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Edgard Neuman

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Posts posted by Edgard Neuman

  1. 2 hours ago, swansont said:

    Solar wind is fairly weak in terrestrial terms (1 ATM being ~10^5 Pa)

    "The wind exerts a pressure at AU typically in the range of 1–6 nPa ((1–6)×10−9 N/m2)"

    https://en.wikipedia.org/wiki/Solar_wind

    The differential pressure for a slightly off-center sphere would be much smaller. Not much "correction" would be happening

    I totally understand that the solar wind is 1–6 nPa ((1–6)×10−9 N/m2) at 1 AU
    For a 1 UA sphere, the pressure necessary to support 1 ton / m² is 5.9641110164 Pa  
    (since the solar wind pressure is also proportional to 1/D², the factor is always the same)

    BUT : if we prevent the solar wind from escaping, the pressure should increase rapidly inside the sphere. 
    All we have to do is to put vents that only open when the pressure gets dangerously high (here that would be >6 Pa at 1 AU).. 

    It's a "closed" sphere : the wind can't escape : it's a balloon, a sort of pressure cooker.

    The sphere would be filled with gas from the star at least at the necessary pressure
    (it would be incredibly difficult to construct before the pressure gets high enough) 

    And the pressure gets greater when the surface get closer to the star : the correction is totally happening.  Also I suppose the scale would make it extremely hard to manage the constraints provoked by any variation of the pressure around the sphere, and solar storm would break everything.. it would need a very calm star, with highly symmetrical wind and pressure. 
     

  2. 8 hours ago, et pet said:

    A primer of sorts was done some years back by Brandon Weigel

    you should be able to just GOOGEL something like "    Dyson Spheres /  Brandon Weigel    "

     

    https://medium.com/our-space/dyson-spheres-450146a7c13b
    Thanks.. read this : no mention of pressure inside the Dyson sphere and its ability to thwart gravity.. so that don't answer my question.. 

    I did google Dyson, and nowhere did I found any mention of pressure inside.. everybody assume the sphere is structurally stabilized by centrifugal force, like it's a structure in orbit. Here I ask about inner gas pressure actively supporting the sphere.. that's totally different. 

    You can read that
    https://en.wikipedia.org/wiki/Dyson_sphere#Feasibility
    They talk about the gravity of the sphere, but they don't talk about the pressure generated by solar wind and inner gas pressure. 

    Think about it. Suppose the totally closed sphere weight 1 ton by m² of surface (inside the sphere)... 1 ton by m² is already a heavy structure.  The sun gravity for 1 ton, is relatively low if the sphere is big enough.. we can then compute
    the gas pressure inside the sphere necessary.
    Let's assume Sun mass = 2×10^30 kg
    Sphere ray = 57909050000 m (the orbit of mercury)
    Gravity force for 1 m² = 1 ton of sphere = G * Sun mass * 1 ton /  r² 
    I get a force of 39,8 Newton 
    So 39,8 Pascal for 1 m² of sphere
    And the bigger the sphere, the lower the pressure
    It seems to me totally achievable if the sphere is filled with the gas from the star,  no ? 

    I totally understand that the solar wind is 1–6 nPa ((1–6)×10−9 N/m2) at 1 AU
    For a 1 UA sphere, the pressure necessary to support 1 ton / m² is 5.9641110164 Pa  
    (since the solar wind pressure is also proportionnal to 1/D², the factor is always the same)

    BUT : if we prevent the solar wind from escaping, the pressure should increase rapidly
    I wouldn't be a "solid" sphere, but rather a space balloon, filled by the pressure of the star

  3. Hi,

    Here is my question, until now, I thought "of course, it's impossible". The matter will never be hard enough to resist, and the whole thing is in meta stable equilibrium anyway : any deviation would pull the closest sides of the sphere and break the whole thing. ("That's dumb !.")
    Until I thought about this : what about solar wind and matter production from the star...? 
    It seems to me now, that if you really close the star into a solid sphere, it will still produce a powerful solar wind, and temperature and pressure that would fill the solid sphere, until it increase enough to push the sphere away. 
    So here is my question : is a "self pressured" Dyson sphere, where solar wind and matter pushes in every direction the sphere (and thwart gravity) totally impossible ? (it would then "only" require "pressure control", by venting enough Gaz to stabilize the sphere)
    (I know the true answer would probably require serious modeling : has it been done ?)

  4. hi,

    there's a thing that i think is a good candidate for "time", and that has been under our noses the whole time : decoherence..
    Decoherence doesn't work backward.. a choice is made..
    Any thoughts about that ? 

    thks

  5. 17 minutes ago, geordief said:

    You are unfortunate with your misspellings (flow/flaw earlier)

    Perhaps you are a victim of autospell or autocomplete

    😉

    That's a big problem I have. I am too enthusiastic, I always want to answer the fastest, and I usually have to edit my answers many times.. when I hear the notification sound, I can't wait to answer.. I always have trouble understanding people don't understand me.. I usually suppose that I already said enough, because in the first message I send, I usually consider that I closed every loop hole.. A lot of things are supposed to be deducible from a single text.  
    (for instance If I say "ultimately, each point in the universe because the speed of light is finite, receive some photons from the CMB"
    You should not ask after that "where does the information come from" and ask about the conservation of information.. my first message imply the information come from outside the universe at each point of time.  And for instance, I know the CMB is not "outside of the universe".. ) So I feel annoyed to have to explain each point one by one. It seems to me people should not waste time criticizing the form of the message, but the "idea" itself, once understood. I'm not here to write an essay, but to discuss ideas.

    I know that plays against me. Sorry for that. 
     

  6. 4 minutes ago, joigus said:

    Being wrong requires making sense. Bye.

    Sorry if you don't understand me. 🤷‍♂️
    Information, meaning "minimum causalities" from "outsides of system" is what ultimately animates them.. It's like "things happens" because you know "outside exists"
    I think it's simple.

  7. 9 minutes ago, joigus said:

    Not even plastic surgeons can do that.

    You say stable systems don't exist ? The moon, left in the cold space, does its entropy change ? The fact that entropy always increased (I think I mixed up the law before sorry).. doesn't mean It "has" to increase. 

    Quote

    You're 1 non-sensical/non-sequitur comment away from my ignore list. Time is indeed precious.

    sorry I admit I go too fast. Anyway, I've said enough. The question is "what is time". You have my answer, if you can explain why I am wrong, do go one, but I don't need your answer.  

  8. 15 minutes ago, joigus said:

    Fine-grained, or microscopic entropy, never changes. It's a constant. It's the volume of phase space; a measure of how much information is in the system. That's called Liouville's theorem. Dynamical systems conserve the distinctions, the amount of information.

    Dynamic "closed" system.. Or has I said from the beginning.. The universe IS EXPANDING. You get "new photons" at any point of the universe (directly or indirectly).. (and I suppose "photons" are not the only carrier of information, gravitational waves, any particle.. any event.. any "information".. that's just to explain that because of relativity : any point of space time get to interact with new points of space time as time go one)..
     No system is really closed.. that's why I say information is time. 

    Quote

     

    It's just that evolution always de-correlates most of your system's dynamical variables with the "macroscopic handles" you may establish to study it (volume, pressure, fields). So most of this dynamical information is lost for your macroscopic "description handles", in my figure of speech.

    I don't disagree with that.. I almost wrote a text that said that "measurements" are just summaries of reality (classification into sets)

    Quote

    Coarse-grained, or macroscopic entropy, always increases for closed systems.

    I was explaining that if entropy  (a property of a system can go backward) can go backward. As I said entropy is a statistical property, in reality, law of physics are time reversible.. So the real reason why entropy "always increase" is because of initial conditions. And reversed system, that goes back into a ordered stable state, is perfectly possible in respect to the laws of physics. 

    Quote

    Time? You're trying to take too big a leap here. Time has to do with entropy growth (its direction), but it's not defined by it.

    Time doesn't stop. What makes you think it does?

    Entropy can stop changing. I mean therefor it can't define time. But I don't think "time can't stop". You talking about your idea of time, as something that occur spontaneously in matter (like the spining of electrons in atoms, or the "oscillations of wave"). But for a true objective idea of time, independent of scale, can stop. You know, when nothing happen.  The "quantum" time, is just a level of time..

    Quote

    The grandfather paradox has to do with geometry of space-time, not with entropy.


    Therefor it can't be time. That's it. You talked about entropy, you know why you do. I don't ! 

    Quote

    What's that about???

    sorry : *Light*

  9. 22 minutes ago, joigus said:

    That's not what I said. "Reverse entropy" doesn't make any sense. You must mean "reverse entropy change". How could it define time? Entropy doesn't define time.

    I understand that entropy speaks about "closed system".. can't diminish (the laws of thermodynamics)..but when entropy stay the same (because the system is stable) does time stops.. ? and if it stops, what does make it start again ? (information !)
    Suppose you take a empty box . You carefully compute the trajectory of every molecule you throw in the box, in a specific way, that is the exact opposite of where the molecule would have pop up if the box first contained ice. You throw the molecule, close the box. The molecules bounce, and according to your calculation, ends up in the corner of the box.. 


    The subject of the thread is "what is time". I gave you my answer. You talk about the classic theory that the arrow of time is somehow explained by the laws of thermodynamics (the entropy thing). So what are you trying to say if you're not talking about that ?? 

    45 minutes ago, studiot said:

    This is a Physics forum.

    What 'matter' are you referring to that has no relationship to reality ?

    Ok that sentence wasn't very clear. 
    I mean that the matter that carries the information (like the screen, a computer, a brain, a book.. information doesn't exist without matter to carry it) does not have a relationship with the reality described by the information (the meaning). A book, without a dictionary, is not enough to recreate the story. Therefor this "information" does not "exist" (something that exists, by definition, is something that can be lost and found..).. the meaning is only in the brains of people.

  10. 3 minutes ago, joigus said:

    Nobody says that. That's not how you formulate irreversibility.

    No. It's a measure of ignorance or "randomness" if you will. And yours is going through the roof.

    So if entropy can be reversed, how could it define time..? Can time be reversed now ? What about the grandfather paradox ? 
    You can't explain time with something that can be reversed. And does the entropy of a single atom change ? So how could we built atomic clocks ? 

  11. 17 minutes ago, joigus said:

    My concept of information comes from Shannon, which fits the definition of entropy given by Boltzmann (information deficit). There are other definitions of entropy that are more useful in different contexts and are qualitatively equivalent. None of those do I recognize in what you say.

    For example, you've got Rényi entropy: https://arxiv.org/pdf/1102.2098.pdf

    In some respects it's a more solid definition, meaning that in some systems for which Boltzmann entropy is not well defined, Rényi entropy is.

    And you still haven't answered: What's the connection between time and entropy? Information defines a thermodynamic arrow of time, but not its units.

    Another thing you haven't answered: Nature goes from more information to less information. It's the opposite of what you suggested.

