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The science fantasy behind Faster-Than-Light anything
Faster-than-light travel, communication, whatever -- it all violates Science As We Know It.
I will use the acronym FTL [faster than light] freely in this page.
Larry Niven, in "N-Space", presents an excellent explanation of why any sort of interstellar
politics almost requires FTL travel and communication. I need this politics for my science
Exorcising time travel from the universe: FTL travel/communications does not imply time travel,
contrary to what has been repeatedly published.
The physics in Iskandria's universe is forgiving: all of the classic FTL travel paradigms can be constructed.
Hyperdrive: Lost In Hyperspace
Teleportation (and how to keep it from turning into hyperdrive)
The common reasoning behind FTL travel automatically allowing time travel is as follows:
- For simplicity, let's consider a drive that travels at twice the speed of light. The question is,
"which reference frame?" The idea is that by traveling at twice the speed of light from the
viewpoint of Earth, and then traveling at twice the speed of light with respect to (say) some
cosmic ray, we could end up in the past compared to when we started. I will not go into all of
the standard horrors this entails. These horrors are definitely worth excluding.
- Note, however, that the above argument falls apart if there is a physically preferred way of
measuring FTL travel. This amounts to an "FTL ether", by analogy to the search for "ether" in
a late 1800's attempt to reconcile electromagnetic theory [Maxwell's equations] and the
conventional Newtonian mechanics.
- Maxwell's equations are not preserved by the coordinate transformations of classical
mechanics. They are preserved by the Lorentz transformations of General Relativity.
- Newton's Three Laws are preserved under Lorentz transformations. This is not
intuitive. In fact, Newton formulated his laws to account for the possibility that the
mass of an object might depend on its velocity.
- It was known, in 1876, that classical mechanics applied to Maxwell's equations
predicted no magnetism. Thus, the telegraph (around before 1876) was direct proof
that classical mechanics was not completely correct -- just a good approximation in the
Earth-normal physics regime. [This is in some chemistry textbook in one of the
Johnson County, KS libraries. I read it in 1988 or 1989.]
- The "ether" was an attempt to impose a preferred reference frame for electromagnetism.
Such a preferred frame would make it impossible to apply classical mechanics to
- The Michelson-Morley experiment used a rapidly-spinning series of mirrors to measure
the speed of light. It was thought that at different points in the Earth's orbit, the Earth's
motion relative to the "ether" [the correct frame of reference for electromagnetism]
would change the measured velocity of light. No such change was measurable.
- Mathematically, a physically preferred way of measuring FTL travel would immediately result
in a preferred factorization of space-time into space and time. I don't have access to physical
evidence that either requires, or excludes, such a factorization. If you know of any evidence
relevant to this, please email me with a description of this evidence. This preferred
factorization would have no obvious effects on how to do computational General Relativity
- An "FTL ether" prevents time travel by guaranteeing that no sequence of FTL travels can end
in the past relative to the starting point. It does not affect most phenomena operating
Hyperdrives are supposed to operate at a finite FTL speed.
The following commentary does not depend on the 'exorcism of time travel' comment, above:
changes in coordinate systems merely alter the apparent FTL speed, not the fact it is faster than
- For a finite FTL speed v, the Lorentz contraction factor is a purely imaginary
- EXERCISE: We are taking the square root of a negative number.
- A mathematically clean way to interpret this is that a hyperdrive travels at right angles to the
universe in all four coordinates -- when departing and arriving. One should think of "going
out a certain distance", then "returning to a different place in space-time". My motivation for this
is the coordinate expression of 4-momentum in General Relativity.
- Unfortunately, an error in the return position that cannot be measured, results in completely
missing the universe we want to return to.
Teleportation, for my purposes, is the relocation of the spacecraft (or other object/being) on time
scales approaching the Planck time.
- Both the departure point, and the arrival point, will radiate gravity waves.
- I haven't researched whether this can be worked to preserve the locality principle. Then again,
the locality principle may not be that meaningful at Planck time scales.
- In the absence of a preferred space-time factorization for FTL phenomena, almost all
coordinate-changes turn teleportation into de-facto hyperdrive (with the usual problems).
Warp drives are supposed to work by cleverly warping space-time so that the spacecraft need not
go faster than light itself, even if the rest of the universe thinks it is going FTL.
- Anders' links & mirror [FTL section] to a metadesign for a warp drive --
and an attempt to use Quantum Mechanics+General Relativity to show it can't be built.
- Quantum Gravity has not been formulated -- yet. The attempt may, or may not, be
- Observe that this metadesign assumes a preferred reference frame for the calculations, in spite of the construction being for two space-like related points.
I have not seen a demonstration that warp drives require a preferred space-time
factorization for FTL.
- The gravitational fields around a warp drive are not to be mocked.
- The energy required to create these gravitational fields is also not to be mocked.
- While wormholes are related, these shortcuts do not cause FTL effects.
Opinions, comments, criticism, etc.? Let me know about it.
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