Nothing

Silence: the scale goes below zero#

A sound level in decibels compares a pressure with a reference of 20 micropascals, close to the faintest sound a young, healthy ear can hear. Zero decibels is that threshold, not silence, and anything quieter gets a negative number. A whisper is about 30 dB, a normal conversation about 60, a power lawn mower about 90. Every 20 dB down divides the pressure by ten.

In 2015 Guinness World Records listed an anechoic chamber in Building 87 at Microsoft in Redmond as the quietest place on Earth, with an average of −20.35 dBA. It took the title from Orfield Laboratories in Minneapolis, measured at −13 dBA in 2012. In 2021 Orfield took it back with −24.9 dBA, the record Guinness lists today; visitors to such rooms describe hearing their own blood pumping.

Around 1951 the composer John Cage sat in an anechoic chamber at Harvard, expecting silence. He heard two sounds, one high and one low. The engineer told him the high one was his nervous system and the low one his blood circulating. Cage concluded that silence cannot be achieved. On 29 August 1952 the pianist David Tudor gave the first performance of Cage’s 4′33″, three movements in which the performer plays nothing.

Sound also needs something to travel through. At a thousandth of a millibar, an air molecule goes about 6.7 centimetres before it hits another, so the molecules no longer pass on the pressure of a sound wave as a gas does. In the room, the sound dial stops working once the matter dial gets that low.

Darkness: the walls glow#

Direct summer sun gives about 100,000 lux; an office, a few hundred; a full moon, 0.1 to 0.3; a clear night with no moon, about 0.001; an overcast night with no moon, about 0.0001 or less. Each step on the light dial is ten times less light.

Shutting the light out is the easy part. Anything warm glows, mostly in the infrared, which the eye cannot see. A closed box at room temperature is full of this radiation: about 500 million photons in every cubic centimetre. Their number falls with the cube of the temperature, so in the room, once the shutters are closed, only the heat dial can remove them. The red glow on the screen stands for that infrared light.

Deep space is dark to the eye, but it is not empty of light. The radiation left from the early universe, measured at 2.725 K, puts about 411 photons in each cubic centimetre of it. Even the blackest coatings, such as a carbon-nanotube material made at MIT in 2019, return a small part of the light that falls on them: that one absorbs at least 99.995%.

Cold: the last step takes forever#

The lowest temperature measured is 38 trillionths of a degree above absolute zero. In 2021 a team at the Bremen drop tower let a cloud of rubidium atoms fall and slowed its spread with magnetic lenses. The figure describes how slowly the atoms moved, and it held for about two seconds.

Nature’s coldest known object is the Boomerang Nebula, at about 1 K, colder even than the 2.7 K glow of the space around it because its gas is expanding fast.

In 2017 Lluís Masanes and Jonathan Oppenheim derived the third law of thermodynamics: under general assumptions (a bath whose heat capacity is positive), cooling anything to absolute zero would take an infinite number of steps or an infinite time.

Even at the bottom, motion does not stop. Quantum mechanics leaves every particle held in place a lowest energy above zero. Helium shows it on a large scale: at ordinary pressure it stays liquid however cold it gets, and freezes only when squeezed at about 25 atmospheres. The slight tremble of the dust in the room stands for this motion.

Empty: the vacuum keeps an energy#

Air at sea level holds about 25 billion billion molecules in each cubic centimetre. The beam pipes of CERN’s Large Hadron Collider are pumped to 10⁻¹⁰–10⁻¹¹ millibar, a pressure about ten trillion times lower than the air’s. In a run reported in 2017, the BASE experiment at CERN kept antiprotons in a cold trap for 405 days with none lost to decay or to collisions with gas, which put the gas inside below about 3×10⁻¹⁸ millibar: at most a few molecules per cubic centimetre, about as many as in the solar wind near the Earth. The average for the whole universe is about one proton in every four cubic metres.

Take away every atom and the vacuum is still there. In quantum theory, empty space keeps a lowest energy that cannot be removed, and the usual explanation of the Casimir effect rests on it: two metal surfaces a few micrometres apart or closer are pushed together. Steve Lamoreaux measured the force in 1997, and Umar Mohideen and Anushree Roy measured it to about 1% in 1998. The flickering pairs in the room are a picture of this idea, not of anything that can be seen.

Zero: named, never reached#

Physics only approaches zero; mathematics can simply name it. The earliest surviving written rules for computing with zero are in Brahmagupta’s Brāhmasphuṭasiddhānta, from 628: a number times zero is zero, and zero added to zero is zero. In 1202 Fibonacci’s Liber Abaci made the Indian figures and the sign 0 widely known in Latin Europe, the sign “which the Arabs call zephir”.

