Galileo & Einstein - second thoughts

Discussion in 'Physics & Math' started by c'est moi, May 12, 2002.

  1. c'est moi all is energy and entropy Registered Senior Member

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    583
    taken from that other thread:

    """In fact, there is no experiment you can do inside the ship which will distinguish the ship moving at a constant velocity from when it is at rest. That's the basis of relativity. There simply is no universal standard of rest."""

    An observer outside the boat will be happy to tell you if it is moving or not.

    This prinicple of relativity in regard to FOR's has been mistakenly seen as representing a scientific principle. It is not. It is a prinicple that is based on a variable, ie INFORMATION, and nothing else. It has nothing to do with how Nature works.

    There is still no absolute FOR needed if there is no aether out there. Each situation simply has to be looked at in a different way.

    If we are all inside the boat and nobody is outside to tell us the situation we're in, then we shouldn't be making up silly principles because we lack information. We should simply understand that science requires the factor of Observation but that the Observer is limited in his capibilities.
     
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  3. (Q) Encephaloid Martini Valued Senior Member

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    An observer outside the boat will be happy to tell you if it is moving or not.

    Unfortunately, the observer outside the boat cannot tell you *absolutely* if the boat is moving across the water or if the water is moving under the boat.
     
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  5. c'est moi all is energy and entropy Registered Senior Member

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    """Unfortunately, the observer outside the boat cannot tell you *absolutely* if the boat is moving across the water or if the water is moving under the boat."""

    Luckily we know how waves of the ocean work (quite complex if I'm not mistaken). Both the boat and the waves are in motion.
     
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  7. (Q) Encephaloid Martini Valued Senior Member

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    Luckily we know how waves of the ocean work (quite complex if I'm not mistaken). Both the boat and the waves are in motion.

    You're missing the point. The outside observer cannot tell whether the boat is moving and the ocean, the Earth, the Solar System, and the Galaxy are *absolutely* stationary or whether the boat is *absolutely* stationary and the ocean, the Earth, the Solar System, the Galaxy are moving underneath it.

    It has nothing to do with how waves work.
     
  8. Prosoothus Registered Senior Member

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    1,973
    Q,

    What you refer to as "relativity" I see as simple inertia.

    Inertia: The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force.

    Regardless of the speed of an object, the object will continue moving at that constant speed, and in a straight line. This explains why the observer can't tell if the ship is moving or not. It has nothing to do with Einstein or the Theory of Relativity.

    Also, you, Crisp, and others on this forum are constantly claiming that the mass of an object increases as it speeds up. If that were the case, then the observer could find the true speed of the ship by measuring it's increased gravitational field. In other words, the observer's weight is dependent on the speed of the ship.

    Funny, it appears that Einstein contradicted himself, again.

    Tom
     
  9. (Q) Encephaloid Martini Valued Senior Member

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    20,855
    Prosoothus

    Actually the conversation between cest moi and myself is in regards to frames of reference. I don't know how you managed to read any differently, but somehow you did. :bugeye:
     
  10. Prosoothus Registered Senior Member

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    1,973
    Q,

    My post must have been misunderstood. I was stating that the reason the observer in his frame of reference could not tell if the ship is moving or not, is the result of the nature of inertia.

    Tom
     
  11. c'est moi all is energy and entropy Registered Senior Member

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    583
    I'll tell you a little secret

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    You are the one who keeps missing the point. The observer is LIMITED. You cannot, read CANNOT, make this LIMITATION into a PRINCIPLE of NATURE

    (and you can take the bottom of the ocean as a reference to see if the boats is moving and obviously it IS ALWAYS moving cause the water surface is never at rest -> absolute rest is a phantasy)

    """The outside observer cannot tell whether the boat is moving and the ocean, the Earth, the Solar System, and the Galaxy are *absolutely* stationary or whether the boat is *absolutely* stationary and the ocean, the Earth, the Solar System, the Galaxy are moving underneath it."""

    they are not moving underneath it
    the ocean and the boat are in the momentum of the earth
    and the earth in the momentum of the galaxy
    if I am walking in a train you won't tell me if I am the walking in that direction or I am standing still and the train is moving
    OBVIOUSLY the train is ALSO moving at that moment, but as I have its momentum with me its motion is COMPLETELY irrelevant as to where I am walking
     
  12. thed IT Gopher Registered Senior Member

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    1,105
    C'est Moi

    You're boat analogy is carefully chosen to be falsifiable.

    It is better to generalise the analogy. Are you stationary? Can an outside observor determine your real FOR or would their FOR determine the observation.

    There are two obvious answers. Yes or no. If you chose a third, being 'it depends', you ubnderstand Relativity.
     
  13. c'est moi all is energy and entropy Registered Senior Member

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    Thed, why don't you answer more directly to my statement?

