Cosmic Conundrum [Brief essay on multiple universes and the Anthropic Principle]

Time ^ | Monday, November 22, 2004 | Michael D. Lemonick; J. Madeleine Nash

[snarks_when_bored]

Cosmic Conundrum

The universe seems uncannily well suited to the existence of life. Could that really be an accident?

[snip]

[snarks_when_bored]

 

Because I don't know whether excerpts from "Time" magazine are permitted, I'm providing only the essay's title and teaser.

The Anthropic Principle is controversial. For a negative reaction to the "Time" essay, see, for example, Aliens' answer to the anthropic principle.

 

[muawiyah]

Ah, yes, it's all done with smoke and mirrors.

[Rudder]

The universe seems uncannily well suited to the existence of life. Could that really be an accident?

The sun is well-suited to emit light and heat. Could that really be an accident?

Talk about begging the question...

[snarks_when_bored]

I've just done a few (very rough) calculations aimed at showing just how rare life is in our immediate cosmic neighborhood. Wherever '=' occurs below, just consider it to mean 'roughly equal to'. Details of the calculations are available upon request.

As far as we know right now, life in our immediate cosmic neighborhood exists only on a strip of the Earth's surface a few miles thick. Let's be generous and assume this strip to be 200 miles thick. Let BS—BioSphere— stand for the volume (in cubic miles) of this strip. Then

BS = 156,861,815,589 cubic miles

Now, aside from our Sun, the next nearest star to us, Proxima Centauri, is about 5 light years away (roughly 6 trillion miles). Let PC stand for the volume (in cubic miles) of the sphere of space centered on the Earth with radius 5 light years. Then

PC = 1.131 x 10⁴¹ cubic miles

The ratio of BS to PC gives the relative volume of space occupied by life in a sphere of radius 5 light years centered on the Earth:

BS / PC = 1.4 x 10^-30

or

BS / PC = .000000000000000000000000000000014

To say this in words, life occupies no more than about

14 billionths of a trillionth of a trillionth

of the spatial volume in a sphere of radius 5 light years centered on the Earth.

And, of course, when we take into account the fact that a sphere of radius 5 light years contains essentially no spatial volume at all when compared to the spatial volume of the entire visible cosmos (and even less when compared to the spatial volume of our entire inflationary bubble), we begin to get an inkling of just how exiguous life appears to be within the vast scheme of things.

From this point of view, it does seem a bit odd to say that "[t]he universe seems uncannily well suited to the existence of life". If it were so well suited to life, one would think that life would occupy much more of it. Energy is ubiquitous in the universe, life appears to be at the other extreme (as far as we now know).

---

As a snide aside, let me point out that, using the ordinary acceptations of the acronyms BS and PC, the ratio of BS to PC seems to be pretty nearly 1. But I'll defer a more detailed examination of that ratio to another day.

[snarks_when_bored]

Correction to previous post:

1 light year is approximately 6 trillion miles, so 5 light years is approximately 30 trillion miles.

Hence the sentence

Now, aside from our Sun, the next nearest star to us, Proxima Centauri, is about 5 light years away (roughly 6 trillion miles).

should read

Now, aside from our Sun, the next nearest star to us, Proxima Centauri, is about 5 light years away (roughly 30 trillion miles).

[JustDoItAlways]

good number crunching snarks.

But you stopped half-way.

Take your extremely low ratio and extend it across the universe and you end up with lots and lots of places that have life.

But since we are never going to be able to travel to the stars, it is meaningless because we will never ever meet any of that other life.

[snarks_when_bored]

And for anyone who's actually reading this stuff, I used 30 trillion in my calculations, not 6 trillion; the '6 trillion' was a writing error only.

[snarks_when_bored]

Well, somebody is reading this stuff!

I find myself in the camp that holds that even low-level, microbial life is pretty rare, while high-level, intelligent life is incredibly rare (I think it's quite possible that Earth holds the only instances in the entire Milky Way galaxy). But I wouldn't care to dispute heatedly with anybody who thinks otherwise, because we're still a ways from having enough information to draw sound conclusions on the question.