The words keep the idea of emptiness. Zero and cipher both come from the Arabic ṣifr, “empty”, itself a translation of the Sanskrit śūnya, “void”. Nothing is simply no thing. In Romanian, nimic comes from the Latin nemica, which old dictionaries read as “not a crumb”.

In the 1920s John von Neumann defined each number as the set of all the numbers before it, starting from the empty set. Written out with nothing but brackets, a number n needs 2ⁿ pairs: 3 is {{},{{}},{{},{{}}}}, eight pairs. Each step up doubles everything that came before, which is why each picture in the section above holds the one before it at half size, and everything inside that one again.

What the room shows#

Each dial runs on a logarithmic scale: every turn down by the same angle divides the quantity by the same factor, so zero would lie infinitely far down. The bottom of each dial is the lowest value measured; for light it is a closed room, and for matter the average of the universe. The dust, its speed, the beam and the waves are drawn on compressed scales so that all four can share one screen. The amplitude of the hiss, when sound is on, follows the decibels: it falls by a factor of ten for every 20 dB.

Three things in the room are linked as they are in nature. A beam of light is only visible from the side when something scatters it, so it fades as the air goes. Sound stops when the molecules are too far apart to carry it. The infrared glow depends on the heat dial. The heartbeat appears once the room is quieter than the threshold of hearing, the way Cage heard his own blood. It stands for the listener’s own.

Sources#

• NIOSH (2001). General estimates of work-related noises. DHHS (NIOSH) Publication 2001-104. stacks.cdc.gov
• Guinness World Records (2015). Microsoft lab sets new record for the world’s quietest place. www.guinnessworldrecords.com
• Guinness World Records. Quietest place: Orfield Laboratories, −24.9 dBA, 19 November 2021. www.guinnessworldrecords.com
• Guinness World Records (2024). Inside the quietest place on Earth. www.guinnessworldrecords.com
• Cage, J. (1961). Experimental Music. In Silence: Lectures and Writings, p. 8. Wesleyan University Press. users.drew.edu
• NPR, Composers Datebook: 4′33″ (first performance, Woodstock, 29 August 1952). www.npr.org
• Leybold (2001). Fundamentals of Vacuum Technology, Table III: mean free path of air. physics.uwo.ca
• IES VE. Examples of illuminance (sunlight, interiors). help.iesve.com
• Bedrosian, T. A. & Nelson, R. J. (2017). Timing of light exposure affects mood and brain circuits. Translational Psychiatry 7: e1017, Table 1 (night-time illuminance). pmc.ncbi.nlm.nih.gov
• Fixsen, D. J. (2009). The temperature of the cosmic microwave background. The Astrophysical Journal 707: 916–920. arxiv.org
• Anchordoqui, L. Black-body photon number density (lecture problem set). lehman.edu
• Cui, K. & Wardle, B. L. (2019). Breakdown of native oxide enables multifunctional, free-form carbon nanotube–metal hierarchical architectures. ACS Applied Materials & Interfaces 11: 35212–35220. news.mit.edu
• Deppner, C. et al. (2021). Collective-mode enhanced matter-wave optics. Physical Review Letters 127: 100401. doi.org
• ALMA Observatory (2013). ALMA reveals ghostly shape of “coldest place in the universe”. www.almaobservatory.org
• Masanes, Ll. & Oppenheim, J. (2017). A general derivation and quantification of the third law of thermodynamics. Nature Communications 8: 14538. doi.org
• Enss, C. & Hunklinger, S. (2005). Low-Temperature Physics. Springer (helium solidifies only above about 25 bar). doi.org
• NIST CODATA. Loschmidt constant. physics.nist.gov
• CERN. A vacuum as empty as interstellar space. home.cern
• Sellner, S. et al. (2017). Improved limit on the directly measured antiproton lifetime. New Journal of Physics 19: 083023. doi.org
• NASA Goddard. The solar wind. umbra.nascom.nasa.gov
• Planck Collaboration (2020). Planck 2018 results VI. Cosmological parameters. Astronomy & Astrophysics 641: A6. arxiv.org
• Lamoreaux, S. K. (1997). Demonstration of the Casimir force in the 0.6 to 6 μm range. Physical Review Letters 78: 5–8. doi.org
• Mohideen, U. & Roy, A. (1998). Precision measurement of the Casimir force from 0.1 to 0.9 μm. Physical Review Letters 81: 4549. arxiv.org
• MacTutor. A history of zero. mathshistory.st-andrews.ac.uk
• Sigler, L. E. (2002). Fibonacci’s Liber Abaci: a translation into modern English, ch. 1. Springer. doi.org
• Stanford Encyclopedia of Philosophy. Set theory (von Neumann ordinals). plato.stanford.edu
• Wiktionary. zero; cipher; nothing (citing the OED). en.wiktionary.org
• dexonline. nimic (DEX, DER, CADE, Șăineanu); zero. dexonline.ro