A Blog for the Curious and the Scientifically Perplexed

This is the story of a great journey that started with a great thought. One day in 1895 a boy looked into a mirror and wondered what the universe would look like if he could travel on a beam of light. That sixteen year old boy was Albert Einstein and that one thought started him on the road to discover his Theory of Relativity. The great man has been reinvented as Albert 2.0 to come back and blog about a journey through space on a beam of light and explain the science behind everything from atoms, blackholes to global warming. If you've just joined and want to start at the beginning use the index on the left. If you're bored try these links below just for fun.


Saturday, October 6, 2007

Are we Alone? Listening for extra-terrestrial life

“Is that the Earth straight ahead?”

That's the Earth, in all its glory. Only five seconds and the best part of a million miles to go.

“Pretty place, with all those bluey, greeny whitey bits. A bit small though.”

At this distance it certainly looks small. Amazingly no earthling has ever seen the Earth from this distance with their own eyes. The farthest humans have been is the moon which is only a quarter of a million miles away, just over a light second.

“We’ve been 3000 light years across space on this journey and human astronauts have only travelled one light second! That’s a bit pathetic isn’t it?”

Well, earthlings are only just starting to explore space. NASA is back talking about going to Mars which is at least a planet away.

“And how far is Mars?”

At its nearest a few light minutes.

“A few light minutes? And they’re still only talking about that? I guess it’ll be a while before humans make the return visit to our star.”

They have sent machines, or space probes as they call them, off into the outer solar system to Saturn and beyond. Remember we talked about voyager and the golden disc a while back?

“Not exactly Star Trek is it? Will humanity ever travel into space and meet aliens?”

We might but it is more likely they will visit us than the other way around.

“Why is that?”

Well, we have only just started wondering about life on other planets in the last hundred years – a mere blink of the eye in terms of the age of the universe. Humans only discovered the first planet around another star ten years ago. If there are other civilisations out there asking the same question as us, the chances are they are more advanced.

“I don’t see why?”

If there are lots of intelligent civilisations who know that planets exist around other stars and we have only just discovered this, then we must be the newest member of the galactic civilisations club. So it stands to reason that the other members have been in the club for longer and so will be more technologically advanced.

“Unless we are the only member of the club.”

True, but that is the real question - are we alone?

“How can we answer that question without just waiting for someone to visit.

We can try and listen for their signals. When we talked about this last time, I explained how radio and TV signals from earth can’t have travelled very far into the galaxy because we’ve haven’t been transmitting for that long. The signals from other planets, if they are more advanced and using radio waves for thousands of years, should have been travelling for far longer so could have spread out across the whole galaxy by now. This is what the organisation SETI, which stands for Search for Extra-Terrestrial Intelligence, does – listen for radio signals from space.

“Have they found anything yet?”

Not yet but there is a lot of space out there. They have been getting ordinary people to help by using their own computers, almost 3 million people are helping in the search.

“But if they have found nothing so far is there any point in keeping trying?”

Heavens above, what a question, of course. Scientists have tried to calculate the chances of there being other civilisations in our galaxy and it seems unlikely that we are completely on our own.

“How can they know that?”

One of the founders and now president of SETI, Dr. Frank Drake, came up with a way of came up with a way of caculating the chances of finding intelligent life in our galaxy by listening to radiowaves from space – The Drake Equation. To work it out you need to first answer seven questions. I’ll take you through a slightly simplified version of the Drake Equation and we can answer them together as they are tricky enough. First, we need to know how many stars there are in the galaxy. Any ideas?

“A hundred million?”

Oh, a lot more than that, perhaps a hundred billion or more. Now the next question is how many stars have planets around them. When Dr Drake thought up his equation in 1961 astronomers had no idea how to answer that question. With all the planets discovered in the last few years we now know planets are common so it might be as much as half of all stars.

“Just what I was about to say.”

The next question is how many planets are capable of supporting life, with a temperature that is not too hot or cold and an atmosphere. If there are lots of planets around these stars then the chances of one in the right zone goes up. So there might be one suitable planet around every one or two stars that have planets. So can you guess what’s the next thing we need to know?

“How often life starts on these planets?”

Exactly, well done. Even though it seems remarkable that life could start out of nothing, if it could start on earth then there is no reason that it couldn’t start anywhere else. So life might be very common, so common that some form of life might start whenever there is a suitable planet.

“But would it be intelligent life?”

Good question. On earth chimpanzees and dolphins undoubtedly have some form of intelligence. So if there are at least three intelligent species on earth then given enough time evolution should be able to create intelligent life anywhere. The sixth question is the chance that this intelligent life could build machines to send radio signals into space. This could be difficult for dolphins even if they evolved to be ten times smarter than humans because they only have flippers, so not every intelligent life form may be able to send radio waves or want to.

“How about 10% of intelligent life being able to send radio waves?”

Not a bad guess. Now the seventh and last question is how long an intelligent alien species would use radio waves for.

“Once they discover radio waves, why would they stop?”

