Without an observer to the experiment the photons behaved in a predictable way.
That may not actually be what the double slit experiment proves, and after 100 years of study it is becoming increasingly unlikely that the above interpretation is correct. It is an early misconception which most now understand to be false. What the double slit experiment more correctly shows us (and what we can observe directly with quantum computers), is that entanglement is at the root of classical behavior. Even without a conscious observer, increasing entanglement with the environment eventually leads to a situation in which the wave function is no longer reversible and we stop seeing wave behavior in favor of particle like behavior.
But it is really the test apparatus itself that creates the entanglement necessary to collapse the wave behavior, not the observer. The quantum eraser experiment additionally shows us that if we can catch and stop the entanglement early enough, we can restore the wave behavior before it becomes essentially irreversible. A quantum particle entangled with too many other particles in the environment has a wave function that can not be easily reversed, and thus behaves classically. Unfortunately, since we can not duplicate quantum information, removing the entanglement also means deleting copies of the information.
None of this is to say that consciousness can not influence the quantum world. I definitely believe our brain is structured as a quantum amplifier. But I think our understanding of how it all works is still way too primitive, and my belief is merely a personal bias. Until we genuinely understand all of this better, we need to be very careful believing we actually understand anything, especially when it comes to dangerous experiments with molecules like DNA. We have no business playing around with that at our level of intelligence. It is like giving a monkey a dangerous explosive and waiting to see what he will do. Sooner or later he is going to do something monumentally stupid.
That may not actually be what the double slit experiment proves, and after 100 years of study it is becoming increasingly unlikely that the above interpretation is correct. It is an early misconception which most now understand to be false. What the double slit experiment more correctly shows us (and what we can observe directly with quantum computers), is that entanglement is at the root of classical behavior. Even without a conscious observer, increasing entanglement with the environment eventually leads to a situation in which the wave function is no longer reversible and we stop seeing wave behavior in favor of particle like behavior.
But it is really the test apparatus itself that creates the entanglement necessary to collapse the wave behavior, not the observer. The quantum eraser experiment additionally shows us that if we can catch and stop the entanglement early enough, we can restore the wave behavior before it becomes essentially irreversible. A quantum particle entangled with too many other particles in the environment has a wave function that can not be easily reversed, and thus behaves classically. Unfortunately, since we can not duplicate quantum information, removing the entanglement also means deleting copies of the information.
None of this is to say that consciousness can not influence the quantum world. I definitely believe our brain is structured as a quantum amplifier. But I think our understanding of how it all works is still way too primitive, and my belief is merely a personal bias. Until we genuinely understand all of this better, we need to be very careful believing we actually understand anything, especially when it comes to dangerous experiments with molecules like DNA. We have no business playing around with that at our level of intelligence. It is like giving a monkey a dangerous explosive and waiting to see what he will do. Sooner or later he is going to do something monumentally stupid.