
The Anthropic Principle (2000) - lainon
http://www.physics.sfsu.edu/~lwilliam/sota/anth/anthropic_principle_index.html
======
putzdown
Every time I read about the Anthropic principle I get the feeling I'm missing
something. Enthusiasts of the principle seem to be committing a fallacy;
perhaps someone can explain why they're not, or why they are. I compare the
principle to this. A group of friends get together and decide they'll roll a
d20 to decide how to spend the evening. There are various options afoot, but
they decide that only if they roll a 20 will they play board games that night.
Lo and behold, they roll a 20 and spend the evening playing board games. Later
someone says, "How lucky we are to be playing board games!" A skeptic says,
"Whatever do you mean by 'lucky'?" Reply: "Well, there was a 1 in 20 chance,
and we hit it! That's pretty lucky." The Anthropicist snorts and says,
"Hardly! We're not lucky at all. There was a 100% chance. After all, we're
playing them." Is that a good analogy? Or does it miss something crucial on
one side of the argument or the other?

~~~
whack
Here's a better analogy. Joe has OCD. Every morning, he rolls a d100, and if
it comes up 1, he hosts a board-game party that night.

On day XX/YY/ZZZZ, Joe hosts a board-game party and a bunch of people show up.
During the course of the party, Joe reveals to everyone his d100 policy.

Tim asks him what his die-roll this morning was. Joe tells Tim that he rolled
a 1. Tim exclaims _" The only reason we're here is because you rolled a 1! How
did this incredible piece of luck come to pass?"_

Adam responds _" There's nothing incredible about what happened. If Joe hadn't
rolled a 1 today, we wouldn't be here. We would never have this discussion, or
have it on some other day when he does roll a 1."_

~~~
mjewkes
To extend this even further...

~This~ morning Joe rolled a dice, and it came up 1, so he hosted a board-game
party.

During the party Joe hints that the die he rolls may be very large, but stops
short of outright saying so.

Joe also refuses to say whether he rolls the die every morning, or if it was
just this morning.

The interesting questions are:

How big is the die?

How often is it rolled?

Does Joe do anything at all if he rolls almost anything other than a 1, or
does he just lie in bed?

If the very large die is only rolled once, and all non-1s are very boring,
then it is remarkable that we're here.

~~~
whack
_" Does Joe do anything at all if he rolls almost anything other than a 1, or
does he just lie in bed? If the very large die is only rolled once, and all
non-1s are very boring, then it is remarkable that we're here."_

That's a very interesting point you raised, and I was thinking about this as
well. If the universe only "exists once", and life is very unlikely but it
still came to be, then it does seem remarkable.

However, this is based on the presumption that life is non-boring, and all
other potential universes devoid of life are boring. This seems like a very
subjective presumption. Clearly we are biased towards thinking that our own
existence, or the similar existence of "life" is special. But a skeptic would
claim that from a purely scientific perspective, there's no reason to believe
that a universe without life is any more boring than our universe.

~~~
putzdown
Well, but there is something fundamentally and essentially special about
conscious minds. A universe that is complete unperceived is, first of all,
harder to even imagine than it first appears and, second, would be neither
boring nor interesting, since both of those words, and all other assessments,
only have meaning within the context of conscious perception. So I would
affirm the presumption that "life", in the sense of the existence of conscious
minds, is non-boring and universes devoid of life are either boring, or
inconceivable.

~~~
enkid
Spoken like a conscious mind

------
jzl
Also relevant: Boltzmann Brains

[https://en.wikipedia.org/wiki/Boltzmann_brain](https://en.wikipedia.org/wiki/Boltzmann_brain)

A Boltzmann Brain is (very roughly) a "brain", i.e. self-aware entity, that
appears spontaneously in the middle of the universe due to random quantum
fluctuations. In an infinitely old and infinitely large universe this should
actually be a common occurrence. So why are we not Boltzmann Brains ourselves?
Why are we all here observing the universe clustered together on this one
planet a mere 15 billion years since it came into being? Why is there so much
structure?

~~~
jbmorgado
_> "In an infinitely old and infinitely large universe this should actually be
a common occurrence. So why are we not Boltzmann Brains ourselves?"_

Because our Universe is neither infinitely old (is about ~14 thousand millions
years old) nor infinitely large (is about 90 thousand millions ly in
diameter).

