Jump to content


Senior Members
  • Posts

  • Joined

  • Last visited

Everything posted by DrRocket

  1. I found no log for hardware device and driver checks, nor for anything else. Task Mgr. did not show hplamp.exe. Still get error message "could not initialize. scanner not found'. It does not get as far as warming up the lamp.
  2. no multiple devices Performance monitor. Did not see anything remarkable. Only save option was type -Mocrosoft common console document , HTML not available. File not attachable with forum software.
  3. At the undergraduate level none of the scientific or engineering disciplines are particularly difficult. They are logical and tests are objective. For a truly difficult major, look towards those that are more subjective, with test evaluation being perhaps capricious and/or that require a high level of physical talent which is also evaluated subjectively. I would think that modern dance in the College of Fine Arts might qualify. Graduate research degrees requiring not only knowledge, but also creativity, are an entirely different matter.
  4. Hardware: Dell T7400 workstation, dual processor @ 300 G SAS hard drives, Raid 2 configuration, Windows XP 32 bit HP 7400c flatbed scanner, USB connection Background: Things were running fine,including scanner operation, until a software problem, perhaps introduced in a Windows update caused the machine to fail to recognize the existence of the hard drives -- would not boot up. This was corrected by wiping the hard drives and re-installing Windows XP. Of course all data was lost and all software needed to reinstalled. (Makes one wonder about the usefulness of Raid 2) . The Problem: The scanner comes with a software package, HP Pro Scan. The software appears to install properly, but cannot initiate a scan. The error message "scanner not found" is displayed. However, the scanner does is recognized by Windows, and operates to scan single pages which can be saved as bit maps. The scanner can also be initiated from Corel Draw. This demonstrates that the hardware and USB connections are working, but leaves the scanner functionally useless for the intended use. Cannot create multipage PDF documents directly from the scanner. The same software disk can be used on another computer (wife's laptop), also running Windows XP, to install HP Pro Scan, and the scanner operates as desired. Installing the software from the HP web site produces the same problem as installing from the disk. Erasing the Pro Scan elements in the registry prior to software installation has no effect. Neither Dell nor HP have any idea what the problem might be. Any ideas ?
  5. It seems that the negative voters outnumber those of us who can cast positive votes. This says something about the voting process. The OP was not only reasonable, but ought to be helpful to newbies. If anything it deserves a large positive point count. The -9 that I saw at the time that I voted is just ridiculous. Fortunately it has zero impact on the OP, whose rep seems quite secure. This is, of course, anecdotal, but my observation is that rep points have no correlation to the merits of the posts for which they are cast. I have gotten some positive votes on posts that even I thought were rather mediocre. The whole idea of "reputation points" strikes me as silly. One ought to be able to judge the value of a post on the basis of its content, not just the gold stars of the poster. Nobel Laureates have been known to espouse nonsense -- Hans Alfven and Brian Josephson leap to mind.
  6. The distinction lies in the objective of and motivation for the research No cigar. 1. Too non-specific. 2. There is no reason to believe quantum gravity is significant in understanding how to create black holes. GR appears to be adequate -- it is the means by which the existence of black holes was predicted. That certainly seems to be the pattern in the past.
  7. In general relativity spacetime is a 4-dimensional Lorentzian manifold. Under the assumptions of homogeneity and isotropy it can be decomposed as a one-parameter foliation of space-like 3-dimensional hypersurfaces (aka "slices"), without boundary. Those slices are spaces of constant curvature and are what is called "space" in cosmology. Homogeneous and globally isotropic spaces of constant curvature are of one of three types: the zero curvature case -- Euclidean 3-space, the positive curvature case -- the 3-sphere, and the negative curvature case -- hyperbolic space. Only the 3-sphere is compact, aka "finite". It is not known which, if any, case represents the physical universe. An infinite expansion rate is not allowed by general relativity. There is no boundary. The universe could be finite. It is not infinitely old. In the homogeneous, large-scale approximation the temperature is uniform. The universe is neither homogeneous nor isotropic except as an approximation on the largest scales. No.
  8. "Understanding" is the subject of fundamental researxh. In fact the seeking of fundamental understanding as opposed to the use of that understanding is what distinguishes basic from applied science. In short you did not meet the challenge. Of course a less fundamental example might make it easier for you, but that is not the point of the challenge that you issued. Since quantum gravity seems to be important in the interior of the event horizon of black holes and in the initial 10^-33 seconds or so following the big bang, while existing theories are rather good otherwise, it is not surprising that "practical applications" are difficult to identify.
