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What is spacetime exactly?

  1. Sep 19, 2010 #1
    I know that spacetime is a Lorentzian manifold,
    but what kind of properties has to be required exactly?
    for example orientable, connected, Haussdorff, ...
  2. jcsd
  3. Sep 19, 2010 #2
    It is not even sure that it is a Lorentzian manifold. Different physicists try different models. Lorentzian, Finsler, dgenerate metrics, metrics changing signatures, pure affine, multi-dimensional. You need to distinguish space and time of physics from their mathematical models.
    The Lorentzian model is most popular and seems to work for weak field approximations and when you do not take into account quantum effects.
    It is up to you which assumptions you choose - depending on applications that you may have in your mind.
  4. Sep 19, 2010 #3


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    Gold Member

    I would rephrase this to

    Spacetime can be modelled by a Lorentzian manifold

    A Lorentzian manifold is an abstraction that lives in our minds ( or in my case visits now and again), it can't be awarded the same ontological status as charge and mass, say.
  5. Sep 20, 2010 #4
    Ok, but lets see the conventional Lorentzian manifold.
    What are the conventional properties?
  6. Sep 20, 2010 #5
    You may like to assume that it admits a http://en.wikipedia.org/w/index.php?title=Sven-S._Porst&action=edit&redlink=1" [Broken].
    Last edited by a moderator: May 4, 2017
  7. Sep 20, 2010 #6
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