Friday, May 18, 2007

Family of Science

I won't make a habit of this. But I thought posting this here would give the reader some sense of the environment that leads a young man to grow up and start Blog of Science!
For reasons unclear to me, my family has chosen to comment on my recent post "Not the end of the world" elsewhere, rather than on Blog of Science, so I have reproduced our discussion here. GML is my father, KAL my mother and JAL my brother. The following messages are in approximately chronological order:

The great physicist Enrico Fermi pointed out that interstellar travel is not very difficult for a technologically advanced and rich civilization, as long as it is designed for travel times of decades or centuries (or longer if a big colony is sent in a "generation ship". Each new colony would then grow and develop for some centuries, even a millennium, and then send out new ships (first to scout and then to colonize), and that this process would spread a civilization about our galaxy in a fairly short time, astronomically speaking, perhaps a few million years. Surely, the idea goes, at least one species somewhere would do this. This led to his famous question, "Where is everyone?" Many answers have been suggested, but the relevant one here is self-destruction, probably not by a physics experiment gone wrong, but by war within the species.
Our species has been said to need a "Moral Equivalent of War" to give us some outlet for our natural aggressive and us-them tendencies. This MEOW idea appeals to me, but I am not clear what it would be.
-GML

Dad, correct me if I'm wrong, but it was my impression that ETs wouldn't need to travel between stars for us to notice them. I thought even the level of radio noise that we currently produce would be plenty for us to notice if anyone were producing it within a few zillion light years. So the fact that we haven't heard anything (despite SETI and other projects looking for non-random radio signals) suggests not just that no one out there is traveling, but that no one out there is using radio waves, i.e., is technically advanced at all. Is that not right?
-JAL


There are a lot of assumptions we are making here.
Of which these are a few:
1. We are assuming that an advanced civilization uses radio waves to
communicate. Why do we assume this? We think we are advanced, and we
use radio waves. Perhaps radio is grossly inferior to something else we
ain't thought of yet, so nobody uses it.
2. They don't care if we hear them or not. Why do we assume this? We
don't worry about ETs detecting us, so we think they don't care if they
are detectable or not. Perhaps for one reason or another, many
civilizations consider it unwise or undesirable to broadcast their
presence.
3. We assume that if they are out there broadcasting radio, we would
pick up the signal. I don't know how far off we could pick up
broadcasts from a planet transmitting like Earth, unless we
specifically targeted that point in space, but I assume it is a
relatively small section of the galaxy.
4. We assume that if we picked up their signal, we would recognize it
as nonrandom. Given that we have no idea what form life on other
planets would take, it seems hubristic to assume that we would
recognize their transmissions as a sign of intelligent life.
5. We assume that if they picked up our signals, they would then
continue behaving in a way that would allow us to detect them. Imagine
there are technologically advanced aliens 100 light years away. They
detect rapid environmental change on earth, infer a rapidly developing
early technological civilization that behaves rather voraciously. Until
they know more, do they want the aliens (us) to know they are there?
The overarching point is that we know too little to know anything
except that we don't know. If we assume we are looking for ourselves,
which is what we often assume, we are wrong. The aliens are not going
to be biologically, psychologically or technologically familiar. they
are not going to live in a niche that would be amenable to us, and they
are not going to develop all the same technologies or develop them in
the same order. They are not going to have the same weaknesses and
strengths. They are not going to be in the same phase of develoopment,
or a similar one, to where we are. They are not necessarily going to
match our current definitions of either intelligence or life. It is fun
to speculate about and make up hypotheses, but we don't know enough to
draw any conclusions or moral lessons from. We know that either there
is no one out there, or that they are undetectable given our current
technology, or for one reason or another we have failed to detect them,
or have failed to notice detecting them. Everything else is SciFi.
-DAL

There is no reason why alien "life" should be carbon-based, or have discrete "bodies," or use the same senses we do (light, sound), or be on the same size scale as we - they might be miles across or microscopic or made up of filaments - or need the same amount of ambient radiation, heat, pressure, or environmental stability. There need not even be "individuals" with separate lives and separate mortalities. Probably some relatively fluid medium is needed - it would be hard to imagine solid rock being able to assume the complexity necessary for communication and reproduction. Otherwise I think that most human thought about the topic uses way too many chauvinistic assumptions. Long, thin necks and three-fingered hands, indeed!
-KAL

