SafekipediaVacuum
Adapted from Wikipedia · Adventurer experience
A vacuum (pl.: vacuums or vacua) is space with no matter. The word comes from the Latin vacuus, meaning "empty." In science, a vacuum is a place where the pressure of gas is much lower than normal air pressure. Physicists talk about a perfect vacuum, but in real life, we usually deal with a partial vacuum, like in a laboratory or outer space.
The quality of a vacuum is measured by how close it gets to a perfect vacuum. A typical vacuum cleaner can reduce air pressure by about 20%, but much higher-quality vacuums exist. For example, ultra-high vacuum chambers used in science can have pressures below one trillionth of normal air pressure. Outer space is an even better vacuum, with only a few hydrogen atoms in a cubic meter.
People have been interested in vacuums for a long time. It wasn’t until the 1600s that scientists like Evangelista Torricelli created the first laboratory vacuum. Today, vacuums are important in many technologies, such as incandescent light bulbs and vacuum tubes.
Etymology
The word vacuum comes from Latin, meaning "an empty space" or "void". It is based on the word vacuus, which also means "empty".
"Vacuum" is one of the few English words that has two u letters next to each other.
Historical understanding
Ancient Greek philosophers wondered if empty space, called a vacuum, could exist. They talked about this idea while studying tiny particles called atoms. Later thinkers, like Lucretius and Hero of Alexandria, also asked if humans could make an artificial vacuum.
Many people believed that nature "hated" a vacuum, a view called horror vacui. Some medieval scholars even thought only God could create a vacuum. Over time, ideas changed. By the 17th century, many accepted that a vacuum might exist beyond our world. Important experiments, like those by Evangelista Torricelli and Otto von Guericke, showed that partial vacuums could be created and measured for the first time.
Classical field theories
A vacuum is a space with no matter, energy, or movement. In physics, this means no particles or energy-carrying fields are there.
In the study of gravity, a vacuum can still show curves in space-time because of gravitational forces and waves, even though there is no matter. For example, black holes are areas of vacuum with very strong gravity.
In electromagnetism, a vacuum is used as a standard reference. In this perfect vacuum, light moves at its full speed of 299,792,458 meters per second, and electric and magnetic fields act in very predictable ways.
Quantum mechanics
Main article: Quantum vacuum state
In quantum mechanics and quantum field theory, the vacuum is the state with the lowest possible energy. In quantum electrodynamics, this is called the 'QED vacuum'. It has no matter particles or photons. Even though we can't create this perfect vacuum in experiments, it helps explain many observations.
The QED vacuum has special properties. While the average values of electric and magnetic fields are zero, they fluctuate. These fluctuations create temporary particles and give the vacuum energy. They help explain things like spontaneous emission and the Lamb shift. They also change how Coulomb's law and electric potential work near electric charges.
Outer space
Main article: Outer space
Outer space is almost like a perfect vacuum. It has very little matter in it, with only a few hydrogen atoms in every cubic meter. Even though outer space is mostly empty, it is not a perfect vacuum.
Stars, planets, and moons keep their atmospheres because of gravity. The Earth's atmosphere gets thinner as you go higher. At about 100 kilometers up, called the Kármán line, it becomes outer space. Beyond this point, the air is so thin that it hardly affects anything. However, there is still enough air up there to slow down satellites in low Earth orbit, so they need to use their engines to stay in place.
Measurement
Main article: Pressure measurement
The quality of a vacuum depends on how much matter is left in it. A good vacuum has very little matter. We measure vacuum by its absolute pressure, but we also need to know the temperature and the types of gases present.
One important factor is the mean free path (MFP) — the average distance gas molecules travel before bumping into each other. As gas gets thinner, the MFP grows. When the MFP is longer than the size of the container, special rules apply, and this is called high vacuum.
Vacuum quality is grouped into ranges based on the tools needed to create or measure them. For example, atmospheric pressure is around 101 kilopascals. Deep space is usually emptier than any vacuum we can make on Earth. Perfect vacuum means no particles at all — this can’t be achieved in labs, but tiny areas may briefly have no matter at all. Even then, there would still be things like light particles (photons), energy, and other effects.
