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# Astrophysics/Alcubierre drive theory?

Question
If a star is 500 light years away, the light we get from it was emitted 500 years ago, so if I used an Alcubierre drive to travel to that location (assuming it works) would the time of the destination AND the point of departure remain the same actual times? Or am I going into the past?

Hello,

Miguel Alcubierre's warp drive is predicated on a "local expansion of space-time" behind a spacecraft, while at the same time there’s an opposite contraction of space-time in front of it.

But, there is this important difference to warp drives as depicted in science fiction (e.g. Star Trek): In the Alcubierre warp drive travelers are never really moving faster than the speed of light, since technically they always remain “in their own light cones”. So, rather than an FTL (faster-than-light) displacement of their inertial reference frame (attached to the ship) itself, it is the expansion of space-time that creates the enormous speed of separation.

To obtain this, the appropriate metric must be found, e.g. to “push” the craft along a trajectory described by an arbitrary function of time, say S(t).

The primary proviso for the above, is that the 3-metric be ‘positive-definite’ for all values of t, so the space time is then globally ‘hyperbolic’. The key point is that for the conditions set out, there’ll be no "causal curves", generating the sort of paradox described in the experiment on the laser pulse at NEC Research Institute some years ago (where the pulse was seemingly received before the laser was activated)

It’s important to bear in mind that proper time always applies to the coordinates of the starting and destination points, as well as to the craft(though the latter will be subject to time dilation during the initial and final stages of the trip when moving through flat space-time). This means that only the time on the craft is affected, but that the home world of the travelers, say if at immense distance, would long since have changed by their return.

Rather than "going into the past" it would more be a case of going into the future. (N.B. from the conditions given above, one cannot ensure that the times of destination and departure points remain the same)
Questioner's Rating
 Rating(1-10) Knowledgeability = 8 Clarity of Response = 8 Politeness = 10 Comment As thorough response as I hoped for, thank you!

Astrophysics

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#### Philip A. Stahl

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I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars – as well as the magnetohydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: http://members.shaw.ca/warmbeach/FAQ.htm purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.

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Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

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American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

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Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

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B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

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Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

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Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).