Speed of Light May Not Be Constant
Some scientists are exploring the possibility that the cosmic speed limit changes.
Did you own a toy race-car track as a child? Ever crash your model trains into one another just to see what happened? If you did, then congratulations, you already know some of the basic principles behind the Large Hadron Collider (LHC). Built by the European Organization for Nuclear Research (CERN), the 27-kilometer tunnel buried in the Swiss countryside exists to smash particle beams into each other at velocities approaching the speed of light. The idea is to use the resulting data to better understand the structure and origins of the universe. We're talking heavy questions and even heavier answers. Perhaps it's understandable that some critics, conspiracy theorists, crackpots and (alleged) time travelers might fear something more substantial than the Higgs boson particle. In this article, we'll run through some of the more popular misconceptions about the LHC and how little you have to fear about it causing the end of the world as we know it.
5. CERN Is Making an Antimatter Bomb
The Dan Brown detective novel (and movie adaptation) "Angels and Demons" centers on a plot to steal an antimatter bomb from CERN and blow up the Vatican with it. While the blockbuster delivered its share of action and intrigue, it fell short on facts. Two of the film's biggest mistakes revolved around antimatter's potential use as both an energy source and a weapon. Yes, when an antimatter particle comes in contact with normal matter, the two particles destroy each other and release energy. But CERN is quick to point out that the energy payoff simply isn't there. In fact, the transaction is so inefficient that scientists only get a tenth of a billionth of their invested energy back when an antimatter particle meets its matter counterpart. As for developing an antimatter bomb, the same principles apply. CERN points out that, at current production rates, it would take billions of years for the organization to produce enough antimatter to generate an explosion equal to an atomic blast.
4. Fun-sized Black Holes
Some concepts don't become tamer when you tack a "micro-" or a "mini-" prefix in front of them. For example, a mini-stroke is still an excellent reason to visit the hospital, and you'd certainly be ill advised to question the power of a minigun. So when CERN scientists mention that they might create microscopic black holes in the midst of their particle smashing, it's easy to understand some of the ensuing panic. Based on Einstein's theory of relativity, a few speculative theories lend a sheen of possibility to micro-black hole creation. The good news is that these theories also predict the micro-black holes would disintegrate immediately. If these black hole welterweights did hang around a little longer, it would take billions of years to consume the mass of a tiny grain of sand. That means no reducing the European countryside to a singularity and certainly no destroying the planet "Star Trek" style.
3. Attack of the Strangelets
Read enough space publications and your perception of the universe changes pretty fast. Once you get beyond the absurd vastness of the cosmos, you encounter such mind-rending notions as black holes, antimatter and dark matter. After you've swallowed the notion of a gigantic star collapsing into something smaller than a pinhead, it's easy to get bowled over by the idea of universe-destroying strangelets. Strange matter is presumed to be 10 million times denser than lead and was birthed during the Big Bang from the hearts of dense stars. The fear, which originated with the start-up of the Relativistic Heavy Ion Collider (RHIC) in 2000, is that the LHC will inadvertently produce strangelets -- tiny particles of strange matter -- and that these particles will swiftly convert surrounding normal matter into even more strange matter. It only takes a thousand-millionth of a second for the chain reaction to convert the entire planet. Strangelets, however, are purely speculative, and haven't surfaced in over eight years of RHIC operation. CERN says that the RHIC was far more likely to produce the theoretical matter than the LHC, so there's really no chance of it consuming the planet.
2. Time Travelers Hate It
In "Bill & Ted's Excellent Adventure," the titular slacker duo wields time travel with the logic of a 12-year-old. When Bill and Ted need a cell key to bust a few historical figures out of a modern California jail, they simply make a mental note for their future selves to travel back in time and plant the key where they can find it. While the 1989 buddy comedy is pretty much the antithesis of hard science fiction, its view of time-travel logic is shockingly similar to a 2009 theory regarding the LHC. Danish string theory pioneer Holger Bech Nielsen and Japanese physicist Masao Ninomiya, in a series of posted physics articles, laid out their theory that the Higgs boson particle is so abhorrent to nature that its future creation will send a ripple back through time to keep it from being made. Naturally, this theory summons images of T-800s, Jean-Claude Van Damme and Hermione Granger all galloping back through time to prevent future disasters, but not everyone is busy cracking jokes and reminiscing about time-travel movies. The two scientists aren't even talking about shadowy strangers from the future, but merely "something" looping back through the fourth dimension. Imagine a poorly designed bomb that, upon creation, destroys half the bomb factory. Now expand that example out from the confines of linear time.
1. Gateway to Hell
Black holes, antimatter explosions and even strangelets all originate from scientific fact and theory (albeit with a bit of imagination thrown in). Forget all that for the moment and consider the "Satan's Stargate" theory, proposed by Chris Constantine, better known on the Internet as YouTube user gorilla199. Constantine charges that the LHC exists "to disrupt a hole in the Van Allen belt that surrounds the Earth" and "to allow the return of the Annunaki from the planet Nibiru in order that they can come here, corrupt the rest of the Earth and do battle with God at Armageddon." There's also some stuff in there about freemasonry, cosmic rays and the Old Testament offspring of humans and fallen angels. According to BBC News, Constantine received a suspended sentence for DVD pirating after his defense attorney charged that Constantine suffered from a serious psychiatric condition. The Antichrist could not be reached for comment.