Different tools are used to measure vacuum pressure, depending on how empty the space is. Some gauges use liquid columns, like mercury, to show pressure changes. Others use metal parts that bend with pressure, or heat to see how well gases conduct heat. For very empty spaces, ionization gauges are used, where electric currents help count gas particles.
| Pressure range | Definition | The reasoning for the definition of the ranges is as follows (typical circumstances): |
|---|---|---|
| Prevailing atmospheric pressure (31 kPa to 110 kPa) to 100 Pa | low (rough) vacuum | Pressure can be achieved by simple materials (e.g. regular steel) and positive displacement vacuum pumps; viscous flow regime for gases |
| medium (fine) vacuum | Pressure can be achieved by elaborate materials (e.g. stainless steel) and positive displacement vacuum pumps; transitional flow regime for gases | |
| −6 Pa | high vacuum (HV) | Pressure can be achieved by elaborate materials (e.g. stainless steel), elastomer sealings and high vacuum pumps; molecular flow regime for gases |
| −6 Pa to 1×10−9 Pa | ultra-high vacuum (UHV) | Pressure can be achieved by elaborate materials (e.g. low-carbon stainless steel), metal sealings, special surface preparations and cleaning, bake-out and high vacuum pumps; molecular flow regime for gases |
| below 1×10−9 Pa | extreme-high vacuum (XHV) | Pressure can be achieved by sophisticated materials (e.g. vacuum fired low-carbon stainless steel, aluminium, copper-beryllium, titanium), metal sealings, special surface preparations and cleaning, bake-out and additional getter pumps; molecular flow regime for gases |
Uses
Vacuum is useful in many processes and devices. Its first big use was in the incandescent light bulb to protect the filament. The lack of air in a vacuum also helps in electron-beam welding, cold welding, vacuum packing, and vacuum frying. Very clean vacuums are used to study surfaces at the atomic level.
High vacuums remove air, letting particles add or remove materials cleanly. This is important for making semiconductors and optical coatings. Vacuums also help keep things cold, like in thermos bottles. They can lower the temperature at which liquids boil, which is useful in processes like freeze drying.
Vacuums are also used to create suction, which has many uses. Early steam engines used vacuum to move pistons. Vacuum was once used to help trains stop, and it still powers some car parts like brake boosters. Some airplane instruments run on vacuum. Keeping a vacuum in steam turbines helps them work better.
Effects on humans and animals
See also: Space exposure and Uncontrolled decompression
When humans or animals are in a vacuum, they can lose consciousness quickly because there is no oxygen. The effects are not as big as they look in movies. Lower pressure can make tiny bubbles in body fluids, but this often does not hurt much. Special clothing, like the suits astronauts wear, helps keep them safe.
Animals, like chimps in some tests, have lived through short times in a vacuum. Plants can also stay alive for a little while in places with very low pressure. In space, astronauts need special suits because the air pressure is much lower than on Earth. Very fast changes in pressure can be unsafe, but slower changes are better. Some tiny living things, like tardigrades, can stay alive in a vacuum for many days.
Examples
A vacuum is space with very little matter in it. The word "vacuum" comes from a Latin word meaning "empty" or "void". We can create something close to a vacuum using tools like a Vacuum pump. This tool can remove air and lower the pressure in a space. This helps scientists study how things behave without air getting in the way.
| Pressure (Pa if not explained) | Pressure (Torr, atm) | Mean free path | Molecules per cm3 | |
|---|---|---|---|---|
| Standard atmosphere, for comparison | 101.325 kPa | 760 torrs (1.00 atm) | 66 nm | 2.5×1019 |
| Intense hurricane | approx. 87 to 95 kPa | 650 to 710 | ||
| Vacuum cleaner | approximately 80 kPa | 600 | 70 nm | 1019 |
| Steam turbine exhaust (Condenser backpressure) | 9 kPa | |||
| liquid ring vacuum pump | approximately 3.2 kPa | 24 torrs (0.032 atm) | 1.75 μm | 1018 |
| Mars atmosphere | 1.155 kPa to 0.03 kPa (mean 0.6 kPa) | 8.66 to 0.23 torrs (0.01139 to 0.00030 atm) | ||
| Freeze drying | 100 to 10 | 1 to 0.1 | 100 μm to 1 mm | 1016 to 1015 |
| Incandescent light bulb | 10 to 1 | 0.1 to 0.01 torrs (0.000132 to 1.3×10−5 atm) | 1 mm to 1 cm | 1015 to 1014 |
| Thermos bottle | 1 to 0.01 | 1×10−2 to 1×10−4 torrs (1.316×10−5 to 1.3×10−7 atm) | 1 cm to 1 m | 1014 to 1012 |
| Earth thermosphere | 1 Pa to 1×10−7 | 10−2 to 10−9 | 1 cm to 100 km | 1014 to 107 |
| Vacuum tube | 1×10−5 to 1×10−8 | 10−7 to 10−10 | 1 to 1,000 km | 109 to 106 |
| Pressure on the Moon | approximately 1×10−9 | 10−11 | 10,000 km | 4×105 |
| Cryopumped MBE chamber | 1×10−6 to 1×10−10 | 10−8 to 10−12 | 10 to 100,000 km | 108 to 104 |
| Dense nebula | 10,000 | |||
| Interplanetary space | 11 | |||
| Interstellar space | 1 | |||
| Intergalactic space | 10−6 |
Images
This article is a child-friendly adaptation of the Wikipedia article on Vacuum, available under CC BY-SA 4.0.
Images from Wikimedia Commons. Tap any image to view credits and license.