Chronological and Biological age

Sir/Madam,

I got a question in a thread that got closed before I had time to answer it.

Quote from the thread:

Sorry that I was unclear. I thought that "twin roundabout time" was clear, but a was clearly wrong. I need to focus more on how I write. A time unit is an event or a series of events (as with the current definition of one second), we can freely choose "twin roundabout time" to be a time unit. That is not the same as "proper time (Minkowski) for the roundabout twin".

Chronological age of a person is something that is well established and has nothing to do with SR.

Chronological age (YYYY.MM.DD) = Current date (YYYY.MM.DD) - Date of Birth (YYYY.MM.DD).

If we have two twins, one going on a space roundabout and the other one staying on earth, when they reunite their chronological age will be the same. That´s have nothing to do with physics but with the definition of chronological age.

Biological age of a person can be global or just about some attributes (like mental age or bone age). To determine the biological age of a person you compare some attributes to a "age standard" for that attribute. The relevant field of science regarding biological age is not physics but medicine. We have limited evidence of the effect space travel has on the biological age of humans. The best evidence to this date has we from Soviet/Russian cosmonauts that had stayed at space stations for a prolonged time. Such space travels seams to transient increase the biological age in some aspects. The biological effect of a space travel as in the twin paradox can not be resolved by theoretical physics but by medical research.

But the twin paradox is basically not about the biological or chronological age of twins. It´s about if there is a logical flaw in the SR or not.

Best regards

 

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No further testing is needed, and no medical studies either. You simply have to accept that time is relative between inertial and moving reference frames. Each twin ages one second per second of his own clock. But the clocks don't agree. So when the traveling twin returns, he/he will be biologically younger than the twin who stayed behind.

 

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Hi lukmaa,
You seem to use the words "Chronological age" to mean "the time that passed on the stay-at-home clocks."
This actually has everything to do with SR and the twin paradox.

In SR, we call it the "ïnvariant interval." It's the time that passes between two events that happen at the same spot in some inertial reference frame, measured by a clock that stays in that one spot. Any clock that departs from that spot and comes back later is going to measure less time passing.

In the twin paradox, the two events are "The twins separate", and "the twins rejoin".
The heart of the paradox is the idea that the time that has passed on the stay home clocks is nothing special, that the time passing on the travelling clocks is an equally valid measure of time.
But, you know and I know that the time passing on Earth's clocks is special, because they are the only clocks that measure the invariant interval.

It's about how much time SR says passes on travelling clocks compared to stay at home clocks.

 

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Simplifying the twin paradox

Yes, I read it & wanted to post to it but it was closed. "Timewarp" opened the tread with the question, "Can the Twin Paradox be simplified?" I was about to start a thread when I spotted yours. My answer to him and to you is yes, it can. I did after trying to understand what even the teachers don't understand, and I used nothing new under the Modern Physics' sun. My intent was to see if I could understand what has been well observed and confirmed, but in a way it makes sense and requires only a HS reading comprehension level and no math at all. I will post part of an essay I wrote that includes not just the TWin Paradox example but also a second even more-simple example of so-called "time dilation." It can be read at http://nomathphysic.wordpress.com in its entirety. The following is about 1/2 of the essay. I welcome all questions and comments.

NO-MATH ESSAYS IN THEORETICAL PHYSICS
By Thomas Garcia
Copyright 1996/Revised 2012/All Rights Reserved

