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

Discrete Spacetime.

  1. Aug 3, 2005 #1
    If spacetime is discrete at the Quantum/Sub-quantum scale, what "joins" and keeps spacetime together at GR scales?

    P.S. What "Separates" spacetime at Quantum scales?
  2. jcsd
  3. Aug 3, 2005 #2


    User Avatar
    Gold Member

    The first question is easy. A coarse grained surface looks smooth from a distance.

    The second question is more philosophical. In a discrete space-time it is assumed that distances and times come in fixed irreducible chunks.

    One attraction of a discrete space time flows from how renormalization is done. Without renormalization, QM equations "blow up" into infinitities, while renormalization sets an arbitrary and consistent cutoff to prevent that from happening and this provides real answers. A discrete space time elevates renormalization from being a mere mathematical trick to an actual feature of space time, and since there is a naturally plausible set of discrete spaces and times (the Planck scale) it is plausible to look to that as the cutoff.

    Discrete space-time theories like causal set theory, CDT and LQG all approach quantum gravity from the point of view of time space following GR which views gravity as a time-space curvature issue, rather than from the QM approach of creating a graviton.
  4. Aug 6, 2005 #3
    Since spacetime is discrete at the Quantum/Sub-quantum scale, is it possible that something that occupied a discrete spacetime move to the other discrete through straight line?
  5. Aug 10, 2005 #4
    the definition of straight line does not make sense when alluding to sites which are just neighbors, since the space between two adjacent sites don't have, in principle, a physical status.

    Best Regards

  6. Aug 13, 2005 #5
    I agree with your opinion. So how do they travel? Do a matter, in Quantum/Subquantum scale, actually travel through higher dimension?
  7. Aug 13, 2005 #6
    I would suggest something which is typical in the quantum formalism. I would suppose the existence of some system of coordinates in which, using this smallest scale, the triples would be always integer numbers. Then I would suggest that movement is in fact the consequence of existing a matrix of transition probability. Transitions from one triple to the other. Due the correspondence principle, adjacent site transitions generally are given higher probabilities when coming to macroscopic objects.
  8. Aug 14, 2005 #7
    Logically a Macro entity by virtue of size, will always have this as a limit to "hitting-quantum-targets", for instance if you have two marble's, one the size of Earth and one 'normal' size, then the Earth size will have a problem colliding with a small 'normal' size marble. Conversely, a normal size marble will have no problem at all in being directed to a marble the size of Earth.

    Quantum entities have no HUP factors when being directed at Macro Targets, they are sure-fire probable certainties in hitting their targets.

    HUP has a 'two-size' dependant principle factoring
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook