So what about the consequence that comes out of it all that "nothing"no kind of energy or other causal influencecan travel faster than light? It's probably the most popularly quoted line whenever relativity is mentioned, and so some words on it wouldn't be out of order here, although they are necessarily speculative.
The limit follows from the form of the equations that express velocity as a fraction of the speed of lightyou can't have anything greater than a hundred percent of itself. Put that way it sounds a bit trite, rather than expressing anything especially profound. The same fraction forms the basis of all the velocity-dependence equations, such as that for mass, which increases to infinity as velocity approaches lightspeed, and time, which tends to a standstill. So accelerating a massive object to lightspeed would require an infinite input of energy, and since that's impossible the implication is you can't get there. All experiments on fast-moving particles confirm the predictions, and as far as some kinds of minds are concerned, those that seem to need limits and restrictions to guide their lives, that closes the subject. If all of the human race thought that way we'd never have bothered trying to build flying machines because the eminences who knew better had proved them impossible.
One person who didn't think that way was the aerospace engineer, science-fact and science-fiction writer G. Harry Stine. 83 As Stine pointed out, and we have spent space enough being reminded of here, relativity theory derives primarily from Maxwell's equations of electromagnetics, and the evidence supporting it comes from a narrow range of experiments using charged particles accelerated by electric or magnetic fields. The way mass is determined (or, strictly speaking, the mass-charge ratio) is by measuring the reaction to other fields or the momentum transfer of impacts with other particles. It's an extremely restricted sample for building overall pictures of the world.
Maxwell's equations, in essence, state that a charged particle, (a) at rest possesses an electric field; (b) moving at a steady velocity generates a magnetic field; (c) accelerating, radiates away some of the applied energy, i.e., not all of the accelerating energy will appear as motion of the particle. The theory derived from those statements and the experiments designed to test it say that the "deficit" not appearing as acceleration increases with velocity. It's as if energy is being supplied faster than the system can absorb it by changing its state motion. It sheds the excess by radiation, and the faster it moves the greater a proportion it has to get rid of until it's radiating all of it, at which point it can't be accelerated further. Interestingly, the equations of aerodynamics for propeller-driven aircraft take the same form, approaching a limit at the speed of sound through air. As a plane approaches the speed of sound, more of the propulsion energy goes into generating shock waves that radiate it away, and accelerating the plane further becomes progressively harder. It exhibits an increase of "aerodynamic mass."
In his general field equations, Einstein theorized that a gravitational "charge" (mass) would produce a field analogous to the magnetic field when in motion. Furthering the analogy, it should produce a gravitational radiation when accelerated. This would be true, for example, of any spinning mass. What is the nature, Stine wonders, of the peculiar forces we're all familiar with that hold gyros at strange angles when intuition says they ought to fall over, and play havoc when you try to carry them around corners? All of the second-derivative Newtonian forces are already accounted for, since a rotating mass undergoes constant acceleration. [Second-derivative of space with respect to time, hence d2x/dt2 , or d/dt(momentum).] Stine hypothesizes a Newtonian-like third-derivative force that's proportional to rate of change of acceleration (d3x/dt3)a quantity referred to as "surge"and associated with it, a combined gravitational and inertial "GI" field playing a role comparable to the electromagnetic field, but one derivative step up from the counterpart in the charged domain. This field is also able to accept excess energy beyond the ability of an accelerating body to absorb quickly enough. But in the case of a charged body, electromagnetic reactions account for all the energy supplied by the time lightspeed is reached, and no further acceleration beyond that limit is possible.
But if that "barrier" could be overcome, the GI field would still be available to continue absorbing excess energy, meaning that acceleration could be pushed further. In other words, only charged particlesthe magnetic-propeller-driven kinds used in all our relativistic experimentsare limited to lightspeed. Uncharged matterproviding you had a means of accelerating itwould have a limiting velocity set by the currently unknown properties of GI propagation. What might that be? Anybody's guess, really. But Stine cites an estimate made in 1961 by William Davis, S. A. Korff, and E. L. Victory, based on the apparent stability and relative sizes of structures from binary stars, up through galaxies, to the entire universe, that gave a range of from 10,000 to 15,000 times lightspeed. He gives them the unit "Mikes," after A. A. Michelson.
In considering possibilities of this kind, mention should also be made of the intriguing "field distortion theory" (FDT) developed by Steve Dinowitz. 84 As with other alternatives that we've looked at, the classical Galilean transforms hold, and the same experimental results are expected that support SRT. FDT begins with a model of propagation in which the field lines around a charged body such as an electron behave like radial compressible springs (recalling the charge redistribution treated by Beckmann) and exhibit an aerodynamic-like distortion when the source moves through a gravitational field. The body's inertial mass is then related to this distortion of its field, resulting in an expression for mass in which the determining factor is the motion through the locally dominant gravitational field and the field's energy density. As a consequence, mass-increase and time-slowing are not pure velocity effects but also depend on the comparative field energy densities of the body being accelerated and other bodies in the vicinity. These effects would not occur to anywhere near the degree expressed by the relativistic limits when the gravitational field due to the accelerated body predominates. This condition is never realized on the Earth's surface, where the gravitation of accelerated particles like electrons or protons is vanishingly small compared to the Earth's, and the equations of FDT reduce to those of SRT. But it would occur naturally in the case of, say, a spacecraft leaving the Solar System.
Little of this impresses the custodians of the sacred dogma, however. Heretical findings have been reported in connection with things like experiments performed on rotating platforms where light beams seem clearly to be traveling around in opposite directions at different speedsthe basic operating principle of the laser-ring gyro, which works just fineand the synchronization of GPS satellites. 85 True enough, a relativistic explanation can usually be produced eventuallytypically in the form of wheeling in GRT to account for a contradiction of something that SRT said in the first placebut always after the event, uncomfortably suggestive of the way in which with enough ingenuity a new epicycle could always be added to Ptolemy's hopelessly over-elaborate system to explain the latest data. Otherwise the problem is declared "meaningless." But if the underlying premises of relativity are inconsistent as some have argued it's really immaterial, since it can be proved that logic based on inconsistent premises can be made to agree with any conclusion. 86
As with the Church of old, it seems to be "political" scientists of an authoritarian bent who end up directing and bureaucratizing the system. This becomes particularly true of "Big" science, where so much of what will be rewarded by recognition, funding, and appointments depends on political approval. But good science works best when left to muddle through in its own sloppy and democratic ways. Maybe what we need is a Constitutional amendment separating Science and State. Government should no more be deciding what good science shall be than dictating or suppressing religion.