dac

I actually just started quantum physics today. I can't say I'm the least bit excited.

__________________

lucifer_sam

I recommend:
Fundamentals of Physics, Part 5 by Halliday, Resnick & Walker.
Enough of this philosophical shit, quantum mechanics operates on a mathematical basis.

and cardboard when did you give up the modship?

__________________
first.am

dac

I hope you're not serious with that. That book is the most dry fucking read of all time. It's like reading random segments of numbers.

__________________

Freebase Dali

Go to TED.com and check out some of the talks regarding quantum sciences. Some short, but good introductory talks.

__________________

Filotrillian

Lol physics is math.

Filotrillian

Quantum Mechanics by Claude Cohen-Tannoudji.

Read it.

After Halliday of course.

And Differential Equations.

cardboard adolescent

i found this paper i wrote a while back, might be interesting food for thought for some of you or at least get you thinking about theoretical physics :P

Choosing Sides:
The Argument for the Many-Worlds Interpretation as
the Best Alternative to Copenhagen Quantum Mechanics
t-om

As I start to write this paper, my mind can not help but wander. I consider that, in my imagination at least, there exists a Tom who stopped after writing that first sentence and went back to daydreaming about transtemporal identity. I'm willing to accept that as this other Tom gets closer to the deadline the probability that he writes a second sentence will increase; however, if we discretely branch off Toms, eventually there will remain one who never writes the paper. At face level, all this tells me about my self-identity is that I have a low likelihood of acting particularly irresponsibly. If, however, I assume that all these Toms actually exist, as the Many Worlds Interpretation of quantum mechanics suggests, what distinguishes me, the Tom who wrote this particular paper, from the one who wrote a much better paper, or the one who didn't write it at all? Ultimately, the issues of philosophy are the issues of quantum mechanics. As such, the ambiguity of philosophy is reflected in the ambiguity of quantum mechanics. The empirical underdetermination of quantum mechanics almost inevitably leads interpretational arguments into the domain of philosophy, where abstractions like “realism” and “locality” become trading cards to score points for your theory. The playing field has been wide open since the early thirties, and is still the source of heated debate. On the grounds of restoring realism to quantum mechanics, however, one theory has slowly risen and accumulated credibility over the last five decades to provide a “complete” picture of the universe. The Many Worlds Interpretation of quantum mechanics (MWI) preserves intuitive notions while accounting for quantum weirdness more completely than any other non-Copenhagen interpretation.
Our logical first step is to define the Many Worlds Interpretation. This term, however, has come to mean different things over the years. Its history begins with Hugh Everett's 1957 “Relative State Formulation of Quantum Mechanics”, in which Everett attempted to solve the “measurement problem” by reducing measurement to an interaction between two quantum systems which could become entangled. In other words, he postulated that the Schrödinger wave function described the complete state of an isolated system at all times and that “collapse” of the wave function was an illusion of subjective experience. Everett's theory was highly mathematical, and left a lot of glaring ambiguities. As a result, there are a number of modern theories which expand on Everett's ideas. The MWI was first introduced by Bryce DeWitt in his 1970 paper, “Quantum Mechanics and Reality.” According to the MWI, measurement does not cause the wave function to collapse, rather, it causes our universe to split into universes corresponding to all the possible measurement outcomes. Thus, according to this theory, the universe we perceive doesn't constitute the whole of reality; instead, it is part of a larger structure known as the “multiverse,” which consists of an infinite amount of constantly branching universes (Vaidman, 2002). At first this structure seems blatantly counter-intuitive and unnecessarily extravagant, but the former is never a suitable reason for abandoning a theory and the latter is ultimately very subjective and questionable.
What possible reasons could one have to adopt such a theory? The most obvious is, as mentioned before, that it solves the measurement problem of standard quantum mechanics. This problem states that the observation of a quantum system indeterministically changes its state in a way which requires a discrete extension of the quantum formalism. This problem was at the root of Schrödinger's cat paradox, and is rendered meaningless by the MWI. Similarly, the MWI allows us to restore determinism because all systems evolve deterministically according to the wave function, and realism, because all elements of a system are completely described by the wave function. These two standards, determinism and realism, are at the core of our inherited classical intuitions. If the MWI can restore these ideals without necessitating a super- or sub-structure independent from Schrödinger's wave function, it would seem to be the ideal “alternative” interpretation. Whether this can actually be accomplished, however, is the subject of much debate.
Before we balance the MWI on the edge of Ockham's razor, however, there are other advantages it offers us which should be considered. One of these is locality, which is violated by hidden-variables theories like Bohm's. Locality is considered especially important in resolving Quantum Mechanics with Special Relativity, and is a key element to the study of Quantum Field Theory (Berkovitz, 2007). In some aspects though, it would seem as though the MWI is not a completely local theory. After all, it seems to say that a quantum observation here on Earth results in the duplication of a star system light-years away. However, this view of the MWI is quickly becoming replaced with localized splitting based on decoherence. According to this view, splitting occurs when a thermodynamically irreversible process has occurred and interference effects can no longer occur. A Geiger counter measurement is one such thermodynamic process (Zeh, 2005). Thus, when we detect the presence of a particle, splitting occurs locally at the microscopic level, and spreads throughout the universe causally. It is in this way that the MWI can be best understood as preserving locality.
...

