Absolute rest - What does it mean?

Discussion in 'Physics & Math' started by Quantum Quack, Jun 20, 2009.

  1. Quantum Quack Life's a tease... Valued Senior Member

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    Hi Guys, I am familiar that it is often mentioned that Absolute rest is forbidden under certain theories. Having done some research has proved that defining this term precisely has certain difficulties.

    So what does it actuallly mean to the various fields of physics? Do they share a similar definition or are dealing with ambiguity as well.
     
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  3. James R Just this guy, you know? Staff Member

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    I don't see much problem with defining the term.

    The idea of absolute rest is that you can point to at least one object or thing in the universe and say "That object is stationary." If you can do that, then you have a standard of absolute rest; if you can't then you don't.

    The importance of the concept is mostly historical, and tied up with the "aether" theory of light. The idea was that some kind of mysterious substance, the aether, was the stationary thing. The speed of light would then always be the same relative to the aether, but not relative to anything moving relative to the aether.

    Of course, you can do an experiment with light to try to detect the aether. And if you do, you discover that the aether is undetectable. Instead of having a thing at absolute rest, we now believe that light travels at the same speed relative to ALL inertial observers, no matter what their state of motion. And that idea leads directly to Einstein's relativity.
     
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  5. AlphaNumeric Fully ionized Moderator

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    This is QQ's way of saying "I've done no research, no searching, no reading and I don't know what it means because I misused it in a discussion with AlphaNumeric over in pseudo and now I realise, for once, I need to know what a word means before making claims about it".
     
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  7. Quantum Quack Life's a tease... Valued Senior Member

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    When you say stationary, do you differentiate between "non-changing" and "no motion" or are they treated the same?
     
  8. James R Just this guy, you know? Staff Member

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    Absolute standard of rest refers only to motion through space. It has nothing to do with changes that don't involve motion.
     
  9. Quantum Quack Life's a tease... Valued Senior Member

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    interesting!
    qu: Can change ever not involve motion and what example would you use to demonstrate change without motion?
     
  10. James R Just this guy, you know? Staff Member

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    I think you've misunderstood me.

    As I sit here in my chair, there are lots of changes going on in my body. My heart is beating, my blood is circulating, my nerves are firing, my digestive system is doing its thing, and so on. All of those things involve some things moving. But my body as a whole is not moving relative to the room I am in. And there's no way that you can show that my body (or, let's be specific, its centre of mass) is not at "absolute rest" as I sit here.

    The problem with absolute rest, though, is that if I sit in my car as I drive down the road, there's also no way you can show that (the centre of mass of) my body is not at rest. Thus, we have two apparent standards of "absolute rest" that conflict with each other - my room and my car. Since you can't prove which of these is "really" at rest, it follows that neither of them is a good candidate for absolute rest. And the same applies to anything you want to put up as a candidate for absolute rest.
     
  11. Quantum Quack Life's a tease... Valued Senior Member

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    So if I have a pendulum clock with the pendulum swinging from side to side it could be considered as being at absolute rest by your definition?
    Sorry about being so pedantic.
     
  12. Enmos Staff Member

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    If QQ doesn't mind I have a little side-track question.

    James, can you explain to me how light slowing down in a denser medium does not contradict the statement below ? Thanks

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  13. Quantum Quack Life's a tease... Valued Senior Member

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    Just reading this aspect of the post and wonder if the universe as a whole could be considered at absolute rest like you have considered your body to be at absolute rest.
    Afterall it must have a centre of gravity and it certainly has a lot of moving parts to it....do you see what I am on about?
     
  14. Quantum Quack Life's a tease... Valued Senior Member

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    yeah I deleted it because I thought it was a bit rude to answer for JamesR.
    I believe JamesR's sttatement you refer to is necessarily brief as he was respondng to my question and limited it. Other wise he would have to give a complete rendition of SR to supply the answer.

    The speed of light is deemed constant and invariant to all observers "in a vacuum". Dense mediums are just the same but considerably more complex to calculate so the invariance of light is not violated by experiments such as the Bose /Einstein condensate...I am sure AlphaNumerico or JamesR will correct me if I am wrong.
     
  15. Enmos Staff Member

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    But the key word is 'relative'. Light travels at the same speed relative to all inertial observers.
    This would mean that if I flew away from you at near c and you point a flashlight at me, the light would have to travel at nearly 2*c to reach me within the time predicted by James's statement.
     