  9. quantum gravity, whatever it may eventually turn out to be.
  10. As Swansont noted the units for the E and B fields are different. Therefore you cannot say that the E field is greater than the B field. That would be like saying that 1 kilogram is greater than 1/2 meter, and by the same logic then less than 50 centimeters -- an immediate contradiction.
  11. DrRocket


    If it were me I would choose a technique that addressed the given problem.
  12. I have been in academia and I have been in industry. While in industry we maintained cordial and mutually beneficial relations with academics in the physical sciences and engineering, and business schools. On the other hand, if any of the so-called social sciences (e.g. political science) had disappeared we would have neither noticed nor cared. "Academia" is a big place. Some academics are well-acquainted with the "real world". Others are clueless. As Swansont observed the word "theory" may influence opinions. A theory in mathematics or the physical sciences is quite different from a conjecture, and to call something a theory is a sign of high regard. In other areas it may be indistiguishable from a wild-ass guess.
  13. But [math]\Gamma(n) = (n-1)![/math] and [math] \Gamma(1.3) \approx 0.8975[/math]
  14. Right, without open questions science would be moribund. Previous predictions that ultimate knowledge of fundamental rules was "just around the corner" have fallen a wee bit short of the mark. The big difference between a research scientist and a crackpot is that the scientist knows what is known and what is not known and concentrates his efforts on that which is not known. The crackpot questions fundamental theories, within their domain of validity, ignoring the mountain of experimental evidence that supports those theories. Vision [math] \ne [/math] Hallucination Open mind [math] \ne [/math] Empty head
  15. The factorial function is defined only for non-negative integers. There is a generalization in terms of the gamma function, but that may or may not reflect your purpose. http://en.wikipedia.org/wiki/Gamma_function
  16. As far as I can tell you are arguing semantics, not physics. None of "rest mass", "invariant mass" or "invariant mass" are "re-definitions" in any meaningful sense. All go back over three-quarters of a century. All are valid. All have a long history of use. All are recognized terms, with well-defined meanings. The whole point is that "mass" without further qualification is ambiguous in the context of special relativity. If you insist that one be solely entitled to the term "mass" then you can do that, but recognize that in so doing you are being arbitrary. I have seen other physicists argue as vociferously for "rest mass" as you argue for "invariant mass". You will have difficulty communicating with such a pereson since you will be using one word for two distinct concepts. Just out of curiousity, how do you relate "mass" to "inertia" ? I personally try to avoid the term and simply stick to equations of dynamics with the type of mass being clearly specified; e.g. [math] F=\frac {d(mv)}{dt}[/math] where [math] m = \gamma m_0[/math]
  17. How did you get an expression involving c starting from an expression involving only a and b ? You cannot do that without some other expression relating a and b to c.
  18. Fermilab has been conducting proton-antiproton experiments for years. http://www.fnal.gov/ What do you perceive as the issue with anti-matter in a many worlds interpretation of quantum theory ?
  19. This is just plain wrong. Ed Witten, "the father of M theory" has most certainly never been "hooted out of the scientific community". His accomplishments are legendary -- here is an incomplete sample: A greatly simplified of the positive mass theorem of general relativity (first proved by Schoen and Yau using geometric methods0 A supersymmetric solution to the hierarchy problem for the Higgs mass Selberg-Witten theory Dualities in string theory and the M-theory conjecture Understanding of Jones polynomials Fields Medal (only physicist ever) M-theory may or may not ever become a valid physical theory. I certainly have my doubts. But no one who is knowledgeable would ever discount Ed witten. As for Hawking, the Hawking-Penrose singularity theorems for general relativity are as sound as ever. The only problem is that no one knows or has ever presumed to know how they translate to physics beyond "the theory breaks down and we need a theory of quantum gravity". I am quite confident that anything that you posted in any forum has had zero influence on Hawking and that he remains blissfully unaware of your opinion.
