• Mr Bee
    234
    This leads to the interpretation that any restful body is not actually at rest but is moving through time at the speed of light. So in that sense everything moves through spacetime at velocity c, but photons can only move through space, hence no time passes for a photon.Kenosha Kid

    Can you clarify what "movement" means here? Certainly can't mean change in spatial location with respect to time since we are talking about "motion" through time. Of course one can define it in terms of a fifth dimension which objects move with respect to, but there are none beyond those of spacetime that I am aware. It seems like you're using it in a different sense than is normally used.
  • Kenosha Kid
    519
    Can you clarify what "movement" means here? Certainly can't mean change in spatial location with respect to time since we are talking about "motion" through time. Of course one can define it in terms of a fifth dimension which objects move with respect to, but there are none beyond those of spacetime that I am aware. It seems like you're using it in a different sense than is normally used.Mr Bee

    4D velocity is defined with respect to a different measure of time, rather than a different dimension. Within any given reference frame, a body's four-velocity is its rate of change of 4D position (x, y, z, t) with respect to the proper time of the body (t') which is time in that body's rest frame.

    Like other physical four-vectors, this velocity is frame-independent even though its vector components are not. (In the body's rest frame or a comoving frame, all of the velocity is in the time component; in any other frame, some of it is spatial, i.e. the body is seen to move.) The magnitude of all 4D velocities is c, the speed of light.
  • Mr Bee
    234


    Thanks, though from looking at the opinions of other physicists on the matter these past few hours, it doesn't seem like the whole concept of "speed through spacetime" is a popular way of describing things, with alot of people blaming Brian Greene for the concept.
  • Kenosha Kid
    519
    Thanks, though from looking at the opinions of other physicists on the matter these past few hours, it doesn't seem like the whole concept of "speed through spacetime" is a popular way of describing things, with alot of people blaming Brian Greene for the concept.Mr Bee

    It's older than that. The natural reaction to special relativity was to figure out what the invariant properties of objects were. Four-velocity is one of those invariants. It has good explanatory power, for instance in demonstrating why a reference frame change is a rotation and in simply describing time dilation. It encodes a lot of relativity. Beyond that, yeah, not a very useful quantity to work with.
  • Mr Bee
    234


    Oh sorry, I wasn't saying that Greene introduced the concept of 4-velocity, but rather it's description as "speed through spacetime" (or at the very least he seemed to have popularized this way of understanding it). As you can probably tell through my own questions about it, it's can be pretty confusing to implicitly define a second concept of "motion" and apply that to things like time, and from what I can tell for physicists it's not very helpful as a description either. However as you can also tell from Benj96's comments, for the purposes of popularizing science it also sounds cool to describe things that way, sort of like how the Higgs Boson was described as the "God particle" that grants mass even though that isn't really the case.
  • Kenosha Kid
    519

    Velocity generally is an unhelpful concept in modern physics. It is little-used in quantum mechanics for instance. Momentum is the useful quantity of motion. But any concept generalised to 4D is the same. If you accept time as a dimension different from but analogous to space, any temporal component of a four-vector will be likewise different from but analogous to the spatial components. The mixing of these components in frame transformations is testament to the validity of this interpretation. When you transform from a rest frame to a non-rest one, the result is a rotation of a 4D property from purely temporal into partially spatial. And vice versa.
  • Eugen
    235
    Relativity is absurd, wrong and I hope it will soon dissapear. To believe time and space curve it's simply hilarious.
    I would argue relativity also harm science. For example, the pilot wave view which explains Quantum Mechanics in a very nice, non-mystical and deterministic way, it's not popular among scientists is because it is inconsistent with relativity.
    Scientists have to accept that Einsten was at best a cool dude, but not a god, and he was simply wrong.
  • Kenosha Kid
    519
    Scientists have to accept that Einsten was at best a cool dude, but not a god, and he was simply wrong.Eugen

    I think they need a stronger reason to than distaste. Relativity's predictions are numerous and empirically verified (black holes, gravity waves, Mercury's orbit...) and science is empirical. And it's not like they're not considering other options (string theory, for instance).
  • Eugen
    235
    There are many ways in which you could reach the same result. Pilot wave for example is a theory with no less success in empirical results than probabilistic QM, which is totally different. So the empirically verified argument isn't enough to defy the logic and common-sense.
  • Kenosha Kid
    519
    There are many ways in which you could reach the same result.Eugen

    They have to be proposed and tested. Tmk no testable theory contests GR. A testable theory must a) explain everything Newtonian gravity explained, b) explain everything Einsteinian gravity explained, c) explain something unexplained by GR. When we have that, GR is dead. Science in a nutshell!
  • Eugen
    235
    I am not a sciebtist, but I have seen different plausible variants. You can check on YT. But even if we didn't have alternatives, I don't think believing in absurd things like time curvature is a good way to do science. Time is like probabilities - just a human tool.
  • Kenosha Kid
    519
    I am not a sciebtist, but I have seen different plausible variants. You can check on YT. But even if we didn't have alternatives, I don't think believing in absurd things like time curvature is a good way to do science. Time is like probabilities - just a human tool.Eugen

    A good way to do science is to test your hypotheses. Belief is always optional :)
  • Eugen
    235
    True. You will see GR's success fade away soon. And l don't need to know science or to test something illogic. GR's success is due to the fact that it is not entirely wrong, not because it's correct. GR is based on the idealistic thought that the universe revolves around the observer.
  • Eugen
    235
    GR is so illogic. E.g. if you live on Mars and work in London, if you wanna travel by the speed of light (in order to arrive earlier) you have to leave home earlier, which is contrary to all daily empirical tests. So this is an empirical counter-argument. GR is false!
  • Kenosha Kid
    519
    GR is based on the idealistic thought that the universe revolves around the observer.Eugen

    GR is based on the Equivalence Principle (gravity and acceleration are indistinguishable) and special relativity (SR) which decentres the observer and claims there are no special frames of reference. Quite the opposite to what you said.

