Image for Dr. Brian Keating. Image Credit: Edge
“What is fascinating to me is that we are now hoping, with modern measurements, to probe the early Universe. In doing so, we’re encountering deep questions about the scientific method and questions about what is fundamental to physics.”
When we look out on the Universe, we’re looking through this dirty window, literally a dusty window. We look out through dust in our galaxy. And what is that dust? I like to call it nanoplanets, tiny grains of iron and carbon and silicon—all these things that are the matter of our solar system. They’re the very matter that Galileo was looking through when he first glimpsed the Pleiades and the stars beyond the solar system for the first time.
When we look out our telescopes, we never see just what we’re looking for. We have to contend with everything in the foreground. And thank goodness for that dust in the foreground, for without it, we would not be here.
Professor BRIAN KEATING is an astrophysicist with the University of California San Diego’s Department of Physics. He and his team develop instrumentation to study the early universe at radio, microwave, and infrared wavelengths. He is the author of over 100 scientific publications and holds two U.S. patents. Brian Keating’s Edge Bio page
SHUT UP AND MEASURE
What is this cosmic hubris that makes us feel so important about the Universe and our place within it? This is the question that I’m grappling with right now. I’m trying to experimentally shed some light on these extremely heated discussions that have taken over cosmology in the last few months with a debate about the deep past of cosmology and the implications for the future.
Specifically, what concerns me is whether we can drill down to the first moments, nanoseconds, microseconds, trillionths of a second after the Big Bang. And if we do, is it really going to tell us something about the origin of the Universe, or is it merely tacking decimal places onto the primordial collection of stamps? My question is one of bringing data. When people were waxing philosophic and having existential crises of faith about their equations, Feynman used to say, “Shut up and calculate.” And that meant that the implications of what you were doing metaphysically, philosophically, and otherwise didn’t matter; what mattered were the answers that you got at the end of the calculation.
A lot of what my colleagues and I do is shut up and measure. We build equipment that you can’t buy online. We have to design things from scratch that have a very specific purpose. I’ve noticed lately, and it’s of grave concern to me, that many of the scientists, especially young scientists, are in the mode of trying to prove a theory. And that is a very dangerous aspect of science. The thought of being associated with the physicists who have created these ideas that are speaking to the essence of meaning as a human being is intoxicating. How did it all begin? It’s the most primitive question the human mind can ask. It’s natural to want to be associated with that. And further, it’s natural to think that we live in the first time in the history of humanity in which it’s possible to answer these questions using modern technology.
Back in the late 1900s, they thought they understood the nature of the atom. Perhaps they were a little hubristic as well, thinking that everything that came after would be solved by Newton’s equations and thermodynamics and electromagnetism. And lo and behold, there were many forces that they didn’t perceive still yet to come. I feel like we’re in that same phase right now, and the thing that concerns me most is that we’re always going to be in this state of thinking. We’re always going to think that we’re the last generation to be perplexed by these fundamental questions of existence, these Copernican questions.
Are we central to the organization of the Universe? I’ve counted no fewer than five Copernican epochs when we thought we were the center of the solar system, the galaxy, the Universe. The question now comes down to whether we are the center of the multiverse. Essentially, it’s a continuation of the first question. You see it with this quest for life on other planets, which is also a Copernican impulse that humans have. We want to discover other habitable planets, habitable zones within our own solar system, on moons of other planets, past life on other planets. The implication is a Copernican one: Are we somehow special? Is life on Earth special? Or is there deeper organization that permits the utter banality of life of which we’re composed. That’s a fascinating thing that we’re able to shed light on, but I don’t think we’ll be the last generation to wrestle with these questions.
Specifically, what I’m doing is building technology to look at the light left over from the Big Bang, which is called the cosmic microwave background radiation (CMB). It suffuses all of the Universe, as far as we can tell. It originates from an epoch about three minutes long after the Big Bang. I always say it’s the actual formation of the elements, which is called Big Bang nucleosynthesis. That process lasted less than one tenth of the TV show The Big Bang Theory. It is, in that timespan, all the matter that matters. It’s the matter that we’re comprised of: the protons, the neutrons, the croutons. Everything else that matters to humanity was forged in that first three minutes, and in so doing, the die was cast for this all-pervasive radiation to then propagate.
