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Exploring Superstrings in the Lab
ultracool writes "Physicists at Utrecht University in the Netherlands have come up with a way of observing a superstring by utilizing Bose-Einstein condensation (BEC). A one-dimensional BEC in an optical lattice is rapidly rotated, causing a quantized vortex to form. The bosonic part of the superstring consists of this vortex line. Inside the vortex, they would trap an ultracold cloud of fermionic atoms. Hopefully this will allow observation of the supersymmetry between bosons and fermions, thus providing the first experimental evidence to support superstring theory."
A more detailed explanation of http://en.wikipedia.org/wiki/Superstringssuperstri ngs.
...to refer people to more information on Bose-Einstein condensates (BEC):
BEC wikipedia page
BEC home page at Colorado
BEC at NIST
What is a BEC?
this is the first experiment that could confirm the existence or non existance of super strings. This would begin to give emperical evidence to support String Theory. up until now most work on String Theory has been unable to provide a working way to test it. this could easily change the face of theoretical physics in the labs and particle accelerators.
String Theory was unknown to me until I saw the awesome Nova special on it..
from the article : String theorists attempt to explain all the fundamental particles as vibrations on tiny strings on length scales of about 10-33 metres. The theory naturally includes "supersymmetry" - a symmetry that connects particles with integer spin, known as bosons, to particles with half-integer spin, which are known as fermions. The particles that carry the fundamental forces of nature, such as the photon and the gluon, are bosons, while the quarks and leptons that make up matter are fermions. Although superstring theory is the leading candidate for a theory of everything, there is no experimental evidence to date for strings or supersymmetry.
Witten said that proving supersymmetry would be helpful in understanding string theory. From what I understand supersymmetry down the road implies string theory. So if supersymmetry is disproved by implication so is string theory. However if supersymmetry is proved is does not prove string theory. But rather add towards understanding and maybe later proving string theory.
but IANAST.
The best education consists in immunizing people against systematic attempts at education. - Paul Feyerabend
I'm also not a string theorist, but I believe that (string theory) + (supersymmetry) = (superstrings). This seems to be an attempt to construct a condensed matter analog of the superstring theory that could underly particle physics. In other words, it's an analog that doesn't necessarily mean that superstrings are or are not the underlying fundamental theory of physics.
Now, for the reason: if you know some quantum physics, think of taking two composite objects and interchanging them; fermions wavefunctions change sign under this interchange. For the composite object, its wavefunction looks like (an anti-symmetrized) product of single-particle wavefunctions. If those are fermionic and there are an odd number of them in the composite wave function, interchanging the two composite wavefunctions will produce an odd number of sign changes in the product, for an overlal sign change. If there are instead an even number of fermionic single-particle wavefunctions in the composite wavefunction, the resulting even number of sign changes under interchange produces no net sign change in the many-body wavefunction.
This is easily extended to composite objects that are a composite of both bosons and fermions.
http://www.pbs.org/wgbh/nova/elegant/program.html
All 3 hours of it are avaliable on PBS's website.
It's amazing stuff.
The book "The Elegant Universe" by Brain Greene is what the TV Special above is based on.
Definitly worth a look at - if you enjoy the TV special, have a look around for the book... It goes into a LOT more detail.
"Who says nothing is impossible? Some people do it every day!" - Alfred E. Neuman
Intrastellar space is not ultracold, it's pretty darn hot (4 Kelvin) when you contrast that to the temperatures needed to form a BEC (around 170 nanoKelvin).
So what's the definition of a fermion or a boson, and in this specific case, of a fermionic or bosonic nucleus?
Bosons have integer spin, and fermions have half-integer (n+1/2, where n is a nonnegative integer) spin. The spins of the individual quarks in nucleons (protons and neutrons) always add up to a half-integer, so nucleons are fermions. The quarks themselves are too. The spins of the nucleons in a nucleus can add up in different ways, depending on the number of each kind (proton and neutron) present. When the spins add to become an integer, the nucleus is bosonic. When the spins add to a half-integer, the nucleus is fermionic.
If a given nucleus is fermionic, then identical nuclei of that type obey the Pauli exclusion principle. If the nucleus is bosonic, then the Pauli exclusion principle does not apply to it, and the possibility of a collection of that kind of nucleus forming a BEC exists.
