Sean Carroll, Ph.D., Caltech, 2007, The Teaching Company, Dark Matter, Dark Energy: The Dark Side of the Universe, Guidebook Part 2 pp. 46, Accessed 7 October 2013, "...dark matter: An invisible, essentially collisionless component of matter that makes up about 25 percent of the energy density of the universe... it's a different kind of particle... something not yet observed in the laboratory..."
اطلع عليه بتاريخ 21 مارس 2013.  الوسيط |الناشر= تم تجاهله (مساعدة); الوسيط |تاريخ الوصول= تم تجاهله (مساعدة); الوسيط |المسار= تم تجاهله (مساعدة); الوسيط |العنوان= تم تجاهله (مساعدة); الوسيط |التاريخ= تم تجاهله (مساعدة) Sean Carroll, Ph.D., Cal Tech, 2007, The Teaching Company, Dark Matter, Dark Energy: The Dark Side of the Universe, Guidebook Part 2 page 46, Accessed Oct. 7, 2013, "...dark matter: An invisible, essentially collisionless component of matter that makes up about 25 percent of the energy density of the universe... it's a different kind of particle... something not yet observed in the laboratory..."