Measured Against Reality

Thursday, August 16, 2007

We have NOT broken the speed of light

We have broken the speed of light, the article's headline boldly proclaims.

No, we haven't. I absolutely guarantee it. First, let's look at what they did:

The pair say they have conducted an experiment in which microwave photons - energetic packets of light - travelled "instantaneously" between a pair of prisms that had been moved up to 3ft apart.


Well there's not really anything here. My first guess was that this was some issue about Quantum Entanglement, but it might not be (and that doesn't offer FTL communication anyway, that's just a sloppy interpretation of what's happening). If this is about entanglement then it's not news, this has been done dozens of times, and it doesn't break SR.

But if it's not about entanglement it doesn't matter, because there's no way light traveled faster than light. It reminds me of someone who asked me if humidity can be above 100%. My response was, "No, because can't hold more water than it can possibly hold."

Light always travels at the speed of light, and the speed of light varies based on the medium the light is in. This comes straight from Maxwell's Laws (see here if you're interested in why), and it's what inspired Einstein to think about what light would look like if you ran alongside it (of course, he figured out that no matter how fast you were running it would still go at the speed of light). Special relativity comes straight from Maxwell's laws, and if something is found to violate SR, then Maxwell's laws aren't correct.

Now, it's always possible that our current knowledge of the universe isn't correct, even something as old and well-established as the fundamental theory of electricity and magnetism. But the more established and well-tested the theory, the less likely this becomes. It's like evolution, sure it could be wrong, but it almost certainly isn't. The same is true of Maxwell's Laws, they've been so thoroughly tested to such insane limits that if they're wrong it would shake physics to its core (given that those four little equation form an entire section of physics, and form the foundation for relativity, one of the two pillars of modern physics, the other being QM).

So while it's possible that these two researchers have broken the speed of light, I highly doubt it. Besides, if you look at their setup the have light traveling one meter, which happens in about 3 nanoseconds. I think it's more likely that they measured incorrectly (that there's some error in their experiment) than that half of modern physics is wrong. If I never hear about this monumental discovery again, I'll be pretty sure that I'm right.

Update: A different article has more information, this one attributes the FTL travel to quantum tunneling, which is a process by which a particle goes through an energy barrier that it classically shouldn't be able to go through. I'm not very experienced with this phenomenon, but my understanding is that this still doesn't violate SR since it's not actually moving that distance, the wavefunction has just spread over to the other detector. Since the wavefunction covered the whole distance anyway, the particle wasn't localized before measurement, so it can't be said to have traveled FTL in any real sense (keep in mind that could all be wrong). But it's so hard to say what's going on based on these news reports, they don't include reference information and I can't see it here anyway, so I can't check any actual paper for an idea of what's going on.

In any case, I still stand by my original assessment that this isn't revolutionary, but as always, I could be wrong.

UPDATE 2: Wow, I should have checked Eureka Alert a while ago. Here's a reasonable explanation of what happened. It was indeed tunneling, and it also does not violate SR. As is typical with science reporting, the reporter seized upon the most fantastic interpretation of the results, and not the sober analysis presented at the end. We did not break the speed of light, end of story.

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