Well, we know matter can be divided until you reach its fundamental particles (electrons, quarks, whatever), and QM tells us that this is so for energy as well (photons).

 

But then some go further and claim that QM shows spacetime to be composed of fundamental units as well. Usually, what they are refering to are the Planck units (like the Planck length, Planck time, etc.) - those measures of space and time for which we cannot measure anything smaller.

 

But is this warranted? Is it warranted to say that these smallest units of measurement are 'particles' of space and time, that there is no amount of space or duration of time smaller than these amounts? Or is it just a matter of our ability to measure it?

Some sort of fuzziness or discreteness seems to be inherent in most (all?) approaches to quantum gravity. Loop quantum gravity and string theory both suggest a fundamental noncommutative nature to space-time.

 

 

The argument that this should be at the Planck level is mostly "circumstantial" and quantum effects in gravity could be present at a lower energy level. Planck scale is really an upper bound to the scale at which quantum effects of gravity are small.

Some sort of fuzziness or discreteness seems to be inherent in most (all?) approaches to quantum gravity. Loop quantum gravity and string theory both suggest a fundamental noncommutative nature to space-time.

 

 

The argument that this should be at the Planck level is mostly "circumstantial" and quantum effects in gravity could be present at a lower energy level. Planck scale is really an upper bound to the scale at which quantum effects of gravity are small.

 

Thanks ajb, but what is a "noncommutative nature to space-time"?