Time: World Lines and the Block Universe

April 08, 2019

A review of a book by Paul Kalpern called The Quantum Labyrinth.

If you consider spacetime a single unified thing comprised of both space and time (and they do go well very well, mathematically speaking), then you could see your entire life -- everywhere you go, everyone you meet -- in the form of a wiggly line stretching against a backdrop of the other three dimensions.

“Nothing happens in space alone. It must have a timestamp too,” wrote Paul Kalpern in "The Quantum Labyrinth: How Richard Feynman and John Wheeler Revolutionized Time and Reality," a 2017 book.

In fact, every molecule in the universe would be captured in this block, including those that make up your body for a part of their billion year journeys. From this particular dimension, the "Block Universe" as it's known, time does not exist, other than as these trails encased across stretches of space, which are sometimes called 'World Lines.'

“The world lines of everything that existed or will exist -- past, present and future -- would be etched within such a cosmic crystal ball,” Kalpern wrote. “Time would seem as frozen as a block of ice, because it would already be foreseen.” From a distance, this block universe may look smooth and calm, but closer up it appears more "turbulent and frothy."

A review of a book by Paul Kalpern called The Quantum Labyrinth.

Technically speaking, there is no law in physics that prevents causality from going back in time, or of cause always preceding the effect. "Just as right and left could be reversed, so might future and past," Kalpern wrote. "Clearly, causality was real. Humans experienced it every day. But it did not have a bearing on particle interactions." But Time's Arrow appears to depend on the second law of thermodyamics, by way of entropy, "which mandates its non-decrease as time moves forward," Kalpern wrote.

Richard Feynman attributed Time's Arrow to the fact that we know more about the past — and so it has lower entropy — than we do about the future, which by that definition would have a higher entropy. The weird thing about that is everything else in the universe tends to move in the opposite direction — from a lower entropy state to a higher one.

Notes and Quotes

The problem is one of what Einstein called “spooky action at a distance,” or why when you wiggle one electron (or set the “spin”) another one would wiggle instantaneously -- no matter how far away from one another the two are. This occurrence proves that quantum physics is inherently non-local, meaning it operates outside the classical laws of cause and effect, where information can move faster than the speed of light.

"'How does an electron cross the road?' As Feynman and Wheeler showed, the correct quantum answer is that it takes every physically possible path."

"It was as if Groucho March were standing in for a great scientist" -- C.P. Snow on Richard Feynman.

Backstory: Germans had discovered that massive Uranium nuclei could be divided, releasing a mass of energy ("Fission"). In a conference, Niels Bohr announced news of this development to the physics community, who immediately saw the danger of the Germans using the technology to build a bomb. Certain forms of uranium were easier to split than others -- Uranium 235 could be disrupted by relatively slower neutron, as could a then still theoretical isotope Plutonium 239. The idea is that the fission would release more neutrons leading to a "chain reaction" of other nuclei.

"In general relativity, matter and energy warp the fabric of spacetime -- Space and time combined -- like a heavy nest on a flimsy tree branch."

“Electromagnetic waves form a duo of electric and magnetic fields, oscillating perpendicular to each other at the speed of light.” Electromagnetic are also hard to explain in terms of quantum mechanics.

The speed of light, not measurements of space (which can be compressed) or time (which can be dilated), serves as the universal standard

Einstein explained general relativity, as well as 'action-at-a-distance' through a geometric model of gravity. But he had to add in a fudge factor, the Cosmological Constant, to "counteract the destabilizing effect of gravity."

"The amount of energy of per photon depends on the frequency, rate of vibration, of the light with which it is associated. Frequency is, in turn, is inversely proportional to wavelength. The greater the wavelength, the lower the frequency and vice-versa." Long wavelengths (radio waves) are low frequencies and low energy. Higher wavelengths (X-Rays) are high energy, high frequency.

“The purpose of theory is to describe nature, not to explain nature,” in Richard Feynman’s view.

Image: Pablo Picasso's 1909 cubist painting "Woman with Pears" (Detail)