    ""You're boat analogy is carefully chosen to be falsifiable. ""

    I picked it because it is from Galileo
    need I say more?
    btw, it is excellent to test it
    it appears to be wrong logic
    pick out any scenario
    it's never logic
    it's fundamentally wrong

    ""It is better to generalise the analogy.""

    not really, every situation is different
    you should answer the boat scenario
    or even the train scenario

    generalisations have the bad smell that YOU can generalise some kind of principle and make it look REALISTIC but when put to practice it turns out it isn't (see also the "throwing-a-baseball-scene in regard to kinetic energy in that case; note also that the relativity principle in EVERY experiment is a one-way conclusion, it has never been tested in both ways to see if it's true and I don't even think we can put up an experiment to test it and in other words, it's not even science because it is not falsifiable as per Popper)

    ""Are you stationary?""

    """Can an outside observor determine your real FOR or would their FOR determine the observation.
    There are two obvious answers. Yes or no. If you chose a third, being 'it depends', you ubnderstand Relativity."""

    If you want to you can pick a 4th, a 5th or a trillionth observer. It still doesn't turn it into a basic principle of nature. If you look at a particular situation, you need to look at what the observer KNOWS or can see. If he doesn't know, then so be it. Nature is not some kind of quiz where you HAVE TO say yes or no when you don't know. Saying it depends is the answer of wrong logic and fooling yourself by thinking you have solved the problem. You haven't.
     
  14. James R Just this guy, you know? Staff Member

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    39,397
    c'est moi:

    Obviously you still do not understand the principle of relativity.

    <i>...you can take the bottom of the ocean as a reference to see if the boats is moving and obviously it IS ALWAYS moving cause the water surface is never at rest...</i>

    Consider this:

    The boat is moving at 3 m/s across the water.
    The water is moving at 2 m/s across the ocean floor.
    The ocean floor is moving at 1000 km/hr around the centre of the Earth.
    The centre of the Earth is moving at 29 km/second around the sun.
    The sun is moving at 200 km/second around the centre of the galaxy.
    The centre of the galaxy is moving relative to the local group of galaxies.
    The local group is moving relative to other galaxies in the universe.
    We can't determine if the universe is moving, since there's nothing to compare it to.

    So, we cannot calculate how fast the boat is moving in an absolute sense. The best we can do is to say how fast it is moving with respect to the water, or the ocean floor, or the sun, or a small planet orbiting Tau Ceti or whatever.

    All motion is relative to an observer.
     
  15. c'est moi all is energy and entropy Registered Senior Member

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    James R, I have to catch my train now but with all respect, you don't even understand what I am trying say -> do I say I want an absolute frame??????? (btw, it took you many posts in regard to the Sagnac experiment to get to the bottom of it, ie the earth is a non-inertial frame because we DO detect its absolute motion but it doesn't matter 4 rel. cause its non-inertial)

    you on the other hand as the rest can't even answer to my objection on this stupid principle on relativity

    I had a new thought this night and appears that this silly principle is violated by physicists all the time (ie, they measure/caclculate kinetic energy --> but that's for this evening or maybe tomorrow)

    so, has anyone here even the descensy to answer me?
     
  16. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    Out of everyone here, I'm probably one of the least educated in physics, but this is what I see.

    As the Sagnac (if it's the one I think it is) and other experiments demonstrate, regardless of emitter movement or observer movement or any other factors, light (ie. photons, or EM emissions, of any part of the spectrum) travels at a given speed in any given medium. Like sound from a source arriving at two different observers in different places at different times, so light will arrive at different observers at different times. This does not indicate time travel or any other spooky things, it indicates only speed and distance.

    When on a ship, if that ship measures its speed as 30 knots, then it is not necessarily travelling at 30 knots relative to the Earth, or relative to its geographical position. You must take into account the current and such. If there is a 5 knot current going the other way, the ship's instruments may read 30 knots but it will only be travelling at 25 knots relative to the Earth. Relative to an observer off the ship, well, it depends on the movement of the observer too. And the ship's speed is different again relative to the Sun, to the Moon, to Jupiter, and to Andromeda.

    Not only is there no defined stationary point or direction in the universe against which we can measure absolute velocity, there is no need for such. When you get right down to it, you simply don't need such a reference. All you really need is velocity between yourself and whatever objects/effects you give a damn about, such as other ships nearby, the stars, et cetera. We already know light travels at certain speeds in certain media, although the details of the numbers may be refined furtehr in future; and we know how long it will take to walk from here to the corner shop, regardless of how we are moving in relation to Andromeda. Maybe relevent motion is as important as relative motion.

    C'est Moi, sorry if this is not what you were wondering about, I just thought I'd spill some of my thoughts.
     
