1. A Brief History of Time
Predictably, this list must begin with Stephen Hawking's A Brief History of Time. Some may have held off on reading it due to the daunting subject matter — his book may have sold 10 million copies, but Hawking was well aware of its reputation as "the most popular book never read"
Rest assured, A Brief History of Time was written specifically for those of us who don't know our quarks from our gluons. It briefly covers the origin, development, and future of the universe but in a comprehensive, digestible, and — most importantly — enthusiastic way. Here's an excerpt:
Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?
2. The Order of Time
Carlo Rovelli is a theoretical physicist at Axis-Marseille University best known for his Seven Brief Lessons on Physics. Like A Brief History of Time, The Order of Time is designed for the layman, but Rovelli's style differs significantly Hawking's. Rovelli writes in a lyrical, almost poetic style, supplementing the heady physics of time with quotes from figures such as Shakespeare and the Greek philosopher Anaximander. It's a pleasant read, but the combination of hard science and philosophy particularly lends itself to the audio book version narrated by Benedict Cumberbatch. You can listen to a sample of the audio book in the video below.
Benedict Cumberbatch on The Order of Time www.youtube.com
3. Einstein's Clocks, Poincaré's Maps: Empires of Time
There are few concepts more crucial to our modern understanding of time than the theory of relativity, most famously elaborated by Albert Einstein. However, Einstein's theory didn't emerge from a vacuum; his contemporaries were hard at work on relativity, including his rival, Jules Henri Poincaré.
In essence, the theory of relativity showed that there was no such thing as a universal time; time flows differently for different systems. In Einstein's Clocks, Poincaré's Maps: Empires of Time, author Peter Galison explores the extraordinary period of history when this theory was discovered. Rather than serving as a solely scientific exploration of time, Galison's book has been described as "part history, part science, part adventure, part biography."
4. Your Brain is a Time Machine
Part of what makes learning about the physics of time so fascinating is how wildly it differs from our intuitive understanding of time. Though we can conduct experiments and analyses to develop an objective conceptualization of time, we're still stuck with the way our squishy brains like to perceive time. But thinking that our "natural" view of time is less interesting would be wrong.
Physicists and philosophers espouse the idea of eternalism — that there is no fundamental difference between the past, present, and future. "There is absolutely nothing particularly special about the present: under eternalism now is to time as here is to space," writes neuroscientist Dean Buonomano in Your Brain is a Time Machine. But in our perception, "now" is the most important aspect of time, the only accessible portion of it.
In his book, Buonomano explores the myriad ways our brains and bodies keep track of time, how we travel through time in our own way, and how this biological sense of time clashes or connects with the physics of time.
5. Slaughterhouse Five
You don't have to stick to hard science to build an understanding of time. In fact, doing so would provide a lopsided picture of time, leaving out the crucial fact that we are subjective individuals with unique points of view.
To learn more about this aspect of time, we have to turn to literature: Kurt Vonnegut's Slaughterhouse Five traces the contours of how time affects us, our memory, and most of all how trauma distorts our sense of it.
Billy Pilgrim, the book's antagonist, survives the firebombing of Dresden by hiding out in a slaughterhouse — an event that Vonnegut lived through himself — only later to become unstuck in time, forced to witness the events of his life randomly, without any control, over and over again:
Listen:
Billy Pilgrim has come unstuck in time.
Billy has gone to sleep a senile widower and awakened on his wedding day. He has walked through a door in 1955 and come out another one in 1941. He has gone back through that door to find himself in 1963. He has seen his birth and death many times, he says, and pays random visits to all events in between.
6. The Dialogues
One of the intractable problems with physics is how darn abstract it is. Getting a good understanding of science sometimes requires the use of visual aids. That's why The Dialogues made this list; though it doesn't focus specifically on time, it does cover the nature of time, along with numerous other subjects in the sciences as portrayed through illustrated conversations.
7. From Eternity to Here
Sean Carroll's From Eternity to Here focuses on a specific characteristic of time and offers a theory on how time operates. Carroll's book examines what physicists refer to as the arrow of time, or the idea that time always seems to be moving in one direction — into the future, forward, and not backward.
There's no real reason for this to be the case, however. Why doesn't time flow backward? In his book, Carroll posits that it could be because the Big Bang wasn't the start of the universe, that conditions from before the Big Bang have determined that the arrow of time flows forward. Carroll explains this possibility in his TED Talk in the video below:
Cosmology and the arrow of time: Sean Carroll at TEDxCaltech www.youtube.com
8. A World without Time
Einstein's theory of relativity set the scene for our modern understanding of time, but for logician Kurt Gödel — a lifelong friend of Einstein's — it also revealed a bizarre conclusion. Gödel argued that in any universe where the theory of relativity was true, time could not exist at all.
In A World Without Time, Palle Yougrau covers Einstein's and Gödel's friendship, the underpinnings of Gödel's time-less philosophy, and how modern cosmologists and philosophers seem to have forgotten all about Gödel.
