Suggestion for 2 more GR tests

[DanMP]

TL;DR Summary

I want to suggest two GR tests/experiments: 1 - atomic clocks much farther than current GPS clocks/satellites and 2 - an extension of Gravity Probe A experiment.

Although there are tons of experimental tests/confirmations for General Relativity, I noticed that most of them are made on/from Earth, or very close to Earth, so in this thread I'll suggest 2 extensions of past experiments:

1. GSM GPS satellite (preferably with an unmodified atomic clock) far higher than they currently are. The clock should go, progressively, as high as possible, while still orbiting the Earth (close to Earth's Hill sphere radius).

[Mentor Note: GSM-->GPS fixed in above text]

2. an extension of Gravity Probe A experiment going all the way to, and even beyond, Earth's Hill sphere limit/radius.I searched for such experiments and found atomic clocks (most of them on GPS satellites) only below 45,000 km (from the Earth's centre). This is almost nothing compared to 1,471,400 km (Earth's Hill sphere radius). And Gravity Probe A experiment only reached a height of 10,224 km ... There really is room from improvement.[English is not my first language, so please excuse my language/grammar related errors.]

 

[Dale]

What would you expect that those tests would accomplish? That would be further into the Newtonian regime and relativistic effects would be smaller. I don't get it

 

[PeterDonis]

Earth's Hill sphere radius

What significance do you think the Hill sphere has for a test of GR?

 

[DanMP]

What would you expect that those tests would accomplish?

Extend the tested range/domain. That is all I want to say right now regarding my reasons, so please don't insist in this direction.

 

[Ibix]

DanMP has a personal theory that is essentially an entrained ether theory with "dark matter" search-and-replaced instead of ether. The Hill sphere is where he thinks the entraining stops.

This is a test of his personal theory, not of GR.

 

[DanMP]

What significance do you think the Hill sphere has for a test of GR?

Thank you for asking. When I searched for the radius/diameter of Earth's gravity well I got Hill sphere page. See the picture from there.

 

[PeterDonis]

That is all I want to say right now regarding my reasons, so please don't insist in this direction.

With this restriction, there is nothing to discuss. You've suggested a couple of tests. What are we supposed to do?

 

[PeterDonis]

When I searched for the radius/diameter of Earth's gravity well I got Hill sphere page.

Yes, so what? That just pushes the question back to: what significance do you think "the radius/diameter of Earth's gravity well" has for a test of GR?

 

[DanMP]

Yes, so what? That just pushes the question back to: what significance do you think "the radius/diameter of Earth's gravity well" has for a test of GR?

Gravity wells are important for GR, so why not investigate them more, going farther away from the Earth's surface (and even cross the "border")?

Even the clocks/satellites would have a significant Hill sphere of their own, over 1 million km off the surface. This is a difference. Why we shouldn't go and test to see what happens?

With this restriction, there is nothing to discuss. You've suggested a couple of tests. What are we supposed to do?

Nothing. I just wanted my suggestions to be here. That's all I want here/now. Except if you/somebody know of such tests to be already performed ...

DanMP has a personal theory that ...

Please refrain from speculations in this forum.
Keep the thread/forum clean. I do ...

 

[Dale]

Extend the tested range/domain.

That is just silly. You don't extend the domain of a theory by going to a regime where it predicts smaller effects and where it is more similar to the alternative theory.

Why don't we test it with satellites painted pink? Why don't we test it on Tuesdays instead of Fridays? Because there is no GR effect predicted for pink satellites, nor for Tuesdays, nor for further into the Newtonian limit.

 

[DanMP]

You don't extend the domain of a theory by going to a regime where it predicts smaller effects.

The gravity well of a satellite gets much bigger, not smaller, while going up ...

That is just silly.

Ok, I understood your opinion.

I have to go now.

 

[Dale]

Ok, I understood your opinion.

My apologies, @DanMP, I was out of line to call it silly. I think it is wrong, but the reasons indeed are subtle enough that calling it silly was not accurate and was rude.

When we speak of extending the range or domain over which some theory is tested, we are not talking about testing it in new places, but rather we are talking about testing to greater precision.

Gravity probe A, for example, tested gravitational time dilation compared to a ground clock using a maser. Because of the precision of the maser we needed a lot of time dilation, so it was necessary to launch it in a rocket to a certain altitude to measure the effect. Launching it to a lower altitude would have been too small of an effect to detect with the precision of a maser.

Now, extending the domain means testing gravitational time dilation to greater precision. As more accurate frequency standards have been developed, gravitational time dilation could be tested by only going up to the top of a mountain. And now with the most accurate standards it is anticipated that these tests could be performed within a room. Smaller elevation differences require more precise clocks. So extending the domain for gravitational time dilation means using smaller distances, not larger ones.

