O Tannenbaum, O Tannenbaum
How faithfully you blossom
Through summer's heat and winter's chill
Your leaves are green and blooming still
O Tannenbaum, O Tannenbaum
How faithfully you blossom...

I like this song because it's perfectly traditional and also perfectly secular. "O Christmas Tree" is a mistranslation of the line; Tannenbaum really just means "fir tree." The song admires the evergreen for its constancy, its living needles giving hope amidst the blanketing snow, reminding us through the depths of winter that all is not lost.

Of course, this message falls flat on us here in Austin. Almost all of the trees around town are still green, as always, and there's not a flake of snow to be seen (not yet, anyway). There's nothing special about greenery in December. Indeed, we might rather sing:

O cedar tree, O cedar tree
How noxious is your pollen
Your powder blowing far and wide
That leaves us red- and bleary-eyed
O cedar tree, O cedar tree
How noxious is your pollen...

But is there another tree that deserves our praise?

Let me pivot for a moment and quote from Friedrich Nietzsche's Thus Spake Zarathustra. Here, the titular prophet lies dying, and his companion animals, the talking eagle and snake, supply for him his last words:

Now I die and disappear [...] and at once I am nothing. Souls are as mortal as bodies. But the tangle of causes into which I am woven returns—it will create me once again! I myself am part of the causes of the eternal return. I come again with this sun, with this earth, with this eagle, with this snake—not to a new life, or a better life, or a similar life: I come again forever to this identical and selfsame life, in its greatest and its smallest, to teach again the eternal return of all things—to speak again the word of the great noontide of earth and man, to teach again to man the Overman. [Ch. 57]

Now, what is Nietzsche trying to say here? Did he actually believe that time is one big circle, that the universe will repeat itself again and again forever, down to the last and smallest detail?

We could imagine some abstruse physical model in which this is literally true, but I don't think that's what Nietzsche is getting at. Rather, the metaphor of "eternal return" is meant to challenge us: If there is no afterlife, no karma, no divine reckoning of good and evil deeds, then what do we live for? Is this life, here and now, the one you would want to live over and over again for eternity?

If nothing else, to think on this question may impel us to waste less of our precious time, to live out life to its fullest, and not to defer our fulfillment to a later, better life that will never come.

But unlike Nietzsche, there are those of you here tonight who hope for a literal immortality through life extension and cryonics, or at the very least, who care about what happens in this world after you die. If you knew that a big space rock was on a course to strike the Earth in 2150, and you knew it would exterminate all life, wouldn't that make you sad right now?

But then again, this so-called "long-termism" is just kicking the can down the road. After all, by most accounts the universe itself has a finite lifespan. Whether in the heat death of the universe, or the Big Crunch or the Big Rip, someday all of this will be gone. The same abyss that stared back at Nietzsche, stares as well at all existence. We may long for eternity, but the spectre of death remains, at one timescale or another.

We can dispel it only when we understand the truth: that time itself is an illusion.

I don't know if I understand exactly what "timeless physics" is, but I think it's something like this. The state of the whole universe is thought of as a single point in a high-dimensional space, called configuration space. Every point in that space is assigned some measure of probability, called amplitude. And if we know the amplitude at a particular point, the laws of physics dictate what the amplitudes at the nearby points must be.

Naturally, the simplest solution is the trivial one, wherein all points have an amplitude of zero. But there's nothing else that we can say about such a universe, and so it might as well just not exist.

The next simplest solution is when we specify some point as having a certain amplitude, and then work out from there, using the laws to find the amplitudes throughout the rest of configuration space. This singular point we call the Big Bang, and from it springs forth an unfathomably intricate tree of winding, forking paths.

Within this tree is all that is, all that ever was, all that ever will be, all that ever can. Our lives, the lives of our ancestors and of our descendants, the machines we are lucky or unlucky enough to build, countless stars and planets and alien life forms—are all there inside it. Time itself only exists within the tree, emerging from the steady increase of entropy as one traces the tendrils of amplitude away from the Big Bang.

But the tree itself is static, unchanging, fixed and timeless. Every one of us, every decision that we make, is etched indelibly into its branches, a truth no less real than 1+1=2. The tree of worlds then confronts us with a challenge far greater than Nietzsche's: Is this life, is this civilization, is this reality, one worthy of dwelling in this eternity beyond time?

Think on that this longest night, when you see a tree decked out in festive lights.

O tree of worlds, O tree of worlds
How timeless are your branches
Whose measure shines so clear and bright
Our home in dark chaotic night
O tree of worlds, O tree of worlds
How timeless are your branches!