About fifteen years ago, some colleagues and I had an idea to test whether we could use this fossil relic from the Big Bang—the cosmic microwave background radiation—as a film. We know we can’t go farther back in time than this so-called “surface of last scattering,” when the Big Bang was emitting this radiation field we call the CMB, because that epoch corresponds to a fictitious surface, if you will.
Light is prevented from traveling to earlier times and more distant regions of space, just as it is through a mirror. You can’t see through a mirror because it has electrons in it, and electrons are highly mobile and can reflect and scatter light back towards you so you can see your reflection. But you can hear something behind a mirror, right? You can see with sound. We’re using waves of gravity to transcend this fictitious boundary.
Gravitational waves have been known about. The bright young theorist who predicted them, Albert Einstein, would be 150 years old now. He predicted them in 1916 as a consequence of the general theory of relativity. That theory had as a consequence that any gravitational disturbance propagates at the speed of light, and that disturbance, like all disturbances—water waves, for instance—carries energy and momentum with it. In this case, it was in the form of gravitational radiation. We call it gravitational waves, which were detected indirectly in the 1970s by Hulse and Taylor, who watched a pair of pulsars slowly spinning down and orbiting a common barycenter. As they did so, they emitted gravitational waves, just like a New Yorker shaking his fist out a window emits gravitational waves by virtue of mass in motion.
Where did you have the most mass ever? And where did you have that mass in such violent motion that it would produce tremendous amounts of gravitational waves? Our answer was the Big Bang. Did anything precede this epoch of the first three minutes? Are there any other relics left over from the Big Bang that were older than, say, the cosmic microwave background radiation photons? Older than the matter of which we’re comprised?
Physicists are greedy. We’re not content with saying, “Three minutes out of 13.82 billion years is pretty good, right?” Physicists don’t think that way. We think logarithmically. We think in exponential terms. The Universe at 180 seconds is not nearly as interesting as the Universe at one second, two orders of magnitude younger. We think in logarithmic time. If this inflationary paradigm is correct, we want to go back to a trillionth of a trillionth of a trillionth of a second after the Big Bang—a decimal place, approximately thirty-five zeroes and a one. To give you an idea, if a person is sixty years old, they’re roughly 2 billion seconds old. Two billion seconds in sixty years. Sean Carroll likes to say every lifetime has something like 3 billion heartbeats, which is about ninety years. That equates to billions of seconds—1010 seconds. We want to go back forty-six magnitudes in time earlier. We’re talking just a fantastically minute epoch after the Big Bang. And that corresponds to an epoch at which it might be possible to say that time can no longer be further subdivided.
If there’s a true fundamental quantum of time, it would be called the Planck time. The Planck time is maybe two orders of magnitude shorter in duration than this epoch is. What’s incredibly exciting about this is that if it’s true that inflation happened, and it has these properties that many of my theoretical friends and colleagues suspect it does, then we’re not only looking at the Big Bang, we’re looking at the quantization of gravity. Gravity itself would be quantized. That’s a goal that has eluded mathematicians and physicists, Einstein included, for the better part of the last 100 years. Gravity is the only force that persistently resists the quantization of it into fundamental particles—quanta—of energy, namely, short wavelength gravitational waves, or what are called gravitons. Not only would we be doing quantum cosmology, we’d be doing experimental quantum cosmology. This idea intoxicated me. Could we really probe this first epoch?
I’m from New York, so I’ve got a natural neurotic bent to myself, but I began to worry—what if inflation didn’t happen? What if this is a wild goose chase, or as I like to say, wild Guth chase? We’re trying to pursue the signature predicted by, essentially, one or two men. While it seems to match up with a lot of the evidence that we have, circumstantial evidence is not sufficient to convict. A lot of people believe this would be the smoking gun.
