I have DVD called "What the Bleep do we know??!"
It's about Quantum Physics, I don't really think I understand how it really works.
Has anyone seen it? or know anything about Quantum Physics?
| Hayate wrote: |
I have DVD called "What the Bleep do we know??!"
It's about Quantum Physics, I don't really think I understand how it really works.
Has anyone seen it? or know anything about Quantum Physics? |
Yes. That film is ridiculous. -_- It's got about as much real science in it as Buck Rogers in the 25th Century.
Quantum physics encompasses a number of theories that define the elementary particles and interactions to be quantized, which simply means that that they are "digital" in nature. For example, electrical charge can be 1e, 2e, 3e, ne for any integer n, where e is the charge on an electron, but it can never be 1.2e or πe (this is a gross simplification, but it's the idea of it). Because matter is made up of atoms, a monofilament bar can only be 1 atom long, 2 atoms long or n atoms long where n is an integer, but it can't be 3½ atoms long because you can't have half an atom.
There are a number of quantum theories, ranging from quantum mechanics to quantum chromodynamics to string theory. Which theory are you interested in? The "standard model" is the one currently in use, but there's a whole lot of research being done in quantum gravity and string theory.
There are philosophical implications from quantum theories, but that film just goes way off into left field.I haven't seen the film, but I'm very interested in quantum mechanics. On the other hand I don't think I will ever understand it. It's really strange and more time you study it more questions arises. But try to study and you will be rewarded.
| redace wrote: |
| I haven't seen the film, but I'm very interested in quantum mechanics. On the other hand I don't think I will ever understand it. It's really strange and more time you study it more questions arises. But try to study and you will be rewarded. |
Unfortunately, both of your points are true. Quantum mechanics is difficult to understand because it requires that you have a very firm grasp of physics and math to conceptualize it. Classical mechanics is easy to understand because you can directly observe it in action, whereas this isn't the case for quantum - although you can make indirect observations. And it is true that all quantum theories are rather open-ended, because they're so new comparatively. We had classical mechanics pretty much down since Newton (although i'd say since Faraday figured fields out, or even better, since Maxwell), but all quantum theories are still under investigation. | Indi wrote: |
| Quantum mechanics is difficult to understand because it requires that you have a very firm grasp of physics and math to conceptualize it. Classical mechanics is easy to understand because you can directly observe it in action, whereas this isn't the case for quantum. |
Exactly. Most (if not all) of the theories in this field "give very good explanations" for several phenomena. So they are not actually proven, but accepted. And math is absolutely neccesary to understand (not to mention state) these theories.
Also, once you became familiar, it opens a whole new world, and helps understanding everything better.I took it in college. Believe me it was tough. Now that I'm done with the course, i dont' think remember much if any at all. Maybe just the thermodynamics stuff and possibly the derivations
| em0o wrote: |
| I took it in college. Believe me it was tough. Now that I'm done with the course, i dont' think remember much if any at all. Maybe just the thermodynamics stuff and possibly the derivations |
Believe me the basic courses cannot even tell you what is quantum mechanics about. The usual way in this courses is solving some types of potential in Schrödinger equation, then tell you something about harmonic oscillator and the creation and anihilation operators maybe something about spin, which is very unnatural and is 'fully' explained by Dirac and then comes the end of the course. But there is much more to study. Scattering theory is just one amazing topic. Try looking in Sakurai, some quantum optics books, Feynman and Landau (both the classical non-relativistic and quantum electrodynamics theory) and I'm sure you will be amazed how beautiful this theory is when you get behind some basics. But of course I don't say I understand basics, nobody knows what is the collapse of state.I'm absolutely fascinated by quantum physics. Some of the concepts are quite alien to human thought. I can't remember who it was that said "If it doesn't shock you, you don't understand it" (maybe Heisenberg?). The idea of a particle being in more than one place simultaneously and only settling for a particular place when it's observed is mind-boggling. And as for "spooky action at a distance", WTF!
i think the string theory is a load of crap
tons of college students are wasting their lives on a pointless study. even those who are testing it dont fully understand it. If anyone ever finds a flaw in it they just adapt the theory to explain everything. the thing is it can never be proven and will never be proven.
