The setup begins where last week began: the double-slit experiment. Fire single photons at a screen with two slits; you get an interference pattern (wave behavior). Add a detector that tells you which slit each photon went through; the interference pattern collapses (particle behavior). So far, ordinary quantum weirdness.
Now the wrinkle, first proposed by John Archibald Wheeler in 1978 and experimentally realized in increasingly sophisticated forms ever since: delay the measurement. Send the photon on its way. Wait until after it has already passed through the slits. Then decide whether or not to measure which slit it went through. If you decide to measure, the photon retroactively behaves like a particle. If you decide not to measure, the photon retroactively behaves like a wave. The decision now seems to determine the behavior then.
The delayed-choice quantum eraser (Yoon-Ho Kim et al., 1999) goes one step further. Even after the «which-slit» information has been recorded, you can later erase that information — and the photon’s past behavior switches back from particle to wave. Erasing the present record changes what happened in the past.
No serious physicist claims this is backward time travel in any usable sense. (You cannot send signals into the past.) But all serious physicists agree: time, at the quantum level, is not the simple one-way arrow our intuitions assume. The «present moment» is much more entangled with «past» and «future» than common sense imagined. Scripture says God lives on the outside of that entanglement entirely.
9καὶ μνήσθητε τὰ πρότερα ἀπὸ τοῦ αἰῶνος, ὅτι ἐγώ εἰμι ὁ Θεός, καὶ οὐκ ἔστιν ἔτι πλὴν ἐμοῦ· 10ἀναγγέλλων πρότερον τὰ ἔσχατα πρὶν αὐτὰ γενέσθαι, καὶ ἅμα συνετελέσθη·9Remember the former things of old; for I am God, and there is no other; I am God, and there is none like me, 10declaring the end from the beginning and from ancient times things not yet done, saying, ‘My counsel shall stand, and I will accomplish all my purpose.’
1Κύριε, ἐδοκίμασάς με καὶ ἔγνως με· 2σὺ ἔγνως τὴν καθέδραν μου καὶ τὴν ἔγερσίν μου, σὺ συνῆκας τοὺς διαλογισμούς μου ἀπὸ μακρόθεν· 3τὴν τρίβον μου καὶ τὴν σχοῖνόν μου σὺ ἐξιχνίασας, καὶ πάσας τὰς ὁδούς μου προεῖδες· 4ὅτι οὐκ ἔστι λόγος ἐν γλώσσῃ μου.1O LORD, you have searched me and known me! 2You know when I sit down and when I rise up; you discern my thoughts from afar. 3You search out my path and my lying down and are acquainted with all my ways. 4Even before a word is on my tongue, behold, O LORD, you know it altogether.
ὅτι οὓς προέγνω, καὶ προώρισε συμμόρφους τῆς εἰκόνος τοῦ υἱοῦ αὐτοῦ, εἰς τὸ εἶναι αὐτὸν πρωτότοκον ἐν πολλοῖς ἀδελφοῖς·For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers.
24αὐτὸς γὰρ τὴν ὑπ' οὐρανὸν πᾶσαν ἐφορᾷ, εἰδὼς τὰ ἐν τῇ γῇ πάντα ἃ ἐποίησεν… 26ὅτε ἐποίει οὕτως, ὑετὸν ἠρίθμησε, καὶ ὁδὸν ἐν τινάγματι φωνάς, 27τότε εἶδεν αὐτὴν καὶ ἐξηγήσατο αὐτήν, ἑτοιμάσας ἐξιχνίασεν.24For he looks to the ends of the earth and sees everything under the heavens. 25When he gave to the wind its weight and apportioned the waters by measure, 26when he made a decree for the rain and a way for the lightning of the thunder, 27then he saw it and declared it; he established it, and searched it out.
καὶ οὐκ ἔστι κτίσις ἀφανὴς ἐνώπιον αὐτοῦ, πάντα δὲ γυμνὰ καὶ τετραχηλισμένα τοῖς ὀφθαλμοῖς αὐτοῦ, πρὸς ὃν ἡμῖν ὁ λόγος.And no creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account.
ὅτι ἐὰν καταγινώσκῃ ἡμῶν ἡ καρδία, ὅτι μείζων ἐστὶν ὁ Θεὸς τῆς καρδίας ἡμῶν καὶ γινώσκει πάντα.For whenever our heart condemns us, God is greater than our heart, and he knows everything.
αὐτὸς ἀποκαλύπτει βαθέα καὶ ἀπόκρυφα, γινώσκων τὰ ἐν τῷ σκότει, καὶ τὸ φῶς μετ' αὐτοῦ ἐστι.He reveals deep and hidden things; he knows what is in the darkness, and the light dwells with him.
What ‘Omniscience’ Actually Means
Christian theology has never said God knows the future by being a really good guesser. God’s knowledge of all events — past, present, future — flows from his being outside time. He does not look down the timeline and see what is coming; he is equally present to every moment of the timeline at once. Boethius (6th century) called this totum simul: the whole, all at once. Augustine had said much the same. It is a careful theological move that protects both divine knowledge and human freedom (a theme our Soul and Hell study took up under the heading of middle knowledge). The delayed-choice experiment does not prove divine timelessness, but it shows that even at the level of physics, «the present» is not the simple, isolated thing common sense imagines.
Past, Present, and the Quantum Eraser
What the delayed-choice eraser actually demonstrates is that for some quantum events, there is no fact of the matter about whether the particle was a wave or a particle until the relevant measurement is made. The «past» for the photon was, in a sense, undetermined — held open — until the «present» measurement was performed. This is deeply counterintuitive, but it is the consensus reading of the experimental data. It means time at the quantum level is not the simple sequential ledger our brains imagine. There is room in the structure of the world for what scripture has always taught: a Knower who is not bound by the ledger.
Knowledge Is Not Coercion
An old worry comes back to the surface here: if God knows what I will do, am I really free? It is the same worry the Soul and Hell study faced. The answer is the same: knowing what someone will freely do is not the same as making them do it. Your weather app may know it will rain tomorrow without causing the rain. God’s omniscience — including his knowledge of the «future» that, from his vantage, is as visible as the past — does not erase your agency. It simply means he never gets caught off guard by your choices.
Pleasant Springs Church — Discipleship School