If we detect these waves of gravity via their imprint on the CMB’s surface—this fictitious surface—then we would … they won’t say prove inflation, and I think that’s correct. You can’t prove a theory, but you can falsify alternatives to it. What’s raging right now in cosmology is the question of whether inflation is a theory. Is it science? Is it falsifiable? There are many eminent cosmologists and theoreticians, from Roger Penrose, Paul Steinhardt, and many others who are just as eminent as a physicist working on inflationary cosmology, who claim that not only is it not provable, it’s not even science because it cannot in principal be falsified.
What I’ve become fascinated with lately is why falsifiability is a criterion. Why is that so sacrosanct to the physicist? I’m not saying that it’s not, but it has become a cudgel. If I say to you, “I can’t falsify inflation,” then you can say, “Well, then it’s not a theory.”
The person who first proposed falsifiability as a criterion was Karl Popper, in the 1930s. Karl was an Austrian philosopher and mathematician who was deeply influenced by Kurt Gödel. Gödel is famous for the incompleteness axiom theory, which stated that certain aspects of a mathematical set of axioms can never be proven within the framework of those axioms. It’s somehow made to constrain what is knowable in mathematics. I claim that people have now thought that we need the same kind of thing for physical theories. In other words, we need a Gödel’s incompleteness theory for experiments for theoretical science—not that which can be proven purely by axioms, but by evidence.
I’m not taking a position at this moment, but I do want to point out that physicists have this erotic obsession with Popperism and falsifiability criterion. I want to question that because I don’t know that it’s necessarily a sufficient condition to rule something science or not. In fact, Popper himself was a big proponent of the steady state model. We discarded that model long ago for important reasons that are re-emerging when it comes to the inflation versus multiverse versus modern steady state models that have come about from Penrose, Steinhardt, Turok, and others.
It’s interesting to me that people have this obsession with falsifiability. I claim that it’s not necessarily so simple. What Popper had in mind when he talked about falsifiability was the pseudoscience of Marxist thought—the dialectic materialist thought of Marx—and the psychoanalysis of dreams by Freud. He compared them both to astrology, which was so flexible that no combination of observations could falsify an astrological observation. For example, if you tell me you’re a Pisces and I tell you what’s going to happen to you tomorrow, you could say, “You know what? I just realized I’m a Libra.” And I would say, “Well, the same things are going to happen.” It’s so flexible he felt it was total nonsense.
It’s interesting to me that cosmology originated from astrology. We utilized all of the data from early astrologers to come up with our theory of astronomical positions of planets and other things. Now we’re back to the same falsifiability of astrology that’s bleeding over into the question of what science is.
Is inflation science? Recently, there was a petition signed by thirty-three or so eminent physicists including Lisa Randall, Max Tegmark, Alan Guth, along with four Nobel Prize winners including Frank Wilczek and John Mather. It had these incredibly eminent cosmologists responding to an article written by Paul Steinhardt, Anna Ijjas, and Avi Loeb. The question of whether or not inflation is science, I think, is a valid one.
When people trot out Nobel Prize winners, it’s the appeal to authority. But we don’t really care about authority in physics. Einstein was wrong many times; Galileo, inventor of the scientific method, was wrong on many fronts and made many mistakes; it doesn’t take away from their brilliance. I was surprised about this petition in physics. But it reveals the heat. What better way to take away the heat than to shed light using experiments? Can we take a position using data?
I believe it was Mark Twain who said that history doesn’t repeat itself but it rhymes. Each generation of cosmologists accepts things like the Copernican principal, that humanity is not special, and that there is no centrality to our location in time and space in the Universe; nevertheless, they find it not within the bounds of their hubris to claim they are the ones who are going to explain how everything began.
I always say that Aristotle was essentially never right about anything that had to do with physics. Maybe he was right about philosophy, I don’t know; I’ll leave that to the philosophers. Almost everything he said about physics—bodies in motion, gravity, things falling at different speeds depending on their mass and weight—was wrong. He was wrong about the eternality of the Universe as well. Nevertheless, it’s a persistent illusion.