Now this might seem big for you, but it's actually infinitesimal when compared
to the number of necessary permutations in order for higher intelligence to
appear solely by a quantum fluctuation.

This means that the only scientific possibility for higher intelligence to
appear, is then that only a very small set of universe conditions must occur
so that atoms then stars then planets then life then intelligent life has the
time and conditions to form.

~~~
solipsism
_is about 90 thousand millions ly in diameter_

This is the diameter of the _observable_ universe. We don't know if the
universe is infinitely big, but all signs (e.g. the flatness of space as far
as we can measure it) point to it being infinite, or very very much larger
than our observable sphere.

I don't understand why I'm constantly having to inform smart people of this
very basic fact. Is there something wrong with the way we teach astronomy? Can
you help me spread the word?

~~~
jbmorgado
> _" "90 thousand millions ly in diameter" This is the diameter of the
> observable universe. We don't know if the universe is infinitely big, but
> all signs (e.g. the flatness of space as far as we can measure it) point to
> it being infinite, or very very much larger than our observable sphere."_

Our observable sphere is nowhere near 90 thousand million ly in diameter since
that would violate relativity. Our observable sphere in ly is always smaller
than the age of the universe in years (so ~14 thousand million years).

Also, what you said is no fact, basic or not, it's just some misconception you
have about cosmology so you should stop spreading that word since you are
misinforming people you talk to.

In a nutshell: A Universe that begins in a singularity cannot have an infinite
diameter and while it's true that we do calculate the size of the Universe by
assuming the expansion rate right after the Big Bang and that rate might be
wrong, it still cannot be infinite without violating the major principles of
physics and the all big bang theory.

~~~
solipsism
My "fact" doesn't refer to the universe being flat. I would never call this a
fact. The "fact" I referred to is that the universe appears to us to be flat
as far as we can tell.

 _Our observable sphere in ly is always smaller than the age of the universe
in years (so ~14 thousand million years)_

This ignores the basic fact that the universe is expanding at an accelerating
rate. I'm comfortable calling this one a fact. Many 9s behind that confidence
percentage (even if the number of nines was recently lowered).

 _A Universe that begins in a singularity cannot have an infinite diameter_

Based on what logic? You are probably imagining an infinitesimally small
sphere expanding out and becoming the universe. This is a good description of
only our observable universe. There's no reason not to think that point wasn't
part of an infinitely large manifold. This would point to an infinitely large
universe.

I'm not an expert, but in my curiosity I've spoken to Dr. Don Lincoln from
Fermilab about this very topic, so that's the source of my confidence. Along
with my own subsequent (armchair) research. I've since followed up and done my
best to understand why this misconception is so prevalent. I'm convinced it's
because many sources say "universe" when they mean "observable universe",
leading to many misconceptions.

You seem as misinformed as most.

~~~
jbmorgado
> _" This ignores the basic fact that the universe is expanding at an
> accelerating rate."_

And that ignores the basic fact that information about those parts of the
Universe didn't have time to arrive yet (that is where relativity is
violated). You are mixing the concept of "observable universe" with "observed
universe". At a given time, given the expansion rate of the universe you have
an "observable universe" (those ~90E9 ly), but it will only be fully
observable somewhere in the future, in the present you only get to observe
~14E9 ly). In a nutshell what you are proposing is that we are observing
particles with infinite redshift. Or perhaps in a simpler way: You can be
observing _today_ parts of the universe that are (for instance) 25E9 ly away
_today_ , but you are observing particles of light that left that part of the
universe a _long time ago_ so that the _c x t_ condition was never violated.

> _" This is a good description of only our observable universe. There's no
> reason not to think that point wasn't part of an infinitely large manifold.
> This would point to an infinitely large universe."_

Based on the theory of the Big Bang which is the de facto theory accepted by
Cosmology. It is true that you could have an infinitely large manifold and
that is a very interesting theory. But I was answering inside the actual
theory that is the accepted one now-a-days the Big Bang (and I actually
referred that in the answer). Also, even inside the manifold theory theory,
_our universe_ that is what is being discussed here, would still not have an
infinite diameter.

------
RivieraKid
Something vaguely related I've been thinking about: When looking at the
timeline of life (link below), humans are a completely negligable slice of
history. Dinosaurs survived for about 170M years, modern humans have existed
for just 200K, civilization for about 10K, and the technological boom has been
here for roughly 100 years.