    You try to make me understand your ideas (I don't need to, because I already have a answer to the question :) ).. first : entropy is not "irreversible".. you should know that all law of physics ARE time reversible. when people say "entropy" can't be reversed, it's not entirely true. In theory, if you reverse the speed "every molecules" of a gas, the gas go back to the corner.. If you want to unbreak a glass, you just have to put it back and restore the molecular liasons that were broken.. and you can "unmix" liquids (it's just complicated and require skilled chemists)
    so already, there's a "flaw" :D
    Entropy just talk about probabilities for system to be in specific stats. In reality, a set of card, when it's ordered, is not different to when it's not ordered (except in your mind, where "some cards go after some others cards). You choose to believe specific states are "special" because they exhibits symmetries.. but even that's a subjective idea. Symmetries you observe in nature, (like Chrystal) are just minimum states.. minimum states often have symmetries (because they obey local constraints) but not always (like quasi-christals)

    It's all about probabilities : systems flows from states to states, and when the flow of states (in the space of states) converges to some more probable states, matter often ends up in those states. But that's not "time". because... conservation of quantum information precisely and explicitly contradict this "convergence of states".. 🤷‍♂️.. A perfect oscillator (like a isolated atom), or even a chaotic oscillator doesn't gain or lose entropy, while it still "evolves" in time.. 
    I think what you see as entropy is just a redistribution of randomness.

  12. 40 minutes ago, joigus said:

    Neither am I. It's about consistency. I use irony as a tool. Irony is a universal language and helps you make a point. I'm not convinced by your concept of time as information. I don't think you've thought it through.

    how and why ? 
    I can believe you're not convince, but I see no hole in my ideas that I would have forgotten to fill. The problem probably comes from what you call "information" that is not what I call "information". You're seeing it as description..
    In reality "information" as you see it, doesn't even exist.. the letters on this screen describe poorly reality via a code, and that code exist via physical relationship between sensorial neurons  in our brains (those who see things, and those who read letters).. (we share the code, that is the English language)
    But in reality, the matter that carries this "information" doesn't have any relationship to reality itself. If you don't have the code, you have don't have a book, but a inked paper. Some alien reading this text would find regularities, symmetries and even some rules. But without pictures, there's no way they would understand the meaning of the text.
    Now if you talk about a series of "bit" as information (as a mathematical property of a set of 0s and 1s).. that's just symmetries.. You can't really compress anything without a code. To zip or unzip a file, you need a specific software. Without knowing the software, you could never read a zip file, because the bits could be anything.. Suppose you code the bits "00000" into somehow 5 x "0" (the bits would be "1010" in some unrealistic software the already know that the first 3 bits are a number)... how do you know that "1010" isn't the bits you coded at first ? or 2 x "10" ?.. 
    By "information" I mean the minimum (the Greek "atom") of causality.. (that's the meaning used in relativity.. "no information can't travel faster than life" really speaks about causality)

     

  13. 30 minutes ago, joigus said:

    I think you just put your finger on it. It's definitely a flaw of information we're talking about.

    sorry (I'm not a native English speaker). 
    By the way you seem to love "bits".. here is some facts :
    by definition, probabilities carry "less" than bits. If I tell you "the memory has 60% chance to contain a 1".. how many "bits" did I transfer to you ? 
    - any mathematical continuity, implies infinity of "bits".. between to real numbers, you can always find a infinity of new numbers.. and you can have some with a infinity of  uncompressible digits.. so you know you can always find a number, whose writing would need more bits than the first 2

     

  14. 7 hours ago, Edgard Neuman said:

    I don't wish to discuss it, as metaphysics is by definition out of provability.

    I'm sorry, our way of thinking are too different for me to even have the will to try to understand and describe every difference between us.. 
    (OK I can't resist)


    If you "understand physics", and you don't see how "information makes time at every level of complexity".. (ok maybe, because you don't see information as the minimum causality possible).. try to understand dominos.. our even how computer works.. or this thread your reading.. or your mind.. or special relativity.. ("information can't go faster than light".. if information can't go faster than light.. try to understand what it implies in terms of flow of information.. picture any system, and how information flows in it..what would happen if it wouldn't).. When you try to define a clock in relativity.. what travels between the parts of your clock ? at least a particle, a signal right ? What is the minimum of a signal ? (information !)

    You can't define a "wave" (any wave.. quantum wave. The "idea" of wave) without talking about a field and a perturbation travelling in it, from points to points continuously  (in any type of mathematical structure you can imagine).. what is a wave, if it carry a perturbation across space, but neither matter, nor energy ? (a wave of information..! )

    And for the "rules" don't make the system predictable.. so new information pops up everywhere you think (because there's no "between the two"). you can roll the quantum dice, and you get new random numbers on the screen (are numbers not information ? can't I fill my hard drive with random quantum numbers ?).. wouldn't that contradict the conservation of information "https://en.wikipedia.org/wiki/No-hiding_theorem"  
    Apparently (according to MIT) a photon carries 10 bits of information.. how many virtual photons are usually in the void ? 

    Bye !
     

  15. Hi, 
    Can I give you my point of view ?
    The question is in metaphysics, not really physics but not "quackery" philosophy about "inner feelings of time" either (as if humans would be the center of the universe).. I don't wish to discuss it, as metaphysics is by definition out of provability.
    I'm placing my thought about the particular laws of physics : I speak only about states of structures in space, laws (how structure's state are related localy) and interactions between structures (without specifying anything more, or any geometry), because I think it's enough to define time. 

