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Online Rama Set

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Re: Cavendish experiment
« Reply #220 on: May 12, 2021, 11:39:26 AM »
The Cavendish experiment is not the only test of gravity, so his awareness of the imprecision of the Cavendish Experiment isn't evidence that "gravity is merely a belief".

He is aware that he can't measure gravity. Refer to the previous quotations.

He is talking about the Cavendish Experiment and it's pretty clear in the broader context that it was a matter of unsatisfactory precision.  This position is supported by the comments of other astrophysicists, as I showed you earlier.  He was not talking about the observation and measurement of gravity broadly, so your interpretation is untenable.
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Offline Iceman

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Re: Cavendish experiment
« Reply #221 on: May 12, 2021, 11:52:26 AM »
...Terence Quinn is a British physicist who spent many years studying gravity and was emeritus director of the International Bureau of Weights and Measures. If he says it, it's golden.

Okay great, he said this in a nature piece:
"Who needs a more accurate numerical value of G (the current recommended value is 6.67408 ± 0.00031 × 10−11 kg−1 m3 s−2)? The short answer is, nobody, for the moment..."

https://www.nature.com/articles/nphys3651?proof=t


 I guess were done here?

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Offline Tom Bishop

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Re: Cavendish experiment
« Reply #222 on: May 12, 2021, 12:01:44 PM »
...Terence Quinn is a British physicist who spent many years studying gravity and was emeritus director of the International Bureau of Weights and Measures. If he says it, it's golden.

Okay great, he said this in a nature piece:
"Who needs a more accurate numerical value of G (the current recommended value is 6.67408 ± 0.00031 × 10−11 kg−1 m3 s−2)? The short answer is, nobody, for the moment..."

https://www.nature.com/articles/nphys3651?proof=t


 I guess were done here?

Here is his quote:

"Who needs a more accurate numerical value of G (the current recommended value6 is 6.67408 ± 0.00031 × 10−11 kg−1 m3 s−2)? The short answer is, nobody, for the moment, but being apparently unable to converge on a value for G undermines our confidence in the metrology of small forces. Although it is true that the orbits of the planets depend on the product of G and the mass of the Sun — the structures of all astrophysical objects are determined by the balance of gravity and other forces produced by, for example, gas, photon or degeneracy pressure — ab initio models of the Sun are still an order of magnitude away from predicting a value of G at a level comparable with laboratory determinations. We do not need a value of G to test for departures from the inverse square law or the equivalence principle. There is as yet no prospect of a theory of quantum gravity that would predict a value for G that could be tested by experiment."

The part you cut out after "nobody for the moment..." says that this value undermines their science in the metrology of small forces. He clearly suggests the recommended range is invalid and questionable there, rather than your suggestion that he is supporting it wholeheartedly. This is another point against you.

Trivializing the need for G doesn't directly address the matter of whether he thinks that he measured it. He is talking about the practical purpose for the such a measurement, in non-cavendish situations and measurements. He is correct that G is not needed for the equivalence principle tests. That's something else, showing that gravity does not depart on various ranges and situations from the concept that the Earth is accelerating upwards. The EP tests are highly and accurately verified.

Quinn's "we should be able to measure gravity" statement says that he cannot measure gravity in the Cavendish Experiment. In the quote you referenced we see a statement that the recommended range undermines their science in the metrology of small forces, showing that he is certainly not endorsing it. You're right. We are done here. We have talked about this for pages and you are still unable to substantiate your argument.
« Last Edit: May 12, 2021, 04:55:23 PM by Tom Bishop »

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Offline Iceman

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Re: Cavendish experiment
« Reply #223 on: May 12, 2021, 01:04:48 PM »
Yes that's great, the more quotes we can get from Dr. Quinn the better :) hes smarter than all of us on the matter!

"Could these unresolved discrepancies in G hide some new physics? This seems unlikely. I believe undiscovered systematic errors in all or some of these new experiments is the answer — G is difficult to measure but it should not be too difficult!"
- from the nature piece linked above

Now someone else's turn!

