Time Dilation

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BoJangles

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<p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">If you look at a light beam that has traversed a billion light years, how old is that light, taking into consideration time dilation, i.e. time dilation at the speed of light it quite large I understand is it not ?</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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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If you look at a light beam that has traversed a billion light years, how old is that light, taking into consideration time dilation, i.e. time dilation at the speed of light it quite large I understand is it not ? <br /> Posted by Manwh0re</DIV><br /></p><p>If you are considering this from a time dilation perspective, the photon doesn't have an age.&nbsp; The photons gamma factor is infinite... it doesn't experience time and doesn't age.&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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BoJangles

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If you are considering this from a time dilation perspective, the photon doesn't have an age.&nbsp; The photons gamma factor is infinite... it doesn't experience time and doesn't age.&nbsp; <br />Posted by derekmcd</DIV><br /><br /><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">The time dilation affects as you approach the speed of light is a lot greater than at half the speed of light. </font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">Although a photon doesn&rsquo;t age, is it possible to hypothetically calculate the age of the photon in regards to dilation as experienced by the photon travelling say a billion light years. I.e. if you were that photon, how much would you age? , or dose the maths run into infinity.</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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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The time dilation affects as you approach the speed of light is a lot greater than at half the speed of light. Although a photon doesn&rsquo;t age, is it possible to hypothetically calculate the age of the photon in regards to dilation as experienced by the photon travelling say a billion light years. I.e. if you were that photon, how much would you age? , or dose the maths run into infinity. <br /> Posted by Manwh0re</DIV></p><p>Anything traveling at C will not age due the length contraction being infinite.&nbsp; In other words, the travel time for the photon between any events it might experience is instantaneous.&nbsp;&nbsp; If you, in a spacship, traveled to Alpha Centauri (some 4.2 light years distance from Earth) at the speed of light, you wouldn't experience and time changing.&nbsp; You would arrive instantly in your reference frame.&nbsp; In your reference frame, the length contraction would be such that AC would appear right infront of you as soon as you hit light speed.&nbsp; Your clock wouldn't have ticked at all and your ships odometer wouldn't register any mileage. </p><p>An observer on Earth would see that the trip took you 4.2 years and that you travelled 4.2 light years distance.</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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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Anything traveling at C will not age due the length contraction being infinite.&nbsp; In other words, the travel time for the photon between any events it might experience is instantaneous.&nbsp;&nbsp; If you, in a spacship, traveled to Alpha Centauri (some 4.2 light years distance from Earth) at the speed of light, you wouldn't experience and time changing.&nbsp; You would arrive instantly in your reference frame.&nbsp; In your reference frame, the length contraction would be such that AC would appear right infront of you as soon as you hit light speed.&nbsp; Your clock wouldn't have ticked at all and your ships odometer wouldn't register any mileage. An observer on Earth would see that the trip took you 4.2 years and that you travelled 4.2 light years distance. <br />Posted by derekmcd</DIV><br /><br /><font face="Calibri"><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3">Wow that&rsquo;s heavy&hellip; </font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3">An seems a little anti intuitive and way too far out, but i can live with it.</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3">Relativity certainly as some splaining to do (for me anyway).</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3">Being inquisitive as I am, I'm wondering if Einstein didn&rsquo;t hack time, what would need to be changed to make up for observations, i.e. e=mc^2 in relation to mass or speed or something I suppose.</font></p></font> <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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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Wow that&rsquo;s heavy&hellip; An seems a little anti intuitive and way too far out, but i can live with it.Relativity certainly as some splaining to do (for me anyway).Being inquisitive as I am, I'm wondering if Einstein didn&rsquo;t hack time, what would need to be changed to make up for observations, i.e. e=mc^2 in relation to mass or speed or something I suppose. <br /> Posted by Manwh0re</DIV></p><p>&nbsp;</p><p>Not really heavy at all... it' light!!! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-laughing.gif" border="0" alt="Laughing" title="Laughing" /></p><p>Einstein may have hacked time with Special Relativity, but he couldn't have done it without Hendrik Lorentz writing the software first.&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'>Wow that&rsquo;s heavy&hellip; An seems a little anti intuitive and way too far out, but i can live with it.Relativity certainly as some splaining to do (for me anyway).Being inquisitive as I am, I'm wondering if Einstein didn&rsquo;t hack time, what would need to be changed to make up for observations, i.e. e=mc^2 in relation to mass or speed or something I suppose. <br />Posted by Manwh0re</DIV></p><p>Before Einstein proposed the special theory of relativity bits and pieces had been proposed in an ad hoc manner to explain what seen experimentally.&nbsp; The&nbsp;research in progress would probably have come up with the special theory even if Einstein himself had not proposed it (the general theory did not have such early signals).&nbsp; So, the answer to your question is that to explain the observations we pretty well need the special theory and if Einstein had not proposed it someone else would have.&nbsp; <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'>Before Einstein proposed the special theory of relativity bits and pieces had been proposed in an ad hoc manner to explain what seen experimentally.&nbsp; The&nbsp;research in progress would probably have come up with the special theory even if Einstein himself had not proposed it (the general theory did not have such early signals).&nbsp; So, the answer to your question is that to explain the observations we pretty well need the special theory and if Einstein had not proposed it someone else would have.&nbsp; <br /> Posted by DrRocket</DIV></p><p>I think Einstein happened to be the first to completely abandon the idea of Aether and that's why SR was successful.&nbsp; I agree... It was just a matter of time.&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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killium

