EDIT: this is now pretty much retracted, see the following thread.
If the reductionist thesis is “we use multi-level models for computational reasons, but physical reality has only a single level”, then what kind of evidence could support it against the thesis “we use multi-level models for computational reasons AND physical reality has multiple levels?”
Lower level models are more accurate than abstract models, and you can observe the consequences of this on multiple levels of abstraction. Therefore if physical reality has multiple levels then they must be incompatible and parallel in a very peculiar way. This makes the idea more complex and therefore less probable than the reductionist thesis.
Even if the argument “Occam’s Razor says that since reality having only one level is simpler than reality having multiple levels, then the first option is more likely to be true.” was valid, there is a problem.
Contrarily to other contexts where Occam’s Razor is actually useful, none of these options lead us to anticipate differently under any circumstance, so the rational thing to do here is not to apply Occam’s Razor, but to reject the question “Does physical reality have one level or multiple levels?”
Edit: Note that I did not mean to say that you should not apply Occam’s Razor at all in this scenario. Perhaps, given the hypothesis that reality has multiple levels, Occam’s Razor makes certain phenomena more likely, and observations regarding these phenomena could be used to argue for or against the reductionist thesis. The point is that I cannot find examples of such phenomena, specially if the kind of multiple levels that we are talking about are purely physical.
Wait. Perhaps one of such predictions would be that we should find universal laws involving higher-level entities, while it seems that at that level, we only find ceteris paribus laws. By contrast, at the lower level, we do find universal laws. This should be evidence in favour of the reductionist thesis.
Which would indicate that I was wrong in my initial claim.
Actually when I first responded to you I was thinking about biology, psychology and such as the higher level. In this case the claim seems to make sense. However, if I understood EHeller correctly, this doesn’t hold water inside the realm of modern physics. Besides, we can in principle never know if we’re at the lowest level.
The whole point of the renormalization group is that lower level models aren’t more accurate, the lower level effects average out.
The multiple levels of reality are “parallel in a peculiar way” governed by RG. It might be “more complex” but it’s also the backbone of modern physics.
The whole point of the renormalization group is that lower level models aren’t more accurate, the lower level effects average out.
I tried to read about RG but it went way over my head. Is the universe in principle inexplicable by lower level theories alone according to modern physics? Doesn’t “averaging out” lose information? Are different levels of abstraction considered equally real by RG? Does this question even matter or is it in the realm of unobservables in the vein of Copenhagen vs MW interpretation?
The point of RG is that “higher level” physics is independent of most “lower level” physics. There are infinitely many low level theories that could lead to a plane flying.
There are infinitely many lower level theories that could lead to quarks behaving as they do,etc. So 1. you can’t deduce low level physics from high level physics (i.e. you could never figure out quarks by making careful measurements of tennis balls), and you can never know if you have truly found the lowest level theory (there might be a totally different theory if you only had the ability to probe higher energies).
This is super convenient for us- we don’t need to know the mass of the top quark to figure out the hydrogen atom,etc. Also, it’s a nice explanation for why the laws of physics look so simple- the laws of physics are the fixed points of renormalization group flow.
Thanks, my reality got just a bit weirder. It’s almost as if someone set up a convenient playground for us, but that must be my apophenia speaking. If there are infinite possibilities of lower level theories, are successful predictions in particle physics just a matter of parsimony? Is there profuse survival bias when it comes to hyping successful predictions?
I think I’m communicating a little poorly. So start with atomic level physics- it’s characterized by energy scales of 13.6 eV or so. Making measurements at that scale will tell you a lot about atomic level physics, but it won’t tell you anything about lower level physics- there is an infinite number of of lower level physics theories that will be compatible with your atomic theory (which is why you don’t need the mass of the top quark to calculate the hydrogen energy levels- conversely you can’t find the mass of the top quark by measuring those levels).
So you build a more powerful microscope, now you can get to 200*10^6 eV. Now you’ll start creating all sorts of subatomic particles and you can build QCD up as a theory (which is one of the infinitely many theories compatible with atomic theory). But you can’t infer anything about the physics that might live at even lower levels.
So you build a yet more powerful microscope, now you can get 10^14 eV, and you start to see the second generation of quarks,etc.
At every new level you get to, there might be yet more physics below that length scale. The fundamental length scale is maybe the planck scale, and we are still 13 orders of magnitude above that.
I think I’m the one communicating poorly since it seems I understood your first explanation, thanks for making it sure anyways and thanks for the link!
When I was wondering about successful predictions in particle physics, I was in particular thinking about Higgs boson. We needed to build a massive “microscope” to detect it, yet could predict its existence four decades ago with much lower energy scale equipment, right?
The existence of the Higg’s is one of the rare bits of physics that doesn’t average out under renormalization.
The reason is that the Higgs is deeply related to the overall symmetry of the whole standard model- you start with a symmetry group SU(2)xU(1) and then the Higgs messes with the symmetry so you end up with just U(1) symmetry. What the theory predicts is relationships between the Higgs, the W and Z boson, but not the absolute scale. The general rule is RG flow respects symmetries, but other stuff gets washed out.
This is why the prediction was actually “at least 1 scalar particle that interacts with W and Z bosons”. But there are lots of models consistent with this- it could have been a composite particle made of new quark-like-things (technicolor models), there could be multiple Higgs (2 in SUSY, dozens in some grand unified models),etc. So it’s sort of an existence proof with no details.
