“Outcomes really do follow probabilities.” She turned to Daniel. “What happens tomorrow between you and me? Will we be together or not?”
Without waiting for an answer from Daniel, she turned to Marie. “What will you do next at NASA? Will you wear the headband again now that you know it hasn’t been destroyed? Will you visit Haiti after our chat? None of these outcomes, the important stuff and the trivial, has been determined. But there are plenty of probabilities, and some outcomes are more likely than others.”
Nala gripped their hands tightly. “If you ask me, that’s the multiverse in a nutshell. We live it every day. Today is the result of yesterday’s probabilities, and tomorrow will materialize from today’s.”
“Sounds more like philosophy than science,” Daniel said.
Nala smiled. “Yeah, it does, doesn’t it? And here I thought I was strictly a scientist.” She lifted Daniel’s hand and kissed it and then did the same to Marie’s. “The quantum world will do that to you.”
Afterword
I hope you enjoyed the story. I had a lot of fun writing it. Like most people I relish a good adventure, but I could spend days contemplating the unanswered questions of our fascinating world. If this story spurred deep thoughts about the structure of the universe or why it works the way it does, then I’ve been successful.
I also had fun writing this story because I’ve developed an affection for the three scientists that held hands in the final chapter. I would love to join them in their conversation out on the hotel patio in Austin. It makes me think of Stranger than Fiction, the movie with Will Ferrell and Emma Thompson in which an author meets her character. That would be fun.
Just as I did after the first book (Quantum Space) I thought I’d write one more chapter. I’ll step out of the story and talk about the science and the science fiction by diving into three scientific topics: critical density, nothingness and quantum superposition. Don’t roll your eyes; I’ll be nice.
Critical Density
While drifting effortlessly in her float pod, Nala contemplates the density of space in Chapter 6, Bosons. Later, in Chapter 38 and 40, she explains that the universe is flat because its density exactly matches critical density, measured to be 9.47 × 10–27 kg/m3.
First, let me say that every bit of this is real science, as accurately as I could write it. Second, it absolutely blows my mind that our universe is flat, and it doubly blows my mind that so few people realize how mind-blowing this bizarre coincidence is!
Allow me to expound. In 1915, Albert Einstein published his Theory of General Relativity, which is all about gravity and the shape of space. Space, Einstein said, is curved wherever there is mass. The curvature is what we experience as gravity. But curved into what? Einstein’s explanation required extra dimensions of space that we cannot see.
Fast-forward a hundred years and dozens of confirmations of Einstein’s theory. As it turns out, space really is curved into an extra dimension and remarkably this curvature is measurable with highly accurate lasers. How?
Space can have positive or negative curvature, or it can have no curvature at all (flat). Like this:
You probably learned in high school geometry that the sum of the angles inside any triangle always equals 180 degrees. Right? But when space is positively curved (the top image), the sum of those angles is slightly more than 180. And when space is curved negatively, the sum is slightly less than 180. Only when space is flat do the angles inside a triangle sum to 180.
For our routine life on Earth, the curvature of space is negligible, and sure enough, any triangle you measure will sum to 180 degrees. But shine three lasers between Earth, Venus and Mars to precisely measure the triangle formed by the planets. You won’t get exactly 180 degrees; the sum of the angles will be a little larger as a result of the positive curvature of space around the sun. (Full disclosure: No one has ever performed this specific experiment, but NASA’s Gravity Probe B in 2004 and the LAGEOS satellite in 1976 both did something similar to measure the warping of space around the Earth. Answer: space is indeed curved.)
What if you wanted to measure the curvature of the whole universe? Is the universe itself curved? If so, does it curve like a sphere or a Pringles potato chip?
Astronomers have been eager to find out ever since Einstein explained how space curved. They got their chance in 2001 when NASA launched the Wilkinson Microwave Anisotropy Probe (WMAP). The probe took pictures in every direction, measuring the 2.7 Kelvin cosmic microwave background (CMB) radiation, the residual radiation left over from the Big Bang. The results looked like this (which Nala explains in Chapter 40 Density):
With WMAP’s sensitive instruments and some clever thinking, mission scientists measured overall curvature. What did they find? The universe is flat. Not everywhere—there are local positive curvatures and local negative curvatures—but as a whole it all balances out to perfectly flat. An enormous triangle spread across the whole universe would have angles that add to exactly 180 degrees. That’s important. But before I cover why, let’s talk about density.
Measuring triangles with lasers or estimating curvature from the CMB radiation map is what scientists call the geometric approach but there’s another way to measure the shape of the universe, called the accounting approach.
In Chapter 40, Nala takes a stab at explaining it:
“The universe is expanding, right?” she says. “And gravity tries to halt that expansion by pulling things together. More mass, more gravity. Critical density is a number with deep meaning. It tells you the precise amount of mass that is needed to exactly cancel expansion.”
In this story, these two forces are represented as the interaction between quarks and the HP boson. In our real world, quarks are well established as the foundation for matter, and matter is what causes gravity. But in the real-world HP bosons don’t exist. Oh well, the story is science fiction.
