Satellite testing of relativity (split from measuring distance to satellite)

[Bjarne]

You send a signal with a response request then devide the time for the signal to get back to you by two. This way you can calibrate signal delay including electronic process delays.

A more accurate method though could be sending a request to the RTC (real time clock) on the satellite requesting the time of receiving a signal. Then compare to two precalibrated atomic clocks. One on Earth one on satellite.

From that data one can calculate the distance to a satellite. Granted we don't rely on one method. If you combine the previous data with parallax you can fine tune the distance/rate of signal.

 

After all a signal moving through a medium can cause delays so you will need to study and test that medium. (Ie atmosphere). After years of transmission though we have an extremely high degree of accuracy in knowing the properties of the atmosphere and local spacetime medium. (Though we still continually test it for changes).

 

That's one aspect ppl fail to recognize in science. We continously test. Particularly on something as critical on distance measures, redshift, luminosity/distance relation and relativity.

This continous testing leads to extreme fine tuning.

As such numerous tests are continuously developed to help strengthen our accuracy.

Sounds good, thanks

 

Another question which satellites/ orbis are used for testing relativity?

I mean most satellite have only GPS purposes,- I suppose

But which satellites are also used for systematical scientific test of relativity ?

Edited January 19, 2016 by Bjarne

[ajb]

Another question which satellites/ orbis are used for testing relativity?[/size]

I mean most satellite have only GPS purposes,- I suppose [/size]

The fact that GPS works is already a reasonable test of relativity, even it they were never intended specifically for that purpose.

 

 

But which satellites are also used for systematical scientific test of relativity ?[/size]

Interesting, two of the Galileo satellites intended for GPS were placed in incorrect orbits. The plan now is that they could be used to test relativity by using their clocks.

 

http://www.nature.com/news/wayward-satellites-repurposed-to-test-general-relativity-1.18780

 

-----------------------------------------------------

Wider than this, you should take a good look at Clifford M. Will, The Confrontation between General Relativity and Experiment, Living Rev. Relativity 17 (2014). You can download the paper for free from the journals website.

 

 

Edited January 19, 2016 by ajb

[Bjarne]

The fact that GPS works is already a reasonable test of relativity, even it they were never intended specifically for that purpose.

 

 

 

So why continue testing relativity ?

 

Chernobyl was also working very well (until it exploded),- just joking

 

[Strange]

So why continue testing relativity ?

 

Because that is what science does. It continually tests established theories. Things are never taken for granted. After all, finding errors in current theory is how advances are made.

[ajb]

So why continue testing relativity ?[/size]

Nobody really expects that there will be any results that conflict with general relativity, at least at the scales we can currently examine. Still, one should still test the theory as best we can.

 

It would be great if some clear signal of a more complete theory than GR could be found, that could help us understand quantum gravity for example. This I think would have to come from more extreme situations, maybe some 'fingerprint' from the early Universe or maybe from the physics of black holes.

[Mordred]

To improve upon its confidence level and accuracy. Relativity is a big pill for many to swallow. However if you think about it we test one aspect of relativity in particle accelerators 100's of times every day. That being inertial mass and the amount of energy required to accelerate the protons.

 

We even have an atomic clock on Mount Everest testing time dilation. Then you also have muon decay. Normally muons couldn't reach the Earths surface. But they do thanks to good ole time dilation.

 

Comments on the tests of relativity.

 

http://arxiv.org/pdf/0806.0528

 

http://www.astro.sunysb.edu/rosalba/astro2030/GeneralRelativity_tests.pdf

[Mordred]

 

No matter how confident we are in any theory the scientific method always considers some error. No theory is ever claimed 100%. So we continue to improve our confidence in a theory.

[Bjarne]

No matter how confident we are in any theory the scientific method always considers some error. No theory is ever claimed 100%. So we continue to improve our confidence in a theory.

Excactly

[Mordred]

Just to note if you plan on tackling relativity. You better have conclusive experimental evidence. I saw the thread that was locked. For lack of such. The Pioneer anomoly for example was figured out to be caused by anisotropic radiation loss due to the crafts own heat. You can get the paper in the reference on this page.