Mario Livio wrote a book called Brilliant Blunders, where he debunks the myth that Albert Einstein actually said that adding dark energy, cosmological constant, to his equations of gravitational general relativity, he called that his biggest blunder. It turns out that’s apocryphal. Nevertheless, he believed so strongly that the Universe was static and eternal that he didn’t realize his equations were smarter than him. And this keeps on happening in cosmology. It happened again in the ’40s and ’50s with the early steady state model, trying to grapple with evidence from Hubble. Hubble was a brilliant astronomer who unknowingly repeated some of the arguments that Lemaître, a Belgian Catholic priest, had come up with, which was this nature notion that somehow space and time began from a primeval atom. We now call this the Big Bang.
Lemaître had this model where everything expanded and exploded due to a quantum fluctuation. This was in 1927. He was so prescient. He predicted the Universe from nothing long before our friends Lawrence Krauss and others came up with similar ideas—that essentially, a quantum fluctuation could cause the ultra fast expansion of Universe from early times.
Hubble’s observations were not dispositive. There were many challenging systematics. There were errors lurking in the data that didn’t depend on Hubble himself or his telescope; it had to do with things in the Universe that Hubble was unaware of. Dust, in particular. It’s one of the most important things that there is in the entirety of the Universe, and it’s the thing that’s obscuring and challenging the way that we attempt to study the ultra early Universe and inflation.
Hubble didn’t realize that these galaxies were being obscured by dust, so he ascribed to them great distances and velocities in order to get there, receding away from every other galaxy at speeds we now know to be about seven times too big. If those were taken at face value, it implied that the Universe was younger than the objects within it. As I always say, it’s as embarrassing as finding your stepmother is younger than you are.
What we ended up learning from that was that there were flaws in the Big Bang. It wasn’t this cosmological savior, by any means. It had deep problems in it. Many eminent theorists and experimentalists grappled with this from the ’60s and the ’70s, even after the discovery of the microwave background. There’s a misperception that the discovery of the cosmic microwave background radiation, which is what I study now, cemented and solidified the Big Bang, killing off any alternatives to it. There are a number of problems with that.
In Steven Weinberg’s book The First Three Minutes, and even in his technical books on cosmology, he stated as late as the mid-’70s that the steady state had challenges, but it was philosophically more attractive in many regards, most of all because it was the one that least resembled Genesis 1:1. In other words, it had no origin. It was as Copernican as you could possibly get, in both space and time—no particular specificity to our location in space and no beginning. If you have a beginning, that’s the ultimate anti-Copernican. That means there’s some special moment in time.
The steady state was very seductive to cosmologists in the ’70s and even as late as the ’80s, when Alan Guth was a young soon-to-be-unemployed post doc working at SLAC in Stanford. He luckily had just heard a lecture by Bob Dicke, who was famously scooped out of his Nobel Prize by Arno Penzias and Robert Wilson in 1965. Dicke was looking for a signature of a hot thermal origin of the Universe. He didn’t call it the Big Bang. He was looking at a cyclic model of the Universe, along with Jim Peebles and David Wilkinson, who was my grand PhD advisor. They were looking at cyclic models. As a consequence, there would be an early epoch after the previous cycle of the Universe collapsed and condensed to very high but not infinite density, and that would produce a thermal relic of the Big Bang that Penzias and Wilson discovered in 1965 called the CMB.
That discovery did not kill the steady state; in fact, it highlighted many problems with the Big Bang model. Into that milieu arose the physicists of the ’70s who were concerned with particles and fields, phase transitions, and unification of theories. They developed models to unite models of the very small with the very big—particle physics, cosmology, unified via field theories, unified via phase transitions.
Dicke and Peebles pointed out that there were certain aspects of the Universe that made it too facund, if you will, for it to not have an underlying explanation. Dicke said the Universe is basically flat. It has, within an order of magnitude, the amount of matter density that we now know it does, which is very strange. It’s as if you throw a razor blade and it ends perfectly on its edge, not flipping to one side or the other. It’s highly unstable that the Universe should have the exact curvature, and it’s very unlikely.
