Best I can think of are Indiana, and perhaps Waterloo. They have both been the source of a lot of good C++ libraries. Not sure how much of that filters down to the undergraduate courses though.
Because the dickhead is comparing the STS toilet, that just collects waste for later disposal when they get back to Earth, with the Russian system that filters and purifies the liquid waste into potable water.
Right, an important aspect of computer science is the relationship between different processes (I'd say 'algorithms', but that seems to be a politically incorrect word on this thread). This has a real influence on software engineering, via generic programming, OO, etc. And it's all mathematics. What people seem to be forgetting here is that mathematics encompasses a heck of a lot more than just calculus. There was even a comment earlier from some guy that said he sucked at math but was great at logic! Heh, I don't think so;-)
Yes, it is common teminology in high-end computing, but no it does not have anything to do with distributed computing. It predates multi-processing by a long time. See this comment. As far as I know, the usage shows no sign of falling out of favor.
It depends on the subculture. In scientific computing and high-performance computing, it is common to refer to programs as 'codes'. This language originates from one of the original supercomputer applications, hydrocodes.
If you went to the system administrator of a large computing cluster and asked "what codes are you running now?", he would immediately grok that you know what you're talking about. I wouldn't be at all surprised if big iron Oracle people used the same terminology.
I think that is absolutely the wrong advice. Tourism is the problem, not the solution. Even an `environmentally aware' tourist is not as good as no tourist at all.
The existing tourism is obviously unsustainable (as is the fishing), so eventually it will be reduced - either by lowering quotas or, of that is not done, by destroying the place until no tourist wants to go. But putting pressure on the number of tourists wanting to go is not going to help!
Well, we could go back and forth on this all day. But unless I was asleep while the rest of the class learned the definition of 'unique', I would say that being 'unique' is exactly what makes that frame of reference special. Note that the word word I have consistently used is 'special', I have never referred to it as 'fundamentally different', you are trying to put words into my mouth. Indeed, I even agree with you that
it doesn't appear as a fundamental entity in relativity
You started off saying I was wrong:
IWannaBeAnAc: General relativity tells us that the passage of time depends on your movements in space, but it doesn't forbit the presence of some 'special' reference frame...
xaonon: Actually, that's exactly what it forbids.
You now seem to be backing away from that statement and instead simply saying that "there is nothing in physics that makes that frame of reference fundamentally different than any other". But that is still not correct. The fact that such a reference frame exists is not implied by general relativity, but is apparently a consequence of our particular cosmology. Whether it is some random chance the universe ended up this way (which is what string theory rather vacuously implies), or whether it is a natural consequence of some deeper physical law, is an interesting question. But the fact that it exists is most definitely a special property of our universe.
What? Of course it has special physical significance, it is the uniquely defined frame that is stationary with respect to the cosmic microwave background! Just because it doesn't appear as a fundamental entity in relativity, but is instead an emergent property of our particular cosmology, doesn't make it any less special. In some sense, that makes it even more special: in some other universe, different to ours but still allowed by general relativity, such a frame might not exist!
There is a fundamental difference though. The classical 'equivalent' of a C-NOT is indeed just an XOR gate where one of the inputs is duplicated as the second output line. This follows a common tool in classical circuits, where one output line can drive a large number of different inputs. You never need a two-output gate in a classical circuit because you could always produce the same effect by having two one-output gates and copying the inputs to each gate.
But in a quantum circuit, there is a fundamental theorem that says you cannot do this - the no cloning theorem. This means that you cannot construct a C-NOT gate out of some quantum version of an XOR and a copy of one of the inputs, as neither of these operations exist. It must be done as a single two-input two-output gate.
The C-NOT name is justified because you can increase the number of control lines. Eg, the C-C-NOT gate, which acts similarly to a 2-bit adder.
I think you're still missing the point. MS's argument about requiring a new driver model for DX10 is FUD. It may be the case that a redesigned driver model makes it easier to implement the DX10 API, but it isn't plausible that it would actually be necessary.
