Relativity

Why can't anything go faster than the speed of light?
• ### Science Channel

1. There aren't many sure things in the world of gambling, but you should never bet against a beam of light in a drag race through space. If Albert Einstein were around, he'd tell you the same thing: The speed of light constitutes a universal speed limit. Einstein's theory of special relativity dictates that an object gains mass as it accelerates. The faster it goes, the more massive it becomes. The more massive it becomes, the more thrust or push it requires in order to maintain its speed. According to relativistic predictions, if an object with any mass were to achieve the speed of light, its mass would become infinite, which seems impossible in its own right. But assuming that the object did achieve infinite mass during light-speed travel, to keep moving, the power behind its thrust or push would need to be infinite as well. No force in the known universe can achieve this, short of space-time itself.

There are several potential exceptions to the idea that nothing can go faster than the speed of light. For example, right after the Big Bang occurred, it appears that the universe expanded at a rate faster than the speed of light. However, this does not necessarily violate the mass-energy paradox of light-speed travel, since the empty space that was (and still is) expanding has zero mass. Many physicists also believe in faster-than-light action at a distance on the quantum scale -- for instance, quantum entanglement shows that subatomic particles can react to information about one another instantly, even if they are separated by long distances [source: Kaku].

Light-speed or faster-than-light travel is not merely an academic subject -- such a possibility would have practical applications. For example, according to relativity theory, an object moving at the speed of light does not experience the passage of time. Essentially, time stops. The idea of a carousel spinning at the speed of light, and its time-stopping effect on someone riding it, has merit. To a carousel rider looking out, days would go by extremely quickly. As such, relative to people who are not riding the carousel, the people on the ride would age at a much slower rate. In essence, such a contraption would have the effect of creating a time machine for its passengers, enabling them to travel to the future.

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