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<p>repling to:</p><p>Anything traveling at C will not age due the length contraction being infinite.&nbsp; In other words, the travel time for the photon between any events it might experience is instantaneous.&nbsp;&nbsp; If you, in a spacship, traveled to Alpha Centauri (some 4.2 light years distance from Earth) at the speed of light, you wouldn't experience and time changing.&nbsp; You would arrive instantly in your reference frame.&nbsp; In your reference frame, the length contraction would be such that AC would appear right infront of you as soon as you hit light speed.&nbsp; Your clock wouldn't have ticked at all and your ships odometer wouldn't register any mileage.</p><p>-----------------------------------------------------------------------------------------------------------------------</p><p>So it means that once your vehicle reach speed of light (let's suppose it's possible), the rest of the ride is free ? (you can't expense energy if you have no time to do so...).</p><p>&nbsp;</p><p>Something about all this just jumped to my eyes: Red-Shift. This is due to photons loosing energy while in transit right ? If a photon experiences no time, how could one (or many) of its caracteristics (like energy level) change ? And how does that change can then be proportionnal to time ? Can someone points me to where i goofed ? lol!</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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SpeedFreek

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So it means that once your vehicle reach speed of light (let's suppose it's possible), the rest of the ride is free ? (you can't expense energy if you have no time to do so...) <br /> Posted by killium</DIV></p><p>Well, as you are aware you are trying to describe the impossible, what sort of answer do you expect to get? Nothing with any mass can be accelerated to the speed of light. If we just "suppose" it is possible, without modifying the theory that says it is impossible, the results will be nonsensical.</p><p>Unless subject to other forces (like gravity), once you reach <em>any</em> speed you need not expend any more energy to stay at that speed - if you push something in space it keeps on moving.&nbsp;</p><p>Consider this... if you were moving at the speed of light and no time was passing for you or your vehicle, and you could, from your point of view, instantaneously travel to anywhere in the universe, <em>how could you stop when you got there?</em> </p><p>&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Something about all this just jumped to my eyes: Red-Shift. This is due to photons loosing energy while in transit right ? If a photon experiences no time, how could one (or many) of its caracteristics (like energy level) change ? And how does that change can then be proportionnal to time ? Can someone points me to where i goofed ? lol!&nbsp; <br /> Posted by killium</DIV></p><p>You are assuming that redshift is <em>due</em> to photons losing energy, but have you considered that <strong>both</strong> the redshift and the loss of energy are due to another cause? If you think of the doppler shift of sound as a train approaches and then recedes, the sound itself is not changed in any way during the process - the sound would be normal for a listener that is moving alongside the train. It is the frame of reference of the listener, or the observer, that is changing, not the light or the sound.</p><p>The expansion of the universe is described in cosmology as the <em>change in the scale factor of the background metric</em>. The change in this scale factor during the billions of years between the emission and detection of the light is what can be thought to cause an apparent redshift. It is as if we are moving away from the source of the light which results in a similar effect to the lowering of the frequency of the sound of the train as it recedes from us. The sound itself remains at the same frequency throughout, but that frequency apparently changes depeding on the frame of reference of the listener.</p><p>If you fire a ball-bearing at a target and it leaves the muzzle of the gun at 200mph, but the target is receding at 100mph, the ball-bearing will be moving at 100mph relative to the target when it hits it. But the ball-bearing did not lose that energy... </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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Ranjha

