Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mach's principle

  1. Sep 20, 2010 #1
    I don't understand the Mach's principle completly.

    In the base situation when there are only two objects in the Universe.
    I think there is no question, because we cannot observe anything,
    since there are no photons etc. in the Universe.
     
  2. jcsd
  3. Sep 20, 2010 #2
    Well, even when there are photons, but you are not there - you will not be able to observe anything. For instance before you are born. That does not mean that the universe does not make sense and you can't discuss what happens when when you are not there.
     
  4. Sep 20, 2010 #3
    Its not about me or you
     
  5. Sep 20, 2010 #4
    You wrote "because we cannot observe anything". Whom did you have in mind writing "we"?
     
  6. Sep 20, 2010 #5
    Somebody on the object.
     
  7. Sep 20, 2010 #6
    So, you need "somebodies". Photons, as far as we know, are not "somebodies". Photons are modes of a quantized electromagnetic field.
     
  8. Sep 20, 2010 #7
    What about Mach's principle do you not understand? It's not obvious from your three sentences what you are asking.
     
  9. Sep 20, 2010 #8

    epenguin

    User Avatar
    Homework Helper
    Gold Member

    I have never read Mach but only read of Mach indirectly. This is not the Mach's principle I know of, but it sounds like the sort of thing he would have enunciated.

    For the purposes of philosophical argument it is permissible to take a naive view of e.g. vision, and imagine like you do before knowing any physics, that stuff is just there and you can see it. You would have to know what a 'body' is. A structureless particle even if conscious cannot see another object move. It needs a third object in order to see it move with respect to. Or it needs to be a body with a structure of its own - well that is really a particular example of the former case. It cannot have any experience (e.g. of something moving) unless it has a memory or a means of recording a past situation and comparing with present. Three bodies in the Universe is a minimum and even that is pushing it!

    If you are interested in this sort of reflection but in connection with real physics there is a book called "The end of time" by Julian Barbour plus, I just saw, a website and stuff on the web..
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook