Author Topic: Loose Thoughts About Physical Reality  (Read 460 times)

Offline trdsf (OP)

Re: Loose Thoughts About Physical Reality
« Reply #30 on: July 06, 2017, 03:25:48 PM »
Even worse, THOSE quasars have the same distance on the other side from us.  And so to those.

When "they" say the universe is 13 billion years old, they only mean the part we can see.  It logically spreads further.

I'm not sure if there's a meaningful difference between something being 92 billion light-years away in a universe with a 13.8 billion light-year horizon, and that something just being in another universe.

Which kind of leads to the idea of the multiverse being really overlapping universes rather than parallel ones... ow again.
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"Confused? At a loss for what to do? Wow, sounds like you're human. Good luck." -- Welcome to Night Vale

Re: Loose Thoughts About Physical Reality
« Reply #31 on: July 06, 2017, 05:40:33 PM »
I'm not sure if there's a meaningful difference between something being 92 billion light-years away in a universe with a 13.8 billion light-year horizon, and that something just being in another universe.

Which kind of leads to the idea of the multiverse being really overlapping universes rather than parallel ones... ow again.
That would be the case for the level one multiverse, I think, since each point in space-time has its own observable bubble (a Hubble Bubble) around it. For the other kinds of multiverse, though, there may be more definite separation, I guess.
God Not Found
"I am an expert of electricity. My father occupied the chair of applied electricity at the state prison."
W. C. Fields

Offline trdsf (OP)

Re: Loose Thoughts About Physical Reality
« Reply #32 on: July 11, 2017, 01:08:36 AM »
The main problem with the Fermi Paradox is that it assumes an eternal, steady-state universe in which time is ultimately not a consideration and civilizations can be arbitrarily old. In the universe we live in that is closed in time at one end, there are some good -- not necessarily convincing or definitive, merely in accord with our current understanding -- reasons why we shouldn’t be surprised no one’s come calling yet.

The first is, as Douglas Adams said, space is big.  Really big.

The maximum range at which any ETI might be able to look at our world and think there’s something sentient going on is about 200 lightyears. That’s because about 200 years ago, we started pumping pollutants into our atmosphere as the Industrial Revolution started up. Now, first of all, there needs to be another intelligent life form within that sphere that has sufficient technology not only to detect the Earth from underneath the much larger optical/gravitational signals of the four big outer worlds, but also can resolve it enough to permit spectrographic analysis of our atmosphere. Detecting oxygen is about as dead a giveaway as there is for life, because so far as we can tell, oxygen atmospheres are unstable and something needs to continually replenish the oxygen supply and there aren’t any good candidate non-living physical systems that can do that.

Finding oxygen only says life, though, and doesn’t imply there has to be anything more complicated than algae. The industrial byproducts -- air pollution -- are what indicate the presence of a technological civilization. Fundamentally, gunk in the air implies intelligence. Not necessarily wisdom, but intelligence.

So, worst case, let’s posit there’s one other world at the 200LY marker that just discovered there might be someone here. How abundant does intelligent life have to be to make that more likely than not?

Well, the volume of the Milky Way galaxy is about 3.3×1061 cubic meters. The volume of our 200 light year sphere is around 2.8×1055 cubic meters -- not quite one-one millionth the volume of our home galaxy, so we would expect a bit over a million sentient species in the galaxy to have a better than 50% chance of having one only 200LY away. I’m leaving out some refinements for now, like uninhabitable areas towards the galactic core, but it’ll do within an order of magnitude, and I’ll come back to those later.

We’ll take an average of 250 billion stars for the total in the galaxy, since the range is 100-400 billion -- and again, I’m not going to get into the details of which stars theoretically can and cannot host life-bearing planets, this is all back-of-the-envelope, order-of-magnitude stuff. Around one million sentient life forms spread among around 250 billion stars is around one per 250,000 stars -- and as it turns out, there are known to be some 260,000 stars within a 250 light year radius of Earth. So we’re in the right ballpark as far as the numbers go.

