Twin Paradox

[harry]

G'day from the land of ozzzzzz

The Twin Paradox has been dicussed for over 100 yrs.

What is your opinion on the matter?

Was Einstein wrong?

[rstevenson]

The Twin Paradox has been dicussed for over 100 yrs.

Indeed.

What is your opinion on the matter?

There is no paradox.

Was Einstein wrong?

Since he agrees with me, I think not.

Rob

[apodman]

I think not.

You must watch what you say. As the story goes, René Descartes was on an airplane when the flight attendant asked him if he'd like cream in his coffee. When he replied, "I think not," he vanished in a puff of logic.

---

Special relativity is only for inertial reference frames, and the twin who feels the force of acceleration is not in one, so there is no actual paradox. The paradox is only in name and only in the question which is immediately answered.

[rstevenson]

I think not.

You must watch what you say. As the story goes, René Descartes was on an airplane when the flight attendant asked him if he'd like cream in his coffee. When he replied, "I think not," he vanished in a puff of logic.

---

Special relativity is only for inertial reference frames, and the twin who feels the force of acceleration is not in one, so there is no actual paradox. The paradox is only in name and only in the question which is immediately answered.

Exactly so. This is one of those things that is paradoxical only when an attempt is made to express the issue in a spoken language, like English. Mathematically speaking, the paradox is not evident. For more on that, the curious can see http://en.wikipedia.org/wiki/Twin_Paradox

Rob

[Chris Peterson]

The Twin Paradox has been dicussed for over 100 yrs.

The term "paradox" is only there because some people found (or continue to find) the concept non-intuitive. There is no paradox in the true sense.

What is your opinion on the matter?

There should be no difference of "opinion" in this matter; the effect is easily observed experimentally.

Was Einstein wrong?

See previous.

[The Code]

Hi harry...And everybody



If the clocks were at different times at a low speed,, At what speed and point can they no longer see each other, When they get back to the start point? How can i see a person sitting on a bench last week, or that same person on the same bench next week. If the clock goes fast or slow enough when does the man on the bench in both future and past time zones see the clock?

If i had a twin... How could i come back and see, two different time zones at the same time? If ''I'' was a photon,, how long did my journey take ,, from 500 million years after the BB to earth?
If speed says that all time must flow at our ticking clock. Is all of time ''at one point'' minus speed?
Mark

[BMAONE23]

Theoretically speaking (with a little science fiction thrown in)
You would need 3 things,
1) a ship capable of traveling faster than light
2) a telescope capable of seeing the person on the bench at that distance.
3) faster than light communication

Launch this super telescope to a point that is 7 light days away and focus it on the bench. The light it sees is 7 days old or last weeks light thereby seeing 7 days in the past. Without being able to send the signal faster than light, the experiment will still only show you what was there as the light time is still 7 days for the signal to reach you.

[harry]

G'day from the land of ozzzzz

I hope this answers the issue

http://aps.arxiv.org/abs/physics/0501131
Einstein's concept of a clock and clock paradox

Authors: Wang Guowen
(Submitted on 25 Jan 2005)

Abstract: A geometric illustration of the Lorentz transformations is given. According to similarity between space and time and correspondence between a ruler and a clock, like the division number in a moving ruler, the tick number of a moving clock is independent of its relative speed and hence invariant under the Lorentz transformations. So the hand of the moving clock never runs slow but the time interval between its two consecutive ticks contracts. Thus it is Einstein's concept of slowing of the hands of moving clocks to create the clock paradox or twin paradox. Regrettably, the concept of the clock that Einstein retained is equivalent to Newton's concept of absolute time that he rejected. This is a blemish in Einstein's otherwise perfect special relativity.

5 Conclusion
We have seen that, like the division number in a moving ruler, the tick number of a
moving clock is independent of its relative speed and hence invariant under the Lorentz
transformations. So the hand of the moving clock never runs slow but the time interval
between its two consecutive ticks contracts. Thus it is Einstein’s concept of slowing of
the hands of moving clocks to create the clock paradox or twin paradox. Regrettably,
his way to measure time is identical with Newton’s. In other words, the concept of
the clock that he retained is equivalent to Newton’s concept of absolute time that he
rejected.
Similar to the clock’s ticking, the heart beating of the travelling twin never runs really
slow but according to special relativity the beating period between two consecutive
beats contracts. Since the human lifetime may be considered as being basically determined
by the total number of the heart beats, no one of the twins will become younger
than the other when they reunite. Thus, the general relativity is not required to resolve
the twin paradox. It is Einstein’s assertion of slowing of the hands of moving clocks to
create the paradox and hencemake many physicists believe slowing of all physical processes
with the increased speed, including chemistry reactions, nuclear reactions, life
process and others. This is a blemish in Einstein’s otherwise perfect special relativity.
Finally, the author would say that if the present conclusion is correct, it will prohibits
us from believing the assertion that some related experiments [8,9] have confirmed
the Einstein’s prediction of slowing of moving clocks that creates the clock
paradox.

