This is the second part of an unusual timeline. It records the moments when humankind realizes that its notion of reality is shockingly mistaken. The first part of the timeline took us to the beginning of the 20th century. Now the pace of disillusionment quickens.
1905: Bern, Switzerland
Albert Einstein, was working as a young examiner at the patent office, but his life’s preoccupation was theoretical physics. With a brilliant mind and an education in math and physics, he published speculative papers that would change the world forever.
The Special Theory of Relativity
He realized what the Michelson-Morley experiment meant: the ether, an invisible medium said to pervade all of space, did not exist and therefore could not affect the speed of light. Furthermore, light must travel through the vacuum of space at a constant speed that nothing in the universe could equal or exceed!
He saw the consequences of putting an absolute limit on speed. For instance, if a moving train shines a light ahead, the speed of the light is not increased by the speed of the train. He did “thought experiments” like this one: imagine the train passing point A, and at that moment two clocks start, one on the train and one beside an observer, at an embankment across from A. If we arbitrarily pick a point B farther down the tracks and check both clocks as the train passes it, we’ll see that less time will have elapsed on the train’s clock than on the observer’s clock! This is known as time dilation. The discrepancy gets larger as the speed of an object (like our train) increases. In our daily lives, the discrepancy is negligible, but to subatomic particles and bodies in space, the difference is considerable. For example, time passes differently on Mars than on Earth.
Einstein would say the observer and the train are in different reference frames. That is, they have different coordinates in spacetime, the 4-dimensional medium in which everything exists. The passage of time in one reference frame is relative to the passage of time in the other. The differentiating factor is speed, or velocity, as physicists call it. And there’s yet more to it. Velocity affects size as well. Specifically, if Star Ship 1 is moving faster than Star Ship 2, an observer in Star Ship 2 will see that Star Ship 1 has become somewhat smaller! This is known as length contraction.
These speculations, taken together, are Einstein’s Special Theory of Relativity. “Special” because objects are assumed to move in a straight line at a constant velocity, which is a special case of motion. He would have a great deal more to say about relativity later.
Energy and mass
It was well known that if you applied energy to a moving object, its velocity would increase. However, continuing to add energy became a less and less effective way to produce this effect. Einstein realized that as energy was added, some of it converted into mass; that is, the moving object became heavier! Energy became matter! He calculated that the conversion could be expressed as m=e/c2, where m is the added mass, e is the added energy, and c2 is the speed of light squared. (Commonly, the equation is written as e=mc2, of course.)
1915: Berlin, Germany
Einstein had long been uneasy about Newton’s use of gravitational acceleration in calculating the orbits of the planets. His equations didn’t work for Mercury, the closest planet to the Sun. What’s more, he claimed that if the Sun vaporized, all the planets would immediately fly off into space. But “immediately” is impossible because the gravity waves that brought news of this catastrophe would have to travel faster that light! Worst of all, Newton had no idea what caused the phenomenon of gravity. Why did it weaken as the mass of respective bodies decreased or as the distance between them increased? He asked his readers to conjecture for themselves.
Einstein theorized that mass distorts spacetime, much as a bowling ball would bow the surface of a rubber sheet. The effect is what we call gravity. In a gravitational field, the spatial dimensions of spacetime warp and time dilates. To illustrate, suppose we visit the Empire State Building with clocks set to the same time. If I stay on the ground floor and you take the elevator to the top, where the Earth’s gravity is weaker, your clock will show more time on it than mine when you return.
Gravity also bends the path of light, even though light has no mass. It must be so because light travels through spacetime, and spacetime itself is bent. This was confirmed by the total solar eclipse of 1919, and Einstein became world famous.
1923: Mount Wilson Observatory, California
Edwin Hubble, an American astronomer, discovered that many objects thought to be nebulae, clouds of gas and dust, were in fact galaxies beyond the Milky Way. So our grandparents and great-grandparents were the first humans to experience the shock that the Milky Way was not the entire universe — not by a long shot.
Hubble also confirmed the belief that galaxies were not only moving farther away from Earth, but were doing so at velocities that increased proportionately to their distance. This phenomenon came to be called “Hubble’s Law.”
The picture at the left was taken 67 years later by the Hubble Space Telescope. Every object in it is a galaxy! Today, astrophysicists estimate there are at least 2 trillion galaxies in the observable universe.
1925: Leuven, Belgium
Georges LeMaitre was a Catholic priest, astronomer, and professor of physics rolled into one. In the magazine Nature, he proposed that the universe had been created by an exploding “Primeval Atom,” which he late referred to as the “Cosmic Egg.” This is what we now call the “Big Bang Theory.” The term was coined by another astronomer, Fred Hoyle, who used it derisively.
LeMaitre was first to calculate the universe’s rate of expansion, a number that unfairly came to be known as “Hubble’s Constant.”
1927: Copenhagen, Denmark
For nearly 30 years, a new kind of physics had been developing. Its focus was quantifying the properties of subatomic particles. The act of assigning a value to a property was quantizing it. The practice of quantizing properties was called quantum mechanics or quantum physics.
Quantum physicists were active experimenters. They soon discovered oddities that were a surprising departure from what classical physics had led them to expect. The double-slit experiment is a famous example of their work. It’s explained in Part 1 and Part 2 of a helpful video.
From this and other experiments, Werner Heisenberg concluded that certain pairs of subatomic properties — for example, the position and momentum of an electron — could not be measured simultaneously, and only to a degree of probability. This observation is known as the Heisenberg Uncertainty Principle. It tells me something unsettling: I can describe a chair or a lamp to a fare-the-well, but when I try to describe their subatomic components, I can only make guesses — even if I’m a Nobelist in physics. That turns the foundations of reality into fuzz.
Note: For more about the oddities of quantum physics, see my post “The Final Frontier.”
1928: London, England
Paul Dirac was interested in combining quantum physics with special relativity. To that end, he published an equation that described the behavior of an electron traveling in a relativistic context. To his surprise, the equation had two solutions. One assigned a positive energy to the electron; the other assigned a negative energy to it!
Dirac proposed a way both results could be true. For every kind of particle with positive energy, there must exist a corresponding particle with negative energy, and vice versa. The opposites of the particles in the atom were antimatter. His conclusion was confirmed four years later when Carl David Anderson discovered the positron, the positive counterpart of an electron, in cosmic rays.
When matter and antimatter meet, they annihilate each other and produce gamma rays. If 1 kilogram of one should meet with 1 kilogram of the other, the gamma radiation released would melt most of Mount Everest. We needn’t worry because not long after the Big Bang, antimatter became rare. Nevertheless, physicists don’t rule out the possibility that antimatter might be more common in other galaxies.
1938: Berlin, Germany
For many decades, physicists had known about nuclear decay, the tendency of unstable nuclei to spontaneously emit particles. In doing so, an atom of one element could become an atom of a lighter element. However, no one had thought that a nucleus might be split and thereby produce nuclei of much lighter elements. To do so would be a case of nuclear fission.
Otto Hahn repeatedly bombarded uranium atoms with neutrons and examined the results. By doing so, he created transuranium elements — elements with a greater atomic number than uranium. Then a colleague suggested that by modifying the experiment, he might be able to split uranium atoms. He took her advice and discovered, to his astonishment, he could produce barium, cerium, and lanthanum from uranium. Modern day alchemy!
The upshot was profoundly consequential in opposite ways: the building of horrific nuclear weapons and the building of reactors that produce unlimited cheap energy.
1948: Ithaca, New York
Richard Feynman and his colleagues, while working at Cornell, developed the theory of quantum electrodynamics. They argued that the notion of an electromagnetic field wasn’t needed to explain electromagnetic force. Instead, the force could be propagated by a virtual photon — a short-lived particle of light — being absorbed by an electron, then emitted by the same electron, then absorbed by another electron, and so on ad infinitum. (Warning: Paranoids should read no further!)
The virtual proton is a messenger particle. It transfers momentum to any electron than absorbs it and so changes the electron’s direction. It belongs to a class of particles called gauge bosons. A fascinating question is, what else, besides momentum, do gauge bosons communicate from particle to particle? Do they function as a kind of subatomic hotline? The question seems pertinent given the mystery of quantum entanglement.