    My current definition is : 
    - time is the accumulation of information in each system. Any structure and history can be "distorted rotated" inverted etc.. But any system is in a state that depends its previous interactions.. most complex system tends to be described as what I call "vortex"  : it's a loop of causality, with some data entering, and some going out, and some of it staying in the loop. Just like what conscience is. Or a rock. Or a molecule (I'm not 100% sure about that : that would need the confirmation of a quantum mechanic expert). And the structure of a system contains partially "memory" that is the component of the state of structure that was added over time.. (but of course, not all data is stored in a system).. (and for us, as systems,  memory is really what we call time)
    Somehow, I would suppose that a closed system could only be in one of the three states : not changing, cycling, or chaotic. That's disputable but it seems that reality has laws, and that, in a closed system : each state depends only on the previous one (in a infinitesimal part of space that is).
    So for everything, every event that come into it from the outside, perturbate the set of states that were previously reachable.. every data make the system more complex.. 
    Consider a book containing a story. If the story obey laws, the story can be deduced from the premises : the start of the book implies the end of the book. The book is just information. Now if somehow, at a point in the book , you "intervene" in the story : the story change into states that depends on what you did. The end of the story can't be explained without mentioning your particular intervention : you added information to the story. 

    Another good way of seeing is this : ultimately, each point in the universe because the speed of light is finite, receive some photons from the CMB, photons that were previously out of the visible universe for the point .
    Each structure in the universe sees the visible universe constantly growing. So at the very list, at a deeper levels, everything in constantly gaining information. In other words, when a structure interact with an other structure, because of relativity : some part of the past cone of the other structure never were in your past cone : so every interaction you get depends on something new from your history. (You could say that laws are not necessarily bijective, but I think the conservation of information in quantum mechanics exclude that).
    It's kind of like in Conway's game of life : each state of a square depends chaotically on its cone of previous squares, and each square depends on at least some squares different from its neighbours.  (I think that "explains" what you measure as time in relativity, but I really fear being banned for this highly speculative idea of mine.. )


    At a deeper level, if you consider reality as a mathematical structure, where identity is truly absolute (not depending of where the structure is)  : I think of time as a the creations of new informations (by mixing previous informations) .. and the diffusion of the new information to mix with previous informations.. It's like a big problems that constantly tries to solve itself.

  16. 20 minutes ago, Strange said:
    !

    Moderator Note

    If what you are saying is that physics is the same whether you use Imperial measurements, CGS, MKS or furlongs per fortnight, then this is trivially true and the thread can be closed.

    If you are trying to say something different then you need to state that clearly, ideally mathematically, so that it an be understood. If you can't do that, then this thread will be closed.

    Over to you.

     

    I'm saying that the changing of scale (and ok, maybe a more complex thing that defines a transformation of vectors) .. not what you call "scale" that is applying to some laws and not the others, I mean "the scale of the universe, and everything in it, every laws".. This is by definition a relative value, because it's undefined outside of the universe and the matter in it..
    So I'm saying that this value could change from region of space to region of space, and that would be "general relativity".. 
    That was my point.. I had to countlessly explain what "scale" is..  because you don't want to "properly scale" the universe and everything in it in your mind..(that was not a problem for me. When I mean scale I mean "scale".. if you scale a system you scale everything in it obviously... I think the problem came because you consider space to be something that exist independently of matter...I suppose the only thing that exist, is what define the propagation of information.. and in my idea, that is the scale field)
    But that was not the important part. The important part, is that there is a equivalence principle involved between two universe with different scales, and that implies the existence of a field. You could then use a Gauge principle, to deduce there is a particle that "carry" that information from place to place, and that would be the graviton.
    But as you said, for the laws of universe to be invariant by the scale change, you have to put all others law "under" the influence of this scale defining field..
    Ok, you can say, that's just indeed some deeper interpretation of general relativity. 
    There's nothing else to say, I am not asking something really, I'm suggesting a speculative theory. If somebody think of something that contradict it, I would be happy to read it..the problem is, you didn't understand my definition of scale, but if once you understand it, you can contradict it, go ahead. I don't see why you would forbid people to contradict me.

  17. 1 hour ago, swansont said:

    You keep using "scale" so this doesn't solve the confusion about how you are using the term.

     

    If length were scaled, interactions would change.

    The Coulomb interaction, which varies as 1/r^2, would change relative to the magnetic interaction, which scales as 1/r^3 (for a dipole). Which means that the Hyperfine splitting (magnetic) would change at a different rate than the energy-level spacing (electrostatic).   

    Certain molecular bonds vary differently with distance, so you wouldn't necessarily get the same chemistry.

    Given that we have not unified the gravitational interaction with the others, I don't see what the basis is for this confidence that GR tells you anything about other interactions. Changing gravity would have no known effect on the other interactions. The dynamics of stellar and planetary evolution would change, of course, because multiple interactions are present.

    Further, space has the same laws everywhere because momentum is conserved (and vice-versa) — the laws are symmetric under translational symmetry.  If this were not true, we would be able to see the effect, and we don't see it. The above-mentioned hyperfine transition in hydrogen would be an obvious thing to check, but no, we see 1420 MHz coming from everywhere (adjusted for known effects, of course)

     

     

    you still don't understand, that I scale "everything". every law. I change all the dimensionless constants accordingly..  Interaction would be transformed accordingly. 
    (In reality, you should really understand that I'm really talking about changing the speed of light, assuming of course "light" drive time or length at the deepest level.. which I suppose true because of special relativity... that would be equivalent..  )...It a very simple  transformation of coordinates.. I'm scaling every particle, every wavelength, every speed (so the speed of light).. Relative to itself, It's the same universe.. relative to the observer, it's a different universe with a different set of constants.. 
    I scale the universe, without changing the story inside of it.. It's a different set of law. Mathematically what I do is exactly equivalent to changing meters to inches or other simple unit change.. in reality all measures are nothing but numbers.. Now I compare "2 universes" .. one being the homothetic version of the other.. They change only by the very most numerical definition of length, and one relative to the other.
    Imaging a atom in a void space. How can you measure the size of the atom ? The only answer is "the atom is 1 atom length"... There is nothing in this universe except the atom to compare to.. there is no "scale frame" except the content of the universe itself.. you can say "it's x time the speed of light when the atom vibrate n times..".. but you would use the light from the atom and the time from the atom... (because there is no other photons in this universe). The things you could use to measure distance.. are made of particles.. particles make the length.. 
    You can't say how big is a atom without..atoms (or particles).. 

     

  18. 38 minutes ago, swansont said:

    This seems contradictory. You say you are scaling the length, but then you are saying you aren't scaling the length.

     

    The length relative to the matter that obey the physical laws versus the length relative to some other universe with a scaled set of laws.. 

    - A given atom is "always"  X meter, because a meter is defined by the local laws of physics (the speed of light, the fine structure constant,etc).
    - two universe, with different set of laws, scaled differently, could have the same atoms, and there would be no way to define why one is bigger or the other. Special relativity tends to show that matter organize itself depending of the flaw of information.
    If the laws of physics defines a constant length (like the size of a atom or planck length).. that already mean that "space and the law in it" defines "length". There is no reason that it is a absolute constant.. no more than there is a absolute 0 position or an absolute 0 speed in that space.
    My idea is that : a field define the scale of local laws and the atom (yes ok a rank 2 tensor field define the matrix transformation between the set of laws).. There is no reason why "space" has exactly the same scale of laws everywhere : that's why I suppose that's what general relativity is : the effect of the variation of the scale of laws. 

     

  19. 10 minutes ago, MigL said:

    I understood the OP to be asking whether GR can be expressed in terms of changing scales of the 4 constituent dimensions, NOT whether GR can be expressed as a scalar field.
    I think we all agree it cannot be expressed as a scalar field, but neither can changing scales in 4 dimensions.

    I believe I've read some of K thorne's work where he claims aspects of GR can be expressed as either 'changing lengths/intervals' at constant scales, or 'changing scales' at constant lengths/intervals.
    I'll have to look into the standard model Lagrangian problem with changing scales.

    Let's just say this : my definition of "scaling" is from the start precisely the same as changing the length units.. (not relative to something else in the same set of laws)
    It's a very naive and simple scaling, not a change of length relative to matter. There's no point in talking about "just scaling the length".. I've never said "that" would work, and that's not the object of this thread. It's really the idea that "a dimensionless space" can't define the size of what's in it.. so that can vary (and ok it's not a simple scalar). 

  20. 25 minutes ago, swansont said:

    You keep using that word, but it makes no sense. If you scale length by a factor of 2, there are other parameters that do not scale by a factor of 2. If you are simply changing the value of all terms as you might if you went from MKS to cgs (or other) units, that's not scaling.

     

     

    I'm scaling "the universe" relative to another universe. That's very important. I discussed why a closed universe would have a certain size, and relative to what .
    I understand what you say, so please consider what I say : I'm placing myself out of the universe. You seem to have some preconceived idea about what scaling is..
    So that's not "that scaling" I'm talking about. When I say "matter defines length and time".. that tells the same thing that "you can't change only the length". .i agree with that from the start !! (the lenght of the atom is defined by the strength of the EM force, by some relativity etc.. of course !)

    I'm talking about the property of space and a medium transmitting information.. I don't see why I can't scale (absolutely) everything.. You take the whole movie, and you project it onto a bigger screen. Length are defined relative to matter, ok, but if you were outside of the universe, what would length mean ? From the beginning, I said : if you scale the universe by 2, that's equivalent to double the speed of light etc.. that's because one of my axiom is that speed of information through space (or light) defines everything and everyother law (you can see it in special relativity.. that what I explained with ABC blind particles)
    Take a spaceship with a certain speed, seen from outside : apply the lorentz transformation.. is the life in the spaceship changed  ?? NO.  Are the length you measure from outside different  ? Yes : it's the lorentz transformation.. the ship is compressed. And yet, the picture you have from outside totally respect law of physics. So that already contradict the idea that "you can"t scale the universe".. you can obviously squeeze it : we call it the lorentz transformation.

     

  21. 1 hour ago, Markus Hanke said:

    The model contains coupling constants that define the relative strengths of the various interactions. They are dimensionless themselves, but are related in specific ways to other fundamental constants that do have dimensions. This (along with boundary conditions in the Euler-Lagrange equations) defines a unique scale for the model as a whole, that cannot be changed without affecting physically detectable changes.

    Of course you can express the SM in inches, if you are so inclined - but that is not the same as resling the Lagrangian. When you scale something, you are scaling the actual dynamics of the system, which is a physical change; using different units just means expressing the same physics in a different way. Today's temperature can be 20 celsius or 68 fahrenheit - this isn't a scaling, because it refers to the same physical temperature. You can say 'this house's temp is 20C' and 'that house's temp is 68F', and there is no difference whatsoever between them.

    so the explanation is "i'm not resling the Lagrangian".. I'm not scaling the actual "dynamics of the system". I'm scaling "the system". I'm scaling "every" constant.. You saying that somehow, dimensionless constant define the size of atoms : I agree with that. The atoms is measured relative to atoms, anyway. But you can still suppose that 2 unrelated systems have a different scale relative to each other.. 