Now, that count of stars in our galaxy is all stars, not just the F, G, K and M stars that are long-lived enough to permit the slow process of biological evolution to unfold. And I am strongly skeptical of the ability of M-class stars -- red dwarfs -- to host intelligent life, because these are worlds that will both be very close and rapidly become tidally locked and therefore not have great variability in weather over the course of their very short years. And M-class stars make up 80% of all stars in the galaxy. F, G and K stars make up only 13.5% of the stars in the galaxy, and that cuts our number of available stars from 250 billion to just shy of 34 billion. And of those, the current estimates are that of those 34 billion roughly sun-like stars, there are 2-3 billion with planets in habitable zones -- call it 2.5 billion, or 1% of the total stars in the galaxy.

Now, we still need those million civilizations to get one near enough, volumetrically. But now they need to be not one in every 250,000 stars, but one in every 2,500 habitable stars. And that tallies close enough to 1% of all the stars within our detectability radius, since we know there are 260,000 within 250LY, we're actually doing much better than just staying within an order of magnitude.  We calculated that we need 2,500 within 200LY radius, we know there are 2,600 within 250LY radius, and that's much closer than an order up (25,000) or down (250).

So now we can dispense with part of Fermi’s objection: we are only just now at the very beginning of entering an era in which, statistically, we can expect to have been detected only and not yet replied to, and that’s if intelligent life is common enough that there are a million ETIs in this galaxy. So we should not be surprised that we haven’t heard from anyone yet, and the Fermi Paradox fails spatially.

And for the record, while I’m bullish on ETIs in our galaxy, I’m not bullish to the tune of a million. I always seem to come up with 5-10 total when I plug my numbers into the Drake Equation. And that means on average the nearest one would be a long, long way away. I think life is easy, complex life is tricky but do-able, and intelligent life is even trickier, but obviously still do-able.

I suggest that the Fermi Paradox also fails temporally.

It’s pretty clear that complex life could not develop in the earliest days of the universe, since the only elements available in any quantity were hydrogen and helium, and vanishingly small traces of anything bigger. Isolated individual stars going supernova won’t turn the trick either -- you need galaxy-scale masses so that the heavier elements can collect and condense over time, and it takes a long time to collect enough to build metal-rich stellar systems.

I don’t say that it’s necessarily probable, but I think that it’s possible that we’re entering the first epoch of the universe in which complex life can have evolved all the way to intelligence, simply because you need a few generations of exploding stars to enrich the interstellar medium with heavy elements before you can even start a potentially life-bearing stellar system, much less start the process of biological evolution. So several billion years had to pass before things could even get started, and then a few billion years more to just barely get to the point where we can look up and go, “Hey, where is everyone?”

It’s possible that a species might be millions of years more advanced than we, but I think it’s highly unlikely in terms of both stellar and biological evolution that there would be anything out there billions of years more advanced. And given the distances involved, the expense in both materials and sentients, and the speed limit of light, that’s the kind of time frames we’re talking about to fully explore and/or colonize a galaxy. In the steady-state universe -- which was still a plausible theory with the evidence at hand when Fermi proposed his paradox -- you have the time. In a Big Bang universe, you don’t. So, no paradox temporally either -- we haven’t seen anyone yet because there hasn’t been the time for anyone to randomly stumble across us.

Lastly, I think it fails from sheer perspective. First of all, to the question of “Where is everyone?”, it’s perfectly legitimate to answer, “I don’t know!” And not only that, it’s appropriate to counter, “Why should they come here in the first place?” As indicated above, no one outside 200 light years can know we’re here (and the radius was less than 150LY in Fermi’s day) -- and if you want to go by our radio bubble, it’s barely 100LY today. Fermi’s assumption that they should come to Earth to see us is nothing more than latter-day geocentrism, the assumption that we’re special somehow that the rest of the galaxy should come to us because we’re the Earth.

And there’s no reason to think that. At least half the galaxy can’t even see our star, and of the remainder that can, they have no particular reason to think we’re anything special. We’re just a catalog number, a boring little yellow dwarf that maybe they can devote a little telescope time to some day, but there’s no hurry.

And when they do, even if they can detect the presence of the Earth, even if they can resolve it just enough to do an analysis of our atmosphere -- all that will tell the vast majority of them is that at least some sort of microbe that excretes oxygen exists here.

