In physics, the observer effect is the fact that simply observing a situation or phenomenon necessarily changes that phenomenon. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner.
Quantum physicists argued that a photon is a wave that only becomes a particle once something observes it.
What causes quantum physicists to argue that a photon had some physical form even before being observed?
How do we know that a photon has some physical form before we observe it?
Is it clear at all that "we know that a photon has some physical form", whatever the circumstances?