Posted on 02/28/2003 2:59:02 PM PST by sourcery
Quantum physics predicts the existence of an underlying sea of zero-point energy at every point in the universe. This is different from the cosmic microwave background and is also referred to as the electromagnetic quantum vacuum since it is the lowest state of otherwise empty space. This energy is so enormous that most physicists believe that even though zero-point energy seems to be an inescapable consequence of elementary quantum theory, it cannot be physically real, and so is subtracted away in calculations.
A minority of physicists accept it as real energy which we cannot directly sense since it is the same everywhere, even inside our bodies and measuring devices. From this perspective, the ordinary world of matter and energy is like a foam atop the quantum vacuum sea. It does not matter to a ship how deep the ocean is below it. If the zero-point energy is real, there is the possibility that it can be tapped as a source of power or be harnassed to generate a propulsive force for space travel.
The propellor or the jet engine of an aircraft push air backwards to propel the aircraft forward. A ship or boat propellor does the same thing with water. On Earth there is always air or water available to push against. But a rocket in space has nothing to push against, and so it needs to carry propellant to eject in place of air or water. The fundamental problem is that a deep space rocket would have to start out with all the propellant it will ever need. This quickly results in the need to carry more and more propellant just to propel the propellant. The breakthrough one wishes for deep space travel is to overcome the need to carry propellant at all. How can one generate a propulsive force without carrying and ejecting propellant?
There is a force associated with the electromagnetic quantum vacuum: the Casimir force. This force is an attraction between parallel metallic plates that has now been well measured and can be attributed to a minutely tiny imbalance in the zero-point energy in the cavity between versus the region outside the plates. This is not useful for propulsion since it symmetrically pulls on the plates. However if some asymmetric variation of the Casimir force could be identified one could in effect sail through space as if propelled by a kind of quantum fluctuation wind. This is pure speculation.
The other requirement for space travel is energy. A thought experiment published by physicist Robert Forward in 1984 demonstrated how the Casimir force could in principle be used to extract energy from the quantum vacuum (Phys. Rev. B, 30, 1700, 1984). Theoretical studies in the early 1990s (Phys. Rev. E, 48, 1562, 1993) verified that this was not contradictory to the laws of thermodynamics (since the zero-point energy is different from a thermal reservoir of heat). Unfortunately the Forward process cannot be cycled to yield a continuous extraction of energy. A Casimir engine would be one whose cylinders could only fire once, after which the engine become useless.
ORIGIN OF ZERO-POINT ENERGY
The basis of zero-point energy is the Heisenberg uncertainty principle, one of the fundamental laws of quantum physics. According to this principle, the more precisely one measures the position of a moving particle, such as an electron, the less exact the best possible measurement of momentum (mass times velocity) will be, and vice versa. The least possible uncertainty of position times momentum is specified by Planck's constant, h. A parallel uncertainty exists between measurements involving time and energy. This minimum uncertainty is not due to any correctable flaws in measurement, but rather reflects an intrinsic quantum fuzziness in the very nature of energy and matter.
A useful calculational tool in physics is the ideal harmonic oscillator: a hypothetical mass on a perfect spring moving back and forth. The Heisenberg uncertainty principle dictates that such an ideal harmonic oscillator -- one small enough to be subject to quantum laws -- can never come entirely to rest, since that would be a state of exactly zero energy, which is forbidden. In this case the average minimum energy is one-half h times the frequency, hf/2.
Radio waves, light, X-rays, and gamma rays are all forms of electromagnetic radiation. Classically, electromagnetic radiation can be pictured as waves flowing through space at the speed of light. The waves are not waves of anything substantive, but are in fact ripples in a state of a field. These waves do carry energy, and each wave has a specific direction, frequency and polarization state. This is called a "propagating mode of the electromagnetic field."