I’m all for extraterrestrial life, but even I would question sending a probe hundreds or thousands of light-years to look at pond scum. You save those for the big finds, because of the extreme times and resources involved to get even a small ship across interstellar distances. There’s no reason to assume that ETIs have unlimited resources to fling out probes -- much less staffed survey ships -- to every little speck of light they see.

tl;dr: “Where is everyone?” “Who knows?” :D
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"Confused? At a loss for what to do? Wow, sounds like you're human. Good luck." -- Welcome to Night Vale

Offline Cavebear

Re: Loose Thoughts About Physical Reality
« Reply #33 on: July 11, 2017, 04:55:22 AM »
The easiest answer to "where is everyone" might just be that long-distance inter-stellar travel is just impossible for intelligent life.  Lack of speed, no hibernation works, cosmic rays are unstoppable, etc.

I don't especially like the idea that no problem is unsolvable, but it might be the case.

To get more esoteric, we might be the first.  Or only.  Or it could be that every intelligent species causes an individual universe around itself by existing.

Do I think that?  No, not really, but it's possible.  And maybe we don't want to meet a space-faring species.  Our history suggests that less-advanced cultures don't do very well when confronted by more advanced ones.
Atheist born, atheist bred.  And when I die, atheist dead

Offline Baruch

Re: Loose Thoughts About Physical Reality
« Reply #34 on: July 11, 2017, 07:25:13 AM »
"The easiest answer to "where is everyone" might just be that long-distance inter-stellar travel is just impossible for intelligent life."

Thank goodness we are unintelligent life!  The possibilities are endless for us ;-)
שלום

Re: Loose Thoughts About Physical Reality
« Reply #35 on: July 11, 2017, 07:47:50 AM »
I tend to see in the x-rated portion of the spectrum.
We 'new atheists' have a reputation for being militant, but make no mistake  we didn't start this war. If you want to place blame put it on the the religious zealots who have been poisoning the minds of the  young for a long long time."
PZ Myers

Offline Cavebear

Re: Loose Thoughts About Physical Reality
« Reply #36 on: July 11, 2017, 08:32:28 AM »
I tend to see in the x-rated portion of the spectrum.
Whatever your um "spectrum" is, it is yours to enjoy. 
Atheist born, atheist bred.  And when I die, atheist dead

Offline Baruch

Re: Loose Thoughts About Physical Reality
« Reply #37 on: July 11, 2017, 01:11:40 PM »
I tend to see in the x-rated portion of the spectrum.

But "The Man With The X-Ray Eyes" ... a 1950s B movie ... the protagonist goes insane.  Not enough to just see beneath people's clothing.  He starts seeing everyone as skeletons!
« Last Edit: July 12, 2017, 02:48:44 AM by Baruch »
שלום

Re: Loose Thoughts About Physical Reality
« Reply #38 on: July 11, 2017, 05:13:07 PM »
In cosmic terms, the universe has just begun. We are living at the dawn of time, with hundreds of billions of years to go before things get completely unsuitable for life. We may well be the first of our kind in our Hubble bubble. But looking is fun, and so why not?
God Not Found
"I am an expert of electricity. My father occupied the chair of applied electricity at the state prison."
W. C. Fields

Offline trdsf (OP)

Re: Loose Thoughts About Physical Reality
« Reply #39 on: July 11, 2017, 11:17:26 PM »
The easiest answer to "where is everyone" might just be that long-distance inter-stellar travel is just impossible for intelligent life.  Lack of speed, no hibernation works, cosmic rays are unstoppable, etc.

I don't especially like the idea that no problem is unsolvable, but it might be the case.

To get more esoteric, we might be the first.  Or only.  Or it could be that every intelligent species causes an individual universe around itself by existing.

Do I think that?  No, not really, but it's possible.  And maybe we don't want to meet a space-faring species.  Our history suggests that less-advanced cultures don't do very well when confronted by more advanced ones.
Well, sure.  Someone has to be first.  It could as reasonably be us as anyone else.  Of course, there's just no knowing at this point in time.  By the principle of mediocrity, we assume that on average we are not, but we could be.