anyone willing to back me up on this?
| Wahwah Man wrote: |
| i think the string theory is a load of crap |
Ok?
| Wahwah Man wrote: |
| tons of college students are wasting their lives on a pointless study. |
And this makes it unique among college courses how?
| Wahwah Man wrote: |
| even those who are testing it dont fully understand it. |
Then how are they "testing" it? Randomly? "Gee, Bill, I want to test a part of string theory. What do you think I should do?" "Well, Al, maybe we could set up a few particle collisions. Measure some voltages. Some crap like that, eh?" "Sure sounds good, what the hell? I got grant money to burn."
| Wahwah Man wrote: |
| If anyone ever finds a flaw in it they just adapt the theory to explain everything. |
*blink*
Isn't that the point?
| Wahwah Man wrote: |
| the thing is it can never be proven and will never be proven. |
Define "proven".Pretty much agree with a lot that has been posted. I'll post some links at the end which may help if you are determined to go for it. They link to resources on my site which you can download and use as a basis for a self-study course in physics which will take you up to the level of QM.
The documents are several megabytes long so be aware that it may take some time to download depending on your link.
A couple of points to emphasise before you decide whether to go for it or not:
1. QM is difficult. The math is non-trivial to put it mildly, and you need to be very familiar with calculus before even starting to try and get to grips with QM
2. QM is also counter-intuitive to a very high level. As Feynman said - we know exactly what is happening [in QM] and can predict outcomes to an astonishing degree of accuracy, but we can't describe the mechanisms, because it's just plain screwy, so we don't try anymore. In the QM world things behave in very strange ways - in ways that things in our world (the Macro universe) do not behave. It is therefore impossible to teach QM using analogies because there are no suitable analogies. You cannot say - 'it is like....', because it is not like anything...
OK....if you still want to go for it and learn QM then here is my suggested list of d/loads......
1. Download a Physics text book as the basis for study. T
Click here to load Physics text book (Adobe Acrobat format)
2. If your math is weak (if you know no calculus for example), or if you could do with a refresher on math, then you will need some calculus texts. Download the two texts below. (Word format)
Click here to load math text 1
Click here to load math text 2
3. Here is a link to Chapter 21 (on QM) of Roger Penrose's excellent book 'The Road to Reality'. I downloaded this a while ago from a bookseller site.
NB - All the above materials (with the exception of the Penrose chapter) are either copyright free or free for educational use. The license and other information can be checked HERE
Regards
Chris | Bikerman wrote: |
Pretty much agree with a lot that has been posted. I'll post some links at the end which may help if you are determined to go for it. They link to resources on my site which you can download and use as a basis for a self-study course in physics which will take you up to the level of QM.
The documents are several megabytes long so be aware that it may take some time to download depending on your link.
A couple of points to emphasise before you decide whether to go for it or not:
1. QM is difficult. The math is non-trivial to put it mildly, and you need to be very familiar with calculus before even starting to try and get to grips with QM
2. QM is also counter-intuitive to a very high level. As Feynman said - we know exactly what is happening [in QM] and can predict outcomes to an astonishing degree of accuracy, but we can't describe the mechanisms, because it's just plain screwy, so we don't try anymore. In the QM world things behave in very strange ways - in ways that things in our world (the Macro universe) do not behave. It is therefore impossible to teach QM using analogies because there are no suitable analogies. You cannot say - 'it is like....', because it is not like anything...
OK....if you still want to go for it and learn QM then here is my suggested list of d/loads......
1. Download a Physics text book as the basis for study. T
Click here to load Physics text book (Adobe Acrobat format)
2. If your math is weak (if you know no calculus for example), or if you could do with a refresher on math, then you will need some calculus texts. Download the two texts below. (Word format)
Click here to load math text 1
Click here to load math text 2
3. Here is a link to Chapter 21 (on QM) of Roger Penrose's excellent book 'The Road to Reality'. I downloaded this a while ago from a bookseller site.
