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.

Why I hate science reporting

I've only been reading Digg for about a minute, and already I've seen two stupid science stories on the front page. The first is about time travel:

Could all our blunders be reversed, our failings eliminated? Perhaps so, if an Israeli scientist's research is to be believed. With the help of Prof. Amos Ori, we might just be able to go back and stop the screw-ups from happening in the first place.

No, they can't, because it doesn't work that way. Here's why (from later in the same damn article):

But don't pack your bags and get ready to go dinosaur-hunting yet. "We, however," he cautions, "could not return to previous ages because our predecessors did not create this infrastructure for us."

If time travel is ever invented it will only be able to take you back to the point where it was initially invented, and I don't think it could be used to go appreciably into the future (the accounts I've heard all require time dilation in order to move into the future. How exactly it works is irrelevant since it's impossible anyway).

The other is about the Casimir effect (if you know what it is, you're probably already groaning).

The article's headline is "Levitation breakthrough proposed". The last paragraph of the article says:

The scientists say there is no likelihood in the foreseeable future of humans being able to levitate. "At the moment, in practice it is only going to be possible for micro-objects with the current technology, since this quantum force is small and acts only at short ranges," said Prof Leonhardt. "For now, human levitation remains the subject of cartoons, fairytales and tales of the paranormal."

I hate editors. Why do they put these ridiculous titles and lead-ins that are flatly contradicted later in the article? Why can't they report science breakthroughs (or theoretical developments) for what they are, and not a pile of sci-fi garbage that they're not? It boils my blood because this is science that anyone who's taken "Intro to Modern Physics" wouldn't get wrong, you don't need a PhD to see that it's crap.

And it's not like the actual science is boring. The Casimir effect article is talking about negative refractive index materials being used to eliminate the quantum attraction between two nanomachines. Why isn't that exciting enough? Why do they need to add levitation? (I find nothing redeeming about the time travel one, since he just proposed a new technical mechanism for something that's beyond our technology but we already knew was plausible. It's not news.)

All of this reminds me about an article where someone claimed to have "solved" the "Twin Paradox" (this was months, probably a full year ago, I have no chance of finding the offending article). My head nearly exploded, because there's nothing to solve. It's only a paradox if you're not thinking about it right, and again, any intro physics class should explain why it's not a paradox (or any book that contains any real treatment of relativity).

It's just so aggravating to see science distorted into something it's not, when what it actually is is so fantastic to begin with.

Nothing Can Move Faster Than Light

As a physicist-in-training, seeing physics misrepresented gets me angry. Some of the most common misrepresentations of physics involve the speed of light.

Occasionally I’ll see over-zealous headlines that proclaim “Scientists send [something] faster than light!” This is completely impossible. To explain why, we have to deal with Einstein’s theory of special relativity.

The speed of light (c) is hardwired into Maxwell’s equations, the equations governing electricity and magnetism. It is the speed at which light propagates in a vacuum, 2.99792 m/s. It’s a very fundamental constant.

There are three main reasons that no massive particle can move faster than (or at) the speed of light, the first has to do with velocity addition. In relativity, velocities don’t add simply, they follow the formula:



Close inspection of this formula reveals that nothing can accelerate to the speed of light by velocity addition. C is quite literally the speed limit.

Another reason has to do with energy. In relativity, the energy of a particle is equal to:



where the factor gamma is equal to:



As v approaches c, gamma approaches infinity, and so does the energy of the particle. That means any particle that has any mass needs infinite energy to move at the speed of light, which is impossible.

The last reason that nothing can move faster than c is that it would make gamma imaginary, which would render every equation of special relativity unintelligible.

You might have noticed that everything I said above only applies to massive particles, but the story is pretty much the same for massless particles, except they can only move at the speed of light.

What’s usually going on with those headlines is that the researchers have “slowed light down”, which is misleading as well, because light always moves at the speed of light. The only way it can be slowed down is by entering a medium with an index of refraction that’s greater than one (which is why I previously said “the speed of light in a vacuum”). Slowing light down in this way is possible, and it happens all the time. It’s why things appear to bend at the water-level (which has an index of refraction of about 1.3).