ESSAY ONE: The Time and Motion Relationship
When asked about the nature of time, I can answer only in terms of my own frame of reference - that is, as a student of human group interactions and as an activist in the American sociopolitical arena, and with a layman’s whetted interest in science and an analytical eye out for straight thinking in the formulation of reasonable thought.
Where it concerns time theory, my candid inquiries have led me to propose that the passage of time varies at a rate set inversely proportional to the state of motion of discrete matter in space, and therefore time to me is a distinct property of matter. I believe this very simple time and motion relationship, which I defend with logical arguments, is at least as relevant to science today as is the incredible concept of Albert Einstein’s curved Space-Time Continuum. I hope to convince the reader of the validity of my claim by the end of this essay.
It is obvious to me that while we’ve known for quite some time now the rate of the passage of time depends on the speed of objects, we have not used this information as well as we should have. That may be simply because we are continually being led and pushed into considering ever more-exotic and quite complicated concepts that purport to explain, at least to some extent, the riddles of light, energy, motion, and even space. Consequently, we have not put as much importance as we should have into what we do know about time.
That may well be the reason why, after all the centuries of people asking each other “Just what is time?”, we have progressed essentially no farther in Theoretical Physics than Albert Einstein’s standpoint of time and space interdependence and his premise that they are both flexible and dependent upon the state of motion of an observer.
Indeed, it is difficult to figure out time. We cannot get beyond Dr. Einstein’s premise of time-space interdependence because it bonds time and space as partners absolutely and forever, where one cannot exist without the other. The result of that is the creation of a virtual “blind alley” from which there seems to be nowhere else to go because the premise discourages any in-depth consideration of the idea that there may be more relevance to time other than our usual understanding of it as simply the Siamese twin of space and not much else than that.
Therefore, when we think about time, it is usually as a “continuum” or “fabric” in our universe in which all things exist equally subject to the “force” of time’s irresistible and unwavering flow. However, such a concept requires time to have or to be a force of its own - it requires that time must either be energy or must contain energy.
Subsequently, we are led to another blind alley where we find we cannot explain certain “loose ends” or apparent natural contradictions. For example, time must contain energy in order for it to be a force that is imposed onto objects as well as onto space. Although most people believe that time has such energy, it remains a belief without substance, based only on the effect and not the cause of it.
In order to support the idea of the existence of a time and space continuum, scientists have had to come up with the notion that there must be such things as time and space so-called “fluctuations” in the form of “time warps,” “curved space,” “dilations,” and so forth.
For many of us, though, it is just too hard to successfully imagine the warping of time and the curving of boundless space in any way other than as the literary trick used in science fiction stories as a relatively quick and easy way to travel around the universe.
It is a task too difficult for us because we are unable to reasonably extend the concept of ordinary space far enough to reconcile in our inquiring minds how it could be that empty space can “do”, “act”, or “perform” any sort of physical act. For scientists to take ideas from science fiction or nature’s effects is a risky adventure as it can too easily become a case of the tail wagging the dog, as it were.
“Absolute space” is commonly defined as: “…physical space independent of whatever occupies it.” Of course, time passes and matter moves, but can we really bestow to empty space the capacity to actually do something? And if space could do something, how would we ever know it? Even so, if we wish to (perhaps only to resolve these nagging questions), we can imagine the concept of time being something quite separate and independent indeed from the concept of space, contrary to what most scientists believe today. I shall later herein discuss just how this may be done.
In a common textbook example of Special Relativity theory, two observers - one of whom is seated inside a moving passenger train while the other is positioned outside as the train goes by – take accurate measurements with their synchronized clocks of the amount of time it takes light to travel from a ceiling lamp to the floor of the train car. The experiment proves (in a surprising conclusion) that time passes slower for the observer riding on the train, but only in comparison to the rate of the passage of time for the other observer standing alongside the railroad tracks. That doesn’t seem right, how can an experiment show such a thing, and why does it apply only to the two observers? It does that by having the only relevant difference between the two observers being that they are not moving at the same speed with respect to each other.
