Atomic Clock Exp on Ballistic Flight: Proving Clocks are Accelerometers

[dom_quixote]

In the past, scientists have experimented with atomic clocks aboard airplanes in order to prove the Special Theory of Relativity.

In our humble opinion, ALL watches are accelerometers.

Effect observed in a chaotic pendulum in free fall:



Too bad they didn't do the same experiment with an ordinary pendulum ...

We propose an atomic clock experiment on board a ballistic flight:

https://eoportal.org/web/eoportal/airborne-sensors/airbus-a310-zero-g

Is twenty seconds enough to prove that clocks are accelerometers?

 

[jbriggs444]

A properly functioning clock measures time, not local acceleration.

https://en.wikipedia.org/wiki/Time_dilation#Clock_hypothesis

 

[A.T.]

We propose an atomic clock experiment on board a ballistic flight:

We already have atomic clocks on free falling satellites for decades. Why bother with ballistic flights?

 

[Dale]

In our humble opinion, ALL watches are accelerometers.

This is called the clock hypothesis, and has been tested to about $10^{18}$ g. Clocks are not accelerometers.

 

[Ibix]

This is called the clock hypothesis,

To be pedantic, it is the inverse of the part you quoted that is the clock hypothesis - that clocks are not accelerometers.

 

[hutchphd]

Individual clocks are not accelerometers.

 

[PeterDonis]

In our humble opinion, ALL watches are accelerometers.

A pendulum is not even a good clock under stable proper acceleration, since its "ticking" is only uniform for small enough amplitudes. But even leaving that aside, a pendulum, chaotic or not, is obviously not going to be a good clock in free fall since its mechanism depends on the presence of proper acceleration.

Since other types of clocks do not share this unwanted property, basing a claim about the behavior of all clocks with regard to acceleration on the behavior of pendulums is not valid.

 

[dom_quixote]

This is called the clock hypothesis, and has been tested to about $10^{18}$ g. Clocks are not accelerometers.

Dale,
Thanks for your reply. Please send me more data about this experiment, as this subject interests me a lot.

 

[Motore]

Dale,
Thanks for your reply. Please send me more data about this experiment, as this subject interests me a lot.

In post #2 @jbriggs444 refernced you the Wiki article where you can find this reference for example (unfortunately is behind a paywall):
https://www.nature.com/articles/286244a0

 

[Dale]

Dale,
Thanks for your reply. Please send me more data about this experiment, as this subject interests me a lot.

In addition to the one mentioned by @Motore the “experimental basis of special relativity” page lists 2 more relevant experiments in section 5: https://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

One measured muons in a storage ring and another used a Mossbauer rotor

 

[dom_quixote]

Thanks, Dale!
Thanks Motore!

What about this proposal? Is this viable?

"
Geophysical applicability of atomic clocks: direct continental geoid mapping
Ruxandra Bondarescu, Mihai Bondarescu, György Hetényi, Lapo Boschi, Philippe Jetzer, Jayashree Balakrishna
Geophysical Journal International, Volume 191, Issue 1, October 2012, Pages 78–82, https://doi.org/10.1111/j.1365-246X.2012.05636.xSummary

The geoid is the true physical figure of the Earth, a particular equipotential surface of the Earth's gravity field that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General relativity theory predicts constant clock rate at sea level, and faster (slower) clock rate above (below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate (frequency ratio inaccuracy of 10−18), which is equivalent to 1 cm in determining equipotential surface (including geoid) height. We discuss the value and future applicability of such measurements including direct geoid mapping on continents, and joint gravity-geopotential surveying to invert for subsurface density anomalies. Our synthetic calculations show that the geoid perturbation caused by a 1.5-km radius sphere with 20 per cent density anomaly buried at 2-km depth in the Earth's crust is already detectable by atomic clocks of achievable accuracy. Therefore atomic clock geopotential surveys, used together with relative gravity data to benefit from their different depth sensitivities, can become a useful tool in mapping density anomalies within the Eart. "

Source:
https://academic.oup.com/gji/article/191/1/78/2007166

 

[Dale]

What about this proposal? Is this viable?

"
Geophysical applicability of atomic clocks: direct continental geoid mapping
Ruxandra Bondarescu, Mihai Bondarescu, György Hetényi, Lapo Boschi, Philippe Jetzer, Jayashree Balakrishna
Geophysical Journal International, Volume 191, Issue 1, October 2012, Pages 78–82, https://doi.org/10.1111/j.1365-246X.2012.05636.x

Yes. That seems completely viable with current technology. And in a few years it will probably not even be very expensive.

By the way, the Geophysical Journal International is the #3 ranked journal in the field of Geochemistry and Geophysics according to Eigenfactor http://www.eigenfactor.org/projects...year=2014&searchby=isicat&orderby=eigenfactor

 

[vanhees71]

Time/frequency measurements are the most accurate measurements feasible. It's just amazing, what can be done with modern technology. This week's Nature issue had this (on gravitational red-shift measurements at the mm scale):

https://www.nature.com/articles/s41586-021-04349-7
https://www.nature.com/articles/d41586-022-00379-x

 

[A.T.]

What about this proposal? Is this viable?