NB - All the above materials (with the exception of the Penrose chapter) are either copyright free or free for educational use. The license and other information can be checked HERE
Regards
Chris |
I agree with you. But it is not only about calculus. One have to understand very deeply classical mechanics. Poisson brackets, Hamilton-Jacobi and so on. There are also many analogies with classical mechanics. For example Heisenberg picture of world and his (Dirac's) equation of motion for operators is very nice and in the limit it gives classical mechanic equation. But of course opposite way is not possible. Also a lot of algebra is needed and I think more than calculus, because when one doesn't understand Hilbert space, hermicity and so on, almoust all fields of quantum mechanics are prohibited to him. A calculus of complex variable is needed. And of course some special function for solving Schr. equation. By the way what about quantum electrodynamics?It is cute to derive a propagator of photon and all that slash, slash seems like everythings is wrong:) Do you have some interesting materials on this topic?quote="Wahwah Man"]i think the string theory is a load of crap
tons of college students are wasting their lives on a pointless study. even those who are testing it dont fully understand it. If anyone ever finds a flaw in it they just adapt the theory to explain everything. the thing is it can never be proven and will never be proven.
anyone willing to back me up on this?[/quote]
Um, well maybe a little. First, believe me, there's not tons of college students taking string theory. It's one of the most tricky mathmatical adventures that science has ever been on, and no undergraduate is ready for that. Secondly, how many people do you know that have ever even taken advanced graduate courses? Take that small number, divide by about 4, and thats about how many would take such a course in graduate physics.
To say that the people 'testing' it don't fully understand it is an incorrect statement as well. Nobody is testing anything in string theory, but this is where you might have an argument. If the theory is not testable, is it still physics (or science for that matter)? I argue that it's not. I won't give up hope that someday we might find a way to test the theory, but until then science has not been done. Therefore, in my mind, it cannot ever be labeled a valid scientific theory.
Another note on that statement as well. Nobody every fully understands ANY theory in physics. Study any branch of physics. You'll never hit the end of the road.
| Bikerman wrote: |
Pretty much agree with a lot that has been posted. I'll post some links at the end which may help if you are determined to go for it. They link to resources on my site which you can download and use as a basis for a self-study course in physics which will take you up to the level of QM.
The documents are several megabytes long so be aware that it may take some time to download depending on your link.
A couple of points to emphasise before you decide whether to go for it or not:
1. QM is difficult. The math is non-trivial to put it mildly, and you need to be very familiar with calculus before even starting to try and get to grips with QM
2. QM is also counter-intuitive to a very high level. As Feynman said - we know exactly what is happening [in QM] and can predict outcomes to an astonishing degree of accuracy, but we can't describe the mechanisms, because it's just plain screwy, so we don't try anymore. In the QM world things behave in very strange ways - in ways that things in our world (the Macro universe) do not behave. It is therefore impossible to teach QM using analogies because there are no suitable analogies. You cannot say - 'it is like....', because it is not like anything...
OK....if you still want to go for it and learn QM then here is my suggested list of d/loads......
1. Download a Physics text book as the basis for study. T
Click here to load Physics text book (Adobe Acrobat format)
2. If your math is weak (if you know no calculus for example), or if you could do with a refresher on math, then you will need some calculus texts. Download the two texts below. (Word format)
Click here to load math text 1
Click here to load math text 2
3. Here is a link to Chapter 21 (on QM) of Roger Penrose's excellent book 'The Road to Reality'. I downloaded this a while ago from a bookseller site.
NB - All the above materials (with the exception of the Penrose chapter) are either copyright free or free for educational use. The license and other information can be checked HERE
Regards
Chris |
You'll need not only calculus, but linear algebra, ODE and even PDE is helpful.May i ask for confirmation on general definition of quantum physic, is it the study of the behavior of particle at subatomic level ?? Other than that, i thought the theory is quite randomized and have a lots of uncertainty...
sorry if anything i post sound ridiculous.... 
QM, is in two words " a game".
The NATURE said that you humans should made a game.
Some body like Boler and Hesinberger or Shrodinger jump out and seted up a game.
Thousands of Physicists later began to play with it, and thousands of Physicists are now playing with it and some time later thounsands of Physicists will play with it or just make another game......
