Slashdot Mirror
Particle-Wave Duality Demonstrated With Largest Molecules Yet
An anonymous reader tips news that researchers have successfully demonstrated particle-wave duality in molecules that have masses of 514 and 1,298 atomic mass units. The academic paper can be found in Nature Nanotechnology.
"Thomas Juffmann et al. fired molecules composed of over 100 atoms at a barrier with openings designed to minimize molecular interactions, and observed the build-up of an interference pattern. The experiment approaches the regime where macroscopic and quantum physics overlap, offering a possible way to study the transition that has frustrated many scientists for decades. ... The relatively large phthalocyanine (C32H18N8) and derivative molecules (C48H26F24N8O8) have more mass than anything in which quantum interference has previously been observed. To have wavelengths that are relatively large compared to their sizes, the molecules need to move very slowly. Juffmann et al. achieved this by directing a blue diode laser onto a very thin film of molecules in a vacuum chamber, effectively boiling off individual molecules directly under the beam while leaving the rest unaffected. ... The researchers observed the particle nature of the molecules in the form of individual light spots appearing singly in the fluorescent detector as they arrived. But, over time, these spots formed an interference pattern due to the molecules' wavelike character.'"
Yes and no.
Scientists are currently trying, albeit with somewhat smaller objects than a person. What you should understand is that the tunneling probability is exponentially damped in both the width of the barrier and the size of the object.
Already for a hydrogen nucleus tunneling through the (electrostatic) potential barrier presented by another hydrogen nucleus, the probability is around 10^-30 (if memory serves correctly). This fact is what keeps the sun burning for billions of years, and not exploding like a hydrogen bomb in a split second, since it limits the rate of fusion processes in the sun.
for i in `facebook friends "=bday" 2>/dev/null | cut -d " " -f 3-`; do facebook wallpost $i "Happy birthday!"; done
It's great to study, understand and use Feynman's path integral, especially since it leads to new insights about the nature of Quantum Mechanics (plus, seeing the familiar face of the principle of least action in the quantum world is just awesome). But it seems counter-productive to limit yourself to it. For example, some problems that are relatively simple to solve using the "usual" methods (i.e., thinking about waves and using the Schrodinger equation) can become intractable math nightmares with Feynman's path integral. I'm sure there are problems for which the reverse is true, too.
Most people who work with QM seem to take a very pragmatic approach when dealing with problems outside the foundations of QM: use whatever works for you for the problem at hand. Peter Shor (the guy who invented the quantum algorithm to factor numbers in polynomial time) once wrote:
Interpretations of quantum mechanics, unlike Gods, are not jealous, and thus it is safe to believe in more than one at the same time. So if the many-worlds interpretation makes it easier to think about the research you’re doing in April, and the Copenhagen interpretation makes it easier to think about the research you’re doing in June, the Copenhagen interpretation is not going to smite you for praying to the many-worlds interpretation.
(Source)
And I agree that people should read QED: it's very easy to read, and it's great.
There is no particle-wave duality. Every particle is only a wave and sometimes, if you look from very far (or at high temperatures) it seems to behave as a point-like object.
In any case it is not like path integrals are alternative to the normal schroedinger wavefunction formulation. See the work of Dyson for that, or simply the Feynman-Kac formula. At the fundamental level path-integrals ar just combinations of double-slits experiments in a very abstract space (Trotter's formula).
And yes, in the path integral a particle interferes with itself. You'll notice that you have to take into account and sum paths going through different slits.
I do work in the path integral formulation because I think it is more elegant, but it is not an alternative to the "traditional" wavefunction approach (hey, path integral is not exactly new anymore). It is the same as choosing cartesian or spherical coordinates.
The tagline is: path integrals do not describe different physics.
Alright, let me clarify what I meant. In fusion, the main factors in determining the reaction speed is the energy and the density. While the energy is comparable in the sun and a hydrogen bomb, the density is 2 orders of magnitude higher in a hydrogen bomb than at the sun's core. The tunneling probability is exponentially sensitive to the density; so sensitive that a third of the way out from the sun's core, fusion can no longer happen. This means that those 2 orders of magnitude are translated into 20 orders of magnitude slower explosion. At that point, I wouldn't call it an explosion.
Just to highlight this point: the power production per volume at the sun's core is 280 W/m^3. This is less than for a human being, it's roughly the same power as a crocodile produces per volume.
TL;DR: You're saying that the smoldering pile of flour on my kitchen bench is exactly like a dust explosion. I beg to differ.
for i in `facebook friends "=bday" 2>/dev/null | cut -d " " -f 3-`; do facebook wallpost $i "Happy birthday!"; done