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length of a piece of string

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Comments

  • #32
    Son Goku
    Closed Accounts Posts: 1,475 ✭✭✭Son Goku


    stevenmu wrote:
    Therefore the length of a piece of string is determined by the person measuring it, and if one measurement is taken which takes space-time curvature (and other relativistic effects) into account and another disregards it then are both measurements not equally correct within there own terms of reference?

    A reference frame isn't a point of view though. It is simply a machine for labelling events.

    Also in curved space there are no true frames of reference.


  • #33
    stevenmu
    Moderators, Society & Culture Moderators Posts: 9,689 Mod ✭✭✭✭stevenmu


    I should really be more carefull with my use of terminology on the physics forum :) By "terms of reference" I'm referring to the terms of the measurement. I think a measurement should really be treated almost like an experiment, as a basic example there could be a case where you need to run a piece of string from the centre of one galaxy to the centre of another another, in that case you would need to take relativistic effects into account or you may end up several million kilometres out. Another example may be that you need a piece of string to go the distance between your sofa and your coffee table, any spatial distortions in this region are almost certainly going to be too trivial to be worth measuring, so disregarding them would still give you a measurement within an acceptable level of error.

    To summarise, how long a piece of string is depends on why on you want to measure it in the first place :)


  • #34
    nesf
    Registered Users, Registered Users 2 Posts: 27,644 ✭✭✭✭nesf


    stevenmu wrote:
    I should really be more carefull with my use of terminology on the physics forum :) By "terms of reference" I'm referring to the terms of the measurement. I think a measurement should really be treated almost like an experiment, as a basic example there could be a case where you need to run a piece of string from the centre of one galaxy to the centre of another another, in that case you would need to take relativistic effects into account or you may end up several million kilometres out. Another example may be that you need a piece of string to go the distance between your sofa and your coffee table, any spatial distortions in this region are almost certainly going to be too trivial to be worth measuring, so disregarding them would still give you a measurement within an acceptable level of error.

    To summarise, how long a piece of string is depends on why on you want to measure it in the first place :)

    See. A physicist will measure it because it's there, an engineer because he has to and a philosopher won't because he'd prefer to talk about it.


  • #35
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 94,804 Mod ✭✭✭✭Capt'n Midnight


    nesf wrote:
    If you assume the piece of string is on earth then it's a much simpler issue.
    Measuring string at the bottom of a gravity well :eek:
    You can't use the speed of light as a reference because it's no longer a vacuum, the speed will vary according to temperature, isobars and humidity ! Also you have to take into account the time dialation effects of the increased gravity (which varies depending on where you are) which makes it very difficult to get an accurate time/speed to turn meters per second back into meters.

    Not to mention the humidity would probably affect the length of the string too.


  • #36
    planck2
    Closed Accounts Posts: 242 ✭✭planck2


    look if I have a piece of sting, be it an imaginary string, string theory string or an actual string and I am moving with respect to all of you then according to me the length of the string is according to SR is the proper length and rest of you can go do what you like if you are in flat space-time. If its a piece of string in a black hole the piece of string will be torn apart by the a few seconds after it has crossed the event horizon and in any case there'd be no light so you'd have no light to carry out any measurements.


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  • #37
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 94,804 Mod ✭✭✭✭Capt'n Midnight


    Is the black hole rotating ?

    If the back hole is big enough then the tidal forces won't be that strong over the length of the string and it may pass the event horizon unharmed , taking days to fall into whatever... Hang on - won't it be travelling close to the speed of light by the time it gets there. So that string will have ZERO length for all practical purposes.


  • #38
    nesf
    Registered Users, Registered Users 2 Posts: 27,644 ✭✭✭✭nesf


    planck2 wrote:
    look if I have a piece of sting, be it an imaginary string, string theory string or an actual string and I am moving with respect to all of you then according to me the length of the string is according to SR is the proper length and rest of you can go do what you like if you are in flat space-time. If its a piece of string in a black hole the piece of string will be torn apart by the a few seconds after it has crossed the event horizon and in any case there'd be no light so you'd have no light to carry out any measurements.

    Actually. The scale of the string makes a huge difference. It's a different ballgame at quantum and cosmic scales. Best just to keep it in normal scales.


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