How does the Twins Paradox challenge our understanding of ageing?

[jadgerz]

Janus is correct. An accelerometer detects proper acceleration, not coordinate acceleration. So an accelerometer in orbit (or any free fall) reads 0. A spacecraft is not always in free fall, so the fact that it reads 0 in orbit doesn't prevent it from being useful.

I didn't say he was wrong. I just wanted to give him the opportunity to say it correctly. Unfortunately you had to say it for him.

 

[jadgerz]

What about lateral red shift? That is if an light emitting object in space is moving toward us we see a blue shift and if it is moving away from us we see a red shift. If an object is moving laterally we should also see a red shift due to the time dilation effect slowing the frequency of the particular transition observed. This may have already been done? If not this seems like a great experiment waiting to be done. How exactly you determine the motion of the object by means other than red shift is the question. I would think jets emitted from things that have jets (i.e. neutron stars with accreting matter?) would work.

I'm being lazy about this but has anyone figured out how fast an object is receding at the furthest distance observed by the Hubble telescope (using the Hubble constant). Is it 13 billion years? Maybe we can observe Cepheid variables in those far away galaxies and be able to infer something about time dilation by this observation? Just a thought.

 

[edpell]

This called the transverse Doppler effect and has been observed:

http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Tests_of_time_dilation

I did the Mossbauer experiment in a senior lab class. It is so impressive to see the sample crawl along at millimeters per second and still be able to easily see the Doppler effect. I was thinking that some variation would be usable for a time dilation experiment and yes here it is 1960 :|

# Hay et al., Phys. Rev. Lett. 4 (1960), pg 165.

A Mössbauer absorber on a rotor.
# Kuendig, Phys. Rev. 129 no. 6 (1963), pg 2371.

A Mössbauer absorber on a rotor was used to verify the transverse Doppler effect of SR to 1.1%.

I find this much more compelling than the airplane experiment. This is so much easier to understand.

 

[edpell]

and the 1.1% is much better than the airplane experiment accuracy

thanks jtbell

 

[jadgerz]

What about lateral red shift? That is if an light emitting object in space is moving toward us we see a blue shift and if it is moving away from us we see a red shift. If an object is moving laterally we should also see a red shift due to the time dilation effect slowing the frequency of the particular transition observed. This may have already been done? If not this seems like a great experiment waiting to be done. How exactly you determine the motion of the object by means other than red shift is the question. I would think jets emitted from things that have jets (i.e. neutron stars with accreting matter?) would work.

I believe Edpell "hit the nail on the head". Jets emitted from neutron stars are purported to be 99.8 percent the speed of light. Where do we get an opportunity to observe near light speed with ordinary matter like this? Can any of you geniuses out there propose a test to observe time dilation phenomena by taking advantage of this opportunity? Let's see you put your money where your mouth is.

 

[edpell]

In fact this is so simple and compelling I would say it is worth doing again with today's technology to lower the experimental error down from 1.1% to whatever we can get to today.

 

[edpell]

Can any of you geniuses out there ...

I appreciate the support but lighten up. Most folks here are friendly.

 

[Dale]

Where do we get an opportunity to observe near light speed with ordinary matter like this?

In Upton, New York

http://en.wikipedia.org/wiki/Relativistic_Heavy_Ion_Collider

 

[edpell]

In Upton, New York

http://en.wikipedia.org/wiki/Relativistic_Heavy_Ion_Collider

Yes and no. At Brookhaven matter goes in a circle not a straight line. In a jet once it has cleared the source object by a few light hours (where the gravitational potential is changing slowly/little) it is simple motion in a straight line. I have nothing against Brookhaven data I would just like to know what the jet data says.

 

[edpell]

OK yes at the interaction points it is a straight line and if spilled from the accelerator it is a straight line. Peace.

 

[edpell]

Has anyone done an experiment at Brookhaven with radioactive ions and measuring the decay rate in the straight sections?

 

[Dale]

Yes and no. At Brookhaven matter goes in a circle not a straight line.

So what? It is still ordinary matter at highly relativistic speeds. And the path is actually a rounded off hexagon with six straight sections where the detectors are placed.

We have a lot more control over accelerator experiments than astronomical observations like you are talking about. In my mind looking at neutron star jets is like the H&K experiment and looking at accelerator data is like the Mossbauer absorber. Sure, you could do the jets, but there are so many uncontrolled variables that it would just be messy data. That said, I wouldn't be surprised if it has already been observed, in fact, that is probably how they got the estimate for the speed of the jets.

 

[edpell]

There is another interesting article in PRL 4(4) 1960 p176 by Cocconi and Salpeter "Upper Limit for the Anisotropy of Inertia from the Mossbauer Effect". I would love to read this now but I will have to wait until a day I am in a library with PRL.

