Sky Matters: Whether we are alone in the Universe has exercised many great minds

The question as to whether we are alone in the Universe has exercised many great minds. It has spawned several impressive global experiments whose purpose is the Search for Extra-Terrestrial Intelligence (SETI) by listening for faint radio signals.

After almost 70 years of trying the search goes on, but so far nothing has been found.

Nevertheless, during the seven decades we have transformed our understanding of how planets form and discovered that planets are very common.

In fact, they’re likely to be much more common than stars, and there are a LOT of stars, numbering in the region of ten trillion trillion (give or take).

The magnitude of this number is so large that the prospect of our planet harbouring the only intelligent life in the universe is really hard to get your head around.

It would make us the rarest of the rare, the one-off of one-off’s, a habitat that has somehow gained a footing on a small rocky ball orbiting a star which appears remarkable for being unremarkable on a cosmic scale — unremarkable that is, except to us.

The Sun has been powering the evolution of life on Earth for about four billion years and will continue to do so for another four billion. Life on Earth has learned to make good use of this energy in incredibly clever ways, from plants which use the energy directly, to animals who take advantage of the plants.

It is hard to conceive that amongst the trillions of sun-like stars, accompanied by their orbiting planets, that some form of life hasn’t learned similarly clever lessons.

And so the SETI programmes continue to listen for the faint hiss of a radio signal whose origin is decidedly unnatural. For despite the apparent complexity of the Universe, stars and planets have only ever been found to emit relatively “simple” signals that show no underlying thought processes, no attempt to communicate, to share ideas or announce their existence. If the stakes weren’t so high, SETI would likely have ceased some time ago.

But the stakes could hardly be higher. It drives teams of researchers to develop ever-more sensitive techniques and to keep looking. It has been commented that if the oceans of the world represented all the available possibilities where life might exist, we have examined only a bathtub to date — in some ways, our search has only begun.

The importance of our Sun is visibly evident in March as new buds appear and green shoots begin to replace brown stalks.

We now know that a similar warming of the landscape is occurring billions of times across the Universe on different planets. We know the energy to power evolution is abundantly present. We don’t know if there is any evolution elsewhere to be powered.

Of course the universe may be teeming with life that is incapable of communicating beyond its own surroundings.

Indeed on Earth, we humans are the only species who have developed that capacity. And we have only reached it in the last 100 years as our radio and TV transmissions bleed out into the cosmos.

Alongside the efforts of the SETI folk we have others looking for signatures of life in the atmospheres of planets beyond our solar system, produced by molecules like methane that may come from living or decaying biological material.

In fact pretty much every molecule in the air around you has been generated by some interaction with living organisms, so if we find a molecule-rich atmosphere it will give us tentative evidence that life exists there.

On March 21 we will have the Spring Equinox, the date when night and day are of equal length across the globe.

It is a reminder that we all share this one planet. Our search for life elsewhere adds to this understanding and teaches us that sharing a planet is a rarity in our vast cosmos ... and a privilege to be protected.