[apodman]

Poppycock.

[Chris Peterson]

I hope this answers the issue

http://aps.arxiv.org/abs/physics/0501131
Einstein's concept of a clock and clock paradox

I'd argue that for the vast majority of interested people, that just makes the whole thing a lot harder to understand. A much better discussion is found in the Wikipedia article on the Twin Paradox, which describes quite clearly, using arguments from both Special Relativity and General Relativity, why there is no paradox. (In all cases, the important point being simply that relativity is not violated because one of the twins is not traveling in an inertial frame for the entire journey.)

As a rule, primary sources (regardless of quality) are generally the wrong sort of references to use for answering general astronomical questions. If you're going to answer a question, how about simply answering it in your own words, and possibly supplying an additional reference or two to Wikipedia or one of the many sites that offer articles written for intelligent, interested, non-specialists? Original research papers are best reserved for discussions around very fine points- discussions which usually don't occur (and usually shouldn't occur) on this forum.

[neufer]

I once worked for a Prof. Carroll 0. Alley at the Univ. of Md. who sent atomic clocks on jet aircraft such that the eastbound clocks were closer to being in free fall and hence ran faster than gravitationally slowed earth clocks or clocks on westbound jet aircraft:

In 1972, scientists flew extremely accurate clocks around the world in both directions on commercial airlines, and were directly able to observe the relativistic "twin paradox" the eastbound clock gained 273 ns and the westbound clock lost 59 ns, matching the predictions of general relativity to within experimental accuracy.

[Chris Peterson]

I once worked for a Prof. Carroll 0. Alley at the Univ. of Md. who sent atomic clocks on jet aircraft such that the eastbound clocks were closer to being in free fall and hence ran faster than gravitationally slowed earth clocks or clocks on westbound jet aircraft...

Indeed. However, the "paradox" aspect doesn't stem from the fact that the effect occurs (which is easily observed), but from the fact that- superficially- it seems as if it shouldn't. That's because relativity seems to suggest that either twin should see the other as moving and himself as stationary. So there appears to be an asymmetry that violates relativity. In fact, the actual system is asymmetric because one of the twins experiences acceleration (including a change in direction), so you don't have a pair of inertial frames and there is no requirement for symmetry- either under SR or GR.

[The Code]

hi

So what changes the clock, baring in mind A jet air craft's speed is nothing to what speed our planet is traveling at,, around the sun, around the galaxy,, Did i once here our galaxy is moving very fast also? seems A large clock movement ,, for 3,000,000 mph + or minus (500) mph differance? Our earth is not a clock at rest is it?

That's because relativity seems to suggest that either twin should see the other as moving and himself as stationary.

What is absolute stationary? How can you tell what that figure is?

Mark

[Chris Peterson]

What is absolute stationary? How can you tell what that figure is?

There's no such thing as "absolute stationary"- that's a big part of what relativity is all about. As far as comparing a pair of clocks (which is a pretty easy experiment), you don't care if both are on a moving planet in a moving star system in a moving galaxy. All you care about is the relative motion between the two. So you call the one on the ground "stationary" and the one in the airplane "moving".

[makc]

All you care about is the relative motion between the two.

but then haven't you just lost an effect of "real", "absolute" acceleration right there? twins are out of sync because space is differently "curved" for them, but if you simply look at their relative motion, you are throwing this difference out of the window, and end up in paradox.

[Chris Peterson]

All you care about is the relative motion between the two.

but then haven't you just lost an effect of "real", "absolute" acceleration right there? twins are out of sync because space is differently "curved" for them, but if you simply look at their relative motion, you are throwing this difference out of the window, and end up in paradox.

I don't see the problem. The asymmetry comes from the fact that you can only compare the clocks (or the twins) once they are back in the same place, and the only way to get them back in the same place again is for one or both to be moving at some point in a non-inertial frame. At its simplest, we consider that to be the clock (or twin) in the spaceship. There's no way that the ship can return to its starting point while remaining in an inertial frame the entire trip.

I'm not saying you can ignore velocity changes, only that you can ignore the effects of any larger frames that contain both twins, such as the motion of the galaxy as a whole.

[geckzilla]

I tried going to the Wikipedia article a few times in the past couple of days to figure this out but my feeble mind can't seem to grasp it. This thread isn't helping either. It's funny, I have heard of this before and even though I can't understand it, I just give the scientists the benefit of the doubt and say ok, I guess that's what happens when someone travels at the speed of light.