How much money does PR make from selling articles that are older than 20 years old? Is it worthwhile to restrict everyone's access for that amount of money?

 

[edpell]

Has anyone done an experiment at Brookhaven with radioactive ions and measuring the decay rate in the straight sections?

or muon life times? if it has been done what is the accuracy?

 

[edpell]

that is probably how they got the estimate for the speed of the jets.

I would guess you are right. In which case it is not a useful way to measure time dilation.

When people talk about accelerators they talk about muon tracks that are many times longer than the track length traveled in one muon lifetime. But has the SR affected muon lifetime in fact been measured? To what level of accuracy?

 

[Dale]

has the SR affected muon lifetime in fact been measured?

You know, I am a little tired now, so I may be a little over-sensitive, but I am finding this question rather obnoxious when such experiments have already been cited at least 3 times in this thread alone, twice by me. How many times in a single conversation do I have to provide references before others can be bothered to look at them?

Please, at a minimum, look at the FAQ in the section on time dilation. The experimental evidence is overwhelming.

 

[atyy]

When people talk about accelerators they talk about muon tracks that are many times longer than the track length traveled in one muon lifetime. But has the SR affected muon lifetime in fact been measured? To what level of accuracy?

http://pdg.lbl.gov/2009/tables/contents_tables.html
http://arxiv.org/abs/0902.1756
http://relativity.livingreviews.org/Articles/lrr-2005-5/

 

[Al68]

So the Earth twin will see no change in the tick rate of the traveling clock during the trip?

Yes, since the relative velocity drops to zero at one point. But the traveling clock runs faster as it slows down, to a max of the same rate of Earth's clock, then runs slower as the relative velocity increases again. Certainly we can't say the acceleration slowed down the ship clock when it runs the slowest during inertial motion.

I thought that "change in v" = "acceleration".

Yes, but not necessarily acceleration of the clock. The change in the rate of a clock depends on a change in v in exactly the same way whether the clock accelerates or the reference frame accelerates instead.

 

[Mentz114]

For the umpteenth time, may I point out the confusion between 'time dilation', the fact that IFRs in relative motion see each others clocks slowed by the gamma factor, and differential ageing. The first is an observer dependent effect, the second is not.

If you believe that the mutual apparent slowing of clocks is not observer dependent, then this leads to an apparent paradox.

Instantaneous observations of another frames clock cannot be used to extrapolate to what will happen when the clocks meet and are compared. They are different phenomena.

I don't expect this post to make any difference because some posters here (jadgerz ) don't understand SR and are clearly driven by some prejudice or other.

 

[Dale]

While we are pointing out confusions I would also like to point out that time dilation is actually a function of speed in the inertial frame, not velocity nor acceleration. Different velocities with the same speed will exhibit the same time dilation and accelerations that change velocity without changing speed will not change time dilation.

I will make an effort to use the correct terminology in the hopes that it will avoid some of this confusion in the future.

 

[jadgerz]

For the umpteenth time, may I point out the confusion between 'time dilation', the fact that IFRs in relative motion see each others clocks slowed by the gamma factor, and differential ageing. The first is an observer dependent effect, the second is not.

If you believe that the mutual apparent slowing of clocks is not observer dependent, then this leads to an apparent paradox.

Instantaneous observations of another frames clock cannot be used to extrapolate to what will happen when the clocks meet and are compared. They are different phenomena.

I don't expect this post to make any difference because some posters here (jadgerz ) don't understand SR and are clearly driven by some prejudice or other.

I guess after that remark I'm going to have to pull out "The Big Guns"! Okay, first, here is my position on all this. Yes! The MATH for SR and GR all work out well on paper. It's comprehensible by anyone who has taken any math course up to differential equations. But math equations can be made to fit any theory. The problem comes from physical testing of the phenomena. Although people quote various experiments which "prove" relativity a scrutiny of those tests show remarkable flaws. The H&K experiment from 1971 was discredited by Dr. A.G. Kelly's critique in the 1990's. I strongly recommend it be read. I'll even print excerpts here later to press my point. "Ahaa!" you say, but later experiments with more accurate methods proved it! Here's where Dr. Louis Essen's work comes in. For anybody who does not who Dr. Essen is he is the inventor of the atomic clock. His "complaint" was that atomic clocks can not be used to accurately test relativity due to intrinsic problems related to atomic clocks themselves. Thus any test on relativity using atomic clocks must be suspect. Note however, that neither of these gentlemen deny relativistic effects. They simply critique the means used to test it.

