As a kid, the late theoretical physicist Stephen Hawking was not a great student, by his own admission. What he was always good at, however, was asking big questions, queries so daunting and seemingly impossible to answer that many of us avoid considering them.
In a slender new book, Brief Answers to the Big Questions, released last month, Hawking shared his final thoughts, both scientific and personal. He died in March at 76 years old, but not before making the abstract propositions of cosmology and theoretical physics if not simple at least accessible and comprehensible.
He also shed light on his own life, humorously illuminating his path from middling student to world-renowned scientific genius, a mean feat made all the more impressive by the fact that Hawking was diagnosed with the degenerative motor neuron disease amyotrophic lateral sclerosis in his twenties.
Hawking wasn’t expected to live very long. This early death sentence gave the scientist a unique appreciation of existence, and a sense of urgency. “After my expectations had been reduced to zero, every new day became a bonus, and I began to appreciate everything I did have,” he explained. “While there’s life, there is hope.”
This appreciation for life, coupled with his sense that there was no afterlife, pushed Hawking to continuously explore the universe in his mind and through science. He didn’t think he’d have much time and so he made the moments count.
So let us bravely go where Hawking led us, diving into the biggest question to have preoccupied mystics, philosophers, artists, scientists, and writers for as long as humans have been contemplating existence: Is there a God?
Hawking was not a religious man. He did not believe in God. He believed in scientific laws. Yet he provided a scientific definition of God and argued that we can know this deity’s “mind” because “knowing the mind of God is knowing the laws of nature.”
“My prediction is that we will know the mind of God by the end of this century,” he wrote.
The dictates of nature might be a definition of God, Hawking conceded, but he didn’t see these as proof of a deity’s existence, merely a description of an impersonal almighty, one who doesn’t actually decide how things go in our personal lives or judge us. “I don’t have a grudge against God,” he explained. “I don’t want to give the impression that my work is about proving or disproving the existence of God. My work is about finding a rational framework to understand the universe around us.”
With this declaration, Hawking proceeded to do just that, explaining the “recipe” for the universe and how it came to create itself.
Although the universe is complex, it’s made up of just three ingredients—matter, energy, and space. And if you think of matter, or mass—dust, rock, ice, and liquids—as just another form of energy, as Albert Einstein proved it was with his equation E=mc2, then really there are only two key components to the universe: energy and space.
There’s the stuff, mass or matter, and there’s what contains the stuff and is all around it, or space. Einstein’s equation, which states that energy is equal to mass multiplied by the speed of light squared, basically proves that mass and energy are interchangeable, The cosmic pantry is super simple yet the number of recipes the three—or two—ingredients yield is astoundingly numerous.
Hawking believed that these things came to create the universe, spontaneously. “At the moment of the Big Bang, an entire universe came into existence, and with it space. It all inflated like a big balloon being blown up,” he wrote.
When the Big Bang produced a massive amount of positive energy, it also produced an equal amount of negative energy—we know this because the universe has a kind of perfect symmetry. Hawking explained this symmetry with a simple analogy. If you build a hill, you also dig a hole, taking from one area to add to another. That’s what the universe does with positive and negative energy. Everything must always add up to zero, according to the laws of nature.
Space is a vast store of negative energy balancing out the positive energy of matter. Hawking likened the universe to “an enormous battery” that stores negative energy. The negative energy (the hole) is spread throughout space and the positives (the hill) are the mass and energy of the material world, including ourselves, mountains, the Earth, and much more.
Here’s where it gets a bit tricky. To understand how the universe could have created itself from nothing, we must consider quantum mechanics. At the tiniest scales, energy acts randomly and something can ever-so-briefly appear from nothing. Hawking calls the universe “the ultimate free lunch” because it came into being on a minuscule scale out of nothingness with no “cause” or “creator” beyond the laws of quantum mechanics, which allow for randomness.
We usually think of everything, any effect, as being caused by something else, something that occurred earlier. In that case, it’s arguable that God caused the universe to come into existence. Hawking didn’t think so, though, explaining:
The law of nature itself tell us that not only could the universe have popped into existence without any assistance, like a proton, and have required nothing in terms of energy, but also it is possible that nothing caused the Big Bang. Nothing.
The scientist argued that when the Big Bang occurred, time began. Based on the relationship between space and time, as illuminated by Einstein, we know that the two are fundamentally intertwined. So, if there was no time “before” the Big Bang, there’s no need for a creator to explain how the universe spontaneously came into existence.
“You can’t get to a time before the Big Bang became there was no time before the Big Bang. We have finally found something that has no cause, because there was no time for a cause to exist in,” according to Hawking.
Asking what came before the Big Bang is thus a meaningless question, Hawking argued, because there was no such thing as time. It’s an irrelevant, nonexistent reference. It would be like asking, “What is South of the South pole?”
If the concept of time only exists within our universe and the universe came to be spontaneously, on a microscopic level, and with it, brought time into existence, there’s simply no “before” to consider. Time itself is bound by the Big Bang.
After the Big Bang, which brought time into existence, the universe expanded at a rapid rate. We know this because we have a kind of fossil record of the universe’s beginnings based on very faint microwaves, like static on the radio, which provide a sort of map of the past.
Scientists in the 1960s posited that the Big Bang scattered matter that condensed into galaxies and released a blast of radiation that could be detected in microwaves. The waves are like reverberations that we can now measure, “the afterglow radiation left over from the hot Big Bang,” NASA explains.
All over the sky, the temperature is extremely uniform, with tiny variations or fluctuations at the part-per-million level that provide insight into the origin, evolution, and content of the universe. The cosmic microwave temperature fluctuations are believed to trace differences in the density of matter in the early universe, which gave rise to the formation of galaxies and, ultimately, our existence.
In 1982, Hawking proposed the theory that quantum fluctuations—random temperature differences at the tiniest levels—were the seeds for structures in the universe, eventually leading to the formation of galaxies, stars, and people. About two decades later, NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) provided the evidence that backs this proposition, showing those tiny fluctuations in radiation that prove different densities in the universe at the start of time.
As Hawking put it in his book, “WMAP produced a wonderful map of the temperature of the cosmic microwave sky, a snapshot of the universe at about one-hundredth of its present age.” The irregularities in the map reveal that some areas of the universe had a higher density than others. In those dense areas, gravitational expansion was slower, causing a collapse of matter into galaxies and stars. Hawking called the map “the blueprint for all structure in the universe” and humanity “the product of quantum fluctuations in the very early universe.”
Among his final predictions, Hawking posited that eventually the amount of matter in the universe will slow down its expansion altogether, leading to a Big Crunch. Essentially, the gravitational attraction between galaxies will cause them to fall toward each other until they are all crunched into one.
The other option for the future of the universe that the cosmologist proposed was no more heartening. If the density of the universe falls below a critical value, and gravity becomes too weak to stop the galaxies from flying apart forever, the universe will get emptier and emptier and colder and colder as all the stars burn out.
Either way, whether through a crunch or an expansion, Hawking believed the universe could reach an end point, just as it seems to have a beginning. But don’t despair, the end of history is billions of years away, he predicted.
In the interim, we can still do a lot with the time remaining. ”Be brave, be curious, be determined, overcome the odds. It can be done,” Hawking urged. “We are all time travelers, journeying together into the future. But let us make that future a place we want to visit.”