Wine are talking about writing an implementation of DX10 that works on top of OpenGL. This won't require DX10 drivers, it will only require OpenGL drivers. And they already exist. So, in not too long it might be possible to download a DX10 emulation layer for WinXP that 'just works', no extra drivers necessary.
You made that up, didn't you? Even the Wikipedia article you mention doesn't say anything about a 2-input gate called 'NOT'. I've never heard of A NOT B as shorthand for A AND (NOT B) before, but I'll forgive you if you can post a link to where that terminology is used. But that gate has nothing to do with XOR, and definitely has nothing to do with the quantum C-NOT gate. The whole point of quantum gates is that they are reversible, of which AND and OR (and there negative-true counterparts) are not.
This isn't an ordinary NOT gate, it's a controlled NOT, or C-NOT. This gate does have two inputs. The state of the first input is either inverted or not inverted, depending on the state of the second input. So it is actually very similar to a conventional XOR gate.
By all means, pull numbers out your ass on what your predictions on when you think a quantum computer will be built, but you should at least put in a disclaimer that you have no idea what you are talking about. WTF is a `quantum transitor' ? There are a lot of designs of transistors that depend on quantum mechanical effects to operate, and are therefore called `quantum transistors'. These exist today, but these are ordinary transistors and have nothing to do with quantum computing. If you are trying to refer to some device that has a similar relationship to a quantum gate that a transistor has to a conventional gate, then I'm afraid you are out of luck - AFAIK there is no such device. For the designs referred to in the article, a Josephson junction could maybe be considered a fundamental building block - but it acts nothing like a transistor.
Note that we're talking about coordinate time in a particular reference frame
Right - here the obvious reference frame is the inertial frame in which both the Earth and Eta C are stationary.
Again, I'm not talking at all about when things are observed. I'm talking about when they actually happened according to various observers (which they would deduce from when they observe something, how far away it is, and the speed of light).
Exactly. We're on the same wavelength here.
Everyone will certainly agree on what the time ordering is in a specific frame of reference. What I said is that someone in a different frame of reference will say that, according to his own time keeping, the Slashdot story was published before Eta C went supernova. It is not just that he will observe them in this order, he will say (according to the time in his frame of reference) that they actually happened in this order. One such observer would be someone in a space ship passing by Earth at the instant the story was published moving at 0.99c away from Eta C. You can verify this using the Lorentz transformations.
This is where we have a fundamental disagreement. When the observer calculates the time at which Eta C went supernova, he would of course take into account the fact that he is moving away from it at 0.99c (ie, he would calculate the proper time in Eta C's frame of reference). It doesn't make any sense to do otherwise. Suppose, for example, there is an observer on Eta C. In 7500 years he will observe the Slashdot story and, simultaneously (as in at the same coordinates in spacetime, so everyone can agree it was simultaneous) the space ship passing by. Now suppose that 10 minutes later, the observer on Eta C sees the space ship blow up. Now, given that the observer on Eta C has seen 10 minutes elapse, how long was the spaceman travelling for since he left Earth? The answer is of course much less than 10 minutes, it is about 1.4 minutes.
The fundamental point, which you seem to be missing, is that Earth and Eta C are both in the same inertial frame, and within an inertial frame simultaneity is well defined. If some other observer is flying past in his spaceship, he can still determine whether the two events are simultaneous or not because there is a unique inertial reference frame in which both objects are stationary, he just has to do a Lorentz transformation into that frame. In other words, a clock on Earth will move at exactly the same rate as a clock on Eta C, so the time difference between an event happening on Earth and an event happening on Eta C is well defined, and everyone will be able to agree on what it is (after they do a Lorentz transformation to the common inertial frame).
The case where simultaneity is not well defined is when the Earth and Eta C are moving relative to each other. In this case, the spaceman flying past cannot determine an inertial frame that is common to both objects. He could choose a frame in which Earth is stationary, or he chooses a frame in which Eta C is stationary, but neither is any help in answering the question of whether the events were simultaneous.
