Universe is fine tuned for life

1. Nov 2, 2013

{~}

universe is "fine tuned" for life

http://web.mit.edu/rog/www/papers/fine_tuning.pdf

There is some evidence that the universe is "fine tuned" for life. If the fundamental constants of the universe were a little bit different then we couldn't exist. Roger White considers this evidence of a rational actor. Others see this argument being consistent with a multiverse hypothesis. Personally, I don't think fine tuning is convincing of either unless you are already predisposed to think that there might be a god or a multiverse.

I am unconvinced possible life supporting universe are sufficiently rare to need an explanation.
It may be true that adjusting any one of the fundamental constants will result in a universe which doesn't support life, but it doesn't necessarily follow that life supporting universes are rare.

Suppose that the gravitational constant, $G$ in $F = \frac{GmM}{r^{2}}$, is slightly stronger. This might create a universe which immediately collapses in on itself or a universe which only contains blackholes. But suppose at the same time you adjusted the cosmological constant λ to prevent collapse and electromagnetism to allow "normal" matter to form ect. I believe thinking of the constants as settings on a dial might be fallacious, they are more like weights on a complex balance.

Furthermore the constants might not be a fundamental feature of the universe but an artifact of our limited understanding. Proposed theories of everything are generally trying to unify the disparate forces in the universe. Such a unified theory might show that constants can only have certain values. In our current understanding we don't know what if any range of values the constants might have. If the possible life supporting universes require a finite subset of values out of an infinite range then life supporting universes are rare indeed. But we simply don't have any particular reason to suppose that to be the case.

2. Nov 3, 2013

mathman

This is the most likely - to me at least.

3. Nov 4, 2013

skydivephil

I see no physcial reason to say the unvierse is fine tuned for life than top say its fine tuned for potato soup. There are a lot of phenemenon in the universe, why life and not potato soup? please explain that too me.

4. Nov 4, 2013

Chronos

Why belongs to the realm of philosophy, not science.

5. Nov 4, 2013

skydivephil

In that case the question itself is also philosphy and not science. We can asky how did the constants of nature get their values , that seems a proper scientific questions. But to assume they are fine tuned for life and not potato soup is just an excercise in human arrogance.

6. Nov 4, 2013

mathman

If these constants are fine tuned, then all of biology as well as chemistry benefit.

7. Nov 14, 2013

rbj

need to understand the difference between a dimensionful universal constant (which $G$ is) and a dimensionless universal constant (say $\alpha$ or $m_p/m_e$).

only values of the latter (the dimensionless constants) have meaning in an of themselves.

the rest of the fine-tuning issues you bring up are all well and good. maybe check out the Wikipedia article on the topic as well as on the Anthropic principle.

bestest.

8. Nov 22, 2013

yogi

Agreed. IMO the idea of G as constant is suspect. In particular, the dimensional units are based upon changing velocity and our present concept of mass as fixed. {Volumetric acceleration per unit mass}, in mks units Meters cubed per second squared per unit of mass. It may well be that one of the dimensions changed as the universe transitioned from what it was to what it is. I know, the long term experiments to measure changes in the lunar orbits of planetary moons failed and therefore conclusions were drawn that G is invariant - but such experiments only confirm the invariance of the MG product during the experimental period - not G alone. We know that the inertia of mass changes with relative velocity - and the velocity of expansion in the standard model has not been constant.

9. Nov 24, 2013

Truenorthnatur

The issue with fine tuning, is that it assumes that 'life' is somehow a special entity. It isn't. Biology is chemistry and chemistry is physics....matter and energy.

A carbon molecule has the same properties whether it is part of a supernova explosion or in a human brain. Life is just a macro level of how we try and explain other 'stuff'...matter and energy. Nothing special about life in General Relativity or Quantum mechanics.

10. Nov 24, 2013

yogi

True but the broader question is whether fine tuning is necessary for anything to exist as a functional cosmos - not just life Einstein once said:, "what I really want to know is whether God had any choice in the creation of the world" Perhaps the holistic nature of things requires everything be the way it is - - alternatives are illusory

11. Nov 26, 2013

skydivephil

But the problems is what you define as a functional cosmos depends on the things you observe in it. A different set fo constants might generate different things and that could be considered functional.

12. Nov 26, 2013

Chronos

If the 'fine tuned' properties of the universe are emergent, instead of fundamental, it would seem to greatly simplify matters. That would suggest they are relational, hence self tuning. I can picture a universe where only one, or a very small number of properties are truly fundamental. It is suspected that the four fundamental forces of the universe emerged from some sort of superunified force. If we figure out that part perhaps all of the pieces that came afterwards will make sense.

Last edited: Nov 26, 2013
13. Nov 26, 2013

Jonathan Scott

For a start, whenever you start suggesting that something might vary in a non-standard way, you have to be very careful about the implications for standard equations and results. In many cases the experimental predictions end up remaining unchanged and all you have done is redefine some physical quantities in an unusual way. (This applies especially to cosmological redshift, but also to variation in G).

Theories based directly on Mach's principle certainly do provide a large amount of automatic "fine tuning" by making G variable, effectively becoming an abbreviation for the effect of the potential due to all of the masses in the universe. This means that G typically has to vary both with location (according to the distribution of masses) and with the age of the universe, both of which appear at first to be contradicted by the experimental evidence, at least within the solar system, so if you want to explore such theories any further you need to understand the constraints.

