[QUOTE=Falubii;40085090]Okay, then why is an average of energy a base unit? Energy is a derived unit.[/QUOTE]
I thought all units are essentially arbitrary, so I don't see how there can be "base units".
Average energy is just a useful quantity when it comes to statistical mechanics. That or I don't understand your question.
[QUOTE=Number-41;40094146]I thought all units are essentially arbitrary, so I don't see how there can be "base units".
Average energy is just a useful quantity when it comes to statistical mechanics. That or I don't understand your question.[/QUOTE]
A base unit is supposed to be based on a natural quantity. For example, 273K is the melting point of water, 1 meter is the distance covered by light in 1/300000000th of a second, etc. Speed for example is a derived unit, because it can be expressed in base units - meters/second.
He's asking why/if kelvins can be defined in terms of joules.
Don't think that's possible. You can always derive a relation between mean energy and temperature, using the appropriate [URL="http://en.wikipedia.org/wiki/Partition_function_(statistical_mechanics)"]partition function[/URL] (it basically is a function that allows you to derive all useful macroscopic quantities for a given system), but that doesn't make it fundamental, as I don't think there's a partition function for "everything" (i.e. all particle types).
You might be over thinking it. Temperature = average energy in a system, so it really could be given in joules (kg*m^2/s^2). So obviously mass, distance, and time are fundamental, but temperature just seems to be a derived unit consisting of those.
[QUOTE=Falubii;40098525]You might be over thinking it. Temperature = average energy in a system, so it really could be given in joules (kg*m^2/s^2). So obviously mass, distance, and time are fundamental, but temperature just seems to be a derived unit consisting of those.[/QUOTE]
You are using this relation (I guess)
[IMG]http://upload.wikimedia.org/math/0/4/c/04cda6fe2db68be35df1747b16964984.png[/IMG]
but that assumes that every substance has the same (in this case 3) amount of degrees of freedom (which is not always the case, think diatomic, solids,things with a magnetic moment in a magnetic field, etc). If temperature really could be expressed in an absolute amount of energy, then that would mean that systems that are in thermodynamic equilibrium (and have the same T) would also contain the same amount of energy, which is certainly not true for systems containing particles with a different amount of degrees of freedom(~ways of storing energy).
It's that 3 in the 3/2 that differs for each type of particle. If that 3/2 would be constant for various kinds of gasses & solids, it'd be possible.
Actually, you can define it for specific substances, and that would be the specific heat C.
New question: What happens to the excess energy of a photon when an electron jumps to a higher energy state? If the photon has more energy than is necessary to put an electron to first level, but not quite enough to get to the second level.
Just finished a quantum homework that's due on tuesday and one of the questions was to write the quantum harmonic oscillator potential in momentum space so I just made the substitution x = i(hbar)[(partial)[sup]2[/sup]/(partial)p[sup]2[/sup]]
Am I missing something because that took about 10 seconds and was worth 1/6 of the points on the homework
[QUOTE=Falubii;40101621]New question: What happens to the excess energy of a photon when an electron jumps to a higher energy state? If the photon has more energy than is necessary to put an electron to first level, but not quite enough to get to the second level.[/QUOTE]
Well, if it doesn't have the exact amount of energy, the photon isn't absorbed and goes through the electronic cloud. As an 11th grader, teacher never told us anything about this case.
Also my current physics teacher (guy's barely 10 year older than I am) admits that everything we learn in high school in physics-chemistry is a LIE. Fuck this shit. Also asked him how the LHC produced its particles with collsions, he didn't know what to answer. After some Wikipedia I found: mass of particles changes at relativistic speeds because while they gain kinetic energy they also gain mass with E=mc². So higher speed implies greater energy for the collisions. Last thing is to explain what creates antiparticles, bosons and leptons with all that energy... Note that I shouldn't have any of the knowledge to answer this, I'm just tryin'.
The idea of relativistic mass is a bit dated. Mass is usually considered invariant now and it's energy that changes.
[QUOTE=Falubii;40085108]Not what I was asking, but thank you for replying.
Damn you Nikita.[/QUOTE]
Ah, I misunderstood what you meant. I thought you literally meant why is Kelvin the unit, and not so much why is temperature itself a base unit. Makes more sense now.
So if a particle can borrow energy from the universe, what would happen if it never returned the borrowed energy?
Could this principle be done on a much larger scale?
it can't not return it
I see, but from "where" does this energy come from? And could humans harness/borrow this energy? Or is it something way out of our grasp?
So I talked to the other string theorist in the department today. His graduate advisors were Joe Polchinski and Steven Weinberg, and his post-doc advisor was Edward Witten. Holy shit, this man has a pedigree.
He talked to me about research in string theory and told me that it's practically impossible to get a job as a string theorist since the field is so saturated with brilliant people that it's ridiculously competitive. He said that Polchinski gave him the same talk 25 years ago when he was a grad student. So basically I spoke to Joe Polchinski indirectly today and he told me, "So you want to get into string theory, lol good luck"
Strings are lame anyway.
God fucking dammit I'm forced to use matlab for my Geophysics master all the time and I've never experienced such a hatelove, why, why, WHYYYYY?
Everything it does is done by Mathematica and BETTER.
Given the "in time" checks and all around development environment is pretty nice but it has so many.... stupid design decisions. And the synthax is not consistent AT ALL
Matlab is the best thing that ever happened to me
Also what's wrong with the syntax?