The next point of the argument is that GPS proves relativity. Well, here is what the NAVY (the people who developed and run the GPS program) themselves have to say about that. This is an excerpt from an article published by the military in 1996 on the matter:


["The Operational Control System (OCS) of the Global Positioning System (GPS) does not include the rigorous transformations between coordinate systems that Einstein's general theory of relativity would seem to require - transformations to and from the individual space vehicles (SVs), the Monitor Stations (MSs), and the users on the surface of the rotating earth, and the geocentric Earth Centered Inertial System (ECI) in which the SV orbits are calculated. There is a very good reason for the omission: the effects of relativity, where they are different from the effects predicted by classical mechanics and electromagnetic theory, are too small to matter - less than one centimeter, for users on or near the earth."]

Note the phrase: "...(GPS) does NOT include the rigorous transformations between..."

Want more? Here it is:

[Tom Van Flandern, an astronomer hired to work on GPS in the late 1990s, concluded that "The GPS programmers don't need relativity." He was quoted as saying that the GPS programmers "have basically blown off Einstein." Asynchronization can be easily addressed through communications between the satellites and ground stations, so it is unclear why any theory would be needed for GPS. But other obscure physicists having no connection with GPS design claim that Van Flandern is wrong about GPS, and insist that relativity provides the best explanation for its timing adjustments.]

Even more from Dr. Neil Ashby, Univ. of Colorado, who has published a few professional articles on GPS states:

["Currently, GPS satellites are synchronized to Coordinated Universal Time by radio signals from the ground; therefore, they cannot currently be used to test general relativity."]

As that little old lady used to say: "Where's the beef?!" Indeed!

 

[atyy]

Ashby, Relativity in the Global Positioning System
http://relativity.livingreviews.org/Articles/lrr-2003-1/

"Also, experimental tests of relativity can be performed with GPS, although generally speaking these are not at a level of precision any better than previously existing tests."

"There is an interesting story about this frequency offset. At the time of launch of the NTS-2 satellite (23 June 1977), which contained the first Cesium atomic clock to be placed in orbit, it was recognized that orbiting clocks would require a relativistic correction, but there was uncertainty as to its magnitude as well as its sign. Indeed, there were some who doubted that relativistic effects were truths that would need to be incorporated [5]! A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by general relativity, then the synthesizer could be turned on, bringing the clock to the coordinate rate necessary for operation. After the Cesium clock was turned on in NTS-2, it was operated for about 20 days to measure its clock rate before turning on the synthesizer [11]. The frequency measured during that interval was +442.5 parts in 10¹² compared to clocks on the ground, while general relativity predicted +446.5 parts in 1012. The difference was well within the accuracy capabilities of the orbiting clock. This then gave about a 1% verification of the combined second-order Doppler and gravitational frequency shift effects for a clock at 4.2 Earth radii. "

 

[jadgerz]

Ashby, Relativity in the Global Positioning System
http://relativity.livingreviews.org/Articles/lrr-2003-1/

"Also, experimental tests of relativity can be performed with GPS, although generally speaking these are not at a level of precision any better than previously existing tests."

"There is an interesting story about this frequency offset. At the time of launch of the NTS-2 satellite (23 June 1977), which contained the first Cesium atomic clock to be placed in orbit, it was recognized that orbiting clocks would require a relativistic correction, but there was uncertainty as to its magnitude as well as its sign. Indeed, there were some who doubted that relativistic effects were truths that would need to be incorporated [5]! A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by general relativity, then the synthesizer could be turned on, bringing the clock to the coordinate rate necessary for operation. After the Cesium clock was turned on in NTS-2, it was operated for about 20 days to measure its clock rate before turning on the synthesizer [11]. The frequency measured during that interval was +442.5 parts in 10¹² compared to clocks on the ground, while general relativity predicted +446.5 parts in 1012. The difference was well within the accuracy capabilities of the orbiting clock. This then gave about a 1% verification of the combined second-order Doppler and gravitational frequency shift effects for a clock at 4.2 Earth radii. "

Dr. Ashby also wrote in another article:

At present one cannot easily perform tests of relativity with the system because the SV clocks are actively steered to be within 1 microsecond of Universal Coordinated Time (USNO).

Several relativistic effects are too small to affect the system at current accuracy levels, but may become important as the system is improved; these include gravitational time delays, frequency shifts of clocks in satellites due to Earth's quadrupole potential, and space curvature.

Dr. Ashby also mentions the fact that any real scientific scrutiny of GPS is not possible due to the fact that the operations of GPS are classified by the military. The military itself, in the 1996 article states that it does not include relativistic adjustments in it's programming. No need. Dr. Ashby mentions it would be a great tool in the study of relativistic effects and indeed it would. But validation would only be possible if or when the military declassifies the GPS operations.