On the other hand, it's unlikely we're a latecomer to the party.  If there were a millions-year-old species in the universe, we should have detected it by now, even given the half-assed way we've gone about SETI -- and by half-assed, I mean in terms of governmental support, not in terms of the science.
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"Confused? At a loss for what to do? Wow, sounds like you're human. Good luck." -- Welcome to Night Vale

Offline Cavebear

Re: Loose Thoughts About Physical Reality
« Reply #40 on: July 14, 2017, 06:28:36 AM »
Well, sure.  Someone has to be first.  It could as reasonably be us as anyone else.  Of course, there's just no knowing at this point in time.  By the principle of mediocrity, we assume that on average we are not, but we could be.

On the other hand, it's unlikely we're a latecomer to the party.  If there were a millions-year-old species in the universe, we should have detected it by now, even given the half-assed way we've gone about SETI -- and by half-assed, I mean in terms of governmental support, not in terms of the science.

Well, as mentioned elsewhere here, signals seem to deteriorate faster than we thought.  Our original TV signals have spread out 60-70 light years, but apparently they are merely static after a few stars away.
Atheist born, atheist bred.  And when I die, atheist dead

Offline trdsf (OP)

Re: Loose Thoughts About Physical Reality
« Reply #41 on: July 14, 2017, 10:54:07 AM »
Well, as mentioned elsewhere here, signals seem to deteriorate faster than we thought.  Our original TV signals have spread out 60-70 light years, but apparently they are merely static after a few stars away.
Oh, definitely.  The limit for direct detection of our radio and TV signals appears to be Proxima Centauri.  But a deliberate broadcast is another matter entirely.  Using the Arecibo dish as a transmitter rather than as a receiver, we could be 'heard' clear to the center of the Milky Way.  Radio detection will probably be of species *wanting* to be heard, barring discovery of any refining technique that would allow picking up such fantastically weak signals and separating them from the other sources of radio noise.
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"Confused? At a loss for what to do? Wow, sounds like you're human. Good luck." -- Welcome to Night Vale

Offline Cavebear

Re: Loose Thoughts About Physical Reality
« Reply #42 on: July 14, 2017, 01:53:25 PM »
Oh, definitely.  The limit for direct detection of our radio and TV signals appears to be Proxima Centauri.  But a deliberate broadcast is another matter entirely.  Using the Arecibo dish as a transmitter rather than as a receiver, we could be 'heard' clear to the center of the Milky Way.  Radio detection will probably be of species *wanting* to be heard, barring discovery of any refining technique that would allow picking up such fantastically weak signals and separating them from the other sources of radio noise.

The most exciting AND scariest moment of my life would be the reception of a signal of a series of prime numbers (or anything equally unnatural) not created by humans.  I probably would live to see it, but I suspect some humans will.  What will happen then? 

Will it be Nightfall, or Utopia?  Alpha or Omega?
Atheist born, atheist bred.  And when I die, atheist dead

Offline trdsf (OP)

Re: Loose Thoughts About Physical Reality
« Reply #43 on: July 14, 2017, 04:13:03 PM »
The most exciting AND scariest moment of my life would be the reception of a signal of a series of prime numbers (or anything equally unnatural) not created by humans.  I probably would live to see it, but I suspect some humans will.  What will happen then? 

Will it be Nightfall, or Utopia?  Alpha or Omega?
I can't think of a better attention-getter than a sequence of primes; that's what you send if you want to be heard.

I can imagine a fear reaction to the definite discovery of an alien signal.  I would be overjoyed, personally.  I think I would be, anyway.
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"Confused? At a loss for what to do? Wow, sounds like you're human. Good luck." -- Welcome to Night Vale

Offline Cavebear

Re: Loose Thoughts About Physical Reality
« Reply #44 on: July 14, 2017, 04:29:34 PM »
I can't think of a better attention-getter than a sequence of primes; that's what you send if you want to be heard.

I can imagine a fear reaction to the definite discovery of an alien signal.  I would be overjoyed, personally.  I think I would be, anyway.

Well, in a sense, I suppose we might as well be thrilled if we contacted an alien intelligence.  We would have much choice if detected.

I can imagine the greatest human debate of all time if we received a signal.  Respond or not.  But I know the answer.  Someone would respond.

Then we would wait a few generations to find out if we are the Incans or the Europeans.

If it is beneficent, great.  If not, we are out of luck.  There wouldn't be any equivalence.  If they come here, we're behind.
Atheist born, atheist bred.  And when I die, atheist dead