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    No, what I am trying to say is that all atoms of the same kind have the same structure regardless of where and when they are, because their fundamental constituents are subject to the same laws and dynamics. And you can't keep those laws and dynamics the same if you rescale them. It's about the dynamics of the system. As for relativity, the Standard Model is CPT invariant, which implies Lorentz invariance, so compliance with the laws of relativity is both guaranteed and required.
    Essentially, the dynamics of a system isn't the same as its spatiotemporal embedding.

    that makes no sense.. you can' tell the size of the universe "from outside" the universe.. It's not a "physics" fact, it's a deep logical fact.

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    Actually, all this if off-topic, because the original question was whether GR can be rewritten in terms of just a scalar field. The answer to this is "no", because a scalar field (irrespective of what it physically refers to) cannot capture all the dynamics of gravity. Even a vector field can't. You need at least a rank-2 tensor field. You can see this most clearly if you consider that gravity can propagate as gravitational radiation fields - such fields have two polarisation modes (+ and x) that are distinct, so you will need at least a rank-2 tensor to fully capture all its degrees of freedom. A scalar field simply can't do the job, which can even be formally proven.

    ok but if I follow my logic, what make the difference between two system, is basically the "scaling", the matrix describing two set of dimensionless space.. I realize why I was wrong, but the thought experiments still works. I will say it again. Picture 2 closed universes. In each of them, the same matter organize the same way : in each, the size of atoms is equal, relative to rulers inside of each other respectively.
    But since there are no topological connection between the 2, can you tell if one is bigger than the other ? A property of space must tell this one is this size, the other one is the other size. Something must represent the way each other are related.. it's a field. And so ok, a scalar isn't enough : maybe one universe is "squeezed", maybe one is "compressed in one direction".. so what would describe the transformation of one into the other, from a local point of view  ? Maybe it's a rank-2 tensor field ! (that would be funny if a rank-2 tensor simply describe the transformation of a infinitesimal local spacetime frame into an other... )
    That would still be interesting to understand that there is a field and a particle that carry it.. 
    You have to understand, that I think from a metaphysical point of view.. What is absolute, what is not.. 

    2 hours ago, swansont said:

    You don't seem to be using this consistently. Scaling something up or down is not the same as using a different set of units.

    My thought experiment is "just scaling everything".. you supposed scaling some part of the laws and not others, or the metrics and not the energy etc.... I've never said that.
    but my scaling is from the start precisely scaling the length units.. My idea of scaling is the simplest scaling possible : the same universe, the same story, the same laws,
    but I discuss the absolute meaning of "length", not relative to "the content" of course : I know that wouldn't work. As I said repeatedly : the matter defines its own length (and time).. 

    It's really a abstract consideration (a simple one, I'll admit I don't understand what a rank-2 tensor exactly is).. but because it's a metaphysical consideration, that doesn't mean I'm wrong.. What is the "length"  of the universe, not relative to what's inside, but in a no dimension space, and could it be something else.. 

  22. 33 minutes ago, Markus Hanke said:

    Well then, I don't suppose you have any need for my - or anyone else's - input.

    I'm talking about information and metaphysical consideration. 
    "if quantum mechanic (or standard model or any theory) is not invariant, it means something in space has to define length"
    How would you contradict that ? 

    18 minutes ago, Markus Hanke said:

    The Lagrangian contains very many terms - some of them contain units of space and time, others do not; some contain mixes of different parameters, others contain higher powers of some dimensions, but not others. If you simply scale units, then some parts of the Lagrangian change, whereas other parts do not, so the overall Lagrangian is never the same. That's the point - because the Lagrangian is so complicated, it is simply not possible to adjust everything in such a way that it remains overall invariant. Especially the weak and strong interaction parts will cause problems here.

    And then of course, even if it did somehow remain invariant, you still can't recover the dynamics of gravity from a simple scalar field. You need at least a rank-2 tensor.

    If you change scale, it's just equivalent of changing the length units. For instance using "inches" instead of "meters". Are you saying that the standard model can't be expressed in inches ? ?? I don't understand everything you say, but I don't have to, because I just can prove this can't work. How complicated is your theory, there is no way you can't replace a arbitrary unit by another unit. 🤷‍♂️
    In the other hand if you trying to say that a given atom always has the same size : I agree !! The ruler you can use to measure "length" is made of atoms. There's nothing surprising here. That doesn't mean that the length can't vary from places to places (the fact that a atoms is squeezed from a inertial frame is in special relativity).. .. On the contrary : the fact that "something" is absolute locally implies it can vary globally..(it's the same thing as the elevator thought experiment).. because the whole universe can't have "absolute" measurement, without an external frame of reference (that would be outside of it, contradicting the "whole universe" hypothesis). That's a metaphysical consideration.
     

  23. 13 minutes ago, Markus Hanke said:

    I didn't say this. I said that the Standard Model (taken as a whole, or specific parts in it) are not scale invariant.

    Can you show this mathematically?

    Multiplicating "every" length in a theory, you get the same theory with bigger length. Instead of meter, for instance, you use "centimeters". So every 1 length units , become 100 length units. You can't "prove" a change in axiomatic you made arbitrarily. Also, the fact something is "arbitrary" should indicate that it could vary from place to place, and that a "field" exists. It's somehow a metaphysical  requirement of every constants, because the opposite would imply there is a "reference" somewhere outside of the theory (so out of the universe). 
     

