Some Pysics Insights


The question is not "Why would we want to find evidence of extraterrestrial intelligence?";  for most of us the answer to that question is so obvious it's not worth asking.  If someone's talking to us, we'd like to know!

Rather, it's "Why do we think it's possible to find evidence of extraterrestrial intelligence?".  After all, if it's impossible on the face of it, then there's no point in doing it.

With current technology, we won't be able to detect any other civilization unless they're intentionally sending signals our way.  Random radio noise wouldn't be loud or coherent enough.  So, we won't find ET unless ET wants to be found.  Does it make sense to even bother to search in such a situation?

Would You Rather Ask, "What is SETI?"

The Search for Extra-Terrestrial Intelligence.   Check out these links if you are curious:

Planetary Society SETI Page
The SETI Institute

Now let's get back to the "why" question.

But First ... Does ET exist?

The only honest answer at this time is "We don't know".

Naively, one might think that any reasonable model of the cosmos would lead to the conclusion that it's teeming with life.  For, suppose otherwise ... suppose, in particular, that there's just one planet with intelligent life in the entire universe.  There are something like 1027 stars in the universe.  If just one has intelligent life, then we must conclude that such life is incredibly unlikely ... but it is obviously possible.   In other words, it's just barely possible, and it has happened, exactly once.  Intuition rebels.  The universe can't be so finely balanced as that; if it's possible at all, and there are 1027 stars, it seems like it must have happened many times.  The notion that it could have happened exactly once seems completely absurd.

Sadly, there are cosmological models which make the notion that life might have arisen exactly once in our cosmos seem far more reasonable.  In brief, suppose that, as Arthur Clarke put it many years ago, universes float like bubbles in the stream of time ... or in the Higgs field, or in a Superverse filled with perpetual inflation, or what have you.  Modern theories of cosmology include the notion that there are many, many universes; perhaps there are an infinite number.   The natural laws may be different in every universe.  If we assume for the moment that in most of these universes life is impossible, and that only in a relative few is the balance right for life to form, then we are led to a distressing possibility:  It may be that in most universes where life is possible, it is barely possible.  One consequence may be that, if we plot the percentage of all universes against the number of life-bearing planets in each one, we find that as we increase the number of life-bearing planets in each universe, the number of universes which contain so many living worlds decreases rapidly.  We don't know the shapes of any of the curves, but it seems quite plausible that, when one sums all the universes with various "life levels", one could find that most living worlds are in universes which contain just one life-bearing planet!

But again, we don't know.  We can imagine a universe in which life is common; we can imagine a "multiverse" in which lonely living planets in otherwise lifeless universes are the most likely scenario.   Speculation won't answer this.  The only way to tell what kind of universe we're in is to look for ET, and find out.

If ET Exists, Why Don't We Have Visitors?

Of course, many people think we do have visitors.  But if we assume there are no aliens in Area 51, and there was really nothing to "cover up" at Roswell, and we disallow the testimony of alien abductees, and ignore the opinions of those who think the Earth is hollow, and the Sun is a solid ball of ferrite, and the Sun revolves around the Earth ... then we're left wondering why we don't have visitors.

In this case the simple answer may be the correct one, and in simplest terms, it can be stated as: C.

Interstellar distances are large on a scale that's hard to grasp, and the speed of light is a crawl by comparison.  You can't just casually bop over to see what the neighbors are doing.

Current theory doesn't just fail to provide provide a mechanism for traveling faster than the speed of light.  It actively forbids both superluminal travel and communication (see, e.g., the CCentipede tale).  If current theory is correct, then interstellar travel is likely to remain forever either very difficult or impossible.  If we assume, reasonably, that the density of advanced civilizations is not very high in our galaxy, then we might not expect our nearest neighbors to be closer than a few hundred light years away.  That's a few hundred years of travel time, best case.  Furthermore, they don't even know we're here, because several hundred years ago we were emitting no radiation they could detect and everything we've emitted more recently hasn't gotten to them yet -- so why would they be visiting us?

What's worse, traveling close to the speed of light requires prodigious amounts of energy.  A traveler going close to C is enormously energetic, and that energy must come from someplace -- it's not free.

One can imagine ways around these problems (that don't violate current theory) but it's not obvious they could ever really be made to work.  When we combine that fact with the plausible assumption that there are, at most, one advanced civilization per several thousand stars, it's easy to believe that we have no visitors just because nobody happens to be visiting us.  If our nearest neighbors are 100 light years away, there might very well be 50,000 stars which are closer to them than we are; even if they're touring nearby stars they may just not have gotten around to coming by our way as yet.

Certainly the apparent lack of visitors is not any sort of evidence that ET doesn't exist.

So Why does ET Want to Talk To Us?

With all this said, let's just assume ET exists and hasn't chosen to (or can't) physically visit us.  Furthermore, ET is so far away that we can't hold a conversation.  Finally, using current technology, we can only detect signals from ET if they're beamed at us, so the only way we'll hear anything is if ET really has something to say to us.  Why would ET do that?   We'd need to assume ET is subject to some sort of overpowering urge to communicate, to think ET even might spend time beaming signals to other stars which are so far away they'll never be able to reply to those signals.  Does that make any sense?

Ask a different question.

Why does this web page exist?  It's a "send-only" medium -- there's no conversation involved.   I can't even tell if anyone's ever looked at it (unless I check the logs, of course).  Yet I'm writing it anyway, and sending my signal out into the Great Beyond of the Internet, to be received -- or not -- by strangers I will never meet.  And millions of other people are doing exactly the same thing.  Web pages are signals sent out into the darkness ... just like ET's signals sent into interstellar space.  Web pages aren't free (they cost time, if nothing else) and for most of us, they have no payback.

I don't have a good answer to the question of why there are so many web pages, but it's a fact that they are there.  And those web pages provide an "existence proof" of the kind of urge to communicate which could drive ET to beam radio signals at every star within range which was of the right sort to support life.

By listening for signals from other stars, we're really just trying to connect up to the interstellar Internet.

Page added 8/15/05