Each mode is subject to the Heisenberg uncertainty principle. To understand the meaning of this, the theory of electromagnetic radiation is quantized by treating each mode as an equivalent harmonic oscillator. From this analogy, every mode of the field must have hf/2 as its average minimum energy. That is a tiny amount of energy, but the number of modes is enormous, and indeed increases as the square of the frequency. The product of the tiny energy per mode times the huge spatial density of modes yields a very high theoretical energy density per cubic centimeter.
From this line of reasoning, quantum physics predicts that all of space must be filled with electromagnetic zero-point fluctuations (also called the zero-point field) creating a universal sea of zero-point energy. The density of this energy depends critically on where in frequency the zero-point fluctuations cease. Since space itself is thought to break up into a kind of quantum foam at a tiny distance scale called the Planck scale (10-33 cm), it is argued that the zero point fluctuations must cease at a corresponding Planck frequency (1043 Hz). If that is the case, the zero-point energy density would be 110 orders of magnitude greater than the radiant energy at the center of the Sun.
CONNECTION TO INERTIA AND GRAVITATION
When a passenger in an airplane feels pushed against his seat as the airplane accelerates down the runway, or when a driver feels pushed to the left when her car makes a sharp turn to the right, what is doing the pushing? Since the time of Newton, this has been attributed to an innate property of matter called inertia. In 1994 a process was discovered whereby the zero-point fluctuations could be the source of the push one feels when changing speed or direction, both being forms of acceleration. The zero-point fluctuations could be the underlying cause of inertia. If that is the case, then we are actually sensing the zero-point energy with every move we make (see origin of inertia).
The principle of equivalence would require an analogous connection for gravitation. Einstein's general relativity successfully accounts for the motions of freely-falling objects on geodesics (the "shortest" distance between two points in curved spacetime), but does not provide a mechanism for generating a gravitational force for objects when they are forced to deviate from geodesic tracks. It has been found that an object undergoing acceleration or one held fixed in a gravitational field would experience the same kind of asymmetric pattern in the zero-point field giving rise to such a reaction force. The weight you measure on a scale would therefore be due to zero-point energy (see gravitation).
The possibility that electromagnetic zero-point energy may be involved in the production of inertial and gravitational forces opens the possibility that both inertia and gravitation might someday be controlled and manipulated. This could have a profound impact on propulsion and space travel.
Yeah. That sourcery character would be a bit of a drag on me if we were yoked together, I suppose.
It was once thought that black holes did raise problems for entropy and the second law. Does a black hole retain all the entropy of all the stuff that it eats and if so how does it show it? That kind of thing. Even Hawking thought that BHs violated the second law.
Kip Thorne*, after many convolutions, describes the bottom line as follows: A black hole's entropy is the logarithm of the number of ways that the hole could have been made. This entropy does not disappear but is retained in the surface area of the hole's event horizon as the evaporation-radiation particle "atmosphere."
The second law is obeyed. The dim glow of a black hole may be a free lunch to local systems, but only in the same way the sun is to local systems. The entropy of the universe goes up when the black hole eats something. It goes up more as the BH evaporates.
* Black Holes and Time Warps, W. W. Norton, 1994.
Fascinating. So ZPE is not associated with the mechanism for EM wave propagation through a vacuum?
That's not what I said. What I said was that ZPE is not the medium in which EM propogation occurs. ZPE is a consequence of QED/QCD, not the other way around.
I'm not trying to criticize, I'm trying to understand. Can you give me a thumbnail sketch of EM wave propagation?
For the discussion, here are two signficiant zero point energy related articles:
THE CASIMIR FORCE, a 1948 theoretical prediction in which the seemingly desolate "vacuum" creates a tiny force between a pair of conductors, has been precisely measured for the first time. According to quantum mechanics, empty space (the "vacuum") is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence. However, when the vacuum is bounded by a pair of conducting surfaces, the only electromagnetic waves that can exist are those with wavelengths shorter than the distance between the surfaces. The exclusion of the longer wavelengths results in a tiny force between the conductors. To measure the Casimir force, Steve Lamoreaux, now at Los Alamos (505-667-5005), employs a torsion pendulum, a twisting horizontal bar suspended by a tungsten wire. The attraction between a gold-plated sphere and a second gold plate causes a small twisting force in the bar. By applying a voltage sufficient to keep the twisting angle of the bar fixed, Lamoreaux determined the force caused by the attraction of the plates. His results agree with theory to a 5% level. (Upcoming paper in Physical Review Letters.) Researchers previously measured the Casimir-Polder force (Update 122), a different but related effect in which the vacuum creates an attraction between a conducting plate and a neutral atom.
