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pmb

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Posts posted by pmb

  1. If you believe someone is doggedly responding with an answer contrary to the convention then they deserve to be neg repped...it is important in the science part of these forums for the benefit of layman like myself. I confess to being somewhat confused now to the true status of W/P Duality in the physics community today.

    Check your PM. I sent you a treatment of the Wave-Particle Duality. You should find it very helpful.

     

    Not necessarily. If they're responding contrary to the mainstream of physics, I expect the bar on their evidence to be that much higher, but I don't automatically dismiss their claims unless, as pmb said, they are simply blatantly wrong, or putting forth arguments that have been repeatedly addressed and found lacking.

    Those kinds of thing belong in the forum where people post speculations, not in the physics forums.

  2. Thank you.

    Note: A photon doesn't have a 4-velocity. A 4-vlocity requires dividing by a proper time interval on the photons world line and that's always zero, hence there's no 4-velocity for photons (or any other luxon).

  3. Looks ok to me...point no.7 on your minus list would depend on how and with what they were pursing their point. If they are presenting a novel speculation and throw everything they've got, logically and amiably, in support of it then it doesn't deserve neg repping imo but I would expect them to concede when they hit an insurmountable counter-argument eventually.

    Example: Almost every QM text that I have explains the wave-particle duality and what it means. This is a well-defined and unbiversally accepted phenomena with endles reams of data to sup[port it. Yet there are places where people claim that there is no such thing as a wave-particle duality. When I see people say that I neg-rep them. Then there's relativistic mass. People claim that nobody uses it and yet the majority of current relavity textbooks uses the concept. So when I see people claim that nobody uses it I neg-rep them. Its always something which I have a lot of evidence which demonstrates that they're wrong. There was a time that someone was trying to convince me that a photon had a 4-velocity, which it doesn't. I would have neg repper them if there was a system in place to do that. But its all objective things that I'm referring to. Not mere disagreement over something.

  4. Which is what I keep saying.

    I appologize for being unclear. I'm very cautious whn I say things like that because, at least in my eyes, its quite tricky. For example: What exactly is an experimental set up? If I have 10,000 doub;e slit experiments set up each of which only one particle goes through. In each case the electron is localized when it hits the screen, where the position is then recorded. In each experiment there is no wave property other than the wave being used to prdict where the electron will be. The ensemble of experimental set ups shows that there is intereference as an enemble but there's no way that it can be said that electrons are interfering with each other. Do you see why I'm cautious?

  5. Artificially influencing rep by the use of sockpuppet accounts or other 'illegal' method should be combed for if suspected...my point was really just towards people who use the system normally but whose pattern of choices one may not agree with...let 'em get on with it.

    Here's how I used to use it.

     

    Reasons for a + rep

     

    (1) Funny post

    (2) Good physics

    (3) Beautiful way of saying something

    (4) When someone refrains from lashing out

    (5) Positive emotions

     

    Reason for a - rep

    (1) When someone intults someone else

    (2) A veiled attempt at insulting someone

    (3) Negative emotions

    (4) When someone lashes out

    (5) Angry comments

    (6) Arrogance

    (7) Saying things which goes against textbook physics

     

    If nobody has a problem with that then I'd feel comfortable using it again. Anybody?

  6. It is ironic that a poster gives an old quote from Dirac about wavefunctions in her/his personal attacks to posters who do not buy the duality myth.

    Nobody used a personal attack against anybody else in this thread. We disagree with you. I scanned and PMd the section of the wave-particle duality from my graduate text on quantum mechanics to the people in this thread. They already know what its all about.

     

    Historical Note: It was Author Eddington who coined the term wavicle

     

    The following is, in essence, what the wave-particle duality is all about.

     

    Simply put: All experiments on diffraction and interference effecs with articles show that a definite wavelength is associated with partilces of a a given momentum.

     

    That's the very definition of wave-particle duality. This is just straight textbook quantum mechanics. Has C. Ohanian describes it as follows in his text Modern Physics - 2nd Ed. on page 147

    Are electrons classical particles or waves? They are niether. They are wavicles, or quantunm-mechanical particles--they have some properties of a classical partilce and some properties of a classical wave. We say that electrons exhibit duality: they sometimes behave like particles, and sometimes behave like classical waves. The electrons behave in one way or another depending on the experimental arrangement.

    This is the definition of what the term wave-particle duality means. Anyh atempt to claim otherwise is just plain wrong.

  7. The time vanishing from GR is a result of quantizing the EFE equations and out of which you get the Wheeler de Witt equation, which is the timelessness one speaks about at the heart of GR.

    That doesn't downplay the concept of time. Einstein's field quations are about defining a gravitational field. That field may vary with time and free particles which are in the field change their position as a function of time.

     

    At this point in time I'm going to back out and leave it be. I've said all I've had to say and anything more would just be repetition. We'll just have to agree to disagree my friend.

  8. Further you need to state whether you are using manifold in the general sense as just a collection of elements of a set.

    I disagree. First off its the context which tells you what the manifold is. Second, quite often when one uses the term manifold its because they want to emphasize that its not physical space.

  9. Read my description again, in post#64.

    Consider it done.

