![]() ![]() However, to clarify physical meaning of quantities calculated, a local observer is required. The metric ( 2.1) describes the global geometry of the spacetime. ![]() 2.2 Frame of reference in the warp drive spacetime Since there is no fundamental limit on the parameter \(v_s\), we can take it as large as possible, so the warp bubble can take a distant trip with arbitrarily short time. Recall that R is the radius of the warp bubble, we see the spacetime outside the warp bubble remains quasi-Minkowskian, while the “internal” of the bubble propagates along the x axis with an apparent velocity \(v_s\). In this limit, f approaches a step function with \(f=1\) for \(r_s R\). We can understand the warp drive geometry more easily in the limiting case \(\sigma \rightarrow \infty \). 4, and the total effect on collision between spaceship and interstellar matter is presented in Sect. After that, the geodesic of matter in the warp drive spacetime is studied in Sect. 2, and then work out the distortion force exerted on the spaceship in Sect. We briefly introduce the warp drive scenario in Sect. We find that, although in both cases the pressure depends on \(v_s\) linearly when the spaceship is placed at the center, the \(v_s\) dependence of photon comes from the energy shift, while that of dust comes from the collision frequency. Then we combine all these results and get the dependence of pressure felt by spaceship on its apparent velocity \(v_s\). We study the case for two typical interstellar matter, dusts and photons, and work out the condition for them to collide with the spaceship, the energy shift when the collision happens, and the collision frequency. Secondly, as indicated by, the warp drive metric will accumulate particles in the front part of the bubble, so interstellar matters will be “attracted” and collide with the spacecraft. Firstly, a real spacecraft with non-zero volume will feel a “distortional” force due to the nontrivial curvature gradient. We consider two situations that occurs during the interstellar travel. That is, even if we could overcome all puzzles listed above and construct a warp bubble, the additional challenges preventing us from superluminal travel is still severe. The above works are concerned with the feasibility of a warp drive metric, while we focus on the potential problems arise in the process superluminal travel. In this paper, we investigate the possibility of superluminal travel through warp drive scenario in another prospective. ![]() One of the main focuses of this field is to solve the above theoretical puzzles, see for example. It thus becomes a chicken-and-egg problem of how to move the NEC-violating matter in a superluminal way in order to start the warp drive. (v) To move the warp drive, the flux of the NEC-violating matter is superluminal. (iv) A superluminal warp drive metric leads to quantum instabilities. (iii) In the superluminal region, the warp bubble suffers from a “horizon problem”: there are event horizons that prevent any observers inside the spaceship to interact with the bubble. (ii) The Alcubierre drive requires an unphysically large amount of negative energy, so there appears no practical way to create an Alcubierre drive even if we have control of NEC-violating matter. It is realized that the NEC violation is a generic feature of warp drive spacetimes. Superluminal travel and NEC violation are closely related. For example: (i) To generate a warp drive spacetime, exotic matters violating the Weak Energy Condition (WEC) and Null Energy Condition (NEC) are required. There are several theoretical challenges on the warp drive geometry currently. Hence, the spacecraft inside the warp bubble can travel between two distant points in an arbitrarily short period and remain inside its local lightcones. By a proper parameter setting, the propagating speed of the warp bubble can be arbitrarily large, while the internal spacetime of the warp bubble remains quasi-Minkovskian. In this scenario, the warp bubble, a region of the spacetime deviating from the flat metric, is driven by the local expansion or contraction in its neighboring spacetime. ![]() The warp drive solution provides a possible way for timelike observers to travel superluminally within the framework of classical General Relativity (GR). ![]()
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