4 ms·

I wonder if this is like ancient astronomers finding more and more epicycles.

by lacker 5y ago

at_a_remove 5y ago
Not especially, no. This is more akin to finding new molecules (hadrons), given known kinds of atoms (quarks).
eddieh 5y ago
Nah, they're more like elements, but they're made of quarks not nucleons (protons/neutrons). I think the modern equivalent of epicycles is string theory. Find an inconstancy? No problem, add a dimension.
- s1dev 5y ago
  That's not quite true. The dimension of the ambient space is constrained to be exactly 10 (in strings, 11 in M-theory) by consistency considerations. The important question is what is the geometry of the extra dimensions, if they exist. You need a large amount of energy to probe the extra dimensions, so it would appear just like some extra particles in the theory to a low energy observer. (Of course, the observer has to have enough energy to find even those particles). The standard model also has seemingly arbitrary particle content and interactions without much to constrain it. A majority of the particle content was put in the theory by hand after seeing a failure of the theory. In strings, this choice has been moved from the theory to the initial data (choice of geometry of the extra dimensions).
  - eddieh 5y ago
    I'm not a theoretical physicist and only took a few math courses beyond which were required by my major, but it was my understanding that mainstream string theories have 10, 11, and 26 dimensions, but I recall, and could be wrong, that there can be infinitely many string theories with 4 dimensions being the lower bound and some unspecified upper bound. But I'm not an expert and I was mostly being hyperbolic with my original reply. Corrections are always welcome.
    - evanb 5y ago
      26 is for theories with bosons only. If you want fermions you need 10; 11 in M-theory as GP suggested.
- chriswarbo 5y ago
  > I think the modern equivalent of epicycles is string theory. Find an inconstancy? No problem, add a dimension. A very common trick is to bump things to higher energy/mass. Your expensive collider didn't find the particle I predicted? The particle's mass must be larger than I thought; probably just beyond your collider's ability. You'd better build a bigger collider! My theory of dark-matter/dark-energy/quantum-gravity/etc. doesn't fit known observations? This tweaked version only has discrepancies above a certain energy, which coincidentally is just beyond current colliders. This is arguably how we found the W, Z and Higgs bosons; the charm, top and bottom quarks; and the tau. On the other hand, supersymmetry has been playing this game for decades, claiming that each new collider was sure to find (or rule out) the plethora of particles it predicted. Each time, the mass estimates were revised upwards.
  - jfengel 5y ago
    The physicists knew all along what the potential mass range was. They hope they can find it at the lower range, because that's what's cheaper, as well as feasible with the engineering capability. Arguably, the biggest problem with the Higgs boson is that it was found exactly where they were expecting it. They'd ruled out other ranges; anything bigger would no longer be a Higgs boson. So all it did was tell them what they already knew. Failing to find it would actually have been more interesting -- though finding something different would have been even more interesting. So they don't really say "we're sure to find it". They're hoping to find it -- and hoping not to. They'll always need a bigger collider. That's where new results will always be. They're hoping for results they can't predict, and that makes it really hard to write a justification for the expense. (I personally would just as soon spend much less on Big Science like that, but you'll find a ton of people willing to defend it. Fundamental physics has a history of producing results that are unexpected but economically immense, from lasers to the Web, as well as driving human intellectual curiosity.)
    - chriswarbo 5y ago
      > They'll always need a bigger collider. That's where new results will always be. Bigger colliders are a low-risk approach: we'll definitely learn something, even if it's just better constraints on our models. This was a no-brainer back when colliders took up rooms or buildings. We've gone so far down this path that colliders are now measured in kilometres (and straddle national borders!), making it harder to justify the expense. Higher-risk approaches can be much cheaper, by looking for new paths (where we haven't hit diminishing returns yet). EmDrive is an example; wakefield accelerators are another. These have a greater chance of going nowhere (again, EmDrive), but cost so little that we can fund a whole bunch for the equivalent of a bigger collider. Of course, in best approach is to strike a balance between these two extremes: don't spend everything on the biggest possible collider; but likewise don't avoid projects just for being expensive. Another good example is ITER versus the various fusion startups.
petertodd 5y ago
Worth noting that those ancient astronomers weren't wrong so to speak: each additional epicycle predicted the data better. What they were doing wasn't fraud the way that, say, dowsing would be. Rather, they hadn't made the mental and cultural leap to the the much simpler model that made epicycles (almost always) obsolete. I think it's fair to say that physicists are well aware of the fact that this could be like finding more and more epicycles. In the sense that they're hoping they one day find a much simpler model to explain all this stuff than a big list of particles without a simpler theory behind all of it.

