Drake's Equation

How many alien civilisations in our Milky Way?

Some scientists have suggested that the reason why we haven't heard from the ETs by now is because the number of alien civilisations in the Milky Way (and, by implications, the rest of the universe) is few and far between. Is this true?

Are there enough technological civilizations in our galaxy to communicate with?

There is a famous equation developed by Dr Frank D. Drake known, naturally enough, as Drake's Equation. This mathematical equation gives scientists an estimate on the number of civilizations there are likely to be in our galaxy (or the entire Universe if you like; however scientists prefer them to be close by for easier communication) at this moment in time.

The equation that determines the number of technically-advanced civilizations (i.e. the ones that can communicate with us) that have evolved on a planet with Earth-like conditions at this moment in time is given by:

N = R.fs.fm.fp.ne.fl.fi.ft.L

To work out roughly how many civilizations there are in our Milky Way, let us substitute a few figures into the above terms.

The factor R

The average rate of star formation over the lifetime of the galaxy

When we evaluate the age of the oldest stars—located in what are known as globular clusters strewn about the halo of our Milky Way galaxy—we are also determining an approximate age of the galaxy. Astronomers have estimated this age to be at least 18,000 million years. Therefore, given that there are roughly 400,000 million stars in the Milky Way, the average rate of star formation is:

R = 400,000 million / 18,000 million, or about 22 stars per year.

The factor fs

The fraction of stars in the Milky Way that are single and sun-like

Although scientists have argued that it might be possible to find intelligent, technological life around a solar system with more than one star, we shall assume life can only arise on a single star like our Sun. Therefore, astronomers estimate than the percentage of stars in the Milky Way that are single stars is about 25 percent. And another 25 percent of those stars are said to be sun-like.

fs = 0.25 x 0.25 = 0.0625

The factor fm

The fraction of single sun-like stars in the Milky Way that are metal rich

To estimate the number of stars likely to lead to the development of a technology for communicating with other civilizations, a single sun-like star should have a reasonable abundance of metals in its chemical composition. This means planets associated with these stars will almost certainly be rich with metals.

Although some sun-like stars can be richer in metals than others, we will assume virtually all single sun-like stars will have enough metals to help a fledging civilization develop a technology.

fm = 0.9

The factor fp

The fraction of stars with a planetary system

Planetary systems appear to be common throughout the Milky Way galaxy. But to be on the safe side, let us assume a little over half the stars develop a planetary system of their own, or:

fp = 0.6

NOTE: In the most recent data obtained from the Kepler probe, the probability of finding planets around other stars is now considered very high. Therefore, a figure of between 0.9 and 1 would be much closer to what is happening out there.

The factor ne

The average number of planets per star that have evolved a suitable ecosphere

Earth is our only fine example of a planet possessing a suitable ecosphere at this moment in time, so set:

ne = 1

The factor fl

The fraction of those planets that eventually lead to life

Dr Stanley Miller's famous experiment on the origin of life, a study of those meteorites containing organic substances that resemble the tarry oils found on Earth (i.e. Carbonaceous Chondrites), and the fossilised remains of animals and plants that appeared on Earth over the past 4,500 million years suggests there is good indication for life to arise very quickly. Hence let:

fl = 0.9

The factors fi and ft

The fraction of those planets that eventually lead to intelligent, technological life

Whenever there is a highly competitive, harsh and unforgiving environment for life to develop and grow, the propensity for intelligence will arise given enough time. On Earth, one type of intelligence has seen the development of creatures capable of affecting all other forms of intelligent life through its technology. Although this may suggest an inevitable trend on all other life-bearing worlds, the hundreds of millions of years it has taken for humans to evolve suggests the road to a technically-advanced society can be somewhat long and precarious. Of particular concern in this regard are those extraterrestrial threats of large asteroids or comets colliding with a life-bearing planet which could extinguish all forms of life. Consequently, some evolutionary biologists have given a conservative estimate for the product fi.ft to be about 0.02.