From the viewpoint of the outside observer who took his measurement as the train went by, the light traveled “distance x” in moving from the ceiling to the floor, plus “distance y,” which is the distance the train moved in the time it took for the light to travel to the floor of the car. For him, a line tracing the path of a single light particle as it fell would show a diagonal line of travel drawn downward but curving in the direction of the train’s movement. For the passenger, the light fell plumb downward from the ceiling light bulb to the floor of the train, but for the outside observer, the same light did not fall straight downward.
For him, the falling light curved as it fell simply because the train was moving faster than he was as it passed by. For the observer in the train, however, the light particle traveled only the “distance x” because the falling light was moving down but not moving past her since she was on the same train as the light she measured. For the train rider, then, a line drawn based on her observation would be a vertical line because she is moving along inside the train with the photon as it falls. Thus, there is no “distance y” involved in her measurement.
In comparing the length of the two lines, the diagonal curved line is longer, meaning that it had to have taken more time for the light to reach the floor, so far as the stationary observer is concerned, but less time than that as it pertains to the measurements of the train passenger observer.
If for the stationary observer the event took, e.g., two seconds to occur by his clock, and if for the train passenger it took, say, only one second to occur by her clock, it means that in this bilateral relationship, time passed for the stationary observer at twice the rate that the train passenger underwent, and therefore he aged faster, or more, than the passenger in the moving train. This experiment clearly illustrates the time and motion relationship of inverse proportionality in that the observer moving relatively faster than the other observer accrued and underwent a slower time rate.
Here is an instance where we have obtained two accurate but different time measurements of the same event; yet, this hardly seems possible. The speed of light is constant; therefore, it cannot be that which changed and caused the differences in the time measurements of the two observers. If the speed of light did vary in order to accommodate the situation, that would explain the time differences and we could then say that the speed of light “adjusted” to that particular situation, and then it would not be necessary for time and space to warp or curve.
If it was the case that the speed of light varied instead of the rate of the passage of time (as opposed to just the passage of time), then time could be a force of the universe, and if that was so, it seems all objects in the universe should age at the same rate. However, we would still need to wrestle with the same question as with space, e.g., how could time have the energy required for it to be a force?
However, if it cannot be the case that the speed of light varied during the experiment, it seems then that the reason for the time differences must indeed have to do with the fact that the measurements were made while each observer was in a different state of motion relative to the other. Thus, the rate of time varied for each observer inversely proportional to their particular state of motion. Up to this point, many already agree with the latter case, as we shall see below.
Within the context of Einstein’s time-space interdependence premise, it is said that both time and space must at some unknown point warp, fold, flex, bend, dilate, or curve so as to reconcile the differences in the rates of the passage of time as measured by our two observers. The premise is a conclusion necessarily adopted to explain the time differences, I believe, since we believe the speed of light does not vary in the vacuum of space. Beyond that context, however, it is extremely difficult if at all possible to apply such physical terms to time and space because neither can be so easily studied as can discrete objects.
If we think that the rate of the passage of time (i.e., the rate of aging) is universal - that is to say, for those who think that time is, or is part of, a medium or “continuum” in which all things are held equally captive in time - and are thus held equally subject to its immutable flow - then it becomes necessary indeed to invent such terms as time and space “warps” and imbue space and time with forces impossible to confirm. The necessity arises, I think, when we are confronted with such natural inconsistencies of the type shown in the experiment above and we cannot come up with better explanations for them.
For the rest of us, however, if we can agree that in our experiment above the rate of the passage of time varies for the observers due to the difference in the states of motion between them, it becomes easier for us then to think that the reason for the time differences is because each observer measured the event from within a time rate corresponding to his and her own state of motion.
Remember that we said both measurements in our train example are accurate and so, essentially, the only difference in the situation between the observers is that one is moving faster than the other at the instant they each measure the light traveling from the ceiling to the floor inside the train car. They are both moving in space along with planet Earth, but on the planet, the train has a different state of motion.
