Speed of Time
in [Relativity]
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From: PD on 5 Jan 2010 16:52 On Dec 26 2009, 4:37 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 26 Dec, 04:03, "Inertial" <relativ...(a)rest.com> wrote: > > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > >news:c6d4ea67-9711-4b79-b35f-7bc54e086b76(a)n35g2000yqm.googlegroups.com.... > > > > On 26 Dec, 00:30, "Androcles" <Headmas...(a)Hogwarts.physics_q> wrote: > > > >> You should read Dork's twin paradox analysis. He can > > >> pick up the origin of frame of reference and move it, > > >> so if you go from London to New York you can do it > > >> twice without ever going from New York to London. > > > >> He says > > >> quote/ > > >> "We use 3 inertial reference frames. > > >> S: The frame of the "stay at home" twin. > > >> S': The frame of the "outbound part of the trip". > > >> S": The frame of the "inbound part of the trip". > > >> http://users.telenet.be/vdmoortel/dirk/Physics/TwinsEvents.html > > > >> So if T = 5 years and v = 0.8c, then the stay at home twin will > > >> have aged 10 years while his travelling twin sister will have aged > > >> 6 years. > > >> /unquote > > > > I'm afraid I don't understand how he arrives at that conclusion. > > > He was using the Lorentz transforms of SR > > But the same transformation applied with the astronaut in the fixed > frame of reference (which, according to relativity, is a perfectly > legitimate switch of frame) will yield *the opposite* result. Clearly > there is something wrong there - and I think the answer is in good ole > classical mechanics. > > > > It > > > rubbishes relativity. > > > Nope > > If the argument is correct it does. Of course, really I think the > problem lies in the argument, not in relativity. > > > > Relativity says that both twins will perceive > > > the same effects, relative to their own frame of reference. > > > No .. it does not. This is something many novices stumble over. The two > > twins are no equivalent as one remains at rest in his initial frame of > > reference, the other twin changes frames of reference (ie does not remain at > > rest in his initial frame of reference). > > An absurd position. Of course the astronaut remains at rest in his own > frame of reference. It is the *universe* that is accelerating around > the astronaut, according to relativity. > > Believe it or not though, this contrivance of "moving reference > frames" is closer to the truth than you might think. What changes is > not the reference frame. What changes is the astronaut's relative > length (i.e. length contraction). And soon in separate post, I'll tell > you why length contraction is not the same for the homebody as it is > for the astronaut. > > > In fact he changes inertial frames > > three times (given instantaneous acceleration) .. once when he leave his > > twin, one when re turns around to come back, and another when he stops when > > he gets back to the stay-at-home-twin. The stay-at-home twin stays at rest > > in his inertial frame of reference through out. > > A ludicrous argument, that if true rubbishes relativity! Relativity > says that an astronaut accelerating through space, is > indistinguishable from space accelerating around the astronaut. If you > accept relativity, then you cannot deny this. Relativity does NOT say that. I don't know where you got the impression that it does. > > > NOTE: You can avoid two of the changes by starting the experiment the > > instance after the twin starts to move away, and finishing the instant > > before he stops .. then there is just one change in inertial frame. > > > NOTE: You can also eliminate the instantaneous (infinite) acceleration > > altogether by having three 'twins' (triplets then). I'll explain if you > > like. What really makes a difference is the change of inertial frame of > > reference. > > But according to relativity, there has been no change of reference > frame, because all reference frames are equal. There has only been a > change of reference frame relative to the other twin - both will say > the other twin's reference frame changed in the middle of the journey > (one will say the rocket turned around and came back, the other will > say the earth turned around and came back). If both reference frames > are equal, then we're left with the paradox. If both reference frames > are not equal, then we must discard relativity. > > The question is, if we retain relativity, then what force or factor > does the astronaut suffer to a greater extent, that the homebody > suffers to a lesser extent? > > > > If that is > > > true, then the astronaut cannot return younger than the homebody - it > > > cannot happen. > > > Sorry .. it does > > And therein lies the contradiction. We observe that the astronaut > comes back younger - the observation cannot be denied. We must > therefore deny the coherence of the explanation. > > > > Because if you change the analysis and have the > > > astronaut in the fixed frame of reference, and have the universe > > > accelerate around him, then by exactly the same logic the *homebody* > > > will be the younger twin when the astronaut returns to earth. > > > Nope .. you can do the analysis from either point of view, and you get the > > same result > > That is not possible. You cannot possibly do an analysis that involves > the earth accelerating away from the astronaut, and still have the > astronaut come back younger, because by your own argument the *earth* > has changed reference frames at the turnaround, and the astronaut's > reference frame has remained constant. > > Clearly, this "changing reference frame" business is a gratuitous > failure to grasp relativity. > > > > If the astronaut is younger when he returns, then either relativity is > > > false, or there is another factor in play that applies differently to > > > the astronaut than the homebody. > > > > Incidentally, what evidence is there exactly to suggest that such > > > twins ages would differ once the astronaut returned to earth? > > > Because less time has elapsed for the travelling twin. > > In other words, my question is "why is the twin younger", and your > answer is "because the twin has aged less". Thankyou for that dynamite > response. > > I was actually looking for you to name studies that have proven the > effect. I presume astronauts themselves have not come back discernibly > any younger than their earth-bound families. > > > Unlike spatial dimensions, where the shortest distance between two point is > > a straight line (and so a twisty path is longer) for the temporal dimension > > the straight line is the longest temporal distance (elapsed time). The more > > you move in your path from one event to another, the shorter the time taken. > > Naturally. If I travel at 10mph, 1 mile of distance takes 6 minutes to > cover. If I travel at 60mph, 1 mile of distance takes 1 minute to > cover. That does not explain why, when I come back from my journey, I > will be any younger than my housebound family.
