World Lines & (x, y, z, t)

Discussion in 'Physics & Math' started by Dinosaur, May 4, 2014.

  1. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    Quote the pseudoscience that I supposedly said, and give a reason why it's pseudoscience, explain it to me the proper way, and show me where my error is.
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  3. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

    The buzz phrase, "Query, quest, and quantify", comes to mind as the operative plan when a science enthusiast sets out to understand the universe. The query phase is the start, and that phase is an ongoing active part as you follow the path. The query stage soon becomes a quest to sort out science and nature, so give it your best effort to put everything together in a personal understanding of cosmology, a personal model of the universe.

    As the model unfolds out of your queries and quest, you naturally begin to address the quantification of your model, and that is where it is really handy to be a trained physicist and mathematician. If you aren't qualified to speak the language of physics, then your personal model might not get any meaningful attention, and maybe it shouldn't. If it is not in the language of science, it is not "science", it is the personal model of a layman science enthusiast who wonders, researches and explores, and gradually draws conclusions that begin to fit together to your own satisfaction. But you get all the fun of doing it, and learning as you do. Maybe it is just a hobby. Remember that as you talk about what you are doing.

    You certainly can use the science forums and internet to learn, ask questions, and post and discuss ideas. That way there will be a record of your quest that you can always refer to by looking back over your posts and threads, and you can continually update your views as they evolve.

    What is wrong with that? Nothing, unless you pretend it is science if it is not, or unless you state your speculations and hypotheses as if they were fact, and unless you disparage real scientists and generally accepted science. Don't do those things if you want your quest to be ongoing, and to evolve in the direction you want it to go. That direction should be that of continual learning, and continually picking out of the research and contemplations those things that work in your view.

    How do you know what works and doesn't work? What works are those pieces that are consistent with each other and work together, i.e. internal consistency, and what doesn't work are those pieces that are inconsistent with scientific observations and data.

    Follow those rules, be reasonable and responsible, stick with the quest, and contemplate and deliberate as you go, and your personal understanding of the universe will take shape. Keep track of what you include in it, what you exclude from it, and revisit those things often, because if you have an early flaw in terms of the rules of internal consistency and external compatibility, it won't be any fun going back to where the fatal error crept in, and starting over from there.

    A word of warning. It will not ever be smooth sailing, and if people in the forums you frequent start saying you are pretending to be "doing" science, or saying you are presenting your speculations and hypotheses as if they were fact, or that you are disparaging real scientists and generally accepted science, make them quote what you said that causes them to make those accusations. If they do respond with examples, admit when you are wrong, and if they don't show you the specific quote they are referring to, ignore them, they are trying to disrupt your path and discredit you personally.
    Last edited: May 8, 2014
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  5. paddoboy Valued Senior Member


    Interesting comment.
    Let me say that as one who has fervently pushed and adhered to the reality of time, I would agree that the point is far from settled, and is debatable.
    When I did admit this point to undefined in a forlorn effort for some common ground, it was literally drowned once again in a conglomeration of inane lengthy gobblydook and completely denied...So no common ground obtained.

    I suppose that's another point to consider with differences between mainstream scientists, and some of those pushing all encompassing alternatives are discussed.
    Last edited: May 9, 2014
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  7. Secret Registered Senior Member

    Q1 Bump and with elaborations:

    when I watch this video it instantly reminds of this "worldline set" interpretation of yours

    The dance moves looks seemlessly connected in the video, but each frame in the movie are events that are separated in varying amount of spacetime interval in the guy's rest frame.

