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Thread: Cosmic Speed Limit

  1. Top | #21
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    Quote Originally Posted by skepticalbip View Post
    Quote Originally Posted by Loren Pechtel View Post
    I must nitpick: Mr. One Mug effectively says you can't accelerate anything to superluminal velocity. That does not, however, preclude the existence of particles whose only existence is at superluminal velocity. Useless for travel, not useless for communications.

    After all, the same equation says you can't accelerate anything to lightspeed, yet we talk by radio all the time.

    (Now, the paradoxes are another matter.)
    Not exactly. It is anything with rest mass (fermions) that can't be accelerated to lightspeed. We talk by radio using photons (EM radiation) which have no rest mass and can only exist at c... at least according to uncle Al and cousin Max.

    ETA:
    Now if you come up with a way of using tachyons (which may or may not exist) for communication it would earn you Nobel prizes in a couple different fields.
    Fermions--always below lightspeed. Photons--always at lightspeed, but we can manipulate them to great benefit. Tachyons, if they exist, would obviously always be above lightspeed. We have no evidence of them--but neither do they go against physics. When the rules permit something there's a good chance it exists.

  2. Top | #22
    Administrator lpetrich's Avatar
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    Quote Originally Posted by skepticalbip View Post
    Quote Originally Posted by bilby View Post
    c as a limit applies equally in EVERY inertial frame. That's the great and extraordinary finding that made Einstein famous.
    Uncle Albert's unique step here is that he dared to accept the result of the many, many measurements that showed c was constant for any observer. No other scientist at the time dared to risk their reputation by contradicting Newton... that is if they even considered that Newton could have been wrong. The common interpretation was that either the measurements or set ups were wrong.
    There was a good reason to want to stick with Newtonian mechanics. It was enormously successful. Like being able to predict the motions of the celestial bodies. Not only their two-body limits, but also their perturbations on each other. That's how Neptune was predicted from discrepancies between Uranus's calculated and observed motions.

  3. Top | #23
    Veteran Member skepticalbip's Avatar
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    Quote Originally Posted by lpetrich View Post
    Quote Originally Posted by skepticalbip View Post
    Quote Originally Posted by bilby View Post
    c as a limit applies equally in EVERY inertial frame. That's the great and extraordinary finding that made Einstein famous.
    Uncle Albert's unique step here is that he dared to accept the result of the many, many measurements that showed c was constant for any observer. No other scientist at the time dared to risk their reputation by contradicting Newton... that is if they even considered that Newton could have been wrong. The common interpretation was that either the measurements or set ups were wrong.
    There was a good reason to want to stick with Newtonian mechanics. It was enormously successful. Like being able to predict the motions of the celestial bodies. Not only their two-body limits, but also their perturbations on each other. That's how Neptune was predicted from discrepancies between Uranus's calculated and observed motions.
    Hey, I am a big Newton fan. Personally, I think he was more of an original thinker than Einstein. Newton's physics came damn close and his work made Einstein's possible. Newtonian mechanics did allow for the prediction of Neptune however they also predicted a planet, Vulcan, inside Mercury's orbit to account for the precession of Mercury's orbital eccentricity around the sun. There was a long unsuccessful search for Vulcan. Relativity was able to account for the precession so no one looks for Vulcan any longer.

  4. Top | #24
    Administrator lpetrich's Avatar
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    Quote Originally Posted by skepticalbip View Post
    Hey, I am a big Newton fan. Personally, I think he was more of an original thinker than Einstein. Newton's physics came damn close and his work made Einstein's possible. Newtonian mechanics did allow for the prediction of Neptune however they also predicted a planet, Vulcan, inside Mercury's orbit to account for the precession of Mercury's orbital eccentricity around the sun. There was a long unsuccessful search for Vulcan. Relativity was able to account for the precession so no one looks for Vulcan any longer.
    Except that there have been searches for intra-Mercurian asteroids.

    A New Observational Search for Vulcanoids in SOHO/LASCO Coronagraph Images - ScienceDirect - 2000
    The search for vulcanoids in the 2008 total solar eclipse | SpringerLink - 2008
    A search for Vulcanoids with the STEREO Heliospheric Imager - ScienceDirect - 2013

  5. Top | #25
    Fair dinkum thinkum bilby's Avatar
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    Quote Originally Posted by lpetrich View Post
    Quote Originally Posted by skepticalbip View Post
    Hey, I am a big Newton fan. Personally, I think he was more of an original thinker than Einstein. Newton's physics came damn close and his work made Einstein's possible. Newtonian mechanics did allow for the prediction of Neptune however they also predicted a planet, Vulcan, inside Mercury's orbit to account for the precession of Mercury's orbital eccentricity around the sun. There was a long unsuccessful search for Vulcan. Relativity was able to account for the precession so no one looks for Vulcan any longer.
    Except that there have been searches for intra-Mercurian asteroids.

    A New Observational Search for Vulcanoids in SOHO/LASCO Coronagraph Images - ScienceDirect - 2000
    The search for vulcanoids in the 2008 total solar eclipse | SpringerLink - 2008
    A search for Vulcanoids with the STEREO Heliospheric Imager - ScienceDirect - 2013
    There's a rather nice map of the Solar System's asteroids and other objects above 10km here.

    It shows a few Mercury crossing asteroids, but only one that was inside Mercury's orbit at the time of the snapshot (New Year's Eve 1999)

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