# Centripetal force, gravity, and relativity

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#### BoJangles

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<p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">1)<span>&nbsp; </span>Could Centripetal force somehow be related to gravity? </font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">If you spun me in a giant centrifuge I would definitely feel a sense of gravity. In fact we can measure the force applied to my body spun in a centrifuge in g&rsquo;s. As far as my body would be concerned they will feel like similar forces (gravity and centripetal force), seems like they are one and the same, jsut described in diffrent ways.</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">2) Now if you spun an atomic clock in a centrifuge would it time dilate in rearguards to relativity, would it lose time in the classical sense. <span>&nbsp;</span>I.e. would it experience time dilation as far as relativity is concerned? Has anyone done this?</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">The reason I'm asking, is because it seems the proof for time dilation is atomic clocks. Could the effect seen with atomic clocks be somehow related to superficial changes in the sub atomic nature of the electron, or of how an atomic clock works, and not a real time affect?</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">I suppose I'm probably fundamentally confused with the question, is time dilation a speed thing, a mass thing or a gravity thing in regards to relativity.</font></p><p style="margin:0cm0cm10pt" class="MsoNormal"><font face="Calibri" size="3">Ps. I realise this post is very disjointed :/</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'>1)&nbsp; Could Centripetal force somehow be related to gravity? If you spun me in a giant centrifuge I would definitely feel a sense of gravity. In fact we can measure the force applied to my body spun in a centrifuge in g&rsquo;s. As far as my body would be concerned they will feel like similar forces (gravity and centripetal force), seems like they are one and the same, jsut described in diffrent ways.2) Now if you spun an atomic clock in a centrifuge would it time dilate in rearguards to relativity, would it lose time in the classical sense. &nbsp;I.e. would it experience time dilation as far as relativity is concerned? Has anyone done this?The reason I'm asking, is because it seems the proof for time dilation is atomic clocks. Could the effect seen with atomic clocks be somehow related to superficial changes in the sub atomic nature of the electron, or of how an atomic clock works, and not a real time affect?I suppose I'm probably fundamentally confused with the question, is time dilation a speed thing, a mass thing or a gravity thing in regards to relativity.Ps. I realise this post is very disjointed :/ <br /> Posted by Manwh0re</DIV></p><p>Anytime you find yourself asking, "does time dilation affect ______ ?".&nbsp; The answer is <strong><em>always</em></strong> yes.&nbsp;&nbsp; So yes, an atomic clock in a centrifuge would experience time dilation.&nbsp; You can see this in action with the decay rates of particles in particle accelerators.</p><p>Time dilation is a <em>velocity</em> thing and through the equivalence principle you have a velocity standing on earth which slows your clock down compared to someone in a lesser gravity well.&nbsp; So, time dilation cal also be a gravity thing, but it is still related to velocity and Special Relativity.&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'>Anytime you find yourself asking, "does time dilation affect ______ ?".&nbsp; The answer is always yes.&nbsp;&nbsp; So yes, an atomic clock in a centrifuge would experience time dilation.&nbsp; You can see this in action with the decay rates of particles in particle accelerators.Time dilation is a velocity thing and through the equivalence principle you have a velocity standing on earth which slows your clock down compared to someone in a lesser gravity well.&nbsp; So, time dilation cal also be a gravity thing, but it is still related to velocity and Special Relativity.&nbsp; <br />Posted by derekmcd</DIV><br /><br />Ok thanks guys <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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#### vandivx