1957: Urbana-Champaign, Illinois
A team of physicists — John Bardeen, Leon Cooper, and John Schrieffer — investigated a phenomenon known as the Meisner effect: when an electrical conductor is cooled, its resistance to an electrical current decreases, and at a temperature somewhat above absolute zero, the resistance disappears. The conductor becomes a superconductor, which means no electrical energy is lost as light or heat. Furthermore, the phenomenon of quantum locking occurs. Namely, if a superconductor is placed somewhat above or below a magnet it will hover in space as if locked above or below the magnet. If a superconductor is started forward along a closed magnetic track, it will continually travel around the track without any loss of energy!
The BCS team — the initials of the physicists’ last names — theorized that superconductivity was caused by the way pairs of electrons interacted with the lattice of positively charged atoms in the frozen conductor.
A new age of super-efficient electricity awaits the discovery of materials that can become superconductors at warmer temperatures. Room-temperature superconductivity is now a kind of Holy Grail.
1965: London, England
After earning a Ph.D. in algebraic geometry from Cambridge, Roger Penrose began to turn his attention to astrophysics. He was drawn to a possibility that Einstein foresaw: bodies of enormous density that were formed by the collapse of massive stars. Their gravitation would be so powerful, not even light could escape, making the bodies invisible. Their presence could only be inferred by a whirlpool of visible matter spinning around them. They came to be known as black holes.
Penrose was soon joined in his studies by his friend Stephen Hawking, a theoretical physicist from Cambridge. Hawking theorized that at the center of a black hole was a singularity, an infinitely small space of infinite density, infinite gravity, and infinite spacetime curvature. At a singularity, the known laws of physics would cease to operate.
A black hole is bounded by its event horizon. Anything below it is inevitably drawn in and never seen again. Anything beyond it can escape given a sufficient velocity.
At an event horizon, just as anywhere else in spacetime, pairs of virtual particles, matter and antimatter, pop into existence. They usually annihilate each other in short order, but not at an event horizon. The antimatter particle falls into the black hole, and annihilates a minuscule part of the mass there; the other particle escapes as radiation. As eons pass, the antiparticles take a critical toll. The black hole, very much reduced in mass, explodes.
Note: Black holes are critical to the stability of galaxies. A giant one is likely to be at a galaxy’s center. When it deteriorates, what happens to the galaxy? I haven’t found a speculation about this question.
1979: Ithaca, New York
Alan Guth theorized that an instant after the Big Bang, the infant universe expanded at an extraordinary rate — exponentially faster than the speed of light — for less than a trillionth of a second. This was sufficient time for its size to grow from infinitesimal to the size of a grapefruit. Theoretical physicists call this episode inflation. The universe has continued to expand, but at a considerably slower rate.
A minority of physicists disbelieve Guth’s theory, but there are three strong reasons to think it’s true:
- If we look at distant regions of the universe that lie in different directions, we see their properties are largely homogeneous. For example, their temperatures are practically the same. This could only be true if the regions were in a single homogeneous space immediately after the Big Bang and then accelerated apart so quickly that gravity had very little chance to affect them.
- By combining astronomical observations with advanced geometry, we know the universe is practically flat, like a discus. This would occur if the universe began that way and then expanded quickly. A slower expansion would have produced a rounder universe.
- Particle physics predicts that the universe should contain magnetic particles with only one pole. However, no such particle has ever been observed. Physicists who endorse the inflation theory claim these particles could not form in the post-inflation universe.
1980: Washington, D.C.
At the Carnegie Institution for Science, Vera Rubin was trying to solve the galaxy rotation problem. Astronomers had earlier discovered that spiral galaxies, given their mass distributions, were rotating much faster than gravity should allow. As one writer put it, they should be “flying apart like a smoothie in a lidless blender.” Rubin offered a plausible explanation for the stability of the galaxies: they must contain a great deal of extra mass that doesn’t emit or reflect light or produce detectable particles. She called the extra mass dark matter.
According to recent calculations, dark matter makes up almost 27% of all the matter and energy in the universe. Only 5% is visible matter. Imagine, what we see through our most powerful telescopes is only 1/20 of the pie! Until we know what dark matter is, we can regard our knowledge of the universe as minuscule.