I wonder if this is like ancient astronomers finding more and more epicycles.

by lacker 5y ago

I wonder if this is like ancient astronomers finding more and more epicycles.

at_a_remove 5y ago

Not especially, no. This is more akin to finding new molecules (hadrons), given known kinds of atoms (quarks).

eddieh 5y ago

Nah, they're more like elements, but they're made of quarks not nucleons (protons/neutrons). I think the modern equivalent of epicycles is string theory. Find an inconstancy? No problem, add a dimension.

s1dev 5y ago
That's not quite true. The dimension of the ambient space is constrained to be exactly 10 (in strings, 11 in M-theory) by consistency considerations. The important question is what is the geometry of the extra dimensions, if they exist. You need a large amount of energy to probe the extra dimensions, so it would appear just like some extra particles in the theory to a low energy observer. (Of course, the observer has to have enough energy to find even those particles). The standard model also has seemingly arbitrary particle content and interactions without much to constrain it. A majority of the particle content was put in the theory by hand after seeing a failure of the theory. In strings, this choice has been moved from the theory to the initial data (choice of geometry of the extra dimensions).
- eddieh 5y ago
  I'm not a theoretical physicist and only took a few math courses beyond which were required by my major, but it was my understanding that mainstream string theories have 10, 11, and 26 dimensions, but I recall, and could be wrong, that there can be infinitely many string theories with 4 dimensions being the lower bound and some unspecified upper bound. But I'm not an expert and I was mostly being hyperbolic with my original reply. Corrections are always welcome.
  - evanb 5y ago
    26 is for theories with bosons only. If you want fermions you need 10; 11 in M-theory as GP suggested.
chriswarbo 5y ago
> I think the modern equivalent of epicycles is string theory. Find an inconstancy? No problem, add a dimension. A very common trick is to bump things to higher energy/mass. Your expensive collider didn't find the particle I predicted? The particle's mass must be larger than I thought; probably just beyond your collider's ability. You'd better build a bigger collider! My theory of dark-matter/dark-energy/quantum-gravity/etc. doesn't fit known observations? This tweaked version only has discrepancies above a certain energy, which coincidentally is just beyond current colliders. This is arguably how we found the W, Z and Higgs bosons; the charm, top and bottom quarks; and the tau. On the other hand, supersymmetry has been playing this game for decades, claiming that each new collider was sure to find (or rule out) the plethora of particles it predicted. Each time, the mass estimates were revised upwards.
- jfengel 5y ago
  The physicists knew all along what the potential mass range was. They hope they can find it at the lower range, because that's what's cheaper, as well as feasible with the engineering capability. Arguably, the biggest problem with the Higgs boson is that it was found exactly where they were expecting it. They'd ruled out other ranges; anything bigger would no longer be a Higgs boson. So all it did was tell them what they already knew. Failing to find it would actually have been more interesting -- though finding something different would have been even more interesting. So they don't really say "we're sure to find it". They're hoping to find it -- and hoping not to. They'll always need a bigger collider. That's where new results will always be. They're hoping for results they can't predict, and that makes it really hard to write a justification for the expense. (I personally would just as soon spend much less on Big Science like that, but you'll find a ton of people willing to defend it. Fundamental physics has a history of producing results that are unexpected but economically immense, from lasers to the Web, as well as driving human intellectual curiosity.)
  - chriswarbo 5y ago
    > They'll always need a bigger collider. That's where new results will always be. Bigger colliders are a low-risk approach: we'll definitely learn something, even if it's just better constraints on our models. This was a no-brainer back when colliders took up rooms or buildings. We've gone so far down this path that colliders are now measured in kilometres (and straddle national borders!), making it harder to justify the expense. Higher-risk approaches can be much cheaper, by looking for new paths (where we haven't hit diminishing returns yet). EmDrive is an example; wakefield accelerators are another. These have a greater chance of going nowhere (again, EmDrive), but cost so little that we can fund a whole bunch for the equivalent of a bigger collider. Of course, in best approach is to strike a balance between these two extremes: don't spend everything on the biggest possible collider; but likewise don't avoid projects just for being expensive. Another good example is ITER versus the various fusion startups.

petertodd 5y ago

Worth noting that those ancient astronomers weren't wrong so to speak: each additional epicycle predicted the data better. What they were doing wasn't fraud the way that, say, dowsing would be. Rather, they hadn't made the mental and cultural leap to the the much simpler model that made epicycles (almost always) obsolete. I think it's fair to say that physicists are well aware of the fact that this could be like finding more and more epicycles. In the sense that they're hoping they one day find a much simpler model to explain all this stuff than a big list of particles without a simpler theory behind all of it.