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    Again, this isn't about QM, it's about the Standard Model specifically. Different terms (and there are many!) scale differently within the Lagrangian, and most of the coupling constants are dimensionless and don't scale at all. So no matter what you change in terms of the constants, you can't get a consistent scaling for the overall Lagrangian.

    I'm simply pointing out to you how the maths work - it's up to yourself what you do with that information. Ideally, you shouldn't take my word for it at all, and instead learn to do the maths yourself. 

    Well then, I don't suppose you have any need for my - or anyone else's - input.

    I've published my answer too fast, your answer was useful


    What I think you physicist should do is frontly define the "equivalence principle" for all "constants" of physics, and always suppose that if you see a constant (just like the size of a atom) it must imply that a "field" defines it, and that a particle carries the information. 

  24. 5 hours ago, Markus Hanke said:

    This would be the case in Newtonian gravity, but in GR it's much more complex than that. Here, the source of gravity is the stress-energy-momentum tensor, which is a tensorial quantity with 16 (not necessarily independent) components. Energy density is in there as well, but so are other things such momentum fluxes, stresses, strains, momentum density etc.

    Also, it has to be remembered that the GR field equations are a local constraint - so even in the vacuum of free space where there are no local sources of energy-momentum, you still get gravity. Lastly, unlike in Newtonian gravity, the field equations are non-linear, which physically means that in some sense gravity is also its own source, i.e. gravity is self-interacting. You can in fact get gravitational constructs in the complete absence of any sources of energy-momentum.

    See above - the source term is a rank-2 tensor, not a scalar. Also, in GR gravity is described purely geometrically, it doesn't use the notion of 'force' as such.

    Some laws of physics may be scale invariant, but most are not. Specifically, the Standard Model is not scale invariant, and there isn't any self-consistent way to make it so.

    You don't need matter to have gravity. Also, space isn't 'around' matter - spacetime is everywhere, both in the exterior and the interior of energy-momentum distributions.

    The coupling constants for the three fundamental interactions are dimensionless; they wouldn't scale along with your clocks and ruler. And if they did scale, you would break the weak and strong interactions in the process, because their Lagrangians are not invariant under such changes.

    You'd have two regions of spacetime where the fundamental interactions work in two different ways. This is obviously not what we observe in the real world.

    I understand perfectly well, thank you. I'm simply trying to point out that this can't work.

    Thanks for your answer.. Ok I know general relativity is complicated. 
    I understand your way of understanding space time ("space time" with objects in it). I understand it (I understand at least special relativity). There is no point in trying to "tell me how it is". I'm not trying to understand relativity, but to make you understand it differently. that's the object of this thread.. I'm telling you, that you can understand it differently : the matter structuring itself in the information medium.. it should gives you back special relativity and general relativity, I don't see what you risk in trying to see things the way I do.
    For instance you say "quantum mechanic is not invariant by scaling". If you scale everything, including the metrics and the time, the definition of length, it's invariant (because you made it so). You scale the speed of light, you scale the planck length. You scale "every length of the theory". If you just project "the reality" and everything that happens in it, into a "bigger space" . The same things happen in both case (because you scale everything).. In that case it's obviously invariant (but of course you have to really think about what i'm saying instead of repeating old arguments). Now suppose that the definition of length vary for place to place (that's general relativity really).. and that graviton is the vector of this information. 

    In a broader sense the fact that quantum mechanics is not invariant by scale is easy to understand : a atom at rest "defines" a length and a time. BUT. If you define length and time as the size and frequency a atom organize itself in space, you can define a specific data that is in that space, and that give you the scale. (In quantum mechanic, it's coded into the constant lengths of the theory)..
    I know I'm right of a simple reason : IF quantum mechanic is not invariant, it means something in space has to define length. You put a atom in space : it take "a certain length". Why ? Where does this length come from, and could vary from place to place ? (you would say "because of quantum mechanics that use constants.." but why those constants have those values ??) I simply suppose the value depends on a scale field. 
    That's the field I'm talking about. I suppose that ultimately it is the speed of light, the speed of information, because it also conveniently define special relativity and general relativity. 

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    I also understand that the complete Lagrangian of the Standard Model isn't invariant under scalings, regardless of how you try to twist the fundamental constants - in fact, because many of the constants have mutual dependencies, and some are dimensionless, it isn't possible to scale them all simultaneously in a consistent manner.

    What is a "meter".. 
    What you say, is equivalent to "matter define length"  that I understand, that's what I 'm saying.. but, that doesn't mean that this metrics can't vary relatively from place to place ! (and in fact, that's what General Relativity says). Imagine two atoms, in two space : if you stand close to them and measure them, you always get the same length (that's obvious, because your ruler is made of atoms).. but that doesn't mean that you can't imagine two different scale frame exists.

     

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    When I first participated on online forums, many years ago, the idea of "shrinking matter" was in vogue for a time - the idea was that the universe is actually static, and just appears to be expanding because all matter in it is shrinking in such a way as to be locally undetectable. The mechanism was supposed to be the same - a scaling of local frames. So not only I am familiar with the essential idea of scaling fundamental laws, I've even been through some of the maths to show why it doesn't work (and can't work).

