# The speed of light

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#### BoJangles

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<p style="margin-top:0cm;margin-left:0cm;margin-right:0cm" class="MsoNormal"><font face="Calibri" size="3">Everyone knows we are moving, our continents are drifting, our earth is spinning, the earth is orbiting the sun, the sun is orbiting the Milky Way, the Milky Way is moving in our local galactic cluster, and our galactic cluster is moving compared to the cosmic background radiation. </font></p><p style="margin-top:0cm;margin-left:0cm;margin-right:0cm" class="MsoNormal"><font face="Calibri" size="3">By searching the weird and wonderful internet we can find answers for the speed of light and varying speeds in which we are moving in relation to all the above rest frames. </font></p><p style="margin-top:0cm;margin-left:0cm;margin-right:0cm" class="MsoNormal"><font face="Calibri" size="3">Thought experiment: <span>&nbsp;</span>if we measure the speed of light, in direction A, B and C, knowing we are flying through space at massive speed (100&rsquo;s km/s) and knowing the speed of light is constant, should not the measurements be dramatically different? <span>&nbsp;</span>In fact couldn&rsquo;t we infer our exact speed and direction through space just by measuring the speed at which light takes to travel the same distance in 3 directions?</font></p> <div class="Discussion_UserSignature"> <p align="center"><font color="#808080">-------------- </font></p><p align="center"><font size="1" color="#808080"><em>Let me start out with the standard disclaimer ... I am an idiot, I know almost nothing, I haven’t taken calculus, I don’t work for NASA, and I am one-quarter Bulgarian sheep dog.  With that out of the way, I have several stupid questions... </em></font></p><p align="center"><font size="1" color="#808080"><em>*** A few months blogging can save a few hours in research ***</em></font></p> </div>

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#### MeteorWayne

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Everyone knows we are moving, our continents are drifting, our earth is spinning, the earth is orbiting the sun, the sun is orbiting the Milky Way, the Milky Way is moving in our local galactic cluster, and our galactic cluster is moving compared to the cosmic background radiation. By searching the weird and wonderful internet we can find answers for the speed of light and varying speeds in which we are moving in relation to all the above rest frames. Thought experiment: &nbsp;if we measure the speed of light, in direction A, B and C, knowing we are flying through space at massive speed (100&rsquo;s km/s) and knowing the speed of light is constant, should not the measurements be dramatically different? &nbsp;In fact couldn&rsquo;t we infer our exact speed and direction through space just by measuring the speed at which light takes to travel the same distance in 3 directions? <br />Posted by Manwh0re</DIV><br /><br />That is what was expected back before the 20th century. But in fact, light measures exavtly the same speed in all directions. Google the Michelson-Morley experiment. This discover was the foundation of Einsteins theories of relativity. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Everyone knows we are moving, our continents are drifting, our earth is spinning, the earth is orbiting the sun, the sun is orbiting the Milky Way, the Milky Way is moving in our local galactic cluster, and our galactic cluster is moving compared to the cosmic background radiation. By searching the weird and wonderful internet we can find answers for the speed of light and varying speeds in which we are moving in relation to all the above rest frames. Thought experiment: &nbsp;if we measure the speed of light, in direction A, B and C, knowing we are flying through space at massive speed (100&rsquo;s km/s) and knowing the speed of light is constant, should not the measurements be dramatically different? &nbsp;In fact couldn&rsquo;t we infer our exact speed and direction through space just by measuring the speed at which light takes to travel the same distance in 3 directions? <br />Posted by Manwh0re</DIV></p><p>As Wayne noted, the Michelson-Morley experiment was undertaken to find just the effect that you described, but instead found no effect whatever.&nbsp; Einstein's theory of special relativity took that one step further and adopted as a fundamental postulate that the speed of light is a constant, independent of the inertial reference frame in which it is measured.</p><p>While this result may seem counter-intuitive, it has been verified experimentally many times since the Michelson-Morley experiment and has profound implications for our understanding of physics.&nbsp; Among other things it shows that the concept of time is also dependent on the reference frame in which it is measured and this correction for time is important in our use of the Global Positioning System, which relies on very precise time measurements.&nbsp;</p><p>When you "Google" the Michelson-Morely experiment, I suggest that you also look at Special Relativity.<br /></p> <div class="Discussion_UserSignature"> </div>

