Einstein’s Telescope

"That’s right, so after two more theoretical books I thought it would be a good idea to have a more down-to-earth book that really looks at how we know all of these wonderful things about the universe. All of the books I chose are fairly recent. There are classic books on cosmology, but the field has changed so much over the past few decades that you really need to read the more recent books. We know a lot more. We know about dark matter and dark energy. We know about the cosmic microwave background. We have learned about the early universe and how tiny ripples at early times grew into galaxies and stars. These were things we had imagined 30 years ago and now they are things that we can observe. That is why people need to read this book! It is all about the tools that cosmologists have used to be able to do this. Evalyn is an expert in gravitational lensing, which is the idea that by measuring the deflection of light around a cosmic object we can measure the object’s mass. As light passes by matter and energy, it gets bent. Einstein predicted this a long time ago and now we use it to probe the universe in very precise ways. We can figure out how much matter there is in a galaxy or cluster galaxy by seeing how it deflects the light of galaxies behind it. So we don’t need to count up the stars, we can actually measure all of the matter – and that is how we can find that there is much more matter there than can be counted. Yes. We have entered the era of precision cosmology. Back in the old days we were lucky if we knew numbers to within the right order of magnitude. Now we know a lot of numbers to within a few percent, which is just amazing."