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Time dilation is a velocity thing and through the equivalence principle you have a velocity standing on earth which slows your clock down compared to someone in a lesser gravity well.&nbsp; So, time dilation cal also be a gravity thing, but it is still related to velocity and Special Relativity.&nbsp; <br /> Posted by derekmcd</DIV></p><p>the principle you mention means the equivalence of gravitation and acceleration, not gravitation and velocity (for nitpickers - equivalence of gravitational and inertial forces such as those arising in a gravitational field and accelerated reference frame or in other words the equivalence of gravitational and inertial mass) </p><p>while acceleration is changing velocity, it is not in my books quite the same as velocity given that the former is accompanied by force while the latter is not</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>1)&nbsp; Could Centripetal force somehow be related to gravity? If you spun me in a giant centrifuge I would definitely feel a sense of gravity. In fact we can measure the force applied to my body spun in a centrifuge in g&rsquo;s. As far as my body would be concerned they will feel like similar forces (gravity and centripetal force), seems like they are one and the same, jsut described in diffrent ways.2) Now if you spun an atomic clock in a centrifuge would it time dilate in rearguards to relativity, would it lose time in the classical sense. &nbsp;I.e. would it experience time dilation as far as relativity is concerned? Has anyone done this?The reason I'm asking, is because it seems the proof for time dilation is atomic clocks. Could the effect seen with atomic clocks be somehow related to superficial changes in the sub atomic nature of the electron, or of how an atomic clock works, and not a real time affect?I suppose I'm probably fundamentally confused with the question, is time dilation a speed thing, a mass thing or a gravity thing in regards to relativity.Ps. I realise this post is very disjointed :/ <br />Posted by Manwh0re</DIV></p><p>In special relativity time dilation is the result of relative velocity.&nbsp; But special relativity only covers cases in which gravity and acceleration can be neglected.</p><p>In general relativity&nbsp;space-time is curved by the presence of mass.&nbsp; This curvature in space-time results in the "slowing down" of time in regions of high curvature, or equivalently high gravitational fields.&nbsp; This effect can actually be measured in terms of changes in time with elevation near the surface of the earth -- see a link I posted for you in another thread.</p><p>So both speed and gravity can affect time.&nbsp; And mass is obviously related to gravity so there is an effect of mass in that sense.</p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### kg

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In special relativity time dilation is the result of relative velocity.&nbsp; But special relativity only covers cases in which gravity and acceleration can be neglected.In general relativity&nbsp;space-time is curved by the presence of mass.&nbsp; This curvature in space-time results in the "slowing down" of time in regions of high curvature, or equivalently high gravitational fields.&nbsp; This effect can actually be measured in terms of changes in time with elevation near the surface of the earth -- see a link I posted for you in another thread.So both speed and gravity can affect time.&nbsp; And mass is obviously related to gravity so there is an effect of mass in that sense.&nbsp; <br />Posted by DrRocket</DIV><br /><br />I think the question being asked is...&nbsp;an object in a centrifuge experiences something similar to&nbsp;a stronger gravitational field.&nbsp; However the object&nbsp;isnt in a stronger gravitational field.&nbsp; So if you spin this object up to say 1000gs will it experience the "slowing down" of time that it would if it were&nbsp;on a planet that was massive enough to give you 1000gs&nbsp;on its surface?&nbsp;

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#### vandivx

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I think the question being asked is...&nbsp;an object in a centrifuge experiences something similar to&nbsp;a stronger gravitational field.&nbsp; However the object&nbsp;isnt in a stronger gravitational field.&nbsp; So if you spin this object up to say 1000gs will it experience the "slowing down" of time that it would if it were&nbsp;on a planet that was massive enough to give you 1000gs&nbsp;on its surface?&nbsp; <br /> Posted by kg</DIV></p><p>&nbsp;</p><p>yes, precisely that would happen, that's what the equivalence principle is about - it is 'exactly' the same being in a given gravitational field or in a centrifuge that supplied the same acceleration, time dilation will be the same in both cases if the acceleration will be the same in both cases regardles if it is due to motional acceleration or gravitational acceleration </p><p>&nbsp;</p><p>-----&nbsp;</p><p>I put the word 'exactly' into qualifying brackets for the nitpickers: there is some difference in 'artificial' gravitational field of the centrifuge from the real gravitational field (so called tidal effects by which one might tell real gravitation from that generated by a centrifuge) but that is nothing that would affect time dilation</p> <div class="Discussion_UserSignature"> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I am wondering whether you realize or believe that 'time dilation due to speed alone' implies absolute motion (absolute space) if what we are talking about is time dilation with lasting effects, such as that in twin 'paradox' thought experiment&nbsp;&nbsp;in arguments around differential twin aging it is often argued that the twin that went on the trip was 'really moving' because he was the one who accelerated... but relativity of motion means there is no such thing as 'real motion' or 'really moving', it is all relative motion - and that implies that linear motion (speed) should only lead to apparent time dilation by relativity books, that is one without lasting effects - time dilation should be relative and the twins shouldn't age differently because of this, opponents of absolute space (defenders of relativity) argue that the real timeshift between the twins is due to either acceleration (at the begining and middle of the journey during turnaround - but that had been refuted, acceleration by itself cannot account for all the time difference btw twins) or else they say its due to (abrupt) shifting of the reference frame during turnaround in the middle of the journey relative to the 'stay at home twin' (this latter attribution smacks almost of unreality, that is magic)&nbsp;&nbsp;...Posted by vandivx</DIV></p><p>It is really not magic.&nbsp; A completely rigorous resolution of the twin paradox can be accomplished through the use of general relativity.&nbsp; It shows that the twin who goes away and comes back does in fact age less.&nbsp; This has been demonstrated experimentally by flying one atomic clock on an aircraft and comparing it to one that has remained on the ground.</p><p>General relativity has been thoroughly tested in experiments and has been found to pass with flying colors.&nbsp; The only known issues involve situations in which quantum effects are important.&nbsp; There we have a problem since quantum theory and general relativity are not compatible.&nbsp; At least one of them needs to be revised to cover such situations.</p><p>http://en.wikipedia.org/wiki/Tests_of_general_relativity<br /></p> <div class="Discussion_UserSignature"> </div>

