- In 1916 Albert Einstein published his General Theory of Relativity which stated that gravity is created because a mass bends the fabric of space-time. That mass changes the behavior of its surroundings as a result of these space-time changes. It is the warped space-time that causes objects to fall towards the larger mass. If the mass is rotating it will drag the object along as space-time rotates.
- This process, called frame-dragging, drags the fabric of space-time along with the rotation. It is like a rotating ball in a pool of honey. The honey rotates too.
- Newton’s law states that the force of gravity is dependent on the mass of the two objects. Newton’s law has no effect for the masses rotating. Newton’s equation is correct but it is incomplete. With Einstein’s equations for General Relativity a mass’s space-time does have an effect if the mass is rotating. The effect is very small, 1 part in 10^12, one part in a trillion. To measure the effect you need a very large mass or very sensitive and precise instruments.
- The Earth is the largest mass we have access to. The technology to design the most sensitive gyroscope is available. The plan was to put the gyroscopes in orbit around the Earth. The spinning axis of the gyros would point to a guide star and any shift in the direction of the axis due to passing through the bent space-time created by the Earth’s mass would be measured.
- There were two separate effects that needed to be measured:
--------------- (1) The “ geodetic effect” is a shift solely resulting from the curvature of space time. Einstein’s calculations were for the satellite to be shifted 6,606 milli-arc seconds per year due to the geodetic effect.
-------------- (2) The “ frame dragging effect” is due solely to the rotation of space-time would result in a 39 milli- arc second per year shift. The measurement were made over a period of 5 years.
- The satellite was orbiting 399 miles high taking 97.5 minutes to complete each orbit. The satellite contained 4 gyros, two spinning clockwise and two spinning counterclockwise. Each gyro was spinning 4,000 revolutions per minute. These gyroscopes were the most precise every made. The spheres used in the gyros were perfectly smooth to 1 part in 10^17.
- Each sphere was made of niobium, 1 ½ inches in diameter. Each sphere was a super conductor encased in 645 gallons of liquid helium at - 271 C. The spin axis of each gyro was pointed to the guide star 1M Pegasis. The spinning spheres created a magnetic moment that allowed precise measurements of the direction of the spin axis of each gyro.
- After 5 years data measured for the geodetic effect was 6,602 milli-arc seconds per year with a + or - ½ percent uncertainty in the measurement. Remember the calculation was for 6,606 milli-arc seconds.
- The measurement of the frame-dragging effect was 37.2 milli-arc seconds with a + or -7.2 milli-arc second uncertainty in the measurement. This 19% accuracy was not what the scientists wanted. The calculation expected a 39 milli-arc second shift.
- The problem in the measurement accuracy had to do with the spheres not be perfectly electrically spherical. They were perfectly mechanically spherical, but, electrical distortions caused magnetic distortions that caused measurement uncertainty the scientists had not bargained for. It took years to unravel the real data out of these distortions. The results were not released until May, 2011.
- The project to verify Einstein’s predictions for the bending of space-time started in 1976 with the launch of Gravity Probe A. It showed that atomic clocks ran slower as their velocity increased in orbit. The atomic clocks in orbit controlled microwave signals of 1.42*10^9 cycles per second frequency. The clocks on the ground were compared to the ones in the rocket. The increases velocity made the clock run slower, but, the decreased gravity made the clock run faster. The clock’s ran faster 1.4 parts per 10,000 consistent with the Theory’s calculations.
- The Gravity Probe B experiment took 50 years to complete. The satellite was finally launched April 20, 2005. 5 years of data and 2 years of analysis later and the results still confirm that Einstein’s calculations nearly 100 years ago were correct. Using the Earth mass the effects are small and science needs more precision. But, the effects around a mass of a Blackhole are significant.
- The Blackhole’s mass actually bends space-time back on itself so nothing can escape. To an outside observer time stops. Space is frozen at the Event Horizon of the Blackhole. The effect of a rotating Blackhole’s frame dragging is to observe light traveling in the direction of rotation to travel faster the light traveling against the direction of rotation. This effect actually makes it very difficult for an object to fall directly in to a Blackhole. Instead the dragging of space-time accelerated the in falling object in to an orbit in the direction of rotation.
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707-536-3272, Tuesday, February 7, 2012
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