Interesting point. There are several factors to consider. The radio-based SETI and similar programs (mostly piggy-backing onto other equipment since Senator Proxmire made fun of it and got the U.S.Gov't to make it illegal to spend gov't money for it) make various reasonable (but not necessarily correct) assumptions about what frequencies would be used, as most free of background noise, etc., but at moderate interstellar distances such signals would be very hard to sort out, anyway. Also, higher-tech systems than radio (tachyons, gravity waves, links through space warps, etc.??) could be used, so lack of radio broadcasts does not mean lack of high technology. Another thought is that any sensible advanced species would carefully refrain from broadcasting its location, for fear of hostiles killing off possible competitors. No-one really knows, but the pay-off could be so great, technically and intellectually, that it seems worthwhile to put a little money into listening for interesting patterns; even if we do not find ETs, we may hear some natural phenomena worth knowing about. This has already happened, as when the pulsars (at first jokingly termed LGM for Little Green Men) were discovered.
-GML

Dan is quite correct in all his points, except perhaps in regard to our ability to recognize non-randomness. This is based on mathematics, mainly, not on biology or (I hope) human psychology. I certainly think that mathematics is universal; though I have no non-human examples as evidence. I believe that in some sense we discover mathematics, and do not just invent it.
-GML

Once mathematics is applied to trying to recognize patterns in real data, it becomes science, and all the limitations that come with science apply. We have to look at a particular set of time scales on a particular set of frequencies for a deviation from some mathematically defined but psychologically chosen null hypothesis. And all that means we don't really know if we could detect an alien deviation from random.
Regarding mom's point, it is very true, there is no reason to assume life on other planets would be carbon based. I wouldn't dismiss some sort of solid state lifeform though. Silicon can do amazing things.
-DAL

How about my idea that "life" elsewhere may accept very different conditions re solid/not solid "body" (or no actual body at all), tolerance/requirements for temperature conditions or radiation exposure, apparent passage of time per actual time passage, inevitability of mortality, use of other senses than sight/hearing, etc? Perhaps we haven't heard from anyone because we are actually very atypical in our characteristics and wouldn't think of the more common communication modalities. Or maybe no one else is out there and we are truly unique. Sometimes I think we exist only because the universe requires at least one set of observers in order for it to exist.
-KAL

Very true, that any collisions that CERN will make have happened, more powerfully, many times out in space, with no-one to register and measure them.
The Big BAng, from what I read, supposedly did not create any mass-energy, hard as that is to believe. The idea is that the expansion of the universe is, in proper physical book-keeping, measured in negative units, while the mass-energy is in positive units, and that these just cancel each other out. As you note that Stephen said, "on a minute scale the universe is a froth of energymass popping in and out of existence, but that these things were usually so small and numerous they mostly canceled each other out, leaving the energymass in the universe very close to
constant." Larger sized quantum fluctuations are shorter-lived than smaller ones, and if the universe is thought of as a nearly-zero mass virtual particle, it can last a very long time. Mass-energy versus time is one of those complementary trade-offs found in quantum physics, such as (knowledge of?) a particle's momentum vs. (knowledge of?) its position.
-GML

So we can get de novo mass-energy as long as we are willing to accept an equal amount of de novo space-time with it?
-DAL

Yes, in a sense, we can get more mass-energy along with more space-time, but only in a new universe, I gather. A prominent current theory is that black holes create new baby big bangs which then expand as full fledged universes; if the characteristics of a given universe leads to lots of black holes, that kind of universe will end up with lots of descendant universes with similar (but not identical) properties, leading to universes with successful characteristics (physical constants, etc.) becoming more numerous and predominating, in a Darwinian fitness paradigm. This theory is supposedly testable by figuring out what set of physical constants, etc., should be most successful in making black holes of the right sorts, and seeing how well this matches our universe.
-GML

But Darwinian evolution requires:
1. Mutations leading to variation
2. Heritability of that variation
3. Fitness differentials based on the heritable mutations
With regard to black holes as baby universes, we have no reason to assume 1 or 2, only that if 1 and 2 were to be true, that 3 could be true.
Also, your last comment implied that in order to be stable, a big bang event would have to result in something that in some strange sort of reckoning had zero mass. Black holes are not known for having zero mass.
There also seems to be the difficulty that black holes are not closed systems. Mass can go in and through quantum variation of location, evaporate off. Universes on the other hand are generally thought to be closed.
-DAL

3 comments:

Stephen said...

