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> The issue with fine tuning is that the curvature of the universe is directly tied to the mass/energy density and any deviation from an extremely narrow range

> The issue with fine tuning is that the curvature of the universe is directly tied to the mass/energy density and any deviation from an extremely narrow range which our universe seems to sit in out of all possible values would not just produce a universe with triangles with fewer or more degrees than 180 but would either produce a universe that would collapse on itself within a blink of an eye or expand so fast that gravity would never be strong enough to cause even the most basic structures to form. Well, the notion of "extremely narrow range" is arbitrary. There is no mathematical notion of "large numbers" vs "small numbers". If the constants you speak about were 10^-g64 (Graham's number) times larger or smaller than they are, nothing would really change. If they were 2 times smaller, the universe would be extremely different. But 2 and 10^-g64 are just numbers. Neither of them is inherently large or small. We just happen to understand 1, 2, 3, ... much better than g64. You could say that there is a surprising amount of leg-room in the values of some constants of nature, while others can only vary in a reasonable range. While the fine-structure constant can vary within a reasonable +-1/1000 range without massive changes, other values can vary by massive numbers such as +-2!

dogma1138 5y ago
The range doesn’t have anything to do with “numbers” directly because yes you can always say there is an infinity between any two numbers no matter how close they are to each other. The very limited range is actually captured in physical quantities. Back to the original analogy Pi is always exactly Pi not because we count it as 3.14~… but because of the relationship between the various innate properties of a circle. So fine tuning isn’t that oh gosh we got very oddly specific values here is that we have problems such as https://en.m.wikipedia.org/wiki/Hierarchy_problem https://en.m.wikipedia.org/wiki/Hierarchy_problem that are only solvable through fine tuning. So back to the circle it’s really a case of use not understanding the relationship between the circumference and the radius and just brute forcing the value of Pi which is really what fine tuning is.
- tsimionescu 5y ago
  Sure, but none of this must have a fundamental explanation. It could just be the way the universe is, nothing in maths requires this 'problem' to have a solution. Conversely, things like the measurement problem, quantum gravity, dark matter, dark energy, the mass of neutrinos and others must have some answer - they are facts we can see that just don't mesh with current theories. So why study a problem that there is no reason to believe will have an ultimate answer, when you can study problems that must have such an answer?
  - dogma1138 5y ago
    Ok let me try to maybe make it simpler. Back to the circle… take a string and pin trace a circle with it, take another piece of string and trace it. Cut the traced string in half each half would not have the value Pi (granted the original string you had used to draw the circle has a value of one). That relationship is fundamental and the answer we are trying to find is exactly is this fundamental relationship that would explain why the constants have the values they have. As in there needs to be a certain mechanism that defined those values in relationship to each other in a manner that does not require “fine tuning” because that would require either an infinite number of other universes which can have different values regardless of the fate of those universes or a cycle of death and rebirth in which these values somehow can be randomized (which opens a whole other question how does that happen?).
    - tsimionescu 5y ago
      The circle is a nice example where there is a simple analytical relationship between the radius and the circumference (1:2pi). Other basic shapes, like the ellipse, have no such simple relationship, even in pure maths. And when performing the experiment you mentioned, the strings are very unlikely to be in 1:2pi ratio, they will be within some range of that ratio. The universe has some set of independent initial parameters. Whether they are the ones we know or there are some other, more fundamental ones, ultimately some parameters are there. Even with a single fundamental parameter, that parameter will have some range within which variations in value don't affect the universe at all (like the 1/g64 example), and some range where changes in them would lead to a very different universe, potentially one that can't sustain life. This idea of "probability" of the observed values of these parameters is then meaningless. What is the probability distribution of the "universes"? To say that the "fine tuned" universe is "unlikely" you have to posit a probability distribution, but there is no empirical data to then verify if this distribution is correct, and, crucially, there can never be such empirical data. You might as well ask yourself why the universe is four-dimensional (or 11-dimensional) and not 2-dimensional.
panda-giddiness 5y ago
I'm not sure I understand your point. There is such a thing as "large" and "small" in physics, but they're relative to the scale you're considering. For example, if you're a million miles from the Earth, then from a gravitational perspective you may as well be infinitely far away (a ~ 10^-5 g). But if you were the same distance from the sun, gravity would be extremely relevant for you (a ~ 5 g). Moreover, I find it unfathomable that the scale 1/g64 would be relevant anywhere in physics – I certainly can't think of any examples!
- simiones 5y ago
  There is such a thing as "large" and "small" as related to measurement and impact. But a change in a base parameter of the laws of physics is different. If a change of 1/10% in the value of one parameter is detectable, than it is "a large change". If a change of 200% in the value of another parameter is not detectable, then it is "a small change". But the fine tuning argument relies on defining an absolute idea of "large" and "small". In the fine tuning problem definition, 1/10% is "small" and 200% is "large", and it's the parameters themselves that behave strangely, since one parameter produces visible results for "small" changes while another doesn't. Get rid of the absolute ideas of "small" and "large" numbers, and the fine tuning problem goes away entirely. > Moreover, I find it unfathomable that the scale 1/g64 would be relevant anywhere in physics – I certainly can't think of any examples! My point about 1/g64 was that, for all physical quantities, there is some scale at which they can vary without measurable differences. I took such a fantastically small number exactly to make sure I'm not risking a case where the factor I gave as an example would in fact cause detectable differences.

