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Name: Amanda
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A


Question:
A long time ago, I read an article about atoms affecting each other without actually reacting with each other. I am very, very vague on the details (so I cannot just Google it). Is it possible that atoms can affect each others' frequencies even over large distances? Across vacuums? I am trying to give a full answer to a question about action at a distance to a student, but I am teaching history (scientific revolution) and am woefully ignorant about physics after Newton. The student is too young (8, but brilliant) to get too deep into atomic theory by himself, but I would really like to encourage this line of inquiry. I do not know enough about it to give him a direction even. Please help!

Dear Amanda,

We have tried to figure out what you are talking about, but failed. Is there any other shred of information that may help us? If one atom affects another, it is considered an interaction. We are not clear on what you mean by "each others' frequencies". Please clarify.

---sysop---

Dear NEWTON-

HAHA! I do not know what I am talking about either! Can atoms affect each other at a distance? Can they affect each other without reacting in the traditional electron sharing/swapping way? Is there such a thing as action at a distance in modern physics or quantum mechanics?

We have been talking about the pre-scientific revolution way of thinking about the world. Action at a distance was an accepted thing then, but it was more like voodoo as I am sure you know. So action at a distance is obviously *not* true in the way they thought of it, but is there a sense in which we currently think action at a distance could be true?

From Googling this I have come up with "quantum teleportation." What the heck is that? Sadly, even Wiki is over my head on that one. That might well be what I am asking about though. Any Quantum Mechanics for Dummies resources out there?



Replies:
Amanda,

My guess is that you are referring to entanglement, of which quantum teleportation is an application. Entanglement is not easy to understand, even for a brilliant student, as the best physicists are still trying to figure out all of the implications. Einstein even disliked the idea that this could even occur. The Wiki on "quantum entanglement" might help explain a little as well as these other sites:

http://searchsmb.techtarget.com/sDefinition/0,,sid44_gci341428,00.html

http://en.wikipedia.org/wiki/Quantum_entanglement

http://plato.stanford.edu/entries/qt-entangle/

None of them are light reading, by any means, but the first couple sentences of the first link might be enough of a definition for you. It is very difficult to describe entanglement in lay terms because it requires an innate understanding of quantum mechanics to understand more than the basic: two particles can be correlated to each other to predictably interact, regardless of the distance. I hope at least helping you put a name to the phenomenon helps!

Matt Voss


Amanda,

One "simple" way that atoms affect each other without coming near is through light. Electrons are constantly emitting and absorbing photons. Photons are "units" of light, sometimes called particles and sometimes called bundles of energy. Photons can pass through anything. Radio waves are made of photons. Visual light is made of photons. Gamma rays are made of photons. They carry energy. In some ways, they carry information. The random emission and absorption affects the energy temporarily stored in an atom. It affects the motion of the atom. It affects how the atom interacts with its neighbors.

Distant atoms interact less often. Neighboring atoms interact frequently. Electromagnetic energy has no true limit of distance or time. A large number of photons together can act as a light wave, oscillating through space. A single photon, more common at the level of individual atoms, acts more as a particle.

When people try to figure out what a photon is "made of", they find it to be a quite unique object. It has no mass, and has no electric charge. Still, it has momentum and kinetic energy. It has a frequency, but it is not a wave. It can be absorbed by any atom, but is more likely to be absorbed by some more than others. This depends on the photon's energy. If the energy perfectly matches the energy gap between states of an atom, the photon can be absorbed quite easily. The energy from the photon might remain in the atom forever. If the photon energy does not match the atom, it is less likely to be absorbed. If absorbed, it will be released very quickly. This is why light travels more slowly through transparent materials than through empty space.

Richard Feynman once commented that anyone who claims to understand quantum physics is not telling the truth. I have found it to be completely against common sense at the day-to-day level. Distance and time take on whole new meanings. Whether something is a particle or a wave depends on what it does and how you measure it. If you have a group of quantum particles joined together (such as all the particles making all the atoms making all the molecules of a baseball), the average effect obeys what we call Newton's Laws. At the level of single particles, Newton's Laws fall apart. A particle does not even have a specific position until the position is measured.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Amanda,

In classical physics, action-at-a-distance is accomplished by fields: gravitational fields, electric fields, magnetic fields. Certainly, atoms can affect each other over distances: the changing electric fields created as their electrons move around the atomic nuclei affect (and attract) other atoms in the neighborhood.

Modern physics formally dispenses with fields, making action-at-a-distance a more tenuous concept. In general relativity, the force of gravity is created by a warped geometry of space-time rather than by a specific gravitational field. By the same token, general relativity replaces magnetic fields with electric fields affected by warped space-time.

Quantum electrodynamics dispenses with the electric field, instead invoking virtual particles to mediate the action-at-a-distance. So interacting particles actually exchange virtual particles, so that there is not really any action-at-a-distance when you consider that the particles are interacting directly with virtual particles they contact.

There is a force particle (boson) for every force in quantum mechanics: a photon for the electromagnetic force, a gluon for the strong nuclear force, three weak bosons for the weak nuclear force, and maybe, just maybe, a graviton for the gravitational force.

Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming



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