why is the universe quantized?

Early philosophers like Democritus (around 400 BC) deduced that the universe is made up of tiny objects which cannot be subdivided, which he called "

atoms". He came to this deduction via logic despite the fact that atoms are so small that he had absolutely no way to detect them.

Today we would add something like "they cannot be subdivided without fundamentally changing their characteristics". Because we can now smash atoms into electrons and protons, but these behave radically different from the parent atom.

You could apply the same logic to anything - the brightness of a light (which we know is quantized), the wavelength of light from a Hydrogen atom (which we know is quantized), the strength of an electric charge (which we know is quantized), the strength of magnetic flux (which we know is quantized) or the wavelength of light from thermal sources (which we

*don't* know is quantized, and is classically described as a "continuous spectrum").

*If* the continuous spectrum is quantized, it is on such a fine scale that it looks continuous to our most sensitive instruments.

- To detect quantization, you need instruments able to measure on the quantum scale.

- Some have suggested that length might be quantized on the Plank Scale; but at 10

^{-35} m, this scale is so small that our instruments can't measure these lengths at all.

- The LHC has managed to generate Higgs Bosons with a lifetime of around 10

^{-22} s. Traveling at almost the speed of light, these will travel about 10

^{-16} m before they decay (ie not even the diameter of a proton). This is about 20 orders of magnitude larger than the Plank length.

- So length seems to be a continuous measure to us.

doesn't a quantum universe, by only allowing certain values, make the universe more deterministic, compared to a continuous function universe? A quantum universe reduces randomness.

I agree that a quantized value reduces choice. Restricting the flip of a coin to heads or tails certainly reduces the number of states that the coin can be in; there are 2 states, so you can guess the state with 50% probability. However, it still doesn't let you determine ahead of time whether the coin will turn up heads or tails the next time you toss it - it is still random.

- A measure like the spin direction of a subatomic particle (up or down compared to a magnetic field) is a discrete function.

- A measure like the velocity of a subatomic particle is a continuous function.

- But the Heisenberg uncertainty principle places constraints on the accuracy to which you can measure either one of them

PS: I can remember a science teacher who grabbed a coin-shaped object to illustrate head/tails probability; he and our class were astonished to see it land on the thin edge, and roll along the floor... It sort of spoiled the illustration.