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Impact from a water drop causes an upward &quo...
Impact from a water drop causes an upward “rebound” jet surrounded by circular capillary waves. (Photo credit: Wikipedia)

The title of my post may look odd, but it represents one of the most important chemical compounds on earth. Without it, life would not exist and the search for evidence of the possible existence of life on other planets often comes down to looking for this molecule. It is of course, water.

If you still don’t understand my title, the formula for water is H2O, where the “2” should be subscript representing the fact that there are two Hydrogen atoms in water and one Oxygen atom. This could be misheard as “H to O”, hence my title.

The water molecule with its electric charges
The water molecule with its electric charges (Photo credit: Wikipedia)

Water could be considered to be an oxide of hydrogen, or hydrogen oxide. There is a closely related compound called hydrogen peroxide (which has two oxygen atoms) which is sometimes used as a bleach and disinfectant. Surely everyone over a certain age has heard of “peroxide blondes“.

Water is sometimes referred to, usually jokingly, as dihydogen monoxide. This silly pseudo-scientific name in sometimes used to create fake polemics against water to trick gullible people, causing them to call for a ban on this noxious and toxic chemical!

The logo of DHMO.org, primary current residenc...
The logo of DHMO.org, primary current residence of the dihydrogen monoxide hoax (Photo credit: Wikipedia)

We see water all around us, in all three normal states of matter, solid, liquid and gas. Well, ice and water can be nearly transparent, and water in the gaseous state is invisible – we can only see the water vapour that forms when water in the gaseous state condenses into small particles of liquid water suspended in the air.

Water molecules have a slight “V” shape which gives it some amazing properties. it has a minimum density at 4 degrees Centigrade. It freezes at 0 degrees Centigrade so ice is slightly less dense than liquid water and the ice floats. This results in icebergs and the inevitable reference to the Titanic, which as everyone knows hit an iceberg on its maiden voyage, and endless discussions on whether or not both Jack and Rose could have survived the disaster.

TITANIC life boats on way to CARPATHIA
TITANIC life boats on way to CARPATHIA (Photo credit: Wikipedia)

Not only does ice keep our drinks cool, but it also forms a skin over ponds and puddles in winter which has the effect of protecting small plants and animals from the worst of winter. This is because the ice acts as an insulating layer and allows some warmth to remain in the waters of the pond.

Most animals can’t survive freezing but some really small ones, like certain frogs and toads and some spiders and insects survive being frozen solid. It is believed that this is because of some constituents of their blood acting as an anti-freeze agent, prevention the destructive formation of ice crystals in the cells and blood of the animal.

English: Frozen pond The water here has frozen...
English: Frozen pond The water here has frozen hard. It is believed to be excess field water not a natural pond. (Photo credit: Wikipedia)

Gaseous water is found all around us. It is dissolved, as it were, in air. It’s the water in the air which gives it its humidity. Gaseous water is swept up by the air and boosted to high altitudes by air currents and condenses to clouds, which are masses of water vapour. Ultimately the water falls to earth as rain and runs off into the seas. This whole cycle is driven by heat energy from the sun which causes the evaporation.

On average a human being’s body contains approximately 60% water. It can be higher as in a new-born baby or lower as in obese persons. If a normal person refrains from drinking liquids he or she may become dehydrated, which can result in mental issues and physical ones (which usually go away if the person is rehydrated.

(From source) This cholera patient is drinking...
(From source) This cholera patient is drinking oral rehydration solution (ORS) in order to counteract his cholera-induced dehydration. The cholera patient should be encouraged to drink the Oral Rehydration Solution (ORS). Even patients who are vomiting can often be treated orally if they take small frequent sips. Their vomiting will subside when their acidosis is corrected. (Photo credit: Wikipedia)

A person loses water by sweating and by urinating. If he or she is in an arid environment, such as a desert, he or she will lose water faster than usual, and if it is not replaced, the dehydration could kill. In hot humid climates, sweating is less effective in controlling the person’s temperature and he or she may die of overheating.

Our planet is (mostly) blue from space mainly because the presence of the water that makes up the seas. However in small quantities and in very shallow depths the colour of water is often due more to the mineral content of the water than anything else. This leads to rivers being called “Blue Nile” (because of the black sediment carried by the river – the word for black is also used for blue in the local dialect) or “White Nile” (because of the light clay sediment carried by the river) for example.

The Earth seen from Apollo 17.
The Earth seen from Apollo 17. (Photo credit: Wikipedia)

Apart from making up most of our bodies, and being essential for the body’s proper functioning, water has a myriad of uses to humans. It forms a part of many industrial processes for example, and it often provides the power for them, by way of hydroelectric generation. It helps make our crops grow, and we use it and flavour it to provide our beverages.

We also use water for recreation. We swim in the seas and rivers, we sail on them and we dive under them. We hike many kilometres in some cases to view places where water flows over a drop, and we even explore the caves created by the action of water on some rocks.

A windsurfer with modern gear tilts the rig an...
A windsurfer with modern gear tilts the rig and carves the board to perform a planing jibe (downwind turn) close to shore in Maui, Hawaii, one of the popular destinations for windsurfing. (Photo credit: Wikipedia)

The deep waters of the seas provide much of our food. Our fishermen haul great numbers of them from the seas with some difficulty and at some expense. There are people who believe that we are doing great damage to the planet by doing this, and that we are causing much marine life to become extinct, which seems to be a big risk to us in the future.

We look for water on other planets, to determine whether or not they will or have supported life. The reasoning behind this is that our way of life, and the way of life of all creatures on Earth depends on water. We cannot conceive of a life form that does not depend on water in some ways. That doesn’t mean, of course, that such life forms do not exist, but just that we can’t currently conceive of a way that such a life form could exist. As Mr Spock might say “It’s life, Jim, but not as we know it”.

