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.
Correct. Except in Hollywood where one can shoot someone with a recoilless pistol and have the target fly backwards as if struck with a 500lb sandbag.
Earth should be upperclass too, but it doesn't always happen that way.
OF course they do, if that is their intended audience. You ever have to write an "Executive Summary"? They are one of the better examples of "dumbing down". When you must "dumb down" and/or use common terminology, sometimes technical inaccuracies creep in. :)
The concept of graphing was developed by Rene DeCartes, but is called Cartesian System because his nom de plume was Cartius -- he wrote in latin as did all scholars of the day. the "m" is m for monter, french for to climb (mountains). The b is because polynomials use the coefficients ax^n, bx^n-1, etc. In the Slope-intercept form m is the slope and the usual "a" woldn't carry the meaning.
That's true, but at one point E=MC^2 might have been thought of as "free lunch". Properly understood, it's not of course, but it MAY turn out that neither is the "vacumn energy".
They "push the air backwards, true. But, the expelled air "pushing against" the stationary air, is not what makes them work. This whole line of discussion goes back to some people, not any real scientists you understand, in the days before spaceflight, saying that rockets would not work in space, becaue there is nothing for them to "push against". But since they do not rely on "pushing against" anything, although they certainly push their propellents out, they work just fine in space.
In Einstein's theories, neither. Rather modeled as a distortion of "space-time". However Einstein's theories do not include quantum effects. At the time he wasn't very fond of quantum mechanics, saying "God does not play dice with the universe", later he modified his views. Someone else, Hawking maybe, later responded, "Not only does God play dice with the universe, He sometimes throws them where they can't be seen". :)
More modern treatments attempt to include quantum effects, but a satisfactory general quantum theory of gravitation still does not exist. If it did, one suspects it would settle this "zero point energy" question. But maybe not.
Surely we'd at least have vacumn tube switches? :) Of course even a tube has quantum mechanical aspects. In fact one of the early "quantum" effects, the "Edison effect" was first observed in a vacumn tube!
I agree, "Common sense" has little to do with quantum mechanics, or relativity for that matter. For the simple reason that neither (directly!) manifests itself under the conditions of everyday life, where common sense is presumably developed, although I wouldn't know, since I have very little of it myself. Or so my father was fond of telling me when I was younger. :) He may have been right too!
The ship must push against the propellant. If it didn't there would be no pressure inside the rocket nozzle.
There is no medium, or really no external medium. In short a time varying magnetic field results in an electic field, also time varying. But a time varying electric field also results in a time varying magnetic field. The "wave", which need NOT be sinusoidal, just sort of pulls itself along by it's bootstraps, so to speak. (that might not be a very good description, but it's about as good as it gets without the math). Sinusoidal is the easiest and most common solution to Maxwell's Equations, but not the only one. They come in several forms, see Maxwell's Equations all of which are equivalent. My favorite version of the equations, usually the most general version, either of the two forms shown at the link above, above which is written, "And God said:" and below which is written. "And there was light!" :)
The death knoll of the "ether" theory of electomagnetic propagaton was the Michaelson-Morely experiments, which in turn led to Einstein's special theory of relativity, and the famous E=MC^2. The "ether" was the postulatd medium for the propagation of light and other EM waves.
Hope you don't mind a totally amateurish question. Doesn't entropy have to be expressed in terms of dimensions of some sort, like energy/temperature, or temperature/energy? Can a logarithm have such dimensions?
Well, I guess that goes to show, a black hole is but a storm, full of sound and fury, signifying nothing. Then again, Shakespeare and thermodynamics probably don't mix...
Seriously though, when you say it's just a number, I assume you're referring to the fact that it's a coefficient? (just to make sure we're on the same page)
Actually a good question. Logarithm-of-states entropy is also called logical entropy and there's been no end of confusion on these threads (and in my head) about how equivalent that concept is to thermodynamic entropy (useless background energy).
A good starting point is here. The concepts are highly related but a key difference is that logical entropy depends upon the arbitrary concept of "recognizeable states." Because of this you can have a non-zero change in logical entropy accompanied by a zero change in thermodynamic entropy as Klyce shows on that web page.
OK, you got me.
If one is changing while the other is not, even though they both represent the same thing when it comes down to it, would this not be evidence of a limitation of the method of measurement as applied to logical entropy? How would that impact upon Thorne's formulation?
From Alamo-Girl Post 144.
It's a "Why is the sky blue" kind of question. But it's a serious question, especially since it came from a genuine mathematician (my prof, not me) and he is training us to question everything.
Theorems link concepts: Proofs establish links
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