Well, I agree with Sean Carrol about there being shades of grey as to what constitutes a scientific or unscientific theory. I also agree with him regarding some people taking falsification to extremes, even if the references he cites don't actually demonstrate this.
I agree with the other authors that the multiverse isn't business as usual, because you can't test - not falsify, but merely even evaluate it against other theories - its major prediction. I think the Nature article linked by Carrol says it best :
As we see it, theoretical physics risks becoming a no-man's-land between mathematics, physics and philosophy that does not truly meet the requirements of any.
Cosomology, someone once said, is always on the edge of mysticism. And regarding the Many Worlds interpretation - surely the philosophical next of kin to the inflationary multiverse - someome else once said, "surely it doesn't take the creation of an entire universe to kill one cat." And again from the Nature article :
In our view, cosmologists should heed mathematician David Hilbert's warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.
However, I take issue with a couple of points in the Nature article :
In our view, the issue boils down to clarifying one question: what potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory... Dawid argues that the veracity of string theory can be established through philosophical and probabilistic arguments about the research process... Instead of belief in a scientific theory increasing when observational evidence arises to support it, he suggests that theoretical discoveries bolster belief.
Well, this clearly does show that Carrol was not attacking a straw man when he said that some people take falsification and even testability too far. Yet while it's wrong to suggest that belief in a theory should increase because of theoretical arguments, that doesn't mean that theoretical arguments can't lend a preference for it. It's a very good thing, in my opinion, to prefer simple ideas that avoid infinities. You just shouldn't cling militantly to that mere preference in the face of the evidence.
I'll further muddy the waters by noting that "scientific" and "useful" are certainly not the same thing, nor is being useful even necessary for a scientific theory. The idea that the Universe may extend beyond the visible horizon is logical, rational, eminently scientific and perhaps even escapable given current knowledge. The idea that it extends to infinity and perhaps contains other spacetimes with different physical laws, well, I don't know if that's scientific or not - it's certainly not pseudoscience or mystical woo, so perhaps it's a new class of weird - but it's definitely useless (though see Hossenfelder's blog post).
Also :
http://astrorhysy.blogspot.cz/2017/05/i-told-you-he-was-tricksy.html
http://astrorhysy.blogspot.cz/2016/03/youll-have-your-eye-out-with-that.html
Originally shared by Abhijeet Borkar
Some really interesting discussions going on in the field of Philosophy of Science:
https://www.preposterousuniverse.com/blog/2018/01/17/beyond-falsifiability/
http://www.math.columbia.edu/~woit/wordpress/?p=9938
https://platofootnote.wordpress.com/2018/01/22/peter-woit-vs-sean-carroll-string-theory-the-multiverse-and-popperazism/
and
https://www.npr.org/sections/13.7/2018/01/22/579666359/scientific-theory-and-the-multiverse-madness
https://www.preposterousuniverse.com/blog/2018/01/17/beyond-falsifiability/
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Science doesn't need to be useful to us to be both true, and valid. In order for us to know science though, and whether any part of that science is true, we must be able to measure it, repeat that measurement, and that measurement must be consistent, even if the measurement remains consistently inconsistent . Then, and only then can we comprehend the content within that science, and whether it is true, or not.
ReplyDeleteWhether some theory might be true about our multiverse is irrelevant with respect to everything except to testing that theory. If it might be true it continues to need to be tested, until it can be verified as true, ...or not, in which case the theory collapses.
Same goes for any "grey" areas. If there is a grey area, then the theory, or measurement of that theory is not complete, or the theory contains some incorrect components, scientifically speaking.
Placeholder theories have their place. They act as placeholders until something better comes along. E.g., Rydberg's spectral equation, or Bohr's orbital equation. Of course with the acceptances of a "placeholder", its not apparent that the incumbent theory will be replaced.
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In our view, cosmologists should heed mathematician David Hilbert's warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.
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"Infinity" is just another name for "unbounded". Because these are abstract concepts you can just say well say "as n approaches infinity", and call n finite. If you ask how big the universe is ... as how big can a reference length be?
There are certainly interesting theories which are useful, useless theories which are interesting, and useless theories which are not interesting. The infinite multiverse (and its variants) currently fall in the middle ground, in my opinion. It might be true. But "everything happens somewhere" currently lacks much credence to be a scientific theory even if it is true. It's the measure problem : you can't have meaningful probabilities if reality is infinite. Worse, multiversers seem (often) to use this as an asset, trying to explain specific problems because "everything happens somewhere" whilst trying to stick to hard, proper physics elsewhere. It's trying to have your cake and eat it.
ReplyDeleteI would venture to go even further, and say that any statistical explanation for why the Universe is the way it is (i.e. just chance alone) is not really science. You have to have a mechanism by which things act. Electrons don't flow "because that's just the way they happened to be moving", objects don't fall to the ground "because they just do", the value of G isn't 6.67E-11 because "why not ?". It takes more than dice to make a theory.
Which does not preclude the proto-science multiverse or string theory from becoming genuine science, one day. If the measure problem could be solved, so that you could somehow assign a probability even given infinities, and still show that physical processes could remain meaningful (i.e. not everything is occuring due to chance, but that there really are actual fundamental mechanisms driving physical processes), then it would be much more interesting and maybe even useful.