I did my masters thesis some years ago on statistical models of quark-gluon plasma (QGP). As said by others, temperature is a statistical thing. A measure of the average kinetic energy of the particles in the particular statistical ensemble. What is suprising is that such a small number of particles can behave in such a way that they can be described by a statistical ensemble at all. Point is that treating the collision like this works. The theoretical curves fit *most* of the data exceedingly well. This is how one can infer the temperature of the QGP: namely assume a thermalized statistical ensemble (of some sort: either grand canonical or more sophisticated) and find what temperature fits the data. This is the "temperature" of your QGP. (If there is such a thing for such a small ensemble.)
Yes, I have not read "The Emotional Brain" either. I'll go and read it, and you go and read Lawson and then we will see. I never wanted to say humans act rationally all the time. I wanted to suggest that rational behaviour is one of many innate traits of humans necessary for our survival. Whether it is genetically hard-wired or fostered early in development through interaction with the surrounding environment is not worth arguing over though. Point is that it is there. Isn't it funny though how people turn off their rational thinking capabilities as soon as they see anything "scientific".:)
Let me make it explicit then. An IQ test is meant to test innate brain capacity right? So for example a smarter person would have a larger short term memory capacity than a stupider person. This is tested by getting the subject to memorize a random string of numbers say. The more you can memorize, the higher your innate intelligence.
THe point of the example is to argue that there can be no independent unbiased test of such a thing as short term memory. Someone who has a "gift for numbers" or who is a mathematics expert would be able to memorize more than someone who is not. Maybe the other one can memorize lots of words and infact his short term memory is better. You can try and give absolutely random combinations of stuff to reduce this effect, but I would argue that you can never remove context dependence completely. There are too many factors which can affect the outcome. I would argue that IQ tests are inherently bad at best and extremely damaging to society as a whole at worst. The ideas of memorizing random strings of stuff to measure short term memory have been discredited for 50 years. (plusminus 10 years).
I want to add my two cents on this IQ debate. Simon and Chase and Simon did a number of studies on chess players in the 70's. Give an expert a chess position - s/he can memorize the entire board in one look. Give it to a novice chess player, s/he can memorize just a few pieces. THEN they gave the experts and novices RANDOM positions (pieces just mixed up everywhere) and there was no difference in ability to remember the position. Both the experts and novices were unable to remember more than a few pieces. The explanation is that experts have deep and complex schemas which they use to memorize large patterns and relational structures on the chess board. When they cannot use them, they are in the same position as a novice. Carry this over to the IQ test. Someone who is a mathematics expert will be able to memorize far more numbers in a random string than someone who is an expert in poetry for the same reasons mentioned above. Basically the IQ test is a test of expertise in an extremely limited range of subjects chosen mostly for historical reasons I guess.
Second point. Someone said that humans are not naturally "rational" or words to that effect. Absolute rubbish! First of all what do you mean by "rational"? If you will accept my (and others) definition of "rational" - which is roughly ability to engage in logical reasoning ala the "scientific method" then humans are innately rational. Humans engage in hypothetico-deductive reasoning all the time just in order to function. Read Anton Lawson (1993) in Cognition and Instruction, for complete explanation.
Yes, mod me offtopic if you like. I think why people whine about the spelling errors is simply because/. is not a little news service for a bunch of computer geeks. Millions of people all over the world (90% of them smartarses like myself) read it and it seems really embarrassingly pathetic when the author and the editor do not know the difference between milli (m) and mega (M) and the fact that the P4 must be running at GigaHertz (GHz). Well... I am embarrassed for them.
I am not sure if anyone has suggested this already, but you can give a cool demonstration of the crushing force of atmospheric pressure in the following way:
Find the biggest hunk/jock in the crowd as a volunteer. Wrap him up in a trash bag up to his neck. Obviously leave his head sticking out. Then take a vacuum cleaner and suck the air out of the bag. This takes a little practice since you have to wrap the tube up in the bag and stick it down his back and make sure that everything seals reasonably well. Then ask him to move. He will be so stuck he cannot do anything at all...
Words of caution: Don't get his head involved. I am quite sure this will collapse your lungs if they got involved in the demo. Also, I never saw this tried with someone standing and probably with good reason because as the air is sucked out I am sure he/she would fall over like a rigid pole and injure themselves. Sit the victim on a chair or something like that.
I saw a fireball in Cape Town once. It was moving fast though, and gave off a white light. There is no doubt in my mind that it was a meteor. I actually heard a crackling noise after it wizzed overhead and broke up into lots of little pieces. And no, it was not a firework.
So, I will keep trying to post some thoughtful questions and ideas on these space matters and hope for some intelligent replies.