  16. Quantum Quack Life's a tease... Valued Senior Member

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    Just trying to nail this absolute rest phrase better.
    As I would have thought it meant literally what it says.
    absolute rest meaning absolutely "still" in absolute terms with out any relativity involved.
    Which is why I thought it was "forbidden" because nothing of substance in this universe can be at absolute rest whilst the universe exists as the universe must continue to move through time or cease existing.
     
    Last edited: Jun 20, 2009
  17. Quantum Quack Life's a tease... Valued Senior Member

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    hate to say it but there are a few gedankens in archives that deal with this issue....and yes SR deals with it...due to length contraction and time dilation along vector...me t'inks....associated with doppler effects If I am not mistaken..
     
  18. Enmos Staff Member

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    Ok, I'll stop polluting your thread now

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  19. Quantum Quack Life's a tease... Valued Senior Member

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    Wow interesting responses guys...!
    All I see at the moment is that science appears to consider absolute rest as absolutely not absolute.....In philosophical terms and most schools on languages terms like "Absolute" are unconditional. They are indeed absolute. Yet here we have conditions placed upon the absolute nature of the term "absolute". A bit like saying something is "sort of infinite" or "sort of zero" or "sort of absolute"

    ahhh confusion reigns supreme!

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  20. Quantum Quack Life's a tease... Valued Senior Member

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    Well then it appears you have to redefine the use of the term "absolute zero" to maybe pseudo absolute or some other qualified statement.
    Non-zero ground state energy implies heat so there for using absolute zero [temp] is inappropriate I would have thought as it is obviously contradictory.

    So when I ask about Absolute Rest are you guys interpreting this as pseudo absolute rest? As this certainly seems to be the case.
     
  21. Quantum Quack Life's a tease... Valued Senior Member

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    Found this little ditti at:

    A brief history of Einsteins STR

    Of course at the time absolute rest/space/time was acheived via an aether as JamesR mentioned earlier in this thread.
    So Einstein basically stated that there can be no Absolute Rest and was directly referring to the historical use of a mysterious aether of some unknown or knowable substance. [ a basic premise of an Aether being maintained by Newtonians]
     
    Last edited: Jun 21, 2009
  22. James R Just this guy, you know? Staff Member

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    My point was that absolute rest is a useless concept, because you can't point to any object and state categorically "this thing is at absolute rest".

    A pendulum is an extended object, like most objects. You can look at the motion of its centre of mass, or you can look at the motion of its individual parts. In the case of the centre of mass of a swinging pendulum, the centre of mass oscillates backwards and forwards as the pendulum swings. On average, the centre of mass does not move; to be precise, its velocity averaged over one cycle of the motion is zero relative to the pendulum's support.

    The concept of "absolute rest" would be applicable to motion of the entire pendulum through space - if such a concept was useful, which it isn't.

    If the universe had a centre then you could say that the centre of mass of the universe was at rest, just as you could say that any part of the universe was at rest. The problem is that the universe has no centre. And if it is infinite the universe probably doesn't have a centre of gravity.

    You should insert the words "in a vacuum" into my statement. It only applies in a vacuum.

    The thing is, physicists when talking about relativity and light tend to automatically assume a vacuum unless they explicitly state otherwise. Sorry if this is confusing.

    That makes sense, but it is absolutely not true. And that is what the theory of relativity tells us. In fact, if you fly away from me at close to c and I point my flashlight at you, the light from the flashlight will travel at c as seen by me and (this is the important part) at c as seen by you, even though you are travelling relative to me.

    How can that be? Answer: your perceptions of space and time are different to mine as you travel away from me. As I watch you, I see your time running slower than normal. As you watch me, you see the distance that the light has to travel to you from the flashlight as being shorter than the distance that I measure, so the light can still reach you travelling at c.

    Irrelevant. Physics is full of idealisations.

    No. A BEC is just a bunch of very cold particles.

    I defined absolute rest correctly in my first post to this thread. Your definition is nonsense.

    Absolute zero is talking about temperature. It has nothing to do with absolute rest.
     
  23. Quantum Quack Life's a tease... Valued Senior Member

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    agrees entirely the term is absolutely useless as science has removed it from it's theoretics since the abolition of an Aether by the MM experiments.
    [ I have since found out ]
    So why not say that as the definition?:
    Absolute rest : defined as "...a currently obsolete notion that was in use prior to MM experiments."
    btw...thanks JamesR well put!
     

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