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#### derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Everyone knows we are moving, our continents are drifting, our earth is spinning, the earth is orbiting the sun, the sun is orbiting the Milky Way, the Milky Way is moving in our local galactic cluster, and our galactic cluster is moving compared to the cosmic background radiation. By searching the weird and wonderful internet we can find answers for the speed of light and varying speeds in which we are moving in relation to all the above rest frames. Thought experiment: &nbsp;if we measure the speed of light, in direction A, B and C, knowing we are flying through space at massive speed (100&rsquo;s km/s) and knowing the speed of light is constant, should not the measurements be dramatically different? &nbsp;In fact couldn&rsquo;t we infer our exact speed and direction through space just by measuring the speed at which light takes to travel the same distance in 3 directions? <br /> Posted by Manwh0re</DIV></p><p>&nbsp;</p><p>I think the only way this might be possible if the astronaut was travelling in a closed circle and the photons also travel the same path within the closed circle.&nbsp; No matter what speed the astronaut is travelling, should he/she emit two photons when at the "12 o'clock" position (one released in the direction being travelled, and the other in the opposite direction), both photons will circumnavigate the circle at the same speed and still meet at the point they were released.&nbsp; However, due to closing speed, the astronaut will meet the photon that was released from behind sooner than the one that was released in the forward direction.&nbsp; From this, the speed of the craft could be determined.</p><p>Unfortunately, this can't happen in the real world because photons can't travel in a circle unless you can somehow get the photon to fall into orbit around a black hole right on the event horizon.&nbsp;&nbsp; Not sure any astronauts wan't to go there.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I think the only way this might be possible if the astronaut was travelling in a closed circle and the photons also travel the same path within the closed circle.&nbsp; No matter what speed the astronaut is travelling, should he/she emit two photons when at the "12 o'clock" position (one released in the direction being travelled, and the other in the opposite direction), both photons will circumnavigate the circle at the same speed and still meet at the point they were released.&nbsp; However, due to closing speed, the astronaut will meet the photon that was released from behind sooner than the one that was released in the forward direction.&nbsp; From this, the speed of the craft could be determined.Unfortunately, this can't happen in the real world because photons can't travel in a circle unless you can somehow get the photon to fall into orbit around a black hole right on the event horizon.&nbsp;&nbsp; Not sure any astronauts wan't to go there.&nbsp; <br />Posted by derekmcd</DIV></p><p>My head is starting to hurt on this one, but you can get light to go in a circle.&nbsp; Just use fiber optics.&nbsp; The speed will be a bit slower than c but it will be pretty close.&nbsp; However, you still will not be able to detect uniform motion or determine any sort of preferred rest frame.&nbsp; Without going through the problem in detail I'm pretty certain that your scenario will run into trouble determining when the astronaut intercepts the photon -- basically running into the issue of relativity of simultaneity.<br /></p> <div class="Discussion_UserSignature"> </div>

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#### derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>My head is starting to hurt on this one, but you can get light to go in a circle.&nbsp; Just use fiber optics.&nbsp; The speed will be a bit slower than c but it will be pretty close.&nbsp; However, you still will not be able to detect uniform motion or determine any sort of preferred rest frame.&nbsp; Without going through the problem in detail I'm pretty certain that your scenario will run into trouble determining when the astronaut intercepts the photon -- basically running into the issue of relativity of simultaneity. <br /> Posted by DrRocket</DIV></p><p>A photon travelling in a fiber optic cable made into a circle wouldn't be travelling in a circle.&nbsp; The beam of light, as whole, would be, but the individual photons are not.&nbsp; </p><p>Simultaneity still confuses me a bit, but for the astronaut travelling in a closed circle, I'm not sure if it would be an issue.&nbsp; Wouldn't the astronaut's entire reference frame be contracted.&nbsp; The distance all the way up to his exhaust pipe would be contracted.&nbsp; I would think that if the astronaut can "see" the entire circular path, then the whole path in the direction he is travelling would be contracted.&nbsp; This might mean there would be no issues.&nbsp; Honestly, I'm not quite sure.</p><p>I was thinking more along the line of non-relativistic speeds.&nbsp; Like 2 cars on a race track and me jogging in one direction.&nbsp; I'm going to meet the car travelling the opposite direction first, but the cars will meet where they started.&nbsp; I was just trying to provide a simple picture.</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### BoJangles

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<p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">Thanks I appreciate all your comments</font></p> <div class="Discussion_UserSignature"> <p align="center"><font color="#808080">-------------- </font></p><p align="center"><font size="1" color="#808080"><em>Let me start out with the standard disclaimer ... I am an idiot, I know almost nothing, I haven’t taken calculus, I don’t work for NASA, and I am one-quarter Bulgarian sheep dog.  With that out of the way, I have several stupid questions... </em></font></p><p align="center"><font size="1" color="#808080"><em>*** A few months blogging can save a few hours in research ***</em></font></p> </div>

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#### Mee_n_Mac

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>A photon travelling in a fiber optic cable made into a circle wouldn't be travelling in a circle.&nbsp; The beam of light, as whole, would be, but the individual photons are not.&nbsp; Simultaneity still confuses me a bit, but for the astronaut travelling in a closed circle, I'm not sure if it would be an issue.&nbsp; Wouldn't the astronaut's entire reference frame be contracted.&nbsp; The distance all the way up to his exhaust pipe would be contracted.&nbsp; I would think that if the astronaut can "see" the entire circular path, then the whole path in the direction he is travelling would be contracted.&nbsp; This might mean there would be no issues.&nbsp; Honestly, I'm not quite sure.<u>I was thinking more along the line of non-relativistic speeds.&nbsp; Like 2 cars on a race track and me jogging in one direction.&nbsp; I'm going to meet the car travelling the opposite direction first, but the cars will meet where they started.&nbsp; I was just trying to provide a simple picture.</u> <br />Posted by <strong>derekmcd</strong></DIV><br /><br />This is the basic operating priniciple behing a ring laser (or fiber optic)&nbsp;gyro.&nbsp; There's Doppler shift in those devices as well but I see no reason, given&nbsp;a long enough&nbsp;path length, that relative timing between 2 photons or packets of photons couldn't be used to determing rotation rate of the detector (astronaut).&nbsp; I think the grey dots in this wiki animation show what you're trying to say. </p><p>BTW this doesn't answer the OP's question.&nbsp; Let me ponder that for a bit but my inclination is say no you can't measure your velocity his way.</p> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

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