I am curious what would happen if there was a space debris or micro-meteorite collision. The articles did not leave me with any comfortable feelings in this regard. The possibility of the cable simply snapping after a collision was glossed over. For those of you who think that 20000km of falling cable is nothing, read Kim Stanley Robinson's account of the falling cable in his Mars Trilogy.
Another curious point: Every modern idea for a cable seems to have dispensed with the idea of towing a large asteroid into geostationary orbit to make sure that the final cable's centre of mass is in geostationary orbit. Now they want to extend the cable an extra 60000km outwards to produce the same effect. So, saves the trouble of towing an asteroid, but raises two issues:
Lots of extra cable to manufacture
Tremendous strain on the cable. A shorter cable with an asteroid on the end seems a far more stable and less stressful configuration to me.
What about wind. You are going to have to contend with the jet stream blowing one way in the stratosphere and some other wind (whose name I don't remember) blowing in the opposite direction above it at about 400km/h or something like that.
And so, what is the earth and the moon if not two bodies in close orbit around each other? Ya think the earth isn't orbiting around the moon? Think again brother.
Secondly, what alternative definition would you suggest for a planet other than that it has to be massive enough? (And probably be in orbit around the sun...which is kind of trivially obvious I guess.)
My Very Energetic MOther Just Served Us Nine Pizzas Quickly/Quietly/Quantumly/Quaintly/....
Um, well it doen't solve the problem of 10 planets, but on the other hand we could leave it as "Nine". Just imagine our grandchildren will tell their children that the "Nine" is an artifact of history when people thought there were only nine planets in the Solar System...
Duh, I solved Tic Tac Toe when I was just a wee bairn. I was replying to the dude who thinks that mathematicians have "solved" chess. (which by the way I am pretty sure they have not.)
Re:oh man. The punsters are gonna have a field day
on
New Moon for Uranus
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· Score: 1
Come to think about it, naming a planet uranus was probably not one of the brightest events.
On the other hand, the creation of the USA and its rather quirky pronunciation of the English language was not one of humanity's brightest events either, come to think of it...
Sorry for trolling slightly, but if you want to learn some basic physics, don't read popular science. I mean "Brief History of Time" and "The First Three Minutes" and "The Dancing Wu Li Masters" and all that sort of thing. I do not believe that they will teach you much physics or give you an idea of what physics is about. My recommendation for a good beginning physics textbook is "Physics for the Inquiring Mind" by Eric M. Rogers. It is out of print (sorry) but if you can find a copy, it would be worth the search.
For quantum Mechanics, there is nothing good really. I think Griffiths is ok (David Griffiths that is...). A.S. Davydov is better if you are very brave. Again, it is out of print.:( Also, French and Taylor is pretty good at the "easy" level. As is Eisberg and Resnick although they really do tend to ramble sometimes. One wishes they would just get to the point!
Yes, you get the prize for being a good physicist, but not for being smart. A little internet research should reveal that these figures of mach 5 or whatever are GENERALLY quoted in sea-level sonic units where the speed of sound is 340m/s. After all, an orbital speed of mach 25 is rather slow if you are in space where the speed of sound is zero.:)
"modern physics won't be able to make any large advances until we realize that time isn't a dimension."
I just love this comment. Someone please mod it up. You are quite correct. But Science is a social creation. If you examine how time is viewed in English (or any other european language), all our vocabulary is based on the idea that we can view time as a spatial dimension upon which a sequence of events either passes us by. Or alternatively we pass by the sequence of events. This spatial metaphor is encapsulated in the idea of space-time where time is given explicit spatial status and becomes part of the metric of the space. I would agree with you in a sense. It seems like the spatial metaphor of time has been extended probably to almost its fullest extent. (We will have to wait and see if string theory produces anything useful or not...) One of these days a paradigm shift will take place. Time will be expressed in terms of different metaphors and we will generate new ideas and views of how the world works... Until then we are stuck with the current paradigm.
If I am interpretting you correctly, I don't think there is anything paradoxical here at all. Whenever the spacecraft pass each other by their clocks should agree. Yes, I know some relativity.
The twin paradox as raised by wolftrap is correct. The paradox is not in the fact that one twin is older when they meet again. The paradox is that viewed from the reference frame of each twin, it looks like the other twin should be younger when they meet again. The resolution is however fairly simple. The key is to understand that the LONGEST distance between two points in space-time is a straight line. (That is motion with constant speed.) The twin in the rocket has to accelerate to go away from his brother and return to the same point in space. Thus his space-time interval is shorter and he arrives there "first" so to speak. IE: younger... The paradox arises from not realising that the twin in the rocket is not an inertial reference frame. (ie: he is accelerating).