  20. Whether he was a proponent has not been the real issue. The question arose when I correctly stated that the equation [math] E=mc^2[/math] is valid in any inertial reference frame if "m" is taken as relativistic mass. Variability of mass with energy, the equivalence of mass and energy, comes straight from Einstein's work. But see the observation at the end of this post. Einstein initially used "none of the above". I don't follow this at all. None of the quantities, mass (any version) or energy are defined in terms of more fundamental ideas or derived in special relativity. Relativistic mass in the form of [math] m = E/c^2 [/math], valid in any reference frame is as much derived as is [math]m_0=E/c^2[/math], which is valid only in the rest frame of the particle. Even in Newtonian mechanics [math]F=ma[/math] serves only to define either force or mass in terms of the other, but no independent definition of either is extant. Mass is simply taken as a primitive. In special relativity we have three versions of mass and any of the two are definable in term of the third. This then seems to me to be an inconsistent position. Rest mass ([math]m_0[/math]) requires referral to a special reference frame -- the rest frame. But as you originally stated, does not change with motion. It has the appealing property of being the scalar factor relating 4-velocity to 4-momentum, or equivalently it is the Minkowski norm of the 4-momentum vector (in units in which c=1). In this sense rest mass really is invariant in the sense of Lorentz invariance. Relativistic mass ([math]m = \gamma m_0[/math]) is frame-dependent and very definitely does change with motion. It is not invariant in any sense. Invariant mass is most commonly applied to a system of particles. In the case of a single particle it coincides with rest mass. In the case of many particles (as with the molecules in a macroscopic system) invariant mass is the sum of the relativistic masses of the particles plus any potential energy from interactions,, in the reference frame in which the total momemtum of the system is 0 -- the center-of-mass frame. So to deal with invariant mass you must first accept relativistic mass and then go further and consider a system-specific reference frame. Invariant mass is actually the most conceptually difficult of the three ideas. Invariant mass varies with thermal motion and so does not conform with your statement that mass does not vary with motion. One needs a bit of care with invariant mass. this is because in general invariant mass[math](A \cup B) \ne [/math] invariant mass [math] (A) + [/math] invariant mass[math](B) [/math]. Consider two bodies moving at relativistic speed along paths at right angles. Then individually their invariant masses are their rest masses, but the invariant mass of the system is not just the sum of the rest masses. The center of mass is moving along a 45 degree line in our "fixed" frame and the "invariant mass" is referred to a frame with that point as the origin. For large systems in thermal motion this problem goes away. As with any quantitative analysis using special relativity, one must select a reference frame. Einstein selected the rest frame of the body as the most convenient one in which to write his equations. What is revealing is his statement, "If a body gives off the energy L in the form of radiation, its mass diminishes by L/c². The fact that the energy withdrawn from the body becomes energy of radiation evidently makes no difference, so that we are led to the more general conclusion that The mass of a body is a measure of its energy-content; if the energy changes by L, the mass changes in the same sense by L/9 × 1020, the energy being measured in ergs, and the mass in grammes." -- bold added In more usual notation L=E and 9 × 1020= c^2 Hence what this equation states is quite simply [math]E=mc^2[/math] Changing of mass momentumin the rest frame makes limited sense (only when electromagnetic energy is emitted or absorbed), since as you have said, rest mass is invariant and rest mass and "invariant mass" are the same thing for the monolithic body that Einstein was addressing. Einstein's statement in greater generality would seem to apply to kinetic as well as electromagnetic energy. Remember that in 1905 when Einstein wrote the paper the atomic hypothesis was not universally accepted, so the equivalence of "invariant mass" with the mass of Newton was not so clear. I don't know if "invariant mass" was even a concept in use at the time. I will admit, however, that others interpret m in that same paper to be rest mass. I don't ascribe to that interpretation because of the words in bold above. With regard to what Einstein used in the early years, I have done a little research. The answer is a bit ugly. Relativistic mass was introduced by Tolman in 1932. Einstein and Lorentz, prior to that, used the notions of longitudinal and transverse mass -- [math]m_T= \gamma m_0[/math], [math]m_L= \gamma ^3 m_0[/math]. Dynamics in this formulation is repulsive. With relativistic mass one has simply [math] F= \frac {dp}{dt} = \frac {d(mv)}{dt}[/math] just as with Newton, simple and elegant. http://en.wikipedia....cial_relativity My only point in bringing up Einstein was to counter the statement that [math]E=mc^2[/math] is any sort of "new equation" or invalid. It is neither. Using Einstein's early writings from a technical perspective is probably not a good idea. Any good physicist or physics student today probably understands relativity better than did Einstein. They should. Einstein's genius was in developing relativity from scratch. Modern scholars have the benefit of over a century of work on the subject by a boat load of geniuses. You are free to stick to one and only one version of mass if you wish. I will continue to use whatever is most convenient for me in the application at hand, being clear as to what concept is being used. I doubt that you will see me using longitudinal or transverse mass (Ohanian in his book says that Einstein himself made mistakes with those concepts). In my first course involving relativity, we used relativistic mass, and I seem to have survived without permanent damage.