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What if we ARE moving at the speed of light?&nbsp; How do we experimentally check that we are NOT? <div class="Discussion_UserSignature"> <p><font size="2" color="#cc33cc"><font color="#000000">"I'm normally not a praying man, but if you're up there, please save me Superman."<br /></font><span style="font-size:11px;color:#339999">By: Homer Simpson<br /></span></font></p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>What if we ARE moving at the speed of light?&nbsp; How do we experimentally check that we are NOT? <br />Posted by Ranjha</DIV></p><p>Relative to&nbsp; what ?</p> <div class="Discussion_UserSignature"> </div>
 
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SpeedFreek

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>What if we ARE moving at the speed of light?&nbsp; How do we experimentally check that we are NOT? <br /> Posted by Ranjha</DIV></p><p>As DrRocket asked, relative to what?</p><p>As we look out into the universe we see that, the further away a galaxy is from us, the faster it is apparently receding from us. Any galaxy with a redshift of z>1.4, which equates to a light travel time of over 9 billion years, is apparently receding from us faster than the speed of light. The cosmological principle tells us that, from the point of view of those galaxies today, they would see <em>our</em> galaxy (or more accurately, what was here 9 billion years ago) as receding from <em>them</em> at a speed faster than light.</p><p>I should point out that no galaxy is actually moving through space at the speed of light or faster, but rather the scale factor of the universe is increasing in such a way that objects will seem to have receded at those speeds. Nothing ever overtakes a photon.&nbsp;</p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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trumptor

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<p>With the whole time dilation discussion finally here, I get to try out my theory<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" /></p><p>&nbsp;</p><p>I assume everyone agrees that a person that runs every day tends to live longer than a couch potato. Is it really that the "running" itself is making him/her live longer or the fact that time is slightly dialating for them everytime they run as opposed to the couch potato??? If that's the case then I'd much rather hop in my car and ride around for 5 miles a day than run!<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><em><font color="#0000ff">______________</font></em></p><p><em><font color="#0000ff">Caution, I may not know what I'm talking about.</font></em></p> </div>
 