9. The Fabric of the Cosmos
Physicist Brian Greene lays out the fundamental nature of the universe in this book, dedicating one out of its five parts to time and experience. In it, he explores the flow of time, how the laws of physics apply equally as well when time flows backwards as it does when it flows forwards, and the nature of time in the quantum realm.
Greene also explores many other aspects of the universe, including some ideas that are controversial amongst scientists, making this a valuable read for those interested in more than just time. "Cosmology," writes Greene, "is among the oldest subjects to captivate our species. And it's no wonder. We're storytellers, and what could be more grand than the story of creation?"
10. The Direction of Time
Hans Reichenbach was a philosopher of science from the 20th century, and as such, his perspective is a little different than that of career physicists. In his work, The Direction of Time, Reichenbach analyzed the philosophical implications of the many exciting findings of the theorists of his day. In fact, Rovelli, author of The Order of Time, cited it as one of his favorite books on time. In a review of The Direction of Time, Rovelli writes,
He was the first, as far as I know, to fully grasp the implications of the fact that the growth of entropy is the only law of physics that distinguishes the past from the future. This means that the existence of traces, memories and causation are just byproducts of entropy growth. This is a shocking realisation, which I believe has not been fully digested yet.
Our universe may be having itself quite a great time it seems. Cosmologists from Uppsala University came up with a new model that proposes the universe may be riding on an ever-expanding bubble in an extra dimension.
In particular, according to this theory, published in Physical Review Letters, the researchers offer a novel explanation for how the universe may be getting bigger. The fact of its accelerating expansion has been known for about the past 20 years but the explanation for that has relied rather unsatisfyingly on the mysterious "dark energy".
In their new paper, the Swedish scientists approach this topic from the direction of string theory, which maintains that all matter is made of tiny vibrating strings. The theory also allows for the existence of extra dimensions, in addition to the three spatial ones we experience on a daily basis.
The groundbreaking new idea by the researchers says that the universe may be sitting on the edge of an expanding bubble, while all matter exists on strings that reach outward from it into an extra dimension. Dark energy would be the inflating force in this bubble, the existence of which is supported by string theory, claim the scientists.
In case you're wondering, they think such bubbles should be rather stable, writing there's "a strong indication in favor of the stability of these bubbles."
Perhaps even more excitingly, there could be more bubbles than just the one with our universe on it. Each one of those carrying another universe.
'In this context, the cosmology we see as 4D observers is not due to vacuum energy, but rather arises as an effective description on a dynamical object embedded in a higher dimensional space,' the researchers explain.
The Uppsala University team included Souvik Banerjee, Ulf Danielsson, Giuseppe Dibitetto, Suvendu Giri, and Marjorie Schillo.
As they write in their paper, black holes can also be re-defined by this new theory:
"Gravitational collapse of the string endpoints in four dimensions results in an unstable black string solution in five dimensions," state the scientists.
Check out their research for yourself here.
Michio Kaku: The multiverse has 11 dimensions
Perhaps it's not the most cheerful thought, but people have preoccupied themselves with how the world around them could end for millennia. Now in the scientific age, one such dire prediction comes from math and physics. The theory of the Big Rip says that at some point in the distant future, the universe could rip itself apart, with everything in existence from animals to atoms becoming shredded.
''In some ways it sounds more like science fiction than fact,'' said physicist Dr. Robert Caldwell of Dartmouth, who first proposed this dramatic idea in a 2003 paper he wrote with Dr. Marc Kamionkowski and Dr. Nevin Weinberg from the California Institute of Technology.
The cosmological model of the Big Rip is predicated on the notion that if the universe continues to accelerate in its expansion, it will eventually reach the point where all the forces that hold it together would be overcome by dark energy. Dark energy is the rather mysterious force that is predicted to make up 68% of the energy of the observable universe. If it overwhelms gravitational, electromagnetic and weak nuclear forces, the universe would literally come apart.
A new model of the Big Rip theory published in 2015 actually came up with the date when the Universe would meet its demise - about 22 billion years from now. The 2015 model was developed by professor Marcelo Disconzi of Vanderbilt University in collaboration with physics professors Thomas Kephart and Robert Scherrer.
The timeline of how life universe ends up in a Big Rip.
Credit: Jeremy Teaford, Vanderbilt University
Disconzi's hypothesis says that a Big Rip can occur when dark energy will become stronger than gravity, reaching a point when it can rip apart single atoms. The professor's model shows that as its expansion becomes infinite, the viscosity of the universe will be responsible for its destruction. Cosmological viscosity measures how sticky or resistant the universe is to expanding or contracting.
If the Big Rip theory is correct, one day we could reach a moment when planets and everything on them will be torn apart. Then the atomic and molecular forces will be ripped open, electrons splitting from atoms, all the way down to the quarks and anything smaller. But until then, check out his video for more on the Big Rip:
