From Eternity to Here

by Sean Carroll

Nicholson Baker’s novel The Fermata

F. Scott Fitzgerald’s short story “The Curious Case of Benjamin Button”—more

Martin Amis’s novel Time’s Arrow

Philosophers speak of the distinction between Being—existence in the world—and Becoming—a dynamical process of change, bringing reality into existence.

If you know the exact state of the universe, and all of the laws of physics, the future as well as the past is rigidly determined beyond John Calvin’s wildest dreams of predestination.

It’s a bit embarrassing, frankly, that with all of the progress made by modern physics and cosmology, we still don’t have a final answer for why the universe exhibits such a profound asymmetry in time.

The future of our universe is dilute, cold, and lonely.

His image as the rumpled, absentminded professor, with unruly hair and baggy sweaters, contributes to the impression of someone who embodied the life of the mind, disdainful of the mundane realities around him.

And / or he was autistic.

a left turn into yesterday.)

Extraneous motion decreases the time elapsed between two events in spacetime, whereas it increases the distance traveled between two points in space.

We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.

If it’s the Solar System you are interested in, the state is the position and momentum of each planet, as well as of the Sun. Or, if we want to be even more comprehensive and realistic, we can admit that the state is really the position and momentum of every single particle constituting these objects. If it’s your boyfriend or girlfriend you are interested in, all you need to do is precisely specify the position and momentum of every atom in his or her body. The rules of classical mechanics give unambiguous predictions for how the system will involve, using only the information of its current state. Once you specify that list, Laplace’s Demon takes over, and the rest of history is determined. You are not as smart as Laplace’s Demon, nor do you have access to the same amount of information, so boyfriends and girlfriends are going to remain mysterious. Besides, they are open systems, so you would have to know about the rest of the world as well.

A system that has the maximum entropy it can have is in equilibrium.

High entropy implies equilibrium, which implies that the energy is useless,

As long as the fundamental laws of physics are perfectly reversible, given the precise state of the entire universe (or any closed system) at any one moment in time, we can use those laws to determine what the state will be at any future time, or what it was at any past time.

It is impossible to use reversible laws of physics to derive an irreversible result.

All of these would be completely independent events, each individually unlikely, and the combination of all of them is fantastically unlikely. But if you truly have eternity to wait, even the most unlikely things will eventually happen.

And an infinite number of times.

Essentially Epicurus suggested that, in addition to the basic tendency of atoms to move along straight lines, there is a random component to their motion that occasionally kicks them from side to side. It’s vaguely reminiscent of modern quantum mechanics, although we shouldn’t get carried away. (Epicurus didn’t know anything about blackbody radiation, atomic spectra, the photoelectric effect, or any of the other experimental results motivating quantum mechanics.) Part of Epicurus’s reason for introducing the swerve was to leave room for free will—basically, to escape the implications of Laplace’s Demon, long before that mischievous beast had ever reared his ugly head.

“On the Nature of Things”

“If I were a Boltzmann brain, there would be a strong prediction: Everything else about the universe should be in equilibrium. But it’s not. Therefore the universe is not a random fluctuation.”

What if the Boltzmann brain formed randomly to contain the observations of the universe it believes it observes?

this mysterious irreversibility is of precisely the same character as the mysterious irreversibility in thermodynamics, as codified in the Second Law: It’s a consequence of making approximations and throwing away information,

The loss of information is one meaning of "entropy."

The quantum state of a two-state system is described by a “qubit.”)

Her quantum state is described by a superposition of the two distinct possibilities we would have in classical mechanics. It’s not even that “they are both true at once”; it’s that there is no “true” place where the cat is.

The wave function of the universe assigns distinct amplitudes to all the alternative configurations of the combined system of Miss Kitty, us, and the outside world. After we observe Miss Kitty’s location, the wave function evolves into something of the form (sofa, you see her on the sofa, world1) + (table, you see her under the table, world2), where the last piece describes the (unknown) configuration of the external world, which will be different in the two cases. Because we don’t know anything about that state, we simply ignore the entanglement with the outside world, and keep the knowledge of Miss Kitty’s location and our own mental perceptions. Those are clearly correlated: If she is on the sofa, we believe we have seen her on the sofa, and so forth. But after throwing away the configuration of the outside world, we’re no longer in a real quantum superposition. Rather, there are two alternatives that seem for all intents and purposes classical: Miss Kitty is on the sofa and we saw her on the sofa, or she’s under the table and we saw her under the table. That’s what we mean when we talk about the branching of the wave function into different “worlds.” Some small system in a true quantum superposition is observed by a macroscopic measuring apparatus, but the apparatus is entangled with the outside world; we ignore the state of the outside world and are left with two classical alternative worlds. From the point of view of either classical alternative, the wave function ha...