ZERO-POINT MOTION IN A BOSE-EINSTEIN CONDENSATE has been quantitatively measured for the first time, allowing researchers, in effect, to study matter at a temperature of absolute zero. According to quantum mechanics, objects cooled to absolute zero do not freeze to a complete standstill; instead they jiggle around by some minimum amount. MIT researchers (Wolfgang Ketterle, 617-253-6815) measured such "zero-point motion" in a sodium BEC, a collection of gas atoms that are collectively in the lowest possible energy state (Update 233). According to Ketterle, "the condensate has no entropy and behaves like matter at absolute zero." The MIT physicists measured the motion (or lack thereof) by taking advantage of the fact that atoms absorb light at slightly lower (higher) frequencies if they are moving away from (towards) the light. To determine these Doppler shifts (100 billion times smaller than those of moving galaxies), the researchers used a technique known as Bragg scattering. In this technique, atoms absorb photons at one energy from a laser beam and are stimulated by a second laser to emit a photon at another energy which can be shifted upward or downward depending on the atoms' motion towards or away from the lasers. Measuring the range in energies of the emitted photons allowed the researchers to determine the range of momentum values in the condensate. Multiplying this measured momentum spread (delta p) by the size of the condensate (delta x) gave an answer of approximately h-bar (Planck's constant divided by 2 pi)--the minimum value allowed by Heisenberg's uncertainty relation and quantum physics. While earlier BECs surely harvested this zero-point motion, previous measurements of BEC momentum spreads were done with exploding condensates having energies hundreds of times larger than the zero-point energy. (J. Stenger et al., Physical Review Letters, 7 June 1999.)
tpaine shows his stupidity. He should stick to his paid spamming on his drug legalization threads. His motto: Ecstasy in every pocket.
It makes sense to the uneducated laymen that has no concept of aerodynamics.
What do you mean: "Ooops"?
OK. Go ask 100 high school drop outs how a propellor gets it's thrust. Then ask them how a rocket gets it's thrust in outer space where their is NO air to push against! You will get 100 shrugged shoulders.
Are you saying momentum is not conserved and that the "pressure gradient" contributes but not in a way that conserves momentum? I think I will have to take issue with that.
Is there a problem using Webster's as an authority?
Oof. That's not what I meant, but I see why you might take it that way. The fault lies entirely with my wording.
An electric field is measured/defined by the intensity of the force (accelerative effect on mass) that is produced by the field. An electric field propagates as a wave. The wave is produced by oscillation (to and fro movement) of an electric charge. So an electric field wave is simply the change over time in the strength of an electric field, produced as a result of the oscillative movement of the charge that produces the field.
Magnetic fields are more complicated, but the analogous distinction exists between magnetic fields and magnetic waves.
How fields themselves work, and their relation to space, time, matter and energy, is the core subject of any unifield theory of physics. For a very good discussion, I recommend Brian Greene's "The Elegant Universe."
Magnetic fields are induced by currents and time-varying electric fields. Waves in an electric field make the field strength vary over time. Time-varying magnetic fields produce electric fields. Waves in the magnetic field make the field strength vary over time. It should be obvious, then, that electric field waves cause magnetic field waves, and magnetic field waves cause electric field waves. It is this process of A causing B causing A by which electromagnetic wave propagation occurs. An electromagnetic wave is both an electric field wave, and also a magnetic field wave. One wave causes the other, recursively.
You can see a graphical depiction here: Animation of the Propagation of Electromagnetic Waves
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