Can this be seen as evidence that the timeline of humanity will be relatively
short in the big picture? Because it would seem like a strange coincidence to
be born at the beginning of it. This is even more true for the survival time
of humans with modern technology. Assuming the era of technologically advanced
humans will last for, say 200M years, it's extremely unlikely to be born at
the first 100 years (0.00005 %).

It's interesting to think about how civilization would develop over hundreds,
thousands or _thousands of thousands_ years. There have been some pretty
significant changes in just the last 100 years, what could happen in millions
of years? Civilisation is not a stable system, it seems to be quite volatile.
And unlike before, changes and disruptions are not as locally constrained.
Perhaps after many thousands of years, there will come a low-probability event
that civilization won't recover from.

[https://en.wikipedia.org/wiki/Template:Life_timeline](https://en.wikipedia.org/wiki/Template:Life_timeline)

~~~
jodrellblank
It's a nonsensical idea.

Imagine you are a soul, in limbo, somewhere outside the universe and elsewhere
in another part of reality the universe is progressing through its motions as
time goes on. You are an other-reality-style being, yet somehow still
allocated as "going to be a homosapiens on Milky Way\Sol\Earth", and your
birth will be random during the era of homo sapiens.

Now you can argue about the likliehood of where this random birth happens.

On the other hand, take away the other place, and the souls, and the spooky
assignment of types, and just look at the universe as a thing of matter and
energy. Some configuration of matter was born to your parents, from their DNA.
It is intimately connected to its surroundings by a continual stream of light,
heat, air pressure, physical pressure; over millions of seconds it learns. It
learns the patterns of air pressure that correspond to other people talking to
it, and it learns what things it can and can't push by trying, and what other
people talk about.

And it says "isn't it unlikely that I was born here and now, instead of some
other time?"

And the question makes no sense. _What_ could have been born somewhere else?
or somewhen else? Without its parents DNA, without its particular twenty
continuous years of sensory input that it learned from, it would not be
itself.

Some other matter, born to other parents, with other DNA, and other childhood
experiences, and other knowledge patterns. It would be someone else. Entirely
someone else. And ... that happens, we call it "other people".

If you don't believe in a soul, or something like it, what does it mean for
you to possibly "be born somewhen else"?

~~~
grkvlt
The question is, what is the probability that _a person_ picked at random from
the human population, would be born during a technological era. We can work
this out. Then, what is the probability that the part of the technological era
they were born in was the first 100 years. This is easier to work out, it's
100/L_years(technological_era) but, unfortunately that's also the probability
they are born in the second 100 years of a technological era of the same
length, the third 100, the last 100 etc. so I don't think it gives us any
predictive power?

~~~
jodrellblank
No, the question asked by the parent poster is "what is the probability that
_I_ would be born at this time in a long time frame".

Which is what I was answering. You can't pick a human at random including from
the future, unless you're outside the system somehow.

~~~
grkvlt
That just leads you down the road of discarding probabilities. Since something
either happens or doesn't happen, the probability is either 100% for the
things that _will happen_ or 0% for those that do not. This is not a helpful
position to take, although it is technically correct, in some not very useful
sense.

Humans are good at dealing in counterfactuals. 'What would have happened if I
hadn't missed the bus?' is a useful question to ask, even if you _did miss the
bus_. What would I be like if I hadn't gone to university/had taken that
job/never killed my parents? Obviously the 'I' in those questions cannot be
_you_ , exactly, since you did or didn't do those things. But it's still a
useful concept or thought experiment, and can give us valuable insights.

The commenter is using 'I' in that counterfactual sense. And certainly, I
understood what they _meant_ by it, so they were successful in communicating
(at least, to me) which is what matters with language.

------
bo1024
Not complete without mention of Terry Pratchett:

> _The UU Professor of Anthropics had developed the Special and Inevitable
> Anthropic Principle, which was that the entire reason for the existence of
> the universe was the eventual evolution of the UU Professor of Anthropics.