There’s an infinite number of real numbers between zero and infinity, and yet the Universe picked the number one. In certain units, it picked the number one, 1.001, which is as great a position as we’ll ever get on it. It’s a known scientific fact that the Universe is flat, and yet it’s the most unstable. It’s the razor’s edge of possibilities. How did it get to be like that? How did it get to be so smooth and uniform in the Universe, excepting local variations? How did it get so smooth that structure was inhibited from forming? Galaxies couldn’t form, stars, planets, people, et cetera, could not form until just the right moment. It seemed like a cop out to say it was so that life could arise, and so that we wouldn’t be here asking the question of why it’s so perfectly fit for life.
That was a mystery to cosmologists. A young post doc named Alan Guth heard these mysteries and was deeply innervated by them. He couldn’t stop thinking about them. In December 1979, a year after Penzias and Wilson collected their Nobel Prize, Guth had been thinking about this lecture he heard by Dicke. This remarkable synergy of events, revolving around cosmology’s first Nobel Prize, may have influenced this young theorist facing the unemployment line to come up with this model.
I always like to think about Alan Guth, the man. He’s got a kid and a wife, and he makes his living from his brain; this is his shot and he’s got to get something big, otherwise he’s going to be out of a job and out of the career that he loves. He comes up with this serendipitous discovery of inflation. One night he thinks about the Universe as a bottle of champagne, with bubbles trapped in it. When you release the cork the bubbles all rush to the surface, releasing their energy, their entropy, into one big bubble. The surface of the air in the room is like a giant bubble. In doing so, the fluid cools off a little bit. Guth’s thought was, what if there are bubbles of a heretofore unknown substance? He didn’t speculate on what it was. He just said that if there was some field in the early Universe—which he later called the inflaton—it could be super cooled, and it could be like those bubbles that rise exponentially and grow in size exponentially. And in doing so, he would solve these two problems that Dicke had presented to him at a lecture the year before.
One of the problems was called the Flatness Problem: Why is the Universe balanced on the razor’s edge? There’s a famous New Yorker cartoon that shows New York as a flat surface, and the whole world is centered on us here. Reality shows that the Universe is like that. So, it wasn’t just New Yorkers that could have such an egoistic interpretation. Why was that? Inflation. The Universe expanded such that even if it was highly curved from Lemaître’s primeval atom, it could inflate to scales bigger than the observable radius of curvature of the Universe.
There’s also what’s called the Horizon Problem. When I look back to the beginning of time—13.82 billion years ago—in this direction, and then I look in a region of the sky 180 degrees away, why do they have the same temperature? They have the exact same temperature and, for all we know, the exact same physical properties. We are connected to each one of them by the age of the Universe times the speed of light—and expansion factors, which we’ll ignore. But they’ve never been in contact with each other. How can they possibly have dialed their thermostats to within a fraction of a thousandth of a degree Kelvin? It’s impossible. The conspiracy required is much greater than any man-made conspiracy you could possibly think of. But inflation explains it.
At the beginning, there was a primeval atom. Lemaître was absolutely correct. How it got there, what happened before him, Guth said, “I do not know, but it doesn’t matter.” He actually says it doesn’t matter how it got there, inflation is insensitive to what preceded the epoch of the supercooled state. Expansion takes place and blows everything up. In doing so, it would have laid the seeds for the slight deformations in matter and energy. But there was one problem: The process was so effective at expansion, you couldn’t put the cork back in the champagne.
When Guth gave his talk, I believe in the Boston area, there was another young post doc in the audience who got incredibly depressed. It was Paul Steinhardt. Paul Steinhardt was sitting in the audience in 1980 listening to Alan Guth speak. It took almost two years for Guth to publish his paper on inflation, which he called the “spectacular realization.” He was going around on a lecture tour himself, and he ended up getting a job at MIT. That’s where Paul Steinhardt heard about this.
Paul told me recently that it was the most exciting and depressing talk he’d ever heard. It drove him equally mad almost. He thought the idea was so beautiful it couldn’t be abandoned. Whereas Guth was trained on the high-energy physics side of the spectrum, Steinhardt had great knowledge and facility with condensed matter. The physics that traffics in phase transitions, in fluids, in bubbles, and these condensed matter forms of energy. Steinhardt was just the right guy. You look back and history makes sense.