From: PD on 5 Jan 2010 16:53 On Dec 28 2009, 5:43 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > Also those who DO understand physics (SR in particular) will point out the > > mistaken ideas of the crackpots, and that truth makes the resent just about > > everyone. PD, Eric, Tom (and myself) are amongst the few who understand SR > > well. > > Perhaps. But then no one doubts that theologians know their subject. Theologians don't have to be reliant on experimental data. Scientists tend to do that better.
From: PD on 5 Jan 2010 16:59 On Dec 28 2009, 6:37 am, Ste <ste_ro...(a)hotmail.com> wrote: > > I was saying that relativity, or at least the interpretations that I'd > read, all said that all reference frames are equal. That is a loose statement that is easily misinterpreted. There is a more careful statement of the principle of relativity: The laws of physics take the same form regardless of inertial reference frame. Note that this does not mean that physical quantities have the same *value* in all inertial reference frames. It also does not mean that the accounting of events is the same in all inertial reference frames. It also does not mean that everything is the same in all reference frames whether inertial or not (or even "mostly" inertial"). It is these "does not means" that are the subject of teaching puzzles like the twin puzzle, the barn and pole puzzle, the rivet and bug puzzle, and so on. > And I know a guy > with a PhD who suggests to me that the paradox does not exist, because > the astronaut returns to Earth the same age as his homebody twin. A PhD in *physics*? If so, then he should be ashamed of himself. If his PhD is in psychology or law, then he can be forgiven his ignorance, though probably not for the arrogance of being sure of an answer that is wrong. > So > clearly there is a lot of popular misconception about an issue that > should be incredibly simple to explain (and trust me, I'd trawled the > internet and couldn't find any easy and intuitive refutation of this > paradox). You haven't looked very well. :) Have you considered a book? Taylor and Wheeler's book is simple and thorough. Penrose's book called The Road to Reality dispenses with the twin puzzle in a half a paragraph.
From: Androcles on 5 Jan 2010 17:03 "PD" <thedraperfamily(a)gmail.com> wrote in message news:99e431a3-c7f1-481e-afe1-56d8c796852a(a)35g2000yqa.googlegroups.com... On Dec 24 2009, 2:51 pm, Ste <ste_ro...(a)hotmail.com> wrote: > I was just wondering, can anyone tell me at what rate time advances on > earth? Time doesn't really advance. What happens is that what we call "now" by observing an event advances through time. =============================================== The plane doesn't really arrive at the airport. What happens is that the pilot and passengers observe an airport arriving at their plane and call it an "event". In the Newtonian world the plane meets the airport when the airport meets the plane and the time is "now". In the relativistic world the plane meets the airport "now" and the airport meets the plane "then", because the plane and the airport are different frames of reference and are not simultaneous, which is why Phuckwit Duck often misses his flight.
From: PD on 5 Jan 2010 17:06
On Dec 26 2009, 10:53 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > I'm an engineer to my very core. If you can't explain physics to me, > then there is probably a shortfall in your understanding of the world. > Allow me to remark that frankly I'm shocked that you are so lacking in some of the basics in physics and yet claim to be an engineer. Are you LICENSED as an engineer or do you fancy yourself to be of an engineering mind? As for the implicit dare, I'll just point out to you that just because you don't understand something doesn't mean that it's not understandable. That would be the epitome of arrogance, I'm sure you'll agree. Also, declining to try to explain relativity to a shoat or a table leg is no reflection on the instructor or on the subject matter -- it is a personal choice of how best to invest one's time. |