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Posts posted by juanrga

  1. The reason we do not go smaller than the Planck time (or even work in mixed fractions of time that require fractions of the Planck time) is because our current math fails spectacularly at scales smaller than the Planck units - you'd need the mathematics of a working Theory of Everything in order to work on scales smaller than the Planck units. In any case, why would you want to work on such miniscule scales? As I understand it, nothing exists at scales smaller than the Planck units.


    We can go smaller, it is called the sub-Planck regime or scale, and it is studied by the sub-Planck physics. The math works fine, and there is no need to even mention a TOE when working at such scales.

  2. In which way would a photon change it's momentum,


    For instance via Compton scattering, the photon changes its momentum [math]p_\gamma \to p_{\gamma'}[/math] due to collision with an electron at rest. The electron final momentum [math]p_{e^-}[/math] is the difference between the final and the initial momenta of the photon (the law of conservation of total momentum holds)


    [math]p_\gamma - p_{\gamma'} = p_{e^-}[/math]


    it can't change it's velocity and it can't change it,s mass.


    The Newtonian expression [math]p=mv[/math] is only valid for a massive free particle moving at non-relativistic speed. The photon is both massless and relativistic. For a photon [math]p_\gamma=h\omega/c[/math] with [math]\omega[/math] the frequency.

  3. Gravitation is the reality which I fill every day, so to deny it is wrong.


    Who said or insinuated such thing? Precisely on the leading textbooks on general relativity (that by Misner, Thorne, and Wheeler) is titled Gravitation.


    We can not differentiate between mass & energy in relativity.


    Untrue, we can differentiate both and denote mass by "m" and energy by "E" as in the expression


    [math]E = \sqrt{m^2 c^4 + p^2c^2}[/math]


    I have not seen anything wrong in mathematics given in post 5 by mahesh. he has taken care off mass & time changes as per relativity. If this calculation is true, as mass & time changes with observer, weight will also change as per the observer.


    No, mass is an relativistic invariant. E.g. the mass of an electron [math]m_e[/math] which you can find in a table of scientific constants is the same for any observer.


    You and him seem confused by the outdated concept of relativistic mass (which varied with the observer), but precisely due to this variation with the system of reference it could not be considered a property of the object under study: i.e. was not the mass of the object.

  4. A Planck unit of time is about 5.4 x 10^-44 of a second , why cant this unit of time not be divided further


    There is not proof that Planck time was the smallest unit of time. It is just a speculation.


    and why cant the stuff of reality be divided infinitely smaller or larger?


    Because stuff is made of matter and this has a discrete structure. You cannot divide an atom infinitely.

  5. Hi folks, I'm new here, and I'm not a physicist and I simply have to trust their math, even though it arrives at some strange conclusions. This is a general curiouisity and discussion I'd like to bring up. My science is poor relative to those here, but maybe my creative thought is at least intriguing and some might like to entertain an idea that I have.


    I was watching a documentary where the term "before time" was used (referring to pre big bang), and of course I thought "how is that possible?". If you have to use the word "before" to describe anything, then ultimately it still involves time and to say "before time" is a contradictory statement because it still sets up a "before" and "after". So the word "before",actually can never be accurate when discussing this particular idea. So to truly be accurate, one needs to reference a concept that is neither before or after when speaking of pre big bang. At first, I supposed one must step out of time itself to be able to do this.


    Effectively "before time" is a meaningless expression, but physics documentaries have to lack rigour specially those dealing with speculative topics such as cosmology beyond the standard model.


    Some cosmological models introduce a concept of time before the Big Bang. As the Nobel laureate Prigogine likes to say "time precedes existence" by "existence" he means Big Bang energy-matter. In these models, the Big Bang is a kind of phase transition from a previous quantum vacuum.





    Then, I remembered an older idea of time that I always had. I don't look at time like Einstien does (probably from my lack of knowledge) or if I actually do, I wouldn't know it. Rather than it actually being a plane, I think of time stricty as a measurement for movement. There's only movement, and then time as a conceptual way to measure movement. I know that all the math will tell me I'm wrong, but imagine this. Imagine if every single thing in existence, even down to the most minute element were frozen or did not move. If so, how could there be time? Obviously no days, no watching the clock move, not even any thoughts, if you believe that these can't happen without movement in the brain (chemicals....) but even at a quantum level, no movement and therefore no state changes. So if movement is required for state changes, and therefore nothing is changing it's state, I can't see how there could be time.


    So while I hear some very abstract explanations for how there could be something as "before time", none of them completely settle well with me and they seem to have logical holes that brings me right back to the chicken and egg conundrum. But, if the idea above is applied to the problem, then we could very easily explain a lack of time in pre big bang as simply a lack of movement, and it seems as though the paradox gets easily solved. The problem is that this must violate all of the math that says time is a plane, but logically, it seems to work really easily.


    So I'm trying to figure out why this simple idea does not or might not work and I thought I would ask others who are more knowledgeable of physics than I am..




    No, time is not a measurement for movement. In fact, movement is defined with respect to time [math]x=x(t)[/math], [math]v=v(t)[/math]...

  6. Do all photons have equal amounts of energy in 4 dimensional space-time?

    They all travel at the speed of light.


    What matters to us is how frequently they cross through our bit of 3 dimensional space?


    The energy of a photon is given by [math]E=pc[/math], thus photons with different momentum will have different energy. This is similar to what happen with 1000 kg cars. Their energy is given by [math]E=(1/2000) p^2[/math], thus cars with different momentum will have different energy.

  7. What is statistical mechanics ?


    It is an extension of mechanics that considers statistical effects (deviations on the evolution and behaviour of systems prepared initially in the same state) in mechanical systems.


    Has it got something to do with probability?


    Yes, the deviations are not deterministic and thus have to be described in probabilistic terms; i.e. which is the probability that the system will do "this".


    Why are they different statistical mechanics like Bose-Eistein, Fermi mechanics ?


    Are not different statistical mechanics but different statistics or more correctly different distributions. Fermions and bosons have different requirements regarding their quantum mechanical state and thus their quantum statistical mechanics states are also different: Fermi-Dirac distribution describes fermions and the Bose-Einstein distribution describes bosons.


    And is the Kinetic Theory of gases related to this mechanics ?


    I know, I have many question tongue.png , I just can't find any good material on this online.


    Yes. kinetic theory of gases is a subset of statistical mechanics. One often speak of the kinetic regime or kinetic branch of statistical mechanics.

  8. The work done by a variable force with respect to x distance is the integral of the function of that force with respect to x distance. But say we have a variable force as a function of time, can we say that the integral of the force with respect to time is equal to the work done by that variable force as a function of time?


    Also, if I have the acceleration of a particle as a function of term and I have the mass of that particle, can I multiply the mass and acceleration to find a variable force as a function of time?


    My intuition says yes to both question, but calculating the work using distance gives different results from calculating work using time.


    The definition of mechanical work is


    [math]W = \int \mathbf{F} d\mathbf{x}[/math]


    which is valid for both variable and constant forces. Therein [math]\mathbf{F} = \mathbf{F}(\mathbf{x})[/math]. Using [math]\mathbf{x} = \mathbf{x}(t)[/math] and the definition of velocity [math]\mathbf{v} = d\mathbf{x}/dt[/math]


    [math]W = \int \mathbf{F}(\mathbf{x}) d\mathbf{x} = \int \mathbf{F}(t) \mathbf{v} dt \neq \int \mathbf{F}(t) dt[/math]


    Regarding the second question, the expression


    [math]\mathbf{F} = m \mathbf{a}[/math]


    is obtained from


    [math]\mathbf{F} = \frac{d \mathbf{p}}{dt}[/math]


    only when momentum is given by [math]\mathbf{p} = m \mathbf{v}[/math] and the mass is constant [math]dm/dt=0[/math]. Otherwise multiplying mass by the acceleration does not give the real force [math]\mathbf{F}[/math].


    Therefore your intuitions are not correct.

  9. When force force is applied to mass does the mass is set into motion instantaneously


    Depends. If the mass is a simple particle or a rigid body the answer is yes. If the body is not rigid then the answer is "no" if the force is by contact. There is a small delay between the application of the contact force and the motion of the centre of mass. The answer is again yes for non-contact forces (e.g. gravity).