  17. thed IT Gopher Registered Senior Member

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    1,105
    Adam

    A very well thought post. Congratulations.

    C'est Moi I am trying to make you think differently, is all. Galileo was right in his day, and still is in the limits of low velocity. What he said was absolutely correct based on common sense and a lack of knowledge of very high velocities and the wider Universe.

    You seem to be deliberately ignoring the point James R, and myself in a differing style, are trying to get over. Adam's take on it is very wel stated as well. Let me put it this way.

    Am I stationary, obviously yes. But only in respect to the Earth. To use the more prosaic language, in the FOR of the Earth I am stationary. But that is an arbitrary choice. If I choose my FOR to be the Sun, I am anything but stationary. From another Star I am not stationary. You can scale this out as far as you want. In every other FOR I am moving along differing velocity vectors. In the FOR of a very distant galaxy and a putative observor there, I am moving at a significant fraction of light speed.

    The choice of my zero point is totally arbitrary. The speed of a boat across the ocean is 10 knots say, as measured by a stationary observor on the shore. But as measured by an observor stationary with respect to the Sun, say, that boat is travelling at hundreds of Km/h. Who is correct then?

    Let me put it another way.

    Can we measure our real velocity through space? In order to do this you have to measure velocity with respect to a fixed point. Any point you choose is itself moving through space. So all you need do is work out the other things velocity through space. But what do you measure it with respect to. We're moving, it's moving, every moves with respect to every thing else. Movement is relative.

    If you put two astronauts into two ships moving at identical velocities and parallel to each other, they can not determine their velocities. Eventually they may realise the 'fixed stars' are moving so they can measure against that. Once they realise the stars are moving they no longer have a zero point to measure against.

    There are no absolutes all is relative, hence Relativity.
     
  18. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    Holy shit! Forgot to realise that bit, you might say. Someone far enough away may, in relation to me, be moving at whopping great speeds, as Thed said some significant fraction of C. Meanwhile to them, they are only walking about one metre per second toward the corner shop. No big deal to them maybe, but a totally different story for me.

    Now whether that person is moving at one metre per second toward his corner shop, or moving at 1/2 C across a distant point in the sky from my perspective, light still retains its own speed. For all I know that distant galaxy's relative motion to us might possibly exceed C, but that's beside the point. I think therefore that "lightspeed" and "light" can be disregarded from further consideration in this matter or relative motion. We already know light is going a certain speed, no need to worry about that particular piece of information further for the moment.

    That leaves some daft punk on Hoobagoo Prime wandering toward his corner store at 1m/s, and also travelling at ludicrous speed. So we have two speeds to consider in this situation. Only two which are relevent anyway.

    So after all that, it seems to me that the discussion must make a declaration that lightspeed (the speed light travels, referring only to that) is something to be discussed separately from considerations of relative motion. Relative motion may or may not have anything to do with C, may or may not involve speeds greater than C, et cetera, so we can ignore C when discussing relative motion.

    Small example: Two torch beams shining directly away from each other. Relative motion is double C, I would think. C is still C, but relative velocity is double C.

    And that, by the way, it seems, might lead to discussion of an absolute measure of speed: just C, the passage of EM signals through whatever materials. I don't know if the energy/activity of a material has effects on the speed of light through it (for example I don't know if the temperature of air affects how fast light passes through it), but if there is a difference, then C may be relative to the motion of particles blah blha blah. But in any case, even if there is some absolute measure of speed which can be used, it still makes no difference to the relative motion of, well, anything, such as me and that dude on Hoobagoo Prime.
     
  19. c'est moi all is energy and entropy Registered Senior Member

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    you all keep staring your eyes blind on the concept of absolute FOR

    and that's NOTTTTT what it is about

    so again Thed, if you want to, you can now answer my statement against the principle instead of playing around with absolute or not

    I have the feeling you all deliberitly don't want to answer the point I have made and which I won't repeat

    I agree with you Adam, what is relevant is important, the rest is peanuts
     
  20. c'est moi all is energy and entropy Registered Senior Member

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    583
    I see Crisp has mentioned something about kinectic energy which I wanted to point out now

    example: I throw my basball away up in the sky

    using the rel. principle: or it is the ball which is going up away from the earth or it is the earth which is moving away from the earth, no preferred FOR

    --> we do, however, speak in terms of measuring the kinetic energy of that ball which has been provided by your arm

    BUT, from the other point of view, it is the earth who is flying away, at let us say 60 miles/hour
    obviously, the earth must aquire kinetic energy seen from the FOR of that ball

    now two remarks:

    1) the energy has been provided by my body and transferred to that ball (I believe Crips made a comment on this in regard to particle acceleraters, maybe the solution is easy)
    and didn't go to the earth
    where does the earth get its kinetic energy?
    and where did the energy of my arm went if it didn't went to that ball as kinetic energy? (we are seeing all this now from the FOR of the ball)

    2) the very thought that we speak about measuring or calculating kinetic energy of a moving entity from our FOR is against relativity

    Let me make myself clear:

    Someone with an atomic clock is moving at an important fraction of the speed of light and passes by us.

    what does relativity has to say on this:

    --> From our FOR his clock runs slower
    --> From his FOR our time (clock) is running slower

    This is a direct consequence of the pr. of rel. as it doesn't allow you to say that the other one is moving. It depends. A third, imaginary observer is dragged in this and he'll tell you it depends.

