A 25x25x2 Mpc* slice through a multi billion numerical simulation of cosmic structure formation. Brighter colors mark denser regions. [Courtesy N-Body Shop at UW-Seattle, Department of Astronomy.]
By analogy, to appreciate quantized spacetime we can use WiFi. WiFi is radiation found everywhere in our world and used for internet communication. It is quantized at specific channels near 2.4 GHz and 5 GHz. Each channel is at a different frequency. Its quantization allows every channel to be unique.
Q: How “big” is a 5GHz WiFi quantum (photon)?
A: Photons (quanta of radiation) have no mass, but they each have kinetic energy,
E = hf = hc/λ. Here, h = 6.626 x 10–34 Joule-second is Planck’s constant.
A 5GHz photon has Energy = hf = 3.31 x 10–32 J
A 5GHz photon has Length = c/f = 0.6 mm (millimetres)
A 5GHz photon has Time = 1/f = 0.2 nS (nanoseconds)
Gravity. Spacetime is “like” that…and yet different….
*A megaparsec (Mpc) is a measurement of distance equal to one million parsecs, or 3.26 million light years.
Q: Why parsec?
A: The parallax-second, or parsec, was directly assigned without reference to any other measurement but the one at hand. The “second” here refers to angular second. As a measurement for cataloging of distant stars groups, it serves a utilitarian purpose and handy standard. It was separate from the measurement of light speed.
It represents the distance from Earth to an object if that object changes position by one arc-second in the sky over 6 months (when the Earth is at opposite ends of it orbit). It was never meant to be accurate. Really. It already has the accuracy limitation and system function of any astronomical instrument.
At the IAU conferences in 2012 and later, in 2015, a number of proposals on defining an absolute scale for bolometric measurements were written that may influence the idea of the parsec, but not its practical measurement (below).