  10. Why would I need to redo what has already been done.


    Because science is accumulative and one of the requirements of a new theory is that it must explain what is already known.


    Electron scattering treats electrons as point particles, even though they have spin


    Electrons are pointlike particles. Their spin is quantum and not due to motion around an axis.


    You're mistaken, there are sound proofs which show that the measurement problem leads to a contradiction in quantum mechanics and it is unavoidable. Either Schroedinger's wavefunction isn't all there is or the wavefunction isn't right.

    A general argument against the universal validity of the superposition principle - Angelo Bassi and Ghirardi

    This is one proof and much more stronger version of that proof has been proved by Bernard.

    No. As explained in any QM textbook there are two possible evolutions of a given quantum system and each evolution is described by a different postulate of quantum mechanics: Schrödinger postulate vs von Neumann postulate. Evidently the latter is not reducible to the former (something already proven by von Neumann in his foundational papers) because otherwise you would not need two postulates. In von Neuman's own words:


    • The probabilistic, non-unitary, non-local, discontinuous change brought about by observation and measurement, as outlined above.
    • The deterministic, unitary, continuous time evolution of an isolated system that obeys Schrödinger's equation (or nowadays some relativistic, local equivalent, i.e. Dirac's equation).


    Bassi and Ghirardi just verify that the evolution associated to the von Neumann postulate is nonlinear. Something which has been known for many decades; this is why the dynamical laws postulated since the 60s to describe collapse are all nonlinear...

    Adam did not invented any laws or theorems, it discovered previously unknown genes which codes for particular enzymes all by itself which is no surprising than a evolutionary algorithm coming up with new design solutions which were previously unknown to human beings.

    First I would like to link to the computer who discovered Newtonian laws by itself before replying about Adam


    About what Adam did/does I will simply quote the Science paper cited before:

    The basis of science is the hypothetico-deductive method and the recording of experiments in sufficient detail to enable reproducibility. We report the development of Robot Scientist "Adam", which advances the automation of both. Adam has autonomously generated functional genomics hypotheses about the yeast Saccharomyces cerevisiae and experimentally tested these hypotheses by using laboratory automation. We have confirmed Adam’s conclusions through manual experiments.


    With robot scientists, comprehensive metadata are produced as a natural by-product of the way they work. Because the experiments are conceived and executed automatically by computer, it is possible to completely capture and digitally curate all aspects of the scientific process (11, 12). To demonstrate that the robot scientist methodology can be both automated and be made effective enough to contribute to scientific knowledge, we have developed Robot Scientist "Adam" (13).


    Adam formulated and tested 20 hypotheses concerning genes encoding 13 orphan enzymes (16) (Table 1).


    To further test Adam's conclusions, we examined the scientific literature on the 20 genes investigated (Table 1) (16). This revealed the existence of strong empirical evidence for the correctness of six of the hypotheses

    Tested hypothesis are the laws and theorems associated to the underlying formal systems. The physicists concept of law is not the only possible in science, biology and chemistry have their own laws.
  12. I guess you're talking of this textbook.


    Quantum Theory and Reality


    I wrote "textbooks", which is plural. But the above textbook is specially good because addresses, in a direct way, some of the more typical misunderstandings of quantum mechanics.


    However Griffiths is wrong, there are theorems which have been proved to show that the measurement problem is unavoidable and it leads to a contradiction in quantum mechanics, either the Schroedinger wavefunction is not all there is or the wavefunction isn't right.


    The same link that you gave mentions the measurements:


    Measurements play no fundamental role in quantum mechanics, just as they play no fundamental role in classical mechanics. In both cases, measurement apparatus and the process of measurement are described using the same basic mechanical principles which apply to all other physical objects and physical processes. Quantum measurements, when interpreted using a suitable framework, can be understood as revealing properties of a measured system before the measurement took place, in a manner which was taken for granted in classical physics. See the discussion in Chs. 17 and 18. (It may be worth adding that there is no special role for human consciousness in the quantum measurement process, again in agreement with classical physics.)


    There is no theorem that proves him wrong.


