Once in a while, a student will ask me a question that sends me back to the books (as it were) to learn something new. He wanted to know about zero point energy (ZPE), and Wikipedia was not helping him out much.

I couldn’t either at the time, so I dutifully poked around the web to learn more about ZPE. For a “zero,” the concept has some pretty far-reaching effects.

As it turns out, ZPE (and its cousin, the zero point field) is connected to the very questions of where mass and inertia come from, and may provide an explanation of why electrons, for example, have both wave and particle properties.

Anyone who spends any time at all learning physics sooner or later learns that everything in the science is connected. So it is with the ZPE, it seems.

First, we need to understand what the ZPE is, then we can investigate how it connects to all these other basic physical phenomena.

In classical physics, it was assumed that the internal kinetic energy of a substance could theoretically be reduced to zero, by cooling the substance to absolute zero (-273 C or 0K). And indeed, we can chill things down to a mere fraction of a degree above absolute zero. It is, for a couple of reasons, impossible to reach zero, however.

One reason involves the laws of thermodynamics. It becomes harder and harder to extract energy from a sample, since to do so requires expending energy at an exponential rate. In other words, it substantially harder to cool a substance from -253 C to -273 C than it is to cool it from 20 C to 0 C.

The other big reason involves quantum physics, which introduces a certain fuzziness to the classical concepts of mass, energy, momentum and location. Heisenberg’s Uncertainty Principle says there is a limit to the precision to which we can measure two simultaneous physical values. Loosely speaking, the more precisely we know the speed of a particle, the less precisely we can pinpoint its location, and the better we know how long a particle has a certain energy, the less precisely we can measure the value of the energy.

Planck, Einstein, de Broglie and others, meanwhile, concluded that matter and energy (including light) have both particle and wave properties. Particles have definite locations, while waves do not. This fact of nature gives us a picture of the atom that is far different from the popular conception of tiny ball-like electrons whizzing around a ball-like nucleus. Atoms are more like fuzzy clouds than tiny solar systems.

So, to make a long story short, we cannot possibly cool a substance down to exactly absolute zero, because of the quantum nature of matter and energy. There will always be a teeny tiny amount of energy present in the coldest matter or the emptiest vacuum. That’s the zero point energy.

Now the universe, to paraphrase Douglas Adams, is really, really big, so there should be a substantial amount of ZPE. According to the Calphysics Institute, the value of ZPE for the universe is 110 orders of magnitude greater than the energy at the center of the Sun. [Note: By this we mean 110 more decimal places, as in 10¹¹⁰ greater, NOT 110 times greater.] That’s a lot of energy, brother!

So where is it? Quantum physics once again confounds our common sense. The Uncertainty Principle and the wave-particle nature of matter and energy tells us the particles carrying the ZPE travel only a fraction of a subatomic distance before disappearing. At the macroscopic level, where most of us spend our time, the ZPE might as well not be there. At the quantum level, though, ZPE is quite noticeable.

Imagine taking two perfectly flat, parallel metal plates and gradually bringing them closer together. Electromagnetic waves that are naturally present between them will eventually be damped out, like muting a vibrating string, leaving a “vacuum” of energy between the plates. The higher radiation pressure on the other sides of the plates will tend to force the plates together. This attractive force is known as the Casimir effect, after the physicist who first proposed it.

Recent experiments have verified Casimir’s calculations, but it remains to be seen whether ZPE is the reason for the Casimir force (or effect), or if they are other more conventional explanations.

This force, however tiny, has led some to wonder whether we can get useful work out of ZPE. Is the ZPE a huge energy well that we can draw from? Fringe “scientists” worldwide have developed “perpetual motion” machines that purport to extract ZPE from the environment, running with no apparent addition from conventional energy sources. Alas, these machines have typically proved to be fraudulent or non-functional. There’s no such thing as a free lunch, even in quantum mechanics.

Legitimate theoreticians, however, have found in ZPE and the ZPF possible explanations for the fundamental properties of matter and energy.

In physics, we talk about mass and inertia all the time, but generally avoid the question of why they are there in the first place. Sure, we have definitions for both concepts and laws using them, but no one has really offered a decent explanation why matter has to have inertia.

There are actually three kinds of mass. Conveniently, they all seem to have the same values, so informally we do not distinguish among them. Formally, we need to address the trinitarian model of mass.

Gravitational mass results from, well, gravity. It’s the kind of mass the nurse measures when he/she puts you on the scales at the doctor’s office, or the kind you measure in the lab with a triple-beam balance. The scales compare an unknown mass to a known mass by balancing the force of gravity of one against the other.

