arfa's musings on Elastic surfaces

Discussion in 'Free Thoughts' started by arfa brane, Feb 3, 2022.

  1. arfa brane call me arf Valued Senior Member

    This 'elastic surface' thing, is actually what whole lot of physics is about. An 'inelastic' interaction is just one where the transfer of momentum includes some 'erasure' from the local system; the total system--the universe--just sees a change in state somewhere, and carries on.

    Inelastic interactions are locally observed events.

    I once read in an article (I saw the author was Ph.D-ed), that once the universe was 'big' enough it started ringing, like a bell, and these ancient 'tones' are still around--still ringing 'elastically'. This suggests that the spacetime is an elastic 'space', a medium. Or the three dimensional space is an elastic surface of the 4d-spacetime.

    Math, huh?
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  3. arfa brane call me arf Valued Senior Member

    What is information? Why would I say I've had some kind of insight?

    The insight sounds pretty ordinary. Information about a system of particles is something we want (the system isn't interested in communicating).
    That part of the insight is why Maxwell conjured up his demon, and explaining why it doesn't solve a problem (a problem with . . . gaining information) has taken over 100 years.

    But gaining information means some particles have to "leave" the system, after they "leave behind" some information, about their position, or their momentum, or just their "relative energy"; electrons and other tiny bits of matter make "dots" in a reactive medium. => There has to be a mark we can see, a sound we can hear; something we can convert into a more manageable form. It's why particle accelerators also need detectors. It explains why we see inelastic interactions.
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  5. arfa brane call me arf Valued Senior Member

    Another correction, the 3 should be a 4 in the post about Helium. I get them confused sometimes; but they are both superfluids, except the isotope (the 3 version) has to be in the milliKelvin temperature range.

    One thing that's been researched is what a superfluid does when you rotate the container. How does it deal with moments of inertia, and so on.
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  7. James R Just this guy, you know? Staff Member

    Maybe it's not the place that has the issue. Maybe look closer to home.
    Now, dig out those year 11 physics notes - or first year uni notes if you prefer. Refresh your memory.

    Is it really true that in the air-track collision when the two carts end up stuck together, total momentum is not conserved? Are you sure about that? How sure are you that this "inelastic collision" does not conserve total momentum?

    If you'd like to change your mind before you make an even greater fool of yourself, now might be a good time. Please let me know, either way. Can you admit you were wrong, or are you too old for that?
  8. James R Just this guy, you know? Staff Member

    Maybe you owe the guys an apology, because you made a silly mistake. Are you too old to apologise, too?
  9. arfa brane call me arf Valued Senior Member

    Well, I'm fairly sure about you being sure about the principle applying to an isolated system; so, where do we observe this system from?

    I mean, do we throw in an isolated demon?
    And, I hope this doesn't all go to the same place our little discussion about energy, via Feynman, went. I still think you misquoted him. I still think he might have been almost speaking the truth about what he knew about energy, quantum states, elastic and inelastic scattering, or whatever.
  10. James R Just this guy, you know? Staff Member

    You may assume that we're observing it from the lab frame. Or, if you prefer, you can assume we observe it from the centre-of-mass frame. In fact, any inertial frame of reference will do. Take your pick.

    Now, is total momentum conserved in an "inelastic collision" between two carts on an air track (in the impulsive collision approximation), or not? There is a "yes" or "no" answer to this question. Do you know what it is? Can you answer this year 11 physics question correctly, or can't you?
  11. arfa brane call me arf Valued Senior Member

    For an observer who is isolated with the carts (comoving), and assuming they can ignore a few things, yes. But it isn't true for a remote observer who sees momentum transferred out of the "isolated system".

    Let's try, for argument's sake, to connect a pair of carts sticking together on an air track, to two electrons, one in a detector, the other being detected. How does the apparently irreversible change around the electron in the detector, if that's how it gets measured, say the system is isolated?

    Momentum is conserved, but kinetic energy is lost when an electron 'hits' a screen. Now there is something you can print copies of; the electron is lost along with an amount of heat it generated, leaving a mark, in a sort of permanent-ink way. You should now, according to Bennet and Landauer, consider what it would take to erase all evidence of this mark having been made.

    You already have no possible information in your future concerning the electron that left this mark, . . . in the case of two carts, the analogy is the heat and sound the collision made, these can in principle 'leave a mark' if you can record them, like with electrons.

    I should add the obvious, if you're in a lab and you hear two carts colliding, you remember it. For long enough the "mark it left behind" stays coherent; in signal-processing terms.

    So say the scenario is, you do the carts on an air track experiment. You finish up and the professor asks you, did you hear a sound when the carts collided inelastically?.

    You say, yeah, and he says, then you weren't in the comoving frame, you only saw momentum conserved because in that frame there are only two carts, no air track, and no sound. You can choose which cart to be comoving with, of course, but it doesn't make a difference to what you're constrained to observe.

    In short, if you're a cart momentum is always conserved--there are no inelastic collisions, even when you suddenly become two carts. Unless you're the kind of cart who responds to second or higher order effects of a collision.
    Last edited: Feb 7, 2022
  12. arfa brane call me arf Valued Senior Member

    The impulse-collision; an example

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    The bullet striking a wood block. This might be a reasonable example for high school, but there are some problems.

    One is, wood usually splinters when a bullet hits it at high speed. This is a bit of a hail mary on the conservation of mass. Maybe suppress the splintering with a layer of something that's good at absorbing the shock. Then hope it doesn't get too warm.

