OpenCourser
Learn skills that shape your future
Visit OpenCourser.com
All the matter and light we can see in the universe makes up a trivial 5 per cent of everything. The rest is hidden.
Since the 1970s, astronomers have been aware that galaxies have far too little matter in them to account for the way they spin around: they should fly apart like clay off a potter’s wheel, but something concealed holds them together. This ‘something’ is dark matter – invisible material in five times the quantity of the familiar stuff of stars and planets. By the 1990s we also knew that the expansion of the universe was accelerating. Something, named dark energy, was pushing it to expand faster and faster. Across the universe, this requires enough energy that the equivalent mass would be nearly 14 times greater than all the known material in existence.
With dark matter and dark energy making up 95 per cent of reality, cosmologists have uncovered the biggest puzzle that science has ever faced.
Save
Protected by Amazon A-to-z Guarantee & generous return policies
Every book purchase is protected by the Amazon A-to-z Guarantee. This guarantee covers both the condition of your book and its timely delivery, providing full buyer protection whether you purchase directly from Amazon or from third-party marketplace sellers.
Generous 30-day return policy on physical books. Amazon makes returns effortless with self-service return labels, drop-off at thousands of local locations (Kohl's, Whole Foods, UPS Stores), and free return shipping on eligible book purchases.
Maximize your savings with competitive pricing, deep discounts on new and used marketplace copies, bundled textbook rentals, and exclusive member savings through Amazon Prime with free fast delivery.
Read your way across versatile digital and physical formats: instant delivery via Kindle eBooks, unlimited reading with a Kindle Unlimited subscription, audiobook listening with Audible (often featuring a 30-day free trial), or traditional paperback and hardcover editions.
OpenCourser helps millions of learners each year. People visit us to learn workspace skills, ace their exams, and nurture their curiosity.
Our extensive catalog contains over 50,000 courses and twice as many books. Browse by search, by topic, or even by career interests. We'll match you to the right resources quickly.
Find this site helpful? Tell a friend about us.
We're supported by our community of learners. When you purchase or subscribe to courses and programs or purchase books, we may earn a commission from our partners.
Your purchases help us maintain our catalog and keep our servers humming without ads.
Thank you for supporting OpenCourser.
