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Posts posted by J.C.MacSwell

  1. That's the way it is. You can see it clearly from the argument which is being developed here.


    Yep, Lorentz and Galileo. Clearly there ain't enough room in this town for the two of them.


    Now, a kinder, gentler town (read lower the relative speeds of them yardsticks). I can see maybe they might get along a little better there. (not perfectly though)

  2. .....................................................



    If instead we use the Galilean transformations' date=' there would have been a moment in time, in your reference frame F where things would have been this way:



    Ruler 1:......A_____________B

    Ruler 2:......A`____________B`


    In other words the ends would have coincided [i']simultaneously[/i]. But because we assumed that your friends ruler contracts if it has a nonzero speed V in frame F, then as your friends ruler passes by yours, it is impossible for the ends to coincide simultaneously.


    So there is a reductio ad absurdum proof that can be used (not circular reasoning), which can allow you to conclude that the LCF is false.


    I haven't shown it all yet. But I've shown enough where someone else can figure out the problems caused by assuming LFC is true.


    This proves that, assuming LCF and your other assumptions are correct, that Galilean transformatons (especially at those speeds) are incorrect.

  3. I read it' date=' and the joining links too. I still don't see where its a paradox[b']. If space is expanding [/b] (the space between galaxies I mean) then the light from those distant stars may never reach us. How could they if the "total" expansion is faster than light itself. I don't see that light ever getting to us no matter how much time we wait.


    Sorry, I need more links I think. :confused:




    If you believed that back in Olber's time "they locked you up". :D


    Olber was a 19th century German astromomer. The expansion of space was not popularized until the 1920s.

  4. I see! Interesting to look at these old models.

    since the Hubble parameter was constant' date=' the Hubble radius could not go roaring out into space the way it has been doing

    so light from any galaxy receding at speed c or better would never reach us. the Hubble radius was constant and therefore acted as a bound on the observable universe. So in that steadystate model the night sky could be dark!


    fascinating. and then our own hubble volume of space would tend to get emptier and emptier, so hoyle had to postulate something that kept replenishing it, the constant creation of atoms out there in the void.


    I guess the "steady state" school of cosmologists are getting pretty old now. I saw a news item about the passing of one of the founders of that model, just last week I think.[/quote']


    So what background temperature would the Hoyle Model be?

    I don't know if Hoyle looked at it, although he was pretty thorough in a lot of his work which contributed to the big bang models also, even though he didn't believe in them.


    Edit: OK, I just read (in "Companion to the Cosmos" by John Gribbin) that Hoyle didn't think that his creation field model would have a background radiation. Anyone have an idea why not? I can't picture that. It seems to me that this model puts a limit on "Olber", not snuff him out.

  5. There's radiation heat transfer. Since you're radiating to a 2.7 K background, and it's the only game in town, it's significant. Radiation goes as T4[/sup']. You would eventually get cold.


    Inspite of virtually no conduction or convection losses you would freeze your butt in a hurry without adequate protection/spacesuit, would you not?

  6. and if you accept Gen Rel then the only solutions are ones where there was no matter explosion but space itself is either expanding or contracting. there is no steadystate stable solution to the Gen Rel equation (and this is the equation that is so successful in predicting experimental measurement)




    Steady State Models can account for GR. The Hoyle model used "continuous creation" to fill in the ever increasing "void" of space-time.


    It could not reasonably explain the CMB, though there may be other reasons as well that it fell out of favour.

  7. hey everyone


    sorry i just got back from a big night out last night and yeah hard to think' date=' so that sort of explains the title :P


    anyways.... my query (this is not a homework question of anything, just a general th0ouoght i had when reading a physics text)


    why is it that when a pendulum is swinging that you can assume it has maximum KE at the bottom of its swinging arc?






    When the air resistance matches the acceleration (due to gravity and the centripetal force) on the downward swing the maximum KE will be achieved.

    This would be at the bottom in a vacuum, and before that otherwise with less KE at the bottom due to the friction component exceeding the force due to the PE.

  8. in Newton 3, what does it mean by equal and opposite force? i mean, the force I exert on the earth is far less than what the earth exerts on me;[/b']so how can they be equal?


    This is not correct.

  9. http://www.metaresearch.org/cosmology/speed_of_gravity.asp



    I would love to know if this could be possible also I remember in my youth riding a pedal cycle at night seemed to be easier than riding in daylight & sound seems to travel further when it's dark; is this just imaginable or maybe light does slow things down slightly? And if gravitity is faster than light can we somehow store it for space tr :confused: avel?...us.2u


    Less background noise, less wind/turbulence generally.

    and colder air, again generally.