 

https://en.m.wikipedia.org/wiki/Pioneer_anomaly

 

Just a side note forums are battered with posters that assume something is wrong, believe they have the solution but can't even do the mathematical side of the theory they are fighting against.

Edited January 19, 2016 by Mordred

[Bjarne]

Do you have further questions on measuring satellite distance,?

 

Which satellites/ orbis are used for testing relativity?

I mean most satellite have only GPS purposes,- I suppose

But which satellites are also used for systematical scientific test of relativity ?

All Galileo sattelites send out by ESA ?

Others ?

[ajb]

Which satellites/ orbis are used for testing relativity?[/size]

I mean most satellite have only GPS purposes,- I suppose [/size]

But which satellites are also used for systematical scientific test of relativity ?[/size]

All Galileo sattelites send out by ESA ?

Others ?

To be perfectly honest, I am sure you can find the answers to these questions via google.

 

Look up Gravity Probe B for example...

Edited January 19, 2016 by ajb

[Bjarne]

To be perfectly honest, I am sure you can find the answers to these questions via google.

Off course but can be time consuming

[ajb]

Off course but can be time consuming

So you would rather we do the donkey work for you?

 

Well, I have done some... a good example of a satellite whose purpose is to test GR is Gravity Probe B. You can find out lots of information about this on their official website. Google will find that for you.

[Bjarne]

So you would rather we do the donkey work for you?

 

Well, I have done some... a good example of a satellite whose purpose is to test GR is Gravity Probe B. You can find out lots of information about this on their official website. Google will find that for you.

I read these few articles, nothing about atomic clock on board ??

 

http://www.nature.com/news/2004/040412/full/news040412-11.html

https://en.wikipedia.org/wiki/Gravity_Probe_B

 

I think the probe did not do any SR test right ?

 

Bjarne - I still don't know what more you want from satellites in order to be a valid experimental test-bed. The early Galileo test satellites had three independent and differently designed atomic clocks - whilst Major Tim Peake (and his friends - but he gets a mention from a fellow Brit) are useful and great for the media - human intervention is not essential; there are oodles of experiments and comparisons with predictions that can be done with an array of satellites all with 10^-14ish sec accuracy clocks.

I start reading about Galileo GPS satellites, so far I have understood only 2 (Galileo 5 and 6) will undergo systematically scientific test, - of the theory of relativity - is this correct ,

http://gpsworld.com/esa-releases-diagrams-showing-galileo-5-and-6-orbit/

Edited January 19, 2016 by Bjarne

[imatfaal]

I read these few articles, nothing about atomic clock on board ??

 

http://www.nature.com/news/2004/040412/full/news040412-11.html

https://en.wikipedia.org/wiki/Gravity_Probe_B

 

I think the probe did not do any SR test right ?

I start reading about Galileo GPS satellites, so far I have understood only 2 (Galileo 5 and 6) will undergo systematically scientific test, - of the theory of relativity - is this correct ,

http://gpsworld.com/esa-releases-diagrams-showing-galileo-5-and-6-orbit/

 

Bjarne - all the atomic clocks satellites in all the various GPS systems need to be adjusted for their relative velocity and the change in gravitational potential; how is this not a wide-spread, on-going, real-world test of relativity?

 

If GR (remember SR is a limited case of GR) was not correct - ie if its predictions of time dilation were askew - then your GPS, my mobile phone, and his aircraft navigation system would go awry in a matter of days.

 

The time corrections predicted by GR are on the order of tens of microseconds per day - but the accuracy of GPS is on the order of the distance light travels in nanoseconds (a light nano-second is about a foot - lovely coincidence n'est-ce pas?). So for triangulation to work (ok it is not simple triangulation) the time signal sent from each clock must be corrected adjusted. The triangulation does work so the adjustment is correct. It is too much of a logical leap to say therefore GR works - but it is very persuasive. And any theory that says that GR is wrong has to explain (without the use of GR) why the time adjustment is what it is.

[swansont]

Excactly

 

I doubt you would have agreed if you understood what Mordred meant. The testing is not so much to check that the theory might be overturned — there's way to much corroborating evidence for that to happen. It's to see if there is disagreement out at some distant decimal place, to see if there's new physics needed. Relativity for the things we use it for already would be unaffected, much like classical calculations of e.g. kinetic energy still work for most problems. They only diverge from correct values for energy that's above some noticeable fraction of the rest mass energy.