The stationary observer is at constant velocity with respect to the earth, but the train passenger is not because while the train has all the motions imposed upon it by the moving planet, it also has the added motion, as it moves along the tracks, of moving with respect to the earth. This experiment has also been explained by using a spaceship in place of a train, but I think it is more easily understood using the surface of the planet as the reference base.
In the resolution to the so-called Twin Paradox (another common textbook example), it is proposed that a twin who goes off in a spaceship for a few years will return to greet a much older twin brother or sister because Nature apparently grants a slower time rate to the accelerating space traveler. That conclusion has prompted many to work out mathematical calculations which purportedly show how that happens. However, of the many proposed resolutions to this paradox, not one explains why nature should grant different time rates to moving objects, as I’ve done herein.
The Twin Paradox is just another example where there has been for widespread agreement for some time now that the time rates of discrete objects are set inversely proportional to their states of motion, although I have found no one willing to propose that as a fact. Although questions abound, I have found very little has been written about time, in fact. Centuries back, the argument was whether time passes in a continuous flow or in brief spurts. The issue was not resolved then and it has been forgotten today, perhaps rightly so if it is as unimportant an issue as it seems.
If someone has lately argued time concepts in print, I’ve missed them and thus felt compelled to poke further into what to me seems quite an important discovery about time. I’ve come to believe that at any time when it seems Nature simply and freely “grants” us something, we should be wary of accepting her “gift” too readily because in so doing we could miss a good clue. Greek philosopher/scientist Aristotle argued that all heavenly objects traveled around the earth because it was in their nature to do so. That had a ring of logic to it then, and even though apparently no better argument was offered as to why it was in their nature to do so, many accepted the proposition, probably because then no exception to it could be observed, or perhaps because it just suited them to accept it. We know now that under that “logic,” there couldn’t have been any exceptions, as today heavenly bodies other than our moon still seem to revolve pell-mell around the earth.
We may have acted too eagerly then in accepting Aristotle’s logic as if the question of “why” is of little importance to our insatiable thirst for knowledge. Yet, it would be just as nice for us to be able to think that we can know why nature should choose one observer over another, as in our examples above, as it would be for us to be able to imagine the quite-unimaginable physical feat of the “warping” or “curving” of time and space, as Modern Physics so argues today.
Because I believe our universe is one of cause and effect and that the “why” of any effect is the cause of it, I felt there had to be a reason why Nature would “gift” one observer over the other with a slower time rate. After long deliberations, I was able to develop the following hypothesis about time.
If we agree that an object has a longer life-span (due to a slower time rate) than another similar object moving at a slower speed, then we are saying that for any discrete object time passes at a rate of inverse proportion to its state of motion. If that is so, then the aging rate of the twin and the spaceship would be slower than on earth at any instant whenever the spaceship’s speed would become higher in relation to the earth’s state of motion in space, rather than at some arbitrary or unknown point in time and space. Thus, upon returning to earth, the traveling twin will have aged less as far as the earthbound twin and all the rest of the people on earth are concerned, simply because the spaceship would have to accelerate faster than the earth’s state of motion in order to leave it and then return.
Yet another reason why this idea has not been further developed (that time rates vary as a function of the state of motion of matter in space) may be due to another Relativity postulate which states that motion is meaningful only between two bodies moving relatively to each other. Since the universe is expanding, all observable matter in it must be in motion; therefore, we cannot locate a stationary point in the universe from which to measure the motion of a single body. Any and all of our measurements of motion may only be obtained by comparison to the relative motion and position of other objects.
Nevertheless, is not Einstein’s other premise (noted on page one in the third paragraph) that time and space are dependent on the state of motion of an observer - simply the one exception where motion is meaningful to something other than the relative motion of two bodies? The premise of the paragraph above holds true when we wish to measure the motion of objects in space because that requires other bodies to enable us to compare their motions.
Still, my contention that motion is meaningful to something other than just the motion of two bodies, where time is dependent on the state of motion of objects, is also relevant and holds true to measurements taken by observers whose states of motion differ, as they do in our moving-train and space-traveler-twin experiments. We have already noted above that it is the difference in the states of motion of the observers that yields consequential outcomes in measurements of time.