The player now has already forgoten why should they play with the game.....
QM is leaving far and far way from what it supposed to be developed to.
| y06hci0088 wrote: |
May i ask for confirmation on general definition of quantum physic, is it the study of the behavior of particle at subatomic level ?? Other than that, i thought the theory is quite randomized and have a lots of uncertainty...
sorry if anything i post sound ridiculous.... |
Not only at subatomic level. You can almost see the laws of quantum mechanics when you are at very low teperatures. Superfluidity, superconductivity are the examples. And superconductivity can be seen at very "high" temperatures now. And by the way quantum mechanics is just better model of our world then th classical physics. We are using classical physics in situations where this theory is a good approximation, but when not we most use a more sophisticated theories like general relativity and quantum physics. This theories are quite good models but better is hopefully on the way, but it doesn't mean that our old model was wrong. Every new model must have old models inside itself in the limit of some kind. | y06hci0088 wrote: |
May i ask for confirmation on general definition of quantum physic, is it the study of the behavior of particle at subatomic level ?? Other than that, i thought the theory is quite randomized and have a lots of uncertainty...
sorry if anything i post sound ridiculous.... |
QM is defined as | Quote: |
| the physical science used to calculate and analyze the energies and spatial distributions of small particles confined to very small regions of space. |
The theory is not at all randomised and does not have lots of uncertainty. This is a common misunderstanding arising from the fact that QM is based on the fact that particles behave in a probabilistic manner rather than a deterministic manner - ie you cannot, for example, say for sure whether a particular photon will reflect back from a glass surface or pass through it. You can, however, say for sure that a certain percentage will do so.
Regards
Chris | Bikerman wrote: |
| you cannot, for example, say for sure whether a particular photon will reflect back from a glass surface or pass through it. You can, however, say for sure that a certain percentage will do so. |
(mmmm >_< *remains silent* ^_^; )
Bikerman's definition is technically correct, but when i explain quantum mechanics to non-scientists, i try to put it in simple terms that - while they may not be technically useful - take the confusion and fear out of the concept.
First you have to de-mystify the word "quantum". When things are "quantized", they occur in discrete packets. For example, crowds are quantized, because they are made up of people, and you can't have half a person. You can only have a crowd the size of 0, 1, 2, 3... N people, where N is an integer. You can never have a crowd of 100.45 people. It's either 100 or 101. Therefore, crowds are quantized, and the quantum is a person (two people are two quanta of a crowd).
Old school physics has some quantized concepts, like charge. The smallest unit of negative charge is the electron, and you can't have half an electron. Therefore, the charge of something must be N × e, where e is the charge of an electron and N is an integer. You can have a charge of 0e, 1e, 2e, 3e... Ne, but you can never have a charge of 100.45e - it's either 100e or 101e. Therefore, charge is quantized, and the quantum of negative charge is the electron.
Even matter was (mostly) quantized in classical physics. You can have no atoms of oxygen, or 1, 2, 3... N atoms of oxygen, but you can never have 100.45 atoms of oxygen - it's 100 or 101. And even within atoms, you can never have 3.6 neutrons, 7.9 protons and π electrons. Every one of those numbers must be an integer. So you can always express the amount of matter that you have as an integer number of protons, neutrons and electrons.
What quantum mechanics added was that things that we didn't think were quantized before turn out to be quantized. You wouldn't think that things like force and momentum could be discretely quantized, but they can. And the old model of the atom has electrons orbiting about the nucleus like planets around the sun, but it turns out that they can only exist in certain orbits - their orbits are quantized.
Unfortunately, once you start quantizing things, the math starts to get really icky. You need continuous functions for most things in math, like calculus. Discrete math is easy at basic levels, but gets brutal fast. Discrete (or finite) math means you start getting into things like probabilities and Markov chains and so on. Brutal.
But experimental evidence says these things are quantized, so we need to use discrete math to understand them. And when we do, we start getting into the "weirdness" that most people associate with quantum mechanics - where everything becomes probabilities.