Yes, but you did not answer my questions. How do you practically apply it to getting into space? People abandoned scramjets because they could not make them practical. Scramjets breathe air therefore requiring less fuel and the craft can get some lift from the atmosphere as opposed to using a rocket to go straight up. BUT here is the price you pay:
Huge amts of dead weight from other engines needed to get up to scramjet operating speeds
Tiny operation window: mach 6 to mach 12 maybe... (Someone who knows more can correct me here.) Bear in mind that you need to get to mach 25 to get into orbit.
Flying "horizontally" through the atmosphere at hypersonic speeds means large amounts of energy lost to friction. Vertical launch means you do not have to deal with these problems to such an extent.
Considering all the points I have made above, I fail to see how a scramjet can be practically implemented to get into orbit. What has changed technologically which would make a scramjet practical now as opposed to 30+ years ago when people abandoned the idea?
Slashdot Mirror
I did my masters thesis some years ago on statistical models of quark-gluon plasma (QGP). As said by others, temperature is a statistical thing. A measure of the average kinetic energy of the particles in the particular statistical ensemble. What is suprising is that such a small number of particles can behave in such a way that they can be described by a statistical ensemble at all. Point is that treating the collision like this works. The theoretical curves fit *most* of the data exceedingly well. This is how one can infer the temperature of the QGP: namely assume a thermalized statistical ensemble (of some sort: either grand canonical or more sophisticated) and find what temperature fits the data. This is the "temperature" of your QGP. (If there is such a thing for such a small ensemble.)
Yes, I have not read "The Emotional Brain" either. I'll go and read it, and you go and read Lawson and then we will see. I never wanted to say humans act rationally all the time. I wanted to suggest that rational behaviour is one of many innate traits of humans necessary for our survival. Whether it is genetically hard-wired or fostered early in development through interaction with the surrounding environment is not worth arguing over though. Point is that it is there. Isn't it funny though how people turn off their rational thinking capabilities as soon as they see anything "scientific". :)
Let me make it explicit then. An IQ test is meant to test innate brain capacity right? So for example a smarter person would have a larger short term memory capacity than a stupider person. This is tested by getting the subject to memorize a random string of numbers say. The more you can memorize, the higher your innate intelligence. THe point of the example is to argue that there can be no independent unbiased test of such a thing as short term memory. Someone who has a "gift for numbers" or who is a mathematics expert would be able to memorize more than someone who is not. Maybe the other one can memorize lots of words and infact his short term memory is better. You can try and give absolutely random combinations of stuff to reduce this effect, but I would argue that you can never remove context dependence completely. There are too many factors which can affect the outcome. I would argue that IQ tests are inherently bad at best and extremely damaging to society as a whole at worst. The ideas of memorizing random strings of stuff to measure short term memory have been discredited for 50 years. (plusminus 10 years).
I want to add my two cents on this IQ debate. Simon and Chase and Simon did a number of studies on chess players in the 70's. Give an expert a chess position - s/he can memorize the entire board in one look. Give it to a novice chess player, s/he can memorize just a few pieces. THEN they gave the experts and novices RANDOM positions (pieces just mixed up everywhere) and there was no difference in ability to remember the position. Both the experts and novices were unable to remember more than a few pieces. The explanation is that experts have deep and complex schemas which they use to memorize large patterns and relational structures on the chess board. When they cannot use them, they are in the same position as a novice. Carry this over to the IQ test. Someone who is a mathematics expert will be able to memorize far more numbers in a random string than someone who is an expert in poetry for the same reasons mentioned above. Basically the IQ test is a test of expertise in an extremely limited range of subjects chosen mostly for historical reasons I guess.
Second point. Someone said that humans are not naturally "rational" or words to that effect. Absolute rubbish! First of all what do you mean by "rational"? If you will accept my (and others) definition of "rational" - which is roughly ability to engage in logical reasoning ala the "scientific method" then humans are innately rational. Humans engage in hypothetico-deductive reasoning all the time just in order to function. Read Anton Lawson (1993) in Cognition and Instruction, for complete explanation.
Yes, mod me offtopic if you like. I think why people whine about the spelling errors is simply because /. is not a little news service for a bunch of computer geeks. Millions of people all over the world (90% of them smartarses like myself) read it and it seems really embarrassingly pathetic when the author and the editor do not know the difference between milli (m) and mega (M) and the fact that the P4 must be running at GigaHertz (GHz). Well... I am embarrassed for them.
I am not sure if anyone has suggested this already, but you can give a cool demonstration of the crushing force of atmospheric pressure in the following way:
Find the biggest hunk/jock in the crowd as a volunteer. Wrap him up in a trash bag up to his neck. Obviously leave his head sticking out. Then take a vacuum cleaner and suck the air out of the bag. This takes a little practice since you have to wrap the tube up in the bag and stick it down his back and make sure that everything seals reasonably well. Then ask him to move. He will be so stuck he cannot do anything at all...
