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Fine tuning, muitverse and a double standard

  1. Oct 1, 2015 #1
    I just watched a talk from George Ellis about cosmology. I believe there is a serious double standard implied in it.
    He says
    (A) the universe is fine tuned for life. Change one of the constants of nature like the mass of the electron and you wont have life in the universe.
    He also says
    (B)the multiverse might explain this fine tuning, but the multiverse is based on extrapolating physics to unknown realms that we cant observe and is therefore questionable science.

    However doesnt the statement (A) that life cant exist unless we have these very finely tuned constants also depend on extrapolating physics into realms we cant observe? After all no one can ever do an experiment whereby we change a constant of nature and then see if life still emerges. Perhaps changing one constant leads another to move to compensate, who knows? The conclusion of fine tuning seems to be based on just such an an unverifiable extrapolation that Ellis accuses the multiverse proponents of being guilty of .
    it seems to be if we allow for such extrapolations then both A and B can be fair game, but if we don't then neither A nor B is fair game.
  2. jcsd
  3. Oct 1, 2015 #2
    You can do computer simulations with tweaked constants.

    I'm sure he was referring to life like us, we require atoms and they have to act a very particular way, our chemistry is incredibly advanced. Making a small tweak in a big engine can easily break the engine.
  4. Oct 1, 2015 #3
    A simulation in a computer is not the same as doing an experiment or collecting data from nature. You cant do that with the constants of nature.
  5. Oct 1, 2015 #4


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    Doesn't even need to be, "life like us." It's very difficult to estimate the probability of life very unlike ourselves, but you can still approach the problem very broadly by examining the fundamental requirements of life, the most fundamental of which is the formation of structure. Life cannot exist if there is no gravitational collapse: you need matter to come together if there is to be any hope of any complex structures. And it turns out that you need a pretty narrow range of the known physical constants for any structures to form at all. The cosmological constant is particularly relevant: if the cosmological constant has a positive value greater than about ##10^{-120}##, then no structures can ever form because everything is blown away from everything else in an accelerated expansion before anything has a chance to form any kind of structure. If the cosmological constant has a negative value less than about ##-10^{-120}##, then the universe almost instantly recollapses and there's no time for any life to form.

    Physicists have, for a long time, tried to get around this conundrum by assuming there there must be some kind of symmetry that sets the cosmological constant to zero. No such symmetry has been found.

    You can delve into this problem a bit more carefully by examining other basic requirements. For example, if gravity is too strong, then anything that does enter into gravitational collapse simply becomes a black hole. If the constants that govern nuclear physics are off a bit then no heavy elements can ever form, so there's no possibility of complex chemistry.

    The real difficulty is that in order to approach the problem, you also need some kind of theory which describes the possible outcomes for the various physical constants. For example, imagine that we have physical constants A and B. A is measured to take the value 0.5, while B is measured to take the value 0.000000005. Naively the value of A=0.5 doesn't seem too weird. There's no need for a detailed explanation for numbers that are close to 1. But the value of 0.000000005? That's odd. It demands an explanation. One possible explanation might be that B can take any value from 0-1, but only values that are close to 0 permit any life to exist, so living organisms always observe values of B close to 0. Another explanation could be that the constants A and B are related: instead of being independent values, there's some fundamental relationship that sets B = A / 1,000,000,000, while A can take any value from 0-1. Suddenly the value for B no longer seems weird: it's a consequence of the way the fundamental laws behave and the random result of A.
  6. Oct 1, 2015 #5
    So a computer simulation of the universe with the initial conditions one million years after the Big Bang would predict bacteria, earthworms, birds, etc?
  7. Oct 1, 2015 #6


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    Theoretically, given a powerful enough computer, the necessary data, and a long enough time to run and it probably would. Of course there's no way to gather the necessary data since we can't go back in time to one-million years after the big bang. And if you don't have those exact conditions, there's no telling what this computer will predict (within reason).
  8. Oct 2, 2015 #7


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    What? No. Definitely not. Firstly, one million years isn't anywhere close to enough time. Our universe was basically nothing but a hydrogen and helium gas at that time. No galaxies, no stars. Just some parts of the gas were a bit more dense than others.

    Second, we don't know anywhere near enough to say definitively what conditions are necessary for life. The best we can do is say that some conditions would make life (any life) impossible. There are probably other ways the universe could be that also make life impossible, but we don't know for sure just how specific the requirements for life are.
  9. Oct 2, 2015 #8
    The issue I'm concerned with is not whether or not one can realistically model the universe and see if life should arise given different conditions. The issue is the very process itsetlf, what status should such a process be given? In particular if theoretical extrapolation beyond what is observable should not be allowed in science as Ellis seems to imply with the multiverse; then the same rules should we should not even talk about a universe with different constants. We cant observe the results and so such discussion is not science.
    Either extraploating beyond what we can directly observe is ok or its not. If it is the both the fine tuning problem and the multiverse as a solution are fair moves. But if its not ok then neither the question (fine tuning ) nor the answer (a mulitverse) should be allowed. I dont see why one is ok and the other is not.
  10. Oct 2, 2015 #9
    Theoretically, if you had a precise equation for the nature of the universe (which we don't) and it's deterministic (which we aren't sure it is) and you knew the exact initial conditions (which isn't possible) you could simulate the universe and after 13.8 billion years, that simulation would ponder the same question and build it's own simulation.
  11. Oct 2, 2015 #10


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    Assumptions are the achilles heel of simulations. Input one that is just slightly off and the consequences can take on a life of their own as the error can propogate exponentially. This factor in and of itself can give the illusion of fine tuning where none is necessary A more important consideration may be the relationship between relevant fundamental constants. I see no compelling reason to assume they exist blindly and arbitrarily. I prefer the idea that nature preserves specific, and likely highly complex relationships between fundamental constants according to rules we would find, assuming we knew and understood them, both logical and mathematically elegant. This would explain why we do not see runaway feedback loops in nature. All known physical processes appear to include a built in dampening mechanism.
  12. Oct 3, 2015 #11


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    But maybe to do that calculation your computer produced so much heat that it influences the universe in the time your calculation is finished in such a way that the macroscopic effect cannot be neglected anymore.
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