On the star travel question, I suspect that within the next few hundred years—provided something really awful doesn't happen—we're going to launch a probe towards Proxima Centauri. It'll be a long-term project, but perhaps we'll find some things of interest. Of course, that's assuming that we don't just innundate our local neighborhood with von Neumann probes, which I suppose could happen.

[snarks_when_bored]

A correction to my post #4. I used too large a value for the radius of the Earth, and hence my estimate of the volume of a 200-mile-deep strip of the Earth's surface was too large (I hate it when that happens!).

Using the roughly correct value of 3963 miles for the radius of the Earth, we have

BS = 37,513,386,749 cubic miles (new, smaller value)

PC = 1.131 x 10⁴¹ cubic miles (no change from earlier post)

and so

BS / PC = 3.32 x 10^-31 (new, smaller value)

or

BS / PC = .00000000000000000000000000000000332

Hence life occupies no more than

3.32 billionths of a trillionth of a trillionth

of the spatial volume in a sphere of radius 5 light years centered on the Earth.

Note that this is a considerably smaller fraction even than was found in post #4 (it's about 24% of the earlier, incorrect result).

[RightWhale]

there are 100 billion neurons in the brain

there are 100 billion stars in the Milky Way

there are 100 billion galaxies in the visible universe

the visible universe is 1 billionth billionth billionth of the whole universe

or so

[Nodoginit]

Where is Carl Sagan when you need him?

Wherever he is, I'm sure he knows the answer now..."billions and billions and billions"

[Rudder]

in a sphere of radius 5 light years centered on the Earth

In a sphere?

Howsabout just calculating surface as being the most hospitable habitat for life, as it is here, on earth?

[Rudder]

Hence life occupies no more than 3.32 billionths of a trillionth of a trillionth of the spatial volume in a sphere of radius 5 light years centered on the Earth.

And no less...

[snarks_when_bored]

I used a 200-mile-deep 'rind' of Earth's surface, assuming (generously) that life occupies the entire rind, which it probably doesn't. So the volume occupied by life (as far as we currently know) is probably well below the figure of 3.32 billionths of a trillionth of a trillionth of the volume of a sphere of radius 5 light years. Why radius 5 light years? Because it's pretty clear that there are no life-bearing planets between us and Proxima Centauri, which is about 5 light years away from us.

But all this doesn't 'prove' anything, of course, nor would I claim that it does. It's just aimed at giving one a feel for how miniscule (and vulnerable and [values alert!] worthy of concern and protection) is the living part of our little backwater of the cosmos.

Best regards...

[boris]

Rare Earth: Why Complex Life Is Uncommon in the Universe -- by Peter Ward, Donald Brownlee

Makes the argument (IMHO very persuasively) that "life is common but intelligent life is exceedingly uncommon").

Basically their method is to look at all of the 0.0001 probabilities that led to us and throw all those factors at Sagans "billions and billions". Some examples:

--Planet in habitable zone
--Planet with lots of liquid water
--Planet with a large, prograde moon to stabilize its axis
--A gas giant (Jupiter) far enough out not to perturb planet's axis--but close enough to sweep up all the debris which would otherwise destroy nascent life
--Events such as the "Snowball Earth", which filtered 2% of 2% (my estimates) of all life through the event(s), meaning that all life on Earth evolved from .0004 of species previously existing--in only about 600 million years(!)

And so on.

My WAG at present is that there are >1 and <10 intelligent species in our Galaxy--which makes us essentially alone.

Then there is the Fermi Paradox...

--Boris

[snarks_when_bored]

When I wrote my post #8 on this thread, I had those sorts of considerations in mind (I've not read the book, but I recall having read a review of it some time ago).

And, yes, there's the Fermi paradox:  Where are they?

[SunkenCiv]

just a topic bump

Refuting Fermi: No Evidence for Extraterrestrial Life?
John B. Alexander
National Institute for Discovery Science
http://www.nidsci.org/pdf/fermi.pdf

related FR topics:

Cosmic Conundrum [Brief essay on multiple universes and the Anthropic Principle]
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