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#### vandivx

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>It is really not magic.&nbsp; A completely rigorous resolution of the twin paradox can be accomplished through the use of general relativity.&nbsp; It shows that the twin who goes away and comes back does in fact age less.&nbsp; This has been demonstrated experimentally by flying one atomic clock on an aircraft and comparing it to one that has remained on the ground.General relativity has been thoroughly tested in experiments and has been found to pass with flying colors.&nbsp; The only known issues involve situations in which quantum effects are important.&nbsp; There we have a problem since quantum theory and general relativity are not compatible.&nbsp; At least one of them needs to be revised to cover such situations.http://en.wikipedia.org/wiki/Tests_of_general_relativity <br /> Posted by DrRocket</DIV><br />we both know that magic doesn't happen of course, I also have no dispute with the difference in passing of time between the twins which I believe is true, experiments confirm it, what I don't agree with is the interpretation of what the time loss is due to in conventional explanations of the twin thought experiment because people try to make it so that time dilation doesn't happen during uniform velocity part of the trip </p><p>&nbsp;</p><p>you have yourself said velocity (was it speed? but that is no matter) is one of the states of matter that leads to time dilation with which I agree, what I am saying then is that that implies existence of absolute space, now because that is not acceptable to offical physics view, people either don't want to acknowledge that or else they try to make it so that all the differential aging happens not during velocity part of the trip but during the acceleration part or during the reference frame change at the turning point</p><p>so what I am saying is that if your calculations (employing GR) imply that traveling twin ages less besides other parts of the journey also during the time he coasted along at uniform speed then I am claiming that that would imply existence of absolute space - that is speed is no longer relative which goes against relativity principle no less </p><p>so I have no dispute that calculations are somehow done wrongly, as you say it all adds up when calculated properly</p><p>&nbsp;</p><p>the part of the trip that happens at uniform speed can be made arbitrarily large making the acceleration parts of the trip negligible, also there is a way (which I invented) to arrange the thought experiment so that the acceleration and even the change of reference frame part of the trip can be eliminated (cancelled out) - both twins start on the journey each in his own rocket, they accelerate side by side to achieve traveling speed and coast together for a bit and then one of them decides to turn back and returns home (where he waits for his brother to return) and the other one continues to travels at that coasting speed for some years before he also decides to turn around and return home</p><p>upon return, this twin that coasted years longer at constant speed will have aged less and because both twins have underwent the same amounts of acceleration in all respects including the change of reference frame, it can be taken out of the calculation altogether, right? [any time dilation that happened during those parts of the trip will affect both twins the same amount] and we are left with just the time dilation due to coasting at uniform velocity which makes for simple calculation and if the longer traveling twin is now younger, I say that means that space has to be absolute, that is speed is absolute same as acceleration is and relativity of motion is not true, <font color="#000000"><strong>because of time dilation, one can tell who was <font size="2">really </font>moving through space and who was not</strong></font></p><p><font color="#993300"><strong>&nbsp;</strong></font></p><p>my position is that time dilation during uniform motion happens and so space is absolute, Einstein notwithstanding&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>we both know that magic doesn't happen of course, I also have no dispute with the difference in passing of time between the twins which I believe is true, experiments confirm it, what I don't agree with is the interpretation of what the time loss is due to in conventional explanations of the twin thought experiment because people try to make it so that time dilation doesn't happen during uniform velocity part of the trip &nbsp;you have yourself said velocity (was it speed? but that is no matter) is one of the states of matter that leads to time dilation with which I agree, what I am saying then is that that implies existence of absolute space, now because that is not acceptable to offical physics view, people either don't want to acknowledge that or else they try to make it so that all the differential aging happens not during velocity part of the trip but during the acceleration part or during the reference frame change at the turning pointso what I am saying is that if your calculations (employing GR) imply that traveling twin ages less besides other parts of the journey also during the time he coasted along at uniform speed then I am claiming that that would imply existence of absolute space - that is speed is no longer relative which goes against relativity principle no less so I have no dispute that calculations are somehow done wrongly, as you say it all adds up when calculated properly&nbsp;the part of the trip that happens at uniform speed can be made arbitrarily large making the acceleration parts of the trip negligible, also there is a way (which I invented) to arrange the thought experiment so that the acceleration and even the change of reference frame part of the trip can be eliminated (cancelled out) - both twins start on the journey each in his own rocket, they accelerate side by side to achieve traveling speed and coast together for a bit and then one of them decides to turn back and returns home (where he waits for his brother to return) and the other one continues to travels at that coasting speed for some years before he also decides to turn around and return homeupon return, this twin that coasted years longer at constant speed will have aged less and because both twins have underwent the same amounts of acceleration in all respects including the change of reference frame, it can be taken out of the calculation altogether, right? [any time dilation that happened during those parts of the trip will affect both twins the same amount] and we are left with just the time dilation due to coasting at uniform velocity which makes for simple calculation and if the longer traveling twin is now younger, I say that means that space has to be absolute, that is speed is absolute same as acceleration is and relativity of motion is not true, because of time dilation, one can tell who was really moving through space and who was not&nbsp;my position is that time dilation during uniform motion happens and so space is absolute, Einstein notwithstanding&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br />Posted by vandivx</DIV></p><p>You have part of the story correct, but have badly misconstrued the basic physics.&nbsp; The difference aging is due almost entirely to the time spent "coasting" at high velocity.&nbsp; What the acceleration does is point out that only one reference frame in the problem can be handled as an inertial reference frame and that is the frame attached to the earth.&nbsp; But the conclusion that there is such a thing as absolute rest has been evaluated and found incorrect numerous times, and verified by all experimental data that has been found to date.</p><p>If you want to see the twin paradox and other "paradoxes" so special relativity explained, I recommend either <em>Introduction to Special Relativity</em> by Wolfgang Rindler or <em>The Road to Reality</em> by Roger Penrose.&nbsp; You will find a good discussion of the twin paradox in either book.<br /></p> <div class="Discussion_UserSignature"> </div>

