Information Theory - Part 4: Relativity


Moving on, Charles Seife next looks at the theory of relativity in Decoding the Universe. One of the most famous dictums of that theory is that “nothing can go faster than the speed of light”.

Except that’s not what the theory says. That statement is an oversimplification:
“Some things can go faster than the speed of light. Even light itself can break light speed, in a sense.”
Huh? Both those statements have been proven in multiple experiments, and no, they don’t necessarily involve quantum mechanics! Even good old non-quantum experiments have shown those two statements to be true.

The exact details of those experiments aren’t relevant to this blog, so I won’t get into them. Regardless, don’t such experiments prove that the speed limit imposed by relativity is being violated? It gets a bit murky, but this is what most scientists say relativity really says:
“The true rule is that information can’t travel faster than the speed of light. You cannot take a bit of information, transmit it, and have it get to a recipient faster than a beam of light can make the same trip.”
And this rule, that information cannot travel faster than light, has not been violated in those experiments. The rule on limit on the speed of information transfer also helps resolve other thought experiments that seem paradoxical at first.

Ok, how about the quantum phenomena that seem to violate the speed limit? Like quantum tunneling where a “particle disappears and reappears somewhere else, all at the same moment”. Instantaneous teleportation: surely that violates the speed of light, right? Again, all experiments till date to use this (and other “weird” quantum phenomena) to transmit information faster than light have failed. Any information that is attempted to be transmitted via these techniques always gets garbled by the time it reaches the recipient.

As more than one popular physics author has said:
“Einstein, once again, would have been relieved… The theory of relativity has withstood all attempts to transmit information faster than light speed.”

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