  21. ????? Did you not make the OP ?
  22. From your question it is fair to stick to classical electrodynamics. There is no such thing as "changes" to a static field, electric or magnetic. If the field varies in time (i.e. if it changes) it is not static. Any time varying electromagnetic field creates a propagating electromagnetic wave, and the speed is c. Note, this is a propagating electromagnetic wave, not a propagating electric wave or a propagating magnetic wave -- both come with the package. There is no classic limit on the frequency of an electromagnetic wave. Quantum mechanical systems, depending on the specific system, may have limits related to the discrete spectrum of the Hamiltonian.
  23. Einstein, at least in his in later years was not a proponent of relativistic mass. But the notion comes directly from his special theory and from [math]E=mc^2[/math] which is perfectly valid, as I proved above. I don'rhink you are interpreting the Einstein paper properly (see end of this post). You are being dogmatic. Unnecessarily.. But it is equally clear that you will not be convinced that there are several different definitions of mass. All are valid, and all are useful in the proper context. You can certainly continue with little penalty, as one can formulate a valid description of physics using only one single concept. But that formulation will be very clumsy in some situations. Since you are wedded to "mass is rest mas" you should, to be consistent to your principles, reject any and all mass measurements made with a labotatory balance or a bathroom scale. You will need to chamge [math]F=ma[/math] to [math]F=\frac {E}{c^2}a[/math] and [math]F=G{m_1m_2}{r^2}[/math] to [math]F=G \dfrac {\frac {E_1}{c^2} \frac {E_2}{c^2}}{r^2}[/math]. You will need to revise what you mean by mass in general relativity, as the mass entry in the stress-energy tensor is relativistic mass, not rest mass, and it is relativistic mass that figures in the momentum flux entries as well. Denying relativistic mass and insisting that "m" always be rest mass will make reading much of the literature at best confusing. There are tons of texts that use the concept of relativistic mass, and to good effect. ALL books on classical mechsanics use" m" to denote "invariant mass", relativistic mass in the center of mass frame. That allows them to measure mass on a labratory scale. Do you propose to revise Goldstein to match your standard ? You can certainly do what you propose. It is most certainly correct. But it is hard to do with a straight face. Addendum Now, with regard to the Einstein paper we have (saving me some typing) this bit from Wiki, with which I agree "Einstein considered a body at rest with mass M. If the body is examined in a frame moving with nonrelativistic velocity v, it is no longer at rest and in the moving frame it has momentum P = Mv.Einstein supposed the body emits two pulses of light to the left and to the right, each carrying an equal amount of energy E/2. In its rest frame, the object remains at rest after the emission since the two beams are equal in strength and carry opposite momentum. But if the same process is considered in a frame moving with velocity v to the left, the pulse moving to the left will be redshifted while the pulse moving to the right will be blue shifted. The blue light carries more momentum than the red light, so that the momentum of the light in the moving frame is not balanced: the light is carrying some net momentum to the right. The object has not changed its velocity before or after the emission. Yet in this frame it has lost some right-momentum to the light. The only way it could have lost momentum is by losing mass. This also solves Poincaré's radiation paradox, discussed above. The velocity is small, so the right-moving light is blueshifted by an amount equal to the nonrelativistic Doppler shift factor 1 − v/c. The momentum of the light is its energy divided by c, and it is increased by a factor of v/c. So the right-moving light is carrying an extra momentum ΔP given by: The left-moving light carries a little less momentum, by the same amount ΔP. So the total right-momentum in the light is twice ΔP. This is the right-momentum that the object lost. The momentum of the object in the moving frame after the emission is reduced by this amount: So the change in the object's mass is equal to the total energy lost divided by c2. Since any emission of energy can be carried out by a two step process, where first the energy is emitted as light and then the light is converted to some other form of energy, any emission of energy is accompanied by a loss of mass. Similarly, by considering absorption, a gain in energy is accompanied by a gain in mass. Einstein concludes that the mass of a body is a measure of its energy content."
  24. Three is not eough, Whar in the world is that supposed to mean ? Any of it.
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.