If the “universe” contains everything that exists, what can be outside it? If the answer is “Things that don’t exist”, then “multiverse” becomes an i… - Frank Wilczek

If you don’t have all the clues, you can still do parts of the puzzle. There may be huge parts of the puzzle that we don’t even know about...It means that future generations can have the same kind of fun that we’re having.

E = mc² really applies only to isolated bodies at rest. In general, when you have moving bodies, or interacting bodies, energy and mass aren't proportional. E = mc² simply doesn't apply. ...For moving bodies, the correct mass-energy equation is
<math>E=\frac {mc^2} {\sqrt{1-\frac{v^2} {c^2}}}</math>
where <math>v</math> is the velocity. For a body at rest <math>(v=0)</math>, this becomes E = mc². ...we must consider the special case of particles with zero mass... examples include photons, color gluons, and gravitons. If we attempt to put m = 0 and <math>v</math> = c in our general mass-energy equation, both the numerator and denominator on the right-hand-side vanish, and we get the nonsensical relation E = 0/0. The correct result is that the energy of a photon can take any value. ...The energy E of a photon is proportional to the frequency f of the light it represents. ...they are related by the Planck-Einstein-Schrödinger equation E = hf, where h is Plank's constant.

The traditional “cosmological” Multiverse considers that there might be physical realms inaccessible to us due to their separation in space-time. The quantum Multiverse arises from entities that occupy the same space-time, but are distant in Hilbert space – or in the jargon, decoherent.