Corry Shores
With Thomas Smid's input, I updated the entry on his critique of relativity's time dilation. Click on this link:
"if you think childlike, you'll stay young. If you keep your energy going, and do everything with a little flair, you're gunna stay young. But most people do things without energy, and they atrophy their mind as well as their body. you have to think young, you have to laugh a lot, and you have to have good feelings for everyone in the world, because if you don't, it's going to come inside, your own poison, and it's over" Jerry Lewis "I don’t believe in the irreversibility of situations" Deleuze
The numerical citations refer to page number. The source's text-space (including footnote region) is divided into four equal portions, a, b, c, d. If the citation is found in one such section, then for example it would be cited p.15c. If the cited text lies at a boundary, then it would be for example p.16cd. If it spans from one section to another, it is rendered either for example p.15a.d or p.15a-d. If it goes from a 'd' section and/or arrives at an 'a' section, the letters are omitted: p.15-16.
this achievement is that of a symbol for expressing composites, not that of something experienced that is capable, as Proust would say, of expressing "a little time in the pure state." (85c)cette conquête est celle d'un symbole pour exprimer les mixtes, non pas celle d'un vécu capable d'exprimer, comme dirait Proust, « un peu de temps à l'état pur ». (87c)
Being, or Time, is a multiplicity. But it is precisely not "multiple"; it is One, in conformity with its type of multiplicity. (85cd)L'Être, ou le Temps, est une multiplicité ; mais précisément il n'est pas «multiple », il est Un, conformément à son type de multiplicité. (87cd)
time, as measured by the speeding space traveler, slows down compared to time as measured by a friend left home on Earth. This is sometimes described as the "twin paradox": two identical twins, one of whom goes off on a voyage close to the speed of light, and the other one stays home. When the space-traveling twin returns home, he or she has aged only a little, while the twin who has remained at home has aged at the regular pace. So we have two identical twins who may be decades apart in age. Or maybe the traveling twin returns in the far future, if you go close enough to the speed of light, and everybody he knows, everybody he ever heard of has died, and it's a very different civilization. ("Sagan on Time Travel.")
Let the twins move apart for some time so that the difference in aging measured by each is substantial; then bring the twins back together and let them stand side by side and compare their appearances. Each will say that his sibling is younger than he, but both cannot be right. Which twin is, in fact, older, or is there any age difference seen at all? (Mook & Vargish 110c)
The resolution of the "paradox" depends upon a careful analysis of how the experiment actually can be carried out. When the twins separate on the tracks it is true that each will claim the other is aging more slowly than he, but notice that this is a conclusion based on measurements made of the other twin. Unless we change the direction of motion of at least one twin (that is, accelerate the twin), the two twins will continue to separate forever, and we cannot directly compare their two ages (this is like bringing two events to the same point in space so that simultaneity can be determined directly). But since we do want to compare the twins' ages directly by comparing their simultaneous appearance, suppose that we accelerate twin #1 and bring him back to stand at rest with respect to twin #2. Notice that now the two twins no longer have identical histories. One twin has undergone an acceleration (and the twins can tell which has been accelerated because the accelerated twin moved in a non-inertial frame for a time and so experienced some sort of force, as described in section 2.4). As we will see in the following chapter, in accelerating, twin #1's clock will be slowed relative to twin #2. When the twins are standing at rest with respect to one another, the twin who suffered the acceleration will have aged less than the other. (Mook & Vargish 110b-111).
The standard textbook approach treats the twin paradox as a straightforward application of special relativity. Here the Earth and the ship are not in a symmetrical relationship: the ship has a "turnaround" in which it undergoes non-inertial motion, while the Earth has no such turnaround. Since there is no symmetry, it is not paradoxical if one twin is younger than the other. Nevertheless it is still useful to show that special relativity is self-consistent, and how the calculation is done from the standpoint of the traveling twin.Special relativity does not claim that all observers are equivalent, only that all observers at rest in inertial reference frames are equivalent. But the space ship jumps frames (accelerates) when it performs a U-turn. In contrast, the twin who stays home remains in the same inertial frame for the whole duration of his brother's flight. No accelerating or decelerating forces apply to the homebound twin.There are indeed not two but three relevant inertial frames: the one in which the stay-at-home twin remains at rest, the one in which the traveling twin is at rest on his outward trip, and the one in which he is at rest on his way home. It is during the acceleration at the U-turn that the traveling twin switches frames. That is when he must adjust his calculated age of the twin at rest. (Twin Paradox)
Some physicists claim that the situation would in practice not be symmetric as one observer has to turn around in order to compare the clocks (see for instance http://www.phys.vt.edu/~jhs/faq/twins.html), but it is clear that this argument does not hold water as the time dilation should already be apparent before one observer turns around. (Smid Time Dilation and Twin Paradox Debunked)
The clocks are started and stopped in each reference frame simultaneously (by definition, the contact starts each clock from zero) and both clocks will thus show identical times (for identical rods and clocks) after having been stopped (and after the clocks have been stopped, it is obviously irrelevant if A or B (or both) turn around to compare the clocks). (Smid Time Dilation and Twin Paradox Debunked)
It should also be pointed out that the signal propagation time from the trigger points to the clocks is actually irrelevant here (whatever way of transmitting the signal is used): if the corresponding distances are identical in both systems, then the delay times will also be identical and there won't be any difference in the clock readings afterwards (Time Dilation and Twin Paradox Debunked)
