{"id":141,"date":"2006-03-24T11:21:02","date_gmt":"2006-03-24T11:21:02","guid":{"rendered":"http:\/\/scienceblogs.com\/principles\/2006\/03\/24\/gravitomagnetic-noise\/"},"modified":"2006-03-24T11:21:02","modified_gmt":"2006-03-24T11:21:02","slug":"gravitomagnetic-noise","status":"publish","type":"post","link":"http:\/\/chadorzel.com\/principles\/2006\/03\/24\/gravitomagnetic-noise\/","title":{"rendered":"Gravitomagnetic Noise"},"content":{"rendered":"

\"i-e4f0a9cc66206220ae942912df2792ef-sm_gravmag.jpg\"<\/a>A reader emails to ask if I can make sense of this announcement from the European Space Agency<\/a>:<\/p>\n

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Scientists funded by the European Space Agency have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. Under certain special conditions the effect is much larger than expected from general relativity and could help physicists to make a significant step towards the long-sought-after quantum theory of gravity.<\/p>\n

Just as a moving electrical charge creates a magnetic field, so a moving mass generates a gravitomagnetic field. According to Einstein’s Theory of General Relativity, the effect is virtually negligible. However, Martin Tajmar, ARC Seibersdorf Research GmbH, Austria; Clovis de Matos, ESA-HQ, Paris; and colleagues have measured the effect in a laboratory.<\/p>\n<\/blockquote>\n

Unfortunately, the answer to “can you explain this?” is “Not really.” I’ll offer some opinions below the fold, though.<\/p>\n

<\/p>\n

The effect they’re trying to measure is related to the general relativistic effect called “frame dragging,” which I also don’t understand, but which involves small changes in the gravitational field of a rotating object. There’s a well-known space experiment with the wonderfully poetic name “Gravity Probe B” (honestly, it’s like they’re not even trying<\/strong>) that’s designed to measure this effect for the Earth.<\/p>\n

In this case, the rotating object is a ring of superconducting material that they spin up to a very high rotation rate (6500 rpm) very, very quickly. While the rotation rate in increasing, there should be a small graviational effect due to the accelerating motion of the “Cooper pairs” of electrons inside the supercondutor. (The BCS theory of superconductivity involes electrons “pairing up” through the mediation of the solid lattice, in order to form composite bosons that then undergo Bose-Einstein Condensation. If that doesn’t make sense, I’ve got a hand-wave for it that I can post at some later time.).<\/p>\n

They can detect the change in gravity with three sets of accelerometers placed near the rotating superconductor. If gravity gets stronger or weaker, that should show up as a slight acceleration of any mass nearby. It’s a very<\/strong> slight acceleration– measured in millionths of the acceleration due to gravity at the Earth’s surface– but it should be there, and be measurable. And, indeed, they seem to see such an acceleration at roughly the times and places that they expect to find an acceleration. It’s not clear to me why they only seem to see an effect right at the transition temperature for the superconductor (or even why the temperature is changing during the runs), but I didn’t read the paper all that closely.<\/p>\n

There’s a PDF pre-print on the ESA site (link in the right column of the page linked above) describing the experiment in detail, and they certainly seem to have gone about this in a responsible manner. They repeat the experiment at different temperatures, with different samples (niobium, where they expect a large effect; lead, where thy expect a small effect; and a ceramic high-temperature superconductor, where they expect no effect), and different directions of rotation, and they see acceleration where they expect acceleration, and don’t see it where they don’t expect it. Reading through the paper, it doesn’t look like kookery– they’ve done the right tests, and I can’t think of any obvious cross-checks they’ve left out.<\/p>\n

But, boy, their data (shown in the image above, click for a slightly larger view) don’t make me want to stand up and cheer. The peaks they highlight (marked with arrows) don’t obviously stand out from the other peaks in the signal, that are presumably noise. There are peaks there, and they show up in the two accelerometers where they ought to, and not so much in the one where they shouldn’t, but… Before I go declaring this proof positive of quantum gravity, I’d sure like to see some more data, and better data. In particular, I’m a little troubled by the reference signal (the bottom data trace), which seems to have spikes in the same places as the biggest spikes in the real signal– that might be an illusion, and ought to be accounted for in their analysis (the top two traces are the difference between the signals from the accelerometers with a real signal, and the reference signal which should just be mechanical noise), but it makes me uneasy.<\/p>\n

Of course, this is the problem with gravity– it’s so damn weak that any experiment looking for gravitational effects is stuck with these crappy, tiny signals (hey to Jeff and Jeff). We’ll just have to wait for either some improvements in accelerometer technology, or for some clever person to come up with another way of doing the experiment that generates a cleaner signal.<\/p>\n

As for the impact, if it holds up, this would be a big deal. But that’s still a big “if” at this point.<\/p>\n","protected":false},"excerpt":{"rendered":"

A reader emails to ask if I can make sense of this announcement from the European Space Agency: Scientists funded by the European Space Agency have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. Under certain special conditions the effect is much larger than expected from general relativity… Continue reading Gravitomagnetic Noise<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"1","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[19,33,7,11],"tags":[],"class_list":["post-141","post","type-post","status-publish","format-standard","hentry","category-experiment","category-in_the_news","category-physics","category-science","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/141","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/comments?post=141"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/141\/revisions"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=141"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=141"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=141"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}