If HP bosons are just a figment of my imagination, what really causes the universe to expand? The answer: unknown. Astronomers call it dark energy, but that term is really just a placeholder. Another way of saying, we don’t really know. Seems like we need some aliens to come along and explain it to us.
But even if scientists haven’t discovered the force itself, they can measure how fast the universe is expanding. It’s called the Hubble constant (H) and WMAP provided the most accurate measure anyone has ever had. Along with Newton’s gravitational constant (G), physicists derived this very simple equation for critical density, ρc.
Critical density is the balance between H and G, between the expansive force and the gravitational force (which derives from mass). Critical density is the bullseye on a target, a what-if calculation of the relationship between these two opposing forces.
To find out whether we’ve hit the bulls-eye, we need to know the actual density of the universe. Can we measure it? Get a really big scale and pile every quark, every atom, every star, planet, nebula—every shred of mass in the entire universe—on one side. Place the mysterious expansive force on the other side of the scale.
What happens? Well, your eyes should pop out of your head when you find that the scale exactly balances. Critical density equals actual density. The amount of mass needed to exactly cancel the expansive force is precisely how much mass there is in our universe. The WMAP mission (and the European Space Agency Planck mission in 2013) both performed something like this humongous scale by accurately measuring real-world values for H and G and plugging them into the equation above.
To the accuracy humans can measure, we live in a universe of critical density, otherwise known as a flat universe. What does this mean? It means the entire universe sums to this digit: 0.
The universe is zero, nothing, nada, zilch. Everything we see around us—the stars, galaxies, everything that floats out there in empty space—is simply a local perturbation of energy and mass. The universe can be thought of as a wave where every trough balances every crest. Taken together the sum is nothing. This tells us with some cert
ainty that the universe sprang from nothing. Exactly how this springing-thing happened is not yet clear, but scientists have confirmed just in the past ten years that nothingness was the original state.
The universe is not just a random pile of stuff—the result of a cataclysmic explosion. We shouldn’t think of the Big Bang as just a larger version of a supernova, it was a very different kind of event. The Big Bang was literally something from nothing.
This newfound knowledge should be disturbing or enlightening or emotional in some way to every person on the planet. We know where we came from. We know what existed prior to the Big Bang—nothing.
Nothingness
So, what is nothing? In this book, I called it the void though physicists and cosmologists use other words depending on the topic. For example, in brane theory they call it the bulk. Sometimes you’ll see references to hyperspace. In mathematical descriptions it’s called Hilbert space. In my opinion, none of these terms are as compelling or as conjuring as the void.
The void is not a place. It’s not space of any kind. It has no dimensions, no contents, no volume, nowhere to put anything of substance. It also has no attributes (length, density, position, etc.) except for the sole attribute that it represents the absence of everything.
Light cannot propagate across the void because there is no “across”. Quarks, leptons and bosons cannot exist within the void because there is no “within”. In Chapter 20 Void, Nala pushes a stick beyond the vertical edge of her prison. The stick disappears into nothingness, crackling and sizzling as it goes. (Just a guess on my part. What exactly is the sound of a trillion quarks simultaneously being eliminated from existence?)
The void is unquestionably crazy stuff. Instead of describing the void, it’s easier to describe space. The void would then be anything else. But a word of warning—it gets crazy from here. My advice, take two aspirin before you continue reading.
The multiverse. Multiple universes.
If you enjoy science fiction, you’ve probably come across a story or two that incorporated the idea of multiple universes, or parallel universes. This is the notion that the universe we see (about 14 billion light-years of space containing billions of galaxies) is not all there is. In fact, there may be many universes like our own, possibly an infinite number of them.
Complete fantasy, right? Certainly unscientific.
I don’t think so. Not every idea related to multiple universes is scientifically testable, but some are. And even if only one idea is testable, it makes the question of multiple universes a valid scientific endeavor. Others agree because quite a few physicists, astronomers and cosmologists are actively working in this field.
Take Max Tegmark, for example. He’s a professor of physics at the Massachusetts Institute of Technology—not exactly a hotbed of crackpots. Tegmark has examined each of the current multiverse ideas in detail and has identified four levels of multiverses.
In a Level I multiverse, we live in a sea of never-ending infinite space. Within that space, we can see only a “small” sphere with a diameter of 13.8 billion light-years (that’s how long it’s been since the Big Bang, thus we have no ability to see objects that might be farther away). But this visible sphere is merely a pocket universe—a bubble within the never-ending sea. The bubble came into existence from a Big Bang and a period of inflation (the few microseconds after the Big Bang during which space inflated faster than the speed of light). If this model represents the true nature of our universe, there could be many other pocket universes out there, far beyond our limited view, each of them also a result of local inflation within the infinite sea.
A Level II multiverse is much the same except that each pocket universe has different versions of the fundamental forces, different elementary particles, etc. For example, the force of gravity might be stronger in one pocket universe than another.
A Level III multiverse is derived from quantum superposition, and I’ll talk about that in the next section. A Level IV multiverse is purely mathematical, and I’ll leave that one to the deep-thinking mathematicians like Tegmark.
