I recently had a surprise chance to meet Max Tegmark, and so I first quickly read his enjoyable new book The Mathematical Universe. It covers many foundations of physics topics that he correctly says are unfairly neglected. Since I’ve collected many opinions on foundation of physics over decades, I can’t resist mentioning the many ways I agree and disagree with him.
"he sees the simulation argument as self-destructing because since we know nothing about the universe that might simulate us, it could also be simulated by another universe, which is a “a reductio ad absurdum.”
There is no need for MWI to assign different versions of you to different worlds. Nothing labels your counterparts other than their having had different histories as a result of having lived in different worlds, which is to say, their identities and the identites of he worlds they live in match up automatically without ant special mechanism.
QM does not assume absolute time and space, the subfield of QED (quantum electrodynamics) incorporates relativistic principles.
Newton's assumption about absolute time and space was wrong but even today his laws of motion still stands (although you have to tweak the math of the second law to make it compatible with relativity). In the same way QM undoubtedly contains principles that will hold no matter what deeper physics will be found and we have some indications of which principles those will be. It is worthwhile to do foundational research into the principles even if a few of them will later be proven false (or more likely, get a correcting term added to them), that is at the current levels of spending (which are low compared to global GDP or even the science budgets of the world's nations), not in the least because this kind of research tends to create useful mathematical spin-off.
The problem seems to me to be that MW doesn't, in fact, provide in-principle determinism: there is no deterministic mechanism (or any mechanism) hypothesized assigning any particular version of "you" to a "world."
Thus in order to explain the just-so-ness of the universe, we postulate the existence of other universes.
What I'm not clear about in the anthropic argument for multiple universes is what's so special or "interesting" about life? Life is just one kind of complexity, as judged by one metric. (Our choice of this metric, our metric, isn't happenstance.)
Is there some absolute metric for complexity? I don't think so: degree of complexity seems language-relative.
Is there really any question that qm is false in its assumption of absolute space and time?
Here's an historical parallel. Newton declined to philosophize about foundations, but Leibnitz accepted the challenge and arrived at a kind of relativistic conception. Newton's absolutist assumptions were false, and laying foundations would have been misleading. (Absolute time and space was [it is said] a necessary assumption at that stage in the development of physical science.)
The basic falsity of this assumption was not a bar to making correct predictions within acceptable tolerance in many practical circumstances, but it was nonetheless a false clue about reality.
On the low status of these researchers. I think that has to do with laymen thinking their will never applications of the research and other scientists suspecting the fundamental researchers of hiding away in an ivory tower and not being productive (even for another physicist it's hard to judge whether a theoretical physicist is working hard or just doodling and drinking coffee most of the day, pretending to work).
"Foundations of physics gets unfairly neglected. People who do it have to hide it to save their careers."Lee Smolin, in the last third of his superb book "The Trouble with Physics," speaks eloquently on this general topic.Smolin [2006] believes that the reason the list of the five biggest outstanding problems in physics hasn't changed at all in 30 years (a situation I believe he characterizes as unprecedented in recent centuries) is thata) unlike the 1930s & 1940s. when the challenge was to do calculations/extend models within an existing framework, the current key problems will require fundamental new insights for their solution (much as in the 1st 2 decades of the 20th century);b) the current sociology of the physics community actively and severely discourages revolutionary thinkers willing to question foundations and generate such insights, in favor of superb technicians who demonstrate the ability to push ahead on currently-favored lines of research.c) one major enabler of b) is that geezers such as himself have way too much power over the young people.Great book, and not just for the physics. If you read the last two pages you will be at risk of reading it backwards to the beginning, so grab a bite to eat first.
Well, if you could collect the "yous" in one universe they would have different memories so they are distinguishable, it's just that you have no way of collecting them. Yet, through QM nature has given us some reason to believe the other "yous" do exist (it is of course also possible the universe really is probabilistic).
"But is it sensible to try to provide foundations for a theory you know must be fundamentally false?"
Well, QM might be entirely true with the fault lying with relativity, or both might have relatively minor flaws or both are true within a certain domain (like classical mechanics), being underpinned by a deeper layer of physics that connects them. It is almost without question that some of the "weird" results from QM will hold even if a deeper theory is eventually found and those results need explaining, in the same way the doppler effect's explanation still stands even though we now know classical mechanics is not the whole story.
The question is whether it is possible to know a truth that is unverifiable. If reality doesn't satisfy us by being verifiable, it may (will?) also fail to satisfy us in being knowable.
(Perhaps the barriers to precision in qm are epistemic rather than ontic, but are absolute, so we never will know the foundations.)
[I don't want to press this point too hard because it requires drawing and motivating a distinction between contingent unverifiability and unverifiability in principle.]
Stephen, you (and truth_machine) appear to be conflating "verifiable truth" and "truth."It would indeed be vastly more satisfying to find/converge toward a *verifiably* (in the sense of passing increasingly stringent tests) true theory of the universe, and all else equal, such theories should be given search priority; but as far as I can see, reality is under no obligation to satisfy us by being verifiable.
"he sees the simulation argument as self-destructing because since we know nothing about the universe that might simulate us, it could also be simulated by another universe, which is a “a reductio ad absurdum.”
There is nothing absurd about that.