It's not consistent, commas are used differently on all occasions, parameters to basic functions like plot are sometimes given as string, sometimes given as extra parameters, symbolic calculation works but looks like ass, little this and thats here and there.
Compared to Mathematica I really don't see why people use it appart from convenient libraries.
You are clearly just requesting that Matlab becomes Mathematica, which is silly.
Matlab is not designed for symbolic calculation (as opposed to Mathematica), rather huge matrix (it's called MATRIX Lab for a reason) operations & shit like that. Or manipulating bulk data.
Also if you want to change the marker size, I think adding 'MarkerSize',5 to the plot function seems pretty straightforward. I don't see how else you would do that in code.
Can you give an example of commas being used differently on all occasions?
Well for example colour and markers are passed via one string like 'r*', stuff like seize and all that jazz is passed through 'MarkerSize',5
I can't really think of exact examples for the commas now but everything about the scripting language just seems counterintuitive after I've used FORTRAN and Mathematica for years now and I also really don't see anything that Matlab does better than Mathematica except for the development environment.
Both of them promote lazy use of ressources though.
Just yesterday someone defended his Master Thesis and was incredibly proud of his picking Algorithm only taking 38 hours to sample a few dozen thousand files, yet when you compare even the most basic calculations, normal programming in a language computes so much faster, FORTRAN being the fastest due to the awesome Intel libraries and of course C with CUDA.
I just don't get why people resort to Matlab for data processing when they could use more accurate and faster tools with a very very similar style of programming/scripting.
Maybe I'm just a bit stressed and needed a vent so thanks or that, thread.
Physics which is not done on pen and paper is for nerds.
I get so annoyed whenever a part of the physics community tries to offer a more nuanced definition of time and then a whole bunch of pop-science websites or internet pseudo-intellectuals jump on them and interpret their message as "time doesn't exist!"
it's even more irritating than when people just flat-out say "time isn't real because clocks are man-made" since they usually wrap their illiteracy in a veil of eloquence and philosophical bullshit and it ends up misinforming even more people
[QUOTE=Killuah;40331385]Well for example colour and markers are passed via one string like 'r*', stuff like seize and all that jazz is passed through 'MarkerSize',5
I can't really think of exact examples for the commas now but everything about the scripting language just seems counterintuitive after I've used FORTRAN and Mathematica for years now and I also really don't see anything that Matlab does better than Mathematica except for the development environment.
Both of them promote lazy use of ressources though.
Just yesterday someone defended his Master Thesis and was incredibly proud of his picking Algorithm only taking 38 hours to sample a few dozen thousand files, yet when you compare even the most basic calculations, normal programming in a language computes so much faster, FORTRAN being the fastest due to the awesome Intel libraries and of course C with CUDA.
I just don't get why people resort to Matlab for data processing when they could use more accurate and faster tools with a very very similar style of programming/scripting.
Maybe I'm just a bit stressed and needed a vent so thanks or that, thread.[/QUOTE]
Well I'm just the opposite (learning CUDA too atm, though, dat speed). I started out with Maple (horrible IMHO) and then started using Matlab, which I love. Never really got into Mathematica, though I'll learn it sometime...
Started reading some Arthur C. Clarke books. And damn they are done with precision and detail, for example in "Rendezvouz with Rama", the amount of detail he goes into the spacecraft is amazing.
Reminds me of the detail used in the book "Contact".
[editline]20th April 2013[/editline]
If I were a good director I'd like to make a movie about this book. With the right actors and good CGI, you could make an amazing movie about this book.
(I decided to post this here since we don't have a "Science Thread" anymore, and I figured a lot of you guys like Sci-fi.)
I only read fiction when I'm assigned to. I like some sci-if movies and though.
If you read the unabridged Jules Verne books they're more like textbooks than adventures, really gets you a knowledge and feeling of the science of that time.
He spends pages upon pages describing the machines.
Anyone here knows kirchhoff's rules well? I need to do a simple exercise by tomorrow, but I probably missed that lecture, so I don't know anything about it. There's a simple circuit with two batteries and a resistor, and I need to find the amperage.
[img]http://i.imgur.com/oYTZdsV.png[/img]
emf1=1, r1=1
emf2=2, r2=2 (w/e that means)
I hate when people ask me about tests after they're done
today we took one and one of the questions involved the flux per unit length of a long skinny loop of wire, ignoring the circular ends
the b field is constant as you go down the length, but it's not constant as you go from one wire to the other
that means you have to integrate from one wire to the other to find one "line" of b field, giving you an answer with ln() in it
but everyone i talked to says the b field will be constant, and has declared it as if it was obviously that, so they never even consider my answer as right, they just sorta assume im fully wrong
im not gonna make a scene and try to prove myself right, i know they dont really care so i just play along and let them pretend to be right
but it still just annoys me, because i could explain it well enough
I don't really get your task. Was it one closed wire loop or multiple?
I think this is the right place to ask this question as it pertains to the theory of relativity. I think it would have an easy answer, but I'm still boggled at it.
Since time is slowed down when near a large object as you know, traveling around a black hole has been hypothesized to mimic time travel because it moves so much slower there than on earth due to its insane mass. This is also true with GPS satellites orbiting earth too - if we didn't correct those daily our navigation could be off by as much as 6 miles.
So this brings me to my question: If you were in empty space without a force of gravity acting on you, would time dilate at an infinitesimally rate? If so, what would it be like coming back to a field of great gravity, with time being dilated less. Would you appeared to have traveled through time (without actually)
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