Macro-quantum

Most recent answer: 10/22/2007

Q:
We say that for macroscopic objects, its wave nature is ignorable because its de-broglie wavelength is too small to measure by any physical means. But, practically, all it takes to see a wave is having a large enough amplitude, not its wavelength. In none of the equations of matter waves has wave amplitude appeared. So dont I need to know that to observe its wavenature. I other words, what is the deep physical meaning of matter waves.(sorry for the ’long-nature’ of the question)
- Aditya (age 17)
India
A:
In a sense you DO see the wave when you see the macroscopic object-say a ball. So it’s not that the wave amplitude is too small to allow any effects to be seen.

What you don’t see is any sort of obvious interference pattern. The usual claim that any such interference pattern would not be observable because the wavelengths are far too small makes sense.

There may be other complications preventing simple application of the pure quantum mechanical wave-like time dependence to large objects, but even if that turns out to be true, no new replacement equations are known.

It’s hard to give a definite answer about ’deep physical meaning’. The world must be made of something. So far as we can tell, it’s made of quantum things obeying quantum mechanical equations. Some of the large scale behavior is describable as if it were made of classical objects obeying classical equations.

Mike W.

Quantum behavior has been exhibited in the laboratory for extended objects of the order of a few tens of atoms -- molecules have been coaxed to produce interference patterns but the experiments are rather difficult. Any perturbation of the internal degrees of freedom that’s different for different paths a molecule can take through a system (and there are lots of ways big molecules can move, rotate, and jiggle) spoils any possible interference.

On the flip side, though, large collections of atoms or of electrons can be coaxed to coalesce into the same quantum state, which can spread over a macroscopically observable range. Bose-Einstein condensates can comprise macroscopically large numbers of atoms, and long-range order in solids is often a manifestation of the underlying wave mechanics of the constituent pieces.

Tom

(published on 10/22/2007)