 

[Dale]

First, I would like to remind you that PhysicsForums is not for personal theories nor for crackpot arguments against mainstream science, there are plenty of other internet forums for that. PhysicsForums is for helping students and others learn about mainstream science. You specifically agreed to those terms when you signed up for your account, and citations of notorious crackpots like Van Flandern are a violation of your agreement.

Yes! The MATH for SR and GR all work out well on paper. It's comprehensible by anyone who has taken any math course up to differential equations. But math equations can be made to fit any theory.

This is simply wrong. The math and how you use the math to make experimental predictions are the theory. So you cannot make math equations fit any theory because if you change the math you have changed the theory.

What you may be thinking of is the fact that you can always produce multiple interpretations of the same theory. I.e. you can ascribe different meanings to the various mathematical quantities. A good example is the relationship between SR and Lorentz's Aether Theory which are both different interpretations of the same mathematical theory, the Lorentz transform. I am not sure if your stance is that the Lorentz transform is correct, but SR is an incorrect interpretation, or if you believe that the Lorentz transform is wrong.

His "complaint" was that atomic clocks can not be used to accurately test relativity due to intrinsic problems related to atomic clocks themselves. Thus any test on relativity using atomic clocks must be suspect. Note however, that neither of these gentlemen deny relativistic effects. They simply critique the means used to test it.

A simple look at history debunks this critique. The first accurate atomic clock was built in 1955. So none of the many experimental confirmations of SR before 1955 could possibly be subject to this weakness. See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html. There are also many experiments after that time, such as Kuendig's 1963 experiment with a Mossbauer absorber on a rotor, that did not rely on atomic clocks.

Let me be clear here, I am not in any way accepting your critique of atomic clocks, but for the sake of argument I am just pointing out that the success of SR does not hinge on that.

 

[jadgerz]

First, I would like to remind you that PhysicsForums is not for personal theories nor for crackpot arguments against mainstream science, there are plenty of other internet forums for that. PhysicsForums is for helping students and others learn about mainstream science. You specifically agreed to those terms when you signed up for your account, and citations of notorious crackpots like Van Flandern are a violation of your agreement. This is simply wrong. The math and how you use the math to make experimental predictions are the theory. So you cannot make math equations fit any theory because if you change the math you have changed the theory.

What you may be thinking of is the fact that you can always produce multiple interpretations of the same theory. I.e. you can ascribe different meanings to the various mathematical quantities. A good example is the relationship between SR and Lorentz's Aether Theory which are both different interpretations of the same mathematical theory, the Lorentz transform. I am not sure if your stance is that the Lorentz transform is correct, but SR is an incorrect interpretation, or if you believe that the Lorentz transform is wrong.

A simple look at history debunks this critique. The first accurate atomic clock was built in 1955. So none of the many experimental confirmations of SR before 1955 could possibly be subject to this weakness. See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html. There are also many experiments after that time, such as Kuendig's 1963 experiment with a Mossbauer absorber on a rotor, that did not rely on atomic clocks.

Let me be clear here, I am not in any way accepting your critique of atomic clocks, but for the sake of argument I am just pointing out that the success of SR does not hinge on that.

So why do they still let you in here? I don't propose any theory "of my own". Your description of Van Flandern as a "notorious crackpot" is pure libel. Lucky for you Van Flandern died of cancer last year and can't defend himself. But I'm sure you knew that. Van Flandern received a scholarship at Yale from the US Naval Observatory, received his PhD and went on to work for the USNO for several years. Much of his work with GPS and contributed quite a bit to it's development. The USNO didn't think he was a crackpot. What's your contribution to the science? And quite frankly, it is YOU who are wrong.

 

[Dale]

So why do they still let you in here? I don't propose any theory "of my own".

I know, that is why I said "PhysicsForums is not for personal theories nor for crackpot arguments against mainstream science". Please review the rules.

quite frankly, it is YOU who are wrong.

Then please, address the substance of my rebuttals and show where I was wrong. The fact remains that the experimental support for SR is broad and overwhelming. It simply does not hinge on a couple of key technologies.

 

[edpell]

may I point out the confusion between 'time dilation', the fact that IFRs in relative motion see each others clocks slowed by the gamma factor, and differential ageing. The first is an observer dependent effect, the second is not.

I agree this is an important point. As the two move away from each other they have to wait for the light from the other clock to traverse the increase distance between them. So they both see the others clock as running slow.

My question is is the boosted clock is time dilated will the Earth oberserve see it double slow. Slow because it is time dilated and slow because the light takes longer to arrive due to the increasing distance?

I also wonder if the biology teach who started this thread is still here. :)

 

[russ_watters]

That's enough of that. Locked.