The Speed of Light might not be the Universe’s ultimate speed limit. Almost a century of testing seemed to show that no particle in the standard model could travel faster than the speed of light. Until now.
An Italian team of physicists firing a beam of neutrinos through more than 700 km of rock has discovered a small discrepancy, in more than 15,000 tests, some of the neutrinos arrived earlier than they should have, suggesting that they were travelling faster than the speed of light.
This is an incredible finding, and if it is validated through independent testing it could overturn the current understanding of physics.
What exactly happened?
The OPERA experiment is a giant underground detector designed to detect spontaneous neutrino transformations in a beam fired from CERN, through 732 km of rock to the OPERA detector in Italy.
Neutrinos are subatomic particles which are created by nuclear reactions and radioactive decay. They have very small, but non-zero mass, are electrically neutral (which allows them to pass through large amounts of matter without interacting with it) and move at speeds very close to the speed of light.
Sometimes, neutrinos can spontaneously change from one type of neutrino to another. The OPERA experiment was firing muon neutrinos and looking for transformations into tau neutrinos. The different types of neutrinos are called “flavours” and these transformations between different flavours are called neutrino flavour oscillations.
The OPERA experiment measured more than 15,000 bundles of neutrinos fired from CERN and discovered that the travel times are a few billionths of a second shorter than they should be. This may seem like a tiny difference. What can you do in a billionth of a second? Humans can’t even detect such a tiny fraction of time without mechanical assistance.
Light would cover the distance between CERN and OPERA in 2.4 thousandths of a second at almost 299,792,458 meters per second. The neutrinos are covering that distance 60 nanoseconds faster than light. 60 billionths of a second.
A fusion reaction inside a hydrogen bomb takes 20 to 40 nanoseconds.
The OPERA experiment may have just demolished the accepted theory that nothing can travel faster than the speed of light.
The speed of light is a fundamental constant in physics; we use it to establish the length of a meter. Until now, the speed of light has been accepted as the maximum speed at which light, energy, matter and information can travel in the universe.
Why is the speed of light the “speed limit”?
Albert Einstein came up with a little calculation in 1905 which goes like this:
E = mc2
If we translate that into English it states that the energy of a particle is equal to its mass multiplied by the square of the speed of light. Because the speed of light is so high, this means that even very low-mass particles contain a LOT of energy (hence the hydrogen bomb).
Einstein’s theory of Special Relativity has two other predictions (proven by experiment):
- The length of moving objects contracts, and this contraction is more extreme the faster the object is travelling.
- Moving clocks run more slowly the faster they are travelling.
For any particle trying to travel at (or extremely close to) the speed of light, these three principles come into play. The object becomes exponentially heavier as it approaches the speed of light, its length contracts and time slows until the factor (y) by which it’s length contracts and time dilates becomes infinite.
Thus, as far as we understand the universe, nothing, no particle, no packet of information, can travel faster than the speed of light.
How do we explain the OPERA observations?
- Oops, we made a mistake. Someone put in a few too many zeroes when they were setting up the calculator and it was all a big misunderstanding. I’m pretty sure that this is not the case. The OPERA team has made a lot of observations, found a consistent result and has gone to great lengths to check all their procedures to make sure that this was not an error, simple or otherwise. That doesn’t mean that the observed phenomenon is not due to some error or a variable that was not fully accounted for, but we won’t know until the paper is printed and put through rigorous scientific scrutiny.
- Oh! They aren’t our neutrinos but come from another source. D’oh! Again, the team has tested so many individual packets that it is probable that they are measuring their own neutrino stream. But, because neutrinos are produced in the nuclear reactions of the stars (amongst other sources) all around us and can travel great distances without interacting with baryonic (normal) matter, it is possible that the “faster than light” neutrinos actually come from somewhere else and were picked up on this detector by accident.
- These neutrinos are actually travelling faster than the speed of light! The results from the OPERA experiment are not conclusive, but they are certainly pointing and waggling their eyebrows. We may just have discovered particles travelling faster than c! Now, we need peer review and attempts to repeat the experiment by other teams which show the same result.
Does this mean that physics is not a good way to know our universe?
Physics and the tools it gives us are the best way that we have to understand our universe. It is built on the incremental removal of doubt. The slow and steady progress of testing and re-testing our ideas to eradicate the wrong ones and built upon the right ones.
This is exactly the kind of (potential) discovery that shows the power of physics and the robust nature of the system to re-evaluate and move forward.
Testing by other teams of physicists is extremely important at this point. We need as many minds as possible to work on this and see if it is what we think it is.
This is not going to give us faster than light spaceships
Because spaceships and everything that goes into them weigh a great deal more than a neutrino. We might be able to go very fast by shooting a stream of neutrinos out of the back of a spaceship, but c is still reserved for light beams and particles with negligible mass.