hilpers


  hilpers > sci.* > sci.physique

 #1  
20/03/2017, 18h34
Pentcho Valev
Philip Ball explains why Frank Wilczek's time crystals are bogus:

[..]
"But to make that happen, the researchers must deliver kicks to the spins,provided by a laser or pulses of microwaves, to keep them out of equilibrium. The time crystals are sustained only by constant kicking, even though -crucially - their oscillation doesn't match the rhythm of the kicking. Theexperiments are ingenious and the results show that this modified version of Wilczek's vision is feasible. But are we right to award the new findingsthis eye-catching new label, or are they really just a new example of a phenomenon that has been going on since the first primeval heart started beating? If these fancy arrangements of quantum spins deserve to be called timecrystals, can we then say that we each already have a time crystal pulsinginside of us, keeping us alive?"

My comment in Prospect magazine:

Insofar as external energy supply is concerned, only three scenarios are conceivable:

1. There is no external energy supply. Such time crystals are obviously impossible - friction will slow down and eventually reduce the "perpetual" motion to zero.

2. The system is receiving regular jerks from the experimentalist. This is the case with sensational, Frank Wilczek's, time crystals (there is nothinginteresting about them, as Philip Ball suggests).

3. Perpetual motion is produced at the expense of ambient heat. That is, heat absorbed from the surroundings drives some perpetual cyclical process but in the end goes back to the surroundings, thanks to friction.

A time crystal of this type can easily be obtained by submerging a capacitor in a dielectric liquid, e.g. water:

[..]
"However, in experiments in which a capacitor is submerged in a dielectric liquid the force per unit area exerted by one plate on another is observed to decrease... [...] This apparent paradox can be explained by taking into account the difference in liquid pressure in the field filled space betweenthe plates and the field free region outside the capacitor."

We have a high pressure between the plates and a lower pressure outside thecapacitor so if we punch a small hole in one of the plates, there will be an ETERNAL FLOW through the hole, from inside (between the plates) to outside. In other words, we will have a SYSTEM IN DYNAMIC EQUILIBRIUM. The eternal flow can be harnessed to do work, in violation of the second law of thermodynamics.

The system can violate the second law in a more traditional way. If the plates of the capacitor are only partially immersed, the pressure between thempushes the liquid upwards:

[..]
I. BREVIK, EXPERIMENTS IN PHENOMENOLOGICAL ELECTRODYNAMICS AND THE ELECTROMAGNETIC ENERGY-MOMENTUM TENSOR, pp. 143-144: "We shall first give some supplementary comments on the well known situation shown in fig. 1, where two parallel condenser plates are partially immersed in a dielectric liquid. When a horizontal electric field E is applied between the plates, the liquid will rise within the condenser to some equilibrium height h."

[..]
I. Brevik, Fluids in electric and magnetic fields: Pressure variation and stability, Can. J . Phys. (1982): "Fig. 1. Two charged condenser plates partly immersed in a dielectric liquid. [...] Fig. 2. The hydrostatic pressurevariation from point 1 to point 5 in Fig. 1."

[..]
Rise in Liquid Level Between Plates of a Capacitor

[..]
Liquid Dielectric Capacitor

[..]
Chapter 11.6.2: Force on a liquid dielectric

But the rising dielectric liquid can do useful work, e.g. by lifting some floating weight, and the crucial question is: At the expense of what energy is the work done? Since, by switching the field on and off, we do no work on the system, the energy supplier can only be the ambient heat. That is, the system can cyclically lift floating weights at the expense of heat absorbed from the surroundings, in violation of the second law of thermodynamics.

Pentcho Valev

 #2  
21/03/2017, 00h05
Pentcho Valev
The "floating water bridge" is analogous to the capacitor-in-dielectric-liquid time crystal - water absorbs heat from the surroundings and uses it to "climb out of the beakers". The system can easily be converted into an obvious time crystal with perpetual cyclical motion if the water bridge is prevented from forming and the lifted water is suitably allowed to fall back inthe beaker:

[..]
"When exposed to a high-voltage electric field, water in two beakers climbs out of the beakers and crosses empty space to meet, forming the water bridge. The liquid bridge, hovering in space, appears to the human eye to defygravity."

[..]
The Floating Water Bridge

Pentcho Valev
 #3  
21/03/2017, 02h36
Pentcho Valev
An obvious time crystal:

[..]
The Formation of the Floating Water Bridge including electric breakdowns

The eternal motion is driven by heat absorbed from the surroundings. This heat eventually returns to the surroundings, due to friction. However the eternal motion can be harnessed - then heat absorbed from the surroundings will be converted into work, in violation of the second law of thermodynamics..

Pentcho Valev

Discussions similaires
Perpetual Motion of the Second Kind: Theoretically Impossible,Actually Commonplace

Water-Based Perpetual Motion Machines in Living Systems

Frank Wilczek's Perpetual Motion

Top 10 Perpetual Motion Machines for 2014


Fuseau horaire GMT +2. Il est actuellement 03h44. | Privacy Policy