> But this was only a fomal statement of the theory which absolutely everyone,
> with only some minor details of a `Fill in name here’ nature, secretly
> believes to be true._

~~~
jzl
One of my favorite Terry Pratchett quotes is from a typical hilarious
character of his pondering the nature of the universe:

"Then there was the question of why the sun came out during the day instead of
at night when it would be more useful."

------
AnimalMuppet
> The Participatory Anthropic Principle states not only that the Universe had
> to develop humanity (or some other intelligent, information-gathering life
> form) but that we are necessary to it’s existence, as it takes an
> intelligent observer to collapse the Universe’s waves and probabilities from
> superposition into relatively concrete reality.

This is a misunderstanding of what quantum waveform collapse is. It requires
an "observation", but not an intelligent observer. For example, in the
Schrodinger's Cat thought experiment, the Geiger Counter is a perfectly valid
observer.

~~~
ggreer
What's the criteria for what counts as an observer? Geiger counters are, but
some photon detectors in a delayed choice quantum eraser experiment[1] aren't?

1\.
[https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser](https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser)

~~~
akvadrako
Basically there is no sharp division, but the more the observation spreads,
the harder it is to reverse. For one isolated particle, it's easiest. Anything
we can reliably read is basically permanent, like a bit flip in a computer.

So once a photon is detected, like by making a mark on a screen or camera,
it's permanent. In the delayed-choice experiment this happens twice, once for
the "interference pattern" and again after the choice.

If you accept that, which I think is intuitive, then it makes the DCQE much
easier to grasp. If you want to understand the experiment better, I would
recommend this thread:

[https://www.physicsforums.com/threads/who-is-puzzled-by-
the-...](https://www.physicsforums.com/threads/who-is-puzzled-by-the-delayed-
choice.402497/)

------
AnimalMuppet
To state the Weak Anthropic Principle in a form that feels (at least to me)
less like philosophical woo: "Universes that cannot be inhabited by
intelligent observers are never observed, because there cannot be anyone there
to do the observing".

~~~
SomeStupidPoint
You just stated it as the contrapositive:

"NOT Universe can support intelligent life -> NOT Universe can be oberved"

... rather than ...

"Universe can be observed -> Universe can support intelligent life (->
Universe has values which can support life)"

I'm not sure either is more useful than the other.

~~~
AnimalMuppet
Right. But the way it was stated in the article makes it easy to think of it
as _the universe requiring_ rather than _the observer requiring_. The other
versions explicitly get into that kind of nonsense; I wanted to state the weak
version in a way that made it clear that it _didn 't_ go there.

(I suspect that this page states the weak version in that way in order to make
the other versions seem more similar.)

~~~
jwatte
An /observed/ universe requires conditions to cause observers to evolve.

I don't but that an "intelligent" observer is needed to collapse the waveform,
BTW. That uses a very non-physical interpretation of "observer." Any particle
that can absorb information, can be said to be "observing." As simple as a
reaction that depends on temperature would do it.

------
edgarvaldes
>The Final Anthropic Principle states that once the Universe has brought
intelligence into being, it will never die out.

How can you propose someting like that? I mean, in a scientific way.

~~~
vorg
The Final Anthropic Principle follows naturally from the Weak/Strong Anthropic
Principle. Once intelligence has evolved and observed the Universe with a
single first thought, why didn't it then die out? Of course the definition of
Intelligence is arguable, anything from a vaguely self-aware rodent to a
literature-reading human, and beyond. If we take some person called Ubuntu who
discovered how to control fire 130,000 years ago at age 23 years and 7 months
in southern Mozambique as having the very first aware thought, then straight
afterwards there'd be no more anthropic principle at work causing intelligence
to exist in the Universe. The fact we're still here, our small tribe of sole
humans not eaten by hyenas or our planet not extinguished by nukes, suggests
there could be a Final Anthropic Principle at work.

~~~
yequalsx
I don't understand how this question is relevant:

"Once intelligence has evolved and observed the Universe with a single first
thought, why didn't it then die out?"

What proof, line of reasoning, logical principle, or evidence do you have to
believe that a single first thought would lead to anything dying out? What
makes you think there is some underlying Anthropic Principle at work in the
universe?