Geophysical applicability of atomic clocks: direct continental geoid mapping
Ruxandra Bondarescu, Mihai Bondarescu, György Hetényi, Lapo Boschi, Philippe Jetzer, Jayashree Balakrishna
Geophysical Journal International, Volume 191, Issue 1, October 2012, Pages 78–82, https://doi.org/10.1111/j.1365-246X.2012.05636.x

This is about using clocks to measure the gravitational potential, not acceleration.

 

[Ibix]

Geophysical applicability of atomic clocks: direct continental geoid mapping

Note that this is measuring gravitational potential variations, not acceleration, which is why it's feasible.

Edit: A.T. was quicker on the draw, I see.

 

[Dale]

This is about using clocks to measure the gravitational potential, not acceleration.

Note that this is measuring gravitational potential variations, not acceleration, which is why it's feasible.

Indeed, as the quoted abstract says:

Therefore atomic clock geopotential surveys, used together with relative gravity data …

In this application the atomic clocks measure the geopotential, and the relative gravity (acceleration) measurements are separate.

 

[dom_quixote]

Sorry if I'm mixing concepts.
It is known that until now there is perfect equivalence between gravitational mass and inertial mass.

Physics is a reductionist science. By the strange redundancy of the equivalence of masses, we are tempted to recognize that one of them is unnecessary.

Would a test with two atomic clocks in the great reservoir of Helsinki help to elucidate the problem?

 

[PeterDonis]

Would a test with two atomic clocks in the great reservoir of Helsinki help to elucidate the problem?

What would you want to show with such a test?

 

[dom_quixote]

Peter,

Thank you for your interest!

I think if the atomic clock is an accelerometer, the readings of the clocks placed at the base and top of the reservoir will not change depending on the variation in the mass of water contained in the reservoir.

It would be great to be able to do the test with gravimeters too. But the variation in the volume of water may not be enough.

Link:
Oldham's Gravimetric Experiment
https://academic.oup.com/gji/article/113/1/83/732878?login=false

 

[Ibix]

An atomic clock is not an accelerometer. The tick rates will vary because the gravitational potential at the top of the tower will vary as water is added.

 

[vanhees71]

The great thing about atomic clocks in fact is that they are pretty insensitive to external influence and thus provide the amazingly accurate definition of the second in the SI. The stability might be topped soon when the "nuclear" Thorium clock becomes as accurate as the atomic clocks.

 

[dom_quixote]

Thank you, Ibix!
Thank you, vanhees71!

Would it be useless and expensive to put this consolidated fact to the test?

 

[Dale]

Would a test with two atomic clocks in the great reservoir of Helsinki help to elucidate the problem?

What problem?

Please try to be clear in your descriptions. We are physicists, not psychics. We cannot read your mind.

What it the problem you are trying to elucidate and how would atomic clocks on the water tower help?

I think if the atomic clock is an accelerometer

Clocks are not accelerometers, we already covered that.

Link:
Oldham's Gravimetric Experiment
https://academic.oup.com/gji/article/113/1/83/732878?login=false

You could do something similar, measuring gravitational potential instead of gravitational acceleration.

What would be the knowledge you would expect to gain from such an experiment? I mean, what is the point or the hypothesis that it would test?

 

[vanhees71]

As already said several times, the "clock hypothesis", according to which an ideal clock always measures its "proper time", which is the well-defined measure of time in both special an general relativity, has been confirmed by experiment to utmost precision, realizing ideal clocks in various ways. Among them are the atomic clocks. The Cs fine structure transition defines the unit of time, the second, in the SI since 1967, since 2019 in the form of defining numerical value of the corresponding frequency. The clock hypothesis has been tested with very high precision also in storage rings with all kinds of unstable particles from elementary ones like the muon to various radioactive nuclei. About this and many more tests of SRT, see Baez's Physics FAQ chapter:

https://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

Also Wikipedia has an article about it

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

and particularly about time dilation and the clock hypothesis

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

 

[PAllen]

Also worth noting is that every lab test of gravitational time dilation using atomic clocks is a complete refutation of the idea that the effect is proportional to acceleration. The potential difference over small heights at the earth’s surface is gh. The difference in acceleration over small heights at earth’s surface is 2gh/r. The latter difference is smaller by 6 orders of magnitude. Atomic clocks have the precision to just measure the former over a centimeter. That they have a positive result of the expected magnitude, versus no result, is a complete refutation of the idea of clocks as accelerometers.

 

[Vanadium 50]

I think if the atomic clock is an accelerometer

It's not.
You've been told multiple times that its not.

 

[cianfa72]

Also worth noting is that every lab test of gravitational time dilation using atomic clocks is a complete refutation of the idea that the effect is proportional to acceleration. The potential difference over small heights at the earth’s surface is gh. The difference in acceleration over small heights at earth’s surface is 2gh/r.

I think you mean actually proper acceleration at Earth's surface as function of (small) heights. So even if both potential and proper acceleration change with height w.r.t the Earth's surface, the results of measurements with atomic clocks at rest at different heights are consistent with their potential difference and not with their negligible proper acceleration difference.

 

[PeterDonis]

if the atomic clock is an accelerometer

We already know atomic clocks are not accelerometers. There is no point in continuing to belabor this.

Thread closed.