According to relativity, clock differences should arise solely due to a constant relative velocity, but as this leads to the twin paradox, a hand-waving argument is being made that one system has to turn around (i.e. accelerate) to compare the clock (which of course doesn't resolve the paradox, as a) you could in principle make the period of acceleration arbitrarily short, and b) it would violate causality as the clock difference would have to build up already before the acceleration occurs). (Smid Relativity Discussion Forum page 4)
To be sure, Peter pastes a label on this time with Paul's name on it; but if he were picturing a conscious Paul, living his own duration and measuring it, he would by that very act see Paul as system of reference and therefore take his place within this single time, inside each system, to which we have just referred; by that very act, moreover, Peter would also take temporary leave of his system of reference, consequently, of his existence as a physicist, and consequently, of his consciousness as well; Peter would no longer see himself as anything but a vision of Paul's. But when Peter attributes a slowed time to Paul's system, he is no longer thinking of Paul as a physicist, nor even a conscious being. He is emptying Paul's visual image of its inner, living consciousness, retaining of the person only its outer envelope (it alone, in fact, is of interest to physics). Then, Peter takes the figures by which Paul would have designated the time intervals of his own system, were he conscious, and multiplies them byso as to make these figures fit into a mathematical representation of the universe conceived from his own point of view and no longer from Paul's. To sum up, whereas the time attributed by Peter to his own system is a time he has lived, the time he attributes to Paul's is neither a time that either Peter or Paul has lived, nor a time that Peter conceives as lived or as capable of being lived by a living, conscious Paul. What is it, then, if not a mere mathematical expression meant to indicate that Peter's not Paul's system has been taken as the system of reference? (52b.d)Sans doute Pierre colle sur ce Temps une étiquette au nom de Paul; mais s'il se représentait Paul conscient, vivant sa propre durée et la mesurant, par là même il verrait Paul prendre son propre système pour système de référence, et se placer alors dans ce Temps unique, intérieur à chaque système, dont nous venons déparier : par là même aussi, d'ailleurs, Pierre ferait provisoirement abandon de son système de référence, et par conséquent de son existence comme physicien, et par conséquent aussi de sa conscience ; Pierre ne se verrait plus lui-même que comme une vision de Paul. Mais quand Pierre attribue au système de Paul un Temps ralenti, il n'envisage plus dans Paul un physicien, ni même un être conscient, ni même un être : il vide de son intérieur conscient et vivant l'image visuelle de Paul, ne retenant du personnage que son enveloppe extérieure (elle seule en effet intéresse la physique) : alors, les nombres par lesquels Paul eût noté les intervalles de temps de son système s'il eût été conscient, Pierre les multiplie parpour les faire entrer dans une représentation mathématique de l'univers prise de son point de vue à lui, et non plus de celui de Paul. Ainsi, en résumé, tandis que le temps attribué par Pierre à son propre système est le temps par lui vécu, le temps que Pierre attribue au système de Paul n'est ni le temps vécu par Pierre, ni le temps vécu par Paul, ni un temps que Pierre conçoive comme vécu ou pouvant être vécu par Paul vivant et conscient. Qu'est-il donc, sinon une simple expression mathématique destinée à marquer que ; c'est le système de Pierre, et non pas le système de Paul, qui est pris pour système de référence? (99-100)
For this space and time which interpenetrate are not the space and time of any physicist, real or conceived as such. The real physicist makes his measurements in the system in which he finds himself, and which he immobilizes by adopting it as his system of reference; time and space there remain separate and mutually impenetrable. Space and time interpenetrate in moving systems in which the real physicist does not exist, in which there live only physicists imagined by him - imagined for the greater good of science. But these physicists are not imaged as real or able to be so; to suppose them real, to attribute a consciousness to them, would be to give; [sic] their system the status of a system of reference, to transport oneself there and become identical with them, to declare that their time and space have ceased to interpenetrate. (Bergson 119d)Car cet Espace et ce Temps qui s'entrepénètrent ne sont l'Espace et le Temps d'aucun physicien réel ou conçu comme tel. Le physicien réel prend ses mesures dans le système où il se trouve, et qu'il immobilise en l'adoptant comme système de référence : Temps et Espace y restent distincts, impénétrables l'un à l'autre. Espace et Temps ne se pénètrent que dans les systèmes en mouvement où le physicien réel n'est pas, où n'habitent que des physiciens par lui imaginés, — imaginés pour le plus grand bien de la science. Mais ces physiciens ne sont pas imaginés comme réels ou comme pouvant l'être : les supposer réels, leur attribuer une conscience, serait ériger leur système en système de référence, se transporter là-bas soi-même et se confondre avec eux, de toute manière déclarer que leur Temps et leur Espace ont cessé de se compénétrer. (234c-235)
Abstract space is, indeed, at bottom, nothing but the mental diagram of infinite divisibility. But with duration it is quite otherwise. The parts of our duration are one with the successive moments of the act which divides it; if we distinguish in it so many instants, so many parts it indeed possesses; and if our consciousness can only distinguish in a given interval a definite number of elementary acts, if it terminates the division at a given point, there also terminates the divisibility. (Bergson 273-274)
L'espace n'est d'ailleurs, au fond, que le schème de la divisibilité indéfinie. Mais il en est tout autrement delà durée. Les parties de notre durée coïncident avec les moments successifs de l'acte qui la divise ; autant nous y fixons d'instants, autant elle a de parties; et si notre conscience ne peut démêler dans un intervalle qu'un nombre déterminé d'actes élémentaires, si elle arrête quelque part la division, là s'arrête aussi la divisibilité. (230)
Bergson, Henri. Matière et mémoire: Essai sur la relation du corps à l'esprit. Ed. Félix Alcan. Paris: Ancienne Librairie Germer Bailliere et Cie, 1903. Available online at:http://www.archive.org/details/matireetmmoiree01berggoog
Bergson, Henri. Matter and Memory. Transl. Nancy Margaret Paul & W. Scott Palmer.