cardboard adolescent

...
The MWI, due admittedly in part to its complexity, offers solutions to other problems as well. For instance, there is the issue of “anthropic bias,” which is the apparent “bias” required in our universe to support the presence of life. If, however, we take the MWI to suggest that all “possible” universes evolve in the multiverse, the very notion of “bias” becomes irrelevant. Instead, there are some universes which can support life and some which can't, and by definition we must necessarily find ourselves in one capable of sustaining life (Ratzsch, 2005). According to David Deutsch, the field of quantum computing also provides support for the MWI. Quantum computing takes advantage of particles' superpositions to do many different calculations simultaneously. An example of this is Shor's algorithm, which factors numbers with hundreds of digits in polynomial time. Factoring a number with 250 digits, for instance, could be done in a realistic amount of time even though it would take “10^500 or so times the computational resources that can be seen to be present.” Deutsch explains this by stating that there are 10^500 universes performing the calculation and they are sharing their results through interference, and challenges detractors to explain how else this is possible. The algorithm itself has been run by an IBM team and found to work, though it was only capable of factoring 15 into 5 and 3 (Deutsch, 1997). The MWI is also often favored by cosmologists, since it allows a complete description of the universe without specifying an external observer, though they are often agnostic regarding the ontological reality of the extra worlds. As shown, the MWI has implications that extend beyond philosophy into the practice of other areas of science.
But is it really as simple as it claims to be? Ockham's razor, as provided by the Stanford Encylopedia of Philosophy, holds “don't multiply entities beyond necessity” (Spade, 2006). It is easy to point out that the MWI does essentially the opposite by multiplying the one world we observe into an infinite of parallel worlds. However, this claim can be rejected on several grounds. The most popular is that the MWI reduces physics to just one entity, the wave function, and thus is the simplest interpretation of Quantum Mechanics. Whether or not the structure which arises from this foundation is simpler is not important to determining its congruence with Ockham's razor, in fact, a complex structure with simple rules seems to be the scientific ideal we are striding towards. Others, such as Deutsch, argue that the simplest realist explanation for interference effects is the existence of multiple universes. A competing construct such as Bohmian mechanics is considered inferior (i.e., more complex) because it requires additional structure to describe particle position and trajectories. Furthermore, Deutsch points out that Bohmian mechanics consists of large interacting sets, which he holds are equivalent to his “worlds,” interacting according to a global wave function, and that it is therefore simply the MWI with disguising excess baggage (Deutsch, 1997, Brown & Wallace, 2004). These claims only hold true, however, if we can show that the wave function does not require excess structure to make the MWI consistent with reality.
According to skeptics the formalism of the MWI fails to account for preferred basis or probability. When a “split” is said to occur, all of the universes formed correspond to elements of the wave function which previously described one universe. Preferred basis is the problem of identifying these elements and justifying how they are decomposed. Most contemporary supporters of the MWI attempt to solve this problem with the theory of decoherence (Bacciagaluppi, 2007). Wallace, for instance, claims that no inherent structure or preferred basis is necessary, and that the classical world emerges from the quantum world through the recurrence of patterns, which can in turn be explained by decoherence (Wallace, 2005). The issue of probability is similar. The argument against the MWI is that while it works perfectly in scenarios where the probability is 50/50, such as Schrödinger's cat, it doesn't account for situations where one outcome is more heighly weighted than another. Consider a Schrödinger's cat experiment, for instance, where the chance of survival is 1% and the chance of death is 99%. Since all the MWI states is that two universes are created it requires some additional formalism to account for the probability not being 50/50. This additional formalism does exist, and is known as the “probability postulate,” which states that the probability constants in the wave function correspond to a “measure of reality.” (Vaidman, 2002) Supporters of this postulate claim that it does not invalidate the MWI because all Quantum Mechanics interpretations require probability postulates, and as such the argument is a moot point. David Deutsch, however, takes a different approach. In his paper, “Quantum Theory of Probability and Decisions,” he combines the axioms of quantum mechanics with classical decision making to derive quantum probabilities. Because the MWI offers such an intuitive way to understand probability, this represents an incredible advancement.
To sum up, the Many Worlds Interpretation of quantum mechanics restores realism, determinism, locality by reducing Quantum Mechanics to just the wave function. Though this sounds ideal, it does so at the cost of a complex ontology. As I have shown, however, it is able to fit all these standards without postulating additional structure, and as such should be seen as the most viable alternative to the standard interpretation. Though there are other relative state formulations which accomplish similar goals, such as the Many Minds Interpretation, the Many Worlds Interpretation follows most clearly from Everett's original description. Also, I believe that the Many Minds Interpretation simply shifts the ontological “weirdness” of Everett's ideas from the physical to the psycho-physical realm, thus making it less accessible.
The implications of the MWI remain mysterious. In a universe of infinite Toms, which one am I? Am I the Tom defined by chance or is there a Tom ideal which all these Toms are simply permutations of? Some have even suggested that paranormal phenomena like poltergeists can be explained by interference effects from parallel universes. The common consensus among MWI proponents seems to be this: we live in a strange world, and a strange world requires a strange explanation.


