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Although the term ''zero-point energy'' applies to all three of these interactions in nature, customarily and hereafter in this article it is used in reference only to the electromagnetic case.
In conventional quantum physics, the origin of zero-point energy is the Heisenberg uncertainty principle, which states that, for a moving particle such as an electron, the more precisely one measures the position, the less exact the best possible measurement of its momentum mass times velocityand 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 and other so-called conjugate variables in quantum mechanics. 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 springing from the wave nature of the various quantum fields.
This leads to the concept of zero-point energy. Zero-point energy is the energy that remains when all other energy is removed from a system. This behaviour is demonstrated by, for example, liquid helium. As the temperature is lowered to absolute zero, helium remains a liquid, rather than freezing to a solid, owing to the irremovable zero-point energy of its atomic motions.
Increasing the pressure to 25 atmospheres will cause helium to freeze. A harmonic oscillator is a useful conceptual tool in physics. Classically a harmonic oscillator, such as a mass on a spring, can always be brought to rest. However a quantum harmonic oscillator does not permit this.
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 ripples in a state of a theoretically defined field. However these waves do carry energy and momentumand each wave has a specific direction, frequency and polarization state.
Each wave represents a ''propagating mode of the electromagnetic field. That is a tiny amount of energy in each mode, but the number of modes is enormous, and indeed increases per unit frequency interval as the square of the frequency.
The spectral energy density is determined by the density of modes times the energy per mode and thus increases as the cube of the frequency per unit frequency per unit volume. The product of the tiny energy per mode times the huge spatial density of modes yields a very high theoretical zero-point 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 cmit is argued that the zero point fluctuations must cease at a corresponding Planck frequency Hz.
If that is the case, the zero-point energy density would be orders of magnitude greater than the radiant energy at the center of the Sun.
How could such an enormous energy not be wildly evident? There is one major difference between zero-point electromagnetic radiation and ordinary electromagnetic radiation. Turning again to the Heisenberg uncertainty principle one finds that the lifetime of a given zero-point photon, viewed as a wave, corresponds to an average distance traveled of only a fraction of its wavelength.
Such a wave ''fragment'' is somewhat different than an ordinary plane wave and it is difficult to know how to interpret this. On the other hand, zero-point energy appears to have been directly measured as current noise in a resistively shunted Josephson junction by Koch, van Harlingen and Clarke up to a frequency of about 0.
That is the only kind of spectrum that has the property of being Lorentz invariant. The effect of motion is to Doppler shift detected electromagnetic radiation, but a frequency-cubed spectrum has the property that up- and down-shifting of the radiation is exactly compensated, i.
A remarkably different phenomenon occurs when accelerating through zero-point radiation. The zero-point radiation acts upon an accelerating detector as if the detector were immersed in a thermal spectrum, even though heat and temperature are not involved.
The perceived ''temperature'' is directly proportional to the acceleration.
They were analyzing the theory of van der Waals forces when Casimir had the opportunity to discuss ideas with Niels Bohr on a walk. According to Casimir, Bohr ''mumbled something about zero-point energy'' being relevant.
This led Casimir to an analysis of zero-point energy effects in the related problem of forces between perfectly conducting parallel plates.
The cavity between such plates cannot sustain all modes of the electromagnetic field.
|Physics Classical Physics Laboratory 1 Lab Manuals You should always print out the lab manual before the lab and bring it with you. Reading it before coming to lab is also a good idea!|
In particular wavelengths comparable to the plate separation and longer are excluded from the region between the plates. This fact leads to the situation that there is a zero-point radiation overpressure outside the plates which acts to push the plates together.
This can be considered analogous to radiation pressure radiation pressure from the Sun pushes comet tails away from the comet nucleusand the resulting effect is now called the Casimir force.
It has the property of increasing in strength with the inverse fourth power of the plate separation. The force ceases when elements of the plates come into contact, the surface smoothness of the plates being a limiting factor, or when the plates are so close that the corresponding zero-point radiation wavelengths no longer ''see'' a perfectly conducting surface.Introduction to Measurements & Error Analysis Department of Physics and Astronomy 3 Accuracy is often reported quantitatively by using relative error: expected value.
For this course you will be required to keep a lab notebook. Everything related to your experiment should be recorded in the lab notebook. Often in physics experiments the details which are important are not apparent straight away, if something important is not recorded it may be lost forever.
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INTRODUCTION Quantum mechanics predicts the existence of what are usually called ''zero-point'' energies for the strong, the weak and the electromagnetic interactions, where ''zero-point'' refers to the energy of the system at temperature T=0, or the lowest quantized energy level of a quantum mechanical system.