Time, old gal of mine, will soon dim out. —Anne Sexton, “For Mr. Death Who Stands with His Door Open”

No matter how stubborn your personality may be, Nature’s rules will not bend to your will,

Hawking radiation originates from virtual particles near the event horizon of a black hole.

Planck length—the tiny distance of 10-33 centimeters at which quantum gravity becomes important—provides a lower limit on what wavelengths are allowed.

So the Boltzmann-brain problem—“Why do we find ourselves in a universe evolving gradually from a state of incredibly low entropy, rather than being isolated creatures that recently fluctuated from the surrounding chaos?”—does not yet have a clear solution.

This state of affairs is known as the flatness problem. Because the universe is so flat today, it had to be incredibly flat in the past. But why?

Rather, we predict on the basis of reasonable extrapolations of gravity and quantum field theory that a multiverse really should exist.

The number of particles within our observable universe is about 1088, which was also the entropy at early times. Now that we have black holes, the entropy of the observable universe is something like 10101, whereas it conceivably could have been as high as 10120. (That same 10120 is also the ratio of the predicted vacuum energy density to the observed density.)

For comparison’s sake, the entropy of a macroscopic object like a cup of coffee is about 1025. That’s related to Avogadro’s Number, 6.02 • 1023, which is approximately the number of atoms in a gram of hydrogen. The number of grains of sand in all the Earth’s beaches is about 1020. The number of stars in a typical galaxy is about 1011, and the number of galaxies in the observable universe is also about 1011, so the number of stars in the observable universe is about 1022—a bit larger than the number of grains of sand on Earth. The basic units that physicists use are time, length, and mass, or combinations thereof. The shortest interesting time is the Planck time, about 10—43 seconds. Inflation is conjectured to have lasted for about 10—30 seconds or less, although that number is extremely uncertain. The universe created helium out of protons and neutrons about 100 seconds after the Big Bang, and it became transparent at the time of recombination, 380,000 years (1013 seconds) after that. (One year is about 3 • 107 seconds.) The observable universe now is 14 billion years old, about 4 • 1017 seconds. In another 10100 years or so, all the black holes will have mostly evaporated away, leaving a cold and empty universe. The shortest length is the Planck length, about 10—33 centimeters. The size of a proton is about 10—13 centimeters, and the size of a human being is about 102 centimeters. (That’s a pretty short human being, but we’re only being very rough here.) The distance fro...

George Pal’s 1960 movie version of H. G. Wells’s The Time Machine;

Elementary particles come in the form of “matter particles,” called “fermions,” and “force particles,” called “bosons.” The known bosons include the photon carrying electromagnetism, the gluons carrying the strong nuclear force, and the W and Z bosons carrying the weak nuclear force. The known fermions fall neatly into two types: six different kinds of “quarks,” which feel the strong force and get bound into composite particles like protons and neutrons, and six different kinds of “leptons,” which do not feel the strong force and fly around freely. These two groups of six are further divided into collections of three particles each; there are three quarks with electric charge +2/3 (the up, charm, and top quarks), three quarks with electric charge -1/3 (the down, strange, and bottom quarks), three leptons with electric charge -1 (the electron, the muon, and the tau), and three leptons with zero charge (the electron neutrino, the muon neutrino, and the tau neutrino). To add to the confusion, every type of quark and lepton has a corresponding antiparticle with the opposite electric charge; there is an anti-up-quark with charge -2/3, and so on. All of which allows us to be a little more specific about the decay of the neutron (two down quarks and one up): it actually creates a proton (two up quarks and one down), an electron, and an electron antineutrino. It’s important that it’s an antineutrino, because that way the net number of leptons doesn’t change; the electron counts as...

page: http://www.theory.caltech.edu/people/preskill/bets.html. For an in-depth explanation of the black