The Weekly Beaker: Infinite Pasts, the Multiverse, and Stardust: Stephen Hawking’s “The Gr
Published: Tuesday, November 6, 2012
Updated: Tuesday, November 6, 2012 22:11
“The Grand Design” by Stephen Hawking and Leonard Mlodinow is chock-full of weird facts about our universe that will make you seriously question your view of reality. Below are a few of the most mind-bending ideas from the book.
One of the amazing concepts discussed came from the work of bongo-playing American physicist Richard Feynman. Feynman analyzed the famous double-slit experiment from a completely new and creative perspective—because previously no one knew how to interpret it. In the double-slit experiment, light particles—photons—were fired one at a time at a recording screen through a plate with one vertical slit. Over time, one band of photons appeared on the recording screen. But when a second slit was added to the plate, rather than two bands of photons showing up, multiple bands appeared, indicating that after passing through the two slits, the photons interfered with each other as if they were waves. Yet, when fired one at a time, what can a single photon interfere with?
It interferes with itself. The strangeness of the quantum world is perfectly encapsulated by this one experiment: the photon traveled through both slits at once to produce the interference pattern. According to the Heisenberg’s uncertainty principle, it is impossible to know an object’s position precisely at a given time, which essentially enables it to exist in more than one place. Our observations limit it to one place, whereas it would have been in many places, each of differing probability, if we hadn’t observed. This means that if we place a detection device at the two slits, we confine the particle pattern to two narrow bands on the recording screen, because our observation changes the phenomena itself and stops the self-interference possible without observation.
Feynman took this explanation a step further. He said a particle takes every possible path to the recording screen simultaneously, and ends up in its particular place because of the probability for that location. And yet if a measuring device is placed just before the recording screen, it confines a particle to a path that it could not have chosen until it was detected. Particles, when measured near the screen, show the two-band pattern rather than interference. But the particle couldn’t have known that it was going to be observed, that it couldn’t take all possible paths, that it would have to choose either one slit or the other, until much later than it actually reached the slitted plate—the decisive moment. Our present observations affect the past. In other words, the unobserved past is a spectrum of infinite possibilities, but one of those possibilities is made real once we shine the light of observation on it.
OK, take a step back and regroup if you need to. That was intense. But it gets cooler. Feynman’s “alternative histories” approach applies to the birth of our universe as well. The universe started in every possible way, with many universes born at the same time, each with different physical laws. The laws of most of these universes cause them to collapse again relatively quickly, before having the chance to develop matter, stars and life. But some of these universes are similar to ours. And again, by peering into the unobserved past with telescopes, satellites and recording equipment, we choose the path of history that led us to where we are, which was previously all possible histories.
And I’m sure you’ve heard that inspirational quote: “We are all made of stardust.” Well this is quite literally true, and here’s why: A heavy element like carbon (the molecular basis for our life) can only be formed under the intense pressure and temperature of a star. But even normal star conditions aren’t enough to generate carbon—only once the star nears the end of its life does its core collapse and rise in temperature, to around 100 million degrees Celsius. Three helium nuclei are able to fuse to form stable carbon. Then, the most epic explosion in the universe happens—a supernova—and the star’s contents are spewed all over, some of which might condense into a little planet like Earth.