    Therefore how close will the worldlines has to be in order to be considered as belonged to the set?


    ||The issue with time and motion||

    Motion is defined as rate of change of position w.r.t. to time, thus it is velocity

    i.e. d(vec(x))/dt

    At every infinitesimal moment in time (e.g. exactly 12:00:00:0000000000....+delta, or zero+a little bit duration), there's an instantaneous motion

    At EXACTLY 12:00:00:0000000, the change in position is not necessary defined, depending on the system in question, thus IN GENERAL for an ARBITRARY system we cannot say whether something is moving or not at an EXACT moment in time

    We are learnt to plot x-t graphs during high school physics lessons, and later when we do general relativity, we also plot spacetime diagrams

    We know that t is a parameter used to keep track on the changes in the system (another example of a parameter that also keep trakc of changes is the gradient: change of some property for every infinitesimal change in position, as mentioned by AquousId)

    We also know from experience that e.g. opening a clock we see cogs moving during a certain interval of time (here I am using this term "time" to refer to the daily life notion of "after a while" but I don't know how to express this more clearly, thus for this sentence, "time" is just a word and not the concept of itself (thus any discussion of its reality is irrelevant in responding to the question that depends on this "see moving cogs" background information)

    There are also many philosophical arguments and debates about what time is, whether it is real or just a convenient mathematical construct to keep track of things

    So I have some subquestions that followed:
    1. what defines a "tick" of proper time in the observer's rest frame, is it just the distance light travel when cesium atom hyperfine splittings have oscillated (also in the rest frame) for 100000 something times?

    *2. If time is just a mathematical parameter, then why we cannot replace it with other parameters say: temperature, mass, distance etc. What makes time as a parameter so different/special from other parameters?

    3. In spacetime diagrams, if spacetime and events in the diagram are just static, non moving, then what give rise to proper time? (since looking the diagram as a whole 4 dimensional volume, nothing is actually movin, and proper time is defined to be the time elapsed measured by a clock moving along the worldline of the observer)

    4. The arrow of time can be explained by 2nd law of thermodynamics and the observation that the big bang is a low entropic state. but is that all it is , or is there something else that is responsible for the arrow of time?

    *5a. (For those who are in the "time is fundamental" camps) What is the origin of the "flow of time/passage of time" commonly encounter in daily life chatting? Or

    *5b. (For those who are in the "time is unreal or non fundamental" camps). In the rest frame (thus neglecting time dilation as the issue is still valid even without time dilation) Why the cogs in this clock will have done e.g. 180 revolutions when say, our heart had beaten e.g. 72 times. Why not e.g. 75 revolutions vs 900 beats. What determine the ratio or relation of frequencies in a periodic system A and a periodic system B?

    *6. Is the measurements of time (whether a real thing measured indirectly or a mathematical parameter measured using some devices) of some changes in the system can only be calibrated with a periodic system. That is if I use an aperiodic system, can I use it to measure the time of my system of interest?

    7. At heat death, where entropy has maximized, do time still retain an arrow, that is could we still tell past from future in our rest frames?

    PS I am currently sitting on the fence of camps 5a and 5b, because I don't understand both enough to decide my side
  8. Dinosaur Rational Skeptic Valued Senior Member

    Secret:From your Post #2
    I wonder if you grok the concept of World Lines. The phrase A set of related World Lines was used in the context of a philosophical discussion which was an issue for at least a few centuries.

    BTW: Note the bolded (by me) phrases in the above. Is English your second language? Perhaps you type fast without mental focus on the syntactic details & do not proof read.

    The discussion related to the claim that a given object (animate or inanimate) has an ongoing identity. Id est: What is meant or implied by the semantic statement that a particular object is the same object today as it was yesterday & is expected to be tomorrow?

    Obviously an object can gain or lose molecules/atoms & the configuration of the molecules/atoms can change (especially in the case of living creatures/plants). Philosophers had pedantic arguments on this issue over a long period of time.

    I would expect modern philosophers who understand the concept of World Lines to be content with the POV that the term set/group of related World Lines provides semantics which strongly imply ongoing identity.

    Proximity of the World Lines is obviously not a critical issue. If I am shot, the bullet in my body is not considered to be part of me, although its World Lines are certainly close to many World Lines in the set considered to belong to me. Defining ongoing identity via the term set of related
    world Lines
    implies an ongoing association of the pertinent World Lines.

    BTW: The notion of a space-time continuum & (x, y, z, t) coordinates for specifying the location of an event provides a static model of particle motion.

    The use of such a model does not deny that there is motion. The model merely allows mathematics associated with geometry to be used to describe the laws of physics.

    BTW: The mathematics used for General Relativity is Differential Geometry.

    Many people do not realize that it is erroneous to view models as realities.
  9. Secret Registered Senior Member

    Technically, I am sort of a beginner of relativity as I am taking this course currently in uni. I learnt from Schurtz's and the course that worldliness are curves in spacetime traced out by an observer. If an observer is at rest , then the worldline will be vertical in their momentary commoving reference frame (MCRF). I also learnt that 4 velocity is a tangent vector on the observer's worldline in their MCRF

    I am indeed a non native English speaker cause I'm Chinese. Few people managed to notice this though and some even comment I use very advanced english

    Would love to read more about that, some good links for reference?

    That sounds logical, but I am wondering whether we can define (or even quantify) the "extent of ongoing identity"?

    Like in maths when one ask what is a geodesic, they will say its the shortest path between two points on a manifold

    So I understand that according to what you mentioned, whether the worldliness belong to a set is determined by how close they are related to each other which one can conclude they represent the ongoing identity of the observer (or event) in question, ad not their spacetime separation. But since this is philosophical (as you have elaborated in an earlier subquote), is it possible to make rigorous what is meant by the extent of relatedness of two worldliness, so we can actually start using some maths to work out how closely related two worldliness are, if yes then how?

    Sometimes I can snap out of it, e.g. when my physics professor reminds me that we actually don't know what an electron really look like, just various ways to describe it that allow us to understand (wavefunctions, point charges etc.) . But often times, maybe because of getting use to the theory when doing many tut problems, sometimes there's this natural tendency to say that the fact is <insert mainstream theory>. In particular, given how physics is taught on using models in order to fit and explain experimental observations, it seems natural to me that one will try to ask whether the model can explain things that we perceive in daily life, such as how in spacetime diagrams we turn everything into geometry thus everything is static since the variable time is part of the geometry of spacetime. I just don't understand how does motion in spacetime diagrams (basically a static model) can relate to the concept of motion in mechanics where it is basically change in space for every unit of time progress

    Or in order words, in spacetime diagrams we don't see motion in the sense that we are used to in daily life since nothing is actually moving in a spacetime diagram. but in mechanics, we can see things moving

    which then brought me a question. How does motion in general is defined? Is it just an equation that relates a parameter known as time with a parameter known as position of an object, so does not require things to be moving (in a daily usage and mechanics sense)?
  10. phyti Registered Senior Member

    secret 124

    Motion is defined as rate of change of position w.r.t. to time, thus it is velocity

    That is a definition of speed.

    Motion is a change of position relative to another object.
    As to your questions:

    I recently abandoned the phrase "a clock measures time", since a ruler does not measure distance. It becomes clear if you compare the clock to a metronome, they both establish a standard beat or rhythm. The ruler sets a standard spatial unit of measure. The clock and ruler are tools that allow a human to make measurements. The only difference, the clock is typically active, it accumulates, where the ruler is typically passive. If a clock is adjusted to run faster, we don't have anymore 'time' than before, thus it isn't measuring time.

    If you are using a light clock, a 'tick' is n light cycles between an emitter and detector, or a finite light distance. Check your Minkowski vertical axis, it should be ct.

    Historically 'time' is a finite amount of motion of an object, earth, moon, sand, etc.

    The Minkowski is an historical record of speed, vt/ct, which allows you to calculate elapsed local time for a moving observer, which is what you just stated. If 'time' is just counting/accumulating ticks, it is a scalar and has no direction, and therefore has no arrow. Minkowski generalized the transformation equations to mathematically treat it as a dimension. It's no different than treating a square as an instance of a rectangle, with W=L. That's what mathematicians do, generalize and symmetrize.

