Understanding why the fundamental constants (which reflect the strength of gravity, the speed of light, and other physical laws) have the values that we measure is one of the most challenging and important problems in physics.
One popular way to explain the constants involves the anthropic principle. It's based on the argument that life is only possible under certain values of the constants, and that we wouldn't be here to measure them if they were even slightly different.
Although it may seem like little more than circular reasoning at first glance, Steven Weinberg (University of Texas) managed to use the anthropic principle to calculate the cosmological constant with surprising accuracy back in the late 1980's, well before observations of the accelerating expansion of the universe gave us a measurement of the constant.
Astrophysicists Glenn Starkman (Oxford) and Roberto Trotta (Case Western), however, take issue with anthropic reasoning in calculations of the cosmological constant.
They claim that the parameters that go into the calculations, such as the number of sentient beings who try to measure the constant, are so poorly defined that anthropic arguments can lead to all sorts of values. They expect that similar problems hamper anthropic rationales for the other fundamental constants as well.
The paper by Starkman and Trotta is just one in a recent series of assaults on anthropic principles in physics. In a paper published in the August 2006 issue of Physical Review D, Roni Harnik et al. described a universe with no weak force at all, which they believe could support life nevertheless (http://link.aps.org/abstract/PRD/v74/e035006).
If true, it undermines anthropic arguments for the values of several fundamental constants. Earlier this year, Harvard's Abraham Loeb published a paper in the Journal of Cosmology and Astroparticle Physics (available on the preprint archives at http://lanl.arxiv.org/PS_cache/astro...04/0604242.pdf) showing that finding planets in dwarf galaxies would prove that habitable conditions could arise even if the cosmological constant were a thousand times larger than the one we measure, potentially eliminating anthropic arguments for the constant's value entirely.
Source: Physical Review Letters
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How timely Tormod. Have you been reading Hypography again‽ I ran across this little tidbit after following the links to links:
Quote:
Originally Posted by Wicky
A major outstanding problem is that most quantum field theories predict a huge cosmological constant from the energy of the quantum vacuum. This would need to be cancelled almost, but not exactly, by an equally large term of the opposite sign. Some supersymmetric theories require a cosmological constant that is exactly zero, which further complicates things. This is the cosmological constant problem, the worst problem of fine-tuning in physics: there is no known natural way to derive the infinitesimal cosmological constant observed in cosmology from particle physics.
I added the bolding as I have to notice Durgatosh is fond of the zip zero approach. For myself, and for the time being, I fairly well like the normalized ΩΛ ~= .7. My biggest problem is that I constantly change my mind.
__________________ Brevity. ~Roger Thelonious George
The anthropic principle is based on faulty assumptions. It assumes life to have appeared as a random event requiring specific constants to occur. This assumption is based on ignorance of how life formed. One needs to take into consideration the affects of the third layer of chemistry or the affect of the hydrogen bonding proton to realize that conditions are more flexible then are currently believed.
The anthropic principle is based on faulty assumptions. It assumes life to have appeared as a random event requiring specific constants to occur. This assumption is based on ignorance of how life formed. One needs to take into consideration the affects of the third layer of chemistry or the affect of the hydrogen bonding proton to realize that conditions are more flexible then are currently believed.
The anthropic principle isn't limited to chemistry. It's all-encompassing as far as science is concerned. For instance, gravity (according to the anthropic principle), has to work inverse squared, else the planets might slowly spiral away or into their stars, and life would have been completely impossible. What we see around us in the universe, where gravity follows a specific set of laws, life is possible - but this is not to say that the universe had a previous incarnation (or an infinity of previous incarnations) where the laws of nature 'condensed' differently our of the starting Bang.
The anthropic principle would be appliccable to anything imaginary, simply because we're here to record it.
This does say a lot about life in the rest of the universe, though. Laws of Nature as observed on Earth is clearly conducive not only to Life, but Intelligent Life as well.
Life didn't appear 'randomly', as stated in your post; rather, Life appeared because the conditions were right, and the conditions were right because the Laws of Nature (in this universe's incarnation, at least) allowed it.
The paper by Starkman and Trotta is just one in a recent series of assaults on anthropic principles in physics. In a paper published in the August 2006 issue of Physical Review D, Roni Harnik et al. described a universe with no weak force at all, which they believe could support life nevertheless (http://link.aps.org/abstract/PRD/v74/e035006).
Lame... Problems in a weakless universe http://arxiv.org/abs/hep-ph/0609050 The fact that life has evolved in our universe constrains the laws of physics. The anthropic principle proposes that these constraints are sometimes very tight and can be used to explain in a sense the corresponding laws. Recently a "disproof" of the anthropic principle has been proposed in the form of a universe without weak interactions, but with other parameters suitably tuned to nevertheless allow life to develop. If a universe with such different physics from ours can generate life, the anthropic principle is undermined. We point out, however, that on closer examination the proposed "weakless" universe strongly inhibits the development of life in several different ways. One of the most critical barriers is that a weakless universe is unlikely to produce enough oxygen to support life. Since oxygen is an essential element in both water, the universal solvent needed for life, and in each of the four bases forming the DNA code for known living beings, we strongly question the hypothesis that a universe without weak interactions could generate life.
