时空是否量子化？由光子瞬时湮灭引发的相关疑问

Great question—this gets right at some of the trickiest, unresolved intersections between quantum mechanics, relativity, and quantum gravity. Let’s unpack this step by step:

First, let’s revisit the premise: Is photon annihilation truly "instantaneous"? #

In quantum mechanics (and specifically quantum field theory, the framework we use to describe particle interactions), "instantaneous" isn’t a clear-cut term. Photons aren’t tiny classical balls—they’re excitations of a quantum field. When we say a photon "annihilates" (like being absorbed by an atom, or pairing with a positron to vanish), we’re describing quantum state evolution: a state containing a photon excitation evolves into one that doesn’t.

This evolution is continuous and unitary (a fancy way of saying it follows quantum rules and is reversible, when no measurement is involved). There’s no hard, absolute "moment" where the photon suddenly flips from "existing" to "not existing." For macroscopic measurements, this process feels instantaneous, but at the quantum scale, we only talk about the probability amplitude of the transition—not a precise "disappearance instant."

Your core confusion: A classic thought trap with continuous spacetime #

The "last moment of existence" and "first moment of non-existence" you’re imagining come from classical, binary "exists/doesn’t exist" logic—and that doesn’t translate to quantum systems:

• Mathematically, on a continuous real-number timeline, you can’t define both a "last existing moment" and a "first non-existing moment." Suppose the photon exists from [0, T]: then non-existence starts at (T, ∞). Here, T is the clear last moment of existence, but there’s no first moment of non-existence (any t > T has a smaller t' between T and t that’s also a non-existence moment). Flip it around: if existence is [0, T), non-existence is [T, ∞)—now there’s a first non-existence moment T, but no last existence moment. This is just a property of continuous numbers, not a physical contradiction.
• Quantum systems don’t sit in some "in-between" state of existing and not existing. Every moment has a well-defined quantum state; when a photon interacts with another system (like an atom), the state evolves into a combined state where the photon is absorbed and the atom is excited. There’s no fuzzy "middle ground"—we just simplify this to "the photon disappeared" when talking about it macroscopically.

How does spacetime quantization factor in? #

Right now, we don’t have an experimentally proven quantum gravity theory, so whether spacetime is quantized (i.e., has a smallest, indivisible unit like the Planck time/length) is still an open question. But even if spacetime is continuous, it doesn’t conflict with the "instantaneous" feel of photon annihilation:

• Quantum field theory works perfectly well in a continuous spacetime framework to describe annihilation processes, with no logical inconsistencies.
• If spacetime turns out to be quantized, that would eliminate the "infinite intermediate points" issue—but it’s not a necessary fix for your confusion. The mathematical properties of continuous spacetime and the rules of quantum state evolution already resolve the contradiction you’re seeing.

To wrap up: Your confusion comes from applying classical binary logic and continuous spacetime math to quantum processes, which operate under different rules. Quantum mechanics already explains photon annihilation without needing spacetime to be quantized—though spacetime quantization is a fascinating area of research, it’s not directly tied to this specific question.

内容的提问来源于stack exchange，提问作者Edo Mor