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BoJangles

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<p><font face="Calibri"><span class="mceitemhidden"><span class="mceitemhidden"><font size="3"><span class="mceitemhidden">I'm wondering&hellip; We should all be time </span><span class="mceitemhiddenspellword1">dilating</span><span class="mceitemhidden"> anyway; with the spin and proper motions of our planet, our solar system, our galaxy. </span><span class="mceitemhiddenspellword1">In fact</span><span class="mceitemhidden"> people on the equator you should be younger then people closer to the earth&rsquo;s axis, which would probably cancel out an affects of running or driving a car ( in some situations ).</span></font></span></span></font></p><p><font face="Calibri"><span class="mceitemhidden"><span class="mceitemhidden"><font size="3"></font><span class="mceitemhidden"><font size="3">Even more to the point if you were to plot our planet in relation to the CMB, we would be doing this very complex spirograph, there will obviously be some point in time where we speed up and slow down n relation to whatever reference frame. I wonder what affect they have on anything.</font></span></span></span></font></p><p><font face="Calibri"><span class="mceitemhidden"><span class="mceitemhidden"><span class="mceitemhidden"><font size="3">A question how does time dilation affect us as a result of all the motion we are feeling because of the moving systems we are in? When calculated some of those are moving quite fast?</font></span></span></span></font></p><p><font face="Calibri"><span class="mceitemhidden"><span class="mceitemhidden"><span class="mceitemhidden"><font size="3">And I still don&rsquo;t see why light is measured the same speed in all directions, these questions seem related. Sorry if I'm sounding like a broken record, I'm slowly understanding this stuff.</font></span></span></span></font> </p><p>&nbsp;</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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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm wondering&hellip; We should all be time dilating anyway; with the spin and proper motions of our planet, our solar system, our galaxy. In fact people on the equator you should be younger then people closer to the earth&rsquo;s axis, which would probably cancel out an affects of running or driving a car ( in some situations ).Even more to the point if you were to plot our planet in relation to the CMB, we would be doing this very complex spirograph, there will obviously be some point in time where we speed up and slow down n relation to whatever reference frame. I wonder what affect they have on anything.A question how does time dilation affect us as a result of all the motion we are feeling because of the moving systems we are in? When calculated some of those are moving quite fast?And I still don&rsquo;t see why light is measured the same speed in all directions, these questions seem related. Sorry if I'm sounding like a broken record, I'm slowly understanding this stuff. &nbsp; <br />Posted by Manwh0re</DIV></p><p>First, motion is relative.&nbsp; We measure life spans in our earthly frame of reference.&nbsp; There is some effect from the items that you mention.&nbsp; But if you consider that the effect of time dilation is exceedingly small except at relative velocities very near the speed of light, then you find that the effects on life span are swamped by other sources of variation.&nbsp; They just are not important.&nbsp; The speeds of those phenomena may seem very high to you, and they are by the standards of normal experience, but they are in fact very very slow when compared to the speed of light.&nbsp; Remember that light travels at 30,000,000 kilometers per second.</p><p>The questionas to WHY light speed is measured to be constant in all directions and independent of the reference frame is not a question that science can answer.&nbsp; What we know is that all measurements show it to be constant and that the theory based on the assumption that it is constant, relativity, has been demonstrated to be very accurate.&nbsp; We don't know WHY light behaves as it does but science has a very good and accurate picture of HOW it behaves.&nbsp; </p> <div class="Discussion_UserSignature"> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm wondering&hellip; We should all be time dilating anyway; with the spin and proper motions of our planet, our solar system, our galaxy. In fact people on the equator you should be younger then people closer to the earth&rsquo;s axis, which would probably cancel out an affects of running or driving a car ( in some situations ).<br /> Posted by Manwh0re</DIV></p><p>In our day to day lives, these differences are statistically insignificant.&nbsp; Atomic clocks on GPS satellites age about 38 millionths of a second per day faster than atomic clocks here on earth.</p><p>I'd be willing to bet medical science wouldn't be able to tell the difference between two twins... one that spent a life time travelling at 1% C (far faster than anything we've accomplished to date) and the other at zero.&nbsp; Unless they were carrying atomic clocks in their pockets, no one could tell.</p><p>Even at 25% C at 103 years old, the twin travelling at 25% C would only be 100 yearls old.</p><p>Gamma factor calculator:</p><p>http://www.1728.com/reltivty.htm</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><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>First, motion is relative.&nbsp; We measure life spans in our earthly frame of reference.&nbsp; There is some effect from the items that you mention.&nbsp; But if you consider that the effect of time dilation is exceedingly small except at relative velocities very near the speed of light, then you find that the effects on life span are swamped by other sources of variation.&nbsp; They just are not important.<br />Posted by DrRocket</DIV></p><p>&nbsp;</p><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3"><font face="Calibri">This is basically what I expected (I&rsquo;m learning something </font><span style="font-family:Wingdings"><span>J</span></span><font face="Calibri"> )</font></font></p><p style="margin:0cm0cm10pt" class="MsoNormal">&nbsp;</p><p><br />Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The questionas to WHY light speed is measured to be constant in all directions and independent of the reference frame is not a question that science can answer. <br />Posted by DrRocket</DIV></p><p>&nbsp;</p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">Now this I find intriguing&hellip; And I&rsquo;ve never quite heard this said this way. So does relativity explain this phenomenon mathematically, i.e. does relativity predict light to do this, or is it a case of (like you said), science just doesn&rsquo;t know.</font></p><p style="margin:0cm0cm10pt" class="MsoNormal">&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In our day to day lives, these differences are statistically insignificant.&nbsp; Atomic clocks on GPS satellites age about 38 millionths of a second per day faster than atomic clocks here on earth.I'd be willing to bet medical science wouldn't be able to tell the difference between two twins... <br />Posted by derekmcd</DIV></p><p>&nbsp;</p><p style="margin:0cm0cm10pt" class="MsoNormal"><font size="3"><font face="Calibri">I wonder if you could do a cell division experiment that involves some sort of fast predictable bacteria division rate. I.e. chuck a bucket of something (bacteria) on&nbsp;the ISS&nbsp;while additionally reproducing the environment on the earth, shake and&nbsp;then leave for a couple of years. <span>&nbsp;</span>However, I expect any biological process to be fraught with uncertainties and this when accumulated would make the experiment null and void. </font><span style="font-family:Wingdings"><span>&szlig;</span></span><font face="Calibri"> I agree this is probably the worst and most inaccurate experiment in history</font></font></p><p>&nbsp;</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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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;This is basically what I expected (I&rsquo;m learning something J )&nbsp;&nbsp;Now this I find intriguing&hellip; And I&rsquo;ve never quite heard this said this way. So does relativity explain this phenomenon mathematically, i.e. does relativity predict light to do this, or is it a case of (like you said), science just doesn&rsquo;t know.&nbsp;,,Posted by Manwh0re</DIV></p><p>Special relativity is actually based on the assumption (backed by experiment) that the speed of light is the same in all inertial reference frames.&nbsp; So it is not really a prediction but a foundation of the theory.</p><p>In special relativity you postulate that 1) the laws of physics are the same in all inertial reference frames and 2) the speed of light is the same in all inertial reference frames.&nbsp; Everything else is a logical consequence of these postulates.</p><p>http://en.wikipedia.org/wiki/Special_relativity</p> <div class="Discussion_UserSignature"> </div>
 
