# Faster than Einstein

Ingo Rammer writes about the theoretical limit to reducing latency. Since 1994, we’ve reduced latency by 10 times, but increased bandwidth by millions. We can make the pipes fatter, but we can’t make the data any faster than the speed of light unless, as Ingo points out, “you prove Einstein wrong”.

According to Einstein’s special theory of relativity, the speed of light is an absolute barrier. Not only is the speed of light itself limited, but anything that communicates information is also bound by that limit.

The reason for this is that the speed of light is the same in all frames of references. Suppose I’m in a train heading east from California to New York at half the speed of light and I pull out a flashlight (maybe it is dark in there). I face the flashlight toward the front of the train (say it is 100 meters away) and turn it on. The beam of light from my frame of reference appears to head east at 186,282.4 miles per second which is denoted by the constant c (as in the c in E=mc2) and reaches the front of the train in a split second.

Now suppose somebody in Nebraska happens to be sitting outside watching the trains go by and sees me turn on the flashlight. From his perspective, the beam of light travels west to east at exactly the same speed c. Interestingly enough though, during that same split second, the beam of light travels farther before it reaches the front of the train, because the train itself is moving. How is it possible that light, travelling at the same speed, travels two different distances in the same amount of time?

It doesn’t. The elapsed time itself is different from our two perspectives. This is the paradoxical (but experimentally verified) phenomena called time dilation.

So what does this have to do with latency? The perceived time dilation is the ratio between an external observer’s perceived time and the time perceived by an observer approaching the speed of light. As the the latter observer gets closer to the speed of light, the ratio approaches zero. This would violate causality. If we could send a ping faster than light, from one frame of reference an obsever would observe that the ping was sent before it was received (as expected by causality), but in another frame of reference, the observer would observe the ping as being sent after it was received.

So is it possible to prove Einstein wrong? Perhaps, but not likely. Time dilation has been experimentally verified. There is promise in Quantum Entanglement, but so far it seems impossible to to transmit information using this approach. There are a class of theoretical particles (non have been observed) that might be faster than light, but these would also run into c as a barrier. In this theory, the speed of light is impossibly slow. Good luck trying to rope one of them in to send your ping packet. Those particles are most likely travelling backwards in time, thus not violating causality. They just exhibit causality in a different direction.

If anything will prove Einstein wrong (and I am skeptical) is discovering that causality itself is not sancrosanct. Perhaps time itself is an illusion.