Will You Live To See EM Pulse Scattering By Ships Nearing Light Speed?
We are all being asked to imagine what it will be like to see electromagnetic pulse scattering by spacecraft nearing light speed. Particularly by Timothy J. Garner, Akhlesh Lakhtakia, James K. Breakall and Craig F. Bohren in their new physics paper:
Humans will launch spacecraft that travel at an appreciable fraction of the speed of light. Spacecraft traffic will be tracked by radar. Scattering of pulsed electromagnetic fields by an object in uniform translational motion at relativistic speed may be computed using the frame-hopping technique. Pulse scattering depends strongly on the velocity, shape, orientation, and composition of the object. The peak magnitude of the backscattered signal varies by many orders of magnitude depending on whether the object is advancing toward or receding away from the source of the interrogating signal. The peak magnitude of the backscattered signal goes to zero as the object recedes from the observer at a velocity very closely approaching light speed, rendering the object invisible to the observer. The energy scattered by an object in motion may increase or decrease relative to the energy scattered by the same object at rest. Both the magnitude and sign of the change depend on the velocity of the object, as well as on its shape, orientation, and composition. In some cases, the change in total scattered energy is greatest when the object is moving transversely to the propagation direction of the interrogating signal, even though the Doppler effect is strongest when the motion is parallel or antiparallel to the propagation direction.
Electromagnetic Pulse Scattering by a Spacecraft Nearing Light Speed
Arthur C. Clarke not only asked us to imagine what it looks like when a craft nears light speed, he made an effort to describe it in his 1953 classic Childhood's End - behold the Stardrive:
...half a million kilometers away, the Stardrive went on. Up from the heart of the spreading moon-glow a tiny spark began to climb towards the zenith.
At first its movement was so slow that it could hardly be perceived, but second by second it was gaining speed. As it climbed it increased in brilliance, then suddenly faded from sight. A moment later it had reappeared, gaining speed and brightness. Waxing and waning with a peculiar rhythm, it ascended ever more swiftly into the sky, drawing a fluctuating line of light across the stars. Even if one did not know its real distance, the impression of speed was breathtaking: when one knew that the departing ship was somewhere beyond the moon, the mind reeled at the speeds and energies involved.
It was an unimportant by-product of those energies, Jan knew, that he was seeing now. The ship itself was invisible, already far ahead of that ascending light. As a high-flying jet may leave a vapour trail behind it, so the outward-bound vessel of the Overlords left its own peculiar wake. The generally accepted theory-and there seemed little doubt of its truth- was that the immense accelerations of the Stardrive caused a local distortion of space. What Jan was seeing, he knew, was nothing less than the light of distant stars, collected and focused into his eye wherever conditions were favorable along the track of the ship. It was a visible proof of relativity-the bending of light in the presence of a colossal gravitational field.
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