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What dictates galaxy and planetary system sizes?
What are the functional relationships dictating
galactic size (presently ~10^22 cm) and star planetary system size (presently ~10^15 cm) contained in a Hubble radius (presently ~10^28 cm) and the voids between? Richard D Saam [[Mod. note -- There is a large body of literature on how planetary systems form. A key factor is what materials are solid vs gaseous as a function of temperature (which is closely tied to distance from the protostar in the protostellar nebula). Alas, I don't seem to have any good references to hand at this moment. Perhaps someone can suggest some good review papers? Until then, Wikipedia offers https://en.wikipedia.org/wiki/Format...em#Format ion -- jt]] |
#2
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What dictates galaxy and planetary system sizes?
On 12/18/16 3:31 PM, Richard D. Saam wrote:
What are the functional relationships dictating galactic size (presently ~10^22 cm) and star planetary system size (presently ~10^15 cm) contained in a Hubble radius (presently ~10^28 cm) and the voids between? Richard D Saam [[Mod. note -- There is a large body of literature on how planetary systems form. A key factor is what materials are solid vs gaseous as a function of temperature (which is closely tied to distance from the protostar in the protostellar nebula). Alas, I don't seem to have any good references to hand at this moment. Perhaps someone can suggest some good review papers? Until then, Wikipedia offers https://en.wikipedia.org/wiki/Format...em#Format ion -- jt]] That covers planetary system size (presently ~10^15 cm) formation but is there an inherent planetary system size relationship to galactic size (presently ~10^22 cm) and Hubble radius (presently ~10^28 cm) that can be explained by fundamental parameters (H,c,h,G,kb) or others? RDS |
#3
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What dictates galaxy and planetary system sizes?
In article , "Richard D.
Saam" writes: What are the functional relationships dictating galactic size (presently ~10^22 cm) and star planetary system size (presently ~10^15 cm) contained in a Hubble radius (presently ~10^28 cm) and the voids between? Keep in mind that galaxies range in size over several orders of magnitude. Also, "size" is difficult to define. Solar systems probably have a much smaller range in size, but again the precise definition is not clear. Sometimes, "numerology" can be used to derive true results, such as the typical mass of a star. Check out the corresponding chapter in Edward Harrison's COSMOLOGY textbook. Keep in mind that the size of the Hubble radius is a) probably not really relevant here and b) changes with time and c) galaxies evolve with time. So, at best, you could hope for some very rough estimate based on the constants of nature and so on. But that's not enough. Sure, some combination of the constants of nature can reproduce anything you want; you need to have an explanation as well. My guess is that there is no such relation. Yes, the quantities are determined, as is everything, by the constants of nature and by initial conditions, but there is no reason to expect a simple relationship of the kind you suggest. |
#4
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What dictates galaxy and planetary system sizes?
On 12/21/16 6:32 AM, Phillip Helbig (undress to reply) wrote:
Sometimes, "numerology" can be used to derive true results, such as the typical mass of a star. Check out the corresponding chapter in Edward Harrison's COSMOLOGY textbook. Please do not confuse "numerology" with dimensional analysis. Would you say that the following dimensional equations properly reflect star dynamics as textually expressed in Harrison's COSMOLOGY textbook chapter 5 relection 7 ? [[Mod. note -- These are aren't "dimensional equations" as the term is usually understood. -- jt]] dM/dr = 4*pi*rho*r^2 dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant) P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant) dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants) luminosity(L) = 4*pi*r^2*stefan_constant*T^4 I can see uncertainties: 1. ideal gas law may not be applicable in this non ideal condition 2. alpha,Cp thermodynamic constants may not be constant with radius(r) It is interesting to note in reflection 7 that Newton did not actually use the Newton dimensional gravity constant as we know it. Richard D Saam |
#5
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What dictates galaxy and planetary system sizes?
In article , "Richard D.
