Gravity Probe B Update

Very Exciting! We attended the previous public presentation in April when Professor Francis Everitt, a very approachable Stanford University physicist and principal investigator of the Gravity Probe B (GP-B) Relativity Mission and his team, “shared what they have found so far—namely that the data from the GP-B gyroscopes clearly confirm Einstein’s predicted geodetic effect to a precision of better than 1 percent.” The privilege of being present among the handful of humans in that room during that announcement was clearly a high point in my own human experience, to date. Since that time, we’ve been patiently awaiting the results measuring the frame-dragging effect.

Today, the update below came in on the mailing list, alerting us to just a little bit more time to get the data analysis right, with a target maximum 5% margin of error. Everitt’s last word from the April meeting were timeless, “Always be suspicious of the news you want to hear.”

============================================ GRAVITY PROBE B MISSION UPDATE FOR DECEMBER 2007 ============================================

PROGRAM STATUS

Over the past three months, GP-B has continued to make outstanding progress.

In our September 25, 2007 status update, we reported that the trapped flux mapping technique had resulted in a dramatic improvement in the determinations of the polhode phase and angle for each gyroscope throughout the entire 353-day experiment period. Applying these results to a central 85-day stretch of data, from December 12, 2004 through March 4, 2005, we obtained a robust and stable measurement of the frame-dragging effect with a reasonable (~30%) error level. We are in process of progressively extending the analysis to increasingly long time intervals in order to reach the full experiment accuracy, potentially to an error margin of less than 5%. Also important is the completion of the study of – and if necessary elimination of – any remaining systematic effects that may bias the results of the experiment.

Our progress and results were intensively reviewed by the GP-B Science Advisory Committee (SAC) at its 17th meeting on November 2, 2007. In its subsequent report, the SAC commented on “the truly extraordinary progress that has been made in data analysis since SAC-16 [March 23-24, 2007]” and unanimously concluded “that GP-B is on an accelerating path toward reaching good science results.”

It is anticipated that approximately another six months until May 2008 will be needed to complete this full coverage and arrive at a definitive final result. We believe the results will be truly significant and will withstand scrutiny at the deepest scientific level. We agree with the SAC that: “This phase must include an adequate opportunity for the SAC to review the final result in some detail before publications are prepared and public announcements are made.”

To this end, we are planning on this review for the May 2008 time frame.

GP-B MISSION NEWS

Web Site Overhaul Nearing Completion

For a number of months now, we have been the process of revising our whole GP-B Web site with the goal of updating and improving its look-and-feel, and more importantly, its ease of navigation. This work in nearing completion, and we expect to “go live” with the new site later this month. The new site will have the same URL (https://einstein.stanford.edu) as our current site, and we will send out an announcement to the GP-B Update email list when the new site is up and running.

=================== PREVIOUS GP-B UPDATES =================== If you wish to read any of our previous updates, our GP-B Web site includes a chronological archive of all the updates/highlights (with photos and drawings) that we have posted over the past 8 years: https://einstein.stanford.edu/highlights/hlindexmain.html

============================= OTHER LINKS THAT MAY INTEREST YOU =============================

Our GP-B Web site, https://einstein.stanford.edu contains lots of information about the Gravity Probe B experiment, general relativity, and the amazing technologies that were developed to carry out this experiment.

Video and/or audio of May 18, 2006 public lecture by Principal Investigator, Professor Francis Everitt, on GP-B. You can view a streaming video of the lecture in your Web browser: https://einstein.stanford.edu/highlights/hl_video_everitt051806.html. You can also download either a video or audio only copy of the lecture to an iPod from the Stanford University iTunes U Web site: https://itunes.stanford.edu, This Web page automatically launches the Apple iTunes program on both Macintosh and Windows computers, with a special Stanford on iTunes U “music store,” containing free downloads of Stanford lectures, performances, and events. Francis Everitt’s “Testing Einstein in Space” lecture is located in the Faculty Lectures section. People with audio-only iPods can download the version under the Audio tab; people with 5th generation (video) iPodfs can download the version under the Video tab.

Visual tour of the GP-B spacecraft and payload from our GP-B Web site: https://einstein.stanford.edu/content/vehicle_tour/index.html

PDF file containing a 1/20 scale, paper model of the GP-B spacecraft that you can download print out, and assemble: https://einstein.stanford.edu/content/paper_model.

NASA’s Marshall Space Flight Center also has a series of Web pages devoted to GP-B: https://www.gravityprobeb.com

The Harvard-Smithsonian Center for Astrophysics (Cambridge) and York University (Toronto), with contributions from the Observatoire de Paris, have been studying the motions of the guide star, IM Pegasi for over a decade. To find out more, visit: https://www.yorku.ca/bartel/guidestar/

In addition, you’ll find information in the Guide Star FAQ on our Web site: https://einstein.stanford.edu/content/faqs/faqs.html#guidestar

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