    You are also wrong about the latter one too(mathematical insight) and both of your misunderstandings has been corrected and tackled in this paper.


    Foreward: A Computable Universe, Understanding Computation and Exploring Nature as Computation - Roger Penrose


    However Penrose has missed a simple puzzle, if he thinks that absolute mathematical truths exist somewhere outside of ourselves then he is looking for it in the wrong place, he is searching for it in the structure of space-time and in the microtubules of the brain but anyone who has studied the Pagan mystery religions very well knows that Platonists i.e. our ancients argued that there is a Nous(Mind) apart from the brain which access the ideal Platonic forms from the intelligible realm. Its as simple as that. I figured this out years back and all evidence is in favour of a hypercosmic God i.e. my God. I am quite happy that brilliant physicists like Bernard do recognize it. Progress in science doesn't come by evading the problem, progress and advancement comes by thinking and solving it and giving up our strongly held prejudices.


    I am pushing forward this as a God hypothesis. A God hypothesis is a reasonable competing hypothesis explaining the origin of the cosmos and our place in it. This is not a god of the gaps argument, this is a argument which fills a gap in our understanding of the cosmos. This time it is religion which is going to correct science.


    He does not say that I am wrong. He simply states his personal opinion (he emphasizes "I do") and next writes:


    But I appreciate that others are sometimes less sympathetic to this kind of viewpoint.


    Indeed! But "less sympathetic" is not the correct term used by critics including myself. He is just wrong.


    I missed the link. Could you take it on faith for the minute that I'm not stupid enough to lie about it and answer the point?


    Computer generated proofs exist.

    So either the machines have God in them too, or proof doesn't need God.


    Adam is a well-known example of a robot scientist inventing new laws and theorems...


    The Automation of Science 2009: Science 324(5923), 85–89. King, Ross D.; Rowland, Jem; Oliver, Stephen G.; Young, Michael; Aubrey, Wayne; Byrne, Emma; Liakata, Maria; Markham, Magdalena; Pir, Pinar; Soldatova, Larisa N.; Sparkes, Andrew; Whelan, Kenneth E.; Clare, Amanda.

  13. Still, the equation seems to suggest that a specific energy value is equal to a specific mass value.

    The physical interpretation of rest energy [math]E_0=mc^2[/math] is not very different from that for the Newtonian kinetic energy [math]E_\mathrm{N}=1/2 m v^2[/math].


    Consider a free massive particle moving at [math]v=c\sqrt{2}[/math]. Then its Newtonian kinetic energy is [math]E_\mathrm{N} = mc^2[/math].

    The first expression of above says you that a free mass at rest has an energy [math]E_0[/math]. The second says that a moving free mass has a Newtonian energy [math]E_\mathrm{N}[/math]. In this particular case both are [math]mc^2[/math].

    The total energy of a free massive particle is given by [math]E = E_0 + E_\mathrm{N} + \cdots [/math], where the dots denote post-Newtonian corrections.


    If this is what it suggest then anything that has a energy value would seem to need to have a mass value.
    Is this not what it is saying?


    No. The expression [math]E=mc^2[/math] is only valid for a free massive particle at rest. Thus, it is not valid for a massless particle such as the photon, for which [math]E=pc[/math]. Thus, the photon has an energy value but it has not mass: [math]m=0[/math].



    Yes, I have lots of proofs and I am not a fool to hold such a radical position without genuine logical reasons or proofs and to take sides with Penrose and Bernard.


    Proof of Bell's theorem


    Violation of Bell's inequality implies either one of these premises or assumptions of science are wrong.


    1. Einsteinian separability - i.e. An event A cannot be the cause of an event B if [latex]( \Delta s) ^2 < 0.[/latex]

    2. Realism - i.e. The assumption that an object has an independent pre-defined properties prior to measurement.

    3. Induction


    Nature indeed violates Bell inequality which means either one of these assumptions must be wrong and experiments were made to allow for non-local influences and tested for realism but even then non-local realistic theories fail to account for observed correlations showing that it is the premise of realism which is wrong. We need to abandon the notion of an objective reality existing independent of us.