    Big consequence is: You CANNOT say: 'Hey, that guy with his clock is moving at such a great speed so his clock must definately be influenced by this great speed and must be absorbing an important amount of Kinetic energy which would influence the atomic levels of that atomic clock explaining why it slows down.'

    BECAUSE, it depends which FOR you take, you are not allowed to think like that. That guy with his clock may be stationary and it is YOU who is moving at an important fraction of the speed of light so you CANNOT explain this slowing down of his clock due to kinetic energy.

    But on the other hand, it seems to be common to speak about kinetic energy of a moving object or entity such as a particle which has been accelerated or as a ball which you throw away. There, it is allowed to speak of kinetic energy INFLUENCING that entity. BUT when talking about clocks moving at high velocity, suddenly, you are not allowed to consider the effects of absorbed kinetic energy (or even gravitational energy) and you are not allowed to explain time dilation nor lenght dilation as a logic consequence. Instead, you have to use the magic of FOR's which is clearly not a true principle of Nature but a fairy tale.
     
  21. thed IT Gopher Registered Senior Member

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    C'est Moi

    What exactly is your objection. Your descriptions of your objections appear to have many unwritten asumptions about what you understand something to mean and what you mean. A clarification may be in order.

    For the moment I will address what I think you mean in the OP.

    But only with respect to that observor. Another observor in another frame will see things differently. The point of transformation equations is to ensure a consenus of agreement can be reached. The Galilean Transform does not work at high velocities and it breaks Maxwell's equations.

    To be blunt, I am not sure what you mean by <i>This prinicple of relativity in regard to FOR's has been mistakenly seen as representing a scientific principle</i>. All relativity does is take the Lorentz transform, assumes the speed of light is invariant beteen frames and that you can't distinguish between inertial frames.

    Which of these do you object to and why? Or are we on about General Relativity which says there is no special intertial frames (no absolute rest) and the Principle of Equivalence.

    I think this is what we are disagreeing on though:-

    In the Galilean transform you can have absolute rest and absolute time. In the Lorentz transform you can not. Time and Space become intertwined entities. I suspect you are trying to argue that the Lorentz equations are mathematically right but the Galilean interpretation is right.

    This is an apparent non-sequitor. You are arguing about Relativities interpretation of frames of reference and not an Aether. I'm glad you agree there is no absolute FOR for no Aether. There is no aether ergo no absolute frame of reference, as relativity says.

    Yep, it's transform equation. Which leads to Relativity.

    But there is no outside the boat in the Universe. It is a self contained system. Assuming we both mean Universe to include all of creation rather then universe being only what we can see with the possibility of other universes comprising the Universe.
     
  22. thed IT Gopher Registered Senior Member

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    C'est moi

    Just read your last post. I see where you are coming from now. But I'm for home. Catch you later.
     
  23. (Q) Encephaloid Martini Valued Senior Member

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    Adam

    I believe you are beginning to get a grasp on Relativity. A couple of points:

    The speed of light is important because it is the one constant that can be relied upon. Although you cannot say for sure what speed the daft punk on Hoobagoo Prime is moving, ie. one meter per second or half the speed of light, you can however know that the speed of light is measured in all inertial reference frames. That is what Special Relativity is all about.

    Secondly you cannot add relative velocities together, as in those near the speed of light because the relative velocity of any two objects never exceeds the velocity of light. You may add the speed of two cars traveling towards one another, for example; A is traveling 90 miles per hour towards B who is also traveling 90 miles per hour towards A. Their combined speeds are 180 miles per hour.

    However if A is traveling .9 the speed of light towards B who is traveling also traveling .9 the speed of light towards A, you cannot say their combined velocities are 1.8 the speed of light. This is due to the fact that length and time are different in different reference frames, especially when approaching these relativistic velocities. Instead we use the Relativistic Addition of Velocities:

    v = (v' + u)/ [1 + (uv'/c2}]

    where v is the proper velocity (at rest)
    v' is the velocity of the object at velocity u

    Plugging in .9 the speed of light we get:

    (1.80/1.81)c = .9945c which is still less than the speed of light.

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