The fabric

My own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose.

J.B.S. Haldane

Our bodies are made of organs and tissues, made of cells, made of organelles, made of proteins, sugars, fats, water, … These molecules are made of elements (hydrogen, carbon, etc.), made of atoms, made of subatomic particles (protons, neutrons, electrons). In addition, in the Standard Model of particle physics, protons and neutrons are composed of quarks that are held together by forces mediated by gluons, yet one of the many other elementary particles.

At some point, the elements forming the proteins of your bones and muscles might as well have been part of my body, the body of an Ardipithecus individual 4 million years ago, or part of Tyrannosaurus rex, for that matter. Long before, and far away, the same elements were part of an old dying star. Same matter, different forms, different information, different behaviors, different selves.

The entire cosmos is made of the same stuff that we are made of. But what is exactly that stuff?

Quantum leaps

In 1900, Max Planck proposed that energy was made of individual units, the quanta 1. Quantum theory was born. For that, he won the Novel Prize in Physics in 1918.

In 1905, Albert Einstein building on Planck’s hypothesis proposed that not just the energy, but the radiation itself was quantized in the form of light corpuscles, the photons. Einstein published his paper on the “photoelectric effect” during his “annum mirabilis” (earning him the Novel Prize in Physics in 1921).

In 1911, Ernest Rutherford came up with a model of the atom. He proposed that a heavy nucleus with a positive charge was surrounded by electrons with a negative charge. From a distance, it would look like a small solar system. Rutherford also won a Nobel Prize, but for something else.

In 1913, Niels Bohr proposed a mathematical model of the atom providing theoretical support for Rutherford’s model. In the model, electrons absorb and emit radiation of fixed wavelengths when jumping between fixed orbits around the nucleus. Bohr became the leading atomic physicist, earning the Nobel Prize in Physics in 1922.

In 1924, Louis de Broglie’s principle of wave-particle duality proposed that at the atomic and subatomic levels, both energy and matter can behave, depending on the conditions as either particles or waves. For this work, de Broglie was awarded the Nobel Prize in Physics in 1929.

In 1926, Erwin Schrödinger, assuming that electrons can also travel in waves, formulated a wave equation that accurately estimated the energy levels of electrons in atoms. The “electron cloud model” substituted the idea that electrons orbited around the nucleus of the atom. For his contribution to atomic theory, he won (together with Paul Dirac), the Nobel Prize in Physics in 1933.

In 1927, Werner Heisenberg’s uncertainty principle put forward that, given the wave-particle duality nature of objects (including light and its photons), at the subatomic level, it is impossible to simultaneously obtain complimentary measurements, such as its position and momentum (= mass x velocity). By measuring subatomic particles, we are affecting them. Heisenberg was awarded in 1932 the Nobel Prize in Physics for, among others, “the creation of quantum mechanics.”

Escaping observable reality

Particles have a defined position in space, mass, density, and volume (just like the speaker in your room, it can only be in one place at a time). On the other hand, waves are delocalized disturbances in space. We can measure their wavelength and frequency, but not their exact position. Furthermore, they can co-exist with others (the sound coming out of your speaker reaches everyone in the room, sometimes interfering with the signal of your old radio receiver).

How can a physical object be a wave?

de Broglie wavelength equation indicates that objects with a large momentum (e.g., a shotted bullet, or even large things such as an elephant moving at a small speed) have tiny wavelengths, in fact, too small to be detected. This is not the case with subatomic particles 2.

How is it that we cannot be sure about the exact location or speed of a particle/wave without affecting it? 3

At the macroscopic level, when light hits your soccer ball, its photons will transfer their momentum to the ball, but the latter will remain unaffected 4. However, when a photon hits an electron, a portion of its small momentum transfers to the electron changing its speed and position in space at a given time (imagine two cars frontally colliding).

Physicists don’t understand their own theory any better than a typical smartphone user understands what’s going on inside the device.

Sean Carroll

Today’s conundrum

How does the microscopic quantum world relate to the macroscopic world we can live in, the one we can touch and see?

The reason why it is difficult to understand what’s going on at the atomic or subatomic level is that we rely on macroscopic tools (from calipers to light detectors) to measure microscopic systems (atoms, protons, neutrons, photons…). The laws of physics that operate on the former (classical “Newtonian” physics) are different than those that apply to the latter (quantum mechanics). The former holds that all variables of particles are measurable, the second states that the measuring process defines our objective reality.

Which one should we use, and why? The available answers are not satisfactory for everyone. These are some popular alternatives:

The Copenhagen Interpretation

It’s the current “convention” of quantum mechanics, named after the university where some of its developers worked trying to explain the implications posed by quantum mechanics. The truth is the disagreements are many, especially between Heisenberg and Bohr.

Heisenberg gave emphasis on separating the observer (or measurement instrument) from the object of study. Like other founders (and current followers) of quantum theory, he stressed the active role of consciousness in quantum theory: There is no reality without observation. The tree would produce no sound if no one were around to hear it.

Bohr had a practical approach, believing that quantum mechanics was a generalization of classical Newtonian physics, which was still valid at the macroscopic scale. He believed in observation independent from a subjective observer, capturing an irreversible object/particle state.

Many-Worlds Interpretation

In 1957, Hugh Everett III proposed this multiverse theory, which is currently defended by notable theoretical physicists such as Stephen Hawking. This theory proposes that the wave function never goes away. There are as many parallel universes as possible states in which an object (plant or person) can exist. Under this view, there is a universe in which Schrödinger’s cat is alive, and another in which is dead, regardless of whether the box is opened.

Scaling down

Several notorious physicists had issues with quantum theory, including some of its founding fathers. For example, Schrödinger was uncomfortable with the implications of quantum theory. As a critique of the Copenhagen interpretation of quantum superposition (based on his own equation), he came up with a famous thought experiment known as “Schrödinger’s cat paradox” of quantum mechanics: A cat inside a box with poison is simultaneously alive and dead (before measuring). However, when one looks inside the box (when one measures) it is revealed that the cat is either alive or dead.

While Einstein did not doubt that quantum mechanics gave correct predictions, he believed that it was not a complete theory. Regarding the role of the observer (or measurement), he once complained that the Moon does not exist only when we look at it. He was not happy either about the putative lack of underlying structure (possibility of randomness) in the cosmos: “God does not play dice with the universe.”

The combined results from the experiments on muons from Fermilab (Chicago) and Brookhaven (Long Island) found that these subatomic particles spin at a much faster speed than can be explained based on the current Standard Model. A likely explanation? Something else is interacting with muons causing them to behave the way they do.

Are there universal laws of Nature that can be approximated by human-made models? Is there an ultimate quantic level? Are we quantum levels of a larger system? Or is the fabric of reality made of strings?

1 E = hv (Energy = Planck’s constant x frequency of the radiation).

2 As an example, de Broglie’s wavelength equation indicate, an African elephant of about 2696 kg moving at 24.9 km/h has a wavelength of 0.0000000000000000000000000000000000000355 m.

3 All this is better explained in this short TED-ed video.

4 The mass of a photon is 0, but its momentum depends on the wavelength of the light carrying it.

The cover image shows traditional wool rolls on a textile factory history exhibit in Terrassa, Barcelona (credit: Museu Nacional de la Ciència i Tècnica de Catalunya).