     

    They do in a beam tetrode or cathode ray tube.

    A beam of electrons is not a trajedctory. If it was possible for an electron to follow a classical trajectory precisely then the curve would have a width of zero. The beam width of an eletron beam is very very very far from being a partilce trajectory. If someone is talking about such a trajectorey thn they are ignoring quantumn effects. That's done quite often in classical mechanics but never in quantum mechanics.

  10. How do you get someone to be convinced that time doesn't really exist, only the experience of time exists?

    You can't. Different people have their own ideas of what time is all about. I explained mine already when I used the analog with the electric field.

     

    It vanishes from the equations ..

    I strongly disagree. Consider the Lorentz force equation

     

    [math]\frac{dp^{\alpha} }{d\tau} = \frac{q}{c} F^{\alpha\beta} U_{\beta}[/math]

     

    That has time explicitly in it.

     

    and in general relativity, the motion of systems aren't even represented by true time evolution's - motion arises as a symmetry of the theory. Worldline's are static as well, so there is no past or future;

    Worldlines are a set of variables which determines a curve. One of those variables is time.

     

    I certainly couldn't add anything more to your posts. Though I'd like to ask you, do you consider there being more to a space than thinking of it as a degree of freedom?

    Yes. I don't think of space as beng a degree of freedom. The number of parameters required to uniquely specify the system is called the number of degrees of freedom. The system that those numbers are decribing isn't a degree of freedom.

  11. To me, a space is just a degree of freedom, of course my mind seems somewhat at odds with that when you think of a Hilbert Space, which could just be a point... in fact, people tend to think that [math]\psi[/math] is some point on a Hilbert Space [math]H[/math]. So I don't know... I guess a space means somewhere with some kind of length and width. Wikipedia's explanation is very mathematical in its use of defining space, but it is perhaps truer.

     

    I guess you could say, ''I have a simple understanding of what a space is''.

    I believe that if you were to think of it simple as a set then you'd bve safe. Hilbert space is a set of functions. I'm just trying to get ytou to understand the difference between physical space a mathematical space.

     

    When I was in college studying to become a physicist I saw that if I took manth courses instead of basket weaving I could have a second majopr in math. And with physics you can't have enough math. That's why I'm familiar with mathematical spaces.

  12. Just as I described in my lecher lines, however they can move along definite trajectories note the key word assuming.

    I think you may have misinterpreted that quote. Electrons cannot follow definite trajectories. That's what it was saying, i.e. its not a particle in the sense that it can move along definite trajectories.

  13. In fact, I think I will write up a thread on time, because it is an interesting subject.

    I'm curious about something so please bear with me. Have you never heard the term space used in any other sense than "place inside a room"? For example when you hear the term Hilbert Space as being a function space, what did the term space mean to you?

     

    Wikipedia defines Space in the mathematical sense as follows

    http://en.wikipedia.org/wiki/Space_(mathematics)

    In mathematics, a space is a set with some added structure.

     

    Mathematical spaces often form a hierarchy, i.e., one space may inherit all the characteristics of a parent space. For instance, all inner product spaces are also normed vector spaces, because the inner product induces a norm on the inner product space such that:

     

    [math]||x|| = \sqrt{<x, x>}[/math]

     

    Modern mathematics treats "space" quite differently compared to classical mathematics.

  14. When staying over at my partners last night, I found myself thinking about ways I could explain myself better. I don't believe time actually points out spatial locations, but the notion that space is inseparable to time is fundamentally unique. Time was just another space dimension, an imaginary space dimension in the Minkowski understanding. It's certainly not a ''real space dimension'' (using real as in the mathematical sense), because when people often talk about the spacetime continuum, is that it has three space dimensions and one temporal dimension. This is true, but time if a very special type of imaginary space dimension.

     

     

    What could be throwing you off my statements, is that I am saying it is a dimension of space - well, what I really am saying it is an ''imaginary space dimension''. As I tried to explain, all time is for the spacetime metric is that time is simply an imaginary leg off the real legs of the spacetime triangle. It's an added dimension which many have dubbed ''the imaginary space dimension.''

    Yes. And as I've been trying to say is that time is a dimension of the spacetime manifold. A manifold is a collection of elements which satisfies certain properties. It is a space in the mathematical sense of the term, not as space as in "position of something inside my living room." It's a space in the abstract sense as I've given examples for in the post above.

     

    I'm glad we got that cleared up. :)

  15. Let's get something straight. The wave-particle duality is no a myth. In fact its a subject that you can find defined and described in all textbooks on quantum mechanics. It has a very precise meaning which is defined here http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality.

     

    I have a graduate level quantum mechanics text called Principles of Quantum mechanics - 2nd Ed. by R. Shanmkar. From page 113

    We found that entities such as the electron are particles in the classical sense in that when detected they seem to carry all their energy, momentum, charge, etc. in localized form: and at the same time that are not particlelike in that assuming they move along definite trajectories leads to conflict with experiment. It appears that each particle has associated with it a wave function [math]\Psi(x, t)[/math], such that [math]|\Psi(x, t)|^2[/math] gives the probability of finding it at a point c at time t. This is called wave-particle duality.