The speed of light is constant, or so textbooks say. But some scientists are exploring the possibility that this cosmic speed limit changes, a consequence of the nature of the vacuum of space.
The definition of the speed of light has some broader implications for fields such as cosmology and astronomy, which assume a stable velocity for light over time. For instance, the speed of light comes up when measuring the fine structure constant (alpha), which defines the strength of the electromagnetic force. And a varying light speed would change the strengths of molecular bonds and the density of nuclear matter itself.
A non-constant speed of light could mean that estimates of the size of the universe might be off. (Unfortunately, it won't necessarily mean we can travel faster than light, because the effects of physics theories such as relativity are a consequence of light's velocity). (10 Implications of Faster-Than-Light Travel)
Two papers, published in the European Physics Journal D in March, attempt to derive the speed of light from the quantum properties of space itself. Both propose somewhat different mechanisms, but the idea is that the speed of light might change as one alters assumptions about how elementary particles interact with radiation. Both treat space as something that isn't empty, but a great big soup of virtual particles that wink in and out of existence in tiny fractions of a second.
Cosmic vacuum and light speed
The first, by lead author Marcel Urban of the Université du Paris-Sud, looks at the cosmic vacuum, which is often assumed to be empty space. The laws of quantum physics, which govern subatomic particles and all things very small, say that the vacuum of space is actually full of fundamental particles like quarks, called "virtual" particles. These matter particles, which are always paired up with their appropriate antiparticle counterpart, pop into existence and almost immediately collide. When matter and antimatter particles touch, they annihilate each other.
Photons of light, as they fly through space, are captured and re-emitted by these virtual particles. Urban and his colleagues propose that the energies of these particles -- specifically the amount of charge they carry -- affect the speed of light. Since the amount of energy a particle will have at the time a photon hits it will be essentially random, the effect on how fast photons move should vary too.
As such, the amount of time the light takes to cross a given distance should vary as the square root of that distance, though the effect would be very tiny -- on the order of 0.05 femtoseconds for every square meter of vacuum. A femtosecond is a millionth of a billionth of a second. The speed of light has been measured over the last century to high precision, on the order of parts per billion, so it is pretty clear that the effect has to be small.
To find this tiny fluctuation, the researchers say, one could measure how light disperses at long distances. Some astronomical phenomena, such as gamma-ray bursts, produce pulses of radiation from far enough away that the fluctuations could be detected. The authors also propose using lasers bounced between mirrors placed about 100 yards apart, with a light beam bouncing between them multiple times, to seek those small changes.
Particle species and light speed
The second paper proposes a different mechanism, but comes to the same conclusion that light speed changes. In that case, Gerd Leuchs and Luis Sánchez-Soto, from the Max Planck Institute for the Physics of Light in Erlangen, Germany, say that the number of species of elementary particle that exist in the universe may be what makes the speed of light what it is.
Leuchs and Sanchez-Soto say that there should be, by their calculations, on the order of 100 "species" of particle that have charges. The current law governing particle physics, the Standard Model, identifies nine: the electron, muon, tauon, the six kinds of quark, photons and the W-boson. (Wacky Physics: The Coolest Little Particles in Nature)
The charges of all these particles are important to their model, because all of them have charges. A quantity called impedance depends on the sum of those charges. The impedance in turn depends on the permittivity of the vacuum, or how much it resists electric fields, as well as its permeability, or how well it supports magnetic fields. Light waves are made up of both an electric and magnetic wave, so changing those quantities (permittivity and permeability) will change the measured speed of light.
"We have calculated the permittivity and permeability of the vacuum as caused by those ephemeral virtual unstable elementary particles," Soto-Sanchez wrote in an email to LiveScience. "It turns out, however, from such a simple model one can discern that those constants contain essentially equal contributions of the different types of electrically charged particle-antiparticle pairs: both, the ones known and those so far unknown to us."
Both papers say that light interacts with virtual particle-antiparticle pairs. In Leuchs' and Sanchez-Soto's model, the impedance of the vacuum (which would speed up or slow down the speed of light) depends on the density of the particles. The impedance relates to the ratio of electric fields to magnetic fields in light; every light wave is made up of both kinds of field, and its measured value, along with the permittivity of space to magnetic fields, governs the speed of light.
Some scientists are a bit skeptical, though. Jay Wacker, a particle physicist at the SLAC National Accelerator Laboratory, said he wasn't confident about the mathematical techniques used, and that it seemed in both cases the scientists weren't applying the mathematical tools in the way that most would.
"The proper way to do this is with the Feynman diagrams," Wacker said. "It's a very interesting question (the speed of light)," he added, but the methods used in these papers are probably not sufficient to investigate it.
The other issue is that if there really are a lot of other particles beyond what's in the Standard Model, then this theory needs some serious revision. But so far its predictions have been borne out, notably with the discovery of the Higgs boson. This doesn't mean there aren't any more particles to be found, but if they are out there they're above the energies currently achievable with particle accelerators, and therefore pretty heavy, and it's possible that their effects would have shown up elsewhere.
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