  10. Hi' date=' I was wondering if anyone knew how cold complete coldness is? Is it measurable? eg its 36 degrees celsius where i'm at at the moment. If I was to zoom straight up beyond the atmosphere, it would be pretty cold but the temperature would still be affected by the sun. If I was then to zoom off out into space well beyond all the stars created by the big bang to a totally isolated spot that is [b']not touched by any light or energy[/b], so you cant see any stars ect, complete black. How cold would it be? Is this known?

    Thanks for any info :)


    It is 2.7 K because of the minimal light or energy you would still receive and, after reaching equlibrium, emit. This is assuming you are "on the big bang track" with the energy coming in balanced/equal from all directions. The "night sky" would look basically the same except you may not recognize the patterns/constellations depending on how far off you moved.

  11. What does it tell you that a Lorentz frame is?



    OK, I have:(from "the international dictionary of physics and electronics, second edition 1961, D. Van Nostrand Co.)


    Rest Frame: Lorentz frame in which the total momentum of a system vanishes.




    Lorentz Frame: Any of the set ofcoordinate systems in Minkowski space for which the square of the interval between two events is c^2dt^2-(dx)^2.


    Any such coordinate system may be obtained from another by means of Lorentz transformation (together perhaps, with an orthagonal transformation of the space axes). With each Lorentz may be associated a point observer, each of whom moves with constant velocity relative to the others.

  12. You cannot feel an acceleration, you feel a force.


    You feel a force and force gradients within yourself. I would say if you feel force gradients in this way you "feel" the acceleration, but I think it is open to interpretation.

  13. I understand what you are saying. I will try to find out the correct definition, or if there is more than one accepted use of the term in physics.


    OK, I have:(from "the international dictionary of physics and electronics, second edition 1961, D. Van Nostrand Co.)


    Rest Frame: Lorentz frame in which the total momentum of a system vanishes.

  14. To any object in the universe' date=' there is a center of mass of that object. You can attach a frame to that object, so that the center of inertia of that object is always located at the origin of the frame. This is what I mean by "rest frame" of something.


    So for example, the rest frame of the moon I was talking about, is a three dimensional coordinate system, whose origin is always the center of inertia of the moon. wherever the moon goes, so does the coordinate system.


    Likewise for the rest frame of the rocket.


    Somewhere inside the rocket, is the center of mass of the rocket.

    Let that point be the origin of a three dimensional rectangular coordinate system.


    Wherever the rocket goes, the coordinate system goes, the coordinate system is the rest frame of the rocket, in other words, the rocket is at rest in the coordinate system, [i']even if [/i] the rocket is accelerating in someone else's frame.


    PS: You didnt bold anything, and I don't understand what you mean by "constantly changing rest frames as it accelerates."


    I understand what you are saying. I will try to find out the correct definition, or if there is more than one accepted use of the term in physics.

  15. Exactly.



    But in the rest frame of the ship' date=' the moon is accelerating.


    In the rest frame of the moon, the ship is accelerating.


    The rest frame of the moon was stipulated to be an inertial reference frame.


    So since, in the rocket frame, the moon is accelerating without an external applied force (no action reaction pair) it necessarily follows that the rest frame of the rocket isn't an inertial reference frame.


    But still, the center of inertia of the moon is accelerating in the rest frame of the ship.


    Yes. :)



    Just switch back and forth between the frames, and you know what I'm taking about.[/quote']



    Not quite. I could be wrong but I would not call these (the ones I bolded) "rest frames". I would say that the ship is constantly changing rest frames as it accelerates.

  16. Let me ask you something then Bob.


    Suppose you are in a rocket' date=' passing by a moon, which is at rest in deep space.


    And your ship's engines are on.


    You look out your spaceship's window.


    Is the moon accelerating?[/quote']


    Not in any inertial frame.

  17. How about in terms of a time frame. Is the CMB/Hubble the "oldest" relative to the big bang? I realize that can vary from body to body depending on it's history (or multiple histories of component parts) but would a particle that has been at rest the longest in this CMB/Hubble frame be the "oldest"? Would a particle that has been at rest "forever" in this CMB/Hubble frame be assumed to be at the age of the Universe (15 billion,say)? I realize a particle that deviated from this "Hubble path" without returning may consider itself "older" (14.9, say, but still considers itself older than the "constant Hubble particle" which it considers to be 14.8,say) .



    Hope this makes some sense.

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