    The tired universe..., will eventually give one last yawn before going to sleep. A closed system may reach a state of equilibrium, yet the universe as a closed system persists. This is the most lopsided argument I've ever encountered. The Hubble telescope provides those beautiful photos of stellar nurseries organizing matter. Seeds of genetic code organize matter into plant, animal, and human forms. Gravity organizes matter into galaxies. There are organizing phenomena from the quantum to the astronomical level, which are not considered in the heat death scenario. Unless these disappear, the dire predictions won't happen. There may be a recycling of energy not yet discovered, or an infusion of energy sufficient to maintain a balance.
    As for order, it exists for a crystal at absolute zero or a high speed nucleus, so what does it have to do with anything.
    People waking from comatose states have no memory of elapsed time. That shouldn't be surprising since it's memory that allows a comparison of the current state to a previous state, which the mind processes continuously and contributes to a 'flow' of time. People with brain damage to specific areas lose their ability to gage elapsed time. Then there are the 'movies', where the viewer watches a sequence of still pictures, and sees moving objects. The mind is still not very well understood.
  11. Dinosaur Rational Skeptic Valued Senior Member

    Arfa Brane: From your Post #9:
    General Relativity uses curved space as a model for gravitational effects. Differential Geometry is the mathematical discipline which provides tools for dealing with curved space. It includes methods for determining geodesics (shortest distance curves), calculating distances, areas, curvature, et cetera relating to curved space. Some consider differential geometry to be isomorphic with gravitational effects/calculations. It is the mathematics used for GR.

    Also from your Post #9:
    The two games are not equivalent; Isomorphic implies same form or structure, not equivalence.

    Secret: I admire those who can use two or more languages well & consider you to be more knowledgeable/intelligent than many who Post at SciForums. There is a joke about linguistic abilities.
    While there was a time when I spent more than a year in Brussels & managed by speaking French poorly, I am basically an American as defined above. Taking French in grades 11-12 helped me in Brussels.

    You asked:
    The above & other questions you raised was in the context of the following remark by me:
    The above concept does not provide help in quantifying or doing calculations relating to on going identity. It merely gets rid of some (not all) annoying discussions by pedantic philosophy professors. It does not stop all such discussions & does not fundamentally answer a lot of reasonable questions about the notion of on going identity. It seems to answer some of the questions & provides a reasonable semantic description of the notion.

    You asked:
    Using (x, y, z, t) coordinates & the concept of a Space-Time Continuum allows the use of geometry to deal with mechanics & other laws of physics. The model does not deny that there is motion. It merely allows geometry to be used to develop insights into the laws of physics.

    Geometry has been studied & developed for many centuries with Euclid & Pythagorus being very important early thinkers.

    In more modern times, Differential Geometry was developed to deal with curved spaces, primarily 2D objects like spheres, ellipsoids, toruses, & saddle-surfaces. It became the mathematics used for General Relativity. I think Minkowski or others might have suggested its use for GR.

    My knowledge of General Relativity is weak, even though I took courses in Diff. Geom. It is my understanding that some developments in GR were discovered due to the insights gained during the many decades of effort used to develop Differential Geometry.

    You asked:
    I am reminded of a judge or lawyer who said he could not define pornography, but could recognize it when he saw it. Perhaps the same can be said of motion.

    I suppose the following is a reasonable definition.

    If the values of (x, y, z) vary continuously & can be defined as functions of time, there is motion.​
    This does not deal with (or avoids) the issue of Quantum level events & the Uncertainty Principle.

    I have a life away from SciForums which is now making demands on me. The above does not address all of your questions/remarks. I will be both willing & interested in more questions/remarks from you.

    BTW: One of my favorite fictional characters is the Master of Sinanju, a Korean. He considers Chinese & other orientals to be slightly superior to Caucasians, but inferior to Koreans. The Destroyer series of novels are interesting, especially the first 10-20. He provided me with one of my favorite ideas.
  12. arfa brane call me arf Valued Senior Member

    "Iso" means equal in Greek. I was referring to the codes used in the games; these are isomorphic. Obviously a card game isn't a tic-tac-toe game.

    p.s. are you in the right thread here?
  13. Secret Registered Senior Member


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    I presumed that most Americans at that time is not good at speaking foreign language?