    No. As explained in quantum mechanics textbooks experiments are compatible with both realism and locality. Quotations from textbooks can be given if required...


    There is no mechanism with in the neuro-chemistry of the brain which can account for how the mathematicians can access the ideal world of the platonic realm and obtain absolute mathematical truths.


    The chemistry behind mathematicians' brains is the same than that behind the rest of us. They are affected by the same drugs, chemicals... Moreover there is not "absolute mathematical truths" in our modern understanding of maths.

  15. I wonder who here is an active twitter user. What's been your experience? Also, please consider PMing me your @username and I will share mine with you. I'm still a noob, though.


    I am one. I did not tweet since Christmas, but I will start again in brief. My username is self-evident.

  16. The truth is that if they would be really irreducible pion particles wouldn't decay spontaneously..

    To add a little to swansont reply. Pions are composite particles and precisely by this reason pions are associated to a reducible representation.

  17. I didn't do anything to original diagram. I thought the other one was this one at a glance. An electron is moving forward in time. It then absorbs a photon travels back in time, discharges that photon and moves forward again.


    Solid line is the electron, dotted is the photon and arrows denote direction. I believe the anti particle of the electron(i think the positron) is created at some point in the diagram, I'm not sure though.


    There some physicists that don't think it so meaningless


    There is no need to reinvent the wheel...




    In the first place, the dotted lines are technically representing anti-photons, not photons (although the photon is its own antiparticle this distinction is needed for a correct interpretation of the diagram, see below).


    In the second place, that diagram is a representation of an electron-photon scattering


    e- + y = e- + y


    Third, the electron travelling backward is not real but a formal representation of the real positron travelling forward. Moreover, this is a virtual particle not a real particle, that is why it is in the middle of the diagram, being immediately absorbed to satisfy conservation laws.

  18. Providing you have up/down and anti-up/down quarks,all other particles will be created as side effect.


    No. quarks are only one of the irreducible representations associated to the known zoo of elementary particles and the interactions involving quarks are limited as well




    My understanding is that particles are thought of as wave packets,and that interaction changes the wave packets.


    No. Ballentine textbook on QM explain very well why a particle cannot be associated to a wave packet.

  19. I will quickly address my ideas on time. I think that time the measurement and actual time within the universe are two things that people confuse. Time the measurement is a man-made invention, it is very useful when predicting events and breaking down sequences of events. But time within the universe no more comes in seconds and minutes then it does miles and fluid ounces.


    Time the measurement can be reversed and manipulated at will. With it we can take “snapshots” of the universe and attach it to individual units (milliseconds, seconds, minutes etc) and interpolate the data from one frame to another. This is an extremely useful tool when it comes to analysing everything around is. It helps define beginnings, middles and ends within a limited framework.


    Because people mix up the idea of time the measurement and time within the universe we can create all sorts of wonderful fictions like Back to the Future, Continuum, Star Trek, and other famous time travelling TV shows. As a writer myself I understand the appeal of assuming time the measurement and time within the universe are the same thing.

    But over the years I’ve considered what time is and I’ve come to a single conclusion.


    Time doesn't exist in the way we are trained to think about it. Instead time boils down to two things.


    Space and Matter.


    In order to observe time, we must observe matter. In order to observe matter we must have a spatial framework. Therefore I conclude that what we perceive as “time” is simply “the motion of matter”. Therefore time, and matter are indeed one and the same. If all interactions between matter ceased and all expansion within the universe stopped then for all intents and purposes there would be no time. But as matter moves throughout the universe in its ever moving flow we get change, and it is this change, or interaction of matter that we perceive as time.


    For what is time, if not change?


    Within this model backwards time travel isn't possible under the current rules of the universe. In order to reverse time, you must reverse every direction and interaction of every piece of matter within the universe. Even a slight change in this will create an “imperfect recreation of previous states of matter” and as we all know, with any process there is always a margin of error. If we did manage to do this I highly suspect we’d have a “corrupted” form of the past. And I don’t mean silly things like, if we reversed time the Nazi’s would have won, or a president or two wouldn't get into power. I'm talking something far more catastrophic, such as every single cell in every single living creature becoming cancerous and damaged. Even rocks themselves becoming corrupted at the molecular level.