Saam" writes: Sometimes, "numerology" can be used to derive true results, such as the typical mass of a star. Check out the corresponding chapter in Edward Harrison's COSMOLOGY textbook. Please do not confuse "numerology" with dimensional analysis. Dimensional analysis is the consideration that a certain quantity must depend on various constants of nature and so on; a combination with the proper dimensions is often right to within a factor of order unity. Numerology is usually a pejorative term for fooling around with various combinations of quantities until, by chance, some coincidence is found, then interpreting this as having some sort of deep meaning. My "numerology" (in quotes) is the more serious form of this, i.e. DERIVING the order of magnitude of something (say, the mass of a star) from general arguments. There is an entire chapter in Harrison's textbook on this. It needs more physics input that dimensional analysis. Would you say that the following dimensional equations properly reflect star dynamics as textually expressed in Harrison's COSMOLOGY textbook chapter 5 relection 7 ? [[Mod. note -- These are aren't "dimensional equations" as the term is usually understood. -- jt]] Right; they are differential equations. dM/dr = 4*pi*rho*r^2 dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant) P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant) dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants) luminosity(L) = 4*pi*r^2*stefan_constant*T^4 I can see uncertainties: 1. ideal gas law may not be applicable in this non ideal condition 2. alpha,Cp thermodynamic constants may not be constant with radius(r) Sure, but this is covered in any book on stellar structure and evolution, such as Kippenhahn and Weigert. |
#6
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What dictates galaxy and planetary system sizes?
"Phillip Helbig (undress to reply)"
writes: My "numerology" (in quotes) is the more serious form of this, i.e. DERIVING the order of magnitude of something (say, the mass of a star) from general arguments. Sometimes known as order, Fermi, or "back of the envelope" estimates: https://en.wikipedia.org/wiki/Back-o...pe_calculation I don't really like calling those "numerology", even in scare quotes. Fermi estimates are motivated by the fundamentals of the relevant physics, while numerology is all about particular values and not at all about fundamentals. -dan |
#7
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What dictates galaxy and planetary system sizes?
On 12/25/16 10:26 AM, Phillip Helbig (undress to reply) wrote:
In article , "Richard D. Saam" writes: Sometimes, "numerology" can be used to derive true results, such as the typical mass of a star. Check out the corresponding chapter in Edward Harrison's COSMOLOGY textbook. Please do not confuse "numerology" with dimensional analysis. Dimensional analysis is the consideration that a certain quantity must depend on various constants of nature and so on; a combination with the proper dimensions is often right to within a factor of order unity. Numerology is usually a pejorative term for fooling around with various combinations of quantities until, by chance, some coincidence is found, then interpreting this as having some sort of deep meaning. My "numerology" (in quotes) is the more serious form of this, i.e. DERIVING the order of magnitude of something (say, the mass of a star) from general arguments. There is an entire chapter in Harrison's textbook on this. It needs more physics input that dimensional analysis. Your logic indicates all physical analysis is some degree of "numerology" which in the case of star mass is "serious form". By this definition, "numerology" can be used as a paper review scare tactic to which there is no defense. To what degree of "numerology" is implied? Whereas if the reviewed work is based on dimensional analysis one can argue this or that dimension is correct or not in the context of real data. I think that Harrison would be offended having any of his work (including chapter 26) termed "numerology". Would you say that the following dimensional equations properly reflect star dynamics as textually expressed in Harrison's COSMOLOGY textbook chapter 5 relection 7 ? [[Mod. note -- These are aren't "dimensional equations" as the term is usually understood. -- jt]] Right; they are differential equations. Differential equations also may be properly expressed in dimensional analysis. jt possibly meant something else. dM/dr = 4*pi*rho*r^2 dP/dr = -G*Mr*rho/r^2 (G Newton gravity constant) P = (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas constant) dT/dr = alpha*g*T/Cp (alpha,Cp are thermodynamic constants) luminosity(L) = 4*pi*r^2*stefan_constant*T^4 I can see uncertainties: 1. ideal gas law may not be applicable in this non ideal condition 2. alpha,Cp thermodynamic constants may not be constant with radius(r) Sure, but this is covered in any book on stellar structure and evolution, such as Kippenhahn and Weigert. |
#8
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What dictates galaxy and planetary system sizes?