"It is nice to know that the computer understands the problem. But I would like to understand it too." --Eugene Wigner
So this is very cool (literally!) science, but NOT a test of superstring theory as a way to describe fundamental particles or interactions. At best, it will provide some interesting checks of the mathematical predictions of string-like theories, but only translated into this system. You still won't know if string theory has any hope of describing real electrons, photons, gravitons, etc.
I *almost* understood it. These books went a long way towards helping...
Though I haven't compleated it yet I'll got "The Elegant Universe. Richard Morris also wrote some good books before he died.
FalconShould there be a Law?
But spin is a vector -- it can point in any direction in space. Thus it has a direction too (hence the plus or minus).
That answers your question, but at this point you might wonder why it is assigned either plus or minus 1/2 and not any arbitrary vector. The answer is that due to the weirdness of the spin space (that is, where the electron's spin "lives"), it can be described as a projection onto the plus and minus 1/2 spin vectors along a particular axis. You are, of course, free to choose your axis.
If you can flow liquid helium up your arm at room temperature, it's time to talk to your landlord ASAP.
The poster is probably just mistaking the instantly condensed nitrogen from the atmosphere for liquid helium. Liquid nitrogen (and oxygen the other gases in our atmosphere) runs down the plumbing of your helium container as the liquid boils off and escapes.
Having LN2 run down your arm is not very pleasant either, however. Stings like electric shock at first, and if it stops stinging you know you're in BIG trouble.
IANAP, but I am an MRI technician.
A side note: Liquid helium is very expensive to produce. The bulk of the cost of production is in harvesting the gas to compress down to liquid form. All the helium that exists on Earth is the product of eons of radioactive decay. When the liquid boils off, the escaping gas rises far above our reach. That's ironic, given that He is the second most abundant element in the universe... yet we have to pay more for it than for oil (around $10 per liter).
Buford "Mad Dog" Tannen
Brian Greens' book "The elegant Universe" talks about the history of string theory and if I recall correctly, there were many branches of string theory. One breakthrough in the 80's was M-Theory which tried to consolidate the ideas of 2, 3 and higher-dimensional string-derivative theories. Unless I have the order mixed up, it was then that super-symmetry was introduced. If I am correct, then super-symmetry was part of an exciting theory that was a superset of conflicting theories which provided a semblance of unification (the fabled grand unification theory).
The point is that, unless my memory of the order of progress is wrong, super-symmetry is relatively new to string-theory and definitely wasn't part of the original models. I do not know that disproving super-symmetry disproves all branches of string-theory. No branch yet has experimental prudence, so it's still possible that after back-tracking, one of the earlier branches was on the right track.
Not just wishful thinking, I'm demonstrating that the disproof of super-symmetry does not end string theory; just string theory as we (read me) know it.
-Michael
The defining property of a fermion and a boson is that a fermions probability amplitudes add with a minus sign and a bosons probablitly amplitudes add with a postive sign[...]
As the saying goes, I don't think those words mean what you think they do.
Fermions and bosons are only defined in the context of more-that-one-particle states. One-particle states couldn't care less. The idea is that for identical particles, a particle permutation has to be a valid symmetry of the system (after all, you can't tell them apart) - and since a permutation squared is the identity, the corresponding eigenvalues of the permutation operator can be 1 and -1, that is symmetric and antisymmetric. Now:
fermions: the total wavefunction of the system is antisymmetric under a particle permutation (P[psi] = -psi)
bosons: the total wavefunction of the system is symmetric under a particle permutation (P[psi] = psi)
Nothing can prove string theory. You can only show that the observed behavior of something is consistent with string theory.
But, from what you say, it sounds like there are a number of competing theories which all predict a certain kind of supersymmetric behavior for fermions and bosons.
So, if this experiment works as string theory predicts, string theory and a number of other theories that predict the same thing get a feather in their collective caps.
Need a Python, C++, Unix, Linux develop
Incorrect! He'll feel electromagnetic fields coursing through his body. This is a valuable experience of one of the four fundamental forces of the universe (jumping out of a fifth story building would give exposure to gravity and technically the strong force though breaking your knuckles with a visegrip is a better demonstration of that force) so it's all to the good. The actual transfer of subatomic particles will be negligiable though. A better choice for him would be putting a highly radioactive isotope in his pants.