Ptolemy's Epicycles and Cutting Edge Physics

[darkmatter4brains]

The ptolemaic model of the solar system, which held sway for many hundreds of years, was a Geocentric model of the solar system. it held that the earth was at the center of the solar system and that the oribits were circles. Obviously, this model would not stand up to observation, but when it did not, the solution was to add another small orbit that orbits around the original circular orbit. By adding these additional orbits (epicycles) you can make the model fit observation. It's sorta like a fourier series - you can add as many sine waves together and make them look like almost anything as long as it's a repeating sequence. Some like to call these epicycles a mathematical trick, because you can use the math to match reality, even though the model is physically wrong.

The question has been raised - is this what modern physicists are doing (especially with String Theory)? When I start hearing that theories like the Standard Model have around 15 free parameters I can't help but wonder if maybe they are. Free parameters are basically values that you tweak until the theory fits observation. Any true unified theory, should have ZERO free parameters (or zero epicycles for that matter!). I don't know much about modern string theory, but from one layman's book I read, M-theory, which is an updated version of string theory, has over 100 free parameters!!

So, have these guys run into some very advanced math, that they can tweak into anything they want, or are they really on the road to progress. One can't help but wonder. Would love to hear other's opinions on this.

 

[ramparts]

Well, the number of free parameters is certainly one of the more worrying things about the standard model for physicists. I'm not entirely sure what the consensus is on free parameters in string theory (of course, not being entirely formulated yet, it's hard to tell!).

I think one of the biggest basic things in string theory's favor is that it predicts the graviton. That's not analogous at all to the epicycles - you end up explaining more than you were trying to explain in the first place, rather than successively tweaking your theory to match the observations. That's pretty important.

This is an interesting question though, because I really don't think we can fault scientists of the time for examining failed theories like epicycles, or the ether a few centuries later, or possibly even string theory today. We use the best models we can to explain the data, and we take those models as far as we can, to see if they really do match up with what we observe. And if they're wrong, then we look for and wait for other theories which explain the data more accurately and more simply. The one thing a scientist can be faulted for is not keeping an open mind.

 

[darkmatter4brains]

Well, the number of free parameters is certainly one of the more worrying things about the standard model for physicists. I'm not entirely sure what the consensus is on free parameters in string theory (of course, not being entirely formulated yet, it's hard to tell!).

It seems like the more they formulate it the larger the free parameter count gets!

This is an interesting question though, because I really don't think we can fault scientists of the time for examining failed theories like epicycles, or the ether a few centuries later, or possibly even string theory today. We use the best models we can to explain the data, and we take those models as far as we can, to see if they really do match up with what we observe. And if they're wrong, then we look for and wait for other theories which explain the data more accurately and more simply. The one thing a scientist can be faulted for is not keeping an open mind.

I definitely agree with that. I think in the end whether it turns out that the theory fails and they've been spinning their wheels, or if it's a huge success, it all just goes to show what a challenge physicists had to face in our day.