    That is the precise meaning of wave-particle duality.

  16. Well it existed yesterday and today so it has time coordinates (y,t)

    I don't understand what you mean by this. The letter "y" usually refers to a spatial variable, not a temporal one. And here you have two variables when a time coorinate only uses one. So what does (y, t) mean?

     

    So it has 4D coordinates (a,b,c,d,ct) and (a,b,c,d,cy) and everything in between.

    Again, you seem to be using a spatial coordinat, y, where a temporal one is usually used.

     

    All this is a roundabout way of saying that in spacetime view time does not flow ie my computer does not cease existing yesterday because it exists today.

    Time does pertain to your computer though. I don't know why you say that in spacetime view time does not flow . Can you elaborate for me?

     

    Some great posts guys,

     

    What about a "Moment in Time" do we ever reach one?, my point being once you think you have reached a point in time it is already gone. A sort of a paradox if you like.

    We can record moments in time. Its just that being human we don't experience moments in time very well. But its not a paradox in any sense of the term.

  17. What's so interesting about staff having more access to information which might, on occasion, be needed to fulfill their duties than everybody else?

    I only mentioned it because I was criticized for my usage of the reputation system. I didn't appreciate that.

     

    Request: This is directed to the person who criticized me. Please don't reveal who you are in open forum. I don't want to drag anybody into this. The other person made the mistake of revealing their identity so please don't do the same thing. Thank you.

  18. I don't understand. Are you saying the first five points did address a point (that his thread served its purpose), but that point was not one you had previously addressed?

    The first five points were about the subject of the thread but had nothing to do with the argument.

     

    Also confused by all this talk of 'personal attacks'. Why the need to talk debate this? Just stick to using 'ad hominem' and we won't have to complicate things by defining yet another term.

    In the opening post I referred to it as an ad hominem. Later on, in post #20, I quoted the definition of it from my text on critical thinking and in that definition it stated that personal attacl was just another name for ad homine, i.e. that they're synonyms. Later, in post #24, swansont started to question the fact that that they're synonyms. I explained why it wasn't and it took on a life of its own after that.

     

    I don't know why people are so interested whethher these two terms are ad hominems. They just keep asking me questions and I keep answerig them. I lost interest in this a very long time ago. People still continue telling me I'm wrong so I continue to explain it to them. If you want to know why they keep bringing it up you'll have to ask them. I'm bored so I don't mind answering them. :P

  19. Oh when did the accepted consensus did not mattered to anyone. One says that the wavefunction is real and physical and other one says that wave-particle duality is a myth. Please keep your crackpot science in a different forum.

    To whom are you referring?

  20. I understand and disagree that you're using the term "personal attack" correctly - i.e.

    I disagree, of course.

     

    1. Making of an abusive remark instead of providing evidence when examining another person's claims or comments.

    The definition you just provided is in essense identical to the one in my text. In fact I've used this one myself in this thread. Your definition states that for somethng to be a personal atack it must be mopre than just an abusive remark. In order to be a personal attack it muist be given instead of elements of an argument against the other persons claim. You're using it as being synoymous with abusive remark which is an incorrect usage.

     

    Thus, in most common usage, the term "personal attack" would be roughly synonymous with insult - substitute insult for personal attack in my post if you wish.

    What you just claimed here is contrary to the definition you just gave in that the insul must be used instead of an arguement. An insult doesn't have to pertain to someones arguement like a personal attack does. And that's according to the definition you yourself just quoted.

  21. This question is not a scientific question, it is a philosophical question, it must be addressed without science because you cannot falsify your conclusions... I had say that time is change, which can happen in any level of matter.

    I dissagree in the sense that this is a topic in the philosophy of science. We're discussing the definitions of t basic terms used in science. Definitions don't need to be falsifiable, oinly hyopotheses do. E.g. if I said that the electric field is defined as force per unit mass then it can't be falsified, but that doesn't mean that its wrong. The same with the concept of time.

  22. Talking of metrics here is an interesting one that declares that every point is the same distance from every other point.

     

    This is (almost) equivalent to the old geocentric view of the universe that projected all the universe onto the celestial sphere.

     

    For any two points r, s in 4D Minkowski space

     

     

    [math]d(r,s) = \left\{ \begin{array}{l} 1,\quad r \ne s \\ 0,\quad r = s \\ \end{array} \right\}[/math]

     

    Remember that for a metric function to be valid d must be non negative.

    The Minkoski metric is defined as the tensor g in

     

    [math]dX*dX = g_{\alpha\beta}dx^{\alpha}dx^{\beta}[/math]

     

    where g = diag(1, -1, -1, -1) or

     

    [math]dX*dX = ds^2 = c^2dt^2 - dx^2 - dy^2 - dz^2[/math]

     

    This metric does not say that every point is the same distance from every other point though. This is the metric used in flat spacetime.

     

    In the early history of relativity they used to use ict as the temporal component of an event, not just ct. That's what Aethelwulf was talking about when he referred to the imaginary space dimension. But the term "space" as used here is in the abstract sense as I've explained about in quite a lot of detail. Nobody uses that nowadays though so that point is moot.

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