Saying something could be at work is more or less saying "God did it". It
doesn't explain or illuminate anything.

~~~
vorg
It only takes a single first thought by an intelligence to observe the
Universe. Everything occurring up to then (e.g. nucleii, carbon, brains) is
highly unlikely and therefore many people suggest an Anthropic Principle to
explain it.

Once that single first thought by an intelligence has occurred, the Weak or
Strong Anthropic Principle is no longer required to explain the existence of
intelligence, and so its continuance has the same unlikeliness as other life
forms, i.e. ultimate extinction. The fact humans became the opposite of
extinct (e.g. fire, scrolls, nukes) suggests that if the Anthropic Principle
applies to the emergence of intelligence, something even "stronger" such as
the Final Anthropic Principle could apply to the continuance of intelligence.

I'm not saying there's an underlying Anthropic Principle in the Universe. I'm
answering the question to show that the Final Anthropic Principle is as
scientific a proposal as anything else.

~~~
yequalsx
That's not a scientific proposal. There is absolutely no reason to think that
anything should cease existing simply because the first thought occurred.

------
DonaldFisk
Why are planetary orbits roughly circular? Is it because

(a) if they were any other shape (e.g. very long isosceles triangles)
conditions wouldn't be suitable for intelligent life to evolve, and we
wouldn't be around to observe it, or

(b) Newton's law of gravity constrains them to conic sections. Stable orbit of
single planets must be circular or elliptical. Any planets with highly
eccentric orbits would have been ejected from the early solar system, leaving
only those which are roughly circular?

Of course, the answer is (b), i.e. instead of the emergence of intelligent
life determining the laws of physics, the laws of physics allow the evolution
of intelligent life. But we only agree on that because we already know
Newton's law of gravity. If we didn't know it, some people would believe (a)
while others would think that one day a law of gravity would be found which
determines planetary motion.

~~~
inimino
Why would they be triangular? There is nothing apparently unparsimonious about
elliptical orbits, thus there is nothing that requires explaining.

The anthropic principle is not about intelligent life determining the laws of
physics. There is no magic there. You have the causality backwards.

~~~
DonaldFisk
No reason. You can decide on any shape you want.

I don't have the causality backwards. We don't have a complete knowledge of
the laws of physics, and we have something which is unexplained. Whenever this
was the case in the past, better laws were found which closed the explanatory
gap. Why should it be any different this time?

~~~
inimino
The point of the anthropic principle isn't to explain it, it's to point out
that an explanation is not required.

We could find that the laws of our universe are the only possible set of
physical laws. This would be the expectation of the Newtonian era. In that
case there is nothing to explain. Or it may be, and currently seems likely,
that there are many possible sets of physical laws. Then the question of why
we happen to have one of the perhaps very few possible sets of physical laws
that allows intelligent life to develop seems to require an explanation. The
anthropic principle explains why it really doesn't, because in the (possible
or actual) universes where intelligent life is impossible, the question simply
doesn't come up.

The point of the anthropic principle is precisely that we shouldn't expect to
close the explanatory gap, because there isn't one. We shouldn't be surprised
if physical laws seem to be "tuned" to allow intelligent life to emerge.

Imagine that planets orbited in randomly selected geometric shapes, and we
happened to be on the only known elliptical one, giving us the conditions
required for life. Would this lucky fact require explanation?

~~~
DonaldFisk
>Imagine that planets orbited in randomly selected geometric shapes, and we
happened to be on the only known elliptical one, giving us the conditions
required for life. Would this lucky fact require explanation?

No more than the existence of a planet of the right size at the right distance
from the sun. You still have physical laws which determine what's possible,
but they probably won't (and, in fact, don't) provide a complete explanation.

The weakest form of the Anthropic Principle is uncontroversial. For example,
we can use it to conclude that physical laws which don't permit intelligent
life to evolve must be wrong. Can we use it to rule out physical laws which
don't _entail_ the evolution of intelligent life? I would argue yes, but that
doesn't require any fine-tuning of dimensionless constants: an infinite (e.g.
Einstein-de Sitter) universe, or Everett's Many Worlds interpretation of
quantum mechanics would entail it, given its possibility.

------
hota_mazi
Here's another way to look at the Anthropic Principle:
[https://goo.gl/O6c0Zi](https://goo.gl/O6c0Zi)

------
elorant
That web site seems like it popped-out from 1997.

~~~
kardos
Last-Modified: Fri, 19 May 2000 20:30:18 GMT

Not a bad guess!

------
posterboy
> [is to observe and understand the universe] a lucky break for the
> intelligent beings that they exist at all?

If we were so intelligent, we wouldn't have to ask, so the answer is 42.