    The thing you don't understand is that it's only a "point of view" problem.. Whether matter shrink or universe expand isn't a real question, it's irrelevant, unless you suppose you has a observer defines a "reference scale".. (that doesn't make sense, because a observer can't be out of the universe). That's the same reasoning behind every equivalence principles.. (does the universe have a scale ? do the universe have a position ? do the universe have a speed ?)..
    The only thing that can be observed (by definition) is a variation of something. That's why I said the universe as a whole should be "invariant by scale". If it's invariant in scale (it means a global scale doesn't make any difference). but each part of it can defines a scale relative to the other parts of it. 

    My solution is simple : matter, with forces, organize itself, therefor creating "spacetime metrics" of space : a atom takes it own size.
    What's fascinating, that if you modify the way information travels in space (for instance, you add a speed to all traveling information), you get special relativity.. (that's just the train explanation)... and if you suppose the speed of information varies from place to place, you get general relativity (that's just the "curvature").

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    As I said already, spacetime curvature is a tensorial quantity (it is in fact a rank-4 tensor) - so how would that work, do you think?


    No, I don't know how it would work . But the problem is somehow Einstein tries to defined relativity as "out of frames".. but that also mean that describing reality in a single frame is enough to describe it in all the other frames.. so I don't see the point of understanding everything in a out of frame.

    Sorry i've not finished my comment.. (i publish too fast)


     

     

  25. 5 hours ago, Markus Hanke said:

    This is only true in spacetimes that are at least static and stationary, but not in the general case. 
    The curvature of spacetime is quantified by the Riemann tensor - its formal mathematical definition aside for now, in the context of GR what this quantity measures is geodesic deviation, i.e. the failure of initially parallel geodesics to remain parallel. This is a more general concept than scale invariance.

    Ok i take your word for it

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    On an even more fundamental level, you cannot capture the dynamics of gravity by a simple scalar quantity (such as a scale factor), since a scalar field would be unable to account for the necessary degrees of freedom. It can be formally shown that you need at least a rank-2 tensor field for that - represented by the metric tensor in GR.

    I mean of course the gravitational force would be the gradient of the scalar.. the scalar would be something like the energy/matter density field....isn't the gravitational field entirely dependent on the energy/mass density ?

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    If you postulate a graviton, then, as massless spin-2 particles, they can only couple to rank-2 tensors, not scalars.

    Well, they are empirically not invariant in that way, so I don’t really get the point you are trying to make?

    you don't understand because "when I mean scale" I mean relative scale.. you have to read how I define Length and time.. you put space time as a frame and matter in it. I suppose matter defines it's own length  and time, that's why the speed of light is invariant in it. If the laws of physics were invariant by scaling, you would not be able to detect it (by definition)
    because everything would be the same. Except when two system have different scale : the difference would be gravitation. 
    That's sad because I understand that you can't understand me, i've no way to explain myself better. I will just ask you to reconsider this : "lengths" and "time" is defined by matter. It's not "space" with "matter in it", it's "matter that create space around it".
    You can't measure "space" without a ruler (made of matter) and time without a "clock" (made of matter). Imagine now a space where there is no frame at all  only a bubble with its own clock and and its own ruler (and those measure are from inside). Now picture 2 bubble like that. How could you tell "which one is bigger" ? (in a frameless space, you can't)
    I you really scale "everything", each particle at a deep level,  you scale the ruler and the clock, so there is no differences at all. Each atom defines its own size and its own frequency : so its invariant.
    You can't because length and time are defined "from the inside of each system".. but what if a variation do exist between the two bubbles ? That would be what I'm talking about. The word "scale" is maybe a poorly chosen world, I speak about the very definition of "time/length" in a structure.. it is equivalent to changing the speed of light as seen from outside and not inside (if you suppose that speed of light is what define scale and not the other way around).. 
    ...and I know you won't understand that.. sorry I can't explain better
     

    Ok I will try to explain it differently. Let's suppose "the speed of information" is "c" (it's more fundamental than the speed of light). In any matter structure, It defines what is "time" and what is "space".. because everything that happens depends on it. Let's suppose you have 2 particle A and B. A sends a message to B. A and B have no clocks, no rulers, they are blind in a dimensionless space. All A and B can do is exchanging message. When A sends a message to B, B can send it back. There is a order relationship that defines "time", as a series of events.. the messages.
    but A and B can't tell how "far"  they are from each others.. they have no clock ! nothing happens at all between the message : A and B don't experience "time". the message exchange IS the clock. So with only A and B, time/length is not defined.
    Now if you have a new particle C. A and B can exchange message with C. Now they can compare how easy it is for them to exchange messages relative to each others. For instance A can now tell if C is twice closer than B if he can exchange twice more message with C than with B.
    In this model, space / time is entirely a relative construct.. You can scale everything, and the relationship between A B and C would be exactly the SAME, because all they can ever know is the ratio of their respective message frequency.
    You can also globally change the speed of messages, there still would be now difference..  Now. Suppose that ABC are particle that self organize, and they use the messages to modify their relationship : message exchange is actively used to change the relative distances, in order to make structures (just like a atom, would resist to compression because it's shape is self-defined by EM forces).. the message could be used to add "impulsion"...for instance, A could choose to make the relative distance between B and C equal, to make a equilateral triangle. 
    (by the way, that is enough to define special relativity : if the speed of messages is "anisotropic", if the message slides in one direction (from outside), the structure could still reorganize to make the distance equal... and seen by some outside observer, you would see... a deformation of the structure : the Lorentz transformation ! )
    Now, what I suppose, is that somehow, the "space" in which ABC are, could have a field the define efficiency to carry message.. if the behavior of ABC is still defined by the message. variation of efficiency of messaging would be equivalent to space time curvature.. (as it directly "curve" the space/time measured by particles)

     

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