 

IOW, at this point it's about the possibility of needing to tweak the theory, not the possibility we need to discard it.

[Mordred]

Correct couldn't have explained it better myself

[Bjarne]

 

Bjarne - all the atomic clocks satellites in all the various GPS systems need to be adjusted for their relative velocity and the change in gravitational potential; how is this not a wide-spread, on-going, real-world test of relativity?

 

If GR (remember SR is a limited case of GR) was not correct - ie if its predictions of time dilation were askew - then your GPS, my mobile phone, and his aircraft navigation system would go awry in a matter of days.

 

The time corrections predicted by GR are on the order of tens of microseconds per day - but the accuracy of GPS is on the order of the distance light travels in nanoseconds (a light nano-second is about a foot - lovely coincidence n'est-ce pas?). So for triangulation to work (ok it is not simple triangulation) the time signal sent from each clock must be corrected adjusted. The triangulation does work so the adjustment is correct. It is too much of a logical leap to say therefore GR works - but it is very persuasive. And any theory that says that GR is wrong has to explain (without the use of GR) why the time adjustment is what it is.

I can easy understand your points, and agree that the theory of relativity seems to have fit the bill very exact for decades, GPS etc..

But I also agree that there are still several good reasons to keep testing.

Furthermore I think that if the attention is 100% scientific, - it is 90% better than if the attention only is 10% scientific..

Lack of attention was for example the cause of the biggest atomic catastrophe in the word. It is human to fail and it often happens if the attention is a different place..

To my opinion, - to get 28 GPS satellites to work perfect and précis together, included all the adjustment for known unwanted effects as well as daily dilation synchronizing, on the one hand of course it require all the knowledge we have - but on the other hand it also take a good part of the attention and scientifically test possibilities away – whereby the possible scientific outcome off course suffers. ,

Therefore I am very interested in space probes and satellites that really are tested to the limit of what is possible. – And as I wrote Galileo 5 and 6 is no so far I understand now100% test satellites,

In my universe this is excellent, and such is where I would put my attention, my energy my mouth and my money.

Edited January 20, 2016 by Bjarne

[swansont]

Lack of attention was for example the cause of the biggest atomic catastrophe in the word. It is human to fail and it often happens if the attention is a different place..

 

That lack of attention in no way showed that we have a fundamental misunderstanding of the science, though. We know why the atomic (well, it's actually nuclear) catastrophe happened, because we do know the science. So this is a non-sequitur.

 

To my opinion, - to get 28 GPS satellites to work perfect and précis together, included all the adjustment for known unwanted effects as well as daily dilation synchronizing, on the one hand of course it require all the knowledge we have - but on the other hand it also take a good part of the attention and scientifically test possibilities away – whereby the possible scientific outcome off course suffers. ,

Therefore I am very interested in space probes and satellites that really are tested to the limit of what is possible. – And as I wrote Galileo 5 and 6 is no so far I understand now100% test satellites,

In my universe this is excellent, and such is where I would put my attention, my energy my mouth and my money.

Testing the limit of what is possible is not the same thing as we were talking about. And testing at the limit of what we can do is only going to potentially find issues at that limit, as I discussed earlier. Relativity will not be shown to be wrong at any lower levels of precision.

[Bjarne]

 

That lack of attention in no way showed that we have a fundamental misunderstanding of the science, though. We know why the atomic (well, it's actually nuclear) catastrophe happened, because we do know the science. So this is a non-sequitur.

 

Testing the limit of what is possible is not the same thing as we were talking about. And testing at the limit of what we can do is only going to potentially find issues at that limit, as I discussed earlier. Relativity will not be shown to be wrong at any lower levels of precision.

An aircraft can today fly around the world, - land and take off in different countries, avoid storms, adjust for wind impact, and much more, - without any need for pilot interaction.

 

I think that satellites are also largely controlled by "auto pilot", where computers even calculates all data, and suggests how much the clocks must be synchronized and how much orbits must be adjusted, and who knows maybe without asking anybody for permission. (I guess) it all can be done fully automatically, - without much help is necessary from any GPS navigators

That's what I mean by, - (human) attention at the GPS control center is not so much based on analyzing different causes of necessary adjustments or synchronizing, either to distinguish between different unwanted impacts, - but primary that GPS must work and be precise.