 

[PeterDonis]

Even the clocks/satellites would have a significant Hill sphere of their own, over 1 million km off the surface.

Huh? The clocks/satellites have negligible gravity. Where are you getting this number from?

 

[PeterDonis]

The gravity well of a satellite gets much bigger, not smaller, while going up ...

What are you talking about?

 

[PeterDonis]

Please refrain from speculations in this forum.

He wasn't speculating. He was pointing out that you have done so in the past.

Keep the thread/forum clean. I do ...

It's been a while, but you haven't always. Please leave it to the moderators to apply the rules. If you think someone else's post violates the rules, use the Report button. Don't respond in the thread.

 

[Vanadium 50]

A space mission of this scale costs hundreds of millions of dollars. If you have hundreds of millions, don't post on PF - just do it. If you don't have hundreds of millions of dollars, you need to convince some person or organization who does. If your best argument is "it's never been done before" the reaction you will get will make you long for the days when it was merely called silly.

Here is the first thing you need to do.

• Figure out exactly what you want to do. e.g. how many orbits, how long it will take to reach insertion, etc. Otherwise you have a proposal that is no clearer than "Hey, let's put on a show".
• Figure out what you are going to measure. "Put an atomic clock in space" is not a measurement. "Use radio to synchronize with an array of earth clocks and compare by radio every minute for a year" gets closer.
• Compare the sensitivity to deviations from GR with every single test done so far. Every single test. Show that you are more sensitive. And not just a little more sensitive. A lot more sensitive. If you are not at least 2-10x better on paper, you won't be better in real life.

A lot of work? Yes. You want a lot of money.

 

[Vanadium 50]

As a PS - that's the first thing. The starting point. There is easily 1000x more work after that.

 

[DanMP]

What are you talking about?

See here:

It is possible for a Hill sphere to be so small that it is impossible to maintain an orbit around a body. For example, an astronaut could not have orbited the 104 ton Space Shuttle at an orbit 300 km above the Earth, because a 104-ton object at that altitude has a Hill sphere of only 120 cm in radius, much smaller than a Space Shuttle. A sphere of this size and mass would be denser than lead, and indeed, in low Earth orbit, a spherical body must be more dense than lead in order to fit inside its own Hill sphere, or else it will be incapable of supporting an orbit. Satellites further out in geostationary orbit, however, would only need to be more than 6% of the density of water to fit inside their own Hill sphere.

Huh? The clocks/satellites have negligible gravity. Where are you getting this number from?

From here. Do the math and see that around 1 million kilometers off the Earth's surface, the Hill sphere for a 440 kg GPS satellite is about 30 meters. And this is a big difference. The clock would be well inside the satellite gravity well. And, to my knowledge, we never had an atomic clock in another gravity well. Did we? We will have on the Moon, but only in few years.

A space mission of this scale costs hundreds of millions of dollars

Nah, there are GPS satellites "in reserve" or close to be retired. We just need to "push" one towards a (much) higher orbit.

Now, extending the domain means testing gravitational time dilation to greater precision.

It isn't just about the gravitational time dilation. In fact it is more about the kinematic one when the clock is situated well inside another gravity well. You, of course, consider that nothing unexpected would happen, but did we really test it?

If your best argument is "it's never been done before"

It isn't. I said that I don't want to discuss it here, now:

That is all I want to say right now regarding my reasons.

I'll offer more clues, but not here. Here I'm just suggesting the tests.As a suggestion, if a maser experiment across the Earth's Hill sphere "border" would be too expensive, maybe we can try with a "candle", a source of light with well defined spectral lines, observed with a telescope + a powerful spectrometer, all the way up and across the "border".

[English is not my first language, so please excuse my language/grammar related errors.]

 

[Dale]

It isn't just about the gravitational time dilation. In fact it is more about the kinematic one when the clock is situated well inside another gravity well. You, of course, consider that nothing unexpected would happen, but did we really test it?

Yes, we really tested it to higher precision already.

 

[Vanadium 50]

Given that we can't say the word "silly", I would say instead that the response was profoundly unserious.

1. If you don't own a GPS satellite, you don't get to decide where it goes.
2. You can't take an existing satellite and just move it willy-nilly to another orbit,
3. You did none of the work needed to start convincing people that this idea has merit. You instead fell back on "Hey, let's put on a show!"

 

[Dale]

At this point I think that further discussion here is pointless. The proposed experiment appears unjustified by the scientific method (it does not extend the tested range of GR) based on current professional scientific theories. That is really all that can be said here.