    GR is so illogic. E.g. if you live on Mars and work in London, if you wanna travel by the speed of light (in order to arrive earlier) you have to leave home earlier, which is contrary to all daily empirical tests. So this is an empirical counter-argument. GR is false!Eugen

    This is SR. If you wish to travel for 5 minutes to get to Mars for 9 am, you have to leave before 8:55 Martian time because of time dilation. Moving clocks run slow, as has been demonstrated by the velocity-dependence of particle decays.
  • Eugen
    235
    This is SR. If you wish to travel for 5 minutes to get to Mars for 9 am, you have to leave before 8:55 Martian time because of time dilation. Moving clocks run slow, as has been demonstrated by the velocity-dependence of particle decays.Kenosha Kid

    I am sure it is a case where many mistakes bring you to the correct answer. It is simply illogic and against common sense and reality cannot be like this.
  • Kenosha Kid
    519
    I am sure it is a case where many mistakes bring you to the correct answer. It is simply illogic and against common sense and reality cannot be like this.Eugen

    It is an exceedingly simple theory, derived exactly from two postulates:
    1. The empirically-verified observer-independence of the speed of light;
    2. The empirically-verified invariability of physical law to inertial motion.
    Without finding a flaw in its postulates or its derivation, it is illogical to dismiss its conclusions.

    Our tastes are our own, but taste is not a scientific criterion. The universe has no obligation to be intuitive; she may have her own rules as long as she sticks to them.
  • Eugen
    235
    I am not a scientist, therefore my language is very limited. But time will eventually tell GR is wrong.
  • Eugen
    235
    It is an exceedingly simple theory, derived exactly from two postulates:
    1. The empirically-verified observer-independence of the speed of light;
    2. The empirically-verified invariability of physical law to inertial motion.
    Without finding a flaw in its postulates or its derivation, it is illogical to dismiss its conclusions.
    Kenosha Kid

    Pilot wave has no empirical flaws and it contradicts both GR and probabilistic QM.
  • Kenosha Kid
    519
    Pilot wave has no empirical flaws and it contradicts both GR and probabilistic QM.Eugen

    Then it ought to yield testable predictions.
  • Eugen
    235
    It did. And of course a thing cannot be in 2 places at once and it doesn't "care" about being observed or not.
  • Kenosha Kid
    519
    Pilot wave has no empirical flaws and it contradicts both GR and probabilistic QM.Eugen

    It's not relativistic by design btw. It is mathematically equivalent to non-relativistic quantum mechanics (i.e. the Schrödinger equation), which is an approximation to relativistic quantum mechanics (i.e. the Dirac equation).
  • Kenosha Kid
    519
    It did. And of course a thing cannot be in 2 places at once and it doesn't "care" about being observed or not.Eugen

    Well, yes, it did. It predicted a sizeable electric dipole moment for hydrogen. This wasn't found, so Bohm went back and put the charge distribution inside the pilot wave instead of the particle, completely undermining the whole point of his own theory.
  • Eugen
    235
    These are technicalities and I cannot get into them because it is not my field, but I can only say I did a research and I haven't found flaws with pilot wave. I did find many with GR though. My point is that there are many different opinions, but at the end of the day common-sense and logic will prevail. GR or probabilistic QM are very against common-sense and logic.
  • Kenosha Kid
    519
    These are technicalities and I cannot get into them because it is not my field, but I can only say I did a research and I haven't found flaws with pilot wave. I did find many with GR though. My point is that there are many different opinions, but at the end of the day common-sense and logic will prevail. GR or probabilistic QM are very against common-sense and logic.Eugen

    We are evolved to model everyday, human-scale phenomena. Limiting nature to be common sense is itself illogical. It is perfectly normal for scientific theories to evolves, spawn, die, succeed, etc. But common sense has nothing to do with it.
  • Eugen
    235
    But common sense has nothing to do with it.Kenosha Kid

    I think it has. Things function in this reality because it has.
  • Eugen
    235
    We are evolved to model everyday,Kenosha Kid

    I think we are at the begining, in that romantic infancy of the process when quarks move their positiom when we look at them, when things are in 2 places at one and when we curve time
  • jgill
    634
    Being an expert is something of a challenge in this forum. :roll:
  • Benj96
    156
    Imagine if you were a snail. At the speed of an elderly woman walking down Main Street with a cane, the same is true. In a way. Yes?Outlander

    Hmm. I'm not sure sure. This assumes the snails conscious perception of the passage of time is proportional to its size/distance travelled. But I dont believe it works that way because many small animals/insects travel vast distances within their short life which would be the equivalent to us travelling throughout our solar system proportionally.

    A bee hurtling along on a wind current isnt going to experience time dilation or relativity just because it's small.
  • Benj96
    156
    I'm at home and my clock seems to me to run at a certain rate. My twin on the spaceship describes exactly the same phenomenon. But on his return I'm sixty years older, and he twenty.tim wood

    Yes but you're referring to things with mass. Things with mass such as a clock or two twins arent ever going to reach the speed of light. So no, for matter -time cannot stop it can only change relatively. But if you imagine a photon at the speed of light surrounded by other photons with the same velocity, the distance between them is negligible, the time it takes to go from their origin to their destination is also negligible so for a photon time doesnt occur.

    Also if the universe has finite energy, it has a finite spectrum/scale of rate for which reactions and interactions can occur. A point of maximum change and a point of minimum change. I would imagine the minimum rate of chnage would be one whereby no information exchange occurs at all (no time).
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