Quote:
Originally Posted by Tormod
If true, it undermines anthropic arguments for the values of several fundamental constants. Earlier this year, Harvard's Abraham Loeb published a paper in the Journal of Cosmology and Astroparticle Physics (available on the preprint archives at http://lanl.arxiv.org/PS_cache/astro...04/0604242.pdf) showing that finding planets in dwarf galaxies would prove that habitable conditions could arise even if the cosmological constant were a thousand times larger than the one we measure, potentially eliminating anthropic arguments for the constant's value entirely.
Equally lame, since the goldilocks enigma predicts that these "dwarf galaxies" with planets will exist, but without life.
Try as they might, the anthropic principle just won't go away... but denial is always easier than it is to honestly look for the reason why we are relevant to the structure and stability of the universe.
I suspect that, if the universe had different physical properties, life could still occur, but it would be different from anything we could know. If this life was able to become intelligent, it would look out at the universe and say, "There are no other conditions under which life could have formed".
I postulate that life conforms to the physics of whatever universe it exists in, and thus is particular to that universe's physics. This will make it seem like any universe in which there is life is "anthropic".
There was a science fiction short story published in the 40's or 50's. I believe the author was A.E. vanVogt. It involves the first ever creation of a time machine, but it was unmanned. It was to shoot further and further back in time, "bouncing" as it were on an "anvil" in the present time. At the peak of each bounce, it would gather a specimen. Each peak would be twice as far back as the one before, until the timecraft "bounced" off the big bang and each successive bounce would be only half as far.
Needless to say, the scientists of the world were worried that any attempt to "observe" the past would alter the past, and therefore alter the present, maybe killing off all life on Earth. So they were all invited to the launch with great assurances of the safety measures that had been taken.
Launch! And the anvil rang as the craft went 1, 2, 4, 8, 16, 32 seconds into the past. The MC said, "See, everybody, nothing has changed!" The craft reached ten thousand years in the past; everybody's skin color changed to black. The MC said, "See, everybody, nothing has changed!"
A million years; everybody had scaly green skin and webbed toes. The MC said, "See, everybody, nothing has changed!"
A billion years; everybody had four eyes and breathed methane gas. The MC said, "See, everybody, nothing has changed!"
The craft bounced off the Big Bang and eventually returned to the present and was still. Under a purple sky filled with glowing skradarks, the people emfeetled joyously. The luminosity of the framdarks grittled the balsomic gorgentures of the preems. The MC said, "See, everybody, nothing has changed!"
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Dave might be right, except he misses is the fact that the anthopic principle is expected to be woven into the structure mechanism via the least action principle, which only offers one possible solution if you don't invoke unproven theoretical speculation.
You need to study the history that led up to the AP to understand why Dirac, Dicke, Carter, Wheeler, Davies and even Dr. Einstein, himself would not buy the hype of modern rationale that hides from the fact that the actual observed structure of the universe occurs in dramatic contrast to the modeled expectation... where *many* fixed balance points are commonly or "coincidentally" pointing directly toward carbon-based life, *does* indicate that there is some good physical reason for this otherwise completely unexpected structuring, that is somehow "specially" related to the existence of carbon-based life.
It is an unavoidable fact that the anthropic coincidences are uniquely related to the structure of the universe, so an evidentially supported implication does necessarily exist that carbon-based life is somehow relevant to the structure mechanism of the universe, and weak, multiverse interpretations do not supercede this fact, unless a multiverse is proven to be more than cutting-edge theoretical speculation.
That's the undeniable fact that makes Richard Dawkins and Leonard Susskind say that the universe "appears designed" for life, and they both "beleive-in" unproven multiverse theories, but their interpretation is only valid against equally non-evidenced "causes", like supernatural forces and intelligent design. These arguments do not erase the fact that the prevailing evidence still most apparentely does indicate that we are intricately connected to the structure mechanism, until they prove it isn't so, so we must remain open to evidence in support of this, or we are not honest scientists, and we are no better than those who would intentionally abuse the science.
Why might we be necessary to the physics of the universe?
Do you know that the AP does not apply to only one galaxy, and one planet?
Carter called scientists' inisistence on unobserved mediocrity, "anticentrist dogma"... because it is **equally** anti-fanatical to geocentrism, since the cosmological principle does not extend to the time domain.
where *many* fixed balance points are commonly or "coincidentally" pointing directly toward carbon-based life, *does* indicate that there is some good physical reason for this otherwise completely unexpected structuring
Correlation does not imply causation. I would argue that the principles don't point to carbon-based life, but rather it is the carbon-based life that points to the principles. We don't say that gravity is proportional to the inverse square of the distance because otherwise things would fall wrong, we say that things fall the way they do because gravity is proportional to the inverse square of the distance.
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Re: The Anthropic Principle Under Fire 
I ran across this little tidbit after following the links to links:
Brevity. ~Roger Thelonious George 