    Seems to me that philosophical questions are hard to investigate by building a physical model. Guess we might need to wait until some time in the future we came across an idea that can provide us a breakthrough in the understanding

    I rmb we have briefly went through the minkovski spacetime history in the course, and how Einstein then build his general relativity using monkovski's maths
    General Relativity is HARD. But I will not give up understanding it, considering its a course I have been waiting to study formally for 10 years

    From the course, it seems Mach's principle also inspire Einstein somewhat in formulating the equivalence principle and later via a series of efforts by other grand figures give him the idea of how matter and energy bend spacetime

    I guess that's precise enough definition and helps resolve the (at least my) problem of how we do not see events moving (as defined in the intuitive sense) in spacetime but the particles themselves are still moving because we can describe their evolution in a continuous manner using time, if I understand it correctly

    For quantum, I tend to think of them as clouds which can fuse and sometimes cancel each other and as long I can visualize whatever quantity this way, I am comfortable enough with it. I do however be constantly aware of my interpretations and cross check with science magazines and even science journals to ensure I interpret things close enough that can describe all known observations form the experiments. In sciforums, I have made a thread to crowd source a list of difference to check against my cloud interpretation (made that up) and reality (or at least the mainstream physics). It is interesting to note that time in quantum mechanics is treated differently compared to general relativity, in that it is closer to the concept of absolute time back in Newtonian periods, for example in how it is one of the parameters in describing the evolution of wavefunctions

    Good luck

    Please Register or Log in to view the hidden image!

    And my response to Master of Sinanju is: The objective reality/Nature does not lie. It does not care whether if the entire population believe it does what it never does

    The change in position w.r.t. time can include direction and magnitude, it does not imply only magnitude, thus it is velocity

    Do you mean this change can be defined using parameters other than time? Like how gradient is a change of something for a change of position? or even without a parameter at all? If it is the 3rd case, how to visualize this?

    Make sense, and yes

    I had a feeling you nailed the point, but I still don't quite get it. Can you elaborate, especially on the point about spatial measurements and how it differs from temporal measurements?


    While they looked ordered in the process in question, if you consider also the surroundings, energy in the surroundings become more spread out and locked in many microscopic places and forever rendered unusable. As far I know, there seemed to be no known case of any macroscopic system violating the 2nd Law of thermodynamics for sufficiently long enough time for the effect to persist (although being statistical in nature, it is violated all the time in the microscopic scale for fleeting amount of time)

    And far from equilibrium systems complicate things further.r Check out the BZ reaction
    And for more extreme cases, This. In both cases, 2nd law is pretty happy despite there is order coming from nowhere. It just that it is more likely to clump together and assemble than to say floating around in solution, and the total classical energy units of each of these arrangement, energy etc. options (S=k_BlnW) just get more spread out in the process in accordance to the 2nd law

    I do always dreamt of one day the 2nd and 3rd law of thermodynamics will be violated since as the saying goes "laws were made to be broken". And imagine all the exotic things that can happen if there exist something called below absolute zero (no we are not talking about negative kelvin here, this only occurs for systems where there is a energy maximum thus pumping more energy in will cause the particles to start to pile up in less and less energy levels, thus making the energy (and particle, velocity etc. distributions) of the system more concentrated\

    I don't get the point about how high speed nucleus lead to order (and I suspect you are talking about high speed nucleus obey the 3rd law of thermodynamics?

    A nice point, I often forgot about that. Though it will brought questions if time turned out to be something fundamental
    But otherwise, it would explain how we perceive "time has elapsed". I often heard of this explanation in science magazines, but since the nature of time is still an unsettled issue, I often tend to be open for other explanations. In particular how little interpretations have been conceived for those in the time is real camp All that we know so far is seems that time seemed to elapse while meanwhile energy (and other things) become more spread out in space and forms (2nd law), and there's even something in particle physics that goes in the opposite direction to what we commonly perceived as time elapsing, but so far (for those in the real camps) we are still clueless on what IS time.