    So if time is simply the motion of matter within a spatial frame work, then time itself is no more than an analytic too created by man, useful for prediction and data gathering but no more than that. Thus time doesn't exist, only motion does.


    Already Newton differentiated both concepts of time:



    Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time...


    Real or absolute time (often denoted by [math]\tau[/math] in the literature although I prefer [math]t[/math]) is the evolution parameter that synchronizes particle correlations. Relative or apparent time (often denoted by [math]t[/math] in the literature although I prefer [math]x^0[/math]) is obtained from reading a clock.


    Usual notation in relativistic dynamics: [math]t = t(\tau)[/math]


    But I dislike that notation and prefer my own notation which reads: [math]x^0 = x^0(t)[/math]. I.e. I denote by [math]t[/math] what they denote by [math]\tau[/math]. I prefer to use [math]\tau[/math] for proper time... use the notation that you prefer.


    An alternative naming for the relative concept of time is operational time, because it is defined in terms of an operational procedure. Einstein always confounded both concepts of time, but modern physics does not confound them any more thanks to the recent works of Stueckelberg, Feynman, Schwinger, Horwitz, Piron, and others:




    In that link absolute time is named "invariant evolution parameter" whereas relative time is named "coordinate time". Notice that it is [math]x^0[/math] which can be reversed (e.g. Stuckelberg/Feynman interpretation of antiparticles as particle travelling backward in 'time'), but real time cannot be inverted ("arrow of time"). This is why you cannot travel backward in real time [math]t[/math] and change the history of universe doing that Nazi’s will won neither you can turn every single cell in every single living creature

    in cancerous and damaged.


    Time cannot be confused with matter (matter is a physical system with properties such as energy and momentum defined at a given instant in time). If all interactions between matter ceased and all expansion within the universe stopped then time, real time, will continue to flow whereas it is [math]x^0[/math], apparent time, which will be stopped, somehow as stooping a clock with your hands does not mean that you have stopped the flow of time.

  20. [math]\text{Since light has energy, there is a small amount of mass equal to that energy.}[/math]


    [math] Given: f=1.0\times10^{15} \text{ Hz}, h=6.626\times10^{-34} J\cdot s, c=299792458 \text{ m/s} [/math]

    [math] Find: \text{mass of photon } m_p [/math]


    [math]E=hf, E=mc^2[/math]

    [math]\text{Equate the 2 values of E:}[/math]






    [math]=7.37242\times10^{-36} kg[/math]


    [math]\text{Compare with mass of electron }m_e=9.10939\times10^{-31} \text{ kg}[/math]




    The modern definition of mass is given as


    [math]m \equiv \frac{\sqrt{E^2 - p^2 c^2}}{c^2}[/math]


    For a photon [math]E_\gamma = pc[/math] therefore [math]m_\gamma=0[/math] and this is the well-known result that photons [math]\gamma[/math] are massless particles. Applying the definition for an electron we obtain the well-known value for [math]m_e[/math] reported below




    Note that the value [math]9.10939\times10^{-31} \mathrm{kg}[/math] that you give for the electron is inaccurate in its last figure. It is [math]9.10938\times10^{-31} \mathrm{kg}[/math] because the figures beyond the 8 are 291(40) and this is less than 500... The last recommended value for electron mass is found in the next table of constants




    Your Quote


    Can you explain this just a little . How you feel this should be applied to the Heisenberg uncertainty Principle


    The statistical interpretation interprets the 'principle' (really a theorem) in terms of the standard deviations associated to a large series of measurements on system(s) prepared in the same way.


    This minimalist interpretation is closer to what one really makes in the laboratory and avoids all the Copenhagen's philosophy about what they imagine that happens prior to measurement or between measurements.


    A rather good discussion is given in http://statintquant.net/siq/siqse2.html

  22. I believe it was Hawkings that suggested going back in time may be impossible because of spacial looping, or something like that. And compaired it to holding an electric guitar to an amplifier.

    This made some sence to me.


    Stuckelberg and Feynman showed how antiparticles can be tough of as particles travelling backward in time. This interpretation is at the core of his diagrammatic approach to QED:



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