    The swingarm might be a rigid material, but it's going to vibrate. If you want just the height in the analysis and enough else is known, it's good enough to demonstrate the idea. I guess.
  13. arfa brane call me arf Valued Senior Member

    A ring of rigid material will oscillate in place if you tip it slightly and let go; the motion is constrained because the ring has to 'roll' in a way that, well, preserves the principle of least action--the coin does the minimum 'passive' amount of work, keeping the minimum surface area in contact with a surface . . . It does this all the way, until the frequency gets quite high, sort of an asymptotic limit. Take a squiz at Euler's disk.

    But, Landauer and Bennet would say, eventually the disc does the minimal amount of work, the Lagrangian reaches the same endpoint as the actual path taken, the disc hits the ground, it runs out of steam. This "not beyond a smallest" thing that eventually sees the disk come to rest, is the same as the minimum write or erase principle--the smallest required.

    Ringdown is a commonly used word in engineering and electronics. If you study power output curves and so-called complex functions of impedance, you know it's all connected to Newtonian mechanics too. Only, the units are different for electromagnetic impedance and mechanical impedance.

    Ringdown is a passive response to a residual 'energy' in the system. after an input is suddenly removed. It's kind of the inverse of an impulse, so not like a bullet striking a target. You see it in dielectric surfaces when an electric potential suddenly goes to zero--the electric field in a glass container resonates like a plucked string, if you 'stretch all the electrons away from the protons' in the glass, then let go.

    So it's in the same category as picado, in the Spanish guitar context, plucking a string. Or plucking a loose-ish spring after hanging a weight vertically.

    E pluribus exponenti. Everything in physics that's a passive response, is an exponential decay.
  14. arfa brane call me arf Valued Senior Member

    About that superfluid Helium. It's a Fermi liquid. What is a Fermi liquid?

    OTOH, it's a matter field in a superfluid state, every molecule is in the same quantum state, but restricted by Fermi-Dirac conditions.

    It's, you know, complicated. But actually this superfluid is more simply arranged than the metal 'particles' in a steel ball bearing.
    Thermodynamics is seriously damped. Friction is in a whole different place.

    Research into the response to applied torque (a rotating superfluid), reveals it imposes a fixed geometry (!). With this new restriction the field of liquid particles 'factors' the inertia tensor. It rearranges into a sequence of small 'microdisks', the experiments continue . . .

    It's an insight into how angular momentum and inertia interact--it actually demonstrates what giving little volumes of matter a fixed address, then rotating them around a common centre, means in terms of tensor calculus--inertial moments can be wrapped up into a more generalised object. It works very well when your matter-field is a rigid body. Hence, rotating superfluids are an example of 'rigidity' in a fluid.
    Last edited: Feb 9, 2022
  15. arfa brane call me arf Valued Senior Member

    Yes, thankyou James for the reminder.

    Since after all, this site is only a place for people to post random unconnected ideas.
    Science is something scientists do, in labs. You don't do it on the back of an envelope.

    Around here you trot out a stream of consciousness that only you can follow, nobody is interested.
    The earth might as well be flat, for all anyone cares. And might I add, I don't.

    I think, because of the actual response from supposed members, somewhere south of a high school education, that I might have learned more instead of bothering with those, than I did just trying to hammer something out. Something the scientists here apparently haven't learned much about at all.

    But, y'know, who gives a fuck? I'm doing my thinking about stuff I have textbooks about, and I know what to type into google.

    Basically I think I can say there isn't really any discourse here, if the most compelling shit is about whether the earth is flat. That's worth a whole day's laughing, don't u think?
  16. river

    arfa , agreed , It took awhile for me to stop laughing ( I still am . ) . !!!!!!!!


    James your response ?
    Last edited: Mar 3, 2022
  17. river

    Just Great Stuff .

    These superfluids are plasma based .
    Last edited: Mar 10, 2022
  18. river


    Both angular momentum and inertia in a confined space , fixed address ( room ) . The you get a common centre . Rigid , but rotating mass .
  19. river

    Rotating Mass Movement , three dimensionally , never stops .
    Last edited: Mar 16, 2022
  20. exchemist Valued Senior Member

    Update on Arfa:

    Arfa may show up here again, as he has now managed to get himself suspended from the .net site for a fortnight, for incivility, a month after joining.

    He seems to be aching to patronise someone, anyone, on the basis of his scientific knowledge. Unfortunately he does not make much sense and keeps introducing extraneous concepts in order to show off. And then gets cross when his contributions are ignored or not taken seriously, and resorts to abuse.

    One hopes he may reflect on this and realise that if a new community finds him as objectionable as he has been found here, then the problem must lie with him, not other people. But if my dementia hypothesis is correct we may find he can't make that connection.
  21. sideshowbob Sorry, wrong number. Valued Senior Member

    "The music goes 'round and around
    And it comes out here."
    -- Songwriters: Ed Farley / Michael Riley / Red Hodgson
  22. arfa brane call me arf Valued Senior Member

    That site is full of retards though. Like this one.
    river likes this.
  23. arfa brane call me arf Valued Senior Member

    Unlike you, who patronises people on no basis whatever.
    One of the extraneous concepts usually found in forums like this one, and that other wasteland of ideas calling itself, is that people know things, and can discuss them rationally. This is not what happens.
    Instead we see wankers like you pontificating about how demented it all is. You got that right, amazingly enough.
    I'm not reflecting on anything except the sheer uselessness of sites like this one, and most of the others. They're a joke, a testament to the inanity of the human condition here at the Western World. I find them offensive, I find you offensive, you opinionated shithead.
    river likes this.

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