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#### vandivx

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> There is no experimental or theoretical evidence anywhere to support the notion of absolute motion.&nbsp; You have not even proposed the reference frame that one would use as the basis for "absolute rest" merely asserting that it exists.&nbsp; If it exists then what is it?&nbsp; If you have a real theory, other than that simply general relativity is "wrong" then present it.&nbsp; <br /> Posted by DrRocket</DIV></p><p>&nbsp;simple deduction that <strong>anybody </strong>here could have done (and I am amazed forum fell silent on this thread given any cranky ideas typically receive numerous comments from various people here, I take that as positive sign in my favour) is as follows: absolute rest frame is that one in which the passage of time is maximized, clocks in any other linearly moving frames (moving in any direction) all run slower than the clock which finds itself at absolute rest in space and whose time passes faster when compared to all other clocks moving relative to it (of course the talk is only of uniform motion) </p><p>&nbsp;</p><p>I happen to have a theory but it is still up here - knocks on his forhead after the fashion of Mozart when being querried where is the written composition for the new opera in Forman's famous movie</p><p>but point is why present more when all I get from you that I don't know anything and that my basic physics are all wrong (I suppose that refers to changes I propose and of course new physics are not likely to agree with old ones) and that I go against what was settled century ago and that experimentalists have determined once and for all that something is so and so, why bother fighting you at each and single point when clearly you are steadfastly sold on defending physics as it stands and arrogant to boot - if physics today is so right why is it stalled for like half a century now, you talk about working on details (on quantum level nonetheless) while arrogantly assuming the basic physics is right and settled once for all times and can't be wrong, how arrogant, a bit more modesty would behoove you I dare say </p><p>&nbsp;
As far as physicists dying&nbsp;and acceptance of absolute motion goes, you are a bit over 100 years too late.&nbsp; The physicists who believed in that concept are now long dead.&nbsp; The smarter ones of that era saw the experimental data from several experiments, including Michelson-Morley and accepted Einstein's special theory of relativity.&nbsp; It has served quite well since then, and with the advent of general relativity a few later the theory has only become stronger.&nbsp; If you are looking to an arena in which general relativity may need to be revised, you might take a look at situations in which quantum effects are important, such as near black hole singularities or the big bang singularity.&nbsp; We know that there are problems with general relativity, quantum mechanics or both that must be resolved to explain what is going on in those situations.&nbsp; But&nbsp;with regard to more mundane situations, you are simply barking up the wrong tree.
</p><p>all I can say, its like if I heard someone say to Copernicus that Ptolemaic theory of heavenly spheres have served us so well for so many centuries, that we only need to reconcile it here and there to iron some details but with regard to its basics we are simply barking up the wrong tree...</p><p>now that is just an analogy and I am not saying today's physics is quite as wrong as Ptolemaic system was but it needs some changes as pig needs rubbing</p> <div class="Discussion_UserSignature"> </div>