1995: Los Angeles, California
Somewhat less than a century ago, physicists discovered that relativity and quantum physics didn’t harmonize — the latter could not account for Einstein’s notion of gravity. They set about to find an idea that would reconcile the two. The idea would triumphantly be called “The Theory of Everything.”
In the late 60s, physicists thought they were on to something. They said subatomic particles were actually one-dimensional, vibrating strings. Particles of the same kind were simply strings vibrating at the same frequency. A string could look like a line (open-ended) or a loop (closed-ended). Naturally, the physicists called these ideas string theory.
This was the first incarnation of the theory, and its problems were soon recognized. One was its requirement for a particle that had no mass and two units of spin (a property no physicist can coherently explain). Such a particle had never been identified. This difficulty was handled neatly in the second incarnation called superstring theory. Some physicists claimed boldly that the massless, two-spin particle was a graviton, a quantum of gravity! In a stroke, relativity and quantum physics were joined under one roof.
By 1995, there were five different mathematical models of superstring theory. How could anyone choose one over another? A way out was proposed by Edward Witten, a mathematical physicist. He pointed out many similarities in the theories and described a way to collapse them into a single theory. Three ideas had to be agreed to, however. One, spacetime had to consist of 11 dimensions because the math said so. (This was one dimension more than superstring theory allowed for.) Two, besides strings, there were multidimensional structures called membranes, or branes for short. Our universe was bounded by a 3-dimensional brane. Three, our universe was one of many universes (a multiverse), in which the laws of physics could differ from one universe to another. Witten called his proposal M-theory. Ever since, M-theory has dominated theoretical physics.
You ask, how can reality possibly be 11-dimensional? Where are the other 7 dimensions? The answer is bizarre. The other seven are so small they’re not directly detectable, and they’re folded together into a strange shape called a Calibi-Yau manifold! It’s been proven mathematically that such a figure could exist. A rendering of it appears at the left.
But what would these dimensions be for? Well, maybe one for time backwards and one for time forwards. Maybe another for time travel to other universes. Maybe another relates to wormholes, theoretical shortcuts for traveling within our universe and between universes.
Why don’t humans have the sensory equipment to be aware of the extra dimensions? Because extra senses were unnecessary. Darwin showed us that life develops whatever senses it needs to exploit a given ecological opportunity. Perhaps Earth provides no ecological niche that requires more senses. Here’s a video that’s probably more convincing than I am.
Note: I believe that dark matter, introduced earlier, is actually hiding in one of the M-theory dimensions. One day, this conjecture will earn me a Nobel Prize. If I’m honored posthumously, I hereby appoint my son, Joshua, to accept the prize on my behalf.
1998: California, Massachusetts, and Northern Chile
Three teams of astrophysicists coordinated an investigation of the expansion of the universe and its causes. They looked for a special type of supernova known to have an intrinsic brightness of a standard candle, the basic unit of brightness measurement. When they compared this brightness to the supernova’s luminosity — the amount of energy it emits per unit of time — they were able to compute how far away it was. To measure how fast it was receding from us, they measured how much its light was shifted toward the red end of the spectrum. To their surprise, they found that the visible universe was not expanding at a fixed rate but at an accelerating rate!
But why was expansion accelerating? Where did the energy come from to cause this phenomenon? Unlike heat or light or any other kind of energy, it was undetectable. So it was given the name dark energy.
Eventually, quantum physicists identified the most plausible source of dark energy: the vacuum of space! It seems the vacuum of space isn’t really a vacuum. In any cubic centimeter of this space, you’ll find pairs of virtual particles, matter and antimatter, continually popping into existence and then annihilating each other. (You’ve met virtual particles before in the discussion of black holes.)
The here-and-gone character of virtual particles creates energy called vacuum energy. This is the mysterious dark energy! It doesn’t amount to much in one cubic centimeter, but spacetime is incredibly vast, so the accumulation of dark energy becomes a remarkably powerful force. Powerful enough to drive the expansion of the universe.
As the universe expands, the vacuum of space gets bigger. Consequently, dark energy increases, and naturally, the expansion keeps accelerating. Dark energy is currently calculated to be 68% of all the matter and energy in the universe. At 5%, the stars and everything star-made are trivial by comparison.