You seem to be confusing 'non-uniform' with 'imprecise'. Of course, if the twin is receiving food parcels that were sent from Earth at regular times, then he will actually get them at irregular intervals because of his motion. You call this 'imprecise', but that isn't good terminology: if he keeps a record of his motion via an accelerometer on his spaceship, then he can calculate precisely when the next food parcel will arrive, based on his motions relative to the Earth. You certainly don't need to be in an inertial frame to do this, you just need to be good at solving horrendous non-linear differential equations;-)
Of course, the universe doesn't need to be expanding at the speed of light, or even at a constant speed, for there to be a functional relationship between the age of the universe and the diameter. What about Hubble's Law?
You think that the twin who heads off with velocity V and comes back with velocity -V defines an intertial reference frame?
No, I can't see anything in my post that even suggests I think there is an inertial frame for the two twins. What makes you think that? I said "Even with the twins `paradox', for each twin separately, there is surely a consistent timeline." That is, for each twin separately, I made no claim that there would be a consistent common timeline for the two twins!
All I am saying is that one twin would be able to use general relativity to calculate the timeline from the point of view of the other twin. Isn't that in fact obvious?
Are you confusing observation of events (which in general different observers will disagree on which happens first), with proper time in an inertial frame?
Firstly, the case of Earth and Eta C is special because they are (approximately) not moving relative to each other and are therefore in the same inertial reference frame. Since this is an inertial frame, we would we able to observe a clock on Eta C going at exactly the same rate as a clock on Earth, just 7500 years slow.
An observer moving relative to us in the right way would disagree. In his frame of reference the supernova explosion has not happened yet by the time this story went up on Slashdot.
That statement is really weird. For a start, on Earth we have not yet observed the supernova explosion, so I'm not sure what the disagreement is supposed to be. Secondly, an observer wouldn't have to be moving relative to us in order for him to observe the explosion before observing this slashdot story, he would just need to be in a different location. 1000 light-years away from us in the direction of Eta C would be plenty - he would have seen the explosion already but he won't see the slashdot story for another 1000 years. But in all cases, any observer would be able to say with certainty that in the inertial frame of the Earth and Eta C, the supernova happened before the Slashdot story, even if they observe them in a different order. In the case of the spaceman 1000 light-years away from us, his reasoning would be (at time 1000 years in the future, when he observes the slashdot story), "I just saw a new slashdot story was posted about Eta C. The message has travelled 1000 light-years, therefore the Slashdot story was posted 1000 years ago. But 1000 years ago, I saw Eta C go supernova. Eta C is 6500 light years away, therefore Eta C went supernova 7500 years ago.". Note that an observer on Earth, 1000 years in the future, would come to exactly the same conclusions - namely that the slashdot story was posted 1000 years ago and Eta C went supernova 7500 years ago! To emphasize, this is possible only because Earth and Eta C are in the same inertial frame.
Right, but you are talking about models. Models are great because you can actually calculate things using them. But a model is not going to correspond to reality in every possible detail (otherwise it wouldn't be a model - it would be a theorem!). I don't care whether it is convenient to model the universe as an infinite (nearly) flat plane or not, I'm asking whether it is an infinite (nearly) flat plane. You seem to be confusing the case of an infinite universe with that of a finite and closed curved universe, or maybe your terminology is just confusing me. If the universe is positively curved, then it is surely also finite. To take your example of reduced dimensions and embedding the 2D surface of a sphere in 3-space, the sphere still has a well-defined radius. The 2-sphere is not, in any sense of the word, infinite. Even if it is negatively curved, then it can still be finite, in the sense of having a well-defined maximum distance between two points that were initially close to each other at the big bang.
Thanks, that mostly makes sense. Except, doesn't the universe have a well-defined diameter, which is given by the age of the universe since the big bang?
