# Why is it more convenient to consider spacetime as a continuum?

I often find that phisicists and cosmologists make use of Planck's units. I have read propositions that sound like

"...at the level of Planck's units many law of physics break down"

"...Planck time, the smallest observable unit of time...before which science is unable do describe the universe"

"... it would become impossible to determine the difference between two locations less than one Planck length apart"

even in string theory:

"* Planck length is the order of magnitude of the oscillating strings that form elementary particles, and shorter lengths do not make physical sense*".

Notwithstanding this and the fact that in QM (almost) everything is quantizied (discrete) I read that in mainstream they are still considered not discrete, cf. Phys.SE link.

I am not particularly aware of any pros, I see only cons; can someone tell me what are the compelling reasons to consider spacetime not discrete? Is it a requisite of relativity? As a corollary, I suppose that they must be both discrete or non discrete, right?

• Even if the univers is discrete in time in space (I like to believe that), it tries real hard to conceal that. For example, ultra-high-frequency light is not slowed down by the coarseness of space, or at least is slowed down much less than one would expect. – John Dvorak Aug 9 '14 at 8:50
• The primary benefit of regarding space as a continuum is calculus. – David H Aug 9 '14 at 9:00
• I have the impression that discrete spacetime will not work with special relativity, which has been tested and validated at the limits of possible measurements. physics.stackexchange.com/q/33273 – anna v Aug 9 '14 at 9:17
• @bobie Because plancke units are too large. Suppose you have a circle with radius equal to one plancke unit. If you try to calculate the area of the circle of this unit circle via "integration" with $dA$ equal one plancke unit-squared, you get an area of 4 units-squared instead of $\pi$. – David H Aug 9 '14 at 10:43
• Strongly related, if not a duplicate: physics.stackexchange.com/q/9720 – Kyle Kanos Jan 28 '15 at 13:58