# What limits the speed of light.

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#### tomorows_scientist

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ok this question seems kind of wierd in a way i guess. So light travels at 299,792,458 m/s if im not mistaken. What is limiting light to this speed?? why cant it travel lets say 299,999,999 m/s ??&nbsp; another question on light.... Does gravity slow down light (and in that case does gravity slow down things such as radio waves and gamma rays ect..). Ive heard that like a blackhole's gravity is so strong light cant escape right ?. so could there be gravity that is so strong that radio waves and such cant escape either ??? and one last question does light have mass ??<br /><h2 class="r"><font size="1"><br /></font></h2> <div class="Discussion_UserSignature"> </div>

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#### origin

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>ok this question seems kind of wierd in a way i guess. So light travels at 299,792,458 m/s if im not mistaken. What is limiting light to this speed?? why cant it travel lets say 299,999,999 m/s ??&nbsp; another question on light.... Does gravity slow down light (and in that case does gravity slow down things such as radio waves and gamma rays ect..). Ive heard that like a blackhole's gravity is so strong light cant escape right ?. so could there be gravity that is so strong that radio waves and such cant escape either ??? and one last question does light have mass ?? <br />Posted by tomorows_scientist</DIV><br /><br />The <em>speed</em> of light is <em>constant</em> so gravity does not slow it down.&nbsp; Radio waves and gamma rays are exactly the same thing as light, they are just at different frequencies.&nbsp; Visible light, radio waves, x-rays, gamma rays and microwaves are all just different frequencies of electro-magnetic waves (EM waves).&nbsp; So gamma and radio waves are not slowed down by gravity.</p><p>Light in a vacuum travels at the speed you indicated - never slower and never faster.&nbsp; However the speed of light in water or glass does travel at slower speeds, but it is still a <em>constant speed</em> in that medium.</p><p>In a black hole it is true that the light cannot escape, so it is also true that radio and gamma rays cannot escape.&nbsp; Immagine a neutron star that is so massive that it is almost a black hole, light would escape the surface of this star and the speed would not be affected, however the light <em>wave length</em> would be greatly affected it would be red shifted, that is to say the wavelength would become much longer.</p><p>Google&nbsp;special relativity and you will be able to learn more about this interesting subject.</p><p>edited to add:&nbsp; I don't think that there is an answer to why the actual speed of light is what it is.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### Saiph

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<p>let me pose your question a slightly different way, instead of "what keeps light at C" or "what slows light down". </p><p>Why does light go that fast?&nbsp; Why does it go that specific speed? </p><p>The reason for reposing the question is because of observation.&nbsp; Light goes at speed C, and only C, no matter what we do.&nbsp; </p><p>And the answer comes down to an analysis of what light itself really is.&nbsp; It is an electric field, and a magnetic field, both working and affecting eachother.&nbsp; They push and pull on eachother moving eachother along.&nbsp; The rate at which they move along is dependent, we find, ONLY on how fast these two forces can affect eachother.&nbsp; If they affect eachother slower than we measure, light would move slower.&nbsp; If the effect was more rapid, light would move faster.</p><p>The result, however, is the speed C, in a vacuum.&nbsp; And we find it entirely independent of any other factor. </p><p>&nbsp;</p><p>&nbsp;</p><p>Caveat:&nbsp; Light goes speed C in a vaccum.&nbsp; In other mediums it goes slower, due essentially to absorption - re-emission lag times. </p> <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

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#### vogon13

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<p>&nbsp;</p><p><br /> <img src="http://sitelife.space.com/ver1.0/Content/images/store/9/9/792d7fef-95a9-483d-9903-4eb15eb52e08.Medium.gif" alt="" /></p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

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#### lildreamer

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>ok this question seems kind of wierd in a way i guess. So light travels at 299,792,458 m/s if im not mistaken. What is limiting light to this speed?? why cant it travel lets say 299,999,999 m/s ??&nbsp; another question on light.... Does gravity slow down light (and in that case does gravity slow down things such as radio waves and gamma rays ect..). Ive heard that like a blackhole's gravity is so strong light cant escape right ?. so could there be gravity that is so strong that radio waves and such cant escape either ??? and one last question does light have mass ?? <br />Posted by tomorows_scientist</DIV><br /><br />I always like to direct people to information and let them discover for themselves the answer...</p><p>http://en.wikipedia.org/wiki/Speed_of_light</p><p>you'll find thats a good place to start to references that would lead you to more questions and therefore more answers...</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### MeteorWayne