Or shortly spoken, whether the theory of relativity is 100% correct plays a secondary role for commercial satellites navigators.

 

When testing scientifically, - the attention is 100% scientifically, for long term uninterrupted periods. I think you will agree there is a difference

Edited January 20, 2016 by Bjarne

[swansont]

An aircraft can today fly around the world, - land and take off in different countries, avoid storms, adjust for wind impact, and much more, - without any need for pilot interaction.

 

I think that satellites are also largely controlled by "auto pilot", where computers even calculates all data, and suggests how much the clocks must be synchronized and how much orbits must be adjusted, and who knows maybe without asking anybody for permission. (I guess) it all can be done fully automatically, - without much help is necessary from any GPS navigators

That's what I mean by, - (human) attention at the GPS control center is not so much based on analyzing different causes of necessary adjustments or synchronizing, either to distinguish between different unwanted impacts, - but primary that GPS must work and be precise.

Or shortly spoken, whether the theory of relativity is 100% correct plays a secondary role for commercial satellites navigators.

 

When testing scientifically, - the attention is 100% scientifically, for long term uninterrupted periods. I think you will agree there is a difference

 

Not so much, no. I think the problem is your caricature of how science happens.

 

I met a scientist who wanted to analyze GPS timing data to see if a certain kind of dark matter can be detected. I have a colleague who used our clocks to put limits on local position invariance (the best limits available at the time of publication), even though that's not why we have our clocks. Data are data, and those data collections don't care what their function is.

 

The bottom line is GPS clocks are systematically monitored, and that allows science to be done if one wants to do it. The fact is that you can use GPS to test relativity. The issue is the precision at which one can do the tests. So if one were to make a prediction about an alternate or modification to relativity, one could use these satellites to test the alternate/modified theory at that level of precision. It is this "level of precision" that seems to correspond to your "100% correct", even though no theory has ever been 100% correct — there are always limits to the model that's part of any theory, and that's one reason why the phrasing "100% correct" is horrible. It likely wouldn't occur to an actual scientist to make that comparison, since it's so ludicrous. What a scientist could/would say of special relativity is that we know it to be correct to some limit of precision, whatever that happens to be.

 

GPS shows the relativistic clock corrections to be correct to something like several nanoseconds over the course of a day. That would exclude any alternate theory that predicted an appreciably larger excursion than that.

[Strange]

That's what I mean by, - (human) attention at the GPS control center is not so much based on analyzing different causes of necessary adjustments or synchronizing, either to distinguish between different unwanted impacts, - but primary that GPS must work and be precise.

Or shortly spoken, whether the theory of relativity is 100% correct plays a secondary role for commercial satellites navigators.

 

The satellites and receivers do make their adjustments automatically. By using the mathematics of GR. If GR were wrong then the results would be wrong and this would very quickly become apparent (very small differences would be apparent as noticeable errors in calculated location).

 

Edit: Swansont's answer is much better (as always).

Edited January 20, 2016 by Strange

[Bjarne]

 

The satellites and receivers do make their adjustments automatically. By using the mathematics of GR. If GR were wrong then the results would be wrong and this would very quickly become apparent (very small differences would be apparent as noticeable errors in calculated location).

 

So what you really is saying is that the test of Relativity these yearsm - regarding ISS and Galileo 5 and 6 is waste of billions of USD taxpayers money ?

[Strange]

So what you really is saying is that the test of Relativity these yearsm - regarding ISS and Galileo 5 and 6 is waste of billions of USD taxpayers money ?

 

No. I don't know what makes you think that. It seems like a good idea to reuse the hardware now it is there in the wrong orbit.

[swansont]

So what you really is saying is that the test of Relativity these yearsm - regarding ISS and Galileo 5 and 6 is waste of billions of USD taxpayers money ?

 

Can't do much about the waste of money regarding the Galileo satellites now. They're in the wrong orbit. That money was wasted already — doing science is salvaging something from that mess.

 

But why would doing this science be a waste of money? These can do experiments that can't be done in other ways, or do them at a higher precision than other experiments.