The first question was asked in 2009; the second in 2015.
Setterfield: This quote can be found in my second response to Mark Kluge, here.
Thank you for this question and bringing my quote back to my attention. Until I had checked on the data a few minutes ago, I was under the impression that tachyons had been experimentally verified. They were first discussed by Gerald Feinberg in 1967 in an article entitled "Possibility of Faster-Than-Light Particles" in Physical Review 159: 1089–1105. I recalled watching some cloud-chamber experiments at Adelaide University in the very late 1960's or early 1970's where the doctoral student pointed out to me some strange particle behavior. The student commented that they thought they might be tachyons, since the tracks had features in time and location which were consistent with that.
Your question has forced me to go back to the verified historical data, and you are right. Despite what I saw and was told, tachyons have not been experimentally observed, and therefore only remain a theoretical possibility. If they do exist, they would travel faster than light, since the speed of light is their minimum speed, not their maximum. In briefly reviewing the literature on tachyons, most thinking about them seems to have been confined by the theory of relativity. It might be wise to consider other options in case they actually do exist with some characteristics that are different from what relativity predicts. The basis of relativity is called into question by several facts. First, the Cosmic Microwave background Radiation (CMBR) presents an absolute universal rest frame against which all velocities can be compared. As Martin Harwit points out, this means that relativity can only be valid on very small scales, and not for macroscopic phenomena. Secondly, since the speed of light is inversely dependent upon the strength of the Zero Point Energy (ZPE) and the ZPE has increased with time, the current speed of light may not be the limiting velocity in the cosmos.
This second point was discussed in a New Scientist article for 1st November 2008, p.28-31 where it was pointed out that "there is a definite but unspecified maximum speed [in the universe] that the sum of individual relative speeds cannot exceed ... Light's special position in relativity is a historical accident ... Not only is light not necessary in relativity - there's no room in the theory for it." So the speed of light as we have it now need not be the maximum speed. Indeed, the ZPE research suggests that the maximum speed which attained at the origin of the cosmos was about 10 billion to 100 billion times higher. This leads to the speed of gravity issue.
Research by the late Tom Van Flandern on double star systems indicates that the speed of gravity may be of the order of 10 billion times the current speed of light or more. If this is so, the propogation of gravitational phenomena may reflect the original upper maximum speed. Since the speed of light is dependent upon the density of virtual particles, gravitational waves may be so long that virtual particles present no hinderance to them. If so, they might then travel at what has always been the upper maximum speed in the cosmos. It will be interesting to see how this aspect of the research develops.
With thanks again for helping me to get this straight,
July 16, 2009
Setterfield: You ask about tachyons and their existence. Yes, they are hypothetical particles; they have never been observed experimentally despite deliberate efforts in that direction. According to Einsteinian relativity theory they can theoretically exist, but if they do they have strange properties. For example, if they lose energy, they accelerate and go faster and faster. The more energy they lose, the faster they go until they reach an infinite speed. This sort of behavior is the direct result of Relativity theory; if the theory is wrong, the particle may not exist. If it does exist, it might have different properties to those relativity imposes upon it.
Another suggestion is that this particle might allow us to go back in time if it goes faster than light. Since relativity claims that light and time are inextricably linked (clocks can only transmit information at the speed of light), then traveling faster than light implies traveling back in time. Note that this prediction again hinges on relativity being correct. If the basis of this theory is wrong, then the prediction is also spurious.
So everything hangs on the correctness of Einstein's relativity. Relativity is based on two postulates, namely (1) The speed of light is a universal constant through all time. (2) There is no absolute reference frame for velocities anywhere in the universe; everything is relative to something else. BOTH of these postulates have been proven wrong.
First, the speed of light has been measured as decreasing with time. Second, the Cosmic Microwave Background Radiation (CMBR) has turned out to be an absolute reference frame for the universe. We have measured the motion of our solar system relative to the CMBR; we have measured the direction and speed of motion of our Galaxy in our Local Group relative to the CMBR; we have measured the speed and direction of motion of the Local Group of galaxies against the CMBR... In other words, the CMBR exists as the absolute reference frame for the whole universe.
So Einstein has been knocked out on both of his two postulates on which relativity has been built. Astrophysicist Martin Harwitt in his book "Astrophysical Concepts" states that because of the CMBR reference system, relativity is only correct on an atomic level, not on a macroscopic level (p.178-179). Therefore we may seriously doubt if tachyons exist in an Einstinian sense.
That having been said, Einstein had some correct predictions made by relativity. It was because of these that it gained widespread acceptance. However, it has been demonstrated in chapter 7 of the Monograph "Cosmology and the Zero Point Energy", along with other authors elsewhere, that all the major predictions of relativity can be produced if the action of the ZPE is considered. These include, the slowing of light in gravitational fields, the slowing of atomic clocks in gravitational fields, the bending of light by gravitational fields, the increase in atomic masses with velocity, the origin of gravitational fields, the advance in the perihelion of the planet Mercury, frame dragging, gravitational waves, gravitational lensing and so on. Since SED physics has demonstrated that the ZPE accounts for quantum phenomena, and it has subsequently been shown to predict relativistic phenomena, it therefore unifies the two branches of physics that scientists have desired to do since the time of Einstein.
On the ZPE approach to relativity, there are NO restrictive postulates, so lightspeed can vary over time, but in a way that is uniform throughout the cosmos at any instant. Because of this, the possibility that tachyons exist is a debatable question. I have not looked at the relevant equations in the ZPE approach to see if their existence is supported. If they do exist, I imagine that some of their properties might be different from Einsteinian expectations. But at the moment, this is all speculation.
I trust that gives you the background that you need.