Re: Cavendish experiment
« Reply #224 on: May 12, 2021, 05:05:13 PM »
Now someone else's turn!
Go on then. I don't think this has any quotes from him, but it's an interesting article about the multiple ways they have of measuring gravity:

https://www.nature.com/articles/35050187?foxtrotcallback=true

For such a weak force it's impressive how accurate they can get the value of G and multiple methods of measuring it show that it can't be coincidence. It will be interesting to see if some of the newer experiments which claim a smaller error margin can do better still.
"On a very clear and chilly day it is possible to see Lighthouse Beach from Lovers Point and vice versa...Upon looking into the telescope I can see children running in and out of the water, splashing and playing. I can see people sun bathing at the shore
- An excerpt from the account of the Bishop Experiment. My emphasis

Re: Cavendish experiment
« Reply #225 on: May 15, 2021, 06:00:32 AM »

He clearly suggests the recommended range is invalid and questionable there, rather than your suggestion that he is supporting it wholeheartedly. This is another point against you.


How do you get to the conclusion that "he clearly suggests the recommended range is invalid and questionable there"? He simply does not say that. He does not mention the range at all in this quote. What he only talks about is our ability to measure small forces. He always talks about being able to take accurate measurements rather than measurements in general.

This is a another article from Quinn:

https://www.nature.com/articles/35050187?foxtrotcallback=true

It starts with "Newton's constant, G, which governs the strength of the gravitational attraction between two masses, is difficult to measure accurately".
He does not even question the existence of gravity as he takes it for granted both in this latest link and in the part from the other article that you quoted.

You can accept what he says or reject it, but you cannot use him as a reference for the notion that gravity does not exist.

Re: Cavendish experiment
« Reply #226 on: July 26, 2021, 03:55:22 PM »
what exactly are all these different competing scientists actually measuring, given that they are all coming up with a number around the 6.67 x 10-11 mark?

It seems like you don't believe there exists corruption in science community. The popular view of science community is no way to guarantee it is truthful.

Online SteelyBob

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Re: Cavendish experiment
« Reply #227 on: July 27, 2021, 10:16:08 PM »
It seems like you don't believe there exists corruption in science community. The popular view of science community is no way to guarantee it is truthful.

Nothing I said in my post supports your contention. Scientists exhibit all of the failings of other human beings - of course they do. I simply pointed out that lots of different scientific teams all measured something, using different methods, and came up with remarkably similar numbers.

I'll repeat my question: what then, exactly, were they measuring, if not G?

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Offline Tom Bishop

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Re: Cavendish experiment
« Reply #228 on: July 27, 2021, 10:19:03 PM »
It's not remarkably similar. The physicist Terence Quinn above says that the range undermines their science of the metrology of the small forces.

https://www.nature.com/articles/nphys3651.pdf?proof=t

"Who needs a more accurate numerical value of G (the current recommended value is 6.67408 ± 0.00031 × 10−11 kg−1 m3 s−2)? The short answer is, nobody, for the moment, but being apparently unable to converge on a value for G undermines our confidence in the metrology of small forces."

"Despite intensified efforts, measurements of the gravitational constant continue to fail to converge, as Terry Quinn explains."
« Last Edit: July 27, 2021, 10:22:19 PM by Tom Bishop »

Online SteelyBob

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Re: Cavendish experiment
« Reply #229 on: July 27, 2021, 11:04:33 PM »
It's not remarkably similar. The physicist Terence Quinn above says that the range undermines their science of the metrology of the small forces.

https://www.nature.com/articles/nphys3651.pdf?proof=t

"Who needs a more accurate numerical value of G (the current recommended value is 6.67408 ± 0.00031 × 10−11 kg−1 m3 s−2)? The short answer is, nobody, for the moment, but being apparently unable to converge on a value for G undermines our confidence in the metrology of small forces."

"Despite intensified efforts, measurements of the gravitational constant continue to fail to converge, as Terry Quinn explains."

I'll repeat my question (again): what then, exactly, were they measuring, if not G?

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Offline Tom Bishop

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Re: Cavendish experiment
« Reply #230 on: July 27, 2021, 11:09:35 PM »
They don't know what they're measuring.

https://www.scientificamerican.com/article/puzzling-measurement-of-big-g-gravitational-constant-ignites-debate-slide-show/

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Although gravity seems like one of the most salient of nature’s forces in our daily lives, it’s actually by far the weakest, making attempts to calculate its strength an uphill battle. “Two one-kilogram masses that are one meter apart attract each other with a force equivalent to the weight of a few human cells,” says University of Washington physicist Jens Gundlach, who worked on a separate 2000 measurement of big G. “Measuring such small forces on kg-objects to 10-4 or 10-5 precision is just not easy. There are a many effects that could overwhelm gravitational effects, and all of these have to be properly understood and taken into account.

https://futurism.com/the-gravitational-constant-is-it-really-constant

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So far as we can tell, the gravitational constant has remained constant throughout the entire history of the universe. This has, however, been VERY difficult to prove! Measurements of the gravitational constant over the past 200 years have been erratic. Even as the techniques that we use now are far more advanced and sensitive than were used two centuries ago, the true value of the gravitational constant remains elusive.

