the sort of work on their machines that would would benefit from having 4 cores.
I think I hear someone muttering something about consistency and hobgoblins.
I have no particular opinion for or against software patents, but have to point out that your reasoning has a hole in it.
consider this scenario: big powerful software company X has a new competitor that has a software patent on some new idea they have developed. big company X considers this software a threat... so they duplicate the patented algorithm in a piece of software they write and provide it for free to their customer's in an effort to stiffle this new competitors primary revenue stream.
If it's okay to violate a patent so long as you do so at no profit to yourself, then the scenario I just described would be perfectly legal.
Which isn't to say that I think software patents should be upheld, but only to say that the line you are trying to draw between when a software patent should and should not apply doesn't seem to make much sense.
But that is how current CISC/RISC processors function in practice. They all contain large bypass networks that feed data directly from the output of one instruction to the input of the next whenever they can. The register file is there, but for instructions on the critical execution path it is largely an abstraction and those critical instructions rarely ever directly read from the register file anyway.
I understand that this new EDGE ISA is apparently aiming to formalize that and abstract the register file away completely. But whether there is really any benefit to doing that formally or whether most of the benefit is already available in how current processor's handle the register bypass network is an open question.
I wish the article linked to at the top of this discussion contained a discussion in those terms rather than what it said, but that's an aside. ;-)
Much of what you list is already in current processors (aggressive branch prediction, memory dependence predictors, direct ALU-ALU bypasses). What current processors do lack is the deep 1024 out-of-order buffer and the large 64 entry cache miss buffers. But current applications don't really benefit much from going that deep and on the few workloads that theoretically could, a compiler that is very aware of the cache sizes and latencies could probably schedule carefully enough to avoid the need for such a deep OOO buffer.
I do understand though that you are saying that your ISA is designed to work around that. I'm dubious that an ISA can make that kind of difference, but maybe it could.
I am wary of an approach that depends so much on the compiler. This can lead to backward compatibility issues. Users expect programs that ran well on revision X of the processor to run better on revision X+1 of the processer and will be annoyed if they have to rebuy their software because they have upgraded their processor. That doesn't have to be an issue. It would depend upon which market these processors are being sold into (assuming something like them is ever sold). It would probably also depend upon the degree to which the information the compiler is communicating through the ISA (with which I am totally unfamiliar) depends upon the compiler's knowledge of the low level details of the internal hardware and whether it needs to be reconstructed (in your case: recompiled) when the hardware changes, in order to perform well.
That particular point is something that on-the-fly construction of the dependency graph in-hardware deals with very well. It gives you a buffer against poorly written or poorly compiled code (which some users are going to run no matter what you may intend) and lets you deal fairly well performance-wise with legacy code that may be decently written but poorly optimized for new hardware. That is something that future ISA's will have to deal with if they ever intend to replace the ISA's that are currently in widespread use (in my only partially educated opinion).
Don't know if yours does though. Just my thoughts.
yes. but that isn't usually why the resources go unused. The more common problem is data dependencies. No amount of widening the core is going to resolve those. What frequently happens on current applications is that there is an instruction in the scope of the OOO buffer that could use the unused resources but there is a data dependency between it and some other un-issued or unfinished instruction in the pipeline that prevents the dependent instruction from issueing. Deepening the OOO buffer can help with that, but that technique hits diminishing returns very fast (though I'll acknowledge that there are some academics who have published papers claiming otherwise [I don't agree with them]). More generally, the current ratios of integer to fp to branch to load/store units in most modern cores tends to reflect the typical number that most applications currently in use will need. Those ratios are not picked at random. Architects analyis typical usage models when deciding how many of each type of pipeline to put in there. FP pipelines are one exception. FP pipelines draw too much power and that tends to be a limiting factor. But only a heavy floating point application would benefit from that and there aren't really that many users running those regularly.
That is food for thought.... thanks! ;-)
That is exactly what Itanium's ISA does... Itanium is designed around the idea that the compiler knows best and provides a lot of tools to the compilers to enable the types of things you are talking about. But compilers either are not making use of it (or are unable to). It's not clear which.
of course loop unwinding works fine... when you have a long loop. it does though have two problems. 1) it only works when you have very long loops where there are very little dependencies between the consecutive iterations of the loop 2) even when it does work, it causes the code footprint of the application to be much bigger which means you end up putting a lot more stress on your cache pipeline, requiring bigger caches and a wider fetch engine. And that all aside, what about the vast majority of code segments where massive parrallelizable loops are not being executed? Loop unwinding isn't going to help at all for those.
