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.
This is why the SR-71 becomes so damned efficient at Mach 3+... most of its thrust is developed by the pressure differentials. The actual engine thrust (momentum flux) is only like 35% of the total thrust, but it is still needed to set up the velocity fields which generate the pressure differentials. If I recall, most of the SR's thrust at high Mach is from pressure differential across the inlet spike (and a lesser amount across the afterburner funnel). The higher the Mach, the less total thrust that is actually coming from engine thrust.
So someone else's comment about engineer's and physicists both not writing well misses the mark. It was clearly written by a physicist since an Aero Engineer or Mechanical Engineer with a fluids background would not make this mistake.
My favorite (and best) prof of all time was, in fact, a German rocket scientist who worked for von Braun in the Fatherland. He was one of "our Germans," (though he was actually Ukranian) brought to the US after WWII. Every shuttle launch, until he retired, NASA would fly him down to the Cape as a consultant. He came to class, always dressed formally, and had the total 1 hour lecture always memorized, and I'm talking heavy duty equations. "Vir haff dis trust tairm, und vir integreeren dees oober tay-ta won to tay-ta too." I had no problem since my grandparents spoke the same way... sounded perfectly natural zu mir.
He insisted on calling the roll every day (like a Prussian schoolmarm), always butchering the names. One day, one of the students corrects him on the pronunciation, and he repronounces it, exactly as he did the first time. The student corrected him again, telling him that the name was Ukranian. Ol' Prof Hnatiuk got red in the face and said "I'm Ukranian, und eets prro-nounced [blah-blah]".
When we got back our first midterm, a four question test, the grades were given by a number in the 0 to 4 range (most likely 2 or below). Some kids were real interested on how this translated to letter grades, so they asked him what the grading scale was. "Zeero to forr," he replied looking perplexed. When they demanded to know letter grades that corresponded to these numbers, he reeled it off the cuff, saying 4 was an A, 3 = B, 2 = C, "und so weiter" (etc.) A whiner complained "that's not fair, you have to get a perfect paper to get an A." The old professor, never really adjusting to uppity American students got red in the face, and proclaimed "Gott, heez an A; Me? I'm a B. You?" and then he just shook his head with a snicker. He went on to say that if anyone had problems with the grades, you could talk to him after class. I debated it, but decided to just listen to how the early ones went before committing. Not only did he not give out a single additional point, but he actually reduced a few grades upon finding extra mistakes.
Professor Bohdan T. Hnatiuk was definitely "take no prisoners" with undergrads, but he had a soft spot for grad students. I never learned more during a semester than when he manned the chalk. God rest his soul.
Do you refer to the existence of ZPE, or to its usability as an energy source?
Half a mo' there. Didn't Hawking propose that Black Holes were detectable because the boundary quantum uncertainty at a critical distance around a black hole would produce a net detectable outflow of photons? A black hole detector seems like it might be a keen working device to me. Or is the critical region around a black hole entropy-irrelevant?
Someone better let the physics community know about this, since most physicists seem to take the casimir confirmation as definitive evidence in ZPE's favor.
If common sense was a relevant criteria for quantum mechanics, we'd still be communicating by vacuum tube, and the internet would have a rotary dial addressing mechanism.
It makes sense if you think of the necessity to "push" on the air to expel it rearward at a high velocity, imparting to it the necessary momentum, which is also increased in the forward velocity of the propellor.
Consider a ZPE-based engine as a pie in the sky, wild blue yonder, very outside chance, extreme longshot lottery ticket. In other words, no one really knows, but I wouldn't count on it.
An airplane passenger's body is not accelerated by the jet engine. It is accelerated by the seat. Thus we feel the seat pushing against us.
Ooops...You just said the same thing as that the vacuum on the front is sucking the propellor forward!
It's not a misconception at all. Pushing against a brick wall (or against the ground) is the same thing as pushing against a mass of air or pushing against a jet of hydrazine in a hard vacuum. In each of these cases, it's Newton's Third Law that moves you about. In the case of a brick wall or a planet, the reaction mass is gigantic (never infinite, however), whereas in the case of hydrazine molecules, the reaction mass is tiny. The principle is the same, though. The differences are only quantitative.
Highly unlikely. It may have started out with a manuscript or notes from a physicist, but it looks like the usual science popularization work of a tech writer trying to make it intelligible for the masses (including those masses providing monetary support for the institution).
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