# Gravity measurement

qaqtos
Someone repeated the Cavendish experiment at about 0 K?

My question: the gravity force is costant when mass is near 0 Kelvin?

It is possible a weakening of G, a 'transition phase'?

Staff Emeritus
Someone repeated the Cavendish experiment at about 0 K?

My question: the gravity force is costant when mass is near 0 Kelvin?

It is possible a weakening of G, a 'transition phase'?

Can you please give an exact, valid reference to this?

All previous measurements of the Newtonian gravitational law has been verified up to micron scale. See experiments coming out of the Adelberg's group out of the U. of Washington.

Or see this experiment:

https://www.physicsforums.com/showpost.php?p=1059881&postcount=15

Zz.

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qaqtos
I contacted several physicists, MAGIA group also, but no answer.

My point: to repeat the Cavendish experiment (torsion balance) to measure the force of gravity between masses at temperature near 0 K or less than 2,7 Kelvin at least.

Instead of solid metallic spheres to put containers filled of liquid helium.

To be more precise: the mass has a gravity force of attraction stable or variable referring to the temperature?

I searched around the net but I find out nothing about this, there are gravimeters using masses of superconductor but they operate at temperature far above 0 K.

Staff Emeritus
Riley Newman at Univ. of California, Irvine uses cryogenics temperatures to reduce some of the errors inherent in assessing G, whose uncertainty is very large compared to most other physical constants.

From http://www.physics.uci.edu/gravity/
The UCI Gravity Lab uses torsion pendulums operating at cryogenic temperature to perform tests of Newtonian gravity, the equivalence principle, and searches for new forces.

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Staff Emeritus
I contacted several physicists, MAGIA group also, but no answer.

My point: to repeat the Cavendish experiment (torsion balance) to measure the force of gravity between masses at temperature near 0 K or less than 2,7 Kelvin at least.

Instead of solid metallic spheres to put containers filled of liquid helium.

To be more precise: the mass has a gravity force of attraction stable or variable referring to the temperature?

I searched around the net but I find out nothing about this, there are gravimeters using masses of superconductor but they operate at temperature far above 0 K.

The use of cryogenics would only eliminate thermal noise from the measurement. I don't see how it would affect anything fundamental out of such an experiment, as pointed out by DH's reference.

Zz.

Staff Emeritus
The use of cryogenics would only eliminate thermal noise from the measurement.
Any experiment is burdened with plant (or process) noise and measurement noise. Cryogenics should reduce both. Process noise in this case includes thermal vibrations in the torsion bar. Riley is also using cryogenics to reduce friction. I don't know how he is accomplishing this through the use of cryogenics and I don't know why this cannot be accomplished by some other means.

The universal gravitational constant is known to five significant digits. This is very low resolution compared to most other physical constants. The stated goal of Riley's group is 2 parts per million, or close to two orders of magnitude improvement.

rbj
The stated goal of Riley's group is 2 parts per million, or close to two orders of magnitude improvement.

i thought they said 20 ppm. nonetheless, that would be a big deal. maybe, someday, the powers that be will redefine the SI base units of length, time, mass, and charge to all be some constant multiples of the respective Planck units (but not until we get a much better handle on the value of G). that should drive the point home to the "varying-G" proponents.

qaqtos
In the Riley's apparatus the balance torsion operate at criogenic temperature but the copper masses are not at crio temperature.

In yours opinions it is possible to carry out the G measurement with copper masses at crio temperature or sobstitute the copper masses with an He masses at crio temperature?

In other words: mass has the same G force at near 0 K?

Staff Emeritus
In the Riley's apparatus the balance torsion operate at criogenic temperature but the copper masses are not at crio temperature.

In yours opinions it is possible to carry out the G measurement with copper masses at crio temperature or sobstitute the copper masses with an He masses at crio temperature?

In other words: mass has the same G force at near 0 K?

Why shouldn't it? And this better not have any hint of the Podkletnov effect.

Zz.

Staff Emeritus
And this better not have any hint of the Podkletnov effect.
Google search results: Your search - Podkletnov site:physics.uci.edu - did not match any documents.

Why crogenic? From http://www.physics.uci.edu/gravity/papers/Rome06.pdf":
Boynton et al said:
This ‘‘frequency method’’ was commonly used in the 20th century for measurements of the gravitational constant G, but with milliradian oscillation amplitude. We
operate at a much larger amplitude, near the value that yields a maximum in signal-to-noise ratio (Boynton, 2000). A downside to the frequency method has been the temperature sensitivity of a torsion fiber’s elastic modulus. Variation in fiber temperature will produce systematic and random errors in the frequency measurement. An effective remedy is to operate the pendulum in a cryogenic environment, providing reduced temperature sensitivity and an opportunity for improved temperature control.

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