{"id":946,"date":"2006-12-20T09:44:24","date_gmt":"2006-12-20T09:44:24","guid":{"rendered":"http:\/\/scienceblogs.com\/principles\/2006\/12\/20\/modified-gravity-eliminates-da\/"},"modified":"2006-12-20T09:44:24","modified_gmt":"2006-12-20T09:44:24","slug":"modified-gravity-eliminates-da","status":"publish","type":"post","link":"http:\/\/chadorzel.com\/principles\/2006\/12\/20\/modified-gravity-eliminates-da\/","title":{"rendered":"Modified Gravity Eliminates Dark Matter?"},"content":{"rendered":"

There’s a news squib from the Institutes of Physics this morning touting new results on a theory of modified gravity<\/a> that the authors say can explain the structure of the universe without needing to invoke dark matter. This is a significant problem in cosmology, as the article explains:<\/p>\n

\n

[O]ur theory of gravitation – Einstein’s theory of general relativity – cannot account for the extent of clumping without invoking the right amount of a mysterious substance called “dark matter”. Originally introduced in the 1930s to explain anomalous galaxy dynamics, dark matter (which cosmologists think could make up to 95% of matter in the universe) is gravitationally attractive yet does not couple to light. But crucially it can describe how the initial plasma fluctuations were sustained for long enough to allow large structures to form – on its own, general relativity attests that they simply petered out. Even though dark matter has never been observed, the majority of physicists now believe that general relativity combined with dark matter is the only satisfactory explanation for the universe’s large-scale structure. <\/p>\n

However, in recent years there has been growing support for alternative theories of gravitation to general relativity that do away with the need for dark matter altogether. One of these, devised by Jacob Bekenstein in 2004 at the Hebrew University of Jerusalem, uses vector and scalar fields in addition to the tensor used in relativity, hence the name “TeVeS” (Tensor Vector Scalar). TeVeS has already been shown to explain galaxy dynamics without the need for dark matter. But now, building upon the numerical studies by Pedro Ferreira and colleagues performed earlier this year, Scott Dodelson and Michele Liguori from Fermilab in the US have confirmed that TeVeS can also provide such sustained plasma fluctuations. (See figure: “Powering galaxy formation”.)<\/p>\n<\/blockquote>\n

On the one hand, this sounds really interesting. However, I thought the Bullet Cluster results<\/a> pretty much nailed the case for dark matter some months back. And yet, it’s apparently a result appearing in Physical Review Letters<\/cite>, a journal not known for publishing kookery (here’s the PRL link<\/a>, for those with institutional access).<\/p>\n

I am confused. So I’ll post it here, and hope that somebody who understands the current state of gravity theory will come along and explain this to me.<\/p>\n","protected":false},"excerpt":{"rendered":"

There’s a news squib from the Institutes of Physics this morning touting new results on a theory of modified gravity that the authors say can explain the structure of the universe without needing to invoke dark matter. This is a significant problem in cosmology, as the article explains: [O]ur theory of gravitation – Einstein’s theory… Continue reading Modified Gravity Eliminates Dark Matter?<\/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":[7],"tags":[],"class_list":["post-946","post","type-post","status-publish","format-standard","hentry","category-physics","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/946","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=946"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/946\/revisions"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=946"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=946"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=946"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}