On 12/25/16 1:27 PM, Daniel S. Riley wrote:
"Phillip Helbig (undress to reply)" writes: My "numerology" (in quotes) is the more serious form of this, i.e. DERIVING the order of magnitude of something (say, the mass of a star) from general arguments. Sometimes known as order, Fermi, or "back of the envelope" estimates: https://en.wikipedia.org/wiki/Back-o...pe_calculation I don't really like calling those "numerology", even in scare quotes. Fermi estimates are motivated by the fundamentals of the relevant physics, while numerology is all about particular values and not at all about fundamentals. -dan I have found it refreshing to look out of an airplane cabin window onto the wing and with a "back of the envelope" calculation establish that I should actually be flying within the multi ton piece of metal contain several hundred people. And calculations are not done with "numerology". Richard D Saam |
#9
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What dictates galaxy and planetary system sizes?
In article , "Richard D.
Saam" writes: On 12/25/16 10:26 AM, Phillip Helbig (undress to reply) wrote: In article , "Richard D. Saam" writes: Sometimes, "numerology" can be used to derive true results, such as t= he typical mass of a star. Check out the corresponding chapter in Edwar= d Harrison's COSMOLOGY textbook. Please do not confuse "numerology" with dimensional analysis. Dimensional analysis is the consideration that a certain quantity must depend on various constants of nature and so on; a combination with the proper dimensions is often right to within a factor of order unity. Numerology is usually a pejorative term for fooling around with various combinations of quantities until, by chance, some coincidence is found, then interpreting this as having some sort of deep meaning. My "numerology" (in quotes) is the more serious form of this, i.e. DERIVIN= G the order of magnitude of something (say, the mass of a star) from general arguments. There is an entire chapter in Harrison's textbook o= n this. It needs more physics input that dimensional analysis. Your logic indicates all physical analysis is some degree of "numerology" which in the case of star mass is "serious form". In some sense, yes. Note that the scare quotes are there because this is NOT what is generally known as numerology, although it might look superficially similar. Certainly all physical analysis must include "numerology" in that the order of magnitude must be correct, it must follow from simple principles, etc. In some cases, that is enough; that is what I meant by the example of Harrison's "numerology". In other cases, it isn't, because the processes are more complicated. By this definition, "numerology" can be used as a paper review scare tactic to which there is no defense. To what degree of "numerology" is implied? Not sure what you mean here. If a back-of-the-envelope calculation indicates that some result is obviously wrong, then OK. There is of course no defense in that there is nothing worth defending. However, it can't be used to discredit ANY claim. Whereas if the reviewed work is based on dimensional analysis one can argue this or that dimension is correct or not in the context of real data. Sure; if the dimensions are wrong, the result is wrong. If the dimensions are right, then the answer is not necessarily right. I think that Harrison would be offended having any of his work (including chapter 26) termed "numerology". The term doesn't matter, as long as it is understood. Perhaps "back-of-the-envelope calculation" is better. Would you say that the following dimensional equations properly reflect star dynamics as textually expressed in Harrison's COSMOLOGY textbook chapter 5 relection 7 ? [[Mod. note -- These are aren't "dimensional equations" as the term is usually understood. -- jt]] Right; they are differential equations. Differential equations also may be properly expressed in dimensional analysis. jt possibly meant something else. I don't think so. Of course, ANY equation has to get the dimensions right. dM/dr =3D 4*pi*rho*r^2 dP/dr =3D -G*Mr*rho/r^2 (G Newton gravity constant) P =3D (rho/Mw)*R*T (P pressure, Mw Molecular weight, R gas consta= nt) dT/dr =3D alpha*g*T/Cp (alpha,Cp are thermodynamic constants) luminosity(L) =3D 4*pi*r^2*stefan_constant*T^4 I can see uncertainties: 1. ideal gas law may not be applicable in this non ideal condition 2. alpha,Cp thermodynamic constants may not be constant with radius(r) Sure, but this is covered in any book on stellar structure and evolution, such as Kippenhahn and Weigert. |
#10
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What dictates galaxy and planetary system sizes?
Le 21/12/2016 à 13:32, Phillip Helbig (undress to reply) a écrit :
the quantities are determined, as is everything, by the constants of nature and by initial conditions, Since most of the mass of a planetary system is in the star, the limit to its mass is the limit of the mass of a star. Now, stars when they become obese, start producing antimatter that destroys the star before it is fully built, the limit on star sizes determines, as a consequence, the size of the planetary systems... Is that correct? |
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