Little Green Men

SETI
SETI

SETI is short for “Search for Extraterrestrial Intelligence”, or in other words, a search for the “Little Green Men”. The main thrust of SETI is to examine the light from other stars for signs of intelligent life, often on well known wavelengths such as wavelengths near the “water hole“,  a section of the electromagnetic spectrum associated with hydrogen and hydroxyl ions emissions lines. Hydrogen and hydroxyl together make water and water is supposedly necessary for life, so the thinking is that technically advanced life would possibly use this frequency to initiate contact with other civilisations.

Denomination of atomic shells and of character...
Denomination of atomic shells and of characteristic emission lines (Photo credit: Wikipedia)

The trouble is that this is just a guess and there are many possible frequencies that might seem plausible to technically advanced civilisations. If the little green men are not made of water, as we essentially are, they might pick a different frequency band to search. XKCD, my favourite web site has a cartoon which makes this point:

XKCD - the search
The Search

Suppose a remote civilisation did decide to broadcast in that waveband. If they are just announcing their presence, they would need to broadcast their signal in all directions, or they would need to pick out some likely looking star systems and send a directed signal in just a few directions.

If they broadcast in all directions, the power that they would require would be huge. The problem is that in any average stellar neighbourhood, there aren’t many stars. In the sun’s neighbourhood there is an average of 0.004 stars in a cubic light year. So the probability of finding a star one light year from a star in a neighbourhood like the sun’s is four in 1,000. If you look two light years out from the star, you will enclose a volume of eight times the volume of the search area up to one light year, meaning that the probability of finding a star in that volume is 0.032. You would need to look further than five light years out for there to be a fifty-fifty chance of finding a star in that volume, which would be 125 time the size of the original volume of one cubic light year. At 15 lightyears, there would likely be at least 10 stars within the search area.

Globular Cluster NGC 6397
Globular Cluster NGC 6397 (Photo credit: Hubble Heritage)

That’s all very well, but most if not all of these stars will be of the wrong type to support planets of the type that will have free water on them. In fact it is extremely unlikely that a suitable star with suitable planets can be found within, say 200 light years of our hypothetical advanced civilisation. (That’s an out and out guess, but see later).

The remnant of a supernova located 6000 light ...
The remnant of a supernova located 6000 light years from Earth in the constellation Taurus. (Photo credit: Smithsonian Institution)

The trouble is that the signal gets weaker and weaker the further it travels. If you use the signal strength at one light year as the yardstick, the strength is reduced to one quarter at two light years, one ninth at three light years and one sixteenth at four light years and so on because the signal is spread over an area proportional to the square of the distance from the source.  So if the signal strength at 200 light years will be 1/40,000th of the strength of the signal at one light year. If the signal has to travel further it will be correspondingly weaker.

My second attempt at illustrating the Inverse ...
My second attempt at illustrating the Inverse Square Law. S represents an ideal source of electromagnetic radiation and A represents an arbitrary segment of the surface of a sphere of radius r. (Photo credit: Wikipedia)

So likely systems are rare and the signal strength will be weak at the distance of a suitable system. This means that the signal needs to be very strong to be detectable.  Very strong means lots of energy. To broadcast to the Universe at large the civilisation would have to expend a considerable amount of its available energy to only potentially contact another civilisation. Imagine trying to get a project like into the planetary budget!

Clark's accompanying book to Civilisation
Clark’s accompanying book to Civilisation (Photo credit: Wikipedia)

So the hypothetical civilisation is probably desperate to make contact. That may be because either they are in trouble themselves, or they want to warn all local civilisations about something. They are unlikely to do it on a whim, as they must know that the chances of success are pretty close to zero. There’s a faint possibility of a sort of “vampire civilisation” that must prey on other civilisations and so chooses to broadcast in the hope of finding a new victim. I consider that highly unlikely, since as I said the chances of success are nearly zero, and such a civilisation would need to find a new host in a relatively short period of time, astronomically speaking.

Mark of the Vampire
Mark of the Vampire (Photo credit: Wikipedia)

If a broadcast signal is very unlikely to find a receiver, how about a directional signal, maybe driven by a laser. The spread of a laser signal is much less than a broadcast signal, but the signal does spread. An advanced civilisation would still have to divert significant resources into sending the signal but it might be possible.

The civilisation would have an issue, though. If they wanted to get a signal to us and they used a ground based laser, their ground station would be in line with us once each local day, and our receiver would be in line with them once in every day too. Since it is unlikely that the day lengths would match, so the window for transmission would be short, even down to a minute or less.

Window of opportunity
Window of opportunity (Photo credit: GioPhotos)

The hypothetical aliens would most likely opt for an orbital laser. That could be pointed in our direction all the time, for every hour of every alien day, unless some local object got in the way. However we have a problem now. We would need to detect that a signal is coming from a point in space, in spite of all the extraneous noise that might mask it, and then we would need to concentrate our resources looking in that direction for a length of time. The hard part would probably be convincing ourselves that a signal is from LGM (little green men).

Littler Green Men
Littler Green Men (Photo credit: JD Hancock)

There’s an equation that purports to estimate the possible frequency of extraterrestrial civilisations, called the “Drake Equation”. It’s the sort of “equation” that gives mathematicians the heebie-jeebies, since it is derived from nothing and nothing is derivable from it. XKCD cruelly lampoons the equation, and while I don’t much like the sentiment expressed, I can understand why the Drake equation raises his ire – it is ad hoc, probabalistic, and presents as constants things which are fundamentally unknown. In other words, your guess is as good as mine, and both will fit comfortably in the Drake equation. I may return to the equation in a later post.

XKCD - the Drake Equation
The Drake equation as extended by XKCD

 

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