Gravity Probe B Testing Einsteins Universe

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Gravity Probe BTesting Einsteins Universe
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• Gravity Probe B (GP-B) was launched on April 20,
  2004 at 957 am from Vandenberg Air Force Base in
  California atop a Boeing Delta II rocket
• It entered an orbit over the Earths poles

Launch of GP-B
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• Gravity Probe B is a relativity gyroscope
  experiment developed by NASA and Stanford
  University to test unverified predictions of
  Albert Einsteins General Theory of Relativity
• It is a 21-foot-tall satellite now orbiting 400
  miles above the Earth

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• The experiment will check, very precisely, tiny
  changes in the direction of spin of 4 gyroscopes
  contained in an Earth satellite
• So free are the gyroscopes from disturbance that
  they will provide an almost perfect space-time
  reference system

Gyroscope rotor in a special clean case to
avoid contamination
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Einsteins Theory of General Relativity
Geodetic Effects

• This theory states that any mass, such as the
  Earth, warps space and time around it
• Any object traveling near the Earth must follow
  the curve or warp in space-time
• The result is that the object falls toward the
  Earth

Warping of space-time top view
Warping of space-time side view
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Einsteins Theory of General Relativity
Frame-Dragging Effects

• Einstein also predicted that the spinning Earth
  should twist space-time around with it
• This is an effect called frame-dragging
• It says that an object in space near the Earth
  should respond to that twist of space-time by
  turning with it

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• These gyroscopes will measure how space and time
  are warped by the presence of the Earth and how
  the Earths rotation drags space-time around with
  it
• These effects have far-reaching implications for
  the nature of matter and the structure of the
  Universe

An artists concept of Gravity Probe B orbiting
Earth to measure space-time
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• Throughout the experiment GP-Bs telescope
  remains pointed at IM Pegasi (a distant guide
  star) to provide a constant reference line for
  measuring any turn in the pointing direction of
  the gyroscopes spin axes
• If Einstein was correct, the twisting of
  space-time near the Earth should cause the spin
  axes to turn away from this reference by the very
  tiny angle of 1/100,000th of a degree over a year

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• Free from external forces, the gyroscopes axis
  should continue pointing at the star forever
• But if the region of space through which the
  gyroscopes orbit is slightly twisted, as
  Einsteins theory predicts, the direction of the
  gyroscopes axis would drift very slightly over
  time
• By noting this change in direction relative to
  the star, the geodetic and subtle frame-dragging
  effect can be measured

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• To measure this miniscule drift, NASA created
  four near-perfect spheres called SQUIDs
  (Super-conducting Quantum Interference Devices)
• Each gyroscope is less than three
  10-millionth-of-an-inch from perfect roundness

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• These spheres spin in near-isolation in a
  near-vacuum, near absolute zero, suspended inside
  a housing, protected from any magnetic, electric,
  or solar forces
• Guinness Book of World Records lists them as
  roundest objects ever made in the world

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• GP-B will be the longest space mission kept near
  absolute zero (it will be kept at -450 degrees F
  below zero for 12 months)
• It can sense any change in the gyroscopes
  position to within on 10-millionth of a degree
• It controls the motion of the satellite with
  thrusters that produce forces softer than a human
  breath

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Was Einstein Right?

• If GP-Bs results are consistent with Einsteins
  theory it will help solidify our understanding of
  phenomena like black holes and quasar jets
• If GP-Bs results are not consistent with
  Einsteins theory, it will require a significant
  revision of our theory of the structure of the
  universe
• After two billion spins of the gyroscopes and
  7,000 orbits of Earth, Gravity Probe B should
  know the answer