In 1935 Einstein wrote what might be considered his parting shot against quantum theory, his paper with Podolsky and Rosen describing entanglement. Einstein thought it highlighted the fact that quantum theory was incomplete or wrong, calling it "spooky action at a distance". Now more than 70 years later physicists are sure entanglement is a real phenomenon, its routinely produced in the laboratory and even being used in some futuristic practical applications like quantum computing.
But its not the practical applications that really interest me. What intrigues me is the notion that two physical entities in the universe can be connected across vast distances of space. I don't care what the quantum computer geeks say, so what if you can't transmit digital information instantaneously with entanglement? What really matters here in my opinion is the connection. The fact particles are connected in this way shows that the universe is a bit more mysterious-maybe way more mysterious-than we ever imagined.
In a recent article about this topic, which mentions (but did not describe in much detail) an experiment where scientists in Switzerland were looking to see if some signal traveled faster than the speed of light, a physicist named Nicolas Gisin remarks that nature seems able to "manifest events in multiple locations". Gisin goes on to assure us no signal can travel faster than the speed of light. Some have imagined that perhaps a faster-than-light signal connects two entangled particles.
I know there is a lot of evidence in support of special relativity-no reputable scientist disputes it and I'm not going to either. But let's not make it a religion. I think physicists are all too eager to dismiss the notion of a signal of some kind traveling faster than the speed of light. We don't want to be new age quacks but at the same time we need to keep an open mind. All too often in the history of science physicists just "knew" such and such was a fact and it turned out not to be. Maybe there are signals that can travel faster than the speed of light.
In any case, something is connecting the two entangled particles. Maybe they have some kind of link through higher dimensions.
Click here to read the article
Friday, August 15, 2008
Thursday, August 14, 2008
Quantum Physics Reverses Collapse of Wave Function
When you encounter quantum mechanics for the first time, one of the hardest things to wrap your mind around is the collapse of the wave function. To make the strangeness of this idea lets say that the state of the wave function describing its position is a superposition of several basis states. For the sake of argument say that each basis state describes the position of the particle at different locations. So we could imagine that prior to measurement if the wavefunction was a superposition of a large number of states you could say that in some sense the particle was distributed throughout the room. Then you make a measurement to find out where the particle is, and detect it somewhere, lets say by the professors desk. The act of measurement causes the wave function to "collapse" to that particular basis state. Then it begins evolving again if you leave it alone for a bit.
The collapse is easy enough to describe if you're talking mathematics. But conceptually it sounds pretty wacky, if not impossible. If a neutron passes through the room you are sitting in right now, surely it isn't in 1,000 places at once in the room? Then you look at it and BAM it just collapses down to one specific location? You can kind of understand this, I suppose, by thinking about the wave nature of a quantum system, so a wave can be widely distributed throughout space.
Well lately in quantum theory people have been talking about so-called "weak measurements" that allow you to measure the state of a quantum system without disturbing it too much. In this interesting article, they describe an idea proposed by Andrew Jordan at the University of Rochester, where using weak measurements, one can unmeasure a particle and return it to its original state. In other words the collapse of the wave function can be reversed.
Click here to read more.
The collapse is easy enough to describe if you're talking mathematics. But conceptually it sounds pretty wacky, if not impossible. If a neutron passes through the room you are sitting in right now, surely it isn't in 1,000 places at once in the room? Then you look at it and BAM it just collapses down to one specific location? You can kind of understand this, I suppose, by thinking about the wave nature of a quantum system, so a wave can be widely distributed throughout space.
Well lately in quantum theory people have been talking about so-called "weak measurements" that allow you to measure the state of a quantum system without disturbing it too much. In this interesting article, they describe an idea proposed by Andrew Jordan at the University of Rochester, where using weak measurements, one can unmeasure a particle and return it to its original state. In other words the collapse of the wave function can be reversed.
Click here to read more.
Large Hadron Collider to Begin Operation
The Large Hadron Collider, the long awaited upgrade to the particle accelerator operated by CERN will begin operation on September 10th. Built out of a 17 mile long ring, the hopes of particle physicists throughout the world hinge on its successful operation. For the first time in years scientists will get a chance to see some new data in particle physics, a field which has pretty much languished in the murky world of theory since the discovery of the top quark way back in 1995.
The next few years should prove to be exciting. In addition to "wrapping up" the standard model by finding the higgs boson, a hypothetical particle believed to give particles their mass, the accelerator may be able to test many radical ideas like the existence of "extra" dimensions. Or who knows, maybe it won't find the higgs. Now that would be an exciting result. Scientists would have to go back to the drawing board to explain where mass comes from.
No matter what happens, one thing is for sure. The long-awaited LHC is going to usher in an exciting new era in physical science.
Read more here
The next few years should prove to be exciting. In addition to "wrapping up" the standard model by finding the higgs boson, a hypothetical particle believed to give particles their mass, the accelerator may be able to test many radical ideas like the existence of "extra" dimensions. Or who knows, maybe it won't find the higgs. Now that would be an exciting result. Scientists would have to go back to the drawing board to explain where mass comes from.
No matter what happens, one thing is for sure. The long-awaited LHC is going to usher in an exciting new era in physical science.
Read more here
Quantum Mechanics Demystified Erratta Sheets
Corrections to know errors in Quantum Mechanics Demystified will be posted here.
Chapter 2:
Chapter 5:
Chapters 7,8, & 9:
Chapter 2:
Chapter 5:
Chapters 7,8, & 9:
Tuesday, May 13, 2008
Erratta Sheets
No word on McGraw Hill putting up an erratta website (at least they haven't told me about it), so in a few days I am going to post the errors I know about here as PDF files. So far we have compiled error sheets for Quantum Mechanics Demystified and Linear Algebra Demystified. That isn't as bad as it sounds because the typesetting for those two books was worse than for the others so they contain a vastly larger number of errors. Stay tuned.
Wednesday, May 7, 2008
Saturday, May 3, 2008
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