The Most Beautiful Experiment
Quantum physics informs us that a system exists in superposition — that is, in all possible states — until we observe that it is only in one specific state.
According to a 2002 poll of Physics World readers, the “most beautiful experiment” in physics is one that simply and elegantly demonstrates how observation affects quantum systems: The double slit experiment. The double slit sets aside causality, determinism, and the notion that reality is “out there” as it blurs the line between the observer and the system being observed.
In the double slit experiment, a series of single photons (light particles) are fired at a solid plate that has two slits. On the other side of the solid plate, a photographic plate is set up to record what comes through those slits.
The question: What will we see on the photographic plate?
The answer: If one neglects to observe which slit a photon passes through, it appears to interfere with itself, suggesting that it behaves as a wave by traveling through both slits at once. But, if one chooses to observe the slits, the interference pattern disappears, and each photon travels through only one of the slits.
The formation of the interference pattern requires the existence of two slits… But how can a single photon pass through two slits simultaneously? At that point, we are forced to consider each photon as a wave that travels through both slits… Or we have to think of the photon as splitting and going through each slit separately — and wondering how the photon “knows” a pair of slits is coming.
The only solution is to abandon the idea of a photon — or any other quantum system — as having a location in spacetime until it is observed.
I am trying to figure out the truth about the current understanding of quantum physics. From my understanding nothing can be measured without at some level interfering with what is being measured. Do you know the details of how they measured which slit the photon goes through and how it may interfere with the behavior of the photon? Thanks.
Re: Details: There have been numerous double-slit experiments carried out since the early nineteenth century — using light, neutrons, atoms, electrons, and even molecules as large as carbon-60 and carbon-70. Some were measured by human observers, and some recorded by detectors which were then observed by human observers — who, I might add, also conceived and built the detectors specifically for the purpose of later observation. So, while a real-time human observer is not needed for the experiment itself, it nevertheless holds that a detector’s results are observed, at some point, by a human. And so the effect occurs.
In QT circles, this phenomenon is known as the “measurement problem.” It’s also an ontological dilemma for many people. To my thinking, it seems a simple enough fact that everything we know about anything in this universe is a direct result of observation, for how could we “know” anything otherwise? From that perspective, it also makes sense that an observer (like, for instance, a human) will have an effect on any observable with which it interacts (like, for instance, a photon).
To quote one of my favorite physicists, Erwin Schrodinger, “Subject and object are only one. The barrier between them cannot be said to have broken down as a result of recent experience in the physical sciences, for this barrier does not exist.”
If you’d like to conduct the original experiment yourself, check out http://www.cavendishscience.org/phys/tyoung/tyoung.htm
what about the reductionist approach? suppose I eliminate one intelligent being after another…when I finally eliminate myself, will the universe ‘as we know it’ still exist? will the bullet which blew my brain, continue to follow a newtonian trajectory? I think yes.
You’re using reductionism to argue in favor of pluralism — neither of which can be reconciled with quantum theory. Although the conclusions you have drawn from your model are (superficially) intuitive, it is through deeper analysis that principles such as entanglement and complementarity have been uncovered — and, thus, the case for emergence/synergy successfully established.
Even macro-cosmically speaking (in this case, bullets and brain spatter), reductionism does not work within the ontological framework of QT, as uncertainties at the micro level are increased.
To quote Ernest Gellner, “Reductionism is rooted not in the nature of things, but in our ideal of explanation.”
I had trouble understanding this experiment at first, but on YouTube there is a cartoon like video from Fred A Wolf (Dr Quantum) than explained it perfectly. It was the understanding of this experiment and how consciousness plays such an active role in our realities that has me so turned on to QP. Love the site!
Thanks for your comment. If you are interested, I have a YouTube channel dedicated to exploring the Observer Effect, featuring over 230 videos at the present time (and I am always adding more!).
You can visit my channel at http://www.youtube.com/kellyneill