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tampaDreamer

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Special relativity is actually based on the assumption (backed by experiment) that the speed of light is the same in all inertial reference frames.&nbsp; So it is not really a prediction but a foundation of the theory.In special relativity you postulate that 1) the laws of physics are the same in all inertial reference frames and 2) the speed of light is the same in all inertial reference frames.&nbsp; Everything else is a logical consequence of these postulates.http://en.wikipedia.org/wiki/Special_relativity <br />Posted by DrRocket</DIV><br /><br />So I wish I understood what you are saying above, but I have wondered this for a long time.&nbsp; To put it in laughable 3rd grade math terms..</p><p>If Train A leaves st. louis travelling east at half the speed of light and&nbsp;Train B&nbsp;decides to leave st. louis travelling west at half the speed of light, will train B find itself unable to accellerate to half the speed of light because then it would be moving at the speed of light relative to Train A?</p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So I wish I understood what you are saying above, but I have wondered this for a long time.&nbsp; To put it in laughable 3rd grade math terms..If Train A leaves st. louis travelling east at half the speed of light and&nbsp;Train B&nbsp;decides to leave st. louis travelling west at half the speed of light, will train B find itself unable to accellerate to half the speed of light because then it would be moving at the speed of light relative to Train A? <br />Posted by tampaDreamer</DIV></p><p>Train B will not be able to accelerate to half the speed of light in the reference frame of A.&nbsp; In the reference frame of the train station he will be to do that.&nbsp; Speeds in special relativity do not add up quite so simply as they do in Newtonian mechanics.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>...So it means that once your vehicle reach speed of light (let's suppose it's possible), the rest of the ride is free ? (you can't expense energy if you have no time to do so...)....Posted by killium</DIV></p><p>Yes, the rest of the ride is free and you will not have to expend any more energy.&nbsp; </p><p>Gut there are two points you ought to consider:</p><p>1.&nbsp; It doesn't take any energy to coast in the absence of friction and gravity anyway at any speed.&nbsp; So it is not really a question of expending energy to coast.&nbsp; That is as true in special relativity as it is in Newtonian mechanics.</p><p>2.&nbsp; It took an infinite amount of energy to accelerate to c in the first place, so you ought to be happy not to have to spend any more from your energy account.&nbsp; This is sort of like getting a "free" handout from the government following a 100& income tax.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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