@Stephen
There is no need for MWI to assign different versions of you to different worlds. Nothing labels your counterparts other than their having had different histories as a result of having lived in different worlds, which is to say, their identities and the identites of he worlds they live in match up automatically without ant special mechanism.
Consider the MWI response to Schrodingers Cat.
@Stephen
MWI gives the correct probabilities for observed outcomes because it uses the standard QM apparatus, which works.
You split along with the worlds, you don't jump from one to the other.
Relative proportions are perfectly meaningful with infinities. Eg even numbers and integers exist in the proportion 1:2.
See The Fabric of Reality.
....and relativity says locality is true, which is how you get from either-nonlocality-or-indeterminism to indeterminism.
QM does not assume absolute time and space, the subfield of QED (quantum electrodynamics) incorporates relativistic principles.
Newton's assumption about absolute time and space was wrong but even today his laws of motion still stands (although you have to tweak the math of the second law to make it compatible with relativity). In the same way QM undoubtedly contains principles that will hold no matter what deeper physics will be found and we have some indications of which principles those will be. It is worthwhile to do foundational research into the principles even if a few of them will later be proven false (or more likely, get a correcting term added to them), that is at the current levels of spending (which are low compared to global GDP or even the science budgets of the world's nations), not in the least because this kind of research tends to create useful mathematical spin-off.
Things are even worse that that, truth_machine. You don't have direct evidence of *this* world.
@StephenPositing that the barriers to precision in QM are epistemic rather than ontic is what leads to hidden variables, nonlocality, etc.
The problem seems to me to be that MW doesn't, in fact, provide in-principle determinism: there is no deterministic mechanism (or any mechanism) hypothesized assigning any particular version of "you" to a "world."
If the many worlds interpretation could offer predictability as well as in-principle determinism , it would be a theory not an interpretation.
Thus in order to explain the just-so-ness of the universe, we postulate the existence of other universes.
What I'm not clear about in the anthropic argument for multiple universes is what's so special or "interesting" about life? Life is just one kind of complexity, as judged by one metric. (Our choice of this metric, our metric, isn't happenstance.)
Is there some absolute metric for complexity? I don't think so: degree of complexity seems language-relative.
Is there really any question that qm is false in its assumption of absolute space and time?
Here's an historical parallel. Newton declined to philosophize about foundations, but Leibnitz accepted the challenge and arrived at a kind of relativistic conception. Newton's absolutist assumptions were false, and laying foundations would have been misleading. (Absolute time and space was [it is said] a necessary assumption at that stage in the development of physical science.)
The basic falsity of this assumption was not a bar to making correct predictions within acceptable tolerance in many practical circumstances, but it was nonetheless a false clue about reality.
On the low status of these researchers. I think that has to do with laymen thinking their will never applications of the research and other scientists suspecting the fundamental researchers of hiding away in an ivory tower and not being productive (even for another physicist it's hard to judge whether a theoretical physicist is working hard or just doodling and drinking coffee most of the day, pretending to work).
"Foundations of physics gets unfairly neglected. People who do it have to hide it to save their careers."Lee Smolin, in the last third of his superb book "The Trouble with Physics," speaks eloquently on this general topic.Smolin [2006] believes that the reason the list of the five biggest outstanding problems in physics hasn't changed at all in 30 years (a situation I believe he characterizes as unprecedented in recent centuries) is thata) unlike the 1930s & 1940s. when the challenge was to do calculations/extend models within an existing framework, the current key problems will require fundamental new insights for their solution (much as in the 1st 2 decades of the 20th century);b) the current sociology of the physics community actively and severely discourages revolutionary thinkers willing to question foundations and generate such insights, in favor of superb technicians who demonstrate the ability to push ahead on currently-favored lines of research.c) one major enabler of b) is that geezers such as himself have way too much power over the young people.Great book, and not just for the physics. If you read the last two pages you will be at risk of reading it backwards to the beginning, so grab a bite to eat first.
Well, if you could collect the "yous" in one universe they would have different memories so they are distinguishable, it's just that you have no way of collecting them. Yet, through QM nature has given us some reason to believe the other "yous" do exist (it is of course also possible the universe really is probabilistic).
"But is it sensible to try to provide foundations for a theory you know must be fundamentally false?"
Well, QM might be entirely true with the fault lying with relativity, or both might have relatively minor flaws or both are true within a certain domain (like classical mechanics), being underpinned by a deeper layer of physics that connects them. It is almost without question that some of the "weird" results from QM will hold even if a deeper theory is eventually found and those results need explaining, in the same way the doppler effect's explanation still stands even though we now know classical mechanics is not the whole story.
The question is whether it is possible to know a truth that is unverifiable. If reality doesn't satisfy us by being verifiable, it may (will?) also fail to satisfy us in being knowable.
(Perhaps the barriers to precision in qm are epistemic rather than ontic, but are absolute, so we never will know the foundations.)
[I don't want to press this point too hard because it requires drawing and motivating a distinction between contingent unverifiability and unverifiability in principle.]
Stephen, you (and truth_machine) appear to be conflating "verifiable truth" and "truth."It would indeed be vastly more satisfying to find/converge toward a *verifiably* (in the sense of passing increasingly stringent tests) true theory of the universe, and all else equal, such theories should be given search priority; but as far as I can see, reality is under no obligation to satisfy us by being verifiable.