No, the star exploded at just a single point in spacetime. If you were not at the same location at the same time, then it is too late to do anything about it. An observer located around 1000 light-years closer to Eta C would be seeing the star explode right about now. But that doesn't mean that the star is exploding at that moment in that reference frame, it just means you are seeing the light hit you from the event 6,500 years ago.
Can you elaborate? If we don't see it go nova within the next 1000 years, then there is something badly wrong with current theories of stellar evolution - which would probably mean there is something wrong with our theories of nuclear fission - but that is a subject that is pretty well understood (at least by nuclear physicists!).
Slashdot Mirror
Best I can think of are Indiana, and perhaps Waterloo. They have both been the source of a lot of good C++ libraries. Not sure how much of that filters down to the undergraduate courses though.
Did you reply to the wrong message? Where did that quote come from?
Right, an important aspect of computer science is the relationship between different processes (I'd say 'algorithms', but that seems to be a politically incorrect word on this thread). This has a real influence on software engineering, via generic programming, OO, etc. And it's all mathematics. What people seem to be forgetting here is that mathematics encompasses a heck of a lot more than just calculus. There was even a comment earlier from some guy that said he sucked at math but was great at logic! Heh, I don't think so ;-)
Yes, it is common teminology in high-end computing, but no it does not have anything to do with distributed computing. It predates multi-processing by a long time. See this comment. As far as I know, the usage shows no sign of falling out of favor.
It depends on the subculture. In scientific computing and high-performance computing, it is common to refer to programs as 'codes'. This language originates from one of the original supercomputer applications, hydrocodes.
If you went to the system administrator of a large computing cluster and asked "what codes are you running now?", he would immediately grok that you know what you're talking about. I wouldn't be at all surprised if big iron Oracle people used the same terminology.
I think that is absolutely the wrong advice. Tourism is the problem, not the solution. Even an `environmentally aware' tourist is not as good as no tourist at all.
The existing tourism is obviously unsustainable (as is the fishing), so eventually it will be reduced - either by lowering quotas or, of that is not done, by destroying the place until no tourist wants to go. But putting pressure on the number of tourists wanting to go is not going to help!
One place I would love to see ... but tourism is killing the place, better to admire it from a distance than be part of the problem.
Look harder, the links are on the left sidebar. No flash or javascript required to get either the transcript or the audio.
Well, we could go back and forth on this all day. But unless I was asleep while the rest of the class learned the definition of 'unique', I would say that being 'unique' is exactly what makes that frame of reference special. Note that the word word I have consistently used is 'special', I have never referred to it as 'fundamentally different', you are trying to put words into my mouth. Indeed, I even agree with you that
You started off saying I was wrong:
You now seem to be backing away from that statement and instead simply saying that "there is nothing in physics that makes that frame of reference fundamentally different than any other". But that is still not correct. The fact that such a reference frame exists is not implied by general relativity, but is apparently a consequence of our particular cosmology. Whether it is some random chance the universe ended up this way (which is what string theory rather vacuously implies), or whether it is a natural consequence of some deeper physical law, is an interesting question. But the fact that it exists is most definitely a special property of our universe.What? Of course it has special physical significance, it is the uniquely defined frame that is stationary with respect to the cosmic microwave background! Just because it doesn't appear as a fundamental entity in relativity, but is instead an emergent property of our particular cosmology, doesn't make it any less special. In some sense, that makes it even more special: in some other universe, different to ours but still allowed by general relativity, such a frame might not exist!
There is a fundamental difference though. The classical 'equivalent' of a C-NOT is indeed just an XOR gate where one of the inputs is duplicated as the second output line. This follows a common tool in classical circuits, where one output line can drive a large number of different inputs. You never need a two-output gate in a classical circuit because you could always produce the same effect by having two one-output gates and copying the inputs to each gate.
But in a quantum circuit, there is a fundamental theorem that says you cannot do this - the no cloning theorem. This means that you cannot construct a C-NOT gate out of some quantum version of an XOR and a copy of one of the inputs, as neither of these operations exist. It must be done as a single two-input two-output gate.