Words of caution: Don't get his head involved. I am quite sure this will collapse your lungs if they got involved in the demo. Also, I never saw this tried with someone standing and probably with good reason because as the air is sucked out I am sure he/she would fall over like a rigid pole and injure themselves. Sit the victim on a chair or something like that.
I saw a fireball in Cape Town once. It was moving fast though, and gave off a white light. There is no doubt in my mind that it was a meteor. I actually heard a crackling noise after it wizzed overhead and broke up into lots of little pieces. And no, it was not a firework.
So, I will keep trying to post some thoughtful questions and ideas on these space matters and hope for some intelligent replies.
Well, there are some thoughts. Any comments?
The standard scrabble rules state in effect that you are not allowed to use proper nouns...
And so, what is the earth and the moon if not two bodies in close orbit around each other? Ya think the earth isn't orbiting around the moon? Think again brother.
Secondly, what alternative definition would you suggest for a planet other than that it has to be massive enough? (And probably be in orbit around the sun...which is kind of trivially obvious I guess.)
My Very Energetic MOther Just Served Us Nine Pizzas Quickly/Quietly/Quantumly/Quaintly/....
Um, well it doen't solve the problem of 10 planets, but on the other hand we could leave it as "Nine". Just imagine our grandchildren will tell their children that the "Nine" is an artifact of history when people thought there were only nine planets in the Solar System...
Duh, I solved Tic Tac Toe when I was just a wee bairn. I was replying to the dude who thinks that mathematicians have "solved" chess. (which by the way I am pretty sure they have not.)
Come to think about it, naming a planet uranus was probably not one of the brightest events. On the other hand, the creation of the USA and its rather quirky pronunciation of the English language was not one of humanity's brightest events either, come to think of it...
I find this hard to believe. Do you have a link, some evidence?
Here here. Computers started kicking GMs' butts at blitz years back. -1 plain wrong.
Idiot. You are talking absolute rubbish. And you got +5 for it. :(
Yup, the moderators are so clueless that they don't even realise that this is meant to be funny :(
D
I stand corrected. Still does not make any sense to quote orbital speeds in local speed of sound units though.
Yes, you get the prize for being a good physicist, but not for being smart. A little internet research should reveal that these figures of mach 5 or whatever are GENERALLY quoted in sea-level sonic units where the speed of sound is 340m/s. After all, an orbital speed of mach 25 is rather slow if you are in space where the speed of sound is zero. :)
"modern physics won't be able to make any large advances until we realize that time isn't a dimension."
I just love this comment. Someone please mod it up. You are quite correct. But Science is a social creation. If you examine how time is viewed in English (or any other european language), all our vocabulary is based on the idea that we can view time as a spatial dimension upon which a sequence of events either passes us by. Or alternatively we pass by the sequence of events. This spatial metaphor is encapsulated in the idea of space-time where time is given explicit spatial status and becomes part of the metric of the space. I would agree with you in a sense. It seems like the spatial metaphor of time has been extended probably to almost its fullest extent. (We will have to wait and see if string theory produces anything useful or not...) One of these days a paradigm shift will take place. Time will be expressed in terms of different metaphors and we will generate new ideas and views of how the world works... Until then we are stuck with the current paradigm.
If I am interpretting you correctly, I don't think there is anything paradoxical here at all. Whenever the spacecraft pass each other by their clocks should agree. Yes, I know some relativity.
The twin paradox as raised by wolftrap is correct. The paradox is not in the fact that one twin is older when they meet again. The paradox is that viewed from the reference frame of each twin, it looks like the other twin should be younger when they meet again. The resolution is however fairly simple. The key is to understand that the LONGEST distance between two points in space-time is a straight line. (That is motion with constant speed.) The twin in the rocket has to accelerate to go away from his brother and return to the same point in space. Thus his space-time interval is shorter and he arrives there "first" so to speak. IE: younger...
The paradox arises from not realising that the twin in the rocket is not an inertial reference frame. (ie: he is accelerating).
- Huge amts of dead weight from other engines needed to get up to scramjet operating speeds
- Tiny operation window: mach 6 to mach 12 maybe... (Someone who knows more can correct me here.) Bear in mind that you need to get to mach 25 to get into orbit.
- Flying "horizontally" through the atmosphere at hypersonic speeds means large amounts of energy lost to friction. Vertical launch means you do not have to deal with these problems to such an extent.
Considering all the points I have made above, I fail to see how a scramjet can be practically implemented to get into orbit. What has changed technologically which would make a scramjet practical now as opposed to 30+ years ago when people abandoned the idea?