(Kaku’s context is our dying Universe, which is a bit in the future: trillions upon trillions of years from now.)

If civilizations require many trillions of years to develop the methods that allow the kind of travel Kaku postulates, the UFOs seen by humankind for thousands of years don’t fit an evolutionary time-line that trillions of years represents.

That is, UFOs observed and photographed (real UFOs, and there are some) do not portray advanced designs, as we’ve noted elsewhere here.

Interstellar cultures or civilizations from other universes that have evolved – and Darwin’s theory applies, as he noted himself – to the point where they can maneuver between universes or galactic distances consisting of incalculable light-years would certainly have vehicles much more refined than what UFO observers have witnessed: chariots of fire, cigar-shaped craft, dirigible-like airships, crude flying saucers, delta-wings, et cetera.

So one can rule out the Kaku beings as the progenitors or occupants of UFOs.

But what about time-travelers, from our not-too-distant future or antedeluvial past?

The designs sported by the elusive UFOs do not provide evidence or encouragement that they come from Earth’s future.

They (the designs) are too prosaic and time-oriented to Earth’s historical time-lines, meaning that UFOs are steeped in aerodynamics that mimic pretty much what the aerodynamics of the time when they’ve appeared; that is, UFOs looked like balloon ships during a time when airships were under design or prominent by standards of the day, or UFOs looked like rocketships and circular craft when both were being considered by aircraft designers extant.