 

No, the definition of Chronological age is a commonly accepted definition and are the basis for things like when you are old enough to marriage or vote in a election (in democracies). Chronological age is not the sum of seconds that a clock attached to your brain had ticked since your birth. It´s measured in years, months and days. Ask a random person that lives in an the "developed" part of the world how old he/she is and you will get her/his chronological age as answer. Perhaps he/she will add something like "but a feel much younger" (a difference between self determined psychological age and chronological age). So the two twins in the twin paradox has the same chronological age when the reunited. SR has no effect on chronological age.

Lets elaborate more about this matter. Let both twins go on two separated journeys into space. Then the reunite somewhere. There will still be no age difference between them regardless of their respective paths through space-time. It could be a difference in the accumulated reading from clocks that they had brought with them, and their biological age will show some difference.

 

Nope, your are missing the point. You are still thinking that the stay at home twin is measuring the "real" time so that is what should be used as the chronological time. The twin that traveled could just as easily say that (according to him) the stay at home twin is biologically older but chronologically they are they are the same. Time is relative and you an pick either time as your basis there is no prefered frame.

 

No, I don't think it's formally defined. But your meaning is clear.
It's standard Earth time. Time according to clocks on Earth. The stay-at-home clocks, as I said.

Now you're stepping beyond what you know, and assuming that Earth-standard time is Universal.
How exactly do you intend to measure their "chronological age" in that scenario?

 

Pete, we have no evidence that humans are not connected to earth. For us Earth standard time equals Universal standard time. If we sometimes in the furture will be able to establish a a presens in deep space we still needs a standard time. Without a standard time a it would be hard to have a working society. The two twins doesn't need to know what theire earth standard time is when they reunite in space to know that they have the same age (even if they doesn't knows how old they are).

An age definition based on "proper time" would be meaningsless because we doesn't knows our "proper time"-age.

A question, which part of a human is the center of "proper proper time". Remember that our bodies are not at rest in regard to itself.

 

Origin, both twins will agree when they catch up on how many years it has been since their births. That's because the definition of a year.

 

Biological aging is depedent of several known and unknown variables. There is strong evidence that psychological stress like social deprivation accelerates biological aging. It is reasonable to believe that the space-trip twin would be exposed to social deprivation and other forms of psychological stress during his journey. There will be nummerous other potential aging important factors besides "proper time" that differ between the two twins in the twin-paradox scenario.

There is no shortcuts in science. To know the answer regarding the biological age in the twin paradox we need to perform research, medical research on humans during such space-flights.

So the answer to the twin paradox scenario is:
Chronological age=same
Biological age=unknown

 

Yes, and he's potentially exposed to more radiation, more G-forces etc. Doesn't matter; military pilots are exposed to that as well and they don't get to vote at an earlier age.

Perform medical research on the effect of spaceflight on humans? Definitely, and we've been doing that since the 1950's.

Perform medical research to resolve the twin paradox? No testing or medical research is needed. It's resolved.

The answer is:

Twin 1's age = chronological age based on a clock that stays with him
Twin 2's age = chronological age based on a clock that stays with him

 

No they won't. The stay at home twin can mark of each day on a calender, and the traveling twin can mark of each day on the calender. When they meet back up they will disagree on how many days, months, or years have passed. You have an earth-centric view of the universe and mistakenly think that the earth is somehow special. You may think that the north pole is at the top of the earth but that is also a silly way to think about the universe.

The only result that is occuring with your insistance that chronological time is earth time is tha you are confusing yourself about the meaning of relativity.

 

Maybe it would help if you just dropped the adjective "biological" altogether. I think this is causing you needless confusion. Suppose we just refer to all things, alive or not, as having an age.

Nevertheless, the space traveler be younger than his twin when he returns.

You mean "are". As you develop in your education, you will discover that Special Relativity is not a shortcut. Your attempt to refute it is the short cut. All you need to do is to wrestle with the math and physics, and over time you'll understand it. That's the "long cut".

You can start by noting that there are already systems in place today that correct for the time difference. One of the ones most familiar is GPS. The satellite clocks run slightly slower than clocks on earth. Precisely locating your latitude and longitude requires that the clocks be precisely synchronized. So the GPS system corrects for the time difference automatically. Without the correction, the system would be useless.

You mean, come up with a way to test their ages. Then send a twin away so fast and so far that the age difference will be noticeable. It's not practical. There are limits to spacecraft speed and the amount of food, water and energy that can be put on the ship. More importantly, since relativity is already understood, there is no purpose to this kind of experiment.

No. Drop the "biological": age is just age. Age is a function of time. Time is relative. Therefore, upon the return of the traveling twin, his age will be less than the stay at home twin. There's no way around it, no matter how many ways you seek a short cut, a switchback or an end-around.

 

Bot attack.