That's pretty much how quantum mechanics came about. No mystery, no magic. That's also why it seems a little weird and counterintuitive - because discrete math gets really complex really fast and they don't really match our experience. You know that if you toss a ball and it travels 100 cm, it will travel 33.33 cm if you only toss it a third as hard. Only if it were macroscopically quantized, it wouldn't. It would go 33 or 34 if 1 were the quantum, or 30 or 40 if 10 were the quantum, or even 0 or 100 if 100 were the quantum, and probability would determine which. Can you wrap your head around what that would be like? You would throw a ball and it would land 100 cm away. Then you throw it half as hard, and you don't know whether it will land 100 cm away... or not go anywhere. Freaky.
But, as i said, experimental evidence verifies all this. At our level of experience, the quanta are so small, and the numbers so huge, that they appear continuous. For the case of a single particle, imagine it can only have an energy of 0 units or 100 units. Imagine you apply 30 units of energy to the particle, and that that means there's a 30% chance it will jump to 100, and a 70% chance it will stay at 0. What will that particle do? You don't know. Chances are it will stay at 0, but maybe not.
Now consider a million such particles, each given 30 units of energy for a total of 30 million units of energy you put into the system. Each particle will either go to 0 or 100, but in general, statistically speaking, 70% of the particles will stay at 0 (700,000 particles at 0), and 30% will go to 100 (300,000 at 100) (like Bikerman, i'm glossing over the process here). So now if you measure the ((700,000 × 0 + 300,000 × 100) = 30,000,000 total energy; 30,000,000 ÷ 1,000,000 = 30 units per particle) average amount of energy in that system, you have 1 million particles that have absorbed 30 million units of energy, which means the average energy of each particle is 30. No particle actually has an energy of 30. They all have an energy of 0 or 100. But on average, it appears that they have an energy of 30.
That's why things appear continuous to us. But they're not. Everything is quantized.
That's pretty much the beginner's guide to quantum mechanics.I'm happy to accept Indi's correction/elaboration above...much better explained than my effort:-)
C
first of all, i myself don't know much about QM. but to those who know something and want to research on it, here is an article from wikipedia:
There are numerous mathematically equivalent formulations of quantum mechanics. One of the oldest and most commonly used formulations is the transformation theory invented by Cambridge theoretical physicist Paul Dirac, which unifies and generalizes the two earliest formulations of quantum mechanics, matrix mechanics (invented by Werner Heisenberg)[1] and wave mechanics (invented by Erwin Schrödinger).
In this formulation, the instantaneous state of a quantum system encodes the probabilities of its measurable properties, or "observables". Examples of observables include energy, position, momentum, and angular momentum. Observables can be either continuous (e.g., the position of a particle) or discrete (e.g., the energy of an electron bound to a hydrogen atom).
Generally, quantum mechanics does not assign definite values to observables. Instead, it makes predictions about probability distributions; that is, the probability of obtaining each of the possible outcomes from measuring an observable. Naturally, these probabilities will depend on the quantum state at the instant of the measurement. There are, however, certain states that are associated with a definite value of a particular observable. These are known as "eigenstates" of the observable ("eigen" meaning "own" in German). In the everyday world, it is natural and intuitive to think of everything being in an eigenstate of every observable. Everything appears to have a definite position, a definite momentum, and a definite time of occurrence. However, quantum mechanics does not pinpoint the exact values for the position or momentum of a certain particle in a given space in a finite time, but, rather, it only provides a range of probabilities of where that particle might be. Therefore, it became necessary to use different words for a) the state of something having an uncertainty relation and b) a state that has a definite value. The latter is called the "eigenstate" of the property being measured.
A concrete example will be useful here. Let us consider a free particle. In quantum mechanics, there is wave-particle duality so the properties of the particle can be described as a wave. Therefore, its quantum state can be represented as a wave, of arbitrary shape and extending over all of space, called a wavefunction. The position and momentum of the particle are observables. The Uncertainty Principle of quantum mechanics states that both the position and the momentum cannot simultaneously be known with infinite precision at the same time. However, we can measure just the position alone of a moving free particle creating an eigenstate of position with a wavefunction that is very large at a particular position x, and zero everywhere else. If we perform a position measurement on such a wavefunction, we will obtain the result x with 100% probability. In other words, we will know the position of the free particle. This is called an eigenstate of position. If the particle is in an eigenstate of position then its momentum is completely unknown. An eigenstate of momentum, on the other hand, has the form of a plane wave. It can be shown that the wavelength is equal to h/p, where h is Planck's constant and p is the momentum of the eigenstate. If the particle is in an eigenstate of momentum then its position is completely blurred out.
