Quantum physics can be endlessly fascinating because of the mind-boggling paradoxes it presents us with. The most famous of these, and probably the most easily explained, involves the so-called double-slit experiment. I have read about this experiment many times, but always seem to have trouble retaining the memory, probably because the experimental outcomes are so counterintuitive that they are hard to absorb and retain.
Maybe if I write it down, I'll be able to remember it better. So here goes.
Though I have put it in my own words, this discussion is based on Chapter 8 of the book Biocentrism by Robert Lanza and Bob Berman. If I've made any mistakes, I trust my more physics-savvy readers will let me know.
Let's say we shoot a beam of photons through two slits in a piece of paper so that the photons make an impression on a screen behind the slits. The stream of light will produce wave interference patterns on the screen, indicating that light functions as a wave.
Now let's say we slow down the stream of photons until only one photon is being released at a time. The photon arrives at the pair of slits and has to "decide" (so to speak) which slit to use. Or so it would seem — but in fact, the photon goes through both slits, and as more and more photons are shot through the slits one at a time, they build up a wave interference pattern on the screen. Thus it appears that even individual photons behave as waves.
So far, so good. But now let's attach a detection device to the slits so that the photon can be observed and measured as it goes through — before it hits the screen. When we do this, we get a totally unexpected result: no more wave interference pattern on the screen! Now each photon behaves like a particle, not a wave.
This is odd. It seems that the mere act of detecting the photon as it goes through the slits is enough to convert it from a wave to a particle. And it's not as if the detection device itself somehow interferes with the photon. All kinds of variations on this experiment have been done, using a variety of detection devices, and the upshot is that it is the very fact of observing and/or measuring the photon that causes it to behave like a particle.
From here, things get even stranger. Suppose we set up two parallel experiments – two sets of double slits in front of two separate screens. Then we fire "correlated" particles at these screens. Correlated particles operate in tandem; by measuring one, we can determine the properties of the other.
If we have no detection device attached to either pair of slits, then the correlated particles will make a set of wave interference patterns on each screen, just as we would expect. If we attach detection devices to both pairs of slits, then the correlated particles will behave like particles — again, just as we would expect.
But suppose we attach a detection device to only one pair of slits, and not the other. What happens then? Both correlated particles behave like particles. In other words, even though only one of the particles is actually being measured as it passes through the slits, the other one behaves as if it has been measured, too. Somehow it seems to "know" that its partner has been detected.
This, however, is not the end of the strangeness. Let's say we modify the experiment so that one correlated particle — call it particle A — travels through a pair of slits with no detection device attached to it and hits the screen, while the other correlated particle — particle B — takes a longer, circuitous route. Particle B eventually passes through a pair of slits fitted with a detection device, but it doesn't reach the slits until after particle A has completed its journey and registered its impression on the screen.
In this case, surely, particle A would behave like a wave, since it will pass through the slits long before its companion particle has reached the slits on its side of the experiment. The fact that particle B will be detected upon reaching the slits should have no effect on particle A, which will already have finished traveling by that point.
But, as you may have guessed, things are not that simple. What actually happens is that both particles behave like particles, not waves. In other words, particle A acts as if its companion particle has been detected and behaves accordingly — even though, in fact, particle B has not yet been detected at all.
It's as if particle A not only "knows" when particle B has been detected, but also "knows" that particle B has not yet been detected but will be detected before the experiment is complete. It alters its present behavior to fit an event that will occur to its companion particle in the future.
Now, it seems to me that paradoxical behavior of this kind simply cannot be explained on the model of an objective reality that exists totally independent of consciousness. The model that I have been looking at lately — here and here — is the virtual reality model suggested by physicist Brian Whitworth (and recommended to me by Ben Iscatus). Whitworth suggests that the paradox of wave/particle duality can be explained if we think of our cosmos as a kind of virtual reality simulation in which all objects exist essentially as information in a database. According to this model, an object always has a potential existence, but it has no actual existence until the calculations are made that allow the object to be "drawn" on the "screen" of our reality.