Bibliography

Bacciagaluppi, G. (2007). The Role of Decoherence in Quantum Mechanics. Stanford Encyclopedia of Philosophy. The Role of Decoherence in Quantum Mechanics (Stanford Encyclopedia of Philosophy).
Berkovitz, J. (2007). Action at a Distance in Quantum Mechanics. Stanford Encyclopedia of Philosophy. Action at a Distance in Quantum Mechanics (Stanford Encyclopedia of Philosophy).
Brown, H. & Wallace, D. (2004). Solving the measurement problem: de Broglie-Bohm loses out to Everett. arXiv:quant-ph/0403094v1.
Deutsch, D. (1997). Fabric of Reality. New York: Penguin Books.
Deutsch, D. (1999). Quantum Theory of Probability and Decisions. arXiv:quant-ph/9906015v1.
Ratzsch, D. (2005). Teological Argument for God's Existence. Stanford Encyclopedia of Philsophy. Teleological Arguments for God's Existence (Stanford Encyclopedia of Philosophy).
Spade, P.V. (2006). William of Ockham. Stanford Encyclopedia of Philosophy. William of Ockham (Stanford Encyclopedia of Philosophy).
Tegmark, M. (1997). The Interpretation of Quantum Mechanics: Many Worlds or Many Words? arXiv:quant-ph/9709032v1.
Vaidman, L. (2002). Many-Worlds Interpretation of Quantum Mechanics. Stanford Encyclopedia of Philosophy. Many-Worlds Interpretation of Quantum Mechanics (Stanford Encyclopedia of Philosophy).
Wallace, D. (2005). Everett and Structure. Studies in the History and Philosophy of Modern Physics 34 (2003), pp. 87-105. arXiv:quant-ph/0107144v2.
Zeh, H. D. (2005). How decoherence can solve the measurement problem. SolveMeas.html.