The factor L

The mean lifetime in years of technically-advanced civilizations

The factor L has been given great discussion by the scientists. This factor depends on how well a technically-advanced civilization has learned to live with itself, other lifeforms, and its technology. Let us define technology as the application of science to fashioning implements, practising manual arts and skills, and collecting materials. With only humans to go by, possibly the Industrial Revolution in England could be considered the beginnings of a truly technical society, so let L = 250 years. Of course, this highly conservative figure assumes that we and all other civilisations in the Milky Way would naturally snuff themselves out of existence after around 250 years of developing a technology. Something is telling us this is probably unlikely. But then again, with us as an exanple, who knows? As Professor Lawrence Krauss, a theoretical physicist with a keen interest in the SETI debate, concedes:

"If the Earth is any example, it is not clear that intelligent life survives for a long time. I mean the way that we're going it's not so clear that we're going to." (1)

Multiplying all the numbers

Multiplying all these numbers together gives us a rather dismal figure of n=3.34 or roughly three technical civilizations (maybe four if we want to be a little more optimistic) scattered somewhere in the galaxy. This means every year there are likely to be three or four technical civilizations (one of which has to be ourselves while we have not become extinct) scattered somewhere in the Milky Way. In other words, the closest one to us could be very far away.

The results really do speak for themselves. It would appear the number of civilizations in our galaxy is an absolute pittance and may well explain why we haven't heard from them. The chances of us communicating with ETs would have to be astonishingly small.

Improving the odds

Yet we must remember, the numbers we have entered in the equation are rough estimates. Furthermore, the factor L is probably the single biggest factor for determining whether plentiful alien civilisations exist, or very few.

Assuming all other estimates are fairly accurate, there are two ways to dramatically increase the factor L:

1. At a personal level

2. Build a spacecraft

However, we should make it clear that even if we fail to apply point 1 properly on our own planet and instead go for point 2 and later discover at least one advanced alien civilisation with the capability of reaching the stars as well, there is another factor we should add to this equation. Let us call it factor Z. Its value is either 0 or 1. Which value we take depends entirely on our attitude toward all living things, both here on Earth and on other planets, and what happens later when we meet up with an alien civilisation that lives on an Earth-like planet around another star system. To put it simply, if our attitude to life is one where we feel we can conquer and use up whatever "resources" we can find out there to help keep us alive (and/or possibly get rich) without any consideration of the recycling requirements as well as searching for alternative and less harmful solutions that do not interfere in the evolution of other life forms (which would otherwise result in an imbalance in the intricate web of life), then the factor Z will have to be zero within a very short spacing of time. In other words, we will not survive for much longer. Neither would we know precise how many alien civilisations actually do exist in the Milky Way. Why? It is because a slightly more advanced alien civilisation that feels threatened by our existence because of our belligerent behaviour and willingness to conquer other worlds can easily deal with a primitive and feeble-minded civilisation such as our own. A simple genetically-engineered virus targeted to exploit some weakness in our biology could ultimately see us become extinct in next to no time. Without putting a finer point on this, it would be a real dampener on your life if this should ever happen. So, if you want to guarantee your survival in this universe (barring any asteroid or comet threat to wipe out our planet), you need to shape up (or ship out). Indeed, learn to love one another (preferably starting at home) and solve the problems in the way it should be done. Show real curiosity. Be compassionate about those that have feelings. And think about your actions, which could possibly lead to negative feelings with your fellow human beings and other lifeforms. We must all do these things now. We have no choice. Because once we get out there and reach the stars, we have to show we have grown up and are practising genuinely the principle of love with all living things. Our existence in the universe depends on it. In fact, this becomes even more imperative when we are dealing with other intelligent creatures who have a technology.

Remember, it does not take much for anyone else to destroy our civilisation if they so choose. Nuclear weapons are a classic example. But for a slightly advanced alien civilisation, they really do not have to show their faces to us. It will be the perfect guerilla warfare tactic. No human defence system can ever deal with this situation. All it takes is a simple introduction of a deadly alien virus on our planet to target a particular weakness and we will disappear before we know what happened to us or precisely how many alien civilisations there are out there.

This is the reality of the universe with other advanced civilisations based on sound sociological and psychological principles.

Don't want to end up becoming extinct? No problems. You know what to do (2). If your attitude is one of great compassion and love to all living things and you make active efforts to preserve our planet and look after each other, then an encounter with any number of alien civilisations advanced enough to reach us through their own technology (or through our own) will reveal the answer on the true number of alien civilisations in this galaxy (and it is likely to be in phenomenal numbers). And at the same time we will understand that all these alien civilisations must have the same positive, curious and loving attitude to life in order for them to guarantee their own survival in this universe, especially among other star-faring alien civilisations (including the more advanced variety), barring any natural catastrophe, of course! So what attitude do you have for life on Earth?

If, what has been said here is true and alien civilisations do achieve the two main points mentioned above (i.e. show love and curiosity, and have the technology to visit the stars), it means the Milky Way should be literally teeming with intelligent and technological-advanced life.

Is there any evidence to support both approaches being taken by ETs? And have people already been observing them to give us an indication that both of these two approaches are taking place as we speak right now?