The C-NOT name is justified because you can increase the number of control lines. Eg, the C-C-NOT gate, which acts similarly to a 2-bit adder.
I think you're still missing the point. MS's argument about requiring a new driver model for DX10 is FUD. It may be the case that a redesigned driver model makes it easier to implement the DX10 API, but it isn't plausible that it would actually be necessary.
Wine are talking about writing an implementation of DX10 that works on top of OpenGL. This won't require DX10 drivers, it will only require OpenGL drivers. And they already exist. So, in not too long it might be possible to download a DX10 emulation layer for WinXP that 'just works', no extra drivers necessary.
You made that up, didn't you? Even the Wikipedia article you mention doesn't say anything about a 2-input gate called 'NOT'. I've never heard of A NOT B as shorthand for A AND (NOT B) before, but I'll forgive you if you can post a link to where that terminology is used. But that gate has nothing to do with XOR, and definitely has nothing to do with the quantum C-NOT gate. The whole point of quantum gates is that they are reversible, of which AND and OR (and there negative-true counterparts) are not.
This isn't an ordinary NOT gate, it's a controlled NOT, or C-NOT. This gate does have two inputs. The state of the first input is either inverted or not inverted, depending on the state of the second input. So it is actually very similar to a conventional XOR gate.
By all means, pull numbers out your ass on what your predictions on when you think a quantum computer will be built, but you should at least put in a disclaimer that you have no idea what you are talking about. WTF is a `quantum transitor' ? There are a lot of designs of transistors that depend on quantum mechanical effects to operate, and are therefore called `quantum transistors'. These exist today, but these are ordinary transistors and have nothing to do with quantum computing. If you are trying to refer to some device that has a similar relationship to a quantum gate that a transistor has to a conventional gate, then I'm afraid you are out of luck - AFAIK there is no such device. For the designs referred to in the article, a Josephson junction could maybe be considered a fundamental building block - but it acts nothing like a transistor.
Right - here the obvious reference frame is the inertial frame in which both the Earth and Eta C are stationary.
Exactly. We're on the same wavelength here.
This is where we have a fundamental disagreement. When the observer calculates the time at which Eta C went supernova, he would of course take into account the fact that he is moving away from it at 0.99c (ie, he would calculate the proper time in Eta C's frame of reference). It doesn't make any sense to do otherwise. Suppose, for example, there is an observer on Eta C. In 7500 years he will observe the Slashdot story and, simultaneously (as in at the same coordinates in spacetime, so everyone can agree it was simultaneous) the space ship passing by. Now suppose that 10 minutes later, the observer on Eta C sees the space ship blow up. Now, given that the observer on Eta C has seen 10 minutes elapse, how long was the spaceman travelling for since he left Earth? The answer is of course much less than 10 minutes, it is about 1.4 minutes.
The fundamental point, which you seem to be missing, is that Earth and Eta C are both in the same inertial frame, and within an inertial frame simultaneity is well defined. If some other observer is flying past in his spaceship, he can still determine whether the two events are simultaneous or not because there is a unique inertial reference frame in which both objects are stationary, he just has to do a Lorentz transformation into that frame. In other words, a clock on Earth will move at exactly the same rate as a clock on Eta C, so the time difference between an event happening on Earth and an event happening on Eta C is well defined, and everyone will be able to agree on what it is (after they do a Lorentz transformation to the common inertial frame).
The case where simultaneity is not well defined is when the Earth and Eta C are moving relative to each other. In this case, the spaceman flying past cannot determine an inertial frame that is common to both objects. He could choose a frame in which Earth is stationary, or he chooses a frame in which Eta C is stationary, but neither is any help in answering the question of whether the events were simultaneous.
