Is Common Sense Possible?
Is there hope for common sense? Perhaps. In at least one earlier column, I talked about the famed "Schrӧdinger's cat". Erwin Schrӧdinger posed the following thought experiment. Suppose you have a cat in a box containing a vial of poison. The poison is released by the decay of a radioactive atom, which activates a mechanism for breaking the vial, thus killing the cat. Unless we open the box we won't know whether the radioactive atom has decayed or not. So, is the cat alive or dead? Obviously, the cat is both dead and alive! "Come on", you say, "that's impossible. It's got to be one or the other."
I agree; it's common sense. Yet, in quantum mechanics the prevailing dogma insists that light, as well as other particles, is both a particle and a wave, sort of like Schrӧdinger's cat. Even more disturbing, a particle can be in various places at the same time. Take the example of the double-slit experiment, well known in the scientific community. Put a source of light behind a barrier of some sort in which are cut a couple of parallel slits. Send light through those slits and have it end up on a film strip beyond the slits. The result will be that the film will end up with bands of light and dark areas, a result expected if light is made up of waves. At the same time, we know that light is made up of individual entities we call photons, which behave like particles even though they don't have mass as do ordinary particles.
To demonstrate this, let's put detectors near each slit so that we can observe the photons passing through the slits one by one. With our detectors, we see that each photon goes through one or the other slit. On the films we see two clusters of dots as we would expect if the photons are particles. We've got a problem. Is light a wave or a particle? Or both? In 1927, the year I was born, not only did Lindberg cross the Atlantic but there was also a historic meeting known as the Solvay conference (number 5 in a series of these conferences) attended by some 29 of the top luminaries in the world of theoretical physics. At this conference, these top scientists tried to agree on just what this new field of quantum mechanics really meant. Not an easy job.
One of the attendees was Albert Einstein; others included Niels Bohr, Louis de Broglie, Werner Heisenberg and Schrӧdinger, he of the cat. His Schrӧdinger equation is the key equation in quantum mechanics that incorporates the wavelike nature of particles. Heisenberg's famed uncertainty principle, another of quantum mechanics' keystones, limits the precision to which an object can be pinned down in space and gave rise to all sorts of philosophical discussions about the indeterminate nature of life itself. Of all the attendees, Niels Bohr turned out to be the dominant player. He and Heisenberg put forth what's become known as the Copenhagen interpretation.
In their view, why try to describe the quantum world when we can't understand it? Everything changes when we measure it. Light is a quantum wave before it enters the slit. If we say light is a particle, then we have to say that before it passes through the particle is spread out like a wave; it's everywhere at once! If we measure it with a detector after passing through the slit, we must say that the quantum wave has "collapsed" into a particle. In other words, it's a different world out there after we measure it. It's sort of like the old question of whether or not a tree falling in the woods makes a noise if there's nobody there to hear it. It's a wave if we don't measure it and a particle if we do.
Well, the Copenhagen interpretation carried the day at the Solvay conference. We humans can only believe what we see and measure; the world is only what we perceive it to be. We can't go beyond that. Quantum mechanics only deals with what we can measure. However, at least three of Solvay group did fight this conclusion; they were Einstein, Schrӧdinger and de Broglie. Unless you've taken certain physics courses you probably haven't heard of de Broglie but he's one of the pioneers of quantum mechanics and a true superstar in the field. So, the dissenters were an impressive bunch. Even so the Copenhagen interpretation won out and eight decades later it is still gospel. If a particle behaves as a wave it's spread out and can't be pinned down - unless measured and the wave "collapses". In spite of Schrӧdinger having come up with quantum mechanics' key equation, he obviously was expressing his skepticism of its interpretation with his cat.
Longtime readers will know that I hold Einstein on the highest of scientific pedestals and I would love to see him once more validated, as he was recently with his constant that he termed a "mistake" but which turns out to be consistent with the newly found dark energy that's pushing the universe apart. I'm heartened that there are still those who question some of the weird things resulting from the Copenhagen interpretation. The June 19 issue of Science has an article by Tim Folger on Antony Valentini at Imperial College in London and the September issue of Discover magazine has an interview with Roger Penrose of Oxford, also in England. Penrose is very well known as a theoretical physicist whose contributions range from origin of black holes to the well known Penrose tiles.
Valentini is a coauthor of a book to be published later this year titled "Quantum Theory at the Crossroads", which contains the first English translation of the proceedings of the 1927 conference. Unfortunately, the arguments of the three dissenters must have been off the record and are lost to history. However, the proceedings do include a lengthy discussion of an alternate approach put forth by one of them, Louis de Broglie. He scoffed at the idea that particles exist in more than one place at the same time.
De Broglie proposed that "pilot waves" guided the particles along their paths and that, while a particle passed through only one slit, the pilot wave could pass through both slits and guide the particle to its destination. In the case where the detector comes into play, de Broglie suggested that the pilot wave of the particle and the detector had to be considered as a single system. The system results in an "apparent collapse", not a real collapse of the quantum wave. It seems that de Broglie's pilot wave approach was so roundly ignored that he gave up the fight. Now Valentini has taken up the cause of the pilot wave. It's not a popular topic and Valentini, even though highly respected by colleagues, has had to fight for support living on a grant-to-grant basis.
Valentini says that quantum mechanics is just a special case that describes the world/universe that has evolved into what he calls its present "equilibrium" state. His calculations have led him to conclude that after the Big Bang there were particles in states that would not be allowed by quantum mechanics. However, he thinks such states are allowed by pilot wave theory. There's actually a chance that his theory can be tested. The recently launched Planck spacecraft will hopefully obtain the most precise measurements of the temperature variations in the cosmic microwave background remaining from the Big Bang. (Remember, we've talked previously about this background, its discovery at Bell Labs and it's confirmation of the Big Bang.)
Valentini says that the pattern or distribution of these variations will not conform to quantum mechanical predictions but will conform to patterns predicted by pilot wave theory. If the Planck measurements confirm this, Mr. Valentini will become a household name around the world and, hopefully, we can retire Schrӧdinger's cat.
I almost forgot Mr. Penrose. In the Discover interview, he also strongly objects to some of the weird interpretations of quantum mechanics and the currently fashionable string theory. The possibilities of parallel universes, 11 dimensions and Schrodinger's cat being both dead and alive don't thrill him at all. In answer to the final question of the interview, "When physicists finally understand the core of quantum physics, what do you think the theory will look like?", Penrose replies, "I think it will be beautiful." Let's hope so!
Next column to be posted, hopefully, on October 1. (For those of you who saw my note on missing my normal posting date, I came down with some kind of 24-hour fever/malaise yesterday and missed the play I mentioned in the note.) I will try to come up with a topic that I can understand next time.
Allen F. Bortrum