I’ve read articles that claim researchers got messages to arrive before they were sent by altering the speed of light, but it’s just not possible. These usually turn out to fit the mold of the aforementioned “index of refraction” changes. Besides, there’s no good reason to believe that causality can be broken, and no current theory allows it.

In short, nothing can move faster than light, get over it.

The Equivalence Principle

The equivalence principle, which is the foundation of general relativity, says that a gravitational field that accelerates an object at rate g is equivalent to applying an acceleration of -g to the object.

For instance, standing on the ground on Earth is the same as being on a platform in space accelerating at 9.8 m/s^2. (If you doubt it, think about being in an elevator. As the elevator is accelerating up, you can feel it pushing up on you. If you stand on a scale while this happens, it will read you gaining weight. The acceleration due to gravity and due to the elevator are impossible to tell apart).

This concept is very simple, and it makes sense. It also has dramatic consequences for the world in which we live.

One of these can be called “falling photons”. Think about the room accelerating at 9.8m/s^2, and think about shining a laser pointer across that room. What will happen? As the photons travel, the room will be accelerating upward, which means that the photons appear (to someone in the room) to arc down. Because of the equivalence principle, we know that this happens in gravitational fields too.

This effect was one of the first predictions of general relativity to be confirmed. The position of light from distant stars was measured during an eclipse and found to be different from measurements made while the stars were in plain view.

There are many other spectacular consequences of general relativity, most of which have been confirmed: time is slower in stronger gravitational fields; light is red-shifted (its frequency shortened) when traveling against a gravitational field; and black holes exist, objects so massive that past a certain point (the event horizon), not even light can escape their gravity.

Einstein figured this all out by simply thinking about gravity and the equivalence principle. The math gets very complicated, but the core concept is so simple it can be entirely explained in one sentence: gravitational fields are equivalent to accelerating reference frames. That’s good physics.

Microwave Propulsion

Roger Shawyer has made a remarkable claim: that he can create thrust using only microwaves. Naturally, skepticism abounds; normally when someone proclaims something so outlandish, they have no proof, neither prototype nor theoretical evidence, to back it up. Roger, however, has both. It also helps that he’s been in the aerospace industry for years, working with commercial and military satellites, as an engineers at Matra Marconi Space, and consulting on the Galileo Project.

His engine works with no moving parts, using only microwaves and esoteric physics. He uses a principle discovered by Maxwell nearly 150 years ago, and the same one behind solar sails: that light exerts a force on any surface it hits. Shawyer uses resonant cavities, (those with lengths in integer multiples of the wavelength of light being used) to produce the force. Unfortunately, with cylindrical cavities the forces on both ends are the same, canceling any force.

Continue reading...However, by making a conically shaped resonant cavity, the waves will travel more slowly in the narrow end, producing an uneven force that results in thrust. According to Shawyer, it’s that simple.

But what actually makes the thrust? That’s where relativity comes in. Because the microwaves are moving close to (or at) the speed of light, relativistic effects must be taken into account. This means “that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.” Very strange indeed.

The chief engineering difficulty is that the cavity tends to release energy, which diminishes the effectiveness of the engine. Shawyer has two prototypes, the better of the two produces about 300 miliNewtons, or 0.067 pounds of thrust. More efficient containers, like those used in particle accelerators and made of superconductors, could vastly improve performance.

One big drawback is that the faster these engines go, the less effective they become. That’s why Shawyer wants to use them to make hover-cars, freeing them from the ground while using conventional propulsion to move them.

As is usually the case with a new, untested technology, some people think it’s meaningless crank science, and others think it’s the wave of the future. However, Shawyer has been meticulous in documenting his research, and independent analysts have been impressed.

It’s hard to say what might come of this, there are many technological hurdles still to be crossed, and .067 pounds of thrust, while a good start, is nowhere near enough to be used in anything practical. Maybe one day when we’re all driving hover-cars around Shawyer will be looked upon as the man who gave us the relativity-drive; but he may also fade into obscurity. It’ll be a few years before we can tell for sure. I’ll be waiting to hear more, that’s for sure.

(From New Scientist, Sept. 08 2006, Reltivity Drive: the End of Wings and Wheels? Subscription required)