Newton's Constant -- Not So Constant?

Newswise ^ | 5/8/2002 | Mike Martin

[VadeRetro]

You want me to save the world again? I'm already fully engaged on the other thread.

Nah! Anyway, I'd rather assume there's a nearby black hole than that G has a true directionality.

If people would stop trying to save the world all our troubles would be canceled. We could just drive our SUVs around and party to the end, whatever the end is. A race between global warming, the meteors, the pulsar beams, the Bug-Eyed Monsters, whatever.

[AmishDude]

Will you physicists ever manage to figure out what you're doing? Compared to my field, you guys look like the Marx Brothers. You should've just accepted Aristotle and given up then.

-- A smug mathematician

;)

[Physicist]

You math geeks are just jealous because we've managed to improve on our Greek predecessors. ;^)

[AmishDude]

We gave you zero! We gave you algebra! Personally, I think we should copyright all of mathematics and charge outrageous fees for you guys to use the results. Then we'll get some respect. Mwahahahahaha . . .

Seriously, do you think there exists a grand unified theory or is that a crazy pipe dream?

[Physicist]

We gave you zero! We gave you algebra!

And we gave you back the Dirac delta function.

<ducks>

Seriously, do you think there exists a grand unified theory or is that a crazy pipe dream?

As the physical universe is constrained to be consistent with mathematical truth, there must be. In fact, just as there is more than one consistent formulation of quantum mechanics, there may be multiple Theories of Everything. A territory can have any number of consistent maps, that are nevertheless not the same map. But some map must be possible, I believe.

[Willie Green]

I have no problems retaining a belief that an ideal "G" is still a constant.
IMHO, they're merely misallocating gravitational effects of other gravitational bodies.
In the real world, an ideal "G" could never be measured because it is impossible to gravitationally isolate two bodies from the influence of other physical entities that exist in the universe.

Obviously, I'm no expert on the subject.
Just a humble engineer.
And when it comes right down to it, I've never had to use Newton's constant in roughly 30 years professional experience anyway.
So who gives a hoot what it is and what I think about it?

;^)

[Physicist]

In the real world, an ideal "G" could never be measured because it is impossible to gravitationally isolate two bodies from the influence of other physical entities that exist in the universe.

You don't need to isolate the two bodies. You can calculate the influence of the other entities and correct for them. Moreover, those outside influences will remain constant over a short timescale; you can make one measurement in your lab, change your setup (by for example moving your test masses closer together, or changing their orientation), make another measurement, and base your measurement of G on the difference between those measurements. The outside influences will cancel out.

What inhibits the accurate measurement of G is simply the fact that it's so damned small. The force between two huge test masses is awfully tiny, and thus hard to measure.

[AmishDude]

Don't forget, you also give us undergraduates who "multiply by dx".

I guess what I'm asking is: Is there a Grand Unified Theory of physics that is describable in terms humans can deal with? For example, xe^x has an inverse for nonnegative x, but it cannot be described in a closed-form.

[Willie Green]

You can calculate the influence of the other entities and correct for them.

Seems to be a pretty daunting task considering the infinite number of them floating around out there. Then somehow you gotta factor in that unknown quantity of black mass (or whatever they call it) that affects their indecision whether the universe is going to simply expand forever or eventually collapse back onto itself.

Well, whatever they come up with, I sure hope that not a whole lot of my tax dollars are being wasted on this. I recognize that there is a valid need to support pure research, but I get frustrated by reading about this esoteric stuff. Just prefer to see quicker progress on more practical infrastructure projects that benefit everybody.

But thanks for replying seriously to my babblings.

[apochromat]

Now that I look at it, it seems that external gravity sources would result in stretching along the attraction direction. The effect would be the opposite of what would be the case if the parts of an object attracted each other more strongly along one direction. Spherical distortion would be prolate for a strong gravity from external sources and oblate distortion would be the result for an internally manifested strong gravity direction.

[KayEyeDoubleDee]

It has been known for a few years that there is an anomalous anisotropy in the polarization of the cosmic microwave radiation background

related FYI: Electromagnetic Anisotroy

[apochromat]

Thanks for posting that. Perhaps there is an electromagnetic explanation for the apparent gravitational anisotropy result, perhaps not. We may be seeing more stories about both types of anisotropy in the science news.

[apochromat]

If the fixed stars were actually spinning to create a Mach-type anisotropic gravity, spherical distortion would be oblate -- which apparently matches the measured effect. I'd think the spin would be obvious from direct observation of the stars' rotation. If the rotation was aligned closely with Earth's orbit however, it seems the spin might be mostly concealed. I really can't yet visualize what it means for the entire universe to be spinning, however.

[savedbygrace]

Isn't it Centripetal Force that acts on a body that is moving like the author (and you) describe? Centripetal = toward the center.

[VadeRetro]

A very curious paper, that one. It's going to be interesting to see how this shakes out.

[r9etb]

And when it comes right down to it, I've never had to use Newton's constant in roughly 30 years professional experience anyway.

I use it a lot, and as I a 0.054% variation in G seems impossibly large. For a GPS orbit, we would see semi-major axis differences on the order of 14 km from plane to plane, not to mention significant seasonal errors in our gravity models -- which we don't.

Certainly it would show up as errors in the GPS clocks, but from what I can tell that sort of uncertainty is not seen. (Indeed, GPS clock data would undoubtedly be quite useful to confirm or disprove this claimed effect.)

This seems like a very bogus claim.

[Willie Green]

I admit, ya got me stumped. Let's see what Physicist has to say.

[r9etb]

What inhibits the accurate measurement of G is simply the fact that it's so damned small. The force between two huge test masses is awfully tiny, and thus hard to measure.

Well, yes, to a point. However, since this proposed variation in G translates directly into changes in mu (the gravitiation constant used for orbit work), such a tremendous variation would seem to be rather difficult to have missed.

In addition to very high accuracy orbit determination for satellites, we have such information such as the planetary ephemerides.

And, as I noted above, things like the clocks on the GPS satellites would show the effect -- they're in 6 discrete orientations w/r the distant stars. Not to mention that the even higher-accuracy atomic clocks available in various spots would show a daily variation due to the fact that they're continually rotating with respect to the "alignment of the distant stars."

I have to think that something this significant would have been noted in other fields by now.

[Physicist]

We can't determine G accurately from the motions of the planets or satellites. This is because the force is proportional to G times the mass of the Earth (or the sun). We measure the mass of the Earth by assuming a value of G and measuring how satellites orbit; we can't then turn around and measure G by using that value for the mass of the Earth. So the uncertainty of one will be no better than the uncertainty of the other, and the errors can be huge, even if we measure MG to within a gnat's eyebrow. Because we have no good way to measure the mass of the Earth without knowing G, we have to measure G in the lab with torsion balances and suchlike.