[neufer]

I tried going to the Wikipedia article a few times in the past couple of days to figure this out but my feeble mind can't seem to grasp it. This thread isn't helping either. It's funny, I have heard of this before and even though I can't understand it, I just give the scientists the benefit of the doubt and say ok, I guess that's what happens when someone travels at the speed of light.

Another Professor that I had was David H. Frisch. If anyone peeked in on his MIT class through the door window Prof. Frisch would toss his piece of chalk so fast & accurately that it would loudly shatter on the door window. I don't know how much time dilation there was on the chalk but he did make this classic film on meson time dilation: http://www.scivee.tv/node/2415

[makc]

All you care about is the relative motion between the two.

but then haven't you just lost an effect of "real", "absolute" acceleration right there? twins are out of sync because space is differently "curved" for them, but if you simply look at their relative motion, you are throwing this difference out of the window, and end up in paradox.

I don't see the problem. The asymmetry comes from the fact that you can only compare the clocks (or the twins) once they are back in the same place, and the only way to get them back in the same place again is for one or both to be moving at some point in a non-inertial frame. At its simplest, we consider that to be the clock (or twin) in the spaceship. There's no way that the ship can return to its starting point while remaining in an inertial frame the entire trip.

right, but that guy in (most) non-inertial frame is also seing the other guy accelerating, as in aceleration = change of velocity in his frame per unit of his time. if he only had to care about relative motion, he would, as the paradox part say, also expect the other guy to get younger, but in fact the other guy gets older at some point. the only choice for our guy therefore, if he wants to see his frame as if it was inertial (just the way we all do, btw, sitting on accelerated planet in accelerated solar system in accelerated galaxy etc etc), is to explain the discrepancy by some exotic "gravity" field that acts in distant areas of space where his fast-aging brother happens to travel - the space would look really distorted ("curved", whatever) to this guy, and this bit is kinda external to their relative motion. Somewhat similar to Coriolis force we are experiencing on Earth.

[harry]

G'day from the land of ozzzzz

Wow!!!!! Chris is right, the paper that I posted may be hard to read and Wiki may be the easier explanation.

Chris hit it on the head when he said

I'd argue that for the vast majority of interested people, that just makes the whole thing a lot harder to understand. A much better discussion is found in the Wikipedia article on the Twin Paradox, which describes quite clearly, using arguments from both Special Relativity and General Relativity, why there is no paradox. (In all cases, the important point being simply that relativity is not violated because one of the twins is not traveling in an inertial frame for the entire journey.)

The simple answer is that the Twin that moves the faster alters the "Matter" and thus alters the time. A difference of inertia.

This paper may also be of interest: Its talks of both asymmetry and symmetry situations.

http://aps.arxiv.org/abs/0804.2008
The Twin Paradox Revisited and Reformulated -- On the Possibility of Detecting Absolute Motion

Authors: G. G. Nyambuya, M. D. Ngobeni
(Submitted on 12 Apr 2008 (v1), last revised 6 Sep 2008 (this version, v3))

Abstract: The famous twin paradox of the Special Theory of Relativity by Einstein (1905) is revisited and revised. This paradox is not a paradox in the true sense of a paradox but a reflection of a misunderstanding of the problem and the Principle of Relativity. The currently accepted solution to this takes into account the accelerations and deceleration of the traveling twin thus introducing an asymmetry that solves the paradox. We argue here that, with the acceleration and deceleration neglected, the problem is asymmetric hence leading to the same conclusion that the traveling twin will age less than the stay at home. We introduce a symmetric twin paradox whose solution can not be found within the currently accepted provinces of the STR if one adopts the currently accepted philosophy of the STR namely that it is impossible for an inertial observer to determine their state of motion. To resolve this, we present (in our modest view) a simple and convincing argument that leads us to conclude that it must be possible for an inertial observer to determine their own state of motion. With this, we are able to solve the symmetric twin paradox. The fact that it is possible for an inertial observer to determine their state of motion -- brings us back to the long rejected idea of an all pervading and permeating medium -- the Aether, namely the Lorentz luminiferous Aether. An experiment capable of validating or invalidating this claim is suggested.

