'If time travel is possible then there is no such thing as time'

That sums up Palle Yourgrau's 2006 book pictured above.

The ostensible subject of the book is the deep friendship between Kurt Gödel and Albert Einstein in Princeton, New Jersey.

Both were early members of Princeton's Institute for Advanced Studies, where the greatest minds in the world were paid to be themselves and simply think about things.

No teaching, no publication requirements, just do what you like each day, forever.

Yourgrau believes that Gödel's 1949 paper proving that there are possible worlds described by Einstein's theory of relativity in which time — as we ordinarily understand it — does not exist, upended the world of philosophy.

Gödel went further: if time is absent from those theoretical universes, he showed, time does not exist in our world either.

Einstein instantly recognized Gödel's paper as a breakthrough but an overwhelming majority of physicists, mathematicians and philosophers have spent the past half-century–plus trying to either ignore or find fault with Gödel's conclusion.

Neither strategy has succeeded.

Gödel's reasoning, compressed, was this: he could mathematically demonstrate a universe that was closed and rotated on itself.

In such a universe time travel was not only possible — it was inevitable.

If, in that universe, time was travel was possible, and by this Gödel meant precisely what you and I think of as time travel, i.e., the ability to go back and see the past as often as desired, then that past wasn't over: in fact, it never disappeared, since you could go back and find it whenever you liked, exactly as you can travel to Paris as often as you like and expect to find it there in all its reality.

Since the past was there, not having gone anywhere, then there was no such thing as time in the sense that we think of it passing, since nothing had passed at all — it was right there, always accessible.

From the book:

From his discussions late in life ..., it emerges that Gödel believed that the proper philosophy should capture axiomatically — though not purely formally — the fundamental concepts that underlie reality, which he took to include "reason, cause, substance, accidens [a traditional Latin term], necessity, value, God, cognition, force, time, form, content, matter, life, truth, idea, reality, possibility."

The goal of the great logician was not to make room in physics for one's favorite episode of "Star Trek," but rather to demonstrate that if one follows the logic of relativity further even than its father was willing to venture, the results will not just illuminate but eliminate the reality of time.

Gödel wrote, "I love everything brief, and find that in general the longer a work is, the less there is in it."

Gödel argued that if it was possible to return to one's past, then what was past never passed at all.

It is provable that time fails to exist in the Gödel universe.

It cannot, therefore, exist in our own: the final step is taken, and time really does disappear.

Wait a sec — what's that song I'm hearing?