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Speed of Light Measurement Using Ping

Posted by timothy on from the noise-assisted-sub-threshold-signal-detection dept.

Thomas Colthurst writes "You've no doubt already read the story of ping, but have you ever used it to measure the speed of light?" Here's a case where all that cat5 on college campuses can actually be used for education ;)

5 of 274 comments (clear)

  1. Re:How can this be accurate? by Score0,+Overrated · · Score: 2, Insightful

    All those things are mentioned are constant - so you can do it with a long wire, and with a short wire.

    Then you use the difference - and you've eliminated your constants.

  2. Re:How can this be accurate? by Score0,+Overrated · · Score: 2, Insightful

    Over 15000 samples it's going to be pretty constant.

    Perhaps you should read the paper?

  3. Re:Delays due to molecular friction? by cyberformer · · Score: 2, Insightful
    Electrons themselves can't travel at the speed of light. (They have a rest mass, and so according to relativity theory, would require infinite energy to accelerate them to this speed). The information is carried by electromagnetic waves (or photons), which pass through the electrons and do travel at the speed of light (because they have zero mass).

    Of course, the speed of light (or photons, or EM waves) in a copper wire is somewhat less than that of light in free space (but, interestingly, somewhat more that that in glass fiber, despite claims that fiber optics is "networking at the speed of light").

  4. Re:How can this be accurate? by TommyBear · · Score: 2, Insightful

    While were splitting hairs....

    That's by no means a constant, rather a mean or average of a group of values.

    This is by no means accurate, anaything can throw the values off (OS, System, Hardware, or disks). This is really a wastes of time, in it's current form, needs more thought.

  5. SI length of the meter? by j-beda · · Score: 4, Insightful
    The first footnote of the paper seems to be incorrect, it reads:

    [1] Since the mid eighties the meter has actually been defined in terms of a fixed, integral number of wavelengths of light from a particular optical transition. Since the frequency of that optical transition is tied up in (what are believed to be fundamental) constants of nature, the speed of light is defined through this definition of the meter.

    I had thought that the meter was defined as the distance light travels in 1/299792458 of a second, with the second being so many vibrations of a particular atom (cesium?).

    Yep, according to NIST the length has been defined this way for quite some time:

    The 1889 definition of the meter, based upon the artifact international prototype of platinum-iridium, was replaced by the CGPM in 1960 using a definition based upon a wavelength of krypton-86 radiation. This definition was adopted in order to reduce the uncertainty with which the meter may be realized. In turn, to further reduce the uncertainty, in 1983 the CGPM replaced this latter definition by the following definition:

    The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.