Suppose we are playing a video game. In our virtual world, we are facing due south, and looking at a building. The building appears as an object in our world because the CPU has done the calculations necessary to draw the building on the screen. Meanwhile, behind us, in the direction of due north, there is a mountain. This mountain is not on the screen; we are not looking in that direction; therefore the CPU does not do the calculations necessary to draw the mountain. It would be a waste of processing power to do so. The mountain exists, for the moment, only as a potential. It is real, in the sense that the information necessary to draw it really exists in the database. But it is potential, in the sense that the drawing has not been done because our attention is not focused in that direction.
If we pivot so that we are now facing due north in our virtual environment, then the mountain will come into view. This means that the CPU now has to do the calculations necessary to draw the mountain on the screen. The mountain has become manifest. It is no longer a potential; it is, for the moment, an actuality. Meanwhile, the building that we were looking at earlier has now vanished from the screen. The CPU no longer has to do the calculations necessary to draw the building, which is now relegated to the status of a potential. Wherever we turn our attention in our virtual environment, the CPU draws that part of our environment. Wherever we are not looking, the CPU does not perform the calculations necessary to draw that part of our environment. Our point of view determines which parts of our virtual world are made manifest at any given time, and which parts remain unmanifest.
Applying this model to the double slit experiment, we can say that detecting the photon (or other particle) as it goes through the slits requires that the "CPU" perform the calculations necessary to "draw" the particle on the "screen" that is our physical reality. Even our conscious intention to detect the particle will trigger the necessary information processing; thus, particle A in the last experiment will be manifested (localized) when it goes through the slits because of our intention to detect particle B, even though our intention has not yet been carried out.
When undetected (unmeasured, unobserved), the particle will behave like a wave — specifically a probability wave, or a probability distribution of all the possible points in space that the particle could inhabit. The particle will not occupy any one particular point because, to do so, the calculations necessary to "draw" it would have to be carried out, and the calculations are not performed when the particle is unobserved. The particle still exists, just as the mountain in our virtual reality environment exists even when it is not on the screen; but, like the mountain, the particle exists as a potential, or (one might say) in an indeterminate form. It is indeterminate because the calculations that would determine its precise location and other characteristics are not presently being made.
The big question, if this model is correct, is what exactly serves as the information processor. My guess, which could be wrong, is that the information processor is consciousness itself. Brian Whitworth has a different view; he regards consciousness as an emergent property of the virtual-reality environment, and sees the information processor as something entirely separate.
In any case, if consciousness is necessary to manifest objects in the universe — if objects exist only as probability distributions until and unless they are observed by a sentient being — then the question arises: How could there be a universe before the appearance of the first living organism? It's no good to say that God's consciousness was observing everything and making it manifest, because if that were true, then presumably God (being omniscient and eternal) would still be observing everything all the time — in which case, particles would always behave like particles and never like waves, since there would never be a time when they were unobserved. In fact, however, particles do behave like waves a great deal of time, specifically when they are unobserved; so if there is an omniscient consciousness overseeing the universe, its observations clearly cannot affect the behavior of subatomic particles.
The logic of wave/particle duality, then, seems to lead to the conclusion that the universe, prior to the appearance of sentient life forms, existed in an indeterminate form, as a vast cloud of possibilities, a dizzying array of probability distributions, none of which had been actualized. This is the conclusion that Robert Lanza and Bob Berman reach in Biocentrism. The chicken-and-egg problem — how could the first sentient lifeform ever exist in actuality if the universe itself was only a potential? – can perhaps be addressed by positing a tangled hierarchy.
It seems too weird to be true … but perhaps, as evolutionary biologist J.B.S. Haldane famously observed, "The universe is not only queerer than we imagine, it is queerer than we can imagine."
Or, to quote astrophysicist Sir James Jeans: "The stream of human knowledge is impartially heading towards a non-mechanical reality. The universe begins to look more like a great thought than a great machine. Mind no longer appears to be an accidental intruder into the realm of matter. We are beginning to suspect that we ought rather to hail it as the creator and governor of this realm."