NASA's Gravity Probe B: Testing Einstein's Theory of Relativity

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Discussion Overview

The discussion centers around NASA's Gravity Probe B satellite and its mission to test predictions of Einstein's general theory of relativity, particularly the concept of frame dragging caused by rotating massive objects. Participants explore the implications of the experiment, the relevant theoretical frameworks, and specific metrics related to spacetime.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants discuss the purpose of Gravity Probe B in testing the twisting of space around Earth as it spins, as predicted by general relativity.
  • Questions are raised about the existence of a 'Terra Metric' space-time and whether a SQUID can provide evidence for such a metric.
  • There is a suggestion that the Kerr metric, which describes the spacetime around a rotating mass, may be applicable to the scenario being tested by Gravity Probe B.
  • One participant inquires about the timeline for the results from the Gravity Probe B experiment.
  • Technical details regarding the Kerr Metric and its angular velocity formula are provided by a participant, indicating a mathematical approach to understanding the experiment's implications.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the metrics and theories applicable to the experiment, with no consensus reached on the specifics of the 'Terra Metric' or the interpretation of the results from Gravity Probe B.

Contextual Notes

Some assumptions about the applicability of the Kerr metric and the nature of the 'Terra Metric' remain unresolved, and the discussion includes varying interpretations of the experimental outcomes.

Orion1
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NASA's Gravity Probe B satellite was launched into orbit Tuesday morning to test a key prediction of Albert Einstein's general theory of relativity.

Einstein's theory states that gravity is a distortion in the fabric of space caused by massive objects. Earth, like a bowling ball dropped on a rubber sheet, stretches the invisible fabric of space and causes smaller objects to move toward it.

That portion of the theory was confirmed by Gravity Probe A, launched in 1975.

But the theory also says that as the Earth spins on its axis, it tends to twist the fabric of space around it slightly. Gravity Probe B is designed to test that.

The heart of the satellite is a perfectly spherical quartz sphere, about the size of a pingpong ball, that is electrostatically floated in a cryogenic chamber and spun at 10,000 revolutions per minute.

The spinning sphere is a highly precise gyroscope, claimed to be the most accurate scientific instrument ever built. Researchers hope it will detect the twisting in the fabric of space, deflecting slightly in response to it. A Superconducting Quantum Interference Device, or SQUID, will detect any changes in the sphere's axis of rotation and send the results back to Earth.

The bulk of the satellite is made up of coolant to maintain both the sphere at the SQUID at a temperature near absolute zero, about minus 460 degrees Fahrenheit.

Reference:
http://www.sltrib.com/2004/apr/04212004/images/nasa.jpg
http://www.sltrib.com/2004/apr/04212004/nation_w/159275.asp
 
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Hello orion1 is there a question here or is this simply a statement?
 
Terran Metric...


What is the equation for the 'Terra Metric' space-time?

[tex]s^2 = ...[/tex] ?

Can a Superconducting Quantum Interference Device, or SQUID, prove such a metric?

[/color]
 
when do the results come in?
 
Orion1 said:
What is the equation for the 'Terra Metric' space-time?

[tex]s^2 = ...[/tex] ?

Can a Superconducting Quantum Interference Device, or SQUID, prove such a metric?

[/color]

I imagine they are using the Kerr metric for the spacetime near the turning earth. That is the solution for an axially symmetric spinning mass, and that is the one in which the frame dragging is manifested.
 
Metric Measurement...

Kerr Metric Boyer-Lindquist angular velocity:
[tex]\omega = \frac{2Mar}{(r^2 + a^2)^2 - a^2 \Delta \sin^2 \theta}[/tex]

Reference:
http://www.gravityprobeb.com/
http://www.astro.ku.dk/~cramer/RelViz/text/geom_web/node4.html
 
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