Heisenberg Uncertainty Principle
From Wise Nano
The Heisenberg Uncertainty Principle says you can´t determine both the speed and the momentum of a particle at the same time. How do you want to build something out of single atoms if you don´t know exactly where they are and what they are doing?
Short answer
With the tools and techniques available, the uncertainty regarding atoms' position and velocity is small compared to their size and to positioning precision required for manipulation, positioning, and bonding. These tools and techniques have become available relatively recently.
Long answer
Another way of stating the Heisenberg uncertainty principle is:
The more we know about where a particle is located, the less we can know about its momentum (velocity), and the more we know about its momentum (velocity), the less we can know about its position.
We can illuminate the meaning of the uncertainty principle by considering how we might measure the trajectory of a baseball and an electron. In the case of the baseball, we could photograph it with a blinking strobe light. The resulting photograph would show us both where the ball was and where it was going at each moment in time. In scientific terms, knowing the path of the baseball means that we are measuring both its location and its velocity at each instant or, equivalently, its location and its momentum. (Recall that momentum is mass times velocity.)
Now imagine trying to observe an electron in the same way. We will detect the electron only if it manages to scatter some of the photons streaming by it. However, whereas the photons are tiny particles of light compared to a baseball, they are quite large compared to the miniscule electron. The precision with which we can pinpoint the electron's location depends on the wavelengths of the photons. If we use visible light with a wavelength of 700 nanometers, we can measure the electron's location only to within 700 nanometers - about 7,000 times the size of a typical atom. That is, if we see a flash from a row of 7,000 atoms, we do not even know which atom contains the electron that caused the flash!
To locate the electron more precisely, we must use shorter-wavelength light, such as ultraviolet or x-rays. Now we encounter our next problem. To determine the electron's path, we must observe the flashes from its interactions with one photon after another. Yet each photon's energy delivers a "kick" that disturbs the electron and thereby changes the momentum we are trying to measure. The higher the energy of the photon - which means the shorter its wavelength - the more it alters the electron's momentum.
Locating the electron precisely requires hitting it with a short-wavelength photon, but the energy of this photon prevents us from determining the electron's momentum. Conversely, measuring the electron's momentum requires hitting it with a low energy photon that will not disturb it much. Because low-energy light has long wavelengths, we'll no longer have a very good idea of where the electron is located.
The uncertainty principle applies to all particles, not just electrons. Just as with the electron, when we look at the baseball with 700 nanometer-wavelength light, we can locate any part of the baseball only to within 700 nanometers (about 0.00002 inch) which is negligible. Moreover, the energy of visible light is so small compared to the energy of the baseball (including its mass energy [e = mc^2 ]) that it has no noticeable effect on the baseball's momentum. That is why Newton's laws work perfectly well when we deal with the motion of maseballs, cars, planets, or other objects in the macroscopic world. Newton's laws fail us in the microscopic and nanoscopic quantum realm, where we must deal with the implications of the uncertainty principle.
So to answer the question of 'how do you build something out of atoms', you must bypass the uncertainty principle by using tools that do not illuminate the subject, but instead give detailed descriptions of the subject, such as the STM. Other tools include the AFM, SPM, LFM, MFM, FMM, and CFM.
Some simple research on the web may be helpful to understand how these techniques are enabling researchers to "see in the dark".
Scanning Tunneling Microscope http://physics.nist.gov/GenInt/STM/text.html
Atomic Force Microscope