dogma1138 5y ago

The range doesn’t have anything to do with “numbers” directly because yes you can always say there is an infinity between any two numbers no matter how close they are to each other. The very limited range is actually captured in physical quantities. Back to the original analogy Pi is always exactly Pi not because we count it as 3.14~… but because of the relationship between the various innate properties of a circle. So fine tuning isn’t that oh gosh we got very oddly specific values here is that we have problems such as https://en.m.wikipedia.org/wiki/Hierarchy_problem https://en.m.wikipedia.org/wiki/Hierarchy_problem that are only solvable through fine tuning. So back to the circle it’s really a case of use not understanding the relationship between the circumference and the radius and just brute forcing the value of Pi which is really what fine tuning is.

tsimionescu 5y ago
Sure, but none of this must have a fundamental explanation. It could just be the way the universe is, nothing in maths requires this 'problem' to have a solution. Conversely, things like the measurement problem, quantum gravity, dark matter, dark energy, the mass of neutrinos and others must have some answer - they are facts we can see that just don't mesh with current theories. So why study a problem that there is no reason to believe will have an ultimate answer, when you can study problems that must have such an answer?
- dogma1138 5y ago
  Ok let me try to maybe make it simpler. Back to the circle… take a string and pin trace a circle with it, take another piece of string and trace it. Cut the traced string in half each half would not have the value Pi (granted the original string you had used to draw the circle has a value of one). That relationship is fundamental and the answer we are trying to find is exactly is this fundamental relationship that would explain why the constants have the values they have. As in there needs to be a certain mechanism that defined those values in relationship to each other in a manner that does not require “fine tuning” because that would require either an infinite number of other universes which can have different values regardless of the fate of those universes or a cycle of death and rebirth in which these values somehow can be randomized (which opens a whole other question how does that happen?).
  - tsimionescu 5y ago
    The circle is a nice example where there is a simple analytical relationship between the radius and the circumference (1:2pi). Other basic shapes, like the ellipse, have no such simple relationship, even in pure maths. And when performing the experiment you mentioned, the strings are very unlikely to be in 1:2pi ratio, they will be within some range of that ratio. The universe has some set of independent initial parameters. Whether they are the ones we know or there are some other, more fundamental ones, ultimately some parameters are there. Even with a single fundamental parameter, that parameter will have some range within which variations in value don't affect the universe at all (like the 1/g64 example), and some range where changes in them would lead to a very different universe, potentially one that can't sustain life. This idea of "probability" of the observed values of these parameters is then meaningless. What is the probability distribution of the "universes"? To say that the "fine tuned" universe is "unlikely" you have to posit a probability distribution, but there is no empirical data to then verify if this distribution is correct, and, crucially, there can never be such empirical data. You might as well ask yourself why the universe is four-dimensional (or 11-dimensional) and not 2-dimensional.

panda-giddiness 5y ago

I'm not sure I understand your point. There is such a thing as "large" and "small" in physics, but they're relative to the scale you're considering. For example, if you're a million miles from the Earth, then from a gravitational perspective you may as well be infinitely far away (a ~ 10^-5 g). But if you were the same distance from the sun, gravity would be extremely relevant for you (a ~ 5 g). Moreover, I find it unfathomable that the scale 1/g64 would be relevant anywhere in physics – I certainly can't think of any examples!

simiones 5y ago
There is such a thing as "large" and "small" as related to measurement and impact. But a change in a base parameter of the laws of physics is different. If a change of 1/10% in the value of one parameter is detectable, than it is "a large change". If a change of 200% in the value of another parameter is not detectable, then it is "a small change". But the fine tuning argument relies on defining an absolute idea of "large" and "small". In the fine tuning problem definition, 1/10% is "small" and 200% is "large", and it's the parameters themselves that behave strangely, since one parameter produces visible results for "small" changes while another doesn't. Get rid of the absolute ideas of "small" and "large" numbers, and the fine tuning problem goes away entirely. > Moreover, I find it unfathomable that the scale 1/g64 would be relevant anywhere in physics – I certainly can't think of any examples! My point about 1/g64 was that, for all physical quantities, there is some scale at which they can vary without measurable differences. I took such a fantastically small number exactly to make sure I'm not risking a case where the factor I gave as an example would in fact cause detectable differences.