Energy

Why do you assume this universe is sole and not one amid billions?

Anyway - Want free energy?
Take a strong magnet and fix in an elevated frame (mag 1).
mag north upward.
Place another below (mag 2) (mag north upward) and it will be sucked upward by mag 1.
Allow for a lever (non-magnetic - wood will do) to prevent mag 2 connecting to mag 1 - At approx 90% ascent.
lever (spacer) triggers rotating arm to bring mag 3 into play (mag south up - north down).
This repels mag 1 & 2 - mag 1 is fixed so is unaffected - mag 2 is repelled downward.
upon full descent mag 2 triggers return of mag 3 and ascends once more....
Rinse and repeat.
There is a lever connected to mag 2 (lightweight) that uses approx 20% of this motion to operate mag 3's rotary-arm.
This allows for 80% of energy from this motion to be used or stored.
This will operate for as long as the earth has a magnetic-field or until lockheed send big blokes to kill you.
I would never dream of designing any operational equipment based on this silly idea because big blokes killing me is scary.
Tesla had a Much better insight into zero-point energy, but big blokes called.
Now..... big blokes have it.

Agreed Mark

Agreed in spades

Some theorize other simultaneous Universes in different "dimensions" but there's no evidence

If there are presently or consecutively other collections of matter like ours but just too far away to detect, then they're part of a single Universe

I agree; without our ability to observe other simultaneous universes, we can only arrive at 'no' until such time we are proven otherwise.

Other assumptions are all guesses without much basis other than imagination.

'Relativity' prevents physical measurement of 'that' beyond our relative bubble.
I apply the term 'Omniverse' to the 'endless' construct - 'Universe' to our, respective, bubble - Which is not 'endless'.

Because the Universe does not create energy - it recycles energy. See the stars? They hold the Universe's energy. See the asteroids? They hold the Universe's iron. It's all a recycled system that exists on a scale that can send billions of people with their brain stem between its membranes running back into their existential shell.