two centuries of gravitation in review michael garelick scott steffin

Two Centuries of Gravitation in Review

Michael Garelick

Scott Steffin

General Relativity Theory

In the theory of General Relativity (GR) a massive object will cause the curvature of the space-time around it producing a gravity field. This theory is used in cosmology and is the current view among most physicists.

Experimental Verification of GR from observing gravity

• Deflection of light path or “bending of light” by gravity.

• Gravitational red shift• Gravitational waves have not been

experimentally confirmed. To date there is no detection of gravity waves as defined in GR. All the possible detections of these waves are experimental anomalies.

• Weak Equivalence principle (still being tested)

The Existence of Gravitons

• Are mass-less particles that exist in the Standard Model.

• Have never been detected experimentally.

• Gravitational force carrier.

Areas for Research at Present Time

• Gravity wave detectors• Satellites for measuring gravity such as

Gravity Probe B (mainly testing GR)• Experiments to detect Gravitons• More accurate balances to measure G• Search for violations of current theories and

general assumptions about gravity.• Theoretical work such as String Theory and

quantum gravity work.

The Search for Violations in Our Theories of Gravity

The Search for Violations in Our Theories of Gravity

• Does the universal constant of gravitation G converge to a single value?

G is not Converging with each measurement

The Search for Violations in Our Theories of Gravity

• Does the universal constant of gravitation G converge to a single value?

• Does the value of G change in value?

The Search for Violations in Our Theories of Gravity

• Does the universal constant of gravitation G converge to a single value?

• Does the value of G change in value?• Is the distance dependence of gravity always

1/r^2?

The Search for Violations in Our Theories of Gravity

• Does the universal constant of gravitation G converge to a single value?

• Does the value of G change in value?• Is the distance dependence of gravity always

1/r^2?• Is there a temperature dependence of G?

The Search for Violations in Our Theories of Gravity

• Does the universal constant of gravitation G converge to a single value?

• Does the value of G change in value?• Is the distance dependence of gravity always

1/r^2?• Is there a temperature dependence of G?• Can G depend on voltage, spatial

configuration, pressure, composition, or other factors?

Extreme Values of G on Accurate Balances

6.6656 E-11 (MKS) +/- 0.0000095, M.P. Fitzgerald and T.R. Armstrong

6.71540 E-11 +/- 0.00056, W. Michaelis, H. Haars, and R. Augustin

6.683 E-11 +/- 0.0017, SJ Richman, TJ Quinn, C.C. Speake and RS Davis

7.27 E-11 +/- , Charles E. Goldblum (1987), Bull. Am. Phys. Soc. v.32 p.1049 George Gillies, Rep. Prog. Phys. Vol.60 p.151(1997)

1986 CODATA value 6.67259 E-11 as set for international standard. The CODATA is now at a different value with a higher allowed uncertainty.

Gravity Inside the Earth

• Values of G measured inside the earths surface show values higher than laboratory balances on the surface.

• Measurements from many mine shafts/bore holes show this anomaly

• Is this a real physical effect?

F.D. Stacy and S.C. Holding, Nature vol. 292 p. 230 1981

F.D. Stacy and G.J. Tuck, Nature vol. 307 p. 714 1984

F.D. Stacy, S.C. Holding and G.J. Tuck , Rev. Mod. Phys. Lett. V.59 p. 157

Here are some values of Gmeasured using an accelerometer

Possible Temperature dependence of G

• The authors of this paper (1) state a temperature effect is >2 E-4 per degree C if it exists.

• The picture on the right is the diagram of the balance used.

1. P.E. Shaw and N. Davy, Phys. Rev. v.21 p.680 (1923)

Gravity as A Fundamental Force

• Most physicists agree that gravity is a fundamental force.

• In the 20th century this question has been raised.

• Vacuum and Ether theories of gravitation