21/08/2025
Republicando conjecturas (em inglês) sobre o que pode significar a palavra "existir" na Ciência Física.
Observation and Existence
The cartoon is funny, but it also cuts to the heart of what “existence” in physics really means:
Can there be particles that don’t interact with reality in any respect?
🔹 Short answer: No.
If a particle had no coupling at all — not electromagnetic, not weak, not strong, not gravitational, not even to the geometry of spacetime — it would be in principle undetectable. Physics could never include it, since no trace, signature, or effect could ever distinguish it from non-existence.
🔹 Closest examples we know:
• Neutrinos — couple only weakly and gravitationally.
• Gravitons (hypothetical) — interact only through gravity, making them effectively undetectable at human scales.
• Dark matter candidates — WIMPs, axions, etc., likely couple almost exclusively via gravity.
• Sterile neutrinos (hypothetical) — would avoid weak interactions, coupling only gravitationally.
All of these are extreme cases of minimal interaction — but not zero. Even gravity, however weak, leaves a principle-observable footprint.
🔹 Key principle:
In physics, to exist is to interact. Existence is not defined in isolation but through coupling — with fields, particles, spacetime, or observers. A particle that never interacted in any way could never enter an equation, leave a signature, or be inferred. Within physics, that is operationally identical to non-existence.
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We experience the reality that interacts with us. This doesn’t mean that unobserved possibilities never “exist” in superposition; it means that our slice of reality is precisely the part that leaves a trace. Physics can only describe what is in principle connected — however faintly — to observation.
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