Although Machian theory predicts that G varies with location, it is easy to overlook the fact that when the Machian potential expression is matched up with the Newtonian or GR effective potential, the value of G in the Machian form is effectively an abbreviation for the gravitational effect of all masses in the universe EXCEPT the local masses for which an explicit potential term is included. This means that the effective local value of G, even in the Machian theory, does not vary significantly with location (given that the relative influence on the potential of other stars, the galaxy and other galaxies is essentially constant over an extremely long time scale).

However, Machian theory says that local experiments to determine G between two bodies at some point, for example on the surface of the Earth, would be expected to show a local value which varies very slightly depending on the current potential of the experiment location. As far as I know such variations are much less than those currently detectable by current Earth-based experiments to determine G, but it is worth noting that such experiments are notorious for giving unexpectedly inconsistent results.

The experimental evidence against variation with time seems stronger, in that it seems to say that any time variation of G is slower than being proportional to (or inversely proportional to) the age of the universe. However, there is a complication that the experimental interpretation in that case is more indirect, relying on assumptions which partly rely on the use of standard theory.

In Machian theories, the Whitrow-Randall-Sciama relation says that the sum of Gm/rc^2 for everything in the universe is a simple constant of order 1. If we call this constant n, then we have G = n/(sum of m/rc^2). We would expect the average value of r to increase linearly with the age of the universe, but it is not clear how the total "mass" (or more practically "rest energy" expressed in frequency units) should be expected to vary with time. This would require a more completely specified Machian theory before any specific experimental tests could be applied.

Another effect of the "relative" nature of Machian theories (which also shows up to some extent in GR) is that space can appear to be isotropic and homogenous (at least to first order) even when the local distribution of masses appears to be extremely non-uniform. This is because the effect of the local gravitational potential on the shape of space has the effect of redistributing the potential sources to make them appear more even. As a trivial example, if you have a large mass nearby on one side of an observer, this curves local flat planes in space in such a way that more of the distant stars appear to be on the other side!

14. Dec 1, 2013

yogi

If G varies as 1/r, then the effective mass would necessarily have to increase in proportion to r in order that the MG product be constant. All attempts to measure G actually measure the affect of G upon some mass M, and therefore the null results of the experiments cannot be attributed to the fact that G is invariant - but to the invariance of the MG product. This is a shocking idea - but it has some interesting consequences - like the equivalence principle, and the interesting possibility that cosmic density is simply an inverse function of a variable G and therefore always appears critical or near critical without the benefit of fine tuned initial conditions. This fantasy should be distinguished from the steady state theory - the universe does not need to add particles - it only needs to enhance the inertial reaction of the existing particles which is a natural consequence of the distending gravitational field which defines the negative energy required to balance the increased positive inertial energy as the universe grows.

Last edited: Dec 1, 2013
15. Dec 10, 2013

rbj

the issue is, yogi, that you can't tell if $G$, in and of itself, is or is not invariant. no one measures (or even experiences) $G$, except in relation to a like-dimensioned standard that might be assumed to be a constant standard. but you don't know.

if the Gravitational coupling constant

$$\alpha_G = \frac{G m_e^2}{\hbar c} = \left( \frac{m_e}{m_P} \right)$$

had changed, we would know it. but we would not know if it were due to a change of $G$ or a change in $m_e$ or $\hbar$ or $c$ or a combination of the four. and it doesn't matter because the value of $G$ or any of those quantities has meaning only in the context of a like dimensioned standard (like $\frac{\hbar c}{m_e^2}$) to express that value in. if it were a different standard (say one based on the meter, kilogram, and second), then that value has as much eternal physical meaning as an arbitrary human choice of units. but $\alpha_G$ has constant meaning despite what units one decides to express physical quantity with.

you cannot measure $G$ alone. express everything in terms of Planck units and $G$ is 1. even if someone changes $G$, it still comes out as 1 if you measure everything in Planck units.

16. Dec 10, 2013

julcab12

..I think fine tuning and stability is an illusion IMO. Nature to me is a state of relative complexity, structures, transformations, interactions and patterns producing diverse behaviors. It is meaningless IMO.

17. Dec 10, 2013

yogi

If G alone varies - it could be detected - that would be true of almost any of the "so called" constants of nature - all is relational - My P.O. is that dimensions have been slighted in all these discussions - I recently posted a number of emails on a thread that evolved to the same subject in the Relativity forum - my view is that when dimensionless constants are formed, some information is lost - as an example take the ratio of the gravitational force acting between two electrons and the electrical force acting between two electrons at the same distance - the ratio is about 10^42 so we might define a constant (call it Beta) that expresses this factor. When we form the ratio the distance squared term cancels in both the numerator and denominator - we have only a dimensionless number that tells us nothing about how it was created - it might just happen in some other universe that the electrical force is like an inverse spring - where the repulsion is inverse linear and the G force is inverse squared - if you didn't know how the Beta constant was created - information is lost....admittedly we can recover it by testing the new constant at various distances - but there may be cases such as alpha where the lost information is critical to an understanding of its value

18. Dec 10, 2013

yogi

BTW, what is the significance of the gravitational coupling constant of post 17

19. Dec 10, 2013

Staff: Mentor

Nobody have mentioned anthropic principle so far?

20. Dec 10, 2013

i did.