Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

According to relativity,nothing can break light barrier.But a recent preprint shows energy transmission of commercial electric power (f=60Hz) is faster than light. (It is not the drift velocity of electrons because energy transport depends on the electromagnetic field instead of charged particles). Moreover, the speed increases as its frequency decreases so the value is infinity for a direct current (f=0).That is action at a distance (instantaneous interaction)!

My question is whether it is possible to design a circuit to compare this speed with c in lab? For example,time-delay of an electromagnetic signal through a free space distance of 3m is $10^{-8}\text{ s}$. As to direct current along a copper wire, however, there should be no delay. Is the difference detectable? I'm interested to the experiment because it is of substantial significance to measure the rate of electric power for electrical engineering not matter the result can exceed c or not.

share|improve this question
Also be aware that you can get a paper on arxiv without peer review. –  Colin K Aug 24 '11 at 3:00
Often times very strange papers make it through the very rudimentary process on arXiv (example: arxiv.org/pdf/0710.3438v1 ). Without link it would be hard to understand what is being said. –  Benjamin Horowitz Aug 24 '11 at 5:03
Looking at the link, I see that it's not just a preprint but an actual published paper - which doesn't necessarily make it true, but this is at least something worth looking into. –  David Z Aug 24 '11 at 8:09
The "speed of light" in a transmission line is lower than c, for the record. There is, of course, a delay when propagating DC down a cable (step function). Not sure what this paper is saying. "They lead to a same conclusion that energy(mass) can exceed the speed of light in vacuum." –  endolith Aug 24 '11 at 19:24
Something similiar from the 1980's gsjournal.net/Science-Journals/Journal%20Reprints-Mechanics%20/… Showing evidence of 2 different superluminal velocities one instantaneous and one at 2*C along coaxial cable. I tried to replicate it in the early nineties using fast photodiodes at different distances picking up a flash of light and relaying through different lengths of co-ax but I did not find anything, but my test equipment was being really pushed. I intend to try again when i retire :) –  Alan Dixon Jan 30 at 8:08
add comment

2 Answers

Ignoring whether the claim is valid or not, there should be no problem in measuring the velocity of a signal on a transmission line compared to the velocity of light.

The in the lab part might present a problem because of the small distances, but in principle a simultaneous signal sent on the transmission line and on a laser beam ( which can go for kilometres) should easily allow to measure which comes first.

share|improve this answer
One problem that was prevalent in the "superluminal tunneling" setup was how the arrival of the signal is actually defined, and what exactly is measured (e.g. group velocity?) –  Lagerbaer Aug 24 '11 at 4:06
If I were setting up the experiment I would make the same pattern, a square pulse for example, the front sent simultaneously and measured as front at the arrival station. I can see problems like that when measuring within solids, but here we are talking about transmission lines. –  anna v Aug 24 '11 at 5:19
@anna: yes, the square pulse on a transmission line will neither be generated or survive transmission as a perfect square. so you need to be very careful when defining the timing if you're measuring very small time differences (like a metre of propagation). but an experiment with a hundred meters of propagation line would be much better :) –  BjornW Aug 24 '11 at 8:24
add comment

In physics where where you make time critical measurements you often use the fast nim signal, which is essential a dc signal. To make e.g one signal arrive later at your electronics you use delay boxes, that is just cable inside a box. You can also use small pieces of cable to make a small delay, and it is usually written on the cable how much delay it corresponds to e.g. 1 nano second (= app 20 cm cable).

The signal speed is not infinite, but around 20 cm/ns depending on the dielectrica in the cable.

share|improve this answer
add comment

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.