Update on the Thomas Smid Twin Paradox Entry

Corry Shores


With Thomas Smid's input, I updated the entry on his critique of relativity's time dilation. Click on this link:

Paradox Regained: The Twin Paradox and Thomas Smid's Critique of Special Relativity

Also see his page on the Twin Paradox [he added the animation from the entry, and I am very grateful for that].

Paradox Regained: The Twin Paradox and Thomas Smid's Critique of Special Relativity

by Corry Shores

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Paradox Regained:

The Twin Paradox and Thomas Smid's Critique of Special Relativity

According to Gilles Deleuze, Einstein's relativity theory, taken strictly, is Bergson's best means to demonstrate that there is only one duration rather than a plurality of them. [Bergson's argumentation is found in his book Duration and Simultaneity]

This insight runs contrary to what many physicists conclude regarding relativity. There seems to be consensus that time slows down for things as their speed increases, relative to an observer. One conclusion from this is the following. Suppose a twin departs on a space-ship, leaving his brother on earth. He travels long and far into outerspace before finally returning much later. Many physicists predict that the traveling twin will actually be younger than his earth-bound sibling. In an interview with NOVA, for example, Carl Sagan narrates this same scenario:

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.")

The twin on earth experiences time flowing at one rate. The traveling twin experiences time flowing at another rate. Bergson, for example, uses this paradox to argue that there is only one flow of time and not a plurality [see this section of Duration and Simultaneity for his account]. He strictly adopts special relativity's premise that there is no absolute frame of reference. As the space-bound twin flies-off (at a constant speed), he feels stationary, while it appears to him that the earth flies-away into the distance. So according to his calculations, he predicts that his earth-bound brother will be younger than him. On what grounds have we to say that one is really younger than the other?

In their book, Inside Relativity, Mook & Vargish explain the paradox this way:

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)

There is a solution that is commonly given to resolve the paradox. It deals with how acceleration affects time. Mook & Vargish continue [and they use the example of trains rather than space-ships]:

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).

For more elaboration, note how the wikipedia entry on the twin paradox explains the solution this way as well:

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)

I am not knowledgeable enough to understand how acceleration is supposed to affect temporality. Fortunately we do not need to even get into that matter, according to Thomas Smid. He devises a way to test special relativity's twin paradox in a way that keeps the systems moving at constant speed, and that involves mechanical means to communicate simultaneities rather than using light signals, for example.

Smid first observes the explanation based on changing inertial frames. He writes:

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)

He then describes his own thought experiment. His image for it is here. There are two systems moving relative to each other, each one maintaining its speed. They have very long arms that allow stop-clocks to be mechanically started-and-stopped. Below is my animation.

Smid writes:

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)

Regarding the mechanisms, he continues:

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)

Hence for Smid, this is no solution to the paradox.

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)

[Smid, by the way, provides here a technical explanation for the inconsistencies he finds in Special Relativity.]

Then there is the question of experimental evidence which seems to demonstrate special relativity. What we wonder is if time itself actually changes, or if perhaps it only appears that way from a given perspective. Many physicists say that time really does change, and hence the traveling twin really would be younger. This is a profound claim. I would expect that before the scientific community accepts it as fact, they will first need to see a mountain of experimental evidence that clearly demonstrates time dilation. This site lists and describes four such experiments. There is one that uses clocks and seems to resemble somewhat a situation like with the space-bound twin. It is the Hafele-Keating experiment [wikipedia entry here]. Atomic clocks were placed in planes and compared to ground clocks. Their results accord with relativity theory.

Smid performs a logical analysis on the time dilation and twin paradox problem, and finds that they cannot exist. Hence his position is that "any alleged experimental evidence for the time dilation must therefore be due to actual physical effects (e.g. charged particles moving in electric and magnetic fields)." He offers alternative explanations which serve as suggestions for a genuine account of the observed results. [Although he has a strong sense that his suggestions are likely on the right tract, they may or may not in fact be correct. Even with access to all the experimental data, he explains, he still might not have enough information to pin down the right theoretical explanation. So his accounts are still somewhat speculative. He is certain nonetheless that a time dilation effect in the sense of Relativity (i.e. clocks in systems moving relatively to each other go at different rates) is a logical impossibility.] He provides here the mathematics for an alternate explanation for the planes' clock-discrepancies. He begins by writing: "In the case of the 'airplane-experiment' the slowdown of the atomic clock could for instance be explained by the Lorentz- Force in the earth's magnetic field" (Smid Relativity Discussion Forum page 1).

The 'muon experiment' also seems to support special relativity. Smid provides his alternate explanation at the top of this page.

My inabilities with math and science prevent me from assessing Smid's theories. I was very interested to see that someone had an alternate view that could lend support to Bergson's theory of unitary time. And I was impressed with his thought experiment involving the mechanically triggered clocks. I just ask that readers with abilities in math and science take Smid's ideas seriously, so that the truth of the matter can be better settled. Dr. Smid's homepage is here: http://www.physicsmyths.org.uk/

"Sagan on Time Travel." NOVA online. http://www.pbs.org/wgbh/nova/time/sagan.html

"Twin Paradox." http://en.wikipedia.org/wiki/Twin_paradox

Mook, Delo E. & Thomas Vargish. Inside Relativity. Princeton: Princeton University Press, 1987.

Smid, Thomas. http://www.physicsmyths.org.uk/discussions/relativity1.htm

Smid, Thomas. http://www.physicsmyths.org.uk/discussions/relativity4.htm

Smid, Thomas. "Time Dilation and Twin Paradox Debunked."

http://www.physicsmyths.org.uk/timedilation.htm