3 ms·

Nah, I don't think she has an axe to grind, except maybe to chop down bad arguments in general. Anyway, her argument about 1 in that particular case is afaiu s

Nah, I don't think she has an axe to grind, except maybe to chop down bad arguments in general. Anyway, her argument about 1 in that particular case is afaiu simply that it's rather preposterous to assume a specific (essentially impossible to know) iv. and then massage the theory around it until the results fit the observations. In data science it would be like determining the model parameters by gut feeling, and then start searching for some kind of model with those parameters that actually fit the data. Almost exactly the opposite of how an parameter search/optimization is usually done. I tend to start with some model and see what parameters that fit instead of randomly deciding one parameter is 1 and then go look for a model that might fit my data with that arbitrarily fixed parameter. I'm no astrophysicist, or anything even remotely close to the authors competence, so I'll refrain from commenting on those points, but I really see no reason to critique her arguments in general because somebody pointed out some possible weakness of one a sub argument. Rather the opposite, if you would only have one counter comment on a physics related blog, then you are probably correct, nobody has read it yet, or the comment function is broken.

cyphar 9y ago
Her tirade about omega=+1 is odd because she talks about how it's incredibly anti-science, but doesn't even try to explain what the opposing view is (going so far as to say that she hasn't the foggiest). The first question I would want to know when evaluating the claim that omega=+1 is bad science is to hear the argument for it. From my brief touches with cosmology, omega=+1 comes from measurements that the universe appears to have a flat topology (both from the size of structure in the CMBR and from a variety of other measurements). The flatness problem effectively is a fine-tuning problem that states if omega has slight deviations from +1 (of the order 1e-62) then the universe of today would not be able to sustain galaxies or other large structures. The measurement of _today's_ omega (omega_0) is also very close to +1 (which is what forces the initial condition limit). From that, it was concluded that if we accept the model of an accelerating universe, then the initial condition must be close to +1. Inflation is the proposed physical solution to explain why that is the case. To use the Newton analogy, you are backtracking the path of an arrow to find where it was fired from. To be clear, I personally don't like how hand-wavey cosmology is as a science, but pretending as though modern cosmologists just came up with a random "cult-like" belief that omega=1 is just ludicrous. [The author calls omega 'k'. While omega and k are related (k is the curvature, and can be used to deduce the critical density -- which omega is a fraction of) I'm not sure if that's quite right. But I'm speaking as a senior undergrad here, I might've missed something.] As for the "possible weakness of a sub-argument", you can go to the reddit discussion of this particular post (others have linked it here) and see for yourself. It's quite a bit more than a "possible weakness of a sub-argument". Effectively the analysis is on her entire thesis (that the Bullet-cluster can be explained with modified gravity perfectly fine). The rest of the complains about modern cosmology are sub-arguments to justify why modified gravity should be considered.

cyphar 9y ago

Her tirade about omega=+1 is odd because she talks about how it's incredibly anti-science, but doesn't even try to explain what the opposing view is (going so far as to say that she hasn't the foggiest). The first question I would want to know when evaluating the claim that omega=+1 is bad science is to hear the argument for it. From my brief touches with cosmology, omega=+1 comes from measurements that the universe appears to have a flat topology (both from the size of structure in the CMBR and from a variety of other measurements). The flatness problem effectively is a fine-tuning problem that states if omega has slight deviations from +1 (of the order 1e-62) then the universe of today would not be able to sustain galaxies or other large structures. The measurement of _today's_ omega (omega_0) is also very close to +1 (which is what forces the initial condition limit). From that, it was concluded that if we accept the model of an accelerating universe, then the initial condition must be close to +1. Inflation is the proposed physical solution to explain why that is the case. To use the Newton analogy, you are backtracking the path of an arrow to find where it was fired from. To be clear, I personally don't like how hand-wavey cosmology is as a science, but pretending as though modern cosmologists just came up with a random "cult-like" belief that omega=1 is just ludicrous. [The author calls omega 'k'. While omega and k are related (k is the curvature, and can be used to deduce the critical density -- which omega is a fraction of) I'm not sure if that's quite right. But I'm speaking as a senior undergrad here, I might've missed something.] As for the "possible weakness of a sub-argument", you can go to the reddit discussion of this particular post (others have linked it here) and see for yourself. It's quite a bit more than a "possible weakness of a sub-argument". Effectively the analysis is on her entire thesis (that the Bullet-cluster can be explained with modified gravity perfectly fine). The rest of the complains about modern cosmology are sub-arguments to justify why modified gravity should be considered.