Three quick things to consider regarding the existence of extraterrestrials:

The closest hypothetically habitable extrasolar planet has been recently discovered, at about 20 light years from here. Gravity would be about twice as strong as on Earth, and it orbits its star once every 13 Earth-days.

http://news.bbc.co.uk/2/hi/science/nature/6589157.stm



Second, ponder the following:

http://kokogiak.com/solarsystembodieslargerthan200miles.html

Note that the object "Eris" is a bit bigger than Pluto, thereby forcing us to either have 8 or 10 official planets in out solar system. Also note how big our moon is.


Third, evidence of one really big gopher:

http://antwrp.gsfc.nasa.gov/apod/astropix.html
http://antwrp.gsfc.nasa.gov/apod/image/0705/marshole_hirise_big.jpg

Stephen said...

The link in the previous post may have been cut off at the end
http://antwrp.gsfc.nasa.gov/
apod/image/0705/marshole_hirise_big.jpg

the alternative link was to the Astronomy Picture of the Day, the day in question was May 28, 2007.

jls said...

As our communications technology improves and we switch from simple modulations like AM, FM and QAM to things like DSSS and OFDM, the radio spectrum of our civilization looks more and more like white noise. In a hundred years or so, I would not expect to see anything that looked remotely like a carrier wave between DC and light.

This gets more convincing if you're looking at the world from a long way away. We are already seeing a shift from highly powerful single transmitters (say, that AM radio transmitter kicking out a megawatt on a few hundred kHz, one per country) to non-synchronized repeaters (say, that FM network at 100 MHz where each transmitter only reaches a few dozen miles). The ranges on the surface are limited because of the curvature of the earth, so the frequencies are reused outside of line of sight. What this looks like from space is noise as all the transmitters interfere with each other- and not in a predictable way, since their master oscillators all drift at different rates.

Then there's the ongoing shift from broadcast (which necessarily uses a small number of very powerful transmitters) to unicast media like cellphones; there isn't the slightest chance you could even tell there was a cellphone network on the ground from space, since the frequencies are reused on a radius of less than 25 km; from a lightyear away picking out a single base station would require an unfeasibly large aperture (which would be no good for a sky search unless you had a ridiculously long time to perform it).

And then there's the modulation issue; while GSM uses GMSK which can be relatively easily found with an untargetted search, UMTS and CDMA use spread spectrum, which is to say, a modulation based on a known pseudorandom number sequence; if you don't know the PN sequence, you have absolutely no chance of figuring out there's even a signal there without a damn strong hint (like a known pilot tone).

This gets even worse with OFDM, where the spectrum is intentionally as similar to a block of white noise as possible (after all, the more similar a signal is to white noise, the more effectively you are using the spectrum).

Try computing the power spectrum for an uncompressed text file a couple hundred kbytes long, and then again for a bzip2 compressed version of the same file.

Therefore the absence of alien signals is quite possibly just because they're a century more advanced than us, or a century less advanced (and thus unable to make strong enough signals to pick up with our primitive VLA or whatever).

Let's say it took us five billion years to evolve (close enough, right?) And it took a few billion years for the stellar nursery our Sun came from to acquire enough "metals" (astrophysics term) to make a star with a dirty enough composition to make complex chemistry. (Let's assume chemistry is a prerequisite for intelligent life.) Therefore the window of possibility for the age of neighbouring civilizations is a few billion years wide.

Two hundred years in a few billion years is not a big window of detectability, but that's all it would take to make them undetectable unless they're actually *trying* (and spending a respectable fraction of their planet's resources on terawatt radio transmitters) to be found.