Kierkegaard said, “Life must be lived forward, but it only makes sense in reverse.” Looking back, these people, from Dicke to Guth to Steinhardt, you couldn’t have had a more perfect arrangement of people. Russians are so creative they can do whatever with a piece of paper and a pencil, so Andrei Linde really stands out on his own. Guth, Steinhardt, and Dicke were all around each other in this period of about a year and a half, and that laid the seeds, literally and figuratively, for what would become the model that I’m testing thirty-seven years later, and trying to falsify whether or not inflation took place.
Paul Steinhardt made equal contributions to the theory of inflation. I always say to Paul that he is one of the fathers of inflation, but he’s the one of the three that’s denying paternity. He believes that not only is inflation incorrect, but it has fatal flaws that, via the incontrovertible existence of the multiverse within inflation, within eternal chaotic inflation of Linde, Guth’s original problem still persists. Inflation is so explosively efficient that it cannot be shut off. You can’t put the cork back in. The multiverse should be creating more and more universes. This scalar field called the inflaton is impossible to turn off. I always say it’s like a rocket: Once you ignite a solid rocket, it’s over; you can’t turn it off. It keeps burning and accelerating and there’s nothing you can do to shut it off. So, too, with inflation.
What’s scary about that is it means that there’s not just one other set of interviews going on just like this one, there are an infinite number of interviews just like this one going on. There are an infinite number of universes exactly like our Universe. There’s an infinite number of universes where the speed of light is one mile per second slower than it is in our Universe. The likelihood of those universes might be very small, but infinity, as Woody Allen said, is a pretty long time to wait, especially towards the end. There aren’t many positives to come out of it. It’s the ultimate Copernican principle.
Steinhardt reduced the neurosis that Guth had. He found a graceful exit to the inflaton problem: How could it create a cold universe at the very beginning that would have the properties that could then be reheated to create particles and energy? What was interesting is that when Steinhardt and his student Andy Albrecht corrected or made modifications to this model of inflation, it became known as new inflation. With the help of Stephen Hawking and others, they actually made the first prediction.
What Guth had done was a retrodiction. He explained problems of the Big Bang model that were known to exist, just like Einstein explained these anomalies of Mercury that were known to exist with general relativity. At first it was a retrodiction, but then Einstein predicted gravitational lensing, and the rest is history. He became somewhat famous, you may have heard of him. So, too, with Steinhardt, Hawking, and others: They had predictions that there would be unavoidable quantum jitters of this inflaton field which would make the Universe expand a little bit over there, a little more over here, a little less over here, and that signature was first observed in 1992 by the COBE Satellite.
The COBE Satellite was a very large team. The P.I. of one of the instruments is named George Smoot. The other instrument that found the spectrum of the CMB to be very accurate, which in my mind was the nail in the coffin for the steady state model, at least at that time, was John Mather.
The COBE Satellite did two things. It firmly established that there was a Big Bang. And it showed for the first time that the Universe had these tiny homogeneities that Isaac Newton had recognized needed to be there 400 years earlier. In other words, if the Universe is homogeneous, the same everywhere, then why should New York form here and not where Kansas is? Why would there be something special about where our galaxy formed? You can’t have it. It’s asking for too much. So, Newton realized something was needed to break the symmetry. COBE found that symmetry was broken.
At the press conference, George Smoot famously said that if you’re religious, it’s like seeing the face of God. I claim that that was a little bit premature. What he was really saying was that we have found evidence for inflation. That’s the subtext of what Smoot meant. And yet there are many models besides inflation that predict fluctuations in the CMB, just like COBE would observe using Smoot and others’ instruments. It wasn’t the smoking gun; it was the heat. The gun was hot, but we didn’t see the actual trigger man.
The trigger man is something that came out of a consequence of what Starobinsky, Abbott, Mark Wise, and others predicted, along with a Russian physicist named Alex Polnarev, that there would be gravitational radiation. This jittery inflaton that Steinhardt and others had proposed would lead to not only waves of matter density, where dark matter and ordinary matter pool together and make stars, galaxies, planets, people, et cetera, but there’d be jittering in spacetime’s fabric, called the gravitational waves.