Each multiverse concept has one thing in common: every universe was created from nothing, springing from a fluctuation in a quantum field that caused a single point of nothingness to blossom.
Something from nothing, many times over. That’s the gist of the multiverse concept. It represents a chain of events that may have been going on forever and will continue forever more. No beginning and no end. Infinite in both space and time with every instance derived from exactly nothing.
Are these multiverse ideas testable? Or is it all just metaphysical nonsense?
First, inflation is testable. The cosmic microwave background measured by the WMAP and Planck missions confirmed that the inflation theory is accurate and the best explanation anyone has given for the parameters of the universe we measure today. Every multiverse theory is based on inflation. Check.
The shape of the universe is also testable. As I described above, these same space missions confirmed that the universe is flat, not spherical or open in shape. Mathematically, a flat plane has no end; it goes on forever. Infinite space certainly supports the Level I or II multiverse idea. Check.
It’s a start, and I think there is more evidence too. To find it, let’s dive into the insanity of superposition.
Quantum Superposition
Starting in Chapter 30, the story moves into the very real but very weird quantum world of superposition. Nala and Thomas (and later Marie) become probabilities with outcomes that are not determined until there is an outside observer.
Can this really happen? To people, who knows? But it happens all the time to quantum particles. The mental gymnastics are easier if you stop thinking of them as particles. Call them a quantum probability wavefunction instead.
The conundrum is best represented by the famous double-slit experiment, the scenario in which a gun shoots a stream of particles toward a barrier containing two slits. (If you’re not familiar, this is a good video: https://www.youtube.com/watch?v=M4_0obIwQ_U or read my blog post here: http://douglasphillipsbooks.com/blog/the-double-slit-experiment).
Blast a stream of particles through two slits, and two bands of particles will come out the other side, right? Wrong. Quantum-sized particles like electrons produce a very different result. Instead of two bands, we see multiple bands just like the interference pattern that waves of water produce. Does that mean quantum particles are really waves?
Modern thinking is that quantum particles are a mathematical probability that is wavelike. The particle isn’t really smeared across space, but its true location might be at point A or it might be at point B. That’s superposition in a nutshell. It’s a roll of the dice. The chance you’ll find the particle at A or B is determined by a mathematical probability called the wavefunction. As Core said in Chapter 22, outcomes follow probabilities.
Superposition ties very well with the idea of a multiverse driven by events, which Max Tegmark identifies as Level III. In this kind of multiverse, events that we perceive to be random such as whether a leaf falling from a tree lands in my yard or my neighbor’s are comparable to the choices we each make every day, such as whether to stop the car when a traffic signal turns yellow. Every random event and every choice we make results in a separate branch—a new path to follow in a never-ending complexity of differing outcomes. (Side note: check out Season 3 Episode 4, Remedial Chaos Theory of the television show, Community, if you want to experience the full comedic impact of a Level III multiverse. It’s a classic.)
In a universe like this, the sheer number of random branches is staggering with downstream effects that go on forever. A woman barely catches a train home and finds her boyfriend in bed with another woman or she misses the train and never learns of the affair (Sliding Doors, 1998). You recognize the idea; it’s been in sci-fi for a long while.
We perceive our universe as the chosen path with randomness that has settled on a specific outcome. But in the multiverse explanation, e
very outcome has occurred, each equally valid and equally real. The other versions of ourselves that follow those other paths are just as sure their outcome was the real one, with no opportunity for us to compare notes.
Is this possible? Does it make any sense? A significant number of physicist and cosmologists not only believe it’s possible, they say it’s a rigorous mathematical explanation for the superposition of quantum particles and thus a reasonable explanation for our reality.
But science doesn’t establish reality by taking a poll. Science requires evidence. Is there any?
Maybe. I’ll throw out two more bits of multiverse evidence for your perusal. First is the CMB radiation, measured by WMAP and in greater detail by Planck. Colors in the CMB image above show slight temperature variations away from the average of 2.7 K. The deviations are tiny, only 0.000018 K(or 18μK), telling us that the CMB is exceedingly smooth. But one spot near the lower right stands out:
It’s called the cold spot, because the temperature there is 70μK below the rest of the map—significant enough that scientists have ruled out random variation. Both WMAP and Planck independently confirmed this cold spot, so it’s not a measurement error either. Something about our universe is different in this direction.
At first, astronomers thought it was a relatively empty area containing fewer galaxies than normal but a study in 2017 demonstrated that this interpretation was false. The mysterious spot is still being studied, but one explanation is remarkable: the cold spot may be a cosmic bruise, a place where our bubble universe collided with another bubble during cosmic inflation. It’s potential evidence that our universe is not the only one.
Cosmic bruises aside, perhaps the most compelling evidence is all around us. The parameters of our universe appear to be fine-tuned to produce stars, galaxies and especially life. For example, if the down quark were just a little bit heavier, hydrogen wouldn’t be the most common element. Helium—an inert gas—would take its place, making the formation of complex molecules far more difficult and making good old H2O very rare. Likewise, if gravity were a little stronger, stars would exhaust their fuel more rapidly and planets like Earth wouldn’t have billions of years to evolve life.
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