Can the anthropic principle be used in science?
 

There are many versions of the anthropic principle, and as I understand it,
physicist Leonard Susskind only uses the least controversial one.


(1) Weak anthropic principle (WAP): It can be defined as saying that the
observed values of physical and cosmological quantities are not equally
probable, but - at least in our universe - have obviously the values
restricted by the requirement that there exist sites where carbon-based life
can evolve. Further, at this time, the Universe must be old enough for life
to have already arisen.

This weak version, as I understand it, is the only one accepted by Susskind.
The question, however, is whether or not one can use this to make testable
predictions. (Maybe not, but can we be certain?)

Note that the weak version appears in several forms.


(2) Strong anthropic principle (SAP): "The Universe must have those
properties which allow life to develop within it at some stage in its
history."

However, another version of SAP is much more bold: "The strong anthropic
principle is simply the classic design argument dressed in the modern garp
of cosmology. It implies that the production of life is part of the intent
of the universe, with the laws of nature and their fundamental constants set
to ensure the development of life as we know it."

I reject this argument as mystical nonsense.

("The Rejection of Pascal's Wager")
[Only registered and activated users can see links. Click Here To Register...]


(3) The participatory anthropic principle (PAP) utilises a well known
phenomena in quantum mechanics called the collapse of the wave function. In
a nutshell this notion involves the peculiar property of the quantum world
(such as the behaviour of an electron in double slit experiments) which
seems to imply that something does not become "definite" until it is
actually measured. Thus ostensibly implying that it takes an act of
observation by a conscious observer to make it "real". PAP, first introduced
by John Wheeler in the book Quantum Theory and Measurement co-authored with
W.H. Zurek, suggests that observers must exist to bring the universe into
being. (Quoted from "The Rejection of Pascal's Wager")

Again, I reject this as mystical nonsense.


(4) Final anthropic principle (FAP): "Intelligent information-processing
must come into existence in the Universe, and, once it comes into existence,
it will never die out." (This too exists in several forms.)

I reject this as obviously wishful nonsense.


I ask readers to consider: Are we rejecting every single interpretation of
the anthropic principle, or just some interpretations? And if you accept
that some form of the weak anthropic principle is true, then might we not
make some testable prediction based on it? If not, how can we be so sure
that no possible prediction can be made?

Adherents of some forms of the anthropic principle are often accused of
argument by lack of imagination. But I am wondering if that may be true of
those who reject any possible predictions being made at all? (I don't know,
I am just wondering.)

[Only registered and activated users can see links. Click Here To Register...]

Perhaps we need a guideline for discussing this topic: When agreeing or
disagreeing with an interpretation of a theory, let's clearly state which
interpretation we are talking about. Unconsciously everyone assumes this
with QM, but I'm not sure that we always do this with the anthropic
principle.


By the way, some people think that the landscape currently predicted by
string theory is far too small. Have you read the following paper by Max
Tegmark? He has multiverses on top of multiverses on top of multiverses! (A
shorter version of this recently appeared in Scientific American.)
[Only registered and activated users can see links. Click Here To Register...]

Tegmark writes:

I survey physics theories involving parallel universes, which form a natural
four-level hierarchy of multiverses allowing progressively greater
diversity.

Level I: A generic prediction of inflation is an infinite ergodic universe,
which contains Hubble volumes realizing all initial conditions - including
an identical copy of you about 10^{10^29} meters away.

Level II: In chaotic inflation, other thermalized regions may have different
effective physical constants, dimensionality and particle content.

Level III: In unitary quantum mechanics, other branches of the wavefunction
add nothing qualitatively new, which is ironic given that this level has
historically been the most controversial.

Level IV: Other mathematical structures give different fundamental equations
of physics. The key question is not whether parallel universes exist (Level
I is the uncontroversial cosmological concordance model), but how many
levels there are. I discuss how multiverse models can be falsified and argue
that there is a severe "measure problem" that must be solved to make
testable predictions at levels II-IV.


Tegmark sounds quite mad. I'd rather enjoy meeting him. :)


Happy reading!

Robert