In 2013, a group of researchers working out of France took the measurement of the gravitational constant, using the same machine that they’d used some 2 years earlier. Improvements were made on the machine to improve the sensitivity and give a more accurate result. The machine, which uses two independent methods to calculate the constant, averages the results of the two. This, in theory, should help reduce systematic errors. What did they find? A different result!

At first it may seem strange that the gravitational constant is so hard to determine. There are four fundamental forces in the universe:

Strong Force
Weak Force
Electromagnetism
Gravity

Gravity is by far the weakest of the four forces, which, may also sound a little strange considering what we see in the universe. When looking out into the cosmos, gravity appears to be the reigning king of all. Gravity is so strong that it causes stars to fuse hydrogen into helium, collapses stellar cores into neutron stars and black holes, creates quasars and dictates the flow of matter within the entire universe.

On a large scale, gravity wins. But, as was previously mentioned, gravity is the weakest of the four forces. The reason for this discrepancy is, as a force, gravity travels further and has a slower fall off. The strongest of the four forces, the Strong Force, becomes almost non-existent at distances outside of a nucleus. What makes gravity stronger in macro circumstances is that it is accumulative. The more matter there is, the more gravity. But still, gravity is weaker. Therefore, when trying to measure it, the other forces can cause systematic errors. It is akin to trying to measure the weight of a feather, outdoors, in a slight breeze, with an old pair of scales.

https://royalsocietypublishing.org/doi/10.1098/rsta.2014.0253

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What matters then is not the actual value of G itself (give or take a percentage or so) but its uncertainty. The real importance of the accuracy of G is arguably that it can be taken as a measure, in popular culture, of how well we understand our most familiar force: the discrepant results may signify some new physics, or they may demonstrate that we do not understand the metrology of measuring weak forces. Owing to the lack of theoretical understanding of gravity, as alluded to earlier, there is an abundance of respectable theories that predict violations of the inverse square law or violations of the universality of free fall. In fact, a growing view is that G is not truly universal and may depend on matter density on astrophysical scales, for example. A misunderstanding of the metrology of weak force physics may in turn imply that the experimental tests that have established the inverse square law and the universality of free fall thus far are flawed in some subtle fashion. This makes for a potentially exciting situation and perhaps explains the general interest shown in our apparently mundane and painstaking work on G.

Either new physics or they are misunderstanding something about the forces that exist at that range.
« Last Edit: July 27, 2021, 11:12:34 PM by Tom Bishop »

Online SteelyBob

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Re: Cavendish experiment
« Reply #231 on: July 28, 2021, 09:13:16 AM »
I didn’t ask you whether or not they understand it. I asked you what they were measuring. Given that different methods are all returning a number for G that is remarkably consistent, considering the challenge, we must surely conclude that G is indeed a thing, and it clearly relates to a force between bodies of mass.

Your argument seems to be that a lack of precision (although you don’t specify what degree of precision would cause you to change your mind) indicates that the experiments aren’t measuring anything. That is an absurd argument.

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Offline Tom Bishop

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Re: Cavendish experiment
« Reply #232 on: July 28, 2021, 07:32:21 PM »
If you are trying to measure the weight of a feather with a crude pair of scales outside during a slight breeze, and the view of the feather was obscured, it's difficult to say whether there is actually a feather on the scale. The feather-scale analogy is the analogy the astrophysicist at Futurism gave.

In the Cavendish Experiment it's trying to measure the force equivalent of the weight of a few cells. Very slight. If they can't target that, it's difficult to say what it's measuring at all.
« Last Edit: July 28, 2021, 09:30:06 PM by Tom Bishop »

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Re: Cavendish experiment
« Reply #233 on: July 28, 2021, 09:01:17 PM »
The feather thing is an analogy. It’s not literally what they are trying to do. Clinging on to that phrase is starting to look a little desperate, frankly.

But if you want to play with the analogy…several different teams of scientists have all tried to weigh the feather, so to speak. They did it using all kinds of different methods - maybe different old scales, to stretch it further, in a variety of wind conditions.

And they all came up with numbers within 400ppm of each other. Most people would conclude that the number must be, give it take a few hundred ppm, the weight of the feather. You are saying the lack of better (non specific - it’s always non specific around here, isn’t it?!) precision means the feather doesn’t exist, and/or the scientists don’t understand the feather.