Usually, a system will not be in an eigenstate of whatever observable we are interested in. However, if we measure the observable, the wavefunction will instantaneously be an eigenstate of that observable. This process is known as wavefunction collapse. It involves expanding the system under study to include the measurement device, so that a detailed quantum calculation would no longer be feasible and a classical description must be used. If we know the wavefunction at the instant before the measurement, we will be able to compute the probability of collapsing into each of the possible eigenstates. For example, the free particle in our previous example will usually have a wavefunction that is a wave packet centered around some mean position x0, neither an eigenstate of position nor of momentum. When we measure the position of the particle, it is impossible for us to predict with certainty the result that we will obtain. It is probable, but not certain, that it will be near x0, where the amplitude of the wavefunction is large. After we perform the measurement, obtaining some result x, the wavefunction collapses into a position eigenstate centered at x.
Wave functions can change as time progresses. An equation known as the Schrödinger equation describes how wave functions change in time, a role similar to Newton's second law in classical mechanics. The Schrödinger equation, applied to our free particle, predicts that the center of a wave packet will move through space at a constant velocity, like a classical particle with no forces acting on it. However, the wave packet will also spread out as time progresses, which means that the position becomes more uncertain. This also has the effect of turning position eigenstates (which can be thought of as infinitely sharp wave packets) into broadened wave packets that are no longer position eigenstates.
Some wave functions produce probability distributions that are constant in time. Many systems that are treated dynamically in classical mechanics are described by such "static" wave functions. For example, a single electron in an unexcited atom is pictured classically as a particle moving in a circular trajectory around the atomic nucleus, whereas in quantum mechanics it is described by a static, spherically symmetric wavefunction surrounding the nucleus (Fig. 1). (Note that only the lowest angular momentum states, labeled s, are spherically symmetric).
The time evolution of wave functions is deterministic in the sense that, given a wavefunction at an initial time, it makes a definite prediction of what the wavefunction will be at any later time. During a measurement, the change of the wavefunction into another one is not deterministic, but rather unpredictable, i.e., random.
The probabilistic nature of quantum mechanics thus stems from the act of measurement. This is one of the most difficult aspects of quantum systems to understand. It was the central topic in the famous Bohr-Einstein debates, in which the two scientists attempted to clarify these fundamental principles by way of thought experiments. In the decades after the formulation of quantum mechanics, the question of what constitutes a "measurement" has been extensively studied. Interpretations of quantum mechanics have been formulated to do away with the concept of "wavefunction collapse"; see, for example, the relative state interpretation. The basic idea is that when a quantum system interacts with a measuring apparatus, their respective wavefunctions become entangled, so that the original quantum system ceases to exist as an independent entity.
just search it there, and you will get all you want. i could have given you a more detailed explanation had i known more about this.........but right now, i am concentrating more on astronomy than genereal physics!!! 
Here's a link to the trailer for that movie
What the bleep do we know
http://www.whatthebleep.com/trailer/drh-trailer.shtml
It has been on cable TV several times.
Check out titantv.com for your local listings for it.
My cable system is going to reshow it
S-EDGE 403 12/17/2006 12:50 PM
S-CINE 409 12/23/2006 5:50 AM
S-CINw 410 12/23/2006 8:
S-CINE 409 12/23/2006 5:20 PM
S-CINw 410 12/23/2006 8:20 PM
It's worth seeing. If you've never heard of it, Raymond Chao did an experiment at the University of California Berkley using quantum physics and managed to achieve faster-than-the-speed-of-light-travel. Unfortunately, it was just the light that was faster than light, not him. But still a good experiment to look at. There's something about it on http://www.vectorsite.net/tarokt_7.html, but I don't remember where the experiment's main site was. (and Google didn't find it.)