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<p>The Physics of the Universe <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-laughing.gif" border="0" alt="Laughing" title="Laughing" /></p> <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'>ok this question seems kind of wierd in a way i guess. So light travels at 299,792,458 m/s if im not mistaken. What is limiting light to this speed?? why cant it travel lets say 299,999,999 m/s ??&nbsp; another question on light.... Does gravity slow down light (and in that case does gravity slow down things such as radio waves and gamma rays ect..). Ive heard that like a blackhole's gravity is so strong light cant escape right ?. so could there be gravity that is so strong that radio waves and such cant escape either ??? and one last question does light have mass ?? <br />Posted by tomorows_scientist</DIV></p><p>Prior to Einstein's special theory of relativity it was thought that light waves propagated through a medium in much the same way that water waves propagate through water or sound waves propagate through air.&nbsp; The medium was postulated something called the "aether" that was present throughout space.&nbsp; Experiments were performed to demonstrate the existence of this aether.&nbsp; Probably the most well-known experiment that attempted to find differences in the speed of light based on the relative motion of the Earth with respect to the aether.&nbsp; No such effects were found.&nbsp; No experiments since then have found any variation in the speed of light.&nbsp; Experimental evidence therefore supports the idea that the speed of light is a constant, independent of the inertial reference frame in which it is measured.</p><p>Einstein developed the special theory of relativity using two and only two assumptions.&nbsp; 1)&nbsp; The speed of light is the same in all inertial reference frames.&nbsp; 2)&nbsp; The laws of physics are the same in all inertial reference frames.&nbsp; You can in fact replace the 1st assumption with the assumption that there is some phenomena that propagates at the same speed, call it "x" in all inertial reference frames.&nbsp; From those two assumptions one can derive the Lorentz transformation that relates lengths and time in one inertial reference to lengths and time in another inertial reference frame.&nbsp; What you find is that the speed "x" is the maximum speed at which either matter or information can propagate, and it is the same in all reference frames.&nbsp; In the case of special relativity, the speed "x" is "c", the speed of light, and the constancy of c in all reference frames is supported by experiment.</p><p>What is also true is that special relativity makes other predictions, time dilation and length contraction for instance, that are also testable by experiment.&nbsp; In all cases the predictions of special relativity have been shown to be in agreement with experiment.&nbsp; So special relativity as a predictive theory seems to be on very firm ground, and it is a fundamental principle of that theory that light travels at one and only one speed in all inertial reference frames.</p><p>You can go further and invoke general relativity, but you still get the speed of light as a constant and as a limiting speed for matter and information.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>

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#### SHU

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<p><font size="2">To answer the last question, a photon is said to have no mass but it does have momentum.&nbsp; </font></p>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>To answer the last question, a photon is said to have no mass but it does have momentum.&nbsp; <br />Posted by SHU</DIV></p><p>Correct.&nbsp; More precisely a photon has no rest mass.&nbsp; It does have energy, and energy and mass are the same thing.</p><p>Also, to answer questions that I did not address in the earlier post,&nbsp;a black hole does not permit light&nbsp;or massive particles to escape.&nbsp; Radio waves are a form of light, just longer wavelength than the visible light&nbsp;that&nbsp;can be detected by&nbsp;human eyes, but photons nonetheless.</p><p>Basically nothing can escape from black hole.&nbsp;&nbsp;There is the possibility of&nbsp;emissions from a black&nbsp;hole in the form of Hawking radiation.&nbsp; But Hawking radiation is a quantum effect&nbsp;and what is being radiated is not anything that comes from the other side of the event horizon.&nbsp; There is also some question as to the fate of information that goes into a black hole.&nbsp;<br /></p> <div class="Discussion_UserSignature"> </div>

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#### lampblack

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; &nbsp;&nbsp;&nbsp; <br /> Posted by vogon13</DIV></p><p><font size="2">That was the first time I've laughed out loud all day -- and it's already 1:15 the following morning. Thanks, man! </font></p> <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

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#### why06

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>ok this question seems kind of wierd in a way i guess. So light travels at 299,792,458 m/s if im not mistaken. What is limiting light to this speed?? why cant it travel lets say 299,999,999 m/s ??&nbsp; another question on light.... Does gravity slow down light (and in that case does gravity slow down things such as radio waves and gamma rays ect..). Ive heard that like a blackhole's gravity is so strong light cant escape right ?. so could there be gravity that is so strong that radio waves and such cant escape either ??? and one last question does light have mass ?? <br /> Posted by tomorows_scientist</DIV></p><p>I've think we've touched on something like this before... It's the idea of what would happen if the speed of light changed. So you can answer your question of "What limits the speed of light?" By asking the question "What would happen if the speed of light did increase like you said?"&nbsp;</p><p>To which I would answer: Nothing.</p><p>Nothing would happen because everything else is limited by the speed of light. And honestly it wouldn't matter anyway because no matter how fast you go light will always be that much faster than you. So I think the speed of light is somehow limited by the speed of time itself. </p> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

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#### The_Science_Kid

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The speed of light is constant so gravity does not slow it down.&nbsp; Radio waves and gamma rays are exactly the same thing as light, they are just at different frequencies.&nbsp; Visible light, radio waves, x-rays, gamma rays and microwaves are all just different frequencies of electro-magnetic waves (EM waves).&nbsp; So gamma and radio waves are not slowed down by gravity.Light in a vacuum travels at the speed you indicated - never slower and never faster.&nbsp; However the speed of light in water or glass does travel at slower speeds, but it is still a constant speed in that medium.In a black hole it is true that the light cannot escape, so it is also true that radio and gamma rays cannot escape.&nbsp; Immagine a neutron star that is so massive that it is almost a black hole, light would escape the surface of this star and the speed would not be affected, however the light wave length would be greatly affected it would be red shifted, that is to say the wavelength would become much longer.Google&nbsp;special relativity and you will be able to learn more about this interesting subject.edited to add:&nbsp; I don't think that there is an answer to why the actual speed of light is what it is.&nbsp; <br />Posted by origin</DIV><br /><br />you forgot abaout relativity..<br />if the sun ceases to exist then we would first se the effect of this in 8 min, 19 sec beacuse it travels at the speed of light

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