    Btw my position is on the fence, although a lot of thinking recently and science magazine reading had caused me to lean towards more to the unreal camps

    About the topic of "elapse of time" philosophy tend to have a lot of arguments on it, such as what if we remove all time measuring devices and hints that tell the date and time (this include heat beat molecular vibrations etc., impractical as it sounds) from your room and then lock you in, will you still be able to tell time has passed? I haven't followed the most recent progress on this question, but myself is still being confused by the scenario. As you mentioned there's a lot more to learn of the mind. Our mind can play tricks on us, for instance
  14. Dinosaur Rational Skeptic Valued Senior Member

    Secret: Circa 1950 I took a course in philosophy. There was a chapter in the text book relating to time which had a lot of verbiage, but seemed to say very little. Mathematics, physics, & sports were my forte, so I asked my father (an engineer with many other interests) about my problems with the text.

    He said that he remembered that some book by Einstein (or about him) had a pertinent paragraph relating to time. I found the book in the college library.

    This is approximately what Einstein wrote, which I think is very succinct and pretty much describes it (paraphrase, not an exact quote)
    It is interesting that Albert used bold or italics for before & after, implying that they should be considered undefined primitive terms, not definable via the use of simpler terms or concepts.

    Note that an axiomatic system requires some undefined primitive terms to avoid various logical problems associated with circular definitions.

    It is interesting that Albert did not mention the concept of the flow of time from past through the present into the future, which does seem to be a construct (illusion?) of the human mind rather than an objective process associated with reality.

    When I showed the above to my philosophy professor, he said he would include the above in future lectures, provide it in a pamphlet, & tell students to ignore the chapter in the text book.

    You displayed an interest in & some knowledge of Quantum Theory. There is an excellent book for non experts (Quantum Reality) by Nick Herbert. It describes all the interpretations.

    I favor the Copenhagen (Bohr) interpretaion & consider the Many Worlds interpretation to be absoulte nonsense although it is accepted by many with serious credentials. It is my opinion that those who favor it prefer an interpretation which is easy to understand over explanations which are difficult to understand & leave some issues basically unexplained.​

    It is interesting that as a graduate student & for several years teaching/working with Quantum Theory, Herbert accepted a disturbance explanation for the Uncertainty Principle. He later came to the conclusion that it was erroneous.

    The UC is not a claim that measurement technology has limitations (although it does); It is a claim that position & momentum cannot both have have precise values at the same time. I consider the properties of a Bose-Einstein condensate to be experimental evidence supporting this view. A group of atoms chilled to nearly absolute zero (momentum closely approximating zero) seem to lose their identity because their position becomes very blurred.
  15. phyti Registered Senior Member

    secret #130

    I wasn't questioning the definition of speed or velocity. Motion can be observed without measurement. If you measure it, then you get the ratio of distance to time, or speed with or without direction. This is where Minkowski did science a favor, not with a 4D theory, but replacing the illusory 'time' with ct (light distance), and a comparison of apples to apples.
    While the light clock speeds along, the light is oscillating up and down. At a selected position, the clock stops, and like the carpenters folding ruler, we unfold all those oscillations and form a straight line representing light motion, which is compared to the clock motion. It's not complicated... like shipping.
    Assigning a time to an event results in a larger value than previous assigned values, since 'time' is cumulative. The typical clock recycles, but a bigger clock transfers the day into a yearly clock, like an odometer. Clocks are synchronized to provide an earthwide common ‘time’. Spatial measurements are typically independent of each other (unless related to a common purpose), and are not ordered in any manner.

    Here is a point to ponder. A simple ruler measures with a uom corresponding to distance. What’s the difference between a light clock and measuring a distance using a pulse of light, and a mechanical clock to ‘time’ it? In terms of physics, there is none, and shouldn't the uom be consistent?
    The intended point (which wasn't clear) was, there is order at low and high energy states. Atoms are highly organized and energetic even in lowest states. Also, with sufficient energy any ordered state can be made chaotic.
    The entropy/temperature issue needs more study.

    Imagine the universe reduced to a cloud of dust, with an approximate uniform heat energy. The gravitational effects would not be uniform.
    Maybe all we need is proof that an ideal equilibrium is not possible.

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