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What is Quantum Physics?
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Clanad: speeds approaching the speed of light? What does that have to do with quantum mechanics?
pebblesnbamb:
ok, so think back to about 1880 or so. and before that time. people like Newton far before this time worked out calculations for things like balls rolling down hills, that sort of stuff. All this sort of thing (basically everyday type of science) is called classical mechancs. bouncing balls, the orbits of the planets, everything you've ever done at GCSE physics, all of that.
then they wanted to know what stuff was made from. you've heard of atoms right? (this is probably more chemistry to you, but trust me, it started out as physics). when they began messing about with this really small stuff, they found that their calculations (based on assuming that the atom is like the sun, with electrons orbiting around it, etc.) didnt work at all. so they knew something strange was going on.
at the same sort of time, it's also important to remember that they thought all energy was continuous. what i mean by this is that a scale can be either continuous or discreet. continuous means you can have values like 2.3434 or 5.343 or whatever. discreet means that they come in certain intervals, like 2,4,6,8 (with values like 3, 5, etc. not existing at all) or 1.1,1.2,1.3,1.4 (with 1.15 or 1.16 etc. simply not existing). if you were to stand by a road and count the number of cars that passed you, you'd end up with discreet data, as you'd count 5 or 6 or 56 or something. never 4.345 cars. however, your height can be continuous, as you could be 1.93m tall, 1.4837m tall, anything at all.
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pebblesnbamb:
ok, so think back to about 1880 or so. and before that time. people like Newton far before this time worked out calculations for things like balls rolling down hills, that sort of stuff. All this sort of thing (basically everyday type of science) is called classical mechancs. bouncing balls, the orbits of the planets, everything you've ever done at GCSE physics, all of that.
then they wanted to know what stuff was made from. you've heard of atoms right? (this is probably more chemistry to you, but trust me, it started out as physics). when they began messing about with this really small stuff, they found that their calculations (based on assuming that the atom is like the sun, with electrons orbiting around it, etc.) didnt work at all. so they knew something strange was going on.
at the same sort of time, it's also important to remember that they thought all energy was continuous. what i mean by this is that a scale can be either continuous or discreet. continuous means you can have values like 2.3434 or 5.343 or whatever. discreet means that they come in certain intervals, like 2,4,6,8 (with values like 3, 5, etc. not existing at all) or 1.1,1.2,1.3,1.4 (with 1.15 or 1.16 etc. simply not existing). if you were to stand by a road and count the number of cars that passed you, you'd end up with discreet data, as you'd count 5 or 6 or 56 or something. never 4.345 cars. however, your height can be continuous, as you could be 1.93m tall, 1.4837m tall, anything at all.
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anyway, to solve some problem (the blackbody problem), he decided that energy came in "quanta", meaning little packets of energy, little blocks that cant be split up. and he said that the gap between these stages of energy was a constant, which we call Planck's constant (denoted by letter "h"). so instead of the energy of a photon (the particle that makes up light) being able to have any energy at all, it has to have an energy band like this:
energy1
... add planck's constant
energy2
... add planck's constnat
energy3
so it is a discreet quantity! where each little bundle of energy that we now know to exist is called a "quanta" of energy, hence quantum mechanics. anything that does not rely on this system of thought is not quantum mechanics, and is therefore classical mechanics. this includes einstein's two theories of relativity.
there were also other developments a bit later on from this too. at this time, some things were thought to be particles, and other things waves. Louis de Broglie had the idea that perhaps everything can be both, and it just depends on how you observe the thing to see if you see it as a wave or a particle.
add Schrodinger's wave mechanics (the mathematics behind modern quantum mechanics), and you get to the meat of the subject. at the same time, Heisenberg also develope a system called matrix mechanics, which gives the same outcome as Schrodinger's wave mechanics. so we call these things representations of the quantum theory. they're just two ways of looking at the same thing. Dirac showed this, and developed a cool notation that is representation-independant. he also went on to develop a quantum theory of the electon, taking einstein's special relativity into account (special relativity just tells you that strange things happen when things go really really fast).
anyway, to solve some problem (the blackbody problem), he decided that energy came in "quanta", meaning little packets of energy, little blocks that cant be split up. and he said that the gap between these stages of energy was a constant, which we call Planck's constant (denoted by letter "h"). so instead of the energy of a photon (the particle that makes up light) being able to have any energy at all, it has to have an energy band like this:
energy1
... add planck's constant
energy2
... add planck's constnat
energy3
so it is a discreet quantity! where each little bundle of energy that we now know to exist is called a "quanta" of energy, hence quantum mechanics. anything that does not rely on this system of thought is not quantum mechanics, and is therefore classical mechanics. this includes einstein's two theories of relativity.
there were also other developments a bit later on from this too. at this time, some things were thought to be particles, and other things waves. Louis de Broglie had the idea that perhaps everything can be both, and it just depends on how you observe the thing to see if you see it as a wave or a particle.
add Schrodinger's wave mechanics (the mathematics behind modern quantum mechanics), and you get to the meat of the subject. at the same time, Heisenberg also develope a system called matrix mechanics, which gives the same outcome as Schrodinger's wave mechanics. so we call these things representations of the quantum theory. they're just two ways of looking at the same thing. Dirac showed this, and developed a cool notation that is representation-independant. he also went on to develop a quantum theory of the electon, taking einstein's special relativity into account (special relativity just tells you that strange things happen when things go really really fast).
So, fo3nix, you reference Planck's Constant as a neccessary component of quanta investigation. Turns out, as explained by Max Planck in 1900, that E = hν. The value of h is described thusly h = 6.626068 10�34 joule-sec. You would agree this is a very small number. In his now legendary investigation into black-body radiation Planck also derived Planck's Length and Planck's Mass (I cannot, due to limitations in this site, produce the equations). Inherent in each equation is the term c. I think this is a reference to the speed of light, is it not? Simply stated an inherent in Quantum Mechanics is that the position of an object can only be determined (due to the Heisenberg Uncertaintity Principle) at a distance equal to Planck's Length. Meaning it would be impossible to distinguish a speed of zero (at rest) from a speed of 22.89 m/s (75.09843 ft/s. I probably should have more accurately said at the speed of light, since it is a requirement for any of Planck's definitions and hence, any discovery of the quantum mechanical affects... In my opinion...
potterfan3: this is the many-worlds theory.
if you look into the Schrodinger cat thought experiment (please, don't turn it into a real experiment!), then you find that it's based on what happens when there's an exactly 50:50 chance of a cat dying in a closed box. What happens? Does it die, or does it stay alive? The thing about the experiment is that you don't know until you open the box and observe what's happened.
The many worlds theory says that when something like this happens (a choice has to be made), the universe splits into two: one where the cat dies, the other where the cat is still alive.
I must stress that it's only a theory, even more so than quantum theory itself.
if you look into the Schrodinger cat thought experiment (please, don't turn it into a real experiment!), then you find that it's based on what happens when there's an exactly 50:50 chance of a cat dying in a closed box. What happens? Does it die, or does it stay alive? The thing about the experiment is that you don't know until you open the box and observe what's happened.
The many worlds theory says that when something like this happens (a choice has to be made), the universe splits into two: one where the cat dies, the other where the cat is still alive.
I must stress that it's only a theory, even more so than quantum theory itself.
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