They might blow themselves up in a war if they are like humans, or die from an asteroid hitting the planets like the dinosaurs. The other reason is that there are probably much better ways of sending signals across space that we haven’t even discovered yet. Imagine how advanced human civilisation might be in a thousand or a hundred thousand or even a millions years? A really advanced civilisation would probably have stopped using radio waves and TV-like signals thousands of years ago, in the same way that we’ve moved on from painting pictures on cave walls. They could be sending signals to us right now and we wouldn’t know because we aren’t advanced enough to know what to listen for.

“How long will humans be using radio waves for?”

We discovered them about a hundred years ago, but I can’t imagine we won’t have discovered something better than radio waves in another thousand years. So earth might be sending out radio waves for only 1000 years. For a planet that will exist in total for 10 billion years this means that there is only a one in a ten million chance of anyone listening in with a radio telescope of catching us at the right moment in our evolution. So that’s the last number we need - the number of years a civilisation sends radio signals into space.

“So what’s the answer? How many planets in the galaxy have intelligent life?”

At least one.

“That’s’ a daft answer, of course there’s at least one, the earth.”

Well you can put in your own numbers and calculate it yourself, but before you do have a wild guess.
When you are ready CLICK HERE.

p.s. If you are interested in helping SETI in the search for extra-terrestrial life please visit http://setiathome.berkeley.edu/

p.p.s If you are an extra-terrestrial life form please leave a message in the comment section.

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  1. Anonymous said...
    We came by in July 1947. You weren't exactly friendly. Kept our space ship and cut one of us up. We've decided to let humanity grow up a bit. We'll look in again in 2047.
    Rick said...
    Food for thought... the Drake equation calculates carbon-based life as we know it, and astrobiologists are starting to consider other chemical processes that may lead to different types of life forms.
    Lapa said...
    Very nice profile.
    TheAtheist said...
    Seriously? The Drake Mistake?

    Come on, mate - you're a fan of Albert Einstein, who wasn't a slouch in the brains department, yet you're using one of the worst pieces of pseudoscience ever on your front page.

    Poor old Fermi posited a question and Drake uses it to justify his vanity.

    The Drake equation can only ever be GIGO - garbage in, garbage out. Aside from the number of stars, everything is an assumption.

    The following are unknowns and therefore cannot be entered into an equation without giving a gibberish answer:

    What conditions are necessary for live to arise?

    Whether those conditions are then conducive to evolution, ie, would the planet support only single-celled organisms?

    Why would alien intelligence behave in ways that we do? Why would they build civilisations? We do so because it has been evolutionarily advantageous. That may well not apply on other planets.

    It is not possible to use any real figures in Drake's mistake and to do so may salve the ego a little, but it's not something I can imagine Einstein having any business with.
    albert2.0 said...
    To quote Stephen Hawking from a recent lecture in Washington...

    "Primitive life is very common and intelligent life is fairly rare. Some would say it has yet to occur on Earth."
    Ephraimite said...
    I did visit a couple of thousand years ago,and I even took on the terrestrial form to better understand the difficulties that humans endure in the flesh.I lived and grew and learned of man's weaknesses in the flesh.They were many.As I grew into adulthood I began to teach a better way to those that had ears to hear, and eyes to see truth.Shortly hereafter things took a turn for the worst for Me and my loyal followers, and mankind in general.I was persecuted, and critized by the scholars of "higher learning",and by your so called religious leaders (hippocrites). So much so, that they convinced the government of the day (who was indifferent to my circumstances) to allow them to kill me.They of course choose the most inhumane method of death, which was however endorsed by the government.So, I was crucified (nailed) on a wooden cross and hung there until cetain death occured.I endured this as part of my teaching which was prophesied long ago in the Old Testament teachings.After the death of my flesh body I was laid to rest in a stone tomb which everyone thought to be My final end.However, little did they know or much less understand, that I their Creator could not be held here by the death of the flesh body, because of my celestial body.
    I now await the correct season to which I will return (My Second Advent)and everyone will know and understand Who I Am,and who they are as well.Watch, watchmen watch.
    Ashvini said...
    I thank u Albert, for the joy u r bringing in reading the articles in this blog site.
    This is the best to date I have read on astronomy [which happens to be my pet subject]and it is so knowledgeable, witty, hilarious etc.
    I thank you from the bottom of my heart. I hope that many more Alberts come forward on other subjects to enliven our lives and ofcourse knowledge too.
    Ashvini from Bangalore India
    Ross said...
    I would advise that you add some error checking in the Drake calculator. It's allowing me to enter nonmeaningful percentages, like -25 and 23957023.
    Anonymous said...
    It would be absolutly amazing if it was found that we were the only life in the universe.
    Gurinder said...
    How arrogant of us to expect that ET should contact humans! If aliens are able to travel the universe easily, they have probably encountered many other intelligent species, far more advanced and evolved than us. There is probably nothing all that remarkable about us and they have already studied us in every way. We may not be all that special or intelligent, much as it flatters us to think so, and they want to leave us alone until we are sufficiently evolved. Humans don't want to "communicate" with insects and they may think of us as just insects.

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