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#### vandivx

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So both speed and gravity can affect time.&nbsp; And mass is obviously related to gravity so there is an effect of mass in that sense.&nbsp; <br /> Posted by DrRocket</DIV></p><p>you should learn some basic physics I'd say </p><p>mass, that is inertial property of matter 'affects time' on its own, quite appart from just being 'related to gravity' - mass (or matter of a given mass to be precise) when made to change velocity (accelerated) slows (affects) the passage of time</p><p>&nbsp;</p><p>'You don't know what you are talking about.' I advise you to read any relativity textbook </p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

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#### derekmcd

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I think the only way you are going to achieve an absolute rest frame would be to bring the universe to absolute zero where there is no motion.&nbsp; AFAIK, this is theoretically impossible and would violate the third law of thermodynamics.<br /> <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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#### vastbluesky92

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>'You don't know what you are talking about.' I advise you to read any relativity textbook &nbsp;&nbsp;&nbsp; <br /> Posted by vandivx</DIV></p><p>Wow, I've seen that said a lot on these forums and even said it a couple times myself, but I never expected someone to say it to DrRocket. He's probably the person on these forums (at least who posts A LOT) who knows the most about physics and I bet he's read higher level relativity tetbooks than you ever will. Plus your post pretty much just refrased what he said. </p> <div class="Discussion_UserSignature"> <p>--____________________________________________--</p><p><font size="1"> Don't be too hard on me...I'm only in PHY 1010 </font></p><p> </p><p><font color="#339966">         The following goes without saying:</font> </p> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I think the only way you are going to achieve an absolute rest frame would be to bring the universe to absolute zero where there is no motion.&nbsp; AFAIK, this is theoretically impossible and would violate the third law of thermodynamics. <br />Posted by derekmcd</DIV></p><p>It would also violate the first and second laws.&nbsp;&nbsp; The first because at absolute zero you are in the state of lowest energy and since it is the entire universe that we are talking about all of that earlier energy ought to be around somewhere.&nbsp; The second because absolute zero is a state of minimal entropy and the overall entropy of the universe can at best only remain constant, but in fact is continually increasing.</p><p>I hadn't thought of it, but the notion of reducing the universe to absolute zero is somewhat unique in that it would simultaneously violate all the laws of thermodynamics.&nbsp; That is pretty impressive. <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'>you should learn some basic physics I'd say mass, that is inertial property of matter 'affects time' on its own, quite appart from just being 'related to gravity' - mass (or matter of a given mass to be precise) when made to change velocity (accelerated) slows (affects) the passage of time&nbsp;'You don't know what you are talking about.' I advise you to read any relativity textbook &nbsp;&nbsp;&nbsp; <br />Posted by vandivx</DIV></p><p>I have read several relativity books.&nbsp; I have even understood them.</p><p>It is pretty clear that at least one of us doesn't know what he is talking about, in a big way.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>

