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(my bold)JesseM said:An obvious reason an object can't form a black hole just because it moves at high speed is because speed is relative to your choice of coordinate system (there is no absolute truth about whether any object is moving at close to light speed), whereasthe formation of an event horizon is an objective physical truth that all coordinate systems agree on.

In Rindler coordinates a "Rindler horizon" forms at a fixed distance below the Rindler observer (accelerating uniformly "vertically upwards" and Born-rigidly in flat spacetime, in the absence of gravity). This horizon has many of the properties of a Schwarzschild horizon around a black hole: a free-falling object takes infinite coordinate time to drop to it, nothing (not even light) passes vertically upward through the horizon, the coordinate speed of light at the horizon is zero, and so on. Yet, it can't be claimed (can it?) that the Rindler horizon "is an objective physical truth that all coordinate systems agree on" because in Minkowski coordinates nothing unusual happens at all.

Now I guess this may depend on precisely how you define what an "event horizon" actually is. Maybe the Rindler horizon doesn't count as an event horizon under some definitions.

So, is an event horizon an artefact of a coordinate chart?