These gravitational waves propagate at the speed of light. They last forever. They go through all matter. They go through the entire Earth. LIGO showed that you can have a gravitational wave enter at Washington state and go all the way through to Louisiana. Beautiful. They go through any matter and any energy. They’re the perfect messengers of the inflationary epoch. They can go back to a trillionth of a trillionth of a trillionth of a second because that’s when the quantum jittering of spacetime was encoded. If spacetime is a bell, that’s when the bell was rung.
Unfortunately, you can’t do that with COBE. COBE could see that there are fluctuations, but it could not understand if those fluctuations were uniquely coming from inflation. Even the Paul Steinhardts and the Roger Penroses, the anti-inflationists, admit that their theories—either conformal cyclic cosmology in the case of Roger Penrose, or the bouncing cosmological models of Paul Steinhardt, Neil Turok, and others—if gravitational waves are proven to exist unequivocally without exception in the CMB’s polarization, which is what I study, then their model is wrong. They still are not convinced that inflation is provable. In other words, it will falsify a model, just like Mather falsified the steady state model. Not Mather himself, of course, it’s always a group of people. I’m just using Mather as shorthand for COBE’s FIRAS instrument. That falsified, really, the last hope of the steady state.
So, too, detections of gravitational waves will falsify the modern incarnation of the steady state, which is a cyclic universe. A universe could be infinite in time, and we know that can’t be the case, thanks to the work of Mather and others. We know it has to have perturbations in it, thanks to Smoot and others. But it could be cyclic. It could be a universe that lives and dies like a phoenix, and explodes and reincarnates itself. It could be infinite in space, where there’s a universe parallel to ours over here and over there. There could be deep connections with string theory and branes and so forth. But all of these things are models. If you believe that falsifiability is a criterion of modern science, which Steinhardt and others do believe, they claim if we don’t detect gravitational waves, we’ll still adhere to the predictions of inflation.
They almost ascribe a cult like following to inflation. Again, I go back to Feynman’s dictum, modified for experimentalists: shut up and measure. That’s what I want to do.
What is fascinating to me is that we are now hoping, with modern measurements, to probe the early Universe. In doing so, we’re encountering deep questions about the scientific method and questions about what is fundamental to physics. When we look out on the Universe, we’re looking through this dirty window, literally a dusty window. We look out through dust in our galaxy. And what is that dust? I like to call it nanoplanets, tiny grains of iron and carbon and silicon—all these things that are the matter of our solar system. They’re the very matter that Galileo was looking through when he first glimpsed the Pleiades and the stars beyond the solar system for the first time.
When we look out our telescopes, we never see just what we’re looking for. We have to contend with everything in the foreground. And thank goodness for that dust in the foreground, for without it, we would not be here. Literally, that dust makes up our solar system.
In the steady state model, that dust made up the CMB. That was the origin of the CMB that Mather et al were able to falsify. Nowadays, we know that we have to look through this dusty window and be cleverer than nature. We need to devise an experiment that sees back to the Big Bang and beyond, to the very earliest epochs after the Big Bang, to the real spark. People like Max Tegmark say we shouldn’t call inflation separate from the Big Bang because it’s the fuel that powers the Big Bang. It’s the Big Bang itself. People argue about that. I call it the spark that ignited the Big Bang. What happened before the Big Bang? Hawking used to say that asking what happened before the Big Bang is as meaningless as asking what happens when you go north of the North Pole? It’s the question that has no meaning. But it has a very good meaning in the cyclic universe. It has a very good meaning in the conformal cosmology of Penrose. And it has a very good meaning in the multiverse models of inflation. With apologies to Stephen, it’s not actually correct that that question is meaningless; it has a good meaning, but it depends on the cosmological underlying model.