This apparent paradox arises from an incorrect application of
the Principle of Relativity to the description of the story by the
traveling twin’s point of view and the widely accepted resolution
of this apparent paradox goes as follows. From his [Taurwi]
point of view, the argument goes; his non-adventurous
stay-at-home brother is the one who travels backward on the
receding Earth, and then returns as the Earth approaches the
spaceship again, while in the frame of reference fixed to the
spaceship, the astronaut twin is not moving at all. It would
then seem that the twin on Earth is the one whose biological
clock should tick more slowly, not the one on the spaceship.
The “flaw” in the reasoning is that the Principle of Relativity
only applies to frames that are in motion at constant velocity
relative to one another, i.e., inertial frames of reference. The
astronaut twin’s frame of reference, is a noninertial system,
because his spaceship must accelerate when it leaves, decelerate
when it reaches its destination, and then repeat the whole
process again on the way back home. Their experiences are
not equivalent, because the astronaut twin feels accelerations
and decelerations thus leading to the conclusion that the traveling
twin will be younger when they are reunited. Given this
solution and that this typically presented in books that deal
with the STR at length, it is suprising that some notable authors
(see e.g. Kark 2007) still regard the twin paradox as a
paradox.
The real trick is the accelerations and decelerations experienced
by the traveling twin; these bring about the asymmetry
which leads to Taurwi being the one that experiences the time
dilation. From the purely idealized point of view, we can neglected
these accelerations and decelerations. If we did this –
will the scenario be symmetric? Since it is these accelerations
and decelerations that bring in the asymmetry, it must follow
that we must have a paradox because symmetry ought in this
case to be restored thus leading to a real paradox.

[makc]

re harry - I wonder how would they able to meet again with zero acceleration? this could only happen with very small universe where their lifetime would be enough to travel all the way right and return to the same spot from the left, but this kind of universe should be very weird in itself already, resembling some sort of mirror room.

edit: I just read that article, and - drum roll - it's crap (kinda explains why I do not normally read papers you post, huh). you should better look at the picture in this article (I have seen animated version of this, but just cant find it again). There, it is clear as day that due to infinite acceleration of B the whole 2 * beta-d interval of A's time is compressed into single moment. If B was slowly accelerating (realistic scenario), we'd see it compressed to shorter interval instead, where all of A's aging happens, according to B.

[harry]

G'day Makc

If you do not read papers they are all crap.

If you did read papers this would be interesting reading.

http://arxiv.org/abs/0908.1834
A variation of the clock paradox and a distinguishing feature of an inertial frame

Authors: Chandru Iyer, G.M. Prabhu
(Submitted on 25 Sep 2008)

Abstract: The clock paradox is analyzed for the case when the onward and return trips cover the same <<distance>> (as observed by the traveling twin) but at unequal velocities. In this case the stationary twin observes the distances covered by her sister during the onward and return trips to be different. The analysis is presented using formulations of special relativity and the only requirement for consistency is that all observations are made from any one chosen inertial frame. The analysis suggests that a defining feature of an inertial frame should be based on the continued maintenance of the distinctive synchronicity of the clocks co-moving with it. Published in Journal of Physical and Natural Sciences Volume 1, Issue 1, 2007 this http URL

Here is one for you MakC

http://aps.arxiv.org/abs/physics/0612126
A trip to the end of the universe and the twin paradox

Authors: Thomas Mueller, Andreas King, Daria Adis
(Submitted on 13 Dec 2006)

Abstract: In principle, the twin paradox offers the possibility to go on a trip to the center of our galaxy or even to the end of our universe within life time. In order to be a most comfortable journey the voyaging twin accelerates with Earth's gravity. We developed some Java applets to visualize what both twins could really measure, namely time signals and light coming from the surrounding sky.

[makc]

Here is one for you MakC

this one looks fine, but what's your point?

[Chris Peterson]

right, but that guy in (most) non-inertial frame is also seing the other guy accelerating, as in aceleration = change of velocity in his frame per unit of his time.

No, that's where the argument fails. Special Relativity is only valid for inertial frames. If an observer in one frame sees an object in another frame apparently changing velocity, he has to toss SR out of the assumptions and calculations. In the case of the Twin Paradox, the one who stays home is in an inertial frame (ignoring stuff like the rotation of the planet), and the one who leaves is not. That could be determined by each using, for instance, local accelerometers. The guy in the space ship could tell without uncertainty that he is in a non-inertial frame; even though he observes a relative change in velocity with respect to the frame of the other twin, there is no way he can assume that he is stationary and the acceleration is being experienced by the twin.

[neufer]

right, but that guy in (most) non-inertial frame is also seing the other guy accelerating, as in aceleration = change of velocity in his frame per unit of his time.

No, that's where the argument fails. Special Relativity is only valid for inertial frames. If an observer in one frame sees an object in another frame apparently changing velocity, he has to toss SR out of the assumptions and calculations.

The stay at home twin can calculate the time dilation of his decelerating traveling twin by simply using SR.
It is rather the decelerating traveling twin who must toss SR out of the assumptions & calculations.

Non-inertial frames (e.g., the surface of a white dwarf) needn't be accelerating.
Accelerating (free fall) frames needn't be non-inertial.