The motivations for this technology provided in the article ignore some rather basic facts.
They point out that current multi-core architectures put a huge burden on the software developer. This is true, but their claim that this technology will relieve that burden is dubious. They mention, for example, that current processing cores can typically only perform 4 simultaneous operations per-core, and imply that this is some kind of weakness. They completely fail to mention that the vast majority of applications running on those processors don't even use the 4 available scheduling resources in each core. In other words, the number of applications that would benefit from being able to execute more than 4 simultaneous instructions in the same core is vanishingly small. This is why most current processors have stopped at 3 or 4. Not because they haven't thought of pushing it beyond that, but because it is expensive, and because it yields very little return on the investment. Very few real-world users would see any performance benefit if the current cores on the market were any wider than 3 or 4. Most of those users aren't even using the 4 that are currently available.
Certainly the ability to do 1024 operations simulatenously in a single core is impressive. But it is not an ability that magically solves any of the current bottlenecks in multi-threaded software design. Most software application developers have difficulty figuring out what to do with multiple-cores. Those same developers would have just as much (if not more) difficult figuring out what to do with a the extra resources in a core that can execute 1024 simultaneous operations.
The review above states that Gore's movie is the thing that has changed public perception regarding Global warming issues. I see no evidence of this. In fact, it seemed to me fairly clear that perception was shifting before the movie was even released. I'm not sure what led to the shift. Probably not any one thing. But I'm hoping the shift sticks. True or not. Overstated or not. Global warming is an issue that has to be taken seriously.
That said, I do have an alternative opinion on that question. I personally think that a major impetus in the shift of recent perceptions on this issue was the recent hurricane that hit New Orleans, and the realization at about that time that the hurricane season in and around the gulf of mexico really have been getting more intense the past few years. that may not even be caused by global warming. It could be an unrelated fluctuation in nominal weather patterns. But that doesn't matter. It's the perception that matters.
And in my opinion, the hurricanes that season struck a nerve with a lot of people. People realized that weather can be serious business and shouldn't be taken lightly. I think those events spooked the nay sayers, and gave the advocates for global warming awareness some needed leverage with the media and, indirectly, the public. I think the timing and reach of Gore's movie is building on that, but not driving it.
>>How often do you see kids playing in your neighborhood on a summer's day? I was visiting my folks this summer and I know for a fact the neighborhood they live in is filled with little kids. Not a single one went outside to play the several days I was there. This is pretty much the norm.
:-b I already ran over one of their bicycles after all (they left it in my driveway right underneath the back tire of my car...). I figure that accidentally running over one of the children is just a matter of time.... They'd best stay inside.
It pretty much is not the norm. Maybe where you live but not here in my corner of California. I can confirm that my neigbors' children are out playing in their yards and in the street every day. Not just some of my neighbors. All of them (it's a young neighborhood). The annoying little pests are everywhere. They seem to like me and my dog well enough. Maybe tomorrow morning while the dog and I are on our morning walk I can corrupt some of them into spending more time inside by introducing them to the video games that have cursed my life. That way I wouldn't have to worry about running them over while driving home from work in the evening.
j/k.
Asheron's Call never was as popular as WoW is. Who cares if AC did it. Why would the people who run WoW look to an MMO that is vastly less successful than they are for examples of how to improve??
As for me: i was WoW player. loved it for a long while. not long after I hit level 60 though, I lost interest and closed my account. I'm glad for the people who are enjoying the game beyond that. The appeal of the grind for more stuff isn't enough to keep me playing. WoW has made the perfect game I think for the people who like that sort of thing above all else....
you are mostly correct about how grinds evolve. one exception to that is probably the first iteration of SWG. There was such a decided lack of quest content in that game that the developer's seemed to intentionally place tedious roadblocks in the path toward finishing them. tedious roadblocks that I would classify as a grind.
as for second life: i can think of one reason why the MMORPG crowd wouldn't flock to second life: the graphics are horrid. worse than EQ1. the fast majority of what you encounter if you can stomach walking around in that gameworld for any significant period of time is utter drivel, more akin to the graphiti on the interior wall of a bathroom stall than it is to anything in one of the more conventional MMOs. the gameplay is also so amorphous that there is no real gameplay at all. second life is to conventional MMORPG's what a blank piece of paper is to pen-and-paper RPG's.