What I care about is how we are going to get rid of this dust. What most people don’t appreciate is that the instruments that we build are so sensitive, we can essentially measure the heat of a match sitting on the Moon. We can measure the properties of gravitational waves propagating from billions of light-years away. What we can’t do is build an experiment that’s outside of our Milky Way. We’d like to. I tried putting in funding to do that. NASA is not too willing to do that because it’s a technological impossibility. It’s like building an LHC, a particle collider, bigger than or as big as our solar system to probe the energies that we’re looking at.
How do we make progress? We are dealing with contaminants that are not instrumental, or psychological, or theoretical; they’re inherent in the cosmos. They’re astrophysics at work. We have to build another experiment that operates in parallel that just measures this contaminant. From that, we can remove it and listen to these waves of gravity, potentially. What’s interesting to me is that eventually we’re going to hit a floor. And I hope that we hit it. That floor is one where both the model of inflation and the models of anti-inflation will have an unavoidable bedrock of spacetimes ringing that can never be removed. And if we hit that, and until we hit that, we can’t really make much progress.
We can’t say for sure if the Universe had inflation or not if that bedrock is hit without seeing waves of gravity. That would be fascinating. That would basically mean that all bets are off, that we will never, with the tools that we have, be able to falsify these alternatives to inflation. That day is a ways off in the future. Again, I don’t want to say we’re the last generation of cosmologists to be able to answer this question, because we’re not. Cosmology will continue to ask questions. We’ll continue to make this Copernican conjecture that we are not central to the Universe, and there will continue to be an infinite number of such questions to be asked.
Galileo, again, is credited with the origination of the modern scientific method. When people talk about method of hypothesis, apparatus, hypothesis testing, iteration—that loop was pioneered by Galileo. What’s so cute to find out in looking at this is that Galileo was a human being. There’s no such thing as a scientist who’s not a human being—not yet, maybe not ever. He had biases of exactly the type that the scientific method is designed to exclude and preclude, namely, confirmation bias. Confirmation bias is this urge that humans have to discard evidence that doesn’t agree with their hypotheses.
What were Galileo’s biggest blunders? I like to say Einstein is famous for his biggest blunder. Mario Livio claims it wasn’t true, that it was apocryphal, and Gamow made that up. Nevertheless, it’s a cute little term to think about. What was Galileo’s biggest blunder? Many people say it was his theory of the tides. Galileo said that tides on Earth are caused not by the Moon, as we know them to be now, but because the Earth is rotating and it’s going around the Sun. The combination of rotation and revolution, which he had only recently motivated the evidence for—but didn’t prove—that the Earth is not the only center of the solar system. That was effectively what his observations of Jupiter’s satellite showed—many centers of the solar system, and the Earth is not unique. You can’t prove the Copernican principle. You can only show other things are falsified. He said the Earth is going around the Sun and rotating, and the sloshing of water makes tides. We now know that’s completely incorrect. It’s because of the interaction of the Moon.
He said one other thing that was incorrect. He said if you look up at the night sky, you see a constellation fragment called the Pleiades, the Seven Sisters. The Japanese call it Subaru. It’s a little cluster of seven stars. He did beautiful sketches in his famous first book, The Starry Messenger, which was self-published, without peer review. He looked at it and said that all the nebulosity, which we now call cloudiness, was because there were stars that his telescope couldn’t resolve. That’s all it was. If he had a bigger telescope, he’d resolve it into tiny stars.
He was really trying to say that the Milky Way is basically made up of stars like our Sun—another nail in the anti-Copernican model. In other words, he was driven by this bias to confirm the Copernican universe at all costs. He claimed that when he looked at the Orion nebula, the exact same thing happened. Scientists, Owen Gingerich and others, now claim that he knew that you couldn’t magnify it to find stars, but he really wanted to see what it was. He claimed it was evidence for what we’d call the Copernican model. He had a bias.
What was he was looking at? We now know it was dust. He was looking through a dusty Universe, too. He was using the first telescope to be used for astronomy, looking at dust and seeing its mirage. We cosmologists are now doing that just the same. Are we immune from the same confirmation biases? Do people that have a theory of inflation or anti-inflation not have urges as humans to know the answer within their lifetimes? It gives people meaning, and scientists, as long as they’re people, will continue to have to grapple with this.