EDIT: this is now pretty much retracted, see the following thread.
Lower level models are more accurate than abstract models, and you can observe the consequences of this on multiple levels of abstraction. Therefore if physical reality has multiple levels then they must be incompatible and parallel in a very peculiar way. This makes the idea more complex and therefore less probable than the reductionist thesis.
Tabooing reality might make things a bit clearer.
Even if the argument “Occam’s Razor says that since reality having only one level is simpler than reality having multiple levels, then the first option is more likely to be true.” was valid, there is a problem.
Contrarily to other contexts where Occam’s Razor is actually useful, none of these options lead us to anticipate differently under any circumstance, so the rational thing to do here is not to apply Occam’s Razor, but to reject the question “Does physical reality have one level or multiple levels?”
Edit: Note that I did not mean to say that you should not apply Occam’s Razor at all in this scenario. Perhaps, given the hypothesis that reality has multiple levels, Occam’s Razor makes certain phenomena more likely, and observations regarding these phenomena could be used to argue for or against the reductionist thesis. The point is that I cannot find examples of such phenomena, specially if the kind of multiple levels that we are talking about are purely physical.
Wait. Perhaps one of such predictions would be that we should find universal laws involving higher-level entities, while it seems that at that level, we only find ceteris paribus laws. By contrast, at the lower level, we do find universal laws. This should be evidence in favour of the reductionist thesis.
Which would indicate that I was wrong in my initial claim.
Actually when I first responded to you I was thinking about biology, psychology and such as the higher level. In this case the claim seems to make sense. However, if I understood EHeller correctly, this doesn’t hold water inside the realm of modern physics. Besides, we can in principle never know if we’re at the lowest level.
The whole point of the renormalization group is that lower level models aren’t more accurate, the lower level effects average out.
The multiple levels of reality are “parallel in a peculiar way” governed by RG. It might be “more complex” but it’s also the backbone of modern physics.
I tried to read about RG but it went way over my head. Is the universe in principle inexplicable by lower level theories alone according to modern physics? Doesn’t “averaging out” lose information? Are different levels of abstraction considered equally real by RG? Does this question even matter or is it in the realm of unobservables in the vein of Copenhagen vs MW interpretation?
The point of RG is that “higher level” physics is independent of most “lower level” physics. There are infinitely many low level theories that could lead to a plane flying.
There are infinitely many lower level theories that could lead to quarks behaving as they do,etc. So 1. you can’t deduce low level physics from high level physics (i.e. you could never figure out quarks by making careful measurements of tennis balls), and you can never know if you have truly found the lowest level theory (there might be a totally different theory if you only had the ability to probe higher energies).
This is super convenient for us- we don’t need to know the mass of the top quark to figure out the hydrogen atom,etc. Also, it’s a nice explanation for why the laws of physics look so simple- the laws of physics are the fixed points of renormalization group flow.
Thanks, my reality got just a bit weirder. It’s almost as if someone set up a convenient playground for us, but that must be my apophenia speaking. If there are infinite possibilities of lower level theories, are successful predictions in particle physics just a matter of parsimony? Is there profuse survival bias when it comes to hyping successful predictions?
I think I’m communicating a little poorly. So start with atomic level physics- it’s characterized by energy scales of 13.6 eV or so. Making measurements at that scale will tell you a lot about atomic level physics, but it won’t tell you anything about lower level physics- there is an infinite number of of lower level physics theories that will be compatible with your atomic theory (which is why you don’t need the mass of the top quark to calculate the hydrogen energy levels- conversely you can’t find the mass of the top quark by measuring those levels).
So you build a more powerful microscope, now you can get to 200*10^6 eV. Now you’ll start creating all sorts of subatomic particles and you can build QCD up as a theory (which is one of the infinitely many theories compatible with atomic theory). But you can’t infer anything about the physics that might live at even lower levels.
So you build a yet more powerful microscope, now you can get 10^14 eV, and you start to see the second generation of quarks,etc.
At every new level you get to, there might be yet more physics below that length scale. The fundamental length scale is maybe the planck scale, and we are still 13 orders of magnitude above that.
Edit: this author is sort of a dick overall, but this was a good piece on the renormalization group- http://su3su2u1.tumblr.com/post/123586152663/renormalization-group-and-deep-learning-part-1
I think I’m the one communicating poorly since it seems I understood your first explanation, thanks for making it sure anyways and thanks for the link!
When I was wondering about successful predictions in particle physics, I was in particular thinking about Higgs boson. We needed to build a massive “microscope” to detect it, yet could predict its existence four decades ago with much lower energy scale equipment, right?
The existence of the Higg’s is one of the rare bits of physics that doesn’t average out under renormalization.
The reason is that the Higgs is deeply related to the overall symmetry of the whole standard model- you start with a symmetry group SU(2)xU(1) and then the Higgs messes with the symmetry so you end up with just U(1) symmetry. What the theory predicts is relationships between the Higgs, the W and Z boson, but not the absolute scale. The general rule is RG flow respects symmetries, but other stuff gets washed out.
This is why the prediction was actually “at least 1 scalar particle that interacts with W and Z bosons”. But there are lots of models consistent with this- it could have been a composite particle made of new quark-like-things (technicolor models), there could be multiple Higgs (2 in SUSY, dozens in some grand unified models),etc. So it’s sort of an existence proof with no details.