What about the multiverse?


Arguably, I think nobody has much of an idea at this point how they are compatible. But they must be…somehow.


There is clearly something missing. Either or both could be fundamentally wrong. Take the case of Newtonian physics. It’s compatible with current physics for many observations. However, the Newtonian mechanics fail in contrast to ‘modern’ theories in very notable situations. The only thing we can say is that whatever new unifying theory or extension comes next must explain the observations we’ve already collected. What theories we develop next will likely have a profound effect on our understanding about the Big Bang (among other things).


Right, but Newtonian physics isn’t “fundamentally wrong.” It’s the “best fit” for certain circumstances. The same could be true for gravity and quantum theories–not “fundamentally wrong” but incomplete. I think that’s the general consensus right now anyway, so it’s nice to know that you and I both agree with some really smart people.


This is a bit of a long quote, but it sums up my thoughts quite well.

For an analogy, suppose that there is a planet called Earthprime, in every respect identical to our own, except that on this planet mankind developed the science of physics without knowing anything about astronomy. (E.g., one might imagine that Earthprime’s surface is perpetually covered by clouds.) Just as on earth, students on Earthprime would find tables of fundamental constants at the back of their physics textbooks. These tables would list the speed of light, the mass of the electron, and so on, and also another “fundamental” constant having the value 1.99 calories of energy per minute per square centimeter, which gives the energy reaching Earthprime’s surface from some unknown source outside. On earth this is called the solar constant because we know that this energy comes from the sun, but no one on Earthprime would have any way of knowing where this energy comes from or why this constant takes this particular value. Some physicist on Earthprime might note that the observed value of this constant is remarkably well suited to the appearance of life. If Earthprime received much more or much less than 2 calories per minute per square centimeter the water of the oceans would instead be vapor or ice, leaving Earthprime with no liquid water or reasonable substitute in which life could have evolved. The physicist might conclude that this constant of 1.99 calories per minute per square centimeter had been finetuned by God for man’s benefit. More skeptical physicists on Earthprime might argue that such constants are eventually going to be explained by the final laws of physics, and that it is just a lucky accident that they have values favorable for life. In fact, both would be wrong. When the inhabitants of Earthprime finally develop a knowledge of astronomy, they learn that their planet receives 1.99 calories per minute per square centimeter because, like earth, it happens to be about 93 million miles away from a sun that produces 5,600 million million million million calories per minute, but they also see that there are other planets closer to their sun that are too hot for life and more planets farther from their sun that are too cold for life and doubtless countless other planets orbiting other stars of which only a small proportion are suitable for life. When they learn something about astronomy, the arguing physicists on Earthprime finally understand that the reason why they live on a world that receives roughly 2 calories per minute per square centimeter is just that there is no other kind of world where they could live. We in our part of the universe may be like the inhabitants of Earthprime before they learn about astronomy, but with other parts of the universe instead of other planets hidden from our view.
(Weinberg, S., “Dreams of a Final Theory,” Pantheon: New York NY, 1992, pp.252-253. Emphasis original)


Right. Now extend that to our situation. The “fine tuning” is in our “universe.” So it’s possible that there are multiple universes. That’s a solution to “fine tuning.” The problem is that it’s completely untestable. We can’t test other universes. So as a model it “works” but it’s more speculation than science. Consider that an inhabitant of Earthprime could, sooner or later, fly above the clouds. We cannot fly outside our universe.


From what I can see, all models (including the “God model”) are currently untestable and based on speculation.


I think Newtonian physics is fundamentally wrong. It is based on a set of principles that we have demonstrated simply aren’t correct (e.g. space-time has curvature). It’s like fitting a line to a hyperbola. A line is a fundamentally incorrect model for a hyperbola but within a finite portion of the curve, a linear model can provide a reasonable approximation.


Yup. So there are other reasons that people use to come to or justify their choice of one over the other.


What do you mean by “model”?

I would submit Jack Fraser’s (the first) answer to the question of the validity of Newton on this Quora thread:



By ‘model’, I mean a linear fit (y=mx + b) to a portion of a hyperbolic curve (y^2/a^2 - x^2/b^2 = 1). A linear model provides a perfectly reasonable approximation over any particular portion of a hyperbola. Similarly, Newtonian mechanics can provide a perfectly reasonable approximation for particular physical conditions. But like a line isn’t fundamentally correct model for a hyperbola, Newtonian physics isn’t a fundamentally correct model for gravitational mechanics. That’s how I’m using the term ‘fundamental’.

(David Heddle) #72

I completely (and respectfully!) disagree. Newton’s Gravitation is derivable from Einstein’s GR in the limit of non-relativistic speeds and flat space. That, to me, does not signify “fundamentally” wrong. It signifies that Netwon’s inverse-square gravitation is an approximation, which is quite different. Ptolemy’s epicycles, which are not derivable from Einstein, are an example of something that is fundamentally wrong.


But a functional model for a great many circumstances. So as a “model,” in those circumstances how can it be “fundamentally flawed” if it’s appropriate for those circumstances?

It might be “fundamentally flawed” for different circumstances, but that’s a misuse of the model, not a problem with the model itself.

Don’t you think?


It’s a bit like getting the math wrong but still getting the right answer on a math test. Getting the right answer may get you some credit, but you may not get full credit. A model that uses flat space and an instantaneous propagation of gravity is (relatively) wrong, even if it gives suitable answers in certain situations. Of course, all theories in science are wrong to a certain extent, so it isn’t like we are picking on Newton or anything like that. “The Relativity of Wrong” is a great essay by Asimov if you want a window into how scientists view these things:

“. . . when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together.”–Isaac Asimov, “The Relativity of Wrong”


That’s why I questioned what you meant by “models.” I think in science it’s less relevant that models are “correct” than they they work.

That’s an INCREDIBLE quote! (…and I don’t mean “incredible” literally; that’s seriously amazing, thanks!)


With the case of classical mechanics and relativity, they both give the good answers at low velocities and low gravity. However, they give different answers at high velocities and high gravity, and relativity gives answers that more closely match reality. This is a fundamental part of doing science, finding experiments where two competing ideas should give different answers, and then doing that experiment.


Right. And in the example I linked to, Newton’s model was more than “good enough.”


Just as a spherical Earth is a good enough model for most calculations, even though it isn’t a sphere.


Sure! The model is “good enough.” Again, many scientists today would talk in terms of “valuable models” or “effective models” rather than “true.”


What gives you this idea? Is there a poll out there showing this to be true?


No, a fair bit of general reading (including some pretty smart people like Stephen Hawking, a self-admitted logical positivist). Are you suggesting my appraisal is incorrect?