2012: near Geneva, Switzerland
Three years earlier, the Large Hadron Collider went into operation. It’s the most powerful particle collider in the world, and the largest machine in the world. Its first mission was to search for the Higgs boson, a hypothetical particle that Peter Higgs and his colleagues described in 1964. Their hypothesis depended on the existence of quantum fields.
Quantum field theory holds that every kind of particle has a corresponding field, a ubiquitous part of spacetime in which excitations of energy appear to us as the particle; for example, the electron field contains excitations we perceive as electrons. Higgs believed the Higgs field was home to Higgs bosons.
We know that some particles have mass (“stuff”) — electrons, for instance. Some particles have no mass — photons, for instance. How do the particles with mass acquire their mass? Higgs said it happens when the field for those particles interacts with the Higgs field and its bosons. Metaphorically, it was like God touching Adam’s finger. Thus the Higgs boson got the nickname “God particle.”
When the Large Hadron Collider had been fine tuned and fully powered, its physicists found a particle that had all the characteristics a Higgs boson would have. Today, physicists are in accord that the Higgs boson has been discovered.
2015: Washington, Louisiana, and Pisa, Italy
Of the forces we know about — the strong nuclear force (it binds nuclei), the weak nuclear force (it causes particle decay in nuclei), the electromagnetic force, and gravity — gravity is by far the weakest. Try to pick up a paper clip with a cheap magnet. The magnet will easily overcome Earth’s gravitational field. No contest. But even so, gravity has the power to shape spacetime.
In his Theory of General Relativity, Einstein predicted the existence of gravitational waves that ripple through spacetime much as a backwash ripples through water in the wake of a boat. Gravitational waves, theoretically, would travel at the speed of light and exert a push-pull on any objects they passed. But because they are weak and invisible, they would be extremely hard to find.
A century after Einstein’s prediction, astrophysicists, working at three different observatories, set out to discover gravitational waves. Most observatories look for light waves that have traveled from afar. But gravitational-wave observatories are built to detect the push-pull of gravitational waves traveling from afar. The astrophysicists trained their instruments on two black holes that were on a collision course 1.3 billion years ago. In 2015, the gravitational waves from their massive collision reached Earth. The sensitive instruments at the observatories independently detected the push-pull exactly as predicted.
Scientists are hopeful that gravitational waves will become, as light waves have been, a rich source of information about the universe.
Adults living in the year 1900 had a vastly different notion of reality than we do today. Atoms were solid, like tiny muffins with embedded fruit. Time passed at the same rate everywhere. An object always had the same apparent size, regardless of its motion relative to an observer. There were no more than three dimensions, period. And gravity had no effect on them. People didn’t age more slowly in a valley than on a mountain top. We lived in a star collection called the Milky Way, which was also the entire universe. The universe began when God created it and has remained unchanged. Nothing about the subatomic world would be surprising; matter was matter. Subatomic particles didn’t have dangerous twins that could cause mutual annihilation; God would never permit His creation to be destroyed. One element could never be turned into another; that was a discredited medieval belief. Subatomic particles couldn’t communicate across distances; could a paperweight in London talk to a paperweight in Hong Kong? The frightening possibility of dark, powerful sinkholes in the heavens was undreamt of. Dropped objects always fell to the ground; they never hovered over it. Anything in nature could be detected by our senses alone or with the assistance of a device. There was only one Creation; imagining an infinite number of them would be heretical. God created the universe, meaning light and all the material things; only God could make “stuff” out of nothing. Gravity couldn’t travel billions of miles through space like a light beam; all the stuff in the universe would get smushed together.
That was a time of certainty. Today is different. We try to learn about fundamental bits of nature by examining them with light or with some other form of energy. This very act changes the properties of those bits. Our best current guess is that reality isn’t composed of bits at all, but of energy excitations in quantum fields.
One more thing. You’ve made it all the way through a long, difficult post. You deserve a reward. For your titillation, here’s my favorite science video. Enjoy!
By now you have surely heard the news. Astronomers at two listening posts in the U.S. have heard a series of chirping sounds that confirm the existence of gravity waves. A century ago, Einstein predicted the existence of such waves, but because of their faintness, they had never been detected before. What made them detectable at last was the collision and coalescence of two black holes 1.3 billion years ago; their “gravity report” has taken a very long time to reach us.
The Scratching Post 