Re:Burn out at work is not always work related!
on
Pay vs. Happiness
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· Score: 1
I disagree with the idea that you can always walk away from a job if you are not in debt. As a student overseas, the only employment that I am allowed to have is employment on-campus or directly related to my PhD.
Thus, the university is pretty much in a position to dictate my job to me. I cannot get another source of employment (even the "directly related to my PhD" caveat requires a professor to say that it is indeed related to my PhD). While I agree with the sentiment, and realise that I have made this desicion myself, it is still not always a reasonable requirement for people to just walk away from their job.
Actually AND/OR and NOR take two inputs and give one output. The total number of inputs is 4 (=2 x 2). A function is a *complete* specification of these four inputs to outputs. As each input can have two values we have 8 (=2 x 4 = 2 x 2 x 2) functions from pairs of binary numbers to a binary number, not 16.
(Includes some boring functions such as setting all values to zero).
If we have n binary inputs and m outputs (usually m=1) then the total number of functions is 2^(n+m). In the case of AND/NOR et al we have n=2, m = 1 and the no. of functions = 8 as above.
In ternary we now have 3^(n+m) functions, and if we have b numbers we have b^(n+m). In the case of the number of functions from 2 variables to 1 in a trinary system we have 3^3 = 27 and in a base 4 system we have 4^3 = 64.
And for those that like to be really perverse we can have mappings from a "ring" b1 and another ring b2 in which case the number of functions is (b1^n) x (b2^m).....
Rob, you seem to have a few misconceptions yourself. Quantum field theories can be slightly counterintuitive, to say the least! However, these theorist are quite correct and it is a little unfair to "jump on them" in such a hostile manner. Let me see if I can explain what the modern view of the vacuum is.
We model the existence of all particles as energy levels. As you pointed out, mass is just a form of energy - the lowest energy rung corrosponds to a particle at rest and the energy is just mc^2. Of course, this is only true for MASSIVE particles, massless particles only have kinetic energy. We have a vacuum state that has "no particles in it".
To make this notion precise, we define the vacuum state of a system to be any state such that trying to eliminate a particle (a photon, a massive particle etc) will give you zero. This way, any process that tries to remove a particle to go ahead (such as destroy a particle at point A and recreate it at point B - this is the way Quantum theories see particles as moving!) will contribute zero if it operates on the vacuum state.
However, operators such as the energy operator do not always have a "remove particle BLAH" in every term. Thus, when they operate on the vacuum state it is possible to have a non-zero mean. By the uncertainity principle, if there is a NON-COMMUTING observable then there also exists a (non-zero) fluctuation of this value - measured by physisicts and mathematicans as the square of the deviation from the average.
Some people choose to interpret these as virtual particles popping in and out of existence. The mathematics works the same, so this is a just a picture in ones head to help one think about these things. The mathematics gives us the option - we can take the "picture" interpretation or just do the maths.
Hope this helps!
Damien Martin
Re:light stopped? Or destroyed and re-emitted...
on
Stop, Light.
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· Score: 1
Iam am afraid I have to disagree with the first statement "Technically taking a quantum snapshot of a photon and then restarting it is...."
True, an individual particle loses it's individuality and becomes a set of properties.
Quantum Field theory takes the view that all paraticles are destroyed and then recreated to do anything (eg. travell across a room at normal speed)
The question however cannot simply be one of "Is it the same particle?" - with this I completly agree. However, one of the key properties of light is that it travels at c: a statment equivelent with it bewing both "real" (ie not a figment of our imaginations) and massless. One of the properties associated with being a photon is always travelling at light speed.
(Before I get "jumped" on by peopel talking about other "slow light effects" such as refraction, the average speed of light can be less then c, as propogration through a medium will cause the light to be absorbed and reemitted. When light is propogating between emissions, however it still travels at c)
You cannot slow light down - this is just stopped and started light.
Slashdot Mirror
I disagree with the idea that you can always walk away from a job if you are not in debt. As a student overseas, the only employment that I am allowed to have is employment on-campus or directly related to my PhD.
Thus, the university is pretty much in a position to dictate my job to me. I cannot get another source of employment (even the "directly related to my PhD" caveat requires a professor to say that it is indeed related to my PhD). While I agree with the sentiment, and realise that I have made this desicion myself, it is still not always a reasonable requirement for people to just walk away from their job.
The gates define the 16 functions
Actually AND/OR and NOR take two inputs and give one output. The total number of inputs is 4 (=2 x 2). A function is a *complete* specification of these four inputs to outputs. As each input can have two values we have 8 (=2 x 4 = 2 x 2 x 2) functions from pairs of binary numbers to a binary number, not 16.
(Includes some boring functions such as setting all values to zero).
If we have n binary inputs and m outputs (usually m=1) then the total number of functions is 2^(n+m). In the case of AND/NOR et al we have n=2, m = 1 and the no. of functions = 8 as above.
In ternary we now have 3^(n+m) functions, and if we have b numbers we have b^(n+m). In the case of the number of functions from 2 variables to 1 in a trinary system we have 3^3 = 27 and in a base 4 system we have 4^3 = 64.
And for those that like to be really perverse we can have mappings from a "ring" b1 and another ring b2 in which case the number of functions is (b1^n) x (b2^m).....
Rob, you seem to have a few misconceptions yourself. Quantum field theories can be slightly counterintuitive, to say the least! However, these theorist are quite correct and it is a little unfair to "jump on them" in such a hostile manner. Let me see if I can explain what the modern view of the vacuum is.
We model the existence of all particles as energy levels. As you pointed out, mass is just a form of energy - the lowest energy rung corrosponds to a particle at rest and the energy is just mc^2. Of course, this is only true for MASSIVE particles, massless particles only have kinetic energy. We have a vacuum state that has "no particles in it".
To make this notion precise, we define the vacuum state of a system to be any state such that trying to eliminate a particle (a photon, a massive particle etc) will give you zero. This way, any process that tries to remove a particle to go ahead (such as destroy a particle at point A and recreate it at point B - this is the way Quantum theories see particles as moving!) will contribute zero if it operates on the vacuum state.
However, operators such as the energy operator do not always have a "remove particle BLAH" in every term. Thus, when they operate on the vacuum state it is possible to have a non-zero mean. By the uncertainity principle, if there is a NON-COMMUTING observable then there also exists a (non-zero) fluctuation of this value - measured by physisicts and mathematicans as the square of the deviation from the average.
Some people choose to interpret these as virtual particles popping in and out of existence. The mathematics works the same, so this is a just a picture in ones head to help one think about these things. The mathematics gives us the option - we can take the "picture" interpretation or just do the maths.
Hope this helps!
Damien Martin
Iam am afraid I have to disagree with the first statement "Technically taking a quantum snapshot of a photon and then restarting it is ...."
True, an individual particle loses it's individuality and becomes a set of properties.
Quantum Field theory takes the view that all paraticles are destroyed and then recreated to do anything (eg. travell across a room at normal speed)
The question however cannot simply be one of "Is it the same particle?" - with this I completly agree. However, one of the key properties of light is that it travels at c: a statment equivelent with it bewing both "real" (ie not a figment of our imaginations) and massless. One of the properties associated with being a photon is always travelling at light speed.
(Before I get "jumped" on by peopel talking about other "slow light effects" such as refraction, the average speed of light can be less then c, as propogration through a medium will cause the light to be absorbed and reemitted. When light is propogating between emissions, however it still travels at c)
You cannot slow light down - this is just stopped and started light.