Vacuums- not a lot in them

A vacuum we all know and love

A vacuum is "a volume of space empty of matter", in other words a something that has absolutely nothing in it, no atoms or particles. The word itself comes from the latin from "empty".

It seems that this is impossible to achieve. There is no container that we can get with a special gate keeper that only lets particles out but not back in. If there was and we managed to get every particle out then there might still be some thermal radiation in there, after all the entire universe is full of the stuff, just take a look at Cosmic Background Radiation (CBR).

CBR as I like to call it, being an old friend and all, is thought to be radiation that was created in the very earliest stages of the universe after the Big Bang. It is one of the main "proofs" to the theory of the Big Bang.

When the Big Bang happened things were very very hot, so hot in fact that it is impossible to try and image just how hot. A hot day, even a very hot one in a desert somewhere, take the hottest day ever recorded, Aziziya, Libya, a blistering 57.8 °C(136 °F) on 13 Sept 1922, is low in comparison.

In addition to the high temparatures there were also some hydrogen particles, helium, my money is on some electrons etc. (Actually, I think the very first things produced where neutrons. Every thing stems from neutrons in my book. )

So even if we could get rid of all the atoms and other sub atomic particles from our container there would still be a fair amount of radiation in there. What is more. I am convinced that if you have a really really high quality vacuum, the likes of which you find in deep space, then before you know it... bingo, a neutron pops into existence. This then decays into a proton and a neutron and your on your way to the components for a star.

But I digress. Let's take a look at just how good the vacuums that we create here on Earth are compared with those out in space. So finding a place to start. Let's use atmospheric pressure. There are a number of different units for pressure, just as there are for speed. For example, in speed  we have meters per second, feet per second, miles per hour, kilometers per hour and so on. In terms of vacuum we have similar varieties.

Pascals, named after Blaise Pascal,  a real genius, he died at the age of 39 having lead a quite remarkable life. Probably best known for Pascal's triangle and Pascal's wager. Pascal's triangle is a rather useful tool for calculating binomial coefficients (you have probably used this at school without realizing it). Pascal's wager is betting on whether God exists or not. He also contributed to numerous other fields including the study of pressure. I am tempted to do a post just on this guy alone. He really was something. Anyway, as a result of his contributions, one unit of pressure is the Pascal.

So if we have a pressure of 1 atmosphere, which is the pressure you feel every day and are normally unaware you are feeling it, the equivalent measurement in Pascals is approximately 101,000 Pa. Another interesting measurement is the number of particles (molecules or atoms) per cubic meter. A cubit meter is the volume of a cube with edges of 1 meter. These are the two that we will use today. The Pascal and the number of particles per cubic meter. So, here we go, a little list;

1 atmosphere (atm)	101000 Pa	2.5x 1025a massive number of particle, bigger than brain can imagine
vacuum cleaner only reduces the pressuse to about 0.8 atm	80,000 Pa	2x 1025
Freeze drying	100 Pa	about 1022 particles
Light bulb , this is about 1/10000 atmospheric pressure.	10 Pa	1021 particles
Thermos (the values vary by a factor of about 100 depending on the quality. We are considering the best here)	0.01 Pa	about 1018 particles
Vacuum tube (these values vary by a factor over over a thousand from 10 micro Pa down to 10 nano Pascals) lets go with the highest vacuum	10 nano Pa (that is 1 billionth of a Pa	about 1012 particles (1000 particles in a cubic millimeter)

The lowest pressure achieved on earth is around about 13 pPa, a thousand times higher than for the best vacuum tube, though this can be reduced by a thousand fold with cryogenic system, actually achieving vacuums with only about 100 particles in 1 cm³, or about 100 million in 1 meter³.

Next, let us see how the best on Earth stacks up against the best in space.

On the moon the vacuum is about 10 times better than the best vacuum tube.

In the space between planets in the solar system the vacuum is about 10 times better than the very best achieved on Earth, about 10 million  particles in 1 meter³.

In the space between stars in our galaxy the vacuum as about 1 particle / cm³, (1 million  particles in 1 meter³) so about 100 times better than anything we have achieved on Earth.

In the space between galaxies there is typically only 1 particle in 1 m³, this is about 100 million times better than anything currently achievable on earth.

Think about that for one minute.

1 single atom in 1 m³ of space.

These numbers are averages of course and so there will be regions of inter galactic space that have more than 1 atom per cubic meter and some that have less than 1 atom per cubic meter. In other words there can be some regions of approximately 1 m³ that sometimes have NO atoms in them. Though they still have the electromagnetic radiation discussed earlier.This is about the closest it gets to a perfect vacuum.

So, this brings us to "horror vacui", nature abhors a vacuum. I don't think nature cares one way or the other about a vacuum, Aristotle was just tripping a bit there I reckon. What is does do though is to take advantage of the conditions of the vacuum of inter galactic space to do something rather clever. I think that the universe uses the vacuum of space-time to create particles.

I am just not sure how yet!