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#### vandivx

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<p>&nbsp;</p><p>&nbsp;<BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'></p><div class="Discussion_PostQuote"><font color="#999999">I think the only way you are going to achieve an absolute rest frame would be to bring the universe to absolute zero where there is no motion.&nbsp; AFAIK, this is theoretically impossible and would violate the third law of thermodynamics. <br />Posted by derekmcd </font></DIV><br /></div><br /> <p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'><font color="#808080">It would also violate the first and second laws.&nbsp;&nbsp; The first because at absolute zero you are in the state of lowest energy and since it is the entire universe that we are talking about all of that earlier energy ought to be around somewhere.&nbsp; The second because absolute zero is a state of minimal entropy and the overall entropy of the universe can at best only remain constant, but in fact is continually increasing.I hadn't thought of it, but the notion of reducing the universe to absolute zero is somewhat unique in that it would simultaneously violate all the laws of thermodynamics.&nbsp; That is pretty impressive. <br /> Posted by DrRocket</font></DIV></p><p>&nbsp;</p><p>yes, coming to rest in that sense (being at zero kinetic energy on particle level) would violate well established physics&nbsp; </p><p>when I said 'at rest in space' I didn't mean that somehow all the oscillations of all particles of matter around their center of mass would stop, that wouldn't happen when a chunk of matter came to rest in absolute space and if we talked about individual particle(s) then they couldn't be brought to rest in space in that sense - that they would stop jiggling around their CM, what I meant was their <strong>translational motion would be zero relative to space</strong> </p><p>&nbsp;</p><p>this oscillatory jiggling and wiggling that particles of matter perform unceasingly at least to some minimal extent as physics today knows is completely different matter from what I talk about and would go on as it ever did even while the gross matter composed of them were to come to be at rest in absolute space, in same way that the stone dorstep at my place here is at rest relative to Earth all the while its particles are oscillating and doing what not within that stone slab, being at rest generally doesn't rule out such oscillatory motions, else we couldn't talk of a rest in regard to anything could we </p><p>&nbsp;</p><p>again, I meant translational motion which is enduring which would cease relative to space, be it particle that performs it or a whole macroscopic chunks of matter, not microscopic particle oscillations around CM, if matter did come to 'rest' in space in that way, it would of course violate some very basic and very securely established laws of physics as you say (I wish you left out the irony contained in the term 'impressive') and while in some fantasy one could imagine that kind of rest in space, it doesn't happen</p><p>&nbsp;</p><p>but just because there is this barrier to absolute rest in space on fundamental particle level, still the idea of rest in space being valid for translational (non-oscilatory in microscopic sense) motion is no less than revolutionary idea, old as it may be, in the end it is not important that matter can't be brought to rest in space in the sense of each particle of it coming to rest but that we have a way to establish reference point for exploration of cosmos such as in the study of CMB and such likes (mainly it would be usefull in macroscopic physics (cosmology), not microscopic ones (particles&nbsp; or physics on relatively small scale) </p><p>the whole point of being able to physically establish state of absolute rest in space is not that one could put matter into that state (in all respects including its individual particles) but that it can serve as a reference point, same as we have the concept of lowest temperature reference point of absolute zero while nobody complains that we can't ever reach it, same with the speed of light which gross matter or its particles individually can't reach</p><p>&nbsp;&nbsp;</p><p>the idea of absolute rest in space of course doesn't throw out the concept of relativity out the window altogether, it still doesn't enable us to mark a definite place in space and in that respect relativity would live on albeit more limited as relativity of place in space but not relativity of motion, furthermore as daily life goes motion would be regarded relative I suppose even after the absolute space were accepted in physics because it is 'common sense' thing with modern man and because the concept has no utility in normal life of peoples, even in physics, the field of classical mechanics for example shouldn't change I think although what would change is hard to determine now, myself I only gave that a passing thought so far because that's not important from my point of view, all I care about is to find out how nature ticks </p> <div class="Discussion_UserSignature"> </div>

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#### DrRocket

##### Guest
<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>...&nbsp;maybe the biggest change would come regarding the (in)famous space contraction in SR which never had any direct experimental basis and was just the result of the theoretical need to enable us to deal with the fact that the speed of light was found to be constant in all reference frames which it still would be in the reworked theory I hasten to say except that we would understand the physical reason why it stays constant and space contraction would be conceived in different way (it has to do with the reason behind constancy of light speed)...Posted by vandivx</DIV></p><p>There is experimental evidence for length contraction.&nbsp; Length contraction and time dilation are two sides of the same coin.&nbsp; The decay of the mu meson (in modern terminology called the muon) is a case in point.&nbsp; These particles are formed high in the atmosphere by cosmic ray collisions and are found to penetrate our atmosphere farther than would be expected from the known decay time of these particles.&nbsp; The explanation for this phenomena lies in the Lorentz transformatin of special relativity.&nbsp; From the viewpoint of an earthbound observer, time dilation allows the muon to penetrate deeper into the atmosphere because it has more time to do so.&nbsp; From the point of view of the muon length contraction in the permits the penetration during a normal lifetime.</p><p>If you accept only two premises: 1) that the laws of physics are the same in all inertial reference frames and 2) that the speed of light is the same in all inertial reference frames, then on the basis of mathematical logic alone you must accept the Lorentz transformation that is derivable from those two assumptions.&nbsp; With the Lorentz transformation you get all of the features of special relativity including length contraction, time dilation, relativity of simultaneity, etc.&nbsp; You cannot accept only part of the package, it either the whole thing or nothing.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>

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