You seem to be confusing 'non-uniform' with 'imprecise'. Of course, if the twin is receiving food parcels that were sent from Earth at regular times, then he will actually get them at irregular intervals because of his motion. You call this 'imprecise', but that isn't good terminology: if he keeps a record of his motion via an accelerometer on his spaceship, then he can calculate precisely when the next food parcel will arrive, based on his motions relative to the Earth. You certainly don't need to be in an inertial frame to do this, you just need to be good at solving horrendous non-linear differential equations ;-)
Of course, the universe doesn't need to be expanding at the speed of light, or even at a constant speed, for there to be a functional relationship between the age of the universe and the diameter. What about Hubble's Law?
Well, I'm not an astrophysicist - all I can do is quote from people who are. The current article says
So, maybe saying it will happen within 1000 years is a stronger statement than is warranted, but do you really care?
No, I can't see anything in my post that even suggests I think there is an inertial frame for the two twins. What makes you think that? I said "Even with the twins `paradox', for each twin separately, there is surely a consistent timeline." That is, for each twin separately, I made no claim that there would be a consistent common timeline for the two twins!
All I am saying is that one twin would be able to use general relativity to calculate the timeline from the point of view of the other twin. Isn't that in fact obvious?
Are you confusing observation of events (which in general different observers will disagree on which happens first), with proper time in an inertial frame?
Firstly, the case of Earth and Eta C is special because they are (approximately) not moving relative to each other and are therefore in the same inertial reference frame. Since this is an inertial frame, we would we able to observe a clock on Eta C going at exactly the same rate as a clock on Earth, just 7500 years slow.
That statement is really weird. For a start, on Earth we have not yet observed the supernova explosion, so I'm not sure what the disagreement is supposed to be. Secondly, an observer wouldn't have to be moving relative to us in order for him to observe the explosion before observing this slashdot story, he would just need to be in a different location. 1000 light-years away from us in the direction of Eta C would be plenty - he would have seen the explosion already but he won't see the slashdot story for another 1000 years. But in all cases, any observer would be able to say with certainty that in the inertial frame of the Earth and Eta C, the supernova happened before the Slashdot story, even if they observe them in a different order. In the case of the spaceman 1000 light-years away from us, his reasoning would be (at time 1000 years in the future, when he observes the slashdot story), "I just saw a new slashdot story was posted about Eta C. The message has travelled 1000 light-years, therefore the Slashdot story was posted 1000 years ago. But 1000 years ago, I saw Eta C go supernova. Eta C is 6500 light years away, therefore Eta C went supernova 7500 years ago.". Note that an observer on Earth, 1000 years in the future, would come to exactly the same conclusions - namely that the slashdot story was posted 1000 years ago and Eta C went supernova 7500 years ago! To emphasize, this is possible only because Earth and Eta C are in the same inertial frame.
Right, but you are talking about models. Models are great because you can actually calculate things using them. But a model is not going to correspond to reality in every possible detail (otherwise it wouldn't be a model - it would be a theorem!). I don't care whether it is convenient to model the universe as an infinite (nearly) flat plane or not, I'm asking whether it is an infinite (nearly) flat plane. You seem to be confusing the case of an infinite universe with that of a finite and closed curved universe, or maybe your terminology is just confusing me. If the universe is positively curved, then it is surely also finite. To take your example of reduced dimensions and embedding the 2D surface of a sphere in 3-space, the sphere still has a well-defined radius. The 2-sphere is not, in any sense of the word, infinite. Even if it is negatively curved, then it can still be finite, in the sense of having a well-defined maximum distance between two points that were initially close to each other at the big bang.
Thanks, that mostly makes sense. Except, doesn't the universe have a well-defined diameter, which is given by the age of the universe since the big bang?
No, the star exploded at just a single point in spacetime. If you were not at the same location at the same time, then it is too late to do anything about it. An observer located around 1000 light-years closer to Eta C would be seeing the star explode right about now. But that doesn't mean that the star is exploding at that moment in that reference frame, it just means you are seeing the light hit you from the event 6,500 years ago.
Can you elaborate? If we don't see it go nova within the next 1000 years, then there is something badly wrong with current theories of stellar evolution - which would probably mean there is something wrong with our theories of nuclear fission - but that is a subject that is pretty well understood (at least by nuclear physicists!).