Inertial mass is what you feel when you accelerate an object, by shaking it back and forth for example, or when you are accelerated yourself. Inertia is the resistance to changes in
motion, as Newton’s Laws state.

Historically, careful measurements of inertial and gravitational mass values for the same object led physicists to assume they are equivalent, at least to within acceptable limits. Einstein instead concluded they had to be absolutely equal to each other, leading to his formulation of the General Theory of Relativity, which tells us that the effects of gravitation are equivalent to the effects of being in an accelerated reference frame.

The third form of mass comes out of Einstein’s Special Relativity. He proposed that mass and energy are equivalent, like ice and water. The conversion equation is E = mc², where c is the speed of light. According to Einstein, energy has mass and matter has energy. Motion affects the energy and mass (actually momentum) of an object in surprising ways, largely due to time dilation.

Relativity also tells us that motion, matter, energy, space and time are all interdependent, so it seems logical to conclude that mass and inertia must somehow result from this interdependence. The rest mass of an object is the mass it has when it’s not moving relative to the observer. The Standard Model of physics predicts that the rest mass derives from the interaction of the object with the space around it, specifically with an energy field named after the physicist who proposed its existence, Peter Higgs.

In Higgs’ conception, the Higgs field (as others besides Higgs termed it) permeates all space and gives each type of subatomic particle its unique rest mass. Wave-particle duality requires there be a particle associated with this field, called the Higgs boson. Particle physicists at CERN hope to detect the Higgs boson once their latest upgrade project is finished. If the boson is found, then the field must exist, and Higgs’ theory will survive its first experimental test.

As it turns out, however, the Higgs mechanism does not provide an explanation for the other two kinds of mass. The atoms that make up most matter have “hidden” mass — the mass-equivalent of the energies that hold atoms together. Where does that mass come from? And why does it seem to bestow inertia on all matter?

Bernard Haisch of Calphysics and Alfonso Rueda of California State University may have the answer, and it depends on — guess what — ZPE and the ZPF.

The zero point field, like the Higgs field, exists everywhere. It’s a very thin “fog” of electromagnetic energy that all matter has to move through.

When a conductor moves through a magnetic field, an electric field forms in the conductor, because electric charges experience a force. That’s the generator effect identified and explored by Joseph Henry and Michael Faraday in the early 1800s. If the charges are not free to move, they exert this force on the conductor. That’s the motor effect.

Inside atoms are tiny charged particles whizzing around at really high speeds. Rueda and Haisch, after churning through the numbers, discovered that the electromagnetic interaction of ordinary matter with the ZPF created an effect identical to inertia! Basically, they had found the reason the m is in F = ma.

As with any new advance in science, these conclusions await further investigation. Haisch and Rueda have not fully explained the origin of gravitational mass, though they have speculated it too results from the interaction of subatomic particles with the ZPF.

They have also elegantly explained the equivalence of inertial mass and gravitational mass using the principles of relativity. With inertial mass, a particle moves through the ZPF. With gravitational mass, the ZPF– caught in the warp of space-time — moves past the particle.

Application of ZPE and the ZPF concepts to other long-standing questions in physics have had some promising results without resorting to quantum effects. ZPE and ZPF have a place in a kind of physics called stochastic electrodynamics (SED), which in essence challenges the whole framework of quantum physics by offering classical explanations for the curious behavior of matter and energy at the subatomic scale.

Why do particles have an associated wave nature? Why do electrons have point-like sizes, but seem much larger? Why do incandescent objects, like stars, have characteristic intensity spectrum (blackbody) radiation curves? Why does the electron in the hydrogen atom have a minimum “allowable” orbit?

Quantum physics already offers useful answers to these questions, but the assumptions seem ad hoc in nature. They answer the questions but fail to provide an underlying reason for why nature should act the way it does. (Why is there wave-particle duality, Daddy?)

This is how science works. Each generation looks at old ideas and explanations, and tries to find new answers. Whether SED ends up in physics texts of the future remains to be seen. Superstring theories have been around for at least 30 years, but are still considered by most physicists to be speculative at best. With no experimental verification of superstring theories, they may forever remain footnotes in textbooks.

ZPE and SED seem to have some experimental basis, so maybe we are witnessing the beginnings of another paradigm shift in physics. Time will tell.

References:
http://www.calphysics.org/articles/chown2007.html
http://www.calphysics.org/mass.html
http://www.calphysics.org/zpe.html
http://en.wikipedia.org/wiki/Zero-point_energy

November 29th, 2007 | Tags: Science | Category: Physics | Subscribe to comments | Leave a comment | Trackback URL