Talk:Breakthrough Propulsion Physics Program/Dumping ground

Diametrical drive
The diametric drive is a hypothetical engine which would create a non-conservative gravitational field with non-zero curl. It was argued that in such circumstances, the side of the field which creates more force on the spacecraft will accelerate the spacecraft in the direction of the force.

One idea for realizing this concept involved hypothetical particles with negative mass, originally proposed by Robert Forward and James Woodward. If one were to construct a block of negative mass, and then attach it to a normal "positive" mass, the negative mass would fall towards the positive as does any mass toward any other. On the other hand, the negative mass would generate "negative gravity", and thus the positive mass (the spaceship itself generally) would fall away from the negative mass. If arranged properly, the distance between the two would not change, while they continued to accelerate forever. It has been argued that stability issues might arise.

The concept is illustrated according to Millis by:


 * $$V = (-m) \begin{bmatrix}\frac {-G}{\sqrt{(x+d)^2 +y^2}} \end{bmatrix} $$ $$ + ( + m) \begin{bmatrix}\frac {-G}{\sqrt{(x+d)^2 +y^2}} \end{bmatrix} $$

where:
 * $$V\!$$ is the gravitational scalar potential


 * $$G\!$$ is Newton's gravitational constant


 * $$m\!$$ is normal mass


 * $$d\!$$ is distance

Disjunction
The disjuction drive is a hypothetical drive based on the separation of the source of a field from the matter with which it would otherwise interact. According to a summary of speculative propulsion ideas : "This concept entertains the possibility that the source of a field and that which reacts to a field can be separated. By displacing them in space, the reactant is shifted to a point where the field has a slope, thus producing reaction forces between the source and the reactant. Although existing evidence strongly suggests that the source, reactant, and inertial mass properties are inseparable, any future evidence to the contrary would have revolutionary implication to this propulsion application."

The concept is expressed mathematically as:


 * $$V = \frac {-Gm_S} {\sqrt{(x-d)^2 + y^2}} $$

Pitch and bias
Two hypothetical field-based propulsion mechanism based on a different principle that of the diametric drive and disjunction drive, which was studied in the BPP, are the pitch drive and the bias drive.

The pitch drive, also called the gradient potential drive, involves a hypothetical disjoint field which would eliminate the need for the field to be generated on the spacecraft itself.

One specific proposal for such a pitch drive is the bias drive. According to this proposal, if it were possible to locally alter the value of the gravitational constant G in front of and behind the craft, one could create a bias drive. While the gravitational constant is a fundamental physical constant in general relativity, the Brans–Dicke theory of gravitation does in a sense allow for a locally varying gravitational constant, so the notion of a locally varying gravitational constant has been seriously discussed in mainstream physics. It is not possible to predict the resulting accelaration, as the bias drive would create a singularity in the field's gradient located inside the vehicle.

The bias drive and pitch drive is expressed qualitatively in mathematics as:

$$V = ( xBe ^{..r^2} + 1) [ - G(m/r)]$$

and

$$V = [( - Gm)/r] + ( - xAe ^{..r^2})$$

respectively.

where:


 * $$e^{..r^2}$$ is the Gaussian distribution over $$r\!$$ dimensionless


 * $$A\!$$ is the magnitude of hypothetical pitch drive effect


 * $$B\!$$ is the magnitude of hypothetical bias drive effect

Alcubierre drive
The Alcubierre drive, also called the warp drive, is a proposal, originally due to the physicist Miguel Alcubierre, who proved mathematically that movement at speeds greater than the speed of light was possible without locally exceeding the speed of light. NASA has an experiment which consists of White–Juday warp-field interferometer utilizing a 633 nm HeNe laser beam which is split in two. One beam passes through an electromagnetic field which attempts to distort space enough to see a phase difference between the two beams when they are brought back together. NASA scientist Harold White indicates that a difference of only one part in ten million would be enough to prove the feasibility of the concept. To many people, this concept is reminiscent of the fictional "warp drive" from the science fiction series Star Trek.

Differential sail
The differential sail was another speculative proposal, which appealed to the zero-point energy field. As the Heisenberg uncertainty principle implies that there is no such thing as an exact amount of energy in an exact location, vacuum fluctuations are known to lead to discernible effects such as the Casimir effect. The differential sail was a speculation that it might be possible to induce differences in the pressure of vacuum fluctuations on either side of a sail-like structure—with the pressure being somehow reduced on the forward surface of the sail, but pushing as normal on the raft surface—and thus propel a vehicle forward.

A quantum vacuum plasma thruster is an example of this type of propulsion source.